The toes are important in forefoot function (Hughes et al 1990). Their control and stability are complex and subtle and symptomatic failure is common. Nevertheless, toe problems are often underestimated and traditionally relegated to the end of the list for the SHO to operate on. There is no comprehensive review of lesser toe function and pathology in the literature: hence the rather extended treatment here.
Normal toe function
The toes are important in force and pressure transfer in the late stance phase of gait (Hughes et al 1990). They take 30-40% of peak force and 70% of peak pressure. The great toe is most important and the others have progressively less importance. Loss of this function may precipitate metatarsalgia.
Normal toe forces and stability
The toes are small structures exposed to large forces. It is perhaps surprising that lesser toe deformities are not more common and troublesome. The forces can be classified as follows:
The reversed windlass effect
Weightbearing depresses the medial arch; this create tension in the plantar aponeurosis, which exerts a plantar flexion force on the toes.
Ground reaction force
In the terminal stance of gait the trunk moves over the plantigrade foot and ground reaction force dorsiflexes the toes. If high-heeled shoes are worn the toes are already dorsiflexed so the forces on the plantar plate and its associated tissues are greater.
Muscle forces
- FDL flexes the DIP joint, but can flex the PIPJ to some extent
- FDB flexes the PIP joint
- EDL and EDB insert into the extensor expansion. This is normally tensed by the intrinsic muscles, and the extrinsic extensors extend the PIP and DIP joints, with ground reaction force being the main MTP joint extensor
- Interossei insert into the extensor expansion, thus tending to flex the MTP joint (but not very efficiently) and contribute to extending the PIP and DIP joints. In addition, plantar interossei draw the toe towards the second metatarsal and dorsal interossei draw away.
- Lumbricals insert into the extensor expansion and effectively function in relation to it much as the interossei do.
Other extrinsic forces
- Shoes may press on toes, especially the longest toe (usually 1st or 2nd)
- Adjacent toes may press on one another, especially if there is a deformity (such as hallux valgus or a varus 2nd toe) or if one toe has a bony prominence causing a soft corn.
Normal stabilisation
Skeletal shape
The MTP joint has little intrinsic bony stability in the dorsoplantar or valgus-varus directions. It does, of course, resist compression, but longitudinal pressure tends to result in dorsiflexion.
The PIP and DIP joints have valgus-varus stability due to the shape of the joint surfaces, but these surfaces do not restrict dorsiflexion-plantarflexion.
Soft tissue joint structures
Each joint has collateral ligaments which restrain valgus-varus. The plantar plate is firmly attached to the base of the next phalanx, more loosely to the collateral ligament apparatus and most loosely to the proximal plantar joint capsule. It is attached to the transverse (via the deep transverse metatarsal ligament) and longitudinal tie-bar systems of the plantar aponeurosis. Through the aponeurosis it is also attached to the plantar fat pad: where the plantar plate goes the fat pad will follow.
Muscle balance
Muscle balance in the toes is delicate and essential, particularly in the late stage of stance phase when the toes need to be straight on the ground to transmit force. However it is also subtle: EMG studies show minimal muscle activity at this vital stage.
The intrinsics are needed to tense the extensor expansion so that long extensor power is expended at the IP joints. FDL and FDB function is then balanced by the extrinsic extensors and the toe remains approximately straight. The low level of EMG activity suggests that this muscle activity is maintaining a balance rather than acting as a motor for forward progression: this comes mainly from the triceps surae and to a certain extent from FHL.
Toe failure
Once the delicate balance of forces and opposing structures outlined above breaks down, the toes cease to function normally and may become deformed or painful. In addition, the loss if toe function may increase stresses elsewhere leading to other problems, particularly metatarsalgia. Thus, deformity is not the only feature of lesser toe disorders and the concept of "toe failure" is useful to draw attention to the larger picture. First we consider the factors which lead to the development of toe failure, then those additional factors which contribute to its persistence.
