Subacromial plica as a cause of impingement in the shoulder

The subacromial bursa is the largest bursa in the body. In 1934, Codman described the presence of subacromial plicae, similar to the suprapatellar plicae found in the knee. It is recognized that plicae in the knee can cause anterior knee pain with impingement against the patella in young persons. We investigated the possibility that a similar situation exists with plicae of the subacromial bursa. The aims of this study were to document the prevalence of bursal plicae seen at bursoscopy during arthroscopic subacromial decompression of the shoulder and to assess whether there is any pattern in the occurrence of these plicae, as well as the relationship to impingement lesions seen at bursoscopy. Between January 1996 and July 2001, all cases undergoing arthroscopic decompression were evaluated for anatomic-pathologic changes of the subacromial bursa, including the presence of plicae and impingement lesions. A total of 1732 cases complying with inclusion criteria were recorded, with plicae observed in 104 (6.0%). The occurrence of plicae showed a highly significant younger age predilection (P = .0008, χ² test) but no differences between sexes or sides. The occurrence of subacromial plicae was highly associated with the combined severity of the impingement lesion on the acromial and bursal side. Plicae were most common in shoulders showing an impingement lesion on the cuff bursal side, with no impingement lesion on the acromial side. The odds of the impingement lesion being milder on the acromial side was 3.41 times higher in shoulders with a plica compared with shoulders without a plica. This suggests that impingement of the cuff may be due to the plica itself. This study is the first to describe the presence of subacromial plicae in living subjects and correlates with previous anatomic studies. The younger age predominance correlates with the findings of plicae in the knee. Our findings suggest that subacromial plicae may be a cause of impingement in young patients.