A risk assessment model for chronic ankle instability: indications for early surgical treatment? An observational prospective cohort - study protocol

Abstract

Background: Chronic ankle instability (CAI) is a common result of an ankle sprain. Even though early surgical treatment yields the best results, overall only professional athletes are eligible for acute surgical stabilization. Treating all patients with early surgical stabilization leads to a high amount of unnecessary invasive interventions, as not all patients progress to CAI. If patients at risk of developing CAI can be identified, treatment policies may be applied more effectively and efficiently. The purpose of this study is to develop a risk assessment model to identify patients at risk for CAI that should receive early surgical treatment.

Methods: In this observational prospective cohort, all patients aged sixteen years and older, reporting at the emergency department of one of the participating hospitals after sustaining a lateral ankle sprain, and filled out 1 out of 3 follow-up questionnaires and the 1 year follow-up are included. A lateral and anteroposterior radiograph is made. Patients are excluded if a fracture or other pathology is present. The included patients receive four questionnaires, including questions focusing on the sprain, treatment and complaints, the Foot and Ankle Outcome Score and the Cumberland Ankle Instability Tool. A total of eleven radiographic variables are assessed for inter- and intra-observer reliability. Additionally, four factors extracted from the questionnaires, will be evaluated for correlation with CAI. Significantly correlating factors (e.a. risk factors) will be implemented in a risk assessment model. For the final model, based on sixteen variables with a minimum of 20 events per variable and a prevalence of 30-40% after an initial sprain, a sample size of 2370 patients is needed to perform both internal and external model validation.

Discussion: This study will develop the first large scale model for the risk at CAI after an ankle sprain combining radiographic and patient characteristics. With this risk assessment model, patients at risk for CAI may be identified and properly informed on the treatment options. Patients identified as being at risk, may receive more adequate follow-up and become eligible for early surgical stabilization. This prevents patients from experiencing unnecessary long-lasting complaints, increasing the success rate of conservative and surgical treatment.

Trial registration: Retrospectively registered: NCT02955485 [Registration date: 3-11-2016]. NTR6139 [Registration date: 3-1-2017].

Keywords: Ankle geometry; Ankle sprain; Chronic instability; Model methodology; Prognosis.

Conflict of interest statement

Ethics approval and consent to participate

IRB approval has been obtained from the IRB of the AMC for the AMC and Flevoziekenhuis (W16_258 # 16.303), the Slotervaart Medical Center (U/16.130/P1654), the VUmc (2016.541).

The IRB provided a waiver for requesting written informed consent as this study concerns an observational cohort only including questionnaires. For use of the radiographs verbal informed consent was declared sufficient by the local IRB and legal department.

Consent for publication

Not applicable.

Competing interests

Dr. Haverkamp is a member of the Editorial Board of BMC Musculoskeletal Disorders.

Dr. ir. L. Blankevoort has (pending) Zimmer-Biomet and Smith&Nephew research grants.

Publisher’s Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Figures

Fig. 1

Study outline. Abbreviations: ER: Emergency Department; T0: 1st baseline questionnaire; T1: 2nd questionnaire at 3 months; T2: 3rd questionnaire at 6 months; T3: 4th questionnaire at 12 months. Blue: Standard care at the ER; Red: Inclusion phase; Green: Included patients

Fig. 2

Alignment assessment using the medial distal tibial angle (b). This angle (arrows) is formed by the tibial axis (a-b) and the joint orientation line of the distal tibia (c). The MDTA was measured in two ways: (1) the absolute angle and whether this angle included a (2) varus (<87o), normal (87-91o) or valgus (>91o)

Fig. 3

The fibular position is assessed drawing two lines from the edge of the anterior tibia to the posterior part of the tibia (b) cq. the anterior part of the fibula (a). The absolute distance is measured using the projected posterior distance in millimeters (mm) of the fibula in relation to the tibia (height a in mm); and the relative fibular position is assessed as a posterior position in terms of percentage (a divided by b in %)

Fig. 4

The tibiotalar contact ratio is assessed using 3 variables: the talar radius (r); the talar height (h); and the tibiotalar sector (α). By drawing a circle digitally fitted to the talar joint surface, the radius is determined by drawing a line to the middle of the circle, measured in millimeters (r). The height is determined drawing a line through the middle of the circle from the surface of the talus to the inferior border, measured in millimeters (h). From the center of the circle two lines are drawn to the anterior and posterior margins of the distal tibia, representing the tibiotalar sector (α)

Fig. 5

Medial Malleolar Height Angle (MMHA) formed by the angle connecting the distal tibial joint line (a-b) and the line from the most lateral point of the tibiotalar joint line to the most distal point of the medial malleolus (b-c)

Fig. 6

The Talar Convexity Angle (TCA) is formed by connecting the posterior talar tubercle (a), the most proximal part of the talus (b), and the deepest point of the transition to the talar neck (c)