Anterior Cruciate Ligament (ACL) injuries are a significant concern in sports medicine, especially among professional footballers. The incidence of these injuries remains a prominent problem, with greater susceptibility observed in female athletes compared to male.

Infrared thermography has proven to be an effective, non-invasive, and objective tool for evaluating skin temperature, aiming to prevent and monitor sports injuries. Specifically, the evolution of skin temperature in the knee has been used to support the return-to-play process and provide valuable information on the progression of knee inflammation and the thermal balance of key body regions such as the quadriceps and hamstrings.

Although various factors have been implicated in the higher risk of ACL injuries in female athletes, including differences in neuromuscular control, hormonal influences, and anatomical variations, there is a scarcity of studies describing differences in knee physiology, specifically related to skin temperature, between male and female athletes with ACL injuries.

This study, published in Isokinetic Conference 2024 (Madrid, Spain), aims to address this gap in the literature by using thermography to evaluate the differences in knee skin temperature between male and female professional footballers with ACL injuries. By clarifying possible differences in the evolution of thermal asymmetry, this research seeks to contribute to a deeper understanding of gender-specific physiological factors.

Methodology.

A total of 666 male athletes and 320 female athletes, both amateur and professional, from various sports disciplines (football, volleyball, American football, basketball, and handball) from professional and amateur teams in different European and American countries were evaluated. Of these, 467 were male professional players and 31 were female professional players.

The inclusion criteria were having been diagnosed and operated on for an ACL injury and having been evaluated at least once with a thermal camera. Thermographic evaluations were conducted indoors under controlled conditions (22.60ºC ± 2.02ºC), following the TISEM protocol standards. Subjects were instructed to avoid any potential factors that could affect their skin temperature (including treatments, ointments, etc.).

A thermography technician used FLIR thermal cameras (Teledyne Flir, Colorado, USA) with a minimum resolution of 320×240 pixels to collect thermal images. The thermograms were analyzed using ThermoHuman software (PEMA THERMO GROUP SL., Madrid, Spain), which automatically recognizes regions of the lower limbs (22 regions) and extracts the average, minimum, maximum temperature, and the skin temperature asymmetry between contralateral regions.

Results.

A total of 1591 sessions of the 986 subjects were analyzed. The trends in knee skin temperature asymmetry for each group are represented in Figure 1 of the study. The equations for each trend line are as follows:

• Trend for all male athletes: Y = (1.7559) + (-0.0034)X
• Trend for all female athletes: Y = (1.0006) + (-0.0036)X
• Trend for male football players: Y = (1.9747) + (-0.0033)X
• Trend for female football players: Y = (1.3865) + (-0.0069)X

The results show that knee thermal asymmetry in male professional players with ACL injuries is greater than in female professional players throughout the rehabilitation process. The trends describe a return to symmetric thermal balance in women around day 275 post-injury, while male players need more than 600 days to achieve the same results. The comparison between all male and female athletes is similar.

Conclusions.

• Knee thermal asymmetry in male professional footballers with ACL injuries is greater than in female professional footballers.
• The trends describe a return to symmetric thermal balance in women by day 275 after the ACL injury, whereas male players need more than 600 days.
• These results confirm thermography as an objective tool for establishing refined gender-based benchmarks to optimize the effectiveness of ACL return-to-play protocols.
• Further studies are needed to understand and explain the reasons for these differences.

References

1. Waldén M et al. The epidemiology of ACL injury in football (soccer): a review of the literature from a gender-related perspective. Knee Surg Sports Traumatol Arthrosc. 2011;(1):3-10.

2. Côrte AC et al. Infrared thermography study as a complementary method of screening and prevention of muscle injuries. BMJ Open Sport Exerc Med. 2019;5(1).

3. Piñonosa S et al. Thermal evolution of lower limbs during a rehabilitation process after ACL surgery. Kinesiology. 2013; 45.(1.):121-129.