A little over a week ago I published a post that addressed some potential causes of metatarsal stress fractures in new barefoot and minimalist runners. That post, by Dr. Casey Kerrigan, got quite a response, so I wanted to follow up with an additional post by a running radiologist by the name of Dr. Andrew Lischuk.
Andrew currently holds the position of Assistant Professor in the field of musculoskeletal radiology at Yale-New Haven Hospital. He did his radiology residency training at Robert Wood Johnson University Hospital in New Jersey, and was fellowship trained in musculoskeletal radiology at Yale-New Haven hospital. He has been an attending radiologist for two years now. In addition to also being a doctor and runner, Andrew let me know that he’s most proud of being a devoted husband to his wife Kim, a dermatologist by trade who keeps him lathered up in sunscreen, and a dad to the best four year old on the planet, Reese!
I asked Andrew if he would share some thoughts on metatarsal stress fractures from the point of view of a radiologist, as he sees more than his fair share of fractures in his line of work. In particular, I asked him if he could address the topic of bone remodeling, or how bones react in response to stress. I hope you find what Andrew has to say both interesting and informative!
Metatarsal Stress Fractures: Thoughts From a Radiologist
For the past thirty years the incidence of metatarsal stress fractures has remained at or about 16% of all stress fractures ( Queen et.al. 2009). Numerous studies have been done over the last few decades looking at the factors involved in the development of stress fractures and how we approach them. In the process of replying to several of the responses I read on the previous Runblogger post on stress fractures, I felt the need to do a little more research and so I did a Pub Med search and selected 22 articles to review which were based on the current literature regarding metatarsal stress fractures. I spent the better half of an entire long weekend reviewing the science behind ground reaction forces, force plate analysis, different footwear (racing flats vs. trainers), case studies claiming the incidence of stress fractures in newer minimalist footwear and the such. My conclusions: I am left with more questions than when I started.
Science is a challenging field. We are taught the scientific method from an early age. Formulate a hypothesis, test the hypothesis, and determine its validity. The literature is full of hypotheses, tested and untested. Ideas are examined and re-examined, papers written and revisited. It reminds me of the long standing argument over butter vs. margarine. Growing up we ate butter, then it was deemed unhealthy, so margarine became the new butter. Lo and behold we discovered trans fats, and suddenly we are back to butter. Suffice it to say, any argument or any hypothesis will be tested and retested and a counter argument can be made.
Keeping the above in mind, let’s get into the details. It is true that second metatarsal stress fractures are more common amongst runners, with third and fifth metatarsals occurring at a lower rate. Interestingly the stress fractures of the second metatarsal in runners tend to be distal as opposed to proximal which was described in ballet dancer (en pointe dancers specifically), suggesting that the latter is due more to compressive axial forces or axial and shearing forces as opposed to bending forces. I would agree with Dr. Kerrigan that the forces across the metatarsals are greatest at mid to late stance and it is the combination of these forces, along with muscle fatigue involving the intrinsic foot muscles, that eventually leads to stress fractures in the metatarsals. I have not come across any articles describing the frequency of stress fractures occurring on either the compressive (dorsal) or tension (plantar) aspect of the foot. When looking at stress fractures at other sites in the body there is a wide range of occurrence on both tension and compression sides of the bone. For instance, a common femoral neck stress fracture is seen in the calcar region, that is the inferior femoral neck or the compression side, although I have seen several cases on the tension side as well. Bones themselves tend to be stronger in compression (pushing together) than in tension (pulling apart), but it is unclear whether they will tend to fail in compression vs. tension when subjected to submaximal forces repeatedly. I would surmise that failure can occur on either aspect based on my experience. As for the metatarsal, I have seen both tension and non tension (medial and lateral) stress fracture lines.
