Proprioception of the Ankle
Introduction[edit | edit source]
Skin sensory receptors and musculoskeletal receptors, including the muscle spindle and the Golgi tendon organ (GTO), are the main sensors controlling the relative position of the body parts and muscle activity. They respond to touch, vibration, pressure and stretch on the skin, changing the length of the muscle and activity of the muscle force. The length and tension of the skeletal muscles are controlled by proprioception in order to coordinate motor control. This article will focus on ankle proprioception and how it can be used in the rehabilitation of ankle injuries.
What Is Proprioception?[edit | edit source]
Proprioception is a "specialised variation of the sensory modality of touch that encompasses the sensation of joint movement (kinesthesia) and joint position (joint position sense)". When tissue deformation occurs, the sensory receptors in the skin, muscles, joints, ligaments and tendons provide proprioceptive feedback to the central nervous system (CNS) via various anatomical pathways. The choice of the pathway depends on the type of the signal being carried. Touch and proprioceptive information reach the CNS through the posterior column-medial lemniscal pathway. The spinothalamic pathways carry pain and temperature information. Additionally, visual and vestibular centres offer afferent information to the central nervous system about body position and balance.
Proprioception is guided by the body's receptors. Because of its direct connection with the brain through the nervous system, an individual without sight is aware of his or her body's activities. When changes in the ankle's muscle length, joint position or movement velocity occur, the CNS uses this information to plan a movement and execute gait.
Mechanoreceptors, thermoreceptors, and nociceptors are all skin sensory receptors. There are six skin mechanoreceptors: Merkel discs, Meissner corpuscles, Pacinian corpuscles, Ruffini endings, and C-fiber low threshold mechanoreceptors. Hair follicles also belong to this group and are responsible for detecting light touch sensation. Meissner corpuscles are located in the dermal papillae and detect fine touch and vibration. High-frequency vibration and touch are also a responsibility of the Pacinian corpuscles located in the dermis. Ruffini corpuscles are able to detect pressure from stretching of the skin. The basal epidermis is a home for the Merkel discs which are responsible for detecting structure and texture. Finally, C-fiber LTMs detect light touch sensations.
Strong proprioceptive information is received by the brain through the receptors located in the muscle. These receptors are called muscle spindles. Muscle spindles are considered the most important proprioceptors. They are activated by the muscle stretch and they are exhibiting high sensitivity to small and rapid muscle length changes. This mechanical stretch sensation is transported to the spinal cord via the dorsal root ganglia and the CNS receives this information via afferent nerve fibres.
Proprioception and Ageing[edit | edit source]
Several studies have found that ageing negatively affects muscle spindles and their neural pathways leading to less sensitivity and less acuity.
In a study conducted by Skinner et al., it was found that older subjects had the worst proprioception in response to passive movement when compared to the younger group. Kaplan and his colleagues looked at age-related changes in proprioception and they confirmed reduced proprioception in older individuals compared to younger people.
At the peripheral level, a decline in proprioception related to ageing involves changes in the muscle spindle and its function, as well as deficits in the processing of sensory input. Changes in the muscle spindle include a decline in the total number of intrafusal muscle fibres and nuclear chain fibres per spindle and an increase in spindle capsule thickness. Processing deficit is characterised by myelin abnormalities, axonal atrophy, and declined nerve conduction velocity. The following changes that occur in the central nervous system are responsible for a decline in proprioception:
- Progressive loss of the dendrite system in the motor cortex
- Losses in the number of neurons and receptors
- Neurochemical changes in the brain
Proprioception and Muscles of the Foot[edit | edit source]
The theory of core stability was first proposed by Panjabi. It describes functional interdependence between the passive (bones and joints structures), active (muscles and tendons), and neural (sensory receptors) subsystems which are responsible for mobility and stability of the spine. The same concept applied to the ankle and foot was introduced by McKeon in 2013. The idea of the "foot core" explains the role of the muscles of the foot. It consists of the plantar intrinsic muscles which have a functional link with both arches of the foot. 
