Sagittal slope angle of lateral atlantoaxial articulation is associated with the severity of basilar invagination with atlantoaxial dislocation and predicts reduction degree after surgery.

OBJECTIVE: To investigate (1) lateral atlantoaxial articulation (LAA) morphology in patients with basilar invagination (BI) with atlantoaxial dislocation (AAD) and healthy individuals and its relationship with the severity of dislocation and (2) the effect of the LAA morphology on reduction degree (RD) after surgery. METHODS: In this retrospective propensity score matching case-control study, imaging and baseline data of 62 patients with BI and AAD from 2011 to 2022 were collected. Six hundred thirteen  participants without occipitocervical junctional deformity served as controls. Logistic regression and receiver operating characteristic (ROC) curve were used for analysis. RESULTS: The age, BMI and sex did not differ significantly between the two groups after propensity score matching. Sagittal slope angle (SSA) and coronal slope angle (CSA) was lower and greater, respectively, in the patient group than in the control group. A negative SSA value usually indicates anteverted LAA. Regression analysis revealed a significant negative correlation between SSA and severity of dislocation. However, no relationship was found between CSA and the severity of dislocation. The multivariate logistic regression analysis revealed that minimum-SSA emerged as an independent predictor of satisfactory reduction (RD ≥ 90%). The ROC curve demonstrated an area under the curve of 0.844, with a cut-off value set at -40.2. CONCLUSION: SSA in patients group was significantly smaller and more asymmetric than that in the control group. Dislocation severity was related to SSA but not to CSA. Minimum-SSA can be used as a predictor of horizontal RD after surgery.

Posterior two-step distraction and reduction for basilar invagination with atlantoaxial dislocation: a novel technique for precise control of reduction degree without traction.

PURPOSE: The pathological changes of basilar invagination (BI) and atlantoaxial dislocation (AAD) include vertical and horizontal dislocations. Current surgical techniques have difficulty in accurately controlling the degree of reduction in these two directions and often require preoperative traction, which increases patients' pain, hospital stay, and medical cost. This study aimed to introduce a novel technique for accurately reducing horizontal and vertical dislocation without preoperative traction and report the radiological and clinical outcomes. METHODS: From 2010 to 2020, patients with BI and AAD underwent posterior two-step distraction and reduction (TSDR) and occipitocervical fixation. Radiological examination was used to evaluate the reduction degree (RD) and compression. Japanese Orthopedic Association (JOA) score was used to evaluate clinical outcome. RESULTS: A total of 55 patients with BI and AAD underwent TSDR and occipitocervical fusion. The clinical symptoms of 98.2% of them improved. JOA score increased significantly after the operation. Appropriate (50% ≤ RD < 80%) or satisfactory (RD ≥ 80%) horizontal reduction was achieved in 92.7% of patients, and 90.9% obtained appropriate or satisfactory vertical reduction. Thirty-one patients did not undergo preoperative skull traction. There was no significant difference in radiological outcomes or JOA scores between the traction and non-traction groups. However, the length of hospital stay in the traction group was longer than that in the non-traction group. CONCLUSION: TSDR enables horizontal and vertical reduction. It is a safe, simple, and effective technique for patients with BI and AAD. Despite the absence of preoperative skull traction, the degree of reduction and clinical outcomes were satisfactory.

Does the Angulation of the Screws in the Zero-P Implant Affect the Clinical and Radiological Outcomes of Patients?

