Clinical Diagnosis of Anterior Cruciate Ligament Instability in the Athlete

by Joseph S. Torg, MD, Wayne Conrad, AB, and Vickie Kalen, AB

Temple University Center for Sports Medicine and Science, Philadelphia, PA

Copyright (c) 1976 The American Journal of Sports Medicine Vol. 4, No. 2

The anterior crucial ligament in the face of trauma has remained an enigma. Diversity of opinion exists regarding mechanism of injury, efficacy of diagnostic techniques. as well as appropriate methods of management. We believe that an understanding of the majority of traumatic knee problems that occur in the athlete begins with the knowledge of the status of the anterior crucial ligament.

The purpose of this paper is to deal with the problem of the clinical diagnosis of anterior cruciate ligament instability. A new diagnostic test will be described. The frequency of injury to the anterior cruciate ligament as well as injury to several other structures of the knee will be determined. Also, correlation of these lesions with several clinical diagnostic tests will be made

LITERATURE REVIEW

Helfet (1) has observed that "occasionally, when operating for a torn medial cartilage, one finds that the anterior cruciate ligament has been torn from its insertions in the tibia... but this knee does not demonstrate anterior -posterior instability preoperatively or postoperatively, and removal of the cartilage cures all symptoms. It is not possible to diagnose the coincidental rupture of the cruciate ligament before operations." Of interest is that Helfet also stated that "isolated ruptures of the cruciate ligament are rare and of little clinical significance.

Smillie (2) has observed that "the drawer sign is 'minimal' in isolated ruptures of the anterior cruciate ligament," He further notes that “if the sign is maximal,” it is almost certain that “the medial ligament has been involved.” Also, in the face of an acute injury, the drawer sign is “not easy to establish and may be masked by pain, muscle spasm, and haemarthrosis.” With regard to treatment, Smillie states that, in the case of isolated rupture, “the anterior cruciate ligament alone is not the factor controlling instability, and a repair does not necessarily improve function. When rupture is associated with a tear of the medial meniscus, treatment is meniscectomy, the ruptured ligament being ignored.”

O'Donoghue, (3) reporting on end results of his series of major injuries to the ligaments of the knee, observed that, of sixty-nine patients with disruptions of the medial joint structure, fifty, or 72 percent, had tears of the anterior cruciate ligament. On the basis of analysis of these cases, he concludes that crucial ligament instability causes definite disability and recommends repair of the ligament as being surgically feasible.

More recently, Kennedy et al (4) studied 50 patients with anterior cruciate ligament tears.  He concludes that isolated tears of this ligament do occur and that there is a high incidence of associated medial meniscal injuries (19 of 50, or 40%). Most interesting was his observation that an acceptable result following an anterior cruciate tear may be anticipated in a high percentage of patients with or without repair!

Feagin et al (5) have reported sixty-four isolated tears of the anterior cruciate ligament diagnosed at surgery at the United States Military Academy between 1965 and 1971. Reexploration of sixteen knees in which the ligament had been repaired revealed 8, or 50 percent, to he intact.  Of interest is that the medial meniscus was torn in twelve, or 75 percent, of these re-explored knees.

Allman (6) has also observed that “complete tear of the anterior cruciate ligament may occur as an isolated injury and that in such cases there is no demonstrable laxity of the knee, thus making the diagnosis extremely difficult.”

Anterior Drawer Test

Classically, the orthopedist has been taught that a clinical diagnosis of anterior cruciate instability is contingent upon demonstration of a positive anterior drawer sign, that is, anterior translation of the tibia in its relationship with the femur when the knee is flexed to 90 degrees and anterior stress is applied. The origin of this maneuver is obscure, but for most, its validity has remained unquestioned. As noted, however, the unreliability of the drawer sign has been pointed out by several authorities. On the basis of our experience with 172 knees with anterior cruciate ligament disruption diagnosed at surgery, we agree with those who reject the reliability of this diagnostic test.  Analysis of the factors involved reveals three causes for a "false negative" drawer test in instances of an isolated tear of the anterior cruciate ligament. First, in the face of acute injury, isolated anterior cruciate tears are often, but not always, accompanied by a tense haemarthrosis and reaction synovitis that precludes flexion of the knee to 90 degrees. Second, protective spasm of the hamstring muscles secondary to joint pain can, in the well-muscled, well-conditioned athlete, generate considerable force. Simple vector analysis dictates that to effect translation of the tibia in the direction opposite to such a force requires an effort on the part of the examiner that would tax the capabilities of most of us. Third, and perhaps most important, a consideration of the anatomy of the medial joint compartment with knee flexed to 90 degrees explains the main cause for difficulty in effecting anterior translation of the tibia on attempting the drawer test.  The posterior surface of the medial femoral condyle is acutely convex in configuration.  This convex femoral articulating surface lies in relationship with the concavity formed by the articulating surface of the medial tibial plateau and attached medial meniscus. The spatial relationship is almost like that of a ball-and-socket joint. Specifically, it is the posterior horn of the medial meniscus buttressed against the posteriormost margin of the medial femoral condyle that precludes forward translation of the tibia (Fig. 1a).  Our observations indicate that significant "anterior drawing" occurs only after peripheral separation of the posterior horn of the medial meniscus or disruption of the medial capsular and/or posterior oblique ligaments.

