Peak tibial axial acceleration during walking is related to intact-side lower limb pain in persons with unilateral transtibial amputation.

BACKGROUND: Persons who undergo unilateral transtibial amputation are at an increased risk of secondary musculoskeletal joint pain and degeneration, which has been linked to excessive loading rates of the intact-side limb. Tibial axial acceleration, a feasible measure of loading rates with wearable sensors, would be clinically useful to relate to joint pain in persons with unilateral transtibial amputation. RESEARCH QUESTION: What is the relationship between peak tibial axial accelerations and intact-side joint pain in persons with unilateral transtibial amputation during walking? METHODS: Persons with unilateral transtibial amputation (n = 51) were separated into two groups based on the presence of intact-side limb pain (with pain: n = 16; without pain: n = 35). Tibial axial accelerations were measured with bilateral shank-mounted IMUs while participants completed three 10-meter walk tests. Peak tibial axial accelerations for each limb and between-limb symmetry were compared between groups using analysis of co-variance; significance was set at 0.05. RESULTS: Between persons with vs. without intact-side limb pain, peak tibial axial accelerations were smaller on the prosthetic side (0.64 vs. 0.81 g; p = 0.04), similar on the intact side (0.82 vs. 0.79 g; p = 0.53), and more asymmetrical between sides (intact > prosthetic) (0.81 vs. 1.03 g; p = 0.01). SIGNIFICANCE: Symmetry in peak tibial axial acceleration can assist with identifying preferential limb loading during walking and, with future research, could serve as a useful clinical target for intact-side limb unloading strategies to help mitigate secondary musculoskeletal pain in persons with unilateral transtibial amputation.

Assessment of glenoid baseplate initial micromotion and fixation strength in reverse total shoulder arthroplasty designs using a direct shear force methodology.

Background: In a reverse total shoulder arthroplasty, the altered glenohumeral joint center of rotation subjects the glenoid baseplate to increased shear forces and potential loosening. Methods: This study examined glenoid baseplate micromotion and initial fixation strength with the application of direct shear force in a Sawbone model. The reverse total shoulder arthroplasty systems examined were the DJO Reverse® Shoulder Prosthesis, the Exactech Equinoxe® Reverse System, and the Tornier AequalisTM Reverse Shoulder Prosthesis. Specimens were cyclically tested with increasing shear loads until 150 µm of displacement between the implant and glenoid was achieved, and subsequently until failure, classified as either 1 cm of implant/glenoid displacement or fracture. Results: The average load withstood for the 150 µm threshold for DJO, Tornier, and Exactech was 460 ± 88 N, 525 ± 100 N, and 585 ± 160 N, respectively. The average total load at device failure for DJO, Tornier, and Exactech was 980 ± 260 N, 1260 ± 120 N, and 1350 ± 230 N, respectively. Discussion: The Exactech implant design trended toward requiring more load to induce micromotion at each threshold and to induce device failure, most commonly seen as inferior screw pull out. This study proposes design features that may enhance fixation and suggests little risk of initial micromotion or failure during initial post-operative recovery.