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Alastair Younger, M.D., MB ChB FRCSC
Head, BC’s Foot and Ankle Clinic,
Providence Health Care,
And Clinical Instructor,
Division of Lower Limb Reconstruction and Oncology,
Department of Orthopaedics,
University of British Columbia,
Vancouver, BC Introduction
Total ankle arthroplasty has had a poor reputation as the first generation of total ankle arthroplasties, such as the Mayo ankle, had poor short and long-term outcome much like similarly constrained designs for the knee, shoulder and elbow. More recent designs, such as the Agility, the STAR (Scandinavian Total Ankle Replacement), and the Buckel Pappas, all with semi-constrained bearing surfaces, are, up to seven years follow-up, clearly outperforming their predecessors, and are likely to outperform ankle fusion1. The role of total ankle arthroplasty for the management of end stage arthritis of the ankle needs to be re-evaluated.
One may question why a surgeon would expose the patient to the risk of polyethylene wear disease and late loosening when on superficial review, the results of ankle fusion seam to be so promising. Is this a misdirected technology? After all, an ankle fusion is the gold standard treatment and it is the impression of many orthopaedic surgeons that an ankle fusion is a good orthopaedic procedure with a predictable outcome.
 | | Figure 1: End stage ankle degeneration secondary to rheumatoid arthritis | The Poor Outcome of Isolated Ankle Fusion
Review of the papers published in the last ten years reveals many faults. Unfortunately, less rigorous studies tend to show a better outcome than reality, as shown by Mafulli et al2. If ankle fusion were a good operation, there would be no need to use an ankle replacement. The average follow up for ankle fusion papers in the last ten years was 54 months (4.5 years). Only three papers evaluating outcome of ankle fusion have used validated outcome scores, and only one paper has assessed the long-term follow up of ankle fusion at 22 years, a short time for an operation often advocated for younger patients3. The author had difficulty finding patients with unilateral isolated ankle arthritis, underscoring the fact that ankle arthritis is rarely an isolated disease. The development of post traumatic arthritis in surrounding joints was significant, with a significant increase in degenerative change found in all of the joints in the midfoot and hindfoot. The assumption is that the rigid position of the ankle places increased stress on the remainder of the foot, increasing the rate of degenerative change. The only consistently reported outcome in all papers was nonunion. There were 307 nonunions (15%) for the 1989 patients studied in 67 papers published since 1990. Other factors affecting outcome such as mal-position, failure to fuse the most symptomatic joint, or hardware in surrounding joints, all seen in clinical practice, were not identified in many papers. As global outcome scores such as SF 36 were not used in all but two papers, there is no way of comparing the outcome of ankle fusion against other procedures. Furthermore, many papers scored the Mazur and AOFAS scale out of 90 instead of 100 by deducting the ten points for ankle motion. This is inappropriate as ankle motion is deemed important by both the surgeon and the pa-tient, and so the loss of ankle motion should be considered in the outcome score.
The Poor Outcome of Extensive Hindfoot Fusions
If the results for isolated ankle fusions result in a nonunion rate of 14% and questionable outcomes, the results of the more common globally involved foot are worse. The rates of fusion of an ankle above a triple arthrodesis or a triple arthrodesis or subtalar fusion under an ankle fusion are much lower than for the isolated fusions alone. On top of this, the patient’s tolerance of slight malposition of the fusion is lowered because of the inability to compensate using the remaining motion in the foot or ankle. Patients with successful pantalar fusions may still request below knee amputation be-cause of the poor function of a rigid limb. It has been our clinical experience that patients with extensive hindfoot arthritis do much better with a total ankle and triple arthrodesis than an extensive hindfoot fusion. This procedure therefore holds more promise in the future compared to pantalar fusion.
 | | Figure 2: Treatment options: A combined ankle and subtalar fusion. | The Treatment of Extensive Hindfoot Arthritis
Surgeons also have to recognize that isolated ankle arthritis is a rare disease. Of the causes of ankle arthritis, many are associated with more global conditions such as rheumatoid arthritis. In posttraumatic arthritis, the force that destroyed the ankle often damages cartilage within the surrounding joints, and the fibrosis associated with the injury and the recovery creates a stiffer foot not able to compensate for loss of ankle motion. Outside of global arthritis, patients may have degenerative change in the ankle secondary to ankle instability, itself associated with a cavus foot position4. Ankle arthritis secondary to a planovalgus foot is by definition associated with a mal-positioned foot with secondary degenerative change often seen in other joints of the hindfoot. In light of these outcomes of ankle and extensive hindfoot arthritis, it is not hard for an ankle joint replacement to be a better procedure than fusion even in the short-term.
The Future Improvements In Ankle Arthroplasty and Ankle Fusion
Ankle arthroplasty remains a procedure with many unknowns, and all of the variables of component position and their effect on the joint motion, well outlined for the knee and hip, have not yet been determined for the ankle. Therefore surgeon experience is still a major factor in positioning of the joint, and total ankle arthroplasty should be performed in a few centres only until these details can be worked out and taught. It is also not clear how an ankle joint replacement will perform above a subtalar fusion or triple arthrodesis. Mid-term outcome information on the agility ankle has shown a rate of subtalar arthrosis development of approximately 50% of the rate of arthrosis after ankle fusion. However, this learning curve, though concerning now, leaves considerable room for improvement in the future as technology advances with better bearing surfaces and bonding techniques to bone. Intraoperative decisions, learnt by experience over the last 30 years for the hip and knee, still have to be learnt for the ankle, which in time may become a reliable operation for a general orthopaedic surgeon if these intraoperative factors can be determined and taught at courses and in residency programmes as has been done for the hip and the knee.
 | | Figure 3: OR ankle replacement and triple arthrodesis. | Patient Demands
Although surgeons advise patients about treatment options for end-stage arthritis; at the end of the day, patient demands drive the future of orthopaedic care. In the past, patients have selected knee and hip joint replacement over fusion despite prior reports by surgeons indicating that fusion was an acceptable operation. Motion at the ankle joint remains a goal of many patients, and few are comfortable with the concept of a rigid ankle joint. It is our duty as surgeons and scientists to improve the quality of the prosthesis and the operation, ensure proper training of the surgeons performing the procedure, monitor outcomes and adjust practice accordingly. We also have to ensure that patients have realistic expectations for ankle joint replacement.
The Future
While there are considerable gains to be made in the outcome of total ankle repla-cement; even with its present success, there are few gains to be made in the outcome of fusion. Even if we can raise fusion rates to 100%, patients will still develop secondary changes in other joints and will still have a stiff foot. While the ultimate goal is to restore the normal cartilage to the joint, we are many years away from achieving this goal. In the meantime, ankle replacement holds the most promise with improvements in surgeon experience, design, and bearing surfaces on the horizon.
References
- Pyevich M.T., Saltzman C.L., Callaghan J.J., Alvine F.G. Total ankle arthroplasty: A unique design. Two to twelve year follow up. J Bone Joint Surg Am. 80(A):1410-20, 2000.
- Tallon C., Coleman B.D., Khan K.M., Maffulli N. Outcome of surgery for chronic Achilles tendinopathy. A critical review. Am J Sports med 29:315-20, 2001
- Coester L.M., Saltzman C.L., Leupold J., Pontarelli W. Long - term results following ankle arthrodesis for post-traumatic arthritis. J Bone Joint Surg Am 83(A):219-28, 2001.
- Van Bergeyk A.B., Younger A., Carson B. CT analysis of hindfoot alignment in chronic lateral ankle instability. Foot Ank Int. 23:37-42, 2002.
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