A stress fracture in even the smallest metatarsal bone can be a big problem, particularly for an athlete. Research suggests that male gender, athletic task, foot type, and shoe design may all contribute to loading on the lateral aspect of the forefoot, increasing injury risk.

by Robin M. Queen, PhD, and James A. Nunley II, MD

Stress fractures are thought to be a result of repetitive overuse of bone.¹ Most believe that stress fractures occur during times of increased activity or repetitive loading in which bone remodeling is not occurring as quickly as breakdown resulting in microfractures.^{1- 3} Many risk factors for stress fracture development have been identified including gender,^4,5 lower extremity alignment,^6-10 bone density and hormonal factors,^11-14 as well as training errors and improper footwear.^15-17 Some of the risk factors for stress fracture development have been examined using plantar pressure measurements.

Stress fractures are fairly common in sports, accounting for approximately 10% of all overuse injuries.¹⁸ The incidence of stress fractures is dependent on both the location of the stress fracture, gender, and the sport. Women tend to suffer between 1.5 and 12 times more stress fractures than men^4,19,20 This large difference in stress fracture incidence has been reported most often in the military literature, while the gender disparity does not appear to be as large in athletic populations.^8,19 Iwamoto and Takeda’s summary of stress fractures²¹ reported that the injury was most most common in athletes between the ages of 15 and 19 (42.9% of reported stress fractures) and between the ages of 20 and 24 years old (34.7%), which corresponds to the time when athletes are playing at their highest intensity—at the end of high school and during college.²¹

The incidence of stress fracture by anatomic location has been reported to be influenced by the sporting activity. For sports such as baseball and rowing, stress fractures are more common in the ribs, where as during sports such as soccer, basketball, and track and field, stress fractures are more common in the tibial shaft and the metatarsals.²¹ Independent of the sport being played, stress fractures are more common in the lower extremities and feet than in the upper extremities. Lower extremity stress fractures have been reported to represent between 61.2% and 97% of all stress fractures.^8,21,22 When examined by anatomic location, women have been reported to have more tibial stress fractures (51.43% of all stress fractures) and more metatarsal stress fractures (10.29%) when compared to the men (46.2% and 6.09%, respectively).⁸ Men, however, have been reported to have a higher rate of tarsal fractures (32.4%) when compared with women (19.4%).

As stated, stress fractures are most frequent in the tibia and the metatarsals, with the tibia being the most common site of injury.^2,19 Metatarsal stress fractures have been reported to account for up to 25% of all stress fractures in the foot. Fifth metatarsal stress fracture is a transverse diaphyseal fracture and can be defined as either a Jones fracture, which occurs at the diaphyseal-metaphyseal junction without extending into the metatarsocubiod joint, or a proximal diaphyseal stress fracture.^23-25

Both surgical and non-surgical management of fifth metatarsal stress fractures have been advocated. Treatments of fifth metatarsal stress fractures have varying degrees of success, but the literature is clear that fifth metatarsal stress fractures are difficult to heal, especially if they are distal to the tuberosity.^26-32 Regardless of treatment, fifth metatarsal stress fractures frequently result in delayed union, non-union or refracture requiring extended time away from sport.^{25,27,28,31,33-36} When a patient elects non-operative treatment and has a delayed union or nonunion, then elects surgical intervention, the time loss would be a minimum of five months, which for most athletes is too much time away from their sport^26,30 and for many could be a season-ending situation.

While there are few studies with large numbers of patients sustaining a fifth metatarsal stress fracture, it is clear from the limited number of reports that men are more likely to sustain a fifth metatarsal stress fracture than women. In a previously published case series of 23 fifth metatarsal stress fractures, only six of the stress fractures were reported in women.37 With the high incidence of delayed union, nonunion and refracture in these patients, it is important to improve our understanding of the potential risk factors for the development of the fracture in an attempt to develop protocols and guidelines to prevent fifth metatarsal injury. Therefore, the purpose of this report is to examine the currently available literature on fifth metatarsal stress fracture injury risk factors as they relate to plantar loading.

