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What is an Osteotomy?

Osteotomy literally means "to cut bone". All osteotomies involve changing the shape of a bone to achieve a change in the way force is transmitted across a joint. When done for knee arthritis osteotomy unloads a worn part of the knee and redistributes the load to a normal part. This can be done on the femur (thigh bone) which is call distal femoral osteotomy (DFO) or on the tibia (shin bone) which is high tibial osteotomy (HTO). The vast majority of knee osteotomies are HTOs.

High Tibial Osteotomy (HTO)

High Tibial Osteotomy (HTO) is a realigning, joint sparing operation for osteoarthritis and mal-alignment of the knee. Unlike a knee replacement (unicompartmental or total) that requires resection and replacement of the worn ends of the bone and in the case of a total knee replacement, resection of the Anterior Cruciate Ligament as well, a HTO preserves the joint and works by shifting load from the worn, arthritic side of the joint to the unworn side. This is achieved by changing the shape of the tibia (shin bone) and therefore where weight is transferred across the knee. HTO is not applicable to all arthritic knees, is harder to predict than knee replacement and is therefore generally reserved for those who are too young or too early in the arthritic disease process for replacement. The indications for HTO are quite specific and outside these indications the technique does not produce worthwhile results. These indications pertain to numerous factors including:

  1. Arthritis: HTO is a treatment for osteoarthritis affecting only one side of the knee (unicompartmental arthritis). If both sides are affected then there is no undamaged side to take the load after the realignment in which case the procedure will not relieve pain but merely move it from one side of the knee to the other. By the same reasoning HTO is not used to treat other types of arthritis that affect the whole joint (Rheumatoid Arthritis, Crystal Arthropathy (gout)). Medial arthritis (inside of the knee) is much more common than lateral arthritis (outside of the knee) and the overwhelming majority of HTOs will be done to take weight off a worn medial side and place it on an undamaged lateral side.

  2. Alignment: HTO is a realigning procedure. This implies that there must be a deformity or mal-alignment present with the arthritis. A HTO is therefore not applicable if the there is unicompartmental arthritis without deformity.

  3. Range of Movement (ROM): Typically an arthritic joint loses ROM as the arthritis progresses. Beyond a certain point a TKR becomes a much better treatment option as this ROM can be improved. HTO does not improve ROM and therefore is done only when there is still good movement in the joint despite the arthritis.

  4. Weight: HTO realigns the limb so nearly all the weight is taken across the undamaged side of the knee. This necessarily involves loading the good side well beyond what it would normally take and excess weight will cause the good side to wear quickly. Lean patients get the best results in terms of both the quality and duration of pain relief.

  5. Smoking: Smoking and HTO do not mix. Non-union (the bone not joining back together) and infection are dreadful complications and are much more likely in smokers. Dr McEwen does not do HTO in smokers.

HTO is a reliable and durable treatment option if done in the right patient and if limb malalignment is corrected to the ideal angle. However, many patients undergoing HTO will need a TKR eventually. Converting an HTO to a TKR in a 65 year old who had an HTO in their 40’s or 50’s is however a vastly better situation than converting a failed TKR to revision TKR.

Types of HTO

Numerous HTO techniques have been developed but the vast majority will be either opening or closing wedge corrections.

The opening wedge technique involves cutting 90% of the way across the tibia close to the knee joint and then distracting the cut surfaces to create a triangular gap. This lengthens one side of the bone and not the other and therefore changes the shape. The correction is held with a titanium device and heals from the thin end of the wedge across. 

The closing wedge technique involves removing a wedge of bone and then compressing the cut surfaces to complete the realignment.

The two techniques are equally effective but do have some differences.

The opening wedge technique lengthens the limb. The closing wedge technique shortens the limb but generally alters limb length less than the opening technique. Limb length inequality is very common so often the appropriate technique is the one that equalises the limb lengths. Other conditions such as cruciate deficiency and reconstruction will often determine which osteotomy technique is appropriate.

Computer assisted surgery, although developed for total knee replacement is easily adaptable to HTO and improved the accuracy of correction.


Before Surgery

HTO is a major procedure that should be undertaken under optimal conditions. ​

  1. Diabetes should be controlled and stable with blood sugar levels checked regularly.

  2.  BMI should be less than 30. BMI is a measure of obesity and is calculated by dividing weight in kg by the square of height in meters. For example someone who weighs 100kg and is 1.89m tall will have a BMI 100/1.89x1.89 = 100/3.57 = 28. The normal range for a BMI is 20-25. If your BMI is over 35 you should lose weight before seeking a HTO. 

  3.  Smoking predictably leads to a non-union after HTO (the bone doesn't knit together). Dr McEwen will not undertake a HTO if you're smoking.

  4. Staphlococcal decolonisation should be done preoperatively. "Golden Staph" is the leading cause of infection after all forms of knee surgery and 40% of people undergoing HTO will walk into the OR covered in it unless it is specifically cleared beforehand.

