The anteroposterior (AP) knee view is a standard X-ray projection with the beam directed front-to-back through the knee. Performed supine or standing with the knee extended or slightly flexed, it images the distal femur, proximal tibia and fibula and joint space. It assesses fractures, bone alignment, and joint space narrowing; weight-bearing AP films better demonstrate osteoarthritic joint space loss.

A bilateral knee X-ray is a radiographic exam that images both knees in one study to compare structures. Typical views include anteroposterior and lateral (and sometimes patellar skyline or weight-bearing). It evaluates fractures, dislocations, osteoarthritis, joint-space narrowing, bone lesions, or foreign bodies. The test is quick, noninvasive and uses low-dose ionizing radiation to guide diagnosis and treatment.

The three standard knee X‑ray views are anteroposterior (AP), lateral, and a patellar skyline (axial/tangential) view. AP shows overall alignment, joint space, and distal femur/proximal tibia. Lateral demonstrates patellofemoral relationship, effusion, and posterior contours. The skyline view assesses patellar alignment, articular surface, and trochlear groove for subluxation or cartilage irregularity.

The AP (anteroposterior) knee single-view CPT is 73560. For bilateral standing knees, report the appropriate bilateral knee CPT (73564–73565, depending on number of views) or bill the unilateral code (73560/73561/73562) with modifier -50 per payer requirements. Confirm specific payer/billing rules for bilateral radiography coding.

Aplasia (patellar aplasia) is a rare congenital condition where the kneecap is absent or underdeveloped. It commonly causes knee instability, difficulty extending the leg, pain, and an altered gait. Diagnosis relies on clinical exam and imaging (X‑ray or ultrasound). Treatment ranges from physiotherapy and bracing for stability to surgical reconstruction for significant functional impairment.

To identify an AP (anteroposterior) radiographic view: first check the image marker or technique note for “AP” or “portable.” If not labeled, look for telltale signs: relatively enlarged cardiac silhouette from magnification, scapulae projected over lung fields, clavicles higher or asymmetric, and evidence of poor inspiration or supine positioning. These features suggest an AP rather than PA projection.