For cervical disc herniation, especially for patients with foraminal stenosis, postoperative nerve root dysfunction is more common and mainly manifests as pain, numbness, or weakness in upper limbs. The causes of its occurrence are multifactorial. Choi et al [9] described a case of motor paralysis after C4-5 posterior cervical foraminotomy, arguing that C5 nerve roots usually cover the entire intervertebral disc space and, therefore, require more excessive retraction than other nerve roots. Youn et al [10] suggested that removing a herniated disc or bone spur could lead to a potential risk of motor paralysis due to excessive retraction, while retraction without discectomy could increase the risk of transient root injury. Lee et al [11] reported transient motor weakness and transient sensory changes after PCF and believed that excessive pulling, mechanical damage, and thermal damage during drilling were the reasons for weakness or sensory changes after posterior cervical foraminotomy/PECD. We believed that the continuous mechanical pressure from the protruding nucleus pulposus tissue preoperatively and the release of tumor necrosis factor alpha caused by it activate neutrophils and monocytes to produce a local inflammatory response [12]. Additionally, the mechanical pulling and stimulation of nerve roots and damage of surrounding soft tissues during the operation lead to the generation and release of inflammatory substances and increase the permeability of surrounding capillaries, further aggravating local inflammation and edema. These inflammatory factors also stimulate the exudation of nerve roots and ganglia, possibly leading to nerve root edema and ischemia, and ultimately causing ischemia-reperfusion injury [12–14]. Makkar and Zhang [15, 16] reported that epidural steroid injections provided significant pain relief and reduced disability in lumbar spine. Shin et al [17] reported that the application of epidural steroids in PELD significantly reduced postoperative back pain and lower limb pain and promoted the early functional recovery of patients because steroids can alleviate inflammatory response by inhibiting the chemotactic aggregation of inflammatory cells, adhesion of leukocytes, and release of histamine and kinase [18]. DU et al [12] introduced the use of gelatin sponge infiltration steroids and ropivacaine to cover nerve roots during lumbar MIS-TLIF surgery and achieved good early analgesic effects. Research by Yang et al [7] confirmed that in PELD, the use of cocktail therapy (dexamethasone, ropivacaine, and vitamin B12) and the placement of nerve roots after infiltration with gelatin sponge can more effectively relieve early postoperative nerve root dysfunction and promote postoperative recovery.
To prevent nerve root edema and irritation after PPECD and avoid the risk of total spinal anesthesia (TSA) and spinal cord injury, epidural administration is not available [19, 20]. The use of DSM for the local infiltration of nerve roots is an emerging method to achieve the aforementioned safety improvements. It is advantageous in that it can use a cocktail treatment of multiple drugs and maintain a high drug concentration and sustained release in the early stage. Additionally, unlike PELD, where gelatin sponge is placed between disc and dorsal dura, we placed gelatin sponge on the dorsal side of the nerve root to prevent epidural hematoma. Due to the limited intraoperative resection scope of the ligamentum flavum, it can play a barrier role, reduce the possibility of drugs entering the dural sac, and improve safety. This study uses gelatin sponge as a raw material biofilm to act as DSM. It has the characteristics of degradability, anti-adhesion, and reduction of disordered hyperplasia of peripheral scars.
Ropivacaine is a long-acting amide local anesthetic, which has low cardiotoxicity and neurotoxicity [21]. Low concentrations of ropivacaine (10 mg/h) has obvious sensory block but no motor block [22]. Dexmedetomidine can effectively reduce the ischemia-reperfusion injury of local tissues, better protect the damaged nerve tissue, and speed up the repair. Topical dexmedetomidine exhibits anti-inflammatory effects against local acute inflammatory reactions by reducing the production of inflammatory cytokines. Moreover, dexmedetomidine as an adjuvant can prolong the action time of ropivacaine and enhance the analgesic effect [23–25]. Vitamin B12 can reduce abnormal nerve discharge and promote nerve regeneration [26]. Dexamethasone is known to reduce the production of prostaglandins and participate in analgesia with anti-inflammatory effects. It can inhibit the secretion of neuropeptides from small nerve fibers, thereby reducing pain. Simultaneously, it can reduce edema, fibrin formation, telangiectasia, white blood cell aggregation, as well as the proliferation of capillaries and fibroblasts, scarring, and so on [27]. Therefore, these four drugs loaded at the gelatin sponge have a close synergistic effect on anti-inflammatory, analgesic, and nerve growth.
In this study, the early pain of the cocktail group was significantly relieved within 1 week postoperatively compared with the control group. However, the single-center, retrospective design of this study and small sample size are its main limitations. Further prospectively designed randomized controlled trials to verify our results are warranted. The proportion of mixed drugs was based on clinical experience. These aspects should be further explored to ensure optimal clinical outcomes.