October 2019

Medial Tibial Stress Syndrome Remains a Challenge for Clinicians, Painful for Patients

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While most agree it is an overuse injury, treating MTSS (aka shin splints) should involve rest, proper diet, and sometimes avoiding NSAIDS.

By Cary Groner

It’s been decades since I had a case of shin splints, but I remember vividly how painful it was. I was 20 years old and overtraining—especially given the sorry state of my running shoes—and I felt as if I had a burning coal lodged along the medial side of my left shank. Every step hurt.

In those days, sports medicine was relatively primitive; I visited a doctor, but his best treatment suggestion was to run a hefty six-inch needle down through the length of the sore area and inject it at intervals with corticosteroids. I didn’t know much about shin splints, but I knew a crazy idea when I heard one, so I declined his offer and hightailed it out of there.

We now call this condition medial tibial stress syndrome, or MTSS, and the good news is that our understanding of it has improved significantly. The bad news is that treatment options, while no longer in the Dark Ages, are still far from optimal.

Defining Terms

MTSS is a common overuse injury consisting of exercise-induced pain over the anterior tibia; incidence runs as high as 20% in runners and up to 35% in military recruits, and it accounts for roughly 16% of all running injuries.1,2

The site of bony injury usually has an overlying periostitis (inflammation of the tissue around the bone) that correlates with the tendonous attachments of the soleus, flexor digitorum longus, and posterior tibialis. Cause and effect can be shaky, though; it isn’t clear whether the periostitis precedes cortical microtrauma or follows it.3 MTSS is usually stubborn, in any case, with recovery measured in months.4

Although overtraining is generally recognized as the primary cause of MTSS, other risk factors are still being elucidated. A 2013 meta-analysis, by researchers at the University of Canberra in Australia, reported that several factors appeared important including female gender, body mass index (BMI), fewer years of running experience, and navicular drop.5

Phillip Newman, PhD, that study’s lead author, told LER that he became interested in MTSS because as a military trainer his treatment outcomes for it were poor.

“It was frustrating,” he said. “I really wanted to identify the best evidence. The papers we reviewed investigated more than 70 risk factors, but only 8 or 9 ended up having a strong evidence base behind them.”

Newman, who is a clinical associate professor of physical therapy at the university’s Research Institute for Sport and Exercise, noted that although clarifying risk factors has been helpful, many of those (such as gender) aren’t easily modifiable. This elevates the importance of addressing aspects of those risks via training and therapy when possible. For example, women may be more prone to MTSS because of “female athlete triad”—high levels of physical activity that can lead to hormonal and menstrual disturbances.6,7

“Combine that with less than optimal nutrition, and musculoskeletal breakdown quickly follows,” Newman explained. “Lower body weight and BMI is one marker for that problem, and in that sense the syndrome can also occur in males.”

Risk factors such as BMI, that is, may not present in the obvious way. While overweight athletes increase their risk of MTSS due to the increased stress placed on bone and adjacent tissues, underweight ones do too.

“Women are probably more prone to the triad and the low energy availability that comes with it, but they also tend to be less muscular and more often hypermobile than men,” Newman pointed out. “That makes me wonder if their increased risk results from a combination of those factors.” Gender might not be easily modifiable, in other words, but an alert trainer would know when an athlete of either sex was taking in too few calories to balance hormones and repair or replace bone—and that’s an easier intervention to make.

Michael Chang, MD, an orthopedist in private practice in Los Angeles, agreed.

“The triad increases risk because the body can’t handle the exercise stress,” he said. “If you can’t remodel the bone to manage that, you’re more likely to have problems, including stress fractures.”

Newman’s findings in the 2013 paper were sometimes perplexing. For example, his team reported that although pronated foot structure was not ultimately a significant risk factor for MTSS, navicular drop was. Given that the latter is often considered a component of a pronated foot, this raised obvious questions.

“I don’t fully understand it,” Newman admitted. “Assessing pronation can be subjective, and involves a variety of measures including calcaneal angle, forefoot and rearfoot angles, arch height, and so on. Navicular drop, by contrast, is a simple, objective measure that may signify hypermobility as well as pronation. This may suggest that training the foot muscles is important in prevention and treatment of MTSS.”

More recent studies have reported that MTSS may be associated with passive range of motion, muscle strength, plantar pressure distributions, and gait kinematics;8 and with BMI, navicular drop, and some ranges of motion.2

Diagnostics

A better understanding of risk factors may help clinicians diagnose MTSS more readily, particularly given that imaging can’t easily identify the problem.9

Part of the diagnosis involves differentiating MTSS from other conditions that may present similarly, however, in which case imaging becomes useful. Care is required because although MTSS itself isn’t considered serious, those other problems—tibial stress fractures and exertional compartment syndrome—can be.

