Knee Injuries

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4 Knee Injuries

S. Brent Brotzman, MD

Anterior Cruciate Ligament Injuries

S. Brent Brotzman, MD

Background

The anterior cruciate ligament (ACL) is the most frequently completely disrupted ligament in the knee; most of these injuries occur in athletes (Fig. 4-1). More than 100,000 ACL reconstructions are done each year in the United States.

Figure 4-1 Anterior cruciate ligament and anatomic knee structures.

(Redrawn with permission from Miller MD, Howard RF, Planchar KD. Surgical Atlas of Sports Medicine. Philadelphia, 2003, Saunders, p. 74, Fig. 10-3.)

About 80% of sports-related ACL tears are noncontact injuries, occurring during pivoting maneuvers or landing from a jump. Noncontact ACL injuries are more common in females than in males (see section on ACL injuries in female athletes). Only 60,000 individuals with ACL deficiency actually undergo reconstruction annually.

Hewett et al. (2005) in a level II study found that prescreened female athletes with subsequent ACL injury demonstrated increased dynamic knee valgus (Fig. 4-2) and high knee abduction loads on landing from a jump. Knee abduction moments, which directly contribute to lower extremity dynamic valgus and joint knee load, had a sensitivity of 78% and specificity of 73% for predicting future ACL injury. Neuromuscular training has been shown to decrease knee adduction moments at the knee (Hewitt et al. 1996), and this will be addressed at great length in the ensuing chapter.

Figure 4-2 A, Dynamic valgus is defined as the position or motion, measured in three dimensions, of the distal femur toward the distal tibia away from the midline of the body. Dynamic valgus includes the indicated motions and moments. B, In individuals with anterior knee pain the alignment may appear rather straight—no excessive genu valgum or valgus—but there is significant internal rotation of the femors, indicating femoral anteversion. The patellae are pointing toward one another (left). This is accentuated when the individual gets in a flexed position: the femur goes into further adduction and internal rotation (right).

(Redrawn with permission from Hewett TE, Myer GD, Ford KR, Heidt RS Jr, Colosimo AJ, McLean SG, van den Bogert AJ, et al. Biomechanical measures of neuromuscular control and valgus loading of the knee predict anterior cruciate ligament injury risk in female athletes. Am J Sports Med 33:4, 2005.).

Although the natural history of the ACL-deficient knee has not been clearly defined, it is known that ACL injury often results in long-term problems, such as subsequent meniscal injuries, failure of secondary stabilizers, and development of osteoarthritis (OA).

Although a number of studies have suggested that OA eventually develops in 60% to 90% of individuals with ACL injuries (Beynnon 2005 Part 1, Andersson et al. 2009), a recent systematic review of the literature (Ojestad et al. 2009) concerning OA of the tibiofemoral joint more than 10 years after ACL injury suggests that these estimates are too high. The lack of a universal methodologic radiographic classification made it difficult to draw firm conclusions, but these investigators determined that in the highest-rated studies the reported prevalence of knee OA after isolated ACL injury was between 0% and 13%, and with meniscal injury, it was between 21% and 48% (level II evidence).

Associated meniscal injury is the most commonly cited factor contributing to the development of OA after ACL injury, followed by articular cartilage injuries. A 7-year prospective study of patients with reconstruction of an acute ACL injury found that 66% of those with concomitant meniscectomy developed OA, compared to only 11% of those without meniscal injury (Jomha et al. 1999). Subjective follow-up of 928 patients 5 to 15 years after ACL reconstruction found normal or nearly normal knees in 87% of patients with both menisci present, compared to 63% of those with partial or total meniscectomies (Shelbourne and Gray 2000). Of 54 National Football League players who had meniscectomy or ACL reconstruction or both, those with both procedures had shorter careers (fewer games started, fewer games played, and fewer years in the sport) than those with either procedure alone (Brophy et al. 2009).

Successful reconstruction of the ACL has been proven to improve short-term function and perhaps decrease the risk of subsequent meniscal injury, but it may not decrease the likelihood of OA (Lohmander and Roos 1994), particularly in patients with concomitant meniscal or articular cartilage injuries.

Treatment of ACL Injuries

Nonoperative Treatment (ACL-Deficient Knee)

• Levy and Meier (2003) reported the incidence of subsequent meniscal tears in ACL-deficient knees is 40% at year 1, 60 percent at year 5, and 80% by 10 years after the initial untreated ACL disruption.

• Lohmander and Roos (1994) in a meta-analysis of 33 studies found that the efficacy of ACL reconstruction in retarding the progression of OA was not substantiated. Presence of meniscal injury at time of ACL injury has a high correlation with eventual development of arthritis.

• Some patients who are ACL-deficient, however, have physiologic responses and motor control strategies that allow successful compensation for their ACL absence (copers). Copers are defined patients who have returned to full sports and preinjury activity without instability for at least 1 year.

• Nakayama and Beard have similiarly demonstrated much improved dynamic knee stability and function in patients with ACL deficiency after rehabilitation that included perturbation training. Perturbation training for nonoperatively treated and postoperative ACL reconstruction in addition to traditional strengthening should be advocated.

Despite the success of current ACL reconstruction methods, not all patients require surgical reconstruction. Currently, there are no firm criteria for determining which patients are candidates for ACL reconstruction versus nonoperative management.

Several authors have suggested criteria for nonoperative treatment in ACL tears: Fitzgerald et al. (2000) developed guidelines for selecting appropriate candidates for nonoperative ACL deficiency management (e.g., initiation of perturbation and strengthening program). The primary criteria were no concomitant ligament (e.g., medial collateral ligament) or meniscal damage and a unilateral ACL injury. Other criteria include the following:

1. Timed hop test score of 80% of the uninjured limb

2. Knee Outcome Survey Activities of Daily Living Scale score of 80% or more

3. Global rating of knee function of 60% or more

4. No more than one episode of giving way in the time from injury to testing

The success rate in Fitzgerald’s perturbation ACL rehabilitation group was 92% (11/12 patients). The likelihood ratio calculated for this study suggested patients would be five times more likely to successfully return to high-level physical activity if they receive the perturbation training than if they receive only a standard ACL rehabilitation strength training program.

Moksnes et al. in a level Ib study (2008) found that 70% of patients classified as potential noncopers in Fitzgerald’s original screening examination were true copers after 1 year of nonoperative treatment.

1. These authors’ observation was that the development of knee function in subjects with nonoperatively treated ACL injuries simply took time.

2. At 1-year followup, 70% of the subjects initially classified by Fitzgerald’s criteria as noncopers were true copers (Beynnon et al. 2005). Other possible criteria for nonoperative ACL treatment include the following:

• Minimal exposure to high-risk activities such as sports and heavy work activities

• Willingness to avoid high-risk activity

• Age older than 40 years

• Success in prolonged coping with or adaptation to ACL deficiency

• Advanced arthritis of the involved joint

• Inability or unwillingness to comply to postoperative rehabilitation

Most reports of successful nonoperative treatment of ACL injuries come from case series (level IV evidence). One prospective cohort study (level II evidence) of 100 consecutive patients with nonoperatively treated (early activity modification and neuromuscular knee rehabilitation) ACL injuries found that at 15-year followup 68% had asymptomatic knees (Neuman et al. 2008).

