Manual Laxity Tests for Anterior Cruciate Ligament Injuries

Transcription

1 Literature Review Manual Laxity Tests for Anterior Cruciate Ligament Injuries KRlS JENSEN, PT' The manual laxity examination is the primary means by which clinicians evaluate ACL injuries. This paper reviews the literature and identifies the following ACL laxity tests: anterior drawer test, Lachman test. Maclntosh test, jerk test, flexion rotation drawer test, Slocum test, and the Losee test. Test technique, grading, limitations, and reliability are discussed for each test. General limitations of manual laxity tests are also presented. A review of ACL anatomy and the biomechanics of the pivot shift sign are provided to facilitate an understanding of the underlying principles of ACL laxity tests. Journal of Orthopaedic & Sports Physical Therapy The first report of an anterior cruciate ligament (ACL) rupture was published by Stark in 1850 (35). Since that time, diagnosis of the ACL deficient knee has captured the interest of numerous investigators (5-1 5, 17-32, 34, 36, 37). The magnitude of this research is, in part, reflective of the potential negative sequelae associated with untreated ACL injuries. Several authors have noted a high incidence of meniscal tears, functional instability, and articular cartilage degeneration in the ACL deficient knee (4, 9, 19, 30). In light of these findings, increased emphasis has been placed on early recognition of ACL tears. The complex biomechanical structure of the knee, however, has made diagnosis of ACL injuries a difficult clinical task. In the search for an accurate and reliable diagnostic test, a variety of approaches have been proposed. These include: manual laxity tests (13, 17, 25, 28, 34, 36), knee ligament arthrometers (5, 27, 31), radiographic procedures (32, 37), arthrography (6), and arthroscopic surgery (1 0, 19, 20, 28). The manual laxity examination has remained the primary means by which clinicians assess ACL injuries (7, 11, 22, 28). Choosing the appropriate laxity test, however, can be a difficult task. A large number of manual tests exist, some with only subtle differences and some with multiple names. Several of the ACL laxity tests are designed to elicit a pivot shift, a somewhat complex biome- ' Supervisor. Sports Medicme Physical Therapy. Unwersity of Wisconsin Hosp~tal and Cltnics. Physcal Therapy Department Unwerstty Avenue. Madson. WI /90/ $02.00/0 THE JOURNAL OF ORTHOPAEDIC AN0 SPORTS PHYSICAL THERAPY Copyright by The Orthopaed~c and Sports Phys~cal Therapy Sect~ons of the Amercan Phys~cal Therapy Assoc~at~on chanical phenomenon, from the knee. To accurately perform and interpret a manual laxity examination, the examiner needs a clear understanding of the pivot shift sign as well as an understanding of the differences between the various laxity tests. An important distinction must be made between the terms laxity and instability when discussing injuries to the ACL. Both terms have acquired ambiguous meanings as a result of the multiple ways they have been used in the literature. The term "laxity" should be used to indicate slackness or looseness of a ligament. It should not be used to describe joint motion or an abnormal joint position. Since some slackness is normal in a ligament, it is important to distinguish between normal and abnormal laxity. "Instability" is a general term which should be used to indicate excessive motion or mobility of a joint. The excessive mobility results in an altered position or subluxation of the joint. Joint instability is usually the result of numerous factors. Abnormal ligament laxity is one of the potential factors that can cause joint instability. The purposes of this paper are to describe the general limitations of ACL manual laxity tests, review the literature, and identify the manual tests for ACL injuries, and to note the distinguishing characteristics and limitations of each test. The manual tests included in this paper are: the anterior drawer test, Lachman test, Maclntosh test, jerk test, flexion rotation drawer test, Slocum test, and Losee test. A brief review of the anatomy and biomechanics of the ACL, and the biomechanical basis of the pivot shift sign will be presented to facilitate an understanding of the various tests. It is hoped that this approach will clarify a rather 474 JENSEN JOSPT 1 1: 10 April 1990

