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Comparison of Long-Term Outcomes between the n-HA/PA66 Cage and the PEEK Cage Used in Transforaminal Lumbar Interbody Fusion for Lumbar Degenerative Disease: A Matched-Pair Case Control Study.

OBJECTIVE
The nanohydroxyapatite/polyamide-66 (n-HA/PA66) cage is a novel bioactive nonmetal cage that is now used in some medical centers, while the polyetheretherketone (PEEK) cage is a typical device that has been widely used for decades with excellent clinical outcomes. This study was performed to compare the long-term radiographic and clinical outcomes of these two different cages used in transforaminal lumbar interbody fusion (TLIF).


METHODS
In this retrospective and matched-pair case control study, we included 200 patients who underwent TLIF from January 2010 to December 2014 with a minimum 7-year follow-up. One hundred patients who used n-HA/PA66 cages were matched with 100 patients who used PEEK cages for age, sex, diagnosis, and fusion level. The independent student's t-test and Pearson's chi-square test were used to compare the two groups regarding radiographic (fusion status, cage subsidence rate, segmental angle [SA], and interbody space height [IH]) and clinical (Oswestry Disability Index [ODI], and Visual Analog Scale [VAS] for back and leg) parameters preoperatively, postoperatively, and at the final follow-up.


RESULTS
The n-HA/PA66 and PEEK groups had similar fusion rates of bone inside and outside the cage at the final follow-up (95.3% vs 91.8%, p = 0.181, 92.4% vs 90.1%, p = 0.435). The cage union ratios exposed to the upper and lower endplates of the n-HA/PA66 group were significantly larger than those of the PEEK group (p < 0.05). The respective cage subsidence rates in the n-HA/PA66 and PEEK groups were 10.5% and 17.5% (p = 0.059). There were no significant differences between the two groups in the SA, IH, ODI scores, or VAS scores at any time point. The n-HA/PA66 group showed high fusion and low subsidence rates during long-term follow-up.


CONCLUSION
Both n-HA/PA66 and PEEK cages can achieve satisfactory long-term clinical and radiographic outcomes in TLIF. However, the n-HA/PA66 group showed significantly larger cage union ratios than the PEEK group. Therefore, the results indicated that the n-HA/PA66 cage is an ideal alternative material comparable to the PEEK cage in TLIF.