In this study, we found that area(rural), occupation(“blue trouser” worker), diabetes, cardiovascular disease, knee joint dislocation, proximal fibula fracture, tibial plateau fracture, vascular injury and hip arthroplasty injury are independent risk factors of motor functional recovery of CPN, while high preoperative muscle strength and postoperative knee joint immobilization are protective factor of motor functional recovery of CPN. Using these factors, we developed a nomogram which could likely predict the level of common peroneal nerve motor recovery after surgery.
The effect of the blood supply to the CPN on prognosis was highlighted after multifactor logistic regression analysis. Reports had found the prognosis of injured CPN at the thigh level was slightly better than that at the hip area. In renent years, a growing number of reports found that the peroneal nerve of the sciatic nerve was more vulnerable and difficult to recover [4, 14, 17]. We also found CPN injuries after hip arthroplasty had better prognosis than that of knee arthroplasty. It was not clear whether this was due to more severe damage to the CPN because of its anatomical location or other factors[15, 21]. Blood supply of CPN had drawn attention of researchers[21, 23-26]. The nutrient arteries of the peripheral nerves are anatomically located in the connective tissue sheath, the nerve bundles and inside the nerve fibers which guarante sufficient blood supply in cases that the vessels are interrupted. The extraneural arterial chain of the sciatic nerve consist of 2-6 nutritive arteries at certain intervals which originated from inferior gluteal artery and popliteal artery branches. The extraneural arterial chain of the tibial nerve was supported by 2-5 nutritive arteries formed by branch of the tibiofibular trunk, peroneal artery, and posterior tibial artery. Thus, one or more of those nutritive arteries interruption had no significant effect on the blood of sciatic nerve and tibial nerve. However, the part of the CPN from the terminal division of the sciatic nerve to the fibular neck were supplied by a single blood vessel (97.2%) . Hence, the CPN tended to have a poor prognosis after injuries with the necrosis of nerve ischemic edema, Wallerian degeneration, and the formation of fibrous scar[14, 16].
We believed that knee joint dislocation, proximal fibula fracture, tibial plateau fracture and hip arthroplasty injury affect the functional recovery because of limited blood supply interruption rather than nerve fiber damage. We also observed that vascular injury diseases, including femoral and popliteal artery embolization, were a risk factor both in univariate and multifactorial analyses, which could be explained by vascular thrombosis or embolism of the CPN associated with inadequate collateral circulation[25, 26].
The fact that diabetic patients were vulnerable to peripheral nerve damage had been reached an agreement[29, 30]. Diabetic tended to develop complications of neuropathy or vasculopathy. An underlying neurologic disease increased the problems for any patient with a nerve injury. Cardiovascular disease and diabetes had been found to increase the incidence of CPN in cardiothoracic operations . Patients with cardiovascular disease may have systemic vascular sclerosis, so that blood supply was not easy to restore after nerve injury. Nerve regeneration of injured nerve in diabetic patients was often impaired because of microangiopathic involvement of the vasa nervorum . The fact that patients with cardiovascular disease or diabetes tended to have poor prognosis in our research, indicated that microcirculation of CPN played an ignored role in the repair of CPN.
We found few reports about the influence of “blue trouser” workers on the recovery of the CPN. Excessive exercise or positional factors of “blue trouser” workers could result in chronic compartment at the neck of the fibula, causing subclinical neuropathy of CPN ,which might have potential influence on the recovery of nerve function after injury. Furthermore, compared with “white-trouser” workers, “blue trouser” workers might have stronger tibialis posterior muscle, so that limited recovery of CPN function could not confront the tibialis posterior muscle. There were few studies on the reason why patients living in urban areas had poor neurological prognosis. Patients from rural areas tended to have good prognosis, which could be related to more increased physical activities because they were in a less populated area. However, living in the urban area was not the cause of failure or surgery, but rather the likelihood of specific injury was more possible. Thus, those factors needed further investigation.
