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Purpose: To evaluate the etiology and natural history of limited thumb flexion after volar plate fixation of distal radius fractures.

Methods: The records of 52 consecutive adult patients who underwent volar plate fixation of a distal radius fracture by a single surgeon were reviewed. Twenty five patients (48%) lost normal active thumb flexion (Group 1), and 27 patients exhibited normal active thumb flexion (Group 2) postoperatively. Twenty-one patients in Group 1 returned for evaluation at a mean of 6.5 months after surgery (range, 5 to 12 months). Outcome assessments included the Disabilities of the Arm, Shoulder and Hand (Quick DASH) questionnaire, a visual analog scale (VAS) of patient satisfaction, joint motion measurements, and grip and key pinch strength measurements. Eight fresh-frozen, above-elbow specimens were used to replicate the flexor carpi radialis approach to the distal radius. The thumb was passively flexed and extended at sequential steps during the dissection, and excursion of the flexor pollicis longus (FPL) tendon was measured.

Results: There were no significant differences in patient age, gender, tourniquet time, fracture pattern, or fracture reduction between Groups 1 and 2 (p > 0.5). Dynamic ultrasound and electromyography of the FPL muscle-tendon unit revealed normal findings in 2 patients from Group 1. Return of normal active thumb flexion was noted at an average of 52 days postoperatively (range, 19 to 143 days). At final evaluation in Group 1, mean Quick DASH score was 13, and most patients expressed a high degree of satisfaction. However, active motion of the thumb interphalangeal joint on the injured side averaged 10 degrees less than the contralateral thumb interphalangeal joint (p < 0.05). In the cadaveric specimens, excursion of the FPL tendon decreased from a mean of 7.9 mm to a mean of 2.1 mm with sequential soft tissue dissection and retraction. Detachment of the distal 6 cm of the FPL muscle from the radial shaft averaged 36% of the longitudinal footprint. A Gantzer’s muscle was detected in 4 cadaveric limbs, whereas there were no tendinous interconnections between the FPL and index flexor digitorum profundus tendon.

Conclusions: Temporary loss of normal thumb flexion following volar plating of distal radius fractures may be a common phenomenon. Active flexion can be expected to return to near normal within 2 months after surgery in the majority of cases. Stripping of the FPL muscle from investing fascia and bone, and retraction of soft tissues are probable causative factors.