Pathological Fractures (Humerus)

Pathological fractures of the humerus occur when bone weakened by disease (cystic, metabolic, or neoplastic) fails under physiological loads. In adults over 40, metastatic disease and myeloma are the overwhelming causes. The humerus is the second most common site for long bone metastases (after femur).

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Pathophysiology of Metastasis

Mirels Scoring System

Used to predict fracture risk in impending pathological fractures.

Key Questions:

• Known history of cancer?
• Constitutional symptoms: Weight loss, night sweat, fatigue.
• Pain history: Mechanical ( fracture) vs Biological (night pain).
• Functional demand.

Night pain typically indicates active tumor.

Examination focuses on finding a primary source.

Imaging & Staging

A destructive humeral lesion in an adult is metastasis or myeloma until proven otherwise, but the differential changes dramatically with age and imaging. Distinguishing these before any fixation is the single most important decision.

Algorithm

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Treatment Decision Making

Fixation Strategy

The examination section flags that "the radial nerve is commonly involved in humeral shaft fractures" and the cheat sheet warns against "ignoring the radial nerve in percutaneous nailing," but the humerus's signature neurovascular structure deserves development — it is what makes fixing a pathological humerus different from any other long bone.

Three reasons it matters here:

• A pre-existing palsy. A pathological shaft lesion at the spiral groove (or the fracture through it) can cause a radial nerve palsy from tumour infiltration, compression or the fracture itself. Document active wrist, finger and thumb extension and first-dorsal-web-space sensation before any intervention — this is both planning and medicolegal protection.
• Iatrogenic risk. The nerve runs in the spiral groove on the posterolateral shaft and is at risk during open plating (particularly posterior approaches and distal-third exposure), during percutaneous or distal interlocking screw placement, and from retraction — all made harder when tumour distorts the normal anatomy.
• Approach choice. Plan the construct around the nerve: an antegrade intramedullary nail avoids open dissection over the nerve along the shaft (but distal interlocking screws still endanger it — place them with the nerve in mind, open if necessary), whereas open plating mandates identifying and protecting the radial nerve, and a posterior approach requires formally exposing it.

Potential Complications

Rehabilitation Protocol

The topic states throughout that post-operative radiotherapy follows fixation, that it should cover "the whole implant," and that "if RT is not given, the tumour continues to grow and destroys the fixation" — the rationale and its orthopaedic consequences deserve to be assembled, because it is a stock examiner question after "how would you fix it?"

Why irradiate, and why the whole bone. Surgery for metastatic disease is palliative and deliberately leaves tumour behind. Post-operative radiotherapy to the entire instrumented field controls the residual and microscopic disease along the canal and around the implant; irradiating only the original lesion risks progression elsewhere along the instrumented bone that would ultimately destroy the construct. This is the reason both for spanning the whole bone surgically and for radiating the whole implant.

Timing. Radiotherapy is started once the wound has healed (commonly around 2 to 3 weeks post-operatively) to avoid wound-healing complications.

The double-edged effect on bone. Radiotherapy impairs osteoblast function and bone healing, so a pathological fracture fixed in irradiated tumour bone may never unite. The corollary defines the whole philosophy of this operation: the construct must be durable enough to outlast the patient independent of bony union — mechanical durability, not biological healing, is the goal (the basis of the Capanna and Katagiri prognosis-matched approach). Antiresorptive therapy (a bisphosphonate or denosumab) complements radiotherapy in reducing skeletal-related events. (Detailed radiotherapy dose/fractionation is developed in the radiotherapy for musculoskeletal tumours topic.)

Prognosis

• Pain Relief: Excellent (80-90% improvement) after fixation.
• Function: Restoration of ability to feed/groom.
• Ambulatory: Upper limb fixation allows use of walking aids.
• Hardware Failure: 5-10%, usually due to disease progression or long survival.

Global epidemiology: Bone is the third most common site of metastatic disease after lung and liver, and the humerus is the second most common long bone affected after the femur (around 20% of long-bone metastases). Breast, lung, thyroid, renal and prostate cancers account for the overwhelming majority. Rising cancer survival worldwide is increasing the absolute burden of skeletal metastases.

A universal principle across all settings: never fix a destructive bone lesion of unknown origin without staging and, where indicated, biopsy.

Self-Assessment Questions