Neurohistology of the subacromial bursa in rotator cuff tear

Abstract

This study was undertaken to identify and quantitate neural elements in the human subacromial bursa. Biopsy specimens of subacromial bursae were obtained from patients with rotator cuff tears and from cadavers of patients with no history of shoulder disorder (controls). We used a modified gold chloride method to characterize neural elements within the subacromial bursa. The population of intrabursal neural elements was calculated by computerized image analysis. The subacromial bursa demonstrated an extensive neural network: four morphological types of mechanoreceptors and many free nerve endings were identified. In general, there was an inverse relationship between the population density of neural elements and the extent of cuff tear. The population density of neural elements of the subacromial bursa associated with massive cuff tear was significantly lower than that observed in control shoulders. With regard to clinical symptoms, a significant correlation was established between the population density of neural elements in the subacromial bursa and shoulder pain at rest. Our investigation strongly suggests that the subacromial bursa is intimately involved in the perception of shoulder pain, providing an anatomical basis for afferent neural input in proprioceptive reflex arcs.