Introduction
Skeletal deformities of the knee are the most common body posture disorders, and the most common of these are the genu varum and the genu valgum. A genu valgum is a type of deformity of the knee in the frontal plane, in which the ankle joints had spaced apart if the knees are in contact with each other in a weight-bearing position.
The genu varum is another deformity in which the internal condyles of the femur become spaced apart if they are in weight-bearing contact with the inner ankles of the ankle. These abnormalities were caused by various causes, including heredity, osteoporosis, osteoarthritis, damage to the growth plates, muscle paralysis, rupture of the capsule and external and internal ligaments of the knee, muscle weakness, and muscle shortening. 
Some posture disorders can cause changes in the direction of a body part relative to the base of support, which restricts the movements needed to maintain a proper posture and balance. It makes children who are less proficient in basic motor skills more likely to have problems in everyday motor areas. There is a possibility that they do not perform well in sports activities and games of childhood and adolescence. Knee deformities are more important in children and adolescents because this group had exposed to undesirable pressure on the knee in different environments such as home and school, which will increase the risk of injury and future problems.
One of the fundamental motor skills is jumping. Children typically start jumping activities early and often learn simple forms of this pattern before two. In jumping skills, the child raises his body from a surface with one or both feet and then land with both feet. To improve foot action, the jumper must first take off, fly, and land symmetrically with both feet. Secondly, he must then fully open the joints of the ankles, knees, and thighs at the moment of taking off the body from the ground. And after entirely pulling the legs with full force when taking the body off the ground, bend the joints of the knees and thighs together in the flight stage in a pair length jump. It is helpful for beginners to identify some of the features of long bipedal jumping. In children’s jumps, the body bends in the preparatory phase, very little, and the legs open when taking off the ground is not complete. 
Materials and Methods
The child has gathered the legs instead of opening the legs entirely in the throwing phase. Jumping and landing are some of the most common sports in sports such as basketball, volleyball, football, and badminton. This study had performed on 45 boys aged 7 to 9 years in Shahr-e-Rey of Tehran province who had randomly selected. In this study, using a caliper and a ruler, the distance between the inner ankles and the distance between the inner epicondyles of the thigh had measured, and a length of more than 2.5 cm had considered as cruciate and brace anomalies. 15 students had a genu varum deformity, 15 had a genu valgum deformity, and 15 had a normal knee.
In this study, the stepwise method of longitudinal pair jumping of Clark and Phillips had used. In this way, the legs had fully extended in the stage of detachment from the ground; in other words, flexion in the knee joint had minimized in the flight stage, the knee joint was bent, or the knee joint flexion had maximized. Finally, in the landing stage, the knee joint opens. In other words, the flexion of the knee joint had minimized in the landing stage. Subjects performed a long jump in front of the camera using the Clark and Phillips step method. The knee joint angle data on the sagittal plate had analyzed in three phases: detachment from the ground, flight, and landing using motion analysis software.
Results
The research variables had analyzed in two sections: descriptive statistics and inferential statistics in SPSS software v. 21. The Shapiro-Wilk test had used to examine the normal distribution of data, and the Kruskal-Wallis test and the Mann-Whitney U test had used to detect differences between groups.
The results showed that the knee joint angle in the genu valgum group in the phase of separation from the ground was significantly different from the normal knee group and was not significantly different from the genu varum group. There is no significant difference in knee joint angle in flight and landing phases between genu varum, genu valgum, and natural knee groups. According to the results, the deviation created in the genu valgum deformity and disturbing the lower limb can negatively affect the performance of children when detached from the ground in the skill of longitudinal pair jumping (Table 1).


Discussion
In the other stage, where there was no difference between the functions of the groups, we can proceed according to the theoretical approach of dynamic body systems, which are composed of different components. Whenever one of them changes, the other body dimensions will change accordingly, and this exchange of different systems and dimensions as a functional unit gives the body a lot of flexibility. Based on this, it can be concluded that this abnormality is probably normal in terms of function, and because it occurred during childhood, it has led to their better adaptation.

Ethical Considerations
Compliance with ethical guidelines
This study has been reviewed and approved in terms of research ethics in the Department of Sports Biomechanics, Faculty of Physical Education and Sports Sciences, Central Tehran Branch, Islamic Azad University, Iran.

Funding
The present article is the result of a part of Hamed Jalalvand's master's thesis in the Faculty of Physical Education and Sports Sciences, Central Tehran Branch, Islamic Azad University, Iran.

Authors' contributions
All authors contributed equally in preparing all parts of the research.

Conflicts of interest
The authors declared no conflict of interest.
 

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