Clinical Features And Evaluation

Posterolateral corner injuries occur from a blow to the antero-

medial aspect of the knee, contact and noncontact hyperexten sion injuries, and varus contact of a flexed knee. There has been some speculation as to certain predisposing factors such as genu varum, pre-existing excess external tibial rotation, ligamentous laxity, recurvatum, and epiphyseal dysplasia. Patients having suf fered an acute injury of the PLC describe a traumatic event and report pain over the posterolateral aspect of the knee. Patients may also complain of lower extremity weakness or numbness secondary to peroneal nerve injury. Patients also may report gait difficulties and instability, particularly complaining of hyperextension during toe off.

Physical examination that specifically isolates the structures of the posterolateral aspect of the knee is critical. Hughston and Norwood18 described two tests, the posterolateral drawer test and the external rotational recurvatum test, as key in detecting posterolateral rotatory instability. The posterolateral drawer test is performed to assess posterolateral rotation with the knee at 90 degrees of flexion. The foot is placed in 15 degrees of external rotation, and knee rotation is assessed while a posterolateral force is applied. An increase in rotation compared to the contralateral side typically reflects injury to the popliteus complex.12 The external rotation recurvatum examination is performed by lifting both lower extremities by the hallux with the patient in the supine position. A positive test refers to increased hyperextension and resultant external rotation.19 The reverse pivot shift is performed by slowly extending the knee from 45 degrees of flexion while applying a valgus and external rotational force to the knee. Reduction of the subluxated knee with extension connotes a positive result. Varus testing should be performed at both 0 and 30 degrees of flexion. Varus opening at 0 degrees is likely indicative of severe combined ligamentous injury, while opening at 30 degrees reflects incompetence of the LCL and possibly of other posterolateral structures.18 The pos-terolateral rotation test, also referred to as the dial test, is performed at both 30 and 90 degrees of knee flexion. Although the test may be performed in the supine or prone position, the senior author prefers the prone position with the knees held tightly together to help eliminate hip rotation. A greater than 15-degree increase in external rotation compared to the contralateral side only with the knee at 30 degrees of flexion suggests an isolated PLC injury. A greater than 15-degree increase at 90 degrees of flexion reflects a concomitant PLC and PCL injury.20 The knee should also be carefully evaluated for anterior and posterior cruciate ligamentous incompetence, in addition to medial-side knee injury. A thorough neurovascular examination is also necessary.

The gait status of an individual with suspected PLC insult will also help confirm clinical findings. Because of the role the PLC has in stabilizing varus forces, patients will typically present with a varus thrust or hyperextension at midstance, due to external rotation of the tibia at full extension.5 Some patients may also walk with a flexed knee2,5,21 to avoid pain and instability experienced with hyperextension. DeLeo et al22 reported in a case study a patient with pain in terminal stance and push-off. In this phase of gait, the knee is flexing rapidly from full extension. Stresses to the lateral structures of the knee are increased here, resulting in decreased stance time on the involved limb.

Radiographic examination should consist of standard standing bilateral posteroanterior, lateral, and Merchant knee views.

Figure 55-1 Posterolateral corner injury. Sagittal spin-echo intermediate-weighted magnetic resonance image (2000/20) through the intercondylar notch shows a thickened posterior cruciate ligament (arrows) with intermediate signal intensity throughout, indicative of a torn posterior cruciate ligament. (From Helms CA: The impact of MR imaging in sports medicine. Radiology 2002;224:631-635.)

Figure 55-3 Transverse fast spin-echo T2-weighted fat suppressed magnetic resonance image (3000/70) at the level of the joint shows the posterior capsule (left arrow) of the medial side of the joint, which is not evident on the lateral side. This indicates a torn arcuate ligament (which should be seen as a thickening of the lateral capsule at the joint line). In addition, the popliteus tendon (right arrow) has high signal intensity within and a distended tendon sheath. (From Helms CA: The impact of MR imaging in sports medicine. Radiology 2002;224:631-635.)

Figure 55-1 Posterolateral corner injury. Sagittal spin-echo intermediate-weighted magnetic resonance image (2000/20) through the intercondylar notch shows a thickened posterior cruciate ligament (arrows) with intermediate signal intensity throughout, indicative of a torn posterior cruciate ligament. (From Helms CA: The impact of MR imaging in sports medicine. Radiology 2002;224:631-635.)

Plain radiographs may reveal an avulsion fracture of the proximal fibula (arcuate sign), an avulsion of Gerdy's tubercle, or a Segond fracture (although more common with an anterior cruciate ligament injury). Stress radiographs may show lateral joint space widening. Chronic instability often reveals changes consistent with post-traumatic degenerative joint disease. If malalignment is also suspected, long-cassette hip-to-ankle films should be taken as they may serve beneficial in the planning of a possible osteotomy as an adjunct to ligament repair or recon-

Figure 55-2 Coronal fast spin-echo T2-weighted fat-suppressed magnetic resonance image (3000/70) reveals a torn lateral collateral ligament (arrow). (From Helms CA: The impact of MR imaging in sports medicine. Radiology 2002;224:631-635.)

Figure 55-3 Transverse fast spin-echo T2-weighted fat suppressed magnetic resonance image (3000/70) at the level of the joint shows the posterior capsule (left arrow) of the medial side of the joint, which is not evident on the lateral side. This indicates a torn arcuate ligament (which should be seen as a thickening of the lateral capsule at the joint line). In addition, the popliteus tendon (right arrow) has high signal intensity within and a distended tendon sheath. (From Helms CA: The impact of MR imaging in sports medicine. Radiology 2002;224:631-635.)

struction. Magnetic resonance imaging is key in the evaluation of the specific individual components of the PLC of the knee. A high-powered magnet of at least 1.5 T is recommended in order to adequately assess the iliotibial band, long and short heads of the biceps femoris, LCL, popliteus, and the poplite-ofibular and fabellofibular ligaments (Figs. 55-1 through 55-4). A bone contusion of the anteromedial femoral condyle is also a common finding.

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