Assessing The Structural And Biomechanical Causes Of Navicular Stress Fracture

In my last blog post, I wrote about a case of bilateral navicular stress fracture in a female track athlete. This month, I want to discuss some biomechanical background on why these types of navicular stress fractures seem to occur.

Gross and Nunley’s article on navicular stress fracture states that, “Typically, patients are running athletes, with one study of elite athletes showing that track and field athletes account for 59 percent of all navicular stress fractures.”¹ Mann and Pedowitz also state that these types of fractures are common in athletes who use explosive force in their activities.² These sports can include those that require jumping and sprinting, like track and field, ball sports, dance and ice skating. Many distance runners have these types of fractures as well, especially those that have a forefoot strike.² 

It has long been believed that the navicular has poor vascularity in the dorsal central region of the bone. However, Gross and Nunley question that finding as they reference a study that found normal vascular structures and function throughout the entire navicular.¹ 

The factors that lead to a navicular stress fracture seem to come primarily from both the bone’s shape and its position in the medial tarsal area of the foot. Both previously mentioned studies refer to the navicular as being “bent” in the sagittal plane and also having a convex shape between both the talus and the cuneiforms.^1,2 The insertion of the tibialis posterior has also been implicated in navicular stress fractures, mainly for its action in midstance as it pulls the medial aspect of the navicular into the talar head.^1,3,4 

In fact, Becker and colleagues implicate the posterior tibial tendon in conjunction with a high velocity of eversion in runners who had a history of navicular fracture.⁴ They hypothesize that the shear force from the tibialis posterior may be partly to blame due to one of its purposes being to control rearfoot eversion and the velocity of that eversion.⁴

Multiple authors have noted that limited ankle joint range of motion is a potential cause of navicular stress fractures along with a long second metatarsal and short first metatarsal. Increased subtalar joint pronation range of motion is implicated in these stress fractures as well as adducted and often cavus foot types. ^2,3,4 

Despite all these potential biomechanical and structural causes of a navicular stress fracture, only one source suggests that the medial prominence of the navicular or a navicular ossicle could also be a factor.⁵  As you can see from the picture below, if the talar head is encompassed by the navicular, then the forces in that area could be a potential cause of stress fracture as well. 

Regardless of the primary cause, it does seem that there are many potential structural and biomechanical causes of navicular stress fracture. Addressing these via orthotics could be a way to alleviate pain in the midfoot area that could become a navicular stress fracture. This is certainly is worth considering for post-fracture orthotic control as well.

References

1. Gross CE, Nunley JA 2^nd. Navicular stress fractures. Foot Ankle Int. 2015;36(9):1117-1122.
2. Mann JA, Pedowitz DI. Evaluation and treatment of navicular stress fractures, including nonunions, revision surgery and persistent pain after treatment. Foot Ankle Clin. 2009;14(2):187-204.
3. Vopat B, Beaulieu-Jones BR, Waryasz G. Epidemiology of navicular injury at the NFL combine and their impact on an athlete’s prospective NFL career. Orthop J Sports Med. 2017;5(8);232596711772328. doi: 10.1177/2325967117723285. Accessed August 16, 2019.
4. Becker J, James S, Osternig L, Chou L-S. Foot kinematics differ between runners with and without a history of navicular stress fractures. Orthop J Sports Med. 2018;6(4). doi: 10.1177/2325967118767363. Accessed August 5, 2019. 
5. Ingalls J, Wissman R. The os supranaviculare and navicular stress fractures. Skelet Radiol. 2011;40(7):937–941.