The spinal column is a complex structure of stacked bones, or vertebrae, which provides stability for the body and protects the delicate spinal cord. When the natural alignment of these vertebrae is disrupted, it can lead to mechanical instability and potential neurological problems. Retrolisthesis is a specific type of misalignment describing the backward displacement of one vertebra relative to the one immediately below it. This condition is most common in the cervical spine (neck) and the lumbar spine (lower back) due to the high degree of movement and stress in these regions.
Defining Retrolisthesis of C4 on C5
Retrolisthesis of C4 on C5 occurs when the C4 vertebral body slips backward over the C5 vertebral body beneath it. The cervical spine (C-spine) consists of the seven topmost vertebrae (C1 through C7). C4 and C5 are in the mid-cervical section, facilitating head and neck movement.
This displacement creates a step-off in the spine’s smooth curvature at that level. This misalignment compromises the structural integrity of the spinal segment, including the intervertebral disc and surrounding ligaments. The severity of the slippage is measured using a grading system based on a lateral X-ray view of the neck.
Grades are assigned based on the percentage of posterior displacement of the vertebral body. A Grade 1 retrolisthesis represents a minor slip of up to 25% of the vertebral body’s width. The grading progresses to Grade 2 (25% to 50%), Grade 3 (50% to 75%), and Grade 4 (75% to 100%). Higher grades indicate greater instability and a higher likelihood of neurological involvement.
Primary Causes and Contributing Risk Factors
The primary mechanism involves a compromise in the stabilizing structures of the spinal motion segment. Degenerative disc disease (DDD) is a frequent factor, causing the C4-C5 intervertebral disc to lose water content and height. This disc shrinkage decreases the space between the vertebrae, allowing the C4 bone to shift backward on the C5 bone.
Osteoarthritic changes (spondylosis) in the facet joints can destabilize the segment. These joints connect the vertebrae and can wear down, leading to abnormal movement and slippage. When the joints and surrounding ligaments become lax or damaged, they fail to hold the C4 vertebra securely in position.
Traumatic injury, such as from a fall, contact sport, or whiplash, can suddenly destabilize the C4-C5 segment. Trauma can tear or overstretch the ligaments and soft tissues that restrain the vertebrae, resulting in acute posterior displacement. Chronic poor posture or weak neck and core musculature can also exacerbate existing instability by placing excessive shearing forces on the compromised segment.
Common Symptoms and Neurological Effects
Symptoms vary widely depending on the degree of slippage and whether nervous tissue is compressed. Localized pain and stiffness in the neck are common complaints, often accompanied by a reduced range of motion. The mechanical irritation from the misaligned vertebrae frequently leads to chronic muscle tension and discomfort.
When the backward slip narrows the intervertebral foramen—the opening where a nerve root exits—it can compress the spinal nerve, causing cervical radiculopathy. Since the C5 nerve root exits near the C4-C5 level, compression often causes radiating pain, numbness, tingling, or weakness traveling down the shoulder and into the arm. Patients may notice difficulty lifting the arm, as the C5 nerve root supplies muscles like the deltoid and biceps.
A more severe consequence is myelopathy, which occurs if displacement narrows the central spinal canal and compresses the spinal cord. Myelopathy manifests as a loss of fine motor skills in the hands, such as struggling with buttoning a shirt or writing. It may also affect balance and gait, causing difficulty walking, and if left untreated, this serious condition can lead to permanent nerve damage.
Diagnostic Procedures and Management Strategies
Diagnosis begins with a detailed physical examination where a physician assesses the patient’s reflexes, muscle strength, sensation, and range of motion. Imaging studies confirm the diagnosis and measure the extent of the slippage. Plain lateral X-rays of the cervical spine are the initial and most effective tool for visualizing vertebral alignment, especially when taken while the patient is standing.
Dynamic X-rays, taken during neck flexion and extension, determine if the C4-C5 segment is unstable and moves excessively. While X-rays show bone structure, a Magnetic Resonance Imaging (MRI) scan is ordered to evaluate soft tissues, including the intervertebral discs, ligaments, spinal cord, and nerve roots. The MRI confirms whether the retrolisthesis is causing nerve root compression or myelopathy.
Initial management is conservative, focusing on pain relief and stabilization. Non-steroidal anti-inflammatory drugs (NSAIDs) may be prescribed to reduce pain and inflammation around the affected segment. Physical therapy is a cornerstone of non-surgical treatment, involving specific exercises to strengthen deep neck flexors and surrounding muscles to improve spinal support and posture.
If conservative measures fail to alleviate nerve-related symptoms, interventional procedures, such as targeted steroid injections near the affected nerve root, may be considered. Surgery is generally reserved for cases involving high-grade instability, persistent pain, or clear signs of progressive neurological deficit like myelopathy or severe radiculopathy. Surgical options often involve fusion procedures, such as an anterior cervical discectomy and fusion (ACDF), which permanently stabilizes the C4-C5 segment to prevent further slippage and relieve pressure on nervous tissue.