Range of Motion (ROM) assessments are routinely used during joint replacement to evaluate joint stability before, during and after surgery to ensure the effective restoration of patient biomechanics. This study aimed to quantify axial torque in the femur during ROM assessment in total hip arthroplasty to define performance criteria against which hip instruments can be verified. Longer term, this information may provide the ability to quantitatively assess joint stability, extending to quantitation of bone preparation and quality.

Joint loads measured with strain-gaged instruments in five cadaveric femurs prepared using posterior approach were analysed. Variables such as surgeon-evaluator, trial offset and specimen leg and weight were used to define 13 individual setups and paired with surgeon appraisal of joint tension for each setup. Peak torque loads were then identified for specific motions within the ROM assessment.

The largest torque measured in most setups was observed during maximum extension and external rotation of the joint, with a peak torque of 13Nm recorded in a specimen weighing 98kg. The largest torque range (19.4Nm) was also recorded in this specimen. Other motions within the trial reduction showed clear peaks in applied torque but with lower magnitude. Relationships between peak torque, torque range and specimen weight produced an R2 value greater than 0.65.

The data indicated that key influencers of torsional loads during ROM were patient weight, joint tension and limb motion. This correlation with patient weight should be further investigated and highlights the need for population representation during cadaveric evaluation. Although this study considered a small sample size, consistent patterns were seen across several users and specimens. Follow-up studies should aim to increase the number of surgeon-evaluators and further vary specimen size and weight. Consideration should also be given to alternative surgical approaches such as the Direct Anterior Approach.

Introduction

Hip arthroplasty is considered common to patients aged 65 and over however, both Jennings, et al., (2012) and Bergmann (2016) found THA patients are substantially younger with more patients expecting to return to preoperative activity levels. With heavier, younger, and often more active patients, devices must be able to support a more demanding loading-regime to meet patient expectations. McClung (2000) demonstrated that obese patients can display lower wear-rates with UHMWPE bearing resulting from post-operative, self-induced reduced ambulatory movement, thus questioning if obese kinematics and loading are indeed the worst-case.

Current loading patterns used to test hip implants are governed by ISO 14242-1 (2014). This study aimed to characterize a heavy and active population (referred to as HA) and investigate how the gait profile may differ to the current ISO profile.

The purpose of the project was to develop a questionnaire for completion by patients with elbow pathologies which is short and practical, internally consistent, valid, responsive and sensitive to changes of clinical importance.

The first, pilot phase included 43 patients who each completed a 19 item questionnaire relating to elbow function. The 19 ADLs produced a total scale Cronbach Alpha of 0.96., two different groups of ADLs were identified by multivariate analysis. Group 1 consisted of ADLs requiring moderate to high isometric loading and Group 2 of ADLs requiring high flexion. From the 19 items the best 10 which represented both groups were selected. A summary score was used to create the Wrightington Elbow Disability Score (WEDS).

In the second phase 89 patients completed the new WEDS form, reliability studies produced a Cronbach’s alpha value of 0.91. Internal validity of the groups of ADLs all correlated at p< 0.001 level with strength (Group1) and flexion (Group 2). A sub set of 40 patients undergoing total elbow arthroplasty were assessed for sensitivity to change in disability, the WEDS indicated a significant improvement at the p< 0.001. Convergent validity was demonstrated by the correlation with the ASES-e score at p< 0.001 level. The WEDS was significantly correlated with the ASES-e but not the DASH score.

Our study confirms that the WEDS questionnaire which is short and practical, is internally consistent, valid, responsive and sensitive to changes of clinical importance.