What is “Shin Splints”?
Exertional shin pain is very common in athletes, particularly distance runners. The term shin splints should probably now be abandoned since it refers to a number of conditions and it means different things to different people. To some people it will cover any cause of exertional shin pain, but to sports medicine specialists it describes an exertional discomfort felt in the third quarter of the shin bone with tenderness just at the back of the shin bone 20cms or so above the heel. This is better termed the “medial tibial stress syndrome”. Typically the pain is felt early on with exertion and it may be possible at least in the early stages for the athlete to run through it. The discomfort will then return towards the end of a work out or training and is commonly a dull ache rather than a sharp or electric-shock type of pain. This is an overuse injury for which we do not know the specific cause. Typically there is an absolutely full range of movement with no discomfort to resisted movement and x-rays are commonly reported as normal. In fact the x-rays often show a bit of thickening of bone with a little reaction around it indicated where the bone has been over loaded. The diagnosis will often be confirmed by an isotope bone scan which is an investigation whereby a solution containing weakly radioactively-labelled phosphonate molecules is injected into a vein and the more active bone cells gobble it up and are traced with a gamma camera (like a Geiger counter). This shows where the bone cells are most active and may help delineate the diffuse increase stress seen in the medial tibial stress syndrome from a very well localised area of increased uptake which will be more typical of a stress fracture or pre-fracture. Similar information can now be obtained from an MRI scan which will also avoid the necessity for an injection.
Apart from over-training, various biomechanical abnormalities have been associated with this syndrome, in particular excessive pronation both in amplitude and velocity. This may throw more strain through the soleus muscle attachment to the tibia and too much strain through the vulnerable area of bone.
The mainstay of treatment is relative rest with correction of the biomechanical abnormality either by modification of the foot wear or an in shoe orthosis or both. It may be helpful to take a course of non-steroidal anti-inflammatory drugs and have some physiotherapy directed at the tender area, but also at stretching out any tightness particularly in the heel cord. Surgery is very much a last resort here, but is often successful in resistant cases.
The tibia is the most common bone to be affected by stress fracture in athletes, particularly women. They can occur in high level as well as recreational athletes. They are associated with some static biomechanical abnormality and in particular by rather narrow tibiae. It may be that slightly stiff feet or poor shock absorbers in the feet will increase the risk. The single stress fracture which gives us most trouble is the “dreaded black line” in the front of the middle of the tibia which is often very slow indeed to heal and will sometimes go on to require surgery. We have recently used various bone-stimulating devices & BMP-2, a drug which stimulates “neutral” cells to become bone-forming cells in this condition, but it is too early to report results. Overall over 90% of the typical stress fractures will heal with relative rest, simply avoiding running activities until pain free. This is usually approximately six weeks, but three months before returning to full training.
Exertional compartment syndrome is the other common cause for shin pain. During exercise the blood supply to exercising muscles increases and the muscles themselves swell. In the tibia the muscles are encased in a “weight-lifters belt” type of sheath and in some individuals when the muscles start to swell, the pressure rises until the muscles’ blood supply is compromised. This will make the muscle “unhappy” and tend to make it swell even more. This typically leads to exertional discomfort in the front of the shin which increases progressively with exercise. It is sometimes associated with pins and needles further down in the foot as a result of squashing the nerves which run through the affected compartment. Again, this condition is associated with over pronation, but is less likely to respond to conservative measures. Radiological imaging is commonly normal and the diagnosis (if it is not clear on the basis of the history and examination) is made by measuring the pressure inside the affected compartment while the athlete is running. We used to do this with a tube filled with salt water and what was effectively an electronic manometer, but we now have a transducer-tipped electrode which will go down a very fine catheter into the compartment and allow the athlete to run with direct pressure measurements taking place. We have been looking at developing a machine which will measure the muscle’s metabolic activity without putting a needle into the skin, but this is not yet a standard diagnostic test.
Once a diagnosis is confirmed, over 80% of patients are cured completely by an operation with a very low risk of recurrence. Often patients will get back to light jogging after about a couple of weeks from the day case surgery.
There are a number of other less common causes of exertional shin pain including various nerve and blood vessel entrapment and problems with the fibula.