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Study Design: Retrospective case-control study., Objective: The aim of this study was to describe and compare the sagittal spinal alignment between patients with and without the ossification of the ligamentum flavum in the thoracic spine (TOLF)., Summary of Background Data: Although mechanical factors play an important role in the development of TOLF, limited evidence exists on the association of sagittal spinal alignment and TOLF in the literature., Methods: The present study assessed the preoperative sagittal alignment parameters in consecutive patients who underwent posterior decompression for TOLF in a single institution between January 2014 and December 2019. The sagittal parameters of the patients with TOLF were compared to those of the age- and sex-matched control group with lumbar spondylosis., Results: The TOLF group (n = 43 [23 men, 20 women]), with a mean age of 69.5 (range: 41-86) years, and the control group (n = 86) were compared. The TOLF group had a significantly smaller sacral slope (27.60 ± 7.49 vs. 30.61 ± 8.15, P = 0.045) and lumbar lordosis (36.84 ± 13.63 vs. 45.08 ± 9.90, P < 0.001) and a larger pelvic incidence minus lumbar lordosis (PI-LL, 8.06 ± 15.05 vs.1.00 ± 11.34, P = 0.004) than the control group. Moreover, the thoracic kyphosis was smaller in the TOLF group, although the difference was not statistically significant (25.73 ± 11.29 vs. 28.22 ± 9.34, P = 0.187). The TOLF group had a significantly smaller slope angle at the inflection point (11.97 ± 5.85 vs. 15.78 ± 5.62, P < 0.001) and a higher tendency to have a Roussouly type 2 morphology (46.5% vs. 36.0%, P = 0.252) than the control group., Conclusion: This is the first study to describe the sagittal alignment in patients with TOLF. The TOLF group showed a hypolordotic spine with a larger PI-LL mismatch compared to the age- and sex-matched control group with lumbar spondylosis.Level of Evidence: 4., (Copyright © 2020 Wolters Kluwer Health, Inc. All rights reserved.)

Study Design: Retrospective analysis., Objective: The aim of this study was to investigate the relationship between bony fusion after anterior cervical discectomy and fusion (ACDF) and heterotopic ossification (HO) after cervical disc arthroplasty (CDA) in hybrid surgery (HS)., Summary of Background Data: The mechanism of postoperative bone formation still remains unknown. It is considered a risk factor in CDA but is essential for a solid union in ACDF. With HS, we could directly study the mechanism and relationship of different forms of postoperative bone formation., Methods: Clinical data of 91 patients who had undergone consecutive two-level HS between January 2011 and January 2018 and with a minimum of 2-year follow-up was analyzed. HO was assessed based on McAfee's classifications, whereas fusion success was evaluated according the Food and Drug Administration approved criteria. Clinical outcomes and radiographic parameters were collected and used for the relevant comparisons., Results: HO was identified in 48.4% of patients (44/91). The fusion rates of patients in the HO group and the non-HO group at 3, 6, and 12 months postoperatively, and the final follow-up were 81.8% and 19.1%, 95.4% and 74.5%, 95.4% and 85.1%, and 97.7% and 93.6%, respectively. The fusion rates were significantly higher at 3 and 6 months after operation in the HO group than in the non-HO group (P < 0.05). Patients in both groups had significant improvements across all clinical outcomes at final follow-up., Conclusion: There was a significant relationship between bony fusion and occurrence of HO after HS, suggesting that both bony fusion and HO are reflections of individual osteogenic capacity. However, a reliable predictor of postoperative bone formation is needed in the future to guarantee a solid bony fusion after ACDF and to further take full advantage of the motion-preserving from CDA., Level of Evidence: 3.

Study Design: Retrospective matched cohort analysis., Objective: The aim of this study was to investigate the impact of adjacent level ossification development (ALOD) on the affected as well as the next-level discs with regards to range of motion (ROM) and degenerative changes., Summary of Background Data: Although ALOD is not a rare condition in patients who undergo anterior cervical fusion procedures, there has been little discussion to date about its clinical implications., Methods: Patients who underwent anterior cervical instrumented fusion with a minimum 2-year follow-up were reviewed. Twelve patients with each respective ossification grade (totally 48 patients) were matched based on age, sex, and number of fusion levels. On the preoperative and final follow-up x-rays, disc height, osteophytes, ROM, and maximal listhesis were assessed at the segments which were one- (the adjacent segment) and two-level cranial (the next segment) to the uppermost fused disc. Then, the patients were divided into two groups according to ALOD degree: group 1 (grade 0-1, N = 24) versus group 2 (grade 2-3, N = 24). The changes of all variables were compared between the two groups., Results: The mean ROM of the adjacent segment increased by 3.6 degree in group 1 and conversely decreased by 2.8 degree in group 2 (P = 0.002). The mean ROM increase of the next segment was significantly greater in group 2 than in group 1 (4.5 vs. 1.2 degree, P = 0.016). The osteophyte growth and the progression of listhesis at the next segment were significantly greater in group 2 (P < 0.05). Disc height of the next segment significantly decreased in group 2, but did not change in group 1., Conclusion: Severe ALOD (grade 2-3) following anterior cervical fusion significantly reduced ROM at the affected segment and conversely increased motion at the next segment. This increased motion probably accelerated the degeneration of the next-level disc., Level of Evidence: 3.

Study Design: Retrospective analysis using data from randomized clinical trials., Objective: To compare the occurrence of heterotopic ossification (HO) between two cervical disc prostheses. Clinical outcome and range of motion (ROM) were also evaluated., Summary of Background Data: Cervical arthroplasty was reported to be able to maintain the segmental ROM. However, controversy exists since the difference of the occurrence of HO concerning cervical prosthesis is still huge., Methods: Patients who underwent anterior cervical discectomy with arthroplasty for a cervical radiculopathy due to a herniated disc from the The Netherlands Cervical Kinematics (NECK) trial (activC; metal endplates with a polyethylene inlay and a keel for primary stability) and the PROCON trial (Bryan; metal-on-polymer with titanium coated endplates without a keel) were analyzed for HO at 12 and 24 months postoperatively. HO was scored according to the McAfee-Mehren classification. Segmental ROM was defined by a custom developed image analysis tool, and global cervical ROM was measured by Cobb's angle. Clinical outcome was evaluated by means of the neck disability index (NDI) as well as physical-component summary (PCS) and mental-component summary (MCS)., Results: At 2-year follow-up, the occurrence of HO was 68% in patients treated with the activC prosthesis (severe HO 55%), which was comparable with 85% (P = 0.12) in patients with the Bryan disc (severe HO 44%; P = 0.43). The HO progression was similar between groups. Clinically, the patients had comparable NDI, PCS, and MCS at 2-year follow-up, and comparable improvement of clinical outcomes. The global ROM in the Bryan group (56.4 ± 10.8°) was significantly higher than in the activC group (49.5 ± 14.0, P = 0.044) at 2-year follow-up., Conclusion: In comparison of two cervical disc prostheses the development of HO is independent on their architecture. Although global ROM was higher in the Bryan prosthesis group, this difference was not deemed clinically important, particularly because the clinical condition of patients with and without severe HO was comparable., Level of Evidence: 2.

