The self-locking standalone cage is introduced and applied in the ACDF to reduce complications, such as soft-tissue damage, chronic dysphagia, and adjacent segment degeneration, that happen in anterior plate fixation. It is widely accepted that adopting the self-locking standalone cage can decrease blood loss, operative time, and length of hospital stay; result in higher JOA scores; effectively restore the cervical physiological curvature; and lead to satisfactory outcomes [14,15,16].

Because there is a trend of population aging and prolongation of healthy life expectancy, the chance of the elderly undergoing cervical surgery is expected to increase. Generally, older age is a factor in blood transfusions, reoperations, extended length of stays, and increased postoperative complications. Consequently, comprehensive work is necessary to analyze the efficacy the self-locking standalone cage in older patients undergoing ACDF procedures. However, in the previous studies of the self-locking standalone cage, patients’ ages were almost all under 80 years [16,17,18,19]. With the life span increasing, an increasing number of older patients receive ACDF, which gives us a chance to investigate the outcome and complications of ACDF with the self-locking standalone cage in patients over 80 years.

The present study showed no significant differences in the radiological outcomes between the older and younger groups. In all, 89.2% of patients in the older group and 92.9% in the younger group got solid fusion at the final follow-up. The mean time to achieve a solid fusion was longer in the older group without significant differences. Six cages in four patients subsided in the older group, and two cages in two patients subsided in the younger group. These slight differences in the radiological outcomes may be due to the osteoporosis in the older group. It has been demonstrated that patients with osteoporosis experience slower and less reliable bone healing, increased risk of interbody cage subsidence, pseudoarthrosis, and progressive kyphosis. Using a self-locking standalone cage is also a factor of subsidence compared with the plate-cage system [9]. However, only four older and two younger patients had subsidence in the current study. Several optimal surgical techniques were adopted in our research. First, the bony endplate was preserved as much as possible. Second, the cage size should be carefully tested before installation, and segmental overdistraction should be avoided. Furthermore, the modulus of the elasticity of polyetheretherketone (PEEK) is similar to that of bone. Consequently, in our study, a small percentage of cages subsided; all the involved patients reported good clinical outcomes.

The neurological functions and symptoms of all the patients in both groups were relieved according to the lower VAS and higher JOA scores evaluated after the operation. The self-locking standalone cage decreases blood loss and operative time. It makes it possible for surgeons to thoroughly remove the compressive tissue and decompress the affected nerve, even in older patients. Although the postoperative VAS and JOA evaluations of the older group are slightly worse than those of the younger group, no significant difference can be found between the two groups.

In some studies, complications and readmissions are more likely to happen in older patients [20, 21]. However, a previous study showed prolonged operative time was associated with an increased risk of complications in the elderly population [22]. It has been demonstrated that the self-locking standalone cage obviously decreases operative duration in patients with traditional anterior cervical plating systems [10, 23]. In this study, the operative duration was comparable in the two groups. Consequently, 19.61% of older and 13.89% of younger patients suffered complications without significant differences in the current study.

Dysphagia is a common complication in ACDF patients, with an incidence between 1 and 79% [24]. Patients undergoing ACDF with anterior plate fixation are more likely to have dysphagia compared with those without plate fixation [25]. Wang et al. believed a zero-profile anchored spacer was associated with a lower risk of postoperative dysphagia for less foreign body stimulation [26]. However, Chen et al. indicated that less traction time and less damage to prevertebral soft tissues during surgery contributed to the relatively low rate of dysphagia [9]. Singh et al. demonstrated that age is an independent predictor for dysphagia in ACDF patients [27]. In pathophysiology, frailty and muscular, endocrine, or psychiatric diseases may contribute to dysphagia in the older population [28]. In this study, a slightly higher dysphagia rate was found in the older group, implying that patients over 80 years still have a higher incidence of dysphagia regardless, which is greatly lessened by using a standalone self-lock cage.

This study is not without limitations. First, the retrospective nature of this study may place the analysis at risk of selection bias. Second, the sample size was small. Third, all patients were evaluated and operated in a single center, thus limiting the generalizability of the study findings. Therefore, large-scale, prospective studies with more details on comorbidities and complications are critical to overcome these limitations.