Factors leading to toe failure
Abnormal outside forces
The only normal forces imposed on the toes are those arising from gait and muscle contraction. The main source of abnormal forces is shoewear:
- narrow toe-box crushes the toes together and imposes valgus-varus and, to some extent, hyperextension forces
- narrow toe-box contributes to the development of hallux valgus which presses on the 2nd toe and tends to push it into hyperextension; hallux valgus also represents a weakening of the transverse tie-bar and thus a loss of one of the restraints on lesser MTP joint hyperextension
- toe-box shorter than the 2nd (occasionally 3rd) toe imposes a longitudinal force on the toe: the toe buckles, usually with hyperextension at the MTP joint and flexion at the PIP joint, while the DIP joint may flex or extend. DIP joint flexion may be part of a general clawtoe deformity, or isolated as a mallet toe
- high heels force the MTP joints to spend the whole gait cycle in extension, thus fatiguing the plantar capsule and plantar pad structures and increasing the tendency to hyperextension at the MTP joint.
In addition, trauma to the toes may damage any of the structures. The commonest injuries are sprains of the joints, followed by fractures. However, probably the most serious injuries are to the plantar plate apparatus which may lead to post-traumatic MTP instability. The incidence of these injuries is unknown: they are probably not common but are usually missed.
Any of the above forces may damage a normal joint. However, in the presence of synovitis, either due to a systemic inflammatory arthropathy or trauma, joint damage, and eventually destruction, may proceed further and faster.
Muscle balance failure
Loss of muscle balance may be primary, due to actual unbalanced muscle weakness, or secondary, where muscle action cannot occur in the usual way because of a deformity primarily created by some other force:
- extrinsic weakness: extensor weakness is commoner, leading to clawtoe deformity as all remaining extensor function is expended at the MTP joint (especially where tibialis anterior is weak and the long toe extensors are recruited to help with ankle dorsiflexion)
- intrinsic weakness: as has been seen above, the intrinsic muscles tense the extensor expansion to allow proper distribution of the force of the extrinsic extensors. If this is absent, the extensors extend the MTP joint instead and there is no resistance to FDL and FDB flexing the IP joints. A clawtoe deformity would than develop. Disorders which cause intrinsic weakness are often also associated with extensor weakness and the two problems tend to have an additive effect.
- intrinsic contracture: may occur after compartment syndrome of the foot and leads to a severe clawing of the toes, often without MTP joint hyperextension. The injuries which cause foot compartment syndrome, especially crush injuries, burns or multiple trauma with fractures of the tibia and foot, may also cause long flexor contractures which increase the clawing.
Joint failure
As a result of the above forces and loss of balance, the toe joints tend to fail in a predictable way:
- MTPJ failure: the plantar capsule weakens, the plantar plate displaces distally and the joint moves into hyperextension. The toe eventually ceases to contact the ground in stance phase. Instead the proximal phalanx comes to lie above the MT head and imposes a downward force vector. In addition, the displacement of the plantar plate draws the plantar fat pad out of position so it comes to lie anterior to the MT head. Thus the toe ceases to share forefoot pressure and instead imposes a new pressure of its own, while at the same time removing the forefoot padding.
- PIPJ failure: with the loss of extensor function at the PIP joint it is subject to unopposed flexion by the extrinsic flexors and adopts a flexed posture which can only be corrected by outside pressure (e.g. the examining finger).
- DIPJ failure: in the mallet toe deformity all the pressure on a long toe is taken by the DIP joint which becomes fixed in flexion. In the more generalised type of toe failure the position of the DIP joint is unpredictable: it may be hyperextended, neutral or flexed and we do not understand what determines the position adopted.
Factors causing toe deformity to persist
Persistent outside forces
Obviously, a deforming force may stop after a period of time (eg a pair of more appropriate shoes are obtained) or may persist, causing continuing toe failure and/or permanent damage.
Soft tissue contracture and the plunger effect
Joints which spend much of their time in a deformed position may become fixed by capsular and ligamentous contractures. In the toes even the skin over the joints tends to become contracted. Myerson and Shereff showed that in clawtoes correction could only be obtained by radical soft tissue release, including skin lengthening, dorsal capsulotomy and collateral ligament release in the MTP joint, and equivalent procedures in the other joint. Repositioning of the plantar plate often requires release of its collateral attachments.
