Biomechanical characteristics of 2 different posterior fixation methods of bilateral pedicle screws: A finite element analysis

Percutaneous distal chevron osteotomy is associated with lower immediate postoperative pain and a greater range of motion than the open technique: A prospective randomized study

PURPOSE

The results of past studies comparing percutaneous techniques with traditional open techniques for hallux valgus are controversial. Therefore, this study aimed to compare the radiologic and clinical outcomes of percutaneous and open distal chevron osteotomies.

METHODS

Seventy-one patients with mild to severe hallux valgus deformity were randomized to undergo percutaneous distal chevron osteotomy (percutaneous group, n = 36) or open distal chevron osteotomy (open group, n = 35) between October 2019 and September 2020. Radiological and clinical outcomes were assessed preoperatively and postoperatively. Outcome measures included the foot and ankle outcome score, foot functional index, visual analogue scale (VAS) scores for pain, range of motion (ROM) of the first metatarsophalangeal (MTP) joint, hallux valgus angle, intermetatarsal angle, and first metatarsal shortening. Additionally, the first metatarsal declination angle was measured to evaluate sagittal malunion.

RESULTS

The mean first metatarsal declination angle decreased significantly at 12 months postoperatively in both groups (p = 0.021 and p < 0.001 in the percutaneous and open groups, respectively), and the decrement was significantly greater in the open group (p = 0.033). The mean VAS score for pain on postoperative day one was 4.2 ± 1.9 and 5.3 ± 1.7 in the percutaneous and open groups, respectively (p = 0.019). The mean ROM of the first MTP joint did not change significantly after surgery, from 72.5 ± 7.5 preoperatively to 71.0 ± 9.5 at 12 months postoperatively in the percutaneous group (p = 0.215); however, it decreased significantly from 70.6 ± 7.3 preoperatively to 63.4 ± 10.4 at 12 months postoperatively in the open group (p < 0.001). There were no significant differences between the groups regarding other clinical outcomes.

CONCLUSION

The percutaneous group showed a lower immediate pain level at postoperative day 1 and better ROM of the first MTP joint at 12 months postoperatively.

Pedicle screw path planning for multi-level vertebral fixation

BACKGROUND

For the spinal internal fixation procedures, connecting rods to the pedicle screws are commonly used in all spinal segments from the cervical to sacral spine. So far, we have only seen single vertebral screw trajectory planning methods in literatures. Joint screw placements in multi-level vertebrae with the constraint of an ipsilateral connecting rod are not considered.

PURPOSE

In this paper, a screw trajectory planning method that considers screw-rod joint system with both multi-level vertebral constraints and individual vertebral safety tolerance are proposed.

METHODS

The proposed method addresses three challenging constraints jointly for multi-level vertebral fixation with pedicle screws. First, a cylindrical screw safe passage model is suggested instead of a unique mathematical optimal trajectory for a single pedicle. Second, the flexible screw cap accessibility model is also included. Third, the connecting rod is modeled to accommodate the spine contour and support the needed gripping capacity. The retrospective clinical data of relative normal shape spines from Beijing Jishuitan hospital were used in the testing. The screw trajectories from the existing methods based on single vertebra and the proposed method based on multi-level vertebrae optimization are calculated and compared.

RESULTS

The results showed that the calculated screw placements by the proposed method can achieve 88% success rate without breaking the pedicle cortex and 100% in clinical class A quality (allow less than 2 mm out of the pedicle cortex) compared to 86.1% and 99.1%, respectively, with the existing methods. Expert evaluation showed that the screw path trajectories and the connecting rod calculated by the new method satisfied the clinical implantation requirements.

CONCLUSIONS

The new screw planning approach that seeks an overall optimization for multi-level vertebral fixation is feasible and more advantageous for clinical use than the single vertebral approaches.

The Effect of Concave-Side Intertransverse Ligament Laxity on the Stress of AIS Lumbar Spine Based on Finite Element Method

(1) Background: Scoliosis has the mechanical characteristic of asymmetric stress distribution, which is one of the reasons for the aggravation of scoliosis. Bracing therapy is the best treatment for AIS, but it is difficult and costly to operate. Is it possible to reduce pressure in the concave side by relaxing the ITL in the concave side of scoliosis, so as to improve the abnormal stress distribution of scoliosis? In this paper, a finite element method was used to simulate the effect of the relaxation of concave-side ITL on the stress of a lumbar spine with scoliosis, which provides some guidance for the treatment of scoliosis. (2) Methods: Using CT images of a patient with scoliosis whose Cobb Angle was 43° and Lordosis Angle was 45, a scoliosis lumbar was established, and Young's modulus of the ITL of the concave-side lumbar spine was reduced by 95% to simulate ligament relaxation. By comparing the stress condition of the model vertebral body with no ligament relaxation, the effect of concave-side ITL relaxation on the mechanical characteristics of scoliosis lumbar spine was explored. (3) Results: An effective and complete model of the lumbar spine was established. The concave ITL relaxed, which only had a great impact on the bending loads. After the ligament was relaxed, the stability of the spine was reduced. Stress concentration on the concave side of vertebrae and the IVD was aggravated. Under loads on the convex side, the maximum stress on the vertebral body and the IVD increased significantly, making lumbar vertebrae more vulnerable to injury. (4) Conclusions: Laxity of the ITL on the concave side of the AIS lumbar only affects the bending load. Laxity of the concave-side ligament will reduce the stability of the lumbar, aggravate the uneven stress distribution of scoliotic lumbar vertebrae, increase the risk of IVD injury, and be unfavorable for the scoliotic lumbar spine. Relaxation of the concave ITL alone is not an effective way to treat scoliosis.