ARTHRODESIS OF THE ANKLE

JOHN WILLIAM VAN MANEN, MD

Many techniques have been described to achieve ankle arthrodesis. A simple technique allowing for consistent results is presented here. Four issues were involved with the evolution of the technique: ease with which foot alignment could be obtained, optimizing fusion-site stability, preventing iatrogenic subtalar joint injury, and minimizing wound complications. The technique has excellent exposure and simple osteotomies, allowing for accurate alignment. Stability is obtained by compressing two broad bone surfaces, using lag screw technique. No plates or bone grafting is used. KEY WORDS: arthrodesis, ankle

Arthrodesis of the ankle has been a procedure associ- ated with an unsatisfactorily high rate of complications. The rates of nonunion, malunion, wound healing prob- lems, and infection have been the impetus for a prolifer- ation of techniques hoping to overcome these prob- lems. 11s A successful union in a satisfactory position predictably results in an excellent gait as long as other joints of the foot (especially subtalar joint) function well. ]9,20

The technique to be described has evolved with the following considerations in mind: (1) positioning of foot in relation to tibia, (2) optimizing fusion-site stability, (3) preventing inatrogenic subtalar joint injury, and (4) min- imizing the risk of wound healing problems. These con- siderations are interrelated, and although one technique may impact favorably on one consideration it may impact unfavorably on another. For example, chevron osteoto- mies 9 may impact favorably on stability but make opti- mum positioning more difficult. Similarly, using various plate devices may enhance stability yet make compres- sion less perfect, exposure more extensive, penetration of the subtalar joint more likely, and perhaps wound clo- sure under more tension. It is believed that the tech- nique described in this article addresses these issues in a satisfactory manner. 21

INDICATIONS

Painful arthrosis is the most common indication for ankle arthrodesis. The cause is usually posttraumatic, al- though it could be caused by an arthritic disease or infec- tion.

Individuals may present with a painful ankle, limited dorsiflexion, and dramatic osteophyte formation. Yet, if evidence of adequate articular cartilage on weight- bearing roentgenograms is observed, satisfactory relief of

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pain may be obtained by joint debridement. Other indi- viduals may present with advanced arthrosis, yet not ex- periencing the degree of pain or disability to warrant sur- gery.

A course of antiinflammatory medications and ambu- latory aids (brace, cane) that lessen demands on a joint should be attempted before surgical intervention. Defor- mity or instability that disturb gait are usually managed by bracing, soft-tissue procedures, or extra-articular pro- cedures. Sometimes they may be best managed by ar- throdesis.

PREOPERATIVE EVALUATION

As with any medical treatment, a thorough examination of the patient is essential. In doing so, the surgeon may be able to minimize the risk of failure or at least inform the patient of certain factors that place them at increased risk of failure. Certain aspects of a patients symptoms may be related to abnormalities other than ankle arthritis. The patient should know Which of their symptoms will and which will not be relieved by arthrodesis. Ultimate patient satisfaction can be impacted by preoperative ed- ucation.

If high-energy trauma was the cause of the event lead- ing to arthrosis there is a higher risk of complications. 22 Prior infection, or a patient history that indicates the pos- sibility of infection, may necessitate further work-up. Medical conditions that cause peripheral neuropathy (es- pecially diabetes) should be noted.

The neurological examination should identify motor or sensory abnormalities and seek evidence of nerve entrap- ment syndromes or neuromas. Circulatory disease, arte- rial or venous, and the presence of edema should be noted. Location of prior surgical incisions and the pres- ence of extensive scarring may require modification of the operative technique.

Rang~ of motion in the hips, knees, and subtalar joints should be assessed in addition to the ankle. Dysfunction in these joints may impact ultimate patient satisfaction. Of particular importance is separating those symptoms related to the ankle and subtalar joints.

Operative Techniques in Orthopaedics, Vol 2, No 3 (July), 1992: pp 137-141 137

Overall assessment of lower extremity alignment is needed if a plantar-grade foot is to be obtained. The alignment must include an assessment of the rotational (coronal plane) relationship of the foot and knee. The position of the contralateral foot is the guide used to po- sition the operative foot before fixation.

Roentgenograms should include weight-bearing views of the foot and the ankle. Abnormalities in other joints should be noted. An assessment of bone quality, bone loss, deformity, or changes consistent with an avascular talus are all required in operative planning.

