These authors evaluated the radiographic and clinical performance of an anatomic total shoulder arthroplasty (TSA) with respect to radial mismatch between the curvatures of the glenoid and humeral components. The study group was divided in two groups, one with mismatch < 4.5mm (n:52) the others with mismatch ≥4.5mm (n:23) and analyzed for confounding variables as indication, primary or revision surgery, age, gender, glenoidmorphology and implant characteristics.
The mean glenohumeral radial mismatch was 3.4mm (range 0.5–6.9).
At median follow-up of 41 months radiographic loosening was present in 7 cases (9.3%).
Lucencies around the glenoid pegs were present in 34 cases (45%).
Radiolucencies were significantly associated with a radial mismatch < 4.5mm.
The pre- to postoperative improvements in Subjective Shoulder Value and absolute Constant Score were significantly better in the group with a mismatch ≥4.5mm.
The authors concluded that lower conformity between the radii of humerus and glenoid seems to improve the loosening performance in TSA.
Comment: It is well recognized that a high degree of conformity between the curvature of the humeral head component and the glenoid component can lead to rocking horse loosening of the glenoid.
The authors concluded that lower conformity between the radii of humerus and glenoid seems to improve the loosening performance in TSA.
Comment: It is well recognized that a high degree of conformity between the curvature of the humeral head component and the glenoid component can lead to rocking horse loosening of the glenoid.
A slight degree of mismatch between the curvatures allows for some translation without rim loading.
However, high degrees of mismatch reduce the joint contact area and increase the local joint pressure.
This can lead, over time, to increased polyethylene wear as shown below.
In our practice, we prefer a mismatch of 6mm in diameter, which is equivalent to a mismatch of 3 mm in radius.
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