By Alison H. Chang, Steven Zartov Rasmussen, Asger Emil Jensen, Thomas Sørensen, and Michael Skovdal Rathleff
Clinical commentaries and expert opinions have suggested that aging, injury, repetitive or prolonged overloading (eg, endurance runners), overweight, improper footwear, steroid injection, and comorbidities (eg, diabetes, rheumatic diseases) may negatively impact the structure and function of the heel fat pad. Prior investigations have focused on plantar fasciopathy, although heel fat pad syndrome (HFPS) seems to be a common cause of plantar heel pain. These proposed risk factors and structural changes may be part of the etiology of HFPS; however, it is unclear if this information is based on high-quality evidence. Universally agreed diagnostic parameters for HFPS is critical for standardized inclusion and exclusion criteria in epidemiological studies and clinical trials.
A systematic overview on evidence-based knowledge of HFPS is greatly needed to fill the gaps and inform clinical practice and future research directions. Therefore, the researchers aimed to identify and synthesize the prevalence, etiology and diagnostic criteria, and conservative management of HFPS.
Methods
A comprehensive search was conducted in May 2021 and updated in April 2022, using MEDLINE, Scopus, Cinahl, EMBASE, Cochrane Library, SPORTDiscus, and PEDro and ClinicalTrials.gov and the World Health Organization’s International Clinical Trials Registry Platform (ICTRP) for pertinent registrations. Abstracts, conference proceedings, and bibliographies in relevant systematic reviews (if available) were hand searched for possible inclusions.
Included participants were men and women of any age with heel fat pad pain as well as those with heel fat pad pain plus diagnoses of diabetes mellitus or rheumatoid arthritis. Among the exclusion criteria were studies of heel fat pad biomechanics, morphologies in healthy individuals, participants with a clinical diagnosis of plantar fasciopathy (defined as localized tenderness at the medial calcaneal tuberosity and morning first-step heel pain that abates after a brief period of walking), and participants with unspecified plantar heel pain without differentiating between plantar fasciopathy and HFPS.
The researchers included all study types and designs describing the prevalence; etiology and diagnostic criteria; and non-pharmacological, non-surgical interventions for HFPS, such as exercise therapy (aerobic, neuromuscular, and strength/resistance), stretching/flexibility program, movement training, manual therapy, foot orthotics, shoe insert, footwear modification/recommendation, taping, electrotherapeutics, therapeutic ultrasound, therapeutic laser, shockwave therapy, and cryotherapy. There were no restrictions on the recruitment setting (eg, clinic, hospital, gym, school, home) in which the interventions were performed.
Results
Figure 1. Summary findings of the scoping review.
Only 7 studies met the inclusion/exclusion criteria with varied study designs and mixed scientific rigor. The study design of the included articles was mostly on the lower hierarchy of evidence pyramid: single case study (n = 1), case series (n = 1), case–control (n = 2), retrospective medical record review (n = 1), quasi-experimental intervention (n = 1); therefore, potentially introducing high risk of bias.
Based on these results, a knowledge gap for this condition was identified: frequent inattention to distinguishing HFPS from plantar fasciopathy when describing plantar heel pain, and an absence of robust clinical trials to support the commonly recommended conservative management of HFPS. HFPS may be the second leading cause of plantar heel pain, based on 2 studies. Several differentiating pain characteristics and behaviors may aid in diagnosing HFPS vs. plantar fasciopathy. Thinning heel fat pad confirmed by ultrasonography may provide imaging corroboration. Randomized controlled trials (RCTs) assessing the efficacy of viscoelastic heel cups or arch taping for managing HFPS do not exist.
HFPS is a distinct pathology contributing to plantar heel pain; its etiology and diagnostic criteria are poorly understood. Clinical practice guidelines or decision support platforms (eg, UpToDate) for plantar heel pain emphasize the importance of differentiating HFPS from plantar fasciopathy and propose conservative treatment options despite scant supporting research. Conservative treatment options to manage HFPS include rest, activity modification, icing, analgesics, low-dye arch taping, and viscoelastic heel cups. However, there is limited evidence on the effectiveness of these recommended approaches. Nor have these studies been systematically examined.
