An epidemiological survey on ossification of ligaments in the cervical and thoracic spine in individuals over 50 years of age

An epidemiological survey on ossification of the spinal ligaments was performed on a total of 1,058 subjects over the age of 50 years by means of roentgenography of the cervical and thoracic spine. Ossification of the posterior longitudinal ligament (OPLL) of the cervical spine was detected in 34 subjects (3.2%) with a predilection for men, whereas OPLL in the thoracic spine was found in 8 (0.8%). There were 325 cases (30.7%) of ossification of the anterior longitudinal ligament (OALL) of stage II or above by Forestier's classification in the region from the cervical to thoracic vertebrae, and these cases included a significantly greater number of men. Ossification of the ligamenta flava (OLF) was observed in 48 cases (4.5%). As for the coexistence of ossification of these ligaments, 364 individuals (34.4%) had at least one instance of OPLL and OALL (stage II or above) in the region from the cervical to thoracic spine, and OLF in the thoracic spine.     

A radiological population study on the ossification of the posterior longitudinal ligament in the spine

This paper reports the results of a radiological population study on the ossification of the posterior longitudinal ligament (OPLL) in both the cervical and the thoracic spine among Japanese. The study was carried out in the Yachiho-mura district in the central part of Japan, where 5074 people were living. X-ray examinations were made of 1058 of the people; there were 440 men and 618 women, 50 or more years of age. The roentgenograms showed 34 cases of OPLL in the cervical spine (3.2%): 19 men (4.3%) and 15 women (2.4%). The condition was most frequently observed at the level of C-4. Radiological classification showed 18 cases of the segmental type, 11 of the continuous type, and five of a mixed type. There were eight cases of OPLL in the thoracic spine (0.8%), four in men (0.9%) and four in women (0.6%). OPLL in the thoracic spine was most frequently observed at the midthoracic levels. All eight cases showed a continuous type of ossification. There were three subjects with OPLL in both the cervical and the thoracic spine. Therefore, the number of subjects with OPLL in either the cervical or the thoracic spine was 39 (3.7%) total.     

Co-existence of ossification of the nuchal ligament is associated with severity of ossification in the whole spine in patients with cervical ossification of the posterior longitudinal ligament -A multi-center CT study-

Background

Previous studies have shown that patients with cervical ossification of the posterior longitudinal ligament (OPLL) often have co-existing ossification of the nuchal ligament (ONL). However, no studies have focused on ONL and its relevance to the severity of OPLL or ossification of other spinal ligaments, such as anterior longitudinal ligament (OALL), ligamentum flavum (OLF), and supraspinous/interspinous ligament (OSIL).

A radiological population study on the ossification of the posterior longitudinal ligament in the spine

Summary This paper reports the results of a radiological population study on the ossification of the posterior longitudinal ligament (OPLL) in both the cervical and the thoracic spine among Japanese. The study was carried out in the Yachiho-mura district in the central part of Japan, where 5074 people were living. X-ray examinations were made of 1058 of the people; there were 440 men and 618 women, 50 or more years of age.The roentgenograms showed 34 cases of OPLL in the cervical spine (3.2%): 19 men (4.3%) and 15 women (2.4%). The condition was most frequently observed at the level of C-4. Radiological classification showed 18 cases of the segmental type, 11 of the continuous type, and five of a mixed type.There were eight cases of OPLL in the thoracic spine (0.8%), four in men (0.9%) and four in women (0.6%). OPLL in the thoracic spine was most frequently observed at the midthoracic levels. All eight cases showed a continuous type of ossification.There were three subjects with OPLL in both the cervical and the thoracic spine. Therefore, the number of subjects with OPLL in either the cervical or the thoracic spine was 39 (3.7%) total.This study was subsidized by the Japanese Ministry of Public Health and Welfare     