Of four randomized controlled studies comparing nonoperative to operative treatment (level I evidence), one reported no difference in outcomes (Sandberg et al. 1987) and three reported superior results with operative treatment (Andersson et al. 1989 and 1991, Odensten et al. 1984).

Although age of more than 40 years has been considered a relative indication for nonoperative treatment, several studies have reported results in older patients similar to those in younger patients, and age alone is not an absolute indicator for nonoperative treatment. Many individuals aged 40 years and older remain athletically active and are not willing to accept the limitations knee instability places on their activities.

Operative ACL Reconstruction

ACL reconstruction is almost universally recommended for patients with high-risk lifestyles that require heavy work or who participate in certain sports or recreational activities. Other indications for ACL reconstruction include repeated episodes of giving way despite rehabilitation, meniscal tears, severe injuries to other knee ligaments, generalized ligamentous laxity, and recurrent instability with activities of daily living (Beynnon et al. 2005 Part 1). Once operative reconstruction is chosen, a number of controversial areas must be considered: timing of surgery; choice of graft, autograft, or allograft; one- or two-bundle technique; fixation method; and rehabilitation protocol (accelerated or nonaccelerated).

A study of National Basketball Association players with ACL injuries and subsequent reconstruction by sports medicine physicians found that 22% did not return to competition and 44% of those who did return had decreases in their levels of performance despite reconstruction (Busfield et al. 2009, level IV evidence).

Timing of surgery. Because many patients had difficulty regaining full knee motion after acute or early reconstruction, delayed reconstruction has been suggested to minimize the possibility of postoperative arthrofibrosis. Good results have been reported after both acute and delayed reconstruction, mostly in retrospective case series. A prospective study compared outcomes in patients who had ACL reconstruction at four time points after injury (Hunter et al. 1996): within 48 hours, between 3 and 7 days, between 1 and 3 weeks, and more than 3 weeks. They found that restoration of knee motion and ACL integrity after ACL reconstruction was independent of the timing of surgery. Shelbourne and Patel (1995) suggested that the timing of ACL surgery should not be based on absolute time limits from injury. They reported that patients who had obtained an excellent range of motion (ROM), little swelling, good leg control, and an excellent mental state before surgery generally had good outcomes, regardless of the timing of surgery. Mayr et al. (2004) confirmed these observations in a retrospective review of 223 patients with ACL reconstructions: 70% of patients with a swollen, inflamed knee at the time of undergoing ACL reconstruction developed postoperative arthrofibrosis. It appears that the timing of reconstruction is not as important as the condition of the knee before surgery: full ROM, minimal effusion, and minimal pain are required (Beynnon et al. 2005, Part 1).

Graft choice. Bone-patellar tendon-bone (BPTB) autografts (Fig. 4-3) have been historically considered the “gold standard” for ACL reconstructions, although good outcomes have been reported with other graft choices, particularly hamstring grafts (Fig. 4-4 A–H). A number of studies have compared BPTB grafts with four-strand hamstring grafts, with most reporting no significant difference in functional outcomes, although difficulty with kneeling was more commonly reported by those with BPTB grafts.

Figure 4-3 A, Bone patellar tendon bone graft harvest. The tendon is exposed, and the paratenon is incised. An appropriately sized graft is measured, and the tendon is incised parallel to its fibers. An oscillating saw is used to remove 25-mm bone blocks from the tibia and the patella. B, An osteotome is used to remove the bone blocks. (Reprinted with permission from Miller MD, Howard RF, Planchar KD. Surgical Atlas of Sports Medicine. Saunders, Philadelphia, 2003, p. 46, Fig. 7-4.) C, Anterior cruciate ligament bone patellar bone graft fixation.

(Reprinted with permission from Miller MD, Howard RF, Planchar KD. Surgical Atlas of Sports Medicine. Saunders, Philadelphia, 2003, p. 57, Fig. 7-14,)

Figure 4-4 A and B, Hamstring graft harvest. Initial dissection beneath sartorial fascia and isolation of gracilis tendon (superior) and semitendinosus tendon (inferior). C, Sutures placed near insertion of each tendon with a whip stitch; harvesting performed with a tendon stripper. D, Passage of the tendon stripper outside of the fascial sling beneath the semimembranous muscle may result in the tendon stripper’s taking an aberrant path into the thigh and causing premature amputation of the semitendinosus graft. E, Muscle is cleared off each tendon with a curette. F, Sutures are placed on the free ends of the graft.G, A fixation device is prepared after the graft has been sized. H, Anterior cruciate ligament graft passage with fixation of the metal EndoButton on the lateral femoral cortex.

(A, B, C, E, F, G Reprinted with permission from Miller MD, Howard RF, Planchar KD. Surgical Atlas of Sports Medicine. Saunders, Philadelphia, 2003, Figs. 7-5A, C, D, 7-8 A, B, C, 7-13. Part D adapted with permission from Brown CH, Sklar JH. Endoscopic anterior cruciate ligament reconstruction using quadrupled hamstring tendons and EndoButton femoral fixation. Tech Orthop 13:285, 1998.)

A meta-analysis by Yunes et al. (2001) found that patients with BPTB grafts had anteroposterior knee laxity values that were closer to normal than did those with four-strand hamstring grafts, and a later meta-analysis by Goldblatt et al. (2005) found that more patients with BPTB grafts had KT-1000 manual-maximum side-to-side laxity differences of less than 3 mm than did those with four-strand hamstring grafts; fewer of those with BPTB grafts had significant flexion loss. Those with hamstring grafts had less patellofemoral crepitance, anterior knee pain, and extension loss.

Autograft versus allograft. Suggested advantages of allografts over autografts include decreased morbidity, preservation of the extensor or flexor mechanisms, decreased operative time, availability of larger grafts, lower incidence of arthrofibrosis, and improved cosmetic result. Disadvantages of allografts include risk of infection, slow or incomplete graft incorporation and remodeling, higher costs, availability, tunnel enlargement, and alteration of the structural properties of the graft by sterilization and storage procedures. Two meta-analyses comparing autografts and allografts found no significant differences in short-term clinical outcomes (Foster et al. 2010, Carey et al. 2009); however, Mehta et al. (2010) found higher revision rates with BPTB allografts than with autografts and higher IKDC (International Knee Documentation Committee) scores in those with autografts.

A prospective comparison (level II evidence) of outcomes of 37 patients with autografts and 47 with allografts found similar clinical outcome scores at 3 to 6 years after surgery (Edgar et al. 2008). A retrospective review of 3126 ACL reconstructions (1777 with autografts and 1349 with allografts) found that the use of an allograft did not increase the risk of infection (less than 1% in both groups); hamstring tendon autografts had a higher frequency of infection than either BPTB autografts or allografts (Barker et al. 2009).

