Objectives: The aims of this study were to define radiological measurements for quantifying the position of a surface replacing implant (CapFlex-PIP) in the proximal interphalangeal (PIP) joint, to test the reliability of these measurements, and to explore whether implant position influences patient-reported and clinical outcomes one year after surgery.
Material and methods: We developed 7 radiographic measurements to quantify the position of the proximal and distal implant components. Two independent surgeons analyzed the 1-year postoperative radiographs of 63 fingers documented in our registry. Inter-rater reliability of these measurements was calculated with the intraclass correlation coefficient (ICC). Correlations between the radiographic measurements and PIP range of motion (ROM), the brief Michigan Hand Outcomes Questionnaire (MHQ), and pain were determined using Spearman's correlation coefficient. Radiographic measurements of patients with the worst and best postoperative ROM were compared using the Mann-Whitney-U test.
Results: Inter-rater reliability was only good for 1 measurement (ICC = 0.89), but poor to moderate for the other measurements (ICC ranging from 0.34 to 0.69). These measurements neither correlated with ROM, brief MHQ nor pain based on correlation coefficients ranging from 0.00 to 0.31. There were no relevant differences in the radiographic measurements between patients with the worst and best ROM.
Conclusion: The position of the CapFlex-PIP implant could not be reliably quantified on plain radiographs. The lack of correlations between implant position and postoperative outcomes can be attributed either to the unreliable measurements or the actual lack of influence of the implant position on pain and function.
Keywords: Arthroplastie; Arthroplasty; CapFlex-PIP; Doigt; Finger; Implant de resurfaçage; Position; Radiological assessment; Resurfacing implant; Évaluation radiologique.
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