严重颈椎后纵韧带骨化症前路和后路手术比较

目的 探讨前路和后路手术治疗严重颈椎后纵韧带骨化症的适应证选择、疗效及并发症.方法 2004年1月至2006年12月,手术治疗椎管狭窄率大于50%的严重颈椎后纵韧带骨化症患者34例(男29例,女5例,平均57.2岁),前路采用椎体次全切除减压钛网植骨内固定术14例(男12例,女2例),后路采用椎板切除减压侧块螺钉固定术20例(男17例,女3例).比较两种手术方式患者的颈椎管矢状径、颈椎曲度、椎管狭窄率、骨化物分型、骨化物范围、脊髓压迫率等的差异.采用JOA评分评价患者术前、术后神经功能,并计算改善率.结果 影像学结果显示前路手术主要为范围在3个节段以内的局限型和分节型骨化患者,而后路手术主要为范围超过3节段的连续型和混合型骨化患者,骨化物的分型及范围是选择的主要依据.所有患者随访6个月～3年,平均1.5年.前路手术组JOA评分从术前平均(9.3+1.8)分提高至术后平均(14.2±1.3)分,平均改善率62.3%±15.2%;后路手术组JOA评分从术前平均(8.7+1.6)分提高至术后平均(11.4±1.2)分,平均改善率33.5%±12.7%.两组患者疗效差异有统计学意义(P＜0.01).结论 对于骨化范围在3个节段以内的患者,前路手术是安全、有效的治疗方式,而后路手术则适用于范围超过3个节段的严重颈椎后纵韧带骨化症患者.     

Long-term follow-up results of anterior interbody fusion applied for cervical myelopathy due to ossification of the posterior longitudinal ligament

STUDY DESIGN: A long-term follow-up study was carried out in 30 patients who underwent anterior interbody fusion for cervical myelopathy associated with ossification of the posterior longitudinal ligament (OPLL). OBJECTIVE: To investigate whether anterior interbody fusion without decompression is an appropriate surgical method for long-term relief of cervical OPLL myelopathy. SUMMARY OF BACKGROUND DATA: Several studies of operative results after posterior decompression for cervical myelopathy due to ossification of the posterior longitudinal ligament have been reported. There has been no report about anterior interbody fusion without decompression. The postoperative results of this treatment method applied in cervical OPLL myelopathy have been evaluated by the authors of the present study for more than 10 years. No reports on such a long-term follow-up study have been published in the literature. METHODS: Thirty patients who underwent anterior interbody fusion for cervical OPLL myelopathy were evaluated clinically and radiographically. The mean follow-up period was 14.7 years (range, 10-23 years). RESULTS: Clinical results were evaluated according to Okamoto's classification. At the time of the final follow-up evaluation, 16 patients had improved in functional score by two grades, and their surgical results were regarded as excellent; eight patients improved by one grade, and their clinical outcomes were regarded as good; five patients showed no change; and the condition of one patient deteriorated. As for radiographic analysis, the type of ossification had changed in four cases. Ossification width and thickness increased in 26 patients. Postoperative alignment of the cervical spine showed kyphosis in three patients, straight spine in 11 patients, and lordosis in 16 patients. CONCLUSION: Anterior interbody fusion without decompression is an effective treatment for cervical OPLL myelopathy that resulted in stable long-lasting conditions.     

Treatment of myelopathy due to cervicothoracic OPLL via open door laminoplasty

STUDY DESIGN: Postoperative long-term follow-up study of open door laminoplasty for the ossification of the posterior longitudinal ligament (OPLL) in the thoracic spine. OBJECTIVES: Techniques and outcomes of open door laminoplasty were described. The efficacy of this procedure was discussed and compared with other surgical methods for thoracic OPLL reported in the literature. SUMMARY OF BACKGROUND DATA: OPLL of the thoracic spine is often associated with cervical OPLL or ossification of the yellow ligament (OYL) of the thoracic spine; therefore, it is extremely difficult to determine the most appropriate surgical therapeutic procedure. There are very few detailed reports about extensive laminoplasty for OPLL of the thoracic spine. METHODS: The subjects included in this study consisted of 13 consecutive patients of thoracic OPLL who were surgically treated between 1994 and 2003 by the open door laminoplasty using the spinal processes and ligament complex as spacers for the open side. The number of manipulated lamina, including the cervical spine, was from 7 to 14 (mean 10 laminae), the follow-up period was 75 months on average. We evaluated the clinical symptoms by the JOA scoring method and postoperative bone union and thoracic kyphosis by plain x-ray photograph and computed tomography. RESULTS: Postoperatively, the JOA score improved from an average of 5.5 to 8.5 out of a maximum of 11 points and the mean recovery rate by Hirabayashi method was 54.5%. In all cases, bone union was seen at the hinge side between the opened lamina and the lateral mass. Neither restenosis of the opened lamina nor marked progression of kyphosis were seen on the final follow-up observation in any patient. There was no postoperative spinal cord injury. CONCLUSIONS: Open door laminoplasty is a useful procedure for OPLL of the thoracic spine. This method enables wide-range posterior decompression, especially for the continuous type OPLL extending from the cervical spine to the thoracic spine, even if the apex of the thoracic kyphosis is included.     

