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:

Click to expand

ASBMR Minor Criteria (not required for diagnosis but supportive):

• Generalized cortical thickening of the diaphysis
• Bilateral prodromal symptoms or fractures
• Delayed fracture healing
• Comorbid conditions (e.g., vitamin D deficiency, RA, hypophosphatasia)
• Use of pharmaceutical agents (bisphosphonates, denosumab, glucocorticoids, PPIs)

These criteria 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.

Click to expand

Important differentials:

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

Management of prodromal/incomplete fractures:

Initial conservative approach:

• Protected weight bearing (crutches, walker)
• Bisphosphonate cessation
• Calcium and vitamin D supplementation
• Serial imaging (X-ray every 4-6 weeks)
• Activity modification

Indications for prophylactic fixation:

• Progression of fracture line on serial imaging
• Persistent pain despite conservative measures
• Greater than 50% cortical involvement
• Patient preference to reduce fracture risk
• Non-compliant with protected weight bearing

Prophylactic IM nailing:

• Same technique as complete fracture
• Reduces risk of complete fracture
• Allows immediate weight bearing
• Should be strongly considered if contralateral complete fracture

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:

Patient positioning:

• Supine on fracture table (radiolucent)
• Boot attached with traction
• Contralateral leg in lithotomy or extended
• C-arm access for AP and lateral views

Reduction:

• Traction and internal rotation typically reduces
• May need external reduction aids if shortening/rotation
• Varus tendency common - ensure proper alignment
• Confirm reduction on fluoroscopy before nailing

Key reduction considerations:

• Atypical fractures often have sharp transverse edges
• May need to open and reduce if closed reduction fails
• Avoid excessive manipulation (bone quality poor)

Proper positioning and reduction are essential before proceeding with nailing.

Entry point:

• Piriformis or trochanteric entry (depends on nail design)
• Standard landmarks apply
• Verify with fluoroscopy

Reaming:

• Ream to 1.5-2mm larger than nail diameter
• Be cautious - bone may be brittle
• Consider under-reaming slightly in very brittle bone

Nail selection:

• Long cephalomedullary nail
• Must span entire femur
• Lag screw or blade for proximal fixation
• Multiple distal interlocking screws

Insertion tips: Advance slowly to avoid propagation, watch for cortical perforation (lateral bowing), and confirm position with orthogonal fluoroscopy.

Lag screw or blade placement:

• Standard technique for chosen implant
• Central-central or slight inferior placement
• Tip-apex distance less than 25mm
• Confirm on AP and lateral

Antirotation screw (if applicable):

• Follow implant-specific technique
• Important for rotational stability

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

Distal interlocking screws:

• At least 2 screws (static locking preferred)
• Use targeting device or freehand technique
• Avoid prominent hardware

Considerations:

• Long nail - ensure screws in good bone
• Avoid anterior cortex perforation
• May add third screw if bone quality concern

Final steps: Confirm alignment on AP and lateral imaging, check rotation clinically, and assess stability with stress maneuvers before wound closure.

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.