Surgical complexity

The location of the tibio-talar ankle joint makes the surgical procedure highly complex. As with all joint replacement surgeries the quality of the surgery can affect the success of the device. The small working area and notorious complexity often results in TAR reoperations to remove unforeseen malleolar impingements which will impact the recovery time (Henricson et al. 2007). It is vital to the joint function that the soft tissues are handled carefully (Hintermann 2005) and the device is implanted accurately, parallel to the ground (Jackson et al. 2003).

Positioning can be difficult with the limited surgical access but malpositioning (Figure 1.12), in any or multiple planes, can be a serious problem (Jackson et al.

2003). Not only will this increase the possibility of lift-off (Tochigi et al. 2005), heighten contact stresses (Espinosa et al. 2010), affect the ligaments (Hintermann 2005) and functionality of the implant but should bearing impingement occur as a result the wear rates will be accelerated (Jackson et al. 2003; Hintermann 2005).

Figure 1.12 displays an example of a well aligned implant compared to an anteriorly implanted talar component.

Anterior placement of the talus and reduction of the joint height can cause problems (Tochigi et al. 2005). Misalignments of greater than 5ᵒ in version could see the polyethylene components reach their yield stress long before the predicted time frame (Espinosa et al. 2010). Similarly, the challenges of correcting a heavily varus or valgus deformities have been recognised. Wood et al. (2009) defined a deformity of greater than 15ᵒ to dramatically increase the six year failure rate, especially in the Beuchel-Pappas design and for cases which did not result in direct failure a higher incidence of edge loading was observed. Morgan et al. (2010) reported a similar correlation between pre-op malalignment and post-op edge loading.

In terms of TAR surgical implantation there is a notable learning curve while the surgeon gets used to the device and operative technique (Haskell et al. 2004;

Hintermann 2005; Henricson et al. 2007). The best outcomes have typically been published by the design surgeons themselves (Gougoulias et al. 2010). Henricson et al. (2007) used the Scandinavian Joint Registry to plot contrasting data for the revision rates for three surgeons for their first 30 STAR devices compared to those later. The five-year survival rate rose from 70% for the early implants to 86% for those after. This suggests the more experienced gained with the surgeon’s Figure 1.12. X-ray of a TAR (A) neutrally aligned, (B) talar centre anterior to tibial axis.

Image obtained from: The effect of three-component total ankle replacement malalignment on clinical outcome: pain relief and functional outcome in 317 consecutive patients. Barg et al. (2011) J Bone Joint Surg Am, 93 (21): pp1969 -1978.

A B

preferred implant the better the success rates will be expected to get, however, such inconsistent initial results may have an effect on the professional or public perception of the implant. This will impact low volume TAR centres which despite having similar functional results have been associated with a higher failure rates compared with the more experienced, high volume centres (Pinar et al. 2012).

However, with low numbers of TAR procedures taking place at centres across the UK it is difficult for the surgeon to get the necessary experience (Henricson et al.

2007). This learning curve is likely to be partly responsible for the ranging success rates which are reported in literature. The Depuy Mobility was the most commonly implanted TAR in the UK despite its varying five year statistics; Ahluwalia et al.

(2013) reported a relatively high, 92.6% success rate while at the lower end of the scale Blundell (2012) recorded 84.1% for a smaller study group. Despite these five-year success rates not being dissimilar to other marketed TARs this device has since been removed from the market.

The Corin Group’s Zenith device, having been implanted since 2007 at this early stage there is limited published information regarding the medium or long term results. This evolution of the Buechal-Pappas is marketed on its “advanced coating technology” and novel instrumentation which allows for improved repeatability and may be the reason for its continued market placement (Millar 2012). Advances in surgical equipment may be able to curb the prominence of the surgical “learning curve”. Mckenzie et al. (2012) have reviewed the 81 Zenith TARs implanted between 2007 and 2011 in what was an inventor study and reported a greater than 95% survivorship at 30 months and no evidence of radiographic loosening on radiographs. This centre published more recent survivorship statistics of 99.0% at three years (n=103), reducing to 94.0% at five years (n=50), and 93.8% at seven years (n=16) (Walter et al. 2015). Millar (2012) published a non-inventor study for the early follow up results for the first 50 implanted TARs outlining that 46 out of the 50 patients with the new TAR design were deemed happy. The alignment was reported within ± 5 degrees for 43 patients out of 50 in the coronal plane and 45 patients in the sagittal plane. After a mean follow up of 30 months only one revision surgery for loosening due to cyst formation was required. This was then followed up to medium term, an average of 5.3 years and showed 96%

survivorship especially considering the learning curve which is associated with TAR surgery but further independent information is required to properly judge the implant performance. The midterm results will be interesting as this is where other designs have seen increasing osteolysis and failure.

Taking into consideration the complexity of this procedure combined with the high load bearing nature of the ankle joint it is no surprise the patient indications for TAR surgery are highly limited. The “ideal” patient for TAR is generally over 50 years of age, weighs less than 200 pounds, has failed to respond to the other non-invasive treatments and will only place low physical demands on the device (Mann et al. 2012). There are many more contraindications which are likely to contribute to the fact ankle fusion remains the preferred treatment method for many surgeons (Jackson et al. 2003). Ideally a TAR should be more widely available, especially for younger more active patients but limited confidence in current designs makes that a chance few are willing to take. If these devices are failing early in the ideal patient demographic this will no doubt be worse for any individual outside of this bracket.