Purpose: Constrained devices, standard implants with large heads, and dual mobility systems have become popular options to manage instability after total hip arthroplasty (THA). Clinical results with these options have shown variable success rates and significant higher rates of aseptic loosening and mechanical failures with constrained implants. Literature suggests potential advantages of dual mobility, however little is known about its biomechanics. We present a comparative biomechanical study of a standard implant, a constrained implant, and a dual mobility system.
Methods: A finite element analysis was developed to assess and compare these acetabular options with regard to the range of motion (ROM) to impingement, the angle of dislocation, the resistive torque, the volume of polyethylene (PE) with a stress above 80% of the elastic limit, and the interfacial cup/bone stress.
Results: Dual mobility implants provided the greatest ROM to impingement and allowed delaying subluxation and dislocation when compared to standard and constrained implants. Dual mobility also demonstrated the lowest resistive torque at subluxation while the constrained implant provided the greatest one. The lowest critical PE volume was observed with the dual mobility implant, and the highest stress at the interfaces was observed with the constrained implant.
Conclusion: This study highlights the biomechanical advantages of dual mobility systems over constrained and standard implants, and is supported by the clinical results reported. Therefore, the use of dual mobility systems in situations at risk for instability should be advocated and constrained implants should be restricted to salvage situations.
Keywords: Biomechanics; Constrained implants; Dislocation; Dual mobility; Instability; Subluxation.