The effectiveness of raising the heel height of shoes to reduce heel pain in patients with calcaneal spurs (2024)

Abstract

[Purpose] To investigate the effect of heel height on the distribution of plantar footforce and heel pain in patients with a heel spur. [Subjects and Methods] Plantar force wasmeasured using 8 force sensors in 16 patients (3 men, 13 women), with symptomatic heelspur for 4 heel heights (0–4 cm). Sensors were located at the hallux (T1); medial tolateral metatarsals (M1 through M3), mid-foot (MF); and at the central, lateral, andmedial heel (CH, LH, and MH). Pain was evaluated using the minimum compression force thatcaused pain and was measured using an algometer. [Results] Load bearing shifted from theheel (CH) to the mid-foot (MF) and hallux (T1) with increasing heel height. Raising theheel from 2 to 3 cm reduced the magnitude of load bearing, relative to the minimumcompression force for pain, by 3.70% at the LH and 2.35% at the MH. Excellent clinicaloutcomes, defined by a 70–100% decrease in pain, were achieved in 10/16 participants withthe use of a 2-cm and 3-cm heel height in men and women, respectively. [Conclusion]Increasing heel height effectively decreases the plantar force on the heel duringweight-bearing activities.

Key words: Calcaneal spur, Heel height shoe, Algometer

INTRODUCTION

Heel pain is a problem frequently seen in orthopedic practice, and treatment is mostlydisappointing. Clinically, pain is the chief presenting complaint that causes difficulty inweight-bearing functions, such as walking and standing, thereby restricting work and sportactivities^{1, 2)}. Treatment for this syndrome is usually conservative and is directedtoward decreasing the pain via a nonsteroidal anti-inflammatory drug and a reduction inactivity level³⁾. Several studies haveattempted to decrease pain in the heel compared to this type of conservative treatment usingextracorporeal shock wave⁴⁾ or pulsed radiofrequency energy⁵⁾ as well as conservativetreatment in combination with extracorporeal shockwave therapy^{6, 7)} or with contrast baths,stretching exercises, or wearing low-heeled shoes⁸⁾. During treatment, the level of pain in each patient was determinedusing a telephone survey³⁾ or by manualpalpation¹⁾.

The pain felt by the calcanea spur patients is due to considerable load in the heel areaduring weight-bearing activities^{2, 9)}. This high loading commonly leads to thedevelopment of calcaneal (heel) spurs and pain¹⁰⁾. Orthotics is generally prescribed to manage the pain associatedwith heel spurs, to reduce load bearing on the heel by increasing the height of theshoe^{11,12,13,14,15)}. Goske et al.¹⁶⁾ noted that high conformity of the orthoticto the heel was essential to increasing the contact surface between the heel and theorthotic. This could then reduce the magnitude of the weight-bearing load on the heel.Thicker and softer orthotics further decreased the calcaneal loads, although the effect ofthe material used was not as important as the appropriate sizing and thickness of theorthotic.

We add to the results of these previous studies by measuring the pressure pain threshold(PPT) in the heels of patients experiencing plantar heel pain syndrome. The pain level wasmeasured using a pressure algometer, which indicates the PPT in a quantitative manner¹⁷⁾, as described in Saban et al¹⁸⁾. In that study, the researchers dividedthe heel region into 5 sites and pressed each site using an algometer probe. However, theexact location of pain suppression was not specified.

In the study presented herein, we assessed 7 pain suppression points that were set aroundthe site of the spur growth. In doing so, we sought to systematically evaluate the effectsof increasing the heel height of a shoe on the distribution of forces on the heel duringstanding and the subsequent pain among patients with a symptomatic heel spur. Apriori, we hypothesized that increasing the height of the shoe would decrease thepeak compressive forces that were exerted on the heel during standing.

SUBJECTS AND METHODS

Sixteen patients with symptomatic heel spurs were recruited from the RSUD (local publichospital) Tugurejo in Semarang. Volunteers were healthy, without notable asymmetries onlower limbs alignment and without history of orthopedic trauma based on the check up by anorthopedic specialist. The patient characteristics are shown in Table 1. The study was approved by the institutional review board and all patientsprovided informed consent. Reporting was in accordance with the proposed guidelines for thereporting of reliability and agreement studies (GRRAS)¹⁹⁾.

