Supramalleolar Osteotomy with Internal Fixation Perspective 3

Varus-type osteoarthritis is characterized by varus deformity combined with anterior opening of the articular surface at the distal end of the tibia.^1,2

It often develops bilaterally in middle-aged and elderly women.

Low tibial osteotomy (LTO) was developed to treat varus-type osteoarthritis of the ankle. Cartilage defects can be repaired with fibrocartilage by resolving the stress concentration.

ANATOMY

The distal joint surface of the tibia appears almost perpendicular to the anterior longitudinal axis of the tibia and slight anterior opening to the lateral longitudinal axis (FIG 1).

PATHOGENESIS

The cause of varus-type osteoarthritis is not clear.

Radiographic measurements showed varus tilt of the distal joint surface (FIG 1). It was thought that the varus tilt was caused by acquired changes, because the ankles of infants are in the valgus position.³

Some biomechanical studies^4,10 showed that varus tilt of the distal joint surface of the tibia caused stress concentration on the medial side of the ankle (FIG 2). The stress moved to the lateral side after valgus osteotomy at a distal portion of the tibia.⁸

NATURAL HISTORY

Osteophyte formation and sclerotic changes of subchondral bone initially appear in a medial gutter and an anteromedial corner of the ankle joint.

Damage of articular cartilage gradually progresses from the medial side to the lateral side.

Varus-type osteoarthritis of the ankle is classified into four stages (FIG. 3)^6,9:

Stage 1: no joint space narrowing, but early sclerosis and osteophyte formation

Stage 2: narrowing of the joint space medially

Stage 3: obliteration of the joint space with subchondral bone contact medially

• Stage 3a: obliteration of the joint space in the facet is limited to the medial malleolus

• Stage 3b: obliteration of the joint space has advanced to the roof of the talar dome

Stage 4: obliteration of the entire joint space with complete bone contact

PATIENT HISTORY AND PHYSICAL FINDINGS

The patient complains of ankle pain at the start of walking and after walking for a long distance.

Pain on movement and swelling become significant as osteoarthritis progresses.

A tender point is present at the medial joint space of the ankle.

Motion of the ankle is retained until relatively advanced stages.

IMAGING AND OTHER DIAGNOSTIC STUDIES

Weight-bearing AP and lateral radiographs should be taken to detect narrowing of the joint space.

The angle between the tibial shaft and the distal joint surface of the tibia is measured on the AP view (TAS angle) and on the lateral view (TLS angle) (FIG 4).^1,2,5 Those angles represent the varus angle and the amount of anterior opening of the joint, respectively.

Normal values are 88 to 90 degrees for the TAS angle and 80 to 81 degrees for the TLS angle.^1,2,5

The tibial axis is defined as the line between the midpoints of the tibial shaft at 8 cm and 13 cm above the tip of the medial malleolus.

Varus tilt of the talus has been observed in some ankles with osteoarthritis. The varus tilt angle is evaluated on a weight-bearing AP radiograph that shows the distal joint surface of the tibia and the upper surface of the talar dome (FIG 5).