Discussion
One prospective population-based cohort study (The Feet First Study by Dunn et al) published nearly 20 years ago showed that HFPS is a common foot problem in U.S. community dwelling older adults with a 4.2% prevalence rate, second to plantar fasciopathy (6.9% prevalence rate). The prevalence of HFPS did not differ between sexes but was significantly higher in Hispanic/Latino than in White or African/Black Americans.
This finding was echoed by a retrospective record review of patients diagnosed with plantar heel pain in South Korea. HFPS was diagnosed by the following criteria: less than 3mm heel fat pad thickness assessed by ultrasound, pain at heel center or margin, worsening pain when barefoot or after a long period of standing. Plantar fasciopathy was diagnosed by tenderness on the medial calcaneal tuberosity and an ultrasonic hypoechoic fusiform-shaped swelling ≥4mm thickness at the origin of plantar fascia. In this sample, 53% had plantar fasciopathy; 15% had HFPS, 10% had pes cavus, 9% had HFPS plus plantar faciopathy, 5% had pes planus, 4% had plantar fibromatosis, 2% had plantar fascia rupture, 2% had neuropathy or small shoe syndrome.
Despite HFPS having a distinct pathology and the appearance that it may be the second-most frequent cause of plantar heel pain, many investigators combined participants with HFPS and plantar fasciopathy in their study sample. This oversight may have contributed to a lack of evidence-based treatment options for this condition. The current conservative treatment recommendations of this condition are mostly anecdotal. Future clinical trials with robust study designs are greatly needed.
Damage or irritation to the heel fat pad could be caused by acute trauma (eg, a single high-impact landing) or chronic overuse (eg, repetitive or excessive jumping, running, or walking on hard surfaces). Fat pad atrophy is often associated with aging, rheumatological conditions, diabetes, or obesity. An accurate diagnosis of HFPS is critical for timely management. Based on Yi and colleagues’ work from 2011, key differentiating pain characteristics and behaviors between HFPS and plantar fasciopathy are summarized in a table of Figure 1.
Comparing patients with vs. without HFPS seen in a podiatry care center, Lopez-Lopez and colleagues (2019) found that ultrasound-measured unloaded heel fat pad thickness was significantly lower in those with HFPS (7.23 ± 1.39 vs. 10.36 ± 1.78 mm, P = 0.001, Cohen’s d = 1.959). The reduced thickness was more pronounced in women than men. Among women, the thickness discrepancy was 7.09 ± 1.44 (with HFPS) vs. 10.13 ± 1.68 mm (without HFPS). Among men, the thickness discrepancy was 7.37 ± 1.33 vs. 8.58 ± 3.43 mm. Applying the area under the Receiver Operating Curve (ROC) for identifying optimal thickness cutpoint for predicting negative HFPS, they determined a threshold of ≥ 8.77 mm for no heel pain, with a sensitivity value of 85.5% and a specificity value of 82.2%.
Another study by Kanatli et al (2019) found no relationship between heel fat pad properties (heel pad thickness, compressibility, and pressure distribution) and the presence of HFPS. Heel pad properties were compared between patients with HFPS vs. younger healthy medical students with a lower BMI and lower proportion of women. Heel pad thickness in loaded and unloaded conditions were measured by radiographs. Unloaded heel pad thickness was 20.45 ± 2.89 mm (HFPS) vs. 19.55 ± 2.52 (healthy); loaded heel pad thickness was 14.02 ± 3.38 mm (HFPS) vs. 11.81 ± 2.84 (healthy). Heel pad compressibility, defined as the ratio of loaded to unloaded thickness, did not differ between groups (0.69 ± 0.14 in HFPS vs. 0.60 ± 0.11 in healthy). Peak barefoot heel plantar pressures during normal-speed walking were quantified using a pressure-recording platform embedded in the walkway. No between-group differences in peak pressure were observed.
