Abstract
Periprosthetic fractures in total hip arthroplasty lead to considerable morbidity in terms of loss of component fixation, bone loss and subsequent function. The prevention, early recognition and appropriate management of such fractures are therefore critical. The pathogenesis of periprosthetic factors is multi-factorial. There are a number of intrinsic patient influences such as bone stock, biomechanics and compliance. There are also a host of extrinsic factors over which the surgeon has more control. The prevention of periprosthetic fractures requires careful pre-operative planning and templating, the availability of the necessary expertise and equipment, and knowledge of the potential pitfalls so that these can be avoided both intra-operatively and in follow-up. The key issues here are around identifying the risk, choosing the correct implant, understanding the anatomy, understanding the possible risks and avoiding them and using appropriate technique.
There are a number of recognized risk factors for periprosthetic hip fractures. The prevalence of intra-operative fractures during total hip arthroplasty is higher in the patient with osteopenia/osteoporosis. Other conditions causing increased bone fragility, such as osteomalacia, Paget's disease, osteopetrosis, and osteogenesis imperfecta are also at a higher risk of intra-operative fracture. The use of more and more press fit cementless components has also increased the number of periprosthetic femoral fractures because of the force required to obtain such a fit. Complex deformities of the proximal femur, particularly when associated with a narrow medullary canal, as seen in secondary degenerative joint disease following developmental dysplasia of the hip may also increase the risk of intra-operative fractures. Revision surgery is associated with a higher risk of intra-operative fracture than primary hip replacement surgery. These fractures typically occur during hip dislocation, cement extraction, or reaming through old cement. Other risk factors for post-operative femoral fractures include loosening of the prosthesis with cortical bone loss, local osteolysis, stress risers within the cortex, such as old screw holes, the ends of plates, or impingement of a loose stem against the lateral femoral cortex.
Periprosthetic acetabular fractures are increasingly recognized. This is in part due to the popularity of press fit components, which increase fracture risk both at the time of insertion and later due to medial wall stress shielding and pelvic osteolysis, and partly due to the increasing frequency of severe defects encountered at the time of revision surgery. Both over- and under-reaming are significant risk factors for acetabular fractures during total hip replacement. It is imperative to deal with the osteopenic patient gently and appropriately, being aware of the rim on the acetabular side and having the capacity for screw fixation where needed, having an understanding of where you wish to place your components and creating the appropriate runways for them, thinking about the stability of an implant as it is inserted and understanding that an implant that is less stable than expected probably is associated with either a size mismatch, a fracture or an implant that will not sit properly probably requires more or a different direction of reaming rather than harder blows with a hammer. A typical example where extra care is required is the scenario of a fractured neck of femur that requires total hip arthroplasty. The virgin native acetabulum in a patient likely to have some bony deficiency may be more difficult to deal with as it has a higher fracture risk.
Pre-operative templating helps to identify the correct entry point for preparation of the lateral runway for linear insertion of a femoral stem. If resistance is met during insertion, the situation should be re-appraised to ensure that the direction and level of the rasp and prosthesis are the same. This reduces the risk of varus/valgus positioning which increases the risk of intra- and post-operative fractures. It is also important to avoid a change of version during insertion of the prosthesis as this can lead to high stresses.
