HTO or Unicompartmental Knee Arthroplasty? Choosing Between Two Options for Knee Osteoarthritis (1)

When knee osteoarthritis reaches the surgical stage, total knee replacement is not the only option for every patient. If disease is mainly limited to the medial compartment, high tibial osteotomy (HTO) and unicompartmental knee arthroplasty (UKA) are both common choices.

Both operations can reduce pain and improve walking, but their concepts, ideal candidates, recovery speed, and long-term considerations differ clearly.

Age, degree of varus, cartilage wear, ligament stability, activity demand, and the wish to preserve native joint structures all influence the final decision.

The knee can be divided into medial, lateral, and patellofemoral compartments. In many patients, early osteoarthritis is not equally severe throughout the whole knee; the medial compartment often degenerates first.

This is commonly related to varus alignment. When the leg becomes bow-legged, the mechanical axis passes more through the medial side, increasing cartilage pressure. As cartilage wears and the joint space narrows, medial loading rises further.

HTO and UKA both address this type of unicompartmental disease. HTO cuts and realigns the upper tibia to shift weight from the worn medial compartment toward the healthier lateral compartment while preserving the native knee.

UKA resurfaces the severely damaged compartment while preserving the other compartment, the patellofemoral joint, and most normal structures. Before surgery, doctors judge whether the main problem is abnormal alignment causing medial overload or severe focal joint-surface wear requiring resurfacing.

HTO means high tibial osteotomy. In patients with varus knees, the surgeon performs an osteotomy near the upper tibia and adjusts the angle to change the limb’s weightbearing axis.

A common method is medial opening-wedge HTO (OWHTO). The medial tibial osteotomy gap is opened to the planned angle and fixed with a plate and screws; larger gaps may require bone graft or substitute.

After correction, standing and walking loads are distributed more toward the lateral compartment, reducing pressure on the damaged medial cartilage.

Because HTO preserves the femoral and tibial joint surfaces and ligament structures, it is often considered a joint-preserving procedure, especially for younger, more active patients with clear varus.

In one series of 25 patients aged 47 to 65 treated with HTO plus arthroscopy, all had osteoarthritis and varus deformity, range of motion of at least 110 degrees, Kellgren-Lawrence grade II to III medial degeneration, and mild lateral and patellofemoral degeneration. At 6 months, VAS pain decreased from 6.52 to 0.92 and HSS score improved from 75.16 to 92.36.

UKA means unicompartmental knee arthroplasty. If wear is mainly limited to the medial compartment, the surgeon removes the damaged joint surface in that compartment, implants femoral and tibial components, and places a bearing to restore joint space.

Because only one compartment is treated, the lateral compartment and eligible normal ligaments and tissues can remain.

UKA is generally considered when disease is clearly limited to one compartment, pain is significant, ligament stability is adequate, and range of motion meets requirements.

Compared with HTO, UKA does not require waiting for an osteotomy to unite, so early weightbearing and functional recovery are often faster.

HTO is often discussed for relatively younger patients, higher daily activity, medial-compartment-predominant osteoarthritis, definite varus alignment, relatively preserved lateral cartilage, good anterior-posterior and collateral stability, good range of motion, and a wish to preserve native knee structures.

There is no absolute age cutoff. HTO is often used in active patients under 65, but decisions also depend on general health, bone quality, source of varus, and cartilage damage distribution.

If the medial compartment is already severely degenerated and the lateral or patellofemoral compartments also have clear osteoarthritis, the benefit of HTO becomes much more limited.

UKA often suits patients whose disease is clearly concentrated in one compartment and who want faster recovery in daily life.

A comparative review summarized typical candidates as follows: HTO is more often used in relatively young, active patients with varus deformity, while UKA is more often used in older or lower-demand patients who prioritize pain relief and faster recovery.

In recent practice, UKA should not be described simply as an elderly-patient operation. Eligibility depends on whether disease is limited to one compartment, ligament stability, sufficient range of motion, and the absence of significant degeneration in other compartments.

In a study of patients aged 55 to 65, inclusion required bone-on-bone medial disease on weightbearing X-ray, K-L grade III to IV, varus below 15 degrees, range of motion of at least 90 degrees, and no cruciate or collateral ligament injury. This group lies in the overlap zone where both HTO and UKA may be discussed.