Bicentric bipolar hip prosthesis: A radiological study of movement at the interprosthetic joint

Abstract

Background:The bipolar hip prostheses after some time functions as a unipolar device. There is a need to change the design of bipolar hip prostheses to make it function as a bipolar device over a prolonged period of time. A bicentric bipolar hip prosthesis was used as an implant for various conditions of the hip. We evaluated the movement of this newly developed prosthesis at the interprosthetic joint radiologically at periodic intervals.Materials and Methods:Fifty two cases were operarted with the Bicentric bipolar prosthesis for indications like fracture neck of femur and various other diseases of the hip and were followed up with serial radiographs at periodic intervals to evaluate, what fraction of the total abduction at the hip was occurring at the interprosthetic joint.Results:In cases of intracapsular fracture neck of femur, the percentage of total abduction occurring at the interprosthetic joint at 3 months follow-up was 33.74% (mean value of all the patients), which fell to 25.66% at 1.5 years. In indications for bipolar hemireplacement other than fracture neck of femur, the percentage of total abduction occurring at the interprosthetic joint at 3 months follow-up was 71.71% (mean value) and at 1.5 years it was 67.52%.Conclusion:This study shows the relative preservation of inner bearing movement in the bipolar hip prosthesis with time probably due its refined design. Further refinements are needed to make the prosthesis work better in patients of intracapsular fracture neck femur.

Bicentric Bipolar Prosthesis in Non-Traumatic Hip Pathologies: Maximum 10 Years Follow Up

“…Pa ents based self-assessment was done by modified Harris hip score ques onnaire at each follow up ( We propose changes in the design of BHU bicentric bipolar prosthesis as men oned by Rai et al for the prolonged preserva on of movement at inter-prosthe c joint, and good to excellent modified Harris hip score in majority of 17,18 pa ents in this series. Modifica on of sea ng angle between the stem and the collar has allowed preserva on of the calcar by quarter to 1 cm a er implanta on of the prosthesis.…”

“…Modifica on of sea ng angle between the stem and the collar has allowed preserva on of the calcar by quarter to 1 cm a er implanta on of the prosthesis. Due to low sea ng angle in conven onal bipolar (Bateman type), the calcar has to be sacrificed during the surgery and hence on weight bearing the prosthesis tends 17,18 to sink if cement is not used.…”

“…Thus, reduces wear and debris forma on 17,18 at extremes of the movement. The neck of the prosthesis has been made trapezoidal like the Charnley type neck and the cup has been modified in a staggering fashion to decrease neck cup impingement.…”

“…UHMWPE wear in a bipolar prosthesis is 0.7 mm/year. A 22 mm Charnley head diameter has been used in the BHU bicentric bipolar prosthesis, so that thicker UHMWPE can be provided in outer bearing, thereby increasing the survivorship of the 17,18 prosthesis.…”

“…BHU bicentric bipolar prosthesis is available in 37-55 mm head sizes in 1 mm increments, which provides appropriate head size for replacement and subsequently prevents early failure of the prosthesis, by avoiding Hertzian contact 17,18 stress.…”