This article reviews the anatomic anomalies found during 147 consecutive carpal tunnel releases using a wide surgical exposure between 1983 and 1993. An extensive oblique incision was used across the palm extending from the pisiform to the distal palmar crease in line with the second web space. Variations were classified as Type I, intrinsic to the carpal tunnel, and Type II, extrinsic to the carpal canal. Seventy-four variations were identified in 60 hands, for an incidence of 41%. Patients less than 40 years of age with dominant hand involvement had a 71% incidence of an anatomic anomaly compared to only 24% in patients older than 40 years with carpal tunnel in their non-dominant hand. Intrinsic anomalies included lumbrical and FDS muscles within the canal, lipomas, ganglions, patent median arteries, and cartilage-like thickening of the transverse carpal ligament. Extrinsic anomalies related mainly to variations in muscle anatomy including the thenar, hypothenar and palmaris brevis muscles.
This paper supports an anatomic predisposition carpal tunnel syndrome in many individuals. Most of the reported anatomic variations have been previously described, but few authors have studied the incidence in a surgically treated patient population. While the findings are interesting, the results will probably not have a great impact on current treatment algorithms. Larger studies have shown similar long-term results with more limited incision and arthroscopic techniques when compared to larger open exposures. Surgeons, however, should keep in mind the possibility of anatomic anomalies when performing this common procedure, regardless of which surgical method is chosen.
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