Mark Melnyk

Gender and fatigue have influence on knee joint control strategies during landing

BACKGROUND Gender and fatigue are thought to affect the anterior cruciate ligament injury risk. In spite of much effort, the influence of these factors on knee joint biomechanics is still under discussion. The purpose of this study was to investigate kinematics, kinetics, and active muscle control strategies of the knee joint across gender in fatigue conditions during a landing task. METHODS Thirteen females and thirteen males performed two-legged landings before and after a closed kinetic chain exercise protocol. Knee joint kinematics and vertical ground reaction forces were assessed as well as electromyography of the quadriceps, hamstring, and gastrocnemius muscles. FINDINGS Females landed with increased knee flexion velocities (P<0.001) and knee joint abduction angles (P<0.01). Compared to males, females also showed different muscle activation patterns such as a delayed activation of the lateral hamstring (P<0.05) and the m. vastus lateralis (P<0.05) during the preparatory phase of the landing. Fatigue led to a reduced pre-activation of the medial and lateral hamstrings (P<0.05 and P<0.001) and the gastrocnemius muscle (P<0.05) both in males and females. INTERPRETATION The gender differences in knee flexion velocity, abduction angle, and muscle activation suggest that females and males possess different neuromuscular strategies to control the knee joint during dynamic landing movements. These differences as well as decreased hamstring and gastrocnemius muscle activity, due to fatigue, provide evidence for different knee joint control in females as well as in fatigued conditions.

Novel approach for a precise determination of short-time intervals in ankle sprain experiments

The etiology of ankle sprain injury is still under debate. Therefore, diagnoses of ankle inversion experiments play an important role. Recent studies stress the importance of exact time measurements due to the short inversion period of around 70ms. This paper presents a novel approach using the vertical ground reaction force (vGRF) to determine the short-time intervals in ankle sprain experiments, which are present in the form of short periods from the beginning of the movement to its end and short latencies to following signals, e.g. EMG onset of peroneal muscles. We compare our method to electrogoniometry at the ankle which is considered as the gold standard. During the inversion movement the kinematic action at the ankle can be measured with electrogoniometry, whereas the vGRF quantifies the vertical dynamic reaction of the tested subject entirely. We observe a difference of DeltaT(f,0-->g,0)=10+/-0.5ms between the first observable vGRF response and the first observable electrogoniometer response following platform release. The end of the ankle inversion measured with electrogoniometry is DeltaT(f,1-->g,1)=3+/-0.5ms later than the maximal vGRF peak. The potential supplementary (mechanical) information of this novel approach compared to electrogoniometry and its ease of use, may be not only interesting for researchers when studying ankle sprain simulations but also for clinicians when testing functional ankle stability.

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

Meniscal lesions are among the most common knee injuries and substantially affect the mechanical function of the knee joint. In addition, the presence of mechanoreceptors in the meniscus suggests that the menisci are also involved in the sensorimotor control of the knee. The objective of this study was to investigate the influence of an isolated meniscal lesion on the reflex behaviour of the hamstring muscles, which are involved in the sensorimotor control of the knee joint. For this purpose, we mechanically induced tibial translation in 19 patients in a standing position and analysed the biphasic response of the hamstrings consisting of a short-latency response (SLR) and a medium-latency response (MLR). Moreover, we determined anterior tibial translation. A comparison of electromyographic data for the healthy legs versus the injured legs showed no significant differences in either SLRs or MLRs. Although there was a tendency to an increase in tibial translation, no significant difference between the legs in anterior tibial translation was found. In conclusion, our experimental work did not reveal any substantial effects of a meniscal lesion on the reflex behaviour of the hamstrings. Our data suggest that the menisci appear to play only a minor role for the sensorimotor induced anterior posterior knee stability.

MICHAEL-JÄGER-PREIS 2005

Summary An ACL rupture is generally associated with a deficient proprioception of the knee joint. Previous studies suggested that the hamstrings as synergists of the ACL play an important role in the knee joint stability and are integrated in the sensorimotor control of the knee joint. The purpose of the study was to assess the hamstring activity after anterior tibia translation in 21 patients with isolated ACL rupture. After anamnesis, patients were divided into an acute (n = 7) and a chronic group (n = 14) and in a group with (n = 12) or without giving way sign (n = 9). During standing with 30° knee flexion a posterior-anterior tibia translation was induced by an impact force of 300 N (functional condition). Hamstring activity was measured by surface EMG. A potentiometer detected the maximum tibia translation. Additionally, passive knee laxity was assessed using KT 1000. After ACL rupture the short medium latency (SLR) was unchanged, whereas the medium latency response (MLR) was significantly increased (p