In vivo dynamic motion characteristics of the lower lumbar spine: L4-5 lumbar degenerative disc diseases undergoing unilateral or bilateral pedicle screw fixation combined with TLIF

Objective

To evaluate the short-term in vivo dynamic motion characteristics of the lower lumbar spine (L3–S1) after unilateral pedicle screw fixation (UPSF) or bilateral pedicle screw fixation (BPSF) combined with TLIF for treatment of L4–5 lumbar degenerative disc diseases (DDD).

Methods

Twenty-eight patients were recruited (13 UPSF, 15 BPSF). Each patient was CT-scanned to construct 3D models of the L3–S1 vertebrae. The dual fluoroscopic imaging system (DFIS) was then used to image the lumbar spine while the patient performed seven functional activities (upright standing, maximum extension, flexion, left–right twist, and left–right bend). The in vivo vertebral positions were reproduced using the 3D vertebral models and DFIS images. The ranges of motion (ROMs) of L3–4, L4–5, and L5–S1 segments were analyzed.

Results

At the index L4–5 segment, the primary ROM of left–right twist of the UPSF group (2.11 ± 0.52°) was significantly larger (p = 0.000) than the BPSF group (0.73 ± 0.32°). At the proximal adjacent L3–4 segment, the primary ROMs of left–right twist, and left–right bend of the UPSF group (2.16 ± 0.73°, 2.28 ± 1.03°) were significantly less (p = 0.003, 0.023) than the BPSF group (3.17 ± 0.88, 3.12 ± 1.04°), respectively. However, at distal adjacent L5–S1 segment, no significant difference was found between the two groups during all activities.

Conclusions

The ROM in left–right twisting of UPSF group was significantly larger compared with BPSF group at the index level in the short term. The UPSF has less impact on the cranial adjacent level (L3–4) in left–right twisting and bending activities compared to the BPSF. The data implied that the UPSE and BPSF combined with TLIF would result in different biomechanics in the index and cranial adjacent segment biomechanics. Long-term follow-up studies are necessary to compare the clinical outcomes of the two surgeries.

Electronic supplementary material

The online version of this article (10.1186/s13018-019-1198-6) contains supplementary material, which is available to authorized users.

Do we need a transforaminal lumbar interbody fusion cage to increase the stability of functional spinal unit when comparing unilateral and bilateral fixation?

Transforaminal lumbar interbody fusion was an alternative to posterior lumbar interbody fusion for decompression surgeries. This study investigates the biomechanical responses of the unilateral and bilateral pedicle screw fixations with/without transforaminal lumbar interbody fusion cages under axial compression, flexion, and torsional loads. Ovine vertebrae were used in this study. Cadavers, randomly divided into five, were intact control group, bilateral pedicle screw fixation group, bilateral pedicle screw fixation group with transforaminal lumbar interbody fusion cage, unilateral pedicle screw fixation group, and unilateral pedicle screw fixation group with transforaminal lumbar interbody fusion cage. Axial compression, flexion, and torsion tests were performed on specimens. All study groups provided higher stiffness and yield load values than control group under axial compression. Addition of transforaminal lumbar interbody fusion cage to bilateral fixation increased the stiffness under axial compression. Moreover, additional use of transforaminal lumbar interbody fusion in unilateral fixation increased the yield load values under axial compression. Control group was the stiffest in flexion test. Placing a transforaminal lumbar interbody fusion cage to both unilateral and bilateral fixations did not significantly change the stiffness values. Additional transforaminal lumbar interbody fusion cage increased the yield moment of the bilateral fixation. In torsion test, control group had the highest stiffness and yield torque. The facet joints are the most important parts of the vertebrae on the stability. When comparing the bilateral and unilateral fixations with transforaminal lumbar interbody fusion addition, the more facet preserving approach has significantly higher stability under axial compression, flexion, and torsion. Unilateral fixation with transforaminal lumbar interbody fusion cage can be said biomechanically stable and advantageous fixation system because of the advantage on the less facet and soft tissue resection compared to bilateral fixation with transforaminal lumbar interbody fusion.

Comparison of rigid and semi-rigid instrumentation under acute load on vertebrae treated with posterior lumbar interbody fusion/transforaminal lumbar interbody fusion procedures: An experimental study

Rigid and semi-rigid fixations are investigated several times in order to compare their biomechanical stability. Interbody fusion techniques are also preferable for maintaining the sagittal balance by protecting the disk height. In this study, the biomechanical comparison of semi-rigid and rigid fixations with posterior lumbar interbody fusion or transforaminal lumbar interbody fusion procedures is conducted under trauma. There were four different test groups to analyze the effect of acute load on treated ovine vertebrae. First and second groups were fixed with polyetheretherketone rods and transforaminal lumbar interbody fusion and posterior lumbar interbody fusion cages, respectively. Third and fourth groups were fixed with titanium rods and posterior lumbar interbody fusion and transforaminal lumbar interbody fusion cages, respectively. The drop tests were conducted with 7 kg weight. There were six samples in each group so the drop test repeated 24 times in total. The test samples were photographed and X-rayed (laterally and anteroposteriorly) before and after drop test. Two fractures were observed on group 1. Conversely, there were no fractures observed for group 2. There were no anterior element fractures for both groups 1 and 2. However, one fracture seen on group 3 was anterior element fracture, whereas the other three were posterior element fractures. All three fractures were anterior element fractures for group 4. Treated vertebrae with polyetheretherketone rods and posterior lumbar interbody fusion cages showed the best durability to the drop tests among the groups. Semi-rigid fixation gave better results than rigid fixation according to failed segments. Posterior lumbar interbody fusion cages seem to be better option for semi-rigid fixation, however mentioned surgical disadvantages must be considered.

Slotplates revisited - A retrospective analysis

CONTEXT

Slotplates were specifically designed to meet the special requirements of corrective surgeries of the facial skeleton. This design enables small readjustments of bone fragments in the midface and chin area during surgery without complete removal of plates and screws.

OBJECTIVE, DESIGN, AND SETTING

The aim of this study was to compare morbidity rates of slotplates versus meshplates after Le Fort I osteotomy, genioplasty and/or zygoma 'sandwich' osteotomy performed in a tertiary care centre.

RESULTS

The investigators analyzed chart records of 190 patients, including a total of 257 surgeries. Slotplates were used in 109 patients, meshplates in 81 patients. Plate infection rates were 9.2% in the slotplate group and 7.4% in the meshplate group. Twelve patients (11.0%) from the slotplate group underwent plate removal versus four patients (4.9%) from the meshplate group. In total, there were two cases of delayed union, both in the slotplate group, one progressed to non-union.

CONCLUSION

Due to the low study power significant differences between the two types of plates could not be detected. However, there is a slight tendency towards higher morbidity associated with the use of slotplates. The probability of mechanical weakness of the configuration being responsible for the fatigue fractures is also discussed in this article.