Friday, October 14, 2016

Fixation of the humeral component with impaction auto grafting


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

These authors point out that when the humeral component of a shoulder arthroplasty is fixed with (a) bone ingrowth, (b) a tight diaphyseal press fit, or (c) cement, the patient may encounter problems of malposition, stress shielding,  periprosthetic fracture or difficulty with removal at revision arthroplasty.

The x-ray below shows humeral component malposition resulting from a tight diaphyseal fit and resulting in rocking horse loosening of the glenoid component.




The authors indicate that the challenge in fixation is the highly variable intramedullary anatomy of the humeral canal.


They studied the effectiveness of impaction autografting in which bone graft harvested from the patient's resected humeral head is reinvested in the medullary canal filling in the intramedullary irregularities until snug fixation is achieved.




This approach enables the use of small, canal-preserving stems that can be positioned as desired and that can be easily removed should a revision become necessary.


They studied the radiographic survivorship of impaction-autografted humeral implants using component subsidence as the primary endpoint in 286 primary anatomic shoulder arthroplasties having an average follow-up of 4.9 ± 2.7 years. Initial postoperative radiographs and minimum 2-year follow-up radiographs were evaluated by 3 observers to assess subsidence.


Two different implants were used: the DePuy Humeral Replacement Prosthesis [HRP], below left, and the DePuy Global Advantage [GA] prosthesis, below right. The single piece HRP is made entirely of chrome cobalt while the modular GA prosthesis has a chrome cobalt head and a titanium-alloy body. 



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 more common for the HRP than for the Global Advantage prosthesis 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).


Comment: We have found impaction grafting to be a safe, versatile durable method for biological fixation of the humeral stem.

The x-ray below shows its use in a ream and run procedure for a young high-level athlete with post surgical arthritis.  The goal was to avoid a stress riser at the distal tip of the prosthesis that would increase the risk of periprosthetic fracture on impact.

 



The x-ray below is of a shoulder six years after a ream and run procedure with durably secure fixation.


We have extended the use of impaction grafting to revision surgery, using cancellous allograft. The radiograph on the left shows a failed shoulder arthroplasty with humeral and glenoid component loosening. The film on the right shows revision to a ream and run procedure with impaction allografting of the humeral stem.


In each of these cases, impaction grafting enabled precise adjustment of the height of the humeral component to the berm, as shown in this figure by Steve Lippitt.


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