Ankle distraction arthroplasty: A regenerative solution for osteoarthritis
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Ankle distraction arthroplasty is a mechano-biological treatment for osteoarthritis of the ankle that serves as an alternative to ankle arthrodesis and prosthetic arthroplasty, or total ankle replacement.
The allure of ankle distraction is that the procedure can improve the condition of the ankle joint and reduce pain by harnessing the patient’s own healing potential. Ankle distraction arthroplasty was created for young people who were too active for ankle replacement surgery (where wearing out the components or the bone is a concern). Similarly problematic, ankle fusion in younger patients will inevitability lead to adjacent joint arthritis, making this treatment suboptimal. Ankle distraction arthroplasty has filled this gap in treatment options by providing a method that preserves foot and ankle motion without requiring resurfacing implants. Ankle distraction arthroplasty maintains bone stock and joint geometry. We like to say ankle distraction arthroplasty does not burn bridges for future treatments. With time, it was recognized that older patients could benefit from ankle distraction arthroplasty and enjoyed similar outcomes.
Source: S. Robert Rozbruch, MD
The essence of joint distraction lies in the ability of damaged articular cartilage and subchondral bone to regenerate when placed in an ideal environment. The optimal biomechanical condition for the diarthrodial joints to become biologically active is traction or distraction. Through joint distraction, we can ensure there is no pressure on the injured cartilage and bone. Many joints have been distracted to treat arthritis including the hip, the knee, the subtalar and the metatarsal-phalangeal, but none has received more attention than the ankle joint.
Objective evidence from ankle studies supports a regenerative pathway. MRI has documented thickening of the articular surface (presumed to be cartilage-like-tissue) in response to 3 months of ankle distraction. CT has shown spontaneous resolution of subchondral cysts and decreased subchondral bone sclerosis 2 years after the procedure. Radiographs performed 1 or more years after the surgery often demonstrate increased joint space and reduced sclerosis compared with baseline. Subjectively, many patients report improved pain and ability to be more active with both benefits lasting for years after surgery. Most series report more than 70% of patients enjoy pain relief and functional improvement. Our most recent study showed positive results in 80% of patients at 5 years and lasting improvements beyond 10 years in 67% of patients.
Unfortunately, some patients do not improve after surgery. Presumably, they were unable to generate an adequate healing response despite optimizing the environment for growth. Risk factors for failure have been studied without identifying any strong causation. Some variables that may be correlated with failure include obesity, inflammatory arthritis and intra-articular joint deformity, including joint collapse with altered geometry. While female sex correlates with a higher failure rate, most women benefit greatly from the surgery.
The preoperative evaluation includes history, physical exam and imaging. The history confirms that the patient has OA. The examination confirms there is adequate ankle motion to make ankle distraction arthroplasty worthwhile. An extremely stiff joint that is painful is best treated with fusion surgery. Part of the logic supporting fusion is that the result is more reliable for pain relief and if the joint is stiff then the adjacent joints are already degenerating, and ankle distraction arthroplasty will not protect the adjacent joints from overload in this scenario. Radiographs will identify deformity. CT scans can help pinpoint the location of osteophytes and identify subchondral cysts that may need grafting. MRI will show the condition of the cartilage and serves as a baseline for comparison. MRI and CT scans can document the condition of adjacent joints.
Surgical technique
Ankle OA is often accompanied by large osteophyte formation around the joint. These bone spurs can block joint motion and may be best treated with excision. Often, we approach the ankle anteriorly and re-establish a normal bony contour. Anterior osteophyte resection and deepening of the talar neck will provide immediate improvement in ankle dorsiflexion. Microfracture is a technique that may help expedite cartilage regeneration. This is often accompanied by the injection of bone marrow aspirate concentrate into the drill holes and the joint. Another option is drilling the bone under the subchondral plate without violating the joint surface. Lengthening of the gastrosoleus or Achilles tendon may also be needed to optimize dorsiflexion motion. A posterior subtalar osteophyte may block plantarflexion if the spur is large. A posterolateral approach will allow for excision of the excess bone and improved joint mobility. Bone marrow aspirate is collected from the ipsilateral iliac crest and then injected into the drill holes in the talus and tibia and later into the ankle joint after closure.
The ankle distraction procedure requires applying an external fixator around the ankle and adjusting the ring-to-ring connections to achieve a traction force across the joint. The exact construct of the external frame varies among centers. Our limb lengthening and complex reconstruction service prefers a scaled-down frame with an articulating hinge. A single tibial ring is attached to the distal diaphysis with two Schanz pins (Orthofix). If a pin does not have outstanding purchase in the bone, then a third pin is placed.