Single-or double-bundle reconstruction. The rationale for two-bundle reconstruction is based on the identification of two distinct ACL bundles: the anteromedial (AM) and the posterolateral (PL) bundle (Fig. 4-5). The femoral insertion sites of both bundles are oriented vertically with the knee in extension, but they become horizontal when the knee is flexed 90 degrees, placing the PL insertion site anterior to the AM insertion site. When the knee is extended, the bundles are parallel; when the knee is flexed, they cross. In flexion, the AM bundle tightens as the PL bundle becomes lax, while in extension the PL bundle tightens and the AM bundle relaxes.

Figure 4-5 A Anterior cruciate ligament (ACL) tear of anteromedial and posterolateral bundles, each from femoral insertion. Preoperative examination demonstrated 2+ Lachman test score and 3+ pivot shift test score.

(Reprinted with permission from Cole B. Surgical Techniques of the Shoulder, Elbow, and Knee in Sports Medicine. Philadelphia: Saunders, 2008. p. 664, Fig. 65-4.)

B The ACL is divided into three bundles based on the tibial attachment: the anteromedial (AM), the intermediate (I), and the posterolateral (PL) bundles. With knee flexion, the posterior fibers loosen and the anteromedial fibers coil around the posterolateral ones.

(Redrawn with permission from Baker CL Jr. The Hughston Clinic Sports Medicine Book. Baltimore: Williams & Wilkins, 1995.)

These observations indicate that each bundle has a unique contribution to knee kinematics at different flexion angles. Cadaver studies have shown that double-bundle reconstructions more closely restore normal knee kinematics (Tsai et al. 2009, Morimoto et al. 2009, Yagi et al. 2002), including a more normal tibiofemoral contact area (Morimoto et al. 2009), than do single-bundle reconstructions. Several prospective, randomized comparisons (level I evidence) of the two techniques have shown superior objective results with double-bundle reconstruction but no significant differences in subjective and functional results (Sastre et al. 2010, Jarvela et al. 2008, Aglietti et al. 2010, Siebold et al. 2008) even in high-level athletes (Streich et al. 2008).

A meta-analysis of the literature (Meredick et al. 2008) found no clinically significant differences in KT-1000 or pivot shift results between double-bundle and single- bundle reconstruction. Other authors have reported significantly more rotational stability after double-bundle reconstruction than after single-bundle procedures (Tsai et al. 2009, Hofbauer et al. 2009, Kondo et al. 2008). The primary disadvantage of double-bundle reconstructions is their complexity and technical difficulty. The creation of multiple tunnels increases the risk of tunnel misplacement and makes revision surgery extremely difficult.

Cited advantages of single-bundle techniques include proven success, less technical difficulty, less tunnel widening, fewer complications, easier revision, lower graft cost when allograft is used, lower implant cost, and shorter surgical time (Prodromos et al. 2008).

Method of fixation. A variety of fixation devices are used for ACL reconstruction, with no consensus as to what is best. Generally, fixation can be classified as interference screw-based, cortical, or cross-pin (Prodromos et al. 2008). Interference screw and cortical fixation can be used in both the femur and the tibia. Interference screw fixation functions by generating frictional holding power between the graft and the bone tunnel wall (Prodromos et al. 2008). Cortical fixation can be direct, compressing the graft against the cortex, or indirect, connecting the graft to the cortex with some sort of interface, often a fabric or metal loop through which the graft is passed. Cross-pinning is a relatively new fixation technique for which advocates cite the advantage of being closer to the tunnel opening than cortical fixation. This advantage, however, has not been proved. A meta-analysis showed that cortical fixation provided more stability than aperture fixation (Prodromos et al. 2005), and a prospective comparison of three fixation devices, including cross-pin fixation, found no statistically or clinically relevant differences in results at 2-year follow-up (Harilainen and Sandelin 2009). All currently used fixation techniques appear to provide adequate stability to allow early aggressive rehabilitation after ACL reconstruction (Hapa and Barber 2009).

ACL Rehabilitation Rationale

Protocols for rehabilitation after ACL reconstruction follow several basic guiding principles:

• Achieving full ROM and complete reduction of intra-articular inflammation and swelling before surgery to avoid arthrofibrosis

• Early weightbearing and ROM, with early emphasis on obtaining full passive extension

• Early initiation of quadriceps and hamstring activity

• Efforts to control swelling and pain to limit muscular inhibition and atrophy

• Appropriate use of open and closed kinetic chain exercises, avoiding early open chain exercises that may shear or tear the weak immature ACL graft (see section on open and closed kinetic chain exercises)

• Comprehensive lower extremity muscle stretching and strengthening and conditioning

• Neuromuscular and proprioception retraining including perturbation training (page 219)

• Stepped progression based on achievement of therapeutic goals (i.e., criteria based sequential progression) (Rehabilitation Protocol 4-1).

• Functional testing and functional sport-specific training prior to return to play

REHABILITATION PROTOCOL 4-1 Criteria-Based Postoperative ACL Reconstruction Rehabilitation Protocol

Michael Duke, PT, CSCS, S. Brent Brotzman, MD

Phase I (Days 1–7)

Weightbearing status

Two crutches, locked knee brace, weightbearing as tolerated after nerve block wears off

Exercises

Heel slides/wall slides/sitting assisted knee flexion

Ankle pumps

Isometric quad sets in full extension with and without neuromuscular electrical stimulation (NMES) or biofeedback

Hamstring sets (not for hamstring autograft)

Gluteal sets

Straight leg raise (SLR) flexion, abduction, extension with brace locked in full extension

Prone hangs or heel propped in supine for passive knee extension

Weight shifting in standing for weightbearing tolerance (anteroposterior and side to side)

Continuous passive motion (CPM) 6 hours/day, increasing 5–10 degrees/day

Gait training with crutches and brace, level ground and stairs

Cryotherapy to reduce edema

Manual Therapy

Patellar mobilizations

Soft tissue mobilizations to hamstrings for spasm control

Goals

Active range of motion (AROM) 0–90 degrees within 10 days

Good, active quadriceps contraction

Full weightbearing (FWB) with crutches and brace

Edema control

Graft protection

Wound healing

Criteria to Progress to Phase II

SLR with or without lag in brace

Clean and dry wound

Progressing range of motion (ROM)

Able to bear weight on involved limb

Phase II (Days 8–14)

Weightbearing Status

Weightbearing as tolerated

Two crutches to single crutch

Brace unlocked gradually as quad control improves (SLR without lag before unlocking brace beyond 30 degrees)

Manual Therapy

Continue patellar mobs as indicated

Continue hamstring mobs as indicated

Goals

AROM 0–120 degrees within 3 weeks

SLR without quad lag

Normal gait pattern with single crutch and unlocked brace

Criteria to Progress to Phase III

AROM 0–90 degrees

SLR with minimal quad lag

Normal gait with least restrictive assistive device

Single-leg stance on involved limb with hand-assist

Phase III (Weeks 2–4)

