Non-infective Causes of Failure and Revision in THR – an Analysis and a Novel Prosthesis Designed to Mitigate these Problems

Presenter’s name (Last, First): KIRWAN David

Qualifications: MB.,BS, FRACS, FAOrthA

Affiliations: Insight Private Hospital, ALBURY, NSW

Other authors:


Background / Introduction:

Little change in THR femoral component design has occurred since the first successful implantation, by Sir John Charnley 60 years ago (Nov 1962).Despite high success levels, contemporary failures still occur, due to impingement, instability, loosening, taper problems and peri-prosthetic fracture.
Multiple assistive technologies are available to improve implant placement, ie aiming to reduce the rate and severity of these failures.
Some are proprietary and expensive.
A novel prosthetic design, that aims to reduce impingement and intrinsic prosthetic stability, is presented to reduce reliance on these technologies. It is envisaged that this prosthesis will increase range of motion before impingement occurs and reduce failure rates.

Patients / Methods:

Computer modeling using “Lexi” software and implantation of 3D printed implants into CT derived 3D printed bones, has been undertaken, to assess prosthetic efficacy.
Cadaver implantation and assessment has not yet been undertaken.


Hip joints rotate in 3 planes. The maximum “polar” range of motion(ROM) in 2 planes, is determined by head:neck diameter ratio. Rotation in a 3rd plane, axis centred in the prosthetic neck, is unlimited.
Due to cup orientation, the main axis of hip movement (flexion) largely involves this 3rd plane.
Flexion can be limited (ideally) by external impingement (say knee on chest) or, by anterior bone impingement (ABI), which is a powerful source of posterior instability, or, rarely by anterior prosthetic impingement (API). Hip extension can be limited by posterior prosthetic impingement (a potent cause of prosthetic damage).
A novel prosthetic design has been developed to mitigate all forms of harmful impingement outlined herein. The restoration of normal anterior offset (AO) will reduce ABI and peri-prosthetic fracture rates.
A prosthesis that improves trunnion orientation will reduce impingement and trunnion failure.

A femoral component that reduces impingement, will improve stability and component failure (loosening, subsidence, neck fracture, rim damage and dissociation).Improved taper orientation will reduce taper failure. Restoration of AO will reduce ABI and peri-prosthetic fracture rates.
A novel prosthetic design, that is intended to effect these improvements is presented to the membership and, requires expert orthopaedic consideration.

Level of Evidence & Study type: concept design study only

Declarations of Conflict: The author has unpaid “Development Agreements” in place with Matortho (UK) and Signature Orthopaedics (AU)