Disorders of the inert structures: ligamentous instability CHAPTER CONTENTS Degree of instability Ligamentous instability e270 The degree of instability is demonstrated during stress tests Types of instability . e270 and can be graded on the following scale (Fig. 1): Functional examination . e271 • mild/1+ = 5 mm or less separation of joint surfaces Treatment . e276 • moderate/2+ = between 5 and 10 mm separation • severe/3+ = greater than 10 mm separation. This scale is not very precise but is effective for clinical and Ligamentous instability therapeutic purposes. It should be remembered, however, that under anaesthesia the results of the stress tests are often exag- If the knee becomes unstable after a ligamentous injury, per- gerated so that patients with 2+ instability often show 3+ manent problems may result, especially if the patient is an instability in the test. athlete with high functional demand. If the history indicates that there is possibly instability, an examination to detect the exact location and degree of this is Classification of instability performed. It is important to make this supplementary exami- Instability may be classified as straight or rotatory. nation only when symptoms and signs found in the routine clinical assessment indicate ligamentous instability to be the cause of disability. Indeed, it is important to realize that not Straight instability every lengthened ligament leads to problems.1 If the athlete’s This is defined as an increased range of angular movement in muscles are strong enough to provide dynamic stability, a the frontal plane, i.e. valgus/abduction or varus/adduction slightly unstable knee will not cause trouble. Conversely, it is movement (Fig. 2), or an increased range of gliding movement quite possible that an athlete with slight laxity of one or more in the sagittal plane, i.e. the simultaneous forward or backward ligaments has a chronic painful lesion as well. If the diagnosis gliding movement of the tibial condyles in relation to the of the latter is missed because the routine functional examina- femoral condyles (Fig. 3). tion is not performed, it may well be that the patient is sent for surgery, which will solve the slight instability but does not Rotatory instability cure the main problem. This implies increased rotation movement of the tibia on the femur. The posterior cruciate ligament, located in the centre Types of instability of the joint, is the fundamental stabilizer and is the axis of the joint, both in flexion–extension and in rotation. Consequently, Knee instability is the result of loss of static and dynamic this ligament is always intact in rotatory instabilities; from the function. Stability depends on the tautness of the ligaments, moment the ligament is completely torn, there is no longer a congruency of joint surfaces, effectiveness of the menisci and centre of rotation and any kind of straight instability can 3,4 the well-balanced action of all musculotendinous units acting result. across the knee joint. Of these structures, muscles and tendons There are three types of rotatory instability: play a central role in joint stabilization. They are said to be the • Anteromedial rotatory instability: there is an abnormal ‘first defenders’ in distortion and loading situations.2 forward gliding movement of the medial tibial plateau © Copyright 2013 Elsevier, Ltd. All rights reserved. Disorders of the inert structures: ligamentous instability Fig 1 • Degrees of straight instability in the frontal plane: A, mild; B, severe; C, moderate. 3+ 2+ 1+ (a) (b) (c) with respect to the medial femoral condyle, while the lateral tibial plateau retains a relatively normal relationship with the lateral femoral condyle (Fig. 4b). • Anterolateral rotatory instability: there is an abnormal forward gliding movement of the lateral tibial plateau with respect to the lateral femoral condyle, while the medial tibial plateau retains a relatively normal relationship with the medial femoral condyle (Fig. 4c). • Posterolateral rotatory instability: there is an abnormal backward gliding movement of the lateral tibial plateau with respect to the lateral femoral condyle. Again, as in anterolateral rotatory instability, the medial tibial plateau remains in normal contact with the corresponding femoral condyle (Fig. 4d). Various combinations of these rotatory instabilities can occur. The most commonly encountered are combined anterola- teral and anteromedial, and combined anterolateral and 3+ 2+ 1+ posterolateral. Fig 2 • Degrees of straight instability in the sagittal plane. Posteromedial rotatory instability does not exist because an intact posterior cruciate ligament prevents any backward gliding movement of the medial tibial condyle in relation to the medial femoral condyle. Functional examination If the history or routine clinical examination indicates the possibility of instability, a supplementary examination is per- formed to detect the exact localization and degree of ligamen- tous insufficiency. Acute stage In the acute stage, only the first few hours after the accident are suitable for clinical detection of ligamentous