The Mini Arthrotomy Technique for Ankle Arthrodesis
January 1st, 2003
Mark Myerson MD
Manos Stamatis MD
Abstract
During the last 10 years the majority of ankle arthrodesis procedures has been performed at our institution utilizing a “mini arthrotomy” technique. This technique involves two 1.5 cm incisions, one anteromedial and one anterolateral, through which the ankle joint is visualized. Debridement of cartilage and synovium as well as subchondral bone resection is performed using curettes, rongeurs, and in particular, flexible chisels. The ankle is ideally positioned in the neutral position in the sagittal plane, minimal valgus (up to 5 degrees) and 5 to 10 degrees of external rotation. The arthrodesis is secured with three 6.5mm cannulated screws which are inserted percutaneously. The success rate of this technique has been extremely favorable when compared with that reported in the literature for more extensive methods of arthrodesis. The advantages of this technique are the decreased soft tissue and periosteal dissection, a far easier procedure technically than the more technically demanding arthroscopic method of ankle arthrodesis, and a rapid healing time comparable to that of the largest series of ankle arthrodeses reported.
Historical Perspective
Ankle arthrodesis remains an important procedure in the salvage of the painfully arthritic ankle joint, enabling the surgeon to create a painless, stable, plantigrade foot. Although surgical alternatives for the treatment of ankle joint arthritis (such as total ankle replacement, corrective supramalleolar osteotomy and distraction joint arthroplasty) have undoubtedly improved over the past ten years, for many surgeons ankle arthrodesis remains their treatment of choice (1). These surgical alternatives have focused on changing the distribution of loads on the ankle joint, improving the biomechanics of the lower extremity, or by replacing the joint. These techniques have gained increasing popularity due to the predictable long term consequences and complications of ankle arthrodesis, in particular, the markedly increased loading of the adjacent hindfoot joints.
The operative techniques for reliably obtaining an arthrodesis have steadily improved over the past several decades, and include more than 20 different techniques which have evolved to the present day. What we have learned from this can be succinctly described as the basic surgical principles for a successful ankle arthrodesis: broad, congruent cancellous bleeding surfaces, surfaces which should be stabilized with rigid internal fixation under compression after correct positioning of the foot in the coronal, transverse and sagittal planes (2).
Despite the advances in instrumentation and with the operative approach, problems with ankle arthrodesis still persisted. The frustration with delayed union, particularly nonunion (3,4), led to the evolution of techniques involving minimal exposure such as arthroscopically assisted ankle arthrodesis and the mini arthrotomy procedure. These techniques provided minimal biologic disruption, with subsequent excellent and a rapid rate of fusion with a reduced recovery period (5,6,7,8). On the other hand these techniques were not suitable to address complex deformities and were initially limited to more straightforward arthrodeses. However, for the arthroscopic method of arthrodesis, this was extremely technically demanding with a steep learning curve, and far more time consuming than most other procedures. (5,6,9).
Encouraged by the advantages of arthroscopically assisted ankle arthrodesis the senior author slightly enlarged the two anterior arthroscopic portals to obtain full open visualization of the joint. This led to the gradual evolution of the mini-arthrotomy ankle arthrodesis technique, for which there was a decreased soft tissue “insult”, markedly decreased periosteal stripping, a relatively easy procedure to learn and perform, and a rapid healing time comparable to those of the arthroscopic procedures (10,11,12).
The mini-arthrotomy technique had a firm theoretical basis. The improved healing would be the result of a minimally invasive procedure and avoidance of disruption of small blood vessels, which was certainly not the main characteristic of all alternative ankle arthrodesis procedures. Based upon this hypothesis, we initiated a laboratory study to identify the impact of exposure of the ankle on vascular disruption using digital subtraction angiography. (11). Eight pairs of below knee specimens were obtained from eight cadavers. In each leg the popliteal artery was cannulated and a radiopaque mixture was infused. An ankle arthrodesis was then performed on one leg of each pair via an open arthrotomy and partial fibulectomy, and on the other leg via a mini arthrotomy. Radiographs which had been taken pre- and post-operatively were scrutinized for vascular damage. There was substantial vascular damage and disruption of the peroneal artery in two of the eight ankles, both in the open arthrodesis group. In addition, there was significant loss of the periarticular vessels in all eight of the open arthrotomy group.(11)
The early clinical results of the mini arthrotomy technique were comparable to those of most large series utilizing open procedures as well as to those of the arthroscopic procedures. It was these early successes as well as the continued technical demands of the arthroscopic procedure, that led the senior author to fully adopt this technique for ankle arthrodesis.
