Clinimetric properties of hip abduction strength measurements obtained using a handheld dynamometer in individuals with a lower extremity amputation.

Introduction: Suitable handheld dynamometer (HHD)-techniques to test hip abduction strength in individuals with a lower extremity amputation, irrespective of their amputation level are absent. The aim of this study was to optimise a HHD-technique and to test its reproducibility and validity.

Methods: This study involved three phases, in which two techniques were evaluated. Both HHD-techniques used a lever-arm of 22 centimetre. HHD-technique 1 used a break-technique. After obtaining within-session test-retest reproducibility (phase 1) we optimised the HHD-technique by adding a fixation-belt and using a make-technique (HHD-technique 2). We tested the within-session test-retest and inter-rater reproducibility (phase 2) and the validity (phase 3) of HHD-technique 2 using an isokinetic dynamometer. New cohorts of participants were recruited for each phase.

Results: Phase 1: we tested HHD-technique 1 in 26 participants with a lower extremity amputation. It was test-retest reproducible (ICC3.1agreement: 0.80-0.92, standard error of measurement (SEM): 3.1-4.4 Nm and smallest detectable change (SDC): 8.6-12.3 Nm). There were questions regarding the validity of the measurement, because the mean muscle torque of the residual limb and sound limb were similar, which is uncommon. Phase 2: reproducibility of HHD-technique 2 was tested in 44 participants with a lower extremity amputation. It was test-retest reproducible (ICC3.1agreement: 0.96-0.97, SEM: 3.9-4.7 Nm and SDC: 10.9-12.9 Nm) but not inter-rater reproducible despite having good reliability (ICC3.1agreement: 0.92, SEM: 6.9-7.6 Nm and SDC: 19.2-21.2 Nm). Systematic bias and bias related to the magnitude of the muscle torque was suspected. Phase 3: the concurrent validity was established in 30 healthy participants (r = 0.84). Systematic bias in measurement error was present, including a consistent overestimation of the muscle torque of 28% using the HHD.

Conclusion: HHD-technique 2 is a test-retest reproducible and valid measuring technique The technique may be further optimised by the use of an external device to stabilise the HHD.