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Clinical Observations |
1 Department of Radiology, Duke University Medical Center, Box 3808, Erwin Rd., Durham, NC 27710.
Received September 9, 2004;
accepted after revision January 7, 2005.
Supported by Nike Corporation.
Abstract
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CONCLUSION. Six (12%) of 52 feet showed a signal indicating bone marrow edema in the metatarsals. MRI depicts bone marrow edema in the feet before a fracture becomes evident. Identification of this edema may reveal stress changes, allowing early treatment and prevention of debilitating stress fractures.
Keywords: basketball • metatarsals • MRI • stress fracture
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MRI can detect alterations in bone marrow signal intensity quite readily, as numerous articles have demonstrated. In the foot, in particular, several articles have addressed bone marrow signal alteration as a result of altered biomechanics and increased activity [5-8]. MRI can determine the severity of stress injuries by the intensity of the abnormal signal. These stress changes from altered mechanics are seen as abnormal signal intensity in bone marrow. Marked abnormal signal intensity would then suggest a more significant stress reaction. Continued stress on these bones caused by jumping and landing could lead to the development of stress fractures. It would follow that perhaps MRI could be used to evaluate for bone marrow edema before a stress fracture is apparent clinically [9].
To evaluate the impact of early diagnosis and treatment on metatarsal stress fractures, MRI examinations were performed on asymptomatic elite basketball athletes before the start of the National Collegiate Athletic Association (NCAA) basketball season. The athletes were followed clinically throughout the season, and MRI examinations were repeated at the end of the season.
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Bone marrow edema was defined as increased signal intensity in the shaft of the metatarsal. The criteria for diagnosing stress fracture were bone marrow edema, a low-signal fracture line, and clinical symptoms. The diagnostic criterion for a stress reaction was bone marrow edema with or without symptoms.
Fourteen of the 26 players were examined after the season. Twelve were not available for the postseason follow-up, for a variety of reasons: graduation events, final examinations, family commitments, and exhibitions for professional teams.
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Of the 14 players (28 feet) who underwent MRI 1 week after the season ended, two showed bone marrow edema persisting from preseason imaging—one in the fifth metatarsal, which showed a lower signal intensity than before the season, and one in the second metatarsal, which also showed a fracture line and callus formation. In the player whose preseason study had shown abnormal signal intensity in the third metatarsal, that finding was seen to have resolved on postseason imaging. No other signal abnormality was identified in the metatarsals in the remainder of the feet. Three players who showed a mild increase in signal intensity in the fifth metatarsal on the preseason study remained asymptomatic during the season and showed no signal abnormality on postseason imaging.
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Player 2
An 18-year-old player with an intense signal at the base of the second
metatarsal was asymptomatic at the time of the MRI. Symptoms developed within
1 week. A follow-up MRI examination showed a fracture line
(Fig. 3B). He could not play
for the rest of the season. Postseason MRI showed callus formation at the
fracture site and bone marrow edema around the fracture. At the end of the
season, he was ambulating with mild symptoms.
Player 3
A 19-year-old player showed an intense signal abnormality at the base of
the third metatarsal. At the time of imaging, he was using a self-made,
self-prescribed orthotic. Within 2 weeks of the examination, he reported pain
in the midfoot. His orthotic was removed. He became asymptomatic and
experienced no sequelae from the signal changes. His follow-up MRI showed no
signal abnormality in the bone marrow.
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MRI of stress fractures reveals a spectrum of abnormalities that accompany pain on physical examination. These range from a marked increase in signal intensity in the medullary portion of the bone on a T2-weighted marrow-sensitive sequence to the more significant finding of a transverse, low-signal-intensity medullary line or periosteal reaction.
Signal alterations in the medullary space or bone marrow edema can result from altered biomechanics of the foot [6, 7]. MRI, because it is an excellent technique for examining bone marrow edema, should be effective for identifying stress changes of the metatarsals before the diagnosis of a stress fracture. Because this injury often occurs early in the season, detection of the marrow edema before a fracture line is identified or symptoms are present could alter the course of the injury and the outcome for the player. In effect, the player would not lose a large part of the season recuperating.
