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Malalignment or dysfunction of the foot can increase the risk of landing-related trauma such as anterior cruciate ligament injury, particularly in female athletes. But foot orthoses and bracing can help alter landing mechanics in ways that may decrease that injury risk.

By Douglas Powell, PhD, and Nicholas J. Hanson, MS

Landing is a common maneuver in many athletic events. It involves the dissipation of kinetic energy through passive structures such as connective tissues and eccentric contractions of the lower extremity musculature, including the hip and knee extensors as well as ankle plantar flexors.^{1, 2} The high impact loading and the sudden decelerations associated with landing may have negative effects on the musculoskeletal system, including tendinopathies, cartilage lesions, joint pain, arthritis, bone bruises, fractures, and ligament tears.^3-6

One factor that has been heavily associated with increased risk of injury during landing activities is gender. It has been well documented that female athletes suffer a greater propensity for traumatic lower extremity injury such as anterior cruciate ligament (ACL) rupture.^6-10 Many structural, neuromuscular, physiological, and biomechanical factors have been investigated as possible contributors to the increased rate of traumatic lower extremity injury in female athletes.  However, many researchers believe a central component involves lower extremity landing mechanics.^7-16

Further complicating the assessment of biomechanics in traumatic injury in landing is the role of foot structure in determining the loading pattern of the lower extremity. Malalignment and dysfunction of the foot have been heavily studied as a key factor in lower extremity injury in recent years.^{8, 17-29} Specifically, the structure of the medial longitudinal arch (MLA) has been identified as a major indicator of foot dysfunction.^29-33 The MLA extends from the calcaneus to the first metatarsal head and consists of the calcaneus, talus, navicular, three cuneiforms, and the first three metatarsals.³⁴ Given the importance of the MLA in assessing foot structure and function,^{21, 35-37} many measurements have been used to characterize the height and function of the MLA including foot prints,³¹ plantar pressures,³⁸ relative arch deformity,^{30, 39} arch index ratio,³⁹ and arch stiffness.⁴⁰ Though the MLA and foot type are known to be important structures in determining the pattern of lower extremity loading, few prospective research studies of landing mechanics have controlled for foot type. ^{41, 42}

Injury

The relationship between foot structure and injury has been well researched.^{8, 17-29} Recent studies have revealed that individuals with either high- or low-arched feet have a greater propensity for injury to the lower extremity and back.^22,29,43 Furthermore, these two functionally different groups experience similarly dichotomous injury patterns: high-arched athletes have a greater risk of bony injury to the lateral aspect of the lower extremity, while low-arched athletes experience more soft tissue injuries to the medial aspect of the lower extremity.^18,22,29 Although these unique injury patterns can be attributed to the altered loading patterns experienced by the respective groups due to the interaction of the foot with the ground, these studies examined over-use injuries associated with running rather than traumatic injuries associated with landing. Few studies have examined the structure and function of the foot in relation to traumatic injury of the lower extremity.^8,17,23,44

The link between foot structure and traumatic lower extremity injury patterns has not been well studied. Several research investigations have examined the relationship between common clinical measures of foot structure and the risk of traumatic lower extremity.^8,17,23,44 The consensus of these studies suggests that clinical measures of foot type associated with over-pronation, which include subtalar joint position and navicular drop test, were highly associated with traumatic knee injury, specifically ACL rupture.^17,23,44 However, these studies only present correlational data rather than direct investigations into the underlying mechanisms of ACL rupture. Very limited data exist with regard to the relationship between foot type and landing mechanics associated with lower extremity injury.⁴¹

Powell et al⁴¹ compared landing mechanics between high- and low-arched recreational athletes, but limited the sample population to female athletes. Though the high- and low-arched athletes exhibited similar kinetic profiles in the frontal and sagittal planes, unique joint angles were observed in the frontal plane at key events within the landing phase, including initial contact, peak vertical ground reaction force and peak knee flexion. The investigated events were defined as the beginning (initial contact) and end (peak knee flexion) of the landing movement and the point at which the lower extremity experiences the greatest load (peak vertical ground reaction force). Specifically, the low-arched athletes exhibited significantly greater ankle inversion angles at initial contact compared to the high-arched athletes; however, this difference was no longer present at the time of peak vertical ground reaction force.

