Knee osteoarthritis doesn’t always require joint replacement. High tibial osteotomy (HTO) offers a surgical option designed to help preserve the natural knee by correcting leg alignment, aiming to shift weight-bearing forces away from damaged cartilage to healthier areas of the joint. This procedure targets patients with arthritis confined primarily to the inner (medial) compartment of the knee—often younger, active individuals who want to maintain their lifestyle without the activity restrictions that can accompany joint replacement.
HTO works by cutting and repositioning the tibia (shinbone) to change the mechanical axis of the leg. By converting a bowlegged alignment to a slightly knock-kneed position, the surgery redistributes load across the knee, reducing stress on worn cartilage and potentially slowing disease progression. The procedure has regained popularity as surgical techniques, fixation devices, and patient selection criteria have improved, with outcomes that allow many patients to return to demanding physical activities.
How Leg Alignment Affects Knee Arthritis
The knee joint consists of three compartments: medial (inner), lateral (outer), and patellofemoral (kneecap). In a normally aligned leg, body weight distributes relatively evenly across these compartments. Varus alignment—commonly called bowlegs—shifts the mechanical axis medially, concentrating forces on the inner compartment. This uneven loading accelerates cartilage wear in the medial compartment while the lateral side remains relatively preserved.
Measuring alignment involves drawing a line from the hip centre to the ankle centre. In neutral alignment, this line passes through the knee centre. Varus malalignment shifts this line medially, increasing medial compartment loading with each degree of deviation. HTO aims to shift the weight-bearing line laterally, typically to a point approximately 62% across the tibial plateau from medial to lateral, aiming to unload damaged cartilage and potentially allowing some biological recovery.
This biomechanical principle explains the rationale behind HTO. Patients with isolated medial compartment arthritis and varus alignment frequently represent suitable candidates because correcting their alignment addresses an underlying cause of accelerated wear. Patients with diffuse arthritis affecting multiple compartments typically may not benefit as much, because shifting load simply moves stress to another damaged area.
Suitable Candidates for High Tibial Osteotomy
Age and Activity Considerations
HTO typically suits patients between 40 and 60 years old, though biological age matters more than chronological age. The procedure appeals particularly to individuals who wish to continue sports, manual labour, or high-impact activities that might compromise or wear out a knee replacement prematurely. Younger patients facing decades of activity may find significant benefit in preserving their natural joint.
Activity level influences candidacy significantly. Patients returning to running, cycling, skiing, or physically demanding occupations often prefer HTO because it doesn’t impose the same restrictions as joint replacement. While modern knee replacements have improved, most surgeons still advise against high-impact activities to protect the prosthesis from accelerated wear.
Anatomical Requirements
Favourable HTO outcomes generally require specific anatomical conditions. The lateral compartment must have healthy or near-healthy cartilage to accept the transferred load. Preoperative MRI or arthroscopy assesses cartilage quality throughout the knee. Patients also need adequate range of motion—typically at least 90 degrees of flexion and the ability to fully straighten the knee.
Ligament stability matters as well. While HTO can be combined with ligament reconstruction in some cases, an intact or reconstructable anterior cruciate ligament (ACL) improves outcomes. Knees with significant instability may not achieve the functional results patients expect.
Body weight influences outcomes, with patients closer to normal weight experiencing better long-term results. Obesity increases forces across the knee regardless of alignment, potentially overwhelming the protective effect of realignment surgery.
The Surgical Procedure
Opening Wedge Technique
Contemporary HTO predominantly uses the medial opening wedge technique. The surgeon makes a cut through the upper tibia from the medial side, stopping before reaching the lateral cortex. This creates a controlled fracture that opens to the desired angle, aiming to correct alignment. The opening wedge typically ranges from 8 to 14 millimetres depending on the correction needed.
A locking plate and screws stabilise the osteotomy, designed to provide rigid fixation that helps facilitate early movement. The gap created by opening the bone can be filled with bone graft—either from the patient’s pelvis, from a bone bank, or with synthetic bone substitutes. Some surgeons leave smaller gaps unfilled, allowing them to heal with the patient’s own bone over time.
Closing Wedge Alternative
The lateral closing wedge technique involves removing a wedge of bone from the outer tibia and closing the gap. This method generally heals faster because bone-to-bone contact occurs immediately, but it shortens the leg slightly and requires fibular osteotomy or disruption of the proximal tibiofibular joint. The closing wedge approach has become less common but remains useful in specific situations, such as when a patient has previously undergone an opening wedge procedure.
