Differences in Physical and Psychological Parameters in Sub-Elite, Male, Youth Soccer Players with Jumper’s Knee Following Physical Therapy Compared to Healthy Controls: A Longitudinal Examination

PURPOSE/BACKGROUND: Many adolescent athletes suffer from jumper’s knee (JK) over a long period of time and return to sports before symptoms are fully resolved. Current treatment methods may not reduce pain in the short term, especially not during a competitive season. The purpose of this study was to investigate differences in physical, psychological, and injury-/pain-related parameters in sub-elite male youth soccer players, who previously underwent physical therapy for JK compared to healthy controls (HC) over the course of a season. METHODS: All subjects were tested four times (start of the season [T1], 6 [T2], 16 [T3], and 20 [T4] weeks after the start of the season). Outcome measures included muscle power (drop jump, jump-and-reach), change of direction speed [CODS] (acyclic sprint), speed (tapping, 30-m linear sprint), endurance (Yo-Yo intermittent recovery test level 1), the Achievement Motives Scale (AMS) Sport, and injury-/pain-related data. Univariate analysis of variance was used to compare differences in variables between the two groups over the course of a soccer season. RESULTS: Over the season, the jumper’s knee group (JK; 15.1 ± 0.8 yr) demonstrated significantly worse physical performance in CODS (to the left side: 1.37≤ Cohen’s d ≤ 1.51 [T1-T4]; p < 0.001 / to the right side: 1.24 ≤ d ≤ 1.53 [T1-T4]; p < 0.001) and speed (0.48 ≤ d ≤ 1.26 [T1-T4]; p < 0.007) compared to healthy controls (HC; 15.0 ± 1.0 yr). Further, psychological parameters showed worse values in JK than in HC for the AMS Sport items “hope for success” and “fear of failure” that especially showed a significant difference at T1 (d = 0.65; p = 0.032 / d = 0.68; p = 0.027) and T2 (d = 0.50; p = 0.076 / d = 0.80; p = 0.012). Moreover, the JK group showed significantly higher incident rates for non-contact lower limb injuries (d = 0.69; p = 0.049) per 1,000 hours (i.e., practices/competitions), injury-related rest periods (d = 2.06; p = 0.043), and pain-related training interruptions (d = 1.35; p < 0.001). CONCLUSIONS: The observed findings imply that there are significant differences in physical and psychological performance of youth soccer players after physical therapy for JK compared to HC. When designing rehabilitation and/or training programs, as well as determining the point of return to sport the impact of the injury needs to be taken into account. LEVEL OF EVIDENCE: 1b