Is a patient with a 6mm limb length discrepancy, where the left lower limb is longer than the right, and normal Mechanical Axis of the Proximal Tibia (MPTA) and Lateral Distal Femoral Angle (LDFA) angles, a candidate for high tibial osteotomy and bone graft?

High Tibial Osteotomy is NOT Indicated for This Patient

This patient does not meet the criteria for high tibial osteotomy (HTO) because both the MPTA (97-98°) and LDFA (92-93°) angles are within normal limits, indicating proper knee alignment without varus or valgus deformity. 1 The 6mm limb length discrepancy alone is not an indication for HTO, which is specifically designed to correct malalignment and redistribute load in osteoarthritic knees with varus or valgus deformity.

Why HTO is Not Appropriate

Normal Alignment Parameters

• MPTA angles of 97-98° are normal (normal range: 85-90° is considered varus, >90° approaches neutral to slight valgus). The patient's values indicate no significant coronal plane deformity requiring correction. 2
• LDFA angles of 92-93° are within normal limits (normal range: 85-90°), confirming appropriate femoral alignment. 2
• HTO is indicated for patients with mechanical axis deviation into Zone 2 or greater, which this patient does not have based on the normal angular measurements. 3

Indications for HTO

The ideal HTO candidate requires:

• Isolated medial compartment osteoarthritis with varus malalignment (or lateral compartment OA with valgus malalignment). 1
• Middle-aged patients (60-65 years) with good range of motion and no ligamentous instability. 1
• Mechanical axis deviation requiring correction to redistribute joint loading. 3

Management of the 6mm Limb Length Discrepancy

Clinical Significance

• A 6mm discrepancy is minimal and typically asymptomatic. Most patients tolerate discrepancies up to 20mm without significant functional impairment. 4, 5
• This small discrepancy does not warrant surgical intervention unless accompanied by symptomatic malalignment or functional limitations. 6

Appropriate Management Options

• Observation is the most appropriate initial approach for this minimal discrepancy. 5
• Shoe lift (external) of 6mm can be used if the patient experiences any discomfort, though this is rarely necessary for such small differences. 4
• No surgical intervention is indicated for limb length discrepancy of this magnitude in the absence of other pathology. 5, 6

Critical Pitfalls to Avoid

Inappropriate Use of HTO

• Never perform HTO solely for limb length discrepancy without documented malalignment requiring correction. 1
• HTO actually changes limb length as a side effect: opening wedge HTO increases length by approximately 7-8mm per procedure, while closing wedge HTO decreases length by 1-6mm. 7, 6
• Performing HTO on this patient would create or worsen limb length discrepancy rather than correct it, particularly if opening wedge technique were used. 6

Proper Diagnostic Workup

• Full-length standing hip-to-ankle radiographs are required to accurately assess mechanical axis and determine if any true malalignment exists beyond the angle measurements provided. 2
• Weight-bearing views are essential to evaluate functional alignment under load. 2, 8
• Without evidence of osteoarthritis, malalignment, or functional impairment, no surgical intervention is warranted. 1

Bone Graft Considerations

Bone graft is not indicated because:

• There is no osteotomy planned, eliminating the need for graft material. 1
• Bone graft in HTO is used specifically to fill the gap created in opening wedge osteotomies, which is not applicable here. 1, 7
• The patient has no evidence of bone deficiency, fracture, or other pathology requiring grafting. 5