Open Wedge High Tibial Osteotomy Principles and Techniques

Varus knee, which causes outward bowing of the leg, is a common problem, particularly in Asia. It develops quite early in many patients, commonly from unicompartmental or tricompartmental osteoarthritis.

For less active elderly patients, total or unicompartmental knee arthroplasty (respectively, TKA or UKA) is often the optimal treatment path. However, for those who are younger or very active, knee-preserving surgery is usually more appropriate. One excellent restorative option for varus knee is open wedge high tibial osteotomy.

Advantage of corrective surgery instead of joint replacement

Because osteotomies preserve and protect the knee joint by correcting deformities that cause or exacerbate joint problems, they impose much less on activity as the patient ages. And if the knee joint deteriorates, e.g., due to osteoarthritis, TKA and UKA remain possible.

Osteotomy and religious or social activities

For Asian patients, complete flexion of the knee is particularly necessary to participate fully in religious and social customs. This can mean kneeling to pray or eat, as well as sitting cross-legged or in the lotus position. For people with malaligned knee joints, these positions can be painful or even impossible. The object of the high tibial osteotomy (HTO) is to correct the mechanical axis of the knee, thereby improving load distribution and helping cartilage regeneration. The target outcomes are pain relief, functional recovery and the capacity to withstand heavy functional demands.

Best placement of the mechanical axis for long-term survival free of failure

While most HTOs produce good short-term results, with failure-free implant survival rates hovering around 94% for the first year, longer-term success reflects reasonably close tolerances in surgery. A postoperative valgus angulation of 8-10 degrees has the best long-term prognosis. After roughly four years, patients with 6-7 degrees of angulation fall below 90% survival free of failure, but stabilize at around 87%. With angulations of 5 degrees or less, though, failures become progressively more common. Starting around two years post-surgery, this group’s failure-free survival rate continues to fall in stages, settling after four years at slightly above 60% (Coventry et al.). This failure-free rate is unacceptable.

Complications include inadequate correction (leading to recurrent varus), infections, or injuries to the involved bones, nerves or blood vessels. A number of these commonly result from fibular resection. A good HTO is precise, safe and versatile. In addition to being less invasive than an arthroplasty, it results in stable fixation and fewer complications. This leads not only to faster rehabilitation—meaning shorter hospital stays—but also to an easier conversion to a total knee arthroscopy if that becomes necessary.

While the basic idea of the osteotomy predates modern medicine, recent advances in fixation techniques, beginning in Switzerland around the year 2000, have led to much more predictable results, reduced complications and greater long-term success. One example is medial open wedge HTO using the TomoFix plate, which was developed by Staubli and Lobenhoffer. The recommended high tibial osteotomy offers a mechanically stable joint with excellent short-term benefits (quick recovery) and very little long-term loss of correction. Also, it requires no fibular resection, which is a common source of peroneal palsy.

The main indications for medial open wedge HTO are isolated medial unicompartmental degenerative joint disease, with normal contralateral and patellofemoral joints.

An unsuitable candidate has flexion contracture of more than 15 degrees, bicompartmental disease or prior knee infection, is elderly with difficulty mobilizing, is non-compliant, is obese, or has bone atrophy (particularly if that involves severe tibial or femoral bone loss) and smoking.

Case example: 58-year-old male

The target alignment of weight bearing is based on the lateral tibial eminence. The optimal placement of the mechanical axis (%MA) is 65–70% (slightly valgus). A representative case involved a 58-year-old male who had KL grade 1 deterioration on his right side and grade 3 on his left. Five years after having OWHTO on both knees, he runs daily to prepare for marathons. Patient satisfaction after HTO is very high.

In short, then, OWHTO is a biological treatment that corrects the knee’s mechanical axis. The Tomofix represents a major step forward in the evolution of this procedure, making it much safer and more reliable. This osteotomy procedure is relatively new, but an excellent example of regenerative medicine.