Cervical myelopathy resulting from combined ossification of the ligamentum flavum and posterior longitudinal ligament: report of two cases and literature review

Background contextIn the cervical spine, the combination of ossification of the ligamentum flavum (OLF) and ossification of the posterior longitudinal ligament (OPLL) is rarely seen. There have been only four cases reported in the English literature.PurposeWe describe two more cases that exhibited cervical myelopathy resulting from the combination of cervical OLF and OPLL and required surgery. A literature review with a comparative analysis between previous reports and present cases was also performed.Study designCase report and literature review.Patient sampleTwo patients with combined OLF and OPLL.Outcome measuresPreoperative computed tomography, magnetic resonance imaging, and pathological findings from operative specimens were used to confirm the diagnoses.MethodsA 76-year-old man (Case 1) presented with disturbance of gait and fine finger movement. Magnetic resonance imaging showed severe spinal canal stenosis and cord compression at the C3–C4 level. Computed tomography showed OPLL at the C2–C6 levels (segmental type) and OLF at the left C3–C4 level. The patient underwent posterior decompression and OLF resection. A 75-year-old man (Case 2) presented with sensory disturbance and muscle weakness in his bilateral upper extremities and disturbance in fine finger movements. Magnetic resonance imaging showed severe spinal canal stenosis and cord compression at the C2–C3 and C3 levels. Computed tomography showed OPLL at the C3–C7 levels (mixed type) and OLF at the left C2–C3 and C3 levels. The patient also underwent posterior decompression and OLF resection.ResultsIn both cases, histological examination of the surgical specimens showed osseous tissue and enchondral ossification within the ligamentum flavum, and the diagnosis in each case was OLF. After surgery, both patients' symptoms immediately improved, and no recurrence was observed at 2 years after surgery.ConclusionsWe experienced two cases of cervical myelopathy resulting from the combination of OLF and OPLL in the cervical spine. The symptoms of myelopathy were treated successfully by laminectomy and laminoplasty with OLF resection in both cases. The literature review including the present two cases revealed that cervical OLF tended to occur adjacent or close to the margin of cervical OPLL, suggesting that the increased mechanical stress at the junction of OPLL may be a causative factor.     

前路飘浮法治疗颈椎后纵韧带骨化症初步报告

目的 :对前路飘浮法治疗颈椎后纵韧带骨化症 (OPLL)手术疗效进行初步评析。方法 :对 16例颈椎O PLL患者行前路飘浮法治疗 ,其中连续型 3例 ,节段型 8例 ,混合型 3例 ,孤立型 2例 ;最长手术节段 3节 ;椎管狭窄率 3 0 %～ 70 %。所有患者均采用钛板、钛网行颈椎重建。术后对近期结果随访 ,并按日本矫形外科协会 (JOA)评分系统评分。结果 :平均随访时间 6个月 ,平均恢复率为 68 2 %。无脑脊液漏、神经损伤等并发症发生。颈椎融合良好。结论 :前路飘浮法适合于大多数OPLL患者 ;新型颈椎内固定系统扩大了前路OPLL手术适应证     

胸椎黄韧带骨化症的治疗方法选择

目的研究胸椎黄韧带骨化症（ｏｓｓｉｆｉｃａｔｉｏｎｏｆｌｉｇａｍｅｎｔｕｍｆｌａｖｕｍ,ＯＬＦ）诊断与手术治疗的特点。方法采用回顾性研究方法对手术治疗的胸椎ＯＬＦ的病例进行总结分析。结果总计７２例ＯＬＦ,其中局灶型１５例,连续型４１例,跳跃型１６例;３７．５％合并颈椎后纵韧带骨化症（ｏｓｓｉｆｉｃａｔｉｏｎｏｆｐｏｓｔｅｒｉｏｒｌｏｎｇｉｔｕｄｉｎａｌｌｉｇａｍｅｎｔ,ＯＰＬＬ）,１９．４％合并胸椎ＯＰＬＬ,９．７％合并胸椎间盘突出,１．４％同时合并颈、胸、腰椎ＯＰＬＬ,９．７％合并腰椎间盘突出。结论上述特点是胸椎ＯＬＦ诊断及选择治疗方法时要特别考虑的因素。“揭盖式”椎管后壁切除减压是治疗本病安全、有效的手术方法。     

Ossification of the spinal ligament. A radiographic reevaluation in Bologna, Italy

