Positioning Errors and Anatomical Criteria

Why Positioning Criteria Matter

A radiograph is only clinically useful when the anatomy of interest is shown clearly, completely, and without distortion. Published anatomical criteria—found in references such as Bontrager's Textbook of Radiographic Positioning and Related Anatomy—define exactly what must appear on each projection: which structures must be included, how they should be aligned, and what landmarks should be centered or visible. When a radiograph falls short of those criteria, the interpreting provider may miss pathology, order a repeat exposure, or make an incorrect diagnosis. Repeat exposures add unnecessary radiation dose to the patient, so getting positioning right the first time is both a quality and a safety obligation.

As a limited-scope or entry-level radiographer, your responsibility is to recognize when a finished image meets criteria and, when it does not, to identify the specific error and know how to correct it before—or instead of—repeating the exposure.

Common Categories of Positioning Error

Rotation occurs when the patient's body part is not properly aligned with the image receptor (IR). On a PA chest, rotation is detected by comparing the medial ends of the clavicles: they should be equidistant from the spinous processes of the thoracic vertebrae. If one clavicular head is closer, the patient was rotated toward that side. On an AP pelvis, the obturator foramina should appear symmetric; asymmetry indicates rotation.

Tilt is different from rotation. Tilt describes a superior-to-inferior angling of the part rather than a left-to-right twist. On a lateral lumbar spine, tilt shows as the posterior cortices of the vertebral bodies not being superimposed.

Incorrect centering means the central ray (CR) was directed to the wrong anatomical landmark. For a PA chest, the CR is typically centered to the midsagittal plane at the level of the inferior angle of the scapulae (approximately T7). If the CR is too high, the lung apices may be clipped; if too low, the costophrenic angles may be cut off.

Inadequate collimation means the radiation field is larger than necessary for the anatomy of interest. This increases scatter radiation, reduces image contrast, and delivers unnecessary dose to adjacent tissues. Proper collimation should be visible as a border of unexposed film (or digital equivalent) around the anatomy.

Part positioning errors include failure to achieve the correct projection angle, failure to remove superimposing structures, or failure to place a joint in the required flexion or extension. For example, on a lateral knee, the femoral condyles should be superimposed; a gap indicates the leg was not truly lateral.

Anatomy not fully included means a required structure is clipped at the edge of the image. For extremities, joints proximal and distal to a long-bone fracture site must be included on at least one projection per most protocols.

Evaluating a PA Chest Radiograph

For the PA chest, the accepted anatomical criteria include:

• Both lungs visualized from apices to costophrenic angles
• Ten posterior ribs visible above the diaphragm on full inspiration
• Clavicular medial ends equidistant from spinous processes (no rotation)
• Scapulae projected laterally, outside the lung fields, due to patient positioning with hands on hips and elbows forward
• Trachea visible in the midline
• Sharp cardiac and diaphragmatic borders indicating adequate inspiration and no significant motion

If you see fewer than ten posterior ribs, the patient likely did not fully inspire, or the exposure was taken at the wrong phase of breathing. If the scapulae overlie the lungs, the patient's arms were not correctly positioned.

Evaluating a Lateral Lumbar Spine Radiograph

For the lateral lumbar spine:

• All five lumbar vertebrae and the L5–S1 disc space must be included
• Vertebral end plates should appear as clean horizontal lines, not double-shadowed (indicating true lateral position)
• Intervertebral joint spaces should be open
• A lead marker confirms the side closest to the IR

If the posterior vertebral body margins are not superimposed (double-shadowed posterior cortices), the patient was rotated. The correction is to adjust the patient's pelvis until a true lateral position is achieved, sometimes using positioning sponges under the waist to keep the spine parallel to the IR.

Stating the Corrective Adjustment

Identifying an error is only half the task. You must also state the specific corrective action in terms a colleague could act on:

• "Patient rotated LPO; correct by rotating patient's left shoulder anteriorly until MSP is perpendicular to IR."
• "Lateral lumbar shows double vertebral shadows; support waist with sponge and recheck coronal alignment."
• "PA chest clipped at left costophrenic angle; lower CR to T7 level and verify 14×17 IR oriented lengthwise."

Vague statements like "reposition the patient" are not acceptable. Name the direction of error and the direction of the fix.

Radiation Safety During Image Evaluation Labs

When using a live radiographic unit in lab:

• Only qualified or supervised students may operate the unit
• All persons not essential to the exposure must stand behind the control barrier or wear a lead apron and dosimeter
• Collimate to the anatomy of interest—never leave the beam open to full field
• Confirm the volunteer or phantom is in the correct position before making the exposure to avoid preventable repeats
• Document any repeat exposures as required by your program and facility policy

Patient identification and correct laterality markers (R or L) must be confirmed before every exposure. A mislabeled radiograph can lead to wrong-side surgery or missed diagnosis—both serious patient safety events.