Lateral stability in healthy proximal interphalangeal joints versus surface replacement and silicone arthroplasty:...

The objective of this study was to quantify the lateral stability of healthy proximal interphalangeal (PIP) joints using a three-dimensional motion capture system and compare it to affected joints after surface replacement or silicone arthroplasty. Three study groups comprised healthy participants, patients with PIP joint osteoarthritis treated with a surface replacing implant (CapFlex-PIP) and those with a silicone arthroplasty. All participants were matched on gender and finger, and the two patient groups were also matched on length of follow-up. An optical tracking system was used to measure lateral stability. Radial and ulnar stability of the PIP joint was measured as the maximal lateral deviation angle of the middle phalanx under loads of 40 g, 90 g and 170g at 0°, 20° and 45° PIP joint flexion. Measurement reliability was evaluated with a test-retest trial [intraclass correlation coefficient (ICC)]. A total of 30 joints were assessed with 5 index and 5 middle fingers per test group. Lateral deviation increased proportionally with applied weight. Silicone arthroplasty joints had a higher median lateral deviation angle of 5.1° (range 0.7-7.9) than healthy [3.0° (0.5-11.0)] and surface replacement joints [3.3° (0.3-7.4)] at 45° flexion and under 170g load. Test-retest reliability was high with an ICC of 0.93. Lateral PIP joint stability is highly variable in both healthy participants and patients after PIP joint arthroplasty. PIP joint surface replacement arthroplasty tends to achieve better anatomical stability compared to flexible silicone implants.