Influence of total hip design on dislocation: a computer model and clinical analysis

Area of Science:

• Orthopedic Surgery
• Biomedical Engineering
• Implant Design

Background:

• Dislocation after hip arthroplasty is a significant complication.
• Implant system design is a potential contributing factor to hip dislocation.
• Understanding the biomechanics of implant interaction is crucial for reducing dislocation rates.

Purpose of the Study:

• To evaluate the role of implant design, specifically head size and trunion geometry, in hip arthroplasty dislocation.
• To assess the correlation between computer-aided design (CAD) simulations of range of motion and clinical dislocation rates.
• To determine if CAD modeling can predict dislocation risk in hip implant designs.

Main Methods:

• Virtual range of motion analysis using CAD software for common hip implant designs.
• Prosthetic interference (impingement) was used as the endpoint in simulations.
• Clinical review of 254 primary hip arthroplasties with a specific implant type (type II taper) and minimum 2-year follow-up.

Main Results:

• CAD simulations indicated that implants with 22 mm head size and type II taper impinged in flexion at <90 degrees, suggesting increased dislocation risk.
• Clinical follow-up revealed a 4.8% overall dislocation rate in the series.
• Dislocation rates stratified by head size were 3.6% (28 mm), 4.8% (26 mm), and 18.8% (22 mm), with the smallest head size showing a significantly higher rate.

Conclusions:

• Computer-aided design modeling is a valuable tool for evaluating implant range of motion and predicting potential dislocation risks.
• Implant design features, particularly smaller head sizes combined with specific trunion geometries, are associated with increased hip arthroplasty dislocation.
• These findings support the use of CAD analysis in the development of safer hip implant systems.