An Ankle-Foot Orthosis With a Lateral Extension Reduces Forefoot Abduction in Subjects With Stage II Posterior Tibial Tendon Dysfunction

Abstract

STUDY DESIGN

Controlled laboratory, repeated measures.

BACKGROUND

Posterior tibial tendon dysfunction is a common musculoskeletal problem that includes tendon degeneration and collapse of the medial arch of the foot (flatfoot deformity). Ankle-foot orthoses (AFOs) typically are used to correct flatfoot deformity. Correction of flatfoot deformity involves increasing forefoot adduction, forefoot plantar flexion, and hindfoot inversion.

OBJECTIVES

To test whether a foot orthosis with a lateral extension reduces forefoot abduction in patients with stage II posterior tibial tendon dysfunction while walking.

METHODS

The gait of 15 participants with stage II posterior tibial tendon dysfunction was evaluated under 3 conditions: a standard AFO, an AFO with a lateral extension, and a shoe-only control condition. Kinematic variables of interest were evaluated at designated time points in the gait cycle and included hindfoot inversion/eversion, forefoot plantar flexion/dorsiflexion, and forefoot abduction/adduction. A 3-by-4, repeated-measures analysis of variance (brace condition by gait phase) was used to compare variables across conditions.

RESULTS

The AFO with a lateral extension resulted in a significantly greater change in forefoot adduction compared to the standard AFO (2.6°, P = .02) and shoe-only conditions (4.1°, P<.01) across all phases of stance. Forefoot plantar flexion was significantly increased when comparing the standard AFO and AFO with a lateral extension to the shoe-only condition. The AFO with the lateral extension also demonstrated significantly increased hindfoot inversion during the loading response and terminal stance phases.

CONCLUSION

Off-the-shelf and standard AFOs have been shown to improve forefoot plantar flexion and hindfoot eversion, but not forefoot adduction. A lateral extension added to a standard AFO along the forefoot significantly improved forefoot adduction in participants with posterior tibial tendon dysfunction while walking.

The prevalence of posterior tibial tendon dysfunction (PTTD) is estimated to be 3.3% of the population but is frequently undiagnosed.¹² At the tissue level, the pathology is characterized by progressive degeneration of the tibialis posterior tendon.

A constellation of clinical signs are used to identify the condition, including collapse of the medial arch of the foot, abnormal forefoot abduction, and heel-rise weakness.^1,10 Excessive forefoot abduction is of particular interest because it has been identified as an important component of flatfoot deformity and has not responded favorably to correction using standard ankle-foot orthoses (AFOs).^9,13,26 The presence of forefoot abduction also is one of the signs indicating stage II PTTD.⁵

Progression of PTTD is most commonly described as having 4 stages (I–IV). Stage I is defined as pain with no foot deformity, stage II as pain with a flexible flatfoot deformity, stage III as pain with a fixed flatfoot deformity, and stage IV as the progression to arthritic signs on the lateral foot with fixed flatfoot deformity. ^5,15 Stage II flexible flatfoot deformity is defined by the ability to passively place the foot in a neutral foot posture and by the presence of excessive rearfoot eversion, forefoot abduction, and a lower medial longitudinal arch.

Conservative care has been suggested for treatment of stage II PTTD, including the use of orthotic devices. Orthotic designs vary from in-shoe foot orthoses to more aggressive AFOs.^14,21 Despite varied designs, the goal of orthotic devices is to correct the observed flatfoot deformity, including forefoot abduction. The theoretical goal for using an orthotic device is to correct foot kinematics to protect or unload the tibialis posterior tendon and support structures such as the spring ligament.^3,18

