One contraindication to cervical disk arthroplasty is heterotopic ossification (HO), defined as new bone deposits occurring in abnormal locations as in the connective tissue or in areas surrounding major joints (i.e., hip, knee). HO is graded utilizing the Brooker grades: I/II mild/moderate and III/IV moderate/severe. Prior to performing total hip replacements, Koelbl et al. (7) advocated administering low-dose radiation (7 Gy) in a single fraction the night before surgery; this reduced postoperative HO to grade 1 to 2 levels only. HO can also occur following cervical disk replacements. Leung et al. (8) noted that HO occurred in 16 (17%) of 90 patients undergoing Bryan disk replacements. Pickett et al. (9) observed in another series of 96 patients that 2 (2%) developed HO.

The presence of ossification of the posterior longitudinal ligament (OPLL) poses three contraindications to performing cervical disk replacements. First and foremost is the increased likelihood of spontaneous disk space fusion with continued OPLL progression. The second contraindication is that OPLL often extends beyond the level of the disk space and more frequently warrants corpectomy/fusion rather than a simple single-level diskectomy/decompression. Inadequate exposure for the resection of OPLL may result in increased neurologic injury. A third contraindication to cervical disk arthroplasty is the potential for a cerebrospinal fluid (CSF) fistula to occur in instances where OPLL extends to and through the dura (Figs. 97.1, 97.2 and 97.3). How a persistent CSF leak may affect an artificial disk over either the short or long term is not well documented.

The presence of ossification of the anterior longitudinal ligament (OALL) also poses several risk factors when choosing to place an artificial cervical disk (Fig. 97.4). First is the potential for improperly placing the cervical arthroplasty as the basic anatomical landmarks are altered by the anterior OALL mass extending beyond the normal anterior vertebral body margin. One of two things may occur. If the arthroplasty is placed too anteriorly in the OALL mass itself, it may dislodge, extrude, or loosen. If placed too posteriorly, the anterior OALL mass with its partially decorticated disk/space margins may result in spontaneous fusion. Also, OALL is often combined with OPLL, both of which may contribute to fusion following arthroplasty placement.