OTA 2012 Posters

Scientific Poster #19 Hip/Femur OTA-2012

Inferior Lag Screw Placement: Does the Tip-Apex Distance Really Matter?

Nikhil A. Thakur, MD; Wendell M. Heard, MD; Matt Young, BS;
Patrick M. Kane, MD; David Paller, MS; Christopher T. Born, MD;
Department of Orthopaedics, Brown University, Providence, Rhode Island, USA

Purpose/Hypothesis: The tip-apex distance (TAD) concept was introduced by Baumgaertner et al to help treat peritrochanteric femur fractures. The TAD was recommended to be ≤25 mm to prevent cutout and loss of fixation. To achieve this, Baumgaertner et al advocated placement of the lag screw tip centered on both the AP and lateral radiographs. In a cadaveric study, we have found a low position on AP and centered on lateral position to be biomechanically superior. Clinically, our fixation technique frequently follows this placement strategy and often results in a TAD >25 mm. We hypothesized that the lag screw low-center position results in a TAD >25 mm but has a similar or lower cutout rate than the recommended center-center position of Baumgartner et al.

Methods: A retrospective chart review was conducted on all patients between 2005 and 2010 who underwent fixation of peritrochanteric femur fractures (OTA 31-A1, A2) with cephalomedullary devices. Patient demographic data were collected. TAD was calculated using the same formula employed by Baumgartner et al. Follow up information was obtained on each patient.

Results: 140 patients underwent cephalomedullary nail fixation for peritrochanteric femur fractures (OTA 31-A1, A2). Five patients were lost to follow-up. The remaining 135 patients had a final follow-up visit. Thirty-one patients had lag screw in low-center position (TAD of 30 ± 5.79 mm) versus 65 patients with center-center position (TAD of 22.12 ± 6.42 mm) (P <0.001). There were no cutouts in either group and all patients healed their fractures. 23 patients were in the center posterior position and the remaining 16 in other configurations (7 low anterior, 5 low posterior, and 4 center anterior). There was one cutout in the center-posterior (TAD = 29mm) and one in the center-anterior (TAD = 20 mm), respectively. Other patient factors did not affect the rates of cutout on regression analyses.

Conclusion: Based on our hypothesis, the low-center group had a TAD of ~30 mm and should have resulted in higher cutout rates than the center-center group based on the TAD theory. However, there were no cutouts in the low-center group. Of the two cutouts seen in the cohort, one had a TAD lesser and one had a TAD greater than 25 mm. These lag screws were placed in the center position on the AP view and either anterior or posterior positions on the lateral view. Based on this study and our cadaveric work, we feel the optimal position of the lag screw to be low on the AP and centered on the lateral radiograph. This may result in a TAD >25 mm but does not result in increased cutouts with this lag screw position.

• The FDA has not cleared this drug and/or medical device for the use described in this presentation   (i.e., the drug or medical device is being discussed for an “off label” use).  ◆FDA information not available at time of printing. Δ OTA Grant.