Each patient was asked to perform loaded and unloaded scanning of the foot. Loaded scanningof the foot using a digital footprint was used to determine foot width (FW) and foot length(FL). The footprint image was then used to map the location of pain suppression pointsaround the spur growth. FL is the direct distance from the pterion point to the mostanterior point of the longest toe (first or second) and is measured parallel to the footaxis. FW is the horizontal distance between the tibial metatarsal to the fibularmetatarsal²⁰⁾. The digital footprint wasgenerated using a modified flatbed document scanner and was designed to scan one foot at atime. The scanning process occurs when the research subject is standing in an uprightposture above the platform, as shown in Fig.1a. To obtain the footprint image, the portions of the foot that are not in directcontact with the platform (Fig. 1b) are removedusing MATLAB, which results in the final image as shown in Fig. 1c. The FW and FL are calculated using MATLAB as the differencebetween the nearest and furthest points at the x and y coordinates, respectively, where xrepresents the horizontal coordinates and y represents the vertical coordinates.

The location of the bone spur was obtained from standing plain radiographs, where S is thedistance between the back of the heel and the base of the spur and L is the length of thespur (Fig. 2a). By mapping the results of this radiograph on the footprint image (Fig. 1c), the location and dimensions of the bone spurcan be seen in plantar view. The 7 points used for pain assessment could then be localized,with point 7 being placed at the base of the spur. The remaining 6 points were distributedalong the circumference of a circle, with the base of the spur at its center, and the radiusof the circle being equal to the length of the spur plus 1 cm (Fig. 2b). In all cases, the base of the spur was assumed to be in theheel center line, which was a line drawn from the center of the heel to the tip of thesecond toe (Fig. 2c)²¹⁾.

To measure PPT, the patient lays supine in a relaxed position, and the measurements wereperformed using a mechanical pressure algometer (FDIX 25, Wagner Instruments, Greenwich, CT,USA), as shown in Fig. 3a. This device consists of a flat rubber tip probe of 1 cm in diameter, which isapplied perpendicular to the skin. The voltage signal is transduced and amplified and theoutput is displayed in Newtons or kilograms. The pain test is conducted as follows: 1) markthe 7 pressure points in the heel area to be assessed (Fig 2b); 2) press the skin at point 7 first; 3) increase the pressure graduallyand stop until the patient’s face expression looks like a level 6 or 7, as shown in Fig.3b²³⁾; 4) take a note of the force valuethat causes pain; 5) apply the same procedure to the remaining points 1–6. Suppression atthe end of the spur (around point 6) should produce a minimum compressive force since it isidentical to the cantilever construction. Using the pain test results at those 7 points, itis possible to reveal the pain minimum compressive force and the point location in eachpatient.

The distribution of plantar forces, between the foot and the shoe was measured using an8-sensor array (402 FSR, Interlink Electronics, Camarillo, CA, USA). Determination of thelocation of each sensor was performed using an unloaded foot scan that was produced using a3D foot scanner (ScanPod 3D, Vismach Technology Ltd., Hong Kong, China). In particular, wescanned around the area with the greater z-value coordinates, as shown in the red colorimage (Fig. 4a). Sensors were positioned at the following 8 locations: T1, hallux (sensor 1); M1,metatarsal 1 (sensor 2); M2, metatarsal 2 (sensor 3); M3, metatarsal 3 (sensor 4); MF,midfoot (sensor 5); LH, lateral heel (sensor 6); CH, center of heel (sensor 7); and MH,medial heel (sensor 8), as shown in Fig. 4b.Sensor 7 was always placed at the center of heel, which estimated to be located at 0.15 x FL(Fig. 2c)²²⁾. The standardized position of the 8 sensors was embedded in afabricated orthotic to measure the plantar force between the foot and the shoe (Fig. 4c). For analysis, only the force recorded in thegreater z-value of the sensors positioned at the center, medial, and lateral heel was used(3 of the 8 sensors of the array).

Each participant was fitted with an appropriate shoe size, with custom heel heights of0 cm, 2 cm, 3 cm, and 4 cm (Fig. 5a). To provide foot stability and comfort in the shoe, a custom insole, without contour(flat) or arch support was included. The outer covering was made of Microcel Puff EVA foam(7 mm), with the inner cushion made of Poron cushioning (3 mm)¹⁶⁾ (Fig. 5b). Heelwedges of different heights could be inserted into the shoes. Starting with a heel height of0 cm, the load on the soles of the patient’s feet was measured using FSR sensors. If thepeak load in the heel area F was still greater than the minimum pain force F* or F>F *,patient was asked to use a shoe with a higher heel. The peak load in the heel area wasmeasured again. This process repeated until F≤F *. All measurements for each heel heightshoe are performed when patient is standing in an upright posture guided by the operator

