Abstract
Background
In total knee arthroplasty (TKA), patient reported outcome on pain, function or satisfaction fails to differentiate treatment options. Activity, a consequence of pain-free, well functioning TKA and a satisfied patient, may be a discriminative surrogate metric, especially when objectively measured.
Methods
Habitual activity was measured in TKA patients (n=32, F/M=20/12, age: 72 ±8yrs) at long-term follow-up (9 ±1yrs) and compared to healthy, age matched controls (n=32, F/M=20/12, age: 71 ±9yrs) using a popular questionnaire (SQUASH) and accelerometry. A small 3D accelerometer (X16-mini, GCD Dataconcepts) was worn for 4 successive days during waking hours at the non-affected lateral upper leg. Data was analysed using validated algorithms (Matlab) counting and timing walking bouts, steps, sitting periods and transfers. Stair climbing events or similar activities such as walking steep slopes were classified using the higher mean hip flexion angle as a feature.
Results
SQUASH scores were not sign. different between TKA (mean ±SD: 4551 ±3426) and controls (3659 ±2720, p>0.1). With accelerometry, differences between patients and controls (Median [IQR]) increased from −13% for Time Standing (3.7h [2.6–5.1] vs 4.3h [2.9–5.0], p=0.69), to −26% for Daily Steps (4939 [3796–7910] vs 6731 [5539–8270], p=0.019] and −31% for Sit-Stand Transfers (31.2 [22.1–37.0] vs 45.3 [34.9–58.4], p>0.001). For stair-up events, the difference increased to −74% (6.2 [2.8–22.4] vs 23.9 [10.8–39.1], p>0.001).
Conclusions
Self-report activity could not discriminate between patients and controls. With accelerometry, sign. differences increased with rising levels of effort and difficulty. In TKA, walking alone, either by accelerometry or as the major component of self-report may not serve as powerful outcome measure in orthopaedics were energy expenditure from walking is less relevant than functionally demanding but rarer tasks such as transfer or stair climbing.