The foot active subsystem:
- Offers local dynamic support
- Senses foot position
- Provides postural control
- Actively controls balance in a standing position
- Controls foot position on uneven terrain
- Facilitates higher recruitment of the muscles when additional load is applied
Researchers continue to investigate the role of foot intrinsics in proprioception. It is suggested that the intrinsics provide immediate sensory information when changes in foot alignment occur. Moreover, it has been concluded that these muscles respond well to training and their sensitivity to deformation can be altered. The intrinsic muscles are susceptible to fatigue and, according to Hiemstra et al, muscle fatigue can negatively affect joint position sense in different areas of the lower extremities.
Visual / Vestibular Systems and Proprioception[edit | edit source]
"The vestibular system is an essential sensory system that makes important contributions to our subjective sense of movement and orientation in space."
Vision plays a key role in the ability to sense one’s body in space. It is crucial for movement accuracy, but is not necessary for a person to understand body ownership. The vestibular system is responsible for detecting head movement. This is an important aspect of the sensory system as:
- The position of the head has a significant effect on the human body. Small head movements can lead to postural and perceptual instability.
- Research findings show that abnormal head position changes muscle activity and proprioception.
- The acceleration of the head with compensatory eye movement contributes to proprioception and posture.
Proprioception and Ankle Injury[edit | edit source]
When trauma to tissues occurs, it can result in the interruption of the afferent connection of the nerve cells which are relaying sensory information from the body part to the brain. This can lead to proprioceptive deficits. Several studies investigated the relationship between ankle proprioception and ankle injury:
- Payne et al. found that ankle proprioception could predict ankle injuries in college basketball players.
- Fu and colleagues observed that a group of basketball players with poor ankle proprioception demonstrated different patterns of muscle recruitment and a higher risk of ankle injury during sport-related activities.
- A systematic review by Witchalls et al. showed that ankle proprioception is associated with ankle injury.
- In a systematic review and meta-analysis, Xhu et al. found that patients with chronic ankle instability had impaired kinesthesia and joint position sense when compared with healthy people.
- Studies on chronic ankle instability have shown increased thresholds of mechanoreceptors and decreased proprioceptive acuity.
Individuals with chronic ankle instability experience sensory impairments characterised by increased thresholds of mechanoreceptors and decreased proprioceptive acuity. It is suggested that treatment for these impairments should include sensory pathways.
Proprioception Retraining[edit | edit source]
When an injury occurs it affects more than just tissue. Residual effects of an injury include impaired proprioception with loss of balance, impaired postural control and joint position sense, and alteration in muscle spindle activity. These changes in proprioception should be the focus of rehabilitation through:
- External manipulation
- A variety of sensory integration therapies targeting proprioceptive input
The basic principles when providing proprioception retraining are as follows:
- Start simple and slow
- Provide good instructions
- Do not threaten the patient
- Tasks should not induce more than minimal pain
- Offer a reward
Short Foot Exercises[edit | edit source]
Foot core stability is essential for the effective biomechanical function of the musculoskeletal system of the lower extremity. Balance training to improve ankle proprioception and increase the strength of the intrinsics of the foot is called the short-foot exercise (SFE). The end goal of the SFE is improvement in dynamic standing balance. The SFE training includes exercises that pull the first metatarsal head toward the calcaneus. No curling of the toes should occur. 
The benefits of including short foot exercises in the early stages of the proprioceptive training after ankle injury include:
- Stimulation of the neurocircuitry in the sole of the foot
- Improvement in postural and core stability
- Improvement in proprioception
According to Lee et al., SFE training in individuals with chronic ankle instability leads to improvement in proprioception and dynamic balance. They found that this type of training was more effective than a standard proprioceptive sensory exercise training. The authors further concluded that SFE could facilitate a faster return to activities of everyday life and sports when started early.
