Gross anatomical and histological orientation of the lateral intermuscular septum of the upper arm: a descriptive study

Abstract

Objectives: The lateral intermuscular septum (LIS) is dense and opaque in gross cadaver dissection. It was suggested as source of pain in elbows with lateral epicondylalgia (LE). The study aimed to measure the length of LIS and to describe the fascia orientation and density of LIS in upper extremities of human cadavers. . Methods: 19 upper extremities of 10 formalin preserved human cadavers were dissected using the fascia sparing approach. The LIS was measured from the level of the lateral epicondyle up to the upper arm. The LIS was harvested 5 cm above and below the lateral epicondyle and submitted to a laboratory for histological staining. Prepared slides containing stained LIS were observed under high power microscope. Results: In 17 out of the 19 upper extremities, the LIS attached from the brachioradialis to middle deltoid with a mean of 14.5 (13.8-15.1) cm. 68 out of the 72 fascia images of LIS were linearly oriented in relation to the lateral epicondyle. The LIS was dense on its distal (16/18) and loose (12/16) on its medial sides. Conclusion: The fibers of LIS were linearly arranged near the lateral epicondyle in the upper arm connecting the brachioradialis and the deltoid. The LIS was dense and loose on its distal and medial sides, respectively. Considering the arrangement, connection and density of LIS in the upper arm, the LIS contributes to the inherent tightness of the elbow that may be important in handgrip activities. The connection between brachioradialis and middle deltoid by LIS is important in considering the changes in shoulder movement associated with lateral elbow pain in LE. Keywords: brachioradialis muscle; lateral intermuscular septum; upper arm