Various AFO designs have been evaluated to assess their ability to correct flatfoot deformity. Evidence supports the use of in-shoe orthotic designs, which have been shown to correct arch height and hindfoot posture (increased inversion) when compared to other AFO designs.¹⁴ However, these results were obtained from an in vitro study tested under static conditions, and kinematic changes during walking likely may differ. An off-the-shelf AFO (AirLift PTTD; DJO Global, Vista, CA) was evaluated in a sample of participants with stage II PTTD while walking, with specific attention to the novel use of an air bladder located along the arch. This particular AFO was shown to limit excessive hindfoot eversion and arch collapse but had mixed results in limiting excessive forefoot abduction.²⁴ Interestingly, forefoot abduction has been shown to be harder to correct across other studies as well. In a study comparing the AirLift PTTD AFO and a custom AFO (ArizonaAFO, Inc, Mesa, AZ), forefoot abduction was not corrected across the designs tested.²⁶

It has been suggested that coupled joint motion may lead to improved control of forefoot abduction by correcting hindfoot and arch kinematics.⁴ This would limit the need for specific AFO components to correct forefoot position. However, previous data suggest that this approach may not be successful in persons with flatfoot deformity and stage II PTTD, perhaps owing to the accompanying ligament damage or tendon degeneration.

Due to the limited correction of forefoot abduction using other AFOs, the goal of the current study was to test a specific lateral-extension component applied to a standard AFO. The lateral-extension component was added to a previously tested AFO design (ArizonaAFO, Inc) to correct forefoot abduction by applying a medially directed force on the distal-lateral forefoot (head of the fifth metatarsal) (FIGURE 1). However, the addition of the lateral-extension component would not be expected to adversely affect other foot kinematics (hindfoot eversion and forefoot dorsiflexion). Therefore, the purpose of this study was to test a lateral-extension component in controlling foot kinematics (specifically, forefoot abduction) in participants with stage II PTTD while walking. It was hypothesized that an AFO with a lateral extension would be associated with greater forefoot adduction compared to a standard AFO design and a shoe-only condition. Hindfoot eversion and forefoot dorsiflexion also were evaluated to ensure that the addition of the lateral-extension component did not adversely affect foot kinematics.

FIGURE 1.

The 2 orthotic devices (A, B) used for testing, with modifications needed for motion-analysis testing. The standard-length AFO (A, C). The AFO with lateral extension (B, D). The AFO with kinematic markers (E). Abbreviation: AFO, ankle-foot orthosis.

METHODS

Fifteen participants with a diagnosis of stage II PTTD volunteered to participate in this repeated-measures, laboratory-based study (TABLE 1). The diagnosis of stage II PTTD was made by a fellowship-trained foot-and-ankle orthopaedic surgeon following the diagnostic and classification description provided by others.^15,17,20 Briefly, these criteria required participants to have 1 or more signs related to tendinopathy, including (1) palpable tenderness of the tibialis posterior tendon, (2) swelling of the tibialis posterior tendon sheath, or (3) inability to complete a single-leg heel rise with hindfoot inversion. Additionally, 1 or more signs of flexible flatfoot deformity were required for classification of stage II PTTD. These included excessive nonfixed hindfoot eversion deformity during weight bearing, excessive forefoot abduction (too-many-toes sign), or demonstrated loss of height in the medial longitudinal arch.

TABLE 1.

Demographics of the 15 Participants With Stage II Posterior Tibial Tendon Dysfunction

Characteristic	Value*
Age, y	60.1 ± 8.1
Height, cm	170.9 ± 15.2
Weight, kg	89.2 ± 12.8
Body mass index, kg/m2	31.3 ± 7.6
Sex, n
Female	8
Male	7

^*Values are mean ± SD unless otherwise indicated.