Weightbearing Status

FWB, normal gait without assistive device or brace by 3 weeks

Exercises

Stationary bike with gradual progressive resistance for endurance

Isometric quad sets in full extension and at 90 to 60 degrees flexion with and without NMES or biofeedback until equal quad contraction bilaterally

Closed kinetic chain squat/leg press 0 to 60 degrees, gradual progressive resistance

Balance board bilateral in multiple planes

Single-leg balance eyes open/closed, variable surfaces

Sport cord or treadmill walking forward and backward

Standing SLRs, each LE and with resistance

Manual Therapy

Continue patellar mobilizations as indicated

Initiate scar mobilizations as needed

Manual extension or flexion ROM as needed

Goals

Full AROM, equal to nonsurgical knee

Normal gait without assistive device

Independent activities of daily living (downstairs may still be difficult)

Criteria for Progression to Phase IV

Equal bilateral knee AROM

Normal gait without assistive device

Understanding of precautions regarding state of graft

Single-leg standing without assistance

Phase IV (Weeks 4–8)

Precautions

State of graft at its weakest during this postoperative period. No impact activities such as running, jumping, pivoting, or cutting, and no deep squatting (limits remain 0–60 degrees)

Pay attention to scar mobility; use manual soft tissue mobilizations as indicated

Exercises

Stationary bike: increase resistance and some light intervals

Squats/leg press: bilateral to unilateral (0–60 degrees) with progressive resistance

Lunges (0–60 degrees)

Stairs: concentric and eccentric (not to exceed 60 degrees of knee flexion)

Calf raises: bilateral to unilateral

Contrakicks (steamboats) (Fig. 4-90): progress from anteroposterior to side to side, then circles/random

Figure 4-90 Abduction contrakicks/steamboats.

Rotational stability exercises: static lunge with lateral pulley repetitions

Sport cord resisted walking all four directions

Treadmill walking all four directions

Balance board: multiple planes, bilateral stance

Ball toss to mini-tramp or wall in single-leg stance

Single-leg deadlifts (Fig. 4-91): wait for 6–8 weeks if hamstring autograft

Figure 4-91 Single-leg deadlift.

Core strengthening: supine and prone bridging, standing with pulleys

Gait activities: cone obstacle courses at walking speeds in multiple planes

Criteria for Progression to Phase V

Bilateral squat to 60 degrees (no more) with equal weight distribution

Quiet knee (minimal pain and effusion and no giving way)

Quad girth within 1 to 2 cm of nonsurgical thigh at 10 cm proximal to superior patella

Single-leg balance on involved limb >30 seconds with minimal movement

Phase V (Weeks 8–12)

Things to Watch Out for

Patellar tendinitis

Goals

Equal quad girth (average gain of 1 cm per month after first month with good strength program)

Single-leg squat to 60 degrees with good form

Criteria for Progression to Phase VI

Nearly equal quad girth (within 1cm)

Single-leg squat to 60 degrees

Single-leg balance up to 60 seconds

Minimal, if any, edema with activity

Phase VI (Week 12–16)

Things to Watch Out for/Correct

Landing during exercises at low knee flexion angles (too close to extension)

Landing during exercises with genu varum/valgum (watch for dynamic valgus of knee and correct)

Landing and jumping with uninvolved limb dominating effort

Criteria to Progress to Phase VII

Single-leg squat, 20 repetitions to 60 degrees of knee flexion

Single-leg stance at least 60 seconds

Single-leg calf raise 30 repetitions

Good landing form with bilateral vertical and horizontal jumping

Hop testing †: 80% of uninvolved limb performed prior to running

For Revision ACL Reconstructions

Per specific physician recommendation, follow typically similar protocol until 12 weeks, then extend weeks 12 to 16 through to 5- to 6-month timeline, when patients can then begin running and progress to functional sports activities. See Figure 4-90 for an illustration of abduction contrakicks/steamboats (flexion, extension, and adduction contrakicks can be performed by rotating patient 90 degrees at a time).

Single-leg hop for distance: 80% minimum compared to nonsurgical side for running, 90% minimum for return to sport

Single-leg triple hop for distance: 80% for running, 90% for return to sport

Triple crossover hop for distance: 80% for running, 90% for return to sport

Timed 10-m single-leg hop: 80% for running, 90% for return to sport

Timed vertical hop test: 60 seconds with good form and steady rhythm considered passing

Always begin with warmup on the stationary bike or elliptical for >10 minutes prior to initiation of running.

Patient should have no knee pain following run.

Week 1: Run: walk 30 seconds: 90 seconds every other day (qod) (10–15 minutes)

Week 2: Run: walk 60:60 qod (10–20 minutes)

Week 3: Run: walk 90:30 qod (15–20 minutes)

Week 4: Run: walk 90:30 3-4x/week (20–25 minutes)

Week 5: Run continuously 15–20 minutes 3–5x/week

^* See section on perturbation training for ACL postoperative training progression.

^† Hop Testing

^‡ Progressive running program

Open and Closed Kinetic Chain Exercise

Considerable debate has occurred in recent years regarding the use of closed kinetic chain activity versus open kinetic chain activity after ACL reconstruction. An example of an open kinetic chain exercise is the use of a leg extension machine (Fig. 4-6). An example of closed kinetic chain exercise is the use of a leg press machine (Fig. 4-7). In theory, closed kinetic chain exercises provide a more significant compression force across the knee with activating co-contraction of the quadriceps and hamstring muscles. It has been suggested that these two factors help decrease the anterior shear forces in the knee that would otherwise be placed on the maturing ACL graft. Because of this, closed kinetic chain exercises have been favored over open kinetic chain exercises during rehabilitation after ACL reconstruction. However, the literature supporting this theory is not definitive. Many common activities cannot be clearly classified as open or closed kinetic chain, which adds to the confusion. Walking, running, stair climbing, and jumping all involve a combination of open and closed kinetic chain components to them.

Figure 4-6 Example of an open kinetic chain exercise (leg extension).

Figure 4-7 Example of a closed kinetic chain exercise (leg press).

Jenkins and colleagues (1997) measured side-to-side difference in anterior displacement of the tibia in subjects with unilateral ACL-deficient knees during open kinetic chain exercise (knee extension) and closed kinetic chain exercises (leg press) at 30 and 60 degrees of knee flexion and concluded that open chain exercises at low flexion angles may produce an increase in anterior shear forces, which may cause laxity in the ACL.

Side-to-side Difference in Anterior Displacement

	30 degrees knee flexion (mm)	60 degrees knee flexion (mm)
Open kinetic chain (knee extension)	4.7	1.2
Closed kinetic chain (leg press)	1.3	2.1

(3–5 mm = abnormal; 5 mm = arthrometric failure)

(From Jenkins WL, Munns SW, Jayaraman G. A measurement of anterior tibial displacement in the closed and open kinetic chain. J Orthop Sports Phys Ther 25;49-56, 1997.)

