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Stress Reactions of the Foot

by Gary Vitti
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stress reactions

Illustration (diagram) of Metatarsal fracture types.

The 2019-20 NBA season opened up this week with two Los Angeles Lakers out indefinitely with stress reactions of the foot.  Since I have no specific knowledge about these injuries this blog will be an overview of what a stress reaction in the foot may be.

A stress reaction is classified as an overuse injury.  Wolff’s Law was created by a German anatomist (Julius Wolff) in the 19th century.  The law states that bone will adapt to the loads under which it is placed.  If loading on a particular bone increases, that bone will remodel itself to handle the load.  In essence, lay down more bone to resist the load.

The corollary to Wolff’s law for soft tissue is Davis’s Law (Dr. Henry Gassett Davis). Davis was an American orthopedic surgeon that put forth this principle in his book conservative surgery published in 1867. It is the physiological principle that soft tissue will heal according to how it is mechanically stressed.

In simple terms, the body will lay down more bone and/or soft tissue as you load or stress those structures.  The simplest example of this physiological reaction is when you lift weights your muscles get bigger.

Now here’s the rub.  If you overload the bone or soft tissue before it has had a chance to adapt to the load, that structure will go through a metabolic change and become inflamed.  A word that ends in ITIS means inflammation of.  For instance, tonsillitis is inflammation of the tonsils, appendicitis is inflammation of the appendix.

Applying Davis’s law to the musculoskeletal system, an inflamed tendon is diagnosed as tendinitis caused by micro-tearing of the tendon fibers. If the athlete continues to load an inflamed tendon, the actual properties of the tendon can change to what is called tendinosis or tendinopathy.  This is a degeneration of the actual collagen of the tendon resulting in burning pain, loss of strength and loss of range of motion.

Applying Wolff’s law to the skeletal system, a stress reaction to bone occurs when the bone has not adapted to the loads put upon it causing a metabolic change to the area of the bone that has not laid down sufficient calcium to handle the load.  Continuing to load a bone that is having a stress reaction will cause the bone to begin to come apart resulting in a stress fracture. Loading a bone that has a stress fracture will result in a comminuted fracture where the bone splinters into two fragments.

When explained this way it becomes obvious how important it is to not return too early from a stress reaction.

stress reaction of the footThere are 26 bones in the foot along with two tiny bones engulfed in the tendon under the big toe that are called sesamoid bones. There can be a stress reaction to any of these bones but during my 32-year tenure as the head athletic trainer for the Los Angeles Lakers, the two most common stress injuries in the foot were to the tarsal navicular and the 5th metatarsal.

The navicular is a tarsal bone located at the arch in the middle of the foot.  The geographic location of the bone makes it overly stressed on heel strike by being impinged by two other bones as the arch collapses to absorb the shock of full body weight.  The navicular is at further risk to a stress reaction because the middle third of the bone does not receive a good blood flow (avascular).  Without good blood flow the bone has difficulty regenerating and healing.

The first symptoms of a navicular stress fracture are pain at the arch that gets worse with running and jumping.  X-rays are often negative which would require further diagnostics including bone scan, CT scan, and MRI.  A non-displaced, non-comminuted fracture responds well to 6 weeks of immobilization followed by 6 weeks of rehabilitation before return to play.  If there is not complete healing after 6 weeks to 6 months post-fracture than that fracture is termed a non-union or fibrous union and most likely will require surgery.  Non-union fractures are generally caused by too much motion at the fracture site or poor blood supply.  A fibrous union is when the fracture line fills in with scar tissue instead of bone requiring surgical intervention.
Displaced or comminution fractures will also require surgery with a long healing and rehabilitation period of 3 months or more.

Fifth metatarsal fractures (Jones fracture) are also common in the NBA.  A Jones fracture is a break at the base and shaft of the long bone in the foot that connects to the little toe.  Looking at the architecture of the foot it is obvious that the first toe (big toe) and first metatarsal are bigger than the second.  The second is bigger than the third and so on until you get to last or 5th metatarsal.  The reason for this is on weight-bearing the arch collapses to get the bigger metatarsals and toes on the ground to bear most of the body weight on the toe-off.  The 5th metatarsal is not built to handle that type of load and a stress reaction can occur.  Jones fractures can also occur from the trauma of an ankle sprain causing an avulsion fracture which is a small piece of bone being is pulled off by a tendon or ligament.  As with the navicular, the 5th metatarsal also doe not get a good blood flow which contributes to its vulnerability and slow healing.  Immobilization healing time could be 6 to 12 weeks with 15 to 20% resulting in non-unions or fibrous union requiring surgery with a return to play in 4 to 6 months.

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