The high tibial osteotomy (HTO) is a realignment procedure that corrects varus malalignment of the proximal tibia in order to shift the mechanical axis laterally and unload the damaged medial compartment of the knee. It is a joint-preserving operation for carefully selected younger patients with isolated medial compartment osteoarthritis. The concept was pioneered by Jackson and Waugh and popularised by Coventry at the Mayo Clinic.

The fundamental principle: by realigning the lower limb from varus into slight valgus, the weight-bearing line (WBL) is transferred from the arthritic medial compartment across to the healthier lateral compartment. This reduces medial compartment contact pressures, relieves pain, and slows disease progression.

Indications:

• Age less than 60-65 years (some authors extend to 70 in very active patients)
• Isolated medial compartment OA with preserved lateral compartment (full-thickness cartilage on weight-bearing radiographs and MRI)
• Varus malalignment (correctable, typically less than 15-20 degrees of varus)
• Good range of motion (flexion greater than 90 degrees, flexion contracture less than 15 degrees)
• Active patient who wishes to continue impact sports or heavy labour
• Stable knee or instability that can be addressed simultaneously (ACL reconstruction with HTO)
• Motivated and compliant for the prolonged rehabilitation required

Relative indications:

• ACL-deficient knee with varus thrust (HTO with or without ACL reconstruction)
• Post-traumatic medial compartment OA after tibial plateau fracture
• Osteonecrosis of the medial femoral condyle (early stage)

Proximal tibial anatomy:

• The proximal tibial metaphysis is subcutaneous anteromedially, making the medial approach straightforward. The tibial tubercle (TT) is a critical landmark - the osteotomy is performed distal to the TT to avoid detaching the patellar tendon insertion.
• The medial collateral ligament (MCL) is released or partially detached during opening wedge HTO to allow distraction; in closing wedge the MCL is preserved.
• The common peroneal (fibular) nerve courses around the fibular neck laterally and is at risk during closing wedge HTO, fibular osteotomy, or proximal tibiofibular joint disruption.
• The popliteal fossa contents (popliteal artery, tibial nerve) lie directly posterior to the proximal tibia; the osteotomy must not breach the posterior cortex beyond a controlled depth.

Coronal alignment and planning:

• The mechanical axis runs from the centre of the femoral head to the centre of the ankle mortise. In a normal knee, this passes through or just medial to the centre of the knee.
• In varus malalignment, the mechanical axis falls medial to the knee joint, overloading the medial compartment.
• The weight-bearing line (WBL) is the mechanical axis projected onto the tibial plateau. The goal of HTO is to shift the WBL to 62-66% of the tibial plateau width (measured from the medial edge), placing it just lateral to the tibial eminence.
• Fujisawa point: the classic target, approximately 62-66% across the tibial plateau, corresponds to about 3-5 degrees of valgus femorotibial angle. Overcorrection beyond this risks lateral compartment overload.

Coventry's principles:

• Correct the deformity at or near the site of the deformity
• The osteotomy should be above the tibial tubercle (proximal metaphysis) where bone healing is favourable
• Slight overcorrection into valgus is intentional to account for settling and progressive medial wear

The approach depends on the type of osteotomy:

Opening wedge (medial approach):

• Interval: directly over the anteromedial proximal tibia, between the patellar tendon (fibular collateral ligament side) and the medial collateral ligament. This is a subperiosteal exposure, not a true internervous plane, as the medial proximal tibia is subcutaneous.
• The pes anserinus (gracilis, semitendinosus, sartorius) is encountered and may be released or retracted distally.
• The medial collateral ligament is released from the tibia as a sleeve to allow distraction.
• The superficial medial collateral ligament is the key structure; release must be sufficient to permit opening without spring-back.

Closing wedge (lateral approach):

• Interval: between the iliotibial band (ITB) anteriorly and the lateral collateral ligament (LCL) / biceps femoris posteriorly.
• The common peroneal nerve is at risk as it passes posterior to the fibular head and must be identified and protected if a fibular osteotomy is performed.
• The proximal tibiofibular joint may be disrupted (Coventry technique) or a fibular osteotomy performed at the mid-shaft to allow the tibial fragments to close.

