The association between a low critical shoulder angle and SLAP lesions.

PURPOSE: To evaluate the critical shoulder angle (CSA), acromion index (AI) and further acromion parameters in patients with isolated SLAP lesions compared with patients without SLAP lesions. METHODS: Between 2012 and 2016, the CSA, AI, lateral acromion angle (LAA) and acromion slope (AS) were radiologically examined in consecutive patients > 18 years having had a shoulder arthroscopy with isolated SLAP lesion types II-IV. These were compared to controls without SLAP lesions and without (control group I) or with (control group II) complete supraspinatus tendon (SSP) tears. RESULTS: 75/103 patients with isolated SLAP lesion types II-IV with a mean age of 46.5 years (± 13.0, 18.1-76.3) were analyzed, 61% of them being male. For control, n = 211 consecutive patients (47% male) with an intact SSP and SLAP complex and a mean age of 52.3 years (± 15.0, 18.6-88.4) and n = 115 patients (60% male) with an intact SLAP complex but complete SSP tears, mean age 66.6 years (± 9.3, 44.7-87.9) were examined. The CSA in SLAP patients was 29.6° (± 3.5, 21.0-38.0), 33.8° (± 3.7, 25.1-46.9) in no SLAP and no SSP (p < 0.001) and 36.7° (± 3.6, 29.1-46.6) in no SLAP but SSP (p < 0.001). The area under the curve (AUC) for CSA was 0.83 for SLAP lesions resulting in a probability of 83% for patients with SLAP lesion to be associated with a specific CSA. CONCLUSIONS: Isolated SLAP lesion types II-IV are associated with a low CSA < 30°. The AI, the AS as well as the LAA showed no correlation with SLAP lesions. LEVEL OF EVIDENCE: Retrospective comparative study, Level III.