Plantar plate injury

The plantar plate is a fibrocartilaginous structure located beneath the metatarsophalangeal joints of the toes. It plays an essential role in forefoot stability, in particular by preventing excessive translation of the toe relative to the metatarsal head.

A plantar plate injury may be an irritation, progressive degeneration, a strain, a partial tear or a complete tear. It very frequently involves the 2^nd metatarsophalangeal joint, but can also affect the other rays.

In runners, it may initially present as simple pain under the forefoot before gradually progressing to true metatarsophalangeal instability.

The plantar plate lies beneath the metatarsal head and the metatarsophalangeal joint; it inserts in particular on the base of the proximal phalanx. It is closely related to the joint capsule, the collateral ligaments, the flexor tendons and the transverse stabilising structures of the forefoot: it therefore does not work alone, but is part of a true capsuloligamentous complex that stabilises the toe.

Function of the plantar plate

It contributes to the stability of the metatarsophalangeal joint, resistance to hyperextension of the toe, the distribution of plantar stresses, stabilisation of the toe during push-off and the transmission of forces during walking and running. In particular, it is a major restraint against dorsal translation of the proximal phalanx on the metatarsal head.

Why is the 2^nd joint often affected?

Several factors may explain this: high mechanical stresses, a relatively long second metatarsal, forefoot overload, particular mobility of the second ray, progressive forefoot deformity or associated hallux valgus. When the first ray contributes insufficiently to push-off, some of the stresses may also be transferred to the central metatarsals — the combination of hallux valgus + 2^nd-ray metatarsalgia + 2^nd-toe instability should therefore prompt a search for a plantar plate injury.

Biomechanics during running

With every stride, the forefoot bears significant stresses during push-off: as the heel leaves the ground, body weight shifts forward, the metatarsal heads bear a heavy load, the metatarsophalangeal joints move into extension, the toes help stabilise the foot and the plantar plates are put under tension. These stresses are physiological; the problem arises when their repetition gradually exceeds the tissues’ capacity to adapt, which can weaken the plantar plate. This stress increases in particular with speed, accelerations, uphill running, forefoot exercises and certain shoes.

In runners, the mechanism is generally progressive: repeated overload → irritation → degeneration → strain → partial tear → instability. Acute traumatic injuries also exist (sudden hyperextension of a toe, landing, awkward movement), but they are less common: most injuries to the plantar plates of the lesser toes correspond to a progressive degenerative or microtraumatic process.

Plantar plate injury very frequently affects the second metatarsophalangeal joint, but can also involve the other rays. It is particularly common in runners and in athletes who place heavy demands on the forefoot, as well as in people with hallux valgus, a toe deformity or a relatively long second metatarsal.

Several factors may be associated with overload of the plantar plate.

Anatomical factors

A relatively long second metatarsal, hallux valgus, a toe deformity, a cavus foot in some cases, or abnormal load distribution promote overload of the plantar plate. Hallux valgus in particular can alter load distribution across the forefoot: when the first ray becomes less effective during push-off, stresses may be transferred to the second, or even the third, metatarsal.

Sport-related factors

A sudden increase in mileage, interval training, speed work, hills, a change of shoes or an increase in sessions that load the forefoot are classic contributing factors.

Mechanical factors

Metatarsal overload, functional insufficiency of the first ray, limited ankle mobility or repeated hyperextension of the toes also contribute to overload of the plantar plate.

The main symptom is pain located under a metatarsophalangeal joint, most often the second. The patient may describe pain under the forefoot, a feeling of walking on a pebble, a feeling of a lump, burning, pain on push-off or discomfort when running — the pain may initially be present without any visible deformity of the toe. It is generally located directly under the metatarsal head, and the patient can often point to the exact area with one finger; in an injury of the second plantar plate, the pain is located under the base of the second toe.

