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

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.