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. In children the proximal humerus is the classic site of a unicameral bone cyst, the commonest cause of a pathological fracture through benign bone.

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Epidemiology. Bone is the third most common site of metastatic disease, and the humerus is involved in 20% of bone metastases, second among long bones only to the femur. The number is increasing as cancer survival improves. The primaries to remember are breast, lung, thyroid, kidney and prostate: BLT-KP, a BLT with a Kosher Pickle for lunch.

Prognosis. Median survival depends on the primary, and the fixation must be durable enough for the survival expected.

• Prostate and breast: years (24-36 months)
• Renal and thyroid: intermediate (12 months)
• Lung: short (less than 6 months)

Spread. Metastasis to bone is haematogenous. Tumour emboli deposit in the vascular red marrow, and Batson's plexus, a low-pressure venous system, facilitates spread. Cytokines (RANKL and PTHrP) stimulate osteoclasts.

Lytic or blastic. Lytic lesions destroy bone and lead to fracture; they come from lung, renal and thyroid primaries and from myeloma, with breast giving mixed lesions. Blastic lesions, from prostate and again breast, form bone and leave it brittle. Lytic lesions are the more prone to fracture and the harder to fix.

Biomechanics. The humerus is a non-weight-bearing bone, loaded mainly in torsion and bending rather than axial compression, which allows non-operative management more often than in the femur. Functional demands such as lifting and toileting still require stability. A cortical defect greater than 50% reduces torsional strength by 60%.

Mirels score. Mirels predicts the risk of fracture in an impending pathological fracture from four variables, SPLS: site, pain, lesion and size. Each scores 1 to 3 and the sum runs from a minimum of 4 to a maximum of 12. The score applies to metastatic disease in long bones; it does not apply to primary bone tumours or spinal metastases.

The thresholds. Mirels's own paper recommended prophylactic fixation at 8 or more; the conventional teaching threshold is 9 or more for fixation and 7 or less for radiotherapy. A score of 8 remains a clinical-judgement grey zone in which functional demand and prognosis drive the decision.

Why the score over-treats. Mirels has high sensitivity but low specificity, so a score of 9 or more over-predicts fracture and may lead to over-treatment. A systematic review of fracture-risk methods found a negative predictive value of 86-100% but a positive predictive value of only 23-70%, and concluded that the score "leads to an overtreatment" (Benca, Bone Rep 2016, PMID 28326347). A low score therefore reliably reassures; a high score identifies a group in which most lesions still would not have fractured.

Harrington's criteria. The classic indications for prophylactic fixation of a lytic metastasis:

• Destruction of 50% or more of the cortex
• A lesion 2.5cm or larger
• Pain despite radiotherapy

Read them as femoral criteria. Harrington described them in 1982 for lytic lesions of the femur, in a paper on lower-extremity metastases. His third indication was pain specifically with weight-bearing, which cannot apply literally to the humerus, and his fourth, avulsion of the lesser trochanter, is a hip finding with no upper-limb equivalent. Because the humerus fails in torsion and bending, neither the 50% nor the 2.5cm figure has been validated here, and Mirels scores the upper limb lower than the lower limb precisely because the risk differs.

Using them in the humerus. Neither Harrington's criteria nor Mirels was derived in this bone. Use them to decide who needs a closer look, and let functional pain, lesion geometry on CT and the demands the patient actually places on the arm drive the decision.

History. Ask about a known history of cancer and about constitutional symptoms: weight loss, night sweats and fatigue. Separate mechanical pain from the fracture from biological pain at night, which typically indicates active tumour, and establish the functional demand on the arm.

Examination. The examination focuses on finding a primary source.

• A soft-tissue mass, which raises concern for sarcoma
• Previous mastectomy scars
• Thyroid enlargement
• Axillary and supraclavicular lymph nodes

The radial nerve. It is commonly involved in humeral shaft fractures. 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.

Radiographs. Look for a "moth-eaten" or permeative appearance and cortical destruction. The pathological fracture is transverse, after minimal trauma.