Influence of athletic task on plantar loading

The location of various stress fractures has been linked to the type of sport being played at the time of injury. Therefore, the tasks that are being performed as well as the surface on which the athlete is playing could both influence injury risk. As previously stated, men appear to be at greater risk for the development of fifth metatarsal stress fractures, based on the literature³⁷ as well as clinical practice. In addition to men being at increased risk, fifth metatarsal stress fractures appear to be more common in cleated sports, such as soccer and lacrosse,³⁸ as well as basketball.³⁹

Previous studies have examined the effect of walking speed^40,41 and playing surfaces^42-44 on plantar loading. Increased walking speed has been reported to increase plantar loading, indicating that as people begin to move faster, there will be greater loading on the bones in the foot.^40,41 It appears, however, that each foot region has a unique response to changes in walking speed; with increased walking speed, the pressure beneath the lateral forefoot decreases, while the pressure beneath the heel and hallux increases.⁴¹

In terms of playing surface, studies of fifth metatarsal stress fractures have focused on the differences between natural grass vs. synthetic turf surfaces and natural grass vs. red cinder during cleated sport activities.^43,44 Eils et al⁴³ examined the differences in plantar loading between natural grass and red cinder and found no statistically significant differences in loading between the two surfaces. Ford and co-workers⁴⁴ examined changes in plantar loading during cutting on a natural grass and a synthetic playing surface with a rubber or sand infill. In contrast to the work of Eils, the Ford group found a significant increase in peak pressure beneath the lateral midfoot during the grass condition.⁴⁴ For most of the plantar loading studies, the focus for fifth metatarsal stress fractures will be the loading beneath the lateral midfoot and lateral forefoot due to the proximity to the fifth metatarsal. Although Ford found a significant increase in the peak pressure in the lateral midfoot on natural grass, it is not clear whether this increase could lead to the development of stress fractures,⁴⁴ but does indicate that, potentially, athletes could have a decreased risk of fifth metatarsal injury when playing on a synthetic surface.

Very few studies have examined plantar loading during different athletic tasks. The current studies focus on changes in plantar loading during soccer-specific tasks such as cutting, kicking, and sprinting,^43,45,46 but each differs slightly in terms of the surfaces on which the athletes were tested as well as the tasks that were performed. The subjects of Wong et al⁴⁶ and Queen and co-workers⁴⁵ completed various tasks on a synthetic surface (FieldTurf; Montreal, Canada), whereas the study by Eils’ group⁴³ used both a natural grass surface and a red cinder surface. Each study examined a side cutting task and some form of a running task, although the running task in each study was completed at a different speed. These studies reported that during a 45^o side cutting task to either side, there is a significant increase in plantar loading beneath the medial column of the foot.^43,45,46 The increase in medial column loading also existed during a second side cutting task in which the subjects were asked to cut approximately 180^o to either side.⁴⁶ In contrast, during a cross-over cutting task, an increase in loading was seen beneath the lateral forefoot.⁴⁵ The loading beneath the plant foot during kicking was also examined and demonstrated a significant increase in plantar loading beneath the both lateral heel and the lateral midfoot.⁴³

It appears that the type of task being performed can significantly influence the area of the foot being loaded. In addition, the increased loading beneath the lateral column of the foot during kicking as well as during the cross-over cut task could indicate the importance of focusing on these two tasks when examining risk factors for the development of fifth metatarsal stress fractures. During soccer specifically, these two tasks are performed repetitively, however, during basketball only the cutting task would be of importance. Future work could focus on identifying specific tasks performed in basketball that might influence fifth metatarsal stress fracture injury risk

Influence of foot type on plantar loading

A consensus has not been reached regarding the effect of foot type or arch height on the incidence of foot and ankle injuries. Previous studies have reported that individuals with flat feet are at increased risk for the development of metatarsal stress fractures, and ankle sprains.^7,10,47,48 When specifically examining stress fracture injury risk, however, having a high arch has been associated with an increased risk for the development of femoral and tibial stress fractures, while a low arch has been associated with an increased risk of developing metatarsal stress fractures.¹⁰ In contrast, Giladi et al⁹ reported that having a low arch foot was protective against the development of stress fractures. Adding further to lack of consensus, Williams and colleagues⁴⁸ examined risk factors for running injuries and determined that runners with a high arch were at increased risk for developing fifth metatarsal stress fractures, while runners with a low arch were at increased risk for developing second and third metatarsal stress fractures. Then, there are other studies that have reported no association between foot type and lower extremity injury risk.^7,43

