Three-dimensional analysis of baseplate screw penetration in reverse total shoulder arthroplasty: risk of iatrogenic suprascapular neuropathy by screw violation.

Background: Baseplate screws have been suggested to be a possible cause of suprascapular neuropathy after reverse total shoulder arthroplasty (RTSA). Three-dimensional analyses of screw penetration and confirmation of its clinical impacts are relevant. The study aims to investigate the association between screw penetration and the clinical outcomes.

Materials And Methods: Eighty-two patients who underwent RTSA for a massive rotator cuff tear, cuff tear arthropathy, or osteoarthritis with rotator cuff tear were retrospectively enrolled. They were followed up for a minimum of 12 months, and all underwent computed tomography at 1 year postoperatively. The lengths of the superior and posterior baseplate screws were documented. Postoperative computed tomography images were subjected to 3-dimensional analysis to determine whether superior or posterior screws penetrated the glenoid vault and the location to which they penetrated, and screw-to-nerve distances were measured to estimate risks of screw nerve violation and iatrogenic suprascapular neuropathy. Patients with any screw <5 mm from the suprascapular nerve were deemed to have a high risk. Clinical outcomes (functional scores, ranges of motion, and isometric strengths) of patients in the high- and lower-risk groups were compared.

Results: The mean lengths of the superior and posterior screws were 28 ± 4 mm and 18 ± 3 mm, respectively. Penetration was detected for 13% of superior screws and 64% of posterior screws. Sixty-three percent of penetrating superior screws and 5% of penetrating posterior screws were <5 mm from the suprascapular nerve, and therefore, 12% of patients who received RTSA were assessed to have a high risk of iatrogenic suprascapular neuropathy. However, no significant difference was detected in clinical outcomes between the high- and lower-risk patients after a mean follow-up period of 20 months.

Conclusion: Twelve percent of patients who received RTSA were assessed to be at high risk of iatrogenic suprascapular neuropathy by baseplate screw penetration. However, the clinical outcomes of RTSA at a minimum follow-up of 1 year were similar in the high- and lower-risk groups.