Abstract
Stress-related changes and fractures in the foot are frequent in runners. However, the causative factors, including anatomic and kinematic variables, are not well defined. Footwear choice has also been implicated in contributing to injury patterns with changes in force transmission and gait analyses reported in the biomechanical literature. Despite the benefits of footwear, there has been increased interest among the running community in barefoot running with proposed benefits including a decreased rate of injury. We report 2 cases of metatarsal stress fracture in experienced runners whose only regimen change was the adoption of barefoot-simulating footwear. One was a 19-year-old runner who developed a second metatarsal stress reaction along the entire diaphysis. The second case was a 35-year-old ultra-marathon runner who developed a fracture in the second metatarsal diaphysis after 6 weeks of use of the same footwear. While both stress injuries healed without long-term effects, these injuries are alarming in that they occurred in experienced male runners without any other risk factors for stress injury to bone. The suspected cause for stress injury in these 2 patients is the change to barefoot-simulating footwear. Runners using these shoes should be cautioned on the potential need for gait alterations from a heel-strike to a midfoot-striking pattern, as well as cautioned on the symptoms of stress injury.Drs Giuliani, Masini, Alitz, and Owens are from Keller Army Hospital, West Point, New York.
Drs Giuliani, Masini, Alitz, and Owens have no relevant financial relationships to disclose.
The views and opinions expressed in this article are those of the authors and do not reflect the official policy of the Department of the Army, Department of Defense, or United States government.
Correspondence should be addressed to: Brett D. Owens, MD, Keller Army Hospital, 900 Washington Rd, West Point, NY 10996 (b.owens@us.army.mil).
Drs Giuliani, Masini, Alitz, and Owens have no relevant financial relationships to disclose.
The views and opinions expressed in this article are those of the authors and do not reflect the official policy of the Department of the Army, Department of Defense, or United States government.
Correspondence should be addressed to: Brett D. Owens, MD, Keller Army Hospital, 900 Washington Rd, West Point, NY 10996 (b.owens@us.army.mil).
Posted Online: July 07, 2011
Foot and ankle injuries associated with running, including stress-related changes and fractures, occur frequently. However, causative factors, including anatomic and kinematic variables, are not well-defined. 1 Footwear choice also has been implicated in contributing to injury patterns with changes in force transmission and gait analyses reported in the biomechanical literature. These studies also report conflicting data, particularly in the realm of the benefit of the padded cushioned heel, which typifies modern high-performance distance running shoes. 2–6
Despite the benefits of footwear, interest in barefoot running has increased among the running community, with proposed benefits including a decreased injury rate. Advocates tout the evolutionary success of man as a barefoot bipedal runner. There is also speculation that the development of modern footwear and the associated altered running gait patterns (including a hindfoot strike versus the forefoot or midfoot strike typical of unshod runners) have contributed to injuries seen in runners. However, there is little prospective data to support these claims.
As a response to the rising popularity of barefoot running, several product lines of barefoot-simulating footwear have been developed to allow the proposed benefits of barefoot running while providing protection to the sole from the environment and giving the flexibility and natural feel of barefoot running. Runners with longstanding hindfoot striking gait patterns who have transitioned to footwear developed for a forefoot or midfoot strike may be without specific training or practice in this altered running pattern. This scenario represents a possible risk for repetitive stress injury to the foot or ankle as there is a mismatch between the running style and the footwear design. This article presents 2 cases of experienced runners who sustained metatarsal stress injuries as the result of running in barefoot-simulating footwear.
The patient reported making no changes to his daily routine, mileage, or terrain. He noted pain with weight bearing, but he continued with full weight bearing and had a mildly antalgic gait.
Physical examination revealed no obvious deformity of the left foot; hindfoot alignment and ankle range of motion were normal with no evidence of tendo-Achilles tightness. Dorsomedial soft tissue swelling was noted over the second and third metatarsal shafts. There was no ecchymosis or crepitus; however, the patient had significant tenderness to palpation at the dorsal and plantar aspect of the second metatarsal.
Radiographs of the left foot demonstrated no signs of fracture or dislocation. Magnetic resonance imaging (MRI) was consistent with stress reaction of the entire second metatarsal with adjacent soft tissue edema (Figure ).
The patient was treated with crutch-assisted weight bearing until he no longer ambulated with an antalgic gait. He then was advised to avoid impact aerobics for an additional 8 to 10 weeks and to modify his activity to low-impact aerobic exercise.
