Lateral ankle sprain (LAS) is one of the most common reasons for primary care office and emergency department visits, with an overall incidence of 2.15 per 1,000 person-years in the United States.In its acute phase, LAS is associated with swelling, haematoma and pain over the anterior talofibular and calcaneofibular ligaments, as well as ligamentous laxity of these ligaments. Interventions following acute LAS are based upon the three stages of biological ligament healing: inflammatory phase, proliferation phase (6 weeks to 3 months after trauma) and remodelling or maturation phase (until 1 year after trauma). The initial treatment during inflammatory phase is directed towards avoiding or diminishing excess swelling and ongoing injury, thus optimizing the healing process. Therefore, RICE (Rest, Ice \[cryotherapy\], Compression, Elevation) is the treatment of choice for the first 7 to 10 days to reduce pain and swelling. Cryotherapy has been used for a long time in rehabilitation; mainly using ice, cool packs or cold water. Lately, a new device, the CRYOFOS, has been developed to provide more performing ways to use cryotherapy. CRYOFOS uses a fluid (hyperbaric CO²) that is sprayed in the form of dry ice on the body region to be treated. It leads to a so-called thermal shock, which sees the skin temperature cooled from 32 ˚C to 2-4 ˚C in 30 sec.While CRYOFOS seems, theoretically, better than other cooling procedures, its superiority has never been determined following acute injuries such as LAS. Considering the extensive use of cold in the management of acute LAS, it would be even more relevant to examine the impact of cryotherapy on both the reduction of symptoms and the functional limitations of subjects who sustained a LAS.

The objective of this exploratory randomized control trial is to compare, in participants with acute lateral ankle sprain (LAS) , the reduction of symptoms and functional limitations between two groups of subjects who undergo a conventional rehabilitation program with (experimental group) or without CRYOFOS (comparison group). The hypothesis is that CRYOFOS will lead to a faster reduction of symptoms and functional limitations, and a faster return to daily living activities.Thirty-six participants of 18 years of age and older with acute LAS (sustained a LAS three days or less before the first evaluation session) will be recruited and randomly assigned to either a group receiving conventional rehabilitation program with the addition of CRYOFOS (experimental group; n=18), or to a group only receiving the conventional rehabilitation program (comparison group; n=18). This single-blind (evaluator), parallel-group RCT will include five evaluation sessions over 6 weeks (baseline, day 7, week 2, week 4 and week 6) and 8 treatment sessions (1st and 2nd weeks: 3 sessions/week; 3rd and 4th weeks: 1 session/week) during a 4-week period. The primary outcome will be the functional limitations, evaluated using the Lower Extremity Functional Scale (LEFS). Secondary outcomes will include the level of ankle pain, evaluated using Numeric Pain Rating Scales (NPRS), weight-bearing ankle dorsiflexion range of motion (also called Bent Knee DorsiFlexion test), assessed with the maximal advancement of the tibia over the talus in a weight-bearing position, and joint swelling, using the Figure-of-Eight method.

Both groups will receive the same conventional program consisting of: compression, bracing, early mobilization (including manual therapy), strengthening (isometric and isotonic using elastic bands) and proprioception (using proprioception boards) exercises, according to the grade of the sprain and the stage of biological ligament healing. However, for the experimental group, CRYOFOS will be applied on the ankle at the end of each of the 8 sessions (in accordance to the protocol established).

Descriptive statistics will be used for all outcome measures at each measurement time to summarise results. Baseline demographic data will be compared (independent t-test and Chi-squared tests) to establish the comparability of groups. All data will be tested to check the distributional assumptions for the inferential statistical analyses. An intention-to-treat analysis will be used in which all participants will be analysed in the group to which they were originally assigned. All dropouts and the reason for dropping out of the study will be reported. Any harm or unintended effects during the programs will be recorded. A 2-way ANOVA (2 cryotherapy \[CRYOFOS or Ice\] x 5 Time \[baseline, day 7, week 2, week 4, week 6\]) will be used to analyse the effects of CRYOFOS on primary outcome (LEFS) and secondary outcomes (SPSS 22, proc GENLIN \[Generalized Estimating Equations for repeated measures\]).