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Phyo Kim, Susumu Wakai, Seigo Matsuo, Takashi Moriyama and Takaaki Kirino

Hydroxyapatite (HA) is the main constituent of bone mineral, and synthetic HA serves as a biocompatible and bioactive material. It permits bone growth on its surface and forms a union with the adjacent bone.

Object. The authors have developed implants made of porous HA, which they have used in more than 90 cases in the past 6 years to achieve cervical interbody fusion. The implants were designed to provide maximum durability, biomechanical stability, and alignment preservation and to be technically easy to use. The authors summarize their experience and results with the use of these implants.

Methods. The results of postoperative follow-up observation of 12 months or longer (mean 37.1 ± 2.4 months) are available in 70 patients with underlying disease including: spondylosis, disc extrusion, ossification of the posterior longitudinal ligament (PLL), hypertrophy of the PLL, and trauma. The patients' ages at the time of surgery ranged from 22 to 83 years (mean 50.6 ± 1.3 years).

Flexion—extension radiographs and tomograms, obtained 6 and 12 months after surgery and every year thereafter, were used to demonstrate solid fusion in all cases. Dislocation of the implant occurred in three patients who were treated during the early portion of the series. At 6 to 12 months after surgery, encasement of the implant and formation of union were observed. Normal lordosis, if present prior to surgery, was maintained postsurgery. No neurological deterioration related to the site of fusion occurred during the period of observation.

Conclusions. The authors conclude that satisfactory interbody fusion can be achieved by using HA implants, provided their design is appropriate and adequate surgical techniques are used.

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Keishi Maruo, Tokuhide Moriyama, Toshiya Tachibana, Shinichi Inoue, Fumihiro Arizumi, Takashi Daimon and Shinichi Yoshiya

Object

Laminoplasty is the preferred operation for most patients with cervical myelopathy due to multilevel ossification of the posterior longitudinal ligament (OPLL). Recent studies have demonstrated several significant risk factors for poor clinical outcomes after laminoplasty, including older age, lower preoperative Japanese Orthopaedic Association (JOA) score, postoperative change in cervical alignment, cervical kyphosis, and high occupying ratio of the OPLL (that is, the ratio of the greatest anteroposterior thickness of the OPLL to the anteroposterior diameter of the spinal canal at the same level on a lateral image). However, the impact of dynamic factors on clinical outcomes is unclear. The purpose of this study is to assess the impact of dynamic factors on the clinical outcome after laminoplasty for cervical myelopathy due to OPLL.

Methods

A consecutive series of patients who underwent laminoplasty for cervical myelopathy due to OPLL between 2003 and 2009 was retrospectively reviewed. The indication for laminoplasty at the authors' hospital included preoperative straight or lordotic alignment of the cervical spine and an occupying ratio of OPLL less than 60%. The JOA score and recovery rate were used to evaluate clinical outcomes. A poor clinical outcome was defined as a recovery rate of less than 50%. Patient factors examined along with outcome included age, preoperative JOA score, preoperative somatosensory evoked potentials, preoperative motor evoked potentials, body mass index, and presence of high intensity on MRI. Radiographic measures included the preoperative C2–7 lordotic angle, preoperative C2–7 range of motion (ROM), preoperative segmental ROM at the level of myelopathy, and the occupying ratio of OPLL.

Results

There were 45 patients (33 males and 12 females). The mean follow-up period was 4 years (range 2–6.8 years). The mean patient age was 66.9 years (range 50–85 years). The mean JOA score significantly increased from 9.1 before surgery to 13.1 at the final follow-up. The mean recovery rate was 51.2%. Nineteen patients (42%) had a recovery rate of less than 50%. Patient factors were not associated with surgical outcomes. Only the preoperative C2–7 ROM was significantly greater in the poor surgical outcome group (23.1° vs 14.1°). Receiver operating characteristic curve analysis showed that the optimal preoperative C2–7 ROM cutoff was 20°. Logistic regression analysis revealed that patients with a preoperative C2–7 ROM of greater than 20° had a 4.6 times higher risk (p = 0.021) of a poor clinical outcome, indicating that dynamic factors may have an impact on the surgical outcome of laminoplasty.

Conclusions

Fusion surgery may be a useful strategy in patients with preoperative hypermobility of the cervical spine.