What is a modified triangular transverse pattern in the surgical fixation of an intracapsular femoral neck fracture, particularly in an older adult patient with a history of osteoporosis or other comorbidities?

Modified Triangular Transverse Pattern for Femoral Neck Fracture Fixation

The modified triangular transverse pattern is a specific configuration of three cannulated screws for internal fixation of intracapsular femoral neck fractures, where the screws are positioned in a transverse (horizontal) triangular arrangement on the axial plane, maximizing the area and perimeter of the triangle formed by the screw tips to provide optimal biomechanical stability. 1

Technical Description

The modified triangular transverse configuration differs from traditional screw placement patterns in several key aspects:

Screw Positioning Strategy

• The three cannulated screws are positioned to maximize the triangular area formed between them on the axial cross-section of the femoral neck, with points selected adjacent to the inferior, anterosuperior, and posterior cortex of the femoral neck 2

• This configuration creates a larger area and perimeter compared to conventional inverted isosceles triangle patterns, providing greater fracture stability and support 2

• The apex screw should be positioned 6.5 mm away from the superior border of the femoral neck on anteroposterior radiographs to avoid cortical breach and "in-out-in" (IOI) screw placement, which compromises fixation 3

Biomechanical Advantages

The modified transverse triangular pattern offers superior mechanical properties:

• Finite element analysis demonstrates this fixation scheme provides stronger fracture support and stability compared to conventional configurations 2

• The inverted triangle configuration (two proximal screws, one distal screw) significantly reduces nonunion risk compared to standard triangle configuration (one proximal, two distal screws), with an odds ratio of 2.92 for nonunion when using the standard triangle pattern 4

Critical Technical Considerations

Avoiding Subtrochanteric Complications

• Placing two screws in the inferior part of the femoral neck creates a stress riser in the subtrochanteric region, potentially inducing fractures in weakened osteoporotic bone at approximately 30 days postoperatively 5

• Only one screw should be inserted in the inferior part of the neck to prevent subtrochanteric or intertrochanteric fractures as a technical complication 5

Optimal Screw-to-Bone Distance

• The modified configuration achieves a shorter apex-subchondral bone distance while maintaining adequate purchase, reducing the risk of screw penetration into the femoral head 2

• Screw insertion angles up to 20 degrees do not affect the safety and accuracy of screw placement when using the 6.5 mm offset strategy 3

Clinical Outcomes

Recent evidence supports the efficacy of this modified approach:

• Bone union rates of 89.5% have been reported with the modified triangular transverse configuration, with low rates of femoral neck shortening (5.2%), avascular necrosis, and nonunion 1

• The reoperation rate is approximately 10.5%, primarily due to subsequent trauma rather than fixation failure 1

Patient Selection Context

While guidelines indicate that undisplaced intracapsular fractures in older adults can be treated with cannulated screw fixation 6, several factors must guide decision-making:

• Displaced femoral neck fractures carry an odds ratio of 2.93 for nonunion compared to undisplaced fractures when treated with screw fixation 4

• Poor reduction quality increases nonunion risk by 18.92-fold compared to anatomic reduction 4

• In frail elderly patients with osteoporosis, hemiarthroplasty or total hip replacement may be preferred over internal fixation due to shorter operative time and acceptable functional outcomes 6