High Tibial Osteotomy (HTO)

Definition & Rationale

Indications

• Varus knee malalignment with medial compartment overload (medial proximal tibial angle [mPTA] <90°)
• Isolated medial compartment arthritis (other two compartments free of disease)
• Pain clinically localised to the medial compartment
• Young, active, well-motivated patient — typically ideal candidate is <45–65 years (arthroplasty less appropriate)
• May be combined with osteochondral resurfacing (MACI/OAT), meniscal repair, or ligament reconstruction — corrective osteotomy is required before or simultaneously with cartilage restoration to prevent graft failure from mechanical overload
• PCL insufficiency with posterior tibial slope: a biplanar HTO can address combined malalignment and PCL insufficiency by altering slope
• Spontaneous osteonecrosis of the knee (SONK): proximal tibial osteotomy is an option for joint preservation in younger patients before subchondral collapse

Contraindications

Note: ACL deficiency alone is not a contraindication if all other criteria are met.

Preoperative Planning

1. The weight-bearing line is drawn from the hip centre to the ankle centre
2. The target point on the tibial plateau is 62.5% of the tibial plateau width (lateral to midpoint) — the Fujisawa point
3. The angle of correction (X°) is the angle between the current mechanical axis and the desired axis
4. The osteotomy is performed ~4 cm distal to the joint line, at the level of the fibular head tip
5. The osteotomy gap width (Z mm) is calculated by superimposing the correction angle onto the measured osteotomy line length

Large wedge corrections >8° carry higher complication risk and increased chance of losing correction. — Miller's

Surgical Techniques

1. Medial Opening-Wedge HTO

• Osteotomy is performed medially; a gap is opened to the desired correction angle
• Maintained with a plate and locking screws ± bone graft or substitute
• Modern locking plate fixation allows early weight-bearing and mobilisation
• Advantage: does not require fibular osteotomy; easier to adjust correction intraoperatively

2. Lateral Closing-Wedge HTO

• A bone wedge is removed from the lateral side; the cortices are compressed closed
• Historically required fibular osteotomy
• More inherently stable construct but less adjustable

Complications

Opening-Wedge Technique

• Patella baja (infrapatellar contracture/tendon scarring) — most common complication of both techniques
• Collapse of the open wedge
• Nonunion
• Bone graft harvest site pain

Closing-Wedge Technique

• Patella baja — most common complication → leads to loss of flexion
• Loss of posterior tibial slope → loss of flexion
• Peroneal nerve palsy (from aberrant retractor placement near fibular neck)

General/Other

• Common peroneal nerve injury is a recognised risk of proximal tibial/fibular osteotomy; the nerve supply to extensor hallucis longus is particularly vulnerable — Localization in Clinical Neurology 8th Ed.
• Stress risers from prior HTO fixation holes are a risk factor for periprosthetic fracture if TKA is later performed — Rockwood & Green's 10th Ed.
• Delayed bone healing, especially with stiff locked plate constructs

Outcomes & Survivorship

• Rate of conversion to TKA: ~13% at 6 years (meta-analysis data) — Miller's
• Conversion to TKA after HTO requires longer operative time and more frequent use of revision implants
• The most common long-term failure mode is progression of arthritis to involve additional compartments

HTO vs Distal Femoral Osteotomy (DFO)

HTO in Context of Cartilage Restoration