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Ossification of the cervical ligamentum flavum
234
Surg Neurol 1991;35:234-8
Ossification of the Cervical Ligamentum Flavum Satoshi Kobayashi, M.D., Keiichi Okada, M.D., Kimio Onoda, M.D., and Satoru Horikoshi, M.D. Department of Neurosurgery, Isesaki Municipal Hospital, Gunma, Japan
Kobayashi S, Okada K, Onoda K, Horikoshi S. Ossification of the cervical ligamentum flavum. Surg Neurol 1991;35:234-8.
A case of a 61-year-old man with ossification of the cervical ligamentum flavum is reported. The ossification was located on the left side of C3-4. The symptoms improved with laminectomy and resection. Ossification of the ligamentum flavum usually occurs in the lower thoracic spine, and is rare in the cervical region. Including the present one, only eight cases have been reported to our knowledge. The clinical features and pathogenesis are discussed. KEYWORDS: Cervical spine; Ossification; Ligamentum flavum
The first case of radiculomyelopathy due to ossification of the ligamentum flavum was reported by Yamaguchi et al [15] in 1960. Since then, such reports have been numerous. However, in most cases, it has been found in the thoracic and lumbar regions, and rarely in the cervical region. We encountered a case of ossification of the cervical ligamentum flavum, and its clinical features and pathogenesis are discussed in the following. Case
Report
A 61-year-old man was admitted with spastic left hemiparesis beginning 3 years previously and clumsiness of the left hand for 5 years. Working as a carpenter, he fell from a roof when he was in his twenties and twice in his thirties. Physical examination revealed a mild thoracic scoliosis. Motor testing showed spastic slight left hemiparesis. Muscle tendon reflexes were increased on the left side. Superficial sensation was diminished in the distal part of the left extremities. Deep sensation was diminished below the iliac crest bilaterally. Muscle atrophy and bladder disturbances were not found. Blood and chemical analysis results were within normal limits. X-ray films of the cervical spine showed a Address reprint requests to: Satoshi Kobayashi, M.D., Department of Neurosurgery, Gunma University School of Medicine, 3-39-22, Showa-machi, Maebashi-shi, Gunma-ken, 371, Japan. Received April 30, 1990; accepted August 27, 1990.
© 1991 by ElsevierSciencePublishingCo., Inc.
right cervical scoliosis in the anteroposterior view. Xray films of the thoracic and lumbar spine showed no calcification or ossification of the spinal ligament. Tomography (Figure 1 A) showed an abnormal shadow in the posterior portion of the spinal canal at C3-4. Myelography (Figure 1 B) showed anterior indentation and incomplete block at C3-4 in the lateral view. Metrizamide computed tomography (CT) myelography (Figure 2) showed a nodular mass projecting into the spinal canal from the left posterior medial side at the level of C3-4. A C-3 to C-5 wide laminectomy was performed. The ossification indented the dural sac anteriorly from the left side of the midline at C3-4. It was within the fibrous tissue and 6 × 3 mm in size. No continuity between the ossification and laminae could be found. The ossification did not adhere to the dura mater. Following removal of the ossification, normal dural pulsation became immediately evident. No fracture was found in the resected laminae. Postoperatively, the left hemiparesis improved gradually. Postoperative CT myelography (Figure 3) showed excellent visualization of the subarachnoid space. Histological examination of the surgical specimen (Figure 4) showed elastic bundles and bony tissue. Between the two, a transitional state consisting of cartilage was present. LameUar bone structure and marrow formation were observed within the bony tissue.
Discussion Ossification, calcification, and calcium pyrophosphate dihydrate crystal deposition disease (CPPDcdd) of the ligamentum flavum are sometimes confused because of inadequate histological examination. Kawano et al [4] pointed out that calcification of the ligamentum flavum and CPPDcdd belong to a single category. Histological examination shows ossification and calcification of the ligament flavum to be completely different conditions [9,12]. Based on symptoms and radiological findings, calcification of the ligamentum flavum, fracture of laminae, 0090-3019/91/$3.50
Surg N e u r o l 1991;35:234-8
A
235
B
F i g u r e 1. (A) Cervical tomography, sagittal section: ossification (arrow) is apparent in the posterior portion of the spinal canal at C3°4 as a moundlike bony excrescencearising from the lamina of C-4. (B) Myelography: lateral view showing anterior indentation and incomplete blockage at C3-4 (arrow).
