Intraoperative Direct Mechanical Stimulation of the Anterior Cruciate Ligament Elicits Short- and Medium-Latency Hamstring Reflexes

Abstract

The anterior cruciate ligament (ACL) has not only a mechanical but also a sensorimotor function. Patients with injuries of the ACL frequently complain of knee instability despite good mechanical stabilization after surgical reconstruction. Compared with healthy subjects, their latencies of hamstring reflexes after anterior tibia translation are considerably increased. There is evidence for the existence of a reflex arc between the ACL and the hamstrings. The aim of this study was to determine if there is a direct reflex response after an isolated mechanical stimulation of the ACL in humans. In 10 patients who underwent arthroscopy, hamstring electromyographic (EMG) responses were assessed intraoperatively after applying an isolated load on the ACL. Latencies, amplitudes, and integrals of the EMG responses were analyzed. In four patients, the measurements were repeated after injection of local anesthetics into the ACL. In all subjects, responses with mean latencies of 42 +/- 4.4 (SD) ms corresponding to a medium latency response (MLR) were found. In seven subjects, they were preceded by responses with a short-latency (SLR) of 24 +/- 2.7 ms. The maximum amplitude was 8.6 +/- 7 mV, the integral 0.064 +/- 0.05 mV*s. The injection of local anesthetics reduced the amplitude by 34 +/- 12% and the integral by 50 +/- 20%. Direct mechanical stimulation of the ACL evokes considerably smaller SLRs and MLRs than anterior tibia translation during standing. It is argued that latency changes observed in patients with ACL ruptures may be rather due to changes in the sensorimotor integration of the afferent input from the knee joint than to the absence of the direct ACL reflex.

An Extensive Evaluation of Different Knee Stability Assessment Measures: A Systematic Review

“…For example, the sensitivity and specificity of the Genucom knee analysis system have been reported to be low, at 60% and 65%, respectively [42].On the other hand, the KT-1000 sensitivity at maximum manual force is 93%, and it has a specificity of approximately 93% [16]. Despite the existing studies on the use of the hamstring-stretch reflex [26,[73][74][75], the literature lacks evidence on whether the reflex latency can be a valid objective clinical knee stability measure.…”

“…It is used in operative theatres through a direct pull of the ACL to differentiate short and long latencies [75]. The reflex has been investigated intra-operatively by direct traction under arthroscopic visualization and in a research setting by instrumenting a laboratory-based rig [11]; thus, its clinical usefulness is doubtful.…”

Anatomy and Physiology of Knee Stability

“…This difference in participant populations may have resulted in the disparity in the results obtained from these two studies, as sensorimotor training may enhance neural drive and subsequently improve joint proprioception [50][51][52], thereby reducing the delayed onset of the ACL-hamstring reflex. Friemert et al [53] reported that 10 out of 10 trials (100%) elicited stretch reflex during an intraoperative direct mechanical stimulation of the anterior cruciate ligament. On the other hand, Abulhasan et al [54] tested if ACL-hamstring stretch reflex could be reliably and consistently obtained using knee arthrometer (KT-2000).…”

The influence of meniscal lesions on reflex activity in the hamstring muscles

“…The latency of the short-latency response (SLR) was defined as the time window from the onset of tibial translation (t 0 ) to the first significant hamstring activity. The evaluation algorithm introduced by Friemert et al [12] was used to determine the time window for the medium-latency response (MLR) amplitudes of the first reflex component P-values of 0.361 and 0.514 were calculated, respectively. The comparison for the MLRs between healthy and injured leg also revealed no significant differences for the integrals (P = 0.336) and amplitudes (P = 0.367).…”

“…Intraoperative studies provided evidence that this function is partially ensured by the sensorimotor integration of knee joint receptors and the hamstrings [12,27,28]. Friemert et al [11] were able to show that anterior tibial translation evokes a biphasic reflex response of the hamstrings in standing subjects.…”