May 2018 Issue
Few words on foot orthotic prescriptions cause as much confusion as the term Morton's. Morton's is simultaneously two different foot diagnoses, and three or more distinct orthotic modifications. One misunderstanding stems from the fact that two esteemed doctors, both named Morton, applied their names to unique foot pathologies.
Dudley Joy Morton, MD, was a prolific early 20th century physician who developed the concepts behind Morton's syndrome. This is characterized by a congenitally short first metatarsal bone, hypermobility of the first ray, and callusing under the ball of the foot, specifically at the second and third metatarsal heads. The shorter first metatarsal, and its lack of dorsiflexion stiffness, cause excessive weight to be borne by the second metatarsal head resulting in callus formation. Pain and tenderness are usually felt at the base of the first two metatarsal bones and at the head of the second. This short first metatarsal, relative to the lesser metatarsals, is the most easily recognizable attribute and often results in the second toe appearing longer than the hallux. The appearance of a longer second toe was commonplace in classical Greek sculpture, so this is sometimes referred to as Greek toe.
Typically, patients will seek treatment when there is persistent pain or discomfort either at the base of the first two metatarsal bones, or at the heads of the second and third. Conservative treatment of Morton's syndrome consists of adding a flexible platform or wedge under the first metatarsal and great toe to increase the ground reaction force (GRF) there. By "bringing the ground up" to the first metatarsal, the first metatarsal is assuming extra weight, thereby relieving some of the load on the second. This addition of extra material to the medial-distal portion of a foot orthotic is called a flexible Morton's extension (Figure 1a). It can be made of cork, EVA, or other suitable materials, and is usually 1/8-3/16 inch thick.
Functional Hallux Limitus
Other conditions require decreasing the load at the first metatarsophalangeal joint (first MPJ) to increase the joint range of motion (ROM). Functional hallux limitus occurs when there is a blocking of motion and the great toe is unable to dorsiflex at the first MPJ. This may cause pain and joint deterioration, and it interferes with the pre-swing phase of gait. Patients will often shift weight to the outer border of the foot to prevent painful motion in the big toe.
While the patient is seated and non-weight bearing, check the first MPJ ROM in the sagittal plane by flexing and extending the hallux. Unloaded, there should be 65 degrees of dorsiflexion available. Then load the first metatarsal head with your thumb, repeat the test, and note any restriction. It is not unusual to see a significant decrease in dorsiflexion. This gently simulates the GRF acting on the medial foot during midstance and terminal stance.
A reduction in motion indicates a restriction of the first MPJ at a critical moment in gait and some level of functional hallux limitus. This could obstruct the Windlass mechanism or lead to an impeded gait. Often there will be a pinch callus on the medial hallux and eventually perhaps arthritis of the joint. (For more detailed discussion on functional hallux limitus, refer to "Hallux Limitus and the Vital Operation of the First MPJ," The O&P EDGE, May 2014.)
Performing the weight bearing Hubscher maneuver tests the functional ROM of the first MPJ. With the patient standing in the resting calcaneal stance position, dorsiflex the hallux and note motion at the joint. Less than 12 degrees of dorsiflexion indicates a functional hallux limitus and a restriction of the Windlass. The Windlass mechanism is essential for pulling the plantar fascia taut and stabilizing the midtarsal joint during the propulsive phase of gait.
An effective approach to early stage functional hallux limitus is to provide a reverse Morton's extension on a supportive orthotic. The goal is to increase ROM at the first MPJ. In general, good medial longitudinal arch support helps orient the first metatarsal bone, aligning the first MPJ for optimal function. A reverse Morton's can take two forms. A channel or trough distal to the first metatarsal head allows it to plantarflex (Figure 1b). Alternatively, a platform of 1/8-inch flexible material, albeit a little more bulky, can be used to elevate the second through fifth metatarsals, transferring load laterally (Figure 1c). In either case the objective is to shift GRF locally and allow the first ray to plantarflex, which reduces compression forces in the joint. The prescription may also include a low, broad metatarsal pad. Other conditions such as plantar fasciitis, turf toe, and sesamoiditis can also benefit from this style of modification.
Hallux rigidus is characterized by pain and stiffness in the first MPJ both when the patient is weight bearing and non-weight bearing. There are several techniques available to limit ROM in the forefoot. A rigid Morton's extension is a foot orthotic design where the rigid shell material extends distally under the first MPJ to the tip of the hallux. It is usually made of rigid thermoplastic or carbon graphite materials (Figure 1d). This device may impede gait, and if the extension is not fully rigid it may even exacerbate the condition. If the goal is to eliminate ROM, then it may be preferable to add a sole stiffener to the shoe or place a full-length carbon foot plate under the insole of the shoe. Full-length foot plates have the added advantage of being transferable between shoes. In addition, putting a rocker sole or rocker bar on the shoe will help reduce metatarsal flexion.