Monday, February 8, 2016

Total shoulder arthroplasty: should the humeral components be getting shorter?

Total shoulder arthroplasty: are the humeral components getting shorter?

While the authors opine that "Each generation of total shoulder arthroplasy has improved on the previous," evidence is lacking to support the hope that more recently introduced components yield better results than the established models.

The case for 'shorter' humeral components is usually based on the proposed "theoretical advantages" of preserved bone stock, less stress shielding, eliminating the diaphyseal stress riser, ease of stem removal at revision, and humeral head placement independent from the humeral shaft axis.

The authors point out that seven stemless designs and four short stem designs have recently been introduced and that with these new prostheses have come new problems: metaphyseal cracks, prosthesis decoupling/dissociation, glenoid problems perhaps related to compromised exposure, humeral loosening, periprosthetic fractures, varus positioning, and others.

Comment: Some of the problems related to short stems are shown on the x-rays below of a case recently presenting to us. The glenoid component was not well placed and is loose. While the humeral prosthesis appears properly oriented on the AP view evidence of a healed tuberosity fracture is seen.

The axillary view shows the stem in substantial anterior inclination, with lack of coverage of the posterior proximal humerus and a tendency for anterior subluxation. 

The goals of bone conservation and ease of fit can be obtained without the risk of malposition with the use of a traditional length stem selected after minimal canal reaming with impaction grafting as shown in this link.

Here are the x-rays of a man we saw back one year out from a ream and run procedure with our standard approach to humeral component selection and fixation - no specialized component, no cement, no ingrowth, no loss of endosteal bone through reaming, no valgus, no varus, no angulation, no loosening, no stress shielding, no diaphyseal stress riser, and 12/12 on the Simple Shoulder Test.

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