Yack and colleagues (1993) also found increased anterior displacement during open kinetic chain exercise (knee extension) compared with closed kinetic chain exercise (parallel squat) through a flexion range of 0 to 64 degrees. Kvist and Gillquist (1999) demonstrated that displacement occurs with even low levels of muscular activity: Generation of the first 10% of the peak quadriceps torque produced 80% of the total tibial translation seen with maximal quadriceps torque. Mathematic models also have predicted that shear forces on the ACL are greater with open chain exercises. Jurist and Otis (1985), Zavetsky and coworkers (1994), and Wilk and Andrews (1993) all noted that changing the position of the resistance pad on isokinetic open kinetic chain devices could modify anterior shear force and anterior tibial displacement. Wilk and Andrews also found greater anterior tibial displacements at slower isokinetic speeds.

Beynnon and associates (1997) used implanted transducers to measure the strain in the intact ACL during various exercises and found no consistent distinction between closed kinetic chain and open kinetic chain activities. This finding contradicts the previous studies and indicates that certain closed chain activities, such as squatting, may not be as safe as the mathematic force models would predict, particularly at low flexion angles.

A protective effect of the hamstrings has been suggested based on the findings of minimal or absent strain in the ACL with isolated hamstring contraction or when the hamstrings were simultaneously contracted along with the quadriceps. Co-contraction of the quadriceps and hamstrings occurs in closed kinetic chain exercises, with a progressive decrease in hamstring activity as the flexion angle of the knee increases. Co-contraction does not occur to any significant degree during open kinetic chain exercise.

Other differences between open and closed kinetic chain exercise have been demonstrated. Closed kinetic chain exercises generate greater activity in the vasti musculature, and open kinetic chain exercises generate more rectus femoris activity. Open chain activities generate more isolated muscle activity and thus allow for more specific muscle strengthening. However, with fatigue, any stabilizing effect of these isolated muscles may be lost and can put the ACL at greater risk. Closed chain exercises, by allowing agonist muscle activity, may not provide focused muscle strengthening, but they may provide a safer environment for the ACL in the setting of fatigue.

In summary, closed chain exercises can be used safely during rehabilitation of the ACL because they appear to generate low anterior shear force and tibial displacement through most of the flexion range, although some evidence now exists that low flexion angles during certain closed kinetic chain activities may strain the graft as much as open-chain activities and may not be as safe as previously thought. At what level strain becomes detrimental and whether some degree of strain is beneficial during the graft healing phase are currently unknown. Until these answers are realized, current trends have been to recommend activities that minimize graft strain, so as to put the ACL at the lowest risk for developing laxity. Open chain flexion that is dominated by hamstring activity appears to pose little risk to the ACL throughout the entire flexion arc, but open chain extension places significant strain on the ACL and the patellofemoral joint and should be avoided. An assessment of randomized controlled trials found that closed kinetic chain exercises produced less pain and laxity while promoting better subjective outcome than open kinetic chain exercises (Andersson et al. 2009).

Rank Comparison of Peak Anterior Cruciate Ligament Strain Values during Commonly Prescribed Rehabilitation Activities

From Beynnon BD, Fleming BC. Anterior cruciate ligament strain in-vivo: A review of previous work. J Biomech 31:519–525, 1998.

Rehabilitation Activity	Peak Strain (0%)	Number of Subjects
Isometric quads contraction at 15 degrees (30 Nm of extension torque)	4.4	8
Squatting with Sport Cord	4.0	8
Active flexion–extension of the knee with 45-N weight boot	3.8	9
Lachman test (150 N of anterior shear load)	3.7	10
Squatting	3.6	8
Active flexion–extension (no weight boot) of the knee	2.8	18
Simultaneous quads and hams contraction at 15 degrees	2.8	8
Isometric quads contraction at 30 degrees (30 Nm of extension torque)	2.7	18
Anterior drawer (150 N of anterior shear load)	1.8	10
Stationary bicycling	1.7	8
Isometric hamstring contraction at 15 degrees (to 10 Nm of flexion torque)	0.6	8
Simultaneous quadriceps and hamstring contraction at 30 degrees	0.4	8
Passive flexion–extension of the knee	0.1	10
Isometric quadriceps contraction at 60 degrees (30 Nm of extension torque)	0.0	8
Isometric quadriceps contraction at 90 degrees (30 Nm of extension torque)	0.0	18
Simultaneous quadriceps and hamstring contraction at 60 degrees	0.0	8
Simultaneous quadriceps and hamstring contraction at 90 degrees	0.0	8
Isometric hamstring contraction at 30, 60, and 90 degrees (to 10 Nm of flexion torque)	0.0	8

Other Rehabilitation Considerations After ACL Reconstruction

Pain and Effusion

Pain and swelling are common after any surgical procedure. Because they cause reflex inhibition of muscle activity and thus postoperative muscle atrophy, it is important to control these problems quickly to facilitate early ROM and strengthening activities. Standard therapeutic modalities to reduce pain and swelling include cryotherapy, compression, and elevation.

Cryotherapy is commonly used to reduce pain, inflammation, and effusion after ACL reconstruction. Cryotherapy acts through local effects, causing vasoconstriction, which reduces fluid extravasation; inhibiting afferent nerve conduction, which decreases pain and muscle spasm; and preventing cell death, which limits the release of chemical mediators of pain, inflammation, and edema. Complications such as superficial frostbite and neuropraxia can be prevented by avoiding prolonged placement of the cold source directly on the skin. Contraindications to the use of cryotherapy include hypersensitivity to cold, such as Raynaud’s phenomenon, lupus erythematosus, periarteritis nodosa, and rheumatoid arthritis.

Perturbation Training for Postoperative ACL Reconstruction and Patients Who Were Nonoperatively Treated and ACL Deficient

Michael Duke, PT, CSCS, and S. Brent Brotzman, MD

Perturbation is defined as a small change in a physical system, most often in a system at equilibrium that is disturbed from the outside or an unconscious reaction to a sudden, unexpected outside force or movement—for example, a football running back who reacts to potential tacklers by cutting, side-stepping, stopping, and quickly starting again or a basketball player who avoids defenders by quick changes in direction and speed. Perturbation training involves applying potentially destabilizing forces to the injured knee to enhance the neuromuscular awareness, neuromuscular response, and dynamic stability of the knee to stabilize the joint. The goal of perturbation training is to educate the patient to elicit selective adaptive muscle reactions of the supporting knee musculature in response to force administered on the platform to gain a knee-protective neuromuscular response.

Nonoperative management of ACL rupture has had limited success in patients who wish to return to high levels of activity. Evidence supports surgical intervention for these patients if they plan to return to their high-level sport (Daniel et al. 1994, Engstrom et al. 1993). For some individuals, however, circumstances may warrant a delay in or avoidance of surgical intervention. Such individuals might include an athlete who needs to demonstrate his or her abilities for scholarship or desires to finish the competitive season, seasonal workers who want to postpone surgery until after the busy work season, or individuals for whom life circumstances or stage of life make surgery undesirable but who want to remain active until they are able to undergo surgery.