Our research found that high preoperative muscle strength, and postoperative knee joint immobilization decreased the risk of poor recovery of CPN injury. The prognosis of patients was better with higher preoperative muscle strength, because residual innervation could avoid muscle atrophy, thus enabling better recovery of reinnervation. Knee joint immobilization flexion position could avoid the repeated stimulation of swollen nerves, reduce the probability of vascular occlusion and the duration and degree of edema, and shorten the time of ischemia.
Obesity seemed to have higher complication rates related to nerve surgery[33, 34]. However, fat pad surrounding the fibular head could protect the CPN. Our research suggested that obese patients with higher prevalence of neural injuries did not have worse prognosis compared with normal patients. We also found no difference of neural functional recovery among patient with different BMI. The adverse effects of smoking was found on the functional recovery of peripheral nerves after ischemia/reperfusion injuries in rats. Whereas, a meta-analysis on prognostic associations of peroneal nerve decompression found that although smoking increased the trend of pain, outcomes were not affected by presentation. In our study, smoking had no impaction on the recovery of CPN injuries.
Age and sex showed no correlation with prognosis after surgeries in present studies. A review showed that outcomes did not vary with an advanced age or sex after peroneal nerve decompression. Another review, which included 28 studies to assess the results of repaired CPN, found no significant relationship between outcome and patient age. Our analysis similarly showed that neither age nor sex were prognostic factors of repaired CPN.
Univariate logistic regression analysis showed that the surgical type of neurolysis yielded a worse outcome than end to end suture. Nevertheless, after multifactor logistic regression analysis, there were no statistical difference in outcome of repaired CPN among different surgical types, which was consistent with previous reports[6, 37-39]. Among the variables which could affect the function recovery of repaired CPN, mechanism of injury was one of the crucial determining factors. In experimental nerve injuries, function of injured nerve caused by a sharp transection was easier to restore, compared with that by an avulsion. The avulsed nerves showed no normal nerve architecture at any time period, while the cut specimens showed a progressive resolution in the zone of injury. Prasad et al insisted that stretch/traction injury zone extended into the myoneural junction, creating scar tissue that prevented motor reinnervation, which was the reason of poor functional motor recovery after reconstruction of traction injury to the CPN. However, all the surgical types could not achieve reinnervation of the peroneal innervated muscles because the traction injuries extending beyond what can be perceived optically, even with operating microscope. Besides, stretch/traction injury of CPN provided another perspective on the poor motor function of injured CPN caused or accompanied by knee joint dislocation, proximal fibula fracture, tibial plateau fracture and hip arthroplasty injury in our research.
There were perspectives that tendon transfer should be added in all patients at the time of nerve reconstruction. However, additional surgeries led to greater trauma and increased the risk of uncertain complications, including infection, overcorrection, instability, rupture of tendon transfer and cocked-up hallux. Our research suggested that though traction lesions could be extensive, the prognosis seemed to vary considerably. Therefore, both clinicians and patients need quantified indicators to estimate the prognosis of injured CPN without additional surgeries in early stage of treatment.
To our knowledge, this study is the first to assess factors associated with injured CPN and establish a prediction model to predict the prognosis of injured CPN by using a nomogram. It is generally believed that the model with AUC of 0.50-0.75 is acceptable, and AUC >0.75 indicates that the discrimination of model is prominent . AUC of our prediction model is 0.904, so this nomogram can be used to predict the prognosis of injured CPN well. Our study was carried out in patients with high-risk of poor prognosis, which could improve the efficiency of model for risk factors. Besides, selected factors used to construct prediction model are relatively objective, which is helpful for further application of this model. Using the nomogram, a clinician can eyeball the sum of all predictors’ effect for a given patient with injured CPN, and predict the prognosis of injured CPN. The nomogram could provide evidence for clinicians to assess whether a patient need aggressive surgical strategies in the early treatment stage of injured CPN, such as tendon transfer, ankle foot orthosis, or arthrodesis.
There are limitations of our study that are notable. First, this study was limited as a monocentric analysis. Although there are a lot of cases, we still need evidence from other centers to verify this model. In subsequent research work, therefore, we will persuade other medical center to join in this research project, and provide the corresponding clinical data for further evaluation and validation of the prediction model. Second, our cohort was limited to patients with injured CPN and requirement of surgical treatment.