2 confusing abundance of information and provide the reader with a basic reference on ACL manual laxity tests. ANATOMY AND BIOMECHANICS OF THE ACL The ACL originates from the medial surface of the lateral femoral condyle and inserts anterior and lateral to the tibial spine. As it courses anteriorly, it twists slightly on itself in an outward spiral (2). The ligament is composed of multiple collagenous fascicles. These fascicles have been grouped into two primary bundles: the anteromedial bundle (AMB) and the posterolateral bundle (PLB) (2). When the knee is flexed, the AMB is tight and the PLB is lax. When the knee is extended, the AMB becomes somewhat lax and the PLB tightens. It should be noted that a portion of the ACL is tight and functional at any position of the knee. The primary function of the ACL is to restrict anterior displacement of the tibia on the femur (3, 12). In a classic in vitro study. Butler et al. (3) found that an intact ACL provided 86% of the restraining force in an anterior drawer test. When the ACL is torn, the medial meniscus, medial collateral ligaments, and iliotibial band are the secondary structures which resist anterior translation of the tibia (3, 7). A secondary function of the ACL is to limit excessive internal tibial rotation (1, 7, 23). Noyes (7) has shown that the ACL is most effective in this role when the knee is flexed beyond 30". When the ACL is absent, internal rotation is restricted by the medial collateral ligament, posteromedial joint capsule, and the iliotibial band (7). Due to the geometry and biomechanics of the knee joint, anterior translation of the tibia and internal rotation of the tibia are a coupled motion (5, 7, 12). The amount of tibial anterior translation is, therefore, dependent on the rotational starting position of the tibia. Fukubayashi et al. (12) demonstrated that anterior displacement of the tibia is decreased 30% if internal rotation of the tibia is restricted. This is an important factor when performing manual tests assessing the ACL. This coupled motion is the primary component of the pivot shift sign. THE PIVOT SHIFT SIGN Patients with an ACL-deficient knee often describe a "giving way" or "slipping" sensation that occurs when they turn on their involved knee or stop suddenly while running (7. 9, 38). In 1972, Galway et al. (13) coined the term "pivot shift" to describe this clinical symptom. They described the pivot shift as an anterior subluxation of the lateral tibial plateau when the knee approaches full extension, followed by a sudden reduction of the tibia as the knee reaches approximately 40 of flexion. Other authors have since used the term "anterolateral rotatory instability" (ALRI) to describe the pivot shift sign (lo, 17,21,34). It should be noted that ALRI and pivot shift are not synonymous terms. Although anterior subluxation of the lateral tibial plateau is the primary abnormal motion in a pivot shift, it is not always the only component. The medial tibial plateau may also subluxate anteriorly during a pivot shift. This can occur when the extra-articular structures are abnormally lax. In 1980, Galway and Maclntosh (14) described the Maclntosh test, the first manual laxity test designed to identify the pivot shift. Since that time, numerous pivot shift tests have been developed. It is important to note that all of the pivot shift tests are assessing the same phenomenon: anterior subluxation and/or reduction of the lateral tibial plateau. The biomechanics of the pivot shift can be divided into two components. The first component is an anterior subluxation of the lateral tibial plateau. When the ACL is torn, the tibia is able to subluxate anteriorly and internally rotate. The result is an anterior displacement of the lateral tibial plateau. This step occurs when the knee is positioned in approximately 20" of flexion. If the knee is fully extended, an intact posterior joint capsule will prevent tibial subluxation (7). If there is compression on the knee joint while the tibia is subluxated, the lateral femoral condyle will impinge on the posterolateral margin of the tibia (14, 24). During a manual pivot shift test, compression and impingement will occur when a valgus force is applied to the proximal tibia. In functional activities, weightbearing on the involved limb provides a compression force to the knee joint. The second component of the pivot shift is a sudden reduction of the lateral tibial plateau. This occurs when the knee is flexed beyond 40' of flexion. When the reduction occurs, the examiner and patient may see or feel a "thud" (18), "jerk" (1 7). or "slipu"(24) in the knee joint. Manual pivot shift tests attempt to elicit the same thud sensation that patients feel in their daily activities. The reduction of the tibia is due to the action of the iliotibial band (ITB) (1 4, 18, 24). Because of it's insertion on the lateral tibial plateau, the ITB is an external rotator of the tibia. As the knee is flexed, the ITB tightens and moves from a position anterior to the knee flexion axis to a posterior position. The taut ITB pulls posteriorly on the lateral tibial plateau causing it to externally rotate and quickly reduce. Grading of the pivot shift is often simply noted as positive (present) or negative (absent) (8, 14). Other grading scales have been described. Jakob et al. (1 8) developed a three level grading system JOSPT 11: 10 April 1990 ACL LAXITY TESTS 475

