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Takahiro Makino, Takashi Kaito, Hiroyasu Fujiwara, and Kazuo Yonenobu

Object

Although the anatomy of the thoracic pedicle in adolescent idiopathic scoliosis is well known, that of the lumbar pedicle in degenerative lumbar scoliosis is not. The morphometric differences between the pedicles on the concave and convex sides can result in an increased risk of malpositioned pedicle screws. The purpose of this study was to analyze the lumbar pedicle morphology in degenerative lumbar scoliosis using multiplanar reconstructed CT.

Methods

The study group comprised 16 consecutive patients (1 man and 15 women, mean age 70.9 ± 4.5 years) with degenerative lumbar scoliosis characterized by a Cobb angle of at least 30° who underwent preoperative helical CT scans. The CT data in DICOM format were reconstructed, and the following parameters were measured for each pedicle inside the curves: the inner cortical transverse pedicle width (TPWi) and outer cortical transverse pedicle width (TPWo) and axial angle, all on an axial plane, and the inner cortical minimum pedicle diameter (MPDi) and outer cortical minimum pedicle diameter (MPDo) and cephalocaudal inclination of the pedicle, all on the plane perpendicular to the pedicle axis. The cortical thickness and cortical ratio of the pedicles on the axial plane and the plane perpendicular to the pedicle axis were calculated. Data were obtained for a total of 124 pedicles; L-1, 26 pedicles in 13 patients; L-2, 32 pedicles in 16 patients; L-3, 32 pedicles in 16 patients; L-4, 28 pedicles in 14 patients; and L-5, 6 pedicles in 3 patients.

Results

Among the target vertebrae, the TPWi, MPDi, and MPDo were significantly smaller and the axial angle was significantly larger on the concave side than on the convex side (TPWi, 6.37 vs 6.70 mm, p < 0.01; MPDi, 5.15 vs 5.67 mm, p < 0.01; MPDo, 7.91 vs 8.37 mm, p < 0.05; axial angle, 11.79° vs 10.56°, p < 0.01). The cortical ratio of the pedicles was larger on the concave side than on the convex side (on the axial plane, 0.29 vs 0.26, p < 0.05; on the plane perpendicular to the pedicle axis, 0.36 vs 0.32, p < 0.01). These differences were most evident at L-4.

Conclusions

This study demonstrated lumbar pedicle asymmetry in degenerative lumbar scoliosis. The authors speculate that these asymmetrical changes were attributed to the remodeling caused by axial load imbalance and the limited space available for pedicles on the concave side. On the concave side, because of the narrower pedicle diameter and larger axial angle, surgeons should carefully determine screw size and direction when inserting pedicle screws to prevent possible pedicle wall breakage and neural damage.

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Takahiro Makino, Shota Takenaka, Gensuke Okamura, Yusuke Sakai, Hideki Yoshikawa, and Takashi Kaito

Dorsal spinal cord herniation is reportedly a rare condition. Here, the authors report an unusual case of dorsal spinal cord herniation at the thoracolumbar junction presenting with scalloping of ossification of the ligamentum flavum (OLF). A 75-year-old woman with a 2-year history of bilateral leg dysesthesia presented with progressive gait ataxia. Neurological examination showed bilateral patellar tendon hyperreflexia with loss of vibratory sensation and proprioception in her bilateral lower extremities. CT myelography revealed a posterior kink and dorsal herniation of the spinal cord at T11–12, with OLF between T10–11 and T12–L1. In addition, scalloping of the OLF was observed at T11–12 at the site of the herniated spinal cord. This scalloping was first noted 9 years previously and had been gradually progressing. The patient underwent surgical repair of the spinal cord herniation. Subsequently, her spinal cord herniation and vibratory sensation and proprioception in both legs partly improved, but gait ataxia remained unchanged. Dorsal spinal cord herniation reportedly occurs under conditions of vulnerability of the dorsal dura mater. In this case, acquired vulnerability of the dorsal dura mater owing to previous epidural catheter placement into the thoracolumbar space may have resulted in dorsal spinal cord herniation.

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Takashi Kaito, Noboru Hosono, Yoshihiro Mukai, Takahiro Makino, Takeshi Fuji, and Kazuo Yonenobu

Object

Spinal fusion at the L4–5 disc space alters the normal biomechanics of the spine, and the loss of motion at the fused level is compensated by increased motion and load at the other unfused segments. This may lead to deterioration of the adjacent segments of the lumbar spine, called adjacent-segment disease (ASD). In this study, the authors investigate the distracted disc height of the fused segment, caused by cage or bone insertion during surgery, as a novel risk factor for ASD after posterior lumbar interbody fusion (PLIF).