Next, the center of ankle rotation is localized. A long K-wire (1.8-mm Ilizarov wire) is inserted along the malleolar axis and checked on fluoroscopy. The Ilizarov universal hinges are placed along the axis of the wire and are secured to the tibial ring. The foot ring is then sized and held over the foot in an ideal position. The foot ring is attached to the hinges. The hinges are tested for synchronous motion and adjusted if needed. The foot ring is then anchored to the foot with tension wires. Wires are inserted through the calcaneus, talus and sometimes the midfoot, respecting major neurovascular structures. Olive wires are used in the calcaneus to prevent the heel from sliding on the wire. The talar wire passes through the neck of the talus and is attached to the ring using posts that extend up to the wire. This talar drop wire is tensioned to a lower resistance than the others to minimize ring deflection. The calcaneal wires are tensioned maximally to improve stability.
Postoperative protocol
Some distractions can be performed in the OR. Acute distraction saves time, but there are potential risks. Acutely distracting the frame too much can cause tibial nerve neuropraxia and should be limited to 4 mm in the OR. On the following 2 to 3 days, an additional 1 mm per day may be added while monitoring plantar foot sensation. Acute distraction excessively pulls the skin at the pin sites causing pain and local irritation. Gradual distraction can be achieved by turning the connecting rods in small increments every day until the desired joint space is achieved. Gradual distraction has the advantage of providing the skin and tibial nerve an opportunity to recover from each adjustment prior to the next adjustment. The soft tissue has a chance to undergo stress relaxation with tension reduction in between frame adjustments. A gradual adjustment plan may be to distract the frame 1 mm per day starting on the first day after surgery and continuing for 7 days. Usually, these seven adjustments will yield 5 mm to 6 mm of joint space. A radiograph at the first postoperative visit will confirm the joint space, and additional distraction can be performed as needed.
Ankle range of motion starts the day after surgery and is done by the patient and physical therapist. The external fixator needs to be worn for about 3 months. Patients should be seen at monthly intervals to ensure the wires are holding tension and the joint space has been maintained. Further distraction will resolve both issues. Pain control is achieved with acetaminophen and an NSAID. Oxycodone is prescribed upon discharge from the hospital for 2 weeks and not renewed. The effect of NSAIDs on the biological activity in the distracted ankle joint is unknown. Patients are encouraged to stop taking the anti-inflammatory medication when their pain has subsided and only after ceasing to take narcotics. Having patients walk with two crutches and partial weight-bearing will also reduce pain.
Pin site infection is common and is treated with local wound care for early irritations. For more advanced infection, the patient is started on oral antibiotics. Remember that the first symptom of pin infection is pain. Often patients will ask for more narcotics to remedy an early pin infection. The correct treatment for this pain is antibiotics and not opioids. A short course (10 days) of prophylactic oral antibiotics after surgery does not reduce the incidence of pin infections during the 3-month course (Figures 1 to 3).
Technical tips
- A gastrosoleus recession will improve dorsiflexion and allow for distraction with less resistance.
- Placing the hinge on the correct axis of ankle rotation is important to ensure concentric motion at the ankle joint.
- Gradual distraction is safer than acute distraction. Acute distraction in the OR should be limited to a maximum of 4 mm.
- Pin site infections are common and mild in most cases. Have a low threshold to start oral antibiotics.
- Check for loose or broken wires at each visit. A broken wire can be reattached to the ring in the office.
- Remove the external fixator in the OR under sedation. Hydroxyapatite-coated pins are painful to remove.
- It takes 1 year to see substantial clinical improvement from this procedure. This is frustrating in the early recovery period, so remind yourself and your patient that delayed improvement is expected.
Conclusion
Ankle distraction surgery is exciting in its present iteration with most patients obtaining good results lasting more than 10 years. However, this ankle distraction model provides an ideal environment for hosting advanced cartilage replacement products.
As research on cartilage growth advances, ankle distraction arthroplasty may become more mainstream due to a possible synergy between the biologic cartilage replacement and the mechanical optimization provided by distraction for cartilage growth and subchondral bone remodeling.
- References:
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- For more information:
- Austin T. Fragomen, MD, and S. Robert Rozbruch, MD, can be reached at the Limb Lengthening and Complex Reconstruction Service at Hospital for Special Surgery in New York.
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