In addition, if the plantar plate comes to lie above the MT head, it becomes stuck there by the adjacent displaced plates, the deep transverse metatarsal ligament and the plantar fascial slips, producing a strong downward pressure on the MT head: Stainsby calls this the "plunger effect". The toe will not correct unless the plantar plate is released and reduced. The plunger effect has even been seen after amputation of a lesser toe, when the plate is left on top of the MT head and severe metatarsalgia persists: toe failure without the toe!
Abnormal muscle activity
When a severe MTP joint hyperextension deformity develops, the lumbrical comes to lie behind the joint axis and becomes an extensor, increasing the deforming force. The importance of this effect has been debated.
Clinical presentations
Lesser MTPJ instability
Instability of a lesser MTP joint, usually the 2nd, may present in the absence of a toe deformity. Often deformity develops with time. There may be a history of trauma or inflammatory arthritis, but many of the cases in the (almost exclusively American) literature are athletes, in whom this presumably represents an overuse injury.
The pathology is mainly plantar capsule weakness and plantar plate displacement. One series had a high incidence of plantar plate rupture.
The patient is usually referred as “metatarsalgia”. In most patients it is quickly clear that the site complained of is the MTP joint rather than the sub-metatarsal area, although secondary sub-metatarsal pain and callus formation can occur due to toe failure. The MTP joint is tender and there may be palpable synovitis or an effusion. The draw test is positive to an extent not found in the other toes. An injection of local anaesthetic into the MTP joint may be helpful in making the diagnosis.
Varus 2nd toe
This is usually associated with hallux valgus and there is 2nd MTP joint instability as described above. The MTP joint is usually in hyperextension, overlapping the hallux, but occasionally the 2nd toe under-runs the hallux. The toe may have a hammer or claw deformity or may be straight.
Hammer/claw toe
These terms are used in the literature in an effectively interchangeable way. Although some papers lay down strict definitions, these vary so that what is rigidly defined as a hammertoe in one paper would be (equally rigidly) a clawtoe in another! In the UK, both have hyperextension at the MTP joint and flexion at the PIP joint, but a hammertoe is usually defined as one with a hyperextended DIP joint , while a clawtoe has a flexed DIP joint. As definition is loose and there is no proven difference between them in cause, significance, treatment or prognosis, I have not differentiated between them here.
These deformities may present with:
- pressure and sometimes skin breakdown, usually over the dorsum of the PIP joint, sometimes at the tip
- metatarsalgia due to the MTP joint failure
- rubbing between the toes due to valgus/varus deviation and sometimes little prominences on the phalanges
It is important to evaluate the severity of the contractures of each joint as this affects the non-surgical and surgical treatment which can be offered.
Blackburn classification of hammer/clawtoes:
|
MTPJ |
PIPJ |
Type 1 |
Flexible hyperextension |
Flexible flexion, tight long flexor |
Type 2 |
Flexible hyperextension |
Fixed flexion |
Type 3 |
Fixed hyperextension or subluxation |
Fixed flexion |
Metatarsalgia
As has been outlined above, lesser toe failure removes the load-sharing effect of the toes while increasing the downward pressure on the MT head and removing its protection. It is not surprising that this may cause metatarsalgia with plantar keratoses. Evaluation of any patient presenting with metatarsalgia must include careful examination of the lesser toes. Conversely, any patient with lesser toe problems who complains of sub-metatarsal pain must be evaluated for any of the other causes of metatarsalgia.
Mallet toe
In some toes, usually long 2nd or 3rd toes, longitudinal pressure from the shoe may simply cause flexion of the DIP joint without buckling the whole toe. The reason for this is not understood. These patients usually just have pain over the DIP joint and the tip of the toe. The flexion contracture may be severe and tight.
Assessment
All patients with foot and ankle problems should be asked about:
- diabetes
- inflammatory arthropathy
- neurological disease
- vascular disease
- trauma
Neurological or inflammatory disease may precipitate lesser toe failure - do a general examination.
Ensure that you understand exactly what the patient is complaining of - it may not be what looks abnormal.
Look at the shoes - are they toe-friendly? Don’t assume these are the patient’s normal shoes! Ask what shoes have to be worn at work - women sometimes have to wear certain shoes to “look right”; many workers have to wear protective shoewear which leaves no room for deformed toes.
The foot must be carefully examined in general. Identify any general, neurological or inflammatory problems that may have precipitated or maintained the toe problem.