A radiographic reevaluation of cervical spine films of 1,258 adult patients and of thoraco-lumbar spine films of 488 of these was performed at the Rizzoli Orthopaedic Institute (Bologne, Italy), in order to detect ossification of the posterior longitudinal ligament (OPLL), the anterior longitudinal ligament (OALL), the yellow ligament (OYL) and the nuchal ligament at the cervical level, and OPLL, OALL and OYL at the thoraco-lumbar level. The incidence of OALL, OYL and ossification of the nuchal ligament corresponded with those previously reported in the literature. Cervical OPLL was found in 1.83%, with a definite prevalence in the 45-64 age group where the figure was 2.83%. This incidence is much higher than that hitherto reported in Caucasians, and is nearly the same as that in Japan. Possible explanations for this discrepancy are proposed.     

颈椎后纵韧带骨化症术后骨化进展分析

目的 研究颈椎后纵韧带骨化(ossification of posterior longitudinal ligament,OPLL)症术后骨化进展情况.方法 对2001年1月至2007年12月手术治疗的95例颈椎OPLL患者进行回顾性研究,男72例,女23例;年龄40～73岁,平均56.3岁;随访时间1～6年,平均3.1年.颈椎前路手术36例,颈椎后路全椎板减压固定手术57例,前后路联合手术2例.根据术前、术后随访时的X线、CT及MR影像学资料对骨化进展情况进行测量,并通过统计分析性别、年龄、涉及C3OPLL、伴胸椎OPLL、骨化类型、随访时间、手术方式、日本矫形外科学会评分(Japanese orthopaedic association scores,JOA评分)及改善率与骨化术后进展的关系.结果 95例颈椎OPLL术后随访患者中,术后骨化进展39例,男28例,女11例;手术时年龄41～71岁,平均55.9岁;年龄≤49岁12例,50～59岁12例,60～69岁12例,年龄≥70岁3例.颈椎OPLL后路手术后骨化进展有35例,而前路手术后骨化进展仅4例.以骨化物长度和(或)厚度进展≥2mm为标准,单纯骨化长度进展4例;骨化长度、厚度均进展33例;单纯骨化厚度进展2例.骨化长度进展2～20 mm,平均(7.74±4.71)mm;骨化厚度进展2～6 mm,平均(2.67±1.51)mm.在术后1～3年内骨化进展速度呈下降趋势,4～6年骨化则有部分加速趋势.JOA评分及其改善率在术后3年内达到最佳值.统计结果 显示颈椎OPLL术后骨化进展与患者年龄、手术方式以及涉及C3OPLL明显相关.结论 颈椎OPLL术后骨化进展有相当的发生率,涉及C3OPLL、行颈椎后路全椎板切除手术、年轻的颈椎OPLL患者其骨化进展率相对较高.在中短期(1～6年)随访时间内,JOA评分及其改善率受骨化进展影响不大.     

Association between serum leptin and bone metabolic markers, and the development of heterotopic ossification of the spinal ligament in female patients with ossification of the posterior longitudinal ligament

Obesity is a risk factor for ossification of the posterior longitudinal ligament (OPLL) of the spine, which is characterized by heterotopic bone formation in the posterior longitudinal spinal ligament. Hyperleptinemia is a common feature of obese people and leptin is believed to be an important factor in the pathogenesis of OPLL. However, the association between leptin and bone metabolism and the development of OPLL is not understood fully. The objective of the present study was to determine the association between serum leptin concentration and bone metabolic markers and the extent of heterotopic ossification of the spinal ligament in patients with OPLL. The serum concentrations of leptin, insulin, fructosamine, bone-specific alkaline phosphatase, and carboxyterminal propeptide of type I procollagen, urine deoxypyridinoline levels, and the number of vertebrae with OPLL involvement were measured in 125 (68 males and 57 females) patients with OPLL. The correlation between leptin and these other factors was then examined. Serum leptin and insulin concentrations were increased significantly in OPLL females compared to non-OPLL female controls. In the females with OPLL, serum leptin concentrations corrected for body mass index correlated positively with the number of vertebrae with OPLL involvement. In females, serum leptin levels were significantly higher in patients in whom OPLL extended to the thoracic and/or lumbar spine than in patients in whom OPLL was limited to the cervical spine. Our results suggest that hyperleptinemia, in combination with hyperinsulinemia, may contribute to the development of heterotopic ossification of the spinal ligament in female patients with OPLL.     

