1.    Introduction
Sports injuries not only threaten the health of players but also lead to the waste of substantial financial resources. However, the number of people choosing sports as their profession is increasing every day, and consequently, the associated costs are also rising. Therefore, to prevent the waste of financial resources, it is essential to implement preventive measures to avoid injuries (1). Over 50 percent of all sports injuries occur in the lower extremities, particularly the knee (2). Volleyball is one of the most popular sports in the world. Like other sports, volleyball involves a risk of injuries, which not only incur financial and time costs but also reduce athletes' performance. Therefore, investigating injuries in this sport is important and necessary. Although volleyball is not a contact sport and generally has a lower risk of injury, it involves repetitive overhead arm movements, as well as frequent jumping and landing, which can lead to both acute and chronic injuries in the upper and lower limbs. In volleyball, more than half of sports injuries occur in the lower limbs, particularly the knee. The most common injury sites for volleyball players include the knees, ankles, toes, and back, with knee injuries being especially significant due to their prevalence, treatment costs, and recovery time. The aim of this study was to review the research literature related to knee injuries in volleyball.
2.    Methods
This review research was conducted through a library-based study of articles related to the subject, focusing on both quantitative and qualitative aspects, in the year 1402 (2023). The articles were sourced from reputable domestic and international databases. The criteria for selecting articles included those indexed between 2000 and 2022 for international publications and between 1390 and 1402 for national publications. Only national and international articles published in relevant and reliable sports science journals, with full-text access available, were considered. The exclusion criteria for articles were as follows: studies with small or unclear population characteristics and sample sizes, articles where the research methodology was not clearly defined, and studies that focused on physically or intellectually disabled populations. The selection process involved first reviewing the abstracts and matching them against the inclusion criteria. If the research methodology was well-defined and did not conflict with the exclusion criteria, the articles were accepted for further review. In total, 769 articles were examined for this research, of which 104 were thoroughly evaluated and studied.
3.    Results
and age groups. Various types of ligament, joint, and muscle injuries in the knee area are common in volleyball, with some of the most significant injuries detailed below. Patellar Tendinopathy is one of the most prevalent injuries among volleyball players, especially at the elite level. This injury often results in a decreased level of play and can cause long-term interruptions in training and competition. Factors such as training volume and the type of playing surface contribute to the occurrence of patellar tendinopathy. Anterior Cruciate Ligament (ACL) Injury is another common volleyball-related injury, requiring an extended period of treatment and recovery. ACL injuries often lead to long-term disability and incur very high treatment costs. At least 70% of ACL injuries are non-contact, with evidence showing that most non-contact ACL injuries occur during activities involving landing. The differences in biomechanical structure and hormonal characteristics between men and women result in different physical responses to various movement conditions, leading to variations in the prevalence of knee injuries between male and female athletes. Women are more prone to ligament injuries, while men are more susceptible to tendinopathy. Additionally, factors such as muscle strength, proper technique, flexibility, balance, quick reactions, and the biomechanical characteristics of the lower limbs, particularly during landing, contribute to the risk of injury. As noted, multiple factors contribute to knee injuries. These risk factors are generally divided into two broad categories: external and internal. External factors primarily involve environmental risks, while internal factors are further divided into modifiable and non-modifiable physical risks. Researchers have recommended various training approaches to adjust and improve modifiable internal factors, including strength training, core stability training, neuromuscular training, and combined training (Table 1).

4.    Conclusion
Knee injuries are the second most common type of injury in volleyball and are of particular significance in the research literature due to their long recovery periods and high treatment costs. Research indicates that the prevalence of knee injuries varies across different age and gender groups, with semi-professional female athletes experiencing the highest injury rate—7.07 per 1,000 athlete-exposure hours. It is important to note that studies within the same population group sometimes yield differing and even contradictory results, which may be attributed to variations in the statistical populations studied and differences in biological and biomechanical characteristics. Regarding the types of knee injuries, ligament injuries, especially ligament strains, are the most common, accounting for 31.5% to 47.3% of all knee injuries in volleyball. Concerning injury mechanisms, while various opinions exist in the literature, there is general agreement on the critical role of jumping and landing movements in injury occurrence. During landing, if the body is not properly positioned to control the forces applied to the lower limbs, excessive stress can enter the knee joint, increasing the risk of injury. In terms of injury prevention, the literature suggests strength training, core stability exercises, neuromuscular training, and combined exercises. Among these, combined exercises are particularly emphasized due to their higher relative frequency in research studies. This study highlights the importance of addressing knee injuries in volleyball, especially among female athletes. It is recommended to focus on proper jumping and landing techniques, as well as on effective preventive exercises, including strength training, as supported by the research literature.

Ethical Considerations
Compliance with ethical guidelines
There were no ethical considerations to be addressed in this research.
Funding
This research did not receive any grants from funding agencies in the public, commercial, or non-profit sectors.
Authors' contributions
All authors contributed equally to preparing the article.
Conflicts of interest
The authors declared no conflict of interest.