Is Arthrodesis The Answer For A Severely Deformed Ankle?

Author(s): 
By Jesse B. Burks, DPM, MS

Numerous conditions can result in the need for arthrodesis of the ankle joint. In particular, neuropathic osteoarthropathy, post-polio syndrome, neuromuscular disease and severe degeneration secondary to trauma can all make it especially difficult for podiatric surgeons to achieve a successful fusion.1-4 Although implant arthroplasty is gaining acceptance and distraction arthroplasty may postpone the joint destructive procedure, arthrodesis remains a viable and effective treatment for patients with gross deformity of the ankle.
While all patients will require modifications in surgical technique (and there are numerous articles in the literature addressing this at length), let’s take a brief look at some of the principles in successful surgical management of this condition.

Key Preoperative Considerations
Rotational, angular and limb length deformities necessitate the need for appropriate preoperative planning. The goal is not simply to achieve arthrodesis, but to achieve arthrodesis in the optimum functional position. A plantarflexed foot will force the knee into hyperextension. You will need to address any bone loss from previous talar collapse, prior infection or severe trauma. You need to determine if you can accommodate this with postoperative shoe modifications or surgically with extensive bone grafting.
The amount of autogenous bone will determine the graft harvesting site. In the majority of cases, you will need iliac crest bone. In cases of significant shortening, it may be necessary to perform tibial lengthening via distraction osteogenesis.
You must also correct valgus and varus positions. Typically, the rearfoot to leg relationship is positioned in neutral to slight valgus. Be sure to avoid performing a varus biased ankle arthrodesis as it can place significant stress on the knee joint. When it comes to treating significant deformities, I have found that performing a calcaneal osteotomy may also be necessary to completely align the hindfoot.
Also assess proximal deformity prior to performing an ankle arthrodesis. Especially when you’re dealing with cases of previous trauma, evaluating and considering proximal tibial or femoral deformities is a must. A well-positioned ankle arthrodesis is of little value if the overall position is compromised by proximal deformity.5,6
In an uncomplicated ankle arthrodesis, soft tissue structures are rarely a significant component of the deformity. In fact, a moderately contracted Achilles tendon can actually provide a tension-band effect and aid in successful fusion. This is typically not the case in severely deformed ankles. A long-standing deformity may require surgical treatment of the soft tissue. Ankle equinus or other tendinous contractures may require lengthening or a frank tenotomy. Skin contractures may require release, plasty, grafting or rotation flaps. If you do not assess and treat skin contractures at the time of surgery, skin complications can compromise the entire operation.
The form of fixation is also extremely important in this type of arthrodesis. Since there is a higher risk of non- or malunion, using external fixation or a combination of internal and external fixation can give you the ability to adjust the final position postoperatively. As with any surgery, your choice of fixation should be based upon your experience, the type of procedure and what is most suitable for the patient.

Step-By-Step Surgical Insights
Typically, the patient is in a lateral decubitus position under general or spinal anesthesia with a thigh tourniquet. Place the first incision over the distal aspect of the fibula, beginning approximately 10 cm proximal to the distal tip. You may curve the incision distally over the sinus tarsi to aid in exposure. More often than not, you’ll need to make a medial incision as well. This is due to the fact that a severely deformed ankle often requires extensive bone resection to maximize position. When this incision is necessary, make the approximately 5 cm incision over the anterior-medial aspect of the ankle joint.

Dissecting the lateral incision should reveal the distal fibula. Although many techniques for ankle arthrodesis may preserve the fibula, it is often necessary to resect it not only to gain access to the joint, but also because it is a large factor preventing reduction of the deformity. Once you have resected the fibula at an angle, you can insert lamina spreaders into the joint for removal of the cartilaginous surfaces.
Although the currettage method of joint preparation is very effective, you usually cannot employ this method in the malaligned ankle. Joint resection and extensive planning are often needed to restore alignment.
When resecting articular surfaces, be sure to consider both the sagittal and frontal planes. Be careful to avoid injuring the anterior and the posterior-medial neurovascular structures. Blunt dissection can easily facilitate freeing of the soft tissues from the anterior distal aspect of the tibia. This lessens the chances of neurovascular injury.
Medially, you usually want to leave the malleolus intact. Although you can remove it to facilitate joint access, it can lead to significant medial displacement of the foot in relation to the leg. This results from the tendency of the surgeon to align the medial surface of the talus with the medial border of the tibia. If you leave the malleolus intact, it not only helps in appropriate positioning, but increases the contact area for fusion.
It is at this point that you must consider the transverse plane. Fifteen degrees of external rotation is commonly accepted as the norm for transverse position. Often, you can evaluate this prior to surgery and match the surgical site to the contralateral limb.
It’s also important to address the sagittal and frontal plane for optimum position. The foot should be at a 90-degree angle to the leg or very slightly plantarflexed. Excessive dorsiflexion will reduce the chances of the knee fully extending during gait and excessive plantarflexion will cause the knee to hyperextend. The hindfoot should be neutral to slight valgus.

Other Pertinent Pointers
I often employ a Steinman pin directly from the plantar surface of the calcaneus into the tibia for temporary (or permanent) fixation. (Even in the subtalar joint that is left intact following ankle arthrodesis, there is little chance of degenerative changes simply from pin placement. In reality, any arthrofibrosis or degeneration results from fusion of the ankle joint itself. In the severely deformed ankle, the subtalar joint is already involved and may be autofused.) This technique is used by many surgeons and allows you to place internal or external fixation.
Although you may have given much consideration to choosing appropriate fixation in the preoperative phase, be aware that you may have to modify or completely change the fixation intra-operatively in the severely deformed ankle. In many ankles, such as those affected by rheumatoid arthritis and Charcot, I have found external fixation to provide significant advantages over purely internal fixation. Again, the choice of fixation is dependent upon one’s experience level, the given procedure and whether it is right for the patient. Postoperative care will not usually differ from that of the lesser deformed ankle undergoing arthrodesis.

Conclusion
Arthrodesis of the severely deformed ankle presents a significant challenge to the podiatric foot and ankle surgeon. However, if this procedure is performed correctly, it can provide the patient with decreased pain and increased function.

Dr. Burks is a Fellow of the American College of Foot and Ankle Surgeons. He is board certified in foot surgery and reconstructive rearfoot and ankle surgery. Dr. Burks practices in Little Rock, Arkansas.




References:

References

1.Simon SR, Tejwani SG, Wilson DL, Santner TJ et al: Arthrodesis as an early alternative to nonoperative management of Charcot arthropathy of the diabetic foot. JBJS 82A:939-950, 2000.
2.Stone NC, Daniels TR: Midfoot and hindfoot arthrodesis in diabetic Charcot arthropathy. Can J Surg 43(6): 449-455, 2000.
3.Vogler HW: Surgical Management of neuromuscular deformities of the foot and ankle in children and adolescents. Clin Podiatr Med and Surg. 4 (1): 175-206, 1987.
4.Faillace JJ, Leopold SS, Brage ME: Extended hindfoot fusions and pantalar fusions. History, biomechanics, and clinical results. Foot Ankle Clin 5(4): 777-798, 2000.
5.Glissan DJ. The indications for inducing fusion at the ankle by operation with description of two successful techniques. Aust N Z J Surg; 19:64-71, 1949.
6.Buck P, Morrey BF, Chao EY: The optimum position of the arthrodesis of the ankle: A gait study of the knee and ankle. J Bone Joint Surg 69A: 1052-1062, 1987.

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