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Clinical Orthopaedics and Related Research®

, Volume 472, Issue 8, pp 2492–2498 | Cite as

Is Tip Apex Distance As Important As We Think? A Biomechanical Study Examining Optimal Lag Screw Placement

  • Patrick Kane
  • Bryan Vopat
  • Wendell Heard
  • Nikhil Thakur
  • David Paller
  • Sarath Koruprolu
  • Christopher Born
Basic Research

Abstract

Background

Intertrochanteric hip fractures pose a significant challenge for the orthopaedic community as optimal surgical treatment continues to be debated. Currently, varus collapse with lag screw cutout is the most common mode of failure. Multiple factors contribute to cutout. From a surgical technique perspective, a tip apex distance less than 25 mm has been suggested to decrease the risk of cutout. We hypothesized that a low-center lag screw position in the femoral head, with a tip apex distance greater than 25 mm will provide equal, if not superior, biomechanical stability compared with a center-center position with a tip apex distance less than 25 mm in an unstable intertrochanteric hip fracture stabilized with a long cephalomedullary nail.

Questions/purposes

We attempted to examine the biomechanical characteristics of intertrochanteric fractures instrumented with long cephalomedullary nails with two separate lag screw positions, center-center and low-center. Our first research purpose was to examine if there was a difference between the center-center and low-center groups in cycles to failure and failure load. Second, we analyzed if there was a difference in fracture translation between the study groups during loading.

Methods

Nine matched pairs of femurs were assigned to one of two treatment groups: low-center lag screw position and center-center lag screw position. Cephalomedullary nails were placed and tip apex distance was measured. A standard unstable four-part intertrochanteric fracture was created in all samples. The femurs were loaded dynamically until failure. Cycles to failure and load and displacement data were recorded, and three-dimensional (3-D) motion was recorded using an Optotrak® motion tracking system.

Results

There were no significant differences between the low-center and center-center treatment groups regarding the mean number of cycles to failure and mean failure load. The 3-D kinematic data showed significantly increased motion in the center-center group compared with the low-center group. At the time of failure, the magnitude of fracture translation was statistically significantly greater in the center-center group (20 ± 2.8 mm) compared with the low-center group (15 ± 3.4 mm; p = 0.004). Additionally, there was statistically significantly increased fracture gap distraction (center-center group, 13 ± 2.8 versus low-center group, 7 ± 4; p < 0.001) and shear fracture gap translation (center-center group, 12 ± 2.3 mm; low-center group, 6 ± 2.7 mm; p < 0.001).

Conclusions

Positioning of the lag screw inferior in the head and neck was found to be at least as biomechanically stable as the center-center group although the tip apex distance was greater than 25 mm.

Clinical Relevance

Our findings challenge previously accepted principles of optimal lag screw placement.

Keywords

Femoral Head Failure Load Intramedullary Nail Intertrochanteric Fracture Cephalomedullary Nail 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Notes

Acknowledgments

The research was supported by [RIH Orthopaedic Foundation] and the National Institutes of Health [P20-GM104937 (COBRE Bioengineering Core)].

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Copyright information

© The Association of Bone and Joint Surgeons® 2014

Authors and Affiliations

  • Patrick Kane
    • 1
  • Bryan Vopat
    • 1
  • Wendell Heard
    • 2
  • Nikhil Thakur
    • 3
  • David Paller
    • 4
  • Sarath Koruprolu
    • 4
  • Christopher Born
    • 1
  1. 1.Department of OrthopaedicsRhode Island HospitalProvidenceUSA
  2. 2.Department of Orthopaedic SurgeryTulane University School of MedicineNew OrleansUSA
  3. 3.Department of Orthopaedics, Upstate Bone and Joint Center Upstate Medical University-SUNYSyracuseUSA
  4. 4.RIH Orthopaedic Foundation, IncProvidenceUSA

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