This chapter introduces the reader to “ankle joint preservation arthroplasty” and the role of ankle distraction, or arthrodiastasis, in the treatment of ankle arthritis. Evaluation of, and techniques for correcting, periarticular deformity in the arthritic ankle are presented. The basic science behind ankle distraction, our technique with a ring external fixator, and clinical outcomes are discussed.
Ankle distraction is a lengthy, arduous, involved treatment and patients should be carefully selected. Indications include patients younger than 50 with end-stage osteoarthritis being considered for arthrodesis or replacement, who have failed a minimum of 6 months of conservative treatment. Contraindications include neuropathic, inflammatory, or postseptic arthritides; noncompliant patients; and patients without adequate psychosocial support systems.
Adequate joint debridement must be performed.
Equinus contractures must be addressed.
The concepts of correct application of Ilizarov frames should be applied to minimize in-frame complications.
Early weight-bearing or ankle range of motion must be instituted to generate intermittent increases in intra-articular hydrostatic pressure for the duration of treatment.
Extensive therapy is required during and after treatment, and clinical improvement may not be apparent for 6 to 12 months following treatment. Careful evaluation for, and correction of, periarticular deformities is crucial for a successful outcome.
HISTORY/INTRODUCTION/SCOPE OF THE PROBLEM
Painful degenerative osteoarthritis of the ankle is a difficult problem that lacks an ideal surgical intervention, especially in the young patient. Ankle arthrodesis has been the gold standard for relieving pain and improving function. Ankle arthrodesis is effective in the short term. Long-term follow-up of patients with ankle arthrodesis has shown significant deterioration in results due to increased degeneration, loss of motion, and pain in the ipsilateral foot joints. Total ankle arthroplasty has promising results in select patients but may not be a good option for the young, active patient. Joint distraction preserves the native ankle joint and is an attractive alternative in the young patient with degenerative osteoarthritis of the ankle.
Ankle distraction arthroplasty is a relatively new technique in the treatment of ankle arthritis. The beneficial effects of joint distraction for mobilizing joint contractures were first observed in the 1970s. Volkov et al. used hinged external fixators in the treatment of knee and elbow joint contractures, chronic dislocations, and periarticular fracture nonunions. During the treatment period, the joint surfaces were kept distracted at a predetermined distance. Their results in 31 knees and 28 elbows were encouraging. In 1978, Judet and Judet published their results of distraction arthroplasty in a dog model. An external fixator was placed across the tibiotarsal joints, after excision of the articular cartilage. The external fixator maintained a joint space of 4 to 8 mm. At 1 year, tissue was found covering the joint surfaces that was close to that of normal articular cartilage both macroscopically and microscopically. They also reported 13 of 16 good results in humans treated with a static fixator for 8 weeks.
In vitro and animal studies by van Valburg et al. have shown that intermittent increases in hydrostatic pressure in the absence of mechanical joint stresses improves abnormal proteoglycan metabolism and decreases the production of the catabolic cytokines interleukin-1 and tumor necrosis factor in osteoarthritic cartilage. Intermittent fluid pressure generation (through joint loading or motion) appears to be the key as distraction alone worsens osteoarthritis changes. However, a rabbit study by Karadam et al. demonstrated no beneficial effects of joint distraction, although early microscopic change after joint distraction was the only parameter studied. Clinical studies have shown that joint distraction produces periarticular osteopenia, which has been hypothesized to reduce impact on cartilage through increased stress absorption by the less-dense bone.
It must be acknowledged that we do not fully understand the mechanisms by which joint distraction may be beneficial and therefore the indications for treatment are still being elucidated. Our current indications for treatment are age less than 50 years, end-stage osteoarthritis being considered for arthrodesis, and failure to respond to at least 6 months of conservative treatment measures. The optimal patient for distraction arthroplasty is a compliant, motivated individual who has an appropriate psychosocial support system to facilitate recovery and in-frame care. We believe that a previous history of ankle joint sepsis is a contraindication because these patients, in our experience, have not done well. We do not believe that distraction arthroplasty has a role in the treatment of inflammatory or neuropathic arthritis.
It is important, especially for preoperative planning and patient counseling, to classify the arthritic ankle in terms of etiology, presence or absence of deformity, and arthritis pattern. Etiologies of ankle arthritis include posttraumatic, rheumatoid, osteonecrosis, septic, neuropathic, hemophiliac, gouty, and primary. We have classified ankle arthritis in terms of the predominate location affected within the ankle joint—that is, the “pattern of arthritis.” The pattern of arthritis may be symmetric, anterior, posterior, lateral, medial, or combinations (e.g., anterolateral). In our series, we observed four patterns of arthritis: anterior, symmetric, lateral, and anterolateral. Also in our series, an anterior pattern was most common, followed by a symmetric pattern and a lateral pattern. An anterior pattern of arthritis was associated with a poor outcome in our series. In the group of patients who did not have an anterior joint pattern of arthritis, 83% had a successful outcome versus only 40% of those who did have an anterior joint pattern.
