RESOLVING WHIPLASH INJURIES PART 2 – BIOMECHANICS (continued)
Updated: Oct 14
In Part One of Resolving Whiplash Injuries we reviewed the effects of Stage 1: Vehicle Impact & Stage 2: Neck Hyper-Extension in a whiplash injury (WAD). We also took a look at some of the anatomical structures that are typically involved in these injuries. In Part 2 we will focus on Stage 3 – Neck Hyper-Flexion.
WHIPLASH BIOMECHANICS (continued)
Stage 3 - Neck Hyper-Flexion
Flexion, or the neck bending forward, occurs when the driver’s seat springs forward, causing the driver’s entire torso to move forward at a high velocity. (43) Think of Stage 3 (neck Hyper-Flexion) as a wind-up, or the final moment before a spring releases. During this stage, as the vehicle seat moves forward, the head is still initially moving back.
During Stage 3, almost instantaneously, both the torso and head are flung forward.This forward motion is so strong that if the passenger’s do not have their seat-belt on, they could, depending on the force of impact, be thrown right out of their seat into the steering wheel or even thrown through the window.
This strong forward action causes the driver’s whole spine to flex forward, often past its physiological limits. This violent action often causes a considerable amount of posterior neck, mid-back, shoulder, and even low back damage. (11, 12, 13, 14, 15, 16, 17)
AREAS OF DAMAGE DURING HYPER-FLEXION
Joints, soft tissue, muscles, and ligaments can be severely stressed and damaged during Stage 3: Hyper-Flexion.
Facet joints – As previously mentioned, facet joints are the most commonly injured joints in the neck since they experience extreme stress during both Hyper-Extension and Hyper-Flexion. (12,43)
Soft Tissue Damage
Research has shown that damage to the posterior neck musculature is often evident on MRI studies. In patients who experience chronic neck pain, the MRI shows indications of fatty infiltration in the posterior neck muscles (cervical extensors). This fatty infiltration is associated with sensory, motor, and physical dysfunctions in cases of chronic WAD. (39, 40)
The Suboccipital Triangle – This is an area in the neck located at the base of the skull, and is made up of three key muscles:
The suboccipital muscles are extremely important since they contain very high levels of neurological receptors. Whenever an injury occurs in your neck, it damages not only the ligaments, tendons, and muscle fibres, but also their embedded neurological structures (Golgi tendon organs, muscle spindles, and joint receptors). These neurological structures play an essential role in postural control. Any damage to these structures can affect overall spinal stability, and lead to chronic problems. (55)
The suboccipital muscles also contain very high concentrations of muscle spindle fibres, which are the part of the nervous system that provide postural information to the central nervous system. Damage to muscle spindles can result in gait disturbances and ataxia (an inability to coordinate voluntary muscle movements). (55)
When we compare the density of muscle spindles that pass through, or that occupy the suboccipital area, to that of other muscles in the spine, it becomes obvious just how much this area can affect the function of the whole body.
Take a minute to review the density of muscle spindles per gram of muscle tissue in different parts of the body: (13, 55)
Density of spindles/ gm of muscle tissue
Inferior Oblique (Upper Neck) 242
Superior Oblique (Upper Neck) 190
Rectus Capitis Posterior Major (Upper Neck) 98
Rectus Capitis Posterior Minor (Upper Neck) 98
Longus Colli (Front of Neck) 48.6
Multifidus (Deep back muscle) 24.3
Lateral Pterygoid (Jaw muscle) 20.3
Opponens Pollicis (Hand Muscle) 17.3
Trapezius(Shoulder muscle) 2.2
Latissimus Dorsi (Large back muscle) 1.4
The higher the density of muscle spindles/gm of muscle tissue, the greater the involvement of this area in maintaining whole- body postural control. Given this, you can see that the inferior oblique muscle (located at the base of your skull) contains 242 spindles/gm of muscle tissue, while the very large latissimus dorsi (large back muscle) only contains 1.4 spindles/gm of muscle tissue. (55)
Even though the inferior oblique is a small structure located at the base of your skull, due to the density of muscle spindles in this area, a restriction in this muscle can affect distant structures; from your neck through to your lower back. In fact, research shows that damage to these structures in the suboccipital region (in experimental animals) causes gait disturbances and ataxia (an inability to coordinate voluntary muscle movements). (13, 55)
In addition, we must consider that the suboccipital nerve supplies input to the muscles of the suboccipital triangle. During a MVC, direct compression of the suboccipital nerve can occur at the superior oblique muscle. In fact, suboccipital nerve compression is one of the most common injuries found in whiplash accidents. (13, 55)
The Semispinalis Muscle (capitis, cervicis) is important because the greater occipital nerve is located directly under the semispinalis capitis muscle. Compression of greater occipital nerve is one of the causes of cervicogenic headaches that is often seen after a whiplash accident. (14) This type of headache is often referred to as an occipital neuralgia, and is a medical condition characterized by chronic pain in the upper neck, back of the head, with pain behind the eyes. This is also known as C2 neuralgia or Arnold’s neuralgia. (11) Research has shown that about 85% of patients with whiplash injuries have trigger points in the semispinalis capitis muscle. (14)
The Splenius Muscle (capitis, cervicis) is a prime mover for head extension. It is also involved in lateral flexion and rotation of the neck. This neck extensor is commonly injured in whiplash injuries, and affects all actions of the neck. (15)
The Multifidus Muscle is a deep posterior muscle that is often injured during a MVC anywhere from the neck to the lower lumbar region. Research is showing that the multifidus muscle can increase collision-induced loading of the facet capsular ligaments. (17) Facet capsule damage is often related to chronic neck pain.
When the Trapezius muscle (upper fibers) are injured, it can lead to compression of the third occipital nerve, which travels under the trapezius muscle until it pierces this muscle and ends up in the lower part of the head (occiput). Compression of this nerve causes occipital neuralgias. (13,14)
It is important to note that we have only mentioned some of the common anatomical areas of injury. We have not mentioned injuries to structures of the Jaw and extremity injuries (elbow, wrist, hand, knee, ankle, foot) including peripheral nerve entrapment. All of these can also occur during a MVC.
Part Three: In Part Three of “Resolving Whiplash Injuries”, I will discuss typical symptoms, the physical examination process, and WAD categorization. Please note all references are at the end of Part 5.
DR. BRIAN ABELSON DC.
Dr. Abelson believes in running an Evidence Based Practice (EBP). EBP's strive to adhere to the best research evidence available, while combining their clinical expertise with the specific values of each patient.
Dr. Abelson is the developer of Motion Specific Release (MSR) Treatment Systems. His clinical practice in is located in Calgary, Alberta (Kinetic Health). He has recently authored his 10th publication which will be available later this year.