UW Shoulder and Elbow Academy: Does the innovation of pyrocarbon humeral head prostheses add value for young patients with arthritis?

Mid-term outcomes of pyrocarbon humeral resurfacing hemiarthroplasty compared to metal humeral resurfacing and metal stemmed hemiarthroplasty for osteoarthritis in young patients: Analysis from the Australian Orthopaedic Association National Joint Replacement Registry

These authors point out that humeral resurfacing hemiarthropaslty and stemmed hemiarthroplasty using metallic heads avoid the complications of loosening or wear of the glenoid component seen in total shoulder arthroplasty. but that survivorship has been limited by glenoid erosion when the metal resurfaced head articulates with the native glenoid.

Pyrocarbon articular surfaces have shown to have reduction in wear rates in in vitro testing. Thus pyrocarbon has been proposed as an alternative bearing surface for shoulder arthroplasty.

This study aimed to compare the survivorship of shoulder hemi resurfacing utilizing pyrolytic carbon (n=163) to metal hemi resurfacing (n=163) and metal stemmed hemiarthroplasty (n=67) using data from the Australian Orthopaedic Association National Joint Replacement for patients aged <55 years undergoing primary shoulder replacement for osteoarthritis. It is of interest that >40% of hemiarthroplasties in this series were performed using pyrocarbon.

The authors report the results as follows, "For the diagnosis of osteoarthritis, the cumulative percent revision (CPR) at 6 years was 8.9% (95% confidence interval CI, 3.9, 19.4) for pyrocarbon hemi resurfacing compared to 17.1% (95% CI 11.9, 24.2) for metal hemi resurfacing, and 17.5% (95% CI 10.1, 29.4) for metal hemi stemmed.

Overall, pyrocarbon hemi resurfacing had a lower CPR rate compared to other metal hemi resurfacing (HR=0.41 (95% CI 1.08, 5.52), p=0.032).

There was no difference in CPR rate when pyrocarbon hemi resurfacing was compared to metal stemmed hemiarthroplasty (p=0.067).

In male patients, pyrocarbon hemi resurfacing had a lower CPR compared to metal stemmed hemiarthroplasty (HR=0.32 (95% CI 0.11, 0.93), p=0.037).

There was no difference in the rate of revision for males when pyrocarbon hemi resurfacing was compared to metal hemi resurfacing (p=0.097).

Insufficient data was available for a subanalysis in female patients."

It is noted that pyrocarbon implants have a type of complication not seen with metal implants: prosthesis breakage accounted for >50% of the revisions in the pyrocarbon group.

Comment: While registry data can provide an overview of revision rates with different implants, a major shortcoming is the lack of data on the patient, shoulder and surgeon characteristics of cases receiving each type of implant, for example:

(1) were the patients of comparable health and socioeconomic status, or was pyrocarbon used in "preferred patients"?

(2) were the glenoid types comparable, or was pyrocarbon used in shoulders with less severe pathoanatomy?

(3) were the surgeons comparable or was pyrocarbon used by more experienced surgeons? Since revision was the primary outcome variable, is there evidence that the pyrocarbon surgeons had the same threshold for revision as the metal surgeons?

(4) how did the preoperative and postoperative patient self-assessed shoulder comfort and function compare among the groups, specifically were the clinical outcomes/patient benefit clinically significantly better for pyrocarbon (using an intention to treat analysis)?

(5) since value is benefit/cost, how does the cost compare among the three different implants (see this link)?

As explained in a recent post, Considering new technologies for our practice - understanding bias, it is possible for selection bias, transfer bias, assessor bias, and failure to assess clinical significance to paint an exaggerated view of a new innovation. see below.