Pain may appear after several kilometres, during fast sessions, uphill, when accelerating or on push-off, and gradually come on earlier and earlier; in advanced forms, walking itself may become painful. Walking barefoot on a hard floor is often particularly uncomfortable. Swelling (plantar, dorsal or diffuse around the joint) may appear, sometimes with associated synovitis, which may precede the onset of true instability.

When the plantar plate becomes insufficient, the toe may gradually shift: elevation of the toe, medial or lateral deviation, loss of contact with the ground, overlapping another toe. In advanced forms, the second toe may gradually deviate towards the big toe and then cross over it — this is known as crossover toe, reflecting significant instability and a much more advanced stage than the initial simple plantar pain. A useful sign is loss of toe contact with the ground: when standing, the affected toe may be slightly raised, no longer bear weight properly, and gradually become floating.

Clinical examination

The examination looks for the precise location of the pain, swelling, instability, deformity, loss of toe contact, pain on extension, associated hallux valgus and any forefoot abnormalities; comparison with the other foot is particularly useful. Palpation under the metatarsophalangeal joint generally reproduces the pain, the tender area often lying directly under the base of the proximal phalanx.

The metatarsophalangeal drawer test (Lachman test of the toe) is one of the most important tests: the metatarsal is stabilised and the proximal phalanx is moved dorsally, looking for pain, excessive translation, a feeling of instability or the absence of a firm end point — increased translation compared with the opposite side suggests plantar plate insufficiency. The toe purchase test assesses the toe’s ability to maintain contact with the ground (a sheet of paper is placed under the toe while the examiner pulls on it), and the Kelikian push-up test (pressure under the metatarsal head) observes whether the toe returns to a normal position or shows a reducible or fixed deformity.

Weight-bearing (standing) examination is essential: it looks at toe alignment, hallux valgus, elevation of the second toe, abnormal spreading between the toes (“V” sign, which may indicate early instability), crossover toe and weight distribution — some abnormalities being much less visible when lying down. Analysis of the shoes (narrow forefoot, little room for the toes, very flexible sole) and of running (foot strike, push-off, cadence, first-ray function) usefully completes the examination.

Surgery is not systematic: conservative treatment is preferred in early and stable forms. It may be considered in cases of failed conservative treatment, significant instability, progressive deformity, subluxation, crossover toe or persistent pain that severely limits activities, with the aim of restoring joint stability.

Modern techniques allow direct repair of the plantar plate, through a dorsal or plantar approach depending on the situation, with the plate usually reattached to the base of the proximal phalanx. A Weil osteotomy may be combined with it: it changes the length and position of the metatarsal head, which can reduce stresses, correct an overly long metatarsal, facilitate access to the plantar plate or help correct the deformity — however, it is not necessary for all injuries.

Available studies generally show improvement in pain, function and stability after direct repair in properly selected patients, but much of the data comes from case series and non-randomised studies: surgery should therefore not be offered simply because a tear is visible on MRI. Possible complications include stiffness, persistent pain, swelling, recurrence, residual deformity, floating toe, wound-healing problems or transfer metatarsalgia; recovery may take several months.

The prognosis depends on the stage, how long the injury has been present, the degree of instability, the presence of deformity, the sporting load and any associated abnormalities. An injury diagnosed early, before significant instability develops, generally has more options for conservative treatment.

Early forms may require a few weeks to a few months of recovery. Partial and stable forms can become symptom-free with appropriate conservative management, whereas a major tear associated with instability or deformity has a much more limited potential for spontaneous recovery — the aim of conservative treatment is then mainly to reduce stresses and stabilise the joint. Chronic injuries with instability may require much longer management, and recovery after surgery may take several months.

Prevention is based mainly on progressive training (avoiding sudden increases in mileage, speed, elevation gain or push-off work), suitable footwear that avoids excessive compression of the toes, and maintaining good strength in the triceps surae and intrinsic foot muscles as well as good foot control.

It is also essential not to dismiss persistent pain under a metatarsophalangeal joint: pain can precede visible instability by several months, and early diagnosis helps avoid progression to advanced deformity.