Signs of flatfoot deformity were based on comparison between the involved and uninvolved sides. This required all participants in the PTTD group to have unilateral involvement. The uninvolved side might have exhibited signs of flatfoot deformity, but it was not painful and did not demonstrate the same level of severity of flatfoot deformity as that of the involved side. All of the participants had reported symptoms of less than 2 years in duration (range, 3–23 months) at the time of testing. Participants were excluded if they had pain or pathology in the foot or lower extremity that prevented them from ambulating a distance of greater than 15 m. Additionally, participants were excluded if they reported any loss of sensation on the plantar aspect of the foot, or were less than 40 years of age. The requirement for subjects to be at least 40 years of age was to limit the sample to those with degenerative PTTD as opposed to more acute, overuse tendon pain that sometimes presents in younger individuals. All participants were informed of the experimental procedures and signed a consent form approved by the SUNY Upstate Medical University Institutional Review Board.

AFO Design and Fabrication

For each participant, 2 AFOs were tested (FIGURE 1). The first AFO was a standard Arizona AFO (ArizonaAFO, Inc) that has been described previously in kinematic and clinical studies of patients with PTTD.^2,26 This nonarticulating ankle AFO design extends to the midtarsal joint, ending just proximal to the metatarsals. For the second AFO, a lateral-extension component was added, with a trim line on the lateral side of the foot that wrapped around the fifth metatarsal head to correct forefoot abduction. The lateral extension was added to the AFO during fabrication.

Each participant was casted for the custom AFOs following the guidelines described by the manufacturer (ArizonaAFO, Inc). The foot was positioned in contact with a casting plate on the floor, with the hindfoot in a vertical position. The resulting mold was sent to ArizonaAFO, Inc for manufacturing of the AFOs used for testing. For each of the tested AFOs, a “window” was created so that the calcaneus and rigid-body markers could be visualized during gait analysis (FIGURE 2).

FIGURE 2.

Laboratory setup for kinematic testing with reflective markers.

The custom AFOs were constructed using a 3-mm polypropylene (plastic) ankle shell that was sewn inside a leather cover. The plastic shell covered the medial and lateral ankle (clam shell) and continued around the foot to extend along the plantar aspect of the foot. The plastic shell was extended to the fifth metatarsal head to make up the lateral extension component for the AFO with a lateral extension. The posterior portion of the heel did not have plastic support but was covered with leather, thus the window was removed without altering the plastic support. The window location was chosen to avoid the plastic support structure of the AFOs, as a previous study found decreased plantar-flexion stiffness when holes were drilled into the medial and lateral plastic support.³¹ It was felt that the removal of the leather cover over the heel was largely aesthetic and would not alter the integrity of the AFOs. Openings were also made in the testing shoe in the area of the heel marker and the marker on the dorsal surface of the first metatarsal.

In addition to the necessary openings in the heel and top of the shoe, to maintain the stability of the shoe, a heel strap over the top of the heel marker was added to hold the heel in the shoe and the lacing on the top of the shoe was routed around the first metatarsal marker. A previous study indicated that heel-counter stability was altered by less than 10% following similar shoe alterations.⁸ The modifications made to the shoe and AFOs were completed with input from a pedorthist. The custom AFOs were still appropriate for long-term wear following the modifications and testing protocol. Each participant was seen 7 to 12 (average, 8) days prior to testing to fit the AFOs. Each of the custom AFOs were donned to ensure they fit well, were comfortable, and participants would be able to walk in them after the break-in period.

Each participant was given a wearing schedule to become accustomed to the AFOs over the following week. Each participant was instructed to wear one of the AFOs for 1 hour a day, alternating the AFO worn. This procedure continued for an average of 8 days until the testing occurred. It was determined a priori that any participant who reported having missed more than 1 day of the recommended AFO wear would be considered noncompliant and not be included. Of the 15 participants tested, all met the compliance criteria.

