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The posterior cruciate ligament, situated near the center of the knee, functions as the basic stabilizer and is located close to the axis of motion. We diagnosed and repaired thirty-two consecutive acute tears of the posterior cruciate ligament associated with tears of medial or lateral-compartment ligaments, or of both. Of the twenty-nine knees that we could evaluate, twenty-three demonstrated a 2+ to 3+ positive abduction or adduction stress test done in maximum extension and a positive anterior drawer test done in maximum internal rotation, while only nine had a definitely positive posterior drawer test. In all knees we repaired the tears, using the medial meniscus as a graft in nine knees in which the repair of the posterior cruciate ligament did not produce immediate adequate stability at operation. Five to sixteen years after operation, twenty of these twenty-nine knees were available for evaluation. The objective results were good in thirteen, fair in four, and poor in three.

We reviewed the clinical records and operative notes of seventeen consecutive patients who were treated by surgical repair for acute posterolateral rotatory instability in order to determine the diagnostic features of the instability and the effectiveness of our surgical repair in thirteen patients who returned for objective and subjective evaluation after a mean follow-up of 53.3 months. Sixteen of the seventeen knees had a positive external-rotation recurvatum test; fifteen, a positive adduction-stress test at 30 degrees of knee flexion; and twelve, a positive posterolateral-drawer test. Associated rotatory instabilities were found in ten of the seventeen knees, with anterolateral rotatory instability being the most frequent. Two patients had associated peroneal-nerve palsy. One or more components of the arcuate ligament complex were injured in all seventeen knees. None of the thirteen patients who were followed required subsequent reconstruction for any chronic instability. Of these thirteen, the results in 85 per cent were rated good subjectively and in 77 per cent, good objectively. Eighty-five per cent of these patients had returned to athletic activity at their preinjury level; the remaining 15 per cent did not participate in sports activities. A positive posterolateral-drawer test or external rotation recurvatum test, or both, was diagnostic of posterolateral rotatory instability. The adduction stress test at 30 degrees of knee flexion was usually positive, but was not diagnostic. Accurate diagnosis and treatment of posterolateral rotatory instability in the acute stage can result in subjectively and objectively acceptable knee function.

In summation, the solution to many complications of anterior cruciate ligament surgery seems to be increasing the surgeon's knowledge of its complex anatomy and surgical techniques. Once the surgeon has learned firsthand the details of a relatively successful procedure, he can perform it on anatomic specimens for finesse. All he needs then is appropriate instrumentation and a postoperative protocol for rehabilitation under his direct supervision. Although not necessarily experienced, at that point he should be prepared to perform anterior cruciate ligament reconstructions without too many complications. With careful attention to detail and cumulative experience, he may modify his procedures for his own advantage, for that of the patient, and for the larger orthopedic community.

Functional disability should be proven before surgery is performed. If the knee demonstrates disability and simultaneously demonstrates muscle atonia and atrophy or contracture and imbalance, this dynamic support of the knee should be corrected preoperatively as far as possible and then the disability reevaluated before proceeding with surgery. A complete, documented knee examination must precede ancillary diagnostic procedures. Too often I see patients still in trouble with knees previously operated upon, who relate they had a cursory knee examination or no knee examination and were told that now there are modern diagnostic procedures such as arthrography and arthroscopy so they can be admitted to the hospital for these procedures with a resultant accurate diagnosis. This concept is not true! No ancillary procedure supercedes a knowledgeable history and clinical examination. The surgeon should operate only on the basis of objective demonstration of the need for operation, not on the basis of the history alone. In my estimation, rehabilitation accounts for 50 percent of a successful result following injury or operation. Remember, anatomy is the key to the knee.

Posterolateral drawer tests and external rotational recurvatum tests are used to detect posterolateral rotatory instability. A specific manner of performance of these tests is necessary to properly interpret the nature of acute and chronic knee conditions. The posterolateral drawer test is performed at 80 degrees of knee flexion and is maximum in 15 degrees of external rotation. Since the posterior cruciate ligament is intact in posterolateral rotatory instability, the posterior drawer will be negative on maximum internal tibial rotation. Fibrous scar tissue may conceal an otherwise positive posterolateral drawer sign in the chronic condition. The external rotational recurvatum test examines the knee in extension. Tightness and spasm of the biceps femoris and semimembranosus may obscure a positive external rotational recurvatum test in the acute or chronic condition. The external rotational recurvatum test will be negative when the anteromedial and intermediate bundles of the anterior cruciate ligament are intact owing to their contact with the intercondylar shelf in extension. The posterolateral drawer and the external rotational recurvatum can be subtle tests and require careful observation for accurate evaluation of both the acute or chronic condition of the knee joint.

Lateral instability of the knee is less frequent but more disabling than medial instability of a comparable amount. At the same time the diagnostic tests for lateral instability are more subtle and more frequently misinterpreted. Posterolateral rotatory subluxation is demonstrated by an apparently positive posterior drawer test with the tibia in neutral rotation or by the external rotation-recurvatum test with the knee in extension. Anterolateral rotatory subluxation is present when the anterior drawer test with the tibia in neutral rotation demonstrates that the lateral tibial condyle appears to become more prominent or that both condyles appear to become equally prominent.

Based on the clinical and operative findings in sixty-eight knees with acute tears of the medial compartment and cruciate ligaments, a standardized terminology and classification of knee ligament instability is presented. With an intact posterior cruciate ligament, anteromedial, anterolateral, or posterolateral rotatory instability may occur, but not true posteromedial rotatory instability. With the posterior cruciate ligament ruptured, straight anterior, posterior, medial, or lateral instability may be found.

Posterolateral rotatory instability of the knee, usually accompanied by other instabilities, is easily missed, misdiagnosed, and mistreated. The correct diagnosis requires a complete examination of the knee, including both the external rotation-recurvatum and posterolateral drawer tests. The most effective operative approach when the lesion is interstitial or at the site of the femoral attachment consists of advancing the arcuate ligament complex and its osseous attachment anteriorly and distally on the femur to support the arcuate ligament repair. When the lesion is distal and the arcuate ligament attachment to the tibia and fibula is loose, this area must be stabilized. In a consecutive series of 140 patients, 141 knees were reconstructed with this procedure. Ninety-five patients (ninety-six knees), with a follow-up of two to thirteen years, form the basis for this report. Seventy-one of the patients had undergone a combined total of 112 prior operations on the knee without functional recovery. After surgery directed at the arcuate ligament complex, eighty-two knees (85 per cent) were objectively rated as good; thirteen (14 per cent), as fair; and one, as poor. Subjectively, seventy-five (78 per cent) of the patients considered the result to be good; twenty-one (22 per cent), fair; and none, poor. Functionally, seventy-seven (80 per cent) of the knees were rated by the patient as good; sixteen (16 per cent), as fair; and three (4 per cent), as poor. This is the first report on the long-term results of reconstruction of the arcuate ligament complex for the correction of chronic posterolateral rotatory instability. The results demonstrate the effectiveness of the procedure.

This article defines the anterior cruciate ligament-deficient knee in terms of capsular instabilities. This definition lends itself to a better assessment of the associated pathology consisting of torn capsular ligaments, torn medial and lateral menisci, chondral fractures, subluxation of the patella, and acute contusion of the peroneal nerve. The specific incidence of torn medial meniscus was 70 per cent, with a torn lateral meniscus identified 77 per cent of the time.