A biomechanical study of ligament tethers strengthening for the prevention of proximal junctional kyphosis after posterior long-segment spinal fusion

Biomechanical effects of osteoporosis severity on the occurrence of proximal junctional kyphosis following long-segment posterior thoracolumbar fusion

BACKGROUND

Proximal junctional kyphosis is a common long-term complication in adult spinal deformity surgery that involves long-segment posterior spinal fusion. However, the underlying biomechanical mechanisms of the impact of osteoporosis on proximal junctional kyphosis remain unclear. The present study was to evaluate adjacent segment degeneration and spine mechanical instability in osteoporotic patients who underwent long-segment posterior thoracolumbar fusion.

METHODS

Finite element models of the thoracolumbar spine T1-L5 with posterior long-segment T8-L5 fusion under different degrees of osteoporosis were constructed to analyze intervertebral disc stress characterization, vertebrae mechanical transfer, and pedicle screw system loads during various motions.

FINDINGS

Compared with normal bone mass, the maximum von Mises stresses of T7 and T8 were increased by 20.32%, 22.38%, 44.69%, 4.49% and 29.48%, 17.84%, 40.95%, 3.20% during flexion, extension, lateral bending, and axial rotation in the mild osteoporosis model, and by 21.21%, 18.32%, 88.28%, 2.94% and 37.76%, 15.09%, 61.47%, -0.04% in severe osteoporosis model. The peak stresses among T6/T7, T7/T8, and T8/T9 discs were 14.77 MPa, 11.55 MPa, and 2.39 MPa under lateral bending conditions for the severe osteoporosis model, respectively. As the severity of osteoporosis increased, stress levels on SCR8 and SCR9 intensified during various movements.

INTERPRETATION

Osteoporosis had an adverse effect on proximal junctional kyphosis. The stress levels in cortical bone, intervertebral discs and screws were increased with bone mass loss, which can easily lead to intervertebral disc degeneration, bone destruction as well as screw pullout. These factors have significantly affected or accelerated the occurrence of proximal junctional kyphosis.

Brown Sequard syndrome in a patient with Klippel-Feil syndrome following minor trauma: a case report and literature review

BACKGROUND

There are some cases of Klippel-Feil syndrome with spinal cord injury in clinical work. However, there is no literature report on Brown-Sequard syndrome after trauma. We report a case of Brown-Sequard syndrome following minor trauma in a patient with KFS type III. Her Brown-Sequard syndrome is caused by Klippel-Feil syndrome.

CASE PRESENTATION

We found a 38-year-old female patient with KFS in our clinical work. She was unconscious on the spot following a minor traumatic episode. After treatment, her whole body was numb and limb activity was limited. Half an hour later, she felt numb and weak in the right limb and weak in the left limb. She had no previous hypertension, diabetes, or coronary heart disease. After one-month treatment of medication, hyperbaric oxygen, rehabilitation, and acupuncture in our hospital, her muscle strength partially recovered, but the treatment effect was still not satisfactory. Then, she underwent surgical treatment and postoperative comprehensive treatment, and rehabilitation training. She was able to take care of herself with assistance, and her condition improved from grade B to grade D according to the ASIA (ASIA Impairment Scale) classification.

CONCLUSION

KFS, also known as short neck deformity, is a kind of congenital deformity characterized by impaired formation and faulty segmentation of the cervical spine, often associated with abnormalities of other organs. The cervical deformity in patients with KFS can alter the overall mechanical activity of the spine, as well as the compensatory properties of the spine for decelerating and rotatory forces, thus increasing the chance of spinal cord injury (SCI) following trauma. Many mechanisms can make patients more susceptible to injury. Increased range of motion of the segment adjacent to the fused vertebral body may lead to slippage of the adjacent vertebral body and altered disc stress, as well as cervical instability. SCI can result in complete or incomplete impairment of motor, sensory and autonomic nervous functions below the level of lesion. This woman presented with symptoms of BSS, a rare neurological disorder with incomplete SCI. Judging from the woman's symptoms, we concluded that previously she had KFS, which resulted in SCI without fracture and dislocation following minor trauma, with partial BSS. After the comprehensive treatment of surgery, hyperbaric oxygen, rehabilitation therapy, and neurotrophic drugs, two years later, we found her symptoms significantly improved, with ASIA Impairment Scale from grade B to grade D, and her ability to perform activities of daily living with aids.

Influence of configuration and anchor in ligamentous augmentation to prevent proximal junctional kyphosis: A finite element study

Ligament augmentation has been applied during spinal surgery to prevent proximal junctional kyphosis (PJK), but the configuration and distal anchor strategies are diverse and inconsistent. The biomechanics of different ligament augmentation strategies are, therefore, unclear. We aimed to create a finite element model of the spine for segments T6–S1. Model Intact was the native form, and Model IF was instrumented with a pedicle screw from segments T10 to S1. The remaining models were based on Model IF, with ligament augmentation configurations as common (CM), chained (CH), common and chained (CHM); and distal anchors to the spinous process (SP), crosslink (CL), and pedicle screw (PS), creating SP-CH, PS-CHM, PS-CH, PS-CM, CL-CHM, CL-CH, and CL-CM models. The range of motion (ROM) and maximum stress on the intervertebral disc (IVD), PS, and interspinous and supraspinous ligaments (ISL/SSL) was measured. In the PS-CH model, the ROM for segments T9–T10 was 73% (of Model Intact). In the CL-CHM, CL-CH, CL-CM, PS-CM, and PS-CHM models, the ROM was 8%, 17%, 7%, 13%, and 30%, respectively. The PS-CH method had the highest maximum stress on IVD and ISL/SSL, at 80% and 72%, respectively. The crosslink was more preferable as the distal anchor. In the uppermost instrumented vertebrae (UIV) + 1/UIV segment, the CM was the most effective configuration. The PS-CH model had the highest flexion load on the UIV + 1/UIV segment and the CL-CM model provided the greatest reduction. The CL-CM model should be verified in a clinical trial. The influence of configuration and anchor in ligament augmentation is important for the choice of surgical strategy and improvement of technique.