Lateralized versus medialized glenoid implants in reverse total shoulder arthroplasty for proximal humerus fractures. Comparison between trabecular metal and comprehensive Zimmer Biomet glenoid implants

Reverse total shoulder arthroplasty (rTSA) is widely recognized as an effective treatment for complex proximal humerus fractures (PHFs), providing reliable and predictable outcomes. However, whether glenoid lateralization confers tangible advantages in this setting remains unclear. This study aimed to evaluate the impact of different amounts of glenoid lateralization on clinical and functional outcomes following rTSA for PHFs. To our knowledge, this is the first study to specifically address this question. A total of 132 patients with 3 or 4-part PHFs were treated with rTSA using the same humeral stem (Trabecular Metal Zimmer, TM, a cemented inlay stem, 150° neck-shaft angle), same 36-mm glenosphere, and same surgical team. Patients were allocated into 2 groups according to the glenoid baseplate: Group A received a medializing baseplate (TM Zimmer) and Group B a lateralizing baseplate (Comprehensive Zimmer). Minimum follow-up was 18 months. Functional outcomes were assessed using Constant-Murley Score (CS), range of motion (ROM), and muscle strength recovery with Medical Research Council (MRC) scale. Of the 132 patients initially enrolled (23 males, 109 females; mean age 74.3 years), 15 were excluded due to tuberosity healing failure or deep infection. The final cohort consisted of 117 patients (64 in Group A, 53 in Group B). At final follow-up, the overall cohort demonstrated very good results: mean forward flexion (FF) 157°, abduction 152°, external rotation (ER) 26°, and internal rotation to the L2 vertebral level; mean strength recovery with MRC scale were 4.7/5 for FF and abduction, and 4.3/5 for ER and internal rotation; mean CS was 67.4/100. Compared with Group A, Group B achieved significantly greater ROM in FF (153° vs. 161°) and ER (23° vs. 30°), higher muscle strength recovery (MRC scores), and superior CS (64.0 vs. 70.8), especially in subcategories of ROM (29.8/40 vs. 34.0/40), Pain relief (14.2/15 vs. 14.8/15), and Activities of daily living (14.8/20 vs. 16.1/20). This is the first study to directly compare varying degrees of glenoid lateralization in rTSA for PHFs, with a significant sample size and rigorous selection of both patients and prosthetic components. While excellent mid-term outcomes were observed in all patients, the use of lateralized glenoid components was associated with superior ROM, pain relief, muscle strength, and overall clinical scores. In the context of PHFs managed with rTSA, glenoid lateralization with a humeral inlay stem with neck-shaft angle of 150° appears to provide significant functional advantages in functional outcomes.