Indications/Contraindications
During the last decade we have utilized a variety of surgical alternatives to the ankle arthrodesis (including supramalleolar osteotomy, total ankle replacement, distraction joint arthroplasty and anterior cheilectomy) to address the arthritic ankle joint (1). The choice of surgical technique depends on a variety of factors including the patient’s age, level of activities, general medical status, the position of the foot, and the degree of deformity, the neurovascular status of the limb, bone quality, overall limb alignment and the presence of degeneration in the joints of the foot. Clearly the severely destroyed joint with obliteration of the articular surface can be addressed only by arthrodesis or total ankle replacement and not by the other procedures. Total ankle replacement has very specific indications. The ideal candidate for a total ankle replacement is the person with good bone quality, minimal deformity, reasonable weight, and who places less demand on the lower limb.
There were of course very few limitations to the mini-arthrotomy technique when we initiated this in 1992. The indications for this procedure as they applied in our early series were: a. severe arthritis with marked joint obliteration, b. considerable ankle pain interfering with daily activities and walking ability, c. failure of conservative treatment including non steroidal anti-inflammatory (NSAID) medication, intra-articular steroid injections, physical therapy, and/or use of and ankle-foot orthoses (AFO), d. absence of mechanical malalignment above the ankle joint, e. a minimally deformed ankle joint with varus or valgus less than 10 degrees, f. less than 25% posterior or anterior subluxation, g. avascular necrosis of the talus involving less than 25% of its articular surface, h. articular surface cavitations smaller than 1x2cm, i. Absence of severe neuroarthropathy. From a practical standpoint, these indications were similar to those described for an arthroscopically assisted in situ fusion.
As we were gradually mastering the technique we started expanding its application, and we now recognize and recommend that ankle joints with moderate deformity can be approached with this technique by resecting minimal wedges of bone utilizing flexible chisels and appropriate size osteotomes. To some extent, this has of course become easier as we became more familiar with the technique (the ubiquitous learning curve), but realistically, there are now really very few contraindications to performing this mini arthrotomy procedure. These include severe deformities amenable to correction only by angular and rotational re-alignment, malalignment above or below the ankle joint. We have used this procedure now with avascular necrosis of either the distal tibia or the talus and where large bone defects of the distal tibia are present. The limited skin incisions make this procedure appealing even in the presence of dermatologic, diabetic, autoimmune, vascular, previous surgical incisions which may be relative contra indications to a more extensive surgical procedure. At this time, we use the mini arthrotomy procedure almost exclusively, and more extensive procedures are used to correct massive bone loss requiring structural bone graft.
Pre –Operative Planning
Preoperative evaluation and planning includes careful clinical assessment and a variety of diagnostic studies. When evaluating a patient with a painful “ankle joint”, one should carefully assess the ankle as well as the adjacent foot joints for range of motion, overall alignment, pain, and tenderness on palpation. A manual motor test of the major muscular groups about the foot and ankle is performed, since any weakness may affect the position of the arthrodesis. The degree of ankle joint deformity in all planes (with the patient sitting, standing and walking) is carefully evaluated. The adjacent joints must be carefully evaluated, since the ankle arthrodesis places increased stresses on them, and any preexisting stiffness or arthritis in these joints will likely deteriorate over time. If these adjacent joints appear involved, we evaluate them separately with diagnostic lidocaine blocks. This may be particularly helpful in planning for a more extended ankle and hindfoot arthrodesis. Reduced sensation or vascularity, skin changes, and the presence of venous stasis should be evaluated further before surgery is performed.
Full length, weight bearing bilateral radiographs are obtained, and the overall limb alignment carefully determined, as well as the extent of arthritis, deformity, bone defects in the distal tibia or talus, presence and degree of avascular necrosis (AVN) in either the talar body or the distal tibia, and presence of arthritis in the other foot joints. A CT scan is used preoperatively to confirm and evaluate the extent of arthritis of the subtalar joint and any cavitation or defects in the distal tibia or talus. While these do not present a contraindication to the mini arthrotomy procedure, large defects must be filled with autograft or allograft. If AVN is noted, then an MRI should be obtained to further clarify the extent of the disease. While the mini arthrotomy procedure is not contra-indicated, if extensive, AVN may compromise healing and we plan for internal or external bone stimulation pre rather than postoperatively.