The pain was associated with difficulty ambulating, and radiographs were interpreted as negative for fracture at that time. The patient was instructed to stop running and was referred to the orthopedic clinic for follow-up.
On presentation to the orthopedic clinic 1 month later, the patient was weight bearing with normal footwear and had a mild antalgic gait. Physical examination revealed no obvious deformity of the left foot; hindfoot alignment and ankle range of motion were normal with no evidence of tendo-Achilles tightness. Dorsal soft tissue swelling of the foot was noted. There was no ecchymosis in the area or crepitus to palpation; however, the patient had significant tenderness to palpation over the dorsal and plantar aspect of the second metatarsal shaft.
A repeat radiograph obtained at the clinic demonstrated a periosteal reaction and callus formation of the second metatarsal diaphysis, although no fracture lucency was visualized (Figure ). T2-weighted MRI of the foot demonstrated increased signal within the second metatarsal shaft consistent with stress fracture (Figure ). The patient was instructed to avoid impact aerobics for an additional 6 weeks and to modify his activity to low-impact aerobic exercise.
The resurgence in popularity of barefoot running as an alternative to the wearing of modern footwear has been based in part on the theory that there is reduced risk of injury; however, there is an absence of data supporting this. 8 The need for cushioned soles has been questioned with the launch of several product lines of footwear that simulate barefoot running while offering some protection to runners’ feet. Among these is the shoe that was worn by both patients in this case series. The purpose of this footwear is to facilitate the barefoot running experience while protecting the foot from modern-day elements such as pavement, broken glass, or other hazards that would be directly injurious.
Although the superiority of one footwear style over another is outside the scope of this article, it is relevant to discuss the possibility that there is an association with the transition from modern cushioned-heel footwear to barefoot-simulating footwear with the metatarsal stress injuries described in these 2 cases. Stress injuries to the metatarsals are common in the recreational running population and may be associated with changes in a training routine such as distance, intensity, or frequency. 1
Stress fractures in the foot are also common in military populations. March fracture is the name given to stress fractures of the second and third metatarsals commonly seen in military recruits after long marches. The second and third metatarsals are rigid while marching and are common sites of injury. The majority (75%) of march fractures occur in the distal or middle one-third of the metatarsal shaft. 9
The location of the fractures in our 2 cases was more proximal in the metatarsal shaft than the typical march fracture. Our patients had long-standing running routines prior to presenting with a metatarsal stress fracture in a location not commonly seen in overuse metatarsal stress fractures. For these 2 runners, a common factor appears to be the transition from a cushioned-heel modern running shoe to barefoot-simulating footwear.
The kinematics and biomechanics of shod and barefoot runners has been described in the literature. One notable difference between the 2 styles is the foot-strike pattern typical of each. In a landmark study, Lieberman et al 7 reported on these differences in a comparison of shod and unshod runners that included an evaluation of runners from the Rift Valley region of Africa who have never worn shoes. Runners who regularly wear or who have grown up wearing cushioned-heel footwear primarily have a hindfoot strike gait pattern. Lieberman et al 7 found that this strike persisted when these same runners were tested in an unshod condition. In runners who grew up barefoot running or who have transitioned to barefoot running, a forefoot or midfoot strike predominates. 7
Both of our patients grew up and typically trained wearing cushioned-heel footwear. They can be presumed to have a hindfoot strike typical of this general running population. 10 They also likely continued running with a hindfoot strike as they transitioned to barefoot-simulating footwear consistent with the findings of Lieberman et al. 7
The advantage of the forefoot strike gait in barefoot running is a flatter foot position at impact, which limits the local pressures underneath the heel. Barefoot runners typically adopt a gait pattern with shorter stride length and increased stride frequency. These adaptations facilitate the altered touchdown foot position. 11,12 They also serve to decrease the vertical forces transmitted to the limb, which may have further implications in injury prevention. 13 An additional advantage is gained with the finding of decreased energy expenditure in barefoot versus shod running. 14
In another study evaluating adaptations of stride mechanics in shod and unshod running trials on a treadmill, no in-trial limb position adaptations were noted in barefoot trials whereas shod runners made multiple adjustments in running mechanics during the course of the trial. 13 The authors postulated that this may be due to a natural state of barefoot running that needs no alteration to find the biomechanically efficient gait pattern. However, this also seems to be a risk factor predisposing a runner to repetitive stress injury.
