When Lateral Band Injury Leads To Plantar Fasciitis
Although podiatrists commonly encounter plantar fasciitis, injuries to the lateral band of the fascia are less frequently diagnosed. These authors offer anatomical insights, pertinent diagnostic pearls and key tips on treatment options.
When we think of heel pain, we traditionally think of the anatomy, etiology and the symptomatology of “medial band plantar fasciitis,” and do not give much thought to the lateral band. However, injury to this band does exist both at the calcaneus and at the insertion point at the plantar aspect of the fifth metatarsal base. The symptomatology, etiology and treatments are different from traditional plantar fasciitis so proper evaluation and imaging are paramount for an accurate diagnosis.
There is a common misnomer regarding the actual anatomical structure called the plantar fascia. Is it a true fascial band or is it more of an aponeurosis, ligament or a band of connective tissue? True fascia has multiplanar, three-dimensional movement. While the plantar fascia moves slightly, it is mostly fixed to support and tether the forefoot to the rearfoot so as to support the medial and lateral columns of the foot. The main function of the plantar fascia is to support the foot from splaying proximal to distal due to its strength and fiber orientation. This is partly due to the windlass mechanism.
Hicks originally described the windlass or “cable” like structure of the plantar fascia and how it works to support the triangle orientation or “truss” of the foot. The top part of the truss is comprised of the calcaneus, midtarsal joint and the metatarsals. It is supported plantarly by the tension of the plantar fascia. This truss withstands the ground reactive forces pushing upward and the force downward from the body’s weight.1
Although we often think and describe the fascia to patients as one solid band, it does have three distinct sections. The medial and central bands originate from the larger medial calcaneal tubercle and fan forward toward the metatarsal heads and insert. The lateral band originates from the smaller lateral tubercle and fans distally to the plantar surface of the fifth metatarsal base. These fibers are distinct from the fibers of the peroneus brevis and the midtarsal ligaments in the area. The medial and central bands are cord-like and distinct. It is easy to recognize these bands with imaging modalities as the lateral band is thinner and flat.
Magnetic resonance imaging (MRI) and diagnostic ultrasound have correlated nicely for the medial and central band thickness figures. However, as the sagittal slices move laterally in the foot, MRI is less dependable for accuracy in regard to lateral band thickness. The lateral band is hard to measure due to the convex shape of the calcaneal tubercles and the oblique orientation of the band itself. Under normal circumstances, the proximal medial band measures between 3 and 3.5 mm, the central band measures 2.5 to 3 mm and the lateral band on ultrasound measures 1.7 to 2 mm thick.
Essential Biomechanical Insights
According to the literature as well as our clinical experience, the fascia that undergoes increased traction secondary to overpronation may predispose it to fascial irritation. The increased traction may also predispose the heel to the development of a spur (Wolff’s law).2 During the gait cycle, many things may alter the long arch. Prolonged foot
overpronation can be caused by internal and external factors such as structural/bony foot malalignment and a tight gastroc-soleus complex. This can also be caused by hip and lower extremity weakness.