Long Title: Short to Midterm Outcomes of 139 Pyrocarbon Monopolar Radial Arthroplasties.

ABSTRACT

INTRODUCTION: The MoPyc radial head arthroplasty (RHA) is a monopolar implant with a pyrocarbon head that obtains rigid fixation via controlled expansion of the titanium stem. The aim of this study was to evaluate the short to midterm outcomes of MoPyc RHA. MATERIALS AND METHODS: Between 2002 and 2021, 139 MoPyc RHA were implanted in 139 patients with a RH fracture. The mean follow-up was 5.9 years ±3.5 (range 1-16). Range of motion, mean Mayo Elbow Performance score (MEPS), quick disabilities of the Arm, Shoulder and Hand (quickDASH) score, visual analog scale (VAS), radiographic outcome, and reason for failure were recorded. RESULTS: The mean MEP, QuickDASH, and VAS scores were 89.1± 2.2(range, 45-100), 17.5±16.7(range, 0-78), and 0.8±1.6(range, 0-50), respectively. Stress shielding (SS) and osteolysis around the stem (OAS) were identified in 92(66%) and 20(14%) patients. A total of 47(29%) patients experienced at least one complication; and 29(21%) of them required re-intervention. Persistent stiffness (n=12;9%) was the most common complication. No painful loosening was noted. Osteolysis around the stem, presence of an autoexpanding stem, and overstuffing were associated with a lower MEPS and an increase in VAS (p<0.05). Stress shielding (SS) was associated with an increase in MEPS (aß=6.92; p<0.001) and lower VAS (aß=-0.69; p=0.016). The auto-expending stem increased the likelihood of SS after RHA (aOR=1.49; p=0.001). CONCLUSIONS: A well-fixed MoPyc RHA provided satisfactory short to midterm outcomes, without painful loosening. However, the autoexpanding stem system was associated with poorer functional outcomes and increased the likelihood of SS.