With a transition to barefoot running from cushioned-heel footwear, Lieberman et al 7 described a persistence of a hindfoot strike gait. If a runner of this type does not make gait adaptations, as described by Divert et al, 13 there is potential for perpetuation of a gait that does not provide the efficiency and force reduction expected with barefoot running. An overuse stress injury is the predictable result and may be what was experienced by our 2 patients.
This article presents 2 runners who transitioned from a modern cushioned-heel running shoe to a barefoot-simulating shoe without alteration to their running routine or any specific gait training. Both runners developed a stress injury to their second metatarsal shaft. We propose that the alteration from a cushioned-heel shoe to barefoot-simulating footwear without specific gait training may have contributed to their injuries.
Despite the benefits of footwear, interest in barefoot running has increased among the running community, with proposed benefits including a decreased injury rate. Advocates tout the evolutionary success of man as a barefoot bipedal runner. There is also speculation that the development of modern footwear and the associated altered running gait patterns (including a hindfoot strike versus the forefoot or midfoot strike typical of unshod runners) have contributed to injuries seen in runners. However, there is little prospective data to support these claims.
As a response to the rising popularity of barefoot running, several product lines of barefoot-simulating footwear have been developed to allow the proposed benefits of barefoot running while providing protection to the sole from the environment and giving the flexibility and natural feel of barefoot running. Runners with longstanding hindfoot striking gait patterns who have transitioned to footwear developed for a forefoot or midfoot strike may be without specific training or practice in this altered running pattern. This scenario represents a possible risk for repetitive stress injury to the foot or ankle as there is a mismatch between the running style and the footwear design. This article presents 2 cases of experienced runners who sustained metatarsal stress injuries as the result of running in barefoot-simulating footwear.
Case Reports
Patient 1
A 19-year-old man who ran 3 to 4 times weekly for an average of 20 to 30 miles per week presented with left foot pain and dorsal swelling of 3 to 4 weeks’ duration. The onset of the pain correlated with new footwear (FiveFingers; Vibram, Concord, Massachusetts) the patient was wearing while running.The patient reported making no changes to his daily routine, mileage, or terrain. He noted pain with weight bearing, but he continued with full weight bearing and had a mildly antalgic gait.
Physical examination revealed no obvious deformity of the left foot; hindfoot alignment and ankle range of motion were normal with no evidence of tendo-Achilles tightness. Dorsomedial soft tissue swelling was noted over the second and third metatarsal shafts. There was no ecchymosis or crepitus; however, the patient had significant tenderness to palpation at the dorsal and plantar aspect of the second metatarsal.
Radiographs of the left foot demonstrated no signs of fracture or dislocation. Magnetic resonance imaging (MRI) was consistent with stress reaction of the entire second metatarsal with adjacent soft tissue edema (Figure ).
 | Figure 1:. T1-weighted axial fat-suppressed MRI of the left foot is consistent with stress reaction changes of the second metatarsal. |
Patient 2
A 35-year-old ultra-marathon runner who ran 3 to 4 times weekly for an average of 30 to 40 miles per week presented to the emergency department with sudden-onset left foot pain after running 3 miles. The patient reported making no changes to his training mileage, frequency, or terrain. The only recent change to his training was the incorporation of new footwear (FiveFingers) approximately 6 weeks prior to injury.The pain was associated with difficulty ambulating, and radiographs were interpreted as negative for fracture at that time. The patient was instructed to stop running and was referred to the orthopedic clinic for follow-up.
On presentation to the orthopedic clinic 1 month later, the patient was weight bearing with normal footwear and had a mild antalgic gait. Physical examination revealed no obvious deformity of the left foot; hindfoot alignment and ankle range of motion were normal with no evidence of tendo-Achilles tightness. Dorsal soft tissue swelling of the foot was noted. There was no ecchymosis in the area or crepitus to palpation; however, the patient had significant tenderness to palpation over the dorsal and plantar aspect of the second metatarsal shaft.
