Does lateralisation of the centre of rotation in reverse shoulder arthroplasty avoid scapular notching? Clinical and radiological review of one hundred and forty cases with forty five months of follow-up.

PURPOSE: Our purpose was to evaluate the influence of metallic lateralisation of the centre of rotation (COR) in reverse shoulder arthroplasty (RSA) on the incidence of scapular notching and its eventual clinical and radiological consequences.

METHODS: We analysed 140 RSAs with a lateralised design (Arrow, FH Orthopedics, Mulhouse, France) implanted for massive rotator cuff tear with/without arthritis. Mean follow-up was 45 months (range 24-120, standard deviation 20). Patients were evaluated clinically using the Constant and Murley (Clin Orthop Relat Res 214:160-164, 1987) score and active range of motion (ROM) and radiologically using standard anteroposterior and axillary view. Scapular notching was assessed according to Sirveaux classification Simovitch et al. (J Bone Joint Surg Am, 89:588-600, 2007), and patients were separated into two groups (scapular notch/no scapular notch) and compared.

RESULTS: Forty-one notches (29 %) were found: 20 grade 1, 18 grade 2, and three grade 3. The latter three patients had a follow-up of 44, 70 and 84 months, respectively, and the scapular notch did not evolve in the final two years. Better pre-operative function was significantly associated with scapular notching (p < 0,05 for flexion and abduction), but no final clinical differences in ROM and Constant score were found between groups. A body mass index (BMI) <30 increased the risk of scapular notching, which was observed in 43 % of patients with a BMI < 30 and 30 % of patients with a BMI > 30 p = 0,048). Pre-operative narrowing of the subacromial space increased the risk of scapular notching, but age or gender showed no influence. However, there was a significantly greater number of scapular notches in patients operated on the dominant side (p = 0,04). No significant difference in lateral offset was found between groups (p = 0,99). Glenoid implantation in an excessively high position (p = 0,033) and absence of inferior tilt (p = 0,0029) were significantly associated with scapular notching.

CONCLUSIONS: In this series, metallic lateralisation of the COR in RSA did not impair clinical results, with patients achieving good flexion recovery ROM increase in rotations. Metallic lateralisation of the COR in RSA leads to a lower incidence of scapular notching (29 %) compared with previously reported results using other arthroplastic systems with a more medialised COR. However, although scapular notching was not totally eliminated, those that were found did not evolve over time. Several factors increased the incidence of scapular notching: BMI <30, better preoperative ROM, an excessively high glenoid implant and absence of inferior tilt.