The anterior cruciate ligament (ACL) primarily resists anterior tibial translation on the femur; it also prevents hyperextension and extreme varus, valgus, and rotational movements around the knee.⁷¹ The cruciate ligaments are intracapsular structures, which can produce a joint effusion when injured. This anatomic relationship is contrasted with the medial and lateral collateral ligaments, which are extracapsular structures. When the medial collateral ligament (MCL) is sprained, there is generally less swelling and no intraarticular effusion because the resultant bleeding from the injured tissues can evacuate the area and the fluid is not restrained within the joint capsule.

Etiology

It is well published that female athletes tear their ACLs at a higher rate than their male counterparts.¹ The common mechanism for both contact and noncontact injuries results in a combined force of external rotation of the hip, valgus stress at the knee joint, and internal tibial rotation with or without knee hyperextension while the affected foot is planted (Fig. 18-1).^{24,73,74,77,91,97}

Fig. 18-1 Mechanism of injury to the anterior cruciate ligament (ACL). Typically, the ACL is injured in a noncontact deceleration mechanism of combined forces of external tibial rotation, valgus stress, internal tibial rotation, and knee hyperextension.

Clinical Evaluation

The PTA must be aware of various clinical ligament stability tests to accurately and effectively communicate changes in a patient’s stability to the supervising physical therapist (PT) and physician. Although ligament stability tests are part of the initial evaluation procedures used by the physician and PT, the PTA can better understand the static and dynamic restraints of the knee and develop a more comprehensive view of rehabilitation when exposed to the rudimentary concepts of ligament stability testing.

Perhaps the most common, specific, and clinically useful ligament stability test for the ACL is the Lachman examination (Fig. 18-2).⁴⁷ The patient is supine on an examining table with the affected knee flexed to approximately 25° to 30°. One hand is used to stabilize the distal femur, and the other hand grasps the proximal tibia. An anterior and posterior force is gently directed to the proximal tibia. The integrity of the ACL should be observed, and the degree of anterior tibial translation should be noted.

Fig. 18-2 The Lachman examination. This examination tests the stability of the anterior cruciate ligament (ACL) with the knee flexed 25° to 30°. If the tibia can be displaced anteriorly in reference to the stabilized distal femur, then an injured ACL should be considered.

The anterior drawer test (Fig. 18-3) is another clinical examination used to approximate the degree of anterior tibial translation relative to the fixed femur. This examination is a less sensitive test to challenge the integrity of the ACL, and is instead thought to assess the meniscotibial ligaments and the mobility of the menisci on the tibia.⁴⁷ The examination is performed with the patient supine and the affected knee flexed to approximately 90°. Stabilize the affected limb by sitting on the patient’s foot. Both hands should be used to grasp the proximal posterior tibia, with the thumbs on the anterior joint line of the knee. An anterior and posterior force should be exerted to the proximal tibia, and the amount of joint separation of the tibia relative to the femur should be observed.

Fig. 18-3 The anterior drawer test. With the injured knee flexed to 90°, the clinician grasps the proximal tibia and provides an anteriorly directed force. If the tibia displaces anteriorly in reference to the stabilized distal femur, then the anterior cruciate ligament may be considered injured.

Other relevant tests for the stability of the ACL incorporate multidirectional rotation examinations to acknowledge the presence of anterolateral rotator instability (ALRI), anteromedial rotatory instability (AMRI), posteromedial rotatory instability (PMRI), and posterolateral rotatory instability (PLRI). ALRI is the more common multiplanar instability encountered.47,91 The Hughston jerk test and pivot shift test are commonly used examinations to sublux and reduce the tibia relative to the femur.⁴⁷

Throughout the performance of the examination, complete muscle relaxation of the hamstrings, quadriceps, and gastrocnemius–soleus muscle group must be maintained. Swelling, intraarticular effusion, and muscle spasm falsely stabilize the knee, rendering the examination meaningless.⁵¹

Operative Management

The PTA must recognize the various surgical procedures used to correct functional instabilities related to ACL injuries and be aware of the short- and long-term ramifications of ligament healing to more effectively deliver sound rehabilitation. Therefore this section provides a rudimentary description of the most common ACL surgical procedures as they relate to the scope and practice of the PTA.

