孤立型和复杂型膝关节不稳定

TOPICS IN REVIEW Knee instability: isolated and complex In the past decade, several advances have occurred in the understanding, evaluation, treatment, and rehabilitation of knee instabilities. Despite these advances, an unstable knee still poses many challenges to treating clinicians be- cause of the complexity of its nature and the demands of the patients, who are usually young and active sport en- thusiasts. We present an overview of the various aspects of knee ligament instabilities. STABILITY AND INSTABILITY Stability of the knee joint is maintained by the shape of the condyles and menisci in combination with passive sup- porting structures. These are the 4 major ligaments, the anterior cruciate ligament (ACL), the posterior cruciate ligament (PCL), the medial collateral ligament (MCL), and the lateral collateral ligament (LCL). Significant con- tributions are also made by the posteromedial and pos- terolateral capsular components and the iliotibial tract. The muscles acting over the joint provide secondary dy- namic stability. Instability resulting from ligament injury may result from direct or indirect trauma. The most frequent mecha- nism is “noncontact,” involving cutting, twisting, jump- ing, and sudden deceleration. ASSESSMENT Assessment begins with a detailed history, including a de- scription of the injury. The timing of an effusion (acute hemarthrosis usually occurs within 2 hours) and hearing or feeling a “pop” (highly suggestive of an ACL injury) are significant events. Chronic instabilities present with me- chanical symptoms such as locking, catching, clicking, or giving way, particularly with twisting movements. Age, occupation, lifestyle, level of sporting activity, and past history are all factors considered in subsequent manage- ment. Initially a physical examination may be difficult because of swelling, pain, or muscle spasm. The specific physical signs are described below. Investigations must in- clude plain radiographs of the knee. These may show fractures, avulsions, osteochondral fragments, or the fluid level of a hemarthrosis. If a clear diagnosis is made, a specific treatment can be started. If an adequate examination is possible, but diag- nosis is inconclusive, an expectant policy of mobilization, physiotherapy, and reevaluation in about 2 weeks may be adopted. If adequate examination is not possible because of pain, spasm, etc, the options available are reevaluation, magnetic resonance imaging (MRI), or examination under anesthesia and arthroscopy. MRI is particularly use- ful because of its noninvasive nature, but it is not univer- sally available in the United Kingdom as an emergency investigation. MEDIAL COLLATERAL LIGAMENT Anatomy and function The MCL is attached proximally to the medial femoral condyle and distally to the tibial metaphysis, 4 to 5 cm distal to the medial joint line beneath the pes anserinus insertion. Posterior to the MCL is the posterior oblique ligament, which is a thickening of the capsule. Immedi- ately deep to the MCL is the medial capsular ligament. These constitute the medial ligament complex. In full ex- tension, the posterior oblique ligament and the postero- medial capsule resist valgus stresses. These relax at 20 to 30 degrees of flexion, when the MCL becomes the primary restraint. The MCL together with the posterior oblique ligament also resists abnormal internal tibial rotation. Iso- lated MCL injuries occur usually as a result of a direct blow to the lateral aspect of the knee in a slightly flexed position. When the deforming force includes a rotational component, associated injuries to the cruciate ligaments can occur. Diagnosis of injury Physical examination includes looking for a localized bruise or swelling or localized tenderness and applying a gentle valgus force with the patient’s knee in 15 to 20 degrees of flexion. The degree of medial joint opening compared with the uninjured knee is a measure of damage to the MCL. A difference of only 5 mm indicates sub- stantial structural damage to the MCL. Excessive opening in full extension indicates combined MCL and posterior oblique ligament damage and should alert the examiner to the strong possibility of an associated ACL or PCL injury. If the knee is stable in full extension, it can be safely assumed that the posterior oblique ligament has no sig- nificant damage. Management of injuries The treatment of acute isolated MCL injury is conserva- tive.1 Incomplete tears of the MCL (sprains) without sig- nificant instability are treated with rest, ice, compression, and elevation (RICE) during the first 48 hours. This is .................................. Best Practice Trinath K Kakarlapudi Northern General Hospital Sheffield Derek R Bickerstaff Thornbury Hospital Sheffield S10 3BR UK Correspondence to: Dr Bickerstaff drbickerstaff@ uk-consultants.co.uk Competing interests: None declared This article was published in Br J Sports Med 2000;34:394-400... .