The Correlation between Various Shoulder Anatomical Indices on X‐Ray and Subacromial Impingement and Morphology of Rotator Cuff Tears

OBJECTIVES: Rotator cuff injury caused by subacromial impingement presents different morphologies. This study aims to investigate the correlation between various shoulder anatomical indexes on X‐ray with subacromial impingement and morphology of rotator cuff tears to facilitate surgical management. METHOD: This retrospective study was carried out between January 2020 and May 2022. Patients who were diagnosed as sub‐acromial impingement associated with rotator cuff tears (without tendon retraction) and received arthroscopic surgery were enrolled in this study. The radiographic indexes of acromial slope (AS), acromial tilt (AT), lateral acromial angle (LAA), acromial Index (AI), and sub‐acromial distance (SAD) were measured on preoperative true AP view and outlet view. The location of rotator cuff tear (anterior, middle, posterior, medial, and lateral) and morphology of tear (horizontal, longitudinal, L‐shaped, and irregular shaped) were evaluated by arthroscopy. Groups were set up due to different tear location and tear morphologies, by comparing the various radiographic indices between each group (one‐way analysis of variance and t‐test), the correlation between radiographic indices and tear characteristics was investigated. RESULTS: We analyzed 92 shoulders from 92 patients with a mean age of 57.23 ± 8.45 years. The AS in anterior tear group (29.32 ± 6.91°) was significantly larger than that in middle tear group (18.41 ± 6.13°) (p = 0.000) and posterior tear group (24.01 ± 7.69°) (p = 0.041). The AS in posterior tear group (24.01 ± 7.69°) was significantly larger than that in middle tear group (18.41 ± 6.13°) (p = 0.029). The LAA in middle tear group (67.41 ± 6.54°) was significantly smaller than that in posterior group (72.74 ± 8.78°) (p = 0.046). The AS in longitudinal tear group (26.86 ± 8.41°) was significantly larger than that in horizontal tear group (22.05 ± 9.47°) (p = 0.035) and L‐shaped group (21.56 ± 6.62°) (p = 0.032). The LAA in horizontal group (70.60 ± 6.50°) was significantly larger than that in L‐shaped group (66.39 ± 7.31°) (p = 0.033). The AI in L‐shaped tear group (0.832 ± 0.074) was significantly larger than that in horizontal tear group (0.780 ± 0.084) (p = 0.019) and irregular tear group (0.781 ± 0.068) (p = 0.047). CONCLUSION: Acromion with a larger AS and a smaller LAA tend to cause anterior or posterior rotator cuff tears rather than middle tears in sub‐acromial impingement. Meanwhile acromion with a larger AS tends to cause a longitudinal tear, a larger LAA tends to cause horizontal tears and a larger AI tends to cause L‐shaped tears.