gms | German Medical Science

Objectives/Interrogation: To date, there is no objective quantitative data on the natural lateral stability of healthy proximal interphalangeal (PIP) joints or the postoperative stability of different PIP joint arthroplasties. The objective of this study was to quantify the lateral stability of healthy PIP joints using a three-dimensional (3D) motion capture system, and compare it to affected joints after surface replacement and silicone arthroplasty.

Methods: Three study groups comprised healthy participants, patients with PIP joint osteoarthritis treated with a surface replacing implant (CapFlex-PIP, KLS Martin Group, Tuttlingen, Germany) and those with a silicone arthroplasty. All participants were matched for gender and finger, and the two treated patient groups were also matched according to the follow-up time point. For measuring lateral stability, an optical tracking system was used (CamBar B2 C4, Axios 3D GmbH, Oldenburg, Germany). Radial and ulnar stability of the PIP joint was measured as the maximal lateral deflection angle of the intermediate phalanx under a 170 gram load at 20 degrees PIP joint flexion angle. Measurement reliability was evaluated with a test-retest (intraclass correlation coefficient (ICC)) method. Descriptive statistics were presented as median (range) values.

Results and Conclusions: A total of 30 participants (21 female, 9 male; median age 69 years (52-83)) were assessed including 5 index and 5 middle fingers in each of the three groups. Patients had a median follow-up of 3 years (1-5). The median radial deflection angles were 2.8° (0.8-10.0) for healthy joints, 3.1° (0.7-10.5) for the surface replacement group, and 5.1° (1.0-12.6) for the silicone arthroplasty group; the median ulnar deflection angles were 2.9° (0.5-6.2), 2.8° (0.9-11.0), and 3.9° (1.4-6.9), respectively. Test-retest reliability was high with an ICC of 0.93.

Lateral PIP joint stability shows high variability in both healthy participants and patients after PIP joint arthroplasty. Joints after silicone arthroplasty tend to have higher lateral deflection angles than unaffected healthy joints and joints with a surface replacement arthroplasty. Combined with the possibility to quantify lateral PIP joint stability precisely and reliably, we assume that certain healthy joints show natural joint laxity and that PIP surface replacement arthroplasty tends to achieve anatomical baseline stability with higher intrinsic stability compared to flexible silicone implants.