Changes in plantar loading patterns between subjects with varying foot types have been studied most often during walking. With no consensus on the definition of foot types, comparison across studies is difficult. Previous reports have determined that few differences in plantar loading during walking exist based on foot type.^49,50 When examining plantar loading changes during running based on foot type, however, it appears that there is an anterior shift in loading in subjects with a pes planus foot as well as a decrease in loading beneath the midfoot in pes cavus feet when compared with normal feet.^51,52 Finally, a significant increase in forefoot loading was reported in the pes cavus foot compared to the pes planus foot.⁵¹ One study by Chuckpaiwong et al⁵⁰ reported the differences in plantar loading during walking and running in subjects with a pes planus foot and those with a normal foot alignment. This study reported a significant increase in contact area and maximum force beneath the medial midfoot in subjects with a pes planus foot, along with a significant decrease in peak pressure and maximum force in the lateral forefoot independent of the task being completed.⁵⁰

Little work has been done to examine the changes in plantar loading based on foot type during demanding athletic tasks such as cutting and jumping. One study by Queen et al⁵³ examined the influence of foot type on plantar loading during a side cut, cross-over cut, shuttle run, and landing from a simulated lay-up (jump). The results of this study indicated that during sport specific tasks, foot type has a significant effect on plantar loading. During the side cut and landing tasks, subjects with a pes planus foot demonstrated a significant increase in total foot contact area when compared to subjects with a normal foot type, however, no differences existed when examining the maximum force or the contact time between the two foot types.⁵³ When examining the various foot regions, the subjects with a pes planus foot demonstrated a significant increase in contact area in the rearfoot, medial midfoot and lateral midfoot during the side cut task, while the force-time integral was also increased in the medial and lateral midfoot in the pes planus subjects during the side cut.⁵³ In addition, the maximum force was increased in the medial and lateral midfoot regions during the side cut task in patients with a pes planus foot.⁵³ During the cross-over cut, few differences existed based on foot type. When examining the remaining two tasks, landing from a simulated lay-up and the shuttle run, minor differences based on foot type existed in the medial midfoot region, with contact area and maximum force being higher in the pes planus subjects.⁵³

The current literature appears to support the idea that foot type does have some influence on plantar loading, but that the influence is dependent on the task being performed. It appears as though foot type plays a more pivotal role in plantar loading patterns as the speed and difficulty of the task are increased, such as moving from walking and running to cutting and jumping. Therefore, when examining the changes in plantar loading during various athletic tasks, it may be important to consider foot type and its influence as well as the task being performed.

Influence of gender on plantar loading

While previous literature has examined the effect of gender on injury incidence and has identified gender as a major risk factor in certain types of injuries, it may be surprising that little is known about the differences in plantar loading between men and women. Previous work has determined that foot structure and shape are different between men and women,^54,55 however, little has been done to determine whether these differences are associated with differences in foot loading during different athletic tasks.

During an examination of walking, men demonstrated a increase (although not statistically significant) in normalized contact area and peak pressure in the midfoot when compared to women.⁵⁶ None of the other variables analyzed were found to be different between genders during walking.⁵⁶ Sims et al⁵⁷ examined the differences in plantar loading during soccer specific tasks such as cutting and sprinting, whereas Queen et al⁵⁸ examined gender differences during running. During cross-over cutting tasks, which have been previously been reported to increase loading beneath the lateral column,⁴⁵ men demonstrated a significant increase in force-time integral and maximum force in the lateral forefoot, and force-time integral beneath the lateral midfoot when compared to women.⁵⁷ Neither the side-cut nor acceleration tasks demonstrated significant differences in plantar loading beneath the lateral column of the foot.⁵⁷ During running, however, men demonstrated a significant increase in maximum force beneath the lateral forefoot, medial midfoot and medial forefoot when compared to women.⁵⁸

The gender differences that have been reported during sport specific tasks such as running and cutting indicate that men experience an increase in load beneath the lateral portion of the foot in the region of the fifth metatarsal. This increase in load could indicate men complete these sport specific tasks by using different mechanics than women, which results in increased loading. These results, in combination with the fact that men appear to sustain an increased number of fifth metatarsal stress fractures, indicate the importance of gender when examining the effect of plantar loading on injury risk factors.