A repeat radiograph obtained at the clinic demonstrated a periosteal reaction and callus formation of the second metatarsal diaphysis, although no fracture lucency was visualized (Figure ). T2-weighted MRI of the foot demonstrated increased signal within the second metatarsal shaft consistent with stress fracture (Figure ). The patient was instructed to avoid impact aerobics for an additional 6 weeks and to modify his activity to low-impact aerobic exercise.
 | Figure 2:. AP radiograph of the left foot 1 month after injury shows evidence of a healing second metatarsal diaphysis stress fracture. |
 | Figure 3:. T2-weighted sagittal fat-suppressed MRI shows increased signal and cortical thickening consistent with stress fracture of the second metatarsal. |
Discussion
The transition to cushioned-heel running footwear is a relatively recent phenomenon, with the advent of the modern running shoe only dating to the 1970s. 7 Barefoot running is a modality that by anatomic study dates to early man, and the characteristic gait of native unshod runners has borne the test of time as a successful means of locomotion. 8The resurgence in popularity of barefoot running as an alternative to the wearing of modern footwear has been based in part on the theory that there is reduced risk of injury; however, there is an absence of data supporting this. 8 The need for cushioned soles has been questioned with the launch of several product lines of footwear that simulate barefoot running while offering some protection to runners’ feet. Among these is the shoe that was worn by both patients in this case series. The purpose of this footwear is to facilitate the barefoot running experience while protecting the foot from modern-day elements such as pavement, broken glass, or other hazards that would be directly injurious.
Although the superiority of one footwear style over another is outside the scope of this article, it is relevant to discuss the possibility that there is an association with the transition from modern cushioned-heel footwear to barefoot-simulating footwear with the metatarsal stress injuries described in these 2 cases. Stress injuries to the metatarsals are common in the recreational running population and may be associated with changes in a training routine such as distance, intensity, or frequency. 1
Stress fractures in the foot are also common in military populations. March fracture is the name given to stress fractures of the second and third metatarsals commonly seen in military recruits after long marches. The second and third metatarsals are rigid while marching and are common sites of injury. The majority (75%) of march fractures occur in the distal or middle one-third of the metatarsal shaft. 9
The location of the fractures in our 2 cases was more proximal in the metatarsal shaft than the typical march fracture. Our patients had long-standing running routines prior to presenting with a metatarsal stress fracture in a location not commonly seen in overuse metatarsal stress fractures. For these 2 runners, a common factor appears to be the transition from a cushioned-heel modern running shoe to barefoot-simulating footwear.
The kinematics and biomechanics of shod and barefoot runners has been described in the literature. One notable difference between the 2 styles is the foot-strike pattern typical of each. In a landmark study, Lieberman et al 7 reported on these differences in a comparison of shod and unshod runners that included an evaluation of runners from the Rift Valley region of Africa who have never worn shoes. Runners who regularly wear or who have grown up wearing cushioned-heel footwear primarily have a hindfoot strike gait pattern. Lieberman et al 7 found that this strike persisted when these same runners were tested in an unshod condition. In runners who grew up barefoot running or who have transitioned to barefoot running, a forefoot or midfoot strike predominates. 7
Both of our patients grew up and typically trained wearing cushioned-heel footwear. They can be presumed to have a hindfoot strike typical of this general running population. 10 They also likely continued running with a hindfoot strike as they transitioned to barefoot-simulating footwear consistent with the findings of Lieberman et al. 7
The advantage of the forefoot strike gait in barefoot running is a flatter foot position at impact, which limits the local pressures underneath the heel. Barefoot runners typically adopt a gait pattern with shorter stride length and increased stride frequency. These adaptations facilitate the altered touchdown foot position. 11,12 They also serve to decrease the vertical forces transmitted to the limb, which may have further implications in injury prevention. 13 An additional advantage is gained with the finding of decreased energy expenditure in barefoot versus shod running. 14
In another study evaluating adaptations of stride mechanics in shod and unshod running trials on a treadmill, no in-trial limb position adaptations were noted in barefoot trials whereas shod runners made multiple adjustments in running mechanics during the course of the trial. 13 The authors postulated that this may be due to a natural state of barefoot running that needs no alteration to find the biomechanically efficient gait pattern. However, this also seems to be a risk factor predisposing a runner to repetitive stress injury.
With a transition to barefoot running from cushioned-heel footwear, Lieberman et al 7 described a persistence of a hindfoot strike gait. If a runner of this type does not make gait adaptations, as described by Divert et al, 13 there is potential for perpetuation of a gait that does not provide the efficiency and force reduction expected with barefoot running. An overuse stress injury is the predictable result and may be what was experienced by our 2 patients.
This article presents 2 runners who transitioned from a modern cushioned-heel running shoe to a barefoot-simulating shoe without alteration to their running routine or any specific gait training. Both runners developed a stress injury to their second metatarsal shaft. We propose that the alteration from a cushioned-heel shoe to barefoot-simulating footwear without specific gait training may have contributed to their injuries.
