Ventral screw osteosynthesis is a common surgical method for treating fractures of the odontoid peg, but there is still no consensus about the number and diameter of the screws to be used. The purpose of this study was to develop a more accurate measurement technique for the morphometry of the odontoid peg (dens axis) and to provide a recommendation for ventral screw osteosynthesis.

Images of the cervical spine of 44 Caucasian patients, taken with a 64-line CT scanner, were evaluated using the measuring software MIMICS. All measurements were performed by two independent observers. Intraclass correlation coefficients were used to measure inter-rater variability.

The mean length of the odontoid peg was 39.76 mm (sd 2.68). The mean screw entry angle α was 59.45° (sd 3.45). The mean angle between the screw and the ventral border of C2 was 13.18° (sd 2.70), the maximum possible mean converging angle of two screws was 20.35° (sd 3.24). The measurements were obtained at the level of 66% of the total odontoid peg length and showed mean values of 8.36 mm (sd 0.84) for the inner diameter in the sagittal plane and 7.35 mm (sd 0.97) in the coronal plane. The mean outer diameter of the odontoid peg was 12.88 mm (sd 0.91) in the sagittal plane and 11.77 mm (sd 1.09) in the coronal plane. The results measured at the level of 90% of the total odontoid peg length were a mean of 6.12 mm (sd 1.14) for the sagittal inner diameter and 5.50 mm (sd 1.05) for the coronal inner diameter. The mean outer diameter of the odontoid peg was 11.10 mm (sd 1.0) in the sagittal plane and 10.00 mm (sd 1.07) in the coronal plane. In order to calculate the necessary screw length using 3.5 mm cannulated screws, 1.5 mm should be added to the measured odontoid peg length when anatomical reduction seems possible.

The cross-section of the odontoid peg is not circular but slightly elliptical, with a 10% greater diameter in the sagittal plane. In the majority of cases (70.5%) the odontoid peg offers enough room for two 3.5 mm cannulated cortical screws.

Cite this article: Bone Joint J 2013;95-B:536–42.

Many operations have been recommended to treat Pars Interarticularis fractures that have separated and are persistently symptomatic, but little other than conservative treatment has been recommended for symptomatic incomplete fractures. 10 consecutive patients aged 15–28 [mean 21.7 years] were treated operatively between 2010–2014. All but one were either professional athletes [3 cricketers, 2 athletics, 1 soccer] or academy cricketers [3 patients]. 8 patients had unilateral fractures, and two had bilateral fractures at the same level. The duration of pre-operative pain and disability with exercise ranged from 4–24 months [mean 15.4 months]. The operation consists of a percutaneous compression screw inserted through a 1.5cm midline skin incision under fluoroscopic guidance: 6 cases were also checked with the O-arm intra-operatively. Post-operation the patients were mobilised with a simple corset and discharged the following day with a customised rehabilitation program. All 12 fractures in 10 patients healed as demonstrated on post-operative CT scans at between 3–6 months. One patient had the screw revised at 24 hours for an asymptomatic breach, and one patient developed a halo around the fracture site without screw loosening, and had a successful revision operation to remove the screw and graft the pars from the screw channel. All patients achieved a full return to asymptomatic activity, within a timescale of 4–12 months post-surgery, depending on the sport. Athletes that have persistent symptoms from incomplete pars interarticularis fractures should consider percutaneous fixation rather than undergoing prolonged or repeated periods of rest

Aims

Anchorage of pedicle screw rod instrumentation in the elderly spine with poor bone quality remains challenging. Our study aims to evaluate how the screw bone anchorage is affected by screw design, bone quality, loading conditions, and cementing techniques.