Serial 3D CT analysis of humeral head alignment in relation to glenoid correction and outcomes after total shoulder arthroplasty.

Background: Posterior humeral head (HH) subluxation after anatomic total shoulder arthroplasty (aTSA) is associated with worse outcomes, but it is unclear how corrective glenoid reaming correlates with HH alignment and whether HH alignment changes over time. Therefore, it was aimed to analyze the relationship between HH alignment and the scapula following aTSA to identify anatomic and surgical factors that contribute to realignment of the HH, glenoid loosening, and clinical outcomes. Methods: Three-dimensional scapulohumeral alignment was assessed on three-dimensionally reconstructed computed tomography scans of 23 patients: preoperative (T0), 2 years post-aTSA (T1), and ≥5 years post-aTSA (T2). Anterior-posterior (AP), superior-inferior (SI), and medial-lateral offset measures of the HH center to the scapula were referenced to the HH diameter (scapulohumeral subluxation index). Glenoid version and inclination were measured at T0 and T1. Central peg osteolysis, rotator cuff fatty infiltration, and vault perforation were assessed on two-dimensional computed tomography. Relative Constant Score at T2 measured clinical outcome. Results: Glenoid correction correlated strongly with AP and SI position of the HH (r = 0.733 and r = 0.797, respectively). Each degree of retroversion correction resulted in 0.9% AP scapulohumeral subluxation index offset change toward anterior. Each degree of inclination correction to superior resulted in a 1.0% offset change toward superior. A gradual postoperative proximal (mean difference [MD], -3%; P = .019), anterior (MD, 2%; P = .025), and medial (MD, 3 mm; P < .001) HH migration was observed. Asymmetric progressive rotator cuff fatty infiltration was associated with the direction of change in AP alignment over time (odds ratio, 2.04; P = .046), with progressive subscapularis fatty infiltration as the primary factor associated with gradual anterior HH translation (odds ratio, 15.61; P = .028). Gradual HH medialization was an indicator of glenoid components at risk for loosening (difference between medians, 4 mm; P = .003). Osteolysis around the central glenoid peg was influenced by overcorrection of glenoid version (MD, 7°; P = .038). Preoperative glenoid inclination was the sole anatomical or surgical factor predicting clinical outcome, as larger inferior inclination at T0 was associated with worse relative Constant Score at T2 (P = .016). Conclusion: Corrective glenoid reaming was an effective surgical technique to correct HH alignment in the AP and SI direction. Gradual anterior HH translation after aTSA was associated with progressive subscapularis fatty infiltration, and substantial HH medialization was an important indicator for potential glenoid loosening. While postoperative glenoid version and AP HH alignment were important for radiographic outcome, preoperative glenoid inclination predicted clinical outcome, as larger preoperative inferior inclination resulted in worse clinical scores.