Ultrasonographic Characterization of Scapholunate Joint Interval in Wrist Extended and Neutral Push-up Positions

Research Objectives: To examine the Scapholunate (SL) joint interval changes using Ultrasound (US) imaging in wrist-extended and neutral push-up positions.

Design: Observational study using within-subjects repeated measures design

Setting: Military, outpatient occupational therapy

Participants: Forty-three U.S. military Servicemembers between the ages of 18 and 50 with healthy wrists

Interventions: The participants assumed wrist neutral-unloaded (NU), neutral-loaded (NL), extended-unloaded (EU), and extended-loaded (EL) push-up conditions. Two clinicians completed repeat volar SL joint interval US measurements to establish intra and inter-rater reliability. SL joint interval and arm positions were measured to describe the characteristics of four wrist push-up conditions. Changes in SL joint interval were analyzed to demonstrate kinematic changes amongst the four wrist push-up conditions.

Main Outcome Measures: Intraclass Correlation Coefficient (ICC) was reported as the reliability measure for volar SL interval measurements in four wrist push-up conditions. Relative arm positions, the observed SL intervals, and weight placed on the scale during push-up conditions served as the main characteristics. The measured SL joint interval changes in four wrist push-up conditions were compared using a two-way repeated measures analysis of variance.

Results: ICC for intra-rater reliability of SL interval US measurements ranged from 0.76-0.89, and inter-rater reliability ranged from 0.71-0.80. Each wrist condition's mean SL interval measurements (mm) were NU=4.94+0.85, NL=4.27+0.75, EU=4.65+0.77, and EL=4.38+0.72. A narrower SL interval was observed in the extended wrist compared to the neutral wrist in unloaded conditions (p <.001, mean difference=0.29mm). The SL interval did not significantly differ with wrist positions in loaded conditions (p=.09, mean difference=0.10mm).

Conclusions: This study identified the normal SL kinematics using a reliable US technique that can serve as the baseline for a diagnostic test for SL ligament injuries. Further studies identifying the amount of contribution of SL interval changes to wrist stability will aid in suggesting safe push-up wrist positions.

Author(s) Disclosures: The views expressed herein are those of the author(s) and do not reflect the official policy or position of Madigan Army Medical Center, the Department of Defense, the Defense Health Agency, or any agencies under the U.S. Government.