• Position: supine on a radiolucent table. A bolster under the ipsilateral hip may help control rotation. The leg is draped free to allow full range of motion and fluoroscopic assessment.
• Anaesthesia: general or spinal anaesthesia. A femoral nerve block or adductor canal block may supplement analgesia but should not block assessment of common peroneal nerve function post-operatively.
• Fluoroscopy: essential. The image intensifier is positioned to obtain AP and lateral views of the proximal tibia. The long-leg alignment view (or intra-operative electrocautery cord from hip to ankle) confirms the mechanical axis correction.
• Tourniquet: a high thigh tourniquet is used for a bloodless field but should be released before wound closure to check haemostasis and assess the common peroneal nerve.
• Pre-operative planning: full-length standing lower-limb radiographs (hip-to-ankle) are mandatory for calculating the required correction angle. The Miniaci, Dugdale or Hernigou method is used to plan the correction.

HTO carries a meaningful complication profile. A systematic review reported an overall complication rate of approximately 18-37% depending on technique and definition, with serious complications in approximately 4-10%.

• Common peroneal (fibular) nerve palsy - the most feared nerve complication, predominantly associated with closing wedge HTO, fibular osteotomy, or proximal tibiofibular joint disruption. Most are neuropraxias but some are permanent. Opening wedge HTO largely avoids this risk.
• Nonunion or delayed union - more common in opening wedge HTO with large corrections (greater than 12-15 mm opening) and inadequate fixation or grafting. Smoking is a significant risk factor.
• Loss of correction - collapse of the osteotomy site post-operatively, especially if fixation is insufficient or the lateral hinge fractures.
• Patella baja (infera) - the tibial tubercle-to-joint line distance decreases, particularly after closing wedge HTO. This complicates future TKA exposure (difficulty everting the patella) and alters patellofemoral biomechanics. Opening wedge has less effect or may even increase the TT-TG distance.
• Deep infection - the proximal tibia is subcutaneous; wound dehiscence and deep infection are reported in approximately 1-3% of cases.
• Hardware irritation - prominent plate and screws on the subcutaneous medial tibia frequently require removal after union (approximately 20-40% of cases).
• Compartment syndrome - rare but reported, particularly with extensive soft-tissue dissection or post-operative bleeding.
• Progression of arthritis - lateral compartment OA may develop over time, especially if overcorrected; undercorrection leads to continued medial wear and early failure.
• Vascular injury - the popliteal artery and its branches are at risk if the osteotomy cuts breach the posterior cortex aggressively.
• Fracture into the tibial plateau - intra-articular extension of the osteotomy, particularly if the proximal cut is too close to the joint line or if the lateral hinge fractures into the joint.

There is no single universal guideline for HTO; practice follows the evidence-based principles of patient selection and alignment correction described above. Several international societies have published consensus statements:

Key guidance principles:

• AAOS (US): HTO is recognised as a joint-preserving option in younger patients with varus malalignment and medial compartment OA; the evidence supports strict patient selection criteria. The AAOS clinical practice guideline for knee OA treatment of osteoarthritis (non-arthroplasty) gives a limited recommendation for realignment osteotomy.
• NICE/BOA (UK): osteotomy is supported in national guidance as an option for younger patients with unicompartmental OA and malalignment, often in specialist knee units.
• EFORT/European consensus: European practice has historically been more aggressive in favouring HTO, with large series from France, Germany, and Japan. The European Knee Society has published position statements supporting osteotomy as the first-line joint-preserving procedure for young patients with medial compartment OA and varus.

Registry evidence:

• National joint replacement registries (NJR - UK, AOANJRR - Australia) track conversion from HTO to TKA, providing real-world survivorship data. Registry data generally confirm approximately 85-90% 10-year survivorship free of TKA conversion.
• The Swedish Knee Register and Finnish Arthroplasty Register have published data showing that prior HTO increases the complexity of subsequent TKA (longer operative time, more blood loss, higher complication rate) but does not significantly compromise implant survivorship when the TKA is performed by experienced surgeons.

Global practice variation:

• European and Japanese surgeons have historically performed HTO more frequently than surgeons in North America, where UKA and TKA have been more commonly offered to younger patients. This gap is narrowing as long-term data support HTO durability.
• In low- and middle-income settings, HTO is particularly valued as a durable, lower-cost alternative to arthroplasty in young manual labourers.
• The shift from closing wedge to opening wedge is now nearly universal in high-volume centres, driven by the lower nerve injury rate, preservation of bone stock, and easier TKA conversion.

Conversion to TKA after HTO:

• Conversion is technically more demanding than primary TKA, particularly after closing wedge (patella baja, bone defects, altered tibial anatomy, retained hardware).
• Opening wedge HTO results in less distortion of anatomy and a more straightforward TKA conversion.
• Most registries report good implant survivorship after TKA conversion from HTO, though with slightly higher early complication rates than primary TKA.