Friday, August 28, 2015

Total shoulder arthroplasty - is there a reason to go 'stemless'?

Geometrical analysis of stemless shoulder arthroplasty: a radiological study of seventy TESS total shoulder prostheses.

The authors assert that stem-related complications, such as intra-operative humeral fracture, loosening, stress shielding and periprosthetic fracture can be avoided by stemless humeral implants.

They examined their ability to restore arthritic shoulder anatomy to resemble premorbid anatomy in 69 patients (70 shoulders). The mean difference between premorbid center of rotation (COR) and post-operative COR was 1 ± 2 mm (range -3 to 5.8 mm). The mean difference between premorbid humeral head height (HH) and post-operative HH was -1 ± 3 mm (range -9.7 to 8.5 mm). The mean difference between premorbid neck-shaft angle (NSA) and post-operative NSA was -3 ± 12° (range -26 to 20°).

Comment: For reasons unclear to us, there is a fascination in some parts for 'restoring premorbid anatomy' in shoulder arthroplasty. Instead our view is that the focus of shoulder arthroplasty, like that of hip and knee arthroplasty, is to durably improve mobility and stability of the articulation. This not infrequently requires making adjustments in the diameter of curvature, thickness and offset of the humeral component, rather than trying to match some vision of 'normal'. An illustration is shown in this post.

While the goal of the stemless technique is to 'prevent stem related complications', the authors do not present the complications related to their use of a stemless implant.

In comparison to a humeral component inserted with impaction autografting after conservative reaming and broaching, the use of a 'stemless' humeral component has the following disadvantages: (1) it is more technically difficult, (2) it cannot be used in cases of substantial humeral deformity and (3) it does not provide comparable access to the glenoid for glenoid arthroplasty,  

Impaction grafting of a stemmed implant minimizes the risks of stress shielding, periprosthetic fracture (on insertion or after) and loosening. The head resection with a stemmed implant provides excellent access to the glenoid. 

And finally, the modularity allows adjustment of the head size, thickness and offset to optimize the mobility and stability of the reconstruction as shown in the case below where an anteriorly eccentric head prosthesis was used to manage a tendency for posterior instability.