Word count: 2062



Word count: 2062

Stress Fracture, Lower Leg

Jarmo Karpakka1 and Sakari Orava2

1Department of Sports Medicine,

Deaconess Institute of Oulu, Finland

and 2Hospital Meditori, Turku, Finland.

Stress fractures of the lower leg are common in athletes and their incidence seems to be increasing. This is due to the increased popularity of running and jogging in the training programs of athletes in various sports and among keep-fit athletes. About 60-70 % of athletes' stress fractures occur in the lower leg; the relationship between the number of fibular and tibial stress fractures varying from 1:2 to 1:6. There also seems to have been a change in the location and epidemiology of stress fractures both in athletes and military recruits; the predominance has shifted from metatarsal stress fractures to tibial fractures.

The vertical ground reaction forces during running can be 3-5 times higher and during jumping even 8-10 times higher than those recorded during walking. These forces must be absorbed with a frequency of approximately 500 times per leg per kilometer by a runner. Contrasted with walking they must be attenuated by the body in roughly one-third of the time. The external loading forces generate compressive, tension or shear stresses (force per unit area) within the bone, which results in corresponding strains (changes in the dimensions) of the bone. At low levels of stress the bone will simply deform elastically. The basic reaction of bone to increased work is hypertrophy. When stress above a critical limit is induced, repeated loading will progressively weaken the bone until a fracture occurs. The typical locations of the stress fractures in the lower leg is presented in Figure 1.

Stress fractures have been regarded as typical examples of non-adapted loading caused by too rapid quantitative or qualitative changes in training. The athlete is at risk during the initial four to six months after taking up sport if the commencement of training is too rapid. The runner, on the other hand, is most likely to develop a stress fracture within three months of training modification. Other significant external factors are a hard terrain and low quality shoes. Running along a banked road results in a "short-long leg syndrome", which may cause proximal tibial stress fractures. Important internal and structural factors are anatomical malalignments, i.e. excessive varus of the lower leg and hyperpronation of the foot or pes cavus, leg-length discrepancy, muscular weakness or inflexibility. In military recruits, narrow tibial bone width and a high degree of the external rotation of the hip have been shown to predispose to tibial stress fractures.

Tibia

Tibial stress fractures can be divided into four groups according to anatomical site: plateau, shaft, anterior midshaft and medial malleolus.

Plateau

Stress fractures in the medial tibial plateau are rare and only one case of a stress fracture in the lateral tibial plateau has been reported. The etiological factors are not known, but they seem to be much more common in military recruits than in competitive athletes. They are manifested by pain along the anteromedial aspect of the proximal tibia just below the joint line in weight-bearing activities. Radiographs generally become positive about three weeks after the onset of the symptoms and a bone scan can be needed to confirm the diagnosis. The differential diagnosis includes pes anserinus tendinitis and bursitis.

The treatment is rest from weight-bearing activities and the average length of time to return to athletic activities is approximately four weeks.

Shaft

The majority of the tibial stress fractures are located on the posteromedial compression side of the diaphysis with an almost equal number in the proximal and distal halves. Most of these stress fractures occur in runners. An early diagnosis of a tibial stress fracture is possible with a isotope scan which becomes positive a few days after the onset of the symptoms. Radiographs become positive after the symptoms have persisted for 2-5 weeks. The most common finding is a posteromedially located callus with or without a fracture line. In clinical examination, the callous formation can be palpable, since the tibia is subcutaneous (Fig. 2). The differential diagnosis of tibial stress fracture includes the medial tibial and the compartment syndromes.

Rest from weight-bearing activities is needed with a graduated return to athletic activities in 4 to 6 weeks from the cessation of the weight-bearing activities. Crutches or plaster immobilization are seldom needed. However, a pneumatic leg brace can be used in selected cases. The brace could allow the athlete with tibial stress fracture to begin pain-free ambulation and rehabilitation to limit deconditioning. In general, exercises other than weight-bearing ones should be continued to maintain cardiovascular fitness and to permit an early return to competition. Dislocations and delayed unions are very rare complications of compressive type stress fractures of the tibia.

Most stress fractures of the tibia are transverse or oblique. Few cases have been reported where stress fractures run longitudinally. In these cases, abnormal isotope scans and normal plain radiographs are found and computed tomography may be needed to confirm the diagnosis.

Anterior Midshaft Tibia

Only 15% of tibial stress fractures are located in the mid-tibia. Anterior mid-tibial stress fractures are rare and make up a special clinical entity. A delayed union of this area of the tibia is a potential complication and is a high risk for an athlete, a complete fracture being the most serious complication. This type of a stress fracture is caused by excessive tension forces on the anterior tibial cortex and it has been suggested that the relative hypovascularity of the anterior tibial cortex due to its subcutaneous location may be a factor predisposing towards a delayed union. These stress fractures occur in athletes engaged in jumping sports including ballet and running.

The diagnosis of anterior mid-tibial stress fractures is based on the clinical symptoms and radiographic thickening of the anterior cortex of the tibia with a fissure (Fig. 3). Conventional examinations can be negative for a long time because the fissure develops slowly. The radiological confirmation of the differential diagnosis to a stress fracture can require special projections or examinations. Using isotope scanning, the diagnosis can be confirmed and made earlier than with radiographs.

