We hypothesised that a large acromial cover with
an upwardly tilted glenoid fossa would be associated with degenerative
rotator cuff tears (RCTs), and conversely, that a short acromion
with an inferiorly inclined glenoid would be associated with glenohumeral
osteoarthritis (OA). This hypothesis was tested using a new radiological parameter,
the critical shoulder angle (CSA), which combines the measurements
of inclination of the glenoid and the lateral extension of the acromion
(the acromion index). The CSA was measured on standardised radiographs of three groups:
1) a control group of 94 asymptomatic shoulders with normal rotator
cuffs and no OA; 2) a group of 102 shoulders with MRI-documented
full-thickness RCTs without OA; and 3) a group of 102 shoulders
with primary OA and no RCTs noted during total shoulder replacement.
The mean CSA was 33.1° (26.8° to 38.6°) in the control group, 38.0°
(29.5° to 43.5°) in the RCT group and 28.1° (18.6° to 35.8°) in
the OA group. Of patients with a CSA >
35°, 84% were in the RCT
group and of those with a CSA <
30°, 93% were in the OA group. We therefore concluded that primary glenohumeral OA is associated
with significantly smaller degenerative RCTs with significantly
larger CSAs than asymptomatic shoulders without these pathologies.
These findings suggest that individual quantitative anatomy may
imply biomechanics that are likely to induce specific types of degenerative
joint disorders. Cite this article:
We compared six patients with a mean age of 70 years (49 to 80) with severe bilateral, painful glenohumeral joint destruction who underwent a single-stage bilateral total shoulder replacement, with eight patients of mean age 61 years (22 to 89) who underwent bilateral total shoulder replacement in two stages, at a mean interval of 18 months (6 to 43). The overall function, pain and strength improved significantly in both groups. The subjective shoulder value, relative Constant score, active external rotation and the strength were improved significantly more in the single-stage group. Active elevation, abduction and overall function improved, significantly more in the single-stage group. Both the total duration of hospitalisation and the time off work per shoulder were substantially shorter in the single-stage group. The overall rate of complication was lower in the single-stage group. Our findings indicated that single-stage bilateral total shoulder replacement yielded significantly better clinical results with shorter hospitalisation and rehabilitation than staged replacement, and was not associated with any increase in complications.
