The Heel Pad in Congenital Idiopathic Clubfoot: Implications of Empty Heel for Clinical Severity Assessment

Abstract

Background

Clubfoot has been evaluated in many ways, including the most common classifications of clubfoot, described by Caterrall and Piraniis based on six clinical signs. The purpose of this study was to gain better understanding of the heel pad in relation to the term “empty heel”, and to propose modification of clubfoot severity scoring system based on “empty heel”.

Methods

A combination of prospective study of 79 clubfoot patients treated with Ponseti method and literature review of heel pad anatomy and biomechanics. The setting was a university teaching hospital. The ethical research committee approved study protocol and informed consent of patients' parent obtained. The selection criteria included patients' diagnosed congenital idiopathic clubfoot, age < 2years, no history of previous treatment and tenotomy indicated. An evaluation of patient was assessed by orthopaedic surgeons trained on Ponseti method and has above 5 years experience.

Data analysis performed on the age, sex, Pirani scores at onset of treatment, tenotomy, and 6 month after initial full correction.

Results

One hundred and thirty-two clubfeet in 79 patients (56 males, 23 females) completed Ponseti protocol. The median age at presentation was 5.2 months (range 0.1–23.7 months). The mean right foot abduction after correction 57.30(S.D. 9.20), and for the left foot, was 56.30 (S.D. 9.40). The mean right foot dorsiflexion was −13.70 (S.D. 18.40) before correction while after correction, it was 20.00 (S.D. 4.50) and for the left, the mean was −8.50 (S.D. 9.60) before correction and 21.00 (S.D. 4.30) after correction. Eighteen (22.8%) patients (10 bilateral, 9 unilateral) had clubfeet with empty heel score above zero point at initial full correction (p<0.001). Clinic anatomy shows the heel pad is a solid complex structure existing in normal, moderate and severe atrophied form. Heel pad is attached tightly to calcaneus without a cavity for the calcaneus to drop.

Conclusions

Heel pad probably could replace “empty heel” in modify Pirani scoring system. Clinical indication for repeat tenotomy should be based on equinus, not on the feeling of an empty heel, and families can be advised that the heel pad has a tendency to remodel over time to a normal shape.

Level of Evidence

Level II

Clinical Relevance

Empty heel feeling at initial full correction of congenital idiopathic clubfoot based on Ponseti protocol is not indication for repeat tenotomy.

Introduction

Tenotomy of the Achilles tendon is an integral part of Ponseti method for treatment of club foot¹. Achilles tenotomy is crucial in 80–95% of congenital idiopathic clubfoot (CIC)² to correct the equinus and reduce calcaneum from its plantar flexed position. Clubfoot has been evaluated in many ways³, including the most common classifications of clubfoot described by Caterrall⁴ and Pirani^5,6 based on six clinical signs. (Table 1) This scoring system predicts the number of cast required for correction^6,7 and the likely chance of requiring Achilles tenotomy^4,6-10

Table 1.

Catterall / Pirani Scoring (Normal: 0 points; most abnormal 1.0 points)

Hindfoot contracture (HFCS)	Points	Midfoot Contracture (MFCS)	Points
a.Posterior crease:0, 0.5, or 1.0 points		a.Curvature of lateral border:0,0.5,or 1.0 points
b.Empty heel:0, 0.5, or 1.0 points		b.Medial crease:0, 0.5, or 1.0 points
c.Rigid equinus:0, 0.5, or 1.0 points		c.Lateral head of talus:0, 0.5, or 1.0 points
Total Score (HFCS and MFCS)

The morphological abnormalities of the hindfoot play a major role in the pathoanatomy of the clubfoot^11,12. Malpositioned and deformed talus and calcaneus along with soft tissue contractures account for the ankle equinus and hindfoot varus¹³. Interestingly, the concept of empty heel was described by Catterall⁴ and Pirani^7,10 in their scoring system to reflect the degree of equinus and presence of high riding calcaneus. The emptiness of the heel is one of the signs reflecting the severity of the equinus contracture and its persistence has been considered a sign of not full correction in congenital idiopathic clubfoot (CIC).

However, the description ‘empty heel’ might be misunderstood as a ‘true cavity’ within the heel where the calcaneus should drop with correction. The presence of the feeling of an empty heel after achieving initial full correction of the deformity could be depressive for the parents. This misunderstanding can be a source of worry for the orthopedist, and it is not uncommon to observe indications for a repeated Achilles tenotomy to bring the calcaneus down based on the persistence of the feeling of an empty heel¹⁴.

