CLINICAL ARTICLE J Neurosurg Spine 33:211–218, 2020 How does sagittal spinopelvic alignment of lumbar multisegmental spondylolysis differ from monosegmental spondylolysis? Qing-shuang Zhou, MM,1 Xu Sun, MD,1 Xi Chen, MD,1 Liang Xu, MD,2 Bang-ping Qian, MD,1 Ze-zhang Zhu, MD,1 Bin Wang, MD,1 and Yong Qiu, MD1 1Department of Spine Surgery, Drum Tower Hospital, Clinical College of Nanjing Medical University, Nanjing; and 2Department of Spine Surgery, Drum Tower Hospital, Medical School of Nanjing University, Nanjing, China OBJECTIVE The aim of this study was to investigate sagittal alignment and compensatory mechanisms in patients with monosegmental spondylolysis (mono_lysis) and multisegmental spondylolysis (multi_lysis). METHODS A total of 453 adult patients treated for symptomatic low-grade spondylolytic spondylolisthesis were retro- spectively studied at a single center. Patients were divided into 2 subgroups, the mono_lysis group and the multi_lysis group, based on the number of spondylolysis segments. A total of 158 asymptomatic healthy volunteers were enrolled in this study as the control group. Radiographic parameters measured on standing sagittal radiographs and the ratios of L4–S1 segmental lordosis (SL) to lumbar lordosis (L4–S1 SL/LL) and pelvic tilt to pelvic incidence (PT/PI) were com- pared between all experimental groups. RESULTS There were 51 patients (11.3%) with a diagnosis of multi_lysis in the spondylolysis group. When compared with the control group, the spondylolysis group exhibited larger PI (p < 0.001), PT (p < 0.001), LL (p < 0.001), and L4–S1 SL (p = 0.025) and a smaller L4–S1 SL/LL ratio (p < 0.001). When analyzing the specific spondylolysis subgroups, there were no significant differences in PI, but the multi_lysis group had a higher L5 incidence (p = 0.004), PT (p = 0.018), and PT/PI ratio (p = 0.039). The multi_lysis group also had a smaller L4–S1 SL/LL ratio (p = 0.012) and greater sagittal verti- cal axis (p < 0.001). CONCLUSIONS A high-PI spinopelvic pattern was involved in the development of spondylolytic spondylolisthesis, and a larger L5 incidence might be associated with the occurrence of consecutive multi_lysis. Unlike patients with mono_ly- sis, individuals with multi_lysis were characterized by an anterior trunk, insufficiency of L4–S1 SL, and pelvic retrover- sion. https://thejns.org/doi/abs/10.3171/2020.2.SPINE191415 KEYWORDS spondylolytic spondylolisthesis; multisegment; monosegment; sagittal alignment; lumbar UMBAR spondylolysis, sometimes combined with The pathological mechanisms behind lumbar spondy- spondylolisthesis, predominantly occurs at the lum- lolysis are still not fully understood. Spinopelvic align- bosacral monosegment (mono_lysis).1,2 It is rare ment is an important factor in the occurrence and pro- Lbut possible for spondylolysis to be detected at consecu- gression of single-level spondylolytic spondylolisthesis.6,7 tive multiple regions of the lumbar spine (multi_lysis).3,4 Studies have reported that L5–S1 spondylolytic spondylo- Spondylolysis, with or without spondylolisthesis, is usually listhesis is associated with increased pelvic incidence (PI) asymptomatic; however, some patients may present with compared with that observed in a normal population.7,8 As intractable back pain or radicular symptoms.2 If conserva- demonstrated in biomechanical studies, increased PI gen- tive treatment fails, surgical intervention is an effective so- erates higher repetitive stress at the pars interarticularis lution to achieve solid fusion, neurological decompression, and subsequently results in the development of lumbosa- and restoration of lumbar alignment.5 cral spondylolysis.9 The status of the sagittal plane, such ABBREVIATIONS LDI = lordosis distribution index; LL = lumbar lordosis; L5I = L5 incidence; mono_lysis = monosegmental spondylolysis; multi_lysis = multisegmental spondylolysis; ODI = Oswestry Disability Index; PI = pelvic incidence; PT = pelvic tilt; QOL = quality of life; SA = slip angle; SL = segmental lordosis; SP = slip percentage; SS = sacral slope; SVA = sagittal vertical axis; TK = thoracic kyphosis; VAS = visual analog scale. SUBMITTED November 25, 2019. ACCEPTED February 10, 2020. INCLUDE WHEN CITING Published online April 17, 2020; DOI: 10.3171/2020.2.SPINE191415. ©AANS 2020, except where prohibited by US copyright law J Neurosurg Spine Volume 33 • August 2020 211 Unauthenticated | Downloaded 09/29/21 06:05 AM UTC Zhou et al. as insufficient lordosis, pelvic retroversion, and anterior percentage (SP) and slip angle (SA) of the L3–4, L4–5, sagittal malalignment, has been reported to be associated and L5–S1 levels were measured at the spondylolysis and with clinical presentation.10 Analyses of sagittal spinopel- spondylolisthesis levels, respectively. Pelvic