Contradictions of derotation in scoliosis surgery using the CD principle

Our experience and early results with a complementary implant for the correction of major thoracic curves

PURPOSE

In our article, we would like to introduce a new auxiliary implant called the CAB hook, for use in posterior approach scoliosis surgery.

METHODS

Since 2007, we operated 42 patients with the CAB hook with an average preoperative Cobb angle of 59.3° (28°-92°). In three cases, the posterior approach was preceded by ventral release and Halo traction. In four cases, besides the CAB hooks, SCS hooks and pedicular screws, in three cases both CAB and SCS hooks, in nine cases CAB hooks with SCS pedicular screws, and in 23 cases, only CAB were used. The average follow-up time was 21.6 month (2-51).

RESULTS

All the patients are satisfied with the results. No reoperation was needed due to the loss of correction, pain, implant failure, or infection. The average postoperative Cobb angle decreased to 24.7° (4°-60°). Based on this we calculated the Cincinnati Correction Index (CCI), which was 1.53 (0.7-4.8), which means that our correction exceeded the flexibility of the spine based on the lateral bending X-ray by 53 %.

CONCLUSION

As with all new surgical techniques and implants after the short learning curve, we were able to improve the degree of correction and decrease the time of surgery. One of the advantages of the CAB hook is that besides a few implant-specific instruments, no special instrumentation is required for insertion, and image intensifier need not be used.

Biomechanical examination of the thoracic spine--the axial rotation moment and vertical loading capacity of the transverse process

Our objective was to examine the load-bearing capacity of the transverse processes of human cadaveric thoracic vertebrae to vertical loads and axial rotation moments (i.e., moment applied in the transverse plane). A secondary objective was to examine the effect of the attached rib stumps. We wanted to demonstrate that the transverse process is durable enough to support the CAB hook--a complementary hook to the CD system--and can handle the vertical load or axial rotation moment during correction of scoliosis. We used 107 thoracic vertebrae removed from 10 cadavers. They were prepared in vertebral pairs, and were fixed into a material testing apparatus. Superoinferior vertical loads and axial rotation moments were applied to the transverse process using the CAB hooks at a rate of 30 mm/min and 8.5°/s respectively until it fractured. We recorded 142 measurements, 99 were for vertical load and 43 for axial rotation moment. The average ultimate vertical load was 338 (SD = 128) N and the average ultimate axial rotation moment was 14.4 (SD = 4.52) Nm. The ultimate axial rotation moment for specimens with rib stumps attached was significantly greater than for specimens without rib stumps 15.9 (SD = 4.1) Nm versus 12.5 (SD = 4.4) Nm. Our results showed that both the vertical and axial rotation loading capability of the transverse process are large enough to withstand significant correctional forces, without fracture, through the CAB hooks.

Ex vivo and in vitro determination of the axial rotational axis of the human thoracic spine

STUDY DESIGN

Different geometrical and biomechanical evaluations were performed to determine the axial rotational axis of the thoracic spine.

OBJECTIVE

Our research group has been dealing with the determination of the axial rotational axis of the thoracic spine. Here, we would like to present the geometrical and experimental results of our trials. With our experiments, we are trying to evaluate the contradictions of the related literature.

SUMMARY OF BACKGROUND DATA

In the present state, we know quite a lot about the biomechanics of healthy and pathologic spines. Nevertheless, for a seemingly simple question like the position of the axial rotation of the thoracic spine, the literature gives contradicting results. During correction of a scoliotic deformity, when trying to correct the pathologic rotation, not knowing the physiologic rotation can be hazardous.

METHODS

We wanted to clarify this question, so we examined the thoracic spine in many different ways. First, we examined the problem from a geometrical point of view then we modeled the different rotational axes by studying the change in volume of the spinal canal. Finally, we used cadaver spines that we rotated and examined with radiographs and digital pictures.

RESULTS

Based on the results, we made the following establishments: most of the center points fell on the anterior half of the vertebral body or into the spinal canal, basically on the midsagittal axis of the vertebra. The rib cage has a significant effect on the place of the axis. After removing the ribs, the axis of axial rotation moved forward.

CONCLUSIONS

After evaluating the results, we determined that the most likely place for the rotational axis is on the median-sagittal plane, in the anterior portion of the spinal canal.