Abstract: Extensor Pollicis Brevis Subcompartment Characteristics in the 1st Dorsal Extensor Compartment: An Anatomic Study

Abstract

INTRODUCTION: DeQuervain’s tenosynovitis is a common condition often satisfactorily treated with steroid injections alone. Certain patients, however, ultimately require surgical release of the 1st dorsal extensor compartment. We hypothesize that patients with an EPB subcompartment are more likely to require surgery. The purpose of this study was to better characterize the 1st dorsal compartment anatomy, determine the incidence of EPB subcompartments, and explore potential radiographic correlations related to these findings. METHODS: The 1st dorsal extensor compartment was dissected in ten (10) freshly preserved cadaveric arms. Data including the presence of an EPB subcompartment were collected. Standard posterior/anterior (PA), lateral and oblique x-rays of each wrist were obtained using a portable x-ray machine (Carestream DRX-Revolution, Rochester NY). RESULTS: Nine of the 10 cadaver arms (90%) were male patients and 6 (60%) were left upper extremities. The average age of the donors was 73.7 ± 16.1 years. The average diameter of the 1st dorsal compartment was 13.3 ± 1.3 mm. The mean 1st dorsal compartment length was 29.7 ± 10.2 mm. The abductor pollicis longus tendon was composed of a mean of 3.3 ± 1.3 slips. The extensor pollicis brevis tendon had a single slip in all ten specimens. Seven of ten 1st compartments (70%) had an identifiable EPB subcompartment with an average length of 80.0 ± 10.3% of the 1st dorsal compartment length. Four (57%) subcompartment sheaths were characterized as thick and three (43%) as thin. All 4 thick subsheaths continued well-beyond the edge of the distal radius (min 35%, max 74%) whereas only 1 of 3 thin subsheaths continued beyond the distal radius. An osseous ridge within the compartment was identified in 2 specimens, both of which were associated with a thick EPB subcompartment. CONCLUSION: Seventy percent of the specimens studied had an EPB subcompartment within the 1st dorsal extensor compartment and the majority of these were thick and well-defined, spanning from a portion of the bony tunnel to beyond the distal radius edge; bony ridges within the 1st compartment were only seen in the presence of these well-developed subsheaths. Such characteristics may contribute to the failure of non-operative interventions. The intracompartmental bony ridge may be detectable on preoperative radiographs and, thus, may be a predictor of the presence of thick EPB subcompartment. This could help guide clinical decision-making. DISCLOSURE/FINANCIAL SUPPORT:None of the authors has a financial interest to disclose.