parameters, vic alignment in patients with lumbosacral spondylolytic including PI, pelvic tilt (PT), and sacral slope (SS), were spondylolisthesis have led to the development of surgical measured as previously described.20 The PT/PI ratio was algorithms and assessment of treatment outcomes.11,12 In- computed to investigate pelvic retroversion.21,22 Also, pel- adequate restoration of lumbar alignment is reported to be vic balance was determined on the nomogram of PT and related to poor patient-reported outcomes,11,13 mechanical SS measurements, as described by Hresko et al.23 L5 inci- complications,12,13 and adjacent-segment disease.14,15 dence (L5I) was measured from the middle of the femo- Lumbosacral consecutive multi_lysis often requires ral heads to the middle of the sacrum plateau and a line surgical intervention because of potential segmental insta- perpendicular to the upper endplate of L5.24 Lumbar lor- bility. However, to our knowledge, no studies have ana- dosis (LL) was measured from the upper endplate of the lyzed the spinopelvic alignment of multi_lysis, whereas L1 vertebra to the upper endplate of S1. L4–S1 segmental only sporadic case reports in the literature have mentioned lordosis (SL) was measured from the upper endplate of or described such a rare disease.4,16,17 Comprehensive in- L4 to the upper endplate of S1. The lordosis distribution terpretation of the sagittal alignment pattern and com- index (LDI) was defined as the ratio of L4–S1 SL to LL, pensatory mechanisms of sagittal balance are essential allowing greater understanding of lordosis distribution for surgical intervention to correct multi_lysis. The goals as upper- and lower-arc lordoses.12,13 Thoracic kyphosis of this study were to 1) investigate the pattern of sagit- (TK) was measured from the upper endplate of T5 to the tal alignment in spondylolytic spondylolisthesis patients lower endplate of the T12 vertebra. Global sagittal align- (both mono_lysis and multi_lysis) in comparison with ment was assessed by the sagittal vertical axis (SVA; the healthy individuals and 2) illustrate differences of sagit- distance between a plumb line from the center of the C7 tal alignment and compensatory mechanisms in patients vertebral body and posterior superior corner of S1). An diagnosed with mono_lysis versus multi_lysis. unbalanced alignment was characterized by an SVA ≥ 4 cm, following the Scoliosis Research Society–Schwab Methods adult spinal deformity classification.25 Patient Population Quality of Life Patients diagnosed with symptomatic spondylolysis with spondylolisthesis who previously underwent surgi- Preoperative quality-of-life (QOL) questionnaires were cal intervention at our center between January 2007 and administered to patients. The Oswestry Disability Index January 2018 were retrospectively studied. Enrolled pa- (ODI) and visual analog scale (VAS) for leg pain and back tients had to meet the following inclusion criteria: 1) age pain were used to evaluate the QOL. 18 years or older and 2) symptomatic lumbar spondyloly- sis with at least 1 level of spondylolisthesis (Meyerding’s Statistical Analysis grade I or II). Exclusion criteria preventing a patient from Statistical analyses were performed using IBM SPSS being studied included 1) diagnosis of degenerative spon- (version 20.0, IBM Corp.). The mean and standard devia- dylolisthesis; 2) exhibition of lumbar scoliosis > 10°; and tion were calculated for continuous variables. The inde- 3) a previous history of spinal surgery, trauma, infection, pendent-samples t-test was performed to evaluate the dif- or fracture of the pelvis or lower limbs. All spondyloly- ferences between 2 groups. Differences among 3 groups sis patients were diagnosed by 3D-CT radiography of the were evaluated using one-way ANOVA and chi-square lumbar spine. Spondylolisthesis was defined as a forward tests. We first performed an analysis of the demograph- slip of one vertebral body by at least 5% in relation to the ic data for each experimental group. Next, comparison next most caudal vertebral body on upright neutral lateral 18 analysis of the data obtained from radiological analysis radiography. Patient demographic data, including age, was performed between the control and the spondylolysis sex, BMI, and work status, were recorded. The enrolled groups, and among the control, multi_lysis, and mono_ly- patients with spondylolysis were divided into 2 subgroups: sis groups. Pearson correlations were also performed for the mono_lysis subgroup and the multi_lysis subgroup the multi_lysis group. Lastly, QOL scores were compared (Fig. 1). The mono_lysis group included patients with between the spondylolysis subgroups. A p value < 0.05 monosegmental spondylolytic spondylolisthesis, whereas was considered