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 266 wjm Volume 174 April 2001 www.ewjm.com followed by temporary immobilization and the use of crutches for pain control. Weight bearing as tolerated is encouraged as soon as pain allows. Early mobilization and physiotherapy allow patients to return to activities within about 6 weeks. Chronic MCL insufficiency Chronic MCL insufficiency is rare in isolation and usually is associated with ACL or PCL injury. Careful examina- tion must differentiate between MCL with or without posteromedial rotary instability. Symptomatic medial in- stability not improved with conservative treatment usually requires surgery in the form of proximal advancement of the MCL.2 Posteromedial rotary instability may require reconstruction of the posterior oblique ligament with free hamstring tendon graft. ANTERIOR CRUCIATE LIGAMENT Anatomy and function The femoral attachment is on the lateral wall of the inter- condylar notch posteriorly. The tibial attachment is on the anterior part of the tibial plateau near the tibial spines. The ACL has an anteromedial band that is tighter in flexion and a posterolateral band that is tighter in extension.3 This arrangement allows different portions to be taut through- out the range of motion, allowing the ligament to function throughout flexion and extension. It has also been shown to contain proprioceptive nerve endings.4 The ACL is the primary restraint to anterior translation of the tibia on the femur and to hyperextension.5 It func- tions as a secondary restraint to varus or valgus angulation at full extension. It also resists internal and external rota- tion at nearly full extension. Diagnosis of injury Lachman test. The Lachman test is performed with the knee in 20 to 30 degrees of flexion with the femur stabi- lized. An anterior force is applied to the proximal tibia, and the displacement is assessed. Pivot shift test. This is a dynamic test that shows the subluxation that occurs when the ACL is nonfunctional. In early flexion, the anterolateral quadrant of the tibia is forced to sublux by internal rotation and valgus. This reduces with a clunk by posterior pull of the iliotibial tract with further flexion up to 20 to 40 degrees. Plain radiographs may show an avulsion of the inser- tion of the ACL or a Segond fracture, which is a lateral capsular avulsion fracture from the margin of the lateral tibial plateau. MRI has an overall accuracy of about 90% in assessing the ACL,6 although this is not required rou- tinely. MRI also shows “bone bruises,” seen in about 60% of ACL injuries,7 the significance and long-term sequelae of which have yet to be determined. Instrumented Lach- man testing with an arthrometer (KT1000; Medmetric Corp, San Diego, CA) allows the documentation of an- teroposterior displacement before and after surgery. Ex- amination under anesthesia and arthroscopy for diagnosis are required only if doubt remains after clinical examina- tion and MRI scan. Management of injuries It is widely accepted that an acute repair is associated with poor results, including a higher rerupture rate and arthro- fibrosis.8 Hence, the initial treatment is based on the re- duction of pain and swelling and early restoration of nor- mal joint movement. The goal of treatment of ACL deficiency is to prevent reinjury, which may lead to chon- dral damage, meniscal tear, or laxity of secondary re- straints. These secondary injuries are thought to lead to arthritis, although progression to radiologically detectable osteoarthritis appears to be variable.9 We are aware of no published study proving that ACL reconstruction to sta- bilize the knee prevents the development of arthritis. Once ACL deficiency is diagnosed, the decision be- tween operative and nonoperative treatment is based on variables unique to each person. Among the factors con- sidered are the patient’s age, activity level (recreational and/or occupational), the degree of laxity, associated meniscal or ligamentous disease, ability and willingness to participate in a physiotherapy program, and future expec- tations, including the type of sporting activity in which the patient wishes to participate. Daniel and colleagues have shown that the ability of a patient to cope with ACL insufficiency is related to both the amount of instability present and the willingness to modify lifestyle to avoid high-risk activities.10 This pro- spective outcome study observed 292 patients for an av- erage of 5 years. In total, 19% underwent ACL recon- struction within the first 3 months, 19% requested surgery over the next 5 years, and 62% were able to function satisfactorily without an ACL. Those who had less than 5 mm of side-to-side difference and who participated for 50 hours or less in level 1 or 2 sports had a low risk of needing further surgery. Those with a 7-mm or greater side-to-side difference with more than 50 hours of level 1 or 2 sporting activity were in