A reproducible classification system that allows different surgeons to establish comparable homogeneous patient groups is useful for both therapeutic and prognostic purposes. We defined four types of subscapularis lesions that are easy to identify as either isolated lesions or combined with anterosuperior rotator cuff tears. Long head of biceps tendon abnormalities and fatty degeneration of the shoulder muscles can be added to our classification system. Studies of intraobserver and interobserver reproducibility are needed to complete the process of validating the diagnostic and/or prognostic usefulness of this new classification scheme.

Our study confirms the good clinical and radiological results reported in the literature. Our classification system distinguishing four lesion patterns was applicable during the imaging workup. The main finding from this classification system was the difference in results between Type 2 and Type 3 lesions. The trend towards improvements over time requires confirmation by longer-term studies, which will also have to establish that the increased wasting of the upper subscapularis muscle and fatty degeneration of the muscle belly have no adverse effects.

An original method of CT measurement of the lateralization of the humeral intertubercular groove is described based on geometric construction following Thales theorem. A study of intra- and interobserver reproducibility was done of this measurement and humeral retroversion on 32 healthy volunteers. The results show good reproducibility of these measurements. The average value of humeral retroversion was lower than the average values found in the literature: 11.71 degrees on average on the dominant side and 7.03 degrees on average on the non-dominant side with a large spread of values. The reasons for these differences are discussed. The average values of lateralization of the intertubercular groove were 114.97 degrees on the dominant side and 121.9 degrees on the non-dominant side. These CT measurements are important to consider in the pathophysiology of chronic anterior instability of the shoulder.

Even though all three tests were performed (LOT, BPT, BHT), 24% of the subscapularis tears were only diagnosed during surgery. The role of the Internal Rotation Lag Sign and Belly-Off Sign in improving the diagnosis of tears was not studied in this work.