A pathological fracture is a fracture through diseased bone. Suspect one whenever the trauma involved was minimal, the surrounding bone appears abnormal or if there is a history of malignancy.
In children the cause is often benign. If there is evidence of a localized bone lesion it can be a fracture through a benign tumour, in contrast to the adult skeleton where the cause is often malignant. Common causes are the fractures through:
1) Simple bone cyst
2) Aneurysmal bone cyst
3) Non ossifying fibroma
If more than bone is involved by the process the cause may be:
3) Vascular neoplasms
4) Metastasis (neuroblastoma and Wilms's tumor).
Metabolic and systemic diseases.
1) Osteogenseis imperfecta.
Suspect it if there is a history of many previous fractures with minor trauma. The skeleton is osteopaenic and there are usually other healed and healing fractures. The fractures may lead to bowing of the bones and other angulatory deformities. In Type 1 osteogenesis (dominant inheritance, -ask about a family history of brittle bones.) the sclera are blue. Treat eh fractures as you would any other fracture. If ORIF is needed, prefer intramedullary rods to plates and screws, which may break out of the soft bone. In severe cases with malalignment multiple osteotomies may be needed to straighten the bone. The segments are skewered buy an intramedullary rod such as the Bailey-Dubow rod – a rod that telescopes longer as the child grows. Straightening the bowed limb will lessen the chance of future fractures.
This is caused by lack of Vitamin D. In South Africa, where there is plenty of sun primary rickets is rare, but renal causes are not rare. Pathologic fractures are treated as for any other fracture. The underlying metabolic derangement will also need attention.
Management of a fracture through a cyst
Simple bone cysts tend to disappear once decompressed by the trauma. Treat them as you would any other fracture. In other words the majority will need simple reduction and a plaster cast. The exception is a fracture about the proximal femur. Here open reduction and internal fixation is preferred. If there is enough place for a Paediatric hip screw (sliding screw and plate) between the growth plate and cyst, use one but never violate the epiphysis with this large screw. If the cyst abuts the growth plate, smooth Kircshner wires may be needed – these may be placed so as to cross the growth plate. In this case, additional support in a hip spice will be necessary postoperatively.
Recurrence of a cyst (only about 50% of UBC cysts disappear completely after a fracture) is an indication to do cuttetage and bone graft. Histology is also necessary as it may be an ABC or more aggressive tumour.
Treatment of a known ABC is more aggressive with biopsy, curettege and some form of internal fixation if necessary.
The majority of fibrous cortical defects and non ossifying fibromas are an incidental finding on X ray and they never become symptomatic. Once a NOF occupies more than 50% of the cortex it will become painful as it is in a pre-fracture stage. Large NOFs can be prophylatically curetted and fixed. A fracture through a NOF will probably warrant internal fixation if it is in a weight bearing bone, especially if it is about the hip.
Adult Pathological Fractures:
In the adult a localized lesion will often mean a malignancy. The most common cause is a metastasis.
Suspect Myeloma with any localized lytic bone lesion in a patient over 50yrs of age. In a vertebra there is a vertebra plana or wafer vertebra. In long bones the Myeloma or plasmacytoma will present as a lytic lesion. In myelomatosis a skull x ray may show punched out lytic lesions. Do an ESR in all lytic tumours – in Myeloma it is often markedly raised, typically over 100 mm/hr. Serum electrophoresis will show an abnormal M peak. The protein is lost into the urine and can be identified by the Bence Jones test or by urine electrophoresis.
2) Metastatic tumour
Malignnt tumours that commonly metastasize to bone are:-
· Prostate (sclerotic)
· Thyroid ( lytic, expansile)
· Renal (lytic, expansile)
Basically all pathological fractures through a malignant metastasis need internal fixation. Be wary if the clinical picture is that of a primary bone tumour. These can often be treated by chemotherapy and later a curative resection. ORIF will be contraindicated for a primary without metastases.
For metastases to bone the rationale is to
· Get he patient mobile and out of the hospital
· The fracture will not unite if treated conservatively because:
o The bone will need to be irradiated
o Irradiated bones will not unite via secondary intention.
Make sure the rest of the bone is structurally sound by getting x rays of the whole bone. Get a skeletal technetium scan to determine the spread of other metastases. Where the primary is unknown appropriate investigations as to this need be done:
· Thorough physical examination including breasts in a female, rectal for and prostate in a man.
· Special Investigations:
o Chest X ray
o Thyroid scan
o Abdominal CT or SONAR
Prophylactic fixation of a metastasis:
A large metastasis ideally should have ORIF before it breaks. If a lesion is painful on weitht bearing, and is more than 50% of the cortex in diameter it qualifies for internal fixation. Mirels has published a scoring system for ORIF of metastases. His system awards points for pain, whether the lesion is lytic or blastic and whether it is in the high risk peritrochanteric region of the femur. Of a possible 12 points, as score of more than 8 qualifies the patient for prophylactic fixation.
Osteoporosis is the commonest cause of pathological fractures in the elderly.
The fracture is managed as any other, however the following points must be considered.
· The patient is often elderly and must be mobilized as soon as possible. ORIF is usually necessary.
· Technically ORIF is difficult as screws and plates often pull loose due to the poor bone stock.
· Look for a cause of the osteoporosis and consider long term medical treatment with hormonal replacement, bisphosphonates or calcium supplements.
The treatment of the pathologic fracture is based on the establishment of a diagnosis. Only after establishing the diagnosis with certainty can a proper treatment strategy be formulated.