Staging. CT of the chest, abdomen and pelvis stages the disease, and CT defines the bone stock remaining. A bone scan or PET identifies other skeletal metastases, and whether the lesion is solitary or multiple is prognostic. Stage sufficiently to establish the diagnosis, the extent of disease and a safe treatment plan, tailoring imaging to urgency, known cancer history and the likely primary. A recent negative staging CT does not exclude disease beyond its field: review the scan coverage and image the entire symptomatic bone.

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Laboratory. Rule out myeloma in every patient over 40: serum protein electrophoresis (SPEP), urine Bence-Jones protein and free light chains, with calcium, phosphate and ALP. A normal or equivocal serum electrophoresis does not exclude oligosecretory myeloma. The features of myeloma are CRAB:

• Calcium elevation: hypercalcaemia
• Renal insufficiency: raised creatinine
• Anaemia: normocytic
• Bone lesions: lytic, the "raindrop skull"

Tumour markers point to the primary: PSA for prostate, CEA and CA-125 for gastrointestinal and ovarian cancer, and thyroid function tests for thyroid.

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Biopsy. Biopsy provides the definitive tissue diagnosis. It is indicated when:

• The primary is unknown
• There is a history of cancer but more than 5 years disease free, to confirm the lesion is not a new primary
• The imaging is inconsistent

Core needle biopsy is the gold standard. Open biopsy with frozen section at the time of surgery is an option when fixation is impending.

The biopsy trap. An unplanned nail can contaminate the humeral canal and the soft-tissue compartments if the lesion is a primary sarcoma. Stage first, and place the biopsy tract so it can be excised with a definitive tumour operation.

Vascular metastases. Renal and thyroid metastases may be hypervascular. Consider pre-operative angiography and embolisation when imaging or tumour biology suggests a substantial arterial supply and the planned procedure risks major bleeding. The evidence does not support a blanket mandate, and embolisation is a selective MDT decision.

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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.

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Unknown diagnosis. A destructive or solitary lesion without a known diagnosis is staged and biopsied, by plan, before definitive fixation whenever clinically feasible.

Impending fracture. In a known diagnosis the Mirels bands open the discussion. A score of 7 or less calls for clinical review, and radiotherapy or observation may be appropriate; at 9 or more, consider prophylactic fixation after a humerus-specific assessment.

Complete fracture. In a known diagnosis, stabilise or reconstruct when the benefit outweighs the morbidity, and coordinate the adjuvant treatment.

Non-operative treatment. Consider it when:

• The lesion is mechanically stable and symptoms are controlled
• Surgery is unlikely to improve function or comfort relative to its burden
• Radiotherapy or systemic treatment is expected to control pain and local disease
• Bracing is tolerable and does not compromise skin or function

The options are analgesia, activity adaptation, selective functional bracing, radiotherapy, systemic anticancer treatment and bone-modifying therapy when oncologically indicated.

Operative treatment. Surgery is palliative, for quality of life, not cure. Consider it when:

• A completed fracture or impending structural failure causes pain or loss of useful function
• Immediate stability would restore transfers, self-care or use of walking aids
• The patient can tolerate the intervention and the construct matches expected survival
• Local progression requires resection or reconstruction rather than fixation alone

What the fixation must survive. The goals are immediate stability, immediate loading of the arm, and easier nursing care and transfers. Patients push through the humerus to rise from a chair, to transfer and to use a frame or crutches, and that is the load the fixation has to survive rather than gait.

Solitary renal or thyroid metastasis. For a solitary metastasis from a favourable primary, the balance between palliative fixation and wide resection with endoprosthetic reconstruction is unsettled, and it should be an oncology MDT decision based on prognosis.

Protect what is at risk. Span the diseased bone sufficiently for the observed distribution of disease and the planned local control. Whole-bone protection is not an automatic requirement for every lesion.

Intramedullary nail. The common diaphyseal option, used prophylactically or for an acute fracture. It is a load-sharing device, minimally invasive, preserves the soft tissues and gives immediate stability. Lock it statically, proximally and distally, or augment it with cement screws.

