Tibial Osteotomy for Ankle Arthritis

CHAPTER PREVIEW

CHAPTER SYNOPSIS:

Tibial osteotomies are used to improve the pain of ankle arthritis when there is deformity in the tibia, as seen after trauma or with congenital deformities. Preoperative planning must determine the anatomic location of the deformity and must assess the deformity in three dimensions, considering rotation and angulation in each plane. Meticulous surgical technique should be combined with intraoperative imaging to confirm appropriate alignment has been restored. Tibial shaft malunions can be corrected with a single-cut shaft osteotomy. Tibial pilon malunions may be corrected with a metaphyseal opening or closing wedge osteotomy. This technique also may be used for congenital or developmental deformities in the ankle. Complex deformities including rotation, translation, and shortening may be best managed with distraction osteogenesis (Ilizarov technique).

SURGICAL PEARLS

1

Thorough preoperative planning is mandatory.
2

Minimal periosteal stripping will enhance union.
3

Intraoperative radiographs on large cassettes may be better able to assess alignment than image intensifiers.
4

When considering a tibial osteotomy, it is often necessary to also create a small fibular osteotomy so that the tibia is not tethered.
5

When correcting recurvatum deformities, anterior tibial osteophyte may impinge on the talar neck in dorsiflexion; anterior ankle debridement at the time of osteotomy is a good idea.

INTRODUCTION

In all foot and ankle surgery, limb alignment is essential. Whether in a total ankle arthroplasty or ankle arthrodesis, failure to achieve appropriate alignment results in an increased risk of failure. In simplest terms, the limb is well aligned when the axis of weight-bearing falls from the center of the hip, through the center of the knee, and down to the center of the ankle. The foot should be well centered under the ankle.

Deformity around an ankle, whether congenital or acquired, can itself be a cause of ankle arthritis. Tibial osteotomy can be useful to correct alignment in an arthritic ankle when the deformity arises in the tibia. An osteotomy can also be used to create a deformity in an attempt to alter the distribution of weight-bearing in an ankle with uneven wear.

The first step is to determine the alignment of the limb. Full-length weight-bearing anteroposterior (AP) and lateral radiographs containing the pelvis, hips, knees, and ankles are obtained. The weight-bearing axis falls on the AP view from the center of the hip to the center of the ankle and should pass through the center (or just medial to the center) of the knee. Extensive reviews of assessment of alignment have been presented elsewhere. The entire limb should be assessed, as deformity may arise anywhere, and may arise in multiple locations.

The remainder of this chapter focuses on deformity in the leg and ankle. The long axis of the tibia is both the mechanical and the anatomic axis of that bone. On the AP view, the distal tibial articular surface should be at a right angle to the long tibial axis. (Some propose normal is 1 to 3 degrees of valgus.) In assessing a deformity, a perpendicular line from the distal tibial articular surface is drawn, and the intersection with the proximal shaft axis defines the center of rotational angulation (CORA). Rotation about this point will correct the deformity in the sagittal plane.

Similar calculations can be made on the lateral view to assess for flexion or extension of the ankle relative to the tibia.

In most posttraumatic deformities, the CORA will be somewhere in the tibial shaft ( Figs. 6-1 and 6-2 ). But in cases of congenital deformity, the CORA may be in the joint ( Fig. 6-3 ). To minimize translational deformities, it is ideal to rotate an osteotomy as close to the CORA as possible. A thorough understanding of normal alignment and deformity assessment is essential in formulating an intelligent surgical plan. The remainder of this chapter focuses on several common scenarios in the treatment of ankle arthritis.

INDICATIONS

Tibial osteotomy is indicated for a patient with ankle arthritis under certain circumstances. The ideal candidate is a relatively young patient with a sagittal plane deformity (varus or valgus), who has sufficient remaining cartilage in the joint to permit reasonable function. In many cases, the procedure may be regarded as a temporizing procedure, to delay arthrodesis or arthroplasty, similar to osteotomies about the knee. An osteotomy also may be useful in conjunction with an arthroplasty or arthrodesis; persistence of misalignment after arthroplasty or arthrodesis compromises the results in the long term.

