Sagittal Imbalance Patterns in Degenerative Kyphosis of the Lumbar or Thoracolumbar Spine and Their Impact on Postoperative Complications

Research Background

Degenerative kyphosis (DK) is the most common type of spinal deformity in the elderly. Sagittal imbalance is a typical radiological feature of DK and is associated with a severe decline in quality of life. Corrective surgery aims to restore ideal spinal curvature, but inappropriate correction may lead to mechanical complications (MC). Due to differences in deformity patterns among individuals, the associations between various types of deformities and proximal or distal junctional failure, rod breakage, and other MCs remain unclear. This study aimed to investigate the patterns of sagittal imbalance in patients with lumbar or thoracolumbar DK and determine the impact of each imbalance pattern on postoperative mechanical complications.

Research Institution and Authors

This study was conducted by the spinal surgery team at Nanjing University Affiliated Hospital. The main authors include Li Jie, Tang Ziyang, Hu Zongshan, Xu Yanjie, Liang Bangheng, Qiu Yong, Zhu Zezhang, and Liu Zhen.

Research Methods

Study Subjects

A total of 137 patients who underwent corrective surgery for DK between January 2010 and December 2020, with at least 2 years of follow-up and complete radiological and clinical data, were included. Patients with concomitant scoliosis exceeding 15° or kyphosis caused by trauma, tuberculosis, or Scheuermann’s disease were excluded.

Subtyping Method

1) Based on the location of the kyphotic apex, patients were divided into the TL group (apex at L1 or above) and the L group (apex at L2 or below).

2) Within the TL or L group, patients were further divided into low SS subgroups (SS ≤0° or ≤10°) and high SS subgroups (SS >0° or >10°) based on the sacral slope (SS).

3) Patients were then categorized as imbalanced (+) or balanced (-) based on whether the sagittal vertical axis (SVA) was ≥5 cm.

4) Combining the above conditions, patients were classified into 8 subtypes.

Radiological and Surgical Parameter Evaluation

Radiological parameters, including regional kyphotic angle, lumbar lordotic angle, bone density, and surgical parameters, such as operation time, blood loss, number of fused segments, and the use of sacroiliac fixation, were evaluated.

Complication Assessment

The occurrence of complications, such as proximal or distal junctional failure and rod breakage, was assessed.

Quality of Life Assessment

The SRS-22 questionnaire was used to evaluate the quality of life before and after surgery.

Statistical Analysis

Group comparisons were performed using chi-square tests, t-tests, and other statistical methods.

Main Results

Demographics and General Clinical Characteristics

Among the 137 patients, 95 were in the TL group, and 42 were in the L group. The mean age was 59.5 years, and 66.4% were female. There were no significant differences in age, BMI, bone density, or other demographic characteristics between the two groups.

Sagittal Imbalance Patterns

The L group had more severe regional kyphosis (61.7°±18.9° vs. 38.8°±16.0°), smaller lumbar lordotic angles (27.3°±21.7° vs. 11.6°±16.2°), and larger SVA (94.9±70.1 mm vs. 46.8±53.6 mm) compared to the TL group, indicating more severe global imbalance in the L group.

The distribution of the 8 subtypes was: TLS1(-) 27.7%, TLS1(+) 26.3%, TLS0(-) 11.7%, TLS0(+) 3.6%; LS1(-) 3.6%, LS1(+) 16.1%, LS0(-) 5.2%, LS0(+) 5.8%.

Surgical Situation

Compared to the TL group, the L group had longer fusion segments (12.3±2.2 vs. 9.6±4.2) and a higher rate of sacroiliac fixation (73.8% vs. 55.8%).

Postoperative Correction

Both regional kyphotic angle and SVA were well corrected after surgery, but L group patients had lower preoperative function and pain scores.

Complication Rates

With a minimum follow-up of 2 years, the LS0(+), LS0(-), and TLS0(+) subtypes had MC rates >40%, significantly higher than other subtypes. Patients with MCs had lower bone density; in the TL group, MC patients had larger preoperative SVA and a higher proportion of single-rod fixation, while in the L group, MC patients had lower rates of sacroiliac fixation and three-column osteotomy.

Quality of Life Improvement

After surgery, both groups had significant improvements in function, pain, self-image, and other scores, but there were no significant differences between the two groups.

Research Significance

1) This is the first description of different sagittal imbalance patterns exhibited by severe DK patients with lumbar or thoracolumbar kyphosis, revealing that assessing sagittal imbalance alone is insufficient, and the location of the kyphotic apex should be considered.

2) A subtyping method based on the location of the kyphotic apex, SS, and SVA was proposed, linking subtyping to the prediction of postoperative complication risks.

3) The findings suggest that individualized surgical strategies, such as three-column osteotomy and sacroiliac fixation for L group LS0 subtype patients, are needed to reduce the risk of complications in different sagittal imbalance patterns.

4) Osteoporosis was identified as a risk factor for MCs, and preoperative anti-osteoporosis treatment may reduce complication risks.

5) For severe DK patients, individualized subtyping and strategies based on the location of the kyphotic apex and sagittal balance can help optimize surgical outcomes.

Innovations

1) This is the first study to describe the sagittal imbalance patterns of lumbar or thoracolumbar DK patients from the perspective of the kyphotic apex location.

2) A new subtyping method for DK was proposed, which can aid in preoperative assessment of complication risks and development of individualized treatment strategies.

3) The reasons for the high postoperative complication rates in the LS0 and TLS0 subtypes were interpreted from the perspective of sagittal balance.

4) Theoretical and practical guidance for individualized surgical plans for severe DK patients was provided.

Other Valuable Information

1) The study subjects were severe DK patients requiring long-segment correction, representing a clinically relevant population.

2) Systematic evaluations were conducted on sagittal balance parameters, surgical parameters, complications, and quality of life, providing comprehensive data.

3) The study identified osteoporosis as a risk factor for postoperative complications, highlighting the importance of preoperative osteoporosis treatment.

4) Reasonable explanations were provided for the differences in the high incidence of complications, such as muscle fatigue, between the TL and L groups.

5) A new subtyping tool and strategy selection criteria were provided for individualized treatment of severe DK cases.