Posterior shin splints, or medial tibial stress syndrome (MTSS), cause pain along the inner, lower part of the leg, specifically impacting the shin bone (tibia). This common issue for athletes, particularly runners, can significantly affect physical activity.
Anatomical Basis of Posterior Shin Splints
Posterior shin splints involve the tibia (shin bone) and the tibialis posterior muscle. This muscle, located deep in the calf, stabilizes the foot and ankle. Its tendon extends behind the inner ankle, attaching to foot bones that form the arch.
The tibialis posterior muscle supports the foot’s arch during weight-bearing activities and controls inward foot rolling (pronation). Excessive stress on this muscle and its tendon can cause inflammation or micro-tears where it attaches to the tibia. This irritation of the bone’s outer layer, the periosteum, is the source of the characteristic pain.
Overuse and Repetitive Strain
Posterior shin splints are an overuse injury from cumulative stress on the lower leg. Repeated impact and muscle contractions in activities like running or jumping cause micro-trauma within the tibialis posterior muscle and its shin bone attachments, leading to inflammation and pain.
The frequency and intensity of physical activity influence this condition. When the tibialis posterior muscle’s load exceeds its recovery capacity, it fatigues and weakens. This reduces its effectiveness in supporting the foot’s arch and stabilizing the lower leg, increasing strain on surrounding tissues and bone.
Biomechanical Contributors
An individual’s body mechanics can significantly influence their susceptibility to posterior shin splints. Overpronation, or the excessive inward rolling of the foot during movement, is a common biomechanical factor. When the foot overpronates, the tibialis posterior muscle must work harder to stabilize the arch and control the foot’s motion, placing increased strain on the muscle and its tendon, which can lead to inflammation and pain.
Flat feet or arches that collapse excessively also increase the load on the tibialis posterior. This occurs when the tendon can no longer adequately support the arch. Muscle imbalances can alter gait and distribute forces unevenly through the lower leg. For instance, weakness in the hip abductors or gluteal muscles can affect lower limb alignment and increase stress on the tibialis posterior during activity.
Training Errors and External Factors
Modifiable external factors and training practices contribute significantly to posterior shin splints. A common cause is increasing training intensity, duration, or frequency too quickly, often described as “too much, too soon.” This rapid progression does not allow the body sufficient time to adapt to increased demands, leading to overload of the tibialis posterior muscle and surrounding tissues.
Running on hard or uneven surfaces increases impact forces on the lower legs. Concrete or angled terrain can place additional stress on the tibialis posterior, contributing to micro-trauma.
Improper or worn-out footwear that lacks adequate support or cushioning can further exacerbate the problem. Shoes that do not properly support the foot’s arch or provide sufficient shock absorption can lead to increased strain on the tibialis posterior muscle.
Insufficient warm-up or cool-down routines, along with inadequate stretching or strengthening of relevant lower leg muscles, can also leave the muscles unprepared for activity and more vulnerable to injury.