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OR10.1,OR11.1 | Bone Tumours and Peripheral Nerve Injuries — PBL Case

CLINICAL SETTING

Arjun, a 17-year-old high school athlete, is brought to the orthopaedic outpatient clinic by his parents. He has had progressive pain around his right knee for the past 2 months, initially attributed to a sports injury but not improving with rest and NSAIDs. In the past 3 weeks he has noticed a firm, non-tender swelling just above the knee. His parents also note that he has started to drag his right foot when walking. On examination: a 6 × 5 cm firm, fixed, non-pulsatile mass is palpable over the distal medial femur; there is local warmth but no erythema. Neurological examination reveals inability to dorsiflex the right ankle (foot drop), toe extensor weakness, and sensory loss over the dorsum of the right foot and lateral lower leg. Knee jerk and plantar flexion are intact. The attending orthopaedic surgeon orders plain X-rays of the right femur and knee.

Trigger 1: Plain X-ray Report

X-ray of the right distal femur: There is an aggressive-appearing mixed lytic and sclerotic lesion centred in the metaphysis of the distal femur, measuring approximately 7 cm in length. The cortex appears breached medially with a small soft tissue component. There is a triangular periosteal elevation at the proximal margin of the lesion (Codman's triangle) and a faint sunburst pattern of new bone formation. The physis appears open. No obvious joint involvement. The knee joint space is preserved.

DISCUSSION POINTS

  • What are the characteristic radiological features described, and which primary bone tumour fits this X-ray pattern in a 17-year-old?
  • How does this lesion differ from Ewing's sarcoma and giant cell tumour radiologically, in terms of location (metaphysis vs diaphysis vs epiphysis), periosteal pattern, and patient demographics?
  • What further imaging studies are needed, and what does each one contribute to staging this lesion?
Click to reveal Trigger 2: Staging, Biopsy, and Nerve Injury Workup (discuss previous trigger first!)

Trigger 2: Staging, Biopsy, and Nerve Injury Workup

MRI confirms a 7.2 cm heterogeneous mass in the distal femoral metaphysis with cortical breakthrough and a medial soft tissue extension of 2.1 cm; there is no intra-articular extension. CT chest shows two sub-centimetre pulmonary nodules (indeterminate). Bone scan shows increased uptake at the distal right femur only. A CT-guided core needle biopsy is planned. Nerve conduction studies show absent sensory and motor responses in the right common peroneal nerve distribution; the right tibial nerve responses are normal.

DISCUSSION POINTS

  • Apply the Enneking surgical staging system to this patient. What stage is this tumour, and what surgical margin does that stage mandate?
  • Where should the biopsy needle tract be placed relative to the planned definitive surgical approach, and why? What are the consequences of a poorly placed biopsy?
  • Classify Arjun's nerve injury using Seddon's classification. What deformity and sensory pattern are expected, and what splint should be applied while awaiting recovery or definitive management?
  • How does the presence of indeterminate lung nodules change the management plan, and which additional investigation would clarify their significance?
Click to reveal Trigger 3: MDT Decision and Informed Consent (discuss previous trigger first!)

Trigger 3: MDT Decision and Informed Consent

Histology confirms conventional high-grade osteosarcoma (osteoblastic type). PET-CT shows hypermetabolic activity only at the right distal femur; the lung nodules are metabolically inactive. The MDT decides on: (1) neoadjuvant chemotherapy with MAP protocol (methotrexate, adriamycin, cisplatin) × 3 cycles; (2) wide en bloc resection of the distal femur with distal femoral endoprosthetic replacement for limb salvage; (3) adjuvant chemotherapy based on necrosis response (Huvos grade). Arjun and his parents ask: 'Why can't the doctor just remove the lump now? Will he ever play sports again? Will his foot recover?'

DISCUSSION POINTS

  • Explain to Arjun and his parents (in language a non-clinician can understand) why chemotherapy must come before surgery, and how the tumour's response to chemotherapy determines both the chance of cure and the post-operative chemotherapy plan.
  • What is the expected prognosis for high-grade osteosarcoma without metastases at presentation (5-year survival), and how does the Huvos necrosis grade (good response = >90% necrosis) influence this?
  • Regarding Arjun's foot drop: given the NCS findings (absent common peroneal responses), what does this tell you about the Sunderland grade, the likelihood of spontaneous recovery, and what intervention — conservative or surgical — is most appropriate while the tumour treatment is ongoing?
  • What are the principles of rehabilitation and return to activity after distal femoral endoprosthetic replacement? Which precautions are specific to this reconstruction?

Learning Issues

Research these questions and bring your findings to the discussion.

  1. [OR10.1] What are the aetiopathogenesis, radiological features, differential diagnosis, Enneking staging, biopsy principles, and management of osteosarcoma and other malignant bone tumours?
  2. [OR10.1] How are pathological fractures classified and managed, and what is the role of prophylactic fixation (Mirel's score) in metastatic bone disease?
  3. [OR11.1] How are peripheral nerve injuries classified by Seddon and Sunderland, and what is the expected recovery and splinting for radial, ulnar, median, and common peroneal nerve injuries?
  4. [OR11.1] What are the motor and sensory deficits associated with specific nerve injuries (wrist drop, claw hand, ape thumb, foot drop), and how are they managed with splints and physiotherapy?