The following are the guidelines for SFE:
- Weeks 1–4: sitting position with both feet on the stability trainer, with the hips, knees and ankle at 90º of flexion to stabilise the body
- Weeks 5 – 8: standing on 2 feet
- Weeks 5–9: single-leg stance
- SFE is held for 5 seconds; 12 repetitions per training session, with a 2-min rest period between blocks
- Performed three sets, 3 times a week
You can find out more about a strengthening protocol for the intrinsic muscles of the foot here.
Sensory Targeted Ankle Rehabilitation Strategies[edit | edit source]
Sensory targeted ankle rehabilitation strategies (STARS) consist of three interventions: joint mobilisation, plantar massage, and triceps surae stretching. The treatment protocol includes six, five-minute treatments of each component of the STARS, over two weeks. Research shows that plantar massage and joint mobilisation offer the best outcome in sensorimotor function in individuals with chronic ankle instability. Feldbrugge and colleagues suggested that joint mobilisation and calf stretching can improve ankle dorsiflexion and self-reported functional performance in persons with chronic ankle instability.
- Consists of a combination of petrissage and effleurage to the entire plantar aspect of the foot
- Not specific to the time spent using either technique or the location of the massage
- One study found a 30% improvement in treatment outcomes by doing a plantar massage before performing rehabilitation exercises
External Devices[edit | edit source]
The following methods / devices can be used to stimulate cutaneous proprioceptive signals:
- Textured insoles:
- According to Corbin et al., textured insoles provide increased afferent information to the central nervous system leading to improved postural control in bilateral stance.
- Steinberg et a.l have found that using textured insoles in male dancers improved their dynamic postural balance demonstrating its beneficial effect on foot proprioception.
- Kinesio taping method:
- A study by Halseth et al. revealed that the Kinesio taping method does not appear to enhance proprioception in healthy individuals.
- A systematic review by Wilson and Bialocerkowski provides recommendations for the use of the Kinesio taping method in clinical practice to prevent lateral ankle injuries because of its positive effects on proprioception, muscle endurance and activity performance.
- Training surfaces used in clinical practice: balance half ball, wobble board, multi-station training on 12 different surfaces, BOSU, Swiss ball:
- No improvement in ankle function / stability
- It may need to be started later in the rehabilitation process
- It may cause "freezing" of the patient because the required skill is too demanding
- According to Donovan et al., destabilisation devices introduced in a 4-week rehabilitation program improved dorsiflexion during the stance phase of gait, but had no effect on improving frontal plane motion.
External Supports[edit | edit source]
External supports are not superior to rehabilitation as a stand-alone treatment. The ultimate rehabilitation programme should include the following:
- Combination of dynamic rehabilitation in a closed chain
- Feet placed on a textured surface that is firm and stable with verbal cues, by supervising therapist
- Visual feedback (mirror) plus an external support
A network meta-analysis by Tsikopoulos et al. concluded that external supports (taping, bracing, insoles, a combination of insoles and bracing) did not offer benefit in improving dynamic postural control in individuals with an ankle sprain. The authors suggest that using external supports as a standalone option in the rehabilitation for ankle instability does not lead to a better outcome and that combinations of rehabilitation and external supports could be more effective.
Tests for Proprioception[edit | edit source]
- Star Excursion Balance Test (SEBT)
Resources[edit | edit source]
- Prevent Ankle Sprains With Balance and Proprioception Exercises. Available from: https://www.verywellhealth.com/prevent-ankle-sprains-with-proprioception-training-4115970.
- Effect of proprioceptive training on postural balance in patients with chronic ankle instability. Available from: https://efsupit.ro/images/stories/ianuarie2021/Art%201.pdf
- Pavailler S, Hintzy F, Horvais N, Forestier N. Cutaneous stimulation at the ankle: a differential effect on proprioceptive postural control according to the participants' preferred sensory strategy. J Foot Ankle Res. 2016 Mar 8;9:9.
References[edit | edit source]
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