T a b l e 1. Reported Cases of Ossification of Cervical Ligamentum Flavum Author
Age/sex (years)
Kubota et al [7] Present report (1990) Ohta et al [11] Kamakura et al [3]
39/M 61/M 75/F 61/F
Koizumi [6]
55/M
C2-3 C3-4 C5-6 C5-6 C6-7 Lower
Kirita et al [5] Seichi et al [13]
27/F 70/M
C-7 C6-7
---
Minami et al [8]
40/M
C-7-Th-1
--
Level
Laterality Right, left Left Right Right, left Right --
Location
Ossification of spinal ligament
Initial symptom
Lamina Lamina Lamina Lamina
Th-OYL C-OPLL L-narrow canal (--)
Numbness o f the fingers o f the right hand Clumsiness o f the left hand Numbness and pain o f the extremities Paresthesia o f the extremities
Lamina
C, Th-OPLL, Th-OYL -Th--OYL
Tenseness o f the lower extremities
-Lamina, facet joint --
(--)
Numbness o f the right leg Pain o f the left arm Hypesthesia of the left thigh, weakness o f the left leg
Abbreviations: C, cervical; F, female; L, lumbar; M, male; OPLL, ossification of the posterior longitudinal ligament; OYL, ossification of the ligamentum flavum; Th, thoracic; (--), absent; --, unknown.
236
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1991;35:234-8
A
B
C
D
Figure 2. Metrizamide CT myelography. (A) C2-3, (B) C-3, (C) C3-4, (D) C-4. At the level ofC2-3 and C-3, the left side of the lamina is hypertrophied. The spinal cord and subarachnoid space are deformed posteriorly. At the level of C3-4, the ossification projects mto the spinal canal from the left posterior medial side and the spinal cord is most severely compressed. At the level of C-4, slight ossification of the posterior longtudinal ligament is apparent. A remarkable narrow canal can be seen from C-3 to C-4.
osteoid osteoma, and anomaly of laminae were considered possibilities. Radiological investigation failed to indicate any anomaly of the spine or any other skeletal components associated with congenital disorder. At operation no fracture was recognized in the resected laminae. Histological examination o f the surgical specimen showed endochondral ossification, and lamellar bone structure and marrow formation were observed in the bony tissue. These findings differ from those of calcification. In calcification, calcified granules were deposited within the degenerated ligamentous fibers and no mature
bone had formed within the ligament. The diagnosis of ossification was made on the basis o f these findings. Ossification of the ligamentum flavum is a relatively common disorder. Hasue et al [1] reported it in 49 (41.9%) o f 117 patients. But it usually occurs in thoracic (38.5%) and lumbar regions (26.5%), and rarely in the cervical region (0.9%). The eight cases [ 3,5-8,11,14 ] so far reported showed the following features: (1) All were Japanese. (2) The average age was 53.5 years. (3) The ratio of males to females was 5:3. (4) Four of seven patients showed
Ossification of the Ligamentum Flavum
Figure 3. Postoperative CT myelography at C3-4 shows excellent visualization of the subarachnoid space, but the atrophic cord is unchanged.
ossification of other spinal ligaments. (5) It was found in the middle and lower cervical region. (6) The common initial symptom was sensory disturbance of extremities. Calcification characteristically occurs in the cervical region of older women, and hormonal changes are thought to be involved [10]; this is not the case with ossification. The etiology and mechanism of ossification remain unclear. The reason ossification is frequently observed in thoracic and lumbar vertebrae and rarely in the cervical vertebrae is not known. However, two possible causative factors are considered.
