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Abstract

Purpose:

We prospectively investigated the foot abduction characteristics following Steenbeek foot abduction brace (SFAB) use in corrected clubfeet. The foot abduction achievable in SFAB with knee flexion and extension was calculated to find the effectiveness and stretch exerted by it.

Methods:

Only children with corrected idiopathic clubfeet using SFAB for greater than 3 months were enrolled. The foot abduction with and without brace in knee extended and flexed positions was measured. Hip range of motion (ROM) with and without brace was also recorded.

Results:

The average age of 42 children ( 62 feet) was 24.25 months (range: 5–48 months). There was difference in foot abduction of 22.2° in knee extension and flexion with SFAB on. A significant change in foot stretch of 25.5° observed when the knee was moved from extended to flexed position indicated SFAB dynamicity. The SFAB was found to be an effective orthosis as it brought the corrected clubfoot into maximum abduction permissible in the foot during the phase of knee flexion. The tibial rotation accounted for a major component (61%) of apparent foot abduction with the brace on. A hip ROM of 52.2° was required for SFAB function.

Conclusion:

SFAB is a dynamic brace that functions better in flexed knee position. It is able to induce a near equivalent actual abduction available in the foot in flexed position of knee. There is a significant component of tibial external rotation in SFAB-induced foot abduction. SFAB function is also dependent on hip mechanics.

Keywords

clubfoot CTEV dynamicity foot abduction brace function

Introduction

Foot bracing is now considered an integral part of the overall management of clubfoot by Ponseti method and indispensable for preventing its relapse.^1
–3 Of all the various braces tried, foot abduction brace provided for foot abduction and ankle dorsiflexion is considered most effective.^4,5 Steenbeek foot abduction brace (SFAB) developed by Michiel Steenbeek is one such successful brace widely used in mass clubfoot projects in developing countries.

The retracting fibrosis of the ligaments and musculotendinous units of posterior and the medial foot tissues is believed to be involved in the pathogenesis and relapse of clubfoot.⁶ The foot abduction brace is said to accomplish the abduction and ankle dorsiflexion similar to last cast and provide the necessary stretch to the medial soft tissues.¹ The effectiveness of brace compliance leading to prevention of relapse has been established in several clinical settings.^{1,7

–14} Further quantification of SFAB functionality or correction achieved following its use remains largely undocumented in literature. We prospectively investigated the foot abduction characteristics following SFAB use in corrected clubfeet. The foot abduction achievable in SFAB with knee flexion and extension was calculated to find the effectiveness and stretch exerted by the brace. Also the mechanism by which knee and hip joints interplay with brace functionality was investigated.

Materials and methods

The cross-sectional study was conducted in a CURE Clubfoot Clinic at a tertiary care pediatric super specialty hospital in a low-income country. Forty-two children (62 feet) with corrected idiopathic clubfeet wearing SFAB for over 3 months (using night and nap time bracing only) were enrolled for study during their follow-up visit (July 2015). The 3-month brace usage period was chosen to ensure better adaptability to brace and tissue’s stress relaxation (see discussion). Patients using suboptimal SFAB, that is, ill-fitting braces as well as those with other associated anomalies/syndromes that altered hip and knee mechanics like arthrogryposis, congenital dislocation of hip, limb length discrepancies, hip and knee contractures, and so on were excluded from the study group in the initial screening. Uniformity of fitting of braces and proper tightening of laces were assured by CURE clubfoot supervisors. All the measurements were performed by two authors A.K. (positioner) and A.A. (measurer), the former designated for limb positioning and required manoeuvres in the foot and the latter for recording goniometric measurement in all the cases.

Rationale of the measurements (Figures 1 –3)

When a child with corrected clubfoot wears a foot abduction brace, ipsilateral hip, knee and foot behave as a linked unit. In the extended position of hip and knee, the brace abduction is apparently transmitted to foot, tibia and hip (Figure 3). In the flexed position of hip and knee with both knees at same level, the hip moves into internal rotation and tibia external rotates to compensate for the fixed bar length (Figure 3). We measured the following parameters for this study:

Without brace, in hip and knee flexed 90°:

foot abduction with knee stabilized (hands on distal femur): apparent foot abduction without brace,

foot abduction with tibia stabilized (hands over proximal tibia to prevent external rotation of the tibia): actual foot abduction without brace,

internal rotation available in ipsilateral hip,¹⁵

external rotation available in ipsilateral hip,

Tibial external rotation was calculated from measurements 1 and 2, assuming no rotations at ankle joint.

with brace, keeping both the knee and hip at 90° of flexion and at the same level:

brace abduction and

internal rotation of hip in this position.

