Wednesday, June 8, 2016

Bone-preserving humeral component fixation with impaction autografting

Impaction autografting: bone-preserving, secure fixation of a standard humeral component

Fixation of the humeral component of a shoulder arthroplasty with bone ingrowth, a tight diaphyseal press fit, or cement may present problems of malposition, stress shielding, or periprosthetic fracture as well as difficulty with removal at revision arthroplasty. In order to avoid these risk, these authors explored the use of humeral component fixation using impaction cancellous autografting of the humeral stem, minimizing contact between the prosthetic stem and the humeral cortex. They reviewed 286 primary anatomic shoulder arthroplasties having an average follow-up of 4.9 ± 2.7 years, comparing initial postoperative radiographs and minimum 2-year follow-up radiographs.

Two different implants (Humeral Replacement Prosthesis [HRP] and Global Advantage prosthesis) were used. Of 286 stems, 267 (93.4%) had not subsided. The Global Advantage prosthesis had a subsidence-free survival rate of 98.5% at 5 years. The stiffer-stemmed HRP used early during the study had a higher rate of subsidence compared with the currently used Global Advantage stem (hazard ratio, 5.6; P = .001). Radiolucent lines of 2 mm or greater were less common for the Global Advantage prosthesis than for the HRP in each of 7 zones (P < .001). Total shoulder arthroplasty was associated with a higher rate of subsidence compared with hemiarthroplasty (hazard ratio, 2.6; P = .12).

They concluded that impaction autografting provides a secure, durable, bone-preserving means of humeral component fixation in anatomic shoulder arthroplasty.

Comment: The intramedullary anatomy of the humeral canal is variable making secure fixation with a cylindrical prosthesis a challenge.

Attempts to fix the humeral component with a tight diaphyseal press fit can result in a too-high humeral component and the risk weakening the bone at the tip of the prosthesis

Impaction auto grafting using bone from the resected humeral head 

enables precise positioning of a humeral component with a smaller stem, secure safe fixation, and ease of prosthesis exchange should revision become necessary. Note the absence of cortical contact with the tip of the prosthesis.

The durability of this method of fixation using a titanium stem is shown by the upper solid line in the graph below (the lower dotted line shows the limited durability with a cobalt-chrome stem).

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