Relation of the Sural Nerve and Medial Neurovascular Bundle with the Achilles Tendon in Children with Cerebral Palsy Treated by Percutaneous Achilles Tendon Lengthening

SLR - March 2022 - Tung V. Dao

Reference: Erdal OA, Gorgun B, Yontar NS, Terzibaşioğlu AE, Sarikaya IA, Inan M. Relation of the Sural Nerve and Medial Neurovascular Bundle with the Achilles Tendon in Children with Cerebral Palsy Treated by Percutaneous Achilles Tendon Lengthening. J Pediatr Orthop. 2022 Feb 1;42(2)
 
Level of Evidence: III
 
Scientific Literature Review
 
Reviewed By: Tung V. Dao, DPM
Residency Program: Grant Medical Center – Columbus, OH
 
Podiatric Relevance: Equinus contracture is a common gait abnormality in children with cerebral palsy (CP). Percutaneous Achilles lengthening (PAL), using three hemisections is a popular treatment option for equinus. However, surgeons must be cognizant of anatomy while performing PAL, namely the sural nerve (SN) and medial neurovascular bundle (MNB). This study is the first to describe the anatomical relations of the SN and MNB relative to the AT, define dangerous levels for injury, and mapping these structures via MRI in children with CP who had undergone isolated PAL.
 
Methods: A retrospective cohort study which included children with CP who had undergone isolated PAL at least one year before initiating the study. Triple hemisections were performed in standard fashion starting 1 centimeter proximal to the AT insertion and each cut 2 to 3 centimeters apart. Ankle MRIs were obtained at least one year after surgery. Primary outcomes assessed include AT length. Bimalleolar distance, distance of the AT medial border to the MNB, distance between AT lateral border and SN at each cm from its distal insertion, and distance of SN to tendon at the level of the middle cut. Five millimeters was designated threshold distance for risk of SN injury. Secondary outcomes include range of motion, pain, and neuropathy.
 
Results: Nineteen patients with 30 ankles were included. Mean age was 140.9 ± 38.9 months. Mean follow up was 17.6  ± 4.3 months. Mean AT length was 80.1 ± 23.6 mm. Mean bimalleolar distance was 54.9 ± 5.5 millimeters. SN was within threshold distance of AT lateral border in 1 case in the first 3 cm from the calcaneal insertion, while in the fourth centimeter there were 9/30 cases that were close. At more proximal levels, number of cases with SN within threshold distance increased at each cm. Mean distance between the middle cut and the AT insertion was 59.6 ± 9.6 millimeters. Mean distance of the SN to the AT lateral border at the level of the middle cut was 3.5 ± 3.5 mm. Measurements were positively correlated with patient age. SN was damaged in 5 ankles (16.7%) and severed in one ankle (3.3 percent). No patients had residual equinus or signs of neuropathy. The patient with pain from a severed SN resolved in eight months.

Conclusions: PAL is proven to be an effective treatment option for gastro-soleal equinus in children with CP but can be prone to SN injury. The authors found that the SN passed in the safe zone on the lateral side of the AT in the first 3 centimeters to the tendon insertion and in average-risk zone between 3 and 4 centimeter levels. These regions were considered safe for the middle, lateral directed tendon hemisection. On the medial side, MNB was found to be safe through whole length of the tendon. A limitations of this study includes lack of a control group and MRI results affected by surgical changes in anatomy. Understanding the surgical anatomy of the PAL in children is important in order to obtain good patient outcomes in children with CP and equinus.