A high prevalence of anterior cruciate ligament (ACL) injury amongst adolescent girls aged 14–18 years old is multifactorial [1
]; however, hormonal and biomechanical factors are emerging as primary contributors [2
]. Adolescence is an important stage in the context of female musculoskeletal development, as it typically involves a rapid influx of estrogen and growth factors, commonly referred to as puberty. Considering puberty involves an increase in height, muscle cross sectional area and overall body mass [5
], it’s suspected that these physical characteristics may indeed lead to aberrant lower limb biomechanics related to adolescent female non-contact ACL injury. Specifically, higher external tri-planar knee joint moments, such as the knee abduction moment (KAbM), flexion moment (KFM) and internal rotation moment (KIRM) contribute to a tri-planar mechanism of ACL rupture [6
]. More importantly, it appears that girls at later stages of pubertal development (i.e., late/post-pubertal development) exhibit higher barefoot landing-related knee moments [7
], which may predispose them to a higher risk of injury [10
], highlighting a need for strategies that ameliorate these peak knee moments.
In reality, barefoot participation is impractical for most sports relevant to non-contact ACL injury and, as such, girls wear various types of athletic footwear during sports participation. Surprisingly, there are no published cohort-specific (i.e. puberty) studies investigating the effects of footwear on knee biomechanics. However, previous research involving both healthy [11
] and populations with knee pathology (e.g. older adults with knee osteoarthritis) [16
] have demonstrated a knee load-modifying role of footwear. Specifically, modifying medial and lateral support features of a shoe can influence the resultant frontal (i.e., KAbM) and transverse plane (i.e., KIRM) moments [11
] which may be important in the context of ACL injury, given that combined valgus and rotation increases ACL strain [17
]. The athletic footwear market contains a wide variety of both “high-supportive” and “low-supportive” footwear options. High-supportive shoes commonly feature a medial post, increased longitudinal shoe stiffness and midfoot rotational stability to minimize excessive foot pronation during activity, whilst low-supportive shoes do not contain such features and allow natural pronation to occur [18
It is thought that the biomechanical effects of excessive foot pronation during single-limb landing are transferred up the kinetic chain in female athletes, contributing to elevated KAbM and KIRM [17
]. To counteract these loads, high-supportive shoes with appropriate anti-pronation features [18
], might potentially reduce KAbM and/or KIRM. In support, footwear studies investigating the effects of wedges/insoles and orthotics on knee biomechanics [13
], have demonstrated their influence on knee loads by altering the frontal plane position of the knee relative to the resultant ground reaction force vector [21
]. Specifically, laterally arched/wedged insoles provide a laterally-directed (eversion) bias to the foot shifting the centre of pressure laterally and increasing the KAbM [22
]. By contrast, medially arched/wedged insoles create a foot inversion bias, shifting the centre of pressure medially and lowering the KAbM [21
]. Furthermore, a medial arch support also has the capacity to externally rotate the tibia relative to the femur, thereby limiting internal tibial rotation and the potential magnitude of KIRM during foot-ground contact [23
]. Hence, it’s plausible that high-supportive athletic footwear could attenuate peak KAbM and KIRM during single-limb landing relative to low-supportive footwear and barefoot conditions.
Arguably, athletic footwear also has the potential to increase the risk of non-contact ACL injury by increasing peak KFM during sporting activities. Many athletic shoes possess a raised heel with respect to the forefoot (i.e. pitch) – a feature that has been previously shown to increase peak KFM compared to barefoot in adult runners [11
]. Given that high-supportive shoes often have an increased pitch compared to their low-supportive counterparts, it’s imperative that an examination of high-support footwear includes an analysis of frontal, transverse and sagittal plane knee moments (i.e., KAbM, KIRM and KFM) as many late/post-pubertal girls are likely wearing these types of shoes while playing sport.
Therefore, the aim of this study was to investigate whether a difference in tri-planar knee moments exist between high-support shoes, low-support shoes and barefoot in late/post-pubertal girls. Our primary hypothesis was that the high-supportive shoe would exhibit lower peak KAbM and KIRM compared to both the low support shoes and barefoot. In contrast, our secondary hypothesis was that both high- and low- support shoes would increase peak KFM compared to barefoot.
For the frontal plane KAbM and transverse plane KIRM, no differences were found for all comparisons in either unadjusted (p
> 0.05) or adjusted analyses (p
> 0.05, Table 2
). However, for the peak KFM, there was a main effect for both adjusted and unadjusted analyses (p
< 0.001). Post-hoc
results revealed that both adjusted and unadjusted results were identical, with the high-support shoe exhibiting higher peak KFM (MD = 0.44, 95% CI 0.36 to 0.53 N·m/kg, p
< 0.001, Table 2
) than the barefoot condition. Likewise, results for the low-support shoe were identical for both adjusted and unadjusted FPI whereby higher peak KFM (MD = 0.36, 95% CI 0.25 to 0.48 N·m/kg, p
< 0.001) was observed compared to barefoot. For the between shoe comparison, there was a trend indicating higher KFM in the high-support compared to low-support shoe for both adjusted (p =
0.053) and unadjusted (p
= 0.050) analyses.