Copers

Among patients who opt not to have ACL reconstruction, there is a subset who are better at actively stabilizing the ACL-deficient knee through complex neuromuscular patterns (known as copers). Copers are distinct in their ability to return to full activity despite being ACL deficient with no instability for at least 1 year. They adopt various compensatory patterns of muscle activation that seem to be unrelated to quadriceps strength.

Noncopers

Noncopers are those who are not able to return to full activity and tend to demonstrate a joint-stiffening strategy or a nonadaptive generalized co-contraction of the muscles that stabilize the knee. The noncoper strategy of joint stiffening is commonly seen with early motor learning of unfamiliar activities, and as the task becomes more familiar to the individual, the individual is able to demonstrate more complex motor patterns. Those who are able to return to high functional levels demonstrate alterations in muscle activity that improve stability of the knee joint (Ciccotti et al. 1994, Gauffin and Tropp 1992, Rudolph et al. 1998). Pertubation training has also been shown to improve knee function in noncopers (Logerstedt et al. 2009) with ACL injuries.

Several theories have been proposed to explain the ability to stabilize the knee and other joints. Johansson and Sjolander suggested that an increase in sensitivity of mechanoreceptors in joint structures may result in a higher state of “readiness” of muscles to respond to challenges to joint stability (Fitzgerald et al. 2000, Johansson and Sjolander 1993). The implication is that if the therapist can provide progressively destabilizing challenges to the knee during rehabilitation, the neuromuscular patterns can be altered in a way that improves joint stability despite a lack of passive restraints.

Hartigan et al. (2009) found that those who participated in a perturbation training protocol before ACL reconstruction showed no difference in knee excursion (knee flexion during gait) between the involved and uninvolved knees 6 months after ACL reconstruction. In contrast, a group who participated in only a standard strength ACL program showed significant side-to-side asymmetries. This finding indicates that some form of neuromuscular training, in particular perturbation training, is essential to restore normal movement patterns.

Given that these results show that asymmetries existed at walking speed, the problems are magnified at game speed. Similarly, a clinical trial by Risberg et al. compared a strength-based (ST) rehabilitation program and a neuromuscular control-based (NT) program. Based on their findings, Risberg advocated employing both strength and neuromuscular control based programs.

In reconstructing the ACL, one of the main purposes is to restore passive restraint to anterior translation of the tibia on the femur. Beard et al. (2001) studied tibial translation both preoperatively and postoperatively in patients with ACL deficiency and found that tibial translation actually transiently increased after reconstruction, which the authors attributed to reduction of the protective hypertonicity of the hamstring group, making them less able to restrain tibial movement. Given this finding and the transient loss of the stabilizing effect of the hamstrings, it becomes even more critical to retrain the neuromuscular system to prevent “giving way” episodes with resultant meniscal damage. Perturbation training has been shown to be effective at this.

Several criteria have been described to select the appropriate candidate for a successful outcome with nonoperative treatment of ACL injury (7,8):

• No evidence of joint effusion

• Full passive knee joint ROM, as compared to the uninvolved knee

• Full knee extension during a straight leg raise (SLR) on the involved limb

• A quadriceps femoris maximal voluntary contraction force on the involved limb equivalent to 75% of that on the uninvolved limb

• Tolerance for single-leg hopping on the involved limb without pain

• No concomitant ligamentous or meniscal injury

Once these criteria are met, the screening test is administered as described in Table 4-1. Patients who pass the screening test are considered good candidates for nonoperative rehabilitation.

Table 4-1 Screening Tests for Nonoperative Treatment of ACL Injury

Test	Passing Score
Single, crossover, triple, and timed hop tests (Noyes et al. 1991, Reid et al. 2007)	80% or more of uninvolved limb
Reported number of giving-way episodes from the time of injury to the time of testing	No more than one episode
The Knee Outcome Survey Activities of Daily Living Scale (Irrgang et al. 1998)	80% or more
Subjective global rating of knee function (self-assessed 0%–100%)	60% or more

Augmenting a standard rehabilitation protocol with perturbation training has been shown to greatly increase the likelihood of returning to the competitive season with no episodes of giving way (Fitzgerald et al. 2000). Perturbation training generally is performed in 2 or 3 sessions a week for a total of 8 to 10 sessions, with the patient returning to sport during the last week of training.

The patient is encouraged to respond to the direction and force of the perturbations with purposeful muscle responses designed to prevent or minimize large excursions on the support surface. Gross muscular co-contraction and preparatory stiffening of the joint are discouraged and addressed with additional cues from the physical therapist.

Perturbation training consists of three techniques:

• Roller board translations

• Tilt board perturbations

• Roller board and stationary platform perturbations

Roller board translations consist of the patient standing with both feet on a rolling platform while the therapist applies translational perturbations to the platform (Fig. 4-8). Initially, safety precautions should be used, such as placing the patient in parallel bars or in a doorway, but these can be discontinued once the therapist believes there are no safety issues. The therapist instructs the patient to maintain balance on the board. Progression of the exercise can have various forms, such as the following:

• Predictable and rhythmic to random

• Weak force application to strong force

• Small translations to large translations

• Double-limb stance to single limb

• Visual feedback (watching the board) to eyes closed or looking away

• Patient’s focus directed on the perturbations to sports-specific distractions such as ball tossing or dribbling during perturbations

Figure 4-8 Roller board transitional perturbation technique.

Tilt board perturbations consist of the patient standing on a tilt board while the therapist taps or steps on the edge of the board, causing the board to suddenly tip (Fig. 4-9). The patient is instructed to maintain balance and return to a neutral position after the therapist applies the perturbations. The patient can stand with the board tilting anterior and posterior, medial and lateral, or diagonally in either direction. Progression of the exercise can include all of the aforementioned challenges, with the addition of upright posture progression to progressively deeper squat positions.

Figure 4-9 Tilt board perturbation technique.

Roller board and stationary platform perturbations consist of the patient standing with one limb on the platform and one on the roller board and the therapist applying translational forces to the roller board (Fig. 4-10). The patient is instructed to “match my force” or to prevent the board from moving without co-contraction of the lower limbs. It is important for the therapist to watch for co-contractions and gauge the speed and force of response given by the patient. The patient is learning to selectively activate muscle groups in response to an external challenge. Both the response time and force should improve, indicating the need to further challenge the patient. The following progressions can be made in addition to those already mentioned:

• Side-by-side stance to front or back split stance to sports-specific stance (i.e., baseball infielder stance or quarterback throwing stance)

• Involved limb on roller board to uninvolved limb on roller board

• Wood platform to foam pad (compliant surface)

• Single direction movement to multidirectional

Figure 4-10 Roller board and stationary platform perturbation technique.

