Postoperative Radiographic Early-Onset Adjacent Segment Degeneration after Single-Level L4–L5 Posterior Lumbar Interbody Fusion in Patients without Preoperative Severe Sagittal Spinal Imbalance

STUDY DESIGN: Retrospective study. PURPOSE: To investigate the relationship between preoperative total spinal sagittal alignment and the early onset of adjacent segment degeneration (ASD) after single-level posterior lumbar interbody fusion (PLIF) in patients with normal sagittal spinal alignment. OVERVIEW OF LITERATURE: Postoperative early-onset ASD is one of the complications after L4–L5 PLIF, a common surgical procedure for lumbar degenerative disease in patents without severe sagittal imbalance. A better understanding of the preoperative characteristics of total spinal sagittal alignment associated with early-onset ASD could help prevent the condition. METHODS: The study included 70 consecutive patients diagnosed with lumbar degenerative disease who underwent single-level L4–L5 PLIF between 2011 and 2015. They were divided into two groups based on the radiographic progression of L3–L4 degeneration after 1-year follow-up: the ASD and the non-ASD (NASD) group. The following radiographic parameters were preoperatively and postoperatively measured: sagittal vertebral axis (SVA), thoracic kyphosis (TK), lumbar lordosis, pelvic tilt, and pelvic incidence (PI). RESULTS: Eight of the 70 patients (11%) experienced ASD after PLIF (three males and five females; age, 64.4±7.7 years). The NASD group comprised 20 males and 42 females (age, 67.7±9.3 years). Six patients of the ASD group showed decreased L3–L4 disc height, one had L3–L4 local kyphosis, and one showed both changes. Preoperative SVA, PI, and TK were significantly smaller in the ASD group than in the NASD group (p <0.05). CONCLUSIONS: A preoperative small SVA and TK with small PI were the characteristic alignments for the risk of early-onset ASD in patients without preoperative severe sagittal spinal imbalance undergoing L4–L5 single-level PLIF.

Gait Analysis in Cervical Spondylotic Myelopathy

STUDY DESIGN: Gait analysis of patients with cervical spondylotic myelopathy (CSM) by using a sheet-type gait analysis system. PURPOSE: The aim of this study was to compare the gait patterns of patients with CSM, evaluated by the Nurick grades, and to determine the threshold values of gait parameters predicting the occurrence of a fall by using a gait recorder. OVERVIEW OF LITERATURE: Gait disorder due to CSM may progress to severe paraplegia, following even a minor trauma such as a fall. The indications for the surgery of CSM without severe paralysis remain controversial. The quantitative gait analysis and the decision for decompressive surgery in patients with CSM are important in order to prevent severe paraplegia from a fall. METHODS: One hundred thirty-two subjects (normal, 34; CSM, 98) underwent gait analysis by using a sensor sheet. Measurements of gait cycle parameters included the step and stride length, step width, foot angle, swing phase, and stance phase. CSM was assessed by Nurick grade. RESULTS: Although the clinical symptoms were lacking, Nurick grade 1 had significant abnormalities in the parameters of velocity, step length, and step angle (p<0.05). Regarding the Nurick grade and walking phase, the length of the stance phase was increased to more than 70% of the entire walking cycle in Nurick grade 4. CONCLUSIONS: Gait analysis was an objective tool for evaluating the gait stability. Our results suggested that when the percentage of the stance phase in the gait cycle increases to above 70%, the CSM patients have an increased fall risk.

Kinematic Analysis of the Cervical Cord and Cervical Canal by Dynamic Neck Motion

STUDY DESIGN: Normal cervical sagittal length patterns were measured by magnetic resonance imaging (MRI). PURPOSE: The aim of this study was to evaluate the relationship of sagittal length patterns between the cervical cord and the cervical canal in flexion-extension kinematics. OVERVIEW OF LITERATURE: Cervical dynamic factors sometimes cause a cervical spondylotic myelopathy in elderly subjects and an overstretching myelopathy in juvenile subjects. Previous studies showed the length changing of the cervical cord in flexion and extension. However, there is no detailed literature about the relationship between cervical vertebral motion and cord distortion yet. METHODS: Sixty-two normal subjects (28 male and 34 female, 42.1+/-8.5 years old) without neck motion disturbances and abnormalities on cervical X-ray and MRI were enrolled in this study. RESULTS: The cervical cord length was significantly longer in flexion and significantly shorter in extension in all cervical cord sagittal lines. The cervical canal length pattern was also the same as the cervical cord. The elongation of the cervical cord and canal was the largest at the site of the posterior cervical canal and the shortest at the anterior canal site. The positions of the cerebellar tonsils were verified at each neck position. CONCLUSIONS: The posterior elements of the cervical canal were most affected by neck motion. Movement directions of the upper cervical cord were verified among the various neck positions.

Characteristics of Sagittal Spino-Pelvic Alignment in Japanese Young Adults

STUDY DESIGN: Radiological analysis of normal patterns of sagittal alignment of the spine. PURPOSE: This study aimed to clarify the characteristics of normal sagittal spino-pelvic alignment in Asian people. OVERVIEW OF LITERATURE: It is known that there are differences in these parameters based on age, gender, and race. In order to properly plan for surgical correction of the spine for Asian patients, it is necessary to understand the normal spino-pelvic alignment parameters for this population. METHODS: This study analyzed 86 Japanese healthy young adult volunteers (48 men and 38 women; age 35.9+/-11.1 (mean+/-standard deviation [SD]). The following parameters were measured on lateral standing radiographs of the entire spine: sagittal vertical axis (SVA), horizontal distance between the C7 plumb line and the posterior superior corner of the superior margin of S1, thoracic kyphotic angle (TK), lumbar lordotic angle (LLA), sacral slope (SS), pelvic tilt (PT), and pelvic incidence (PI). RESULTS: The values (mean+/-SD) of SVA, TK, LLA, SS, PT, and PI were 8.45+/-25.7 mm, 27.5+/-9.6degrees, 43.4+/-14.6degrees, 34.6+/-7.8degrees, 13.2+/-8.2degrees, and 46.7+/-8.9degrees, respectively. The Japanese young adults evaluated in this study tended to have a smaller PI, LLA, TK, and SVA than most Caucasian people. Regarding gender differences, SVA was significantly longer and TK was significantly smaller in men; however, there was no statistically significant difference in LLA, SS, PA, and PI. CONCLUSIONS: Japanese young adults apparently have smaller PI and LLA values than Caucasian people. When making decisions for optimal sagittal spinal alignment, racial differences should be considered.