The primary findings of this study demonstrated that medial unloader braces and lateral heel wedges did not alter KAA or KAM during walking gait in healthy subjects. These findings are contrary to our hypotheses and contrast with the decreases in KAA and KAM noted in individuals with knee OA.
The literature regarding the effects of medial unloader braces and lateral heel wedges on gait biomechanics in healthy individuals is equivocal. Our findings agree with those of Ebert et al.55who reported no influence of unloader braces on KAM. Conversely, Orishimo et al.,21 Pagani et al.,23and Kakihana et al.52,56who reported reductions in KAM and KAA with these orthotic devices. The discrepancies between the studies are likely due to differences in the orthotic devices, the testing procedures, and the individuals who were evaluated.
Orishimo et al.21used a different unloader brace (DonJoy OA Adjustor Medial Unloader Brace, DonJoy Orthopedics, Vista, CA) in a slightly older healthy population (32 ± 10 years) compared to our investigation, and reported decreases in KAM and KAA. This discrepancy in results likely can be attributed to the fact that the DonJoy brace induced as much as 20° of valgus correction when loaded maximally.57 Comparatively, the Bledsoe Z-12 OA brace we used provides a maximum of 3° of valgus correction.58 This dramatic difference in valgus loading capacity of the two unloader braces likely explains the difference in results.
Pagani et al.23also reported a decrease in KAM via an unloader brace in healthy subjects. However, these subjects possessed varus deformity. On the contrary, Ebert et al.55reported no effect of an unloader brace on KAM in individuals with normal/neutral knee alignment similar to
the subjects used in our study. In combination, these data suggest that knee alignment influences the efficacy of medial unloader braces, as they reduce medial knee compartment loading in individuals with varus alignment but do not alter frontal plane knee biomechanics in individuals with neutral alignment. This result may be explained by the fact that varus alignment causes joint opening on the lateral side (e.g. greater space between the femoral and tibial contact surfaces). As such, the valgus moment provided by the unloader brace has the potential to alter knee alignment from varus to valgus by approximating the lateral tibial and femoral joint
surfaces. In comparison, the spacing between the joint contact surfaces on the lateral side of the joint in neutrally aligned knees is much smaller, thus limiting the additional approximation that can be caused by the orthotic device.
Kakihana et al.52,56reported significant decreases in KAM with lateral wedges. These investigators used 3° and 6° wedges, but only the 6° wedge decreased KAM. Additionally, these wedges spanned the entire length of the foot. We used a 7° wedge that was placed directly under the calcaneous, and only came into contact with the rearfoot. The foot possesses substantial capacity to adapt to different surfaces via motion between the rearfoot and forefoot segments. As such, the wedge used in our investigation may have produced calcaneal eversion that was countered by forefoot inversion to allow the plantar aspect of the foot to maintain contact with the ground. This compensation for the effects of the lateral heel wedge would have minimized the proximal effects on frontal plane knee biomechanics. Conversely, the wedges used by Kakihana et al. spanned the entire length of the foot, thus limiting compensatory motion between the forefoot and rearfoot, and potentially having a greater proximal effect on frontal plane knee biomechanics.
that matched that of the knee OA patients in their study. This pace may have altered the
subjects’ “normal” gait patterns. In contrast, our subjects walked at a comfortable, self-selected pace. As such, this unfamiliar task may partially explain the discrepancies across studies.
Similar to the effects of medial unloader braces, it is likely that lateral wedges may have minimal effects on neutrally aligned knees while still altering knee frontal plane knee
biomechanics in those with varus alignment. The risk of developing OA increases with age and affects the majority of people above the age of 65.59 An elderly individual is more likely to have cartilage degeneration in the knee than younger individual such as those in our investigation regardless of activity level because of the forces placed on the joint that accumulate over time.59 Even though the subjects assessed by Kakihana et al.52were healthy, they were elderly (average age 65 ± 2 years) and likely had mild degenerative changes in the knee cartilage that were asymptomatic. These mild degenerative changes in the knee cartilage could also allow for a greater joint opening on the lateral side that could make it easier for the wedge to produce valgus orientation at the knee. As such, the difference in populations in the two studies may have contributed to the differential results.
Limitations
The study has limitations that should be considered including the small sample size. There were only 10 subjects who were tested which may have limited our ability to identify differences between the conditions due to relatively high variability. Additionally, we only tested the devices’ effects on frontal plane knee biomechanics. Ankle and hip biomechanics and sagittal and transverse plane knee biomechanics were not studied and could have been affected. The hip, knee, and ankle are aligned to help distribute load by proportionately in all three cardinal planes of motion, thus these devices could indirectly influence factors linked to knee
OA development.60 Examining these relationships could be helpful when drawing conclusions about the devices’ effectiveness in healthy individuals.
Conclusions
In this study, we found that using orthotic devices in healthy subjects had no effect on KAA and KAM. These findings reveal that orthotic devices do not affect healthy subjects in the same way that they do knee OA patients and individuals with varus alignment at the knee. As such, these devices would not likely provide adequate protection for healing cartilage following injury or surgical repair in otherwise healthy individuals with neutrally aligned knees.
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