Normal Tibiofemoral Angle Size on Radiography and MRI
The tibiofemoral angle (TFA) is the angle formed between the mechanical or anatomical axes of the femur and tibia, assessed on weight-bearing anteroposterior knee radiographs. Accurate measurement is essential for evaluating angular deformity, guiding surgical planning for osteotomy, and monitoring progression of conditions such as osteoarthritis and rickets.
Normal Reference Values
| Orientation | Measurement |
|---|---|
| Anteroposterior | <15¡ |
Clinical Significance
A tibiofemoral angle of less than 15° is considered within normal limits. Physiologic valgus of approximately 5–7° is typical in adults due to the anatomical obliquity of the femur; mild deviations within this range are generally not pathologic. Values approaching or exceeding 15° of valgus, or any notable varus angulation, should prompt further clinical correlation.
Abnormal tibiofemoral angles carry important implications for joint loading and long-term cartilage health. Excessive valgus increases lateral compartment stress, while varus malalignment concentrates load on the medial compartment, accelerating osteoarthritis. Precise quantification is critical before corrective procedures such as high tibial osteotomy or distal femoral osteotomy.
- Genu valgum (knock-knee): TFA >15°; associated with lateral compartment OA, iliotibial band syndrome
- Genu varum (bow-leg): medial compartment OA, Blount disease, rickets
- Physiologic childhood valgus: normal developmental variant resolving by age 7
- Post-traumatic malalignment: malunited tibial or femoral fractures
- Inflammatory arthropathy: rheumatoid arthritis causing progressive valgus deformity
Reference: M.D. SB. Radiology Recall, 2e. Lippincott Williams & Wilkins. (2007).
Imaging Notes
On radiography, the tibiofemoral angle is best measured on a full-length standing AP view of the lower extremity with the patellae centered forward. The angle is drawn between the femoral shaft axis and the tibial shaft axis; some protocols use the anatomical axes while others use the mechanical axis — the method should be specified and applied consistently. Weight-bearing is preferred to reflect true physiologic alignment.
On MRI, the TFA can be estimated using coronal sequences, which provide excellent visualization of articular cartilage and menisci alongside angular assessment. MRI is particularly useful when correlating malalignment with cartilage loss or meniscal pathology. However, standard weight-bearing radiography remains the gold standard for angular measurement due to physiologic loading conditions and full-limb visualization.