Distalization and lateralization shoulder angles: do they have a role in predicting postoperative clinical outcomes?

Background

Lateralization Shoulder Angle (LSA) and Distalization Shoulder Angle (DSA) have been proposed to estimate the appropriateness of reverse shoulder arthroplasty (RSA) positioning. The purpose of this study was to evaluate the predictive value of DSA and LSA over clinical outcomes in a group of patients treated by the same surgeon with the same clinical and radiographic follow-up.

Methods

A retrospective analysis of a consecutive series of RSAs performed between 2017 and 2021 was carried out. Inclusion criteria were primary RSA as a treatment for Cuff Tear Arthropathy, Massive Irreparable rotator cuff tear, Osteoarthritis or Rheumatoid arthritis, a true anteroposterior radiograph of the affected shoulder in neutral rotation at final follow-up, a minimum follow-up of 12 months, radiograph used to measure the angles, and clinical evaluation with the same follow-up. Outcome measures were shoulder range of motion (ROM), visual analog scale (VAS) for pain and Constant-Murley score (CS).

Results

A total of 83 patients were included in the study. Patients achieved on average, 130 ± 14.14° of flexion, 97.5 ± 17.67° of abduction, 62.5 ± 3.53° and 72.5 ± 10.60° of external rotation, respectively, at 0° and 90° of abduction, and 5.13° of internal rotation. The mean VAS and CS were, respectively, 2.5 ± 3.5 mm and 69 ± 2.82 points at last follow-up. The mean DSA and LSA were 45 ± 2.72 and 92.99 ± 9.17, respectively. Neither the linear nor the quadratic regression fit for DSA or LSA revealed relevant associations with any of individual ROM measures, except for the quadratic fit correlating LSA and forward flexion (beta = 0.029, P = .027). Linear fit showed a low reverse, but significant, association between DSA and VAS (beta = −0.56, P = .036) and an association of LSA with both CS (beta = −0.344, P = .009) and VAS (beta = 0.091, P = .01). Quadratic models showed higher R squared for all associations, but correlation was significant only between VAS and LSA (beta = 0.006, P = .011)

Conclusion

We present the first evaluation of the predictive value of both DSA and LSA in a group of patients treated by the same surgeon with the same clinical and radiographic follow-up. DSA and LSA play only a marginal to no role in the prediction of RSA postoperative ROM and might have a role in predicting VAS and CS.