Orthopedic Management of the Knee

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18

Orthopedic Management of the Knee

Kenneth Bush, Justin Rossetter, Matthew Smith and Michael Allen

The physical therapist assistant (PTA) is frequently challenged to safely and effectively manage acute, chronic, and postsurgical orthopedic conditions of the knee. This chapter presents common pathologic conditions of the ligaments, meniscus lesions, patellofemoral diseases, extensor mechanism disorders, and fractures of the knee, as well as rehabilitation procedures related to total knee joint replacement. This chapter gives the PTA an appreciation of various knee ailments, mechanisms of injury, and specific tissue healing constraints, and provides an introduction to the rationale behind criterion-based rehabilitation programs for the knee.

Although the knee at first glance appears to be a simple synovial joint, its position and ligamentous and soft tissue support actually reveal a very complex structure. Because of this complexity, the PTA is strongly encouraged to review pertinent knee joint anatomy and functional mechanics before and throughout this study.

LIGAMENT INJURIES

Ligament injuries of the knee refer to various degrees of sprains that may lead to ruptures of the ligament, manifested by loss of joint function. Knee ligament sprains and joint instability are complex problems involving various degrees of straight-plane or combined rotatory instability. Knee ligament sprains may be defined as follows:

Anterior Cruciate Ligament Injuries

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

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.

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.

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.

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 phases91:

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, AC) 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

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 include10:

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:

Moderate-protection phase (6-12 weeks)

To advance to this level the patient must be FWB and should be able to demonstrate proper gait mechanics. Immobilization is generally discontinued around the fifth or sixth week postoperatively.21 Control of pain and swelling with the use of cryotherapy, compression, and elevation continues as indicated.

Closed kinetic chain (CKC) exercises are a system of interdependent articulated links in which motion at one joint produces motion at all other joints in the system in a predictable manner. CKC exercises and progressive proprioceptive tasks (to stimulate the afferent neural input system) are initiated and progressed throughout this phase. Gradual CKC progressive loads are essential to encourage functional muscle control, confidence in the use of the affected limb, and help stimulate neuromuscular coordination. Initial instruction in CKC exercises begins with the patient braced to protect the healing graft. Standing and shifting of body weight from the nonaffected limb to the affected limb is a safe and appropriate introduction to CKC exercises. Once the patient demonstrates confidence, muscle control, and stability, the brace is removed (with prior consultation and concurrence from the supervising PT) and the patient is allowed to shift weight without braced support. The leg press is used as a CKC exercise in a short-arc motion early in the moderate-protection phase while the patient is braced (Fig. 18-6). Progressive ROM exercises are allowed as tolerated. Standing wall slides also are introduced during the moderate-protection phase if the affected limb is braced and the tibia is kept vertical to avoid an anterior tibial translation force (Fig. 18-7). The short-arc step-up is an excellent exercise used to stimulate quadriceps control and strength. A biofeedback system can be used in conjunction with step-ups to encourage appropriate quadriceps firing patterns (Fig. 18-8).

Stationary cycling should be progressed with added time and resistance throughout this phase. The stationary bicycle is used initially to encourage ROM, but during the middle and later stages of this phase the bicycle can be used as an aerobic conditioning tool if the patient has achieved the required ROM, strength, and stability to perform endurance activities. Stair-steppers and inclined walking can also be introduced during this phase if the ROM and intensity of the resistance on the apparatus are modified and controlled initially to allow for protected joint motion (Fig. 18-9). To stimulate greater strength and local muscular endurance of the quadriceps, the patient can be instructed to perform the stair-stepper in a reverse manner.

Throughout this phase the patient is encouraged to maintain patellar, hamstring, and quadriceps-stretching exercises; normal gait mechanics; a general fitness program of strength and endurance activities that do not stress the affected limb; ice application after exercises; and joint-protection principles.

