Baumgaertner (1995) — The value of the tip-apex distance in predicting failure of fixation of peritrochanteric fractures of the hip.

The Value of the Tip-Apex Distance in Predicting Failure of Fixation of Peritrochanteric Fractures of the Hip.

·J Bone Joint Surg Am·1995·1,441 citations·Trauma

This 1995 prospective cohort study of 198 peritrochanteric fractures introduced the tip-apex distance (TAD) as a single, reproducible radiographic measurement to predict lag screw cutout after sliding hip screw fixation. TAD is the magnification-corrected sum of screw-tip-to-femoral-head-apex distances on AP and lateral radiographs. The study tested whether TAD predicts cutout better than previously used zone-based position systems.

Study Snapshot

Design

Retrospective cohort

Setting: Single center, Yale University, New Haven

Funding: Industry (Smith & Nephew)

Objective

Determine whether tip-apex distance predicts lag screw cutout in peritrochanteric fractures

Outcome(s)

Lag screw cutout of femoral head

Subjects

198 fractures (193 patients), peritrochanteric hip fractures

Inclusion

Fixed-angle sliding hip-screw fixation
Complete radiographic and clinical data
≥3 months follow-up or documented early failure

Exclusion

Inadequate documentation (n=138)

Follow-up

Minimum 3 months (mean 13 months)

Statistics

Student t-testChi-square testBivariate logistic regressionMultivariate logistic regression

Key Findings

Zero cutouts occurred in all 120 screws with a TAD ≤25 mm — establishing this as the definitive intraoperative threshold for acceptable lag screw placement in peritrochanteric fixation.
Cutout risk escalates sharply as TAD increases beyond that threshold, making each millimeter of excess placement clinically consequential:
–TAD ≤30 mm → 2% cutout rate
–TAD >30 mm → 27% cutout rate
–TAD >35 mm → 36% cutout rate
–TAD ≥45 mm → 60% cutout rate
Average TAD was 38 mm in cutout cases vs. 24 mm in successes (p = 0.0001), and TAD was the strongest independent predictor of failure on multivariate analysis (p = 0.0002) — outperforming fracture stability, reduction quality, and screw zone.
Once TAD was controlled for, zone-based screw position carried no independent predictive value (p = 0.6), rendering prior 9-zone classification systems insufficient as standalone tools for assessing placement quality.
TAD measurement is highly reliable in practice: interobserver SD 1.7 mm, intraobserver SD 1.2 mm, with r = 0.97 correlation to the true 3D screw-to-apex distance — precise enough to function as a real-time operative decision tool.

Board PearlTAD ≤25 mm eliminates lag screw cutout — zero failures in 120 screws — making this the universal intraoperative benchmark for hip fracture fixation.

Clinical Relevance

When you place a sliding hip screw for a peritrochanteric fracture, measure the TAD on your intraoperative fluoroscopy before finalizing screw position. If the guide pin results in a projected TAD above 25 mm, reposition it — the data show zero cutouts below this threshold across 120 screws.

Prior to this paper, surgeons relied on subjective zone-based systems (9-zone, 11-zone, 17-zone classifications) that had poor predictive value and no statistical validation. Baumgaertner replaced all of them with a single number that any surgeon can calculate in under a minute using the known screw diameter for magnification correction.

This paper is why hip fracture training worldwide emphasizes TAD rather than zone: on multivariate analysis, zone placement became statistically irrelevant once TAD was accounted for. The specific number matters more than the quadrant.

One nuance worth knowing: a 150-degree side-plate angle carried a 21% cutout rate vs. 4% for all other angles. An independent risk factor to keep in mind when implant selection is being made for high-risk patients.

The Value of the Tip-Apex Distance in Predicting Failure of Fixation of Peritrochanteric Fractures of the Hip.

Study Snapshot

Key Findings

Clinical Relevance

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The Value of the Tip-Apex Distance in Predicting Failure of Fixation of Peritrochanteric Fractures of the Hip.

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The Value of the Tip-Apex Distance in Predicting Failure of Fixation of Peritrochanteric Fractures of the Hip.

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The Value of the Tip-Apex Distance in Predicting Failure of Fixation of Peritrochanteric Fractures of the Hip.

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