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.

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.