Wednesday, April 20, 2016

Revision of surface replacement and stemmed arthroplasties

Revision shoulder arthroplasty: does the stem really matter?

These authors reviewed 17 revisions of stemmed arthroplasties (STAs) and 23 revision of surface replacement arthroplasties (SRAs).

95% of the revisions (38 of 40) were due to rotator cuff failure. In 3 cases in each group (6 cases overall), implant loosening was evident as well.

While the operation time, need for humeral osteotomy, need for structural allograft, and number of intraoperative fractures were significantly higher in the STA group, there were no significant  difference between the Constant scores of the 2 groups preoperatively or postoperatively.

Comment: The results of revision arthroplasies depend on many factors, including the diagnosis for which the original arthroplasty was performed. In this series the two groups were not comparable. As shown below surface replacement arthroplasties were used for the simpler pathologies of OA and RA, while stemmed arthroplasties were used for more complex cases, such as fracture, fracture sequelae, and cuff tear arthropathy.

Revisions are highly individualized and depend on factors other than whether the index surgeon felt the need to use a stemmed component.

It is recognized, however, that stemmed arthroplasties need not be fixed with ingrowth or cement, so that revision, if necessary is facilitated. We find that an impaction-grafted humeral component not only preserves but adds bone to the humerus, enables positioning of the humeral articular surface in the desired location (including an eccentric offset when needed as shown in this link) and is applicable to essentially the full range of shoulder arthroplasty indications, rather than being subject to the anatomical restrictions for a resurfacing or stemless device.

We use a chrome cobalt humeral head prosthesis connected to a stem (titanium alloy) the tapered body of which fits inside the humerus.

We note that the humeral canal may be cylindrical or tapered.
and that the cross sectional geometry varies 

We agree that trying to fit a prosthesis by reaming the inside of the bone may substantially weaken it.

and that trying to force a tight fit risks fracture.

Our preferred method for securing the stem within the humeral canal is to use impaction grafting with bone harvested from the arthritic humeral head to conform the inner surface of the bone to the prosthesis. Some have likened this fitting of the patient's bone the prosthesis to the fitting of the traveler to the bed by the inn keeper Procrustes.
As a result, the tapered stem is securely fixed with a biological press fit that safely distributes the load from the prosthesis to the humerus, avoiding stress shielding which has been noted with short stem prostheses (see this link).

The amount of bone removed with an impaction grafted stem is minimal, leaving ample bone stock for revision should it become necessary.


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