Anterolisthesis of C4 on C5 is a spinal condition where the fourth cervical vertebra (C4) has slipped forward over the fifth cervical vertebra (C5) beneath it. This misalignment occurs in the neck, the most flexible region of the spine. Even a small forward shift can potentially affect the delicate nerve structures. The severity of the slippage and its cause determine the resulting symptoms and the required medical approach.
Anatomical Context and Definition
The cervical spine consists of seven stacked bones, designated C1 through C7, which support the head and allow for a wide range of neck motion. C4 and C5 are located in the subaxial region, the most common area for degenerative changes in the neck. Between these two vertebral bodies lies the C4-C5 intervertebral disc, a fluid-filled cushion that functions as a shock absorber. Stability of this segment relies on the paired facet joints located at the back of the vertebrae and a network of supporting ligaments.
Anterolisthesis is the forward translation of a superior vertebral body relative to the one below it; in this case, C4 has moved forward over C5. This displacement places abnormal stress on the surrounding ligaments, discs, and neural structures.
The severity of the slip is routinely quantified using the Meyerding classification system, which measures the percentage of the superior vertebral body that has slipped forward over the one below. A Grade I slip involves a translation of up to 25% of the vertebral body’s length. Grade II ranges from 26% to 50%, Grade III from 51% to 75%, and Grade IV from 76% to 100%. This grading helps determine the degree of mechanical instability and guide treatment.
Common Causes and Risk Factors
The most frequent cause of C4-C5 anterolisthesis is age-related wear and tear, known as degenerative spondylolisthesis. This process begins when the intervertebral disc loses height and hydration, narrowing the disc space. As the disc collapses, the load is improperly transferred to the facet joints, causing their degeneration and failure to maintain spinal alignment.
The C4-C5 level is particularly prone to this degenerative slippage because it often compensates for reduced mobility in the lower cervical segments (C5-C6 and C6-C7). When the lower discs become stiff, the C4-C5 segment may become hypermobile, leading to increased stress and instability. The failure of stabilizing ligaments, such as the posterior longitudinal ligament, then allows the C4 vertebra to slide forward.
A less common cause is traumatic injury to the neck, such as severe whiplash. Acute trauma can damage the facet joints or tear stabilizing ligaments, resulting in immediate instability and forward slippage. Other risk factors include a history of previous cervical surgery or a congenital abnormality that predisposes the spine to misalignment.
Symptoms and Associated Neurological Effects
Not all cases of C4-C5 anterolisthesis are symptomatic; a mild slip may be an incidental finding. When symptoms do occur, they typically fall into two categories: localized neck pain and neurological impairment. Localized symptoms include chronic pain in the posterior neck, stiffness, and a decreased range of motion, particularly when attempting to look upward (extension).
Neurological effects arise when the forward slip compresses the spinal cord or exiting nerve roots. At the C4-C5 level, nerve root compression most commonly affects the C5 nerve root, leading to cervical radiculopathy. C5 radiculopathy presents as pain, tingling, or numbness radiating from the neck into the shoulder and down the upper arm. Motor weakness may also be present, affecting the deltoid (lifting the arm) and the biceps (controlling elbow flexion).
More serious symptoms occur if the spinal cord itself is compressed, a condition known as cervical myelopathy. Anterolisthesis at C4-C5 frequently causes myelopathy, which is often dynamic, meaning compression worsens with neck movement (e.g., extension). Myelopathy symptoms are more generalized and can include difficulty with fine motor skills, such as buttoning a shirt, and gait instability, often described as clumsiness. In advanced cases, myelopathy can cause loss of bowel or bladder control, which is considered a medical emergency.
Diagnosis and Treatment Pathways
The diagnostic process begins with a thorough physical examination, assessing reflexes, muscle strength, and sensation patterns to pinpoint neurological deficits. Imaging studies are then used to confirm the diagnosis and quantify the extent of the slippage. Standard X-rays provide a clear view of bone alignment and are supplemented by dynamic flexion and extension views. These dynamic X-rays are important for determining if the segment is unstable, typically defined as a translation of 3.5 millimeters or more between the vertebrae.
Magnetic Resonance Imaging (MRI) visualizes soft tissues, including the disc, ligaments, spinal cord, and nerve roots. This scan is crucial for determining if the anterolisthesis is causing nerve root impingement or spinal cord compression. A Computed Tomography (CT) scan provides detailed images of the bone structure, especially the facet joints and any contributing bone spurs.
Treatment typically starts with non-operative management for mild to moderate cases without significant neurological symptoms. This pathway includes physical therapy focused on stabilizing the neck by strengthening deep cervical flexor muscles and improving posture. Medications such as non-steroidal anti-inflammatory drugs (NSAIDs) and muscle relaxants can help manage pain and spasms. Steroid injections may be administered near the affected nerve roots or facet joints to provide localized pain relief.
Surgical intervention is reserved for patients who fail conservative treatment, have progressive neurological deficits, or show signs of severe instability or myelopathy. The primary goal of surgery is to decompress neural structures and stabilize the slipped segment. A common procedure is an Anterior Cervical Discectomy and Fusion (ACDF), where the degenerated disc is removed, the C4-C5 segment is realigned, and a bone graft is placed to fuse the two vertebrae together. This fusion prevents further movement and stabilizes the spine, protecting the spinal cord and nerve roots.