12.18 Pathological fractures

In describing the mechanical effect of the environment on materials, cause and effect are related through stress and strain. A fracture occurs when the force applied to bone is greater than the ability of bone to dissipate the stress through its elastic properties as described by strain.

The skeleton which is constituted of bone of normal structure and physiology will require significant force to break at all ages. The patient’s clinical history will register an impact of high energy and the radiographic appearance of the adjacent bone will appear normal. In contrast, bone may be weakened by a pathological process so that a fracture may occur with trivial force. Hence a pathological fracture is defined both by the application of trivial force, and, if sought, evidence of pre-existing weakened bone. It is important to elicit that minimal energy caused the fracture since bony fragments may obscure other evidence of localized bone loss. Consequently, inadvertent reaming of a primary malignant bone tumour or a hypervascular renal-cell cancer metastasis occurs with disappointing regularity and may compromise patient survival. Further evidence of localized bone disease is a subtle history of vague mechanical pain predating the fracture by days or weeks.

Bone may be weakened by:

Although pain often drives a patient to seek the medical attention which results in the diagnosis of a tumorous lesion of bone, pathological fracture is perhaps the first presentation especially in benign lesions. Benign neoplastic lesions are most common in childhood and young adulthood. With increasing age, however, metastatic bone disease eventually becomes the most frequent cause of a localized pathological fracture.

All the benign intramedullary neoplasms of childhood can be associated with pathological fractures. Unicameral (simple) bone cysts are the most frequent but others include aneurysmal bone cyst, enchondroma, fibrous dysplasia, osteofibrous dysplasia, and eosinophilic granuloma.

In young adulthood, simple bone cysts seem to resolve and giant cell tumour can be added to the earlier list. Cortically based lesions such as fibrous cortical defect can result in a unicortical stress fracture. Even a pedunculated osteochondroma may fracture through its stalk and require excision.

Since the histology of new fracture callus includes plump active osteoblasts in a cellular osteoid matrix, it is important to inform the histopathologist of a fracture when sending material, otherwise a spurious diagnosis of osteosarcoma may be entertained.

Primary malignant bone tumours infrequently present as a pathological fracture in childhood, although in osteosarcoma this complication may occur during biopsy or while undergoing neoadjuvant chemotherapy and awaiting surgery. Although univariate analyses suggest that pathological fracture is associated with poor survival, more recent multivariate studies point to other features of tumour aggression as more responsible for this. A chondroid tumour which fractures in one of the proximal long bones may hint of a chondrosarcoma, although in the hand or foot fractures tend to represent a benign enchondroma.

In the patient over 50 years old, a pathological fracture is usually due to metastatic disease. The usual suspect primary tumours are well recognized: breast, prostate, lung, thyroid, and kidney are all carcinomas. Added to this will be the myeloproliferative disorders of myeloma and lymphoma. Except for the special case of a late isolated renal cell carcinoma deposit, it may be impossible to cure the patient. However, an accurate diagnosis will provide the oncologist with the best chance of providing effective palliative treatment.

The importance of identifying that a fracture is pathological cannot be emphasized too strongly. Among some doctors there may be a belief that cancers do not occur in children; others may believe that there can be no harm in promptly fixing all femoral long-bone fractures in the elderly.

Taking a comprehensive history and procuring good quality radiographs will go a long way to ensuring a minimum of mistaken diagnoses.

It is recognized that appropriate investigations may take several days to organize. In the interim it is important to reassure the patient and ensure that adequate analgesia is administered and fracture immobilization achieved. During this period, efforts can be made to maximize patient fitness for surgery—in particular hypercalcaemia of malignancy can be identified and corrected with fluid management and bisphosphonates. Clinical examination of lung fields, abdomen, prostate, and breast may be required. Further imaging may include magnetic resonance imaging of the local area, bone scintigraphy to assess for further skeletal lesions and computed tomography of the chest, abdomen, and pelvis where a primary adenocarcinoma is sought. Where the lesion proves to be solitary, a biopsy should be undertaken with the aim of discriminating a primary malignant bone tumour from a metastasis. This should be discussed with the local or regional bone tumour specialist service to ensure the biopsy method does not compromise further potential optimum management.

In the child and young adult, radiographs alone may be diagnostic, for example, in simple bone cysts of the proximal humerus and digital enchondromas. Age and site and tumour matrix may also be useful pointers in identifying fibrous dysplasia, giant cell tumour and chondroblastoma.