The therapist must be attentive to the patient’s response during the training, constantly assessing response time, strength of response, ability to change directions, stability of the knee, and whether the patient demonstrates significant co-contraction. Verbal cues should be given, and appropriate responses should indicate readiness advancement to more difficult challenges.

Perturbation training also can be an effective tool in rehabilitation after ACL reconstruction. Changes in anatomic knee stability depend on the surgery; however, functional and active knee stability can be altered by rehabilitation programs. The goal of any postoperative ACL reconstruction rehabilitation program should be to enhance long-term functional outcomes, and critical to this is the patient’s ability to stabilize the knee joint during high-level functional activities.

Proprioceptive recovery after ACL reconstruction is critical to joint stability. An intact ACL is known to have mechanoreceptors (Schultz et al. 1984, Schutte et al. 1987), and it has been noted by various authors that some reinnervation occurs in ACL grafts after reconstruction, although timing and extent may vary considerably (Barrack et al. 1997, Barrett 1991, Fremerey et al. 2000, Risberg et al. 2001).

Patients who have had ACL surgery demonstrate co-contraction patterns similar to those who are ACL deficient (Vairo et al. 2008). Considering the time of recovery of quadriceps strength and the need for healing of the hamstring after an autograft reconstruction, we recommend that perturbation training begin around 12 weeks after ACL reconstruction. Several criteria should be met before perturbation training is initiated after ACL reconstructive surgery:

• Normal gait, ROM, straight leg raise, and minimal effusion

• Single-limb balance greater than 60 seconds with minimal movement and eyes open

• Single limb squat on the involved side to 45 degrees with no functional genu varum/valgum during the squat and good pelvic control

Once these criteria are met, a program similar to that outlined for nonoperative treatment of ACL injury can be used.

Although useful for both nonoperative and postoperative management of ACL injuries, perturbation training can be used for any condition that results in abnormal neuromuscular patterns affecting gait or sports movements. Other conditions that also may benefit from perturbation training include the following:

• Other ligament sprains of the knee

• Any joint instability of the ankle, knee, or sacroiliac joint

• Upper extremity conditions (i.e., wrist, elbow, or shoulder), with modifications

• Vestibular conditions

• Knee OA (Fitzgerald et al. 2002)

The concept of improving neuromuscular control of complicated movements through perturbation training can be successfully applied to any sport. Baseball pitchers at various phases of the throwing motion can be perturbed at the upper extremity or trunk or lower extremity. Golfers at various phases of the swing can be similarly challenged. Basketball players while in a post position or while shooting can be perturbed to improve their ability to maintain position or make a steady shot. Any running sport can benefit from single-leg balance and perturbations to improve stability and neuromuscular control to maintain position despite challenges from opponents or surface variations. Extensive study of perturbation training and ACL injury does not imply that this is its only use. Further research is necessary to determine the full extent to which perturbation can be implemented.

There is significant evidence in the literature for the use of the previously described techniques of perturbation training for knee stability. The roller board and rocker board are designed to apply destabilizing forces from the ground up, simulating various neuromuscular patterns during athletic activities where there is no contact with objects or other players. Brotzman and Duke propose that in addition to the current perturbation protocol, athletes will benefit from a variety of perturbations from the top down.

Sports such as wrestling, basketball, football, rugby, and martial arts are all inherently contact sports, and the athletes are repeatedly exposed to external forces to knees, hips, torso, shoulders, upper extremities, head, and neck. By adding perturbing forces that begin light and predictable and progress to functional speeds and intensity, the athlete will be better prepared for the contact that will occur during training and competition.

Standing static push perturbations consist of the patient standing, feet on floor shoulder-width apart, knees slightly bent, and eyes looking forward. The therapist can apply force to knees, hips, and shoulders in varying directions, intensity, and predictability, instructing the patient to maintain position. Add a compliant surface under the feet to increase difficulty. Add sport-specific distractions to further increase difficulty, such as dribbling a basketball, playing catch with a baseball, and the like. Given the use of hands in wrestling and other sports, incorporating upper extremities will also be valuable.

Standing stick pull perturbations consist of the patient standing in a similar position as just described, but the patient holds a stick horizontally with two hands in front, palm-down grip. The therapist can then apply challenges to position in all three planes of movement, again with the patient instructed to resist movement and maintain position. To provide challenges that simulate the athlete’s sport, the therapist may place the athlete in positions of function to their sport including kneeling or half-kneeling or tandem stance or provide the training with the patient’s eyes closed.

Basketball, football, rugby, and other players often encounter outside forces (other players) while in the air. Perturbation training for these athletes may include forces applied while the feet are off the ground.

Midair perturbations consist of having the patient perform vertical jumping while the therapist applies force through a Sport Cord attached around the patient’s waist. With the force being applied while the patient is in midair, the landing direction has a horizontal component to it and challenges the knee stability in that way. The critical part to the exercise is the landing. The therapist should pay close attention to abnormal landing patterns that might indicate poor neuromuscular control and correct these. Jumping technique, angle of force by the therapist, amount of force, direction of jumping, and attention on task or distractions all can be modified as the athlete improves in skill.

These techniques can be applied in conjunction with perturbation training for knee rehabilitation. As with previously described perturbation training, these should be performed after an appropriate level of strength and stability have been achieved. Twelve weeks of rehabilitation should be completed for patients post-ACL surgery prior to beginning this program. The long-term benefit of these three techniques will require further research.

Gender Issues in ACL Injury

Lori A. Bolgla, PT, PhD, ATC

In 1972 the United States passed Title IX of the Educational Act that mandates equal treatment of females in university-level athletic programs. The passage of this act has fostered a dramatic increase in the participation of females at all levels of competition. With this change comes a significant increase in the number of injuries sustained.

ACL Injury in the Female Athlete

Overview

ACL injury represents one of the most serious knee injuries, with annual costs for management exceeding $2 billion. Although surgical reconstruction and rehabilitation significantly improve the return to recreational and occupational activities, outcomes from long-term studies suggest the eventual development of knee osteoarthritis in many ACL-injured knees. The incidence rate of ACL tears for female athletes ranges between 2.4 and 9.7 times their male counterparts competing in similar activities. Together, these findings have led researchers to identify risk factors and develop prevention programs aimed at reducing female ACL injuries.

More than 70% of all ACL injuries occur via a noncontact mechanism during activities such as cutting and landing. Evidence has shown that females perform these activities with the knee positioned in maladaptive femoral adduction, femoral internal rotation, and tibial external rotation (referred to as dynamic valgus). These combined motions apply high valgus loads onto the knee, which can lead to ACL injury (Fig. 4-11). Another contributor to ACL injury is landing from a jump with the knee in a minimally flexed position (rather than the more desired flexed knee position). This position results in greater quadriceps activation relative to the hamstrings, leading to increased anterior tibial translation on the femur.