Surg Neurol 1991;35:234-8
237
The first factor is the anatomical difference between cervical and thoracic ligamentum flavum [2]. The ligamentum flavum consists of an "interlaminar portion" and a "capsular portion." From C2-3 to C5-6, the interlaminar portion is close to the lamina, but elastic fiber disappears in the capsular portion, and the ligamentum flavum does not adhere to the bony tissue directly in such a lateral portion. Below C6-7, including the thoracic and lumbar regions, the ligamentum flavum adheres to the bony tissue directly in both interlaminar and capsular portions. From study on a cadaver, ossification appears at the ligament-osseous junction (enthesis). Ossification of the ligamentum flavum thus hardly occurs in the capsular portion of the cervical spine, where the ligament is not close to the bony tissue directly. Tanaka et al [14] pointed out that above the level of C5-6, ossification occurs in the interlaminar portion, and below the level of C6-7, it always involves the capsular portion. The second factor is the difference in tension operating in the ligamentum flavum [2]. Strong tension affects the cervical ligamentum flavum, while the ligament in the thoracic region seldom becomes loose and the tension is always static. This difference in tension greatly influences the process of ossification. Hotta [2] reported that histological findings for the ligament-osseous junction (enthesis) in the interlaminar portion differ for the cervical and thoracic regions. In the
Figure 4. (A, B) Photomicrograph of a surgical specimen showing elastic bundles and bony tissue. The cartilage layer is present between the two. Lamellar bone structure and marrow formation can be seen within the bony tissue (hematoxylin and eosin stain × 25).
A
238
Surg Neurol 1991;35:234-8
Kobayashi et al
Figure 4. (Continued)
thoracolumbar spine, decreased elastic fibers, hyalinized collagen fibers, emergence of fibrocartilaginoid cells, and intraligamentous calcification were noted. However, in the cervical spine, elastic fibers were close to the bony tissue without the above histological findings. This may possibly be related to difference in tension. In the present case, the patient's occupation was that of a carpenter, and repeated minor trauma may cause ossification of the ligament.
References 1. Hasue M, Kikuchi S, Fujiwara M, Sakuyama Y, Sakamoto T, Miura H, Kawasaki S. Roentgenographic analysis of ossification of the spinal ligament; with special reference to the finding of the whole spine. Seikeigeka 1980;31:1179-86. 2. Hotta Y. Anatomical study of the yellow ligament of spine with special reference to its ossification. J Jpn Orthop Assoc 1985; 59:311-25. 3. Kamakura K, Furukawa T, Takasu T, Mannen T, Toyokura Y. Cervical myelopathy due to ossification of ligamenta flava. Rinsho Shinkeigaku 1978;18:96-102. 4. Kawano N, Matsuno T, Miyazawa S, Iida H, Yada K, Kobayashi N, Iwasaki Y. Calcium pyrophosphate dihydrate crystal deposition disease in the cervical ligamentum flavum. J Neurosurg 1988;68:613-20. 5. Kirita Y, Miyazaki K, Lin D, Nosaka K, Shima M, Yamamura H, Kasahara K, Tamaki S. Surgical treatment for the ossification of the lig. flavum. Cent Jpn J Orthop Traumat 1973;16:814-7.
6. Koizumi M. 3 cases of spinal cord paralysis proved by ligamenta flava ossification. Rinsho Geka 1962;17:1181-8. 7. Kubota M, Baba I, Sumida I. Myelopathy due to ossification of the ligamentum flavum of the cervical spine. A report of two cases. Spine 1981;6:553-9. 8. Minami Y, Maeyama I, Kawakami T, Sakinaga Y. A case of cervical myelopathy due to ossification of the ligamentum flavum. Seikei Geka Saigai Geka 1985;34:335-7. 9. Miyasaka K, Kaneda K, Sato S, Iwasaki Y, Abe S, Takei H, Tsuru M, Tashiro K, Abe H, Fujioka Y. Myelopathy due to ossification or calcification of the ligamentum flavum: radiologic and histologic evaluations. AJNR 1983;4:629-32. 10. Nakajima K, Miyaoka M, Sumie H, Nakazato T, Ishii S. Cervical radiculomyelopathy due to calcification of the ligamenta tiara. Surg Neurol 1984;21:479-88. 11. Ohta S, et al. A case of cervical myelopathy due to ossification of the ligamentum flavum. Cent Jpn J Orthop Traumat 1982; 25:966-8. 12. Oka S. Scanning electron microscopic observation of ossification and calcification of the iigamentum flavum. Arch Jpn Chir 1982; 51:671-94. 13. Seichi A, Katoh H, Tanaka H, Tuzuki N. Radiculomyelopathy due to ossification of the ligamentum flavum of the cervical spine; a case report. Seikeigeka 1988;39:929-32. 14. Tanaka H, et al. Anatomical study of ossification and calcification of the yellow ligament of spine with reference to the distribution of the yellow ligament. Rinsho Seikei Geka 1988;23:411-7. 15. Yamaguchi H, et al. A case of the ossification of the ligamentum flavum with spinal cord tumor symptoms. Seikeigeka 1960;11:951-6.