Criteria that must be met by the patient before progressing to the next phase include the following:

Minimum-protection phase (12-24 weeks)

The minimum-protection phase signals the return to more normalized activities and the introduction of more challenging functional activities. Isolated knee ligament stability tests (e.g., Lachman test, anterior drawer test, and pivot shift test) are performed at the discretion of the PT and physician, usually during the moderate-protection and minimum-protection phases of rehabilitation. Ongoing documentation of the stability of the affected limb is essential to justify progression to more challenging exercises and quantify the clinical results of the surgery. The use of isokinetic testing of the involved limb is also left to the judgment of the PT and physician. Generally, isokinetic examinations are reserved for the moderate-protection and minimum-protection phases. Certain precautions must be taken to minimize the tibial translation forces produced with isokinetic testing and training to protect the healing graft. Positioning the pad proximally on the tibia helps to protect the reconstructed ACL against excessive anterior tibial translation forces.91

More progressive proprioceptive exercises can be initiated when clinical testing demonstrates improved strength, neuromuscular control, and stability of the ligament. The use of a balance board and minitrampoline further challenges the mechanoreceptor system (Fig. 18-10). Standing knee extension with resistance provided by elastic tubing is an excellent CKC exercise that encourages quadriceps control in more functional positions (Fig. 18-11).

A pool running program progressing to a straight-line interval land running program can start later in this phase. Plyometric exercise is also suggested for individuals returning to athletic activities. The inclusion of bilateral ballistic movements, progressing to unilateral movement should be included in the rehabilitation of athletes in order to prepare these individuals for the demands of their sport. It is important to understand that strengthening and plyometric exercises in this phase should not only be progressed from bilateral to unilateral, but also progressed from sagittal, to frontal, to transverse planes of movement.

Progressive strengthening of the entire lower extremity includes isokinetic velocity spectrum training, and isotonic eccentric quadriceps strengthening. The PTA must be constantly aware that rehabilitation after ACL reconstruction involves the entire body and not just the affected limb. Care must be taken to involve all muscle groups, as well as the sensory input systems and aerobic system throughout each phase of rehabilitation. Returning the patient to functional activities is the primary focus of the rehabilitation team.

Frequently, other structures are injured along with the ACL. The rehabilitation plan outlined does not account for possible injury to the meniscus, posterior cruciate ligament (PCL), MCL, lateral collateral ligament (LCL), or joint capsule; associated fractures; or impaired neurovascular structures. The complex nature and vast array of combined injuries dictates modifications at each level of rehabilitation and prolongs the healing process. Common injuries associated with an ACL rupture include a concomitant MCL sprain with a lateral meniscus tear.6,84 In regard to an injured MCL, or débrided meniscus, there will not be a large alteration to the rehabilitation process. In the case of a meniscus repair, it is common for the ACL reconstruction and the meniscal repair to be staged at different times ranging from 3 to 5 months apart. This is done to individually maximize the rehabilitation outcomes of the two surgeries. It has been found that surgical repair of both the ACL and meniscus at the same time yields poorer outcomes than staging the surgeries at separate healing intervals.14

Nonoperative Rehabilitation

The PTA also must be aware that isolated ACL injuries may dictate a nonsurgical course of treatment. The physician must decide if the patient is best suited for surgery or should be treated nonoperatively. If the patient is treated nonoperatively, the rehabilitation program progresses at a faster pace, although the injured knee must still be protected and allowed to heal from the trauma of the initial injury. The maximum-protection phase should range from 2 to 4 weeks, moderate-protection phase should range from 3 to 12 weeks, and minimum-protection phase ranging from 10 to 16 weeks from injury. The aforementioned time frames are approximate and should be based on each individual patient’s prior level of function and current goals with rehabilitation. It is suggested that returning to running after an ACL injury treated nonoperatively should be approximately 12 weeks.21

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

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).

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).

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

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.

Literature shows the higher the grade of MCL lesion, the higher the incidence of an associated ligament injury; with grade III MCL injuries commonly associated with an ACL lesion.30

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