Target soleus related issues associated with medial tibial stress syndrome (MTSS) with the clinically trialled Solushin medical device
Let's meet the soleus
The soleus is a wide flat muscle found in the superficial posterior compartment of the leg. Located deeper (or anterior) to the gastrocnemius muscle heads, the soleus originates just posterior to the head of the fibula and at the mid-diaphysis of the medial border of the tibia before inserting into the calcaneus through the Achilles tendon.
A quick graphic highlighting the soleus muscle
The soleus is a strong plantar flexor that contributes to running, walking and jumping. Along with gastrocnemius and plantaris muscle (or maybe not, depending on who you talk to), the soleus forms the triceps surae.
When running, the soleus acts to propel the athlete forward, mainly through the final phase of propulsion, and act as a shock absorber. Dorn et al. (2012) demonstrated that, while the gastrocnemius might absorb 1-2 times body weight, the soleus undergoes up to 8 times body weight during running!
A quick recap of Medial Tibial Stress Syndrome
MTSS pain presents at the distal 1/3 of the posteromedial border of the tibia
Medial tibial stress syndrome (MTSS) is an overuse injury that affects 4-20% of the general population and has increased prevalence (35%) in athletes and military personnel.
MTSS is described as "pain felt along the middle or distal third of the posteromedial border of the tibia" (Yates et al., 2004). Furthermore, the pain is aggravated with a weight-bearing activity that gradually subsides upon completion of exercise. There is also palpable tenderness along the posteromedial tibial border of the tibia for at least 5cm in clinical examination.
While the pathophysiology is poorly understood and frequently debated, current evidence suggests that MTSS is either associated with myofascial traction or pain disorders, overloading of the tibia, or a combination of the two (Moen et al., 2009).
How is the soleus involved?
Muscle fibre traction via Sharpey's fibres is shown to result in tibial periostitis at the MTSS injury site (Franklyn et al., 2015). This was not the first time this was hypothesised or demonstrated in a study. In fact, as early as 1958 (Devas et al., 1958), the term "shin splints" was linked to a traction injury of the lower leg musculature. However, the traction theory was initially challenged based on the believed fascial attachments to the tibia and the location of pain; the soleus was believed to not attach along the distal-third of the posteromedial tibial border.
Quite often, the tibialis posterior is believed to be the muscle implicated with MTSS; however, in detailed cadaver studies, it has been shown that the tibialis posterior does not attach to the posteromedial tibial border. In fact, it has been demonstrated that only the flexor digitorum longus (FDL) and the soleus muscles actually originate from the medial aspect of the tibia (Beck et al., 1994, Brown, 2016). This does not necessarily answer the question posed above, does the soleus connect along the distal-third?
In a recent cadaveric study, anatomical variability was highlighted in the male and female gender. In roughly 33% of males and 72.5% of females, the soleus was shown to attach to the distal-third of the tibia (Edama et al., 2015). This may also be a contributing factor for the increased prevalence of the injury in female athletes.
Why you should care about the soleus in MTSS sufferers
As previously mentioned, the soleus absorbs up to 8-times your body weight during running (Dorn et al., 2012). High soleus peak electromyography (EMG) amplitude during the propulsion phase of running has also been identified as a contributing factor for MTSS (Naderi et al., 2020).
Imagine going down an off-road, rocky, downhill terrain on a road bike with no suspension. You might pull up sore, and the bike frame may break as there was nothing between you, the frame and the terrain. Hence, the spring and damper on downhill bikes. Like the bike's suspension kit, the soleus helps counteract the bending forces transferred into the tibia. Ensuring the patient has a well-functioning soleus muscle, strength and length, is imperative.
What do you need to do?
When we look at dysfunction, we look at weakness and tightness. The former we can address through strengthening exercises and the latter through stretching or mechanical therapies.
Improving soleus strength
There are plenty of exercises that help isolate the soleus; however, the bent-knee calf raise and its encompassing variations are the real winners here.
Tight calves?
Back in 2012, Anthony H. Wheeler had an article published on Myofascial Pain Disorders. Muscles with activity or injury-related pain are usually shortened with increased tone and tension (Wheeler, 2012). We know mechanical treatments such as the Counter-Traction Technology™ on the Solushin® medical orthosis can target the tight taut-bands ("trigger points") at the origins, and insertions of the soleus can reduce pain and muscle over-contraction. This is backed by a prospective cohort study and numerous case studies.
References
- Dorn, T. W., Schache, A. G., & Pandy, M. G. (2012). Muscular strategy shift in human running: dependence of running speed on hip and ankle muscle performance. Journal of Experimental Biology, 215(11), 1944–1956. https://doi.org/10.1242/jeb.064527
- Yates, B., & White, S. (2004). The Incidence and Risk Factors in the Development of Medial Tibial Stress Syndrome among Naval Recruits. The American Journal of Sports Medicine, 32(3), 772–780. https://doi.org/10.1177/0095399703258776
- Moen, M. H., Tol, J. L., Weir, A., Steunebrink, M., & De Winter, T. C. (2009). Medial Tibial Stress Syndrome. Sports Medicine, 39(7), 523–546. https://doi.org/10.2165/00007256-200939070-00002
- Franklyn, M. (2015). Aetiology and mechanisms of injury in medial tibial stress syndrome: Current and future developments. World Journal of Orthopedics, 6(8), 577. https://doi.org/10.5312/wjo.v6.i8.577
- Devas, M. B. (1958). Stree Fractures of the tibia in athletes or “shin soreness”.” The Journal of Bone and Joint Surgery. British Volume, 40-B(2), 227–239. https://doi.org/10.1302/0301-620x.40b2.227
- Beck, B. R., & Osternig, L. R. (1994). Medial tibial stress syndrome. The location of muscles in the leg in relation to symptoms. The Journal of Bone & Joint Surgery, 76(7), 1057–1061. https://doi.org/10.2106/00004623-199407000-00015
- Brown, A. A. (2016). Medial Tibial Stress Syndrome: Muscles Located at the Site of Pain. Scientifica, 2016, 1–4. https://doi.org/10.1155/2016/7097489
- Dorn, T. W., Schache, A. G., & Pandy, M. G. (2012). Muscular strategy shift in human running: dependence of running speed on hip and ankle muscle performance. Journal of Experimental Biology, 215(11), 1944–1956. https://doi.org/10.1242/jeb.064527
- Naderi, A., Moen, M. H., & Degens, H. (2020). Is high soleus muscle activity during the stance phase of the running cycle a potential risk factor for the development of medial tibial stress syndrome? A prospective study. Journal of Sports Sciences, 38(20), 2350–2358. https://doi.org/10.1080/02640414.2020.1785186
About the author:
Ben Lindsay is the Managing Director and engineer behind the Solushin medical device. A former national medalist swimmer, Ben aspires to learn from physicians, physiotherapists and podiatrists so he can develop tools to improve the quality of care for their patients.