With brace, keeping both the knee and hip at 0° flexion:

hip external rotation in this position.

The measurements for brace abduction with non-flexed hip and knee were found to be same as that in hip and knee flexed 90° as it is constant due to the fixed position of the connecting rod and therefore not separately recorded.

Measurement positions and technique

With a calm child in supine position without brace, foot abduction was first measured by holding the knee in 90° flexed position (counter distal femur), while the other hand brought abduction at midfoot with counter maintained at talar head laterally (Figure 1). This manoeuvre resulted in foot abduction; however, a certain degree of associated tibial rotation was also observed with this manoeuvre. Therefore, this reading was recorded as apparent foot abduction without brace. The second measurement of actual foot abduction without brace was performed while the first observer firmly held the upper leg with one hand with knee flexed 90°, obstructing any palpable tibial rotation, while his other hand achieved midfoot abduction similarly to the above manoeuvre (Figure 1). The degree of abduction was quantified in both these manoeuvres by the second observer using the goniometer with one limb placed along the second metatarsal axis and the other limb perpendicular to the couch. Ipsilateral hip range of motion (ROM) in internal and external rotation was also recorded with knee flexed 90°. Children were next positioned wearing SFAB keeping both the knees and hips (neutral abduction/adduction) at 90° of flexion and at the same level for measuring brace abduction by SFAB (Figure 3). Goniometer measurements were then taken by the second observer keeping one limb along the medial border of the shoe and the other limb perpendicular to the couch (Figure 2). In this same degree of flexion at hip and knee and neutral abduction/adduction at hip, the resultant internal rotation at hip was measured (Figure 3). The limbs were next kept at 0° of hip and knee flexion (extended position) with SFAB on, and any rotation at hip was measured with the reference of an axis perpendicular to the patella (Figure 3).

Figure 1.

(a) Foot abduction with knee stabilized (hands on distal femur): apparent foot abduction without brace; (b–c) foot abduction with tibia stabilized; (inset C hands over proximal tibia to prevent external rotation): actual foot abduction without brace; (d–e) The degree of abduction was quantified in both these manoeuvres by the second observer using the goniometer with one limb placed along the second metatarsal axis and the other limb perpendicular to the couch.

Figure 2.

Child positioned wearing SFAB keeping both the knees and hips in 90° of flexion and at the same level for measuring brace abduction by SFAB keeping one limb of goniometer along the medial border and another perpendicular to the couch. SFAB: Steenbeek foot abduction brace

Figure 3.

In flexed position of hip and knee, with both knees at the same level, the hip moves into internal rotation and tibia external rotates to compensate for the fixed bar length. In extended position of hip and knee, the brace abduction is apparently transmitted to foot, tibia and hip as they behave as a linked unit. (a) Resultant hip IR when a child wearing SFAB is kept at 90° of hip and knee flexion with neutral hip adduction/abduction; (b) resultant hip ER when child with SFAB on lies with extended knees and 0° of hip flexion (normal supine posture of a sleeping child); (c) shows the measurement of IR at hip in flexed position. The leg alignment is determined by two reference points. First is at the anterior tibial tuberosity and the second is at the intersection of line joining the anterior tibial crest and the bimalleolar line. One limb of goniometer is placed along this line and the other limb along the sagittal axis of the body; (d) ER at hip measured using one limb of goniometer along the flat surface of patella and the other perpendicular to the couch. SFAB: Steenbeek foot abduction brace; IR: internal rotation; ER: external rotation.

Statistical differences between measurements were calculated using paired t tests on IBM SPSS Statistics 20 software.

Results

The average age of 42 children was 24.25 months (range: 5–48 months). The male–female ratio was 6:1. There were 20 bilateral and 22 unilateral cases with equal number of right and left feet. The measurements were statistically analysed in Table 1. The actual measurements are enclosed as supplementary data. To demonstrate specific issues, we divided our results into the following sections.

Table 1.

Statistical analysis.

