Bisegmental cervical interbody fusion using hydroxyapatite implants: surgical results and long-term observation in 70 cases

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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.

Article Information

Address reprint requests to: Phyo Kim, M.D., Ph.D., Department of Neurosurgery, Dokkyo University School of Medicine, 880 Mibu, Tochighi, Japan 321–0293.

© AANS, except where prohibited by US copyright law.

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Figures

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    Photographs showing the porous HA (30% porosity) implant used for cervical interbody fusion. Upper: Oblique frontal view of implant resting on its side. Center: Lateral view of implant. Lower: Frontal view. The photographs show an implant 13 mm in height.

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    Designs and dimensions of the HA implants. The implants are available in three different heights: 10, 13, and 15 mm.

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    Photograph of stainless steel instruments used to prepare the fusion bed. Shape of the bone cavity is adjusted to accommodate the instrument securely prior to insertion of the implant.

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    Radiographic images and photograph obtained in a 54-year-old man with spondylosis at C5–6 and progressive myelopathy: preoperative plain radiograph (A) showing an osteophyte; T2-weighted magnetic resonance (MR) image (B) and CT myelogram (C) revealing compression of the spinal cord; intraoperative photograph (D) showing insertion of the implant; postoperative T1-weighted MR image (black-white reversal) (E) demonstrating adequate decompression; flexion—extension tomograms obtained 2 months after surgery (F) revealing the graft construct to be stable; and follow-up CT scan (G) and tomogram (H) obtained 1 year after surgery demonstrating bridging bone at the dorsal aspect of the implant.

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    Radiographs obtained in a 45-year-old man with unilateral facet dislocation and disc extrusion due to cervical injury caused by a motor vehicle accident. Left: Preoperative radiograph revealing anterior subluxation of C-6 and C-7 and disc extrusion. Surgery included reduction, discectomy, interbody fusion with HA, and internal fixation with anterior locking plate system. Right: Postoperative radiograph obtained 2 months after surgery revealing restoration of alignment.

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    Radiographs obtained in a 58-year-old woman with dislocation of the HA implant. The radiographs were obtained immediately after surgery (left) and at 3 days (center) and 9 days (right) after surgery.

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    Tomograms obtained in a 33-year-old man 3 months (left) and 2.5 years (center) after a C6–7 fusion was performed using HA. Note bridging bone surrounding the implant. Encasement of the implant by natural bone is observed on the CT scan (right) obtained 2.5 years after surgery.

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    Plain cervical radiographs obtained in a 43-year-old man with spondylosis preoperatively (left) and 1 year after surgery (right). Restoration of normal cervical lordosis and improvement in alignment are evident.

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