The lesser tuberosity C-block osteotomy for anatomical total shoulder arthroplasty has no negative impact on the volumetric ratio of the transversal force couple.

Background: Mobilization of the subscapularis muscle (SSC) is crucial for optimal access to the glenohumeral joint during anatomical total shoulder arthroplasty (ATSA). However, the ideal mobilization technique remains controversial. This study aimed to assess the impact of the lesser tuberosity C-block osteotomy, a modified lesser tuberosity osteotomy, on the postoperative subscapularis (SSC) volume following anatomical shoulder arthroplasty and compare it to the volume of the infraspinatus/teres minor.

Materials And Methods: All patients between 2006-2022 who received an anatomical total shoulder arthroplasty with the lesser tuberosity C-block osteotomy for primary shoulder osteoarthritis or avascular necrosis of the humeral head with a minimum follow-up of one year and received full scapulae CT scans postop were included in the study. Utilizing imaging software and a validated method established for healthy shoulders, we assessed the postoperative volume of the transversal force couple.

Results: 56 patients (59 shoulders) with an average follow-up of 5 years were included in the study. A strong correlation (rₛ=0.954) was observed between the volumes of the anterior and posterior parts of the transverse force couple, with no statistically significant difference (P=0.207) noted in muscle volumes. The mean transverse force couple ratio was 1.01±0.06, with similar values found across all age groups. Intraobserver and interobserver correlation coefficients were excellent.

Conclusion: Using the lesser tuberosity C-block osteotomy during anatomical total shoulder arthroplasty does not disrupt the essential volumetric balance between the subscapularis and infraspinatus/teres minor, as observed in a well-functioning transverse force couple.