A big toenail that becomes white, lifted or separated along one side is often assumed to have a fungal infection. However, not every separated toenail is fungal.
In some patients, the underlying problem is mechanical and begins much further up the foot, at the alignment of the subtalar joint and ankle.
What causes the nail to separate?
When the foot pronates excessively, the subtalar joint and ankle lean inwards and the hallux, or big toe, can begin to internally rotate.
At the same time, the soft tissues and fibrofatty padding beneath the hallux are displaced laterally, towards the second toe.
Instead of remaining directly underneath the big toe, these tissues repeatedly move and press against the structures beneath and around the nail plate during standing and walking.
With thousands of steps each day, this repetitive movement can create an up-and-down and side-to-side mechanical force beneath the nail.
Over time, the nail plate can gradually be pulled away from the nail bed underneath. This produces a characteristic curved or U-shaped area of separation, particularly along the lateral border of the hallux nail.
This type of nail separation is known as onycholysis, but importantly, onycholysis describes the separation itself. It does not tell us what caused it.
An interesting left-versus-right comparison
This photographic example of the toes and feet provides an excellent example because the severity of the nail changes is different between the two feet.
On the left foot, the ankle/subtalar joint pronates approximately 30 degrees, and the lateral separation of the hallux nail plate is considerably greater.
On the right foot, the subtalar joint pronates approximately 12 degrees, and the lateral nail separation is noticeably less extensive.
The asymmetry is clinically interesting because the foot demonstrating the greater degree of pronation also demonstrates the greater degree of nail separation.
Rather than examining the toenail in isolation, we therefore need to examine what is happening to the whole foot, ankle and hallux during weight-bearing and walking.
Why can this be mistaken for fungal nail disease?
When air gets underneath a separated nail plate, the nail can appear white, yellowish or opaque. Debris may also accumulate beneath the separated portion.
Visually, this can resemble a fungal toenail.
However, treating a mechanically separated nail with antifungal treatment alone does not correct the forces repeatedly acting upon the nail.
Where fungal infection is suspected, appropriate clinical assessment and, when indicated, laboratory testing can help distinguish fungal nail disease from other causes of nail dystrophy and onycholysis.
The relationship with ankle alignment
In our clinical observations at Dubai Podiatry Centre, we frequently begin to see secondary foot and nail changes as subtalar joint pronation increases.
When inward deviation becomes more pronounced, mechanical stress upon the hallux can increase. With greater degrees of pronation, we may see progressively wider and deeper lateral nail separation together with increasing rotation or displacement of the hallux.
At very significant degrees of pronation, other structural changes, including hallux valgus, may also coexist.
These degree measurements should not be interpreted as universal diagnostic thresholds. Every patient is assessed individually because foot structure, joint mobility, footwear, activity, gait and other medical or dermatological factors can also influence the appearance of the toenail.
Treatment must address the cause, not simply the nail
If the separation is predominantly mechanical, our objective is to reduce the abnormal forces acting upon the hallux long enough for a healthier nail to grow forward while remaining attached to the nail bed.
Depending upon the individual assessment, treatment may include:
- Corrective orthotics designed to improve subtalar joint alignment and reduce excessive pronation
- Toe socks to encourage the toes to remain separated and in a more neutral position
- Silicone toe liners or separators between the toes where appropriate to assist alignment
- Footwear with an accommodating toe box, including suitable barefoot-style footwear where clinically appropriate, so that the toes are not compressed or displaced by the shoe
The important principle is consistency.
If a corrective device is worn for only one hour each day but the foot spends the remaining weight-bearing hours returning to its previous position, the mechanical forces responsible for the problem continue.
The objective is to maintain improved foot and toe alignment for as much of the patient’s weight-bearing day as reasonably possible.
How long does the nail take to recover?
Toenails grow slowly.
The recovery period therefore depends partly upon how far backwards the existing separation extends. The damaged portion cannot simply be pushed back onto the nail bed. Instead, we need to reduce the causative mechanical stress and allow healthier nail to gradually grow forward.
For some patients, visible improvement may occur over several months. A mechanically separated area may require approximately four to six months or longer to grow forward sufficiently, depending upon the depth of separation, individual nail-growth rate and how effectively the underlying mechanical problem is controlled.
Look beyond the toenail
A separated toenail does not always mean a fungal toenail.
Sometimes the toenail is simply showing us the end result of a biomechanical problem occurring elsewhere in the foot.
By examining the nail together with the hallux position, plantar soft tissues, subtalar joint, ankle alignment, gait and footwear, we can investigate why the nail is separating rather than treating its appearance alone.
Michelle Duffy Champlin
B.Sc. (Podiatry), M.Ch.S., S.R.Ch. (UK)
Chief Podiatrist
Dubai Podiatry Centre
For more information or to book an appointment please call our clinic +971 4 3435390 or WhatsApp +971 50 3553024