Figure 1a Diagrammatic representation of the relationship of the medial femoral condyle, medial meniscus (MM), and tibia in the sagittal plane with the knee flexed to 90 degrees, the position in which the classical anterior drawer sign is performed. The medial meniscus, being attached to the tibia, abuts against the acutely convex surface of the medial femoral condyle, having a "door stopper" effect, and prevents anterior translation of the tibia and precludes a "positive drawer sign." Disruption of the medial capsular ligament and/or posterior peripheral separation of the medial meniscus, however, will permit a positive drawer sign when the anterior cruciate ligament is torn.

Lachman's Test

John W. Lachman. MD, Chairman and Professor of Orthopedic Surgery at Temple University , has for many years taught a simple, reliable, and reproducible clinical test to demonstrate anterior cruciate ligament instability.(7) The examination is performed with the patient lying supine on the table with the involved extremity on the side of the examiner (Fig. 2). With the patient's knee held between full extension and 15 degree flexion, the femur is stabilized with one hand while firm pressure is applied to the posterior aspect of the proximal tibia in an attempt to translate it anteriorly. A positive test indicating disruption of the anterior cruciate ligament is one in which there is proprioceptive and/or visual anterior translation of the tibia in relation to the femur with a characteristic "mushy" or "soft" end point. This is in contrast to a definite "hard" end point elicited when the anterior cruciate ligament is intact. When the anterior horizon of the knee is viewed from the lateral aspect, the normal slope of the infrapatellar tendon becomes obliterated (Fig. 3a and 3b). A corollary to interpreting the test is that if question remains in the examiner's mind as to whether the test is positive or negative, the ligament is torn.

The Lachman test for anterior cruciate instability obviates those problems mentioned as inherent in the classical "drawer sign." First, the position of comfort of the acutely injured and distended knee joint is one of slight flexion, the position described for performing this test. Second, the force produced by hamstring spasm is negated by testing for anterior translation of the tibia with the knee extended. The physics of static friction resolves the force necessary to translate the tibia in a direction 90 degrees to the opposing force of the hamstring muscles to simply that force necessary to overcome the friction of the two surfaces plus the weight of the leg. By extending the knee, the force of the hamstring is negated, and that force necessary to overcome the friction of articular surfaces is negligible. Third, with the knee extended, that area in contact with the tibial plateau and attached medial meniscus is the slightly convex weight-hearing surface of the femur. The relatively flat configuration of this surface does not obstruct forward motion of the tibia as previously described when the joint is flexed to 90 degrees (Fig. 1b).

Figure 1b With the knee extended, the relationship of the femur, medial meniscus, and tibia is significantly changed. The comparatively flat weight-hearing surface of the femur does not obstruct forward motion of the meniscus and tibia when anterior stress is applied. Thus, in instances where there is an isolated tear of the anterior cruciate ligament, anterior stress of the tibia with the knee extended will demonstrate clinically cruciate instability

MATERIAL AND METHODS

In order to evaluate the several clinical methods for diagnosing traumatic disruption of the anterior cruciate ligament as well as to determine the relative frequency of this lesion as related to injury of other structures, we have reviewed the clinical and operative findings of 250 knees in athletes that came to surgery for several forms of "internal derangement." Included in this retrospective study were a series of consecutive knees operated on for injuries that resulted from participation in recreational and competitive athletics and where operative findings confirmed the diagnosis of injury to one or more of the following structures: anterior cruciate ligament, medial meniscus, lateral meniscus, medial capsular ligament, and tibial collateral ligament.