An autograft reconstruction uses tissue from the body of the patient. Various tissues are used for grafts, including the gracilis tendon, fascia lata, semitendinosus tendon, and quadriceps muscle tendon. The bone–patellar tendon–bone (BPTB) autograft is a commonly used graft because of its boney anchor points. The BPTB and bundled gracilis and semitendinosus autografts have all been shown to have greater tensile strength to sheer forces than the original ACL.20,72 An allograft refers to biologic tissue taken from a human cadaver. The major risks of using allograft involve disease transmission and problems with effective sterilization procedures that do not weaken the graft.²⁸

The arthroscopic central one-third BPTB autograft procedure involves harvesting the graft from the involved knee (Fig. 18-4, A) and surgically routing this structure through tunnels placed in the femur and tibia in a way that duplicates normal ACL anatomy, then securing the graft to the bone to allow for stable healing (Fig. 18-4, B-C). A small incision is made in the knee, and a small diameter drainage tube is inserted to help evacuate the joint of residual bleeding, which may increase the risk of arthrofibrosis if allowed to accumulate. This small drain is usually removed after a few days when the bleeding is controlled. Even with the placement of the drain, postoperative arthrofibrosis is a clinically significant problem that can occur.⁴⁵ Sterile bandages are placed over the incisions, and the patient’s leg is often placed in a hinged brace locked in 0° of flexion.

Fig. 18-4 Arthroscopic central one-third bone–patellar tendon–bone (BPTB) autograft procedure. A, BPTB harvest. A pedicle of bone from the tibial tubercle and patella is removed along with a full-thickness graft of the patellar tendon to be used to anatomically reconstruct the anterior cruciate ligament. B, The graft is placed within the knee joint, through tunnels drilled in the tibia and femur. C, The graft tissue and bone pedicles are secured with anchor screws.

Healing of the graft after surgery

Ligament healing processes and revascularization of graft material are vital concerns in the prescribed rehabilitation program designed by the supervising PT. The appropriate progression of the rehabilitation program depends on the PTA’s awareness of the various stages of healing after an autograft procedure. Once the graft is harvested and surgically routed within the knee, it begins a gradual process of avascular necrosis over the first 6 to 8 weeks.²⁸ The graft gradually loses strength and is quite fragile during the first 2 months after surgery, so excessive loads and forces that would compromise the healing of the graft must be avoided during this time period. The graft slowly revascularizes, and at approximately 3 months the tensile strength of the graft is less than 50% of its original strength.^28,75 Graft strength may take as long as a year to mature and may never reach preoperative tensile strength after the graft cell death and subsequent revascularization process.

Postoperative rehabilitation

The rehabilitation program after ACL reconstruction is designed to protect the graft; reduce pain and swelling; increase joint motion while improving strength, endurance (local muscular endurance, as well as aerobic fitness), flexibility, and proprioception; and ultimately return the knee to full function. This task is organized sequentially and is constantly modified, based on the patient’s individual response to surgery and rehabilitation. The PT and PTA must work together to assess and adjust programs based on the individual’s ability and goals.

In general terms, ACL reconstruction rehabilitation can be organized into three broad, interconnecting phases ⁹¹:

1. Maximum-protection phase: From the first day postoperatively to approximately the sixth week after surgery.

2. Moderate-protection phase: From approximately the 7th to the 12th weeks after surgery.

3. Minimum-protection phase: From the 13th week after surgery until return to activity.

This section reviews each phase separately and introduces the PTA to the many variables and individual differences among patients. The importance of reassessment of initial evaluation data and the need for open communication and teamwork with the supervising PT cannot be emphasized too strongly.

Maximum-protection phase (0-8 weeks)

As the graft slowly loses its strength (6 to 8 weeks after surgery), excessive loads and forces that stress the ACL must be avoided. These forces are controlled primarily by joint protection with range-limiting hinged braces and avoidance of anterior tibial translation, shearing forces, and rotational motions.

Control of swelling is important throughout each phase of rehabilitation. Postoperative swelling can have a profound negative effect on the progress of the patient, even with suction drains inserted at the time of surgery. Swelling inhibits muscle contractions, contributes significantly to pain, limits joint motion, and can stimulate arthrofibrosis.⁸⁵ Cryotherapy, elevation of the limb, and the use of a compression wrap help to minimize swelling.

The patient’s ability to achieve early active range of motion (AROM) is an essential component of the maximum-protection phase. Patellar motion (caudal, cephalic, medial, and lateral glide) must be an immediate goal for the restoration of knee motion. Scarring from the graft harvest site and the suprapatellar pouch typically inhibits free patellar motion and full knee ROM.⁸⁵ Initially the PTA must provide gentle stretching of the patella (Fig. 18-5, A–C) and instruct the patient to perform these stretches two to three times daily. Generally, full knee extension is achieved soon after surgery; if not, passive prone or supine knee extension stretches can be used judiciously to gradually increase knee extension (Fig. 18-5, D). In addition to active and passive knee flexion and extension, some authors advocate the use of a continuous passive motion (CPM) device for a limited time very early in this phase.^28,76,91 The use of a CPM device has been suggested to help maintain a normal articular surface as well as to help evacuate synovial joint hemarthrosis and aid in the prevention of joint contracture.^28,76,91 The use of CPM generally is limited to the period immediately after hospitalization.²⁸

Fig. 18-5 Postoperative manual patellar stretching is used to enhance knee motion. If the patella becomes adhered to surrounding tissues, normal knee flexion and extension cannot occur. A, A caudal (inferior)-directed force applied to the patella. B, A cephalic (superior)-directed force. C, The patella being directed medially. D, Prone passive knee-extension stretch. Note the application of a folded towel under the thigh to elevate the leg and avoid compression of the patella and patellar tendon against the end of the table.

