What HTO Can and Cannot Do for a Worn Knee

For many patients facing medial knee osteoarthritis, the first real question is not anatomical — it is practical: will this operation actually buy me time before a knee replacement? The short answer, based on the available evidence, is yes. High tibial osteotomy (HTO) is a genuine joint-preservation procedure with established capacity to delay total knee arthroplasty (TKA) and, in carefully selected patients, to avoid it altogether.

The mechanism is mechanical rather than biological. Varus deformity — a bow-legged alignment — concentrates weight-bearing load on the medial compartment of the knee, accelerating cartilage breakdown in a joint already compromised by osteoarthritis. HTO corrects that alignment surgically, shifting the weight-bearing axis toward the lateral compartment, which is typically intact. Less load on the damaged side means less pain, slower cartilage loss, and a longer window before replacement becomes necessary.

Meaningful pain relief and functional restoration are consistent findings in the literature. HTO is not, however, the right answer for every worn knee. It is most relevant to younger, more active patients with isolated medial compartment disease — and it sits at a specific point in the treatment continuum, after conservative and injection-based strategies have been explored and before joint replacement becomes the only remaining option.

How Realigning the Leg Offloads a Damaged Compartment

Think of how a car with misaligned wheels wears through one tyre far faster than the other: no amount of tyre quality helps if the geometry is wrong. The knee works on the same principle. In genu varum — the bow-legged posture introduced above — the mechanical axis of the limb runs too far medially, funnelling a disproportionate share of bodyweight through the already-damaged medial compartment with every step.

HTO corrects that geometry at the proximal tibia, just below the joint line. The surgeon cuts partway through the bone, opens a wedge on the medial side, and holds it open with a modern locking plate while healing occurs — around 10 mm of outer (lateral) tibial cortex is left intact to act as a stable hinge. This repositions the tibia so that the mechanical axis — the straight line from hip to ankle — now passes through the centre or slightly lateral aspect of the knee, distributing load more evenly and relieving pressure on the worn medial surface.

This medial opening-wedge technique is the preferred approach for most suitable younger patients. When the patella sits lower than average, a lateral closing-wedge HTO is preferred instead: rather than opening a gap on the inner side of the tibia, a small wedge of bone is removed from the outer side. This avoids lowering the kneecap further, which the opening-wedge variant can otherwise do.

Many surgeons now favour a biplanar osteotomy — adding a second cut in a perpendicular plane — because it confers greater rotational stability and promotes more reliable bone healing. Computer navigation systems can also guide the degree of correction intraoperatively, reducing the risk of undercorrecting or overcorrecting the alignment.

The Patient Profile That Gets the Best Results

Strong HTO candidates tend to share a recognisable cluster of features. Most are under 60, though chronological age matters less than physiological age and activity level — a fit 62-year-old who runs and cycles regularly may be a better candidate than a sedentary 48-year-old. Isolated medial compartment osteoarthritis with confirmed varus deformity is the clinical starting point; diffuse or bicompartmental disease shifts the balance toward arthroplasty.

Beyond the diagnosis, three physical factors determine whether the knee can withstand and benefit from realignment:

• Range of motion (ROM): Adequate knee flexion and extension are prerequisites. Restricted ROM before the operation is an established predictor of poorer outcomes, and the degree of available motion is assessed formally at the preoperative evaluation.
• Ligamentous stability: The corrected knee needs a stable soft-tissue envelope to function under the realigned load. Significant ligamentous insufficiency is a contraindication in its own right.
• Lateral compartment cartilage: Because HTO shifts load toward the lateral compartment, the cartilage on that side must be capable of absorbing it. Arthroscopy immediately before the osteotomy is considered mandatory — not optional — to assess lateral compartment quality directly. If that cartilage is already substantially compromised, the expected benefit of the procedure falls significantly.

Patient motivation is a fourth practical filter. Recovery requires sustained engagement with physiotherapy, progressive strengthening, and mobilisation protocols; candidates who are unlikely to complete structured rehabilitation are assessed accordingly during the surgical planning process.

When HTO Is Not the Right Path

Not every patient with medial compartment OA and varus malalignment is a candidate. Several conditions make HTO either unsuitable or significantly higher risk, and being clear about them is part of honest joint-preservation planning.