laxity. After this, effusion and muscle spasm resulting from the capsulitis will prevent a detailed examination. This is particularly the case in lesions of the medial collateral ligament because of Fig 3 • Straight instability: increased range of gliding movement in its close relationship with the capsule. So assessment should the sagittal plane. be made as soon as possible, preferably at the scene of the © Copyright 2013 Elsevier, Ltd. All rights reserved. e271 The Knee (a) (b) )c( )d( Fig 4 • Rotatory instability: (a) starting position; (b) anteromedial; (c) anterolateral; (d) posterolateral. accident. If intra-articular bleeding is present, which especially accompanies tears of the anterior and posterior cruciate ligaments as well as of the medial collateral ligament, the first few minutes are often the only time available to make a proper clinical assessment of ligamentous laxity. When time has elapsed, examination under general anaesthesia, even- tually followed by arthroscopy, is the only course of action. However, if the lesion seems to be less serious, supplementary examination can wait until a proper clinical evaluation can be made. Chronic stage In the chronic stage thorough clinical examination suffices to estimate, in almost all instances, the degree of functional instability and to determine the type of treatment required. Tests Passive abduction or valgus stress test in 30° of flexion The patient is placed supine on the couch, the head resting on a pillow to enable observation of the examiner without active raising of the head (which often causes tightening of the ham- strings). The thigh rests on the couch and the lower leg hangs over the side, with the knee in 30° of flexion. One hand is placed about the lateral aspect of the knee, the other grasps Fig 5 • Passive abduction or valgus stress test in 30° of flexion. the lower leg at the ankle (Fig. 5). Then abduction stress is applied gently and repeatedly, gradually increasing up to the point of pain. The degree of movement and the end-feel are Passive adduction or varus stress test in estimated. 30° of flexion The normal limb is assessed first, especially in acutely This test is performed in the same position as the previous one, injured patients, because this shows the patient that the but the hands are changed; so one hand is placed about the examination will not be rough and is unlikely to be painful. medial aspect of the knee while the other grasps the lower leg The examiner also gets a measure of the stability of the at the outer side of the ankle (Fig. 6). The degree of movement unaffected knee. and end-feel are estimated. Instability indicates a tear limited to one or more of the Adduction stress is applied to test the stability of the medial compartment ligaments, i.e. the medial collateral liga- lateral compartment ligaments: the lateral collateral ligament, ment, meniscotibial or meniscofemoral capsular ligaments and meniscotibial or meniscofemoral capsular ligaments and the the posterior oblique ligament. arcuate ligament. If the abduction stress test in full extension also shows Instability of the lateral compartment is less common but instability, the posterior cruciate ligament is probably also rup- causes significantly more disability than a comparable amount tured. It should be borne in mind that, in the fully extended of instability medially. position, an intact posterior cruciate ligament still holds the Lateral instability cannot be detected when the test is per- joint surfaces in firm apposition, even in complete tears of the formed with the knee in full extension because the intact tight medial compartment ligaments. posterior cruciate ligament precludes any movement in this © Copyright 2013 Elsevier, Ltd. All rights reserved. e272 Disorders of the inert structures: ligamentous instability Anterior drawer test in external and internal rotation The patient is positioned as for the abduction–adduction stress tests. The hip is flexed to 45°, the knee to 80–90°. The foot is placed on the couch, well fixed by a portion of the examiner’s buttock resting on the dorsum of the forefoot. The examiner places both hands around the upper part of the tibia with the index fingers palpating the hamstring tendons to make sure they are relaxed. Both thumbs are placed at the anterior border of the joint so that they can estimate the range of movement. Then the proximal part of the lower leg is pulled forward repeatedly, first gently then with a somewhat stronger pull. The test is first performed with the lower leg and foot externally rotated beyond the neutral position and as far as is comfortably possible, then internally rotated (Fig. 8). The findings are compared with those of the basic examina- tion, for example in 0° rotation, as well as with the other knee. With the tibia in external rotation Fig 6 • Passive adduction or varus stress test in 30° of flexion. Anteromedial rotatory instability is indicative of a tear of one or more of the medial compartment ligaments: the medial collateral ligament, meniscotibial or meniscofemoral capsular ligaments and the posterior oblique ligament.