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Stress fractures of the foot

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Description

Stress fractures, also known as fatigue fractures, occur with overuse when excessive repetitive force is applied to a localized area of bone.  Stress fractures occur when excessive repetitive force is applied to normal bone or when normal repetitive loads are applied to weaker bone (ex. osteoporosis).  Activities such as walking, running, and repeated jumping can subject the bones of the foot to large forces that often lead to microscopic cracks in the bone, called “microfractures”. Stress fractures are commonly seen in the 2nd or 3rd metatarsal neck region, the base of 5th metatarsal (Jones Fracture), the sesamoid of the great toe, and the navicular bone.

Structure and function

Stress fractures do not occur in random locations. They occur in certain bones, and locations within those bones, that are absorbing excessive repetitive force. Each person’s foot absorbs force in a slightly different manner that is dictated by that person’s foot shape, alignment, foot stiffness, and gait pattern.

Each foot contains five metatarsals. These are the long bones that lead to the base of each toe. The metatarsals are numbered 1-5 starting on the inside and leading outward (from big toe to smallest). Each metatarsal is a long bone that joins with the mid-foot at its base, a joint called the tarsal-metatarsal joint, or Lisfranc joint. In general, the first three metatarsals are more rigidly held in place than the last two, although in some individuals there is increased motion associated with the 1st metatarsal where it joins the midfoot (at the 1st tarso-metatarsal joint) and this increased motion may predispose them to develop a bunion.

The long part of the metatarsal bone is known as the metatarsal “shaft”, and the thick end of the bone nearest the toes is known as the metatarsal “head” (the metatarsal neck lies between the shaft and head). The head serves two very important functions. First, the metatarsal heads are the locations where weight bearing takes place. Second, the phalanges connect to the foot at the metatarsal heads at a joint called the metatarsal-phalangeal joint. These joints are very flexible, allowing the metatarsal heads to continuously support the weight of the body as the foot moves from heel to toe.  Common locations for stress fractures include the 2nd and 3rd metatarsal neck region and the base of the 5th metatarsal.

Lesser metatarsal stress fractures, which usually involve the 2nd or 3rd metatarsal bone (K or L in Figure 1 below), are associated with pain in the midfoot to forefoot. They typically occur following prolonged or repetitive walking or running and are sometimes called “march fractures.” Risk factors for development of a stress fractures include an increase in activity level, a foot shape that overloads those metatarsals, and/or relatively weak bones (as might be seen with osteoporosis).  A foot with a relatively long second metatarsal will have an increased predisposition to develop a stress fracture in the second metatarsal shaft or neck region.  This will be especially true if the first ray (great toe and first metatarsal) is hypermobile and does not take its share of force during walking or running.

A “Jones’ fracture” is a special type of stress fracture of the base of the 5th metatarsal (N in Figure 1). Jones’ fractures generally occur following activities that repetitively load the foot (for example sports with running). These fractures tend to occur in people that have a high arched foot shape or a leg shape that results in increased loading on the outside part of the foot.

Figure 1a, Navicular: E, metatarsals: JKLMN

Figure 1b, Medio-lateral view

The navicular bone is one of the tarsal bones, found in the foot. Its name derives from the bone's resemblance to a small boat, caused by the strongly concave proximal articular surface. Located on the medial side of the foot, the navicular bone articulates proximally with the talus, distally with the three cuneiform bones, and occasionally laterally with the cuboid. Navicular stress fractures are an uncommon but serious injuries characterized by a chronic midfoot ache.  The cause is a repetitive chronic load to the midfoot often from dynamic sporting-type activities. Risk factors for stress fractures include a stiffer (high arched) foot, a relatively long second metatarsal, and activities that involve repetitive loading through the forefoot such as sprinting.  The mechanism of injury is felt to be repetitive loading through the second metatarsal that channels the force through the middle cuneiform and into the navicular.

A sesamoid bone is a bone that is also part of a tendon. An easy example of such a bone is the kneecap (patella). In the foot there are two sesamoid bones (Figure 2), each of which is located directly underneath the first metatarsal head. These sesamoids are part of the flexor hallucis brevis tendon, and act to increase the force of the tendon on the proximal phalanx. They also act to absorb shock and allow the joint to glide smoothly during motion.