Examining the toe itself:
- is the MTP joint irritable and/or unstable? Always do the draw test.
- where is the plantar fat pad? If displaced, can it be reduced by correcting the toe?
- is the MTP joint dislocated? Can the MTP, PIP and DIP joints be reduced fully?
- are there calluses or areas of skin breakdown? Is the patient complaining of them?
What measures have been tried? Has the patient modified his/her footwear; is this practical for their occupation?
Is the patient basically after accommodation and padding, or surgical correction?
Non-surgical treatment
Footwear which accommodates the deformities, along with padding on prominences and a metatarsal dome insole if necessary, will satisfy many patients. “Accommodative” shoes may simply be more sensible shoes from a high street shop, obtained from a specialist outlet (our orthotist keeps a list of these), or provided by the orthotist. Realism on shoes is essential.
If there is an underlying inflammatory disease, this should be brought under control as far as is possible. A joint rheumatology/orthopaedic foot clinic appointment may be useful.
Surgical
Consideration needs to be given to the measures needed at each joint, determined by the degree of fixed contracture and, at the MTP joint, instability.
- MTP instability and fixed hyperextension may co-exist, so the toe may have to be reduced first before stabilisation will be useful
- MTP hyperextension may require a soft tissue release, with dorsal capsulotomy, collateral ligament release and plantar plate reduction. In some tight deformities this will not be enough to produce a stable reduction and bony shortening may be necessary. A small amount (1-3mm) of bony shortening can be produced with a metatarsal head arthroplasty. Greater amounts of shortening require a Stainsby or Weil procedure.
- MTP instability is usually improved by transfer of the FDL to the dorsum of the proximal phalanx. The toe is usually more stable, although the transfer often acts as a tenodesis rather than an active transfer and the patient may be unable to voluntarily bring the toe to the floor.
- A PIP joint flexion deformity that it wholly passively correctable (unusual, in my experience, after about the age of 25) usually corrects after a flexor transfer.
- A fixed PIP joint flexion deformity can be corrected with an excision arthroplasty. There are many variants of this operation, some of which involve an attempted fusion or soft tissue repair of the PIP joint. While these have theoretical advantages there is no evidence that they improve the clinical outcome of the procedure.
In type 1 toes, a flexor-extensor transfer may be enough to correct the toe, although a PIPJ arthroplasty or MTPJ release may be required.
In type 2 toes a PIPJ arthroplasty is first performed and stabilised with a K-wire. If there is residual hyperextension at the MTPJ with the ankle plantigrade, a sequential release of the MTPJ is carried out:
- Extensor tendon release
- Dorsal capsulotomy
- Collateral ligament release
Type 3 toes present the greatest challenge:
- If the MTPJ is of good quality, a PIPJ arthroplasty and full MTPJ soft tissue release will usually reduce the toe fully. Sometimes a Weil osteotomy is necessary to make enough space. A flexor-extensor transfer may be necessary to stabilise the MTPJ. This will usually give a straight toe, but some deformities recur, the MTPJ may be painful, and about 10% of toes feel “odd”
- If the MTPJ is of poor quality (classically in rheumatoid toes) or the patient is not suitable for an extended procedure, a Stainsby procedure will give good correction at the price of a floppy toe, which is sometimes unstable and may feel ”odd”
- Severely deformed, stiff toes in elderly patients may be better off amputated – a simple, quick procedure with a high satisfaction rate in appropriate patients. A plastic spacer may be required to prevent the hallux falling against the 3 rd toe
Other toe deformities
- Congenital curly toes in children can usually be corrected with a flexor tenotomy. In adults there is usually a deformity of the middle phalanx and a phalangeal osteotomy or corrective arthroplasty of the PIP and/or DIPJ is needed.
- A mallet toe can be corrected with an excision arthroplasty of the DIP joint. Release of the FDL tendon from the distal phalanx may produce a marginal improvement in results.
- A severe mallet toe in the elderly, especially if the toe is very long, is suitable for terminalisation, usually through the neck of the middle phalanx. The pulp is brought up as a rotation flap and the cosmetic result is good in this patient group. As with all amputations, care must be taken to leave the flap loose initially as it will tighten with healing.
References
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