Posttraumatic arthritis is by far the most common cause of ankle arthritis and is commonly associated with deformity. Also, up to 50% of cases of primary ankle arthritis are reported to be associated with foot deformities. For a successful outcome, it is important to correct these underlying deformities. We have classified ankle deformities into those that are intra-articular and those that are extra-articular ( Table 8-1 ). Intra-articular deformities are those in which the talus and tibial plafond are not collinear due to either bony or ligamentous abnormalities. Bony intra-articular deformities are usually secondary to malreduced intra-articular fractures. Ligamentous intra-articular deformities are due to chronic lateral, medial, or syndesmotic ligamentous instability. Frequently, there is asymmetric wear, resulting in nonlinearity between the talus and tibial plafond. In these cases, there will be an existing extra-articular deformity causing the asymmetric joint wear. Extra-articular deformities may be congenital, acquired/nontraumatic, or acquired/traumatic. Extra-articular deformities are subclassified into proximal or distal deformities. Distal deformities are hindfoot deformities along with any primary or compensatory midfoot and forefoot deformities.
|Both—equal or unequal|
Ankle joint distraction is but one component of what we have termed “ankle joint preservation arthroplasty.” This technique involves the careful evaluation for and measurement of coexisting deformity. Hindfoot/foot deformities are corrected acutely, unless the complexity or size of the deformity precludes acute correction. Thorough ankle joint debridement and, as indicated, Achilles lengthening with or without posterior capsular release are performed to correct any equinus deformity and to achieve at least 5 degrees of dorsiflexion. Ligament reconstruction is added in the cases of chronic instability. Any tibia/fibula deformities are corrected acutely or gradually, and an Ilizarov distraction frame is applied followed by a minimum of 3 months of distraction therapy.
Precise measurement of deformity requires radiographs obtained in a typical orthopedic office. Standard weight-bearing radiographs provide sufficient information for the majority of ankle deformities. Computed tomography scans, with or without reformations, are occasionally ordered to better evaluate complex deformity.
Radiographic evaluation of distal tibia and foot deformity includes weight-bearing tibial, ankle, hindfoot, and foot radiographs ( Table 8-2 ). The radiographic angles for the ankle described later are general guidelines used in comparison with the uninvolved limb. Anteroposterior (AP) tibial radiographs are made with the patella facing forward. If a rotational deformity of the limb is present on clinical examination, an AP ankle radiograph is made in the foot-forward position to evaluate intra-articular wear or malalignment. Lateral ankle radiographs are made in the plane of the ankle malleoli.
|Standing anteroposterior and lateral tibia|
|Standing anteroposterior, lateral and mortise ankle|
|Hindfoot alignment standing view or long axial non–weight-bearing view|
|Standing anteroposterior and lateral foot|
|Stress radiographs of the ankle|
|Fluoroscopy to assess arc of ankle motion|
The hindfoot alignment view is a weight-bearing radiograph that enables observation of the tibia, ankle joint, and calcaneal tuberosity on a single view. It is the only radiograph that requires a specialized mounting box to angle the radiographic plate 20 degrees from the vertical plane. An alternative radiograph is the long axial view, which is usually done non–weight-bearing and visualizes the tibia, subtalar joint, and calcaneal tuberosity. A line drawn on the vertical axis of the midbody of the calcaneus should be parallel and approximately 1 cm lateral to the mid-diaphyseal line of the tibia. Valgus deformity and lateral translation indicate a pes planus deformity, and varus angulation and medial translation indicate cavovarus type deformity.
The weight-bearing AP foot radiograph is measured for talo–first metatarsal angle, navicular coverage, and joint subluxation or arthritis. The lateral foot view is measured for talo–first metatarsal angle, calcaneal pitch, and joint subluxation or arthritis. Other angles are used when necessary. If the opposite limb is pain free and has no obvious deformity, comparison radiographs may be made for preoperative planning. Rotational deformity usually is not measured radiographically.
Measurement of Deformity
On an AP radiograph of the distal tibia, the frontal plane joint angle (varus, normal, or valgus) is measured between the anatomic axis of the tibia and the line parallel to the distal tibial plafond, defined as the lateral distal tibial angle (LDTA). The normal average LDTA is 89 degrees (normal range, 86 to 92 degrees). In cases of bilateral deformities, a normal LDTA of 90 degrees is assumed.
Distal tibial metaphyseal and juxta-articular ankle deformities are measured as the intersection of the proximal tibial anatomic axis and a line perpendicular to the tibial plafond. These types of deformities are common after distal tibial growth arrest or intra-articular collapse from pilon fractures.
In the sagittal plane, the anterior distal tibial angle (ADTA), defined as the angle between the mid-diaphyseal line of the tibia and the articular surface of the tibial plafond, is 80 degrees (normal range, 78 to 82 degrees). As in the evaluation of the frontal plane, comparison radiographs are useful and a standard ADTA of 80 degrees is assumed when there are bilateral deformities.
Further distal in the foot, tibial varus deformity is compensated by pronation in the forefoot. When a distal tibial varus deformity is not fully compensated by subtalar joint eversion, further compensation may occur from plantarflexion of the first ray with associated rise of the arch of the foot. Similarly, compensation from first ray plantarflexion may occur when the distal tibia is normal but there is fixed subtalar joint inversion or hindfoot varus, as in a cavovarus foot.
Correction of angular deformities by osteotomy involves angulating one bone segment relative to another around an imaginary axis—the angulation correction axis (ACA). In common orthopedic nomenclature, the point at which the proximal and distal anatomic or mechanical axes intersect is termed the apex of the deformity ( Fig. 8-1 ). The apex is the optimal location for the osteotomy and angulation, so it also has been termed the center of rotation of angulation (CORA). Correction with osteotomy at or near the CORA avoids secondary translations. However, if the CORA is at or near the joint, the osteotomy may be made proximal or distal to the CORA; in this case, angulation may be accompanied by translation, and this translation must be corrected, either acutely at surgery or gradually in the frame, to correctly realign the proximal and distal anatomic or mechanical axes.