Motion-Analysis Testing

The laboratory testing session consisted of a series of walking trials to test each of the AFOs in random order. The walking trials began by attaching marker triads to the skin through the openings in the AFO, which allowed the shoe to be donned without disrupting the kinematic markers (FIGURE 1). The participant was then asked to walk along a 5-m walkway at a self-selected, comfortable walking velocity. The velocity of each participant was maintained within 5% using an infrared timing system for all walking trials. This allowed comparison between AFOs at a constant velocity for this repeated-measures study. The average walking velocity chosen was 1.20 ± 0.2 m/s, within a range of 0.96 to 1.46 m/s, which was consistent with the preferred walking velocity in similar study samples.⁶

Following 5 successful trials in which the involved foot landed completely on the force plate and all markers were in view, the shoe was removed by unlacing the front and unhooking the custom heel counter attached to the back of the shoe. This was done without removing the marker triads. Each custom AFO could be slipped on or taken off by unlacing the front and holding the leather tongue aside to avoid the forefoot marker. To allow removal of each AFO without disrupting the position of the heel marker, a custom marker (FIGURE 2), from which the marker wands could be removed without removing the skin-mounted base, was used. This custom marker (FIGURE 2) consisted of 2 parts (a part to which the marker wands attached and a thermoplastic heel cup attached to the skin) that were held together with 2 small screws. The design and accuracy of this method have been described previously.²⁶

Kinematic data were collected using a 3-segment foot model that included the tibia, calcaneus (hindfoot), and first metatarsal (forefoot).³⁴ All angles were calculated as the distal segment relative to the next proximal segment: forefoot abduction was calculated as the forefoot segment relative to the hindfoot segment in the transverse plane; and hindfoot eversion was calculated using the hindfoot segment relative to the shank segment in the frontal plane. Sets of 3 reflective markers were mounted on rigid thermoplastic platforms and then attached using double-sided adhesive tape to the segments of interest. Anatomic landmarks were digitized to establish local anatomically based coordinate systems for each segment using a static standing trial that occurred separately from the walking trials. The static standing trial was completed by asking participants to stand in a comfortable position with their feet shoulder-width apart and their weight equally distributed between their feet. Motion of the distalmost foot segment was then calculated relative to the adjacent proximal segment based on the Euler rotation sequence of flexion/extension, inversion/eversion, and abduction/adduction.⁷

The model used for the current study included the first metatarsal, which was used to determine the flexion/extension angle as well as the abduction/adduction angle between the forefoot and hindfoot segments. This was a modification of our original model, in which the flexion/extension angle was calculated from movement of the first metatarsal but forefoot abduction/adduction angle was calculated from the lateral forefoot segment (second, third, and fourth metatarsals).³⁴ Consistent with a previous study,²⁵ the lateral forefoot segment could not be observed, owing to the use of the AFO and shoes.

A 12-camera Vicon 512 motion-analysis system and Workstation Version 5.2 software (OMG plc, Oxford, UK) were used to collect marker data at a sampling rate of 60 Hz, while MotionMonitor Version 8.52 software (Innovative Sports Training, Inc, Chicago, IL) was used to develop and analyze the kinematic model. The Vicon cameras were focused on a field of view of approximately 1.5 m² centered on the force plate within the walkway. This allowed use of small reflective spheres (6–10 mm) to be used in the kinematic model. The manufacturer reports accuracy of tracking of an individual reflective marker to be ±0.1 mm, with additional studies also reporting excellent precision and repeatability using the Vicon motion-analysis system.^16,19 Initial contact and toe-off points of the gait cycle were identified from the ground reaction force while walking. The unfiltered signal collected at 1080 Hz from an embedded force plate (model 9287; Kistler Group, Winterthur, Switzerland) was used to indicate when contact with the floor and toe-off occurred (10-N vertical force threshold). Kinematic data were smoothed using a fourth-order, zero–phase lag, Butterworth filter with a cutoff frequency of 6 Hz.

Data Analysis

The primary variables of interest included hindfoot inversion/eversion, forefoot plantar flexion/dorsiflexion, and forefoot abduction/adduction. The midpoint of each of the 4 stance phases of gait (10%, 35%, 75%, 90% stance) was chosen as representative of the various mechanical demands placed on the foot across the gait cycle and used as points to compare kinematic data among orthotic conditions.²⁸ Additionally, this method seemed most appropriate from the review of the raw data to capture the “AFO offsets” at mechanically distinct points without a biased representation of maximum or minimum features that may not be representative of the trends across the phase or AFO.

