Posterior shoulder instability is rare, appears in varying clinical patterns and can be the main symptom in patients with instability in more than one direction. The purpose was to analyze and categorize our patients and to report on the results of operative treatment by arthroscopy.

A consecutive first series of 32 shoulders from a 7-year period were chosen for retrospective clinical evaluation with VAS, Rowe Score, Constant Score and Simple Shoulder Test. Allocation based on clinical and intraoperative criteria resulted in the 4 groups A to D characterized by an increasing traumatic impact: group A=predominantly posterior multidirectional (PPM), group B=recurrent posterior subluxation (RPS), group C=unidirectional, group D=bi-directional. A second series of up to now 18 shoulders have been operated since and are still being followed-up prospectively; the whole series now includes 50 shoulders. Patients were operated in beach-chair position receiving a posterior Bankart repair with bone-anchors in 37 or capsular plication to the intact labrum in 13 cases.

The clinical outcome scores were generally good and all showed a trend towards better results from A to D, but without significance. In the first series (n=32) pain on VAS pre- and postoperatively showed a significant (P<0.0001) overall decline from 7.4 to 1.8. The Rowe Score increased significantly (P<0.0001) from a mean value of 41.4 to 89.5 points. Three patients were operated a second time and satisfied, four patients not satisfied at follow-up. In the second series of 18 shoulders with shorter follow-up, no complications were observed. Subgroup allocation resulted in the following distribution: 12 patients qualified for group A, 20 for B, 12 for C and 6 patients for group D. Graphic display of labral lesions, called « labral mapping », revealed typical patterns for the groups. The second prospective series confirms the previously established categorization and allows a more precise demarcation between groups A and B using 4 secondary criteria.

In patients with posteroinferior shoulder instability good results can be obtained with the arthroscopic treatment of all identified pathologies. Categorization based on labral mapping and clearly defined additional criteria into one of four subgroups seems to be a valuable tool regarding the choice of the operative treatment options.