RESULTS

Among the 16 patients in our study group, 7 had symptomatic bilateral heel spurs. Sincecompressive pain was measured bilaterally in these patients, a total of 23 feet wereevaluated. The length of the heel spur ranged between 1.2 and 9 mm. The compressive painforce ranged between 5.04 and 28.40 N. We observed a linear relationship (correlationcoefficient: 0.68) between the length of the spur and the minimum compression force forpain, as shown in Fig. 6. According to the BMI classification from WHO²⁴⁾, there was a relationship between BMI classification and theminimum compression force for pain (i.e., as BMI increased, the minimum compression forcefor pain decreased). In the normal weight group (BMI between 18.5–24.9 kg/m²),the average minimum compression force for pain was 18.07 ± 5.75 N. In the overweight group(BMI between 25.0–29.9 kg/m²), the average minimum compression force for pain was12.02 ± 4.57 N. In the obese group (BMI ≥30 kg/m²), the average minimumcompression force for pain was 8.42 ± 3.08 N.

The minimum compression force for pain, at each reference point around the heel spur, wasas follows: point 1, pain in 11 feet (7.03–28.4 N); point 2, pain in 2 feet (13.06–17.85 N);point 3, pain in 1 foot (9.0 N); point 4, no cases identified; point 5, pain in 1 foot (8.45N); point 6, pain in 7 feet (5.04–25.10 N); and point 7, pain in 1 foot (17.8 N). Whenconsidering the smallest pain force in the patients with bilateral heel spurs, we found thatthe average minimum compressive force for pain was 14.37 ± 6.20 N.

The distribution of load bearing on the plantar surface of the foot, expressed as aproportion of body weight (z-force/BW, %), is reported in Table 2 for the different heel heights. As heel height increased, peak force shiftedaway from the heel to the mid-foot (MF) and fore-foot. Loading on the MF increased as afunction of increasing heel height, from 1.06% at the baseline (0 cm) heel height to 10.01%for the 2-cm height, 10.68% for the 3-cm height, and 11.43% for the 4-cm height. The hallux(T1) supported the highest proportion of load bearing, with peak magnitudes sustained with aheel height of 4 cm. In comparison, the proportion of load bearing was lowest on the medialforefoot (M1) for all heel heights in comparison to all other regions of the foot, and thisfor all heel heights from baseline. The load bearing on the metatarsal region (M2) increasedfrom 0.95% (0 cm) to a peak magnitude of 9.45% (3 cm), while load bearing on the M3 regionincreased from 2.45% (0 cm) to a peak magnitude of 6.10% (2 cm), decreasing to below thebaseline magnitude with heel heights of 3 and 4 cm (0.77% and 0.87%, respectively). Withregard to load bearing specifically on the heel, the proportion of load bearing increasedgenerally as a function of heel height on the medial (MH) and lateral (LH) heel, compared tobaseline (0 cm), with the peak magnitudes sustained on the LH and MH with the 4-cm heelheight. For the central heel (CH), the peak load bearing was at baseline (0 cm), with amarked decrease with increasing heel height, from 14.32% (0 cm) to 1.36% (2 cm), 0.91%(3 cm), and 0.89% (4 cm). The distribution of loading on the MH, LH, and CH for the 4 heelheights is summarized in Fig. 7. The force applied at the CH was lower than the minimum pain force (F*) withincreasing heel height from 0 cm, while the magnitude of force on the LH was comparable toF* at heel heights of 2 cm (5.45% of F*) and 3 cm (1.75% of F*). Load bearing magnitudeswere significantly greater than F* on the MH, at 2 cm (33.65% of F*) and 3 cm (31.30% ofF*). The magnitude of force both on the LH and MH were significantly increased with a heelheight of 4 cm.

The reference measurements of the foot for the location of the sensor at CH are summarizedin Table 3, including the difference between the center point of the heel (used for forcemeasurement) and the base of the spur (used for pain measurement). For some participants,this difference was negative, thereby indicating that the CH sensor was posterior to thebase of the spur. The greater distance difference was seen in patients no. 3 and no. 15(i.e. 5.9 and 6.9 mm, respectively). However, the average difference between the centerpoint of the heel and the base of the spur in these cases was small (1.17 ± 2.79 mm) or −1.6to 3.9 mm. Overall, the sensor was localized close to the base of the heel spur (−1.5 to2.3 mm), except for 2 cases with a difference of 5.9 and 6.9 mm.