A 3-by-4, repeated-measures analysis of variance (ANOVA) model was used to compare kinematic variables (hindfoot inversion/eversion, forefoot plantar flexion/dorsiflexion, and forefoot abduction/adduction) across the AFO conditions. The factors in the model included the 3 AFO conditions (shoe, standard AFO, and AFO with lateral-extension component) and the 4 phases of stance (loading response, midstance, terminal stance, and preswing). In the event of an AFO–stance phase interaction, the main effects were ignored and pairwise comparisons between AFO conditions at each phase were explored. If no interaction was found but a main effect for AFO was present, the data across phases were collapsed. An alpha level of .05 was defined as a cutoff for the comparisons planned a priori.

In addition to the ANOVA model, an intraclass correlation coefficient (model 3,1) was calculated from the control (shoe-only) walking trials and used to determine the standard error of the measurement (SEM) for each of the kinematic variables. This allowed an estimate of the total errors across the study to be evaluated.^29,33 An alternative convention of interpreting any change that exceeds 2° has been suggested and used,¹¹ but with the limited reliability data available using the specific kinematic model and analysis techniques described in this study, it was deemed appropriate to utilize a direct measure of errors in the study to aid data interpretation. Two times the SEM was used to assess those changes that exceeded measurement error.

RESULTS

Reliability

The 2-SEM values were 2.2° for hindfoot eversion/inversion, 2.4° for forefoot plantar flexion/dorsiflexion, and 2.5° for forefoot abduction/adduction.

Forefoot Adduction/Abduction

No interaction was found between the AFO conditions and phases of gait, but a significant main effect for AFO (P<.01) was observed. For this reason, the data were averaged across phases to represent the average effect of each AFO for all phases (TABLE 2). When averaged across all gait phases, the AFO with the lateral extension resulted in significantly greater forefoot adduction (1.3° ± 8.6°) compared to both the shoe-only condition (−2.8° ± 8.8°) and the standard AFO (−1.3° ± 7.7°) (P<.01 and P = .02, respectively). No differences were observed between the standard AFO and the shoe-only condition.

TABLE 2.

Outcome Data for Kinematic Variables at the Midpoint of the Phases of Gait^*

Kinematic Variable/Stance Phase	Shoe Only	Standard AFO	AFO With Lateral Extension
Hindfoot inversion/eversion
Loading response	1.0 ± 5.4†	2.3 ± 5.7	2.7 ± 5.9‡
Midstance	1.1 ± 4.1	1.6 ± 5.1	1.8 ± 5.5
Terminal stance	1.2 ± 3.7†§	3.5 ± 4.8‡	3.2 ± 5.4‡
Preswing	3.7 ± 3.7	5.7 ± 3.7	5.1 ± 4.2
Average across phases	1.8 ± 1.3	3.3 ± 1.8	3.2 ± 1.4
Forefoot plantar flexion/dorsiflexion
Loading response	14.6 ± 8.6	20.0 ± 8.3	21.7 ± 6.4
Midstance	10.9 ± 5.9	16.6 ± 6.1	18.3 ± 5.8
Terminal stance	4.6 ± 6.1	9.2 ± 4.6	10.9 ± 4.3
Preswing	8.8 ± 7.4	12.0 ± 5.5	13.4 ± 6.5
Average across phases	9.7 ± 7.0†§	14.4 ± 6.1†‡	15.9 ± 5.8‡§
Forefoot abduction/adduction
Loading response	−3.5 ± 7.4	−1.6 ± 6.1	0.4 ± 7.3
Midstance	−4.3 ± 10.1	−2.8 ± 8.5	0.0 ± 9.1
Terminal stance	−1.7 ± 7.9	−0.5 ± 7.1	2.4 ± 7.8
Preswing	−1.7 ± 9.9	−0.3 ± 8.9	2.2 ± 9.9
Average across phases	−2.8 ± 8.8†	−1.3 ± 7.7†	1.3 ± 8.6‡§

Abbreviation: AFO, ankle-foot orthosis.

