These authors report a case of a pyrocarbon humeral head resurfacing implant fracture, occurring 6 years following its implantation, without any obvious trauma or dislocation. Initial radiographs showed a proud and oversized pyrocarbon resurfacing implant. On clinical examination, patient had a painful and pseudoparalyzed shoulder with subscapularis insufficiency. Intraoperatively, the implant was found to be fractured with multiple pyrocarbon debris in the glenohumeral joint.
The authors concluded that the use of pyrocarbon as a humeral head resurfacing implant must be questioned "because the material seems to be too fragile to be used as a resurfacing implant and cannot achieve fixation of the implant to bone".
Comment: It is interesting to consider this outcome in light of a previous assertion that "Pyrocarbon has superior tribologic properties than metal because it can slide against bone and cartilage without causing pain or damage." However as shown in the article below, it offers no clinical advantage over standard metal implants. The lesson from this experience is that exciting new technologies may initially appear to be "superior", until longer term followup reveals their short comings.
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.
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