Peroneal nerve entrapment at the knee

Diagnosis and treatment of the most common neuropathies following knee injuries and reconstructive surgery - A narrative review

The main nerves in the knee region are the tibial nerve, the common peroneal nerve, and the saphenous nerve. These three nerves innervate the lower leg and foot, providing sensory and motor function. The large sciatic nerve splits just above the knee to form the tibial and common peroneal nerves. The tibial nerve travels down in the posterior region, while the common peroneal nerve runs around the lateral side of the knee and runs down the front of the leg to the foot. Although all these nerves can be affected by injuries of the knee, the infrapatellar branch of the saphenous nerve (IPBSN) and the common peroneal nerve (CPN) are most affected. In this narrative review we focus on neuropathies associated with nerves located in the region of the knee joint in the context of their injuries and possible iatrogenic damage during reconstructive surgery.

Subclinical Peroneal Neuropathy Affects Ambulatory, Community-Dwelling Adults and Is Associated with Falling

BACKGROUND

Peroneal neuropathy with an overt foot drop is a known risk factor for falling. Subclinical peroneal neuropathy caused by compression at the fibular neck is subtler and does not have foot drop. A previous study found subclinical peroneal neuropathy in 31 percent of hospitalized patients. This was associated with having fallen. The purpose of this study was to determine the prevalence of subclinical peroneal neuropathy in ambulatory adults and investigate if it is associated with falling.

METHODS

A cross-sectional study of 397 ambulatory adults presenting to outpatient clinics at a large academic hospital was conducted from 2016 to 2017. Patients were examined for dorsiflexion weakness and signs of localizing peroneal nerve compression to the fibular neck. Fall risk was assessed with the Activities-Specific Balance Confidence Scale and self-reported history of falling. Multivariate logistic regression was used to correlate subclinical peroneal neuropathy with fall risk and a history of falls.

RESULTS

The mean patient age was 54 ± 15 years and 248 patients (62 percent) were women. Thirteen patients (3.3 percent) were found to have subclinical peroneal neuropathy. After controlling for various factors known to increase fall risk, patients with subclinical peroneal neuropathy were 3.74 times (95 percent CI, 1.06 to 13.14) (p = 0.04) more likely to report having fallen multiple times in the past year than patients without subclinical peroneal neuropathy. Similarly, patients with subclinical peroneal neuropathy were 7.22 times (95 percent CI, 1.48 to 35.30) (p = 0.02) more likely to have an elevated fall risk on the Activities-Specific Balance Confidence fall risk scale.

CONCLUSION

Subclinical peroneal neuropathy affects 3.3 percent of adult outpatients and may predispose them to falling.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Risk, III.

External neurolysis as a treatment for foot drop secondary to weight loss: a retrospective analysis of 200 cases

BACKGROUND

Peroneal nerve entrapment is the most common peripheral mononeuropathy of the lower limbs. Foot drop, a common presentation, leads to an impaired eversion and dorsiflexion of the foot. An intriguing observation is the occurrence of foot drop secondary to weight loss.

METHODS

A retrospective study of patients surgically treated for peroneal nerve entrapment was performed between January 1, 1995 and December 31, 2016, at the Department of Neurosurgery, Genk, Belgium. Out of a total of 421 patients, 200 patients with foot drop secondary to weight loss were included. For each subject, motor and sensory outcomes after external neurolysis were investigated. As a primary objective, we examined the postoperative outcomes of external neurolysis as a treatment for foot drop in patients with peroneal nerve entrapment at the fibular head secondary to weight loss. As a secondary objective, we analyzed the correlation between patient characteristics and the success rate of external neurolysis.

RESULTS

When defining success as a postoperative MRC score of 4 or 5, external neurolysis has a success rate of 85% in patients with foot drop secondary to weight loss. A significant difference (P = < 0.0001) between postoperative and preoperative MRC scores indicates that external neurolysis leads to significant improvement of motor function in patients with foot drop secondary to weight loss. A multiple logistic regression model showed that "preoperative MRC scores" and "duration of symptoms" were the only variables with an impact on postoperative MRC scores. Other variables such as "age," "gender," and "side of entrapment" had no significant impact on postoperative results.

CONCLUSIONS

Statistical analysis emphasizes the important role of external neurolysis in the treatment of peripheral peroneal nerve entrapment. Therefore, external neurolysis at the fibular head should be regarded as a very effective and safe procedure in patients with foot drop secondary to weight loss.