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Assessing The Impact Of Plantar Fat Pad Atrophy And Emerging Treatments
Painful plantar fat pad atrophy is a common, yet poorly understood patient concern. Here the authors share their experience, along with evidence from the literature, regarding available treatment options for both the forefoot and heel along including autograft and allograft approaches.
“I will drive around the parking lot for a half hour to find a parking spot because I have very limited steps before my feet begin to hurt.”
“I have spent thousands of dollars on pads, shoes and orthotics but my feet continue to ache and I feel like I am walking on bone.”
“I just want to play with my children or walk the grocery store without foot pain. I am not looking to wear fancy shoes.”
These are the common complaints heard during consultations for plantar fat pad atrophy. The frustration and desperation of patients suffering with fat pad atrophy of the forefoot or heel are immeasurable. Patients often report depression, loss of work, decreased productivity and a void of recreational activity, mostly due to their foot pain.1
Foot fat pad atrophy may be due to multiple etiologies including age, trauma, repetitive steroid injections, burns, iatrogenic surgical causes and prolonged activity on a foot with abnormal mechanics and bone pathology (see first photo above).2-4 Forefoot and heel fat pad atrophy are among a large list of differential diagnoses for metatarsalgia and heel pain. The fat pads contain specialized compartments, especially in the heel, that help with absorption of force during gait. Currently there is no established tissue thickness criteria when trying to diagnose pedal fat pad atrophy, although many patients will present with imaging studies stating there is loss of fat pad thickness. Fat pad atrophy is therefore a diagnosis of exclusion. Most patients presenting for evaluation of fat pad atrophy have seen several providers and have tried multiple treatment modalities.
The current treatment protocol for fat pad atrophy includes external pads, orthotics and shock absorbing shoe gear.5 These options may mitigate some pain, but patients remain extremely limited in their activity even when using their external devices. Patient compliance with external devices is always questionable and foot mechanics may render one’s foot uncomfortable with padded insoles or orthotics.5 One commonly sees this in the high arched foot, which is predisposed to fat pad atrophy since this foot type bears weight on the heel and forefoot through the gait cycle. Therefore, internal augmentation with soft tissue fillers, acellular dermal matrix, allograft adipose matrix and autologous fat are currently explored options for treatment of pedal fat pad atrophy.
Exploring The Evolution Of Internal Augmentation
There is minimal data describing the use of augmentation of the pedal fat pad with internal techniques. In 1994, Edward L. Chairman, DPM performed a study in which he subjectively interviewed 50 patients over nine to 28 months postoperatively after fat pad autotransplantation.6 Fat grafting was an adjunct to osseous correction of deformities. While patients noted improved pain, differentiating between the benefit of the bone surgery versus the fat grafting was indeterminable.5
In 2008, a case study described the use of an acellular dermal graft to close a chronic plantar calcaneal ulcer.7 Application of a GRAFTJACKET™ regenerative tissue matrix (Wright Medical) took place for a calcaneal ulcer of two years duration using a “parachute technique.” The ulceration partially closed with the matrix and partially through delayed wound healing.7 The parachute technique is a more invasive approach disrupting the natural attachments between the skin and soft tissue structures that comprise the specialized fat pads, however, it does avoid the morbidity of harvesting an autograft. There is little evidence-based research to date on this subject matter in the foot.
Over the past few decades, injectable fillers have gained popularity as a treatment for foot fat pad deficiency. Fillers are not FDA-approved in the foot, however they offer patients temporary foot pain relief quickly, easily and with minimal risk. There is little down time post-injection. While they may be a quick, off-the-shelf solution, these modalities are expensive and introduce a foreign material with risk of an inflammatory response or nodule formation.8 Long-lasting hyaluronic acid fillers could cost as much as $600 for 1ml and even more for fillers such as poly-l-lactic acid. Poly-l-lactic acid requires rehydration, so much of what one injects will dissipate, possibly requiring multiple rounds of injection at high cost and unpredictable distribution. Despite many practitioners using these products, there remains no randomized, controlled published data as to their benefit. Much of the data in the past dealt with injectable silicone, but this fell out of favor due to infection risk and migration to lymph nodes.9
Another injectable alternative emerging in the past few years for fat pad atrophy is allograft adipose matrix (Leneva®, MTF Biologics). Allograft adipose matrix comes in a hydrated injectable form. While this may be an easy off-the-shelf solution, there is limited objective clinical data outside of case reports.10 This product may produce an intense inflammatory response, worthy of warning to patients, whereas autologous fat does not have this response. The allograft is donated human cadaver adipose, processed in a sterile fashion while maintaining key matrix proteins.11,12 The allograft matrix serves as a scaffold for patient adipose cells to multiply when injected into areas of pedal fat atrophy. In very lean patients in whom liposuction is difficult, the injectable allograft may be a promising option for fat pad augmentation. In most patients that have their own fat to donate, convincing them that cadaver fat is a better option without the necessary objective data is a tough sell. It can, however, avoid donor site morbidity from liposuction such as contour irregularity, seroma, bruising or pain; albeit these risks are low in small volume fat grafting.
