Elsevier

Clinical Biomechanics

Volume 23, Issue 3, March 2008, Pages 313-319
Clinical Biomechanics

Influence of trunk flexion on hip and knee joint kinematics during a controlled drop landing

https://doi.org/10.1016/j.clinbiomech.2007.10.003Get rights and content

Abstract

Background

An erect posture and greater knee valgus during landing have been implicated as anterior cruciate ligament injury risk factors. While previous research suggests coupling of knee and hip kinematics, the influence of trunk positioning on lower extremity kinematics has yet to be determined. We hypothesized that greater trunk flexion during landing would result in greater knee and hip flexion and lesser knee valgus. Identification of a modifiable factor (e.g. trunk flexion) which positively influences kinematics of multiple lower extremity joints would be invaluable for anterior cruciate ligament injury prevention efforts.

Methods

Forty healthy individuals completed two drop landing tasks while knee, hip, and trunk kinematics were sampled. The first task constituted the natural/preferred landing strategy (Preferred), while in the second task, subjects actively flexed the trunk upon landing (Flexed).

Findings

Peak trunk flexion angle was 47° greater for Flexed compared to Preferred (P < 0.001), and was associated with increases in peak hip flexion angle of 31° (P < 0.001) and peak knee flexion angle of 22° (P < 0.001).

Interpretation

Active trunk flexion during landing produces concomitant increases in knee and hip flexion angles. A more flexed/less erect posture during landing is associated with a reduced anterior cruciate ligament injury risk. As such, incorporating greater trunk flexion as an integral component of anterior cruciate ligament injury prevention programs may be warranted.

Introduction

Recent research on anterior cruciate ligament (ACL) injury mechanisms has begun to evaluate influences of kinematic factors proximal to the knee joint. Given the closed-kinematic-chain nature of the lower extremity following ground contact during landing and gait activities, it has been suggested that segmental motion of the mass superincumbent to the knee directly influences knee joint motion and loading. Specifically, it has been suggested that hip internal rotation and adduction contribute to knee valgus (McLean et al., 2004b, Zeller et al., 2003), a kinematic factor which has been linked to ACL injury risk (Hewett et al., 2005). This notion coincides with the “position of no return” during which non-contact ACL injury is hypothesized to occur, characterized by hip adduction and internal rotation, knee valgus and external tibial rotation, and subtalar pronation (Ireland, 1999). Additionally, females, a population which is at heightened risk for ACL injury (Arendt et al., 1999, Gwinn et al., 2000), simultaneously display lesser knee, hip, and trunk flexion during gait and landing tasks compared to males (McLean et al., 2004b, DiStefano et al., 2005, Salci et al., 2004, Yu et al., 2006, Decker et al., 2003), suggesting sagittal-plane coupling of these joints. Furthermore, females also demonstrate greater knee valgus during these tasks compared to males (Russell et al., 2006, Ford et al., 2003), suggesting the coupling of lower extremity kinematics has a mulitplanar influence on ACL injury risk. As excessive knee valgus and a more erect landing posture (evidenced by a more extended knee, hip, and trunk) have been postulated as ACL injury risk factors (Griffin et al., 2000), continued research regarding the coupling of these joints is warranted.

Previous research supports a link between landing forces and knee injury (Dufek and Bates, 1991), and numerous investigations have demonstrated relationships between landing forces and frontal and sagittal plane kinetics and kinematics. In a prospective study, Hewett et al. (2005) reported a significant correlation between peak knee valgus angle and peak vertical ground reaction force in individuals who sustained ACL injury, and that the vertical ground reaction force was 20% greater in individuals who sustained ACL injury compared to those who did not. Furthermore, those who sustained ACL injury displayed lesser knee flexion compared to those who did not, and knee flexion angle was correlated with the vertical ground reaction force in these individuals. McLean et al. (2005) demonstrated the dependency of peak knee valgus moments during cutting tasks on hip and knee joint kinematics. Yu et al. (2006) demonstrated that hip and knee joint angular velocities were correlated with posterior and vertical ground reaction forces. Lastly, videotape feedback has been demonstrated to increase knee flexion displacement and decrease vertical ground reaction forces simultaneously (Onate et al., 2005), supporting the link between landing kinematics and kinetics. These data suggest that lower extremity landing kinetics and kinematics and the subsequent load placed on the ACL are highly interlinked in a multiplanar manner, a notion which is supported by investigations of the effects of various knee joint kinematic configurations on ACL stress and strain in cadaveric specimens (Durselen et al., 1995, Fukuda et al., 2003, Kanamori et al., 2002).

The aforementioned relationships between frontal and sagittal plane kinematics and landing forces suggest that greater hip and knee flexion and a smaller knee valgus angle are associated with lesser ground reaction forces, potentially shielding the ACL from excessive loading. While the coupling of hip and knee kinematics and the link between lower extremity kinematics, landing forces, and ACL injury are supported in the literature, it is unclear how trunk motion influences these factors. Specifically, it is unclear how the sagittal-plane positioning of the trunk influences hip and knee joint kinematics. Identification of a single modifiable factor (e.g. trunk flexion angle) which has the potential to alter lower extremity kinematics in a multiplanar manner that is associated with a lesser ACL injury risk would be invaluable to injury prevention efforts. Therefore, the purpose of this investigation was to evaluate the influence of trunk motion in the sagittal plane on hip and knee joint kinematics. It was hypothesized that trunk flexion during landing would result in greater knee and hip flexion, lesser knee valgus, and lesser hip adduction and internal rotation.

Section snippets

Subjects

Forty healthy volunteers (20 males, 20 females: age = 21.5 (SD 1.9) years, height = 1.73 m (SD 0.10), mass = 74.6 kg (SD 17.47) constituted the sample for this investigation. All subjects were physically active, participating in physical activity a minimum of 20 min 3 times per week, and had no history of (1) ACL injury, (2) lower extremity surgery, (3) neurological disorder, (4) chronic lower extremity injury, or (5) lower extremity injury within the six months prior to data collection. Subjects read

Results

The Task main effect and Task × Phase interaction effect were significant for trunk flexion, knee flexion, and hip flexion (P < 0.001 for each analysis). No other main effect or interaction effect reached statistical significance. With respect to post hoc analyses, the trunk, hip, and knee displayed significantly greater flexion for Flexed compared to Preferred on average (i.e. collapsed across landing phases). Additionally, this difference was significant at both landing phases (IGC and Loading)

Discussion

The primary finding of this investigation was that active trunk flexion during landing produced concomitant increases in knee and hip flexion compared to a more erect/extended trunk posture. These results are in agreement with previous evidence of coupling of the knee and hip joints in the closed-kinematic-chain. Previous literature suggests that a more erect posture during landing, gait, and cutting activities as identified by more extended trunk, hip, and knee positions, may be a risk factor

Clinical implications

Considerable debate exists regarding the precise mechanisms of ACL injury and the greater incidence of ACL injury in females. While some investigators have implicated sagittal plane mechanisms as the primary contributors with minimal influence from the frontal plane (Chappell et al., 2002), others suggest that frontal plane factors are the culprits with sagittal plane mechanisms playing insignificant roles (Hewett et al., 2005, McLean et al., 2004a). Given the predisposition for females to

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