Background There is an incidence of 1 per 10 000 people suffering collateral ligament sprain per day. In healthy people there is no difference, but in teenager sport practice, females have prevalence than males in ankle sprains production. 85% of ankle sprains are of the collateral ligament, because it usually happens by a varus or valgus with flexion or rotation movements, being the most frequent one injured its anterior beam, or peroneal-talar anterior ligament.

Methods To value morphologic sonographic changes in the cross-sectional area (CSA) in athletes between 18–30 years old who had 2 or more lateral ligament ankle sprains in the same joint through daily propioceptive exercise program about 30 min sessions for 3 weeks. The person who made the sonographic measurements was a muscleskeletal sonographer level 2, with more than 5 years experience. Our sample was with 2? in control group and other 2? In other group which included propioceptive exercises. The distance between the head and the peroneal malleolus was divided in three thirds giving from proximal to distal, 3 same measures, CSA1, CSA2 y CSA3.

Results Baseline characteristics of both groups were similar in both groups: 100% ?, age 23,5±2,1 years, weight 83±11,13 kg, height 1,81±0,09 and a BMI of 24,55±1,68. After intervention therapy with propioceptive exercises. The diferences between pre and post measurements in CSA1 level was −0,27±1,9 (F 3,93; P 0,19), in CSA2 was 0,32±0,64 (F 2,45; P 0,26), and in CSA3 was −0,06±0,83 (F 1,62; P 0,33).

Conclusions Despite the sample being extremely small, and in view of the data obtained, we can recomend as an optimum point to find changes of the CSA in the distal point of peroneal muscles (CSA1), as most sensitive point for objectify sonographic changes after doing propioceptive exercise.