Weight-bearing status remains a controversial subject in the literature. In general, weight bearing with crutches is allowed as tolerated immediately after surgery, and patients should be full weight bearing somewhere between 2 and 6 weeks from surgery.21,28,91

The primary focus of strengthening the postoperative ACL patient during the maximum-protection phase is to encourage quadriceps control and hamstring strength. Strengthening exercises during the maximum-protection phase focus on isometric co-contractions of the quadriceps and hamstrings. Hamstring strengthening is emphasized during this phase of maximum protection because they act as dynamic stabilizers to limit anterior tibial shearing forces.28,63,76,77,91 Both standing leg curls and supine leg curls can be initiated during this phase if a brace is used.

Exercises that do not strain the ACL include ¹⁰:

Isometric hamstring muscle contraction exercises at 15°, 30°, 60°, and 90°

Isometric quadriceps contractions at 0° and 90°

Simultaneous contraction of the quadriceps and hamstring muscles at 60° and 90°

Active flexion-extension motion of the knee from 60° to full flexion ⁸¹

Passive flexion-extension motion of the knee without muscle contraction

Open kinetic chain (OKC) active knee extension, with or without resistance, causes an anterior tibial translation force relative to the femur that stresses the new graft. The largest anterior tibial translational forces occur between the knee flexion angles of 30° to 50°.⁸¹ This stated knee range of motion (ROM) should be completely avoided when performing OKC knee extension exercise in the early rehabilitation phases of ACL reconstruction.

Four-way hip (flexion, extension, abduction, and adduction) and calf-strengthening exercises as well as stationary bicycling are also encouraged during this phase. The criteria to be achieved by the patient before advancing to the moderate-protection phase include the following:

ROM from 0° extension to 120° of flexion

Full weight bearing (FWB) with normal gait mechanics

Quadriceps control

Hamstring control

Controlled pain and swelling

A minimum of 6 weeks from the day of surgery

Posterior Cruciate Ligament Injuries

The primary function of the PCL complex is to restrict posterior tibial translation. It acts as a secondary restraint to tibial varus, valgus, and external rotations.¹⁰⁰ Isolated PCL injuries occur less often than ACL injuries.^7,17,22 PCL injuries are most commonly the result of some sort of trauma to the knee. Although high-velocity knee injuries often result in PCL tears in combination with other ligamentous injuries, this chapter will deal only with isolated PCL injuries.¹⁰⁰

Etiology

The most common mechanism of PCL injury is a fall on a hyperflexed knee that results in a posterior translation of the tibia on the femur (Fig. 18-12).^22,47,100 Other mechanisms include a dashboard injury from a motor vehicle accident that also causes the tibia to translate posteriorly on the femur. Hyperextension injuries can also tear the PCL, however this commonly will result in a concomitant ACL injury.¹⁰⁰

Fig. 18-12 Mechanism of posterior cruciate ligament injury. With the knee flexed, the proximal tibia is driven in a posterior direction.

Clinical Evaluation

Clinical examination of the PCL may be very complex and begins with a careful history to determine the mechanism of injury. When eliciting a history from a patient with an acute, isolated PCL tear, unlike with an ACL tear, the patient will often not report feeling a pop or tear.¹⁰⁰ Patients with acute PCL tears will typically have mild to moderate knee effusion, a slight limp, pain in the back of the knee, and will often lack full flexion of the knee. More instability is experienced with combined injuries than with isolated tears. Patients with chronic PCL tears may complain more of disability, having difficulty doing things such as walking up or down inclines secondary to increased tibial movement on the femur.¹⁰⁰

The most accurate test for the integrity of the PCL is the posterior drawer test.¹⁰⁰ This test is performed with the patient supine, the knee at 90° flexion, and the tibia in neutral, external, and internal rotations. As seen in Figure 18-13, A, a positive posterior drawer test is observed when the tibia sags, or subluxes, posteriorly relative to the femur. In cases of isolated PCL tears, there is less posterior tibial translation with internal tibial rotation because the MCL and posterior oblique ligament contribute to this as a secondary restraint. Therefore there will be greater posterior tibial translation with the tibia in external rotation when the MCL and posterior oblique ligaments are not compromised. The examiner may produce a false-positive anterior drawer sign, where the posterior tibial sag actually is being reoriented to the neutral position rather than a true anterior translation occurring (Fig. 18-13, B).