Surg Neurol 1991;35:234-8
Ossification of the Cervical Ligamentum Flavum Satoshi Kobayashi, M.D., Keiichi Okada, M.D., Kimio Onoda, M.D., and Satoru Horikoshi, M.D. Department of Neurosurgery, Isesaki Municipal Hospital, Gunma, Japan
Kobayashi S, Okada K, Onoda K, Horikoshi S. Ossification of the cervical ligamentum flavum. Surg Neurol 1991;35:234-8.
A case of a 61-year-old man with ossification of the cervical ligamentum flavum is reported. The ossification was located on the left side of C3-4. The symptoms improved with laminectomy and resection. Ossification of the ligamentum flavum usually occurs in the lower thoracic spine, and is rare in the cervical region. Including the present one, only eight cases have been reported to our knowledge. The clinical features and pathogenesis are discussed. KEYWORDS: Cervical spine; Ossification; Ligamentum flavum
The first case of radiculomyelopathy due to ossification of the ligamentum flavum was reported by Yamaguchi et al [15] in 1960. Since then, such reports have been numerous. However, in most cases, it has been found in the thoracic and lumbar regions, and rarely in the cervical region. We encountered a case of ossification of the cervical ligamentum flavum, and its clinical features and pathogenesis are discussed in the following. Case
Report
A 61-year-old man was admitted with spastic left hemiparesis beginning 3 years previously and clumsiness of the left hand for 5 years. Working as a carpenter, he fell from a roof when he was in his twenties and twice in his thirties. Physical examination revealed a mild thoracic scoliosis. Motor testing showed spastic slight left hemiparesis. Muscle tendon reflexes were increased on the left side. Superficial sensation was diminished in the distal part of the left extremities. Deep sensation was diminished below the iliac crest bilaterally. Muscle atrophy and bladder disturbances were not found. Blood and chemical analysis results were within normal limits. X-ray films of the cervical spine showed a Address reprint requests to: Satoshi Kobayashi, M.D., Department of Neurosurgery, Gunma University School of Medicine, 3-39-22, Showa-machi, Maebashi-shi, Gunma-ken, 371, Japan. Received April 30, 1990; accepted August 27, 1990.
© 1991 by ElsevierSciencePublishingCo., Inc.
right cervical scoliosis in the anteroposterior view. Xray films of the thoracic and lumbar spine showed no calcification or ossification of the spinal ligament. Tomography (Figure 1 A) showed an abnormal shadow in the posterior portion of the spinal canal at C3-4. Myelography (Figure 1 B) showed anterior indentation and incomplete block at C3-4 in the lateral view. Metrizamide computed tomography (CT) myelography (Figure 2) showed a nodular mass projecting into the spinal canal from the left posterior medial side at the level of C3-4. A C-3 to C-5 wide laminectomy was performed. The ossification indented the dural sac anteriorly from the left side of the midline at C3-4. It was within the fibrous tissue and 6 × 3 mm in size. No continuity between the ossification and laminae could be found. The ossification did not adhere to the dura mater. Following removal of the ossification, normal dural pulsation became immediately evident. No fracture was found in the resected laminae. Postoperatively, the left hemiparesis improved gradually. Postoperative CT myelography (Figure 3) showed excellent visualization of the subarachnoid space. Histological examination of the surgical specimen (Figure 4) showed elastic bundles and bony tissue. Between the two, a transitional state consisting of cartilage was present. LameUar bone structure and marrow formation were observed within the bony tissue.
Discussion Ossification, calcification, and calcium pyrophosphate dihydrate crystal deposition disease (CPPDcdd) of the ligamentum flavum are sometimes confused because of inadequate histological examination. Kawano et al [4] pointed out that calcification of the ligamentum flavum and CPPDcdd belong to a single category. Histological examination shows ossification and calcification of the ligament flavum to be completely different conditions [9,12]. Based on symptoms and radiological findings, calcification of the ligamentum flavum, fracture of laminae, 0090-3019/91/$3.50
Surg N e u r o l 1991;35:234-8
A
235
B
F i g u r e 1. (A) Cervical tomography, sagittal section: ossification (arrow) is apparent in the posterior portion of the spinal canal at C3°4 as a moundlike bony excrescencearising from the lamina of C-4. (B) Myelography: lateral view showing anterior indentation and incomplete blockage at C3-4 (arrow).
