Anatomic Relationship of Hand Intrinsic Tendons at the Metacarpal Head as It Relates to the Diagnosis of Saddle Syndrome: A Cadaveric Study

Abstract

The purpose of this cadaveric study was to investigate the intrinsic anatomy surrounding the metacarpal head and the relationship between the interosseous-lumbrical junction (ILJ) and transverse metacarpal ligament (TML) as it pertains to saddle deformity-posttraumatic adhesions at the ILJ that cause impingement during intrinsic activation. Ten fresh frozen cadaveric arms underwent dissections, identifying the intrinsic musculature within the second through fourth webspaces. The TML and ILJ, or "true tendon," were identified. A separate area of nontendinous fibrous tissue identified proximal to the ILJ was referred to as "pseudotendon." Measurements were made within each webspace to identify distances between these structures in full finger extension and intrinsic plus position to assess for changes during simulated motion. The true tendon to TML distance progressively decreased toward the ulnar digits. In the intrinsic plus position, the pseudotendon to TML distance was 0 mm at all webspaces for each specimen. When moving from neutral to intrinsic plus, the true tendon to TML distance decreased the most in the third and fourth webspaces compared with the second, consistent with the trend toward a smaller ILJ to TML gap in the ulnar digits. There is a fibrous pseudotendinous region proximal to the ILJ that abuts the TML in the intrinsic plus position, which may cause impingement when inflamed in the setting of saddle syndrome. Furthermore, a decreased ILJ to TML gap in the ulnar digits may be related to an increased predilection for saddle deformity in those areas. These results suggest that there is a fibrous region present proximal to the ILJ that may be implicated in the pathology of saddle deformity. Furthermore, decreased distances found between the ILJ and TML invivo may be an explanation for increased occurrence of saddle syndrome in the third and fourth webspaces in clinical practice.