	TOT_ABD	FOOT_ABD	HIP_IR	HIP_ER	BRACE_ABD	HIP_IR_BRACE	HIP_ER_BRACE	TIB	R_STRETCH_FLEX	R_STRETCH_EXT	EXCESS_ STRETCH_FOOT
Mean	66.5	25.7	59.8	75.2	62.9	26.7	25.5	40.8	22.1	−3.4	37.2
N	62	62	62	62	62	62	62	62	62	62	62
Std. deviation	15	12.1	15.5	14.4	8.6	6.7	10	13.6	14.9	17	15.2
Minimum	25	5	25	30	40	15	10	13	−15	−50	−15
Maximum	90	75	85	100	80	45	45	75	50	35	70
Range	65	70	60	70	40	30	35	62	65	85	85

Abbreviations: TOT_ABD: apparent foot abduction without brace; FOOT_ABD: actual foot abduction without brace; TIB (TOT_ABD − FOOT_ABD): tibial rotation; HIP_IR: hip internal rotation available in ipsilateral hip; HIP_ER: hip external rotation available in ipsilateral hip; BRACE_ABD: abduction provided by the brace; HIP_IR_BRACE: hip internal rotation measured with brace on in 90° flexion of hip and knee and neutral abduction/adduction at the hip; HIP_ER_BRACE: hip external rotation measured with brace on in extended position (0°degree hip and knee flexion); R_STRETCH_FLEX (BRACE_ABD – TIB): residual stretch on foot by brace in flexed position after compensating tibial external rotation; R_STRETCH_EXT: residual stretch on foot by brace in extended position after compensating tibial and hip external rotation; EXCESS_STRETCH_FOOT (BRACE_ABD – FOOT_ABD): Extra stretch present on foot due to the brace.

The tibial effect on foot abduction

One of the significant findings of the study was the realization of actual foot abduction without brace measured with tibia fixed being smaller/different from apparent foot abduction without brace with just the femur fixed. The apparent foot abduction without brace when tibial movements were not restricted was 66.5° (Standard Deviation [SD] 15). With restriction of tibial external rotation, the actual foot abduction without brace was only 25.7° (SD 12.1). The tibial rotation therefore accounted for a major component of (40.8/ 66.5) 61.3% of apparent foot abduction.

Tibia external rotation and hip external rotation takes the extra stretch

In both flexed and extended positions of the knee, there was an average 37.2° (SD 15.2) of extra stretch (brace abduction − actual foot abduction) produced by the brace. This extra stretch of SFAB on statistical analysis had strong significant correlation with tibial external rotation (Pearson correlation 0.346 and Sig. [two tailed] 0.006) and highly significant correlation with a sum of tibial external rotation and external rotation of the hip (Pearson correlation 0.411 and Sig. [two tailed] 0.001). The tibia is the only other structure involved in taking the extra stretch of SFAB in knee flexed position with hip in neutral position with respect to abduction/adduction and internal rotation. In extended knee and 0° of hip flexion, the addition of hip external rotation as an added mechanism to counter the stretch of SFAB comes into play along with tibial external rotation.

Differences in foot abduction in knee extension and flexion with SFAB on

In both extended and flexed knee positions, the mean observed brace abduction due to SFAB was 62.9° (SD 8.6). In extended position of knee with brace on, the mean external rotation at hip was 25.5° (SD 9.9). Assuming that full tibial external rotation was also present (40.8°; SD 13.6), the mean effective foot abduction in knee extension was (62.9 [brace abduction] −25.5 [hip component] −40.8 [tibial component] = −3.4°[ SD 17]). Thus, the effective foot abduction in knee extension despite SFAB use was practically found to be nil because of counteraction by hip and tibial external rotations.

In flexed knee position, the hip rotations became internal. Subtracting only the tibial external rotation from SFAB abduction provided the effective foot abduction in knee flexion (62.9 −40.8 = 22.1°; SD 14.9). The SFAB therefore required knee flexion to produce effective foot abduction.

The SFAB dynamicity

As calculated above, from a practical nil stretch (−3.4°; SD 17) on foot in extended position of knee, the SFAB brought the foot into mean 22.2° (SD 14.9) abduction in knee flexed position, thus exerting a stretch of 25.6° (22.2° + 3.4°). This change in foot abduction was statistically significant (Table 1). The SFAB was thus dynamic in nature, bringing a change in foot abduction with knee ROM.

The working of SFAB

The SFAB considered mean 22.1° (SD 14.9) effective foot abduction in knee flexion. The actual foot abduction measured in the foot without SFAB was 25.7° (SD 12.1). Thus, SFAB in knee flexed position was able to bring the corrected clubfoot to almost similar degrees to actual foot abduction (22.1–25.7). The SFAB therefore works and is effective as it brought the corrected clubfoot to maximum abduction permissible at least on one limb position.

The hip arch required for successful SFAB function

The mean hip internal and external rotation in children without SFAB was 59.6° (SD 15.5) and 75.2° (SD 14.4), respectively. Thus, the mean arch of ipsilateral hip ROM without brace in clubfoot children was (59.8+ 75.2) 135°. In SFAB, the mean hip internal and external rotation was 26.7° (SD 6.7) and 25.5° (SD 10), respectively. With SFAB, the hip ROM was (26.7+ 25.5) 52.2°. Thus, a minimum of 38.7% (52.2/135) of hip ROM was required for the SFAB function.

