Link ANALYSIS OF CEMENT PENETRATION IN HIP RESURFACING
R.M. Gillies; J.H. Gan; G.M. Hawdon; and S.J. McMahonMay 2007
Introduction: Prevalence of femoral neck fracture in
resurfacing hip arthroplasty continues to question if
failure is technique-related or due to the inherent bone
quality. This study aimed to correlate cement penetration
profile during resurfacing hip with inherent bone density.
The hypothesis is that osteoporotic bone is unable to
support the prosthesis leading to fatigue failure.
Methods: Fifteen patients scheduled for total hip
replacement (THR) were recruited to undergo resurfacing
arthroplasty prior to THR. Each patient was implanted with a
resurfacing femoral component (BHR, Smith & Nephew, Memphis,
TN). Antibiotic simplex cement was inserted one minute after
mixing at 18°C to fill 10% of the femoral component volume.
The femoral head-implant section was removed and kept in
buffered formalin. The patients then proceeded with standard
THR. The femoral head-cement-prosthesis section was
separated using electrical discharge (ED) machining
technique and CT-scanned. The depth and volume of cement
penetration were measured from the CT scans and correlated
with femoral neck bone densities.
Results: Cement penetration was compared for three groups of
bone density: normal, osteopenic, osteoporotic. Average
cement thickness were found to be 0.36 ± 0.16mm (proximal),
0.28 ± 0.11 mm (centre) and 0.12 ± 0.05 mm. During hip
resurfacing, cement is forced into the porous structure,
e.g. the trabeculae and airspaces when the femoral component
is fixed onto the head of the femur. In normal bone, the
trabeculae is dense and air spaces occupy a small volume of
the bone. Greater cement penetration was expected in
osteopenic and osteoporotic bones. However, no significant
difference was found between cement thickness and volume
against inherent patient bone density (p>0.05). High
viscosity of the cement may have prevented more cement to
penetrate the bone. While the exterior cortex of the femoral
head is strengthened by a cement layer, the interior
structure of the femoral neck is still susceptible to
fracture at high loads. In addition, increased bone necrosis
due to the exothermic reaction during cement fixation may
predispose patients to fracture.
Discussion: Resurfacing hip replacement is a viable
technique if the fracture risk can be reduced by gaining the
best possible cement penetration. This would provide
continuous cement stiffness with the bone.