Use of Total Ankle Arthroplasty in the Varus or Valgus Ankle

CHAPTER PREVIEW

CHAPTER SYNOPSIS:

This chapter deals with the very complicated issue of dealing with varus or valgus deformities in the ankle in conjunction with an ankle replacement. A classification system and algorithm for treatment are given for varus deformities. It is of utmost importance to determine every facet of the instability pattern and to correct it at the time of the replacement. It is also important to realize that some of the deformities are so severe that an ankle fusion is the best treatment option.

IMPORTANT POINTS:

1

Always look for foot deformities that can contribute to the ankle deformity.
2

Always look for, and treat, an equines contracture.
3

Never leave the operating room until the ankle is well aligned and stable.

CLINICAL/SURGICAL PEARLS:

1

Always obtain long leg radiographs to determine any alignment issues in the leg.
2

With a valgus deformity, distract the ankle until the deltoid endpoint is found. If there is no deltoid, a reconstruction has to be done, or convert to a fusion.
3

With lateral ligament instability, the lateral gutter fills with heterotopic bone. This has to be removed to allow the talus to reduce in the mortise.

CLINICAL/SURGICAL PITFALLS:

1

If there is no deltoid, it might be best to fuse the ankle.
2

In chronic varus instability, the medial malleolus might be very thin due to wear.

VIDEO AVAILABLE:

•

Varus Ankle [J. Chris Coetzee]

HISTORY/INTRODUCTION/SCOPE OF THE PROBLEM

With the advent of the total ankle arthroplasty as a mode of therapy for end-stage arthritis, multiple challenges have been encountered in treating not only the ankle that has worn out in neutral but those that are worn out in a deformed position. The etiology of the arthritis should be ascertained as to whether it is systemic (i.e., rheumatoid) versus traumatic versus primary. Each of these broad classifications has its unique problems when it comes to correcting deformity, and on occasion, fusion may be the better option if certain characteristics of the deformity (i.e., absent deltoid ligament) can be appreciated preoperatively.

In patients with rheumatoid arthritis or other systemic collagen–type diseases, the factors to consider are the quality of the bone, the amount of bone remaining (i.e., medial malleolus or lateral talar dome wear or erosion), the condition of the skin (i.e., how much deformity can be corrected and the skin can be closed), and associated deformities of the foot. Frequently, in these conditions, there is associated osteoporosis with marked weakening of the bone, thereby increasing the chance of fractures when corrective forces are applied. In valgus deformity with associated planovalgus of the foot (a common combination), closure of the skin can be difficult, leading to skin loss.

In cases that are considered traumatic in origin, a great deal of variability can be encountered in the presentation of the ankle, either varus or valgus, depending on the type of the initial fracture, how the ankle settled, the remaining bone, and how ankylosed the joint has become. Not infrequently, the ankle will be ankylosed to the point that it simply cannot be distracted, and reaching the deltoid endpoint can be achieved only with considerable difficulty. On occasion, the tibial cut has to be made initially followed by tibial bone removal, in essence performing a posterior capsulectomy. This then allows the surgeon to correct any varus, valgus, or equines deformity and allows the ankle to lengthen, thereby allowing identification of the deltoid endpoint. This is important to determine ultimate stability and aid in determining the level of bone resection.

In the case of primary arthritis with angular deformity, the joints are often quite loose with considerable bone loss on both sides of the joint. Distraction is usually very easy but can be alarming in that the joint can be widely distracted before the deltoid endpoint is reached. Distraction on occasion can be carried out to over 1 cm before any tension is achieved medially and stability is obtained.

The angular deformity of the ankle has to be taken into consideration with other adjacent joints, especially the knee and the foot, and these are addressed in Chapter 12 . The biomechanical aspects of the ankle joint are extremely important if one is going to appreciate how the ankle became deformed and apply the necessary procedures to correct the deformity. Others have suspected chronic lateral ligament instability as playing a role in late-onset ankle arthritis, particularly in the varus deformity. Ultimate ligament stability is mandatory if the ankle is going to function properly following the insertion of the joint. Ligaments stabilize the ankle in the sagittal, coronal or rotational, and transverse planes. All three modes must be stable to preclude subluxation or recurrent angulation following insertion of an ankle.

BIOMECHANICS

The deltoid ligament is extremely important in stabilizing the ankle medially, and without it progressive valgus deformity will occur. Progressive lateral loading was reported with concomitant unloading medially with dorsiflexion and associated external rotation. The converse is true with plantiflexion. The deltoid ligament is composed of both the superficial and a deep portion with the superficial portion, taking its origin from the medial malleolus and with its insertion broadly into the calcaneus, talar neck, and navicular. The deep portion originates from the medial aspect of the medial malleolus and consists of anterior, intermediate, and posterior fascicles inserting into the medial wall of the talus. Harper found no lateral displacement or valgus tilt of the talus with an intact deltoid ligament. He noted no increase in valgus tilt with sectioning of the deep or the superficial portions of the deltoid ligament individually. However, valgus tilt was possible with sectioning of both deep and superficial portions. Further sectioning of the posterior ankle joint capsule resulted in increased valgus tilt. Sectioning of the superficial deltoid ligament did not result in increased anterior translation or lateral shift of the talus, whereas sections with deep deltoid ligament resulted in significant lateral shift and anterior translation of the talus. The lateral ligaments are equally important when it comes to stabilizing the ankle joint, with the lateral ligament complex consisting of the anterior talofibular, calcaneofibular, and posterior talofibular ligaments. The anterior talofibular ligament originates from the anterior margin of the distal fibula and inserts at the lateral tubercle of the talus. The calcaneofibular ligament originates at the distal tip of the fibula and inserts at the lateral wall of the calcaneus, spanning both the ankle and subtalar joints. However, because of its unique position parallel to the axis of rotation of the subtalar joint, the calcaneofibular ligament stabilizes the ankle while not restricting subtalar motion. The anterior talofibular and calcaneofibular ligaments are oriented approximately 90 degrees from one another. Inversion stress is resisted by the anterior talofibular ligament in plantiflexion and the calcaneofibular ligament as the ankle is dorsiflexed. Harper determined these structures to be the primary restraint to anterior translation of the talus.

Similar to an arthroplasty of the knee joint, ligament stability must be achieved at the time of insertion of an ankle arthroplasty. In some instances, it is readily apparent to the surgeon in his or her preoperative evaluation that ligament stability has been completely lost and that, with present techniques, ligament stability cannot be achieved and fusion will be necessary. This is particularly true with deltoid insufficiency with gross valgus tilt of the talus and lateral translation.

OPERATIVE TECHNIQUE

The distracter has been an integral part of the Agility ankle system and is used to correct deformity and to assess and define the deltoid ligament. The lateral collateral structures can be reconstructed at time of surgery and their status need not be determined or be essential to proceed with the surgical procedure. The deltoid endpoint must be clearly defined at time of surgery, and its absence would preclude proceeding with insertion.

Varus deformity is divided into stages I, II, and III ( Figs. 11-1 through 11-3 ). In stage I, the varus deformity is secondary to erosion into the medial subchondral plate with no widening of the lateral joint line, indicating no laxity of the lateral collateral ligaments. There is no bony buildup in either the medial or lateral aspect of the joint, and usually there is no erosive change into the medial malleolus.