# How sex and gender differences influence in ACL rupture probabilities: anatomic, biomechanics, hormonal and social factors

> Anterior cruciate ligament (ACL) injuries are the most common ligament injury of the knee, with approximately 100,000 to 200,000 injuries occurring among athletes per year.

## Introduction
The anterior cruciate ligament (ACL) is a band of dense connective tissue extending from the femur to the tibia. It is a critical structure in the knee joint that resists anterior tibial translation and rotational loads. The ACL originates at the medial wall of the lateral femoral condyle and inserts into the middle of the intercondylar area, playing a significant role in the stabilization and kinematics of the knee joint.

## ACL Injury Mechanisms
ACL injuries are the most common ligament injury of the knee. They occur through both contact and non-contact mechanisms, with contact injuries being more common in males and non-contact injuries more prevalent in females. These injuries typically require surgical reconstruction, involve long rehabilitation times, and carry high re-rupture rates. The most common mechanisms of rupture include decelerating, cutting, and rotational movements, particularly during landing.

## Anatomic and Biomechanical Factors
Female injury rates per exposure are higher than those of males, which may be attributed to anatomic differences in the lower kinematic chain, such as the Q angle (quadriceps angle). A wider Q angle increases the lateral pull of the quadriceps femoris muscle on the patella and places medial stress on the knee. Females typically have wider pelvises, which increases this angle.

Research into dynamic knee valgus—which places significant tensile forces on the ACL—shows it is more common in women, partly due to wider hips. Furthermore, females often generate less force in the hip abductors and may rely more on quadriceps activation, leading to higher muscle fatigue and increased injury risk. Poor trunk kinetics and core stability have also been identified as factors that may predispose women to knee injuries.

Regarding the ACL attachment location, studies have investigated whether this differs between sexes. While no significant differences in attachment location were found between males and females, the study noted that a more posterior and proximal femoral ACL attachment origin might predispose individuals to rupture regardless of gender.

## Hormonal Influences
Evidence suggests that estrogen and progesterone receptor sites exist in human ACL cells. Estradiol levels have a dose-dependent effect on fibroblasts, which produce collagen—the primary load-bearing component of the ACL. Alterations in fibroblast metabolism may influence the quantity, type, and stability of collagen, potentially reducing the strength of the ligament and predisposing female athletes to injury.

## The Role of Social and Environmental Factors
Traditional research has focused heavily on biological factors; however, annual ACL injury rates have remained unchanged in females while decreasing in males. This suggests that biological explanations are insufficient. Recent research highlights the impact of social environments:
* **Pre-sport environment:** Mothers often underestimate the crawling abilities of daughters compared to sons, impacting physical development.
* **Training environment:** Female athletes may hold back during training due to social pressures regarding body image and the desire to avoid becoming "bulky."

A more holistic approach that integrates social and environmental factors is necessary to effectively address the disparity in ACL injury rates.

## Authors
* **Rivada López Noa**, Physiotherapy student, Universidade da Coruña, Spain
* **Busto Acedo Melania**, Physiotherapy student, Universidade da Coruña, Spain
* **Otero Fraga Pablo**, Physiotherapy student, Universidade da Coruña, Spain
* **Haukka Sonja-Susanna**, Physiotherapy student, Savonia University of Applied Sciences, Kuopio, Finland
* **Hyvärinen, Johanna**, Physiotherapy student, Savonia University of Applied Sciences, Kuopio, Finland
* **Lehtinen Maiju**, Physiotherapy student, Savonia University of Applied Sciences, Kuopio, Finland
* **Marja Äijö**, PhD, Principal lecturer of gerontology and rehabilitation, Savonia University of Applied Sciences, Finland
* **Mari Tuppurainen**, physiotherapy lecture, Savonia University of Applied Sciences, Kuopio, Finland
* **Dagmar Pavlu**, Physiotherapist, Assoc. Prof. Charles University, Czech Republic
* **Ivana Vláčilová**, Professor, Charles University, Czech Republic
* **Jamile Vivas Costa**, PhD, MSc, PT, Lecturer at Department of Physical Therapy, Medicine and Biomedical Sciences, Faculty of Physiotherapy and Researcher at Psychosocial intervention and functional rehabilitation group, Universidade da Coruña, Spain
* **Montserrat Fernández Pereira**, MSc, PT, Lecturer at Department of Physical Therapy, Medicine and Biomedical Sciences, Faculty of Physiotherapy and Physiotherapist at Spinal Cord Injury Unit, A Coruña Hospital (CHUAC), Spain
* **Verónica Robles García**, PhD, MSc, PT, OT, Lecturer at Department of Physical Therapy, Medicine and Biomedical Sciences, Faculty of Physiotherapy and Researcher at the Neuroscience and motor control group, Universidade da Coruña and Biomedical Institute of A Coruña, Spain

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