Interfragmentary compression across a simulated scaphoid fracture—analysis of 3 screws1

https://doi.org/10.1016/j.jhsa.2003.12.006Get rights and content

Abstract

Purpose

To measure the interfragmentary compression generated across a simulated fracture in cadaveric scaphoids by 3 different headless compression screws.

Methods

A transverse osteotomy was made through the waist of each scaphoid and a load cell to measure compression was interposed between the fragments, which were then fixed internally retrograde with either an Acutrak Standard (n = 10), Acutrak Mini (n = 12), or Bold (n = 10) screw. The surgeon was blinded to the measured compression, which was recorded during screw insertion and for the following 5 minutes. As a measure of scaphoid bone quality the modulus of elasticity of the trabecular bone of each specimen was then calculated from uniaxial compression tests.

Results

The mean interfragmentary compression generated by the Acutrak Standard screw was significantly greater and more consistent than the Bold screw or the Acutrak Mini screw. The compression achieved by the Acutrak Standard screw was also more consistent than that obtained by either the Bold or the Acutrak Mini screws as reflected by the lower standard deviation. The mean modulus of elasticity of the scaphoid trabecular bone was similar for each screw group.

Conclusions

The interfragmentary compression generated by the Acutrak Standard screw was significantly greater and more consistent than that generated by either the Bold or Acutrak Mini screws. The compression generated by the Acutrak Standard and Mini screws was significantly better sustained over time than that generated by the Bold screw; however, these differences were small and may not be clinically important. The optimal compression required to promote scaphoid fracture union remains unknown and clinical trials are needed to further evaluate the outcome from using these devices.

Section snippets

Materials and methods

Thirty-two fresh frozen cadaveric scaphoids were used and all soft tissues were removed before storage at −20°C until testing. The average specimen age was 72 years (range, 40–88 years). Three different scaphoid screw systems were tested: the Acutrak Standard, the Acutrak Mini, and the Bold. The gender and side of the specimens were similar between the groups (Table 1).

The Bold screw (Fig. 1) is of similar design to the Herbert screw12 with a central threadless shaft and differential pitch

Results

The average screw length and range were 26.3 mm (22.5–30.0 mm) for the Acutrak Standard, 25.8 mm (24.0–26.0 mm) for the Acutrak Mini, and 28.8 mm (26.0–32.0 mm) for the Bold. This length incorporates the interposing load cell; therefore screw lengths in vivo would be approximately 2 sizes (5 mm) shorter.

Five minutes after screw insertion we found a significant difference in the magnitude of interfragmentary compression produced by the 3 different screws (p = .01) (Table 2, Fig. 3). The

Discussion

We found that the Acutrak Standard screw produced significantly more compression across a simulated scaphoid fracture (152 ± 21 N) than either the Bold (103 ± 46 N) or Acutrak Mini screws (92 ± 56 N) (p = .01) and that it was more consistent, as reflected by the lower standard deviation. The compressive force achieved by the Acutrak Standard and Mini screws was better sustained over time than that of the Bold screw, with which a small but significant loss of compression was noted in the 5

Acknowledgements

The authors would like to thank Acumed (Hillsboro, OR) and Wright (Arlington, TN) for providing their respective screws and instruments for testing.

References (22)

  • R. Belsole

    Scaphoid reconstruction

  • Cited by (65)

    • Scaphoid waist fractures fixation with staple. Retrospective study of a not widespread procedure.

      2020, Injury
      Citation Excerpt :

      In the screw introduction, performed by percutaneous or open approach, (anterograde or retrograde, depending on the location of the fracture), it is imperative that the fracture gap is positioned between the two threads to obtain compression [35]. To overcome some of the criticalities in the use of the double-pitch screw, screws of a different shape have been developed, such as the truncated-conical screw, which allows fracture compression even in the case of more proximal or distal localizations [13,36]. However, the fixation still remain technically demanding and potential cause of joint damage, when the measurement of the screw length is longer than it should be, after fracture compaction [11,15,16,35,37].

    • Headless compression screw for horizontal medial malleolus fractures

      2018, Clinical Biomechanics
      Citation Excerpt :

      Furthermore, the variable pitch results in the head advancing through the bone faster than the finer trailing threads, enabling the screw to generate interfragmentary compression across the fracture site (Borse et al., 2010). The combination of continuous threading and varying pitch enhances the compressive strength of the Acutrak 2 screw (Beadel et al., 2004). The design of the headless compression screw is ideal for stable screw purchase in cancellous bone (Fowler and Ilyas, 2010).

    View all citing articles on Scopus
    1

    No benefits in any form have been received or will be received by a commercial party related directly or indirectly to the subject of this article.

    View full text