Assessing The Role Of Ultrasound With Fat Pad Atrophy And Restoration

When a patient presents to the office, the evaluation and diagnosis of fat pad atrophy is typically via a clinical examination. Patients often feel they are “walking on pebbles” or feel they are hitting the ground very hard with their bones. Some may relate a shooting or burning pain. Patients may have an associated neuroma, heel spur syndrome/plantar fasciitis or tarsal tunnel syndrome, which one needs to differentiate as part of the diagnosis. Ultimately, one would identify high pressure areas on the ball of the foot, the heel, medial or lateral column or the digits through the physical examination.

A patient history is also essential. The most common causes of fat pad atrophy are trauma; autoimmune conditions such as rheumatoid arthritis; osteoarthritis; joint dislocations and deviations; cavus foot type with anterior displacement; iatrogenic cortisone injection therapy (typically more than three in a location); and natural aging.

Keys to the diagnosis include classical signs of hyperkeratotic lesions, intractable plantar keratomas, areas of erythema, bursas and direct palpation of the bones in the area of pain.

Radiographic analysis is good to show the structure of the foot and identify key deformities, but radiographs will not show the amount of cushion atrophy. Magnetic resonance imaging (MRI) is expensive and time-consuming, and patients do not want to have an MRI unless absolutely necessary. Sometimes it is helpful to get an MRI to rule out other underlying conditions.

One of my favorite modalities is musculoskeletal ultrasound. Ultrasound can be a useful tool in the diagnosis and evaluation of atrophy of the fat pad on the plantar foot, whether it is the forefoot or the heel. This diagnostic tool is helpful to detect fat atrophy in high pressure areas. Musculoskeletal ultrasound is inexpensive, portable, reliable, quick and free of radiation. From a diagnostic standpoint, evaluation of the plantar foot pad on the heel has historically shown a thickness between 7.6 mm and 9.0 mm.¹ Unfortunately, most studies have assessed the heel fat pad in a non-weightbearing position. Weightbearing analysis would be more appropriate for the indication of fat atrophy as most patients complain of symptoms during activity. Moreover, one must still evaluate fat pad measurements to the ball of the foot.

Often, patients will inquire about performing the fat pad injections under the guidance of an ultrasound. Although ultrasound-guided injection therapy may be helpful for some indications, I do not find it necessary for fat pad injection therapy. It is a fancy tool that patients think is high-tech but I honestly think it is a bit unnecessary.

Post-procedure evaluation of the injections with the use of an ultrasound is good to show the patient the impressive before and after improvement of fat cushion thickness. Some fillers are very visible on ultrasound immediately after the injections. These fillers include Radiesse (Merz Aesthetics) and Juvederm Voluma (Allergan). Sculptra (Galderma Laboratories) injections that rely on collagen formation over the course of six to eight weeks are more visible at a follow-up visit.

Although the use of ultrasound to evaluate the progress of the patients’ fat cushioning therapies can help guide injection therapy, the best guide is patient feedback on foot and ankle pain via Visual Analogue Scales.

Reference

1. Wall JR, Harkness MA, Crawford A. Ultrasound diagnosis of plantar fasciitis. Foot Ankle. 1993; 14(8):465–70.

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