The synovial fold of the humeroradial joint: anatomical and histological features, and clinical relevance in lateral epicondylalgia of the elbow.
The synovial fold of the humeroradial joint is known, and sometimes considered as a meniscus that could be injured by chronic repeated trauma related to pronation and supination. The aims of this study were to determine the gross anatomy and histological structure of this fold, and to clarify its participation in the painful lateral syndromes of the elbow. Fifty elbows from adult cadavers were dissected. The capsule of the humeroradial part of the elbow joint was resected with the annular ligament. The presence of a synovial fold, and its location relative to the cranial edge of the annular ligament divided into five sectors (ventral, ventrolateral, lateral, laterodorsal and dorsal) were noted; morphological parameters such as thickness, width and length were measured. The histological examination determined the structure of the folds. Five synovial folds were resected during surgery for epicondylalgia in five patients who suffered from pain precisely at the level of the joint between the capitulum and the fovea radialis, and were also examined. A fold was present in 43 cases, and in two cases two folds were seen at the deep side of the junction between the capsule and the annular ligament. The most frequent positions were: dorsal ( n=11), laterodorsal and dorsal ( n=6;), lateral to dorsal ( n=5), lateral ( n=5), ventral ( n=4) and circular ( n=4). The mean length was 21.4 mm (range from 9-51 mm). The mean width was 2.9 mm (range 1-10 mm), and the mean maximal thickness 1.7 mm (range 1-4 mm). The histological study showed two types of folds: a rigid structure, with oriented fibrous tissue, triangular with a peripheral capsular base, covered on its two sides and along the free edge by a synovial layer; and a pliable structure, formed of two synovial layers that surrounded a thin fatty tissue, with a villous appearance of the free edge. No fibromyxoid structure, as in a real meniscus, was observed. Some nerve fibers were seen in the folds. The five folds resected in operated patients were hypertrophic, and showed an increased number of nerve fibers, along the capsule but also close to the synovial layer. Some painful syndromes of the lateral side of the elbow are not related to tendinitis or to posterior interosseous nerve compression, but have an intra-articular origin. This study showed that the synovial fold is not a meniscus, and may be involved in the etiology of lateral epicondylalgia.