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Changes in Stretch Reflex Excitability Are Related to "Giving Way" Symptoms in Patients With Anterior Cruciate Ligament Rupture

¹Institute of Orthopaedic Research and Biomechanics, University of Ulm, Ulm; ²Department of Neurology, University of Freiburg, Freiburg; and ³Department of Trauma and Reconstructive Surgery, University Hospital Rechts der Isar of the Technical University of Munich, Munich, Germany

Submitted 17 May 2006; accepted in final form 18 August 2006

A rupture of the anterior cruciate ligament (ACL) usually leads to an altered stretch reflex excitability of the thigh muscles that stabilize the knee. The purpose of this study was to quantitatively assess reflex activity in the m. semitendinosus/semimembranosus after anterior tibial translation in 21 patients with isolated ACL ruptures. The patients were divided into a group with "giving way" symptoms (noncopers, n = 12) and a group without "giving way" symptoms (copers, n = 9). While the patients were standing upright with 30° knee flexion, a force of 300 N was applied to the knee to induce posterior–anterior tibial translation. Activity of m. semitendinosus/semimembranosus was measured using surface electromyography (EMG). A linear potentiometer was placed on the tibial tuberosity and measured maximum tibial translation during standing (i.e., functional condition). In addition, knee laxity was assessed with a KT1000 arthrometer under passive conditions. After ACL rupture, the short-latency response (SLR) latency remained unchanged (P = 0.21), whereas for the medium-latency response (MLR) it was significantly longer (P < 0.001). Significantly longer MLR latencies were noted for noncopers compared with copers (P < 0.01), whereas SLR latencies were similar. Significant differences between healthy and injured legs were noted after tibial translations using KT1000 (P < 0.001) and during stance (P < 0.001). Mechanical knee instability was found to be unchanged between copers and noncopers (KT1000: P = 0.97; tibial translation: P = 0.31). These results indicate that ACL rupture is associated with altered stretch reflex excitability, which may lead to "giving way" symptoms, and that altered stretch reflex excitability may be more important for the development of "giving way" than the mechanical instability of the knee.

This article has been cited by other articles:

				T. L. Chmielewski and L. Snyder-Mackler Appropriate Interpretation and Application of a Clinical Classification Scheme to Describe Dynamic Knee Stability After ACL Injury J Neurophysiol, July 1, 2007; 98(1): 557 - 557. [Full Text] [PDF]