Study Design: Systematic review., Objectives: The purpose of the current study is to determine the overall incidence of Heterotopic Ossification (HO) following cervical disc arthroplasty (CDA) as well as per annum rates., Summary of Background Data: CDA is a well-established surgical modality for treatment of one- and two-level degenerative disc disease that has failed conservative treatment. Despite its proven mid-term clinical success, the potential for accelerated HO following CDA remains an area of clinical concern., Methods: A MEDLINE literature search was performed using PubMed, the Cochrane Database of Systematic Reviews, and Embase from January 1980 to February 2018. We included studies involving adult patients, who underwent CDA, documentation of HO, with >12 month follow-up. The pooled results were obtained by calculating the effect size based on the logit event rate. Per annum rates were determined based on weighted averages according to average follow-up period., Results: The initial database review resulted in 230 articles, with 19 articles that met inclusion and exclusion criteria. These pooled results included 2151-disc levels and 1732 patients (50% men and 50% women) who underwent CDA and were evaluated for postoperative HO. The mean age was 45 years with a mean follow-up of 60 months. Sixteen studies reported the occurrence of severe HO resulting in 22.8% of disc levels developing severe HO. When stratifying these studies based on funding type, severe HO was reported at a rate of 21.6% by IDE studies and 27.9% by independent studies., Conclusion: The findings of the pooled data show the incidence of severe HO following CDA to be 22.8%. However, there is a significant difference in reported rates of mild and severe HO between IDE and independent data. This alludes to possible underreporting of HO and severity of HO in the industry sponsored IDE studies when compared with independent studies., Level of Evidence: 2.

Study Design: A nonrandomized, prospective, and single-center clinical trial of the ProDisc Vivo prosthesis., Objective: The aim of this study was to investigate the clinical and radiological results of a refined total cervical disc replacement (cTDR), the ProDisc Vivo, with two years of follow-up (FU). The incidence of implant-related complications was recorded as a secondary outcome variable., Summary of Background Data: Previous generations of the ProDisc artificial cervical disc replacement generate high primary stability due to keel-based designs with opening of the anterior cortex during the implantation and subsequent high rates of heterotopic ossifications., Methods: Clinical outcome scores included the Neck Disability Index (NDI), Visual Analogue Scale (VAS), arm and neck pain self-assessment questionnaires. The radiological outcome included the range of motion (ROM) and the occurrence of heterotopic ossifications. The incidence of implant-related complications with new implant design was recorded as a secondary outcome variable., Results: A total of 55 patients received a single-level treatment with the ProDisc Vivo cTDR between C3/4 and C6/7, with a follow-up rate of 78%. The clinical outcome scores improved in all parameters significantly (P = 0.0001) (NDI: 68.3 → 17.4; VAS arm: 6.3 → 1.4; VAS neck: 4.9 → 1.6). The ROM of the index-segment did not show a significant change (P = 0.26) (7.9° → 9.2°). Heterotopic ossifications at the index segment was found as grade 0 in 58%, grade 1 in 22%, grade 2 in 10%, grade 3 (with functional impairment of the prosthesis) in 7%, and grade 4 in 3% of the cases. We observed three implant-related complications (5.5%), with two implant dislocations anteriorly and one low-grade infect., Conclusion: cTDR with ProDisc Vivo demonstrated a significant and sustained improvement of all clinical outcome parameters. A less invasive implantation mechanism with lower primary stability of the cTDR might be a reason for a higher dislocation rate than the keel-based previous generation ProDisc C., Level of Evidence: 4.

Study Design: A case-control study; clinical prediction rule., Objective: The aim of this study was to construct and internally validate a clinical prediction rule to identify patients at high risk of developing heterotopic ossification (HO) after spinal cord injury (SCI)., Summary of Background Data: HO after SCI can lead to loss of joint mobility, loss of function, peripheral nerve entrapment, and pressure sores. HO is usually diagnosed on the basis of clinical symptoms, as no laboratory tests are yet available to identify patients with early HO formation. Risk factors include a complete SCI; patient age; spasticity; urinary tract infection (UTI); pneumonia; pelvic trauma; cervical or thoracic injury; and pressure sores., Methods: We analyzed a total of 558 patients with SCI, of whom 221 developed HO of the hip. A parametric survival model was fitted to estimate the probability of developing HO of the hip within 3 months of a SCI. Hazard ratios (HRs) calculation, internal validation, calibration, and model reduction were performed over 200 bootstrapped resamples. A risk score for clinical used was developed., Results: Risk factors contributing to the risk score were completeness of the injury, age, sex, UTI, spasticity, and pneumonia. The model demonstrated good discrimination (AUC = 0.72). According to the risk score quintiles, the risk of developing HO after SCI was 1.0 for persons with a score of 0 to 17 and increased 2.47-fold for persons with a score of 1 to 21, 4.75-fold for persons with a score of 22 to 27, 6.95-fold for persons with a score of 28 to 31, and 9.23-fold for persons with a score of 32-35., Conclusion: The risk score demonstrated good discrimination in predicting the occurrence of HO within 3 months of a SCI. Further development and validation of the model in other populations is warranted., Level of Evidence: 3.