Figure 2 Lachman's test for anterior cruciate ligament instability is performed with the patient lying supine on the examining table with the involved extremity to the side of the examiner. With the involved extremity in slight external rotation and the knee held between full extension and 15° flexion, the femur is stabilized with one hand and firm pressure is applied to the posterior aspect of the proximal tibia, lifting it forward in an attempt to translate it anteriorly. Position of the examiners hands is important in performing the test properly. One hand should firmly stabilize the femur, while the other grips the proximal tibia in such a manner that the thumb lies on the anteromedial joint margin. When an anteriorly directed lifting force is applied by the palm and four fingers, anterior translation of the tibia in relationship to the femur can he palpated by the thumb. Anterior translation of the tibia associated with a soft or a mushy endpoint indicates a positive test.

Figure 3 (a) When viewed from the lateral aspect, the silhouette of the inferior pole of patella, infrapatellar tendon, and proximal tibia is one of a slight concavity. (b) With disruption of the anterior cruciate ligament, anterior translation of the tibia obliterates the infrapatellar tendon slope.

RESULTS

Incidence of various derangements in 250 knees was as follows: (1) isolated tear of the lateral meniscus-43, or 17 percent; (2) combined tears involving the lateral meniscus and anterior cruciate ligament-7, or 3 percent: (3) combined tears involving the lateral meniscus, medial meniscus, and anterior cruciate ligament-twelve, or 5 percent; (4) isolated tear of the medial meniscus-35, or 14 percent: (5) combined tears of the medial meniscus and anterior cruciate ligament-93, or 37 percent: (6) combined tears of medial meniscus, anterior cruciate ligament, and medial capsular ligament-43, or 17 percent; and (7) triads-17, or 7 percent (Table 1).

The incidence of specific anatomic lesions in 250 knees was as follows: (I) lateral meniscus-62, or 25 percent; (2) medial meniscus-200, or 80 percent: (3) anterior cruciate ligament-172, or 69 percent; and (4) medial capsular and/or tibial collateral ligament-60, or 24 percent (Table 2).

In 171 knees, arthrotomy and meniscectomy was performed because of primary derangement of the medial meniscus. At surgery, meticulous examination documented that 136, or 79 percent. had associated tears of the anterior cruciate ligament (Table 3).

Operative findings were correlated with the classic anterior drawer sign; rotatory instability test as described by Slocum, and Lachman's test.  Of the 43 knees diagnosed at surgery as having isolated tears of the lateral meniscus, all three tests were negative pre- and postoperatively.  Of the 35 knees diagnosed at surgery as having an isolated tear of the medial meniscus, all three tests were negative pre- and postoperatively.  Of the 93 knees with combined tears of the medial meniscus and anterior cruciate ligament without valgus laxity, preoperative anterior drawer test was negative in 42, equivocal in 14, and positive in 37. All except 5 with bucket-handle tears demonstrated positive Lachman's sign, and none had rotatory instability. Postsurgery, all 93 demonstrated both positive Lachman's sign and anterior drawing. Six had rotatory instability.  Of the 43 knees with combined tears of the medial meniscus and anterior cruciate ligament with valgus laxity, preoperative anterior drawer test was negative in 4, equivocal in 5, and positive in 34. All 43 demonstrated positive Lachman's test.  Rotatory instability was negative in 30, equivocal in l, and positive in 12.  Postoperatively, all 43 had both positive Lachman's and anterior drawer tests. Most significant was that all but 10 which had static stabilizing procedures demonstrated rotatory instability post operatively.

DISCUSSION

An analysis of 250 knees operated on for injuries sustained in recreational and competitive athletics has demonstrated to our satisfaction the value of testing for anterior cruciate ligament instability with the knee held in 0 to 15° flexion. In none of the 35 isolated tears of the medial meniscus was the test positive prior to or following meniscectomy. Likewise, the 43 isolated tears of the lateral meniscus demonstrated negative Lachman tests both before and following lateral meniscectomy. It should he noted that in some instances following meniscectomy, there is slight increase in anterior-posterior translation of the tibia in relationship to the femur when stressed in extension, but in all instances there is an abrupt end point with an intact anterior ligament.

