GCT Recurrence After BKA with THR

Clinical Scenario

A 38-year-old male presents with 3 months of worsening left knee pain at night. He had a left below-knee amputation (BKA) 15 years ago for a giant cell tumour (GCT) of the distal tibia. He subsequently developed symptomatic osteoarthritis of the left knee and underwent total hip replacement on the left 18 months ago. He is otherwise fit and well.

History:

Left distal tibia GCT diagnosed age 23
Treated with extended curettage, high-speed burr, phenol, cement
Recurred twice over 5 years
Eventually required BKA at age 28
Left THR 18 months ago for hip OA (presumed gait-related)
Now 3-month history of:
- Left knee pain (residual limb)
- Worse at night
- Mild swelling above BKA stump
- No constitutional symptoms

Examination Findings:

Below-knee amputation stump, well-healed
Mild swelling in distal thigh/knee region
Tenderness over medial femoral condyle
No warmth or erythema
THR scar well-healed
Hip ROM: Full and painless
Knee (prosthetic): Not assessed
No palpable lymphadenopathy
Chest clear

Investigations

Laboratory Results

Imaging

Plain X-ray Left Femur/Knee:

BKA stump with tibial remnant
THR in situ, appears well-fixed
Lytic lesion in left medial femoral condyle, 4 x 3 cm
Geographic pattern with narrow zone of transition
No periosteal reaction
No matrix calcification
Cortical thinning but no pathological fracture

MRI Left Femur:

4.2 x 3.5 x 3.0 cm lesion in medial femoral condyle
T1: Intermediate signal
T2: Heterogeneous high signal
Gadolinium: Solid enhancement
No soft tissue extension
No skip lesions
Clear of THR stem

CT Chest:

3 pulmonary nodules identified:
- Right lower lobe: 12mm
- Right middle lobe: 8mm
- Left lower lobe: 6mm
No mediastinal lymphadenopathy
Concerning for pulmonary metastases

Bone Scan:

Increased uptake in medial femoral condyle
No other skeletal lesions

Questions & Model Answers

What are the differential diagnoses for this lytic lesion, and what is the most likely diagnosis?

Describe the Campanacci grading system for GCT and how it guides treatment.

How do you manage the pulmonary nodules in this patient with GCT?

What is the role of denosumab in GCT management?

What surgical treatment would you recommend for the femoral lesion?

What is the prognosis and follow-up plan for this patient?

Key Teaching Points

Concept	Detail
GCT Recurrence	15-25% after curettage, can occur years later
Lung Metastases	2-3%, 'benign pulmonary implants', often indolent
Campanacci Grading	I/II = curettage; III = consider wide resection
Recurrent GCT	Treat more aggressively than initial presentation
Denosumab	RANK-L inhibitor, effective but rebound on cessation
Prognosis	Good even with lung mets (>75% 5-year survival)

Common Examiner Follow-up Questions

"What adjuvants can be used after curettage?"
- High-speed burr (mechanical)
- Phenol (chemical cautery)
- Hydrogen peroxide
- Liquid nitrogen (cryotherapy)
- Argon beam coagulation
- PMMA cement (thermal necrosis at cement-bone interface)
"Why use cement instead of bone graft?"
- Thermal necrosis at cement-bone interface may kill residual tumour cells
- Easier to detect recurrence on X-ray (lytic line at cement-bone interface)
- Immediate structural support
- Bone graft: better for young patients, small defects, away from joint
"What is the rebound effect with denosumab?"
- Rapid tumour regrowth after stopping denosumab
- Can occur within months of cessation
- Tumour may be more aggressive than before treatment
- Must plan surgery or ongoing treatment before stopping
- Some advocate lifelong treatment for unresectable disease

GCT Recurrence After BKA