T a b l e 1. Reported Cases of Ossification of Cervical Ligamentum Flavum Author
Age/sex (years)
Kubota et al [7] Present report (1990) Ohta et al [11] Kamakura et al [3]
39/M 61/M 75/F 61/F
Koizumi [6]
55/M
C2-3 C3-4 C5-6 C5-6 C6-7 Lower
Kirita et al [5] Seichi et al [13]
27/F 70/M
C-7 C6-7
---
Minami et al [8]
40/M
C-7-Th-1
--
Level
Laterality Right, left Left Right Right, left Right --
Location
Ossification of spinal ligament
Initial symptom
Lamina Lamina Lamina Lamina
Th-OYL C-OPLL L-narrow canal (--)
Numbness o f the fingers o f the right hand Clumsiness o f the left hand Numbness and pain o f the extremities Paresthesia o f the extremities
Lamina
C, Th-OPLL, Th-OYL -Th--OYL
Tenseness o f the lower extremities
-Lamina, facet joint --
(--)
Numbness o f the right leg Pain o f the left arm Hypesthesia of the left thigh, weakness o f the left leg
Abbreviations: C, cervical; F, female; L, lumbar; M, male; OPLL, ossification of the posterior longitudinal ligament; OYL, ossification of the ligamentum flavum; Th, thoracic; (--), absent; --, unknown.
236
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K0bayashiet al
1991;35:234-8
A
B
C
D
Figure 2. Metrizamide CT myelography. (A) C2-3, (B) C-3, (C) C3-4, (D) C-4. At the level ofC2-3 and C-3, the left side of the lamina is hypertrophied. The spinal cord and subarachnoid space are deformed posteriorly. At the level of C3-4, the ossification projects mto the spinal canal from the left posterior medial side and the spinal cord is most severely compressed. At the level of C-4, slight ossification of the posterior longtudinal ligament is apparent. A remarkable narrow canal can be seen from C-3 to C-4.
osteoid osteoma, and anomaly of laminae were considered possibilities. Radiological investigation failed to indicate any anomaly of the spine or any other skeletal components associated with congenital disorder. At operation no fracture was recognized in the resected laminae. Histological examination o f the surgical specimen showed endochondral ossification, and lamellar bone structure and marrow formation were observed in the bony tissue. These findings differ from those of calcification. In calcification, calcified granules were deposited within the degenerated ligamentous fibers and no mature
bone had formed within the ligament. The diagnosis of ossification was made on the basis o f these findings. Ossification of the ligamentum flavum is a relatively common disorder. Hasue et al [1] reported it in 49 (41.9%) o f 117 patients. But it usually occurs in thoracic (38.5%) and lumbar regions (26.5%), and rarely in the cervical region (0.9%). The eight cases [ 3,5-8,11,14 ] so far reported showed the following features: (1) All were Japanese. (2) The average age was 53.5 years. (3) The ratio of males to females was 5:3. (4) Four of seven patients showed
Ossification of the Ligamentum Flavum
Figure 3. Postoperative CT myelography at C3-4 shows excellent visualization of the subarachnoid space, but the atrophic cord is unchanged.
ossification of other spinal ligaments. (5) It was found in the middle and lower cervical region. (6) The common initial symptom was sensory disturbance of extremities. Calcification characteristically occurs in the cervical region of older women, and hormonal changes are thought to be involved [10]; this is not the case with ossification. The etiology and mechanism of ossification remain unclear. The reason ossification is frequently observed in thoracic and lumbar vertebrae and rarely in the cervical vertebrae is not known. However, two possible causative factors are considered.
Surg Neurol 1991;35:234-8
237
The first factor is the anatomical difference between cervical and thoracic ligamentum flavum [2]. The ligamentum flavum consists of an "interlaminar portion" and a "capsular portion." From C2-3 to C5-6, the interlaminar portion is close to the lamina, but elastic fiber disappears in the capsular portion, and the ligamentum flavum does not adhere to the bony tissue directly in such a lateral portion. Below C6-7, including the thoracic and lumbar regions, the ligamentum flavum adheres to the bony tissue directly in both interlaminar and capsular portions. From study on a cadaver, ossification appears at the ligament-osseous junction (enthesis). Ossification of the ligamentum flavum thus hardly occurs in the capsular portion of the cervical spine, where the ligament is not close to the bony tissue directly. Tanaka et al [14] pointed out that above the level of C5-6, ossification occurs in the interlaminar portion, and below the level of C6-7, it always involves the capsular portion. The second factor is the difference in tension operating in the ligamentum flavum [2]. Strong tension affects the cervical ligamentum flavum, while the ligament in the thoracic region seldom becomes loose and the tension is always static. This difference in tension greatly influences the process of ossification. Hotta [2] reported that histological findings for the ligament-osseous junction (enthesis) in the interlaminar portion differ for the cervical and thoracic regions. In the
Figure 4. (A, B) Photomicrograph of a surgical specimen showing elastic bundles and bony tissue. The cartilage layer is present between the two. Lamellar bone structure and marrow formation can be seen within the bony tissue (hematoxylin and eosin stain × 25).
