Shin splints (also known as medial tibial stress syndrome) affects between 5-35% of runners. In my experience, it most commonly occurs in those who suddenly increase their running mileage, oftentimes in a rush to “clock up the miles” for an upcoming race. New runners are particularly prone to shin splints as they may not have developed the strength in the shin muscles to withstand the cumulative load involved in distance running.
One of the issues in treating shin splints is that the pathology of the condition is unclear. The insertion points of the tibialis posterior and flexor digitorum longus muscles into the tibia bone are generally considered to be the site of pain with shin splints. A case study by Winters et al. (2017) attempted to determine the structures involved in shin splints. Ultrasound assessment of the lower leg was performed in those suffering from shin splints and compared to those with no history of the condition. Edema (swelling) of the outer layer of bone (periosteal edema) and abnormalities in the tibialis posterior tendon were present equally in both the shin pain and asymptomatic subjects. This study demonstrates that there are no visible changes in the tendons or bone of those suffering from shin splints. The lack of clear structural changes behind the condition makes it more difficult to monitor the impact of treatments and formulate effective treatment interventions.
Despite the lack of visible structural changes, there are certain physical characteristics that have been shown to correlate with shin splints. Zachary et al. (2016) performed a systematic review of 21 studies in an attempt to identify the main risk factors for developing the condition. They found the following risk factors correlated with an increased risk of developing shin splints:
- Increased body mass index
- Increased navicular drop
- Greater hip external-rotation range of motion
- Greater ankle plantar-flexion range of motion
A systematic review of the literature by Newman et al. (2013) reported similar findings but added additional factors to the list above.
- Increased body mass index
- Navicular drop
- Navicular drop >10mm
- Increased hip external rotation in males
- Prior use of orthotics
- Fewer years of running experience
- Female gender
- Prior history of shin splints
Is Muscle Stiffness a Driver of Shin Pain?
It would appear logical to consider muscle stiffness as a potential driver of shin splints. Tightness of the muscles inserting into the tibia (shin) bone, in theory, should create greater traction on the insertion point on the tibia bone and increase the risk of shin pain. Saeki et al. (2017) assessed the relationship between shin splints and muscle stiffness of all of the posterior lower leg muscles. They found that the muscle stiffness of the flexor digitorum longus and tibialis posterior were significantly higher in subjects with a history of shin splints. However, there was no significant difference in the tightness of the gastrocnemius, soleus, peroneus and flexor halluces longus muscles. This finding ties in with the premise that the flexor digitorum longus and tibialis posterior are primary drivers of pain with shin splints.
Body Weight & Running Surface
It is logical to assume that a decrease in body mass decreases the likelihood of shin pain by decreasing the ground reaction forces. Likewise, running on a softer surface should help to lessen the load going through the shin with foot strike. When the foot strikes the ground, the joints are exposed to three to four times body weight. In those with a history of shin pain, decreasing running distance and decreasing the amount of time spent running on a hard surface should be discussed as part of the overall management plan in controlling symptoms.
Impaired Hip Strength as a Driver of Shin Pain
Much of the research on risk factors has focused on muscle strength around the hip joint as a potential correlate of knee & shin pain. One of the primary determinants of stability of the lower limbs at foot strike is the activation of the muscles of the hip & trunk. They also act to control the movement of the leg during the swing phase of gait and thus determine the joint angles of the ankle and knee with foot strike. With this logic in mind one would expect hip muscle activation to play a role in the development of shin pain; however, while the strength characteristics of the hip have demonstrated a clear link to knee pain, the link with shin pain is less clear-cut.
Verreist et al. (2014) performed a prospective analysis on a group of 95 female athletes. The prospective design meant that the characteristics of participants were analysed prior to the onset of injury. This is important because any biomechanical changes identified at the outset were present before the injury occurred as opposed to being a response to injury. Of the 95 participants, 21 of the women went on to be diagnosed with shin splints at follow-up. The initial tests performed included isokinetic hip strength measurements of the abductors, adductors, internal and external rotators. The researchers found that decreased abductor concentric strength was a significant predictor of shin splints in females. Interestingly, no link was found between external rotator strength and shin splints.
These findings conflict with those of Luedke (2015). In a prospective study of 600 novice athletes they found that runners with higher eccentric hip abductor strength had a lower risk of developing patellofemoral pain syndrome (pain under the kneecap); however, no link between hip and thigh muscle strength was found to exist for shin pain.
Overall, the research does suggest a probable link between hip strength and shin pain and therefore any deficiency in hip strength identified in the physical exam should be addressed in those suffering from shin splints as part of the overall physiotherapy management programme.
Impaired Ankle Strength as a Driver of Shin Pain
The insertion point of the flexor digitorum longus muscle on the back of the tibia is the most common location for shin splints. This muscle is responsible for flexing the toes & assists in plantarflexing the ankle. Because this muscle is implicated as a source of pain in shin splints it may be expected that the flexion strength of the toes may be affected in those suffering from the condition. Research by Saeki et al. (2017) showed that the strength of the big toe was significantly higher in runners with a history of shin splints compared with those without it. There was; however, no significant difference in the strength of the other toes which the flexor digitorum longus supplies. The authors suggested that runners with a history of shin splints may adopt a strategy of loading the big toe as a means of reducing the load on the medial tibia to reduce shin pain.