Autologous fat is a natural and minimally invasive strategy gaining momentum for the treatment of pedal fat pad atrophy. It involves grafting a patient’s own tissue, often from the abdomen, flanks or thighs through liposuction and transplanting it to areas of plantar fat pad atrophy. The procedure typically takes place in the office setting under local anesthesia. After numbing the donor site with tumescent fluid, a plastic surgeon aspirates the fat with small cannulas into 10 ml syringes. Centrifugation then processes the fat to allow the oil and aqueous portions to separate, before transfer into one ml syringes for injection into the foot. Fat graft placement uses a cross-hatch pattern to avoid large boluses of fat that will result in cell death. No sutures are necessary and patients can walk out of the office after the procedure. Typical post-operative care involves limiting walking on the fat graft and compression of the donor site for six weeks. Modified shoe gear with pads helps offload the fat grafted area. Some patients like to use crutches or knee scooters. Non- weightbearing range of motion exercises are mandatory. Alternating acetaminophen and ibuprofen are sufficient for pain control and ice is not permitted to avoid vasoconstriction near the grafts.
Special Considerations In Forefoot Fat Grafting
Pedal fat pad atrophy affects roughly one-third of adults 60 years and older and 50 percent of adults age 70 years and older.13 Younger patients (age 30 to 60 years) may present with fat pad atrophy secondary to injury and/or multiple surgeries. Many patients undergo removal of fat at the time of a neuroma excision or have a history of multiple steroid injections which can lead to dissolving of the fat (see second and third photos above). Most patients state that they feel like they are “walking on bone.”
The first objective data from a one-year randomized crossover clinical trial of fat grafting to the forefoot demonstrated improved pain and quality of life and limited progression of fat pad atrophy.14 The control group experienced decreased tissue thickness over the course of the year. When studying the same population out to two years, the data confirmed a significant improvement in pain and disability.15 Ultrasound assessed tissue thickness under the metatarsal heads. Thickness after fat autograft injection was not long lasting despite pain improvement.14
To better understand these results, another study utilized magnetic resonance imaging (MRI) to evaluate volumetric differences in the forefoot with autologous foot fat grafting.16 The MRI data showed that there was a significant increase in retained volume in the forefoot, potentially protecting the metatarsal bone, despite loss of fat directly under the metatarsal head by ultrasound.16 This data supports the notion that with increasing ambulation on the grafts, the fat likely re-distributes around the metatarsal heads to provide long term relief. Another study of forefoot autologous fat grafting for systemic sclerosis demonstrated promising results but lacked objective measurement of pain or tissue thickness.17 Fat grafting has data supporting benefits on skin quality, including benefits to collagen, elastin, dermal vascularity and dermal thickness.18,19 Ultrasound data from a two-year randomized, crossover clinical trial demonstrated improved dermal thickness and skin quality with decreased callous formation.20 Improved skin integrity may also help explain increased patient comfort with autologous fat injections despite the loss of tissue thickness directly under the metatarsals.
What Do We Know About Fat Grafting To The Heel?
The most common podiatric foot complaint is heel pain. Plantar fasciitis is the predominant diagnosis and comprises 11 to 15 percent of all pedal complaints seeking medical attention.2,3 The incidence of heel pain is 10 percent of the United States population.4 Heel fat pad atrophy, however, is the next most common cause of heel pain. A combination of both fat pad atrophy and plantar fasciitis ranks as the third highest incidence of heel pain.21 Many patients undergo steroid injections for plantar fasciitis, which can migrate and dissolve the heel fat pad (see fourth and fifth photos above).