Figure 4-11 A, Dynamic knee valgus resulting from excessive hip adduction and internal rotation after landing from a box jump. Because the foot is fixed to the floor, excessive frontal and transverse plane motion at the hip can cause medial motion of the knee joint, tibia abduction, and foot pronation. B, Frontal plane motions of the pelvis and trunk can influence the moment at the knee. This example illustrates landing from a jump on one foot. (1) With the pelvis level, the resultant ground reaction force vector passes medial to the knee joint center, thereby creating a varus moment at the knee. (2) Hip abductor weakness can cause a contralateral pelvic drop and a shift in the center of mass away from the stance limb. This increases the varus moment at the knee (i.e., the perpendicular distance from the resultant ground reaction force vector and the knee joint center increases). (3) Shifting the center of mass over the stance limb to compensate for hip abductor weakness can create knee valgus moment (i.e., the ground reaction force vector passes lateral with respect to the knee joint center). In this scenario, medial movement of the knee joint center (i.e., valgus collapse) exacerbates the problem. C, Low-risk and high-risk landings. The figure on the left shows a high-risk participant where the patella has moved inward and ended up medial to the first toe. The figure on the right shoes a low-risk participant where the patella has remained inward in line with the first toe.

Of note, female athletes have been shown to perform athletic maneuvers with maladaptive variation from their male counterparts on landing including decreased knee and hip flexion, increased quadriceps activation, and greater dynamic knee valgus angles and moments (Powers 2010).

Intrinsic and extrinsic factors (Table 4-2) may account for the higher incidence of ACL injury in the female athlete. Intrinsic factors are anatomic or physiologic in nature and are not amenable to change. Extrinsic factors are biomechanical or neuromuscular in nature and are potentially modifiable. Clinicians have focused much attention on these extrinsic factors for the development and implementation of ACL injury prevention and rehabilitation programs.

Table 4-2 ACL Injury in the Female Athlete

Intrinsic Factors Associated with Female ACL Injury

Intercondylar notch size

ACL size

Physiologic laxity (generalized joint and ligamentous)

Hormonal fluctuations

Extrinsic Factors Associated with Female ACL Injury

Intrinsic Risk Factors

ACL injury commonly occurs with the knee positioned and stressed close to full extension, causing an abutment of the ACL within the intercondylar notch. Although a decreased intercondylar notch size may contribute to ACL injury, data have not supported a sex difference between intercondylar notch size and ACL injury. Instead, individuals with a smaller intercondylar notch appear to be more susceptible to ACL injury, regardless of sex.

Recent attention has focused on ligament stiffness. Hashemi et al. (2008) reported that the ACL from female cadavers exhibited a decrease in length, cross-sectional area, and volume compared to males. They concluded that inherent ligament weakness, in combination with a smaller intercondylar notch size, might contribute to the ACL injury gender bias.

Physiologic laxity (e.g., general joint laxity and ligamentous laxity) represents another intrinsic factor. Because the ACL primarily limits excessive anterior tibial translation relative to the femur, injury can occur when joint movement exceeds ligamentous strength. Uhorchak et al. (2003) have reported that females with physiologic laxity have a 2.7 times higher risk for sustaining an ACL injury.

Finally, increased estrogen levels during the ovulatory and luteal phases of the menstrual cycle may increase ACL laxity, making the female athlete more prone to injury. To date, prior works have not shown a strong association between hormone fluctuations and ACL injury. The reader should note that prior works have used small sample sizes and relied on subjective histories to determine the phase of the menstrual cycle that an injury occurred. Additional investigations are needed to better understand this influence.

Extrinsic Risk Factors

Extrinsic factors include biomechanical (e.g., kinematics and kinetics) and neuromuscular (e.g., muscle strength, endurance, and activation) characteristics. Unlike intrinsic factors, clinicians can modify these factors with interventions, providing the basis for many ACL injury prevention and rehabilitation programs.

As mentioned previously, dynamic knee valgus applies high loads onto the ACL that can cause injury. During the past 10 years, researchers have ascertained that female athletes perform higher demanding activities in positions making them more vulnerable to ACL injury. It is important to note that structures both proximal and distal to the knee can influence ACL loading. Ireland (1999) has described the position of no return to explain gender differences regarding trunk and lower extremity kinematics and muscle activity (Fig. 4-12). The following summarizes extrinsic factors making the female athlete more vulnerable to ACL injury during running, cutting, and landing tasks:

• Overwhelming data infer that females perform these tasks (e.g., landing) with increased dynamic knee valgus from femoral internal rotation, femoral adduction, and tibial external rotation (Fig. 4-11A).

• Females utilize greater quadriceps activation relative to the hamstrings. This muscle imbalance can lead to excessive tibial anterior translation, especially with the knee positioned close to full extension.

• Females tend to activate the quadriceps more than other muscle groups such as the hip extensors and ankle plantar flexors. Muscle activation throughout the entire lower extremity can dampen applied ground reaction forces and reduce valgus knee loading.

• Females with evident hip musculature weakness perform demanding tasks with increased dynamic valgus. The amount of dynamic valgus exhibited during demanding tasks further increases with the onset of gluteus medius fatigue.

• Preliminary evidence infers decreased trunk neuromuscular control as a predictor of ACL injury.

Figure 4-12 A, Position of no return.

B In the “position of no return” (i.e., the high-risk position), the head is forward, the lumbar spine is hyperlordotic, and the pelvis is anteriorly rotated. Internal rotation at the relatively straight knee and subsequent tibial external rotation and foot pronation are also seen. The safe position shown on the left is more neutral and more flexed.

(Reprinted with permission from Ireland M. The Female Athlete. Saunders, Philadelphia, 2002. Fig 43-4.)

ACL Injury Prevention and Rehabilitation Programs in Female Athletes

Identification of these extrinsic factors thought to contribute to ACL injury in the female athlete has provided the basis for the development and implementation of ACL injury prevention and rehabilitation programs. These programs typically include strengthening and neuromuscular training in combination with instruction on proper lower extremity alignment during cutting and landing tasks. Preliminary data have shown promising results for the effectiveness of these programs for preventing ACL injury in high school and collegiate-level female athletes.

ACL injury prevention programs should incorporate strengthening and neuromuscular training for the knee, hip, and trunk muscles on both stable and unstable surfaces (Figs. 4-13 through 4-16). The athlete should perform all plyometric-type exercises with the knees in a more varus, flexed position to reduce valgus loading and facilitate quadriceps/hamstring co-contraction (Fig. 4-17). Sport-specific drills that emphasize proper lower extremity alignment are another important consideration (Figs. 4-18 and 4-19). Throughout the process, the clinician should provide the athlete continual feedback regarding proper technique when performing cutting and landing activities. The female athlete should practice proper deceleration techniques during cutting maneuvers, with a special emphasis on the avoidance of pivoting on a fixed foot. She should perform landing activities with an emphasis on keeping the knees over the toes (to minimize knee valgus) and landing as soft as possible using increased knee flexion (to dampen ground reaction forces).