The impact of pre-existing ulnar nerve instability on the surgical treatment of cubital tunnel syndrome: a systematic review

Background: The decision to perform nerve transposition (NT) or in situ decompression (SD) during surgical treatment of cubital tunnel syndrome is often based on nerve subluxation through elbow motion. This review assesses what impact nerve instability has on study design and reported outcomes. Methods: A search was performed with Boolean operators: “ulnar nerve” OR “cubital tunnel” AND “decompression” OR “transposition” on PubMed, Clinical Key, and CINAHL to identify primary studies comparing NT and SD that report pre-existing nerve instability. Primary outcome was the effect of instability on study design. Secondary outcomes were nerve instability, patient-reported scores, and complications. Results: Five studies met criteria after screening 134 articles. In 3 studies, nerve instability dictated treatment. Prospective randomization was maintained in 1 study. Included cases totaled 464 SD and 304 NT. The complication rate was 8.6% overall, 4.3% for SD and 21.1% for NT. Bishop scores were 56.9% excellent and 37.3% good for stable nerves and 62.0% excellent and 29.3% good for unstable nerves. Conclusions: Very few studies report ulnar nerve instability, and study design is biased by ulnar nerve subluxation. Outcomes showed similar symptomatic improvement for both decompressed and transposed groups with higher complication rates for the transposed group.