Reaming. Reaming improves nail fit, but it can spread tumour and raises intramedullary pressure, with a theoretical risk of tumour and fat embolism. Whether to ream remains debated; ream carefully, and many advocate venting or unreamed nails in patients with poor pulmonary reserve.

Plate and cement. Indicated for:

• Meta-diaphyseal fractures
• The distal humerus
• The need for open tumour debulking

Curette the lesion to create a cavity, fill it with PMMA cement (the "rebar" concept) and apply a locking plate over the cement. The cement restores compressive strength; the plate provides neutralisation.

Nail or plate. No randomised data favour intramedullary nailing over locked plating with cement augmentation for the humeral shaft. The nail protects the whole bone; the plate allows debulking and direct control of the lesion. The choice depends on lesion location and the surgeon.

Resection arthroplasty. Indicated for:

• Extensive proximal humeral destruction
• Articular involvement
• Failed fixation

The implant is a proximal humeral replacement (endoprosthesis), or a reverse total shoulder if the cuff is compromised. Resection arthroplasty allows immediate function but carries a high dislocation risk.

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The radial nerve is what makes fixing a pathological humerus different from any other long bone.

Iatrogenic risk. The nerve runs in the spiral groove on the posterolateral shaft. It 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.

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. Open plating mandates identifying and protecting the radial nerve, and a posterior approach requires formally exposing it.

Local tumour progression. Progression can occur with or without postoperative radiotherapy, and it can compromise fixation despite a technically satisfactory initial reduction. Surveillance and the systemic and local-control plans must match the tumour biology and the chosen construct. When progression appears, re-stage, biopsy if the diagnosis remains uncertain, and reconsider whether fixation alone can provide durable control.

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Haemorrhage. Intra-operative haemorrhage is the risk in renal, thyroid and other hypervascular lesions. Assess vascularity before operating on them, and use embolisation selectively when a target arterial supply and a meaningful bleeding risk are demonstrated.

Nonunion. Tumour, systemic therapy and radiotherapy can impair healing, so the construct should not depend on union when union is unlikely.

Embolic and cardiopulmonary risk. Reaming and cementation may increase intramedullary pressure. Plan anaesthesia, venting and implant technique according to the patient's cardiopulmonary reserve.

Coordinate, do not automate. Postoperative radiotherapy is not an automatic whole-implant rule. After fixation, request radiation-oncology review and state the residual disease, the implant extent and the operative contamination. Whether and how it is delivered then depends on tumour radiosensitivity, residual disease, surgical margins, prior irradiation, systemic therapy, wound status and expected survival.

The field. When radiotherapy is selected after stabilisation of metastatic long-bone disease, field design traditionally covered the instrumented bone because reaming may seed tumour cells along the canal. Contemporary retrospective data remain mixed: some series support broader coverage for local control, while others show no implant-failure benefit and substantial selection bias. The field must therefore be planned by the treating radiation oncologist, not prescribed by a fixed orthopaedic template.

Timing. Timing follows wound recovery, the urgency of systemic treatment and the radiotherapy technique rather than a universal two-to-three-week date. Build fixation that is durable without assuming either fracture union or radiotherapy failure.

Outcomes are driven by tumour biology, systemic disease, pre-fracture function and the match between lesion and construct. Report pain relief, useful hand-to-mouth function, ability to transfer or use walking aids, neurological status, local progression, revision and implant survival. Avoid quoting one universal success or failure percentage across nails, plates and endoprostheses.

Related pages: Pathological Fractures - Femur for the lower-limb counterpart; Pathologic Fracture Management for general principles and prognostic scores; Metastatic Bone Disease for systemic treatment; Humeral Shaft Fractures and Radial Nerve Anatomy for construct and nerve planning; Multiple Myeloma and Osteosarcoma for critical differentials; and Radiotherapy for Musculoskeletal Tumours for indication, timing and field planning.

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