Methods

Radiographic L3–4 ASD is defined by development of spondylolisthesis greater than 3 mm, a decrease in disc height of more than 3 mm, or intervertebral angle at flexion smaller than −5°. Symptomatic ASD is defined by a decrease of 4 points or more on the Japanese Orthopaedic Association scale. Eighty-five patients with L-4 spondylolisthesis treated by L4–5 PLIF underwent follow-up for more than 2 years (mean 38.8 ± 17.1 months). The patients were divided into 3 groups according to the final outcome. Group A comprised those patients without ASD (58), Group B patients had radiographic ASD (14), and Group C patients had symptomatic ASD (13).

Results

The L4–5 disc space distraction by cage insertion was 3.1 mm in the group without ASD, 4.4 mm in the group with radiographic ASD, and 6.2 mm in the group with symptomatic ASD, as measured using lateral spinal radiographs just after surgery. Multivariate analysis showed that distraction was the most significant risk factor.

Conclusions

The excessive distraction of the L4–5 disc space during PLIF surgery is a significant and potentially avoidable risk factor for the development of radiographic, symptomatic ASD.

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Takashi Kaito, Noboru Hosono, Takahiro Makino, Noriyoshi Kaneko, Masato Namekata, and Takeshi Fuji

Object

Double-door laminoplasty using hydroxyapatite (HA) spacers has been widely performed for compressive cervical myelopathy and has provided good neurological outcome. Although HA spacers are used for preventing reclosure of the opened laminae, they are often displaced or dislocated from their original position. The authors investigated the incidence and patterns of postoperative HA spacer displacement to determine the reasons for this unfavorable event.

Methods

Eighty-six patients with compressive myelopathy underwent double-door laminoplasty in which a total of 278 HA spacers were used. The displacement of HA spacers and opened laminae were assessed using postoperative lateral radiographs and CT scans.

Results

Postoperative dorsal migration > 2 mm was found in 116 (42%) of 278 implanted HA spacers. In addition, 33 (38%) of 86 HA spacers rotated > 10° and 29 (34%) of the 86 opened laminae tilted > 10°. Moreover, deformation of the newly formed spinal canal was observed in 51 (59%) of 86 cases, and bone fusion between the HA spacer and spinous process was achieved in only 15 (8.7%) of 172 cases. Neurological worsening and neck pain, however, were not associated with displacement of HA spacers or deformation of the spinal canal.

Conclusions

In double-door laminoplasty, postoperative displacement of the HA spacer with deformation of the enlarged spinal canal occurred frequently. Hydroxyapatite spacers tend to become displaced after surgery. Placing the HA spacer at the base of the spinous process close to the dura mater may prevent postoperative displacement.

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Tsuyoshi Sugiura, Yukitaka Nagamoto, Motoki Iwasaki, Masafumi Kashii, Takashi Kaito, Tsuyoshi Murase, Tetsuya Tomita, Hideki Yoshikawa, and Kazuomi Sugamoto

Object

The upper cervical spine is commonly involved in persons with rheumatoid arthritis (RA). Although 2D measurements have long been used in the evaluation of cervical lesions caused by RA, 2D measurements are limited in their effectiveness for detecting subtle and complex morphological and kinematic changes. The purpose of this study was to elucidate the 3D kinematics of the upper cervical spine in RA and the relationship between 3D morphological changes and decreased segmental rotational motion.

Methods

Twenty-five consecutive patients (2 men and 23 women, mean age 63.5 years, range 42–77 years) with RA (the RA group) and 10 patients (5 men and 5 women, mean age 69.9 years, range 57–82 years) with cervical spondylosis and no involvement of the upper cervical spine (the control group) underwent 3D CT of the cervical spine in 3 positions (neutral, 45° head rotation to the left, and 45° head rotation to the right). The segmental rotation angle from the occiput (Oc) to C-2 was calculated for each participant using a voxel-based registration method, and the 3D destruction of articular facets was quantified using the authors' own parameter, the articular facet index.

Results

The segmental rotation angle was significantly smaller at C1–2 and larger at Oc–C1 in the RA group compared with the control group. The degree of the destruction of the articular facet at C-1 and C-2 correlated with the segmental rotation angle.

Conclusions

In vivo 3D kinematics of the upper cervical spine during head rotation in patients with RA were accurately measured, allowing quantification of the degree of joint destruction for the first time. Joint destruction may play an important role in decreasing segmental motion of the upper cervical spine in RA.

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Noboru Hosono, Masato Namekata, Takahiro Makino, Toshitada Miwa, Takashi Kaito, Noriyoshi Kaneko, and Takeshi Fuji

Object

Although posterior lumbar interbody fusion (PLIF) is an excellent procedure to attain circumferential decompression, it is technically demanding and can lead to various surgical complications. The authors retrospectively reviewed consecutive patients with nonisthmic spondylolisthesis who underwent PLIF to reveal the incidence and risk factors for perioperative complications of PLIF.