OBJECTIVE: When implanting the Zero-P device, the screws of Zero-P form a bone wedge with a 40 ± 5° cranial and caudal angle (CCA). However, no study has been performed in the optimal CCA of the Zero-P implant. To investigate whether the cranial/caudal angles (CCA) of the screws affect the clinical and radiological outcomes in patients undergoing ACDF with the Zero-P implant. METHODS: From January 2016 to December 2023, we retrospectively analyzed 186 patients who underwent 1-level ACDF with the Zero-P device. The patients were divided into four groups: group A (cranial angle ≤40°, caudal angle ≤40°); group B (cranial angle ≤40°, caudal angle >40°); group C (cranial angle >40°, caudal angle ≤40°); and group D (cranial angle >40°, caudal angle >40°). The clinical outcomes, including Japanese Orthopaedic Association (JOA), neck disability index (NDI), and visual analogue scale (VAS) scores, the radiological parameters, including cervical lordosis (CL), cervical lordosis of operated segments (OPCL), intervertebral space height (ISH) and fusion rate (FR), and the complications, were evaluated and compared. Parametric tests, non-parametric tests, and chi-square tests were conducted to analyze the data. RESULTS: The OPCL of group A was significantly less than that of the other groups at the final follow-up (p < 0.05). The ISH of group D was significantly less than that of group A at the final follow-up (p < 0.05). The subsidence rate of group A was significantly less than that of group D at the final follow-up (p < 0.05). At the final follow-up, the upper adjacent-level degeneration (ASD) of group D was significantly less severe than that of groups A and B (p < 0.05). The clinical outcomes do not differ among groups (p > 0.05). CONCLUSION: A larger CCA of the screws (cranial angle >40°, caudal angle >40°) was better for maintaining OPCL and reducing the incidence of ASD. A smaller CCA of the screws (cranial angle ≤40°, caudal angle ≤40°) was better for maintaining ISH and reducing the rate of subsidence.

Incidence of Heterotopic Ossification at 10 years After Cervical Disk Replacement: A Systematic Review and Meta-analysis.

STUDY DESIGN: Systematic review and meta-analysis. OBJECTIVE: This study aimed to assess the incidence of heterotopic ossification (HO) 10 years after cervical disk replacement (CDR). SUMMARY OF BACKGROUND DATA: HO is a common complication after CDR and may limit the range of motion of the artificial disk. As HO usually progresses slowly, a long-term follow-up is required to better understand its incidence. In recent years, the increasing number of original articles reporting 10-year outcomes gives us the opportunity to better understand the long-term incidence of HO. MATERIALS AND METHODS: We searched PubMed, Medline, Embase, and Cochrane Library databases to identify eligible studies. The incidence of HO was pooled, and subgroup analysis was performed. Meta-regression analyses were conducted to identify factors contributing to heterogeneity. RESULTS: Eleven studies with at least 10 years of follow-up comprising 1140 patients who underwent CDR were included. The pooled incidence of overall HO was 70% (95% CI, 60%-81%) at 10 years postoperatively, 60% (95% CI, 44%-75%) at five or six years postoperatively, and 50% (95% CI, 27%-72%) at one or two years postoperatively. The pooled incidence of severe HO (grade 3 or 4) was 37% (95% CI, 29%-45%), and mild HO (grade 1 to 2) was 30% (95% CI, 17%-44%) at 10 years of follow-up. Pooled range of motion decreased from 8.59° before surgery to 7.40° 10 years after surgery. Subgroup analysis showed that HO incidence differed according to the prosthesis type. The earlier publication was associated with a higher pooled incidence of severe HO in the meta-regression analysis. CONCLUSIONS: This is the first meta-analysis providing detailed information on the pooled 10-year incidence of HO after CDR. The incidence of HO seems to increase with the length of follow-up. LEVEL OF EVIDENCE: 3.

Uncovertebral Joint Fusion Versus End Plate Space Fusion in Anterior Cervical Spine Surgery: A Prospective Randomized Controlled Trial.

BACKGROUND: The uncovertebral joint is a potential region for anterior cervical fusion. Currently, we are aware of no clinical trials on human uncovertebral joint fusion (UJF). The purpose of this study was to compare the time it took to achieve osseous union/fusion and the clinical efficacy of UJF to end plate space fusion (ESF)-i.e., traditional anterior cervical discectomy and fusion (ACDF)-in anterior cervical surgery. METHODS: Patients with single-level cervical spondylosis were recruited from April 2021 through October 2022 and randomly divided into the UJF and ESF groups, with 40 patients in each group. Autologous iliac bone was used for bone grafting in both groups. The primary outcome was the early fusion rate at 3 months postoperatively. Secondary outcomes included the prevalence of complications and patient-reported outcome measures (PROMs), including the Japanese Orthopaedic Association (JOA) score, Neck Disability Index (NDI), and visual analog scale (VAS) scores for arm and neck pain. RESULTS: A total of 74 patients (92.5%) with an average age of 49.8 years (range, 26 to 65 years) completed the trial and were included in the analysis. There was no significant difference between the 2 groups at baseline. The operative duration and intraoperative blood loss were also comparable between the 2 groups. The fusion rate in the UJF group was significantly higher than that in the ESF group at 3 months (66.7% compared with 13.2%, p < 0.0001) and 6 months (94.1% compared with 66.7%, p = 0.006) after the operation. No significant difference was found in the fusion rate between the 2 groups 12 months postoperatively. Overall, the PROMs significantly improved after surgery in both groups and did not differ significantly between the groups at any follow-up time point. The prevalence of complications was not significantly different between the 2 groups. CONCLUSIONS: In our study of anterior cervical fusion surgery, we found that the early fusion rate after UJF was significantly higher than that after ESF. LEVEL OF EVIDENCE: Therapeutic Level I . See Instructions for Authors for a complete description of levels of evidence.

