Muscle co-activation, knee joint kinematics, and ground reaction forces are altered in the operated leg of meniscectomized patients at high risk of knee osteoarthritis

Abstract

Purpose: Every other meniscectomized patient develop knee osteoarthritis (OA) 10-15 years after surgery. Thus, meniscectomized patients constitute a useful model to study changes in neuromuscular activity and knee joint biomechanics, which are factors suggested to play a role in OA development. Recently, we were unable to detect differences in neuromuscular activity and knee joint kinetics/kinematics betweenmeniscectomized patients and controls during stair descent. Furthermore, only modest leg-to-leg differences were observed between the operated and contra-lateral leg of the patients. More demanding motor tasks may be needed to detect early changes in knee joint kinetics/kinematics and neuromuscular activity in meniscectomized patients at high risk of knee OA. The aim of this study was therefore to investigate knee joint kinematics, ground reaction force (GRF) kinetics and level of muscle co-activation during a standardized forward lunge maneuver in meniscectomized patients at high risk of knee osteoarthritis. We hypothesized that patients would display increased levels of muscle co-activation along with reduced knee joint range of motion (ROM) and altered GRF kinetics in the operated compared to the contra-lateral leg. Methods: Patients: Twenty-two patients meniscectomized uni-laterally for a medial meniscal tear in the posterior half of the meniscus (15 men and 7 women, 45.4 5.1 years, 174.3 7.1 cm, 77.3 15.4 kg, BMI 25.4 kg/ m2, values are mean SD) were investigated during a standardized forward lunge with synchronous electromyography (EMG), goniometer and force plate recording. In the analyseswe focusedon threedifferent phasesof the forward lunge; the loading phase (foot-strike to 80% peak GRF), the unloading phase (80% peak GRF to toe-off) and mean of the entire stance phase (foot strike to toe-off). Knee joint range of motion (ROM): Knee joint ROM during the loading phase (ROMload), unloading phase (ROMunload) and from foot strike to peak knee flexion (ROMpeakflex) were measured using a flexible electrogoniometer. Ground reaction forces (GRF): The vertical GRF signal during the forward lunge was used to calculate the rate of loading (Loadslope), rate of unloading (Unloadslope) and average magnitude of GRF during the entire stance phase (GRFmean). Co-activation: Thigh muscle co-activation in the above phases of the forward lunge was quantified using normalized EMG signals obtained in the vastus lateralis (VL), vastus medialis (VM), biceps femoris (BF) and semitendinosus (ST) muscles. Statistics: Paired t-test with 0.05 level of significance was used to assess differences between the operated and contra-lateral leg of the patients. Results: All results are reported as mean SE. Consistent differences were observed between the operated leg and contra-lateral leg during the impact phase (loading phase) of the forward lunge. These differences were manifested as increased levels of muscle co-activation (38.0 4.0 vs. 30.1 3.1 %MVC, p1⁄40.02), reduced ROM (23.4 2.9 vs. 29.7 2.7 degrees, p1⁄40.01) and a higher loading rate (Loadslope) (985 160 vs. 696 82 %BW s-1, p1⁄40.01). Furthermore, ROMpeakflex was reduced in the operated compared with the contra-lateral leg (59.4 2.3 vs. 64.9 2.0 degrees, p1⁄40.01). No differences were observed in ROMunload, Unloadslope or muscle co-activation during the unloading phase. In addition, no differences were observed in GRFmean and averagemuscle co-activation during the entire stance phase. Conclusions: The findings of increasedmuscle co-activation, reduced ROM and increased rate of loading during the loading phase between the operated and contra-lateral leg support the hypothesis that meniscectomized patients demonstrate early modulations in knee joint kinetics, kinematics and neuromuscular activity in the operated leg. Future studies should include more demanding motor tasks than stair walking. Representing such a task, the forward lunge test appears to provide a sensitive approach to identify leg-to-leg differences in relevant neuromuscular and biomechanical variables in middle-aged patients at risk of OA.