Figure 2a: Sesamoid bones (arrows) at the base of the first MTP joint, credit: Wikipedia.org 

Figure 2b: Sesamoid bones embedded in flexor hallucis brevis tendons (in red)

credit: Wikipedia.org

The sesamoid bones beneath the great toe rarely develop stress fractures, which is often confused with the more common problem of sesamoiditis combined with a congenital bipartite (split) sesamoid. When sesamoid stress fractures do occur, they usually result from an episode of increased repetitive loading such as an increase in running distance. Pain under the great toe that is aggravated by standing and walking is common. It is not unusual for patients who suffer a sesamoid stress fracture to have a high arched foot type

Normally, the body is able to sufficiently heal these microfractures, leading to a stronger bone to accommodate these higher forces in the future.  However, when the rate of loading on the foot is such that the body’s healing response cannot keep up, a stress reaction can develop. Eventually, if the forces continue, the bone structure can fail and a stress fracture will occur. An individual’s lack of sufficient biology to heal microfractures (i.e., low calcium, vitamin D, or thyroid hormone) can also contribute or lead to stress fractures.

Stress fractures occur in the same manner that you would break a paper clip – excessive wiggling back and force will lead to breakage. Stress fractures can occur in normal bone that is subject to abnormally excessive repetitive loading (fatigue fracture). An example of this would be a new army recruit going on a long march as part of basic training who as a result of this dramatic increase in repetitive loading develops a stress fracture (often called a “March” fracture). Stress fractures can also occur in weakened bone that is subject to seemingly normal repetitive forces (insufficiency fracture). For example a person with thin bone (ex. osteoporosis) who walks much more than they are used to.

Patient presentation

Patients with stress fractures will usually report localized aching pain in the affected area.  They will give a history of some increase in their normal activity level (ex. went for a long hike this weekend, increased training in preparation for a marathon).  This pain typically increases with activity and decreases with rest. They may have a history of a condition that predisposes them to weaker bones such as osteoporosis (weak thin bone), amenorrhea (loss of normal menstrual cycle), or a history of smoking.

Metatarsal Stress fractures

Stress fractures involving the lesser metatarsal bones (typically 2nd or 3rd) will often present with pain and swelling in the midfoot to forefoot. On examination, there will be some degree of swelling and tenderness directly over the affected metatarsal. There may also be some associated forefoot swelling. The foot type in general may be flat, often with a long second and possibly third toe. There may also be an associated callus under the ball of the foot, at the base of the second or third toe. It is the repetitive absorption of the loading force beyond the capacity of the bone to withstand this force that causes the stress fracture. Patients usually can walk on the foot, though there will be a limp.

Jones (5th metatarsal stress fracture)

Individuals who suffer a Jones’ fracture will report pain on the outside of the midfoot (Figure 2). They have difficulty bearing weight and may walk with a limp. In most instances the patient will describe exactly when the fracture occurred, often after landing heavily or performing some other demanding but routine activity. However, sometimes the main symptom will be a chronic (long-term) ache in the outside part of the foot – representing a developing stress fracture of the base of the fifth metatarsal.  Many patients will report a history of some pain in the foot prior to the actual break. It is possible to have the problem in both feet, although usually one side hurts more. Patients with a Jones’ fracture will have pain at the fracture site (Figure 3). Often they will have high arched feet and/or an alignment of the lower extremity that tends to load the outside part of their feet (Figure 4). Sometimes, when looking at these patients’ shoes, one will see excessive wear of the outside of the sole because of the pressure put on that part of the foot and shoe.

Figure 3, Location of pain: Jones’ fracture

Figure 4, High-arched foot pattern in patient with a Jones’ fracture

Navicular Stress Fractures

Patients who develop navicular stress fractures will present with a chronic mid-foot ache.  Although anyone can get a navicular stress fracture, the most common presentation is in the athlete.  The injury may begin after a series of repetitive loading episodes.  However, unlike a typical stress fracture of the metatarsals (which are much more common), these loading episodes tend to be more dynamic.   Some examples include the lead foot of an active golfer, a middle distance runner, or any college or professional athlete performing dynamic repetitive activities.

The symptoms of a navicular stress fracture are often generalized to the mid-foot.  The relatively nonspecific location of the symptoms makes this condition difficult to diagnose.  Pain may be with athletic activities only, but some patients might even have a limp with walking. Physical examination will demonstrate a generalized tenderness around the top of the mid-foot. An astute physician may be able to localize the tenderness to the top of the navicular bone (the "N-Spot").  Certainly, attempts to hop or rise up on the toes of the affected foot will be painful.  There is some suggestion that patients with slightly higher arch feet and also patients with relatively long second toe and second metatarsal may have an increased risk of developing navicular stress fractures. These two situations may increase the concentration of force into the navicular, particularly in patients doing activities that involve them getting up on their toes such as sprinting and jumping.  But most commonly, the person with a navicular stress fracture has a normally-aligned foot.

