Approach to Hip Arthroplasty in Pagetï¿½s Disease
Remember a few points about Pagetï¿½s disease:
– a disease set off by excessive osteoclast resorption of bone, coupled with a desperate response by the osteoblasts to lay down new bone which is disorganized and ultrastructurally inadequate.
– involves an osteolytic phase, followed by a mixed lytic/blastic phase, followed by a final osteosclerotic phase
– can be followed in the lab by elevated alk phos and urine hydroxyproline levels
In the Hip:
– varus bowing of the proximal femur and coxa vara
– acetabular protrusio
– stress fractures on the lateral, tension side
– osteoarthritis is probably secondary to altered morphology and biomechanics of weightbearing
1. Start by making sure that the pain is actually coming from the hip – MAKE SURE THEY DONï¿½T HAVE A PAGETOID SARCOMA!!! Also, rule out RADICULOPATHY from spinal involvement, STRESS FRACTURE, and simple PAGETï¿½S BONE PAIN. Coinsider an intra-articular marcaine injection to sort this out.
2. Check alk phos and urine hydroxyproline to just get a baseline for their Pagetï¿½s disease
3. Consult internal medicine/Rheumatology if considering surgery – will the patient benefit from being put on bisphosphonates and calcitonin preop?
4. Get full length standing films to assess the deformity of the entire femur
5. Make sure cardiac status is okay – 15% involvement of bone can lead to cardiac changes (high output failure)
6. Anticipate that heterotopic bone formation is a problem in these patients – postop they will need NSAIDs or XRT
Technical Considerations – Femur
– on the femoral side, despite the limitations, cemented fixation is still the gold standard – have lots of cement!
1. Hypervascularity – may impair visualization, require measures such as a cell saver, and may compromise cement fixation because of an inability to achieve a really dry field for cement interdigitation; also, theoretically there is a potential risk for osteolytic bone resorption during the hypervascular stage. May also be an issue for acetabular fixation; you might have to consider cementing both the femur and the acetabulum!
– be ready for this preop with calcitonin or bisphosphonates
2. Bone sclerosis – it can be extremely hard; have sharp reamers and the midas rex. May not be able to use the broaches, because the bone is so hard and you may just break it by pounding down the reamers.
3. Varus bowing – anticipate the need to get an intraoperative x-ray to confirm that you are down the middle. Also be ready to osteotomize the femur to get it straight, and preoperatively template to make sure you can bypass this.
4. Size of canal – it is often very wide; need a huge cement restrictor (or bone plug) with lots of cement
Technical Considerations – Acetabulum
– on the acetabular side, cemented or cementless are acceptable (no good comparisons) – have to decide once you see the quality of bone
1. Protrusio – makes the exposure more difficult; anticipate the need for a wide exposure; be prepared to osteotomize in situ, be prepared to bone graft or use a protrusio cage, with rim reaming only to open the mouth of the acetabulum but not deepen it.
Results: as a whole, the results in this patient population are inferior, with a much higher revision rate