the high-risk group. Activities can be graded by the risk to the ACL- deficient knee. Low risk (level 3) includes cycling, swim- ming, stair climbing, and rowing, and medium risk (level 2) includes skiing, tennis, and golf. Although level 2 sports involve pivoting, this is predictable, and a patient can usually prepare for it. High-risk (level 1) sports include high-level skiing, basketball, football, and volleyball where there is considerable risk that the patient can be caught off guard and suffer a twisting injury without time to prepare. Patients with ACL insufficiency are best advised to avoid participating in level 1 sports. .................................. Best Practice Volume 174 April 2001 wjm 267www.ewjm.com Older people are often more willing to modify their activities, but surgery may be required if the laxity level is so great that their activities of daily living are impaired. Because patients do not tolerate instability in 2 major ligaments well, the presence of associated injuries also influences the decision in favor of surgical treatment. Also, ACL reconstruction is advisable in patients in whom meniscal repair is undertaken because the failure rate of meniscal repair is too large in the presence of ACL instability.11 Conservative management: Nonoperative management of acute ACL tears is likely to be successful in patients who have no associated injuries and who are willing to give up highly demanding sports. The rehabilitation program em- phasizes proprioceptive training to maximize the dynamic stability. Nonoperative management also includes coun- seling about high-risk activities and measures to prevent recurrent injuries. The role of functional knee bracing remains contro- versial.12 A knee brace may provide protection by improv- ing joint position sense and by providing mechanical con- straint of joint motion. Some patients report that they can participate in an increased level of sporting activity; how- ever, the use of a brace cannot substitute for a lack of quadriceps or hamstring training and cannot ensure pro- tection from further injury. Surgical management: Surgical techniques have been described for intra-articular and extra-articular reconstruc- tions of the ACL, using the iliotibial band, the semiten- dinosus and gracilis tendons, the patella tendon, allograft tissue, and various synthetic materials. Currently intra- articular techniques are most commonly used. The surgi- cal technique requires proper placement and tensioning of the graft, avoidance of impingement and stress risers on the implanted tissue, and adequate fixation. The available graft materials are broadly divided into autografts, allografts, and synthetic grafts. Autogenous grafts are most commonly used in ACL reconstruction. They provide a framework for revascularization and re- generation of the ligament and, with modern fixation techniques, allow rapid rehabilitation. Allografts heal in a similar manner but at a slower rate. There is also a risk of disease transmission. They are, therefore, more widely used when there is no autograft alternative. Synthetic grafts, although theoretically the most attractive, have not proved successful in the long term. Surgeons differ in their preference for autogenous tissue. The patella tendon graft (ie, bone-patellar tendon- bone [B-PT-B]) allows more secure bone-to-bone fixa- tion. Most surgeons report 80% to 90% good or excellent results with the use of autogenous B-PT-B (figure 1). Patellar fracture, tendinitis, anterior knee pain, and an increased incidence of infrapatellar contracture have been described with its use. Patellar fracture can usually be avoided by careful technique. Patellar tendinitis is usually short-lived and after 1 year is generally not a prob- lem. Anterior knee pain, however, appears to be more significant with this graft source than with hamstring reconstruction. The use of combined semitendinosus and gracilis ten- don grafts for reconstructing the ACL has also been well established. Their stiffness characteristics mimic the nor- mal ACL more closely than the stiffer patellar tendon graft. Multiple strands of the hamstring grafts may allow a better opportunity for revascularization. They offer an al- ternative in skeletally immature patients (where harvesting patellar graft would jeopardize the tibial apophysis), in women for cosmetic reasons, or in patients with extensor mechanism disease. Hamstring harvest is associated with minimal graft-site morbidity.13 Both direct and indirect clinical comparisons have shown that B-PT-B grafts and hamstring grafts have similar rates of effectiveness in adults with only minimal variations in knee stability and muscle strength at an average of 3 years after implantation.14 Rehabilitation Postoperative rehabilitation is an important aspect of care of the ACL reconstruction. Shelbourne and Nitz have advocated accelerated rehabilitation, with an objective be- ing early and