Is there a Difference in Interfragmentary Compression Strength Between Fully or Partially Threaded Screws? Results of an Experimental Biomechanical Pilot Study

Abstract

Objective This study assessed differences between fully- and partially-threaded screws in the initial interfragmentary compression strength. Our hypothesis was that there would be an increased loss in initial compression strength with the partially-threaded screw.

Methods A 45-degree oblique fracture line was created in artificial bone samples. The first group (FULL, n = 6) was fixed using a 3.5-mm fully-threaded lag screw, while the second group (PARTIAL, n = 6) used a 3.5-mm partially-threaded lag screw. Torsional stiffness for both rotational directions were evaluated. The groups were compared based on biomechanical parameters: angle-moment-stiffness, time-moment-stiffness, maximal torsional moment (failure load), and calibrated compression force based on pressure sensor measurement.

Results After loss of one PARTIAL sample, no statistically significant differences in calibrated compression force measurement were observed between both groups: [median (interquartile range)] FULL: 112.6 (10.5) N versus PARTIAL: 106.9 (7.1) N, Mann-Whitney U-test: p = 0.8). In addition, after exclusion of 3 samples for mechanical testing (FULL n = 5, PARTIAL n = 4), no statistically significant differences were observed between FULL and PARTIAL constructs in angle-moment-stiffness, time-moment-stiffness, nor maximum torsional moment (failure load).

Conclusion There is no apparent difference in the initial compression strength (compression force or construct stiffness or failure load) achieved using either fully- or partially-threaded screws in this biomechanical model in high-density artificial bone. Fully-threaded screws could, therefore, be more useful in diaphyseal fracture treatment. Further research on the impact in softer osteoporotic, or metaphyseal bone models, and to evaluate the clinical significance is required.

Keywords

biomechanical phenomena - bone cements - bone screws - fractures, bone

Authors Contributions

All authors contributed to the study conception and design. Material acquisition, preparation and data collection were performed by T. O., M. L., G. R., D. W., and M. H. Data analysis was performed by T. O., E. A., and M. H. The first draft of the manuscript was written by T. O., E. A., M. H. and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.

Berlin Institute of Health at Charité – Universitätsmedizin Berlin, Julius Wolff Institute for Biomechanics and Musculoskeletal Regeneration, Berlin, Germany.

Publication History

Received: 22 March 2022

Accepted: 28 April 2022

Article published online:
22 July 2022

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