An additional 17 knees, examined under anesthesia, but not operated upon, were diagnosed as having "incomplete tears of the medial collateral ligament." or, more specifically. of the medial capsular ligament. In no instance of isolated tears of the medial capsular ligament was anterior translation of the tibia in relation to the femur discernible when the knee was stressed in extension.

In 88 of the 93 combined lesions involving the anterior cruciate ligament and medial meniscus, the test was positive both pre- and post-operatively. The false negative tests were attributed to incarcerated bucket-handle tears blocking forward translation of the tibia. On the basis of our observations, we believe that testing for the instability of the anterior cruciate ligament by stressing the knee between 0 and 15° of flexion is a reliable and readily discernible diagnostic procedure. The test can be positive only in the presence of partial or complete disruption of the anterior cruciate ligament.

Analysis of the data reveals that, of the 250 knees in this study, operative diagnosis demonstrated tear of the lateral meniscus in 25 per cent, tear of the medial meniscus in 80 per cent, tear of the anterior cruciate ligament in 69 per cent, and tears of one or more components of the medial collateral ligament in 24 per cent. Noteworthy is the extraordinary high incidence of partial and complete tears of the anterior cruciate ligament in the knees of these patients. We believe that injury to the anterior cruciate ligament is common in the athlete and that this structure is the second most frequently injured in those knees that come to surgery. Furthermore, in those 171 knees in which meniscectomies were performed because of injury to the medial meniscus, 136, or 79 per cent, demonstrated associated disruption of the integrity of the anterior cruciate ligament.

The value of the above observations is not limited to the demonstration of a previously undescribed and reliable clinical test for anterior cruciate ligament instability or the demonstration of the high frequency of this lesion, particularly associated with tears of the medial meniscus in athletes.  Rather, the data indicate the value of interpreting several clinical signs with regard to specifically delineating the various combinations of common structural defects occurring and affecting anterior and medial knee joint stability.

Table 4 summarizes the correlation of operative findings with the several clinical tests for anterior and medial instability. The clinical findings include evaluation of valgus laxity, Lachman's test, anterior drawer test, and rotators instability test.   In instances of tears of the medial or lateral meniscus, all these clinical tests and signs are negative both pre- and post-meniscectomy.   In instances of an isolated tear of the medial capsular ligament, valgus laxity is present: all others are negative.   In instances of a combined lesion involving the anterior cruciate ligament and medial meniscus without valgus laxity, Lachman's test is positive. However, 50 per cent have negative anterior drawer sign prior to meniscectomy. Following meniscectomy, all have positive drawer sign. Valgus strain and rotatory instability tests are negative.   In instances of a combined lesion involving the anterior cruciate ligament and medial meniscus with medial capsular ligament laxity prior to meniscectomy, all tests except that for rotatory instability are positive. In 75'% of these knees, the test for rotators instability is prevented from being positive by the presence of the medial meniscus. Following meniscectomy, all tests, including that for rotatory instability, are positive.

CONCLUSIONS

1. Lachman's test is a simple, reliable, and reproducible method for demonstrating anterior cruciate ligament instability. In our experience, this is the only test specific for this lesion.

2. Injury to the anterior cruciate ligament is extremely common in the athlete and occurs in 69 per cent of those knees that came to surgery for the various forms of internal derangement.

3. Partial or complete disruption of the anterior cruciate ligament was observed in 79 per cent of the knees with tears of the medial meniscus.

4. Clinical evaluation of the status of the anterior cruciate ligament in the face of injury must include consideration of the status of all joint structures, particularly the medial meniscus and the medial capsular ligament. This necessitates the utilization of the various clinical tests evaluated in this study. It is intended that the clinical-pathologic correlation presented will assist the clinician's understanding of the majority of traumatic knee problems which occur in the athlete and involve the anterior cruciate ligament.

REFERENCES

1. Helfet A: Disorders of the Knee, pp. 92 93, J.B. Lippincott Co., Philadelphia, Pa.. 1974.

2. Smillie IS: Injuries of the Knee Joint, p. 152. The Williams and Wilkins Co., Baltimore, Md.. 1970.

3. O'Donoghue DH: An analysis of end results of surgical treatment of major injuries to the ligaments of the knee. JBJS, 37A: 1-13, 1955.