A
238
Surg Neurol 1991;35:234-8
Kobayashi et al
Figure 4. (Continued)
thoracolumbar spine, decreased elastic fibers, hyalinized collagen fibers, emergence of fibrocartilaginoid cells, and intraligamentous calcification were noted. However, in the cervical spine, elastic fibers were close to the bony tissue without the above histological findings. This may possibly be related to difference in tension. In the present case, the patient's occupation was that of a carpenter, and repeated minor trauma may cause ossification of the ligament.
References 1. Hasue M, Kikuchi S, Fujiwara M, Sakuyama Y, Sakamoto T, Miura H, Kawasaki S. Roentgenographic analysis of ossification of the spinal ligament; with special reference to the finding of the whole spine. Seikeigeka 1980;31:1179-86. 2. Hotta Y. Anatomical study of the yellow ligament of spine with special reference to its ossification. J Jpn Orthop Assoc 1985; 59:311-25. 3. Kamakura K, Furukawa T, Takasu T, Mannen T, Toyokura Y. Cervical myelopathy due to ossification of ligamenta flava. Rinsho Shinkeigaku 1978;18:96-102. 4. Kawano N, Matsuno T, Miyazawa S, Iida H, Yada K, Kobayashi N, Iwasaki Y. Calcium pyrophosphate dihydrate crystal deposition disease in the cervical ligamentum flavum. J Neurosurg 1988;68:613-20. 5. Kirita Y, Miyazaki K, Lin D, Nosaka K, Shima M, Yamamura H, Kasahara K, Tamaki S. Surgical treatment for the ossification of the lig. flavum. Cent Jpn J Orthop Traumat 1973;16:814-7.
6. Koizumi M. 3 cases of spinal cord paralysis proved by ligamenta flava ossification. Rinsho Geka 1962;17:1181-8. 7. Kubota M, Baba I, Sumida I. Myelopathy due to ossification of the ligamentum flavum of the cervical spine. A report of two cases. Spine 1981;6:553-9. 8. Minami Y, Maeyama I, Kawakami T, Sakinaga Y. A case of cervical myelopathy due to ossification of the ligamentum flavum. Seikei Geka Saigai Geka 1985;34:335-7. 9. Miyasaka K, Kaneda K, Sato S, Iwasaki Y, Abe S, Takei H, Tsuru M, Tashiro K, Abe H, Fujioka Y. Myelopathy due to ossification or calcification of the ligamentum flavum: radiologic and histologic evaluations. AJNR 1983;4:629-32. 10. Nakajima K, Miyaoka M, Sumie H, Nakazato T, Ishii S. Cervical radiculomyelopathy due to calcification of the ligamenta tiara. Surg Neurol 1984;21:479-88. 11. Ohta S, et al. A case of cervical myelopathy due to ossification of the ligamentum flavum. Cent Jpn J Orthop Traumat 1982; 25:966-8. 12. Oka S. Scanning electron microscopic observation of ossification and calcification of the iigamentum flavum. Arch Jpn Chir 1982; 51:671-94. 13. Seichi A, Katoh H, Tanaka H, Tuzuki N. Radiculomyelopathy due to ossification of the ligamentum flavum of the cervical spine; a case report. Seikeigeka 1988;39:929-32. 14. Tanaka H, et al. Anatomical study of ossification and calcification of the yellow ligament of spine with reference to the distribution of the yellow ligament. Rinsho Seikei Geka 1988;23:411-7. 15. Yamaguchi H, et al. A case of the ossification of the ligamentum flavum with spinal cord tumor symptoms. Seikeigeka 1960;11:951-6.