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

  • Basic Research
  • Published:
Clinical Orthopaedics and Related Research®

An Erratum to this article was published on 06 June 2014

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.

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Acknowledgments

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

Author information

Authors and Affiliations

  1. Department of Orthopaedics, Rhode Island Hospital, 593 Eddy Street, Providence, RI, 02903, USA

    Patrick Kane MD, Bryan Vopat MD & Christopher Born MD

  2. Department of Orthopaedic Surgery, Tulane University School of Medicine, New Orleans, LA, USA

    Wendell Heard MD

  3. Department of Orthopaedics, Upstate Bone and Joint Center, Upstate Medical University-SUNY, Syracuse, NY, USA

    Nikhil Thakur MD

  4. RIH Orthopaedic Foundation, Inc, Providence, RI, USA

    David Paller MD & Sarath Koruprolu BS

Authors
  1. Patrick Kane MD
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  2. Bryan Vopat MD
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  3. Wendell Heard MD
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  4. Nikhil Thakur MD
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  5. David Paller MD
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  6. Sarath Koruprolu BS
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  7. Christopher Born MD
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Corresponding author

Correspondence to Patrick Kane MD.

Additional information

One of the authors (CB) certifies that he, or a member of his immediate family, has or may receive payments or benefits, during the study period, an amount of USD 10,000–USD 100,000 from Stryker Orthopaedics (Mahwah, NJ, USA); one author (CB) has stock in BioIntraface (North Kingston, RI, USA) and IlluminOss (Riverside, RI, USA).

Intramedullary nails and instrumentation equipment were provided by Stryker.

All ICMJE Conflict of Interest Forms for authors and Clinical Orthopaedics and Related Research editors and board members are on file with the publication and can be viewed on request.

Clinical Orthopaedics and Related Research neither advocates nor endorses the use of any treatment, drug, or device. Readers are encouraged to always seek additional information, including FDA-approval status, of any drug or device prior to clinical use.

Each author certifies that his or her institution approved the human protocol for this investigation, that all investigations were conducted in conformity with ethical principles of research, and that informed consent for participation in the study was obtained.

This work was performed at RIH Orthopaedic Foundation, Inc, Providence, RI, USA.

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Kane, P., Vopat, B., Heard, W. et al. Is Tip Apex Distance As Important As We Think? A Biomechanical Study Examining Optimal Lag Screw Placement. Clin Orthop Relat Res 472, 2492–2498 (2014). https://doi.org/10.1007/s11999-014-3594-x

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  • DOI: https://doi.org/10.1007/s11999-014-3594-x

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