C. L. Hubley-Kozey G. Hatfield W. D. Stanish;
Dalhousie Univ. Halifax NS CANADA.
While muscle activation patterns during walking show that differences are specific to disease severity whether pattern differences are related to progression have not been examined. This follow up study tested two hypotheses: i) that knee extensor knee flexor and plantar flexor strength will be lower and ii) muscle activation patterns (same muscle groups) will have higher with more prolonged activity during walking in those at baseline diagnosed with medial compartment knee OA who at 8 year follow up had progressed to a total knee arthroplasty (TKA) and those that did not.Methods:
50 participants with moderate medial compartment knee OA were tested at baseline. WOMAC scores were recorded and standard anterior posterior radiographs were graded using the Kellgren Lawrence grading scale. Strength testing consisted of maximum voluntary isometric contraction (MVIC) exercises on an isokinetic dynamometer for plantar flexors knee extensors and flexors. Torque was calculated for each exercise as the peak 1 second steady state amplitude from two trials (Nm). Surface electromyograms (EMG) were sampled at 2000 Hz from 7 sites (vastus lateralis/medialis rectus femoris lateral/medial hamstrings and lateral/medial gastrocnemius muscles) using a standardized protocol during the exercises and while participants walked at their self-selected speed. EMG waveforms were averaged for 5 trials time-normalized to percent of gait cycle and amplitude-normalized to %MVIC. EMG waveform amplitude and temporal characteristics were determined using Principal Component Analysis (PCA). At follow up (mean 7.8 years) 25 patients reported undergoing TKA surgery. Unpaired Student’s t-tests examined differences in baseline demographic symptoms walking velocity and muscle strength between groups (α=0.05). Two factor (group muscle) analysis of variance models tested for significant interactions and main effects for waveform characteristics (PC scores) within each muscle group.Results:
There were no between-group differences (p>0.05) in age body mass index gait speed WOMAC or muscle strength measures (Table 1). The No-TKA group had 17 males and the TKA group had 19 males. Radiographic disease severity distribution was similar between groups at baseline (Table 1). Significant group main effects were found for PC1 (overall amplitude) for all muscles and PC2 (prolonged activation) for the quadriceps and hamstrings (p<0.05). See figure 1. The TKA group had significantly higher overall activity of all muscles at baseline (PC1 p<0.05) compared to the group that did not. The TKA group also had prolonged stance phase activity of quadriceps and hamstrings (PC2 p<0.05) at baseline.Conclusions:
Despite similar anthropometrics structural impairment symptoms walking velocity and muscle strength the group that progressed to TKA had higher hamstrings and quadriceps activity throughout the gait cycle with prolonged activity during mid-stance indicative of higher co-activation. In contrast to OA severity findings the gastrocnemius activity increased. This combination of patterns in the TKA group is consistent with increased risk of compressive loading on the knee joint and increased risk of muscle fatigue. Furthermore they provide clinical findings that support animal experimental models that showed increased muscle co-activation was related to OA progression through increased joint compressive loads. This novel longitudinal study provides evidence that muscle activation patterns during gait not just muscle strength deficits are related to knee OA progression.
Table 1 Demograhic WOMAC total Kellgren Lawrence grades walking speed and muscle strength
|Age (years)||58 (8)||59 (10)||0.49|
|Mass (kg)||93.8 (18.8)||93.5 (13.5)||0.95|
|BMI (kg/m2)||30.8 (5.3)||30.6 (4.8)||0.92|
|WOMAC (Total)||29.0 (20.4)||36.8 (14.6)||0.14|
|KL Distribution||2 KL110 KL211 KL32 KL4||3 KL16 KL212 KL34 KL4|
|Walking Velocity||1.27 (0.22)||1.23 (0.16)||0.42|
|Knee Extension (Nm)||123.8 (42.0)||113.6 (41.7)||0.40|
|Knee Flexion (Nm)||60.0 (24.3)||56.6 (25.8)||0.64|
|Plantar flexion (Nm)||98.2 (37.1)||84.9 (30.2)||0.18|