bisphosphonateatypical fractureASBMR criteriaprodromal paincontralateral imagingcephalomedullary nail
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CIM Case: Atypical Femoral Fracture
Clinical Scenario
Patient: 72-year-old woman
Presentation: Fall from standing while walking, sudden right thigh pain and inability to weight-bear
Relevant history: Postmenopausal osteoporosis on alendronate for 8 years, left thigh aching for past 4 months (intermittent, worse with walking), rheumatoid arthritis on low-dose prednisolone, previous vertebral compression fractures (T11, L1), vitamin D deficiency (treated)
Examination findings:
BMI 22, thin habitus
Right leg shortened and externally rotated
Tenderness at mid-thigh level
Unable to perform straight leg raise
Neurovascularly intact distally
Left thigh: tenderness over lateral mid-femur on palpation
No wounds or bruising
Kyphotic thoracic spine
Investigations Provided
Laboratory Results
Test
Result
Normal Range
Interpretation
Hb
118 g/L
115-155 g/L
Normal
WCC
7.2 ×10⁹/L
4-11 ×10⁹/L
Normal
Platelets
245 ×10⁹/L
150-400 ×10⁹/L
Normal
CRP
8 mg/L
<5 mg/L
Mildly elevated
Calcium
2.35 mmol/L
2.2-2.6 mmol/L
Normal
Phosphate
1.1 mmol/L
0.8-1.5 mmol/L
Normal
ALP
95 U/L
30-120 U/L
Normal
Vitamin D
65 nmol/L
>50 nmol/L
Adequate (supplemented)
PTH
4.5 pmol/L
1.5-6.5 pmol/L
Normal
Creatinine
82 μmol/L
45-90 μmol/L
Normal
eGFR
68 mL/min
>60
Mildly reduced
Imaging
Image 1: AP and Lateral Radiographs of Right Femur
Radiological features:
Transverse fracture through lateral cortex of femoral diaphysis
Located distal to lesser trochanter, proximal to supracondylar flare
Non-comminuted (simple fracture pattern)
Short oblique component
Focal lateral cortical thickening ("beaking") at fracture site
Medial spike (characteristic morphology)
Generalised cortical thickening of diaphysis
No periosteal reaction beyond immediate fracture site
Image 2: Full-Length Bilateral Femur X-rays
Findings:
Right: Complete atypical femoral fracture as described
Left: Lateral cortical thickening ("dreaded black line") at mid-diaphysis
Localised periosteal reaction over lateral cortex
Incomplete stress fracture (lateral cortex only)
No complete fracture
Questions & Model Answers
Q1
What is the diagnosis and what criteria define it?
Q2
What is the association with bisphosphonates and what is the mechanism?
Q3
Describe your initial management of this patient.
Q4
Describe your operative technique for this fracture.
Q5
How do you manage the contralateral incomplete fracture?
Q6
What are the expected outcomes and long-term considerations?
Key Teaching Points
Pattern Recognition
This pattern suggests Atypical Femoral Fracture:
Postmenopausal woman on long-term bisphosphonate (>5 years)
Minimal trauma mechanism (standing fall)
Subtrochanteric or diaphyseal location
Transverse/short oblique pattern (NOT spiral)
Lateral cortical beaking on X-ray
Prodromal thigh pain (may have had for weeks/months)
Distinguishing from Typical Osteoporotic Fracture:
Feature
Atypical
Typical
Location
Subtrochanteric/diaphyseal
Femoral neck, intertrochanteric
Pattern
Transverse, non-comminuted
Variable, often comminuted
Lateral cortex
Beaking, thickening
Normal
Prodromal pain
Common (weeks-months)
Rare
Healing
Delayed
Usually uneventful
Critical Management Points
Full-length bilateral X-rays - 30-40% have contralateral involvement
Stop bisphosphonate - but continue calcium and vitamin D
Long cephalomedullary nail - never short nails
Expect delayed union - warn patient, consider teriparatide
Prophylactic fixation - for symptomatic incomplete fractures
The dreaded black line refers to the radiolucent line visible on the lateral cortex of the femur in incomplete atypical femoral fractures. It represents the stress fracture propagating through cortical bone. Its presence indicates high risk of progression to complete fracture and is an indication for prophylactic nailing if symptomatic.
Q: "Should all patients on bisphosphonates have a drug holiday?"
Drug holiday considerations:
After 5 years of oral bisphosphonate (or 3 years IV)
For patients at moderate fracture risk
Continue in high-risk patients (previous fragility fracture, very low BMD)
Monitor during holiday with DEXA and bone turnover markers
Resume if fracture risk increases
Current guidelines (ASBMR 2016, NICE 2017):
Individualise based on fracture risk
Benefits of treatment generally outweigh risks of atypical fracture
Reassess after 3-5 years of treatment
Q: "What is the role of teriparatide?"
Teriparatide (recombinant PTH 1-34):
Anabolic agent - stimulates bone formation
May promote healing of atypical fractures
Duration: 24 months maximum (lifetime)
Contraindicated if prior radiation, Paget's, hypercalcaemia
Expensive, requires daily injection
Consider for incomplete fractures or delayed union
Evidence: Case series suggest improved healing, but no RCTs specifically for atypical fractures.
Q: "How do you counsel a patient who presents with prodromal thigh pain on long-term bisphosphonate?"
Counselling approach:
Explain concern for stress reaction/incomplete fracture
Order full-length bilateral femur X-rays
If positive: discuss prophylactic fixation vs observation
If negative: consider MRI if high clinical suspicion