Peak tri-planar knee moments for each footwear condition
−0.43 ± 0.18
−0.43 ± 0.18
2.90 ± 0.42
2.85 ± 0.43
−0.23 ± 0.11
−0.23 ± 0.11
− 0.41 ± 0.20
−0.41 ± 0.21
3.3 ± 0.39 a
3.3 ± 0.39 a
−0.25 ± 0.11
−0.25 ± 0.11
− 0.44 ± 0.16
−0.47 ± 0.16
3.22 ± 0.41a
3.22 ± 0.41a
−0.23 ± 0.09
−0.23 ± 0.09
This is the first study to compare the effects of different footwear conditions on tri-planar knee moments in a cohort of girls classified as late/post-pubertal development during a single-limb landing task. Our findings reject our primary hypothesis, as the high-support shoe did not ameliorate peak KAbM and KIRM compared to low-support and barefoot conditions. However, as expected, we confirmed our secondary hypothesis that both shoe types would increase peak KFM compared to barefoot. Given these findings, it appears that both high- and low-supportive styles of footwear are inadequate at reducing peak KAbM and KIRM and in fact increase peak KFM, which may be detrimental for reducing the risk of non-contact ACL injury in this cohort [6
Regarding the primary hypothesis related to both KAbM and KIRM, results from this study extend those reported by Bisesti and colleagues [37
], who reported no difference in KAbM between barefoot and low support shoes in a mixed cohort of adult participants who performed a single limb 45° cutting task. However, findings from the present study are in contrast to previous studies investigating the effect of orthotics during single limb landing [38
] and medial post/wedges during double limb drop vertical jumps [14
]. Specifically, two studies by Joseph and colleagues [14
], highlight that knee valgus, foot pronation and hip adduction are all reduced when female college athletes wore a 5° medial post in their shoes compared to no post. In light of these findings, the supportive features incorporated within the high-support shoes tested in this study may be inadequate to substantially influence frontal and transverse plane knee moments, and increasing the medial post of the shoes (e.g. addition of a medial wedge/orthotic) could potentially ameliorate knee moments.
Furthermore, adjusting for FPI did not affect either frontal or transverse plane loading results. As the average FPI in this cohort was 2.5 ± 3.6 which is categorised as a normal foot posture, it may be that the high- and low-support shoe effects on moments were diminished and may be more pronounced in pronated foot types. Indeed, support for this theory comes from a recent randomized controlled trial investigating the effect of standard and motion control footwear in runners, that demonstrated lower injury risk in runners who wore the motion control shoe and had a higher FPI score (i.e. pronated foot; [40
]). Therefore, we recommend further FPI sub-group analysis be conducted in the future.
We confirmed the secondary hypothesis of higher peak KFM (≈10–12%) when landing in shoes compared to barefoot. Although we did not explore the mechanism by which shoes elevate peak KFM, elevated pitch wearing shoes compared to barefoot is a likely contributor [15
]. For instance, we speculate that higher pitch (i.e., shoes) simultaneously reduces the sagittal plane ankle excursion while increasing the knee flexion angle during the stance phase of landing. Consequently, this may lead to a larger sagittal plane knee joint moment arm and higher peak KFM. In support, previous drop-landing studies have demonstrated a 22% increase in knee flexion angle at initial contact and a gradual increase in peak knee flexion angle with increasing heel heights (i.e. pitch; [15
]). Moreover, despite the biomechanics of running and jumping being quite different, previous running-related research demonstrates approximately 18% lower peak KFM when running barefoot (i.e., lower pitch) compared to supportive athletic footwear (i.e., higher pitch; [12
]). Hence, the present study in combination with the aforementioned previous running and landing studies provide evidence for future studies to examine if modifying footwear features can ameliorate peak tri-planar knee moments.
While this study provides new insights into the effect of athletic footwear of late/post-pubertal girls, several limitations should be acknowledged. Firstly, a cross-sectional study design does not answer whether different types of footwear influence knee moments over time. We speculate that an adaptation period may be required for participants to become accustomed to different types of footwear, which may ultimately lead to neuromuscular changes that result in lower peak knee moments, rather than instantaneous change measured in our study. Secondly, footwear was selected based on criteria outlined in previous literature [18
], yet there is the potential limitation of extrapolating results to other footwear styles, or similar styles from other footwear manufacturers. Finally, both adjusted and unadjusted FPI values were reported to determine if FPI influenced results, yet we do not know whether FPI sub-types, particularly those with a pronated foot, are influenced to a further extent than supinated counterparts while wearing different shoes.