This study provides recommendations on the position
of the implant in reverse shoulder replacement in order to minimise
scapular notching and osteophyte formation. Radiographs from 151
patients who underwent primary reverse shoulder replacement with
a single prosthesis were analysed at a mean follow-up of 28.3 months
(24 to 44) for notching, osteophytes, the position of the glenoid
baseplate, the overhang of the glenosphere, and the prosthesis scapular
neck angle (PSNA). A total of 20 patients (13.2%) had a notch (16 Grade 1 and four
Grade 2) and 47 (31.1%) had an osteophyte. In patients without either
notching or an osteophyte the baseplate was found to be positioned
lower on the glenoid, with greater overhang of the glenosphere and
a lower PSNA than those with notching and an osteophyte. Female patients
had a higher rate of notching than males (13.3% Based on these findings we make recommendations on the placement
of the implant in both male and female patients to avoid notching
and osteophyte formation. Cite this article:
Reversed shoulder prostheses are increasingly being used for the treatment of glenohumeral arthropathy associated with a deficient rotator cuff. These non-anatomical implants attempt to balance the joint forces by means of a semi-constrained articular surface and a medialised centre of rotation. A finite element model was used to compare a reversed prosthesis with an anatomical implant. Active abduction was simulated from 0° to 150° of elevation. With the anatomical prosthesis, the joint force almost reached the equivalence of body weight. The joint force was half this for the reversed prosthesis. The direction of force was much more vertically aligned for the reverse prosthesis, in the first 90° of abduction. With the reversed prosthesis, abduction was possible without rotator cuff muscles and required 20% less deltoid force to achieve it. This force analysis confirms the potential mechanical advantage of reversed prostheses when rotator cuff muscles are deficient.
