Ankle distraction arthroplasty is a new technique for the treatment of ankle arthritis in younger patients who wish to defer ankle arthrodesis or ankle replacement.
Distraction arthroplasty is based on the hypothesis that healing of arthritic cartilage can occur when the joint is unloaded and subjected to intermittent intra-articular fluid pressure changes. Unloading is achieved with an Ilizarov external fixator, which is applied for 3 months to distract the joint.9 During this time, it is essential that patients are weight bearing to provide the stimulus for fluid pressure changes. The flexibility of the fine wires used to construct the frame allows sufficient motion for this to occur.9,10
In vitro and animal studies have shown that distraction with intermittent pressure change can reduce inflammation and normalize cartilage matrix turnover.9 Clinical studies have demonstrated an increase in joint space and improvement in pain symptoms.5,7,10
As this technique evolves, the optimal patient and arthritis stage and pattern for distraction arthroplasty will become better defined.
ANATOMY
The anatomy of the arthritic ankle joint selected for ankle distraction arthroplasty should be carefully assessed. A well-aligned limb with a foot that is plantigrade to the long axis of the leg is essential to a good outcome in all distraction arthroplasty patients. Deformity can be present from articular wear or collapse, from bony deformity in the tibia or foot, and lastly from ligamentous laxity.
The ideal arthritic pattern for ankle distraction treatment has uniform cartilage loss across the tibiotalar joint with no extra-articular bony malalignment or ligamentous laxity. Ankles with intra-articular collapse or uneven wear patterns can be treated successfully with ankle distraction only if extra-articular bony deformities and ligamentous laxity are addressed. The stage of ankle arthritis does not determine who is the ideal patient for distraction arthroplasty. If patients are able to maintain ankle range of motion, then satisfactory outcomes have been achieved even with advanced arthritic changes.
Extra-articular deformities in the distal tibia will need to be corrected before or at the same time as the ankle distraction technique. The methods to correct angular deformity, acutely with osteotomy or gradually with an osteotomy followed by distraction osteogenesis, are not included in this chapter but have been well detailed in recent texts.2,4,6
Deformities in the hindfoot and forefoot will also need to be corrected before or in conjunction with ankle distraction. This usually entails careful assessment of heel varus or valgus and compensatory forefoot deformities of forefoot valgus and varus. For most patients presenting with a primary complaint of ankle arthritis, it has been possible to acutely correct foot deformities at the same stage as ankle distraction arthroplasty. A calcaneal osteotomy or subtalar arthrodesis is performed to correct hindfoot deformity. A first metatarsal osteotomy or medial column arthrodesis is used to correct the forefoot.
The presence of joint contractures will need to be carefully assessed. Ankle equinus is extremely common in ankle arthritis patients and clinically the most important feature limiting comfortable gait. It is essential to obtain 7 to 10 degrees of ankle dorsiflexion before or during ankle distraction arthroplasty to obtain a satisfactory outcome. Extra-articular contractures of the gastroc–soleus complex are less common and are readily treated with a percutaneous Achilles tendon lengthening during the frame application. Intra-articular contractures of the ankle can be corrected with the ankle distraction frame using universal hinges along the ankle joint axis and gradual correction of equinus simultaneous to ankle distraction. A more recent option is the use of Taylor Spatial struts to correct the equinus.
Ligamentous stability will need to be assessed. Lateral ankle ligament instability is corrected before distraction. In general, medial deltoid ligament instability is addressed primarily by correcting planovalgus foot deformity or distal tibia valgus. The deltoid ligament can be tightened with nonabsorbable suture after a medial ankle arthrotomy to débride the joint, which is usually performed in these patients.
PATHOGENESIS
Normal ankle articular cartilage is durable and resilient and distributes loads far in excess of single limb body weight. Articular cartilage has a highly organized structure consisting of chondrocytes and an extracellular matrix. The chondrocyte is responsible for synthesis and organization of the matrix molecules. The extracellular matrix consists of tissue fluid (water and cations); a collagen fibril meshwork, which provides form and tensile strength; and proteoglycans, which are responsible for stiffness and durability.
Osteoarthritis in the ankle is the sequential change in the chondrocytes and matrix, resulting in the degradation of articular cartilage through the sequential loss of cartilage structure and chondrocyte number and metabolism.
Stage 1 osteoarthritis consists of matrix disruption with fibrillation, increasing water content and permeability, and changes in the matrix organization.
Stage 2 consists of a chondrocytic response with cellular proliferation, increased matrix turnover, and a repair response.
Stage 3 is the start of cartilage loss, with declining cellular response, bony changes, and progressive clinical symptoms.
NATURAL HISTORY
Most patients have a history of trauma to the ankle, from an ankle or talus fracture or repetitive ankle sprains.
The time between the initial trauma and presentation for ankle distraction is highly variable.
Patients with ankle pilon fractures tend to be younger and usually develop the most rapid posttraumatic arthritis; therefore, they constitute the group to receive distraction arthroplasty closest to the time of their initial injury.
PATIENT HISTORY AND PHYSICAL FINDINGS
Patient evaluation for ankle distraction arthroplasty includes a thorough history and physical examination.
The optimal candidate is a compliant, motivated patient younger than 50 years of age who has posttraumatic arthritis or chronic ankle instability with arthritis, no previous history of ankle joint sepsis or ankylosis, no history of neuropathy, and an appropriate psychosocial support system to facilitate recovery and in-frame care.
