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. 2022 May 3;23(1):414.
doi: 10.1186/s12891-022-05379-6.

Thoracic kyphosis in light of lumbosacral alignment in thoracic adolescent idiopathic scoliosis: recognition of thoracic hypokyphosis and therapeutic implications

Takuya Iimura  1 , Haruki Ueda  2 , Satoshi Inami  1 , Hiroshi Moridaira  1 , Daisaku Takeuchi  1 , Hiromichi Aoki  1 , Hiroshi Taneichi  1
Affiliations

Thoracic kyphosis in light of lumbosacral alignment in thoracic adolescent idiopathic scoliosis: recognition of thoracic hypokyphosis and therapeutic implications

Takuya Iimura et al. BMC Musculoskelet Disord. .

Abstract

Background: The uniqueness of spinal sagittal alignment in thoracic adolescent idiopathic scoliosis (AIS), for example, the drastically smaller thoracic kyphosis seen in some patients, has been recognized but not yet fully understood. The purpose of this study was to clarify the characteristics of sagittal alignment of thoracic AIS and to determine the contributing factors.

Methods: Whole spine radiographs of 83 thoracic AIS patients (73 females) were analyzed. The measured radiographic parameters were the Cobb angle of thoracic scoliosis, thoracic kyphosis (TK), lumbar lordosis (LL), C7 sagittal vertical axis (C7 SVA), pelvic incidence (PI), pelvic tilt (PT), and sacral slope (SS). Additionally, max-LL, which was defined as the maximum lordosis angle from the S1 endplate, the inflection point between thoracic kyphosis and lumbar lordosis, and the SVA of the inflection point (IP SVA) were measured. The factors significantly related to a decrease in TK were assessed by stepwise logistic regression analysis. In addition, cluster analysis was performed to classify the global sagittal alignment.

Results: The significant factors for a decrease in TK were an increase in SS (p = 0.0003, [OR]: 1.16) and a decrease in max-LL (p = 0.0005, [OR]: 0.89). According to the cluster analysis, the global sagittal alignment was categorized into the following three types: Type 1 (low SS, low max-LL, n = 28); Type 2 (high SS, low max-LL, n = 22); and Type 3 (high SS, high max-LL, n = 33).

Conclusions: In thoracic AIS, a decreased TK corresponded to an increased SS or a decreased max-LL. The sagittal alignment of thoracic AIS patients could be classified into three types based on SS and max-LL. One of these three types includes the unique sagittal profile of very small TK.

Keywords: Hypokyphosis; Inflection point; Max-LL; Sacral slope; Sagittal alignment; Thoracic AIS.

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Figures

Fig. 1
Fig. 1
Radiographic parameters were measured on lateral images of the whole spine while the patients were standing. Max-LL: maximum lordotic Cobb angle from S1, IP: inflection point between thoracic kyphosis and lumbar lordosis, IP SVA: sagittal vertical axis of IP
Fig. 2
Fig. 2
Cluster analysis of sagittal alignment in thoracic AIS. Cases were classified into three types based on their SS and Max-LL
Fig. 3
Fig. 3
Lateral X-ray films of representative cases. Type 1 is generally manifests with a flat sagittal profile with a smaller SS and Max-LL. Type 2 demonstrates a larger SS, small Max-LL and a significantly small TK. Type 3 shows a large SS and Max-LL
Fig. 4
Fig. 4
The comparison of radiographic parameters between three types. (One-way ANOVA, JMP 10.0.2 software) A Pelvic parameters. Type 1 has outstandingly small PI and SS values compared to the other types. B Spinal parameters. These are all significantly different among the three types. C Levels of inflexion points and SVAs. Type 2 has a significantly anterior IP SVA compared to the other types. Despite their similar PI and SS measurements, type 2 and type 3 have significantly different TK, LL, max-LL, and IP SVA measurements
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