The genu varum/valgum was determined by measuring the intercondylar (IC) and intermalleolar (IM) distance. The measurement of the IC–IM distance was done by asking the subject to take a relaxed erect standing position on a specially developed instrument with the feet at shoulder width, each foot on a different platform (Fig. 1). The subjects were instructed to position their feet in such a manner that the medial border of the feet was above the inner border of the platform. This positioning made sure that all subjects pointed their feet straight forward. Then, using a motor, the two platforms were moved to each other at a constant low speed until the medial condyles or malleoli touched. Subsequently, in subjects with genu varum, in whom only the medial malleoli touched, the bony IC distance (mm) was measured with a caliper using the method described by Arazi et al. (2). In subjects with genu valgum, in whom only the medial femoral condyles touched, the bony IM distance (mm) was measured. Both measurements were combined to one parameter: the IC–IM distance. In the subjects with genu varum, the IC–IM distance was expressed as a positive value. In the subjects with genu valgum, the IC–IM distance was expressed as a negative value. If, in an individual, both the medial malleoli and femoral condyles touched, the IC–IM distance was defined as zero. In some subjects, during the IC–IM measurement, the medial sides of both feet touched with neither the malleoli nor the condyles touching. In these subjects, the bony IC and IM distance was measured, and the distance between the malleoli was subtracted from the distance between the condyles. This resulted, in all subjects in whom this occurred, in a positive IC–IM distance value. All IC–IM distances from all subjects were measured by the same examiner. The intraclass correlation coefficient (ICC) for the used technique for measuring the IC–IM distance proves to be high for the intertester reliability (ICC = 0.95) and the intratester reliability (ICC = 0.96) (27).
Statistical analysis was performed using SPSS 15.0 for Windows (SPSS, Inc., Chicago, IL). Within the group of sporting and nonsporting boys, a one-way ANOVA was performed to analyze differences between the five age groups separately. Post hoc tests were performed with Bonferroni correction. For each age group, the sporting and nonsporting boys were compared on the basis of IC–IM distance by ANOVA with post hoc Bonferroni corrections. Statistical significance was accepted at the level of P < 0.05.
The nonsporting boys showed a negative IC–IM measurement (genu valgum) until the age group of 13–15 yr. In this group of nonsporting boys, the IC–IM distance turned slightly positive in the age group of 16–18 yr (Fig. 2).
The sporting boys showed a negative IC–IM distance until the age of 10–12 yr. Within this group, the IC–IM distance turned positive (genu varum) from 13 to 15 yr or older and showed an increasing evolution in the age group of 16–18 yr (Fig. 2).
In the sporting boys, statistical analyses revealed a significant difference in IC–IM distance between age group 4 and age groups 1, 2, and 3 (P < 0.001) and between age group 3 and age groups 1 and 2 (P = 0.001 and P < 0.001, respectively). The difference in IC–IM distance between age groups 1 and 2 was not significant (P = 1.00).
In the nonsporting boys, the IC–IM distance was significantly different between age group 4 and age groups 1 and 2 (P = 0.001 and P < 0.001, respectively) and between age groups 3 and 2 (P < 0.001). The differences in IC–IM distance between age group 1 and age groups 2 and 3 (P = 0.95 and P = 0.12, respectively) and between age group 3 and age group 4 (P = 0.11) were nonsignificant within the nonsporting boys.
A comparison between the sporting and nonsporting boys showed a significantly different IC–IM distance in groups 3 and 4 (P = 0.01 and P < 0.001, respectively). In these age groups, the sporting boys showed a significantly greater IC–IM distance, indicating a higher degree of knee varus angulation, than the nonsporting boys. The mean IC–IM values and SD of the sporting and nonsporting boys for the different age groups are shown in Table 3.
The results of this study show that from the age period of 13 to 15 yr, a varus evolution was present in the measured sporting and nonsporting boys (Fig. 2). This finding is in agreement with a study by Cahuzac et al. (6), who demonstrated that a certain varus pattern is noticeable in boys at the end of the growth spurt. Striking in this present study, however, is that from 13 to 15 yr or older, the IC–IM distance was significantly larger in the sporting boys compared with the boys who did not practice any kind of sports. In this age group, the knees of the nonsporting boys still showed a slight valgus angulation, whereas the knees of the sporting boys showed a varus angulation. This indicates that from this age on, the boys who practiced load bearing impact sports markedly developed a greater degree of genu varum than the boys who did not practice any kind of sports.
Interestingly, the age period at which this significant difference in knee alignment was observed between both groups corresponds with the period of the growth spurt in boys (17,24). Therefore, the results of this study support the hypothesis that stress and strain imposed on the knee joint during growth through practicing load bearing impact sports might be related to a varus axed growth deformity in the knee. According to the Hueter–Volkmann law, compression forces will halt physeal growth, whereas distraction will lead to overgrowth. Hence, as stated earlier by Yaniv et al. (28), proximal tibial growth changes due to repeated altered stress over the growing growth plate may be a possible mechanism of axis change. Cook et al. (8) provided evidence that mechanical overload of the proximal medial tibial physis plays a major role in the development of genu varum and proved that restricted physeal growth due to excessive compressive loading leads to progressive varus deformity in the knee.
However, the question of which specific activities during the participation of load bearing sports may lead to this asymmetric excessive compressive loading of the knee and might be associated with a varus angulation in the knee in growing adolescents remains. Reports of previous studies have suggested that in soccer players, kicking the ball may play a prominent role in the development of bowlegs in male soccer players (27,28). This kicking action requires an important adduction moment, which may develop strong adductor muscles leading to an alteration in the players’ normal adductor/abductor strength ratio and the possible development of a varus knee axis deviation (27).