SURGICAL PROCEDURE

Preparation The procedure is performed while the patient is under regional or general anesthetic. A padded bolster i s placed under the ipsilateral hemipelvis to allow easier access to the lateral ankle. A tourniquet is placed on the thigh. The leg is prepared and draped to above the knee to allow unhindered visualization of alignment in the frontal, sagittal, and coronal planes.

Exposure The skin incision is lateral and centered over the fibula. The incision extends from 4 to 6 cm proximal to the tibial plafond to the tip of the fibula. Here the incision curves anteriorly 3 to 4 cm directed toward the base of the fourth metatarsal. Cutaneous nerves are avoided. As this is an internervous interval in most patients, painful neuroma formation is avoided (Fig 1).

Over the fibula the incision is deepened to bone. Sub- periosteal dissection around the fibula distally will enter the ankle joint (anteriorly and posteriorly) as the capsule

f ~

Fig 1. Lateral approach is between sural nerve and superfi- cial perineal nerve.

and ligaments are elevated. The fibula is resected ob- liquely about 11/2 cm proximal to the plafond.

Elevating the origin of the extensor digitorum brevis and the roots of the inferior extensor retinaculum from the floor of the sinus tarsi (calcaneus) is performed. This allows for visualization of the posterior facet of the sub- talar joint and, above that, the lateral process of the talus. Also visualized is the base of the talar neck. Stripping soft tissues from the talar neck should be avoided as much as possible to preserve blood supply.

Returning attention to the ankle shows good visualiza- tion of the talus and tibia. Placing a Cobb elevator deep to the capsule (intra-articular), the capsule is elevated from its tibial attachments both anteriorly and posteri- orly. The elevation is carried about one centimeter prox- imally and carried medially as far as the medial malleolus. By staying deep to the capsule and periosteum, neural and vascular structures are protected. Elevating capsular attachments from the talus is not generally necessary nor recommended. Exposure is now complete with minimal soft-tissue trauma as all dissection has been subperiosteal or subcapsular.

Osteotomies Two bone cuts are made. The first resects the tibial plafond but leaves the medial malleolus intact. The sec- ond resects the talar dome. The amount of bone re- moved is minimal, only as much needed to allow flat surfaces of bone (Fig 2). The final alignment of. the foot is crucial for a successful procedure, proper alignment of the cuts is crucial. Excellent success in gaining proper alignment has been experienced using the following tech- nique. 21

Malleable retractors are placed anterior and posterior to the distal tibia, protecting the soft tissues. A power saw is used to excise the articular surface of the tibia perpen- dicular to its long axis. The surgeon operating the saw judges the angle of the cut from the sagittal perspective (flexion/extension). An assistant, while stabilizing the leg, judges the angle of cut from the frontal perspective (varus/valgus). A good view of the leg is required to make accurate cuts, which is why the patient is draped above the knee. The saw cut is ended at the level of the

Fig 2. Diagramatic representation of bone resection.

138 JOHN WILLIAM VAN MANEN

medial maIleolus (see Fig 2). An osteotome can be used to complete the plafond excision, leaving the medial mal- leolus intact. With an assistant holding the foot in proper position (neutral flexion/extension, 0 ~ to 5 ~ valgus), the surgeon resects the talar dome parallel to the tibial cut. No more bone than is needed to achieve a broad, flat surface is resected. Cartilage is removed from the medial malleolus and the medial facet of the talus. Distracting the bony surfaces with a lamina spreader can improve exposure while removing this cartilage. The flat bone surfaces are now placed together. If they do not contact medially, it is due to the talus abutting the medial malle- olus. Resecting the distal 5 to 10 mm of the medial mal- leolus will correct this problem. While final assessment of alignment is made, a small bishop clamp is used to hold the joint together. Correcting alignment in the fron- tal (varus/valgus) plane or the sagittal (flexion/extension) plane can be easily done by resecting bone on the tibia. Proper rotational alignment needs to be confirmed before internal fixation. Usually the first or second interspace of the foot aligns with the midline of the patella with the knee flexed. Preoperative assessment should document each individuals alignment on their contralateral extrem- ity. The fused ankle should be aligned to match. The surgeon has now achieved two broad, flat surfaces of cancellous bone that can be perfectly opposed with the foot in opt imum position.