Finally the most important step is to determine the proper position of the arthrodesis site. The optimal position for an ankle arthrodesis has been debated, but there is still a consensus that the ankle should be in neutral position in the sagittal plane, minimal valgus (up to 5 degrees) and external rotation symmetric with the contralateral uninvolved side which is usually about 5 to 10 degrees. (2,14). Malunion of the arthrodesis in the sagittal plane is a problem; a plantar flexed or equinus arthrodesis results in a dynamic genu recurvatum and a vaulting type of gait pattern as well as symptomatic transverse tarsal arthritis. A dorsal malunion produces increased stresses on the calcaneus during the heel phase of gait, which may lead to heel pain, and diminished push-off strength. The calcaneus malunion position is very difficult to treat, and even with appropriate heel support and cushioning, further surgery may be necessary. A valgus malunion leads to a pronated flatfoot and increased stresses along the medial side of the knee and hindfoot joints, while a varus malposition leads to increased stress along the lateral aspect of the foot especially under the fifth metatarsal. Increased internal or external rotation of the fused ankle, results in abnormal rotation of the lower extremity during gait with painful foot, and ipsilateral hip and knee joints.
Since the majority of ankle fusions do not require manipulation for correction, positioning of the ankle joint is not difficult because there is little preoperative deformity.When arthroscopic and later the mini arthrotomy arthrodesis became popular, there was always a question based upon prior laboratory work regarding the need to translate the talus posteriorly with respect to the tibia (4,14). Theoretically, this translation reduces the anterior lever arm of the foot on the fusion site and improves its ground clearance during gait. While this is anatomically correct, we have never found that it is necessary to perform such a translation, and no awkwardness or difficulty with gait has ever been noted as a result of the in situ position of the ankle.
When correcting moderate deformity the position of the arthrodesis really becomes critical, and we will use everything possible to produce a plantigrade foot. By and large, the positioning is based upon the knee- foot-ground axis, and this is carefully determined intraoperatively. Any other pathology of the lower extremity above the arthrodesis site is taken into account. For example, when there is a quadriceps weakness, one should preferably position the ankle in 5-10 degrees of plantar flexion. As the plantar flexed arthrodesed ankle leads to genu recurvatum, this stabilizes the knee joint with the deficient extensor mechanism. Finally, the alignment of the foot distal to the fusion site must be carefully assessed and taken into account in order to create a plantigrade foot. A forefoot deformity dictates a compromised position of the ankle joint arthrodesis or other procedures (such as osteotomies). For example, in the presence of fixed mid or forefoot equinus deformity, it is preferable to position the ankle in slight dorsiflexion to accommodate the above mentioned deformity.
Technique
The ankle arthrodesis utilizing the “mini-arthrotomy” technique is performed with the patient under regional ankle or popliteal block and intravenous sedation (15) as an out patient procedure. It is rare that we will use general anesthesia, although this is decided upon by the patient and the anesthesiologist. The patient is positioned supine and a tourniquet is applied to the thigh, although in our practice we do not routinely use the tourniquet. It is important to drape the leg well above the knee joint so as to use the patella as a reference point for the final positioning of the ankle. Two small 1.5 cm incisions are used, one anteromedial and one anterolateral, in approximately the same positions as the arthroscopic portals.
The first incision is just medial to the anterior tibial tendon taking care to avoid inadvertent injury of the saphenous vein and nerve. The second incision is performed immediately lateral to the peroneus tertius tendon, with more careful subcutaneous dissection to avoid injury of the dorsal cutaneous branch of the superficial peroneal nerve. The ankle retinaculum is identified and incised along the same line with the skin incision. By retracting the tendons, the joint capsule is identified and opened in the same way.
The key to this procedure is adequate visualization, and this is facilitated by internal joint distraction with a lamina spreader, and exposure of the anterior joint with a Weitlander retractor. A rongeur is used to remove the hypertrophied synovial tissue from the anterior aspect of the joint further improving the working space and visualization. Any visible cartilage of the anterior ankle joint is resected with curettes of various sizes and shapes, and a set of small rongeurs. Although it is not necessary, we remove most osteophytes off the anterior tibia with flexible chisels, also to improve visualization.