3 based on the presence of the pivot shift in different positions of tibial rotation. Noyes (7) has also described a grading system. His four level scale is based on how dramatic the shift or thud appears when the pivot shift occurs. Both scales are qualitative. GENERAL LIMITATIONS OF MANUAL LAXITY TESTS The lack of objective measurement is a basic shortcoming of ACL manual laxity tests. In the majority of ACL laxity tests, the examiner makes a subjective assessment as to whether the test is positive or negative. Examiners are asked to base their decisions on "proprioceptive" feel (36), awareness of a "mushy" endpoint (36), presence of a "thud" (7), "jerk" (17), or "slip" (25) in the knee joint. In many cases the actual change in joint position is very small and its detection requires acute attention on the part of the examiner (7, 29). As a result, a high degree of examiner experience is needed to accurately perform and interpret most ACL laxity tests (6, 14, 18, 33). The small force levels used in ACL laxity tests can be a significant factor in testing error. The amount of ACL laxity that will be found during a manual test is, in part, dependent on the amount of force that is applied to the knee joint (3, 5. 29). The force exerted on the knee during laxity testing is typically quite low. In an anterior drawer test, 90 N of force are applied to the ACL (3). In contrast, the ACL can be subjected to over 400 N of force during strenuous physical activity (3). Despite the presence of abnormal laxity, the use of such small test forces may allow the abnormal laxity to go undetected. The presence of taut, secondary support structures can also mask an ACL injury. When the ACL is torn, the secondary restraints provide stability to the knee. If the secondary supports are functionally tight, abnormal laxity may be difficult to detect during the ACL tests (3, 7, 29). Similarly, a patient's inability to relax can significantly affect the outcome of a laxity test (26). Donaldson et al. (6) reviewed a series of 100 patients with an ACL tear comparing the preoperative results of a laxity examination to the results obtained while the patient was under anesthesia. Preoperatively, the pivot shift test was positive in 35% of the knees, and the anterior drawer was positive in 70% of the knees. When the patient was under anesthesia, the percentage increased to 98% and 91 %, respectively. Several authors have recommended examining the patient under anesthesia or with arthroscopy when relaxation is a problem (1 0, 19, 20). ACL LAXITY TESTS The most frequently used tests for assessing ACL laxity are the anterior drawer test, Lachman test, Maclntosh test, jerk test, flexion rotation drawer test, Slocum test, and Losee test. The anterior drawer test and Lachman test are the only tests in this review which are not designed to elicit a pivot shift from the knee. The technique for performing each of these tests will be presented. In addition, specific test limitations, grading scales, and test reliability will be discussed. Anterior Drawer Test The patient lies supine on the examination table with his involved knee flexed to 90' and his foot flat on the table. The examiner may or may not stabilize the foot by sitting on it. (By keeping the foot free, tibial rotation is not limited and the coupled motion of anterior tibial translation with internal rotation is not restricted.) (7, 22) The examiner cups the posterior aspect of the tibia with both hands, resting the thumbs across the anterior joint line (Fig. 1). An anterior force is then applied to the proximal tibia. The test is positive if the examiner sees or feels the tibia slide anteriorly (1 6). The uninvolved knee should be tested first to provide a normative reference. The anterior drawer test can be graded to reflect the amount of anterior tibial translation. The most commonly used scale is as follows: grade 1: 5 mm; grade 11: 5-10 mm; grade Ill: more than 30 mm (22). Grade determination is based on the examiner's subjective assessment of tibial translation. The anterior drawer test can also be performed with the tibia internally or externally rotated to assess the laxity of capsular structures (1 6, 17). The anterior drawer test was the classic test for ACL injuries for many years. In 1976, however, Torg et al. (36) criticized the test for it's poor Figure 1. The Anterior Drawer Test. An anterior force is applied to the posterior proximal tibia with the knee in 90 of flexion. From: Feagin JA (ed), The Crucial Ligaments, p 8. New York: Churchill Livingstone, Reprinted with permission. 476 JENSEN JOSPT 1 1:10 April 1990

