Chiropractors use a combination of hands-on feel, visual observation, patient history, and sometimes technology to decide exactly which joints to adjust. The process is more systematic than it looks from the patient’s perspective. Before anything “cracks,” a chiropractor has typically run through several layers of assessment to narrow down which spinal segments are restricted, misaligned, or contributing to your symptoms.
Feeling for Restricted Joints
The most fundamental skill chiropractors rely on is palpation, which simply means using their hands to feel what’s happening in your spine. There are two main types. Static palpation involves pressing gently along the spine and surrounding muscles to find points of tenderness, muscle tightness, or swelling. If you wince or tense up when they press a specific spot, that’s useful information.
Motion palpation goes a step further. The chiropractor moves you through different directions of movement (bending forward, backward, side to side, and rotating) while their hands rest across several vertebrae at once. They’re feeling for segments that don’t glide the way they should. A joint that moves freely in one direction but feels stuck in another tells the chiropractor something specific about what’s going on at that level. Rather than trying to detect tiny movements at a single vertebra, practitioners are trained to feel for obvious restrictions across a broader area, then zero in from there.
What They See Before They Touch You
Most chiropractors perform a visual postural assessment before any hands-on work begins. A UK survey of practicing chiropractors found that practitioners observe up to 44 specific anatomical landmarks during this step. Over 96% assess you from behind, about 80% look from the front, and roughly 72% check both side profiles.
From behind, the main thing they’re checking is symmetry. Are your shoulders level? Do your shoulder blades sit at the same height? Are your hips even? The gaps between your arms and your torso (sometimes called “keyholes”) can reveal whether your trunk is shifting to one side. They also look at your rib cage, the curves of your spine, and whether one set of muscles appears more developed or wasted than the other.
From the side, the focus shifts to spinal curves. They’re checking whether your head sits forward over your shoulders, whether the upper back rounds excessively, whether the lower back curves too much or too little, and whether your pelvis tilts forward or backward. Some chiropractors also look for rotational patterns, checking whether your head, shoulders, and pelvis are twisted relative to each other and to where your feet point. All of these visual cues help build a map of which areas of the spine are likely under the most mechanical stress.
The Leg Length Check
If you’ve ever been asked to lie face down while the chiropractor lifts both your feet and compares them, that’s a leg length assessment. It’s a hallmark of the Activator Method, one of the most widely used low-force techniques. The chiropractor looks for whether one leg appears functionally shorter than the other, which they interpret as a sign that the pelvis or spine is out of balance.
A study of two experienced practitioners using this method found 85% agreement between them when assessing the same 34 patients, which suggests the test is reasonably reproducible. That said, the study’s authors noted that reproducibility doesn’t necessarily prove the test measures what it claims to measure. It’s one data point chiropractors use alongside other findings rather than a standalone diagnostic tool.
Technology Some Chiropractors Use
Some clinics go beyond hands and eyes. Surface electromyography (EMG) uses electrodes placed on the skin along your spine to measure electrical activity in the muscles on either side. The idea is that if one side is firing much harder than the other, or if certain segments show unusually high or low muscle activity, that asymmetry points to areas where the nervous system is compensating for a problem.
Thermal scanning works on a similar principle but measures temperature differences along the spine. Uneven temperatures on the left versus right side may reflect changes in how the autonomic nervous system is regulating blood flow in that area. Neither of these tools is universal in chiropractic practice, but clinics that use them treat the readings as objective data to complement what they find by hand.
When X-Rays Come Into Play
There’s genuine disagreement within the profession about when imaging is necessary. The prevailing clinical guidelines recommend against routine X-rays for most patients under 65 during the first four to six weeks of care, since the vast majority of people don’t have serious underlying conditions like fractures, infections, or tumors. Under this approach, imaging is reserved for red flag situations.
Other factions within chiropractic take a different view, arguing that X-rays are a routine part of practice for both adults and children because they reveal biomechanical details (like how individual vertebrae are positioned relative to each other) that hands alone can’t detect. In practice, whether you get X-rayed depends heavily on your chiropractor’s training philosophy, your symptoms, your age, and your health history.
What Actually Makes the Cracking Sound
The “crack” itself has nothing to do with bones snapping or grinding. Your spinal joints are enclosed in capsules filled with synovial fluid, a thick liquid that lubricates the joint surfaces. When a chiropractor applies a quick, controlled thrust, the joint surfaces separate rapidly. That sudden separation creates negative pressure inside the capsule, and a gas cavity forms in the fluid, much like pulling apart two wet surfaces that have been stuck together. Research using real-time MRI imaging confirmed that the cracking sound happens at the exact moment this gas cavity forms, not when it collapses later. The process is called tribonucleation.
This is also why you can’t crack the same joint again immediately. The gas cavity needs time to reabsorb into the fluid before the joint can cavitate again, which typically takes about 20 minutes.
Safety Screening Happens First
Before choosing where (and how) to adjust, chiropractors are trained to screen for conditions that make spinal manipulation risky. Certain vascular issues are a particular concern in the neck. Cadaver research on vertebral arteries has shown that rotational manipulation of the cervical spine can stretch and compress these blood vessels, and in patients with hardened or calcified arterial walls, that mechanical stress could contribute to vascular injury. This is one reason chiropractors ask about cardiovascular history, stroke risk factors, and symptoms like dizziness or visual disturbances before working on the neck.
The screening process also covers recent injuries, osteoporosis, inflammatory joint diseases, and any neurological symptoms that might suggest something more serious than a stiff back. These findings don’t just determine where to adjust. They determine whether a traditional high-velocity thrust is appropriate at all, or whether a gentler instrument-based or mobilization approach makes more sense.