Abstract
Category:
Ankle; Sports
Introduction/Purpose:
Entrapment of the First Branch of the Lateral Plantar Nerve (FBLPN), also known as Baxter’s Nerve (BN), has been identified as a cause of plantar heel pain in up to 20% of cases. Treatments for entrapment of the FBLPN often involve ultrasound guidance to ensure accurate placement of the treatment or injection. Knowledge of the gross anatomy of neurovascular structures is required to facilitate accurate placement of the therapeutic treatment. The purpose of this study was to utilize radiography to describe the course of the FBLPN relative to palpable anatomic landmarks that can be used to guide ultrasound interventions for plantar heel pain.
Methods:
Ten preserved feet from five cadaveric donors were dissected beginning with an incision 25 cm proximal to the medial malleolus. The skin and soft tissues were carefully dissected to identify the origin of the lateral plantar nerve and FBLPN. A radiopaque wire was inserted distally in each of the two nerves and a lateral radiograph was obtained. (Figure 1) A line designated as the malleolar-calcaneal (MCN) line was drawn from the center of the medial malleolus (point A) to the most distal tip of the calcaneus (point B). The distance between the point at which the FBLPN intersected the MCN line (point C) and the origin of the FBLPN (point D) was measured in millimeters. Using the MCN line, the distance from the medial malleolus (point A) to the point at which the FBLPN transected the MCN line (point C) was measured in millimeters.
Results:
In all ten cases, the FBLPN arose proximal to the malleolar-calcaneal line and originated directly from the lateral plantar nerve. The average distance from the malleolar-calcaneal line to the origin of the FBLPN was 25.70 ± 19.56 mm with a range of 10mm to 76mm. The average distance between the medial malleolus and the intersection of the FBLPN and the MCN line was 65.90 ± 33.80mm with a range of 15mm to 138mm.
Conclusion:
Plantar heel pain is a common reason to visit the orthopedic clinic and entrapment of the FBLPN is a common etiology for this pain. Treatments for entrapment of the FBLPN such as radiofrequency ablation and steroid injections rely on precise placement of the probe or needle in order to maximize therapeutic benefit and minimize side effects. Bony landmarks which are palpable on the patient’s intact skin such as the center of the medial malleolus and the distal tip of the calcaneus can serve to identify the likely course of the FBLPN.
Lateral radiograph of a right foot
Point A: center of the medial malleolus, Point B: Distal Calcaneus, Point C: intersection of the First Branch of the Lateral Plantar Nerve and the Malleolar-Calcaneal line, Point D: origin of the First Branch of the Lateral Plantar Nerve. Line A-B: Malleolar-Calcaneal line.