Foot Posture Analysis & Orthotics
Overpronation of the feet has long been proposed as a cause of shin pain. Pronation of the feet is believed to alter the load distribution throught the lower limb and create traction on the insertion of the tibilais posterior and the flexor digitorum longus muscles at their insertion point on the tibia.
Static analysis of foot posture is a standard component of the physical assessment of those with shin pain; however, the correlation between static findings and shin pain is uncertain. A systematic review by Geoffrey (2014) reported that static measurement of foot pronation was associated with an increased risk of shin splints and patellofemoral pain. However, they suggest that the small effects are unclear and that static measures may not adequately represent dynamic foot function. Furthermore, another systematic review reported that pronated foot type was not associated with higher incidence of shin splints (Newman et al. 2013). Based on this evidence, static foot analysis is of questionable benefit when performing assessment in patients presenting with shin splints.
Orthotics are commonly used as a means of decreasing foot pronation during gait with the aim of preventing shin pain. Although reducing dynamic pronation should in theory reduce traction on the muscles inserting into the tibia, the evidence for orthotics in reducing shin splints is inconclusive at present. A systematic review by Collins et al. (2007) concluded that ‘there is some evidence to support the use of foot orthoses in preventing lower limb injuries but little evidence to support their use in treating overuse conditions. Also, Newman et al. (2013) reported that prior orthotic use is a highly significant risk factor for the development of shin splints. The authors report that orthotic use is a causative risk factor and therefore they are not useful for preventing shin splints. It may be that there are certain subtypes of patients that derive benefit from using orthotics while others do not. Based on the risk factors discussed above, it appears that navicular drop may be a more accurate means of assessing foot posture in patients suffering from shin splints.
Functional Characteristics of those who develop shin pain
Research by Verrelst and colleagues published in the British Medical Journal analysed the biomechanical characteristics of athletes that went on to develop shin splints. Eighty-six female students were analysed performing a single-leg drop jump (SLDJ). The authors found that there was a significantly greater lateral translation of the hip & trunk evident in women that developed shin pain compared with those who avoided a shin injury. The authors report that this can be interpreted as impaired ability to maintain dynamic joint stability resulting in increased accessory movements. They suggest that altered trunk control may lead to excessive eccentric contraction of the lower limb musculature.
As most people will experience shin pain due to running it is logical to consider whether there are running technique variations evident between those that develop shin pain and those that do not. Loudon & Reiman (2012) assessed the running technique in individuals with shin splints and compared this to individuals without a history of the condition. Three-dimensional analysis in runners measured peak hip internal rotation, frontal plane pelvic tilt excursion, and knee flexion. The authors reported that the runners that had a history of shin pain demonstrated significantly greater frontal plane pelvic tilt, hip internal rotation and less knee flexion than the pain-free group. The authors suggest that increased pelvic tilt can create valgus moment due to the body’s center of mass shifting medially. This increased valgus moment at the knee can cause pronation of the foot and overload the shin. As discussed above in relation to ankle strength, individuals suffering from shin splints can alter their movement patterns to decrease loading of the involved structures. Given that this study was retrospective in nature, meaning that it looks backwards in time to collect data, it is difficult to ascertain whether the changes are a result of pain or were present prior to onset of symptoms.
There has been a considerable focus on running technique modifications in recent years as a means of decreasing injury risk. Much of the focus has been on decreasing step length and increasing step rate as a means of reducing impact forces through the lower limb. For example, research by Luedke et al. (2016) found that a lower running step rate was associated with a greater likelihood of shin injury.
Prevention & Treatment
As with most injuries, a previous history of shin splints is one of the primary risk factors for future development of the condition (Saeki et al. 2017). Training volume is a key consideration when trying to avoid shin pain. It is wise to avoid any rapid increase in mileage or running speed. Most guidelines recommend adding no more than 10% to your mileage per week to minimise injury risk. The tendons of the lower limb take time to adapt and develop the tensile strength required to cope with an increase in load.
The first often posed by patients is: “can I continue running if it is sore.” As I say to most of my patients in this scenario, it is very difficult to eradicate pain by inducing pain. In other words, pushing yourself to the point of pain is going to slow down your recovery. In many cases an athlete has an upcoming event that they are determined to complete. After this there may be a window of time during which rehab can be emphasised. In a case such as this, then a plan needs to be agreed with your physiotherapist, where training is adapted to get through the event, after which a period of rest or adapted training may be required.
Strengthening of the calf muscles should help to increase the load tolerance of the muscles and bones of the shin. The resultant increase in bone density and muscle mass should aid in load dissipation, thereby decreasing injury risk. Research is lacking in terms of strengthening exercises and shin splints; however, some research has been done looking at the incidence of stress fracture and there link to calf muscle mass. Stress fractures of the tibia can occur in runners due to progressive bone overload and therefore the mechanism behind such an injury is similar to that of shin splints. Winkelmann et al. (2016) performed an evidence-based review of the literature and reported that an increase calf muscle girth was associated with a significant decrease in stress fracture risk. This correlates with research by Bennell et al. (1996) who reported that greater muscle mass was protective for stress fracture injuries in track and field athletes. It would be interesting to see more research into the correlation between muscle and bone density and shin splints but at present such research is lacking.
This blog is brought to you by Ross Allen from Naas Physio Clinic.
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