Computer Navigation and Planning
Preoperative planning using full-leg standing X-rays allows precise calculation of the correction angle. Computer navigation during surgery can improve accuracy, providing real-time feedback on alignment as the surgeon positions the osteotomy. Studies suggest navigation reduces outliers—patients whose final alignment falls outside the target range—improving consistency across surgeons with varying experience levels.
Recovery and Rehabilitation
Initial Weeks
Most patients stay in hospital for one to two nights following HTO. Weight-bearing protocols vary among surgeons; some allow immediate partial weight-bearing with crutches, while others restrict loading for several weeks to protect the healing bone. Early range of motion exercises begin immediately to prevent stiffness.
Pain management typically involves a combination of oral medications and sometimes regional nerve blocks. Swelling persists for several weeks and responds to elevation, compression, and ice application.
Bone Healing Phase
The osteotomy requires approximately 6 to 12 weeks to achieve initial bone union, with full healing taking several months. X-rays at regular intervals monitor bone consolidation. During this phase, patients gradually increase weight-bearing as healing progresses, transitioning from two crutches to one, then to walking unaided.
Physical therapy focuses on restoring quadriceps strength, which weakens rapidly after knee surgery. Stationary cycling typically begins around six weeks when bone healing permits. Swimming and pool exercises provide low-impact conditioning during the healing phase.
Return to Activities
Most patients return to desk work within two to four weeks, though jobs requiring standing or walking may need six to eight weeks of modified duties. Driving resumes when patients can safely control the vehicle, typically around six weeks for right knee surgery.
Return to sport follows a graduated timeline. Low-impact activities like cycling and swimming resume around three months. Higher-impact activities including running and court sports typically wait until six months or longer, depending on bone healing and strength recovery. Some patients return to competitive sports within nine to twelve months.
💡 Did You Know?
The opening wedge technique preserves bone stock, making future conversion to knee replacement technically easier if needed. The lateral closing wedge removes bone permanently, though this rarely affects subsequent procedures significantly.
Expected Outcomes and Longevity
Pain Relief and Function
Many patients experience meaningful pain reduction following HTO. Functional improvement often allows a return to activities that had become difficult or impossible due to knee pain. Patients commonly report the knee feeling more natural than an artificial joint, maintaining proprioception and normal movement patterns.
Studies tracking patients over time show favourable results in appropriately selected individuals. The procedure generally yields more reliable outcomes when patient selection criteria are followed strictly—medial compartment disease, varus alignment, adequate lateral cartilage, and appropriate activity expectations.
How Long Does HTO Last?
HTO functions as a temporising procedure for many patients, delaying knee replacement rather than eliminating the possibility entirely. The realigned knee continues to experience wear, though at a reduced rate. Many patients maintain satisfactory function for 10 to 15 years, with some exceeding 20 years before considering joint replacement.
Factors influencing longevity include:
- Accuracy of correction (undercorrection limits benefit; overcorrection causes lateral compartment problems)
- Cartilage condition at surgery
- Body weight
- Activity level
- Progression of underlying arthritis
Conversion to Knee Replacement
When HTO eventually fails to provide adequate function, conversion to total knee replacement remains an option. The presence of hardware and altered anatomy makes the replacement procedure technically more demanding, though surgeons experienced in these conversions perform them routinely. Studies examining patients who underwent knee replacement after previous HTO show comparable outcomes to primary knee replacement, particularly when the HTO was performed using the opening wedge technique.
Potential Complications
Bone Healing Problems
Non-union (failure of bone to heal) occurs in a small percentage of patients. Risk factors include smoking, diabetes, and inadequate fixation. Treatment may involve additional surgery with bone grafting and revised fixation. Delayed union—slower than expected healing—occurs more commonly and usually resolves with additional time and protected weight-bearing.
Infection and Hardware Issues
Surgical site infection requires prompt treatment, sometimes including hardware removal and intravenous antibiotics. Hardware irritation from prominent plates or screws affects some patients, particularly those with thin soft tissue coverage. Symptomatic hardware is typically removed after bone healing completes, usually at 12 to 18 months.
Overcorrection and Undercorrection
Achieving the target alignment requires precision. Undercorrection may fail to adequately unload the medial compartment, limiting pain relief. Overcorrection shifts excessive load to the lateral compartment, potentially accelerating wear there. Modern techniques including computer navigation have helped reduce alignment outliers, aiming to improve overall results.