In a case series of 9 patients with HFPS by Balius et al (2021), ultrasound and/or MRI detected pathological heel fat pad morphologies were qualitatively described, including atrophy, fibrosis, edema, and defects in the fat pad septa with fluid in the surrounding tissues. Quantitatively by ultrasound, the unloaded and loaded heel fat pad thickness was 19.8 ± 2.9mm and 12.3 ± 2.9mm, respectively; the compressibility index was 0.60 ± 0.09.
In addition to clinical presentations, ultrasonography and magnetic resonance images (MRIs) have been used to corroborate and confirm the diagnosis of HFPS. Ultrasound quantified fat pad thickness ≤ 9mm may be predicative of HFPS. Contrarily, another study reported no thickness difference between HFPS and healthy controls. An important caveat of this null finding—in this observational case–control study, the disparate age, body mass index (BMI), and sex distribution between the case and control groups were unaccounted for in statistical analyses, potentially biasing study findings. The wide range (12–29mm) of heel fat pad thickness in healthy adults may have complicated the effort to benchmark fat pad thickness as a diagnostic criterion. According to the Physical Stress Theory, thicker fat pad may be present in taller/heavier persons or in endurance athletes who frequently load their heel. Healthy men had thicker fat pad than women. BMI or sex may need to be factored into fat pad thickness interpretation of these studies. Some studies computed fat pad compressibility index, operationalized as the ratio of loaded to unloaded thickness, to ascertain tissue stiffness. A lack of standardized compressive force applied by the ultrasound probe to simulate loaded condition precludes across-study comparisons. Although less economical, practical, and convenient than ultrasonography, MRI could provide more nuanced morphological assessment and qualitatively characterize heel fat pad atrophy, fibrosis, edema, and septal defects.
Viscoelastic heel cups and arch taping have been recommended for conservative management of HFPS. However, the researchers were unable to find even a single randomized controlled trial to substantiate the efficacy of these treatment strategies for HFPS. In contrast, they identified 2 recent systematic reviews and meta-analyses on the efficacy of foot orthoses for treating plantar fasciopathy. Low-dye arch taping has been shown to reduce the first-step pain in high-quality clinical trials and supported by clinical experts and patients as a reasonable first-line management for symptoms during weightbearing activities. Their search yielded 2 interventional studies for HFPS: a single case and a quasi-experimental study. In a 33-year-old man with bilateral HFPS, heel pain decreased after 1-month and 3-month application of silicone gel heel cups. Low-dye taping and low-dye plus figure-of-8 taping provided pain relief by 2 to 3 points on a 0–10 numeric pain rating scale when compared to barefoot walking. In the absence of a control group, the change in self-reported pain observed in this study could be a result of regression-to-the-mean phenomenon or placebo effects. This review brings to light the dire need for RCTs with scientific rigor to support evidence-based recommendations in conservative management of HFPS.
Conclusion
In the limited evidence that was reviewed, it appears that HFPS may be the second leading cause of plantar heel pain. Several differentiating pain characteristics and behaviors may aid in diagnosing HFPS vs. plantar fasciopathy. Thinning heel fat pad quantified by ultrasound may provide imaging corroboration of HFPS. The researchers have identified a substantial knowledge gap for this condition, frequent inattention to distinguishing HFPS from plantar fasciopathy when describing plantar heel pain, and a glaring absence of robust clinical trials examining the efficacy of commonly recommended conservative management of HFPS.
This article has been excerpted from “What do we actually know about a common cause of plantar heel pain? A scoping review of heel fat pad syndrome.” Journal of Foot and Ankle Research. 2022;15:60. doi.org/10.1186/s13047-022-00568-x. Editing has occurred, including the renumbering of tables, and references have been removed for brevity. Use is per CC BY.
