Large Metal Heads and Vitamin E Polyethylene Increase Frictional Torque in Total Hip Arthroplasty.
OBJECTIVE
Trunnionosis has reemerged in modern total hip arthroplasty for reasons that remain unclear. Bearing frictional torque transmits forces to the modular head-neck interface, which may contribute to taper corrosion. The purpose of this study is to compare frictional torque of modern bearing couples in total hip arthroplasty.


METHODS
Mechanical testing based on in vivo loading conditions was used to measure frictional torque. All bearing couples were lubricated and tested at 1 Hz for more than 2000 cycles. The bearing couples tested included conventional, highly crosslinked (XLPE) and vitamin E polyethylene, CoCr, and ceramic femoral heads and dual-mobility bearings. Statistical analysis was performed using Student t test for single-variable and analysis of variance for multivariant analysis. P ≤ .05 was considered statistically significant.


RESULTS
Large CoCr metal heads (≥36 mm) substantially increased frictional torque against XLPE liners (P = .01), a finding not observed in ceramic heads. Vitamin E polyethylene substantially increased frictional torque compared with XLPE in CoCr and ceramic heads (P = .001), whereas a difference between conventional and XLPE was not observed (P = .69) with the numbers available. Dual-mobility bearing with ceramic inner head demonstrated the lowest mean frictional torque of all bearing couples.


CONCLUSIONS
In this simulated in vivo model, large-diameter CoCr femoral heads and vitamin E polyethylene liners are associated with increased frictional torque compared with smaller metal heads and XLPE, respectively. The increased frictional torque of vitamin E polyethylene and larger-diameter femoral heads should be considered and further studied, along with reported benefits of these modern bearing couples.
Department of Orthopaedic Surgery, Indiana University School of Medicine, Fishers, Indiana; Orthopedics and Sports Medicine, Indiana University Health Physicians, Fishers, Indiana.
R Michael
RM
Meneghini
Orthopedics and Sports Medicine, Indiana University Health Physicians, Fishers, Indiana.
Luke R
LR
Lovro
Department of Biomedical Engineering, Purdue School of Engineering and Technology at Indiana University-Purdue University, Indianapolis, Indiana.
Joseph M
JM
Wallace
Orthopedics and Sports Medicine, Indiana University Health Physicians, Fishers, Indiana.
Mary
M
Ziemba-Davis
D019644:Arthroplasty, Replacement, Hip / Q000295:instrumentation*; D002516:Ceramics; D002858:Chromium Alloys; D003343:Corrosion; D005270:Femur Head; D017276:Friction; D006622:Hip Prosthesis; D006801:Humans; D020959:Polyethylene; D011474:Prosthesis Design; D011475:Prosthesis Failure; D019415:Torque; D014810:Vitamin E
D002858:Chromium Alloys; D014810:Vitamin E; D020959:Polyethylene
frictional torque; highly crosslinked polyethylene; total hip arthroplasty; trunnionosis; vitamin E polyethylene