These authors conducted a systematic review using Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines of 3 publicly available free databases to determine if a difference exists between RTSA prostheses with a 135° vs 155° humeral component inclination angle with respect to dislocation rates and scapular notching rates.
Data were available on 1762 shoulders with a 155° inclination prosthesis and 460 with a 135° inclination prosthesis with a lateralized glenosphere.
The rate of scapular notching was 2.83% in the 135° group and 16.80% in the 155° group (P < .0001, z = -7.7107).
The rate of dislocation was 1.74% in the 135° group and 2.33% in the 155° group (P = .4432, z = -0.7669).
Comment: We suggest that the 155° was proposed because of concern about superior instability with lesser angles. However, when a 135° prosthesis is combined with some lateral offset, this concern has not been realized because of the effectiveness of East-West tensioning in stabilizing the articulation.
The redrawing of one of the figures from this article demonstrates, there are three concerns about 155°. A - it moves the humerus distally. B - the center of the humeral socket may not align with the center of rotation of the glenosphere, C - contact between the medial aspect of the humeral component polyethylene may not only cause notching, but may also enable the humeral component to lever away from full contact with the glenosphere.
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