Whiplash is an injury mechanism caused by a rapid, forceful back-and-forth movement of the neck, similar to the cracking of a whip. This motion, common in vehicle collisions but also possible from sports injuries or falls, generates significant force that the neck’s soft tissues must absorb. The resulting condition is known as a whiplash-associated disorder (WAD), which includes a range of injuries affecting the muscles and ligaments.
Key Neck Muscles Strained by Whiplash
The neck’s complex musculature is vulnerable to the acceleration-deceleration forces of whiplash. The muscles at the front and sides of the neck are often the first strained as they try to control the head’s motion. This impact can lead to microtrauma in muscle groups responsible for head movement and stability, which is a primary source of the pain and stiffness following a whiplash event.
A prominent muscle affected is the sternocleidomastoid (SCM), a large muscle running from behind the ear to the collarbone and sternum. The SCM allows you to turn your head side to side and tilt it forward. During a whiplash event, it can be overstretched, leading to pain, stiffness, and a reduced range of motion. An SCM injury is also associated with headaches originating at the base of the skull and feelings of dizziness or imbalance.
The scalene muscles are a set of three muscles on each side of the neck involved in neck flexion and assisting with breathing. When these muscles are strained during whiplash, the injury can cause pain that radiates from the neck down into the shoulder and arm. This is because the brachial plexus, a bundle of nerves supplying the arm and hand, passes through the scalene muscles, and inflammation or spasms can cause compression.
Deeper within the neck lie the deep neck flexors, with the longus colli being a primary example. These muscles provide segmental stability to the vertebrae rather than performing large movements. The longus colli is often one of the first muscles injured in a whiplash event, suffering microscopic tears. Weakness in these deep flexors is a common finding in those with chronic issues, as their failure to properly support the neck can lead to instability and pain.
Affected Shoulder and Upper Back Musculature
The forces from a whiplash event do not stop at the neck, often dissipating downwards to the large muscles of the upper back and shoulders. Because these muscles are connected to the cervical spine, symptoms are rarely confined to the neck alone. The muscles in this region are strained as they contract to stabilize the head and shoulders, leading to pain and dysfunction in the upper torso.
The trapezius is a large, diamond-shaped muscle extending from the base of the skull, across the shoulders, and down to the middle of the back. It moves, rotates, and stabilizes the shoulder blades, as well as extending the neck. Its broad area and connection to the neck and shoulders make the trapezius highly susceptible to strain. Dysfunction of the trapezius is a consistent finding in people with long-term whiplash symptoms, presenting as tension and tenderness.
The rhomboid muscles are located between the spine and the shoulder blades. Their primary function is to retract the scapula, pulling the shoulder blades together. During a whiplash injury, the shoulders are often thrown forward, and the rhomboids can become strained as they work to counteract this momentum. This can lead to sharp pain between the shoulder blades, worsened by movement or deep breathing.
The Process of Muscle Healing
Following the microscopic tears caused by whiplash, the body initiates a natural healing process that occurs in distinct but overlapping phases. This sequence explains why symptoms like pain, swelling, and stiffness evolve as the muscles repair themselves. The process is a coordinated effort to clear out damaged cells and lay down new tissue.
The first stage is the inflammation phase, the body’s immediate response to injury. Blood vessels in the damaged area dilate, and immune cells rush to the site to clear away damaged muscle fibers. This influx of fluid and cells results in the characteristic signs of inflammation: swelling, redness, heat, and pain. This phase is a “clean-up” operation that prepares the area for repair.
Next is the repair phase, which can begin within a couple of days and last for several weeks. During this stage, fibroblasts arrive at the injury site and produce new collagen fibers. This new tissue is laid down in a disorganized manner, forming scar tissue to bridge the gap in the torn muscle. This new tissue restores some integrity but is initially weaker and less flexible than the original.
The final stage is the remodeling phase, a long-term process that can last for many months or even years. The body works to reorganize the disorganized collagen fibers into a more linear structure that aligns with the direction of muscle stress. This realignment makes the repaired tissue stronger and more flexible. Controlled movement and rehabilitation are introduced as healing progresses to help guide the proper alignment of the new fibers.