Assessing and Treating Interosseous Muscle Strains Did you know you have interosseous muscles in your foot? You know your leg has various large muscles as the aductors in your upper leg or the tibial muscles in your lower leg. Well your foot too has very powerful muscles which control the direction of your toes. As all muscles the interosseous muscles can abduct and flex, in this case their action is to abduct and flex the toes. Obviously abduction is less important in the midfoot compared to flexion but let’s first understand the anatomy of the interosseous musculature in relation to the metatarsal bones of the foot, as well as the circulatory and nervous systems. Anatomy of the Interosseous Musculatre of the Foot: Muscles, Tendons and ligaments The 4 interossei muscles are situated between the 5 long metatarsal bones of the midfoot. They are bipenniform muscles, arranged on each side of a tendon. Each interossei muscle originates by two heads from the proximal half of the sides of adjacent metatarsal bones. The two heads of the muscle form a central tendon which passes deep into the metatarsal ligament. The first tendon is inserted into the medial side of the second toe; the other three are inserted into the lateral sides of the second, third, and fourth toes. As mentioned the interosseous muscles’ action is to abduct and flex the toes. Abduction is less important in the foot compared to flexion at the joints between the metatarsal bones and the phalanges (toes). These powerful muscles control the direction of the toes during violent activity, allowing the long and short flexors to perform their actions. The interosseous muscles also contribute to maintaining the anterior metatarsal arch of the foot, as well as to the medial and lateral longitudinal arches of the foot, due to the position of the joints between the metatarsal bones and the phalanges (toes). They basically stabilize the foot while walking and running. The Circulatory and Nervous systems: Nerves and Arteries: The interosseous muscles are innervated by the lateral plantar nerve. The perforating arteries pass to the dorsum of the foot between the heads of the three lateral interosseous muscles. While the deep plantar branch of the dorsalis pedis artery passes through the space between the heads of the first interossei muscle entering the sole of the foot. How and why the Interosseous Musculature Gets Injured Interosseous Muscle Strains as all strains are muscle and ligament injuries without dislocation or fracture. They are divided into stable strains and unstable more severe strains. The interosseous muscle strain is most often a stable strain caused by overstretching or overexertion of the interosseous musculature. A strain or tear of one of the small dorsal interosseous muscles may cause sharp pains, felt between the metatarsal bones of the feet, on the top or beneath the foot. These precipitate sharp pains may even occur between several metatarsals simultaneously. In the acute phase of the injury due to these severe pains most patients will have serious difficulties bearing their full weight on the injured foot. Additional symptoms are swelling and tenderness painful to touch as well as bruising on the plantar medial aspect of the foot. All these symptoms cause for a very limited range of motion of the injured foot. An attempt to perform a provocative maneuver as one of the medical examinations called the ‘piano key test’ or a pronation abduction of the foot will elicit unbearable levels of pain. There are various scenarios causing for this kind of injury or creating this type of severe pain. The injury may be caused by either direct or indirect loads. Crush injuries due to a blow to the foot for example are caused by a direct loading mechanism. This type of injury often results in severe soft tissue damage as well as compartment syndrome which is a serious condition involving increased pressure in the muscle compartment which may lead to damage to the interosseous musculature, damage to the nervous system in the foot and additional blood circulation problems. The typical indirect loading mechanism is caused by forced abduction/adduction or hyperplantarflexion with axial loading. This type of injury often results in various degrees of soft tissue damage or displacement. Common causes for this type of injury can occur due to a fall from a great height or even off a curb or other scenarios causing twisting of the foot; excessive standing or running activities which may bring on fatigue of the foot; inappropriate footwear as excessively tight shoes or very high heels; or even walking barefoot on a surface that requires a shoe for support. Foot injuries are fairly common among athletes. However fractures of the midfoot are uncommon due to the constrained arrangement of multiple articular surfaces, which is improved by capsular attachments and strong ligaments and tendons. Midfoot injuries usually involve fractures or dislocations of bones together with soft tissue injuries yet midfoot sprains and other soft tissue injuries can occur on their own or may continue to cause pain after the fractured bones have healed. Despite the fact injuries to the midfoot are less common; they have a high risk of ending an athlete's season or even career. Interosseus muscle injuries or midfoot sprains as they are often called seem to be challenging to diagnose since the rate of missed or delayed diagnoses ranges from 13% to 24%. However timely diagnosis and proper treatment highly improve the chance of successful healing and reduce the odds for complications. It’s worth mentioning that certain medical illnesses may contribute to these missed or delayed diagnoses. For example diabetes patients suffering from peripheral neuropathy may have a higher threshold for pain and therefore not be aware of the high level of pain caused by a midfoot sprain. Interosseus muscle injuries or a midfoot sprain is commonly caused by a Lisfranc ligament injury. The Lisfranc ligament is a large and strong interosseous ligament attaching the first cuneiform bone to the second metatarsal bone. Midfoot sprains can occur at all ages even to children as young as 3 years old but the they are much more common in athletes participating in many types of sporting and recreational activities, including football, baseball, basketball, hockey, soccer, ballet, mountain biking, and windsurfing. Football players in particular are found to have a high incidence of midfoot sprains (estimated at 4% per year), often occurring in linemen. The classic mechanism of injury occurs in football linemen when an axial load is applied to the heel of a fixed plantarflexed ankle with the toes in dorsiflexion. Treatment Conservative treatment of pain in the acute period consists of rest, compression, and elevation of the foot to reduce swelling and allow for proper healing. Pain medication as NSAID’s may also be needed. These types of injuries often take weeks or months to heal. The recommendation for at least the next 6 weeks following the acute period is immobilization and non-weight bearing with a cast. In the case of continued pain after 6 weeks the recommendation is to wear a controlled ankle motion boot for protected weight bearing together with the use of crutches for an additional month. Once the pain has subsided a gradual return to activity is recommended while wearing proper shoes and arch supports.
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