Abstract
Category:
Ankle, Hindfoot, Trauma
Introduction/Purpose:
Lateral talar process fractures (LTPF) constitute 15% of ankle injuries in snowboarders. They are often misdiagnosed on conventional radiographs, which are also susceptible to rotational malpositioning due to pain. A positive V sign is an interruption of the contour of the lateral talar process. It has been suggested to be pathognomonic for LTPF. However, there are very few studies about this topic. The objectives were to study whether the V sign is useful in diagnosing LTPF.
Methods:
In an experimental study, two investigators evaluated lateral radiographs (n=108) of high resolution, solid foam, radiopaque distal foot and ankle models. Two other investigators, who obtained the radiographs, defined the gold standard. Four different models (no fracture, type A, B, or C fractures according to Hawkins) and three varying ankle joint positions (0°, 20°, and 40° of inversion, plantar flexion, and internal rotation) were the independent variables. The correct detection of a V sign on lateral radiographs (Figure 2 showing a positive V sign on a lateral radiograph in a type B LTPF) was the primary dependent variable and the detection of the fracture type and uncertainty in making this decision were the secondary dependent variables. The chosen study size surpassed the sample size calculation. The chi-squared test was used for categorical data.
Results:
There were fair interobserver agreements on the V sign and fracture types (kappa coefficient [k]=0.35, 95% confidence interval [CI] 0.18-0.53, p<0.001 and k=0.37, 95% CI 0.26-0.48, p<0.001). For the detection of the V sign, the mean sensitivity, specificity, positive predictive value, negative predictive value, likelihood ratio, and mean uncertainty were 77% (95% CI 67-86%), 59% (95% CI 39-78%), 85% (95% CI 75-92%), 46% (95% CI 29-63%), 2, and 38%. Increased inversion and type B fractures were associated with better detection of the V sign (p=0.035 and p=0.011 as well as p=0.001 and p=0.013, for each investigator). Plantar flexion and internal rotation were not associated with the V sign (p=0.31 and 0.33 as well as 0.35 and 0.53, for each investigator).
Conclusion:
It is not recommended to exclusively use the V sign for the evaluation of LTPF. If negative, LTPF cannot be excluded. However, if positive, it may be a helpful surrogate parameter for the presence of LTPF, especially type B fractures. Inversion may lead to better visualization of the V sign. This knowledge about the V sign is a valuable asset for the diagnostic skillset of an orthopaedic surgeon. Future clinical studies may focus on validating these experimental findings.
[Notes: Level of evidence is not applicable to this study. This abstract has also been submitted to the swiss orthopaedics congress 2017.]