long-term maintenance of full knee exten- sion.15 This protocol was based on the use of patellar tendon graft, although the principles are similar with other types of grafts. Figure 1 Lateral radiograph of the knee showing 2 interference screws used to secure a patella tendon graft in reconstruction of the anterior cruciate ligament .................................. Best Practice 268 wjm Volume 174 April 2001 www.ewjm.com LATERAL COLLATERAL LIGAMENT AND POSTEROLATERAL CORNER Anatomy and function The LCL originates on the lateral epicondyle of the femur and is attached distally on the fibular head. An LCL injury in isolation is relatively rare; injury usually occurs as part of a complex involving the posterolateral corner, the PCL, or the ACL. The posterolateral corner is a complex ana- tomic region of the knee consisting of the popliteus ten- don, the popliteofibular ligament, the arcuate ligament, and the posterolateral joint capsule. The lateral and pos- terolateral corner complex can be considered to comprise 3 layers: the iliotibial tract and the superficial portion of the biceps femoris form the first layer; the LCL the second layer; and the joint capsule, the arcuate ligament, the pop- liteofibular ligament, and the popliteal tendon constitute the third layer. The LCL is the primary static stabilizer to the lateral opening of the joint, supplemented by the pop- liteofibular ligament and the cruciate ligaments. The pop- liteofibular ligament is the primary restraint to posterolat- eral rotation, supplemented by the LCL and the popliteus tendon.16 The following tests are most useful in differentiating between isolated LCL, PCL, and posterolateral corner or combined PCL-posterolateral corner injuries. Care must be taken to ensure that there is no neurovascular injury, in particular to the common peroneal nerve. Varus stress test. The varus stress test is performed at full extension and at 15 degrees of flexion. Increased lateral opening at 15 degrees of flexion indicates LCL and pos- sibly posterolateral corner injury. Slightly increased lateral opening even at full extension is consistent with combined injury to the LCL and posterolateral corner. Significant opening at full extension indicates additional injury to the PCL and possibly the ACL. Comparison with the unin- jured side is important. Passive external rotation of the tibia (relative to the femur) with the knee at 30 and 90 degrees of flexion. This is best performed with the patient prone. In the rare case of isolated posterolateral injury, increased external rotation is noted at 30 degrees but not at 90 degrees. When com- bined PCL and posterolateral corner injuries are present, increased external rotation is noted in both positions. Ex- ternal rotation of the injured knee of 10 degrees or more compared with the uninjured knee is considered signifi- cant. In addition, the tibial condyles are palpated to de- termine their position relative to the femur to ensure that the increased external rotation is from posterolateral rotary instability and not anteromedial instability. Tests such as the external rotation recurvatum test, reversed-pivot shift test, and a posterior drawer test per- formed with the foot in external rotation—that is, the posterolateral drawer test—may also be performed for ad- ditional confirmation but are not particularly specific. Limb alignment and gait pattern must be observed to ensure that there is no lateral thrust on walking. If this is not recognized, the ligament reconstruction may fail in the absence of a corrective osteotomy. MRI scanning is useful in the patients with acute injury, not only to identify associated cruciate injury but also to help plan surgery by identifying the site of injury to the structures in the pos- terolateral corner. Management of LCL and posterolateral corner injuries The data available on surgical outcomes for posterolateral reconstruction are limited. The wide variety of procedures used to treat patients with posterolateral instability makes it difficult to derive a consensus on the most effective and appropriate approach to this clinical disorder. With inju- ries of the posterolateral corner, surgical intervention within 2 weeks of the initial injury is optimal, with the direct repair of all injured structures where possible.17 If the LCL or the popliteofibular ligament is ruptured mid substance, then consideration should be given to recon- structing these structures because direct repair in isolation may be insufficient. In patients with a chronic condition, direct repair is rarely possible and various techniques can be used, including tissue advancement and augmentation with autograft or allograft tissues. We use hamstring ten- don autografts to reconstruct the LCL and popliteofibular ligament similar to the technique of Larson, as described by Kumar et al18 (figure 2). If there is a varus thrust, we prefer to perform an opening medial wedge osteotomy to