Atypical Femoral Fractures

How bisphosphonates contribute to AFFs:

1. Suppressed bone turnover:

   • Bisphosphonates inhibit osteoclast activity
   • Bone remodeling is suppressed
   • Microdamage accumulates without repair

2. Altered bone quality:

   • Increased mineralization over time
   • More homogeneous bone matrix
   • Reduced ability to absorb energy (more brittle)

3. Stress fracture progression:

   • Microcracks develop in lateral cortex
   • Unable to heal due to suppressed turnover
   • Progress to complete fracture

The lateral cortex is under maximum tension during weight-bearing, making it vulnerable to stress fracture development.

Why the lateral cortex?

During normal gait, the femur experiences bending moments:

• Lateral cortex: Under tension (stretching)
• Medial cortex: Under compression

Tension forces cause the stress fracture to initiate laterally and propagate medially, explaining the characteristic radiographic appearance.

Femoral geometry effects: Varus alignment increases lateral cortex stress, femoral bowing increases bending moment, and Asian patients often have more varus/bowing contributing to higher incidence.

Effects on bone material properties:

ASBMR 2013 Revised Major Criteria

To diagnose an atypical femoral fracture, 4 of 5 major criteria must be present:

ASBMR 2013 Minor Features (supportive, not required for diagnosis):

• Generalised increase in cortical thickness of the femoral diaphysis
• Unilateral or bilateral prodromal symptoms (dull, aching thigh/groin pain)
• Bilateral incomplete or complete femoral diaphyseal fractures
• Delayed fracture healing

These four minor features support the diagnosis but are not required to meet the definition.

Classification by Completeness:

Incomplete fractures:

• Represent early stress fractures
• May have only cortical beaking visible
• Often painful (prodromal thigh pain)
• At risk for progression to complete fracture
• Consider prophylactic nailing if persistent pain or progression

Complete fractures require operative fixation. Incomplete fractures may be managed conservatively initially but often progress.

Important differentials:

Radiographic assessment:

Plain X-rays (AP and lateral femur):

• Full-length femur views essential
• Look for lateral cortex beaking/thickening
• Transverse fracture line orientation
• Check for contralateral changes (bilateral imaging mandatory)

Key X-ray findings:

Surgical fixation is required for all complete AFFs.

Preferred fixation: Intramedullary nail

• Cephalomedullary nail (e.g., gamma nail, PFNA)
• Provides load-sharing fixation
• Protects entire femur
• Allows immediate weight bearing (depending on fixation)
• Enables bilateral fixation at same sitting

Surgical considerations:

• Entry point: piriformis or trochanteric entry based on nail design
• Ensure good distal locking
• Consider supplementary fixation if comminuted
• Assess and address contralateral femur

The decision for prophylactic fixation balances surgical risk against fracture risk. Most surgeons have a low threshold for prophylactic nailing given the morbidity of complete fracture.

Bilateral involvement occurs in 28%:

Assessment:

• Always image contralateral femur
• Full-length X-rays
• MRI if symptomatic with normal X-rays

Management of contralateral findings:

Staged vs same-session surgery: If complete fracture on one side and incomplete on other, consider fixing both at same surgery. This reduces second anesthetic and total recovery time. Discuss with patient preoperatively.

Drug holiday considerations:

After AFF, decisions about ongoing osteoporosis treatment are complex:

• Bisphosphonate cessation recommended (drug holiday)
• Duration of holiday variable (1-2 years typical)
• Balance fracture prevention vs AFF risk
• Endocrinology/bone specialist referral recommended

Alternative treatments:

Proper positioning and reduction are essential before proceeding with nailing.

Proximal fixation follows standard cephalomedullary nail principles. The atypical fracture location is usually below the proximal screws.

Technique for incomplete fracture:

Same technique as complete fracture with some modifications:

• No reduction needed (bone is intact)
• Entry point and reaming as usual
• Consider smaller diameter nail (less reaming)
• Full-length nail to protect entire femur

Bilateral fixation at same session:

• Start with complete fracture side
• Then prophylactically fix contralateral
• Consider staged if prolonged surgery/blood loss
• Discuss with anesthesia preoperatively

Prophylactic nailing is effective in preventing complete fracture and allows immediate weight bearing.