This study was designed to determine the correlation of a subacromial spur formation with instability of the shoulder to the frequency of impingement syndrome including degenerative rotator cuff tears. Fifty five shoulders with subacromial impingement syndrome including degenerative rotator cuff tears treated from 2006 to 2008 were evaluated. The patients' mean age was 65 years old (range, 40 to 80). The sizes of subacromial spur were measured using X-rays of 30 degrees caudal tilt view and classified into 3 groups: non-spur size (0 to 5mm), medium spur (5 to 10), large spur (over 10). The head of the humerus descending ratio was measured in X-rays of 5kg downward stressed view and classified into 3 groups: non-instability (0 to 10%), moderate instability (10 to 30), high instability (over 30). The results showed that 27% (8 shoulders) in non-spur group had instability, 80% (20 shoulders) in spur group had instability. In spur group, 7 shoulders (100%) of patients under 60 years old had instability, 9 shoulders (75%) of patients between 60 and 70years old had instability, and 4 shoulders (57%) of patients over 70 years old had instability. In shoulder impingement syndrome including degenerative rotator cuff tears, most patients in the medium and large spur group had shoulder instability. Patients under 60 years old with shoulder instability, tended to have a large subacromial spur. A large spur may cause rotator cuff tear at an early age.
