Abstract
Introduction
Unicompartmental knee arthroplasty is in particular promoted for knee OA patients with high demands on function and activity. This study used wearable inertial sensors to objectively assess function during specific motion tasks and to monitor activities of daily living to verify if UKA permits better function or more activity in particular with demanding tasks.
Methods
In this retrospective, cross-sectional study, UKA patients (Oxford, n=26, 13m/13f, age at FU: 66.5 ±7.6yrs) were compared to TKA patients (Vanguard, n=26, 13m/13f, age: 66.0 ±6.9yrs) matched for gender, age and BMI (29.5 ±4.6) at 5 years follow-up.
Subjective evaluation of pain, function, physical activity and awareness of the joint arthroplasty was performed by means of four PROMs: VAS pain, KOOS-PS, SQUASH (activity) and Forgotten Joint Score (FJS),
Objective measurement of function was performed using a 3D inertia sensor attached to the sacrum while performing gait test, sit-stand and block-step tests. To derive functional parameters such as walking cadence or sway during transfers or step-up previously validated algorithms were used (Bolink et al., 2012).
Daily physical activity was objectively monitored with a 3D accelerometer attached to the lateral side of the unaffected upper leg during four consecutive days. Activity parameters (counts and times of postures, steps, stairs, transfers, etc.) were also derived using validated algorithms. Data was analysed using independent T-test, Mann-Whitney U test and Pearson's correlation.
Results
PROM's did not show any significant difference between UKA and TKA especially for the routinely used VAS-Pain and KOOS-PS (p>0.57) while higher (better) mean scores were recorded for UKA using more specialist measures such as self-reported activity (SQUASH; UKA vs TKA: 5659 ±3753 vs 4245 ±2489, p=0.12) and joint awareness (FJS; UKA vs TKA: 50.7 ±24.3 vs 41.4 ±29.2, p=0.08).
Sensor based measures of function showed significantly higher walking cadence for UKA (107.9 ±10.5 steps/min) than TKA (102.2 ±10.9 steps/min, p=0.049). Other functional parameters also indicated better UKA function, e.g. forward sway during sit-stand (UKA vs TKA: 38.0 ±13.2 deg vs 43.2 ±10.7 deg, p=0.06).
The wearable activity monitors showed that UKA patients perform significantly more steps downwards on stairs or slopes (89.0 ±77.4) than TKA patients (46.9 ±51.3, p=0.03). Other, less demanding activity counts such as daily steps (6522 vs 6343, p=0.85) or sit-stand transfers (39.4 vs 42.3, p=0.37) were not different.
Discussion and Conclusion
PROM's could not differentiate UKA from TKA although more specialist or demanding scores such SQUASH (activity) or FJS (joint awareness) seem to have more power.
Objective assessment could show for UKA faster cadence and more steps down on stairs and slopes, indicating that UKA benefits functional quality and enables demanding activities.
Objective measures of function and activity may be required in routine clinical follow-up to provide evidence and wearable sensors may facilitate this.
