Appoach to subtalar instability of the ankle

Introduction

Ankle sprains are the most common sports injuries and they account for between 3 and 5% of all Emergency Department visits. Ankle sprain has high societal economic costs associated with the diagnosis, treatment and loss of work productivity with an estimated annual cost of €187.2 million in the Netherlands alone.

Most patients are able to return to normal activity within 4 to 8 weeks. However, up to 50% of patients are reported to have residual complaints affecting their daily life activities. The most common causes are incomplete rehabilitation, chronic instability, intra-articular lesions, undetected syndesmotic or deltoid sprains and chronic tendon degeneration.

Between 10 to 30% of patients with an ankle sprain develop chronic ankle instability(CAI). CAI can be distinguished into mechanical and functional. Mechanical instability is defined as a pathologic laxity of the tibiotalar joint (with reproducible increased motion) in association with complaints of giving way. Functional instability is a subjective feeling of giving way that may occur despite an absence of deviation beyond the normal physiological range of motion of the talus.

In patients with persisting symptomatic mechanical instability surgical treatment should be considered. In terms of surgical treatment, a distinction is made between repair and reconstruction. A repair is defined as suturing of the torn lateral ligaments. A reconstruction refers to the replacement of the chronically deficient lateral ligaments with local tissues or with graft tissue. The Broström-Gould repair is still considered the gold-standard first-line surgical procedure. In case of failure of a surgical repair, an ankle ligament reconstruction is recommended. Some patients (high BMI, heavy labour occupation or sports requirements,…) may benefit from a ligament reconstruction as a primary procedure. Talocrural instability is often associated with subtalar instability, and unrecognized subtalar instability is a possible cause of failure of the surgical treatment.

The precise cause of functional instability remains unknown, but multiple possible causes are suggested, such as proprioceptive and neuromuscular deficit; unrecognized true subtalar instability; damaged ligaments; scar tissue; and micro-instability. This makes treatment in this group of patients difficult, and the role of surgery controversial, both with regards to timing and the type of procedure.

Subtalar instability has been associated with failure of treatment in patients with mechanical instability as well as functional instability. The incidence of subtalar instability remains unknown but has been estimated from 10 to 80%. Currently, subtalar instability is still difficult to diagnose and is often overlooked [1, 2]. Several methods of stress radiographs have been described but more recent publications question the reliability of those methods. As the normal mobility of the subtalar joint occurs in tridimensional plane, it is difficult to assess this mobility with conventional two dimensional X-rays.

The difficulties in diagnosing cause improper treatment of the patients with suspected subtalar instability. Currently there are no evidence based guidelines according the best treatment strategy. The advent of newer implants and less invasive surgical techniques offers opportunities but still many questions remain unanswered, such as: How  frequent is subtalar instability in patients with CAI? How to treat patients with persistent complaints of subtalar instability? What about patients with a combination of subtalar and tibiotalar instability? At what timing a surgical treatment should be considered? Which surgical technique should be used? Which ligaments should be repaired or reconstructed? Are the newer techniques save and how can we improve them?

Several studies have already been done by our research group about the treatment of talocrural instability in collaboration with the ESSKA AFAS Ankle Instability Group. The aim of this project is to continue this research with a focus on the subtalar instability. General hypothesis

Subtalar instability is a common problem but often overlooked that causes unadapted treatment.

Aims of the project

to improve diagnostic tools to assess subtalar instability.

to improve the surgical treatment and offer some guidelines

Methodology

Exploratory studies

Three exploratory studies will be performed to assess the current knowledge, diagnosis and treatment.

The aim of the first study is to conduct a systematic review regarding the diagnostic accuracy of various modalities used to diagnose subtalar instability. Our main objectives are to determine if there are reliable and usable tests to assess subtalar ankle instability.

The second study should assess the current attitude in the approach of patients with lateral ankle instability and the current approach to subtalar instability. A survey among surgeons with clinical and scientific experience in the treatment of ankle instability will be done in collaboration with the ESSKA AFAS Ankle Instability Group. The survey would look for points of agreement concerning the best strategy for the treatment of CAI.

A third study will assess some epidemiologic aspects. Records of the emergency unit and the orthopaedic department will be assessed to study the appearance of residual symptoms after an ankle sprain with special attention to the subtalar joint.

Developing a diagnostic tool to assess ankle instability.

Improving the treatment of subtalar instability

The data from the first two parts will be integrated in the third part of the study.

A biomechanical study to address subtalar instability. A biomechanical model of the reconstructed ligaments should be tested. The feasibility of the tunnels and the fixation strength of the graft into the tunnels should be estimated.