Radiographic Evaluation of Knee Joint

Standard Radiographic Projections

The American College of Radiology recommends that routine radiography for evaluation of knee joint in weight-bearing position consists of anteroposterior (AP) and lateral views in bipedestation, plus an axial tangential view of the patellofemoral joint 1, 2
Some specialists also use full-length leg radiographs (hip-ankle) in bipedestation for optimal evaluation of alignment 1, 3
The standard AP radiograph of the knee is a valid alternative to the hip-ankle radiograph for determining coronal alignment, but the longer hip-ankle radiograph provides accurate information about the mechanical axis of loading in patients with suspected lower limb malalignment 1, 2

AP radiographs with 10° internal rotation improve interpretation of varus and valgus alignment compared to neutral AP views 1, 2, 4

Radiographic evaluation of wear is based on weight-bearing AP and lateral radiographs, and axial radiographs 1, 2
Linear wear is observed as narrowing of the joint space, and may be accompanied by effusion 1, 3
Annual weight-bearing radiographs are recommended to detect subclinical wear 1, 2
Measurements on frontal radiographs of the knee in bipedestation have an accuracy of approximately 1 mm for evaluating polyethylene thickness in prostheses 1, 3

Axial (tangential) radiographs demonstrate the degree of patellar tilt or subluxation 2, 4
Weight-bearing axial radiographs provide a superior evaluation of patellofemoral kinematics compared to non-weight-bearing views 4

Instability is evaluated on radiographs obtained in extension-flexion position, under varus-valgus stress, and during anterior and posterior drawer maneuvers 2
Malalignment refers to suboptimal alignment of prosthetic components with each other and is evaluated on full-length radiographs in bipedestation 2

Follow-up is recommended every 1-2 years, continued long-term (>10 years) 1, 3
Serial radiographs are important for identifying subtle interval changes 3, 5
80% of orthopedic surgeons recommend annual or biennial radiographic examinations, and more frequent follow-up if there are signs of failure or sepsis, subnormal periprosthetic bone quality, or a history of previous revision 1, 3

The American College of Radiology recommends a standing full-length hip-to-ankle radiograph as the gold standard for assessing knee valgus deformity, as it provides accurate information on the weight-bearing mechanical axis necessary to evaluate lower limb malalignment 6, 7
A full-length hip-to-ankle radiograph must be obtained in a standing (weight-bearing) position to accurately reflect functional alignment under load 6, 7
This radiograph provides a comprehensive evaluation of the mechanical axis in patients with suspected lower limb malalignment 6, 7

The American College of Radiology suggests using a standing full-length hip-to-ankle radiograph as the primary study for initial assessment of valgus deformity 6, 7
A standing AP knee view with 10° internal rotation is recommended for detailed joint assessment 6, 7

The American College of Radiology advises against relying on standard AP knee radiographs alone for valgus assessment, as they cannot accurately measure the mechanical axis 6, 7
Non-weight-bearing radiographs should be avoided, as they fail to demonstrate true functional alignment under physiologic load 6, 7
Radiographs should not be obtained in neutral rotation when assessing valgus/varus alignment; 10° internal rotation significantly improves accuracy 6, 7

After establishing baseline alignment with a full-length hip-to-ankle radiograph, subsequent monitoring can utilize targeted standing AP knee radiographs with 10° internal rotation 6, 7
Serial full-length films remain the gold standard for tracking progression of valgus deformity over time 6, 7