Kinetic Changes in the Forefoot With Metatarsal Pad and Domes
There are many common forefoot conditions to prescribe a metatarsal pad or dome such as:
- Morton’s neuroma
- Plantar plate tear / rupture
- Synovitis of the MPJ’s
- Capsulitis of the MPJ’s
- Stress fractures
- Freiberg disease
- Midfoot arthritis
Please read for a technical look at the reasons to prescribe a metatarsal dome and how they minimize forefoot pressures.
The effectiveness of a metatarsal dome to reduce plantar pressures depends on:
- Placement of the metatarsal dome relative to the metatarsal head
- Material density of the metatarsal dome
- Length of the metatarsal dome
For a metatarsal dome to alter plantar pressures under the forefoot it should alter:
- Force under the met head
- Surface area of contact
Position or placement of metatarsal dome relative to metatarsal head: 1 and 2 are domes, 3 and 4 are met pad or met cover. The X is the location of met heads. 1 and 3 are placed proximal to the metatarsal head and 2 and 4 are distal to the metatarsal head. The metatarsal dome or even a metatarsal pad has two surfaces. The peak and the descent. The proximal location has the tip of the dome below the line of the metatarsal head. The distal location has the tip of the dome over the distal edge of the metatarsal head so that the apex of the dome sits at the neck of the metatarsal head.
Metatarsal dome placed distally (fig 2) – Reduced peak plantar pressures under the forefoot (metatarsal heads up to midshaft) under the forefoot. But no change in the surface area of contact.
Metatarsal dome placed proximally, met bar and met cover – Increased surface area of contact more than distally placed dome. Reduced peak plantar pressures (PP) to a lesser extent than distally placed metatarsal dome. Both dome and pads irrespective of the location and shape significantly reduced maximum force under the forefoot.
Precisely, when the forefoot was divided into 3 regions, proximal to metatarsal head, under the metatarsal head and distal to metatarsal head the outcome measures were as follows:
Proximal placed met dome – Reduced peak PP and maximum force proximal to metatarsal head and underneath the metatarsal head. Softer pad was more effective than harder in reducing PP and force.
Distally placed met dome – Reduced peak PP and maximum force distal to the metatarsal head. Harder pad was more effective in reducing PP and force.
Interestingly, the contact area under these regions was significantly greater only in the region proximal to the metatarsal head. The dome located proximal to the metatarsal head had increased contact area than distal. So, if we are treating a corn under a met head and aim to increase surface area of contact under the corn, a proximally placed dome will be effective of any density.
The metatarsal dome and pad positioned distal to the metatarsal heads reduced maximum force and Peak pressures in the forefoot (Pressure = Force/Area). In other words pressure and force are inversely proportional to area; as surface area increases plantar pressures should reduce. However, the surface area with a distally placed met dome did not increase. So how did the peak pressure lowered in a distally placed metatarsal dome? Impulse = Force x Time. Distally placed metatarsal dome spent approx 10 ms longer than other conditions, this time difference was not statistically significant, but still 10 ms is long enough to consider the time factor. So, a metatarsal dome in fig 2 reduces peak pressures under the forefoot not by increasing the surface area of contact but by lowering impulse.
Since dome placement alters pressure and force distribution relative to metatarsal heads, consideration should be given to onset of symptoms to choose the optimal location of the dome. If symptoms are during early to late stance a proximal located dome is recommended, if the symptoms are towards the end of late stance a distally placed dome could be effective. If the plan is to reduce PP as in pts with fat pad atrophy consider a met cushioning pad (1 -5) and longer the better in reducing total pressures under the FF.
Finite element analysis reported using a metatarsal dome in an orthotic increases tensile forces in the plantar fascia but metatarsal pad or plantar cover or thick forefoot padding (12 mm) lowers the tensile forces in the plantar structures. something to consider in treating heel P. fasciitis.
This article was researched (comprehensive review of up to date research articles) and written by David Survepalli, one of our very talented podiatrists at Foot focus Podiatry. Should you like to read the orignal articles please call 9258 4152 or email us.