Does kyphotic configuration on upright lateral radiograph correlate with instability in patients with degenerative lumbar spondylolisthesis?
Introduction
The combinationof disc degeneration, facet joint hypertrophy, ligament thickening and segmental instability in degenerative lumbar spondylolisthesis (DLS) often results in back pain and neurogenic claudication, which frequently requires surgical intervention [1,2]. Although there are multiple modalities of surgical treatment for symptomatic DLS, including decompression, fusion with or without instrumentation, and interbody fusion, controversy persists for determining the optimal surgical option for DLS in certain clinical scenarios [3]. According to recent surveys on surgical intervention for DLS, segmental instability is a key factor in determining the treatment algorithm, which is largely based on concerns about iatrogenic destabilization of the olisthetic segment leading to poor long-term results [[4], [5], [6]].
From a radiographic view, segmental instability of DLS is defined as either the abnormal alignment of spinal segments or, in a broader definition, excessive mobility and angulation at the olisthetic segment [7]. Because degenerative changes of the disc and facet joint may hinder angular motion, abnormal angulation is a poor method to reveal segmental instability [2]. Therefore, the criterion of instability is commonly set as a translational motion >3 mm and/or >8% of the width of the above adjacent vertebra [2,8]. Various positions of patients have been measured to estimate the instability on roentgenography, among which lateral dynamic flexion and extension radiography (FE) is typically used to evaluate intersegmental hypermobility [9]. Additionally, a combination of upright lateral X-ray and supine MR images has been reported to yield results at least comparable to those of FE in evaluating instability of DLS, which is an easily available, alternative diagnostic modality to FE [8].
However, controversy remains as to whether disc degeneration or facet joint arthrosis is the initiating cause of DLS. Moreover, disc degeneration is a common pathway in pathology of DLS, which results in decreases in disc height [10]. In terms of slip configuration at the olisthetic level, two distinct subtypes separated by slip angle and kyphotic and non-kyphotic angulation were identified in clinical practice. A kyphotic configuration is primarily characterized by a kyphotic slip angle on a neutral lateral radiograph and a posterior disc height higher than the anterior disc height, whereas a non-kyphotic slip angle has a lordotic slip angle with a higher anterior disc height [5].
Recently, increased concern has arisen regarding the subset of DLS patients with a kyphotic configuration [11]. This kyphotic subset and those a with decreased segmental lordosis need to be identified as a separate group of DLS, as discussed in recent classification schemes of DLS [11,12]. However, there remains a paucity of data on the stability of DLS patients with different slip configurations. Furthermore, the modalities that can provide a more accurate assessment of stability in DLS with different slip configurations are unclear. Therefore, the current study was performed to determine the segmental stability and motion characteristics of kyphotic versus non-kyphotic spondylolisthesis through FE and US modalities and to determine whether US or FE is better able to identify instability.
Section snippets
Patients
After obtaining institutional review board approval, we retrospectively reviewed the records of patients with symptomatic DLS who underwent surgical intervention at our center between July 2010 and May 2016. Patients enrolled in this study had to meet the following inclusion criteria: (1) mono-segment L4/5 DLS; (2) low-grade lumbar spondylolisthesis (Meyerding’s grade I-II); and (3) a complete set of radiological examinations, including upright neutral, flexion/extension radiographs, and supine
Baseline characteristics analysis
A total of 227 consecutive patients (45 males and 182 females) were included in this study. The average age was 59.6 ± 10.4 years (range: 41–75 years). Twenty-six (11.5%) patients were assigned to Group K. No difference was observed in age, gender, BMI and work status between Group K and Group NK (Table 1).
As revealed in the preoperative neutral radiographs, Group K was characterized by a prominently intradiscal kyphotic angulation (−3.1°±2.3° vs. 7.9°±4.7°, P < 0.05), collapse of the anterior
Discussion
Our study demonstrated that patients with kyphotic configuration at the olisthetic segment constituted a distinct subgroup with regards to preoperative patient-reported outcomes, which is consistent with a very recent study [11]. Compared with Group NK, Group K is characterized by worse preoperative VAS back pain and ODI scores. However, previous publications did not determine how a kyphotic configuration contributed to these worse patient-reported outcomes [11,12]. Although the cause of lower
Conclusions
A kyphotic configuration presented on the upright lateral radiograph in DLS should be seen as a sign of instability, which impacts patients-reported outcomes. The US is the most clinically relevant modality for DS with a kyphotic configuration, based on the results that the US is superior to the traditional FE for measuring the sagittal translation and identifying instability.
Funding
One of the authors (Xi Chen) has received funding from Postgraduate Research & Practice Innovation Program of Jiangsu Province (Grant No. KYCX17-1277). Another author (Xu Sun) has received funding from the National Natural Science Foundation of China (Grant No. 81772422), and Jiangsu Provincial Medical Youth Talent (Grant No. QNRC2016011).
Conflict of interests
The authors declare that they have no competing interests.
Acknowledgement
None.
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Xi Chen and Qing-shuang Zhou are co-first authors.