Discussion

The deformity correction and relapse in clubfoot is postulated to occur by a phenomenon known as creep and stress relaxation of tendons and ligaments.² Creep is defined as a gradual elongation of tissue when subjected to a constant load; meanwhile stress relaxation is defined as the time-dependent decrease in load when the tissue is subjected to constant elongation.¹⁶ The manipulative correction by Ponseti method is considered creep, whereas the cast immobilization and the SFAB period are considered stress relaxation. When a corrected clubfoot is placed in SFAB, the affected foot is kept at 60°–70° of external rotation and in 10°–15° of dorsiflexion, the posterior and medial ankle soft tissues are kept under stress relaxation by the brace.² As time passes, the contractility of these ligaments and tendons reaches a static equilibrium and the recurrence decreases. The evidence to the above theory has accumulated indirectly through various clinical series showing decreased recurrence rates following brace use.^{1,7

–14} It has also been shown that bar-connected foot ankle orthosis are important in preventing recurrence of clubfeet as they provide the necessary external rotation to stretch the medial soft tissues. A comparative study between bar-connected foot ankle orthosis and the ankle foot orthosis was conducted in 45 children (69 feet) at the University of Toronto.¹ Following initial correction by the Ponseti method, children managed with bar-connected foot ankle orthosis had far fewer recurrences than those managed with ankle foot orthoses.¹

Several designs of foot ankle orthosis are now available. The accrued literature however does not precisely define or quantify the exact functionality of the brace.² We undertook this pilot study in 42 children with 62 clubfeet using the SFAB to evaluate its role in foot abduction.

The tibial external rotation is one of the major components contributing to apparent foot abduction. It is therefore essential to stabilize the tibia to precisely define the available actual foot abduction before tenotomy and brace prescription.

The parents are educated to exercise the child’s knees together as a unit (flex and extend) in the brace. The difference in foot abduction in knee extension and flexion with SFAB on establishes quantitatively the importance of this teaching as the brace becomes more effective in providing foot abduction with both knee flexed.

The statistically significant change in foot abduction when SFAB is moved from extension to flexion (25.48°) demonstrates the dynamicity of SFAB.

The effective working of the brace is demonstrated by the finding that SFAB is able to provide abduction stretch (22.2°) near equivalent to actual foot abduction (25.7°). Since the SFAB is able to provide near complete stretch to medial soft tissues, it is probably capable of preventing relapse when worn properly.

Both hip and knee mechanics play important role in SFAB functionality. The SFAB requires minimum 90° of knee flexion and hip arch of −26.7° to + 25.5° for its proper functioning.

There were several limitations to our study, which we acknowledge. For the purpose of study, age of the patient, age of the brace, SFAB bar length, duration of brace wear and foot sizes were considered non-conforming factors. Further, the child’s foot soft tissue compliance and stretch ability in different age groups was considered uniform. The tibial external rotation was assumed to be full in knee extended position for calculation purpose and this gave negative values (−3.4°) for foot abduction in extension while in brace. Further, no ankle rotations were considered in measurements and calculations. Although there were chances of intra-/inter-observer variations in measurements, the inter-observer factors were minimized by keeping the positioner and measurer unchanged for all feet. We also accept the fact that there can be other mechanisms in pathogenesis and recurrence of clubfoot. There can be other positions of hip and knee (e.g. wide abduction of both hips; extended position of hip in prone child; hyperextended, semi-flexed, fully flexed positions of the knee) while the child wears SFAB. These were not measured for this study. The strengths of our study were first of its kind pilot study to quantify SFAB abduction and the effect on corrected idiopathic clubfoot, at least in one particular limb position. It also provides quantitative evidence of SFAB dynamicity and mechanism for preventing relapse. It also suggests a method to compare different foot abduction braces available for idiopathic clubfoot by means other than clinical data on recurrences.

Conclusion

SFAB is a dynamic brace that functions better in flexed knee position. It is able to induce a near equivalent actual abduction available in the foot in flexed position of the knee. There is a significant component of tibial external rotation in SFAB-induced foot abduction. SFAB function is also dependent on hip mechanics.

Footnotes

Author’s note

The study was carried out at the Department of Pediatric Orthopaedics, Chacha Nehru Bal Chikitsalaya, Geeta Colony, Delhi 110031, India.

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

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