ACL Non-Contact Injuries Part II (by guest contributor Anna Napolitano)


Much emphasis has been placed on proper landing techniques for female volleyball and basketball athletes.  Body position and alignment during jump landings along with proper joint angles and range of motion are important factors to investigate.  Studies have found that NCACL injury possibly occurs in all three planes of motion due to increased knee internal rotation, increased knee valgus and decreased knee flexion during jump landings (Laughlin et al, 2011).  Valgus collapse (knee valgus) may result due to poor timing of the activation of the gluteus medius.  Valgus collapse is also associated with increased ankle pronation and subtalar joint eversion especially during a jump landing.  Decreased knee flexion (most often seen with decreased hip flexion) leads to increased anterior shear forces or increased anterior translation of the tibia over the femur.  With minimal hip and knee flexion occurring, a greater force of the quadriceps occurs to absorb the momentum of the jump landing therefore pulling the tibia forward over the femur.  If the hamstrings are unable to counter this force, then a NCACL injury may occur.  Joseph et al. found increased frontal plane motion during a drop jump test occurring more in females than males and found female athletes exhibiting greater valgus angular velocity (2011).  Increased angular velocity generally occurs during sport specific drills forcing female athletes to adapt to ever changing environments at a quick pace.

Most studies have investigated basketball or volleyball landings separately.  Few studies have compared jump landings between the two sports at one time.  Lee Herrington (2011) investigated knee valgus angles during jump landings between volleyball and basketball athletes.  The results could help identify possible sport specific situations that would place females at greater NCACL risk.  The Herrrington study found no difference between single and bilateral jumping tasks in volleyball athletes (2011).  Basketball athletes showed a decrease in knee valgus angle during the unilateral jump tasks (2011).  A decrease in knee valgus shows greater dynamic hip and knee joint stability and strength.  During the unilateral jumping task volleyball athletes exhibited greater knee valgus than basketball athletes for both the left and right knees (2011).  In contrast the female basketball athletes displayed greater knee valgus angle control during the unilateral task (2011).  The differences here could be related to sport specific skills and demands found unique to that sport.  During volleyball, especially at the middle blocker position, knee, hip and ankle joints are placed at greater risk as the blocker moves across the net to defend the opposing attackers.  Often times when blockers move to the outside or right side of the net to block, their ensuing footwork requires the athlete to maintain stabilization and move quickly to their necessary target.  If there are any imbalances within the lower extremity muscle chain then the forces experienced by the athlete as they move across the net places he/she at possible higher risk of NCACL injury.

Kinematic asymmetries, although not desired, are common among athletes.  Single limb dominance is a common theme however strong research to support it does not exist.  Females could present with greater kinematic asymmetries than males when performing jump landing tasks explaining their “dominance” in NCACL injuries.  During forward jump landings, females displayed greater asymmetry than males in knee valgus and ankle abduction (Pappas and Carpes, 2011).  Ankle abduction increases stress along the medial aspect of the knee joint therefore possibly increasing the amount of knee valgus measured.  Also, the asymmetry presented could have been right limb vs. left limb dominance during landings.  Navicular drop and subtalar pronation are associated with ankle abduction (Pappas and Carpes, 2011).  Females displayed greater asymmetries than males with ankle joint kinematics in the frontal plane as well (Pappas and Carpes, 2011).  Ankle motion in the frontal plane is necessary for shock absorption.  Increased ankle movement leads to internal rotation of the tibia and preloading of the ACL (Pappas and Carpes, 2011).  If the ankle is unable to absorb the extra movements and forces the lower extremity experiences during jump landings, more stress will be placed on the knee and hip joints placing the ACL at greater risk for injury.


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