The athletes were examined with MRI 1 month before the NCAA games were scheduled to begin, that is, before the athletes physically began preparing for the season. Although the numbers were small, this study showed that MRI has a role in identifying stress changes in the metatarsals and that early diagnosis can alter treatment and outcome for a player. Abnormal signal in the marrow suggests altered mechanics, and a stress reaction can result from persistently altered mechanics [7].
Postseason imaging was performed on only 14 players, largely because of the tryout schedule for the National Basketball Association team and the unavailability of athletes for other reasons, such as academic schedules and graduation. Of note, however, is that all players with preseason abnormalities underwent postseason imaging.
One possible explanation for the improvement in bone marrow edema signal in the athletes is the controlled environment in which the athletes play during the NCAA season. These injuries have a propensity to occur early in the season, perhaps because of the off-season, unregulated stresses. Many institutions now have trainers, nutritionists, and conditioning coaches who look after the athletes and help them stay in good physical condition. When not in school, athletes are left to make their own decisions about how often to play and what court surface to play on and are, in essence, not in a "controlled" environment. A combination of these factors may lead to presentation of this injury early in the season.
MRI is the only radiographic tool that allows us to visualize the bone marrow signal intensity differences and degree-of-injury pattern. Player 3 showed that bone marrow edema can result from abnormal stress, because removal of the stress agent (self-prescribed orthotic) resolved the edema. The orthotic altered the normal mechanics of his foot, and the chronicity of the altered mechanics led to the development of increased bone marrow edema and pain. The MRI findings were reported to the training staff. On questioning, the athlete revealed that he was using a self-prescribed stiff orthotic to help with his chronic hip pain. The trainer removed the orthotic, and the athlete's foot pain resolved shortly thereafter.
Player 2 had increased signal intensity at the base of his second metatarsal, diagnostic of a severe stress reaction because of the intensity of the signal abnormality. No fracture line was identified at the time of the MRI. He was not symptomatic when the MRI was performed. Within 2 weeks of the MRI examination, acute pain developed in the midfoot. He was reexamined with MRI and conventional radiography, which showed a fracture line through the area of bone marrow edema. This athlete did not receive treatment at the time the MRI findings became known. He continued to play with no intervention and experienced the season-ending stress fracture.
Player 1, like player 3, also benefited from the preseason MRI. The intense edema noted in his fifth metatarsal was diagnostic of a stress reaction, a likely precursor to a stress fracture, particularly in this injury-susceptible location. Treatment with shock attenuation (different shoe) and an orthotic immediately after diagnosis on MRI more than likely altered the outcome for this individual. The usual course of treatment for a stress fracture of the fifth metatarsal is compression screw fixation, and the athlete watches his season from the bench. The early intervention in this case allowed treatment to begin with the use of a unique orthotic to unload the stress across the fifth metatarsal. When symptoms developed during practice, the player was already being treated with a stress-unloading device. The addition of the sonographic treatment led to complete healing clinically and no loss of time from competition. Although edema may be seen as a response to altered mechanics, all three players went on to experience symptoms shortly after MRI. The metatarsals are particularly susceptible to the development of stress fractures in jumping athletes. Marrow signal abnormalities in this location should be considered ominous and an indicator of a potential impending injury.
This study illustrated the utility of MRI in preventive medicine—in this case, in elite athletes. Limitations of this study included the small number of players enrolled and the small number of players with positive findings. Though the number of players with positive findings was small, that number was in keeping with the usual prevalence of this entity [3]. At Duke University, on average one elite basketball athlete every 2 years is prevented from playing because of this injury. Because of the ability to show anatomic and physiologic information, MRI is the ideal imaging technique for assessing suspected injury to osseous tissues. MRI in the three players presented had a role in diagnosis and affected the treatment of two of the players. In the third player, the diagnosis was made with MRI but the stress fracture occurred before treatment began. Numerous articles have described the utility of MRI for detecting bone marrow, but the literature has not, to my knowledge, discussed MRI as a useful technique in injury prevention. The placement of orthotics and the use of follow-up sonographic therapy will likely be the future mode of treatment for these injuries if their diagnosis is timely.
Although the numbers in this evaluation were small, it revealed that MRI has a role in identifying stress changes in the metatarsals, as shown in three of the 26 players, and that early diagnosis can alter treatment and outcome, as shown in two players. The third player did not receive treatment and sustained a stress fracture. The physicians at my institution will use regular screening.
Acknowledgments
The author thanks Kenny King for his assistance with this study.
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