High Tibial Osteotomy (HTO) — Indications & Techniques

High tibial osteotomy (HTO) is a joint-preserving procedure for medial compartment knee OA in younger active patients with varus malalignment, in which the mechanical axis of the limb is surgically corrected to offload the diseased medial compartment and shift load to the healthier lateral compartment. It delays or avoids arthroplasty by redistributing forces to preserve the joint. HTO is most commonly performed as an opening wedge osteotomy with a locking plate (MOWHTO — medial opening wedge HTO), though closing wedge and dome osteotomies are also described.

• Ideal candidate: young active patient (<60 years); varus malalignment; isolated medial compartment OA; good range of motion (>90°, flexion contracture <15°); intact ligaments; BMI <35 (higher BMI associated with inferior outcomes); high functional demands incompatible with arthroplasty longevity
• HTO is complementary to UKA and TKA — it is a temporising procedure in most patients, delaying arthroplasty by 5–10 years; this is particularly valuable in the very active young patient in whom implant longevity would be a significant concern; a well-performed HTO does not compromise subsequent TKA or UKA conversion; the timing and type of eventual arthroplasty must be planned from the outset

• Long-leg standing alignment X-ray (LSA): essential for pre-operative planning; the mechanical axis (hip-knee-ankle line) passes through the medial compartment in varus; the degree of varus and the planned correction are calculated from this X-ray
• Fujisawa point: the target for the mechanical axis correction after HTO, described by Fujisawa et al.; the mechanical axis should pass through the lateral tibial plateau at 62% of the tibial width (measured from the medial edge) — this corresponds to the lateral third of the tibial plateau; this slight valgus overcorrection (3–5° of mechanical valgus) offloads the medial compartment and produces the best long-term outcomes; under-correction (remaining in varus) produces inferior results; the 62% target is sometimes approximated as `the mechanical axis should pass through the lateral tibial spine`
• Correction calculation: a correction line is drawn on the LSA from the centre of the femoral head to the Fujisawa point (62% of the tibial plateau); the angle between this correction line and the original mechanical axis of the tibia determines the degree of tibial correction required; the osteotomy opening height is calculated from this angle using trigonometry or planning templates
• HKA (hip-knee-ankle) angle: the mechanical axis alignment angle; normal is 0° (neutral); varus = positive angle; the goal of HTO is to change the HKA from varus to 3–5° of valgus

• Lateral hinge fracture in MOWHTO: the lateral hinge is the pivot point of the opening wedge osteotomy — a small bridge of intact lateral cortex and subchondral bone; if the osteotomy is opened too aggressively, the hinge fractures completely, destabilising the construct and requiring additional fixation; safe opening technique includes: stopping the osteotomy cuts approximately 1 cm short of the lateral cortex, using sequential wedge spreaders gradually, and performing intraoperative fluoroscopy to monitor the hinge; if the hinge fractures, it must be fixed before applying the locking plate

• Distal femoral osteotomy (DFO) is the lateral compartment equivalent of HTO: indicated for isolated lateral compartment OA with valgus deformity; a medial closing wedge or lateral opening wedge DFO corrects the valgus mechanical axis; the mechanical axis target is similarly calculated; the principle mirrors HTO but is performed at the distal femur; technically more demanding than HTO; less commonly performed
• DFO for valgus knee: the mechanical axis passes through the lateral compartment in valgus; DFO shifts the load medially; the planned correction target is the lateral Fujisawa-equivalent point, directing the axis through the medial compartment slightly

• Outcomes: 70–90% satisfactory outcomes at 5 years; survivorship (freedom from TKA/UKA) approximately 80% at 10 years; best results with accurate correction to the Fujisawa point; younger patients and lower BMI have the best outcomes
• Conversion HTO to arthroplasty: HTO does not compromise subsequent TKA or UKA provided the tibial component does not impinge on the plate and the anatomy is not significantly distorted; most surgeons remove the plate 12–18 months after HTO (once consolidated) before converting to arthroplasty
• Complications: non-union (more common with MOWHTO, smoking, large corrections >12 mm, inadequate fixation); lateral hinge fracture; correction loss (inadequate fixation); infection (wound and PJI); deep vein thrombosis; peroneal nerve injury (LCWHTO — nerve at risk at the fibular neck); leg length change (lengthening with MOWHTO, shortening with LCWHTO)

• HTO combined with ACL reconstruction: HTO and ACL reconstruction can be performed simultaneously — both procedures are complementary; varus alignment increases the risk of ACL graft re-rupture (increased in-situ forces on the ACL in varus); in a varus knee with ACL deficiency and medial OA, combined HTO + ACLR improves outcomes compared to either procedure alone; the HTO should correct the varus to neutral or slight valgus to protect the ACL graft
• Posterior tibial slope (PTS) in HTO: the slope of the tibial cut in MOWHTO affects the posterior tibial slope; if the anterior cortex is opened more than the posterior (asymmetric opening), the tibial slope increases; increased PTS increases anterior tibial translation and ACL graft strain; conversely, reducing the PTS can be used therapeutically in ACL-deficient patients; careful pre-operative planning and fluoroscopic guidance during osteotomy avoids inadvertent slope change
• HTO vs UKA in the younger patient (40–60 years): a genuine clinical dilemma in medial compartment OA with varus; HTO provides biologic joint preservation and is appropriate for the very active patient who generates high joint loads; UKA provides earlier reliable pain relief and shorter recovery but with a 10–15% revision rate at 10 years; the evidence shows equivalent outcomes at 10 years; patient preference, activity level, and surgeon experience guide the decision; some surgeons reserve HTO for patients with full-thickness medial OA + significant activity level (manual labour, high-impact sport) who are not ready to accept the activity restrictions of arthroplasty

• Ideal HTO candidate: young (<60 years) + active + varus + isolated medial OA + intact ligaments + good ROM + BMI <35 + non-smoker
• Fujisawa point: mechanical axis target at 62% of tibial width from medial edge; slight valgus overcorrection; best long-term outcomes; ~3–5° valgus HKA post-correction
• MOWHTO: most widely used; single medial cut; opens medially; locking plate; no fibula osteotomy; leg lengthening; lateral hinge fracture risk
• LCWHTO: removes lateral bone wedge; requires fibula osteotomy; leg shortening; historically used; largely replaced by MOWHTO
• Lateral hinge fracture: hinge must be preserved in MOWHTO — stops osteotomy 1 cm short of lateral cortex; gradual opening; fluoroscopy monitoring; if it fractures, fix it before applying plate
• DFO: lateral compartment OA + valgus deformity; medial closing wedge or lateral opening wedge at distal femur; mirrors HTO principles
• HTO survivorship: ~80% freedom from arthroplasty at 10 years; 70–90% satisfactory outcomes at 5 years
• HTO + ACL reconstruction: combined procedure for varus knee + ACL deficiency + medial OA; corrects varus to protect ACL graft; superior to either procedure alone
• HTO conversion to arthroplasty: does not compromise TKA or UKA; remove plate at 12–18 months before arthroplasty
• Non-union risk: large corrections (>12 mm), smoking, inadequate fixation; MOWHTO requires good locking plate fixation and bone graft fill