Study Design: Cross-sectional study., Objective: To investigate the prevalence, concomitance, and distribution of various types of ossification of the spinal ligaments in healthy subjects using computed tomography (CT)., Summary of Background Data: CT has better diagnostic accuracy for ossification of the spinal ligaments compared to plain radiography. Currently there is no study that examines the prevalence of ossification of the spinal ligaments using whole spine CT scans., Methods: One thousand five hundred Japanese patients (888 men and 612 women) who underwent positron emission tomography and CT (PETCT) in a private health check center between 2006 and 2013 were included. This PETCT was performed on self-paying participants as a preventive cancer screen. Existence of ossification of the posterior longitudinal ligament (OPLL), ligamentum flavum (OLF), anterior longitudinal ligament (OALL), diffuse idiopathic skeletal hyperostosis (DISH), and nuchal ligament (ONL) was examined., Results: The prevalence of spinal ligament ossifications was found to be 6.3% in cervical OPLL (8.3% in men and 3.4% in women), 23% in ONL (33% in men and 8.8% in women), 1.6% in thoracic OPLL (1.4% in men and 2.0% in women), 12% in thoracic OLF (15% in men and 7.7% in women), 37% in thoracolumbar OALL (45% in men and 26% in women), and 12% in DISH (16% in men and 6.2% in women). Thirteen percent of patients with cervical OPLL had thoracic OPLL, 34% of cervical OPLL had thoracic OLF, 45% of cervical OPLL had ONL, and 36% of cervical OPLL had DISH. The most common level was C5 for cervical OPLL, T1/2 for thoracic OPLL, T11 for thoracic OLF, and T8/9 for OALL., Conclusion: Accurate prevalence of various types of ossification of the spinal ligaments evaluated by CT was revealed. High concomitance was observed in each classification of spinal ligament ossification., Level of Evidence: 3.

Study Design: A cross-sectional study., Objective: To examine the prevalence of ossification of the posterior longitudinal ligament (OPLL) and ossification of the nuchal ligament (ONL) of the cervical spine in the San Francisco area., Summary of Background Data: The prevalence of OPLL and ONL is unknown in the non-Asian population., Methods: This computed tomography-based cross-sectional study assessed the prevalence of OPLL and ONL within the cervical spine of patients treated at a level 1 trauma center between 2009 and 2012. The prevalence of both OPLL and ONL was compared between racial groups., Results: Of the 3161 patients (mean age, 51.2 ± 21.6 yr; 66.1% male), there were 1593 Caucasians (50.4%), 624 Asians (19.7%), 472 Hispanics (14.9%), 326 African Americans (10.3%), 62 Native Americans (2.0%), and 84 Others (2.7%). The prevalence of cervical OPLL was 2.2% (95% confidence interval [CI]: 1.7-2.8). The adjusted prevalence was 1.3% in Caucasian Americans (95% CI: 0.7-2.3), 4.8% in Asian Americans (95% CI: 2.8-8.1), 1.9% in Hispanic Americans (95% CI: 0.9-4.0), 2.1% in African Americans (95% CI: 0.9-4.8), and 3.2% in Native Americans (95% CI: 0.8-12.3). The prevalence of OPLL in Asian Americans was significantly higher than that in Caucasian Americans (P = 0.005). ONL was detected in 346 patients and the prevalence was 10.9% (95% CI: 10.0-12.0). The adjusted prevalence of ONL was 7.3% in Caucasian Americans (95% CI: 5.8-9.3), 26.4% in Asian Americans (95% CI: 21.9-31.5), 7.4% in Hispanic Americans (95% CI: 5.2-10.5), 2.5% in African Americans (95% CI: 1.2-4.9), and 25.8% in Native Americans (95% CI: 16.5-37.5). ONL was significantly more common in Asian Americans than in Caucasian Americans, Hispanic Americans, and African Americans (P = 0.001)., Conclusion: This study also demonstrated that OPLL and ONL were significantly more common in Asian Americans than in Caucasian Americans., Level of Evidence: 3.

Study Design: This is a retrospective study designed to observe the progressive appearance of heterotopic ossification (HO) after cervical artificial disc replacement (ADR)., Objective: To investigate the development and progressive appearance of HO at cervical ADR sites., Summary of Background Data: HO is defined as the formation of bone outside the skeletal system. The reported HO occurrence rate in cervical ADR is high and varied. However, the long-term outcome of HO has not been investigated by longitudinal observation., Methods: Sixty-seven consecutive patients undergoing cervical ADR with complete radiological data were selected for this study. Cervical lateral radiographs and computed tomographic scans were obtained during the first and second studies and compared to identify any transitions in HO. The change in the HO occurrence rate, distribution, and grade of HO were investigated at 2 follow-up time points (18.6 and 36.9 mo postsurgery). To compare the amount of progression between participants' HO rates, the relative increase rate was calculated., Results: HO showed a progressive pattern. The grade of HO was redistributed toward a higher grade in the second study. The number of patients with HO had increased from 31 (46.3%) to 43 (64.2%) of 67 patients at the final follow-up with statistically significant difference (P = 0.037). Twenty-six patients (39.4%) had progressed toward a higher HO grade, but 41 patients (60.6%) showed no change in HO grade. The overall RI rate and the weighted RI rate were 39.4% and 48.7%, respectively., Conclusion: This study found that HO has a progressive appearance and determined that HO is not a static but rather a dynamic phenomenon with progressive pattern. Future elucidation of the environmental factors affecting HO, including genetic or proteomic analyses, is recommended., Level of Evidence: 3.

Study Design: Retrospective clinical data analysis., Objective: This study was conducted to investigate the incidence, related factors, and radiography findings of ossification of the nuchal ligament (ONL) in patient with cervical spondylosis, which could serve as a basis for further studies of the relationships between ONL and cervical spondylosis., Summary of Background Data: Injury to nuchal ligament, which might cause ONL, may aggravate cervical spine instability, leading to cervical spondylosis. Thus, it is important to understand the characteristics of ONL in patients who are diagnosed with cervical spondylosis., Methods: Medical records of 372 patients with cervical spondylosis were reviewed. Data analysis included patients' sex, age, location and classification of ONL, and ossification of the posterior longitudinal ligament (OPLL). Radiological features were evaluated by lateral plain radiography and computed tomography for 2-dimensional sagittal plane reconstruction., Results: Of the 372 patients with cervical spondylosis, 49.7% had a diagnosis of ONL; the incidence of ONL was higher in males than in females (P = 0.001) and in elderly patients than in young patients (P = 0.005). The varying pictures of ONL on the plain radiography were classified into 5 types: local, continuous, segmental, mixed, and unclassified, and the distribution was 49.7%, 33.0%, 3.2%, 8.6%, and 5.4%, respectively. ONL occurred mostly at the level of C4,5 (75.7%) and C5,6 (81.1%). The incidence of ONL was higher in patients with OPLL than others (P < 0.001), and the incidence of multilevel ONL was higher in patients with OPLL than in patients with ONL only (P = 0.038)., Conclusion: The incidence of ONL is 49.7% in patients with cervical spondylosis. Sex, age, and OPLL are related factors of ONL. ONL can be classified into different types through morphology. Local type is the most common type of ONL, and multilevel ONL occurs mostly in patients with OPLL. C4,5 and C5,6 are the levels where ONL occurs mostly., Level of Evidence: 4.

