Saturday, February 25, 2017

Glenohumeral arthritis - management with a spherical implant.

Pyrocarbon interposition shoulder arthroplasty: preliminary results from a prospective multi center study at 2 years of follow-up

It is asserted that "Pyrocarbon has superior tribologic properties than metal because it can slide against bone and cartilage without causing pain or damage".

These authors explored the concept of a free pyrocarbon-coated interposition shoulder arthroplasty in  67 consecutive patients (mean age at surgery was 51 years). The indications for surgery were primary glenohumeral arthritis in 42, avascular necrosis in 13, and secondary arthritis in 12 patients. The criteria for the use of this implant were similar to those the authors use for hemiarthroplasty, notably young age or high activity level, or both.

In this surgery the humeral head resection was performed at the anatomic neck level then a cavity was then reamed in the center of the humeral metaphysis leaving a 2-mm-thick peripheral bony rim at the equator to accept the graphite sphere coated with pyrocarbon. The implant is freely positioned in the reamed cavity within the proximal humerus, articulating directly against the glenoid. 

Revision surgery was performed in 7 patients (10.4%), 2 (3.0%) were lost to follow-up, and the outcome assessments were incomplete in 3 (4.4%). The indications for revision to anatomic or reverse total shoulders included posterior subluxation, inferior glenohumeral impingement causing pain or stiffness, rotator cuff tears, persistent glenoid pain, stiffness and subsidence from wear related to a metal particle. 

In 55 patients at  26.8 ± 3.4 months, the Constant score improved from 34.1±15.1 preoperatively to 66.1±19.7 postoperatively. Here are the x-rays of stable components at > 2 years after surgery.

Progressive glenoid erosion was observed in 6 shoulders and thinning of the tuberosities in 3.

Here is the x-ray of component at > 2 years after surgery with medial erosion of the glenoid

The authors concluded that pyrocarbon-coated interposition shoulder arthroplasty renders clinical scores and implant survival comparable to those of hemiarthroplasty but remain inferior to those results reported for total shoulder arthroplasty. 

Comment: This is an interesting approach to treating glenohumeral arthritis with a free hemiarthroplasty. This device requires removal of metaphyseal bone that may compromise conversation to or revision to a conventional humeral implant should the sphere not provide the desired stability, motion or comfort and, like other hemiarthroplasties, does not address glenoid pathology that may be present.
We concur with the authors that "Until long-term results are available, this type of innovative implant should remain to be tested in a few specialized shoulder centers."