Standardizing Joint-Line determination on anteroposterior knee radiographs: multicenter validation of the adductor ratio and a novel composite index in 3000 knees

Category	Detail
Condition	Joint line (JL) displacement in knee arthroplasty
Key Mechanisms	Alterations in joint line position affect knee stability, patellofemoral forces, range of motion, and risk of aseptic loosening
Target Population	Patients undergoing primary or revision knee arthroplasty without advanced arthritis or prior knee surgery
Care Setting	Orthopedic and traumatology clinics performing radiographic assessment of knee joint line

Small changes in joint line position (≥2 mm) can cause clinical and functional deterioration post-arthroplasty.
Proximal joint line displacement increases patellofemoral compression, anterior knee pain, polyethylene wear, and aseptic loosening risk.
Distal joint line displacement leads to mid-flexion instability, limited range of motion, and increased aseptic loosening risk.

Use standardized anteroposterior (AP) knee radiographs with full extension and no rotation for joint line measurement.
Identify anatomical landmarks such as adductor tubercle, fibular head, medial and lateral femoral epicondyles for measurements.
Calculate indices based on distances from these landmarks to the joint line normalized by femoral width.

Aim to restore joint line to normal anatomical position during primary and revision knee arthroplasty to optimize clinical outcomes.
Avoid joint line displacement greater than 2 mm to prevent instability and functional impairment.

Perform radiographic joint line assessments postoperatively using validated indices to ensure anatomical restoration.
Consider demographic factors such as age, gender, and region when interpreting joint line measurements.

Proximal joint line elevation may cause anterior knee pain and increase risk of implant loosening.
Distal joint line lowering may result in mid-flexion instability and restricted knee motion.
Inaccurate joint line restoration can lead to polyethylene wear and compromised implant longevity.

3000 knees from 10 countries, balanced for sex (1500 female, 1500 male) and stratified by age groups (20–79 years).

Joint line measurement indices vary with demographic factors; composite indices minimizing these influences may improve assessment accuracy.

Use high-quality AP knee radiographs with standardized positioning criteria for joint line assessment.
Measure distances from multiple anatomical landmarks and normalize by femoral width to calculate joint line indices.
Incorporate composite indices that reduce demographic variability for more reliable joint line evaluation.
Exclude patients with advanced arthritis, prior knee surgery, or BMI >30 kg/m2 to ensure measurement validity.
Perform measurements by trained orthopedists and use mean values from multiple observers to enhance reliability.

Clinical Scorecard: Validation of a Composite Index and Adductor Ratio for Joint-Line Assessment in Anteroposterior Knee Radiographs: A Multicenter Study Involving 3000 Knees