Background: Osgood-Schlatter disease (OSD) is a sports-related disorder involving apophysitis, which affects the tibial tuberosity. The identification of factors related to OSD is important for its prevention and early recovery from the disease. This study aimed to compare the passive mechanical properties of the muscle-tendon unit in children affected by an OSD and healthy children, by using ultrasound real-time tissue elastography. Methods: Eighteen legs affected by OSD (OSD group) and 42 healthy legs (control: CON group) were assessed. The elasticity was obtained from the quadriceps muscles and patella tendon (PT) using real-time tissue elastography. The strain ratio (SR; muscle or tendon/reference ratio: strain rate of the muscle or tendon divided by that of the reference material) was calculated as an indicator of the elasticity of the tissue of interest. Results: The SR of the PT in the OSD group was significantly lower than that in the CON group (P<0.05). We found no significant difference between the groups in terms of the SR value of all muscles (P>0.05). Conclusions: The results suggest that a PT with a lower SR may be associated with an OSD and that the passive mechanical properties of the quadriceps muscles have limited association with an OSD. Levels of Evidence: Level IV.

No abstract

The purpose of the present study was to evaluate the normal process of cortical bone acquisition during childhood and adolescence, and the relationship between speed of sound (SOS), measured by the Sound Scan 2000 system, and linear growth. A total of 1689 healthy Japanese children and adolescents (862 males and 827 females, aged 7-19 years) were enrolled in the study. SOS (m/s) was measured at the right tibial midshaft and the standard SOS values in the children and adolescents were generated. Various growth parameters were also measured. SOS of tibia increased significantly with age in both males and females (P < 0.001 each). In both sexes, a spurt in SOS was noted 1 year after the standard age at which Japanese peak height velocity (PHV; cm/year) occurs, and SOS increased markedly after the age at which the length of tibia reached a maximum. Multiple regression equations for SOS were generated as a function of various growth parameters; for males, SOS = 3047 + 6.2 x height (cm) + 2.1 x weight (kg) - 9.8 x length of tibia (cm) (R2 = 0.50; P < 0.001) and for females, SOS = 2713 + 10.3 x height (cm) + 1.8 x weight (kg) - 15.5 x length of tibia (cm) (R2 = 0.49; P < 0.001). In both sexes, SOS correlated positively with body height and weight, but negatively with length of tibia. Our results indicate that SOS is quite useful for evaluating cortical bone status in children and adolescents; the results of these measurements may provide an explanation for the relative weakness of the mechanical properties of the bone during childhood and adolescence.

This study aimed to compare the morphological/mechanical characteristics of muscle-tendon unit (MTU) in children affected by Osgood-Schlatter disease (OSD) and healthy children. The morphological/mechanical properties of MTU were investigated in fifteen subjects (21 legs) who were affected by OSD (OSD group) and 15 subjects (28 legs) found to have no OSD (CON group). Tendon structure stiffness, elongation, and strain of knee extensors were measured using ultrasonography. In addition, we calculated the ratio of fascicle to femur length. Tendon structure stiffness was significantly higher in the OSD group than in the CON group (P = 0.0008).Maximum elongation (P = 0.0006) and maximum strain (P = 0.0003) were significantly lower in the OSD group than in the CON group. There was no significant difference in the MVC values of the knee extensors between the two groups (P > 0.05), nor was there a significant difference in the ratio of fascicle to femur length between the two groups (P > 0.05). These results indicate that mechanical properties of tendon structure are related to the presence of OSD and that an imbalance in the morphological development of muscles and bones has little association with the presence of OSD. K E Y W O R D Ssports injury, stiffness, tibial tuberosity, ultrasound

The rotation speed of the ball spin has been considered a key factor in winning table tennis matches. This study quantiˆed the rotation speed (rotations per second: rps) of service balls delivered by quarter-ˆnalists in the 2009 World Table Tennis Championships. Ball services were recorded during the quarter-ˆnals of both the men's and women's singles, involving 4 matches and 8 players per gender, using a high-speed video camera (1000 fps) for calculation of the rotation speed, and a standard video camera (30 fps) for distinguishing players and aces (including those touched by the receiver). Eventually, the rotation speeds of 329 services were calculated, and these ranged from 13.7 to 62.5 rps. For men, 50 60 rps was the most frequent (40.0) range of the rotation speeds, while for women, the corresponding range was 40 50 rps (43.8); the average (±SD) rotation speed was signiˆcantly greater for men than for women (46.0±9.0 vs. 39.2±9.3 rps, p＜0.001). The fastest rotation speed was 62.5 rps for both genders. Chinese men produced a slower rotation speed than did other men (43.5±8.9 vs. 51.0±6.8 rps, p＜0.001). For women, however, the rotation speed was similar between Chinese players and the others (39.9±10.2 vs. 38.5±8.2 rps). The rotation speeds of aces were scattered over a wide range of 37.0 58.8 rps for men and 27.8 62.5 rps for women, implying a weak association between aces and fast rotation. These pioneering data may help clarify some of the technical and tactical aspects of table tennis, and can be used to develop training and game strategies for successful performance.