The purpose of this review was to gain better understanding of the heel pad in relation to the term “empty heel”, and to emphasize the clinical importance of identifying and treating the equinus element of the deformity to avoid complications associated with manipulating the foot against tight posterior structures. We are not aware of published literature on combine review of basic sciences of heel pad and clinical severity assessment of clubfoot managed with the Ponseti method. The hypothesis was that the empty heel feeling at initial full correction of congenital idiopathic clubfoot based on Ponseti protocol is not indication for repeat tenotomy. The study aims to propose a modification of clubfoot severity scoring system based on empty heel sign

Methods

We performed a literature review as step I about the applied anatomy and biomechanics of the heel pad to gain a better understanding of the term “empty heel”.

The step II involved prospective study of 132 idiopathic clubfeet in seventy-nine patients treated with Ponseti method. The setting was a university teaching hospital. The ethical research committee approved study protocol and informed consent of patients' parent was obtained. The selection criteria include patients' diagnosed congenital idiopathic clubfoot, age ≤ 2 years, no history of previous treatment and prior tenotomy indicated. The standard Ponseti method protocol² administered to all patients. In this study, true contracture of the gastrocnemius-soleus muscle complex is indicated by the equinus assessed with the knee extended. The difference between the equinus recorded with the knee flexed and that measured with it extended indicates the amount of stiffness in the ankle joint and is not ascribed to empty heel. The posterior wall of the calcaneus was palpated carefully when the equines is assessed because the bone could be pulled proximally away from the heel pad and clinically portrayed the empty heel perception¹⁵. An evaluation of patient was assessed by orthopaedic surgeons trained on Ponseti method and had more than 5 years experience in the method.

Data Analysis

All analyses performed based on the intention-to-treat cohort, defined as all clubfoot patients who had tenotomy and maintain full correction within the study period. Data collected included the age, sex, Pirani scores at onset of treatment, tenotomy, and 6month after initial full correction. Data analysis was performed using the statistical package for social sciences (SPSS; Chicago, Illinois) software for Windows version 17. A change in the mean Pirani points was evaluated using Chi-Square test and ANOVA for parametric data. A confidence interval (CI) of 95% with p<0.05 was taken to be significant.

Results

Clinical Assessment

Over two years period between October 2012 and September 2014, seventy nine patients (53 males, 26 females) with 132 clubfeet were treated using the Ponseti method. The median age at presentation was 5.2 months (range: 0.2 −23 months). The distribution of age, sex, foot affected and empty heel score are shown (Table 2). Eighteen (22.8%, 10 bilateral, 9 unilateral) patients had clubfeet with empty heel score above zero point after initial full correction.

Table 2.

Demographic characteristics of 79 clubfoot patients.

Patient Characteristics		Frequency (%)
Age
Birth -12months		67 (84.8)
13–24months		12 (15.2)
Sex
Male		52 (65.8)
Female		27 (34.2)
Foot affected
Bilateral		53 (67.1)
Unilateral		26 (32.9)
Left sided		11 (13.9)
Right sided		15 (19.0)
Empty heel
Before Ponseti casting	0.0	52 (39.4)
	0.5	69 (52.3)
	1.0	11 (8.3)
Empty heel
After full correction	0.0	103(78.0)
	0.5	26 (19.7)
	1.0	3 (2.3)

The mean right foot abduction was −5.3° (S.D 2.9°) with values ranging from −1° to 11° before correction and after correction 53.3°(S.D. 9.2°) with values ranging from 50° to 72°. For the left foot, the mean value was −7.8° (S.D.7.5°) with values ranging from −1° to 13° before correction while after correction, it was 56.3° (S.D. 9.4°) with values ranging from 50° to 70°.

The mean right foot dorsiflexion was −13.7° (S.D. 18.4°) with ranges from −33° to −7° before correction while after correction, it was 19.0° (S.D. 4.5°) with ranges from 16° to 27°. The mean dorsiflexion for the left foot was −8.5° (S.D. 9.7°) with values ranging from −20° to −5° before correction and 20.0° (S.D. 4.3°) with values ranging from 15° tO 31° after correction.

The Pirani scores of affected feet at onset of treatment, tenotomy and six month after full correction is shown in Table 3. The mean Pirani score was above zero points after full correction (p <0.001) reflecting residual empty heel score.