  5. Look after your skin. The skin on the leg being operated on must be free of cuts, scratches, grazes and bites.

Surgical Procedure

The surgery takes approximately 80 minutes. There are a number of components to the procedure: The same enhanced recovery after surgery techniques that are detailed on the total replacement page are employed to minimise pain and swelling.

  1. An arthroscopy of the knee is done to remove any loose pieces of cartilage.

  2. Trackers for the computer navigation system are attached via keyholes to the skeleton above and below the knee.

  3. The arthroscope is reintroduced and the knee is registered, a process by which the navigation system is taught the specifics of the limb and knee.

  4. The osteotomy is done through a 6-10cm long incision.

  5. The correction is done, checked with the computer navigation system and fixed in place with a titanium plate and screws.

After Surgery

An osteotomy in effectively a broken leg. The break is controlled, geometrically precise and immediately stable but the physiology of an osteotomy healing is identical to that of a fracture healing and so is the early management. As such rest, ice therapy, elevation and restricted weight bearing are the mainstay of early management. As with all major knee surgery, swelling drives pain, immobility and complications. It can and should be mitigated from the outset with the simple measures outlines above. Pain medication will of be required and supplied but pain meds are powerful, addictive drugs with some awful side-effects so less is better and prevention of swelling is the key to the whole shooting match. ​

From a structural integrity point of view it is OK to take some weight on an osteotomy immediately but the reality is that it is not comfortable to do so for about 3 weeks. Weight bearing is gradually increased and most people will take full weight by 6 weeks and be off crutches around 8 weeks. How

you walk is much more important than how much weight you take so good technique comes first. 

Physiotherapy begins the day of surgery and will be a daily event until discharge. The aim is to have you independently mobile and self caring as quickly as possible. Crutches will be required. Axillary crutches are best until some weight is being taken at which point Canadian crutches are less cumbersome.

The criteria for discharge are a dry wound, good pain control with oral medications and a pass mark from the physiotherapist including on stairs. Most will achieve this within 24-48 hours. Lots of small walks around the house followed by periods of elevation and ice is the correct approach.

Sleep in whatever position is most comfortable. There is no need to sleep only on your back with the knee straight.

The wound should be clean and dry. Notify Dr McEwen immediately if this is not the case.

You will have a postoperative appointment scheduled for 1-2 weeks after the surgery. Sutures will be removed at this time. A senior musculoskeletal physiotherapist will see you at the same time so leave plenty of time for this. There is no need for supervised physiotherapy between discharge from hospital post-operative appointment

Full recovery from an HTO takes around months. This is the time required for the brain and muscles to adjust to changes in limb length and angle and for inflammation in the arthritic half of the knee to resolve.

Risk and Complications

As with any major surgery, there are potential risks involved. The decision to proceed with the surgery is made because the advantages of surgery outweigh the potential disadvantages

It is important that you are informed of these risks before the surgery takes place.

  • Infection. Infection can occur with any operation. Around an HTO this can be superficial or deep. Superficial infections are treated with antibiotics. Deep infections always require surgical treatment as well as antibiotics. Deep infection is an uncommon but very serious complication and many measures are employed during the course of having a HTO to prevent it. Swelling and haematoma formation put pressure on the skin which can cause the wound to break down. Keeping the limb elevated prevents this and is critical to minimise the risk of a deep infection.

  • Blood Clots (Deep Venous Thrombosis).These can form in the calf muscles and can travel to the lung (Pulmonary Embolism). These can occasionally be serious and even life threatening. If you get calf pain or shortness of breath at any stage, you should notify your doctor. As with infection, many measures are employed to prevent this complication. These include compression stockings, calf compressors, IV fluids, blood thinning medications but by far the most important is early mobility.

  • Neurovascular injury (Damage to nerves and blood vessels). The major nerves and vessels that pass the knee are within a centimetre of the surgical envelope of a HTO. Great care is taken to avoid damage to these important structures. 

  • Non-union. Biologically an HTO healing is exactly the same as a fracture healing. The happens reliably if the HTO is sterile, mechanically rigid and attached to a non-smoker. Non-union is very uncommon but requires bone grafting and revised fixation if it occurs.

  • Numbness. The skin on the outside edge of the incision will be numb after the surgery. Most people are very aware of this in the first 6 months after surgery. The sensation of numbness fades with time but probably never returns absolutely to normal.


HTO changes the shape and therefore the appearance of the limb. Limb length is also affected especially with an opening wedge technique.

Making a bowed leg straighter by opening a wedge invariably lengthens the limb. You will be very aware of the differences in length and angles for at least 6 months. This is especially so if the other leg is also bowed. It takes a while for your brain to stop telling you the limb is different to how it was.

The aim of HTO is not to make the limb dead straight but to slightly over-correct to get weight on the good side of the knee. Bowed legs are made very slightly knock-kneed and knock knees slightly bowed. There will be asymmetry of limb shape. The taller and leaner you are the easier this is to see.

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