Pyrocarbon hemiprostheses show little glenoid erosion and good clinical function at 5.5 years of follow-up

Abstract

The success of traditional shoulder hemiarthroplasty with cobalt-chromium (CoCr) heads is limited by a painful glenoid erosion with problematic bone loss. Hemiprostheses with pyrolytic carbon (PyC) heads have shown reduced glenoid erosion in experimental laboratory studies. Few in vivo data are available. Single-center consecutive cohort study of 31 of 34 patients (91%) who underwent PyC hemiarthroplasty between 09.2013 and 06.2018. For eleven of these concentric glenoid reaming was additionally performed. The mean follow-up was 5.5 (range 3.5 - 7) years. Standardized x-rays were taken and clinical function (Constant score) and pain on the visual analogue scale (VAS) were recorded. AP x-rays were analyzed according to an established method by 2 independent observers: A line parallel to the superior and inferior glenoid rim was translated to the most medial point of the glenoid surface. A further parallel line was placed on the spinoglenoid notch (SGN) and the distance between the two lines was measured. Measurements were scaled using the known diameter of the implanted humeral head component. To assess eccentric erosion AP and axial images were classified according to Favard and Walch respectively. The mean medial glenoid erosion was 1.4 mm over 5.5 years. In the first year there was 0.8 mm of erosion, significantly more than the average erosion per year of 0.3 mm (p < 0.001). Mean erosion per year of patients with glenoid reaming was 0.4 mm, without reaming 0.2 mm (p = 0.09). An evolution of glenoid morphology was observed in 6 patients, of which 4 had a progression of the erosion grade. Prosthesis survival rate was 100%. The Constant score improved from 45.0 preoperatively to 78.0 2-3 years postoperatively and 78.8 at latest follow-up 5.5 years postoperatively (p < 0.001). Pain decreased from VAS 6.7 (3 - 9) preoperatively to 2.2 (0 - 8) at latest follow-up (p < 0.001). There was a weak correlation (r = 0.37) between erosion and pain improvement (p = 0.039) and no correlation between erosion and delta Constant score (r = 0.06). PyC HA caused little glenoid erosion and a sustained improvement in clinical function in our cohort at mid-term follow-up. PyC demonstrates a biphasic development of glenoid erosion, with a reduced rate after the first year. PyC hemiarthroplasty should therefore be considered as an alternative to total shoulder arthroplasty or CoCr hemiarthroplasty for patients with a high risk of glenoid component complications.