As debridement of the synovium and osteophytes from the anterior ankle joint is completed, the available working space and visualization increases. At this point a small lamina spreader is inserted into either the medial or lateral joint space, and further debridement performed. It is not always easy to insert the lamina spreader, and we will use a rongeur on the one side of the joint, and as the joint space opens, then the lamina spreader is inserted on the opposite side. This is alternated between medial and lateral incisions and functions as an internal distractor of the ankle join permitting debridement. It is important to position the lamina spreader correctly is to avoid tilting the talus from the neutral position. With the joint distracted a variety of instruments (rongeurs, curettes, chisels) is utilized to debride any remnants of cartilage, synovial tissue, loose bodies and sclerotic subchondral bone. Smooth bleeding bone surfaces are essential. When we initially began using the mini arthrotomy procedure, a high speed burr was used, but this seemed to burn bone, and was also frequently followed by anterior joint synovitis during healing, probably as a result of the slurry created by the burr. We no longer use the high speed burr, and use predominantly a flexible chisel until bleeding is uniform. This can be deceptive, and the joint must be frequently irrigated to visualize the cancellous bone surfaces.
Small bone wedges may be resected to obtain the ideal joint position particularly when moderate deformity is present. Frequently, once the joint debridement is performed however, the ankle can be moved and manipulated, particularly in the coronal plane for correction without resorting to bone resection or wedges. If any defects remain, they are filled with bone graft, and we routinely use cancellous allograft chips for this purpose. Any dense, sclerotic subchondral bone can be drilled with a 2.5mm drill bit to enhance revascularization. The use of a drill bit is preferable to a K-wire which may compress the bone and potentiate burning and sclerosis.
Particular attention is then paid to the medial and lateral gutters, and any remaining cartilage on the lateral articular surfaces of the talus and the articular surfaces of the malleoli is meticulously taken down. It is questionable to what extent the medial or lateral malleolus participates in the arthrodesis process, but certainly, this can be facilitated by debridement, and filling the void in the gutter with cancellous graft. The “mini-arthrotomy” technique does not allow perfect visualization and debridement of the most posterior portion of the ankle joint. When we began using this procedure, it was apparent that the opening or lack of arthrodesis posteriorly did not in any way affect the success of fusion. In fact there is no reason why it should, if one considers the procedure described for arthrodesis of the ankle in the setting of avascular necrosis where a slotted graft is slid down the anterior aspect of the ankle only avoiding completely the bulk of the (avascular) bone.
At the end of the debridement the joint must be copiously irrigated and the extent of the joint preparation checked, since it can be quite deceiving as to the actual extent of successful debridement with this technique. The ankle is now positioned with the guide pins from a cannulated, self-tapping screw system. We currently use three cannulated, 6.5 mm partially threaded cancellous titanium screws (ACE, DePuy, Warsaw, IN. The guide wires are placed in the following pattern; The first pin (and screw) is inserted from the posterolateral aspect of the tibia in an anteromedial direction into the talar head. The guide pin is inserted immediately adjacent to the Achilles tendon, approximately 3cm proximal to the ankle joint. The second pin (and screw) is inserted from the anteromedial aspect of the tibia directly above the medial malleolus down and anteriorly toward the sinus tarsi The third guide pin is inserted from the lateral aspect of the joint anterior to the fibula, and directed toward the medial talar neck. Occasionally if there is no flare of the distal lateral tibia, there is not sufficient space to insert the pin, and the screw is inserted through the fibula into the talus. The positions of the guide wires and then the screws are checked under fluoroscopy. The screw which seems to cause the most trouble is the one from the medial malleolus, since this is close to the subtalar joint. The screw inserted from the posterolateral tibia is probably the most important one, as it obtains the best purchase in the talus and is in the plane of the most direct line of compression across the joint. places loads across the joint thus improving compression. Because the screws are not introduced parallel to each other, eccentric loading of the arthrodesis site may occur as the first one is inserted. One should avoid that by alternately tightening each until compression is obtained. Once the screws have been inserted, the joint must be manipulated, and the screws tightened or repositioned if any motion is present. Further bone graft can be inserted at this time.
After careful closure of the retinaculum the skin is routinely closed without a drain. A bulky cotton dressing is applied with a medial to lateral coaptation-type splint and posterior mold of plaster. The patient is given oral narcotics, nonsteroidal anti-inflammatory (NSAID) agents and oral antibiotics. If the operation was performed under regional ankle block the patient is discharged home the same day.
