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

A novel classification on degenerative thoracolumbar kyphosis based on sagittal spino-pelvic alignment: should the thoracolumbar segments be intervened?

PURPOSE

There are few researches on characterizing the sagittal alignment of degenerative thoracolumbar kyphosis (DTLK). In addition, the debate on the reasonable surgical strategies, for various patterns of DTLK, still continues. So, the study was to identify the features of DTLK, propose a novel classification of DTLK, and develop surgical strategies for this population.

METHODS

An overall 245 patients diagnosed with DTLK combined with lumbar stenosis performed surgeries (acquired satisfied) were selected from January 2016 to December 2022. The spino-pelvic measurements thoracic kyphosis (TK), thoracolumbar kyphosis (TLK), lumbar lordosis (LL), pelvic incidence (PI), pelvic tilt (PT), sagittal vertical axis (SVA) as well as the severe osteoporosis were recorded. To identify groups with similar spino-pelvic sagittal alignment parameters and clinical features, a 2-step cluster analysis was performed.

RESULTS

Close relationships were found among the parameters. Four types of DTLK based on TLK and balance were classified with Type I: mild kyphosis and balance, Type II: mild kyphosis and imbalance, Type III: severe kyphosis and balance, Type IV: severe kyphosis and imbalance. The probability for imbalance with severe osteoporosis was 8.4 times higher than no osteoporosis (RR = 8.410). The probability for imbalance with PI-LL mismatch was 10 times higher than PI-LL matching (RR = 0.099 in Type II and RR = 0.103 in Type IV). For patients with DTLK, the TK was correlated with LL, PI-LL or PI in Type I to III group but not in Type IV group. Targeted treatment strategies for different types of patients was then addressed.

CONCLUSION

We proposed a novel classifcation with four types of DTLK based on TLK and balance, followed by targeted treatment strategies for various types. Osteoporosis and lumbo-pelvic mismatch were risk factors for DTLK imbalance.

Effect of Posterior Decompression on the Spinal Cord of Thoracic Ossification of the Posterior Longitudinal Ligament: A Finite Element Analysis

OBJECTIVE

Thoracic ossification of the posterior longitudinal ligament (T-OPLL) causes myelopathy. Although posterior decompression for T-OPLL has shown positive results, patients with kyphotic curvatures often endure poor outcomes. Posterior decompression with fusion (PDF) has demonstrated better results compared to posterior decompression alone. This study aims to evaluate the effects of the posterior procedures for T-OPLL.

METHODS

A 3-dimensional finite element model of the C2-T12 spine, created from medical images, was used to develop the following T3-T4 OPLL compression models: an intact model (no surgery), 25% canal occupancy ratio (COR) OPLL, a discontinuous 25% COR OPLL, a continuous 50% COR OPLL, and a discontinuous 50% COR OPLL. These models were analyzed to evaluate the effects of posterior decompression (laminectomy [LN]) with varied fixation lengths (LN T3-T4, PDF T3-T4, LN T2-T5, and PDF T2-T5) in neutral, flexion, and extension positions.

RESULTS

Increased discontinuity in OPLL led to increased stress on the spinal cord. Posterior decompression reduced spinal cord stress in the neutral posture. However, in flexion and extension, spinal cord stress increased for LN T3-T4, LN T2-T5, and PDF T3-T4 compared to the neutral posture. Notably, PDF T2-T5 prevented an increase in spinal cord stress during these motions.

CONCLUSIONS

Effective management of intervertebral mobility and the appropriate length of decompression are crucial for addressing the thickness and mobility of T-OPLL.

Low bone mineral density: a primer for the spine surgeon

Within spinal surgery, low bone mineral density is associated with several postoperative complications, such as proximal junctional kyphosis, pseudoarthrosis, and screw loosening. Although modalities such as CT and MRI can be utilized to assess bone quality, DEXA scans, the "Gold Standard" for diagnosing osteoporosis, is not routinely included in preoperative workup. With an increasing prevalence of osteoporosis in an aging population, it is critical for spine surgeons to understand the importance of evaluating bone mineral density preoperatively to optimize postoperative outcomes. The purpose of this state-of-the-art review is to provide surgeons a summary of the evaluation, treatment, and implications of low bone mineral density in patients who are candidates for spine surgery.