Previous research⁴⁰ has shown high-arched feet to be more rigid than low-arched feet, and the greater inversion angle in the low-arched athletes could be a strategy to decrease ankle stiffness upon landing. Ankle stiffness can be described as the change in ankle joint angle relative to the load creating the change in joint angle. Previous research has shown that methods limiting ankle dorsiflexion range of motion result in decreased knee flexion,⁴⁵ increased knee valgus,⁴⁶ and greater ground reaction forces.⁴⁵ Therefore, a decrease in ankle joint stiffness would functionally increase the range of motion of the knee and limit the ground reaction forces experienced, attenuating the risk of traumatic knee injury. The abolition of increased ankle inversion in the low-arched athletes at the time of peak vertical ground reaction force suggests that this strategy may be effective to decrease ankle stiffness as the ankle exhibited a larger range of motion within the same period of time.

Powell et al⁴¹ also noted differences in frontal plane knee and hip joint angles between the high- and low-arched athletes at the time of peak knee flexion. Though the two groups exhibited differences late in the landing phase, it could be argued that the timing of these unique joint angles does not play a role in the different injury patterns suffered by these two functionally different groups of athletes.

A limitation of the study by Powell et al⁴¹ is the relatively low landing height studied (0.3 meters), which is associated with smaller mechanical demands than may be required to induce injury. It is logical to argue that a greater mechanical demand would exacerbate differences between high- and low-arched athletes. However, previous research has shown that changes in ankle kinetics are minimal when landing from increasing heights, as the hip and knee joints exhibit substantially greater eccentric work and power than the ankle during a landing task.^{2, 6, 47} Yeow et al⁶ reported that male athletes did not alter lower extremity joint angles in the frontal plane when the landing was increased from 0.3 meters to 0.6 meters. However, they significantly increased the contribution of the hip joint to energy dissipation with increased landing height, suggesting males adopt a hip-dominant landing strategy.  These results concur with previous research demonstrating a greater contribution of proximal musculature with increasing demand in male subjects² however, there is a dearth of literature comparing the effects of gender on lower extremity mechanics with increasing mechanical demand.

Recent research has, however, investigated the mechanisms of ACL injury in high-level competition. Boden et al⁴⁸ retrospectively examined select video of ACL ruptures in male and female athletes during collegiate and professional sports, including basketball, soccer and football. Their findings demonstrated differences in kinematic patterns between subjects rupturing their ACL and healthy controls during similar movements. Specifically, those athletes experiencing traumatic knee injury exhibited significantly less ankle plantarflexion at initial contact and had little change in ankle angle during the early stages of load response. The decreased range of motion exhibited by the injured athletes showed that these athletes did not dissipate energy at the level of the ankle; thus the knee experienced greater loading, resulting in traumatic knee injury. It was also revealed that while individuals suffering traumatic knee injury and healthy controls did not exhibit different knee abduction angles at initial contact, the injured athletes did exhibit increasing knee abduction after initial contact compared to healthy controls.  Boden et al⁴⁸ also noted that the female athletes included in their study experienced a “valgus collapse,” indicated by a greater knee abduction position, compared to male athletes.

Further demonstrating the importance of the gender differences previously reported,^9,15,48 research has shown that the ankle musculature makes a greater contribution to energy dissipation during the landing phase in female subjects than in male subjects.^9,15 It is suggested that the unique kinematics and the increased role of the ankle in dissipating energy comprise a strategy adopted by female athletes to avoid placing stresses on the knee joint and in turn reduce the risk of traumatic knee injury. However, it is possible that the altered landing mechanics may actually increase the risk of injury, as it has been previously reported that alterations of as little as two degrees in frontal plane alignment of the knee can decrease the threshold for ACL injury by up to one body weight.¹¹ Therefore, these findings also suggest that aberrant foot function in female athletes may have a greater mechanical effect during landing than in male athletes and may further increase the risk of traumatic injury to the lower extremity. (Although aberrant foot function may disproportionately increase the risk of injury in female athletes compared to male athletes, previous research has suggested that neither gender has a greater propensity of aberrant foot function.⁴⁰) Given this increased risk of ACL injury with aberrant foot function in female athletes and the greater reliance on ankle musculature during landings, it is of utmost importance to address foot and ankle dysfunction in female athletes.

Interventions

Several strategies have been used to improve foot function and reduce lower extremity injury in athletes. Some common forms of intervention include ankle taping and bracing, as well as the introduction of foot orthotics.

