First-generation total ankle arthroplasty (TAA) produced a rather disappointing long-term survival despite various designs. Earlier designs, including cemented, uncemented, constrained, and unconstrained types, had high failure rates compared with hip and knee replacements. However, newer prostheses that have shown lower failure rates with longer-term follow-up have given hope for longer survival rates. The Scandinavian Total Ankle Replacement (STAR) was developed by Dr. Hakon Kofoed, an orthopedic surgeon in Denmark in 1981 (1, 2, 3, 4, 5, 6, 7 and 8). It consists of three parts: a tibial tray, a mobile polyethylene bearing, and a talar cap (Fig. 35.1). He initially developed the prosthesis in which the tibial tray was cemented. In 1986, he modified it to a press-fit component and the prosthesis has remained unchanged since that time. The prosthesis is made of cobalt chrome with titaniumsprayed porous-coated bone contact surface and press-fit over precisely cut bony surfaces (9, 10 and 11).

The indication for the procedure is end-stage ankle arthritis. Relative indications are a patient over the age of 50, who is not involved in heavy labor and who has realistic activity and sports expectations.

The absolute contraindications should be closely adhered to since failure to do so will likely result in premature failure of the prosthesis. These include the following:

Relative contraindications that mean that a good result is more difficult to achieve include the following:

The consideration of ankle replacement surgery begins with a careful history, including details of previous treatment. If there was a previous infection, it is important to determine the severity, prior treatment of the infection, and whether or not there has been any recurrence. If the patients have any significant medical problems, they should receive preoperative clearance from their primary care physician. Assuming the patient is in reasonably good health, the remainder of the patient encounter involves the evaluation of the lower extremity. This begins with examination of the patient standing,
walking, and observing the alignment of the lower extremity. A severe varus or valgus deformity of the knee would be a relative contraindication to the procedure until it has been corrected, after which ankle joint replacement could be considered. The weight-bearing varus/valgus alignment of the hindfoot also needs to be noted.

With the patient seated, the active and passive range of motion of the ankle, subtalar, and transverse tarsal joints needs to be ascertained. The motor function is assessed at the same time. The neurovascular status of the foot is evaluated, and if there is any question about the vascular status of the foot, an arterial Doppler study should be obtained.

The skin needs to be carefully evaluated to be sure that an adequate soft tissue envelope is present. Large adherent scars, particularly about the anterior aspect of the ankle, are a relative contraindication since primary soft tissue healing is a very critical part of the ankle replacement. If there are any questions regarding the quality of the skin, consultation with a plastic surgeon prior to surgery is advised. The ligamentous integrity of the ankle also needs to be assessed, looking for moderate to severe instability, which may require correction at the time of the insertion of the prosthesis by performing a medial release and/or ligament reconstruction.

Weight-bearing radiographs are obtained consisting of an AP, lateral, and oblique ankle x-ray and the Saltzman tibial calcaneal view. Besides the obvious osteoarthritis of the ankle joint, the severity of any coronal plane deformity is noted since correction of more than 25° may be a relative contraindication to the procedure unless other procedures accompany the STAR either before or concomitantly to correct the deformity (12, 13 and 14). In the sagittal plane, anterior or posterior subluxation of the talus is not uncommon and can usually be corrected. The subtalar and transverse tarsal joints are assessed for osteoarthritis, but are rarely a contraindication to the ankle replacement surgery. Consideration can be given at the time of surgery to fuse these joints if they are a source of significant pain.

The overall posture of the foot needs to be very carefully assessed. This begins with the alignment and mobility of the subtalar joint and the alignment and mobility of the forefoot. It is absolutely essential that a plantigrade foot is present under the STAR prosthesis at the conclusion of surgery. Otherwise, failures will occur as a consequence of misaligning the joint. One also needs to determine the alignment of the foot once the ankle coronal plane deformity has been corrected. This can be extremely challenging. The question arises as to whether or not the coronal plane deformity should be corrected before or after the ankle prosthesis has been inserted. As a general rule, a plantigrade foot should be created prior to the insertion of the prosthesis, but occasionally it can be carried out simultaneously or afterward. The important point is that a nonplantigrade foot applies abnormal stress to the prosthesis that will eventually result in failure, requiring either a revision or a fusion.