Cannulated Screw Fixation for Intracapsular Femoral Neck Fractures: Step-by-Step Procedure
Critical Pre-Procedure Decision: Is This the Right Operation?
Cannulated screw (CC screw) fixation is appropriate ONLY for undisplaced or minimally displaced intracapsular femoral neck fractures; displaced fractures require arthroplasty instead. 1
Indications for Cannulated Screw Fixation:
- Undisplaced intracapsular fractures (Garden I-II) are the primary indication for internal fixation with multiple cannulated screws 1
- Displaced intracapsular fractures (Garden III-IV) should undergo arthroplasty, not screw fixation, due to high risk of avascular necrosis and superior outcomes with replacement 1
- If you proceed with screws for displaced fractures, expect failure rates of 12-19% 2
Pre-Operative Risk Assessment:
- Check serum albumin levels - low albumin is an independent predictor of fixation failure and should prompt consideration of arthroplasty instead 2
- Assess posterior tilt on lateral radiograph - angles >20° significantly predict failure (p=0.002) 2
- Ensure adequate reduction is achievable; if not, proceed to arthroplasty 3
Pre-Operative Preparation
Timing and Medical Optimization:
- Perform surgery within 24-48 hours of admission for optimal outcomes 1, 4
- Administer prophylactic antibiotics within 1 hour of skin incision 4, 5
- Do NOT use preoperative traction - it provides no benefit and is specifically not recommended 1, 4
- Implement active warming strategies to prevent hypothermia, particularly critical in elderly patients 4, 5
- Administer preoperative intravenous fluids as many patients are hypovolemic 4
Anesthesia:
- Either spinal or general anesthesia is appropriate with no preference between the two 1, 4
- Implement multimodal analgesia with preoperative nerve block (fascia iliaca or femoral nerve block) 1, 4
- Monitor depth of anesthesia with BIS monitoring to avoid cardiovascular depression in elderly patients 4
Surgical Technique: Step-by-Step Procedure
Patient Positioning:
- Position patient supine on a fracture table with the affected limb in traction
- Ensure the hip is in neutral rotation or slight internal rotation (avoid excessive internal rotation which can cause pressure damage) 4
- Position the unaffected leg in abduction and flexion to allow C-arm access
- Pad all pressure points carefully, especially in elderly patients with fragile skin 4
Closed Reduction (if needed):
- Apply gentle longitudinal traction
- Assess reduction quality with AP and lateral fluoroscopic views
- Anatomical reduction is critical - inadequate reduction significantly increases failure rates 3
- Accept the reduction only if Garden alignment index is satisfactory and posterior tilt is <20° 2
Surgical Approach and Guidewire Placement:
Incision:
- Make a 3-5 cm lateral incision over the proximal lateral femur, starting at or just distal to the vastus ridge
- Incise fascia and split the vastus lateralis muscle fibers bluntly
Guidewire Insertion:
- Under fluoroscopic guidance, insert three guidewires percutaneously through the lateral femoral cortex
- Optimal screw configuration: Modified triangular transverse pattern with screws positioned in a triangular configuration perpendicular to the fracture line 6
- Alternative acceptable configuration: Inverted triangle with one screw inferiorly and two superiorly 6, 7
Guidewire Position (Critical Technical Points):
- All three guidewires must achieve parallel placement 8
- Start guidewires at the level of the lesser trochanter or slightly proximal
- Direct guidewires toward the femoral head with the following targets:
- Superior screw: Aimed toward the superior-posterior quadrant of the femoral head, just beneath subchondral bone
- Inferior screw: Aimed toward the inferior calcar region with maximal purchase in dense bone
- Middle/posterior screw: Positioned to create triangular stability
- Verify guidewire position on both AP and lateral views before proceeding
- Guidewires should be within 5mm of subchondral bone but not penetrate the joint 6
- Ensure adequate spread between screws (minimum 1cm separation at fracture site)
Screw Insertion:
Measurement and Drilling:
- Measure screw length using the calibrated guidewire or depth gauge
- Subtract 5mm from measured length to ensure screws remain subchondral
- Use cannulated drill bit over each guidewire sequentially
- Drill to a depth 5-10mm shorter than final screw length
Screw Placement:
- Insert fully-threaded 6.5mm or 7.0mm cannulated screws over guidewires 6, 7
- Use partially-threaded screws if compression across the fracture is desired (controversial)
- Insert all three screws sequentially, tightening each to achieve interfragmentary compression
- Final screw position should be parallel, with threads crossing the fracture site
- Confirm final position fluoroscopically - screws should be within 5mm of subchondral bone on both AP and lateral views 6
Wound Closure:
- Remove guidewires
- Irrigate wounds copiously
- Close fascia with absorbable suture
- Close skin with staples or subcuticular suture
- Apply sterile dressings
Post-Operative Management
Immediate Post-Operative Care:
- Continue active warming to prevent hypothermia 4, 5
- Administer tranexamic acid to reduce blood loss and transfusion requirements 1
- Continue regular paracetamol throughout the perioperative period 4, 5
Thromboprophylaxis:
- Administer fondaparinux or low molecular weight heparin (LMWH) for DVT prophylaxis 4, 5
- Time LMWH administration between 18:00-20:00 to minimize bleeding risk with neuraxial anesthesia 4
- Use sequential compression devices while hospitalized 4
- Continue pharmacologic prophylaxis for 4 weeks postoperatively 4
Pain Management:
- Continue regular paracetamol 4, 5
- Use opioids cautiously, especially in patients with renal dysfunction; avoid oral opioids in renal dysfunction 4, 5
- Do NOT administer codeine due to constipation, emesis, and association with postoperative cognitive dysfunction 4
- Use NSAIDs with extreme caution and avoid in renal dysfunction 4
Mobilization:
- Implement early mobilization protocols to reduce complications 4, 5
- Allow immediate weight-bearing as tolerated 4
- Physical therapy should begin on postoperative day 1
Follow-Up and Monitoring:
- Radiographs at 6 weeks, 3 months, 6 months, and 1 year to assess for:
- Outpatient DEXA scan and referral to bone health clinic for osteoporosis evaluation and treatment 4
Common Pitfalls and How to Avoid Them
Technical Errors:
- Inadequate reduction is the most common cause of failure - if anatomical reduction cannot be achieved, proceed to arthroplasty 3
- Posterior tilt >20° significantly predicts failure - verify on lateral view before proceeding 2
- Non-parallel screw placement compromises stability - use fluoroscopy meticulously 8
- Screws penetrating the joint causes cartilage damage - stay 5mm from subchondral bone 6
Patient Selection Errors:
- Using screws for displaced fractures (Garden III-IV) - these require arthroplasty per AAOS guidelines 1
- Ignoring low serum albumin - this predicts failure and should prompt consideration of arthroplasty 2
- Proceeding despite inability to achieve reduction - accept failure and convert to arthroplasty 3