Sesamoid Stress Fractures

Perhaps the first thing to realize about great toe sesamoid stress fractures is that in many instances they are not actually stress fractures of one of the two sesamoid bones, but rather, a “bipartite sesamoid” with an associated “sesamoiditis”. A bipartite sesamoid is a variant of a normal sesamoid where the bone remains separated into two fragments during development. “Sesamoiditis” is a general term that refers to pain under the great toe that occurs from repetitive loading to this area in a manner that is similar to metatarsalgia. Patients with deformities to the great toe, in which the sesamoid bones track abnormally, such as a bunion, can also develop a version of sesamoiditis.

However, sesamoid stress fractures do occur and also produce chronic pain under the base of the great toe similar to the symptoms seen in sesamoiditis. Research shows that sesamoid stress fractures are caused by repetitive loading to this area.  This loading can occur during standing, walking or running, particularly in shoes that do not provide adequate protection. A painful sesamoid stress fracture may cause an individual to limp quite noticeably. Symptoms may settle over time, but they will reoccur if a person resumes repetitive load bearing activities, like running or playing sports.  The pain is often quite localized and is associated with the involved sesamoid. It’s not uncommon for a sesamoid stress fracture to occur after a hard training run or another type of activity that is associated with more repetitive loading than normal, such as when an individual’s activity level or training level has increased noticeably. On examination, there will be localized tenderness under the involved sesamoid. Movement of the great toe may exacerbate the symptoms. The pain is usually isolated to under the great toe region. It’s not uncommon for these injuries to occur in patients with high arched feet, as this foot shape tends to cause increased loading at the base of the great toe.

Objective Evidence

Diagnosis of a stress fracture requires a high degree of suspicion as the fracture often does not show up on the initial x-ray. X-rays may initially be negative as it often takes 10 days or more for a callus (new bone) to form and be visualized on x-rays.  A bone scan or MRI will demonstrate a stress fracture or a stress reaction (pre-stress fracture) earlier and one of these studies may be indicated if the diagnosis is in question. It is possible, and in fact common, to see fluid or “edema” in bones on an MRI without having an obvious stress fracture.  This represents a “stress reaction” and is equivalent to microscopic bone fracturing without a complete stress fracture. The fracture, if present, is usually visible on an MRI. If there is concern, a CT scan can usually confirm the diagnosis of stress fracture, as well as clearly define the location and size of the fracture. 

Metatarsal stress fractures typically occur at the neck region or in the mid-part (shaft) of the bone. Occasionally, high-level ballet and modern dancers will generate stress fractures at the base of the metatarsal near the midfoot.

Navicular stress fracture X-rays are often read as normal. Sometimes a subtle fracture line can be identified. In mores advanced cases or cases where there is degeneration of the talonavicular joint, x-rays will be abnormal. Diagnosis can be made with an MRI, a CT scan, or a bone scan. MRI or a CT scan will allow the fracture orientation to be identified. In addition, those studies will allow determination of whether the fracture is complete or incomplete.

Plain x-rays will identify a Jones’ fracture (Figure 5). The fracture itself occurs at the metadiaphyseal area where the more flexible bone at the base of the 5th metatarsal meets the more rigid bone of the shaft of the metatarsal. The fracture is different from a Dancer’s fracture (Figure 6) which occurs when one of the ligaments pulls off (avulses) the tip of the 5th metatarsal base.

Figure 5, Jones fracture x-ray

Figure 6, Dancers fracture

Routine x-rays of the foot can be very helpful in diagnosing sesamoid stress fractures. Typically they will demonstrate two sections of the sesamoid. What differentiates a stress fracture from the bipartite sesamoid is that the bone fragments of a bipartite sesamoid have a clearly identified margin. This is because the congenital nature of a bipartite sesamoid means that it has been present since development, whereas a sesamoid stress fracture has a fracture-like appearance on radiograph. X-rays may be diagnostic although an MRI may be required to clarify the diagnosis.  An MRI can help differentiate a bipartite sesamoid from a sesamoid stress fracture. An MRI may also help differentiate an acute sesamoid fracture from a chronic stress fracture. In addition, it may identify an area of avascular (dead) bone that develops in some sesamoid stress fractures. This happens in some circumstances as the sesamoid bones have a poor blood supply and a chronic stress fracture or bipartite sesamoid may leave one section of the sesamoid with a limited blood supply.