Methods

A total of 240 patients underwent PLIF. The fusion level was at L4–5 in 220, L3–4 in 18, and L5–S1 in 2. The medial walls of the fusion segment's facet joints were resected, and the VSP Spine System was used for the pedicle screw instrumentation. The operations were performed by 7 surgeons, who were divided into 4 groups according to their level of experience with spinal surgery.

Results

The average operation time was 175 ± 49 minutes, and the estimated blood loss was 746 ± 489 ml. A total of 90 patients (37.5%) experienced complications; 41 (17%) experienced transient neurological complications, and 18 (7.5%) experienced permanent neurological complications. The mean neurological score according to the Japanese Orthopaedic Association improved from 14.3 ± 3.8 to 24.7 ± 4.0 in the patients without complications and from 14.8 ± 3.6 to 24.0 ± 3.9 in the patients with complications. Multivariate analysis concerning the relationship between complications and risk factors (operation time, estimated intraoperative blood loss, and surgeon experience) revealed that operation time was the only significant risk factor for complications.

Conclusions

Perioperative complications of PLIF were more frequent in this homogeneous study group than in other studies of various implants. Total excision of the facet joints might preclude neurological complications.

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Takaki Inoue, Satoshi Maki, Toshitaka Yoshii, Takeo Furuya, Satoru Egawa, Kenichiro Sakai, Kazuo Kusano, Yukihiro Nakagawa, Takashi Hirai, Kanichiro Wada, Keiichi Katsumi, Kengo Fujii, Atsushi Kimura, Narihito Nagoshi, Tsukasa Kanchiku, Yukitaka Nagamoto, Yasushi Oshima, Kei Ando, Masahiko Takahata, Kanji Mori, Hideaki Nakajima, Kazuma Murata, Shunji Matsunaga, Takashi Kaito, Kei Yamada, Sho Kobayashi, Satoshi Kato, Tetsuro Ohba, Satoshi Inami, Shunsuke Fujibayashi, Hiroyuki Katoh, Haruo Kanno, Shiro Imagama, Masao Koda, Yoshiharu Kawaguchi, Katsushi Takeshita, Morio Matsumoto, Seiji Ohtori, Masashi Yamazaki, Atsushi Okawa, and

OBJECTIVE

It is unclear whether anterior cervical decompression and fusion (ADF) or laminoplasty (LMP) results in better outcomes for patients with K-line–positive (+) cervical ossification of the posterior longitudinal ligament (OPLL). The purpose of the study is to compare surgical outcomes and complications of ADF versus LMP in patients with K-line (+) OPLL.

METHODS

The study included 478 patients enrolled in the Japanese Multicenter Research Organization for Ossification of the Spinal Ligament and who underwent surgical treatment for cervical OPLL. The patients who underwent anterior-posterior combined surgery or posterior decompression with instrumented fusion were excluded. The patients with a follow-up period of fewer than 2 years were also excluded, leaving 198 patients with K-line (+) OPLL. Propensity score matching was performed on 198 patients with K-line (+) OPLL who underwent ADF (44 patients) or LMP (154 patients), resulting in 39 pairs of patients based on the following predictors for surgical outcomes: age, preoperative Japanese Orthopaedic Association (JOA) score, C2–7 angle, and the occupying ratio of OPLL. Clinical outcomes were assessed 1 and 2 years after surgery using the recovery rate of the JOA score. Complications and reoperation rates were also investigated.

RESULTS

The mean recovery rate of the JOA score 1 year after surgery was 55.3% for patients who underwent ADF and 42.3% (p = 0.06) for patients who underwent LMP. Two years after surgery, the recovery rate was 53.4% for those who underwent ADF and 38.7% for LMP (p = 0.07). Although both surgical procedures yielded good results, the mean recovery rate of JOA scores tended to be higher in the ADF group. The incidence of surgical complications, however, was higher following ADF (33%) than LMP (15%; p = 0.06). The reoperation rate was also higher in the ADF group (15%) than in the LMP group (0%; p = 0.01).

CONCLUSIONS

Clinical outcomes were good for both ADF and LMP, indicating that ADF and LMP are appropriate procedures for patients with K-line (+) OPLL. Clinical outcomes of ADF 1 and 2 years after surgery tended to be better than LMP, but the analysis did not detect any significant difference in clinical outcomes between the groups. Conversely, patients who underwent ADF had a higher incidence of surgery-related complications. When considering indications for ADF or LMP, benefits and risks of the surgical procedures should be carefully weighed.