Hard contraindications — where HTO should not be offered:

• Rheumatoid arthritis or other inflammatory arthropathy
• Fixed valgus deformity greater than 20°
• Severe bicompartmental or tricompartmental osteoarthritis
• Advanced chondral loss in the lateral compartment (the zone that will bear increased load after correction)

Relative contraindications carry meaningful risk: active smoking impairs bone healing at the osteotomy site; osteoporosis undermines the stability of the locking-plate fixation. Neither is an absolute barrier, but both require honest risk assessment before proceeding.

Where varus deformity is substantial or OA has spread beyond a single compartment, unicompartmental knee arthroplasty (UKA) or total knee replacement becomes the more appropriate pathway. The precise threshold of varus deformity at which HTO is preferred over UKA is not firmly established in the current evidence — this remains a genuine clinical grey zone rather than a resolved question, and should be discussed openly during a specialist assessment. For end-stage, diffuse disease, total knee replacement is the right route.

Patients who need a rapid return to full weight-bearing activity, or who are unlikely to sustain the commitment that post-operative rehabilitation requires, may also be better served by an alternative surgical approach.

Combining HTO with Cartilage Repair in One Stage

Fixing alignment without addressing a damaged cartilage surface leaves half the problem unsolved — and the reverse is equally true. Repairing cartilage in a knee that remains mechanically malaligned means the newly treated surface immediately faces the same abnormal loading that caused the damage in the first place. For patients who have both varus malalignment and a focal chondral defect in the medial compartment, a single-stage combined procedure tackles the mechanical root cause and the biological deficit at the same time, potentially extending the joint-preserving benefit beyond what either intervention could achieve alone.

The cartilage repair technique is matched to the defect's size, grade, and location. Options used in this setting include:

• AMIC (matrix-augmented microfracture) — small channels are made through the bone to release the body's own repair cells, and a collagen scaffold is placed over them to guide those cells toward cartilage-like tissue rather than simple scar
• MACI / ACI — cartilage cells harvested from the patient's own healthy knee are grown in a laboratory, then reimplanted on a collagen membrane (MACI) or under a periosteal patch (ACI); this approach suits larger or more complex lesions that benefit from a larger cell population
• OATS / OCA (osteochondral grafting) — a cylinder of bone and cartilage is transferred like a cork into the damaged area, sourced either from elsewhere in the patient's own knee (OATS) or from a donor (OCA) when the defect is larger

Not every HTO candidate requires concurrent cartilage repair. The decision rests on what arthroscopy reveals: the size and grade of any medial lesion, and whether the repaired surface is likely to hold under the realigned load.

What the Evidence Shows About Long-Term Outcomes

In registry studies, roughly 60–80% of patients have not required a knee replacement at ten years following HTO — a figure that represents genuine joint preservation across a meaningful stretch of time, not a modest reprieve. The range is wide, reflecting how much outcomes vary with patient age, severity of pre-operative deformity, surgical precision, and rehabilitation engagement; it describes a population, not a personal forecast.

The available evidence does not precisely quantify how much time HTO adds before TKA becomes necessary for any individual patient. The honest position is that delay is real and clinically significant in most appropriately selected patients, but it is not predictable to a specific number of years. For a younger patient who wants to remain active through their forties and fifties, preserving a native knee joint across that window carries genuine value — even where replacement eventually follows.

When conversion to TKA does become necessary, prior HTO does not prevent it. Surgical planning is more complex, as the team must account for the altered tibial geometry from the earlier osteotomy, but replacement remains achievable in experienced hands. This added complexity should not deter the right candidate from pursuing joint preservation in the first instance.

Improved pre-operative planning tools — including digital alignment simulation and intraoperative verification of the mechanical axis — have helped specialist centres achieve more consistent correction angles than were possible in earlier series, supporting better and more predictable long-term results.

Professor Paul Y. F. Lee at the London Cartilage Clinic assesses patients for HTO and combined joint-preservation procedures, advising on whether osteotomy alone or alongside cartilage repair best fits each individual clinical picture; to arrange an assessment, visit londoncartilage.com.

1. [1] Osteoarthritis. https://en.wikipedia.org/?curid=504841 https://en.wikipedia.org/?curid=504841
2. [2] Unicompartmental knee arthroplasty. https://en.wikipedia.org/?curid=16991704 https://en.wikipedia.org/?curid=16991704
3. [3] High tibial osteotomy. https://en.wikipedia.org/?curid=42896695 https://en.wikipedia.org/?curid=42896695