Segmental Slope is a Predictor of Fusion Rate in Single Level Anterior Cervical Discectomy and Fusion.

STUDY DESIGN: Retrospective study. OBJECTIVES: To explore preoperative segmental slope as a predictor of fusion rate after single-level anterior cervical discectomy and fusion (ACDF). METHODS: Data of consecutive patients with single-level cervical spondylosis who underwent ACDF between 2011 and January 2019 were retrospectively reviewed. Preoperative parameters including baseline characteristics, segment slope, T1 slope, range of motion, intervertebral disk height, and bone density were evaluated. Data were analyzed using Student's t-test, Mann-Whitney U test, χ2 test, Fisher's exact test, multivariate logistic regression analysis, and receiver operating characteristic curve. RESULTS: In total, 253 patients were selected. The mean follow-up was 32.1 months (range 24-99 months). Male sex, body mass index, preoperative segment slope, T1 slope, operative levels, and osteoporosis or osteopenia were associated with non-fusion at an early stage after surgery. However, no statistically significant difference was observed at the last follow-up. Multivariate logistic regression analysis revealed that the preoperative segment slope was an independent predictor for non-fusion at 3, 6, and 12 months postoperatively. Osteoporosis or osteopenia was an independent predictor of non-fusion at 6 and 12 months postoperatively. The area under the curve was .874 at 3 months (P < .001, cutoff value 10.21°), .888 at 6 months (P < .001, cutoff value 14.56°), and .825 at 12 months (P < .001, cutoff value 21.08°). CONCLUSION: Preoperative segment slope can be used as a predictor of early fusion rate after single-level ACDF. We determined detailed cutoff values. This study may help surgeons take measures to promote early fusion in advance.

Is the fusion order of the cranial and caudal levels different in two-level anterior cervical discectomy and fusion for cervical spondylopathy? A retrospective study.

STUDY DESIGN: Retrospective study. OBJECTIVE: This study aimed to compare the fusion order between the cranial and caudal levels in two-level anterior cervical discectomy and fusion (ACDF) with a zero-profile device in the treatment of cervical spondylopathy. Fusion is the standard used to judge the success of ACDF. However, the fusion order in two-level ACDF remains uncertain. The mechanical environment of different levels is different, which may affect the fusion rate or fusion order. METHODS: From 2014 to January 2019, data of consecutive patients with two-level cervical disk degenerative disease who underwent ACDF were retrospectively reviewed. Radiological assessments were based on the range of motion of the fusion level, segment slope, and disk height, and complications were assessed. Data were analyzed using the paired t, Mann-Whitney U, χ2, Fisher exact, and rank-sum tests and logistic regression analysis. RESULTS: In total, 118 patients were ultimately enrolled for analysis in the study. The respective fusion rates of the cranial and caudal levels were 26.27% and 10.17% (p < 0.05) at 3 months, 58.47% and 42.37% (p < 0.05) at 6 months, 86.44% and 82.20% (1 0.05) at 1 year, and 92.37% and 89.83% (p > 0.05) at the last follow-up. Multivariate logistic regression analysis indicated that the preoperative segmental slope and cranial level were independent risk factors for non-fusion. The adjacent segment degeneration (ASD) and subsidence rates were comparable between the two levels. CONCLUSION: The caudal level had a slower fusion process than the cranial level. A higher preoperative segment slope was a risk factor for fusion. However, the subsidence and ASD rate were comparable between the caudal and cranial levels in the two-level ACDF.