Clinically, patients must have pain primarily at the ankle joint along with documented arthritis on radiographs.
Physical examination includes evaluation of ankle and foot range of motion.
Ankle motion (about 25 to 30 degrees), including dorsiflexion (5 to 10 degrees), is preferred for successful ankle distraction arthroplasty.
Subtalar arthrosis may affect the ability to achieve dorsiflexion, so both active and passive subtalar range of motion should be tested with the patient seated.
Hindfoot motion is not required but, if present, may improve the result of distraction arthroplasty.
Foot deformity such as cavovarus or flatfoot deformity is noted.
Ankle joint instability is assessed clinically and may be confirmed with ankle stress radiographs in addition to the radiographic evaluation of the deformity.
Fluoroscopic evaluation is used to assess the arc of ankle motion. Hinge-type ankle motion, instead of the usual gliding tibiotalar motion, or loss of anterior ankle articular cartilage may be associated with less successful results.
IMAGING AND OTHER DIAGNOSTIC STUDIES
Standard weight-bearing radiographs of the tibia, ankle, hindfoot, and foot provide sufficient information for the majority of ankle distraction candidates. CT scans, with or without reformations, are occasionally ordered for evaluation of complex deformity or to assist in defining focal wear patterns in the ankle joint.
Standing full-length lower extremity AP and lateral radiographs from the hip to the ankle are obtained if there is deformity above the distal tibial region or a limb-length discrepancy. The long lateral view of the limb is made with the knee in full extension to assess tibial deformity, knee flexion contracture, or recurvatum from hyperlaxity. AP tibial radiographs are made with the patella facing forward. The x-ray beam is centered on the ankle to include the tibia. 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.
The hindfoot alignment view is a weight-bearing radiograph that enables observation of the tibia, ankle joint, and calcaneal tuberosity on a single view.8 This view requires a specialized mounting box to angle the radiographic plate 20 degrees from the vertical plane.
Another radiograph is the non–weight-bearing long axial view that 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 about 1 cm lateral to the mid-diaphyseal line of the tibia. Valgus deformity and lateral translation indicate a pes planus deformity; varus angulation and medial translation indicate a cavovarus type of deformity.
The weight-bearing AP foot radiograph is measured for the talo–first metatarsal angle, navicular coverage, and joint subluxation or arthritis. The lateral foot view is measured for the talo–first metatarsal angle, calcaneal pitch, and joint subluxation or arthritis.
Comparison radiographs of the contralateral, asymptomatic limb should be obtained for preoperative planning.
DIFFERENTIAL DIAGNOSIS
Arthritis associated with ankle pain is the indication for ankle distraction arthroplasty. As detailed previously, deformity evaluation and correction are needed before or in conjunction with ankle distraction.
In patients with pain out of proportion to the degree of radiographic arthritis, the surgeon should assess for occult infection with joint aspiration for culture and a blood measurement of C-reactive protein.
Any patients who are heavily narcotic-dependent or experience severe preoperative pain associated with early-stage arthritis are poor distraction candidates, as this technique is associated with the usual Ilizarov wire and pin site discomfort, especially in the foot.
These patients may not be able to perform intermittent partial weight bearing of 50 to 75 pounds in their frames and will not receive the intermittent joint pressure changes necessary for the distraction technique.
NONOPERATIVE MANAGEMENT
Conservative treatment of ankle arthritis in younger patients is primarily activity modification.
Running and jumping sports activities are discouraged; cycling, walking, and swimming are encouraged.
Supportive braces, whether soft neoprene or rigid ankle–foot orthoses (AFOs), offer varying degrees of pain relief and can improve function.
Anti-inflammatory medications, acetaminophen, and occasionally narcotics all have a role in alleviating mild to moderate arthritic symptoms.
Homeopathic, naturopathic, or acupuncture remedies can all be used, but these are beyond our expertise for treatment recommendation in ankle arthritis.
SURGICAL MANAGEMENT
All ankle distraction patients should be thoroughly counseled, including preoperative conversations with another patient who has undergone the procedure.
Patient education is facilitated with a preoperative information packet reviewing external fixator and pin site care; this is given to the patient on his or her initial consultation.
Pin and frame care is reviewed with the patient again after surgery.
Preoperative Planning
Deformity analysis is conducted in the clinic from the radiographs.
Previous scars or skin grafts are noted for their impact on planned approaches if joint débridement or tibial deformity correction is needed. The plan includes the need for possible fluoroscopic examination with the patient under anesthesia to assess joint tracking and fluoroscopic stress views to assess ankle joint stability.
Positioning
The patient is positioned supine with a folded blanket under the ipsilateral hip to keep the patella facing upward.
The entire leg to the upper thigh is draped free to allow placement of sterile bath blankets under the distal thigh and foot, leaving the posterior leg from the ankle to the knee free for ease of ring placement and positioning. This also allows optimal lateral fluoroscopic imaging during surgery.
Approach
The ankle distraction procedure is an all-percutaneous surgery and therefore has no single surgical approach.
Safe zones for wire and half-pin placement in the tibia and foot are detailed below (FIG 1). In addition, we do place sagittal half-pins in the tibia, just medial to the tibial crest.
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