A tibial shaft malunion can be a source of deformity proximal to the ankle ( Fig. 6-1 ). Ankle arthritis has been seen to arise in cases of tibial shaft malunions, although it is unclear how much deformity must be present to increase the risk of arthritis. Once arthritis has begun to develop below a tibial shaft malunion, it is reasonable to correct the deformity in the shaft to normalize forces through the ankle. This can usually be done with a single-cut osteotomy.

A malunion of a pilon fracture may lead to deformity in the distal metaphysis, just above the joint ( Fig. 6-2 ). An opening or a closing wedge osteotomy is usually a good choice in this situation.

Growth disturbances during childhood may lead to marked deformity ( Fig. 6-3 ). Opening or closing wedge osteotomies may improve the overall alignment, although they may not be able to restore normal anatomy.

In cases where the deformity includes rotation and translation or marked shortening, gradual correction with distraction (using modified Ilizarov techniques) may be the best choice.

SURGICAL TECHNIQUE

Tibial Shaft Single-Cut Osteotomy

A tibial shaft malunion includes variable amounts of deformity in three planes—rotation (axial plane), varus/valgus (coronal plane), and procurvatum/recurvatum (sagittal plane). A common pattern includes varus, recurvatum, and external rotation. The closer the deformity is to the ankle, the greater is the alteration in pressures in the ankle joint. Pain may arise from altered weight-bearing pressures in the ankle and also from medial or lateral overload in the foot.

When dealing with a tibial shaft malunion, there is always an axis of rotation about which the distal segment can be rotated to bring it back into normal alignment. A single cut of the bone perpendicular to this axis allows rotation about this axis to correct the deformity. A mathematical formula has been calculated to allow the surgeon to define this axis.

Preoperative planning begins with AP and lateral views of the tibia. The axes of the proximal and distal segments are drawn, to calculate sagittal and coronal plane angulation. Torsional deformity (rotation) is determined clinically by comparing the transmalleolar axis to the normal leg.

The calculations result in determination of two angles, theta and phi , which instruct the surgeon in the orientation of the osteotomy. Theta determines the angle of the cut relative to the transverse plane of the tibia. Phi indicates the amount of lateral rotation from the anterior midline for the starting point for the cut. The mathematical formulas to calculate these angles are presented by the surgeons who described the technique.

By following the exact steps of the technique these authors described, anatomic alignment will be restored. However, it is possible to understand the concepts and avoid the geometric calculations.

The technique is actually simpler than it seems once the surgeon understands how to determine the plane of the cut. The steepness or obliquity of the plane of the cut affects the amount of rotation that is achieved. When the cut is fairly short (transverse) across the tibia, rotation will be greater than when the cut is steeply oblique. External rotation results as the foot is moved lateral in relation to the upper leg.

What makes determination of the plane of the cut difficult is that we relate it to the angle of deformity in the traditional sagittal plane, seen on lateral radiographs, and the frontal plane, which is seen on AP radiographs. The angle of deformity occurs only in one plane, but it is usually found between the frontal and sagittal planes. This plane can be determined by using a mathematical formula, but orthopedists are generally not familiar with it. It can be understood much more easily by rotating the beam of a C-arm image intensifier around the leg until the bone looks straight. The beam of the image intensifier then defines the exact plane of the deformity. To confirm that the plane is correct, the C-arm can be rotated until the deformity appears maximal. This should be at a right angle to the plane of deformity just defined by the C-arm when the bone appeared straight.

Classic distal tibial malunion results from nonoperative treatment of an isolated tibia fracture and exhibits extension deformity, shortening, varus, and internal rotation. All of this occurs because the fibula is intact and remains anatomically lateral and posterior to the tibia, maintaining length in that quadrant. This osteotomy technique is ideal for this situation because angulation, rotation, and length (to a limited degree) all can be restored easily with a single cut. Because the fibula is intact, virtually normal anatomy of the lower leg is restored once this is done.

In general terms, an osteotomy to correct pure tibial varus in the frontal plane is made with the blade of a saw in the frontal plane and the distal tibia is simply angulated back to a straight position. The tibia will also rotate externally slightly, but its alignment in the sagittal plane will not change. The more vertical the cut, the less external rotation will take place. If the malunion includes shortening, the fragments can be distracted a bit, but it is difficult to get more than 1 cm of length with this technique. A femoral distractor can be of some assistance for lengthening ( Fig. 6-4 ).