Hip replacement in bone metastasis

Arthroplastic musculoskeletal oncology surgery is generally associated with dramatic resections and megaprosthetic reconstructions in primary neoplasms of the bone and joints. Yet in most general hospitals, an equally significant field of service is joint replacement in cancer patients. In cancer patients with disabling arthritis the approaches to reconstruction are very similar to non cancer-inflicted patients except for a striking increase in the risk of deep vein thrombosis (18% risk reduced to 4% with prophylactic anticoagulation, p=0.006; Nathan et al, 2006), general debility, osteoporosis and, increasingly, complications due to bisphophonate therapy. In cancer patients with metastatic disease the problem is further complicated by issues of massive bone loss, irradiated tissue and expectation of survival. Standard arthroplasty techniques can be adapted to these patients without having to resort to costly tumor prosthesis. 

Hip replacement surgery is routinely performed on cases of varying involvement of the pelvis. The Harrington classification of defects is most applicable to this scenario but nevertheless the Paprosky classification used by joint replacement surgeons offers additional valuable risk stratification. This is incorporated with a protocol for prophylactic anticoagulation using low molecular weight heparin or IVC filters as the individual case warrants. Methods of survival stratification are used such that the most appropriate reconstructive option is selected for the patients depending on the patients’ expectation of survival. Accordingly, the patient with a pathological fracture of the proximal femur with advance lung cancer in extremis should be expediently stabilized whereas a patient with renal cell carcinoma who is otherwise well may require a hip replacement (Nathan et al, 2005). Cryosurgery using Argon gas based probe directed technology (Cryohit, Galil Medical, Israel) is an important adjunct to the standard armamentarium used in these cases.

Results
Most of the cases present to the orthopedic oncology service late having undergone chemotherapy and radiation. Surgery has a high complication rate in this setting with implant loosening, superficial infections and dynamic hip instabilitydue to extreme disuse. Pain relief is virtually complete with all patients having achieved complete relief of pain in the short term. Expectation of ambulation is excellent in the premorbidly ambulant patient and 70% in the patient with pathological acetabular protrusion. There is an at least one grade improvement in all patients based on the ECOG functional scoring system. Cryosurgery is able to afford good local control while preserving host bone tissue which allows more functional reconstructions. Early intervention was far more predictable and desirable in these patients and is the present preferred course of action. 


Conclusions
Hip replacement surgery in metastatic disease should be offered early. Cryosurgery is a useful adjunct in these patients especially after radiation therapy. It appears to offer better control of disease compared to palliative radiation protocols. End-stage reconstructions have very unpredictable outcomes.