What's the Latest Research... Bone Stress Injuries in Runners Using Carbon Fiber Plate Footwear

A study titled "Bone Stress Injuries in Runners Using Carbon Fiber Plate Footwear" by Tenforde et al. (2023) is a Current Opinion article based on a case series of five navicular bone stress injuries in highly competitive running athletes. Before we get into things, I should mention case studies are not a strong form of evidence due to the sample size only being 1 person and there is no control to compare this person against. That is why Randomised Control Trials (RCT's) are considered one of the higher quality forms of evidence.

The article states its 3 intentions:

1. "to raise awareness on possible health concerns around the use of carbon fiber plate footwear"

2. "to suggest a slow gradual transition from habitual to carbon fiber plate footwear"

3. "to foster medical research related to carbon fiber plate technology and injuries."

On May 6th, 2017, in Monza, Italy, Eliud Kipchoge nearly broke the 2 hour marathon barrier. A big part of his campaign was wearing the carbon plated Nike Vaporfly prototypes. Kipchoge failed on the first attempt, but succeeded in Vienna, Austria, on October 12, 2019

running a time of 1:59:40 , by this point the Nike Vaporfly and many other carbon plated shoes had been released publicly with every level of runner needing to get a pair and improve their PB's by 4%.

Running in Carbon plated shoes has found to change your running mechanics compared to running in the traditional running shoe. A longer stride length and decreased cadence has resulted in an increase in ground reaction forces going into the foot when running. It has also been suggested that the carbon plate may reduce force/energy transfer to the ankle joint and muscles and cause the forces to be condensed to the anterior foot.

A bone stress injury (BSI) is an overuse injury where the bone has undergone too much localized cumulative stress resulting in a 'stress response' where the bone can become inflamed and painful. This can progress to the development of stress fracture if the forces continue until the bone can no longer heal itself quickly enough. The Navicular bone is a bone on the inside of the midfoot and can take a lot of sheer forces during running. Because of the high sheer forces alongside its limited blood supply, Navicular BSIs are classified as a high-risk location. Some of these injuries may not effectively heal with non-surgical measures, again, due to the reduced blood supply.

The article contains 4 case studies which may suggest there could be an increase in injury risk with carbon plated shoes.

1. The Male Junior Elite Steeplechase Runner

A 17-year-old elite steeplechase runner used carbon fiber plated (CFP) shoes for track intervals before a race. After a 3000 m steeplechase, he experienced severe midfoot pain. Initial radiographs showed no issues, but persistent pain led to a diagnosis of a navicular stress fracture. Despite a weight-bearing CT confirming a Type III fracture without consolidation. His medical team allowed a gradual return to running without pain, even though the fracture line persisted on follow-up CT scans. He had been training in various types of carbon plated shoes for 2 years.

2. The Female Junior Elite Middle-Distance Runner

A 17-year-old elite middle-distance runner, using CPF shoes exclusively for track intervals, developed midfoot pain. She had a history of a navicular bone stress injury (BSI) in the same foot treated conservatively two years ago. Evaluation revealed bilateral pes planovalgus (flat feet). An MRI showed a navicular bone stress reaction. Initially, she underwent 6 weeks of non-weightbearing in an AirCast, followed by 2 more weeks due to persistent stress reaction. After a total of 8 weeks of non-weightbearing, she resumed training on an Alter-G treadmill, gradually increasing to normal, pain-free training 15 weeks post-diagnosis.

3. The Female Elite 3000 m Steeplechase Runner

An 18-year-old elite steeplechase runner raced in new CPF shoes during a 10 km road race, leading to forefoot pain and swelling. Ignoring the initial discomfort, she continued running, resulting in twisted ankle injury. She then sought medical advise which revealed navicular stress fracture (Type III). After 4 weeks of non-weightbearing in a walker, followed by strength exercises and cross-training, she returned to running pain-free seven weeks post-CT confirmation of the fracture.

4. The Elite Triathlete Who Raced In Unused CFP Shoes

A 38-year-old elite triathlete who raced in unused CFP shoes during a half-marathon, leading to midfoot pain and post-race discomfort and throbbing. With a history of navicular stress injuries in both feet, a CT scan revealed a Type II navicular bone stress injury (BSI). The patient underwent successful healing after open reduction and internal fixation surgery.

5. The Elite Triathlete Training For A Marathon

A 36-year-old elite triathlete, preparing for a marathon, developed midfoot pain after a 22-mile run in relatively new CFP shoes. Despite no prior history of navicular bone stress injuries, a CT scan ruled out a fracture, but diagnosed a navicular BSI ("stress reaction"). Treatment involved a below-knee boot,and some pain relief therapy in the form of shockwave and and electromagnetic transduction therapy (which probably wasn't necessary). After becoming pain-free, he transitioned to cross-training, then resumed running on an anti-gravity treadmill. He ran the marathon pain-free, starting land training about 12 days before the race.

As mentioned before these case studies are not hard evidence that using CFP footwear can increase your risk of getting a navicular stress fracture, but it is certainly something to consider in your training. I am hoping this article will lead to an RCT to clarify whether wearing CFP footwear can increase the risk.

A prior study stated that the time to reach an accurate diagnosis for navicular stress

injuries is almost 9 months (Saxena et al. 2000), and as you can see from the case studies many people require cast/boot for 6-8 weeks. it is vital this injury is detected early in runners to reduce the time out of training and also reduce the risk of further injury and the need for more intrusive measures such as immobilisation or even surgery in rare cases.

James McMurray

Sport and Exercise Health Sciences BSc

Physiotherapy BSc

References:

Tenforde, A., Hoenig, T., Saxena, A., & Hollander, K. (2023). Bone Stress Injuries in Runners Using Carbon Fiber Plate Footwear. Sports medicine (Auckland, N.Z.), 53(8), 1499–1505. https://doi.org/10.1007/s40279-023-01818-z

Saxena A, Fullem B, Hannaford D. Results of treatment of 22

navicular stress fractures and a new proposed radiographic clas-

sifcation system. J Foot Ankle Surg. 2000;39(2):96–103.