Are LDFA (Lateral Distal Femoral Angle) values of 87 degrees on the right and 89 degrees on the left an indication for high tibial osteotomy?

LDFA Values and High Tibial Osteotomy Indication

LDFA values of 87° on the right and 89° on the left are NOT primary indications for high tibial osteotomy (HTO); these values indicate femoral-based deformity requiring distal femoral osteotomy (DFO), not tibial correction. 1, 2

Understanding the Deformity Location

The lateral distal femoral angle (LDFA) measures the angle between the femoral mechanical axis and the distal femoral joint line, with normal values being 85-90° 1, 2. Your values of 87° (right) and 89° (left) fall within or near the normal range, which actually suggests:

• The deformity is NOT primarily femoral - both LDFA measurements are within acceptable limits (≥85°) 1
• You must evaluate the medial proximal tibial angle (MPTA) to determine if the varus deformity originates from the tibia 1, 2
• HTO is only appropriate when the tibial deformity is the primary source of malalignment 1, 3

Critical Decision Algorithm for Osteotomy Level

Step 1: Perform complete deformity analysis 1, 2

• Measure mechanical tibiofemoral angle (mFTA) on full-leg standing radiographs
• Measure MPTA (normal: 85-90°)
• Measure LDFA (normal: 85-90°)
• Calculate joint line convergence angle

Step 2: Determine deformity location using Paley's malalignment test 1

• Tibial deformity: MPTA >90° with normal LDFA (85-90°)
• Femoral deformity: LDFA <85° with normal MPTA (85-90°)
• Combined deformity: Both MPTA >90° AND LDFA <85°
• No bony deformity: Both angles normal (45% of varus knees) 1

Step 3: Select appropriate osteotomy based on deformity location 1, 2

• Isolated HTO: Only when MPTA >90° and correction won't exceed MPTA of 95° 1
• Isolated DFO: When LDFA <85° and MPTA is normal 1, 2
• Double-level osteotomy: When single correction would create excessive MPTA (>95°) or abnormal LDFA (<85°) 1

Why Your LDFA Values Matter

With LDFA of 87-89°, performing an isolated HTO would be appropriate ONLY if:

• The MPTA is significantly elevated (>90-95°) indicating tibial-based varus 1
• Correction to 2-3° valgus won't push MPTA beyond 95° 1
• The mechanical axis deviation can be corrected without creating an oblique joint line 1, 2

Recent evidence shows that only 28% of patients with varus alignment actually have a tibial deformity, and isolated HTO is appropriate in only 57% of varus knees when accepting MPTA up to 95° 1. If anatomic correction (MPTA ≤90°) is required, only 12% qualify for isolated HTO 1.

Common Pitfalls to Avoid

• Performing HTO based solely on varus alignment without analyzing deformity location - this leads to oblique joint lines and poor outcomes 1, 2
• Ignoring the MPTA when planning correction - excessive MPTA (>95°) creates abnormal joint mechanics 1
• Failing to recognize that 45% of varus knees have no bony deformity and may have ligamentous laxity as the primary issue 1
• Not considering that 33-63% of varus knees require double-level osteotomy for proper correction 1

What You Need Before Proceeding

Obtain full-leg standing radiographs and measure 1, 3, 2:

• Mechanical tibiofemoral angle (mFTA)
• Medial proximal tibial angle (MPTA) - this is the critical missing value
• Joint line convergence angle
• Mechanical axis deviation (MAD)

The MPTA value will determine if HTO is appropriate - without this measurement, you cannot make an informed surgical decision 1, 2.