The Utility of Ulnar Nerve Cross-Sectional Area in Predicting Patient Outcomes in the Early Postoperative Period.

Background: Although ulnar nerve cross-sectional area (CSA) can be used to diagnose cubital tunnel syndrome, the predictive value of preoperative CSA for postoperative outcomes remains uncertain. This study's primary aim was to assess the relationship between preoperative ulnar nerve CSA and postoperative changes in Patient-Reported Outcomes Measurement Information System (PROMIS) scores in the early postoperative period.

Methods: A retrospective review was conducted of all cubital tunnel surgeries performed by the senior authors from January 2015 to May 2023. Demographics, preoperative study results, and PROMIS scores were obtained from patient charts. Bivariate and multivariable statistical testing was used to determine statistical significance. After a threshold effect of CSA was observed at 12 weeks post-operation, a Youden analysis was performed to determine the threshold value.

Results: At 12 weeks post-operation, patients with preoperative CSA > 16 mm² had an average change in PROMIS physical function (PF) score of -0.95, which was significantly lower than the 3.41-point improvement experienced by patients with a CSA ≤ 16 mm². Preoperative CSA and postoperative PROMIS scores did not demonstrate a significant linear relationship, either before or after accounting for advanced patient age and type II diabetes mellitus diagnosis.

Conclusions: A preoperative ulnar nerve CSA > 16 mm² was predictive of significantly less improvement in PF at 12 weeks post-operation compared to the progress experienced by patients with smaller ulnar nerve CSA. These findings may aid in preoperative counseling regarding expectations for improvement in hand function during the early postoperative period.