• Projects
• MinimallyInvasiveHipRefixation

Minimally Invasive Refixation of Hip Prostheses

• Theme: Medical Visualisation

• People: Francois Malan (LUMC / TUD), Charl P. Botha, Frits H. Post, Edward Valstar (LUMC), Rob Nelissen (LUMC)

Description

Total hip arthroplasty (THA) is a surgical procedure in which the hip joint is replaced by a prosthetic implant. The procedure is performed to relieve pain and restore functionality - mostly in patients with arthritis or severe joint fractures. Since the 1960s THA has become a routinely performed and very successful orthopaedic procedure.

Each year, despite the high success rate, 350 000 hip prostheses have to be revised (surgically replaced) due to loosening. This corresponds to a 10 year post-operative failure rate of about 10% [1]. When a prosthesis loosens, a layer of weak fibrotic tissue forms in the space between the prosthesis and the anchoring bone. This weak layer has very little rigidity and strength and allows the prosthesis to migrate - in some cases more than two centimetres. These loosened prostheses have very limited functionality and cause intense pain, which creates social dependence among sufferers. Revising an existing hip prosthesis is more demanding on the patient than the original (primary) hip replacement. Due to the high risk of such a major surgical intervention revision is impossible in 100 000 patient cases annually.

Pioneering work in minimally invasive cementing of loose hip prosthesis have already been performed [2], but currently there is no computational way of deciding upon the optimal placement of cement.

The aim of the larger project is to develop a reliable and generally usable minimally invasive surgical procedure in which loosened hip prostheses are refixated based on detailed knowledge of each individual patient. In order to reach this goal, three issues need to be addressed:

• Creating a digital 3D model of each patient's hip. This model will consist of different tissue types (specifically: metal prosthesis, cement, cortical bone, trabecular bone, fibrotic tissue)
• Analysing the mechanical stability of the prosthesis, using the segmented 3D data, and deciding where the (minimally invasive) surgical intervention will be most effective.
• Designing minimally invasive surgical tools and procedures for refixating the prosthesis.

CT is the modality of choice when planing revision surgery [3], but CT image quality suffers from severe scatter and reconstruction artefacts caused by the metal prosthesis. In recent years MRI has also proven to be a promising imaging modality for periprosthetic tissues. However MRI also suffers from severe, albeit different, metal induced image artefacts.

These artefacts need to be dealt with sufficiently well, so that segmenting can proceed. During segmentation we need to identify different tissue zones

Once we have a valid 3D segmentation and of the anatomical and prosthetic structures we can construct a finite element model, which we can use to model the comparative advantage of the refixation options available to us.

The interaction between 3D model, finite element computation and user input will be handled by a pre-operative planning tool (similar to the shoulder replacement planning tool) which will aid the orthopaedic surgeon in planning the procedure.

References:

[1] Malchau H, Herberts P, Söderman P, Odén A "Prognosis of total hip replacement. Update and validation of results from the Swedish national hip arthroplasty registry" 67th Annual meeting of the American Academy of Orthopedic surgeons, Orlando, USA, March 15–19, 2000.

[2] Jolanda J. de Poorter, Rob C. Hoeben, Simone Hogendoorn, Vivien Mautner, John Ellis, Wim R. Obermann, Tom W. J. Huizinga, and Rob G. H.H. Nelissen, “Gene Therapy and Cement Injection for Restabilization of Loosened Hip Prostheses” Human Gene Therapy, Jan. 2008, pp. 83-95.

[3] J. Cahir, A. Toms, T. Marshall, J. Wimhurst, and J. Nolan, “CT and MRI of hip arthroplasty” Clinical Radiology, vol. 62, Dec. 2007, pp. 1163-1171.