Table 3.

Average Pirani score at pre casting, at full correction and at 6month follow up

Pirani score	Mean Pirani Score	F	P value
Total Pirani score before Ponseti casting	5.141 ± 1.018	818.032	<0.001
Pirani score at full correction	0.203±0.342
Pirani score at 6month	0.313±0.070

*Repeated ANOVA measures p<0.001

Applied Heel Pad Anatomy

Location

The heel pad lies between the calcaneus and the skin and consists of neuronal, vascular, fibrous and elastic components intertwined with fat cells¹⁶ (Figure 1). It is securely anchored to skin and to bone, providing stability desirable in gait. The thickness ranges between 14.4 and 24.5mm with an average value of 18mm. The distribution of thickness varies with loading by impacts¹⁷. The heel pad is a complex structure consisting of a fat pad with micro- and macro-chambers divided by an intricate fibroelastic septation (Figure 2).

Figure 1. Heel fat pad in Idiopathic Congenital Idiopathic Clubfoot.

Figure 2. Macrochambers and Microchambers of the Heel Pad.

Relation

Skeletal support to the heel pad is a function of the calcaneal tuberosity, which exhibits two prominent plantar processes off which the plantar fascia originates^18,19. Figure 3 depicted the schematic view of the whorled turbine-shaped fatty-fascial compartments of the human heel pad. Anterior and deep (dorsal) to those processes lie the origins of the two layers of intrinsic plantar muscles: abductors hallucis brevis and digiti quinti flanking flexor digitorum brevis in the first layer, quadratus plantae more deeply together with the long plantar ligament²¹. The proximal plantar surface of the plantar fascia serves for the partial attachment of the fibrofatty heel pad¹⁷.

Figure 3. U-shaped Subcalcaneal fascia septae.

Neurovascular supply

The innervation and arterial supply of heel pad tissues seem primarily dependent upon the posterior tibial artery and nerve²⁰. Also it contained many Vater-Pacini corpuscles, generally felt to be pressure and vibration transducing nerve terminals and characterized as sources of pain^21,22.

Differential Diagnosis

The fat pads are to be differentiated from the “walking pads” which are most pronounced in the fetus but whose residual can still be seen as small, puffy mounds between the metatarsal heads¹⁶.

Disposition

Heel pads also atrophy with old age (loss of collagen, fat atrophy)¹². Owing to the loss of the heel pad, the rubbery, thick, rounded feel of the pad is no longer palpable; instead, one feels the underlying hard os calcis directly under the skin²⁰. Figure 4 shows the heel fat pad cells and septa. Atrophy of heel pads occurs secondary to severe trauma, slough, and infection. Hypertrophy of fat pads and subcutaneous fat is seen most frequently in acromegaly, neurofibromatosis and congenital vascular tumors versus congenital arteriovenous aneurysms which causes more diffuse limb hypertrophy^15,20.

Figure 4. Histological Appearance of the Heel Fat Pad.

Function

The main role is shock absorption, peak force reduction, and protection against excessive local stresses^23-26.

Heel Pad Biomechanics

Morphologically, the thickness of the heel pad can be measured by different methods including ultrasound^12,17. Histologically, the heel pad is a honeycomb pattern of fibroelastic septa that completely enclosed packed fat globules¹⁶ (Figure 2). The tissue septae are U-shaped around the tuberosity and anchored to the calcaneus and the skin. The tight adherence of the heel pad to the calcaneus was described by Tietze²¹ in 1921. The remodeling tendency of the heel pad was first described by Kuhn in 1949¹⁵. MRI studies of the heel showed the heel pad septae to be vertical in the midline and arch shaped adjacent to the calcaneus. Medially and laterally are crescentic with their convex surfaces facing peripherally. On simulated weight bearing, the central fat globules appear flattened and the crescentic globules bend exaggerating their convexity^25,27 (Figure 5). In the heel pad, there is no true cavity²⁸.

Figure 5. Mechanical changes of the Heel pad A. Heel fat pad without compression force. EHFP: Heel fat pad extends posterior to Achilles tendon and that its fibrous septa are connected to it B. Heel fat pad under load is not empty heel.

