The use of pyrocarbon as a bearing surface for shoulder hemiarthroplasty has attracted interest because of the theoretical advantages of increased smoothness and boundary lubrication. The recent literature has been summarized in a recent post: Pyrocarbon shoulder hemiarthroplasty - what do we think we know?
This month, the authors of Pyrocarbon humeral heads for hemi-shoulder arthroplasty grant satisfactory clinical scores with minimal glenoid erosion at 5 to 9 years follow-up report their experience with 37 of 45 patients having hemiarthroplasty (HSA) with the Tornier / Stryker implant (shown below), evaluating the progression of glenoid erosion and clinical scores from short- (2-4 years) to mid-term (5-9 years).
Two of the initial 45 patients had revision surgery due to persistent pain.
For the unrevised patients, the Constant score improved from a mean of 29.3 before surgery to 76.7 at a mean of 2.2 years (first followup) and to 80.8 at a mean of 6.2 years (second followup).
In comparison to immediate postoperative radiographs, 10 shoulders exhibited progression of glenoid erosion by 1 grade (n=9) or 2 grades (n=1). At the second follow-up, glenoid erosion was moderate in 9 (24%) and severe in 3 (8.1%).
Interestingly, the degree of erosion did not correlate with the Constant score.
Comment: The manuscript points out that "This was a case series, with no control group, which does not allow direct comparison with patients that underwent HSA using metallic heads." Thus, the value of this implant in comparison to those in current common use remains to be determined.
As is the case with any design innovation, there are some special considerations with the use of this implant (illustrations below from the paper):
(1) The authors point out that when using the Stryker implant, it is important to be aware that the pyrocarbon heads require an additional metallic tray (see below), which offsets them by about 2mm compared to metallic heads and that this added thickness may increase "tension in the rotator cuff tendons and increase pressure on the glenoid. To take this increased offset into account, the authors recommend that, if in doubt regarding head size, it is better to undersize the pyrocarbon head to prevent overstuffing, as this could lead to lateralization or failure."
(2) Care needs to be taken to avoid overstuffing resulting from too-high and varus positioning of the implant as is shown below.
(3) Humeral bone loss from wear particles or stress shielding may be an issue. The radiograph below was presented as showing "severe" glenoid wear. The bone loss in the upper humerus is visible.
Many of us eagerly await the results of a well controlled comparative study.
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Here are some videos that are of shoulder interest
Shoulder arthritis - what you need to know (see this link).
How to x-ray the shoulder (see this link).
The ream and run procedure (see this link).
The total shoulder arthroplasty (see this link).
The cuff tear arthropathy arthroplasty (see this link).
The reverse total shoulder arthroplasty (see this link).
The smooth and move procedure for irreparable rotator cuff tears (see this link).
Shoulder rehabilitation exercises (see this link).
