Disclaimer: The following neither contains medical or legal advice but is for Informational Purposes Only. Consult a medical professional or attorney for your unique situation.
Numbness and tingling are unpleasant sensations which affect more people than we realize. Most of us have suffered numbness and tingling at least once, usually caused by a blow to or prolonged pressure on a nerve. In most cases, it occurs while sleeping in an awkward position or when hitting an elbow on the outer side. But when it lasts for a longer period of time or when it is caused by an auto accident, then it should raise a concern.1
In case of auto accidents, the location of numbness and tingling is determined by the body part which is injured. In cases of upper body injury, the patient will most likely have numbness or tingling in the arms or hands. Conversely, injury of the lower body can cause numbness or tingling in the legs or feet.
It all comes down to the human anatomy. The human spine plays a role in standing straight, walking, and posture, but it has another important role: it protects the spinal cord which transmit signals from peripheral body parts like hands or feet to the brain and vice versa.2
The spinal cord spans from the base of the skull and down to the lumbar spine (lower back). Every peripheral nerve is connected to the spinal cord. The most important parts of the spinal cord for innervation of extremities are cervical (neck) and lumbar (low back) enlargements. Cervical enlargement is located in the neck and it is the place on the spinal cord where nerves from arms are connected. The same goes for lumbar enlargement, which connects nerves from lower extremities with the lumbar part of the spinal cord.3
Every nerve leaves the spinal cord and creates a pair of nerve roots which are then connected and create a nerve which leaves the spine through a small opening between two vertebrae.
Every nerve has a role in the body. Some are pure motor nerves which have a role to send signals to different muscles and cause a muscle contraction. Other nerves play a role in different sensations like pressure, hot, cold, etc. In the case of numbness and tingling, a sensation nerve is damaged or injured.
Every single nerve has a muscle, muscle group, or body area which it innerves. For example:
- C6 nerve innervates the outer part of the elbow, forearm, thumb and outer part of the index finger
- C7 innerves the middle finger and outer part of the ring finger
- C8 innerves inner part of ring finger and small finger
In lower extremities, L3 innerves outer and anterior parts of the thigh; L4 innerves anterior knee, lateral and part of the posterior calf; L5 innerves lateral calf, anterior foot, inner part of big toe, 2nd toe; S1 innerves heel, little toe, 4th toe, part of 3rd toe, etc.4
In the case of numbness and tingling in arms or hands, the most common mechanism is acceleration/deceleration. When a moving car hits a solid obstacle like another car, wall, etc., the driver’s or passenger’s head will move forward causing the neck to flex above its normal limits. After a very short period of time, the head and neck will reach the maximum of flexion and they will move backwards causing neck extension. This motion will repeat multiple times in a short duration until the head and neck remain still. In case of a hit to the back part of a vehicle, the opposite will occur. At the beginning, neck will be hyperextended followed by hyperflexion.5
In normal circumstances, the neck has a pretty big range of motion and movement, and these limits will not cause any pain or other symptoms. But in the case of acceleration/deceleration injury, the cervical spine is moving out of its normal limits. This will create pathological forces which will have a negative effect on all structures located in the neck area. Muscles, joint capsules, nerves and ligaments will be distended. If enough force is generated, fractures of cervical vertebrae can occur.6
Nerves are very susceptible structures to this type of injury because hyperflexion and hyperextension will cause stretching of nerves and their roots. This will result in a number of symptoms including pain radiation from neck to different areas of the arm or hand, numbness, or tingling in different parts of the arm or hand.6
If you know which nerve root is innerving which part of the arm or hand, you can roughly estimate which part of the spine and which nerve root is injured. For example, if you feel numbness or tingling in the outer part of the shoulder, you most likely have an injury of C5 nerve root, or if you feel numbness or tingling in the thumb, you most likely have an injury of C6 nerve root.4
The similar principle applies to the lumbar spine (low back). It also contains an enlargement in which all lower extremity nerves and their roots are connected to the spinal cord. When it comes to lumbar spine, it has much smaller range of motion than the cervical spine and it is stiffer; however, the rate of injuries is almost the same compared to neck injuries.7
Lumbar spine injuries can also occur during car accidents, especially in case of unrestrained drivers or passengers. In the case of restrained driver/passenger, the seat belt will tighten up and pull the body to the seat, preventing excessive motion. But in case of an unrestrained driver/passenger, there is no belt to prevent excessive motion of the body and excessive flexion or extension of the lumbar spine.
If hyperflexion or hyperextension occur, it will cause stretching of muscles, ligaments, nerves, joint capsules, and excessive force can cause vertebral fracture.
As in the cervical spine, excessive tension on nerve roots will cause their stretching or, in the worst case, tear. Any injury to nerves or nerve roots will cause symptoms. The most common symptoms of lumbar spine injury are lower back pain with radiation of pain down the leg, numbness of certain areas of leg or foot, and tingling in leg or foot.8
The location of numbness or tingling in the leg or foot will reveal the most likely injured nerve root. So, for example, if you have numbness or tingling in the heel, it is most likely that you have an injury of S1 nerve root.4
If the nerve injury is only mild, pain radiation, numbness and tingling will resolve after some time. But in the case of major nerve injuries, like nerve disruption, numbness and tingling will most likely be permanent.
X-rays are usually done after the injury and they can show fracture or dislocation of the spine, but they do not reveal nerve root or nerve injury. To diagnose nerve injury, more sophisticated diagnostic methods are used, usually MRI or EMG.
In conclusion, if you have numbness or tingling in your arms or hands it is most likely that your injury is located in the cervical spine (neck). And if you have numbness or tingling in your legs or feet, the most likely localization of injury is the lumbar spine (lower back).
- “Elbow Injuries.” HealthLink BC. N. p., 2019. Web. 14 Oct. 2019.
- “Understanding Spinal Anatomy: Overview Of The Spine.” Coloradospineinstitute.com. N. p., 2019. Web. 14 Oct. 2019
- Team, Spinal. “Functions Of The Spinal Cord: What You Need To Know.” Spinalcord.com. N. p., 2019. Web. 14 Oct. 2019.
- Benjamin Wedro, FAAEM. “How Do Dermatomes Work? Map, Myotomes Vs. Dermatomes.” eMedicineHealth. N. p., 2019. Web. 14 Oct. 2019.
- Chen HB, et al. “Biomechanics Of Whiplash Injury. – Pubmed – NCBI .” Ncbi.nlm.nih.gov. N. p., 2019. Web. 14 Oct. 2019.
- Tameem, Alifia, Sandeep Kapur, and Hirachand Mutagi. “Whiplash Injury.” Continuing Education in Anaesthesia Critical Care & Pain 14.4 (2014): 167-170. Web. 14 Oct. 2019.
- Mohammadzadeh, Mahdi et al. “Spinal Injury Resulting From Car Accident:Focus To Prevention.” Asian Journal of Neurosurgery 0.0 (2015): 0. Web. 14 Oct. 2019.
- “Spinal Cord Injury: Signs, Causes, And Prevention.” Healthline. N. p., 2019. Web. 14 Oct. 2019.