Study Design: A cross-sectional study., Objective: To gain an insight for the prevalence, morphology, and distribution of thoracic ossification of the yellow ligament (OYL) by computed tomography (CT) and review of the literature., Summary of Background Data: The epidemiology and etiology of OYL remains obscure. To date, to the best of our knowledge, there is no study that comprehensively evaluated thoracic spine by CT to assess the prevalence, distribution, and morphology of OYL in a large enough sample size with wide age distribution., Methods: The participants of this study were the patients who have undergone chest CT for the examination of pulmonary diseases in our institute. The patients with previous thoracic spine surgery and younger than 15 years were excluded. Prevalence, distribution, and morphology of thoracic OYL were reviewed., Results: A total of 3013 patients (1261 females and 1752 males) with the mean age of 65 years were recruited. The CT-based evidence of OYL was noted in 1094 (428 females and 666 males) individuals (36%). Single-level involvement was noted in 532 cases, whereas 562 individuals presented multilevel involvement.Statistical analyses revealed that OYL was noted at a significantly higher rate among the males (P = 0.022). Of a total of 2051 OYLs, 779 central type OYLs, a mushroom-shaped ossification localized at the center of laminae, and 1272 noncentral type OYLs were noted. Distribution of the thoracic OYL formed 2 peaks with the highest and second highest peak found at T10-T11 and T4-T5, respectively. Interestingly, OYL is noted at consistent rates after the age of 30; however, its size increased in age-dependent manners., Conclusion: The prevalence of thoracic OYL in Japanese was 36%. A further study disclosing the association between clinical manifestations and size and/or morphology of OYL is warranted.

Study Design: Case report., Objective: To report the clinical and imaging findings of a patient with arachnoiditis ossificans (AO) 22 years after revision surgery for adolescent idiopathic scoliosis (AIS)., Summary of Background Data: To our knowledge, there are no reports in the literature that describe AO developing after primary or revision surgery for AIS. Ararchnoiditis ossificans is a rare finding and we provide a review of its presentation and management., Methods: We report the patient's history, physical examination, radiographical findings, and management in addition to providing a literature review., Results: A 43 year-old-male who underwent revision surgery for AIS due to intradural migration of a laminar hook presented 22 years after surgery with subjective leg weakness. On physical examination, no weakness was elicited and radiographs demonstrated the instrumentation to be intact. Computed tomographic imaging was performed to assess for adjacent segment disease and diffuse ossification or AO of the thecal sac from L3 to S1 was noted. We recommended observation and nonoperative management because the patient's symptoms were relatively mild., Conclusion: To our knowledge, this is the first report of AO after surgical management of primary or revision AIS. A discussion on the management of AO and a literature review is presented.

Study Design: Retrospective cohort study., Objective: To investigate the differences between single- and multilevel degenerative disc diseases (DDDs) treated with cervical arthroplasty., Summary of Background Data: The US Food and Drug Administration clinical trials compared arthroplasty with anterior cervical discectomy and fusion for single-level DDD. However, cervical arthroplasty for multilevel DDD is rarely addressed in the literature., Methods: A total of 102 consecutive patients who underwent Bryan arthroplasty were divided into either a single- or multilevel group. Clinical outcomes were measured by the visual analogue scale (VAS) of neck and arm, and by the neck disability index with a minimum follow-up of 25 months. Every patient had radiographical evaluations, and computed tomography., Results: Eighty-six patients (84.3%) completed the follow-up with a mean time of 38.3 ± 8.7 months. Postoperatively, there were significant improvements in clinical outcomes (i.e., VAS neck, VAS arm, and neck disability index) at each time point of evaluation (i.e., 3-, 6-, 12-, and 24 mo postoperation). The sex composition and clinical outcome improvements between the single- and multilevel groups were not significantly different. The multilevel group was older (51.3 ± 8.6 vs. 46.3 ± 11.2 yr; P = 0.02), had more intraoperative blood loss (218.0 ± 182.4 vs. 102.8 ± 79.2 mL; P = 0.001), and demonstrated a higher rate of heterotopic ossification (HO) than the single-level group (66.0% vs. 25.0%; P < 0.001). The majority (97.7%) of the artificial discs in this series remained mobile despite HO., Conclusion: Clinical outcomes of cervical arthroplasty in multilevel spondylosis are similar to single-level outcomes. However, the significantly higher rate of HO found in multilevel arthroplasty and its long-term effect warrant further investigation.