Clinical examination and biomechanical investigation indicate that heel pads may be divided into three major classifications¹⁶. The first type, normal heel pad, is thick, resilient, and terse, with most of the weight-bearing forces being absorbed by the relatively high peak pressures within a small area. The second type of heel pad is moderately atrophied, soft, pliable, and “floppy”, as seen in peripheral neuropathy, where the compression forces are distributed over a greater area of heel pad with the weight bearing more evenly distributed among areas of high, medium , and low pressure . The third type, the senescent, severely thin, atrophied heel pad shows a concentrated areas of very high peak pressure within a very small area of contact¹⁶.

Discussion

In this study, the heel pad showed a great amount of remolding in the empty heel score during the course of treatment (Table 2). Lehman et al¹⁰ data and present results revealed some persistence of an empty heel even in those children who underwent tenotomy and achieved full initial correction with the median Pirani score for empty heel at the end of treatment was 0.5. The emptiness of the heel is not more than softness in the consistency of the heel pad tissue. In addition the size of the tarsal bone in clubfoot is smaller compared to the unaffected foot¹¹. The malposition and the smaller size of the tarsal bone probably is compensated by the packing effect of the elastic adipose tissue of the heel fat pad, which makes the heel feels softer and more mobile as if it is empty¹⁵.

Weight bearing may have contributed to the normal size look of heel pad among walking babies. The normalization of heel pad of “empty heel” babies noted before walking age was in keeping with natural remodeling as development occurred. This was a puzzle against solitary weight bearing theory sited for embarking on multiple tenotomy¹⁴. It is essential for truly Ponseti method practitioner to reevaluate idiopathic clubfoot adequately after achieving initial full correction. It would prevent the error of multiple tenotomies in attempt to correct completely all deformities for self or parent's reassurance when “empty heel” persist.

More than 20% of clubfoot patients in this study at initial full correction have mean Pirani score point above zero (Table 3). Our findings was supported by earlier report by Ponseti and Ippolito in 1980 who presented theory of retraction fibrosis of the distal muscles of the calf and the supporting connective tissues¹⁶. These occurrences were attributed to be the cause of clubfoot deformity and for the common recurrence of the deformity after surgery and not the heel pad²⁹. It was noted in severe rigid or complex clubfoot deformity with poor muscle development, relapse or incomplete correction may occur. The Ponseti practitioner may not be able to influence the rigidity of the connective tissue but can change the muscle imbalance by anterior tibia tendon transfer to obtain correction²⁷.

Both clinical examination and biomechanical investigation indicate that heel pads exist in three major forms. The “empty heel” in Pirani scoring could be modify in Table 4 to include, normal heel pad , moderately atrophied, and severely atrophied heel pad¹¹. The zero point score on the Pirani's rating probably related to the degree of softness of the heel pad. Families can be advised that the heel pad in clubfoot remodels over time and becomes of normal shape after few years. Idiopathic clubfoot babies would always have some amount of heel fat pad and do not appeared to influence absolute indication for repeat tenotomy.

Table 4.

Modification of Catterall/ Pirani Scoring (Normal: 0 points; most abnormal 1.0 points)

Hindfoot contracture (HFCS)	Points	Midfoot Contracture (MFCS)	Points
a. Posterior crease:0, 0.5, or 1.0 points		a.Curvature of lateral border:0,0.5,or 1.0 points
b. Heel pad :0, 0.5, or 1.0 points		b.Medial crease:0, 0.5, or 1.0 points
c. Rigid equinus:0, 0.5, or 1.0 points		c.Lateral head of talus:0, 0.5, or 1.0 points
Total Score (HFCS and MFCS)

N.B: Heel pad severity scoring

Normal Heel pad: 0; Moderately atrophied heel pad: 0.5;Severe atrophied heel pad:1.0

Based on the previous anatomical details and from our documentation on fully corrected clubfoot patients, we can conclude that the heel pad is a complex, solid structure that is firmly attached to the periosteum of calcaneal bone with no evidence of a cavity where the calcaneus could drop. The role of Achilles tenotomy in correcting the equinus and reducing the plantar flexed calcaneus is very important; however, repeating the tenotomy based on persistence of empty heel alone is not recommended. Heel pad (normal heel pad, moderately atrophied, and severely atrophied heel pad) probably could replace “empty heel” in a modified Pirani scoring system.

Source of Funding

USAID Grant (2012–2014) to Nigeria for “Clubfoot Disability: Model of Sustainable Health System” enhance patients volume and strengthen Ponseti method adoption during this study.