Coronal Alignment and Ulnar Deviation After Radial-Sided Lateral-Approach Silicone Arthroplasty of the Proximal and Distal Interphalangeal Joints: A Prospective Case Series

Background: Following radial-sided lateral exposure for interphalangeal silicone arthroplasty, the repaired radial collateral ligament must maintain coronal stability against postoperative ulnar drift. Prospective direction-specific alignment data are limited. Methods: Consecutive patients undergoing proximal interphalangeal (PIP) or distal interphalangeal (DIP) silicone arthroplasty through a radial-sided lateral approach with structured collateral ligament repair were prospectively enrolled (minimum follow-up, 12 months). The primary outcome was signed coronal-plane deviation on standardized posteroanterior radiographs, with radial deviation recorded as positive and ulnar deviation as negative. Secondary outcomes included pain, motion, and Quick Disabilities of the Arm, Shoulder, and Hand (QuickDASH). Proximal interphalangeal (PIP) joints constituted the primary cohort; DIP joints were analyzed descriptively. Results: Forty PIP arthroplasties in 26 patients and 13 DIP arthroplasties in 8 patients were analyzed (33 unique patients; mean follow-up, 42.2 and 27.0 months). In the PIP cohort, mean signed deviation improved from −10.9° ± 7.9° preoperatively to −4.0° ± 9.8° at final follow-up, and 75.0% of joints were within ±10° of neutral. Final ulnar deviation >5° occurred in 37.5% of PIP and 15.4% of DIP joints, and >10° in 20.0% of PIP and no DIP joints. Pain, active arc, and QuickDASH improved in both cohorts (all P < .01). Three complications occurred; no implant was permanently removed, and no joint required arthrodesis. Conclusions: Radial-sided lateral-approach silicone arthroplasty with structured collateral ligament repair improved pain and motion while maintaining acceptable coronal alignment in most joints. Direction-specific ulnar deviation remained limited. These findings support feasibility, but not superiority over other approaches.