Treatment with conservative methods can be uncertain and prolonged especially in chronic cases. There does seem to be, however, a good response to conservative therapy if the diagnosis is made early with the aid of an isotope scan. An initial period of rest of up to six months is warranted. In cases of delayed diagnosis, or if there is a suspicion of a possibility of a delayed union or non-union, surgical intervention is recommended. Bone grafting or drilling of the hypertrophied cortex to enhance new bone formation are the methods used.

Medial Malleolus

Stress fractures of the medial malleolus are rare. The etiological factors causing this stress fracture are uncertain. Almost all the athletes reported are involved in running and jumping activities.

The main symptom is local pain. It can be at first poorly localized diffuse medial side pain of the ankle and the lower leg. Later the pain becomes more localized. Radiographs may initially be negative and bone scanning is needed to confirm the diagnosis (Fig. 4). In positive radiographs the fissure line and later intraosseal sclerosis are seen at the medial malleolus-tibial plafond junction extending vertically or obliquely upwards. The differential diagnosis includes medial tibial syndrome, overuse and strain of the medial side tendons and the deltoid ligament.

The risk of a complete fracture is increased in malleolar stress fractures. To estimate the proper healing time more experience is needed. A relatively long rest from all excessive athletic activities of up to four months from the onset of the symptoms is needed. If there is no delay in the diagnosis, the use of an aircast brace can shorten the treatment time to 6-8 weeks. Operative treatment with open reduction and internal fixation may be needed.

Fibula

The stress fracture of the fibula has been called the runner's fracture. The fracture is usually located in the lower part of the fibula 3-8 cm above the tip of the lateral malleolus. In about 25% of the cases, the fracture is located higher up the shaft. It is suggested that fibular stress fractures are caused by either a combination of compression and torsion forces against the lateral malleolus, or by the rhythmic contractions of the plantar and toe flexors. The tension is greatest above the distal fibula, which is firmly fixed at the lateral malleolus.

Fibular stress fractures cause lateral leg and ankle pain. Clinical examinations reveals tenderness and swelling along the affected area. Radiographs become positive after 2-4 weeks so bone scanning is suggested if a fibular stress fracture is suspected. High fibular stress fractures are manifested with lateral leg pain and the differential diagnosis includes biceps femoris tendinitis, compartment syndrome, and peroneal nerve entrapment.

Fibular stress fractures are usually treated with rest from weight-bearing activities. The healing time in most cases is 3-4 weeks. Complications have not been reported.

Prevention

Although stress fractures are preventable, the gradual intensification of athletic training programs in all age groups makes the disappearance of stress fractures unlikely. Malalignments and biomechanical factors that contribute to stress fractures should be recognized. This requires close co-operation between the athlete, the trainer and the physician. There are malalignments that have been observed to be associated especially with stress fractures of the lower leg e.g. flat feet with excessive pronation and leg-length discrepancy. Prophylactic orthotic corrections could be used. However, the benefits of orthoses are not always clear. Shock-absorbing devices inserted into shoe-ware may be helpful in reducing fracture incidence in military recruits. In good quality running shoes the shock-absorption capabilities are usually sufficient.

Training errors are the most common external contributing factors to stress fractures. The bones might not have adapted to excessive mileage, intensive workouts or too rapid quantitative or qualitative changes in training. This is especially important in the training programs of child, adolescent and female athletes who have a more slender bone structure, which requires a longer period to become adapted to the high stresses of running and jumping. The training programs should be modified accordingly. Amenorrhea can be a problem especially in female endurance athletes, and there are many studies that indicate an increase in stress fractures in conjunction with irregular menses. Eating disorders seem to be also more prevalent in female athletes engaged in sports where extra weight is disadvantageous. These athletes usually need a multidisciplinary team for consultations.

The high ground reactions forces during running and jumping should be reduced with good quality sport shoes, the judicious selection of training surfaces and by keeping the leg and foot muscles both strong and flexible. The importance for a runner to stretch and strengthen the leg and foot muscles year-round has been emphasized.

Because stress fractures seem to be inevitable, emphasis should therefore be placed on the earliest possible diagnosis and the provision of effective primary treatment. Both athletes and trainers should be aware of the symptoms of stress fractures.

References

1. Hershman E.B., Mailly T.: Stress fractures. Clin in Sports Med 9(1):183-213, 1990.

2. Hulkko, A.: Stress Fractures In Athletes. Thesis. University of Oulu, Finland, 1988.

3. Matheson, G.O., D.B. Clement, D.C. McKenzie et al.: Stress fractures in athletes. A study of 320 cases. Am J Sports Med 15:46-58, 1987.

4. Orava S., J. Karpakka, , A. Hulkko, et al.: Diagnosis and treatment of stress fractures located at the mid-tibial shaft in athletes. Int J Sports Med 12: 419-422, 1991.

5. Shelbourne K.D., D.A. Fisher , A.C. Rettig et al.: Stress fractures of the medial malleolus. Am J Sports Med 16: 60-63, 1988.

Figure 1. Typical stress fracture sites of the lower leg. Anterior-posterior and side views (modified from Hulkko A, Orava S: Stress fractures of the lower leg. Scan J Sports Sci 9(1):1-8,1987).

Figure 2. Typical tibial stress fracture at the junction of mid-and distal thirds showing periosteal new bone formation (callus).

Figure 3. A transverse stress fracture in mid-tibial shaft involving the anterior cortex (arrow).

Figure 4. Isotope scan with Technetium99 showing a stress fracture of the medial malleolus.

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