The biomechanical function of the anterolateral ligament of the knee.

BACKGROUND: Recent anatomic investigations of the lateral structures of the knee have identified a new ligament, called the anterolateral ligament (ALL). To date, the anterolateral ligament has not been biomechanically tested to determine its function. HYPOTHESIS: The ALL of the knee will resist internal rotation at high angles of flexion but will not resist anterior drawer forces. STUDY DESIGN: Controlled laboratory study. METHODS: Eleven cadaveric knees were subjected to 134 N of anterior drawer at flexion angles between 0° and 90° and separately to 5 N·m of internal rotation at the same flexion angles. The in situ forces of the ALL, anterior cruciate ligament (ACL), and lateral collateral ligament (LCL) were determined by the principle of superposition. RESULTS: The contribution of the ALL during internal rotation increased significantly with increasing flexion, whereas that of the ACL decreased significantly. At knee flexion angles greater than 30°, the contribution of the ALL exceeded that of the ACL. During anterior drawer, the forces in the ALL were significantly less than the forces in the ACL at all flexion angles (P < .001). The forces in the LCL were significantly less than those in either the ACL or the ALL at all flexion angles for both anterior drawer and internal rotation (P < .001). CONCLUSION: The ALL is an important stabilizer of internal rotation at flexion angles greater than 35°; however, it is minimally loaded during anterior drawer at all flexion angles. The ACL is the primary resister during anterior drawer at all flexion angles and during internal rotation at flexion angles less than 35°. CLINICAL RELEVANCE: Damage to the ALL of the knee could result in knee instability at high angles of flexion. It is possible that a positive pivot-shift sign may be observed in some patients with an intact ACL but with damage to the ALL. This work may have implications for extra-articular reconstruction in patients with chronic anterolateral instability.

Liquid cooling system for the vibro-tactile threshold device.

Vibrotactile threshold testing has been used to investigate activation of human somatosensory pathways. A portable vibrotactile threshold testing device called the Vibrotactile Threshold Evaluator for the Workplace (VTEW) was designed for screening of carpal tunnel syndrome in the workplace, and initially contained a small fan for cooling. During subject testing, the device is operated intermittently, which causes the linear actuator to warm the tactile probe. The probe causes discomfort for some subjects. During testing, the probe heated to 42 °C within 90 seconds of continuous operation. A liquid cooling system was implemented to dissipate heat from the probe. The liquid cooling system maintains a steady state temperature of 36 °C for continuous actuation of the probe. The liquid cooling system is capable of maintaining a safe operating temperature, without adding erroneous vibrations to the device. However, the cooling system deters the portability of the device. Further research will investigate how to make the liquid cooling system portable and implements vibrotactile threshold testing in the workplace to quickly evaluate whether or not a person has early symptoms of carpal tunnel syndrome.