As for bone remodeling in response to applied stress, it will occur according to Wolff’s law, that bone remodels according to the location of lines of stress. We see this at the femoral neck most apparently as one can radiographically visualize the curving lines of the trabeculae (little bony plates that make up the inner spongy bone) aligning to support the weight of the body. In one of the articles I read below, differences were seen between runners and soccer players, with soccer players having greater cross sectional diameter of the metatarsals. A suggested reason for this observation was that the bones were subjected to more forward, backward, and side to side motion as opposed to the continually straight ahead motion found in runners.
As for bone remodeling, this is a dynamic process dependent on the interplay between osteoblasts and osteoclasts (cells that respectively build and break down bone). From an imaging standpoint, osteoblastic response to injury can be seen as early as two weeks from onset of injury – with an MRI this can be seen as intramedullary edema (swelling inside the bony shaft, typically called a stress reaction) even before a stress fracture line is visible. It is important to note however that the laying down of new bone in response to stress is disorganized and that a delicate interplay exists between osteoblasts (bone building cells) and osteoclasts (bone removing cells) during the healing process. This interplay eventually allows for the most optimal healing to occur according to the load placed on the affected bone. This balance between osteoblast and osteoclast activity is disrupted with a stress fracture and repeated loading, thus the osteoclast wins out and the bone weakens thus leading to the fracture. Once this point is reached, the bone requires immobilization for optimal healing. All of the literature I’ve come across describes a rest period of approximately 6 to 8 weeks in adults, with shorter periods for children and adolescents. Also, all of the literature recommends a return to activity in a graded fashion to avoid re-injury. There is no description of a window at which point you would risk greater injury because that is variable amongst different individuals. For instance, my body is sore and my bones ache after a 9 mile long run this weekend, to the point that I know I risk injury by running the day after. Dean Karnazes goes out and runs 40 miles today and can do another 40 tomorrow. He’s just different, and so is his body.
There a multitude of suggested risk factors for the development of stress fractures. These include and are not limited to female sex, lower bone mineral density, smoking, malnutrition, poor training habits, being overweight or underweight (probably an aspect of nutrition), shoe wear (although the article that mentioned this as a risk factor did not articulate as to what type of shoe wear), and even a tight Achilles which may play a role in the angle of the metatarsals at push off, which can subject them to increased stresses. One interesting thing, and I have no way to prove it at this time, is that bone mineralization in consistently shod individuals will likely be less in the involved extremity than in the non-shod individual. I base this upon my experience in evaluating the x-rays of individuals who have been casted for any period of time or who have had surgery which resulted in non-weight bearing in an extremity. The trabecular bone density decreases dramatically in those injured or non weight bearing. Now a cast is an extreme example of a “shod” individual, but I firmly believe that the bones in the foot adapt over time to being chronically shod vs. unshod. When I get some good imaging examples I will be sure to share them as I am beginning to collect a series of images of running related injuries evaluated using radiologic technology.
There is certainly a great deal of information out there regarding these injuries. I am concerned that the recent study on stress fractures and Vibram Fivefingers footwear (Giuliani et al., 2011) stepped out so far as to suggest that it was due to the footwear since stress fractures have been around since the dawn of time and the research in runners from as far back as 1978 has shown the same frequency, and I can assure you Vibram was not around back then to take the blame. I am, however, also certain that stress fractures will occur in individuals wearing minimalist footwear and that they could be avoided by appropriately training so as not to disrupt the balance between osteoclast and osteoblast activity in the wrong direction.
Thanks for reading.
Andrew W. Lischuk, MD
Articles on Stress Fractures
1. Brockwell J, Yeung Y, Griffith JF. Stress fractures of the foot and ankle. Sports Med Arthrosc. 2009;17(3):149-59.
2. Carmont MR, Patrick JH, Cassar-Pullicino VN, Postans NJ, Hay SM. Sequential metatarsal fatigue fractures secondary to abnormal foot biomechanics. Mil Med. 2006;171(4):292-7.
