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Tip apex distance in pfn

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"tip apex distance" AND "proximal femoral nail" AND cutout

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Here is a complete summary of Tip Apex Distance (TAD) in PFN / Intertrochanteric Fracture Fixation:

Tip Apex Distance (TAD) in PFN

Definition

TAD is the sum of the distances from the tip of the lag screw to the apex of the femoral head measured on both the AP and lateral radiographic views, after correcting for magnification.
TAD = X_AP + X_LAT
TAD Calculation - distances from screw tip to femoral head apex on AP (X_AP) and lateral (X_LAT) views
(Campbell's Operative Orthopaedics, Fig. 60.32)

Key Threshold

TAD ValueSignificance
< 25 mmTarget - associated with the lowest screw cut-out rate
> 25 mmRisk of cut-out increases exponentially
The ideal placement is center-center in the femoral head with a TAD < 25 mm.
TAD graph showing exponential rise in probability of cut-out as TAD increases beyond 25 mm (n=198)
(Campbell's Operative Orthopaedics, Fig. 60.33 - Baumgaertner et al., JBJS 1995)

Practical Points for PFN

  1. Optimal position: Lag screw should be in the center-center position within the femoral head in both AP and lateral planes.
  2. TAD < 25 mm is the accepted target for both sliding hip screw (SHS) and cephalomedullary nails (PFN/CMN).
  3. Helical blade modification: The 25 mm TAD rule may not apply when a helical blade is used instead of a lag screw - medial blade migration has been reported even with TAD < 20 mm. Helical blades also have higher fixation failure (OR 1.88) compared to standard lag screws.
  4. The relationship between increasing TAD and cut-out risk is an S-shaped (logistic) curve - risk stays low below ~25 mm, then rises steeply.

Original Source

Described by Baumgaertner et al. (JBJS 77A:1058, 1995) - "The value of the tip-apex distance in predicting failure of fixation of peritrochanteric fractures of the hip" - in a series of 198 cases.

Summary Mnemonic

"TAD < 25 = Screw stays" - Keep the tip of your lag screw within 25 mm of the femoral head apex (on combined AP + lateral views) to minimize cut-out.
  • Campbell's Operative Orthopaedics 15th Ed 2026, p. 3453
  • Miller's Review of Orthopaedics 9th Ed, p. 917
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