Fatigue & Stress Fractures of the Metatarsals
Fatigue (Stress Fractures and pre-Stress fracture) Fractures of the Metatarsals
Although commonly called stress fractures, the fact that bones never break unless stressed makes the term a little odd. What are actually meant are fatigue fractures. We all know that you bend plastic over and over again it will finally break. What happens is that repeated bending weakens the plastic so that it breaks with a much smaller force than it would the first time you bent it. All biological materials are also bound by the same law that repeated loading weakens a material. Biological material however gets to repair itself when rested, so that it is as good as new to bear that force again. However if the rate at which damage ours outstrips the rate the tissues can heal then the tissues can still fail. In bone this causes a fracture.
All load bearing bones of the body can get a fatigue fractures, usually where forces are concentrated on weight bearing. The narrow area just short of the metatarsal head is known as the metatarsal neck. Fatigue fractures on metatarsal necks are quite common, mainly at the 2nd, 3rd and 4th metatarsal necks. The first metatarsal is very strong and does suffer fatigue fractures, but the sesamoids beneath can suffer fractures. Occasionally, metatarsals can also fracture higher up into the shaft of the bone, but the neck being the thinnest point is the most common fracture site.
The cause of a stress fracture can be divided into two. The first type is due to the forces being greater than the bone can cope with when the frequency of the force is increased or the about of force is increased. It is most common to see this type is very active people who have perhaps increased the amount of sport they play or the frequency. Training for a marathon can cause fatigue fractures, especially as running on roads and pavement is particularly hard on the foot. However, any activity rapidly increased, especially if involves impact on a hard surface is a potential risk.
The other situation involves bone that is abnormally weak, so that normal repetitive forces causes the bone to crack and break. The most common reason for this is in older people; although it can occur is some younger individuals too. Known as OSTEOPENIA, it causes the bone to be ore fragile than it should be. It is far more common in women, especially postmenopausal women. A strong risk factor is early menopause or hysterectomy before your 50’s. Sadly are bone density is at its greatest in our early 20’s and starts to deteriorate in our 30’s. How dense are bone becomes at its peak is due to a combination of genetic and environmental factors. In particular diet and environmental exposure to vitamin D as we grow from a foetus into adulthood and exercise levels are critically important. Low levels of vitamin D as a foetus, infant, child and teenage, coupled with little exposure to sun light and little exercise would mean you have low bone density. Sadly living in such a dull cold part of the world we are at high risk in the UK, especially if you also have dark skin.
Fatigue (Stress Fractures and pre-Stress fracture) Fractures of the Metatarsals - Treatment
Pain of stress fractures is usually very sharp associated with swelling, but you can get a low level arch usually over the top of the metatarsal for a while before the bone breaks. Known as a pre stress fracture it is difficult to diagnose and often picked up only on MRI. X-rays are not much use even in a full fatigue fracture as the fractures are often very fine. Until the bone starts to heel nothing can be seen on x-ray. Around six weeks after the fracture changes indicating healing usually confirm the diagnosis, but most people will want treatment before then.
Like all fracture the bone immediately needs rest and off loading. If you suspect a stress fracture stop your sport or reduce weight bearing activity straight away and seek advice from a clinician/therapist. Often it will be necessary to use a shoe that prevents you weight bearing on the forefoot, but sometimes this can be achieved with padding and insoles. Early treatment is very important, because untreated the fractured bone can heal deformed, usually elevated. This can lead to over load of the adjacent metatarsal leading to further fractures or other types of metatarsalgia. If your fracture occurred without any reason such as a change in activity level, it may be necessary to get a bone density scan done.