Clinicians can often tell the difference between MTSS and a stress fracture simply by location, Newman said. “Stress fractures are usually much more localized to the top half of the tibia, whereas MTSS is typically in a five-centimeter spread in the distal half.”

Chang noted that how the patient describes the problem is often a key to differential diagnosis.

“You ask them where it hurts and watch their response,” Chang said. “If they have MTSS, they usually rub their hand up and down the medial side of the tibia and say, ‘It hurts from here to here.’ If they have a stress fracture, they’ll point with their index finger and say, ‘It hurts right here.’ It’s very point-specific.” Chang likes to start with a plain x-ray, but will order an MRI if he suspects a fracture that isn’t visible on x-ray.

Compartment syndrome, by contrast, is a sudden-onset emergency that results when injury to a muscle causes so much edema that it cuts off circulation and the tissue begins to die.

“If you see the classic P’s—paresthesia, pulselessness, and pallor—and the anterior or lateral compartment is hard as a rock, they should go straight to the ER or to an orthopedist for treatment,” Chang said.

The Nature of the Beast

MTSS is frustrating to treat partly because no one knows exactly what sort of problem it is. Some experts think it occurs primarily in the bone due to the stresses placed on it; others suspect the periosteal tissues, since that’s often where most of the pain lies; still others propose the adjacent muscles and tendons as an initial source of weakness, from which the subsequent problems arise.1

“We still don’t know exactly what structure is the source of pain,” said Newman. “It could have something to do with the interface between muscle and bone in the lower tibia—how robust the bone and periosteal tissue is in an individual. Bone and muscle have a strong physiologic relationship—muscle signals to bone and vice versa—so when one of them is under stress, the other responds accordingly. When you have a site like that of MTSS, where muscle doesn’t directly attach to bone, it may be more susceptible to undetected load.”

Michael Gross, PT, PhD, a professor of physical therapy at the University of North Carolina, told LER that he suspects several causes for MTSS.

…clarifying risk factors has been helpful, [however] many, such as gender, aren’t easily modifiable. This elevates the importance of addressing aspects of those risks via training and therapy when possible.
Phillip Newman, PhD

“When you’ve got a condition that’s multifactorial, it’s difficult to draw a link between variable A and pathology B,” he acknowledged. “But the typical location of pain in MTSS suggests to me that it could be related to pronation, which can be driven by tibial varum, forefoot varus, and tight triceps surae. That in turn could lead to passive stretching of the tibialis posterior and tugging on the periosteum.”

Gross has seen enough patients with excessive curvature of the tibia in both the frontal and sagittal planes that he’s come to suspect that as a contributing cause of stress fractures. “Would that be associated with MTSS, though?” he asked. “It’s hard for me to buy into that story.”

The Continuum

Increasingly, researchers speculate that MTSS and tibial stress fractures may represent a continuum of injuries that share common sources. For example, several studies have proposed bone stress, a result of tibial bending and remodeling, as a likely cause of MTSS symptoms.5

“A lot of variables go into this,” said Chang. “Is there a continuum? We think there is. Can it be influenced? We really don’t know.”

Kenneth Cameron, PhD, MPH, ATC, is the director of orthopedic and sports medicine research at the U.S. Military Academy at West Point. He’s writing a position statement on MTSS for the National Athletic Trainers Association, and he too considers these conditions part of a whole.

“We have a lot of experience with MTSS in military populations, and I think these injuries do occur on a continuum,” he said. “That includes periostitis, probably caused by muscle forces on the bone, all the way up to stress fractures.”

For Newman, data to assess all this would include finite element models that better analyze where stresses occur in the running gait cycle. “That would help us understand loading patterns, how leg muscles absorb ground reaction forces, and so on,” he said.

As it happens, researchers at Victoria University in Melbourne, Australia, have recently undertaken a study that may help. Karen Mickle, PhD, a research fellow at the university’s Institute for Health and Sport, together with her PhD student Joshua Mattock of the University of Wollongong, hope to shed light on whether lower-leg muscle strength and morphology affect the type of tibial bending that leads to stress fractures and possibly to MTSS.10

“I’m a coach as well as a researcher, and I’m particularly interested in how foot- and leg-muscle weakness can contribute to injuries,” Mickle said. “We see MTSS a lot in our distance runners, and I’d like to keep them injury free.”

