Protecting Ankle Structures During Total Ankle Arthroplasty
Introduction
Total ankle replacements are gaining favor. Multiple implants are currently FDA approved for use in the United States:
Scandinavian Total Ankle Replacement (STAR; Small Bone Innovations, Morrisville, PA)
INBONE (Wright Medical Technology, Arlington, TN)
Agility (DePuy, Warsaw, IN)
Salto Talaris (Tornier, Montbonnot, France).
A number of studies have provided evidence that the implants are gaining in terms of success and longevity.1-7 Ankle replacements preserve joint motion and avoid overloading the other joints, which happens in the case of a fusion.8 Studies also show that they allow patients to maintain gait patterns and may achieve better results than those achieved with a fusion.8-10
Potential complications with total ankle replacements include infection, loosening, and pain.5,11 It is important to educate the patient on these complications before surgery.
Another potential complication is malleolar fracture,12 either to the fibula or the medial malleolus (ie, tibia). Malleolar fracture can occur during bony cuts if too much bone is taken or if the implant is positioned too medially or laterally. The fibula lies behind the talus in a posterior position, and if the direction of the cut is not appropriate, the fibula could be cut as well. This has been well described in the literature.13-15
Damage to the neurovascular structures around the ankle could also occur. The flexor hallucis longus (FHL), flexor digitorum longus (FDL), posterior tibial tendon (PTT), posterior tibial artery, and tibial nerve, which pass around the posterior aspect of the ankle, can be injured with saw cuts or pin placement, particularly those that go from anterior to posterior. This can occur with a variety of ankle systems. 14
Purpose
The purpose of this article is to describe simple ways in which the FHL, FDL, PTT, posterior tibial artery, and tibial nerve can be protected from intraoperative injury.
The medial malleolus can be protected by placing a prophylactic screw, which can be commonly done with a cannulated system.
The tendons and nerves behind the ankle can be protected with a posterior retractor.
Both measures can be done at the beginning of the case in approximately 10 minutes. Not only will this protect patients from the above complications, but it will also save considerable time during surgery that would be spent addressing such injuries.
Technique
Medial Malleolar Screw
The patient is positioned supine with a bump. Small variations of the overall technique depend on the ankle implant system being used. This part of the procedure does not need to be done under tourniquet so as to save time for the later total ankle replacement.
A 1.6 K-wire is then placed percutaneously into the medial malleolus, starting at its tip. An attempt is made to angle this wire up the medial malleolus, taking care not to put it too close to the lower mid-shaft of the tibia, which would interfere with potential implants. This is particularly the case with an INBONE, which has a longer stem. The Salto Talaris has a keel that must be avoided as well.
The wire is aimed to the center on the lateral view in an attempt to avoid going too far anterior or posterior. Once the wire is placed, it is checked with fluoroscopy (Figure 1). If the position is appropriate, a small stab incision is made. The K-wire is then exchanged for a 1.25 K-wire, which easily fits within the hole.
Figure 1. Intraoperative fluoroscopy lateral view demonstrating correct position of K-wire into the medial malleolus
A depth gauge is used to measure the length of this wire to determine the appropriate length of the screw. A 2.7-mm cannulated drill is then used to drill its path (Figure 2) and a 4.0 partially, threaded, cannulated screw is placed and checked with fluoroscopy (Figure 3). The size of the screw again depends on the implant being used and the level that must be avoided; in general, this is anywhere from a 40- to 50-mm screw. It should be placed so as to avoid the eventual implant (Figure 4).
Figure 2. Intraoperative photograph showing 2.7-mm cannulated drill used to drill into the medial malleolus
Figure 3. Intraoperative photograph demonstrating a 4.0 partially-threaded, cannulated screw placed in the medial malleolus
Figure 4. Intraoperative fluoroscopy demonstrating final implant placement.
Protection of Posterior Structures
To protect the posterior structures, an easy dissection is made, which is also performed at the beginning of the case without tourniquet. A 4-cm incision is made off the posterior aspect of the tibia about 4 cm proximal to the medial malleolus (Figure 5). The PTT is usually found directly up against the posterior aspect of the tibia and is left in its position.