Yaniv et al. (28), however, postulated that a combination of internal forces with muscular tension into flexion and varus during side kicking and external forces such as those exerted in crossover cutting maneuvers during play may underlie the deformity evolution in soccer players.
In this present study, however, the investigated sporting boys who did not practice soccer but were enrolled in other load bearing sports (track and field, basketball, volleyball, field hockey, tennis, badminton, and squash) showed a significantly increased degree of genu varum from 13 to 15 yr or older compared with the sedentary boys. In this investigated group of athletes, the side kicking action, which is a typical action for soccer, was not performed during sports participation. However, the external forces during running, sidestepping, and crossover cutting tasks are equally frequently exerted in the knee in these sports.
A major determinant of medial-to-lateral load distribution in the knee joint is the moment that tends to abduct the knee during almost the entire stance phase of normal gait (22,23). This abduction moment is strongly related to the magnitude of the total intrinsic compressive load on the medial compartment of the joint (22). Load bearing sports that involve intensive running cause a strong increase of these abduction moments in the knee. Moreover, Besier et al. (3) measured the external loading in the knee joint during running and cutting maneuvers. They concluded that the external varus/valgus and internal/external rotation loads placed on the joint increased dramatically during cutting tasks compared with normal running. According to the Hueter–Volkmann law and Frost’s chondral modeling theory, these strongly increased abduction moments in the knee during load bearing sports activities may halt physeal growth in the proximal medial tibial physis as a result of repeated supraphysiological compressive loads that they cause over the growing growth plate at that location. This might form a possible explanation for the observed relationship between practicing load bearing sports and the knee varus evolution in the investigated adolescent boys of this study.
Furthermore, during cutting tasks, compression forces may be applied to the proximal medial tibia by repeated contraction of the pes anserinus (sartorius, gracilis, and semitendinosus muscles) and semimembranosus muscle (28). Frequently repeated contractions of these muscles during sports may also contribute to the mechanical overload of the proximal medial tibial physis.
The results of this study suggest that participation in load bearing sports such as track and field, basketball, volleyball, field hockey, tennis, badminton, and squash, in which intense running and cutting maneuvers are highly frequently exerted, is associated with an increased knee varus evolution in adolescent boys. This has a very important implication because a higher than normal abduction moment in the knee joint is related to the development and progression of medial tibiofemoral osteoarthritis (1,23). Several studies in the literature have shown that axial deviations in the knee such as genu varum are associated with the development of knee osteoarthritis in later life (9,14,16). In 1985, Chantraine (7) documented both a higher prevalence of knee varus and a higher incidence of osteoarthritis in the knee in veteran soccer players. Because, today, millions of children over the world are enrolled in and practice load bearing sports, the results of this study warn of the possible deleterious consequences in the knee in later life.
A second important question one should ask is what efforts can be done to reduce this evolution in adolescent athletes. In a previous study in male soccer players, it has been proposed that if a muscular imbalance around the knee joint would prove to be associated with the development of genu varum, prevention should emphasize on preservation of this muscular balance (27). Future studies are, however, needed to investigate this relationship. Further future research is also warranted to investigate whether other preventative measures can be taken to reduce the possible risk of developing bowlegs in millions of sporting growing adolescents and to reduce their risk of developing knee osteoarthritis later on.
There are some limitations of this study that have to be considered. First, the different sport disciplines in which the sporting boys of this study were enrolled were pooled into one group of load bearing sports. However, more accurate information concerning the relationship between sports participation and a varus evolution in the knee may be obtained if the different sport disciplines would be investigated separately because different forces may act on the knee in athletes practicing different types of sports. This should be addressed in future studies examining larger cohorts of subjects. Second, the cross-sectional design of our study does not allow us to establish cause-and-effect relationships. As previously has been hypothesized in soccer players (28), a natural selection might be present in athletes practicing load bearing sports by which varus axed knees may confer an advantage in sports participation. Yaniv et al. (28) suggested that in soccer players, bowlegs may play a role in the player’s balance and stability and may serve the player to adapt more readily to the increased difficulty to maintain balance during the game. This, however, might also apply for athletes practicing other load bearing sports and may result in the fact that more children with genu varum end up being athletes. Furthermore, the observed varus angulation in the sporting boys may also be genetically present and rather might be a product of normal development than a result of training, as previously has been suggested by Chantraine (7). Therefore, future prospective studies would be required to draw any definitive conclusions in this regard.
The present study focused on the relationship between sports participation and the frontal plane knee axis evolution in adolescent boys. However, future studies are also warranted to evaluate whether, in female sporting adolescents, the knee axis evolution follows the same pattern as the one observed in the investigated male adolescents.
From the results of this study, it can be concluded that besides the previously reported soccer participation, participation in other load bearing sports is also significantly related with a greater knee varus alignment in adolescent boys. Future research is necessary to further investigate which biomechanical mechanisms are responsible for the observed knee varus deformation in adolescents practicing load bearing sports.
The present study was unfunded.
The authors declare that there are no conflicts of interest.
The results of the present study do not constitute endorsement by the American College of Sports Medicine.
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Keywords:©2012The American College of Sports Medicine
KNEE VARUS; BOYS; SPORTS PARTICIPATION; OSTEOARTHRITIS