DOS BULLETIN - Dansk Ortopædisk Selskab

2010-378_DOS nr. 3 2010 29/09/10 10:08 Side 107
Does larger heads prevent luxation?
Sara Malmose, Michele Hassing, John Rasmussen, Derek Curtis,
Peter Gebuhr, Christian Wong
Department of Orthopaedic Surgery, University Hospital of Hvidovre;
Institute of medicine and technology, The Danish Technical University;
Department of Mechanical Engineering, Aalborg University;
The Gait laboratory, University Hospital of Hvidovre
Background: Dislocation is serious postoperative complication of the
primary total hip arthroplasty. Restrictions in range of motion are
applied the first 3 months to prevent this. New prosthesis designs using
improved ceramics and polyethylene allow the use of larger femoral
heads for surgical implantation. There are clinical indications that the
use of larger femoral heads provides better range of motion and stability
against dislocation.
Purpose: The purpose of this study was to investigate whether post operative
restrictions in range of motion could be avoided by using larger
femoral heads by analysis of selected high risk dislocation situations. We
used gait analysis and the Anybody Modelling System for motion and
reaction force analysis. In this study we used the design of the R3 cup
system© of Smith and Nephew©.
Methods: Data of motions from ‘bending down from standing’ and ‘getting
up from a deep chair’ were recorded with the Vicon Motion Systems.
These data were transferred to The AnyBody Modelling System
for motion and cup reaction force analysis. Here kinematic and kinetic
data were extracted to evaluate the distance from neutral to impingement
(DTI) and the risk of spontaneous dislocation. DTI was located as a rise
in reaction forces. Head sizes of 28, 32, 36 and 52 mm with corresponding
liners and increasing cup sizes were examined.
Findings: DTI increased with larger head size, only giving impingement
for the 28 mm head. The reaction forces pointed posterior as for posterior
luxation. DTI also increased when the cup size was increased.
Conclusion: Conclusively the most optimal prosthesis design is dependant
of head and cup size, to achieve better ROM and stability. There
were no sign of impingement for femoral heads larger than 28 mm for
the R3 cup©.
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