Figure 5. 4-cm incision made off the posterior aspect of the tibia, about 4 cm proximal to the medial malleolus
The interval between the PTT and the flexor FDL is visualized and then exploited with gentle and careful dissection. Once in this interval, the surgeon uses a Cobb elevator to gain access and perform a periosteal dissection around the back of the tibia. Care is taken to ensure that the elevator can be passed to the lateral and medial aspects of the posterior joint. At this point in the case, the elevator cannot necessarily be seen, but it will be visualized later, once the bony cuts are made.
The Cobb elevator, which has a wide blade, is placed into the back of the ankle during parts of the case that could theoretically injure the posterior structures. The tourniquet is let up and an anterior approach is made. The total ankle technique that is followed depends on which implant is being used.
For most systems, pinning of a tibial cutting guide is done with anterior to posterior pins. This is a very good time to use a Cobb elevator (Figure 6). It is placed medially for medially placed pins and laterally for laterally placed pins. It is also important during the tibial cut (Figure 7). For systems that have a separate talus cut, it is important to also use a Cobb elevator when placing guide wires for the talus from anterior to posterior and when making the anterior to posterior cuts. Some of the posterior capsule is generally also taken after the bone is taken out from the tibial and/or talar cuts. The retractor can commonly be visualized. At times, the FHL can be visualized as well.
Figure 6. Intraoperative photograph showing the position of the Cobb elevator used during the pinning of the tibial cutting guide.
Figure 7. A lateral view showing use of the Cobb elevator, placed through the posterior tibia incision, during tibial cuts.
At the end of the case, once all the implants are in, the closure begins. The subcutaneous layer is closed with an interrupted, buried 3-0 Vicryl. The skin is usually closed with either a running or horizontal mattress, interrupted 3-0 nylon. This wound is usually not an issue and heals quite readily.
The postoperative protocol depends on the total ankle replacement being used, but generally consists of a posterior well-padded splint for a minimum of 2 weeks.
References
Bonnin M, Gaudot F, Laurent JR, Ellis S, Colombier JA, Judet T. The Salto total ankle arthroplasty: survivorship and analysis of failures at 7 to 11 years. Clin Orthop Relat Res 2011; 469 http://www.ncbi.nlm.nih.gov/pubmed/20593253
Devries JG, Berlet GC, Lee TH, Hyer CF, Deorio JK. Revision total ankle replacement: an early look at agility to INBONE. Foot Ankle Spec 2011; 4 http://www.ncbi.nlm.nih.gov/pubmed/21868797
Gougoulias N, Khanna A, Maffulli N. How successful are current ankle replacements? A systematic review of the literature. Clin Orthop Relat Res 2010; 468 http://www.ncbi.nlm.nih.gov/pubmed/19618248
Kopp FJ, Patel MM, Deland JT, O'Malley MJ. Total ankle arthroplasty with the Agility prosthesis: clinical and radiographic evaluation. Foot Ankle Int 2006; 27 http://www.ncbi.nlm.nih.gov/pubmed/16487461
Saltzman CL, Mann RA, Ahrens JE, et al. Prospective controlled trial of STAR total ankle replacement versus ankle fusion: initial results. Foot Ankle Int 2009; 30: 579-596. http://www.ncbi.nlm.nih.gov/pubmed/19589303
Piriou P, Culpan P, Mullins M, Cardon JN, Pozzi D, Judet T. Ankle replacement versus arthrodesis: a comparative gait analysis study. Foot Ankle Int 2008; 29 http://www.ncbi.nlm.nih.gov/pubmed/18275730
Doets HC, van Middelkoop M, Houdijk H, Nelissen RG, Veeger HE. Gait analysis after successful mobile bearing total ankle replacement. Foot Ankle Int 2007 http://www.ncbi.nlm.nih.gov/pubmed/17371655
McGarvey WC, Clanton TO, Lunz D. Malleolar fracture after total ankle arthroplasty: a comparison of two designs. Clin Orthop Relat Res 2004; 424 http://www.ncbi.nlm.nih.gov/pubmed/15241150
Schuberth JM, Patel S, Zarutsky E. Perioperative complications of the Agility total ankle replacement in 50 initial, consecutive cases. J Foot Ankle Surg 2006 http://www.ncbi.nlm.nih.gov/pubmed/16651192
Myerson MS, Mroczek K . Perioperative complications of total ankle arthroplasty. Foot Ankle Int 2003; 24
Conti S, Wong Y. Complications of total ankle replacement Clin Orthop Relat Res 2001; 391.
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