Opening wedge, closing wedge and gradual opening wedge
All forms of high tibial osteotomy (HTO) change the angle of the upper shinbone so that the load line of the leg moves away from the overloaded inner knee. They differ in how and when the correction is made, how it is held and what stays in the body.
Opening-wedge HTO (OWHTO)
During surgery, the upper shinbone is opened on its inner side to the planned angle. The correction is held with an internal plate and screws while the gap fills with new bone.
Closing-wedge HTO (CWHTO)
During surgery, a small wedge of bone is removed from the outer side of the shinbone and the gap is closed. The correction is held with an internal plate or staples and screws. The fibula usually needs to be addressed as well.
Gradual opening-wedge HTO (UniPlasty)
The bone is prepared through a small incision, and a temporary external fixator with an adjustable hinge is attached with four pins. After a waiting period of 5–7 days, the wedge on the inner side is opened step by step: 0.66° a day, 0.33° in the morning and 0.33° in the evening, usually over 1–2 weeks.
Because the correction happens after surgery, the alignment can be checked and fine-tuned on X-rays taken while you stand on the leg. Once the new bone has consolidated, after about 2–3 months, the fixator and its four pins are removed in a simple procedure. No internal plate or screws are used.
At a glance
| Opening wedge | Closing wedge | Gradual opening wedge (UniPlasty) | |
|---|---|---|---|
| When is the angle corrected? | In one step during surgery | In one step during surgery | Gradually after surgery, over about 1–2 weeks |
| Can it be adjusted afterwards? | Generally not | Generally not | Yes, guided by standing X-rays |
| How is the correction held? | Internal plate and screws | Internal plate or staples and screws | Temporary external fixator with four pins |
| What stays in the body? | Plate and screws, unless removed in a later operation | Plate and screws, unless removed in a later operation | Nothing: the fixator and pins are removed after healing |
| Main everyday challenge | Recovery after the operation | Recovery after the operation | Living with an external fixator and pin care for about 3–4 months |
Which technique is right?
No technique is best for everyone. Your surgeon chooses based on where and how large the deformity is, the condition of the bone and soft tissues, and your goals and daily life.
Frequently asked questions
Why correct gradually?
Because the correction takes place after surgery, it can be checked while you stand and put weight on the leg, and adjusted along the way. The aim is to reach the planned alignment under real load.
What do OWHTO and CWHTO mean?
OWHTO stands for opening-wedge high tibial osteotomy and CWHTO for closing-wedge high tibial osteotomy. MOWHTO (medial opening wedge) and LCWHTO (lateral closing wedge) describe the side on which the bone is opened or closed.
More about bow legs and HTO
- Bow legs (varus knee): causes, symptoms and treatmentWhat bow legs are, why they can overload the inner knee and how they are treated.
- Who is HTO for?The patient groups that may benefit from a knee-preserving HTO, and when other options fit better.
- HTO or knee replacement?How HTO and knee replacement differ, and who each is usually considered for.
- Recovery after HTO with UniPlastyA typical recovery timeline: walking, correction, weight bearing, work, exercise and removal.
Questions about UniPlasty?
Contact the Response Ortho team. Treatment suitability requires an orthopaedic consultation.
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