Influence of shoe design on plantar loading

While intrinsic factors such as foot type and gender have been shown to influence plantar loading, it is also important to consider the role of footwear. Previous studies that have examined changes in plantar loading based on shoe design have focused on a range of topics, from clinical populations such as patients with diabetes^59,60 and women with foot pain⁶¹ to differences in military boot design ⁶² and medical walking boots.⁶³ Few studies have examined changes in plantar loading in different sport specific footwear.^{64- 66}

A study of changes in plantar loading in running shoes by Wiegerinck et al⁶⁶ indicated that peak pressure is increased in the lateral midfoot; medial, middle and lateral forefoot; and beneath the hallux and lesser toes when running in a racing flat (which has decreased cushioning properties) compared with a traditional training shoe. In addition, they demonstrated a significant increase in the maximum force beneath the lateral forefoot, hallux and the lesser toes when running in a racing flat. These results suggest that there is an inverse relationship between shoe cushioning and loading beneath the lateral forefoot.

The examination of shoes other than running shoes has been limited at this point to cleated shoes.^64,65 Santos et al⁶⁵ examined the differences in plantar loading between a soccer shoe and a training shoe. Unfortunately, limited information was given to explain the differences in footwear construction between these two shoes. The results of the study indicate that there is an increase in contact area beneath the foot when walking in the training shoe compared to the soccer shoe. However, maximum force and peak pressure were both increased in the soccer shoe compared to the training shoe. The different regions of the foot were not compared between the two shoe conditions.

Queen et al⁶⁴ examined the differences in plantar loading between four different soccer cleat designs (Bladed, Firm Ground, Hard Ground, and Turf) to determine if cleat placement or cleat design influenced plantar loading in the forefoot during a side-cut and cross-over cut task. It was clear from previous studies that the cross-over cut task for the men was the most problematic in terms of loading beneath the lateral portion of the foot.^45,57 The cleat study included both men and women, but because of the aforementioned gender differences, the results for men are most clinically relevant. When comparing the plantar loading between different cleat types during the cross-over cut task for the men, the Turf cleat demonstrated a significant decrease in the force-time integral in the lateral forefoot when compared to the other three cleat types, but there were no differences between the other cleat types. In addition, the force-time integral was significantly decreased in the turf shoe when compared with the bladed cleat. The results of this study are similar to those by Wiegerinck et al, which reported that with increased cushioning there was a decrease in loading beneath the lateral portion of the foot.^64,66 The Turf cleat that was tested in the study by Queen et al featured additional midsole cushioning that was not present in the rest of the cleated conditions.

Footwear appears to play a role in changing the loading beneath the foot, but it is unclear what the effect of changing specific cushioning parameters would be on plantar loading. Future work examining the effect of changes in midsole density on plantar loading could be important in determining an optimal shoe design for the prevention of fifth metatarsal stress fractures, as well as for returning to play following injury.

Conclusions

When examining plantar loading and the potential for identifying risk factors for fifth metatarsal stress fractures, it appears that gender, athletic task, foot type, and shoe design may all play a role. The literature indicates that, independent of the task being performed (running or cutting), men demonstrate an increase in plantar loading beneath the lateral aspect of the foot. This increased loading in men could be one possible explanation for the increased incidence of fifth metatarsal stress fractures. Based on the current literature, it appears that the cross-over cutting task during soccer results in the greatest loading beneath the lateral portion of the foot, but no information exists examining the effect of various basketball specific tasks. Therefore, future work should address plantar loading during basketball specific tasks, as well as examining the differences in basketball shoe construction that could influence loading and therefore injury risk. In addition, continued study of the effect of foot type on plantar loading during more dynamic tasks, as well as additional epidemiological studies, could improve our understanding of how foot type influences injury risk. Future work should focus on changes in plantar loading during sport specific tasks in cleated sports and basketball, specifically in men, in order to better understand how to prevent this injury and how to decrease the re-injury rate.

Robin M. Queen, PhD, is director of the Michael W. Krzyzewski Human Performance Lab and a medical instructor in the division of orthopaedic surgery at Duke University in Durham, NC. James A. Nunley II, MD, is the J. Leonard Goldner Professor in the department of surgery, division of orthopaedic surgery as well as the chief of orthopaedic surgery at Duke University School of Medicine.

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