biomechanical analysis of ankle sprain

Ankle sprains are common among both active and sedentary people. Although they are more prevalent among active people such as joggers and those engaged in sports, ankle sprains are rather a complex form of injury.

One reason for its complexity is the fact that our ankle joints are composed of many bone pieces joined by ligaments. The physiological aspects of ankle sprains involve strong ligaments in the joint structure stretching beyond their elastic limits and either getting injured or tearing completely.

Causes and Severity of Ankle Sprains

Most active people sustain an ankle sprain, which is often caused by pulled or even torn ligaments. Sports enthusiasts, however, such as basket ballers, tennis players, and runners sustain more serious ankle sprains due to the increased momentum compared to more sedentary victims of the same ankle injury.

The severity of ankle injuries depends on the extent of stress placed on the ankle joint ligaments and bones. However, it is generally considered safe to assume that you have suffered a sprained ankle if you have incessant pain on the joint and have trouble placing your weight on the affected foot.

From a biomechanical perspective, ankle sprains cause the ligaments supporting the ankle joint to rupture or tear and affect the ankle’s ability to function or support the victim. Repetitive ankle sprains eventually compromise the ankle’s support ability and may cause chronic pain or worse arthritis.

Biomechanics of the Ankle Joint

biomechanical analysis of an ankle sprain

Our ankle joint moves in a complex manner making it more of a multi-axial joint rather than a hinge one. The main movements are plantar and dorsiflexion, which are movements in the sagittal plane.

The ankle joint moves in the transverse plane causing adduction while the same motion is called inversion in the frontal plane. Combining these movements creates a series of three dimensional motions called supination and pronation. Supination refers to the position of the sole of the foot that faces medially through motion combinations such as plantarflexion, adduction, and inversion.

Many specialists have long considered the tibiotalar joint responsible for rotation of the human ankle joint to be a hinge joint. However, the internal rotation that occurs during the process of dorsiflexion and external rotation characterizes the plantarflexion movement; there have been arguments that this joint is multi-axial. Recent considerations have introduced further revisions to these considerations resulting to the identification of the tibiotalar joint as a uniaxial joint. Because the axis of rotations is oblique, the joint rotates in a manner that cannot be considered fully multi-axial.

The range of motion (ROM) of our ankle joint is not a fixed one due to many factors including geographical location, cultural predisposition, and extent of physical activity.

Geographical Location

Geographical location ankle sprain

The geographical location influences the ROM based on the differences between various locations of the earth. Some regions are sloppier, requiring people to position their feet differently for mundane activities like walking. Other areas may be so flat that the ROM remains largely unchanged relatively.

Cultural Disposition

Cultural disposition influences the ankle joint’s ROM largely through gait. Some cultures require that the people walk with an upright gait while others force people to stoop or even bow. Such cultural predispositions place differing pressures on the peoples’ gait resulting in different ankle joint ROMs.

Extent of Physical Activity

tennis, biomechanical analysis of an ankle sprain

The extent of physical activity determines the extent which the person engages in the physical activities that involve the ankle joint. For example, active lifestyles involving jogging and tennis place increased pressures on the ankle meaning there is greater ROM in the same joint.

The ankle’s ROM mainly occurs in the sagittal plane, where dorsiflexion and plantarflexion occur in the tibiotalar joint.

Most studies on the ROM of the human ankle joint have demonstrated it to be between 60 and 70 degrees of motion. Broken down, this means the ankle moves between 10 and 20 degrees of motion for dorsiflexion and between 40 and 55 degrees for plantarflexion. Therefore, the total range of motion through the frontal plane is about 35 degrees of motion in the sense of 23 degrees for inversion and 12 degrees for eversion.

In addition, lengthy observations have demonstrated that the ROM is necessary for everyday activities such as walking at 30 degrees and 37 degrees for ascending stairs. Descending stairs requires about 56 degrees of motion in the human ankle joint.

Biomechanical Analysis of an Ankle Sprain

woman with a sprained ankle

Injury in one or more ligaments that support the ankle could lead to ankle sprains. Our foot has medial ligaments that support the ankle joint from the inside against forces of inversion. On the outside, the lateral ligaments function the same way.

The main reason for sustaining ankle sprains involves rotating the foot, causing injury or complete tears in the lateral ligaments supporting the bones and ankle joint from the outside part of the foot. One way this form of injury can occur is stepping on an uneven surface as most basketball players do when jumping close to each other and landing on each other’s feet.  The three main lateral ligaments therefore become the main culprits when it comes to ankle sprains.

Lateral Ankle Sprain

Lateral ankle sprain is the most common type of ankle sprain. The three lateral ligaments that are often injured are the Anterior Talofibular ligament (ATF), Posterior talofibular ligament (PTF) and the Calcaneofibular ligament (CF). This type of sprain involves the tearing of fibers in one or more of these ligaments or total tear of the entire tissue, which can result in an unstable ankle joint prone to further damage to the bones.

Inversion sprains

Ankle sprain

Inversion or eversion sprain happens when the lateral ligaments get injured due to unstable landing after a jump or running/walking on an uneven surface. It results from the plantarflexion of the foot injuring the ATL.

To understand this type of injury, you need to know that the ligament involved moves perpendicular to the talus, exposing it to sheer forces. A lot of force applied to the ATL during the inversion sprain may break it and affect the CL. This domino effect occurs because the CL is the next ligament supposed to take the stress.

The CL can be injured if the inversion sprain is extreme enough, specifically when the ankle is in the neutral position and the ligament is near perpendicular. Inversion sprains that result in the tearing of the ATL usually lead to an unstable ankle joint only during plantarflexion. However, should both the ATL and CL, tear as is in cases of more serious forms of ankle sprains, the joint becomes unstable in any position you place your foot.

