Anatomic pronator quadratus repair increases flexor pollicis longus tendon pressure after volar rim plating: a cadaveric study.

BACKGROUND: To quantitatively evaluate the impact of anatomical pronator quadratus muscle (PQM) repair on peak flexor pollicis longus tendon (FPLT) pressure during functional wrist motion following volar rim plate (VRP) fixation. METHODS: This cadaveric study included 16 intact wrists from eight fresh-frozen upper extremities. A modified volar Henry approach was used to apply a 2.4 mm variable-angle VRP (Synthes) in a standardized Soong grade 2 position. A thin (0.15 mm) FlexiForce® piezoresistive sensor was placed between the FPLT and the distal edge of the plate to quantify interface pressure. Peak contact pressures were recorded at three wrist positions (maximum flexion, neutral, and extension) during four active motion cycles. Measurements were obtained in both unrepaired and anatomically repaired PQM states. Pressure values were statistically compared using paired t-tests to assess the effect of PQM repair. RESULTS: Biomechanical testing in 16 cadaveric wrists demonstrated that anatomical PQM repair significantly increased average pressure at the FPLT-implant interface across all wrist positions (p < 0.05). Mean overall pressure rose from 37.5% to 48.5% (p = 0.003), reflecting an 11% absolute and 29.3% relative increase. Position-specific analyses confirmed significant pressure elevations in flexion (Δ + 4.8%, p = 0.013), neutral (Δ + 11.0%, p = 0.005), and dorsiflexion (Δ + 17.2%, p < 0.001), with the greatest rise observed during wrist extension. DISCUSSION: Anatomic PQM repair significantly increases FPLT pressure following VRP by reestablishing a tissue interface that alters tendon-implant contact mechanics. Contrary to prior assumptions, these findings suggest that PQM interposition alone may not reliably mitigate flexor tendon loading. Surgical decision-making should therefore consider both implant positioning and PQM integrity in tandem when addressing tendon-related complications in distal radius fracture fixation.