Improved bone bonding of hydroxyapatite spacers with a high porosity in a quantitative computed tomography-image pixel analysis: A prospective 1-year comparative study of the consecutive cohort undergoing double-door cervical laminoplasty

Yoshiki Takeoka; Takashi Yurube; Koichiro Maeno; Yutaro Kanda; Ryu Tsujimoto; Kunihiko Miyazaki; Yuji Kakiuchi; Shingo Miyazaki; Zhongying Zhang; Toru Takada; Kotaro Nishida; Minoru Doita; Ryosuke Kuroda; Kenichiro Kakutani

doi:10.1002/jsp2.1080

Improved bone bonding of hydroxyapatite spacers with a high porosity in a quantitative computed tomography-image pixel analysis: A prospective 1-year comparative study of the consecutive cohort undergoing double-door cervical laminoplasty

JOR Spine. 2020 Feb 3;3(1):e1080. doi: 10.1002/jsp2.1080. eCollection 2020 Mar.

Affiliations

¹ Department of Orthopaedic Surgery Kobe University Graduate School of Medicine Kobe Japan.
² Maeno Orthopaedic Clinic Himeji Japan.
³ Department of Orthopaedic Surgery Kobe Hokuto Hospital Kobe Japan.
⁴ Department of Orthopedic Surgery Graduate School of Medicine, University of the Ryukyus Okinawa Japan.
⁵ Department of Orthopaedic Surgery Iwate Medical University Graduate School of Medicine Iwate Japan.

Abstract

Laminoplasty using hydroxyapatite (HA) spacers is widely performed in patients with cervical myelopathy. However, spacer dislocation is a critical complication caused by bone absorption and inadequate bone conductivity, and can result in dural damage and restenosis. We thus designed a prospective cohort study to clarify the feasibility of increased porosity HA spacers for double-door laminoplasty by analyzing computed tomography (CT) images. Forty-seven patients underwent cervical laminoplasty. Two different types of CERATITE HA spacer were used, either high porosity (50%) or low porosity (35%). These HA spacers were placed in an alternating manner into the laminae in each patient. In total, 85 high-porosity (50%) HA spacers and 84 low-porosity (35%) HA spacers were implanted. At postoperative 2 weeks, 3 months, 6 months, and 1 year, CT images were obtained. In both groups, the percentage of bone-bonding boundary area of the HA spacer in contact with laminae and bone volume of the spinous process relative to the 2-week value were calculated by a 3D and 2D CT-image pixel analysis. The bone-bonding ratio was significantly higher in high-porosity (50%) than low-porosity (35%) HA spacers at 3 months and thereafter (1 year, 69.3 ± 27.8% and 49.7 ± 32.9% respectively, P < .01). The bone volume in both groups significantly decreased with time (1 year, 73.2 ± 29.8% and 69.0 ± 30.4% respectively, P < .01), indicating bone absorption. This showed no significant difference between the HA spacers (P = .15) but was higher in high-porosity (50%) than low-porosity (35%) HA spacers throughout the study period. Meanwhile, spacer breakage was found in 4.7% of high-porosity (50%) HA spacers and 1.2% of low-porosity (35%) HA spacers (P = .37). In summary, high-porosity (50%) HA spacers have the advantages of accelerated bone bonding and relatively decelerated bone absorption compared to low-porosity (35%) HA spacers; however, possibly more frequent breakage of HA spacers with a high porosity (50%) requires careful, extended postoperative follow-up.

Keywords: bone bonding and absorption; cervical spine; computed tomography (CT); double‐door laminoplasty; hydroxyapatite spacer; porosity and pore size.