3. Chuckpaiwong B, Cook C, Pietrobon R, Nunley JA. Second metatarsal stress fracture in sport: comparative risk factors between proximal and non-proximal locations. Br J Sports Med. 2007;41(8):510-4.
4. Drakonaki EE, Garbi A. Metatarsal stress fracture diagnosed with high-resolution sonography. J Ultrasound Med. 2010;29(3):473-6.
5. Edwards MR, Jack C, Jones GG, Singh SK. Post-operative stress fractures complicating surgery for painful forefoot conditions. Foot (Edinb). 2010;20(2-3):49-51.
6. Finestone A, Milgrom C, Wolf O, Petrov K, Evans R, Moran D. Epidemiology of metatarsal stress fractures versus tibial and femoral stress fractures during elite training. Foot Ankle Int. 2011;32(1):16-20.
7. Fredericson M, Jennings F, Beaulieu C, Matheson GO. Stress fractures in athletes. Top Magn Reson Imaging. 2006;17(5):309-25.
8. Gehrmann RM, Renard RL. Current concepts review: Stress fractures of the foot. Foot Ankle Int. 2006;27(9):750-7.
9. Giuliani J, Masini B, Alitz C, Owens BD. Barefoot-simulating Footwear Associated With Metatarsal Stress Injury in 2 Runners. Orthopedics. 2011;34(7):e320-3.
10. Goud A, Khurana B, Chiodo C, Weissman BN. Women’s Musculoskeletal Foot Conditions Exacerbated by Shoe Wear:An Imaging Perspective. Am J Orthop (Belle Mead NJ). 2011;40(4):183-91.
11. Gu YD, Ren XJ, Li JS, Lake MJ, Zhang QY, Zeng YJ. Computer simulation of stress distribution in the metatarsals at different inversion landing angles using the finite element method. Int Orthop. 2010;34(5):669-76.
12. Hetsroni I, Nyska M, Ben-Sira D, et al. Analysis of foot structure in athletes sustaining proximal fifth metatarsal stress fracture. Foot Ankle Int. 2010;31(3):203-11.
13. Laker SR, Saint-Phard D, Tyburski M, Van Dorsten B. Stress fractures in elite cross-country athletes. Orthopedics. 2007;30(4):313-5.
14. Logan K. Stress fractures in the adolescent athlete. Pediatr Ann. 2007;36(11):738-9, 42, 44-5.
15. Meardon SA, Edwards B, Ward E, Derrick TR. Effects of custom and semi-custom foot orthotics on second metatarsal bone strain during dynamic gait simulation. Foot Ankle Int. 2009;30(10):998-1004.
16. Niva MH, Sormaala MJ, Kiuru MJ, Haataja R, Ahovuo JA, Pihlajamaki HK. Bone stress injuries of the ankle and foot: an 86-month magnetic resonance imaging-based study of physically active young adults. Am J Sports Med. 2007;35(4):643-9.
17. Queen RM, Abbey AN, Chuckpaiwong B, Nunley JA. Plantar loading comparisons between women with a history of second metatarsal stress fractures and normal controls. Am J Sports Med. 2009;37(2):390-5.
18. Queen RM, Mall NA, Nunley JA, Chuckpaiwong B. Differences in plantar loading between flat and normal feet during different athletic tasks. Gait Posture. 2009;29(4):582-6.
19. Umans HR. Imaging sports medicine injuries of the foot and toes. Clin Sports Med. 2006;25(4):763-80.
20. Wall J, Feller JF. Imaging of stress fractures in runners. Clin Sports Med. 2006;25(4):781-802.
21. Wiegerinck JI, Boyd J, Yoder JC, Abbey AN, Nunley JA, Queen RM. Differences in plantar loading between training shoes and racing flats at a self-selected running speed. Gait Posture. 2009;29(3):514-9.
22. Zadpoor AA, Nikooyan AA. The relationship between lower-extremity stress fractures and the ground reaction force: a systematic review. Clin Biomech (Bristol, Avon). 2011;26(1):23-8.