Study Design: Large scale, cross-sectional imaging study of a general population., Objectives: To evaluate the prevalence, morphology, and distribution of ossification of the ligamentum flavum (OLF) in a population, and synthesize the scientific literature on the prevalence of OLF and some factors associated with its occurrence., Summary of Background Data: OLF is a rare disease in which the pathogenesis has not been conclusively established. Little is known about its epidemiology. To date, there is no study that comprehensively assessed the distribution and prevalence of OLF in the whole spine using magnetic resonance imaging (MRI)., Methods: A total of 1736 southern Chinese volunteers (1068 women; 668 men) between 8 and 88 years of age (mean, 38 years) were recruited by open invitation. MRI was administered to all the participants. T2-weighted, 5-mm spin-echo MRI sequences of the whole spine were obtained. Presence of OLF was identified as an area of low signal intensity in the T2 sagittal sequence located in the posterior part of the spinal canal, and subsequently confirmed by computed tomography scans showing areas of ossification within the ligamentum flavum. The distribution of OLF was classified into 3 types: the isolated type, continuous type, and noncontinuous type. While the morphology of the lesion was classified into triangular, round, and beak shapes based on the pattern of ossification on T2-weighted sagittal MRIs., Results: OLF was identified in a total of 66 subjects or 3.8% of the population (52 women and 14 men). In 45(68.2%) cases, OLF was present at a single-level (isolated type), whereas in 21 (31.8%) cases OLF was present at multiple levels. The isolated type was found in 45 (68.2%) cases, continuous type in 11 (16.7%), and noncontinuous type in 10 (15.2%). The most common site of involvement is the lower thoracic spine, but they can also occur in the upper thoracic spine. The majority of the segments had a round morphology (n = 75: 81.5%), while 17 (18.5%) segments were triangular in shape. A literature review of the past 26 years showed only 4 reports on the prevalence of OLF, all were in special patient groups., Conclusion: Case reports have described postoperative paraplegia from failure to identify and decompress all stenotic segments of OLF. This study demonstrated that OLF is not uncommon, and that some 15% of the lesions are noncontinuous, and therefore could be missed. The authors recommend that for patients undergoing surgical decompression for 1 level of OLF, the whole spine should be routinely screened for other stenotic segments. Failure to do so could result in paraplegia from the nondecompressed levels.

Study Design: A retrospective review., Objective: The aim of this study is to highlight one of the under recognized and under reported aspects of ossification of the ligamentum flavum (OLF), namely, dural ossification in OLF and to discuss the incidence, radiologic signs, causes as well as the surgical and prognostic implications of dural ossification in OLF., Summary of Background Data: OLF is being increasingly recognized as a cause of myelopathy. One of the surgical pitfalls in the management of this condition is ossification of the dura mater in OLF. Preoperative identification of ossified dura mater will be helpful to the surgeon to modify the surgical technique and to counsel patients regarding the risks of surgery., Methods: A retrospective analysis of a database of OLF maintained by this author was done to identify cases of OLF where there was intraoperative evidence of dural ossification and dural laceration. Only those patients who had both computed tomography (CT) and magnetic resonance imaging (MRI) were included in the analysis. Patients with MR imaging alone were excluded from the analysis as CT evaluation was not done routinely in the earlier part of the study. Nurick's grading was used to assess the neurologic status before and after surgery. The CT and MR images of these patients were analyzed to identify radiologic signs of dural ossification. The pattern of dural ossification, if present, was noted. The intraoperative and postoperative complications were recorded., Results: During the study period from 1997 to 2006, there were 20 patients with OLF who had both CT and MR imaging evaluation. Of these 20 patients, 8 had intraoperative evidence of dural ossification and these patients also sustained dural laceration during surgery. Of these 8 patients, CT evidence of dural ossification was found in 7. In the remaining one patient, there was no radiologic evidence of dural ossification. The radiologic signs of dural ossification as depicted in the bone windows of CT were of 2 types: (1) the "tram track sign," where there was a hyperdense bony excrescence with a hypodense center and (2) the "comma sign," where there was evidence of ossification of one-half of the circumference of the duramater. Of these 7 patients, 4 developed cerebrospinal fluid (CSF) leak following surgery and 1 of these 4 patients developed meningitis. Neurologic function improved by one Nurick's grade in 5 of the 7 patients. In the remaining 2 patients, there was no change in the neurologic status., Conclusion: Dural ossification is a common finding in OLF. There are 2 radiologic signs of dural ossification, namely, the "tram track sign" and the "comma sign." Preoperative identification of dural ossification might help the surgeon to anticipate and appropriately deal with dural laceration during surgery. This will also help to counsel patients regarding the risks of surgery for OLF. The surgical and prognostic implications of dural ossification are being discussed.

Study Design: Case report and review of the literature., Objective: To report 2 patients, with a history of thoracic tuberculosis, in whom ossification of ligamentum flavum (OLF) was found adjacent to progressive kyphosis and resulted in incomplete paralysis. The relevant literature was also to be reviewed., Summary of Background Data: Progressive kyphosis is the most common cause of late onset paralysis after spinal tuberculosis. However, OLF related to tuberculous kyphosis is rarely observed and this makes surgical treatment become very difficult., Methods: Clinical history, laboratory examination, and radiographic findings of the 2 patients were described. Posterior laminectomy and instrumented fusion were performed for both 2 patients, but additional osteoectomy was performed through posterolateral zygapophysial approach in only 1 patient in whom the kyphotic deformity was partially corrected. A review of the relevant literature was also done., Results: Two patients were observed up for 2 and 6 years, respectively. Neurologic status was significantly improved after operation and no further kyphosis developed. To our knowledge, only 1 article had reported 2 similar cases of spinal stenosis above a healed tuberculous kyphosis., Conclusion: OLF related to tuberculous kyphosis was rarely observed. The local instability and repetitive stimulus of excessive stress could lead to development of OLF. Our experience suggested that decompression of OLF was more important than correction of kyphotic deformity to improve the neurologic status in these patients.

Study Design: Case report., Objective: Describe a complication from the use of bone morphogenetic protein-2 (BMP-2) for posterolateral lumbar fusion., Summary of Background Data: N/A, case report., Methods: The patient is a 69-year-old white male with a 1 year history of back and right leg pain with a foot drop due to spinal stenosis and a degenerative spondylolisthesis at L4-L5. Surgery for decompression and instrumented fusion was performed using BMP., Results: Within 3 months after surgery the patient developed pain along his iliac wing, groin, and greater trochanter on the right side. Work up over the next several months included a bone scan, radiographs, Dexa scan, computed tomography scan, and magnetic resonance imaging with gadolinium and fat suppression. These tests showed extensive bone formation in the psoas and iliacus on the right side. The bone has persisted at least 2 years after surgery and shows no sign of resorption., Conclusion: BMP-2 can cause heterotopic bone formation when used for posterolateral lumbar fusion.