Fig. 18-13 Anterior drawer test. A, Starting position. If the posterior cruciate ligament injury is torn, the proximal tibia will be in a posterior tibial sag initial reference position. B, A false-positive anterior drawer test can be seen when the tibia translates forward during the drawer test because the torn posterior cruciate ligament (PCL) injury places the tibia posterior to the femur; therefore when the clinician directs an anterior force, the tibia appears to actually displace anterior to the femur.

Another PCL laxity test is the Godfrey posterior tibial sag test. The patient is supine with the hip and knee of the affected limb held at 90°. Hold the heel of the affected limb and allow the tibia to translate, sublux, or sag posteriorly by gravity (Fig. 18-14).

Fig. 18-14 Godfrey tibial sag test. This is a clinically sensitive test to view the reference of the proximal tibia in relation to the distal femur with the leg flexed to 90°.

Operative Management

Current surgical indications for PCL injuries include combined ligamentous injuries involving the PCL, symptomatic grade III laxity, and bony avulsion fractures.¹⁰⁰ There are a number of graft options for patients seeking a PCL reconstruction. Autologous tissues that are available include BPTB and hamstring and quadriceps tendons, of which the BPTB is the most frequently used. To decrease harvest site morbidity and surgical time, the Achilles allograft is an alternative to the autografts just listed.^22,29,100

Postoperative rehabilitation

Postoperative treatment may begin as quickly as the day after surgery. Patients may present with use of a knee immobilizer or hinged knee brace most often locked in full extension and use of crutches to decrease stress placed through the surgically repaired knee. Weight-bearing restrictions after PCL reconstruction vary from immediate full weight bearing to partial weight bearing (PWB) for 4 to 6 weeks.22,29

Maximum protection phase

Early physical therapy will include quadriceps setting, multiplane straight leg raises, patella mobilization, and ROM exercises to gain full extension. Hamstring isometrics at angles greater than 30° have been shown to increase strain on the PCL, and therefore should be avoided in the maximum-protection phase.⁶³ Minimizing full knee flexion from 60° to 90° is necessary early in the rehabilitation to protect the healing PCL graft. Generally, full knee flexion ROM can be achieved by 2 months after surgery.²²

Moderate and minimum protection phases

These phases of rehabilitation are similar to that of the postoperative ACL in terms of goals and time frames. Considered an agonist of the PCL, the quadriceps should be emphasized more than when rehabilitating a patient from an ACL reconstruction.⁶³ The goal of the moderate protection phase (6 to 12 weeks from surgery) of rehabilitation is to restore full ROM and progress strength of the affected leg. The minimum protection phase consists of progressing strengthening exercises from bilateral to unilateral. Running and plyometric exercises for the athletic patient should be progressed in a similar fashion to that of rehabilitating the postoperative ACL. Return to sport can range from 6 to 9 months from surgery.

Nonoperative Rehabilitation

Nonoperative treatment is indicated for patients with acute, isolated grade I or II PCL tears.¹⁰⁰ Patients may present with a knee immobilizer or hinged knee brace, along with crutches. Patients will begin physical therapy immediately to focus on decreasing inflammation, maintaining quadriceps tone, and restoring knee ROM. Rehabilitation exercises will include quadriceps isometrics, multiplane straight leg raises, and ROM. CKC strengthening may begin after 2 to 4 weeks as swelling, pain, and ROM improve. As mentioned previously, quadriceps strengthening should be emphasized because of the agonistic nature they have with the PCL to prevent posterior tibial translation.^26,63 Stationary bike, elliptical, or pool work may be implemented to increase cardiovascular fitness. Plyometric and sport specific training may be implemented once adequate strength is demonstrated and the patient shows no signs of pain or swelling. Typical return to sport is approximately 6 to 8 weeks with low grade PCL sprains.¹⁰⁰

Medial Collateral Ligament Injuries

Etiology

Injuries to the MCL are the most common ligament injuries seen in the knee.31,58,98 The MCL can be injured by direct contact to the lateral knee resulting in a valgus stress to the knee (Fig. 18-15, A). Uncommonly, a noncontact valgus or rotational stress to the knee can produce an isolated tear of the MCL when the lower leg is fixed and the tibia rotated externally (Fig. 18-15, B). Upon injury, patients may feel or hear a pop, but more commonly state they felt a tearing or pulling on the medial aspect of the knee. Patients will often present with swelling, and more severe sprains may present with ecchymosis. Patients will also walk with a limp; as they will be very hesitant to fully extend the knee because of increased stress and pain.