A novel nanohydroxyapatite/polyamide-66 cage for reducing the subsidence rate after single-level anterior cervical discectomy and fusion: a comparative study of 7-year follow-up

A novel nanohydroxyapatite/polyamide-66 cage (n-HA/PA66 cage) with a horseshoe shape was designed to lower the subsidence rate of the traditional hollow cylindrical n-HA/PA66 cage. However, no studies have compared the incidence of subsidence in the two cages. The purpose of this study was to compare the long-term clinical and radiological outcomes of the novel n-HA/PA66 cage with the hollow cylindrical n-HA/PA66 cage after anterior cervical discectomy and fusion (ACDF) to treat single-level cervical degenerative disk disease (CDDD). Fifty-two patients with novel n-HA/PA66 cages (Group A) and fifty-five patients with hollow cylindrical n-HA/PA66 cages (Group B) were included. The radiological parameters included intervertebral height (IH), C2-7 angle (C2-7a), segmental alignment (SA), subsidence rate, and fusion rate. The clinical outcomes were visual analog scale (VAS) scores, Japanese Orthopedic Association (JOA) scores, and patient satisfaction rates. The pre- and postoperative SA, C2-7a, and fusion rates of the patients in Groups A and B were similar. The preoperative and 6-month postoperative IHs in both groups were comparable. However, the final follow-up IH in Group B was significantly smaller than that in Group A (35.9 mm vs. 36.7 mm). The difference in the subsidence rates at the final follow-up between Group A (5.8%, 3/52) and Group B (18.2%, 10/55) was significant. The VAS score, JOA score, and patient satisfaction rate were not significantly different. The novel n-HA/PA66 cage had similar favorable SA, C2-7a, fusion rate, and clinical outcomes compared to the hollow cylindrical n-HA/PA66 cage for treating single-level ACDF. Moreover, the novel n-HA/PA66 cage achieved a lower subsidence rate and higher IH than the hollow cylindrical n-HA/PA66 cage at the final follow-up.