Vertical Drop Jump Biomechanics of Patients With a 3- to 10-Year History of Youth Sport–Related Anterior Cruciate Ligament Reconstruction

BACKGROUND: A better understanding of movement biomechanics after anterior cruciate ligament reconstruction (ACLR) could inform injury prevention, knee injury rehabilitation, and osteoarthritis prevention strategies. PURPOSE: To investigate differences in vertical drop jump (VDJ) biomechanics between patients with a 3- to 10-year history of youth sport–related ACLR and uninjured peers of a similar age, sex, and sport. STUDY DESIGN: Cross-sectional study. Level of evidence III. METHODS: Lower limb kinematics and bilateral ground-reaction forces (GRFs) were recorded for participants performing 10 VDJs. Joint angles and GRF data were analyzed, and statistical analysis was performed using 2 multivariate models. Dependent variables included sagittal (ankle, knee, and hip) and coronal (knee and hip) angles at initial contact and maximum knee flexion, the rate of change of coronal knee angles (35%-90% of the support phase; ie, slopes of linear regression lines), and vertical and mediolateral GRFs (normalized to body weight [BW]). Fixed effects included group, sex, and time since injury. Participant clusters, defined by sex and sport, were considered as random effects. RESULTS: Participants included 48 patients with a history of ACLR and 48 uninjured age-, sex-, and sport-matched controls (median age, 22 years [range, 18-26 years]; 67% female). Patients with ACLR demonstrated steeper negative coronal knee angle slopes (β = –0.04 deg/% [95% CI, –0.07 to –0.00 deg/%]; P = .025). A longer time since injury was associated with reduced knee flexion (β = –0.2° [95% CI, –0.3° to –0.0°]; P = .014) and hip flexion (β = –0.1° [95% CI, –0.2° to –0.0°]; P = .018). Regardless of ACLR history, women displayed greater knee valgus at initial contact (β = 2.1° [95% CI, 0.4° to 3.8°]; P = .017), greater coronal knee angle slopes (β = 0.05 deg/% [95% CI, 0.02 to 0.09 deg/%]; P = .004), and larger vertical GRFs (landing: β = –0.34 BW [95% CI, –0.61 to –0.07 BW]; P = .014) (pushoff: β = –0.20 BW [95% CI, –0.32 to –0.08 BW]; P = .001). CONCLUSION: Women and patients with a 3- to 10-year history of ACLR demonstrated VDJ biomechanics that may be associated with knee motion control challenges. CLINICAL RELEVANCE: It is important to consider knee motion control during activities such as VDJs when developing injury prevention and rehabilitation interventions aimed at improving joint health after youth sport–related ACLR.