Clinical analysis of ossified thoracic ligaments and thoracic disc hernia]

Thoracic lesions present several clinical problems, particularly in their diagnosis and treatment, compared with cervical or lumbar lesions. Since 1983, 18 cases of thoracic space lesions, excluding spinal tumors or trauma have been experienced: nine cases of ossification of yellow ligament (OYL), five of ossification of posterior longitudinal ligament (OPLL), and four of disc hernia (DH). In these 18 patients, problems of clinical manifestations, neuroradiological examination, and surgical approaches are analyzed and discussed. As clinical manifestations, there was a preponderant occurrence in males in the OYL group, while in the OPLL group all the patients were females. OYL and DH occurred at lower thoracic levels. Thirteen of the 18 patients showed combined lesions either in the cervical or in the lumbar regions, such as cervical OPLL, cervical spondylosis, lumbar DH, and lumbar canal stenosis. In the neuroradiological examinations diagnosis of the upper thoracic lesions was difficult. Computed tomography (CT) scan with intrathecal metrizamide injection seemed essential for examination of ossified thoracic lesions. However, because CT imaging of the entire spine is impractical, efficient use of this examination requires previous localization of the offending vertebral level from either the neurological findings or other neuroradiological examinations such as myelography. Magnetic resonance imaging seemed most useful for ruling out the thoracic compressing lesions. As for surgical approaches, posterior decompression was effective for OYL and the anterior approach was useful for OPLL and DH. In patients with "tandem lesions," neurological and neuroradiological findings played an important role in deciding the responsible site.     

胸椎后纵韧带骨化的临床特点及治疗策略

目的回顾研究手术治疗胸椎后纵韧带骨化症(OPLL)的临床特点及治疗方法。方法1991至2005年手术治疗胸椎OPLL55例,男19例,女36例;年龄35～73岁,平均51.9岁。均伴有脊髓损害。手术方式包括单纯椎管后壁切除术34例、前方OPLL切除减压术15例以及前后路联合手术6例。结果55例中36例(65.5%)合并胸椎黄韧带骨化(OLF),18例(32.7%)合并颈椎OPLL。单纯发生于上胸椎的OPLL13例(23.6%),中胸椎12例(21.8%),下胸椎及胸腰段17例(30.9%),广泛分布者13例(23.6%)。43例获得随访,平均随访时间47.1个月(6～168个月)。37例神经功能有改善,改善率为76.6%,无改善2例,加重4例。前方入路获随访者13例,其中3例症状加重,余改善率平均为82.9%(42.9%～100%)。后路椎管后壁切除术获随访者25例,1例无改善,1例加重,余改善率平均为72.6%(22.2%～100%)。前后路联合手术获随访5例,1例无改善,余改善率平均为83.9%。结论胸椎OPLL常合并胸椎OLF及颈椎OPLL。上胸椎OPLL合并颈椎管狭窄可一期行颈后路单开门及上胸椎椎管后壁切除术。两个节段以内的OPLL且不合并有造成脊髓压迫的胸椎OLF可行前路OPLL切除减压术,否则行后路椎管后壁切除术。单节段的OPLL合并胸椎OLF可行前后路联合手术。     

Spinal deformity and instability after multilevel cervical laminectomy

Sixty-four patients who had undergone multilevel cervical laminectomy were studied for postoperative spinal deformity and instability. Special attention was given to patients with cervical spondylosis (CS), ossification of the posterior longitudinal ligament (OPLL), and spinal cord tumors. Twenty-three (36%) of 64 patients showed postoperative changes in curvature type and 9 (14%) had developed spinal deformity (kyphotic or meandering-type curvature). In two juvenile patients, the deformity developed soon after operation and spinal fusion was required to prevent neurologic complications. In the adult cases, contrary to the hitherto accepted concept, long-term follow-up revealed the tendency of the deformity to develop more frequently in OPLL cases than in CS cases. Mobility of the cervical spine was reduced considerably after laminectomy, both in CS and OPLL cases. There was no adult patient who required further operation for severe deformity or instability after laminectomy. Extensive laminectomy, even including the C2 lamina, seemed to have no adverse effect on the stability of the cervical spine.     

