Quantitative assessment of the course of distal radioulnar joint instability.

Introduction: There is a lack of methods to objectively evaluate improvement in distal radioulnar joint (DRUJ) instability through treatment. We used ultrasonography to assess DRUJ instability and calculated the minimal detectable change (MDC) in healthy individuals. MDC was used to evaluate post-treatment changes in a patient with triangular fibrocartilage complex (TFCC) injury.

Methods: DRUJ instability was evaluated using force-monitor ultrasonography in eight healthy male participants to determine MDC and in a man in his 60s who underwent surgery and rehabilitation for TFCC injury (Palmer classification: type 2C). In the patient, DRUJ instability was measured pre-operatively, 3 months postoperatively, and 1 year post-operatively. Self-reported hand and upper limb functional ability were also recorded. The transducer of the force-monitor ultrasonographic system was used to apply cyclic compressions to the wrists automatically and measure DRUJ displacements. The amount of displacement was calculated using the distance between the radius and ulna before and during cyclic compression to the wrists. The applied pressure was measured as the force to the wrist, and the displacement-to-force ratio was calculated.

Results: The 95% confidence MDC₉₅ for radioulnar displacement, displacement force, and displacement-to-force ratio were 0.27-0.31 mm, 0.30-0.59 N, and 0.12-0.15 mm/N, respectively. The patient's post-operative decrease in displacement exceeded the MDC₉₅. DRUJ stability, pain, and use of the affected hand in daily life improved.

Discussion: Force-monitor ultrasonography can quantitatively evaluate post-treatment improvement in DRUJ stability over time. MDC for DRUJ instability can assess recovery after treatment or rehabilitation and determine changes resulting from interventions.