What is a Cephalomedullary (CM) nail and how is it performed?

What is a Cephalomedullary (CM) Nail and How is it Performed?

A cephalomedullary nail is an intramedullary rod inserted through the femur that locks into both the femoral head (via screws through the femoral neck) and the distal femur, providing stable fixation for unstable intertrochanteric, subtrochanteric, and reverse oblique femoral fractures. 1, 2

Indications for CM Nail

The CM nail is mandatory for specific fracture patterns where sliding hip screws fail at unacceptably high rates:

• Unstable intertrochanteric fractures with posteromedial comminution or lesser trochanter involvement 1, 2
• Subtrochanteric fractures (strong evidence supports cephalomedullary devices for these patterns) 1
• Reverse oblique fractures (where the fracture line runs from superomedial to inferolateral) 1, 3
• Ipsilateral femoral neck and shaft fractures (complex multifocal patterns) 4, 5

For stable intertrochanteric fractures, a sliding hip screw remains the preferred option, not a CM nail 1, 2. The distinction between stable and unstable patterns is critical—using a CM nail for stable fractures increases cost and surgical time without benefit 1, while using a sliding hip screw for unstable patterns results in failure rates exceeding 50% 2.

Surgical Technique

Preoperative Preparation

• Do not use preoperative traction—it provides no benefit and is specifically not recommended 2
• Administer prophylactic antibiotics within one hour of skin incision 2
• Either spinal or general anesthesia is appropriate with no preference 2

Key Surgical Steps

Entry Portal and Nail Insertion:

• The entry point is at the tip of the greater trochanter or slightly medial (piriformis fossa), which can be technically challenging to locate accurately 6, 5
• A guide wire is inserted through the entry portal down the femoral canal under fluoroscopic guidance in both AP and lateral views 5
• The femoral canal is reamed over the guide wire to accommodate the nail diameter 5
• The cephalomedullary nail is inserted over the guide wire down the femoral shaft 4, 5

Proximal Locking (Into Femoral Head):

• Two screws (or one large lag screw, depending on nail design) are inserted through the nail into the femoral neck and head 6, 4
• These screws should reach within 5-10 mm of the subchondral bone of the femoral head 2
• Tip-apex distance (combined distance of screw tip to apex on AP and lateral views) should be minimized to prevent cutting out 7
• Screws should be placed in Cleveland zones 5,6, or 8 (center-center or inferior positions) for optimal purchase 7

Distal Locking:

• The nail is locked distally with cortical screws (typically 1-2 screws) through the distal femur to prevent rotation and shortening 4
• Static locking (both proximal and distal) is used in 24 of 27 cases in complex fractures 4

Fracture Reduction:

• Anatomic reduction must be achieved before nail insertion, with restoration of the medial cortical continuity and normal neck-shaft angle (approximately 130-135 degrees) 2
• For comminuted fractures, open reduction via Watson-Jones approach may be required (needed in 6 of 16 cases in one series) 5
• Additional cerclage wiring or cables can stabilize the greater trochanter in open procedures (used in 12 of 14 open cases with no failures) 3

Critical Technical Pitfalls to Avoid

The surgery is technically demanding with a definite learning curve 5:

• Incorrect entry portal location is the most common intraoperative problem (occurred in 4 patients in one series), which can lead to nail misdirection 6
• Driving the nail through the intercondylar notch distally (occurred in 1 case) causes catastrophic failure 6
• Inadequate reduction before fixation leads to malunion and hardware failure 2
• Cutting out of proximal screws from the femoral head occurs with poor screw placement or excessive tip-apex distance 6, 3
• Over-compression can cause fracture comminution in osteoporotic bone 2

Despite these technical challenges, when performed correctly, non-experienced surgeons (fewer than 50 cases) achieve similar complication rates and reoperation rates as experienced surgeons (more than 500 cases), though operative time and blood transfusion volume are significantly greater 7.

Postoperative Management

• Immediate weight-bearing as tolerated is appropriate with adequate fixation 2, 8
• DVT prophylaxis with fondaparinux or low molecular weight heparin for 4 weeks 2, 8
• Regular paracetamol for pain management, with cautious opioid use especially in renal dysfunction 2, 8
• Avoid codeine due to constipation and cognitive dysfunction risk 2

Special Considerations

For metastatic/pathologic fractures: CM nails can be used for diaphyseal lesions, though there is no advantage to routine use as new femoral neck lesions after intramedullary nailing are uncommon 1. However, failure to diagnose a femoral neck lesion before implanting increases risks of implant failure and need for additional surgery 1. If both femoral neck and diaphyseal lesions are present, combined approaches (arthroplasty plus plating or long-stem arthroplasty) may be preferred over CM nailing 1.