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.