^*Values are mean ± SD degrees. Positive values indicate hindfoot inversion, plantar flexion, and forefoot adduction. For forefoot abduction and forefoot plantar flexion, there were no significant differences that were dependent on phase of stance (no phase-by-AFO interaction); therefore, averages across phases are presented.

^†Significantly different from extended AFO.

^‡Significantly different from shoe-only condition.

^§Significantly different from standard AFO.

Forefoot Plantar Flexion/Dorsiflexion

No interaction was found between AFO condition and phase of gait, but a significant main effect for AFO (P<.01) was observed. For this reason, the data were averaged across phases to represent the average effect of each AFO for all phases (TABLE 2). When averaged across all gait phases, the standard AFO (14.4° ± 6.1°) and the AFO with a lateral extension (15.9° ± 5.8°) resulted in greater forefoot plantar flexion compared to the shoe-only condition (9.7° ± 7.0°, P<.001). Additionally, the AFO with a lateral extension exhibited greater forefoot plantar flexion compared to the standard AFO (14.4° ± 6.1°, P = .01).

Hindfoot Inversion/Eversion

Differences between the AFOs were dependent on the phase of stance (significant interaction, P = .05), and therefore comparisons between the AFOs occurred across each phase (TABLE 2). The AFO with a lateral extension resulted in greater hindfoot inversion compared to the shoe-only condition at loading response (2.7° ± 5.9° versus 1.0° ± 5.4°, respectively; P = .04) and terminal stance (3.2° ± 5.4° versus 1.2° ± 3.7°, respectively; P = .03). The standard AFO resulted in greater hindfoot inversion (3.5° ± 4.8°) compared to the shoe-only condition (1.2° ± 3.7°) at terminal stance only (P = .049). No other differences in hindfoot frontal plane motion were observed between the different AFO conditions or stance phases.

DISCUSSION

Improved foot kinematics, specifically forefoot adduction, may contribute to improved clinical outcomes when using AFOs in persons with PTTD. Improving foot kinematics has been a focus in the evaluation of orthotic device options for patients with PTTD.^2,22,27,32 Orthotic devices aim to correct abnormal foot kinematics by realigning the foot with the intention of reducing tendon or ligament stress and preventing the progression of degeneration. Recent studies have highlighted the failure of various AFOs to correct forefoot kinematics and, specifically, forefoot abduction.^24–26

A key finding of the current study was that the AFO with the lateral-extension component resulted in a significant increase in forefoot adduction compared to the shoe-only condition and a standard AFO. The standard AFO did not result in a significant increase in forefoot adduction, which is consistent with previous studies.^25,26 The observed change of 1.5° in the standard AFO, however, did not exceed the 2-SEM value of 2.5° (TABLE 2). The standard AFO is designed to increase forefoot adduction through a 3-point pressure system that opposes abnormal forces caused by foot deformity. As part of the standard AFO design, the ankle support and the side of the shoe act in one direction on the lateral side, while the medial arch support serves as the third opposing force. The lateral-extension component added to the standard AFO was hypothesized to further enhance the distal-lateral point on the foot (FIGURE 1). An additional improvement of 2.6° of forefoot adduction with the lateral extension component (compared to the standard AFO) exceeded measurement error. A total correction of 4.1° (2.8° of abduction compared to 1.3° of adduction) was achieved when comparing the shoe-only condition to the AFO with a lateral-extension. This is considered a meaningful change and may serve to enhance already positive clinical outcomes when wearing a custom orthotic device.²

The standard AFO and the AFO with a lateral extension resulted in a significant increase in forefoot plantar flexion, averaging 5.5°, compared to the shoe-only condition (TABLE 2). Compared to the standard AFO, the AFO with a lateral extension further improved forefoot plantar flexion by 1.5°; however, this did not exceed the 2-SEM value of 2.4°. Of importance is that the custom AFO improved forefoot plantar flexion, consistent with previous studies,^25,26 and the addition of the lateral extension did not adversely affect this motion. Therefore, the positive effect of lateral extension on controlling forefoot abduction is not offset by a negative or neutral effect on other foot kinematics.