Study Design: A retrospective study on 9 patients treated for ossification of the ligamentum flavum (OLF) at the lumbar spine., Objective: To evaluate the clinical and radiologic findings as well as the postoperative results of the patients., Summary of Background Data: Ossification of ligamentum flavum (OLF) in the lumbar region causing neurologic impairment is a rare pathologic entity described mainly in Japanese literature. The present study represents the largest surgical series of European patients with OLF at the lumbar spine., Methods: A retrospective study of 9 consecutive patients was conducted between 2000 and 2005. The clinical status was evaluated according to the Japanese Orthopedic Association scale. Potential associated disorders were also recorded. Diagnosis in each case was established using computed tomography and magnetic resonance imaging. Whole-spine magnetic resonance imaging was routinely used in order to reveal possible coexisting spinal lesions. Pathologic confirmation was available in all cases., Results: Radicular pain was the most common presenting symptom. Myotomal weakness was found in most of the cases. A majority of our patients had lesions located at the L3-L5 levels. Thoracic OLF was recorded as a spinal coexisting ossified lesion. Surgery led to neurologic improvement with a statistically significant increase in the Japanese Orthopedic Association score (P = 0.007). The median recovery rate was 91.60% +/- 43.85%., Conclusion: It is possible that OLF is underreported in the Greek population. Surgical treatment is important in order to improve functional outcomes.

Study Design: A study using rat spondylolisthesis models., Objective: To clarify pathomechanism of vertebral rounding deformity in pediatric spondylolisthesis., Summary of Background Data: For high-grade slippage, rounding of sacrum surface associated with L5 spondylolisthesis is reported to be the most responsible risk factor. However, the exact pathomechanism of the rounding deformity is yet to be clarified., Methods: Spondylolisthesis rat model (4-week-old) was used. Radiographs were taken weekly for 5 weeks after the surgery. The lumbar spines were harvested for histology. Hematoxylin and eosin, alcian blue staining, and tartrate-resistant acid phosphatase staining were used. Immunohistochemically, the growth plate cartilage was studied for type II and X collagen. A modified bone histomorphometric analysis was also performed., Results: Radiographs showed slippage 1 week after surgery. Rounding deformity was obvious 2 weeks after surgery. The rounding deformity progressed with time. Three weeks after surgery, the specific columns of growth plate were unclear at the anterior corner, which corresponded to the rounding surface observed on radiographs. Instead, a huge mass of cartilage was observed at that site. Tartrate-resistant acid phosphatase-positive cells were observed in the vicinity of the growth plate except in relation with the anterior corner. The growth plate and cartilage mass at the anterior corner stained positive for type II collagen. Chondrocytes in the hypertrophied layer stained positively for type X collagen; however, staining was faint at the anterior corner. The results suggested that the chondrocytes at the anterior did not form, morphologically and functionally, the normal growth plate. From histomorphometrical analysis, the normal posterior growth plate made endochondral bone growth in 510 +/- 20 microm for a week, whereas the anterior corner in 200 +/- 15 microm., Conclusion: Deficient endochondral ossification of the growth plate in the anterior upper corner of the vertebra could be the pathomechanism of the rounding deformity of the sacrum.

Study Design: We report on a 46-year-old man with atlantoaxial rotatory subluxation and cranio-cervical osseous fusion secondary to cervical dystonia (CD) and concomitant ankylosing spondylitis (AS)., Objective: To describe treatment of CD under these unusual circumstances., Summary of Background Data: CD may cause several complications due to enhanced spinal degeneration. Primary and secondary nonresponders to conservative treatment may benefit from neurosurgical procedures including denervation procedures or functional stereotactic neurosurgery. However, if spinal fixation has occurred, usually, treatment of dystonia is considered to be not appropriate. Nevertheless, in the rare case, neurosurgical intervention may still be useful to improve dystonic pain., Methods: After a 4-year history of severe CD, the head was rotated to the left in a rigidly fixed position. Three-dimensionally rendered computed tomography imaging studies revealed fixed rotation of the occiput and the C1 vertebra at an angle of 45 degrees to the C2 vertebra. There was abnormal ossification of the facet joints and the ligaments of the odontoid., Results: The patient experienced marked relief of his neck pain after deactivation of the dystonic right sternocleidomastoid muscle by partial myectomy and the left posterior neck muscles by selective posterior ramisectomy., Conclusion: Although rare, the concomitant occurrence of AS and CD should alert treating physicians and result in timely treatment of dystonia.

Study Design: Observational study with prospective CT analysis., Objective: To assess the incidence and clinical sequelae of epidural bone formation following the adjunctive use of recombinant bone morphogenetic protein 2 (rhBMP2) with local autogenous bone graft use of (rhBMP2) in minimal access interbody (PLIF and TLIF) fusions., Summary of Background Data: The use of rhBMP2 for interbody fusion is associated with high fusion rates. However, for posterior approaches, concerns regarding heterotopic bone formation within the epidural space have been raised., Methods: An independent CT analysis of 33 consecutive patients following minimal access lumbar fusion (PLIF [n = 10] or TLIF [n = 23]) with [n = 23] and without [n = 10] rhBMP2 was performed. Bone formation was graded in a centrifugal manner (intradiscal, anular/ALL/PLL, epidural [canal/foramen] and beyond the spine). In all BMP cases, a constant dose of 4.2 mg/disc level was administered (lowest commercially available dose). In all cases, local autograft was used. Review and assessment of prospectively collected outcomes data were performed., Results: Average clinical and CT (minimum 6 months) follow-up was 25.0 and 7.9 months, respectively. Bridging bone (fusion) was seen in 100% of the BMP group and 90% without BMP. Epidural bone formation occurred in 20.8% with the use of BMP (5 levels: n = 1 spinal canal and n = 4 within the foramen) compared with 8.3% (1 level: canal) without BMP. Foraminal bone formation was seen only in the TLIF group. All epidural bone formation was heterotopic, and no ectopic bone formation occurred. There were no clinical sequelae associated with heterotopic bone formation. The mean preoperative and postoperative Oswestry Disability Index was 50.2% (range, 25%-75%) and 11.3% (range, 0%-38%) respectively., Conclusion: Although the adjunctive use of rhBMP2 is associated with a higher incidence of heterotopic bone, there does not seem to be any associated clinical sequelae.

