A herniated disc occurs when the soft material from the center of an intervertebral disc pushes out through a tear in the outer ring, often irritating nearby nerves. This displacement can cause pain, numbness, or weakness, particularly in the lower back and legs. Concerns frequently arise about the safety of spinal manipulation (SMT), a common chiropractic technique, and whether the forces involved could cause or worsen this condition. Understanding the actual risk requires examining the scientific evidence and the specific mechanics of the procedure.
Evidence on Causing a New Herniation
The question of whether a chiropractor can cause a new, or de novo, herniated disc is addressed by examining the statistical incidence of severe adverse events following spinal manipulative therapy (SMT). Large-scale studies consistently classify severe complications, such as a new disc herniation, as extremely rare events. One analysis of nearly one million SMT sessions reported a severe adverse event incidence of approximately 0.21 per 100,000 sessions. The few severe cases reported were typically rib fractures in patients with osteoporosis, not disc herniations.
The risk of a patient with a pre-existing lumbar disc herniation experiencing a clinically worsened condition or cauda equina syndrome after SMT is estimated to be less than 1 in 3.7 million. This low figure suggests the procedure is not a common trigger for severe disc pathology. While the risk is not mathematically zero, the likelihood of SMT causing a new disc herniation in a previously healthy spine is negligible.
It is important to differentiate between causing a new injury and exacerbating a pre-existing, often asymptomatic, condition. Manipulation may temporarily increase discomfort in individuals who have disc bulges or small tears that are not causing symptoms. However, studies investigating the safety of SMT for patients with confirmed lumbar disc herniation have found no reports of serious complications.
The current medical consensus is that the forces generated during manipulation are well-tolerated by healthy disc tissue. The low incidence rate of severe adverse events is comparable to or lower than the risks associated with many common medical interventions for back pain. This places the risk of a new herniation in the category of a statistical anomaly.
Biomechanics of Spinal Manipulation
Spinal manipulation primarily involves a High-Velocity Low-Amplitude (HVLA) thrust, which is a controlled, sudden force delivered over a very short distance. The practitioner applies a gentle pre-load force to position the joint near the end of its typical range of motion. The goal is to move the joint complex slightly beyond its normal physiological limit but still within its anatomical boundary.
The thrust is characterized by high speed and minimal amplitude. This quick stretch often results in a popping sound, or cavitation, caused by the sudden release of gas bubbles within the synovial fluid of the facet joints. The forces involved are directed specifically to the targeted spinal segment.
The structural design of the spine, particularly the facet joints, provides a natural safety stop against excessive rotational forces that can damage the disc. The intervertebral disc typically requires about 16 degrees of rotation to tear the outer ring and herniate. However, the facet joints limit rotation to a much smaller range, often just 2 to 3 degrees.
This inherent limitation protects the disc from the extreme rotational stress necessary to cause a tear. The technique is specifically designed to work with the spine’s anatomy to avoid the misdirected or excessively forceful thrust that could overcome this natural protection.
Identifying Patient Risk Factors
Proper patient selection is the primary method practitioners use to mitigate the already low risk of adverse events. A thorough screening process, including a detailed medical history and physical examination, identifies any absolute or relative contraindications. Certain underlying conditions can make a patient more susceptible to injury from the forces of SMT.
Absolute contraindications are conditions where manipulation should not be performed due to the high risk of serious harm. These include severe osteoporosis, which makes bones brittle and prone to fracture, and acute spinal cord compression or cauda equina syndrome. Any progressive neurological deficit, such as rapidly worsening weakness or numbness, warrants immediate referral for medical imaging and different management.
For patients with a known disc issue, such as acute radiculopathy, manipulation is often avoided or substituted with gentler mobilization techniques. The clinician must rule out an extruded disc with myelopathy—disc material pressing on the spinal cord—a condition that could be worsened by mechanical forces. Imaging review, such as an MRI or X-ray, may be necessary to confirm the structural integrity of the spine before proceeding with SMT.
By carefully screening for red flags, such as undiagnosed fractures, tumors, or severe bone-weakening diseases, the practitioner ensures the patient is an appropriate candidate for SMT. This focus on individual patient status, rather than the procedure itself, is the final layer of safety.