Internal Fixation Two screws (6.5 mm cancellous) are now inserted across the arthrodesis site using proper lag technique. The screws are inserted from distal to proximal (talus to tibia) and are roughly parallel. One screw enters at the plantar lateral base of the talar neck. The second enters the talus lateral to the first, just above the posterior facet of the subtalar joint. The screws are directed posteromedially but as perpendicular to the arthrodesis site as possible. The screw threads should engage the posteromedial tibial cortex (see Fig 3).

Broad contact surfaces are critical to stability when the lag technique is used alone: This contact transfers bend- ing moments from the screws to the bone. 23 The loads applied to the screw are then tensile. The fixation leads to excellent stability. No bone grafting is used.

Closure Closure is performed over a drain. Having excised the fibula during the exposure, the skin can be opposed with- out the tension often noted after operations about the ankle. A bulky compression dressing is applied and the ankle is splinted.

Postoperative Care The patients are discharged when analgesia is accom- plished with oral medication. Follow-up for suture re- moval is done at 1 or 2 weeks. At this time a short leg cast is applied, and the patient is kept non-weight bearing. Six weeks after surgery, if the x-rays show satisfactory healing, weight bearing is allowed. Twelve weeks of

Fig 3. Approximate screw position.

casting is usually required, though an occasional delayed union has made the average 14 weeks. 21

DISCUSSION

The four main considerations in the development of this technique, (1) position, (2)stability, (3) wound healing, and (4) protection of the subtalar joint, ,have been dealt with in a logical fashion. Only follow-up with larger numbers of patients and in other surgeons hands will confirm whether this procedure has advantages. There are several key points to reemphasize.

Regarding Position A great deal of emphasis has been given to frontal and sagittal plane a l ignment . Do not fail to recognize and correct abnormalities in rotational alignment. The advan- tage of flat bone cuts is to make positioning in varus/ valgus and flexion/extension simple. Also achieved is freedom in positioning the foot rotationaUy. Loss of leg length is minimal.

Regarding Stability Adhering to fixation principles is critical. One should not expect the screws to directly resist the bending moments across the ankle. The screws must compress the fusion site over a broad area to transfer these stresses to bone. Factors that may prevent broad bony contact or hinder the ability to compress with screws need to be assessed. Bone loss as noted after removing a failed ankle replace- ment arthroplasty or the severe osteoporosis that may be present ' in rheumatoid arthritis are two of these factors. Other methods of achieving stability may need to be con- sidered. It is not believed that using the fibula as a strut across the fusion site adds significantly to stability if good compression is obtained.

ARTHRODESIS OF THE ANKLE 139

neuromas and painful scars should be minimal in this interneural approach.

Fig 4. (A,B) Screws oriented from tibia into talus run risk of penetration into subtalar joint.

Regarding Wound Healing

Tension on the skin with wound closure commonly oc- curs in procedures about the ankle. Bulky internal fixa- tion materials can add to this potential problem. Absence of the fibula allows for a wound closure that is under no tension, and excising the distal fibula has not caused problems with peroneal function or inversion instability in the fused ankle. Cosmetically, the ankle is improved with the fibula discarded as it narrows the ankle. Shoe wear becomes easier for the same reason. Troublesome

Regarding Subtalar Joint

Orienting hardware away from the subtalar joint should eliminate potentially disabling damage to this joint (see Fig 4). Good long-term results in ankle arthrodesis are expected and much of the success depends on good sub- talar joint function. Changes are noted in the subtalar joints after ankle arthrodesis, presumably due to the in- creased stresses they absorb. Damage to joints that will have increased demands on them should be avoided.

Theoretically, limiting soft-tissue dissection from the talus will protect its tenuous blood supply. Some of this bone's nutrient vessels may already be lost if trauma was the event that led to arthrosis. Further damage to the precarious blood supply may be the cause of the higher failure rate noted in the arthrodesis after a history of high-energy trauma.

CONCLUSIONS

The successful outcome of ankle arthrodesis is optimized by several factors: (1) limiting complications, (2) proper patient selection, and (3) patient education regarding ex- pected symptomatic relief. The published results with this technique have been gratifying. 21 Its relative simplic- ity should allow for reproducible results (Figs 5A-C).

Fig 5. (A) Anteroposterior, (B) lateral, and (C) oblique views 9 months after arthrodesis showing union and screw position.

140 JOHN WILLIAM VAN MANEN

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ARTHRODESIS OF THE ANKLE 141