Biomechanical comparison of three different compression screws for treatment of odontoid fractures evaluation of a new screw design
Section snippets
Background
Anterior screw osteosynthesis in patients with Anderson's and D'Alonzo's odontoid type II fracture (Anderson and D'Alonzo, 1974) is the only operative procedure with movement preservation for this type of injury. At the same time, surgical treatment improves survival at a comparable complication rate compared to conservative treatment such as halo-fixation or orthosis immobilization. However, there is a non-union rate of 27% (Robinson et al., 2014). Mechanical factors such as tissue
Investigated compression screws
Three different lag screws for the treatment of the odontoid fracture with different compression principles were selected for testing. These are a classic cannulated spongiosa screw with smooth shaft and screw head (CS, DePuy Synthes, Raynham, US), a non-cannulated double threaded or Herbert screw (Ulrich Medical, Ulm, Germany) and a cannulated spongiosa screw with shaft and sleeve nut (Signus Medizintechnik GmbH, Alzenau Germany) (Figure 1).
The technical details are shown in Table 1. The
Density of the test material, compression force, and torque
All screws show a significant increase in both maximum compressive force and torque with increasing density of the test material (Table 2).
Compressive force
The generated compressive force increases significantly (p < .001) for screws CS 1.25, CS 2.5 and SLN as the density of the test material increases. DTS shows a significant increase in compression force only when the test material density increases by at least 10 pcf. SLN shows superior compression in all densities over all other types of screws (Fig. 3).
Interpretation
The tested lag screws for the treatment of odontoid fractures type II according to Anderson and De'Alonzo (Anderson and D'Alonzo, 1974) show different characteristics in the phase of optimal fragment compression as well as a different vulnerability to overtightening and screw stripping.
Limitations of the experimental technique
The test material used has a very homogeneous structure, which only resembles ideal cancellous bone. A possible contact of the cancellous bone thread with cortical or sclerosed bone is not taken into account. Likewise, a possible bicortical implantation of the cancellous bone screw is not included in the test series. The manual insertion of the screw allows the determination of the moment of cutting the screw only in steps of 90°. The rotational stability of the connection between the two test
Conclusions
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The maximum compression force increases with the screw diameter.
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The quotient of maximum torque and plateau torque can be improved by optimizing the pre-drilling.
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The application torque can be indicative of the stripping torque.
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Compression force and torque are only correlated for CS 1.25, CS 2.5 and SLN.
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DTS and SLN show a higher tolerance to screw tearing than classic CS.
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SLN is superior in compression and as robust as DTS against screw stripping.
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It is unclear how much compression is required for
Funding
No funding was received for this research.
Studies with human participants
This article does not contain any studies with human participants performed by any of the authors.
Declaration of Competing Interest
Jan-Uwe Müller:
Dr. Müller is consultant for Signus and received financial support for travel costs and honoraria for consultation.
Dr. Müller has no other financial relationship to Signus, no direct or indirect profit sharing arrangements, rebates, commissions or compensations in any form.
All other authors:
All other authors certify that they have no affiliations with or involvement in any organization or entity with any financial interest (such as honoraria; educational grants; participation in
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