Closing wedge HTO (CWHTO) still has a role, particularly where FTA is over 182 degrees.

For more complex cases, including severe varus and deformity on two levels, open- and closing-wedge implants can be combined to correct joint alignment, particularly regarding the placement of the mechanical axis. In addition to improving anatomical joint line obliquity, biplane osteotomy offers the advantages of stability against rotation, early rehabilitation and rapid bone healing. However, particularly where the distal femur is concerned, small changes can make large differences; so proceed with caution.

Leg axes, joint angles and anatomy

As deformities are three-dimensional, they require analysis on three planes. The most important is the frontal plane, which shows varus or valgus deformity and medial or lateral translation. From the sagittal plane we can see antecurvation or recurvation, along with anterior/posterior translation. And the axial plane allows us to see internal or external rotation.
Accurate analysis depends on good imaging. A good full-leg x-ray is taken from about three meters, with the patella front and center, meaning the leg is rotated slightly inward. In the x-ray, the lesser trochanter should be visible but not large. If it appears large, the leg is externally rotated. The proximal tibiofibular joint overlap is about one-third of the fibular head; and the shape of the femoral condyle looks normal. If it does not, it is rotated externally or internally.

Comparing standing to supine views, some differences in the mechanical axes are visible. Still, both views are useful. Any length discrepancy should be corrected with blocks under the shorter leg, so that the weight is distributed evenly and alignment is as normal as possible. For purposes of measurement, it’s also useful to place a four- or five-centimeter metal ball at the level of the expected correction.

The Rosenburg view—a PA view with the knee flexed 45 degrees and the camera positioned 10 degrees above the joint—is also important. As this position shortens and narrows the joint space, it makes signs of osteoarthritis much easier to spot.

Analyzing the deformity in the frontal plane allows a check of where the limb’s mechanical axis (MA) crosses through the knee joint. Also called the Mikulicz line, this axis extends from the center of the hip to the center of the ankle. If it does not also pass through the appropriate part of the knee joint, i.e., slightly valgus, the knee is malaligned.

The MA deviation is the distance between the Mikulicz line’s intersection point and an appropriate joint line intersection point. The intersection point is normally expressed as a percentage of the Tibia width from medial to lateral, with the medial edge being 0% and the lateral edge being 100%. Very severe varus values can be negative percentages; extreme valgus values can be greater than 100%. The optimal MA intersection point is 65–70%.

Using a frontal plane view, the relevant angles are measured following Dror Paley’s technique. Rather than using the Mikulicz line, Paley used two separate lines, one running down from the middle of the hip to the target MA/joint-line intersection, and one running up from the middle of the ankle through the same point. With these in place, the angles of the hip, the knee (femur and tibia) and the ankle can all be determined, as well as the mechanical tibiofemoral angle (mTFA) (normally 0-2 degrees). And finally there’s the joint line convergance angle (JLCA), i.e., the angle across the joint between the distal femoral and proximal tibial surfaces. Like the mTFA, the JLCA is normally 0– 2 degrees. A knee with a JLCA greater than 2 degrees is varus; one with a negative JLCA is valgus.

An accurate measurement of the JLCA is vital. Therefore, frontal-plane stress x-rays—one showing the joint angled fully varus, the other fully valgus—are necessary. The difference between these two joint angles (∆JLCA) indicates the amount of change that will be necessary. As the standing x-ray is normally in the centered position, supine position x-rays are more useful for this view.

Uses of software

Several software packages are available not only to calculate the amount of change necessary but to simulate the entire osteotomy. Working with digital images also makes the measurement of distances and angles much quicker. However, all necessary calculations, measurements and markings can also be made manually.

Assuming that you have already determined that the joint is malaligned, the first step of this part of the analysis is to determine the location of the deformity that is causing the malalignment. This is normally where the osteotomy cut will be made. For a varus knee, while a deformed distal femur is sometimes the cause, the most common site of the deformity is the proximal tibia. In those cases, a high tibial open- or closing-wedge osteotomy is normally indicated. For a valgus knee, distal femur deformity is the more common cause. This is usually an indication for a distal femoral medial closing-wedge osteotomy.

