No Difference between Percutaneous and Arthroscopic Techniques in Identifying the Calcaneal Insertion during Ankle Lateral Ligament Reconstruction: A Cadaveric Study

Advantages of ultrasound identification of the distal insertion of the calcaneofibular ligament during ligament reconstructions

INTRODUCTION

In lateral ankle instability, anatomical ligament reconstructions are generally performed using arthroscopy. The ligament graft is passed through the talar, fibular and calcaneal tunnels, reconstructing the anterior talofibular and calcaneofibular (CFL) bundles. However, the calcaneal insertion of the CFL needs to be performed in an extra-articular fashion, and cannot be carried out under arthroscopy, thus requiring specific anatomical landmarks. For obtaining these landmarks, methods based on radiography or surface anatomy have already been described but can only offer an approximate identification of the actual CFL anatomical insertion point. In contrast, an ultrasound technique allows direct visualization of the insertion point and of the sural nerve that may be injured during surgery. Our study aimed to assess the reliability and accuracy of ultrasound visualization when performing calcaneal insertion of the CFL with specific monitoring of the sural nerve.

MATERIALS AND METHODS

Our anatomical study was carried out on 15 ankles available from a body donation program. Ultrasound identification of the sural nerve was obtained first with injection of dye. A needle was positioned at the level of the calcaneal insertion of the CFL. After dissection, in all the ankles, the dye was in contact with the sural nerve and the needle was located in the calcaneal insertion area of the CFL. The mean distance between the sural nerve and the needle was 4.8 mm (range 3-7 mm).

DISCUSSION AND CONCLUSION

A pre- or intra-operative ultrasound technique is a simple and reliable means for obtaining anatomical landmarks when drilling the calcaneal tunnel for ligament reconstruction of the lateral plane of the ankle. This tunnel should preferably be drilled obliquely from the heel towards the subtalar joint (1 h-3 h direction on an ultrasound cross section), which preserves a maximum distance from the sural nerve for safety purposes, while allowing an accurate anatomical positioning of the osseous tunnel.

Current Concepts on Subtalar Instability

Subtalar instability remains a topic of debate, and its precise cause is still unknown. The mechanism of injury and clinical symptoms of ankle and subtalar instabilities largely overlap, resulting in many cases of isolated or combined subtalar instability that are often misdiagnosed. Neglecting the subtalar instability may lead to failure of conservative or surgical treatment and result in chronic ankle instability. Understanding the accurate anatomy and biomechanics of the subtalar joint, their interplay, and the contributions of the different subtalar soft tissue structures is fundamental to correctly diagnose and manage subtalar instability. An accurate diagnosis is crucial to correctly identify those patients with instability who may require conservative or surgical treatment. Many different nonsurgical and surgical approaches have been proposed to manage combined or isolated subtalar instability, and the clinician should be aware of available treatment options to make an informed decision. In this current concepts narrative review, we provide a comprehensive overview of the current knowledge on the anatomy, biomechanics, clinical and imaging diagnosis, nonsurgical and surgical treatment options, and outcomes after subtalar instability treatment.

A calcaneal tunnel for CFL reconstruction should be directed to the posterior inferior medial edge of the calcaneal tuberosity

PURPOSE

Anatomical reconstruction of the calcaneofibular ligament (CFL) is a common technique to treat chronic lateral ankle instability. A bone tunnel is used to fix the graft in the calcaneus. The purpose of this study is to provide some recommendations about tunnel entrance and tunnel direction based on anatomical landmarks.

METHODS

The study consisted of two parts. The first part assessed the lateral tunnel entrance for location and safety. The second part addressed the tunnel direction and safety upon exiting the calcaneum on the medial side. In the first part, 29 specimens were used to locate the anatomical insertion of the CFL based on the intersection of two lines related to the fibular axis and specific landmarks on the lateral malleolus. In the second part, 22 specimens were dissected to determine the position of the neurovascular structures at risk during tunnel drilling. Therefore, a method based on four imaginary squares using external anatomical landmarks was developed.

RESULTS

For the tunnel entrance on the lateral side, the mean distance to the centre of the CFL footprint was 2.8 ± 3.0 mm (0-10.4 mm). The mean distance between both observers was 4.2 ± 3.2 mm (0-10.3 mm). The mean distance to the sural nerve was 1.4 ± 2 mm (0-5.8 mm). The mean distance to the peroneal tendons was 7.3 ± 3.1 mm (1.2-12.4 mm). For the tunnel exit on the medial side, the two anterior squares always contained the neurovascular bundle. A safe zone without important neurovascular structures was found and corresponded to the two posterior squares.

CONCLUSION

Lateral landmarks enabled to locate the CFL footprint. Precautions should be taken to protect the nearby sural nerve. A safe zone on the medial side could be determined to guide safe tunnel direction. A calcaneal tunnel should be directed to the posterior inferior medial edge of the calcaneal tuberosity.