Mickle and her colleagues will study two groups of runners, both of which will receive the same initial assessments, including foot-posture index and cross-sectional thickness measures of the tibialis anterior, the peroneals, the soleus, the flexor digitorum longus, the flexor hallucis longus, and the gastrocs—as well as strength assessments of those muscles. The researchers will also assess subjects’ bone density via ultrasound, and measure kinematics, EMG, and plantar pressure during treadmill tests.

The first cohort comprises uninjured runners who will commit to 30K of running weekly for the next year (or until they’re injured); the second group will consist of runners who’ve been running at that level but have recently developed symptoms suggestive of MTSS. Mickle won’t ask them to keep up that training load, obviously, but she does want to assess them before they cut back, to remove the atrophy variable from the equation.

“We’re interested in how these muscles might be protecting the bone by absorbing ground reaction forces,” Mickle said. “We want to see, prospectively, how structure and function may differ in those who develop MTSS versus those who don’t.”

Although results won’t be available for a year, Mickle said, preliminary data suggest that subjects without MTSS have significantly stronger calves than those who do. However, subjects with MTSS had thicker gastrocs than those without it, even though overall calf girth was roughly the same. It seems paradoxical, but in fact it may not be.

“This may suggest some difference in those deeper plantar flexor muscles,” Mickle said. “I’d like to determine what role these muscles play, because that suggests an approach to rehab and training that could be tailored to the individual athlete with MTSS.”

Training and Rehab

Despite the ongoing uncertainties about the source of MTSS, physicians and trainers have achieved a rough consensus about how best to prevent it from occurring and treat it when it does.

“I think the most important is the training plan,” said Kenneth Cameron. “If you have a proper plan with progressive increases in distance and intensity, you’re much less likely to experience a tibial stress injury.”

For those who have been injured, rest is vital, he added. “Both rest and diet—avoiding energy deficiency—are really important. There’s also compelling evidence emerging that NSAIDs should not be used with bone stress injury, as they may inhibit healing.”11

Said Mike Gross, “Mainly you want to settle down the tissue using ice, and address overuse issues.  Get them to lose weight if they need to. Cycling is a good way for these patients to exercise, especially if you position the malleoli over the pedal so the plantar flexors get a rest.”

Michael Chang emphasized that in the case of MTSS, rest doesn’t mean all rest.

“Ideally, you want to identify the training error, then fall back to a lower level of activity to allow the healing process to occur,” he said. “You want to maintain some level of fitness while allowing the injury to heal—not based on time, but on symptoms.”

Cary Groner is a freelance writer based in the San Francisco Bay area.

REFERENCES
  1. Winters M. The diagnosis and management of medial tibial stress syndrome : an evidence update. Unfallchirurg. 2019.
  2. Winkelmann ZK, Anderson D, Games KE, Eberman LE. Risk factors for medial tibial stress syndrome in active individuals: an evidence-based review. J Athl Train. 2016;51(12):1049-1052.
  3. McClure C, Oh R. Medial Tibial Stress Syndrome. Treasure Island, FL: NCBI / StatPearls Publishing, 2019.
  4. Moen MH, Holtslag L, Bakker E, et al. The treatment of medial tibial stress syndrome in athletes; a randomized clinical trial. Sports Med Arthrosc Rehabil Ther Technol. 2012;4:12.
  5. Newman P, Witchalls J, Waddington G, Adams R. Risk factors associated with medial tibial stress syndrome in runners: a systematic review and meta-analysis. Open Access J Sports Med. 2013;4:229-241.
  6. Nazem TG, Ackerman KE. The female athlete triad. Sports Health. 2012;4(4):302-311.
  7. Mountjoy M, Sundgot-Borgen J, Burke L, et al. The IOC consensus statement: beyond the Female Athlete Triad–Relative Energy Deficiency in Sport (RED-S). Br J Sports Med. 2014;48(7):491-497.
  8. Becker J, Nakajima M, Wu WFW. Factors contributing to medial tibial stress syndrome in runners: a prospective study. Med Sci Sports Exerc. 2018;50(10):2092-2100.
  9. Winters M, Eskes M, Weir A, Moen MH, Backx FJ, Bakker EW. Treatment of medial tibial stress syndrome: a systematic review. Sports Med. 2013;43(12):1315-1333.
  10. Mattock J, Steele JR, Mickle KJ. A protocol to prospectively assess risk factors for medial tibial stress syndrome in distance runners. BMC Sports Sci Med Rehabil. 2018;10:20.9
  11. Hughes JM, McKinnon CJ, Taylor KM, et al. Nonsteroidal anti-inflammatory drug prescriptions are associated with increased stress fracture diagnosis in the US Army population. J Bone Miner Res. 2019;34(3):429-436.

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