In this case, we’re discussing corrections to varus deformities. Regardless of the target outcome, though, it is critically important to make accurate measurements. A poorly-placed osteotomy will result in an oblique joint line, which will cause unnecessary stress on the cartilage.

One possible source of confusion is a deformity quite far-removed from the joint, e.g., midway between the knee and the ankle. In this case, the optimal point for correction is the center of rotation and angulation (CORA). In the case of a badly-bowed tibia, the CORA is the point where the anatomical axes of the proximal and distal parts of the tibia intersect.

In cases where there are two or more deformations, each will contribute separately to the joint malalignment. For example, both the femur and the tibia sometimes have deformities. In such cases, correcting the malalignment entirely in one location will result in an abnormal joint line. Therefore, all deformities require correction.

In every possible case, a frontal weight-bearing long leg radiograph should be taken, along with any other appropriate views, e.g., a Goldberg view. As noted above, the leg rotation should center the patella between the two condyles. Using the available software, you can measure all of the necessary parameters for a thorough deformity analysis. By comparing your measurements with normal values, you can plan for the best possible treatment.

Based on that standard long x-ray, planning an osteotomy has five main steps:

1. Define the malalignment
2. Locate the deformity
3. Define the target alignment axis
4. Decide which osteotomy is required and location of hinge point
5. Measure the correction angle with the Miniaci method

1. Defining the malalignment

To define the malalignment, a Mikulicz line must be drawn, i.e., from the center of the femoral head to the center of the ankle. If that line crosses the knee joint medially of the normal range, the alignment is varus. If the deviation is greater than 15mm, it is considered obvious varus. If it crosses laterally of that range, the alignment is valgus. The threshold for an obvious valgus malalignment is 10mm. The designation of obvious is an important indicator for osteotomy correction.

2. Locating the deformity

As noted earlier, the deformity can be located by drawing the mechanical axes and joint lines, measuring the relevant angles and comparing the results with normal values. Where intraarticular deformity is also present, this will normally self-correct when the bones are realigned. Therefore, we need to remember to subtract the predicted changes in the lateral and medial joint gaps from the overall correction.

3. Defining the target joint-MA alignment

The precise alignment will depend on the patient’s age and activity level, as well as on the condition of the cartilage. For a very active patient with healthy cartilage, a central alignment will be best. For damaged or deteriorated cartilage, the alignment should be closer to or on the Fujisawa point.

4. Most common osteotomy choices and where to locate the hinge point

The most common osteotomies are to correct varus deviations. The choices are a medial open wedge HTO (MOWHTO) with a lateral hinge point, or a lateral closed wedge HTO (LCWHTO) with a medial hinge point.

5. Determining the height of the wedge opening (Miniaci method)

The steps to determine the height of the opening necessary for a medial open wedge osteotomy are listed below.
Once you have decided on the location of your hinge point, you can use the Miniaci method to determine the correction angle.

The Miniaci method of determining the correction angle

1. Draw a target mechanical axis line directly vertically from the center of the femoral head to level of the foot.
2. Draw a second line (line AB) connecting the hinge point (A) to the center of the ankle (B).
3. Keeping the origin of line AB on the hinge point, inscribe an arc from the center of the ankle to where it crosses the mechanical axis. That is point C. Join A to C. You now have two lines—AB and AC—of identical length.
4. The angle between the two lines from the hinge point (to the current and target position of the ankle) is the alpha angle.
5. If there is a self-correction to the joint line convergence angle (JLCA), subtract that from the alpha angle.
6. Transfer this angle to the correction site and use a Hernigou trigonometric chart to match the correction angle (alpha minus the JLCA self-correction) to the cut length to locate an opening size.

AO Trauma is very grateful to the authors of this webinar for their generous assistance.