4. Kennedy JCL et al: The anatomy and function of the anterior cruciate ligament. JBJS. 56A.   223-235. 1974.

5. Feagin. JA et al.: The Isolated Tear of the Anterior cruciate Ligament. Presented, 39th Annual Meeting AAOS. Washington, D.C., February 3. 1972.

6. Allman F: Sports Medicine, p. 244. Academic Press. New York, 1974.

7. Lachman JW, Personal Communication.

EDITORIAL COMMENT

Dr. H. Rover Collins, Cleveland Ohio: It is a pleasure to discuss Doctor Torg's paper.  Doctor Torg has stressed the importance of the anterior cruciate ligament in providing stability of the knee in the pivoting and cutting athlete in contrast to previously held views which stated that this ligament was of no clinical significance. He has discussed the incidence of isolated anterior cruciate tears as well as those associated with other lesions in the knee, particularly meniscus tears. He has stressed the importance of multiple diagnoses in the knee of which the orthopaedist must be aware. Doctor Torg has stated that there is a high incidence of anterior cruciate damage, ie, ligamentous tear associated with medial meniscus tears and that this must be looked for. He has also emphasized the importance of examining the knee after the meniscus has been removed in order to determine whether instability, which was not felt to be present prior to meniscectomy, may now he present when the stabilizing structure has been removed.

The main emphasis of Doctor Torg's paper lies in his discussion of a new test to determine instability or laxity of the anterior cruciate ligament. lie has stressed the point that the usual anterior drawer test is often falsely negative due to tenseness of the knee as a result of hemarthrosis, protective muscle spasm, and posterior horn tear of the medial meniscus which may prevent forward movement of the tibia on the femur, and often will cause the improper positioning of the tibia. He described a test and sign which are new to me, that being Lachman's test.

I have several questions that I would like to ask Doctor Torg:

1 . What does Doctor Torg do when he finds an anterior tear of the cruciate ligament?.

2. What does he do when there is rotatory instability after meniscectomy?.

3. What static stabilizing procedure was he referring to in his paper?

4. What is the natural history of anterior cruciate ligament tears in the athlete?

In conclusion, I would like to state that the anterior cruciate ligament is an extremely important structure in the athlete, and I appreciate the fact that Doctor Torg sent his paper to me in plenty of time to prepare a discussion.

Authors' Reply

I would like to thank Dr. Collins for his kind comments and encouraging evaluation of our paper. We have attempted to present a relatively simple, reliable, inexpensive, and noninvasive clinical test to determine the status of the anterior cruciate ligament. We have found Lachman's test most helpful in evaluating the relatively large number of knee problems that we see in our clinic.

With regard to his question as to what we do in instances of an isolated tear of the anterior cruciate ligament, suffice it to say that the initial management is nonsurgical. "The joint is aspirated, and the individual is immediately placed on an intensive isotonic exercise program for both quadriceps and hamstrings. Early return to activity is encouraged. For individuals involved in vigorous activity, bracing and/or taping is recommended. It is our opinion that attempts to surgically repair an isolated tear of the anterior cruciate ligament, regardless of the location of the disruption, are a fruitless surgical exercise. I am not aware of any evidence in the current literature that would lead me to believe otherwise.

As Dr. Collins has noted, mentioned in this paper was a reference to an extra-articular static stabilizing procedure for anteromedial joint instability-a situation that we believe necessarily requires disruption of the anterior cruciate ligament. Although the initial results of this procedure have been quite encouraging, our series is too small and follow-up too short to share the details with this audience today.

The natural history of the athlete with an isolated tear of his anterior cruciate ligament has been aptly described by Dr. Fred Allman as "the beginning of the end." Disruption of the anterior cruciate ligament, as an isolated phenomenon, results in functional anterior instability of the tibia in relation to the femur, similar to that demonstrated by the Lachman test. When this occurs and a valgus and/or rotatory stress results in forceful incarceration of the medial meniscus between the tibia and femoral condyle, posterior peripheral separation and/or longitudinal tears in the substance of the posterior horn of the medial meniscus occur. It is this event that is responsible for the "knee-going-out" sensation described by the patient. With the meniscus is impinged between the tibial surface and femoral condyle and a force of significant magnitude applied, there can also result tearing and/or stretching of the posteromedial supporting ligamentous structures. Repeated episodes result in increasing ligamentous laxity. When this situation is associated with a lax medial capsular ligament, anteromedial rotatory instability results.