4 reliability. He noted three common causes of a "false negative" drawer test: a tense hemarthrosis that prevents flexion of the knee to 90, protective hamstring spasm, and wedging of the posterior horn of the medial meniscus against the medial femoral condyle. A "false positive" anterior drawer test can occur if the posterior cruciate ligament is torn (3, 11). In this situation, the anterior translation of the tibia is due to the tibia moving from a posteriorly subluxed position back to it's neutral position. A wide range of anterior drawer test reliability scores have been reported in the literature: Noyes et al. (28)(24%), Jonsson et al. (20)(33%), Donaldson et al. (6)(54%), Fetto and Marshall (9)(94%). The discrepancy between these reports is due, in part, to differences in the populations being tested. The studies which included only subjects with an acute or isolated ACL injury reported the lowest test reliability (6, 20, 28). The reliability of the anterior drawer test is reportedly higher when assessing chronic anterior cruciate ligament injuries (6, 20). This change in reliability may be due to a stretching out of the secondary support structures over time (3). Because of the generally poor reliability of the anterior drawer test, it should be used in conjunction with other laxity tests when assessing the status of the ACL. Lachman Test The patient lies supine on the examination table with the involved knee next to the examiner. The examiner holds the knee in approximately 15-20' of flexion. One hand stabilizes the distal femur while the other hand applies an anterior force to the posterior aspect of the proximal tibia (Fig. 2). The test is positive if the examiner sees or feels an anterior translation of the tibia (36). The uninvolved knee should be tested to provide a normative reference. The examiner also evaluates Figure 2. The Lachman Test. An anterior force is applied to the posterior proximal tibia with the knee in of flexion. From: Feagin JA (ed), The Crucial Ligaments, p. 10. New York: Churchill Livingstone, Reprinted with permission. the endpoint of the tibia's translation. A soft or mushy endpoint is characteristic of an ACL tear (6, 7, 36). A positive Lachman test can be graded with the same scale that is used for the anterior drawer test (6). Gurtler et al. (15) described a different grading system with the following classifications: grade I: proprioceptive appreciation of a soft endpoint; grade II: visible anterior translation of the tibia and a soft endpoint; grade Ill: passive anterior subluxation of the tibia occurs when the patient lies in a supine position with a support under the proximal tibia; grade IV: ability of the patient to actively subluxate the proximal tibia. The Lachman test has been hailed as the most reliable clinical test for ACL tears (6, 7, 15, 19, 20, 22, 36). Jonsson et at. (20) found the Lachman test to be positive in 87% of acute ACL tears and 97% of chronic ACL deficient knees. Donaldson et al. (6) found the Lachman test was positive in 100 of 101 ACL deficient knees. The Lachman test minimizes the effect of hamstring spasm and wedging of the medial meniscus by positioning the knee in of flexion. A false negative Lachman test can occur if there is a displaced bucket handle tear of the medial meniscus (20) or if excessive internal rotation is applied to the tibia during the test (1 1). Maclntosh Test The patient lies supine on the examination table. The examiner holds the involved side ankle with one hand and raises the limb off the table (Fig. 3). The knee is in full extension. The examiner's other hand applies a slight valgus force to the proximal lateral tibial plateau. The knee is gradually extended, allowing gravity to cause the femur to drop posteriorly and the lateral tibial plateau to subluxate anteriorly. The anterior tibial subluxation is increased by internally rotating the tibia with the hand holding the ankle. The knee is then slowly flexed while the examiner places a strong valgus force on the lateral tibial plateau. When the knee reaches 30-45' of flexion, tension in the iliotibial tract will cause the lateral tibial plateau to suddenly reduce. The Maclntosh test was the first test described in the literature for assessing the pivot shift phenomenon (14). It is often referred to as simply the "pivot shift test" (6, 7). The test mechanics are dependent on a functionally taut iliotibial band. If the iliotibial band has been lengthened by trauma or surgery, false negative results will be found (24). In order to perform the Maclntosh test, the patient must be relaxed. Relaxation, however, can be difficult to obtain since this test is often painful. JOSPT 1 1: 10 April 1990 ACL LAXITY TESTS 477