Epidemiology

Stress fractures are common and affect people of all ages. They are more likely to occur in females than in males, especially among females with the female athlete triad of amenorrhea, disordered eating, and osteoporosis.  The estimated incidence in athletes and military recruits is 5-30%, depending on the sport and other risk factors.  It is estimated that among people who run regularly for exercise, approximately 50-66% will sustain an injury that keeps them from running for 1 week (PMID:10496574), whether this be shin splints, stress fracture, cartilage breakdown, or osteoarthritis.  Stress fractures do not occur as often in the non-active population unless there is an underlying pathology that causes bone weakness.

Differential diagnosis

Differential diagnoses for stress fractures of the foot include fracture, osteomyelitis, bone metastases, osteoid osteoma, and bone contusion.  MRI can usually differentiate these and therefore is useful in determining the correct diagnosis.

Red flags

The female athlete triad includes amenorrhea, disordered eating, and osteoporosis.  Low estrogen levels from lack of normal menses may predispose women to osteoporosis, and lack of adequate nutrition also plays a role in pathologic bone maintenance. If a female athlete presents with a stress fracture it is important to take a detailed dietary history to ensure that the patient is eating enough calories and nutrients, including calcium and vitamin D.  If she is not, it is important to refer her to a specialist who can address these issues.

When diagnosing a sesamoid disorder, it is critical to determine whether the problem is from a sesamoid stress fracture or a bipartite sesamoid with overlying sesamoiditis. The general non-operative treatment principles are similar, although a true sesamoid stress fracture will tend to have a worse prognosis.

Treatment options and Outcomes

Most stress fractures do not require surgery. Treatment generally involves resting the affected area until the bone adequately heals, often 6-8 weeks or more. This can be accomplished with crutches and a CAM walker boot.  Additionally, correcting any risk factor that may predispose to further stress fractures, including training issues, footwear, and nutritional or hormonal deficiencies.  NSAIDs and other analgesics may be used to limit pain.  Bisphosphonates may be prescribed if lack of healing noted after 2-3 months of rest.  Once healing has occurred, a gradual return to activity in a stiff-soled shoe is advised.

Surgery is rarely indicated for a second or third metatarsal stress fracture. Occasionally, there may be an associated non-union that will need to be treated with surgery. Although it is rare, surgery will usually include fixation with a plate and screws and possibly bone graft.

Certain stress fractures may require surgery in order to aid in healing or prevent non-healing (i.e., non-union) or re-fracture. These “high risk” stress fractures include the Jones' fracture, a displaced navicular stress fracture, and other stress fractures that may not heal adequately with non-surgical treatment.

Jones Fracture:  Treatment

Like most fractures, a Jones’ fracture will usually heal if the foot is protected from the forces of weight bearing for a long enough period of time. However, the area of the bone that is fractured has a relatively poor blood supply so bone healing may be slowed. Furthermore, because the fracture is related to repetitive stress to the fracture site there is always a concern that the fracture may recur. In athletes with a Jones’ fracture, surgery is usually recommended.

The initial surgery involves stabilizing the fracture site by placing a strong screw through the middle of the bone (Figure 7). The stability helps the bone resist the forces that can slow healing and drilling across the break stimulates blood flow to help healing. The after-surgery treatment for this surgery is similar to that described above for non-operative management, but return to high level activities tends to be substantially quicker.

Figure 7: Screw fixation to treat a Jones fracture

The surgery to place a screw across the fracture site can be associated with complications including infection, sural nerve injury, wound healing problems, non-union (failure of the bone to heal, often due to continued loading to the area during a return to walking activities), and Increased fracturing of the bone at the time of surgery. In some instances placing the screw across the fracture site will increase the fracture or resulting in further breakage of the 5th metatarsal.

A patient that has a non-union of the Jones’ fracture or a recurrent fracture after it had appeared to have healed may need more involved reconstructive foot surgery. This reconstructive surgery would repair the fracture (often with bone grafting) and involves changing the shape of the foot by cutting and repositioning one or more bones in the foot or lower leg. Common bone cutting procedures (osteotomies) may include lateralizing calcaneal osteotomy (cutting the heel bone and shifting it more to the outside) and dorsiflexing 1st metatarsal osteotomy (cutting a wedge out of the top of the 1st metatarsal so that it may be realigned).

Navicular Stress Fracture: Treatment

Navicular stress fractures can also be difficult to treat due to the relative lack of blood supply to the navicular (a good blood supply is needed for healing of any bone injury) and the fairly extensive force that this bone absorbs in normal walking and in sporting type activities.

Good results have been reported when treating non-displaced navicular stress fractures with casting and a period of non-weightbearing for 6 weeks.  Success rates of 85-90% have been reported with this treatment method.  Many doctors will also recommend use of a bone stimulator which is designed to encourage bone healing.  However, there is no clear evidence that the stimulator improves the time to healing.