螺旋CT三维重建在颈椎后纵韧带骨化中的应用

目的：探讨螺旋CT三维重建显示颈椎后纵韧带骨化的价值和临床意义。方法：回顾性分析21例颈椎后纵韧带骨化的螺旋CT扫描资料。结果：颈椎后纵韧带骨化按Hirabayashi分型，节段型3例，连续型9例，混合型5例，其它型4例。结论：螺旋CT三维重建能清晰显示颈椎后纵韧带骨化的范围，厚度，形状。三维重建有助于手术入路设计，有助于理解骨化的复杂性。螺旋CT是颈椎后纵韧带骨化最好的检查方法，应该常规使用。     

颈椎后纵韧带骨化症的手术治疗

目的探讨颈椎后纵韧带骨化症手术治疗方法及其疗效。方法回顾性分析2002年1月至2008年1月我院65例颈椎后纵韧带骨化症手术治疗病例。均有程度不等的脊髓压迫症状。41例合并发育性颈椎管狭窄,平均椎管狭窄率42．1％。术前均行X线、CT平扫加矢状位重建和MRI检查。其中23例行前路手术,37例行后路手术,5例行前后路联合手术。结果65例获6～72个月随访,平均随访时间19个月。根据日本矫形外科学会评分标准,颈前路手术平均改善率70％,颈后路手术平均改善率66．3％,颈前后路联合手术平均改善率75．4％。术后并发节段性神经根麻痹5例。结论根据患者病情和影像学表现,尤其是CT矢状位重建,仔细分析后纵韧带骨化部位、范围及椎管狭窄率,选择合适手术方法,方能减少并发症,提高手术疗效。     

后纵韧带钩辅助下颈椎后纵韧带骨化物切除减压术

目的探讨后纵韧带钩辅助下颈椎后纵韧带骨化物前路切除的适应证、方法及其临床效果。方法患者19例,男14例,女5例;年龄51-71岁,平均59岁。术前影像学检查结果示后纵韧带骨化物局限型6例,分节型13例;椎管狭窄率32％-75％,平均54％。术前神经功能JOA评分4-14分,平均9．6分。行颈前路常规手术入路,椎体开槽切骨达椎体后壁,范围超过后纵韧带骨化灶。利用后纵韧带钩插入后纵韧带下,钩起后纵韧带及骨化物,在后纵韧带与硬膜间形成一间隙,直视下用超薄型枪状咬骨钳切除后纵韧带及骨化物,而后植骨固定,恢复颈椎稳定性。结果随访6-36个月,平均16个月。术后JOA评分8～16分,平均12．8分,恢复率42％＇-92％,其中疗效优9例,良7例,可3例,优良率84．2％。4例患者术后并发脑脊液漏,保守治疗后均获得痊愈。术后CT和MR检查显示骨化后纵韧带切除完全,脊髓和硬膜囊形态恢复良好。结论后纵韧带钩可提高颈椎前路手术切除后纵韧带骨化物的安全性和有效性,适用于局限型和分节型、切除范围在两个椎节之间的颈椎后纵韧带骨化症患者。     

Immunohistochemistry of symptomatic hypertrophy of the posterior longitudinal ligament with special reference to ligamentous ossification

STUDY DESIGN: Immnunohistochemical staining of the thickened posterior longitudinal ligament of the cervical spine. OBJECTIVES: To clarify the histological characteristics of hypertrophy of the posterior longitudinal ligament (HPLL) of the cervical spine and the relationship between HPLL and ossification of the posterior longitudinal ligament (OPLL). SETTING: Aichi Medical University, Aichi, Japan. METHODS: Eight specimens of HPLL and two of OPLL were obtained during anterior decompressive surgery on the cervical spine from patients with myelopathy. Hematoxylin and eosin staining, alcian blue staining and immunohistochemical staining with antibodies against bone morphogenetic protein (BMP), transforming growth factor (TGF)-beta, proliferating cell nuclear antigen (PCNA), alkaline phosphatase (ALP) and osteopontin (OPN) were carried out on the specimens. RESULTS: HPLL showed hyalinoid degeneration, the proliferation of chondrocytes and fibroblast-like spindle cells, infiltration of vessels and small ossification. In four cases, chondroid tissue was prominent with chondrocytes, which were expressed by ALP and OPN. The cells in HPLL were weakly or moderately stained by BMP, TGF-beta and PCNA. Their expression was similar to that of OPLL. Immunohistochemical staining was negative for all cells in the control cases. CONCLUSIONS: Histological and biochemical evidence supports the hypothesis that HPLL transforms into OPLL. The positive expression of BMP and TGF-beta in HPLL cells of myelopathic patients, and their similarity to OPLL, suggest that these cells have the potential to differentiate into osteogenic cells. Of note, neither BMP nor TGF-beta was demonstrated in the PLL of control subjects. Furthermore, the expression of chondrocytes by ALP and OPN in cartilage-prominent HPLL suggests that the cartilage can be replaced by new bone.