Posterolateral Knee
Purpose: It has been postulated that the biceps femoris complex can exert a compressive force on the FCL, thus exerting a stabilizing force on the lateral side of the knee. The specific aim of this study was to compare the difference in elongation of the FCL in response to loaded and unloaded conditions of the biceps femoris muscle-tendon complex during clinical limits-of-motion testing for the posterolateral knee. In addition, we sought to determine the clinical tests which resulted in the greatest elongation of the FCL during limits-of- motion testing, in order to determing which clinical tests are most suitable for the detection of FCL injuries. Materials and Methods: Six fresh frozen cadaveric lower extremities were minimally dissected to identify the FCL. Care was taken to preserve the lateral aponeurotic attachments from the long and short heads of the biceps femoris to the FCL, to minimize disruption of important anatomical relationships. A DVRT (Microstrain, Burlington, VT) was implanted into the midsubstance of the FCL to measure the local displacement (local strain) of the ligament produced by clinical motions. The specimen was mounted into a specially designed frame with the femoral shaft fixed intermedullary and the following muscle- tendon units loaded by a pulley system: Quadriceps (44N); medial hamstrings (gracilis, semimembranosus, semitendinosus)(22.5N); medial and lateral gastrocnemius (22.5N) and the iliotibial band (10N). The load on the biceps femoris complex varied depending on the experimental condition (22.5N, loaded; 2N, unloaded). Limits- of-motion testing was then performed for the loaded state with the following clinical tests: Lachman test, posterolateral tibial rotation at 30 degrees ("posterolateral Lachman test"); adduction at 0 degrees; adduction at 30 degrees; posterolateral drawer, and the dial test at 30 and 90 degrees of knee flexion. Each clinical test was performed 3 times and the repeatability of the clinical testing was verified. The entire sequence was repeated with the biceps femoris complex unloaded. Results: The average percent elongation (local strain) of the FCL was as follows: Lachman test (6.2%, loaded; 4.9%, unloaded), posterolateral tibial rotation at 30 degrees of knee flexion (8.3%, loaded; 7.1%, unloaded), adduction at 0 degrees (9.5%, loaded;7.9, unloaded), adduction at 30 degrees (13.3%, loaded; 13.4% unloaded); posterolateral drawer (8.0%, loaded; 7.9%, unloaded); dial test at 0 degrees (9.4%, loaded; 4.9%, unloaded), and the dial test at 90 degrees (10.2%, loaded; 8.0%, unloaded). Paired t-tests (level of significance = p < .05) were used to compare the loaded and unloaded states. There were no significant differences in percent elongation of the FCL for clinical limits- of-motion testing of the posterolateral knee in the biceps femoris loaded versus unloaded state. Conclusions: In this test we were unable to prove a possible dynamic role of the biceps femoris in providing strain relief to the FCL either through its lateral aponeurotic attachments or via direct compression, during clinical limits-of- motion tests specific for the posterolateral knee. It is possible that stability is granted through a more complex mechanism through the multiple attachments of the biceps femoris complex to the posterolateral knee. The clinical tests which produced the greatest local strain of the FCL were adduction at 30 degrees of knee flexion, the dial test at 90 degrees of knee flexion, and adduction at 0 degrees of knee flexion.
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