Where a skeletal metastasis is already identified, the risk of future fracture arises. If this risk is high, prophylactic fixation may be indicated. Where 50% of a single cortex is destroyed, pathological fracture may be regarded as inevitable. Furthermore, avulsion of the lesser trochanter points to an imminent hip fracture. It is recommended that each trauma unit has a named surgeon who has responsibility for liaison with colleagues and other specialists such as oncologists to allow early assessment and treatment of such impending fractures. Mirels has developed a scoring system which ranks radiographic and clinical features as shown in Table 12.18.1.

A score of 8 or above indicates a high likelihood of impending fracture and prophylactic fixation is recommended prior to radiotherapy.

In most generalized conditions, bone will heal as rapidly or almost as rapidly as in normal bone. Choice of treatment depends upon the fracture configuration, comorbid factors, age, and mobility.

In benign lesions, upper limb pathological fractures are perhaps more common than those in the lower limb. However, fractures in the lower limb are more difficult to manage with a higher malunion risk and so surgeons will be more likely to undertake prophylactic treatment of an impending femoral fracture. It is important to advise use of crutches while awaiting surgery, or at least explain the risk of fracture to avoid accusations of neglect.

In many types of benign bone lesions, a fracture may stimulate osteogenesis within the lesion so that both fracture healing and lesional obliteration occur together. This is seen in simple and aneurysmal bone cysts, enchondromas, fibrous cortical defects, and fibrous dysplasia. It is recommended that the patient is followed-up until lesional obliteration. In the lower limb long bones, however, internal fixation may be necessary to achieve an accurate anatomical reduction. A giant cell tumour may represent a difficult reconstructive problem when an intra-articular fracture occurs around the knee. If there is sufficient bone to secure both medial and lateral cortices, then curettage, grafting, and plate fixation may be appropriate. Otherwise an extended tumour prosthesis might be required.

The British Orthopaedic Association has stated that the aim of surgery in a pathological fracture due to metastatic disease is to relieve pain and restore function. An over-riding principle is to provide immediate postoperative stability, allowing weight bearing, and to stabilize all lesions in the affected bone, where possible.

In long-bone biopsy-proven solitary metastases and in multiple bony metastases without biopsy a pathological fracture of the diaphysis or metaphysis is most reliably managed with a load-bearing implant—typically an intramedullary nail. The reason for this is that the fracture cannot be assumed to be capable of healing—at some point the tumour will grow again locally. The aim of surgery is therefore to stabilize the bone for the duration of the patient’s life—typically this is 1–2 years in non-breast cancer, perhaps 2–5 years in breast cancer. Modern intramedullary fixation will not undergo fatigue-failure in cyclical loading within 2 years. It is probably worth stabilizing a long-bone fracture if life expectancy exceeds at least 6 weeks although each case is judged on its own merits with full involvement of patient and family in decision-making. Where surgery is too great a risk, then a portable epidural catheter may allow comfort and even some transfer-mobility. In renal cell metastasis, there is a risk of severe haemorrhage, so that preoperative angiography plus coil-embolization is warranted. In solitary renal cell metastases which have developed some years after nephrectomy, then treatment as for a primary malignant bone cancer might be undertaken with a high chance of cure.

Where a fracture is juxta-articular, then plate fixation together with bone–cement reconstruction is advisable. The exception to this, however, is a peritrochanteric fracture of the femur or proximal humerus fracture which may be treated by an intramedullary nail of reconstruction type, or a cemented joint prosthesis. The latter has a low failure rate. Occasionally, a tumour prosthesis may be required but the loss of some hip or shoulder abductor function will have to be accepted. A fracture through the ilium adjacent or proximal to the hip joint will require hip replacement with acetabular reconstruction. Harrington has described useful principles of surgical treatment depending on the anatomical site of the pathological pelvic fracture. Cement and metal pins will produce a ‘reinforced concrete’ effect proximal to the acetabulum into which a polyethylene cup can be cemented.

All reamings and curetted material should be submitted to histopathological examination to confirm the tumour diagnosis. Oncological postoperative treatment will be guided by the diagnosis and radiotherapy will frequently be directed to the tumour bed.

Certain cancers will not prevent fracture healing when treated with appropriate chemo-, endocrine, or radiation therapy. These include lymphoma, myeloma, thyroid, and breast and prostate cancer. New oncogene inhibitors in renal cell metastases now seem to provide a similar gratifying effect.