However, if the patient is allowed to walk on the cast, the rate of healing may fall as low as 25%. It is common to require three, four, or more months to make a full recovery from an non-displaced navicular stress fracture, and it may be a season-ending injury for an athlete. Furthermore, patients who have developed a navicular stress fracture are at risk for having a recurrent fracture, as the underlying biomechanics are usually unchanged even after the fracture has healed.

Surgery may be recommended for some patients, especially if an initial period of non-operative treatment is not successful.  Surgery may include drilling across the fracture, placement of one or more screws, and possibly the addition of bone graft to improve healing.  Surgery usually results in successful healing, but a period of rest and non-weight bearing is required after surgery, and overall recovery time is still prolonged.

In rare cases, a navicular fracture may go on to displace.  Non-operative treatment is no longer appropriate; a surgeon needs to reduce the fracture (set it in exact position), hold it in place with screws, and possibly add bone graft.

The most obvious and concerning potential problem with non-operative treatment is persistence of the fracture.  If the fracture is not showing signs of healing, then surgery should be considered.

In rare cases, the navicular bone can collapse.  This is probably not the end point of a stress fracture, but may be part of a more complex and rare disease.  Collapse compromises function of the hindfoot joints and is difficult to manage.

If a navicular fracture heals in poor alignment, arthritis of the associated joint (the talonavicular joint) will set in, with pain and stiffness.  Surgery to fuse the talonavicular joint can alleviate much of the midfoot pain associated with talonavicular arthritis. However, it is associated with a fairly prolonged recovery time of six or more weeks of non-weightbearing. In addition, it increases the stiffness of the midfoot.

Sesamoid Stress Fracture: Treatment

Like with other stress fractures, non-operative treatment of a non-displaced acute sesamoid stress fracture requires a period of immobilization and protected weight bearing. The goal is to manage weight bearing through the heel for a period of six to eight weeks in order to give the sesamoid bones the best chance to heal properly. Specifically, the area under the base of the great toe is protected, similarly to managing sesamoiditis. An orthotic that helps to offload this area is used. This is typically an orthotic with a recessed area under the base of the first metatarsal head. This is combined with the cushioned insole and a very stiff sole of the shoe with a slight contour. A stiff sole with a rocker bottom contour will allow for a smoother dispersion of the force away from the base of the great toe. In addition, activity modification to help prevent excessive loading to this area should be performed. Time will often help to settle this condition when combined with activity modification.

Displaced acute stress fractures will need surgical intervention. The results of surgical treatment are not routinely predictable. The treatment involves repairing the fracture with fixation and removing a portion of or the entire fractured sesamoid bone. Removing the sesamoid bone is performed in conjunction with a repair of the associated joint capsule. One of the issues with both operative and non-operative treatment is that the underlying foot shape (usually high arched) that often contributes to the development of this condition remains unchanged. Therefore, the area under the base toe is constantly and repetitively loaded during standing and walking activities.

There is an array of complications that can occur as a result of sesamoid surgery, including but not limited to infection, wound healing problems, and blood clots (DVT and PE). Complications that are specific to sesamoid surgery include irritation to the nerve running to the inside of the big toe, persistence of symptoms as the loading to this area will continue, and great toe deformity (hallux valgus, hallux varus, cock-up toe)

Risk factors and prevention

Risk factors for stress fractures include intrinsic mechanical factors (e.g. decreased bone density, foot structure), nutritional factors, hormonal factors, physical training, and extrinsic mechanical factors (e.g. footwear, running surface) (PMID: 10492029).  Patient's with osteoporosis, osteomalacia, osteogenesis imperfecta, Paget's disease, and fibrous dysplasia are at a higher risk for stress fractures (insufficiency fractures).

Preventative measures to prevent stress fractures include avoiding increasing the intensity of training too quickly, eating a diet with adequate amounts of calcium and vitamin D, and changing out running shoes every 300-500 miles.  A study by Lappe et al. showed that female military recruits given calcium and vitamin D supplements were significantly less likely to sustain a stress fracture than recruits that did not take supplements (PMID: 18433305).

Miscellany

Because women with amenorrhea have low estrogen levels and estrogen is important in bone health, one possible way to reduce the risk of stress fractures in these women may be to put them on oral contraceptive pills (OCPs).  Theoretically, exogenous estrogen may help to decrease bone resorption and increase bone mineral density.    

Key terms

Microfracture; osteoporosis; female athlete triad; Jones’ fracture; calcium; vitamin D; amenorrhea

Skills  

Bedside skills for the diagnosis stress fractures include the ability to take a detailed but focused history and perform a thorough musculoskeletal examination.