Across the AFOs tested in this study, there were smaller changes in hindfoot eversion compared to the other 2 kinematic variables. When testing the AFO with a lateral extension, hindfoot inversion only was statistically significant compared to testing in the shoe-only condition during loading response (1.7°) and terminal stance (2.0°). These changes did not exceed the 2-SEM value of 2.2° and did not occur during the midstance phase, when peak hindfoot eversion occurs. ^28,32 These findings are consistent with recent studies demonstrating that a standard AFO increased hindfoot inversion by a small amount across only select phases of stance.^25,26

A limitation of the current study includes use of a specific kinematic model that targeted movement of the first metatarsal and calcaneus. Alternative models have been proposed and include more segments in the forefoot or midfoot.^23,30,32 It is possible that the shoe, which was a control condition, might have affected foot kinematics compared to an unshod condition. The comparison to a shoe-only condition was chosen for this study to encourage the use of supportive shoes in this population during standing or walking. Another limitation of our study was the use of the classification system used to establish the stage of PTTD. A more general classification for stage II was used in the current study, but others have refined the classification to include subgroups within stage II.⁵ Future research may consider how an AFO with a lateral extension might impact various subgroups of stage II participants. Individual variability might have resulted from the range of severity that exists under the classification of stage II PTTD, with some classifications also including specific subgroups based on forefoot abduction position. These classification schemes may help to identify patients who would be uniquely suited for the AFO lateral-extension component.

Additionally, our study did not provide a comprehensive assessment of all foot kinematics that result from custom orthotic devices, but an evaluation of the effects of a lateral-extension component of an existing AFO. Future studies are needed to determine the clinical effect of the lateral-extension component (ie, pain ratings or self-reported outcomes). The lateral-extension component was considered an individual factor that was tested on a commonly used orthotic device. Further research should test the lateral-extension component in combination with other orthotic devices and shoe designs.

A lateral-extension component applied to a standard AFO significantly increased forefoot adduction. Hindfoot eversion, forefoot dorsiflexion, and forefoot abduction are primary kinematic impairments that contribute to flatfoot deformity. The correction of these kinematics is linked to the unloading of the posterior tibial tendon and associated ligaments, which may result in symptom relief for patients with PTTD. Prior data suggest that custom devices may be successful in correcting hindfoot eversion and forefoot dorsiflexion, but not forefoot abduction. In the current study, adding a lateral-extension component to the solid ankle-support design provided greater correction of forefoot abduction. These results may provide reasoning behind positive clinical outcomes in custom AFOs, and the lateral-extension component may further improve these outcomes.

CONCLUSION

A lateral-extension component added to a standard AFO corrected forefoot abduction by an average of 4.1° compared to not wearing an AFO, and by 2.6° compared to a standard AFO without the lateral-extension component. These changes were significant and exceeded the error of the measurement system used in this study. Hindfoot eversion and forefoot dorsiflexion were also reduced across certain stance phases of gait.

KEY POINTS.

FINDINGS

The addition of a lateral-extension component to a standard AFO improved control of forefoot abduction in participants with stage II PTTD while walking.

IMPLICATIONS

The addition of a lateral-extension component to existing AFO designs should be considered to improve the correction of flatfoot kinematics in participants with stage II PTTD.

CAUTION

The lateral-extension component may have different results in other samples of patients, such as those with stage III or IV PTTD.