One interesting observation that also stresses the complexities of the ankle joint and its injuries is the results of dorsiflexion after ankle sprains that tear both the CL and ATL. As opposed to the plantarflexion motion that results in an unstable ankle joint at all position, tearing both ligaments leads to a stable ankle when the foot is dorsiflexed. Injuring both the anterior and posterior tibiofibular ligaments makes the ankle joint unstable.

Eversion sprains

Eversion sprains are relatively less common than the inversion type partly because of the presence of the lateral malleolus. This bony protrusion reduces the length of ligament exposed to the sheering forces that can could cause ankle sprains. Additionally, the medial ligaments, which eversion sprains target, are stronger compared with lateral ligaments. These shorter ankle ligaments are so strong that tearing them usually requires enough stress and force to fracture the tibia or even fibula. Therefore, eversion-related ankle sprains should be checked in conjunction with fractures as they commonly occur together. In addition, the tibia, fibula, or even talus may be fractured, making eversion sprains particularly severe.

The tearing of the deltoid ligaments, which occur inside the ankle, could result in eversion sprain. These ligaments, also known as medial ligaments, prevent the foot from everting or turning inwards. Tearing them is hard due to the presence of the fibula, which prevents excessive eversion. The medial ligaments are also far shorter, hence stronger than the lateral ones on the outside of the foot.

High Ankle Sprain (Syndesmotic ligament complex)

Sprained Ankle at Soccer Game

Some unique forms of ankle sprains involve the syndesmotic ligaments that connect the ankle joint to the bones forming the shin. Injury to these ligaments results in special types of ankle sprains called “high ankle sprains.” This type of sprain is common among footballers and result in persistent pain as well as residual ankle dysfunction. Additionally, when you have “high ankle sprain,” you’ll require almost twice as long to heal compared with inversion and eversion sprains. One reason for such lengthy healing periods is the syndesmosis ligament, which is hard to heal. Surgery is a common form of treatment for cases where the high ankle sprain is serious and the syndesmosis ligaments are torn.

High ankle sprains occur in three distinct manners. The first is external rotation of the foot. When done in a forceful manner as in sports like skiing and soccer, it may widen the ankle mortise due to the talus being driven into the mortise by external rotation. Such action results in huge stresses on the syndesmotic ligaments and may even tear them, resulting in debilitating high ankle sprain.

The second manner a high ankle sprain may occur is eversion of the talus in a forceful manner leading to the mortise widening. Such action also exerts a lot of strain on the high ankle ligaments because the entire ankle shifts with the talus injuring the syndesmotic ligament.

The third way a high ankle sprain may happen is dorsiflexion, which widens the mortise because the wider anterior aspect of the nearby talar dome invades the joint space. If the dorsiflexion occurs forcefully, as in sports such as soccer and rock climbing, the distal fibula is pushed away laterally and prevented from engaging with the distal fibula in its normal articulation manner.

Further Consideration Supporting the Biomechanical Analysis of an Ankle Sprain

When analyzing the biomechanics of ankle sprains, you cannot distance yourself from considering the different merits of each of the ligaments. The weakest groups of ligaments among the three main groups that are involved in ankle sprains are the lateral ligaments. One of the three lateral ligaments, the anterior talofibular ligament (ATFL) is the weakest of the ligaments supporting the ankle joint. Therefore, it is most prone to injuries surrounding ankle sprains.

The second culprit is the Calcaneofibular Ligament (CFL), which makes it the second ligament that’s most prone to ankle sprains. The last ligament to suffer injury in most cases of normal inversion-type sprains is the posterior talofibular ligament (PTFL). From majority of inversion-type ankle sprains, the sequence follows the individual ligament’s proneness to injury and rupture.

It is easy to assume that only ligaments suffer injury or tears during ankle sprains. However, it’s worth noting that the peroneal tendon also faces injury when inversion-type ankle sprains occur and even subluxate during the healing process that seeks to restore the injured or torn ligaments. Such injury to the tendons supporting the peroneal muscles makes the common ankle sprain more serious as tendons do not heal as fast as ligaments.

Muscles also play their special roles in the biomechanical analysis of an ankle sprain. The peroneus brevis muscle suffers longitudinal sheers when lateral ligaments suffer injury in the event of ankle sprains. Similarly, the peroneus longus muscles also change their activation patterns in case of ankle stability which is a severe outcome of serious ankle sprains. The main cause of such changes in activation process and sequence are caused by restrictive changes in the muscle structure during healing processes targeting the sprained ankle.

References:

  1. 1. Dubin, J. C., Comeau, D., McClelland, R. I., Dubin, R. A., & Ferrel, E. (2011, September). Lateral and syndesmotic ankle sprain injuries: a narrative literature review. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3259913/
  2. 2. Brockett, C. L., & Chapman, G. J. (2016, June). Biomechanics of the ankle. Retrieved from http://www.sciencedirect.com/science/article/pii/S1877132716300483 
  3. 3. Lin, C., Gross, M. T., & Weinhold, P. (2006). Ankle Syndesmosis Injuries: Anatomy, Biomechanics, Mechanism of Injury, and Clinical Guidelines for Diagnosis and Intervention. Retrieved from http://www.jospt.org/doi/pdf/10.2519/jospt.2006.2195?code=jospt-site
  4. 4. Ankle Sprains or Inversion Sprains. (n.d.). Retrieved from http://kinetichealth.ca/ankle-sprains-or-inversion-sprains/