[Pullout test in expansive unilateral open-door laminoplasty of the cervical spine with OsteoMed M3 plate and screws: the screw orientation matters].

OBJECTIVE To study the impact of screw orientation on the pullout strength of OsteoMed M3 titanium screws in expansive unilateral open-door laminoplasty of the cervical spine. METHODS Six fresh human cervical spine specimens were randomly numbered and OsteoMed M3 plate and screws were used for an expansive unilateral open-door laminoplasty. The screws were inserted in the lateral mass at different extraversion angles (0°, 30° and 45°). The maximum pullout strength was tested on the ElectroForce material testing machine. RESULTS The maximum pullout strength was 81.60∓7.33 N, 150.05∓15.57 N, and 160.08∓17.77 N in extraversion angle 0°, 30°, and 45° groups, respectively. The maximum pullout strength was significantly less in extraversion angle 0° group than in 30° and 45° groups (P<0.05), but similar in the latter two groups. CONCLUSION The pullout strength of the screws inserted at an extraversion angle over 30° provides stronger fixation than an angle of 0° in the unilateral open-door laminoplasty using OsteoMed M3 titanium plate and screws.