Tripolar Hip Implant Dislocation Test

Principal Investigator: Daniel J. Berry, M.D.
Project Coordinator: Frank Chen — chen.qingshan@mayo.edu

Dislocation after total hip arthroplasty remains common despite increasing sophistication of implants and techniques. Its prevalence ranges from 1 to 10% for primary procedures and up to 26 % after multiple procedures. Tripolar implants have been proposed to manage this surgical challenge. Using a large inside diameter acetabular cup and a bipolar femoral component this device is expected to reduce dislocation. Several clinical studies with successful outcome have been reported. However, scientific data documenting the mechanism by which these components increase hip stability is lacking.

We performed two dislocation conditions tests on each implant. 1) Shear-out dislocation defined as implant dislocation without impingement between the stem and 2) acetabular cup and lever-out dislocation defined as implant dislocation that occurs due to impingement of the stem and acetabular cup.

The tripolar implant demonstrated better efficacy to prevent lever-out dislocation when impingement occurs. The intermediate retentive UHMW polyethylene insert increases the effective "head" size and delays the occurrence of lever-out dislocation due to impingement.