Nerve and Vessel Injury
The peroneal nerve wraps around the fibular head near the surgical site, placing it at risk during both opening and closing wedge procedures. Nerve injury can cause foot drop and sensory changes. Careful surgical technique aims to minimise this risk, and most nerve injuries recover over time.
⚠️ Important Note
Smoking significantly impairs bone healing. Patients planning HTO should stop smoking at least four weeks before surgery and ideally permanently. Continued smoking substantially increases non-union risk.
HTO Compared to Other Options
Versus Unicompartmental Knee Replacement
Partial knee replacement (unicompartmental arthroplasty) also addresses isolated medial compartment arthritis. Both procedures preserve bone and maintain relatively normal knee kinematics. HTO may suit younger, more active patients and those with significant malalignment. Partial replacement may suit older patients seeking faster recovery and more predictable pain relief, though it carries the activity restrictions associated with any prosthetic joint.
Versus Total Knee Replacement
Total knee replacement is a well-established option to address arthritis regardless of compartment involvement or alignment. It generally provides predictable pain relief and function for most patients. However, prosthetic joints have finite lifespans, and revision surgery carries increased complexity and risk. Younger patients may benefit from delaying joint replacement as long as reasonably possible, making HTO an option worth considering when appropriate.
Versus Non-Surgical Management
Conservative treatment—weight management, exercise, injections, bracing—remains first-line therapy for knee arthritis. HTO enters consideration when conservative measures no longer provide adequate function. Some patients try unloader braces, which work on principles similar to HTO by shifting weight-bearing forces, though braces provide more modest and less consistent relief.
Preparing for High Tibial Osteotomy
- Optimise body weight to reduce forces across the knee during healing and afterwards
- Strengthen quadriceps and hamstrings before surgery to facilitate postoperative rehabilitation
- Arrange home modifications including shower access, toilet height adjustments, and removal of trip hazards
- Stop smoking at least four weeks preoperatively and plan for permanent cessation
- Review medications with your surgeon, particularly blood thinners and anti-inflammatory drugs
When to Seek Professional Help
Consult an orthopaedic surgeon if you experience:
- Inner knee pain worsening with activity despite conservative treatment
- Visible bowing of your legs that has progressed over time
- Difficulty walking distances you previously managed comfortably
- Knee pain limiting work or recreational activities you value
- Morning stiffness lasting more than 30 minutes
- Knee swelling that recurs after activity
Commonly Asked Questions
How long until I can walk normally after HTO?
Most patients walk without crutches by eight to twelve weeks, though this varies based on bone healing and surgeon preference. A normal gait pattern typically returns within three to four months as strength improves and swelling resolves.
Will I need a knee replacement eventually?
Many HTO patients eventually require knee replacement, though this may be delayed by 10 to 20 years in well-selected patients. Some patients never require replacement. The surgery may preserve the natural joint during a patient’s more active years.
Can both knees be done at once?
Bilateral HTO is technically possible but rarely performed simultaneously. The recovery demands make staged procedures—one knee followed by the other after full recovery—safer and more practical for most patients.
Will my leg length change after surgery?
Opening wedge HTO slightly lengthens the leg, typically by a few millimetres that most patients don’t notice. Closing wedge HTO shortens the leg slightly. These changes rarely require treatment and usually don’t affect function.
Can I return to running after HTO?
Many patients return to recreational running following full recovery, typically at six to nine months. Impact loading remains a consideration, and some surgeons advise modifying running volume or transitioning to lower-impact activities to protect long-term results.
Next Steps
HTO is generally well-suited for active patients under 60 with isolated medial compartment arthritis, varus (bowlegged) alignment, and intact lateral cartilage. When patient selection criteria are met, the procedure may potentially delay knee replacement by 10 to 20 years while aiming to preserve normal joint mechanics. Outcomes depend on surgical precision—particularly achieving the target alignment—and consistent rehabilitation focused on restoring quadriceps strength. For patients who eventually require joint replacement, prior HTO does not typically compromise that outcome significantly.
If you are experiencing inner knee pain that worsens with activity, or have been told you have medial compartment arthritis with bowlegged alignment, consult an Orthopaedic Hip & Knee Surgeon to determine whether high tibial osteotomy is appropriate for your condition.
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