The first metatarsal has a critical role in foot stability and propulsion, especially during mid-stance and push-off. A hypermobility of the first ray is associated with hallux valgus deformity and can affect the function of the medial longitudinal arch and other structures.
Studies of orthotic effects on the foot have generally focused on kinematics or general effects without considering how targeted modifications under the first ray might modify force vectors in the sagittal and frontal planes.
Causes
The first metatarsal, also known as the big toe, is the shortest, strongest and most important weight-bearing structure in your foot. It is a vital component in the biomechanics of foot function and can lead to various problems if it does not work properly.
The big toe, along with the medial cuneiform, controls the motion of the first metatarsophalangeal joint. The joint needs to be flexible enough to absorb ground reaction forces and shift the center of gravity forward during ambulation, but at the same time it must be stiff enough to maintain a stable position while bearing weight.
Hypermobility of the first ray can cause abnormal forefoot dynamics that lead to excessive forefoot pronation and hindfoot varus. These abnormal dynamics can lead to metatarsophalangeal joint deformities such as hallux valgus, plantar plate injury, subluxation and hammer toe.
Roukis et al (6) preferred method for assessing first ray mobility consists of placing the subtalar joint (STJ) in neutral position, and stabilizing with one hand the second through fifth metatarsal heads while attempting to dorsiflex and plantarflex the first metatarsal head. This movement is compared to the movement available of the first ray as measured using Root et al’s clinical first ray mobility test. If the first ray has decreased dorsiflexion stiffness it will be unable to accept its normal share of the ground reaction force in the forefoot during loading and stance phases of gait and will shift CoP laterally and overload the second metatarsal head during midfoot rocker.
Symptoms
The first metatarsal bone that leads to the big toe (first metatarsophalangeal joint, 1st MPJ) varies greatly in its functional range of motion. Congenital factors, trauma or foot injury, and systemic conditions such as rheumatoid arthritis can all affect this range of motion. When the first metatarsal is plantar flexed too low, the hallux does not dorsiflex properly during the push off phase of gait. As a result, excessive stress is placed on the second metatarsal head and/or the sesamoids located under the big toe. This can lead to pain, calluses and/or pseudobursitis.
In the seated non-weight bearing Hubscher test, gently dorsiflex the hallux in the sagittal plane and note the range of motion. Unloaded, there should be about 65 degrees of dorsiflexion available. A reduced dorsiflexion indicates a restriction in the ROM at this critical moment in gait and may represent a functional hallux limitus. This could obstruct the Windlass mechanism and interfere with normal function of the first MPJ.
Another diagnostic test is the weight bearing Hubscher maneuver. In this test, the patient is placed in a supine position and the load is transferred to the first metatarsal. Dorsiflexion of the hallux is again noted and less than 12 degrees of dorsiflexion suggests a functional limitation of the ROM at this time point in gait and potentially an obstruction to the Windlass mechanism.
Diagnosis
The first ray is a fundamental stabilizing structure, contributing to foot biomechanics by distributing loads evenly and supporting push-off dynamics. Dysfunction in this area may lead to excessive load on the plantar sesamoids or to other symptoms such as metatarsalgia, foot pain and ankle sprains. Ultimately, if unaddressed, first ray dysfunction may result in neuropathic complications such as ulceration.
The clinical diagnosis of a plantarflexed first ray can be made using a simple squeeze test that requires the examiner to hold down the lesser metatarsals (2nd-5th) while applying dorsal and plantar pressure on the 1st metatarsal phalangeal joint (MTPJ). A hypermobile FR is defined as having significant dorsiflexion with limited plantarflexion while a fixed articulation is defined as having no dorsiflexion and sitting in a plantarflexed position (Fig 2).
Objective measurement methods have been developed for assessing first ray mobility, including radiographic imaging and dynamic squeeze testing. However, despite these advances, it remains challenging to standardize the measurement of FR mobility and interpretation of results. X-ray methods of measuring the dorsiflexion of the FR have been the most popular, but are constrained by projection error. Dynamic squeeze testing is more reliable and easier to perform, but may not be practical in clinical practice. Surgical procedures involving I-MTCJ fusion can be technically demanding, and some investigators recommend that these techniques be reserved for cases where the fusion is necessary for addressing other foot problems such as hallux valgus deformity.
Treatment
The primary objective of treating first ray dysfunction is to reduce load under the first metatarsal head. This is accomplished through a combination of offloading, kinematic corrections, and dynamic evaluation and treatment. This approach is more effective than simple pain management and superficial management of hyperkeratotic lesions, as the latter are a symptom of underlying biomechanical deficits.
First ray dysfunction can be stiff or compliant and is determined by assessing the amount of dorsiflexion at the 1st MTPJ and lesser metatarsals (2nd to 5th). If there is significant plantarflexion but no dorsiflexion, it is called a compliant plantarflexed first ray; if there is more dorsiflexion than plantarflexion, it is referred to as a stiff plantarflexed first ray.
Stiff plantarflexed first rays can be treated by using a 2-5 metatarsal bar or forefoot cushion to decrease the amount of pressure under the 1st MTPJ and lesser métatarsals. This modification can also be used to treat hallux valgus and other forefoot deformities by preventing the lateral deviation of the first metatarsal during gait.
Physical therapy can include calf stretches and Mulligan mobilization techniques to strengthen the intrinsic foot muscles and enhance first-ray stability. Offloading through custom orthoses with first-ray cut-outs and a metatarsal pad can also significantly reduce peak pressure under the first ray. For those with persistent symptoms, surgical intervention may be necessary. DRHC Dubai offers a variety of minimally-invasive procedures to realign the first ray and improve function.