5 Figure 3. The Maclntosh Test. A) The test starts with the knee extended. Gravity causes the femur to subluxate posteriorly. Internal tibial rotation increases the anterior subluxation of the lateral tibial plateau. B) A strong valgus force is applied as the knee is slowly extended. C) When the knee reaches 30-4S0 of flexion, the ITB will cause the lateral tibial plateau to suddenly reduce. From: Feagin JA (ed), The Crucial Ligaments, p New York: Churchill Livingstone, Reprinted with permission. Without patient cooperation, the test reliability can be markedly diminished. In the series by Donaldson et al. (6), the Maclntosh test was positive in only 35% of 101 ACL deficient knees during the preoperative examinations. When the patients were examined under anesthesia, 98% of the tests were positive. Jerk Test The patient lies supine on the examination table. The examiner supports the involved limb by holding the ankle with one hand (Fig.4). The hip is placed in 45O of flexion and the knee is flexed to 90. The examiner's other hand places a valgus stress on the proximal lateral tibial plateau. While the valgus force is being applied to the knee, the examiner internally rotates the tibia with the hand holding the ankle. The knee is then gradually extended. In a positive test, the lateral tibial pla- Figure 4. The Jerk Test. A) The test starts with the knee in 90 of flexion. The tibia is internally rotated and a valgus force is applied to the knee. B) The knee is slowly extended. The lateral tibial plateau will subluxate anteriorly at approximately 30 of flexion. The tibia will suddenly reduce when the knoe approaches full extension. teau will be subluxated anteriorly when the knee approaches 30 of flexion (17). As the knee extends further, the tibia will suddenly reduce. The sudden reduction of the lateral tibial plateau is called a "jerk". The jerk test was described by Hughston et al. (17) in This test elicits a pivot shift by reversing the order of stresses applied to the knee during the Maclntosh test. The pivot shift is elicited by moving the knee from a reduced position (90 of flexion) to a subluxated position (30 of flexion) and then back to a reduced position (approximately 10' of flexion). No reliability studies for the jerk test were found in the literature. Flexion Rotation Drawer Test The patient lies supine on the examination table. The examiner raises the involved limb, supporting the weight of the lower leg with both hands (Fig. 5). The knee is held in 20 of flexion and neutral rotation. In a positive test, gravity will cause the femur to displace posteriorly and externally rotate \ISEN JOSPT 1 1: 10 April 1990

6 Slocum Test Journal of Orthopaedic & Sports Physical Therapy Figure 5. The Flexion-Rotation Drawer Test. A) The knee is held in 20 of flexion and neutral rotation. Gravity will cause the femur to subluxate posteriorly and externally rotate. This results in an anterior subluxation of the lateral tibial plateau. B) The tibia is reduced by applying a posterior force on the proximal tibia as the knee is flexed. From: Noyes FR, Basset RW, Grood ES, et al.: Arthroscopy in acute traumatic hemarthrosis of the knee. J Bone Joint Surg (Am) 62: , Reprinted with permission. (28). This produces an anterior subluxation of the lateral tibial plateau. The examiner then applies a posterior force on the tibia (as in a posterior drawer test) while the knee is slowly flexed. When the knee reaches approximately 40' of flexion, the examiner and patient will usually feel a characteristic "thud" as the lateral tibial plateau reduces. The flexion rotation drawer (FRD) test was initially described by Noyes et al. (28) in This test modifies the Maclntosh test by eliminating the valgus force applied to the knee. Subluxation of the lateral tibial plateau is achieved through the effect of gravity acting on the femur, not with a manual force. This modification makes the FRD test a less painful test. Noyes (28) reported the reliability of the FRD test to be 89% when the patient was under anesthesia and 62% when the patient was not under anesthesia. The patient lies on histher uninvolved side with the pelvis rotated posteriorly approximately 30 (Fig. 6). The medial aspect of the ankle on the involved limb rests on the examination table. The involved knee is flexed 10'. If the ACL is torn, the tibia will internally rotate and subluxate anteriorly in this position. The examiner then places one hand above and one hand below the knee joint. A valgus force is applied to the knee as the examiner pushes the knee into flexion. In a positive test, the tibia will suddenly reduce at approximately 40" of flexion (34). In 1976, Slocum et al. (31) described this modification of the Macintosh test. The test has also been called the "sidelying test" (7) and the "anterolateral rotatory instability test" (22, 25). The advantage of this test is its ease of application with heavy or tense patients. By placing the patient in a sidelying position, gravity is used to subluxate the tibia and provide a valgus force to the knee joint. No scientific reliability studies were found in the literature for this test. Losee Test The patient lies supine on the examination table. The examiner supports the involved side ankle with one hand (Fig. 7). The tibia is externally Figure 6. The Slocum Test. The patient lies on his/ her uninvolved side with the pelvis rotated posteriorly and the involved knee flexed lo0. The tibia will internally rotate producing anterior subluxation of the lateral tibial plateau. A valgus force is applied as the knee is flexed. Tibial reduction will occur at approximately 40 of flexion. From: Slocum DB, James SL, Larson RL, et al.: Clinical test for anterolateral rotatory instability of the knee. Clin Orthop 118:63-69, Reprinted with permission. JOSPT 1 1: 10 April 1990 ACL LAXITY TESTS 479