Results
We have performed this operation since 1992, and published the early results of the first 32 patients with the mini-arthrotomy technique. There were 13 men and 19 women with an average age 52.5 years (range 29 to 76 +/- 13.5 years). Of the 32 patients 27 had posttraumatic arthritis, 1 had rheumatoid arthritis and 4 had degenerative arthritis. For three of them the mini arthrotomy procedure was a revision of a prior arthrodesis attempt. The average follow-up for these patients was 23 months (range: 7 to 37). In 30 of them a radiographic fusion was achieved at an average time of 8 weeks (range: 6 to 22 +/-4). Radiographic fusion was judged as the presence of good bone apposition without hardware loosening and osseous trabeculae across the ankle arthrodesis site. Postoperative radiographs demonstrated a fusion of the anterior three quarters of the joint. As it has been said that was due to inadequate visualization and debridement of the most posterior portion of the ankle joint. Based on our early series results we found out that the lack of bony fusion across the posterior portion of the ankle does not appear to be a clinical problem.
One of the interesting features of this and perhaps other methods of ankle arthrodesis is when fusion actually occurs. This is very difficult to determine radiographically with the mini arthrotomy technique, and we have used clinical as well as radiographic criteria to determine the onset of arthrodesis. This is therefore judged as the absence of pain with weight bearing and ambulation, but most importantly, cessation of warmth and swelling at the joint site.
In the original series of patients, there was one delayed and two non-unions. The one patient with the delayed union was noncompliant with instructions for his recovery process and walked extensively immediately following surgery. Fusion finally occurred at 22 weeks without further intervention. The two patients with non-union were both heavy smokers, and revision surgery was performed at 34 and 40 weeks after their original surgery using the mini arthrotomy technique successfully. Most importantly, we have continued with this technique successfully, with results very similar to those previously reported. At the present time, we have performed this procedure on one hundred and fourteen patients, with successful fusion in one hundred and five patients at an average time to fusion of ten weeks.
Complications
The complications we encountered using the mini arthrotomy technique have been minimal, and mostly related to the burring technique initially used. Seven of 32 patients in our early series experienced swelling and warmth located at, and limited to the anterior aspect of the ankle. This transient inflammation was experienced by the patients 4 to 10 weeks after surgery. There was no concomitant pain and there were no signs of delayed healing or hardware loosening. All patients treated conservatively with nonsteroidal anti-inflammatory (NSAID) medication and three of them required a local steroid injection. This transient inflammation completely resolved in all patients within 4 weeks. We initially attributed this to the leakage of bone slurry, generated by the pneumatic high speed burr which was used in our early series to debride and roughen the subchondral bone. This problem has not occurred since we discontinued the use of a high speed burr producing a slurry in the anterior joint.
Post-Operative Management
Two weeks after surgery the postoperative bulky cotton dressing is changed to a short leg cast, and no bearing of weight is permitted for six weeks or until early radiographic and clinical signs of healing are noted. We do not use a removable walker boot for recovery after ankle arthrodesis. Once walking commences, a short leg cast is applied, with a posteriorly placed rubber heel, until healing of the fusion is radiographicaly and clinically confirmed. The role of such a posterior heel is to provide an axial compressive force across the ankle joint with weight bearing rather than any torque by pressure on the forefoot. The commercially available walking boots all have a rocker type sole, which may increase the force across the anterior ankle, and do not appear as reliable as a more rigid cast. After healing is confirmed patients are gradually weaned to a walker-type boot and then to regular shoes. Most patients find that a rocker bottom shoe assists with a more normal gait.
CONCLUSION
This is our procedure of choice for ankle arthrodesis. Preservation of the fibula is essential regardless of the technique of ankle arthrodesis. This preserves the important blood supply, and more importantly, maintains the anatomy of the ankle for future consideration for conversion to a total ankle replacement. Certainly, in our initial series, the majority of patients had less complex deformity, including both the overall alignment of the ankle and the quality of the bone. Yet, more recently we now use this procedure for correction of deformity associated with almost all types of ankle arthritis, and the results have been well maintained. It has become clear that the mini arthrotomy procedure may be used in the setting of avascular necrosis of the talus, particularly if this is partial. Ankle deformity is now no longer is a contraindication to this procedure, although we would suggest that this is not the first ankle that the surgeon attempts with this technique for arthrodesis.
References
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