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Incidence of Ulnar Nerve Instability in Patients Considered for in Situ Ulnar Nerve Decompression
Jonas Matzon, MD; Kevin Lutsky; C. Edward Hoffler, MD, PhD; Nayoung Kim, BS; Pedro Beredjiklian, MD
Orthopaedics, Rothman Institute at Thomas Jefferson University Hospital, Philadelphia, PA

Introduction: The incidence of ulnar nerve instability in patients considered for in situ ulnar nerve decompression is unknown, and pre-operative risk factors for ulnar nerve instability necessitating transposition have yet to be identified. We hypothesized that a relatively high percentage of patients considered for in situ ulnar nerve decompression will require transposition secondary to ulnar nerve instability.

Methods: Using our surgical database, we retrospectively identified all patients undergoing surgical treatment of cubital tunnel syndrome by three surgeons over a five-year period. We included all patients who were candidates for in situ ulnar nerve decompression. Patients requiring ulnar transposition due to revision surgery, elbow arthritis, or elbow contracture were excluded. Three hundred sixty three patients met inclusion criteria. We collected demographic data including age, weight, height, and body mass index (BMI). Patients with pre-operative radiographs had measurements of ulnar groove and medial epicondyle morphology. We recorded the number of patients who underwent ulnar nerve transposition due to ulnar nerve instability, and we evaluated whether ulnar nerve instability was diagnosed pre-operatively, intra-operatively following decompression, or post-operatively. We performed unpaired t-tests to assess statistical differences between patients undergoing decompression and patients requiring transposition.

Results: Of the 363 patients who were considered for in situ ulnar nerve decompression, 76 patients (21%) required ulnar nerve transposition secondary to ulnar nerve instability. Twenty-nine patients (8%) were diagnosed with instability pre-operatively, while 44 patients (12%) were identified with instability intra-operatively following in situ decompression. Three patients (1%) were not diagnosed with instability until post-operatively and subsequently underwent delayed transposition. Patients who required transposition due to instability were significantly younger (p<0.0002), taller (p<0.03), and had a lower BMI (p<0.05) than patients without instability. For those patients with pre-operative radiographs, height and width of the ulnar groove and slope of the inferior aspect of the medial epicondyle did not correlate with the need for transposition.

Conclusion: In situ ulnar nerve decompression is an acceptable treatment for cubital tunnel syndrome, but a relatively high percentage of patients will require transposition secondary to ulnar nerve instability. While patient age, height, and BMI correlate with the need for ulnar nerve transposition, further research is necessary to determine which patients are at greatest risk for ulnar nerve instability following decompression. Meticulous pre-operative evaluation for ulnar nerve instability is recommended to aid in appropriate patient counseling and surgical scheduling.


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