7 occurs when the tibia subluxates during jumping or deceleration activities. A false negative test can occur if a meniscal tear blocks full knee extension (24). A false positive test can occur when there is posterior subluxation of the lateral tibial plateau (25). No scientific reliability studies for the Losee test were found in the literature. CONCLUSION Journal of Orthopaedic & Sports Physical Therapy Figure 7. The Losee Test. A) The test starts with the knee flexed 45O and the tibia externally rotated. B) The knee is slowly extended as a valgus force is applied. The tibia is allowed to internally rotate. The lateral tibial plateau will subluxate anteriorly at approximately of flexion. C) The tibia will reduce as the knee approaches full extension. From: Feagin JA (ed), The Crucial Ligaments, p New York: Churchill Livingstone, Reprinted with permission. rotated. (The external rotation assures the examiner that the tibia is not subluxated at the start of the test.) The patient's knee is then flexed to approximately 45'. The examiner places his other hand on the lateral side of the knee. The thumb is hooked behind the fibular head and the fingers are placed over the patella. This hand then applies a valgus force to the knee while the thumb lifts upward on the fibular head, internally rotating the tibia. The knee is slowly extended while the valgus force is being applied. The leg and foot are allowed to roll into internal rotation. If the test is positive, the lateral tibial plateau will suddenly subluxate anteriorly as the knee reaches approximately 10-20" of flexion (25). The Losee test was first described in 1978 (25). It is similar to the jerk test in that both tests start with the knee in flexion and the tibia reduced. The two tests differ in their tibial rotation starting position. In the jerk test, the tibia is held in internal rotation. In the Losee test, the tibia starts in external rotation and is allowed to gradually roll into internal rotation. The Losee test reproduces the mechanism of functional knee instability that 480 JENSEN The manual laxity exam remains the primary tool available to clinicians assessing ACL injuries. The laxity tests which have been described in the literature can be divided into two groups: those which assess abnormal anterior tibial translation, and those which assess the coupled motion of anterior tibial translation with internal tibial rotation (the pivot shift). The appropriate use of laxity tests requires an understanding of the inherent limitations of all laxity tests, in addition to specific test limitations. Examiners should be aware that only the Lachman test has been shown to be a consistently reliable examination. While the pivot shift tests are a legitimate means of assessing ACL injuries, their incidence of false negatives is high. Similarly, clinicians must critically review literature which provides grades for laxity test results. Not only do multiple grading scales exist, but determination of a test grade remains a subjective decision. An awareness of these limitations will enhance a clinician's understanding of the role of ACL manual laxity tests in the clinical examination of the knee. 0 REFERENCES Arms SW. Pope NH. Johnson RJ. F~scher RA. Arv~dsson I. Er~ksson E: The b~omechancs of antenor cruclate hgament rehabilttatim and reconstruction. Am J Sports Med Arnoczky SP: Anatomy of the anterlor cruclate I~gament. Clin Orthop 172: Butler DL. Noyes FR. Grood ES: L~gamentous restraints to antenor-postenor drawer in the human knee. J Bone Jomt Surg (Am) Clancy WG Knee ltgamentous Injury In sports the past present and future Med SCI Sports Exerc Damel DM Malcom LL Losee G Stone ML Sachs R Burks R Instrumented measurement of anterlor lax~ty of the knee J Bone Jomt Surg (Am) Donaldson WF Warren RF W~cklewlcz T A comparlson of acute antenor cruclate l~gament exammattons Am J Sports Med Feagtn JA ed The Cruc~al L~gaments New York Churchlll Lwng stone 1988 Fetto JF Marshall JL Injury to the anterlor cruclate hgament producmg the plvot-sh~fl slgn J Bone Jomt Surg (Am) Fetto JF Marshall JL The natural hlstory of antenor cruclate hgament msufflc~ency Clm Orthop Fowler PJ The class~f~cat~on and early d~agnosts of knee jant lnstabhty Clm Orthop Frank C Accurate lnterpretatlon of the Lachman test Clm Orthop Fukubayash~ T Torz~ll~ PA Sherman MF Warren RF An In vltro blomechanlcal evaluat~on of antenor-postenor motlon of the knee J Bone Jomt Surg (Am) Galway RD Beaupre A Naclntosh DL Ptvot sh~fl a cltnlcal slgn of systematic anterlor cruclate ltgament lnsufflclency J Bone Jolnt Surg (Br) JOSPT 11:10 April 1990

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