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.

Introduction: The literature reports an increase in anteroposterior diameter of the common extensor origin (CEO) of the extensor carpi radialis brevis (ECRB) and extensor digitorum communis (EDC) or the radial nerve in painful elbows diagnosed with lateral epicondylalgia (LE) or supinator syndrome. The edge-to-edge measurements of these anatomical structures are quantified using musculoskeletal ultrasound (MSUS). However, in the current literature, reports on the reliability and validity of MSUS measurements of the CEO (of ECRB and EDC) and the radial nerve are not found. In this study, reliability was measured for three testers in determining the anteroposterior diameter of the CEO (of ECRB and EDC) and the radial nerve. Moreover, the concurrent validity was determined of MSUS measurements with Vernier calipre measurements using formalin preserved elbows of human cadavers. Methodology: Cadaver measurements of the CEO (of ECRB and EDC) and the radial nerve were performed. Initially, the sonologist measured the anteroposterior diameter of the CEO (of ECRB and EDC) and the radial nerve. A month after scan, the formalin preserved cadavers were dissected. Consequently, the anteroposterior diameter of the exposed CEO (of ECRB and EDC) and the radial nerve was measured using the Vernier calipre. Results: Eight upper extremities of four embalmed Filipino cadavers (2 males: 2 females) were dissected. A total of seven (7) CEO of EDC, seven (7) CEO of ECRB, and eight (8) radial nerves at the level of the radial head in the elbows of four (4) cadavers were measured using the MSUS and the Vernier calipre. The MSUS and Vernier calipre protocol used in this study was found to be reliable, p > 0.05. However, in all three levels of interest, the MSUS measurements were statistically different from the Vernier calipre measurements, p < 0.05. Conclusion: MSUS and Vernier calipre measurements are reliable methods in measuring the CEO (of ECRB and EDC) and the radial nerve. While each of these methods is reliable in measuring the anteroposterior dimensions of the CEO (of the EDC and ECRB) and the radial nerve, substituting one for the other yielded statistically different measurement results.