The heel is the first point of contact during the gait cycle and subject to significant impact. The shock-absorbing specialized heel pad is comprised of the dermis and two fat pad layers: the deeper, larger, compressible macrochamber (MAC); and more superficial, noncompressible, compact microchamber (MIC).22,23 An ultrasonic evaluation of heel fat pad atrophy patients revealed increased compressibility of the macrochamber while the microchamber remained constant with compression.24 The macrochamber is the zone mostly devoted to shock absorption and is therefore the target for heel fat pad augmentation. There are subjective case reports of autologous fat grafting to the heel secondary to a deficiency from trauma.25 Data from a two-year, prospective, randomized, crossover pilot study for heel fat grafting demonstrated similar results to the forefoot.24 Macrochamber thickness initially increased but was not significantly greater by six months. When loaded with the ultrasound probe, the macrochamber remained significantly thicker in fat grafted feet at 12 months. This corresponded to reduced compressibility as compared to controls.24
The stromal network of the fat pad is important. The heel contains fibrous septae connecting the periosteum of the calcaneus to the overlying reticular dermis.26 The connective tissue network forms a web of viscoelastic pockets around adipocyte clusters which act to resist compression and shear forces while providing elastic recoil during ambulation.27,28 Degeneration of the collagen and elastin fibers has been linked to macrochamber fat pad atrophy in patients tht have diabetes.29 Rejuvenation of this collagen and elastin network from the adipose tissue is a possible explanation for the reduced compressibility seen in fat grafted heels. In addition, autologous fat grafted heels had increased dermal thickness from baseline starting at two months and extending throughout the course of the study. When compared to controls at six and 12 months, fat grafted heels had significantly increased dermal thickness. After fat grafting, dermal thickness increased in a delayed fashion, starting at two months and increasing at each successive time point through 24 months, suggesting that the benefits of fat grafting on the skin keep increasing over time. Foot pain, function and appearance were significantly improved at six and 12 months when compared to controls.24
Predicting The Success Of Fat Grafting
Patient selection is important before engaging in an elective procedure. No documented criteria for fat pad atrophy measurements currently exists. However, certain foot characteristics may help suggest when treatment from autologous fat grafting will be successful.30 When examining 44 patients that received fat injections into the forefoot, 73 percent were women with a mean age of 61 years and a mean body mass index (BMI) of 26 kg/m2. Seventy-five percent had bilateral forefoot injections, 59 percent had a rigid cavus foot, 73 percent had a past history of pedal deformity or surgery, and 43 percent had plantar callous formation. Only female gender correlated with improved pain from the time of fat grafting surgery to 12 months post procedure. Patient BMI and unilateral treatment versus bilateral treatment did not significantly impact the success of fat transfer.30
While these patient characteristics may favor who will have the best outcomes, larger studies are necessary to determine who will ultimately benefit the most from the procedure. Clinical trials of autologous foot fat grafting are challenging since it is hard to discern if failure is due to the quality of the patient’s fat versus individual foot mechanics. In addition, some patients suffer from additional areas of pain (i.e. forefoot patients may have had heel pain not addressed by fat grafting the forefoot only, or heel patients may have had chronic plantar fasciitis in addition to the heel fat pad atrophy treated), and thus may bias the results of the clinical trials.
Concluding Thoughts
Several treatment options are available for augmenting the foot with fat pad atrophy. The body of literature regarding these methods is also increasing, with most data in the autologous fat grafting arena. Replacing “like with like” makes sense, while preserving the natural connections between the skin and underlying structures. Fat is an ideal soft tissue filler in that it creates long-lasting volume augmentation in addition to rejuvenating surrounding tissues including the skin. Allograft adipose is also showing promise but more objective data is necessary on this treatment as well as other off-the-shelf fillers. People are living longer. For one’s mental and physical well-being, it is important to stay active. With age and use, foot fat pad atrophy is inevitable and proves to be symptomatic in 30 to 50 percent of our aging population.13 Although there are new options to treat this problem, the potential regenerative capabilities of autologous fat grafting are intriguing. Studies show that the fat transfer prevents worsening over time, therefore earlier diagnosis and treatment would be beneficial. Autologous fat grafting is a minimally invasive, safe and evidence-based effective procedure.
Dr. Beth Gusenoff is a Fellow of the American College of Foot and Ankle Surgeons and a Clinical Assistant Professor of Plastic Surgery in the Department of Plastic Surgery at the University of Pittsburgh in Pittsburgh, Pa. She is Co- Director of the University of Pittsburgh Medical Center Foot Fat Grafting Program.
Dr. Jeffrey Gusenoff is a Professor of Plastic Surgery in the Department of Plastic Surgery at the University of Pittsburgh in Pittsburgh, Pa. and Co-Director of the University of Pittsburgh Medical Center Foot Fat Grafting Program.
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