Taping and bracing of the ankle are common interventions to reduce or prevent ankle injury and re-injury. Though no direct evidence exits, previous research findings suggest that ankle taping and bracing reduce the kinematic and kinetic variables associated with traumatic knee injury and indirectly suggest that ankle taping and bracing may attenuate the increased risk of traumatic knee injury associated with aberrant foot function. Several studies have examined the effects of ankle bracing and taping on perceived instability,⁴⁹ range of motion,^50,51 and neuromuscular activation patterns.^52,53 In a recent study it was reported that ankle bracing was associated with decreased sagittal plane motion at the ankle, but resulted in increased knee flexion at landing.⁵⁴ Another study examining the effects of ankle taping on lower extremity mechanics during athletic tasks⁵⁵ demonstrated that ankle taping reduced knee internal rotation and varus moments; however, knee valgus moments were increased. Valgus loading of the knee is a common mechanism of ACL injury.⁴⁸ Another recent study⁴⁵ revealed that individuals with a greater sagittal plane range of motion exhibited greater knee-flexion displacement and smaller ground reaction forces.  These mechanics are consistent with decreased loading and may reduce the risk of injury by limiting the forces applied to the lower extremity.^56-58

By design, ankle taping limits ankle range of motion, specifically targeting pronation which is a common mechanism of acute ankle sprain. However, taping functionally limits ankle range of motion in the sagittal plane, possibly limiting the displacement available at the ankle and applying greater loads to the knee joint and its supporting connective tissues.^48,56 Therefore, ankle taping may impair strategies for shock attenuation, resulting in a greater risk of traumatic knee injury.

Another study investigating the efficacy of ankle bracing revealed increased ankle eversion torques and knee external rotation torques when athletes wore ankle braces during a landing task.⁵⁷ Furthermore, there were no changes in knee valgus torques, suggesting that ankle braces may be associated with fewer adverse effects and a lower risk of ACL injury than ankle taping. While ankle bracing and taping may be common interventions for ankle instability, recent literature suggests these two interventions may aid in controlling the transverse plane motions associated with traumatic knee injury.

However, research evidence pertaining to the effects of ankle taping and bracing on the biomechanics of the knee during a landing task is diffuse, with few studies directly investigating these relationships. Current literature suggests that foot position during landing directly modulates lower extremity mechanics. Further, these data suggest that ankle taping and bracing address different mechanisms associated with traumatic knee injury, and no over-arching conclusion can be made regarding their efficacy in reducing the risk of ACL injury.

Another common intervention to prevent lower extremity injury in athletics is the use of semi-custom or custom orthotics to correct for foot malalignment or aberrant foot function. A cross-sectional study investigating the efficacy of orthotics in preventing knee ligament injury in basketball players has demonstrated positive effects.¹⁴ One hundred fifty female basketball players over a 13-year period were assigned to either a control group, which did not receive orthotics, or a treatment group which received orthotics. The control group had an anterior cruciate or collateral ligament injury rate of .50 injuries per 1000 athlete exposures, while the orthotics group had injury rates of .07 and .29 per 1000 exposures for the anterior cruciate and collateral ligaments, respectively. These findings strongly suggest that orthotics decrease the propensity of injury in female athletes during a landing sport.

Further study into the mechanisms of function by which orthotics decrease the rate of injury revealed that orthotics were associated with changes in transverse plane of motion of the lower extremity.⁵⁸ Specifically, the efficacy and lower extremity mechanics associated with over-the-counter and semi-custom orthotic designs were examined. While both orthotics limited transverse plane motion of the lower extremity, the over-the-counter orthotic altered hip internal rotation and the semi-custom orthotic limited tibial internal rotation. Though effectively acting at different locations in the kinetic chain, both orthotic devices limited known mechanisms of ACL injury¹⁴ and, it is logical to argue, would decrease the risk of injury in female athletes. Another recent study pertaining to the efficacy of foot orthotics in reducing kinematics associated with ACL injury ⁵⁹ revealed that orthotics reduce knee valgus and ankle pronation at initial contact during landing. As the transmission of loading through the ankle to more proximal structures happens over a short period of time, the position of the foot at initial contact is central in determining lower extremity loading patterns.⁵⁶

The increased reliance upon an ankle strategy in females suggests that aberrant foot function may disproportionately increase their risk of traumatic knee injury compared to their male counterparts.^9,15 However, data pertaining to the effects of orthotics on lower extremity injury suggest that orthotic interventions not only compensate for aberrant foot function, but act in a manner that limits the mechanics associated with rupture of the ACL.⁵⁸

Conclusions

In summary, proper function of the foot and ankle are paramount in landing. Malalignment or dysfunction of the foot can place an athlete at an increased risk of traumatic injury to the lower extremity. Female athletes are more susceptible to pathomechanics associated with foot dysfunction during a landing task due to their greater reliance upon the ankle for energy dissipation. However, bracing and orthotic interventions have been shown to be effective in limiting lower extremity mechanics associated with traumatic injury of the knee in landing.

Douglas Powell, PhD, is a research fellow in the Department of Physical Therapy at Creighton University in Omaha, NE. Nicholas J. Hanson, MS, is a doctoral student in the College of Education and Human Ecology at The Ohio State University in Columbus, OH.