Study of local cryotherapy methods for the knee joint

BACKGROUND: A promising method for treating musculoskeletal disorders to alleviate symptoms and promote recovery is local cryotherapy (LC). Proper control and regulation of the procedure enable safe interventions with predictable therapeutic effects for various locations.

AIMS: This study aims to identify measurable physical criteria for the effectiveness of the LC procedure and the dosing characteristics and to compare and analyze the capabilities of various methods.

MATERIALS AND METHODS: The experiment involved 16 volunteers who were randomized into 4 groups. The first and second groups underwent LC using ice bags for 20 min with a cooling agent consisting of an ice and water mixture and a 23.1% sodium chloride solution. The third and fourth groups underwent nitrogen (for 3 min) and air (for 20 min) LC, respectively. During the experiment, the skin temperature was measured using a temperature sensor and thermal imaging camera.

RESULTS: The lowest value of the minimum final temperature after cooling was recorded with liquid nitrogen vapor as equal to 0.88 ± 1.75 ℃. The minimum area of the work zone was 33.7 ± 7.1 cm². When cooled with an ice bag with water and ice, the most uniform distribution of the temperature field among the investigated cases was observed, with the highest values of the minimum final temperature (i.e., 6.43 ± 0.90 ℃) and minimum area of the work zone (i.e., 135.2 ± 34.6 cm²) among the investigated methods.

CONCLUSIONS: The main physical criteria for the effectiveness of LC are identified as temperature and the dynamics of its changes on the surface of the object of exposure. A dosing characteristic, i.e., the area of the work zone, was proposed and evaluated. In the area of the work zone, the target temperature is achieved. Based on the main physical criteria, the three main cooling methods are compared. These methods achieve the target result in different ways. The easiest to use and prepare are contact methods using ice bags. Air cooling in the investigated mode is more easily tolerated by the subjects, and in terms of the physical criteria, it is equivalent to contact methods. Cooling with nitrogen vapor leads to the fastest achievement of the target temperature on the surface and the least cooling of internal tissues; therefore, cooling deep into the biological tissue is limited.