Radiological analyses of the dimensions of the pedicle and dorsal part of the transverse process of subaxial vertebrae in the context of cervical spine surgery

The Attallah screw: Where safety meets robustness in posterior subaxial cervical instrumentation

Posterior fixation of the subaxial cervical spine (SCS) commonly relies on the application of lateral mass screws (LMS), with pedicle screws being a less prevalent alternative. The present study provides another option: A recently introduced novel approach, the Attallah screw, intended to ensure a safety profile comparable to that of LMS, combined with a strength profile similar to that of pedicle screws. The focus of the present study is the comparative analysis of peak insertion torques for these three screw types. Employing standard surgical techniques and instruments, Attallah screws were scheduled for insertion on the right side of the SCS in 15 cadavers, pedicle screws on the left side in 8 cadavers, and LMS on the left side in the remaining 7 cadavers. The peak insertion torque was recorded using an electronic torque screwdriver. The results revealed that the peak insertion torques were similar in the pedicle and the Attallah screw at C3, C4 and C7, but differed at C5 (mean ± SD; pedicle, 79.5±19.6 cNm; Attallah, 56.7±18.5 cNm; P=0.029) and C6 (pedicle, 85.4±28.7 cNm; Attallah, 49.8±17.9 cNm; P=0.004) in favor of the superior pedicle screw measurements. The peak insertion torques of the pedicle screw were superior to the corresponding data from the LMS from C4 to C7. By contrast, the peak insertion torques of the Attallah screw were only superior to those of the LMS at C7 (Attallah, 69.5±24.5 cNm; lateral mass, 40.5±21.4 cNm; P=0.030), although similar trends were observed at the other cervical levels. On the whole, the findings presented herein indicate the level-dependent superior robustness of the Attallah screw as a posterior cervical fixation method compared to the LMS. However, from a biomechanical perspective, the pedicle screw remains the preeminent choice for fixation within the C5-C6 range.

Comparison of the maximum possible lengths of insertable screws in the Subaxial Cervical Spine

BACKGROUND

Lateral mass screws are the most commonly used fixation technique in the Subaxial Cervical Spine (SCS), their main advantages being that they are easy to insert and safe in their application. Pedicle screws are significantly longer, are quite challenging to insert in most settings and are accompanied by the risk of serious complications such as vascular and neural injuries. We have therefore developed a new technique, which permits safe insertion of long screws in the SCS.

METHODS

A radiological evaluation was carried out to determine the maximum possible insertable screw length in the SCS when using the following techniques: pedicle, lateral mass (Magerl's) and "Attallah" screws. Scans of 66 cervical spines were analyzed to determine the maximum possible screw lengths of all three screw insertion techniques, based on the standard description through the vertebrae from C3 to C7.

RESULTS

The maximum possible length of the Attallah screw of 20.7 ± 2.5 mm (mean value ± SD) is only 2.4 mm shorter than the pedicle screw (23.1 ± 1.8 mm) along the SCS. The lateral mass screw is with 10.2 ± 1.3 mm full 12.9 mm shorter than the pedicle screw.

CONCLUSIONS

The maximum possible length of the Attallah screw is close to that of the pedicle screw and significantly greater than that of the lateral mass screw. We provide a fixation method comparable to the pedicle screw in its strength and to the lateral mass screw in its safety.