Study Design: Prospective clinical study enrolled in 2 centers (Munich and Liberec) as part of a prospective European multicenter study with ProDisc C (Synthes Inc., Paoli, PA)., Objectives: The first goal of the study was to evaluate the rate of heterotopic ossifications identified with plain radiograph following total cervical disc replacement (TCDR). The second goal was to show whether segmental motion can be preserved, and whether TCDR can provide improvement of the patient's ability to perform activities of daily living as well as a decrease of pain., Summary of Background Data: Only a few reports about the radiologic outcome after TCDR are published so far. Heterotopic ossification is a well-known phenomenon after total hip arthroplasty. The rate of heterotopic ossification following TCDR is unclear., Methods: The radiographs of 54 patients (in total, 77 implanted prostheses) were analyzed 1 year after TCDR with a ProDisc C prosthesis. We classified the heterotopic ossification in 5 grades according to a recently published classification system for lumbar total disc replacement. For clinical parameters, the visual analog scale and the Neck Disability Index were evaluated preoperatively and 1 year postoperatively. The Student t test and Wilcoxon test were used for statistical analysis., Results: In 26 treated segments (33.8%), no heterotopic ossification was detectable. Grade 1 ossifications were present in 6 levels (7.8%). A total of 30 segments (39.0%) showed grade 2 ossifications. Heterotopic ossifications that led to restrictions of the range of motion were present in 8 cases (10.4%). One year postoperatively, 7 cases (9.1%) had a spontaneous fusion of the treated segment. The clinical parameters improved significantly and were similar to previous reports about TCDR., Conclusions: Only 33.8% of the patients did not show any signs of heterotopic ossification, and the rate of spontaneous fusion after TCDR 1 year after surgery was unexpectedly high. There were 49.4% of the patients with grade 2-3 ossification, which lets us suspect an even higher rate of spontaneous fusion after long-term follow-ups. Motion preservation after TCDR is only guaranteed if spontaneous fusion can be prevented. Thus, mobility of the implanted segments needs to be further studied.

Study Design: A series of 14 patients from the French Antilles treated for ossification of the ligamentum flavum (OLF)., Objectives: To describe the clinical and radiologic aspects, as well as disease course in a group of Caribbean patients. Also describe the use of sagittal computerized tomography (CT) reconstructions to distinguish OLF from calcification of the ligamenta flava., Summary of Background Data: OLF is a rare disease described almost exclusively in Japanese patients. Only rarely are patients of African descent affected. No series of OLF in African American or African Caribbean subjects has previously been published., Methods: A retrospective study of 14 consecutive patients, including 7 men and 7 women (mean age, 66.8 years), was conducted from 1996 to 2003. Diagnosis in each case was established using CT. Magnetic resonance imaging was also performed in every case. For the 11 patients treated surgically, pathology studies were performed., Results: Walking difficulties were the most common presenting complaint. A picture of spastic paraparesis associated with sphincter dysfunction was the most common finding on initial examination. In each case, CT provided sufficient information to establish a diagnosis of OLF, while magnetic resonance imaging was helpful for showing spinal cord involvement. In most of the patients, OLF was located in the lower thoracic spine. Surgical decompression through a posterior approach resulted in regression of symptoms in all 11 patients treated surgically., Conclusions: This study is the first reported series of OLF in a group of Caribbean patients. The disease appears to be underreported in the African Caribbean population. OLF can lead to debilitating thoracic myelopathy. Surgery is frequently indicated and achieves favorable results.

Study Design: Skeletal tissues of mice with an inactivated allele of the Col2a1 gene for Type II collagen ("heterozygous knockout") were studied., Objective: To determine whether a heterozygous inactivation of the Col2a1 gene has a role in the etiology of spine disorders such as disc degeneration., Summary of Background Data: Mutations in the COL2A1, COL11A1, COL11A2, and COL9A2 genes have been linked to spine disorders. However, the mechanism by which genetic factors lead to disc degeneration still are largely unknown., Methods: Spine tissues were studied using radiograph analyses; conventional, quantitative, and polarized light microscopy; immunohistochemistry for the major extracellular components, and in situ hybridization for procollagens alpha1(I) and alpha1(II). Voluntary running activity also was monitored in half of the mice., Results: As the findings showed, 1-month-old heterozygous knockout mice had shorter limb bones, skulls, and spines, as well as thicker and more irregular vertebral endplates, which calcified earlier than in the control mice. They also had a lower concentration of glycosaminoglycans in the anulus fibrosus, in the endplates, and in the vertebral bone than the controls. These features in the heterozygous knockout mice were compensated by the age of 15 months. However, the long bones and skulls of the mature heterozygous mice remained shorter than those of the controls. Gene-deficient mice used the running wheel less. However, physical exercise did not induce any marked structural changes in the skeleton., Conclusion: Mice with heterozygous knockout of Col2a1 show subtle early skeletal manifestations that bear some resemblance to those of human spine disorders.

Study Design: This is a case report., Objective: To present a case of osseous bridging between C1 and C2 of posttraumatic origin and with an associated closed head injury and to discuss its pathogenesis and clinical outcome after surgical resection., Summary of Background Data: Heterotopic ossifications of posttraumatic origin in the spine are rare. To the authors' knowledge, no cases have been reported of spontaneous bony bridging between C1 and C2 with a posttraumatic origin., Methods: Heterotopic ossifications were detected when pain and limited axial rotation (left/right 10 degrees/0 degree/20 degrees) were persistent, despite intensive physical therapy. Because heterotopic ossifications were ankylosing C1 and C2, the decision was to resect the osseous bridge in combination with a careful mobilization of the cervical spine. Functional computed tomography was performed for analysis of the postoperative results., Results: Four months after surgery, clinical examination showed asymptomatic increased axial rotation. Functional computed tomography indicated that left C1-C2 axial rotation was reduced, possibly related to impingement caused by residual bony spurs. Pathologic changes in the surrounding soft tissue may be another important factor in the persistent limitation of rotation., Conclusions: Osseous bridging between C1 and C2 may be considered when persistent pain and limited axial rotation are observed after trauma. Operative resection, together with careful intraoperative and postoperative mobilization, may be the treatment of choice.

