Short-term Outcomes and Survival of Pyrocarbon Hemiarthroplasty in the Young Arthritic Shoulder
These authors reported the short-term outcomes and survival of hemiarthroplasty with pyrocarbon heads (HA-PYC) with (n=23) or without (n=41) glenoid reaming for the treatment of shoulder osteoarthritis in patients younger than 60 years (mean age: 53 years) at an average follow-up of 33 months (range 24 to 60 months).
Eight percent of the patients had a revision: 5 patients were revised at a mean of 24 months (range 15–37 months): one conversion to TSA and 4 conversions to RSA.
The Constant score and SSV increased from 36 (26-50) to 75 points (69- 81) and from 35% (20-50) to 80% (75-90), respectively (p<0.001).
42 of 46 patients returned to work and 15 of 17 returned to sport.
The severity of pre and postoperative glenoid wear was not significantly associated with the functional results.
The 26 patients having glenoid reaming had similar Constant and SSV scores to those not requiring glenoid reaming and did not show more progression of glenoid wear.
Non anatomic reconstruction of the proximal humerus (center of rotation of the prosthesis over 3 mm from the anatomical center) occurred in 29% (18/62) and was associated with significantly lower functional and subjective results, more complications (subscapularis insufficiency and/or symptomatic glenoid erosion) and a higher risk of revision.
The additional 1.5 mm of thick metal disc under the pyrocarbon head was found to be the main reason for overstuffing of the prosthetic head.
Comment: The apparent attraction of pyrocarbon is that in an experimental study performed in a dog model, pyrocarbon generated 10 times less cartilage wear and 6 times less microscopic subchondral cracks than cobalt chrome. However in this study, the survival rate free from revision after HA-PYC for OA was not different from those reported for a metal hemiarthroplasty or total shoulder arthroplasty.
Because of issues with breakage, the Aequalis Ascend Flex Pyrocarbon Humeral Head was re-designed in 2013. It is now created by combining the pyrocarbon bearing surface and a CoCr double taper neck. A classical morse taper cannot be used with a pyrocarbon head because of its low Young's modulus and poor resistance to traction: when applying a force of impaction, the risk of breakage of the pyrocarbon is too high. Thus to make the morse taper reliable and safe, a metallic plate abutment was added to stop the pyrocarbon bearing surface seating at an appropriate level and prevent breakage of the pyrocarbon head. For this reason, pyrocarbon heads are about 2 mm thicker than the metallic ones for the same diameter. This increased thickness is related to the addition of the metallic tray to support the pyrocarbon head (+1.5-mm) plus the void under the metallic plate (+0.5-mm) to accommodate the inferior morse taper. As a result the authors downsize (one size) the humeral pyrocarbon head to prevent overstuffing of the cuff tendons and overpressure on the glenoid surface.
Further clinical research will be needed to see whether the patient outcomes with this implant surpass those achieved with standard implants.