DISCUSSION

The highest number of pain points were identified at points 1 and 6, just anterior andanterolateral to the heel spur. This is consistent with our original assumption thatpressure applied to the end of the spur would be associated with the greatest magnitude ofpain. The average minimum compression force for pain at points 5 and 6 (i.e., 8.5 N and 14.5N, respectively), were lower than at points 1 and 2 (i.e., 16.5 N and 15.5 N, respectively).This result is in accordance with the study of Saban et al.¹⁸⁾, except at point 7 in the base of the spur, which noted that theminimum compressive force for pain at sites medially posterior, medially anterior, andcenter, were significantly lower than at sites laterally anterior and laterally posterior.He concludes that this is due to the aggregation of anatomic structure at this location,particularly the nervous tissues. The patients that Saban et al. recruited experiencedplantar heel pain syndrome and were not specifically mentioned due to the presence of acalcaneal spur and since the exact location of pain suppression points 1–5 were notspecified. In this study, in reference to the spur, point 7 was placed at the base, point 6was placed at the end, points 1 and 2 were placed laterally anterior and laterallyposterior, and points 4 and 5 were placed medially posterior and medially anterior. Based onthe placement of the 7 points for pain assessment, it is reasonable if the minimumcompression force for pain at point 7 is higher than at the other points.

The relationship between BMI and the minimum compression force for pain indicated thatpatients with excessive body weight experience more pain²⁵⁾. Meanwhile, the relationship between the length of the spur and theminimum compression force for pain shows that the compression force for pain is lower whenthe length of spur is higher. This agrees with the research of Ozdemir et al.⁸⁾ and Rome et al²⁶⁾. Ozdemir et al. noted that, as spur size increased, theheel pad compressibility index (HPCI) value increased, while Rome et al. demonstrated thatheel pad thickness and HPCI were all significantly greater in patients with plantar heelpain than in normal subjects.

Our measurement of the distribution and magnitudes of forces on the plantar surface of thefoot provides additional insights into the forces at the foot-shoe interface. Withincreasing heel height, we identified a redistribution of plantar force, both in terms ofmagnitude and location, with increasing load bearing on the mid-foot region. Therefore, theincrease in the downward slope of the foot with higher heel height shifts load bearing fromthe heel to the mid- and fore-foot regions¹⁵⁾. This redistribution is characterized by a shift in the proportionof load bearing from CH to M2, which is indicative of increased pronation of the fore-footwith increasing heel height¹³⁾, with anincrease in peak plantar force under the hallux (T1 region) with the 4-cm heel height. Thesefindings agree with those previously reported by Kim et al.¹⁴⁾ and Hessert et al²⁷⁾. Compared to flat shoes, Speksnijder et al. reported an increase of27% in the plantar force on the medial fore-foot at M1, 13% in the central fore-foot (M2),and 27% at the hallux (T1) with high-heeled shoes, with the same redistribution identifiedduring walking, although the peak magnitudes of force were greater²⁸⁾. Increasing heel height also forces the fore-foot intopronation, with a decrease in rear-foot pronation¹¹⁾, which we found resulted in an 89% increase in the proportion ofload bearing on the MH, relative to the LH, in comparison to the baseline (0 cm) heelheight.

Our comparison of average calcaneal loading to the average pain minimum compressive forceindicated a decrease in load bearing on the CH with a 2-cm heel height which is smaller thanthe average pain minimum compressive force, but without decrease in load bearing on the LHand MH. Therefore, there is still a potential for heel pain. However, raising the heelheight from 2 to 3 cm reduced the proportion of load bearing on the LH by 3.70% and on theMH by 2.35% in comparison to the minimum compressive force for pain.

The average difference between the location of the heel center point and the location ofthe base of the spur was 1.17 mm. Therefore, the position of the CH sensory was relativelyaccurate since, at the very least, the edge of the sensor was able to compress the spur.This allowed us to compare the peak load applied to the minimum compression force forpain.

We found that the use of a 2-cm heel height for men and 3-cm heel height for women wassufficient to decrease calcaneal pain and improve comfort during standing and walking.Participants wore their custom shoes from early August to the end of September 2016, for≥4 h/day over a duration of 8 weeks²⁹⁾.Without the use of local anesthetic, the following clinical outcomes were obtained: adecrease in pain from 100% to 70% in 10 individuals (excellent clinical outcome); decreasefrom 70% to 30% in 3 individuals (very good outcome); and a decrease of <30%(satisfactory outcome) in 3 individuals. None of the participants reported an increase inpain or unsatisfactory results. Therefore, increasing heel height provides an effectivestrategy to decrease the plantar force on the heel during weight-bearing activities.

Acknowledgments

This work was supported by an Application and Development Research Grant from the UNDIP(2015) Contract No. DIPA: 023.04.2.1898.152013 and (2016) Contract No. SP DIPA:042.01.2.400898/2016.

REFERENCES