Study Design: Strain distribution in the intervertebral discs was evaluated biomechanically using an engineering true strain calculation formula., Objectives: This study was performed to clarify the involvement of dynamic factors in the progression of ossification of the posterior longitudinal ligament., Summary of Background Data: In patients with ossification of the posterior longitudinal ligament of the cervical spine, ossification frequently progresses after laminectomy. This suggests the involvement of dynamic factors in the progression of ossification. However, these factors have not yet been clarified., Methods: The analysis was performed on 101 patients with ossification of the posterior longitudinal ligament by employing dynamic lateral x-ray films of the cervical spine. The x-ray films were digitized and used as computer data for calculating the strain distribution. X-ray films were obtained again 5 years later, and the strain distribution and the presence or absence of progression of ossification were evaluated., Results: The progression of ossification of the posterior longitudinal ligament was highly correlated with abnormal strain distribution in the intervertebral discs. Progression of ossification was frequently observed in areas having disc distortion in tension and extension on the posterior longitudinal ligament., Conclusions: In this study, the area of progression of ossification corresponded to the area showing uneven strain distribution and resultant concentration of dynamic stress. These results suggest an important role for dynamic factors in the progression of ossification of the posterior longitudinal ligament.

The significance and role of cervical soft disc hernia in ossification of the posterior longitudinal ligament were investigated based on 54 surgical cases. The types of ossification of the posterior longitudinal ligament were divided into three sub-types: segmental, continuous, and mixed types. In the current series, there were 29 segmental type, 12 continuous type, and 13 mixed type. In the 29 segmental type, 23 patients had accompanying cervical disc hernias (79%). In the 12 continuous type, only 2 patients (17%), and in the 13 mixed type, 5 patients (33%), had accompanying disc hernias. According to the current study, an essential difference exists between the segmental type and the continuous or mixed types. In addition, the current result seems to indicate that, at least in the segmental type, disc herniation is not the promoting or initiating factor of ossification of the posterior longitudinal ligament, but that, in these cases, the fragility of the posterior longitudinal ligament may increase the chance of a disc hernia.

This is the first report of the process of formulation of a cervical osteophyte causing dysphagia. The patient had ankylosing spinal hyperostosis and OPLL and was followed radiographically for a long time before the onset of dysphagia. The radiological observation suggested that dysphagia was produced when the immobile part of the esophagus was compressed by the anterior projecting cervical osteophyte. The immobility of the esophagus is an important factor in determining whether dysphagia occurs. Another possible contributing factor to dysphagia in this patient was the ossification of the cervical anterior and posterior longitudinal ligaments. The OPLL affected intervertebral segmental motion and induced the formation of anterior projecting cervical osteophytes.

To study the role of calcium metabolism in the development of ossification of the posterior longitudinal ligament of the cervical spine, 39 patients with affected cervical spines were investigated using an oral calcium tolerance test and followed by cervical spinal radiography to evaluate disease progression. The average follow-up was 6 years. The patients were divided into two groups according to their responsiveness to an oral calcium load: a group of 14 patients with decreased calciuric responses and another group of 25 with normal responses. The incidence of the development of cervical ossification of the posterior longitudinal ligament in the decreased-response group was significantly higher than that in the normal group. Because these patients were managed operatively by laminoplasty, however, the incidence was low irrespective of their calciuric responses. These results suggest that the development of cervical ossification of the posterior longitudinal ligament is associated with decreased intestinal calcium absorption but that treatment with laminoplasty alters the mechanical environment of the cervical spine (eg, range of motion of the cervical spine is limited). The development of cervical ossification of the posterior longitudinal ligament may be controlled by this procedure.

Five patients with single sclerotic vertebral body lesions had serial radiographs demonstrating no change in size of the radiodensities. Radionuclide bone imaging, obtained in 4 of these patients, showed no increased radioisotopic uptake in the areas in question. The absence of growth of the lesions on follow-up radiographs and the presence of negative bone scans support the diagnosis of enostoses of the spine. It is important for the radiologist to realize that benign sclerosis of a single vertebral body may simulate skeletal metastasis.

To study the genetic background in ossification of the posterior longitudinal ligament of the spine (OPLL), 1,030 relatives of probands with cervical OPLL in 347 families were investigated by observing their spinal x-ray films, and the following results were obtained. Ossification of the posterior longitudinal ligament was found in 26.15% of the parents of the probands and 28.89% of the siblings of the probands. These prevalences were significantly higher than in the general population. The segregation rate in the siblings corresponded neither with the hypothesis of autosomal dominant inheritance nor with that of autosomal recessive inheritance. The possibility of polygene inheritance was also ruled out, considering the risk of recurrence in the siblings of the probands. However, owing to the segregation rate in the siblings exceeding 0.25 and the high prevalence of OPLL in the parents, OPLL was suggested to be a disorder possibly controlled by autosomal dominant inheritance.

Although there is considerable literature concerning ossification of the posterior longitudinal ligament or the ligamentous flava (OPLL or OYL) in the cervical and thoracic spine, there are only a few references about OPLL or OYL in the lumbar spine. The authors have described lumbar spinal stenosis due to OPLL or OYL as hyperostotic lumbar spinal stenosis, and analyzed 12 surgically documented cases with this condition. The symptoms and signs of hyperostotic lumbar spinal stenosis are the same as those seen in degenerative lumbar spinal stenosis, but the degree of paraparesis is much more severe in hyperostotic lumbar spinal stenosis. Computed tomography scan imaging clearly demonstrates OPLL or OYL in the lumbar spine, although some lesions can be seen on the lateral view of a plain roentgenogram. The results of 12 surgical cases suggest that decompression laminectomy produces relief of symptoms. An analysis of 2,403 plain lumbar roentgenograms showed an incidence of 8.4% OYL in the lumbar spine, with frequent involvement of the upper and middle lumbar spine. A classification system of OYL in the lumbar spine has been developed. The entire spine should be examined before surgery on a patient with hyperostotic lumbar spinal stenosis because of a tendency to ossify spinal ligaments at other levels.

Although the pathogenesis of ossification of the cervical posterior longitudinal ligament (OPLL) has not yet been clarified, it has come to be widely recognized that severe cervical myelopathy or radiculopathy is caused by OPLL. Fifty-three cases who were operated on for OPLL with myelopathy or radiculopathy in our clinic over the past 16 years were followed up. A recovery rate of approximately 70% was observed. Postoperative progressions of the ossification were observed among 75% of the cases of continuous and mixed type but seldom among those with segmental and other types. As causative factors for these postoperative progressions of the ossification, the authors would like to advocate biological, structural, and mobility-related elements. We concluded that in the ossified stage it is desirable to apply anterior decompression for the segmental and other type, posterior decompression for the continuous and mixed type, and, if necessary, two-stage combined decompression for the mixed type.