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The Whiplash Puzzle: Part 2 - Biomechanical Breakdown

Updated: Sep 9, 2023


In the first instalment of our series on overcoming whiplash injuries, we examined the impacts of Phase 1: Vehicle Collision and Phase 2: Neck Over-Extension in a whiplash-associated disorder (WAD). We also discussed the common anatomical structures affected by these injuries. This second part will concentrate on Phase 3 - Neck Hyper-Flexion.



Phase 3 - Neck Hyper-Flexion


Hyper-flexion, which refers to the neck bending forward excessively, happens when the driver's seat springs back into position, propelling the driver's entire body forward with great speed. You can visualize Phase 3 (neck Hyper-Flexion) as the final tensioning moment before spring is released. In this stage, while the vehicle seat surges forward, the head is still initially moving in the opposite direction.


Almost instantly during Phase 3, both the torso and the head are catapulted forward. The forward momentum is so powerful that, without seatbelts, passengers could be propelled out of their seats, hitting the steering wheel or even being ejected through the window, depending on the collision's force.


This intense forward movement causes the driver's entire spine to flex forward, often beyond normal limits. This violent action can significantly damage the back of the neck, mid-back, shoulder, and even the lower back.


 

Areas Of Damage During Hyper-Flexion


Joints, soft tissue, muscles, and ligaments can be severely stressed and damaged during Phase 3: Hyper-Flexion.


Joint Damage


Facet Joints - As noted earlier, facet joints bear the brunt of a whiplash injury as they are the most frequently affected joints in the neck. They endure tremendous strain during both the Hyper-Extension and Hyper-Flexion phases of the injury.




Soft Tissue Damage


Studies have demonstrated that MRI scans often reveal damage to the muscles at the back of the neck. In patients suffering from persistent neck pain, the MRI results indicate the presence of fat deposits within these posterior neck muscles (cervical extensors). Such fat infiltration has been linked to sensory, motor, and physical impairments in long-term cases of whiplash-associated disorders (WAD).



The Suboccipital Triangle

Nestled at the base of the skull is a region known as the suboccipital triangle, formed by three critical muscles: Obliquus Capitus Superior, Obliquus Capitus Inferior, and Rectus Capitis Posterior.


The significance of these suboccipital muscles lies in their abundance of neurological receptors. When a neck injury occurs, it doesn't just affect the ligaments, tendons, and muscle fibers, but also the neurological structures housed within them, such as Golgi tendon organs, muscle spindles, and joint receptors. These structures are crucial for maintaining posture. Damage to them could compromise spinal stability, potentially leading to persistent issues.


Moreover, these suboccipital muscles are rich in muscle spindle fibers, key nervous system components that relay postural information to the central nervous system. Injuries to these spindles could result in coordination problems, such as gait disturbances and ataxia (a condition that impedes voluntary muscle movements).


Upon comparing the density of muscle spindles in the suboccipital region with that in other spinal muscles, the impact of this area on the body's overall functioning becomes glaringly clear.


Let's consider the concentration of muscle spindles per gram of muscle tissue across various body parts:


  • Spindle density per gram 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 spindle density per gram of muscle tissue, the greater the role that particular region plays in managing our overall posture. For instance, the inferior oblique muscle, located at the base of your skull, possesses 242 spindles per gram of muscle tissue, significantly higher than the large latissimus dorsi (a major back muscle) holds only 1.4 spindles per gram of muscle tissue.


This highlights how a relatively small structure like the inferior oblique, due to its high spindle density, can influence remote areas of the body, from the neck to the lower back. Research has shown that damage to these structures in the suboccipital region can cause gait disturbances and ataxia in experimental animals.


Furthermore, the suboccipital nerve's role in supplying input to the suboccipital triangle's muscles is worth noting. This nerve can be directly compressed during a motor vehicle collision, particularly at the superior oblique muscle. Suboccipital nerve compression is one of the most frequent injuries observed in whiplash incidents.


Semispinalis Muscle

The Semispinalis Muscle, which includes the capitis and cervicis, holds significant importance due to its location directly above the greater occipital nerve. Compression of this nerve is a common cause of cervicogenic headaches often observed following a whiplash accident. These headaches, characterized by chronic pain in the upper neck, back of the head, and behind the eyes, are also referred to as occipital neuralgia, C2 neuralgia, or Arnold’s neuralgia. (11) Studies indicate that approximately 85% of whiplash patients present with trigger points in the semispinalis capitis muscle, further emphasizing the muscle's relevance in these injuries.


Splenius Muscle

The Splenius Muscle, encompassing the capitis and cervicis components, plays a vital role in head extension. It also contributes to the lateral bending and rotation of the neck. Given its significant involvement in neck movements, it's unsurprisingly susceptible to injuries during whiplash incidents. Damage to this muscle impacts all neck actions, potentially leading to restricted mobility and increased pain. This underlines the importance of proper diagnosis and treatment of injuries to the Splenius muscle following whiplash events to ensure optimal recovery and maintenance of neck function.


Multifidus Muscle

The Multifidus Muscle, located deep in the posterior part of the spine, is frequently impacted in motor vehicle collisions, with injuries spanning from the neck down to the lower lumbar region. Emerging research indicates that this muscle can exacerbate the loading on the facet capsular ligaments caused by a collision. Damage to the facet capsules is commonly associated with persistent neck pain. Therefore, injuries to the Multifidus Muscle during a vehicle accident can have lasting implications, potentially contributing to chronic neck discomfort.


When the upper fibers of the Trapezius muscle are compromised, it can constrict the third occipital nerve, which threads under the Trapezius muscle and culminates in the lower region of the head or occiput. This nerve compression can result in occipital neuralgias, a type of chronic headache.


Remember, we have only touched upon some of the frequent anatomical injury sites. We haven't explored injuries to the jaw structures and limb injuries (like those to the elbow, wrist, hand, knee, ankle, and foot) including peripheral nerve entrapments, which can manifest from motor vehicle collisions.


In the third part of "Resolving Whiplash Injuries," we will delve into common symptoms, the process of physical examination, and the classification of Whiplash Associated Disorders (WAD).


 

DR. BRIAN ABELSON DC. - The Author


Dr. Abelson is committed to running an evidence-based practice (EBP) incorporating the most up-to-date research evidence. He combines his clinical expertise with each patient's specific values and needs to deliver effective, patient-centred personalized care.


As the Motion Specific Release (MSR) Treatment Systems developer, Dr. Abelson operates a clinical practice in Calgary, Alberta, under Kinetic Health. He has authored ten publications and continues offering online courses and his live programs to healthcare professionals seeking to expand their knowledge and skills in treating musculoskeletal conditions. By staying current with the latest research and offering innovative treatment options, Dr. Abelson is dedicated to helping his patients achieve optimal health and wellness.

 

Please Note: References for all five sections of this article can be found at the end of Part Five.


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