52 The Zimmer Trabecular Metal Total Ankle System Abstract The Zimmer Trabecular Metal Total Ankle represents a paradigm shift from existing systems. A utilitarian lateral approach through a fibula osteotomy permits sparing of the deltoid ligament and correction of deformities. A frame is used to achieve alignment and stability. The bone-sparing curved shape implant follows the contours of the natural joint. The implant materials are unique including porous tantalum trabecular metal and highly crossed-linked polyethylene. The technique will cover exposure, fibular osteotomy, release of contracture, alignment, bony stabilization, routing of the surfaces, rail guide drilling, trial reduction, implantation of the prosthesis, fixation of the fibula, restoration of the lateral ligaments, closure, and postoperative management.1–5 Keywords: lateral approach, fibular osteotomy, highly crosslinked polyethylene, tantalum trabecular metal, curved implant, alignment, frame • Symptomatic arthritis of the ankle. • A contralateral ankle fusion. • Symptomatic arthritis of the ankle with adjacent joint arthritis. • Ankle deformity that involves a malunion or deformity of the fibula. • Sagittal plane deformity (anterior or posterior translation) of the ankle. • Valgus deformity with shortened or valgus fibula. • Varus deformity with varus fibula and contracted deltoid. • Rotational deformity of the ankle. • Prior ankle fusion with intact fibula. • A lateral approach may be the best option for a patient with compromised anterior tissue. • Prior lateral scar from fracture fixation, lateral ligament reconstruction, or peroneal tendon surgery. • Flat top talus or low domed talus with ankle arthritis.6–8 • Evaluate the range of motion of the ankle, subtalar, and transverse tarsal joints. • Test muscle strength and look for atrophy. • Evaluate the neurovascular status. • With the patient standing, evaluate overall alignment of the lower extremity, and especially the foot. • Watch the patient walk to check for dynamic deformities and mechanical contributions from other lower extremity pathology. • Determine if there is a deformity. If yes, is it passively correctable? • Carefully assess the etiology of ankle malalignment: instability of medial or lateral ligaments, arthritis, contracture, and/or weakness due to a neurologic situation. Is there bony deformity from joint erosion: tibial, fibular, and talar malunion? • Evaluate for pes planovalgus from posterior tibial tendinopathy. • Check for cavovarus from peroneal tendon pathology. • Document previous incisions and the quality of the lateral tissues. Make sure adequate skin bridges will be present with the lateral approach. • Medically optimize the patient by vitamin D replacement to midrange level using 50,000 IU weekly for 12 weeks in patients with low or deficient levels. • For patients with rheumatologic diseases, altering their use of disease-modifying antirheumatic drugs and biologics to increase the drug-free time before and after surgery may decrease infection and wound complications.7,9–11 • Standing anteroposterior (AP) and lateral views of the ankle, including the lower two-thirds of the tibia. An AP view of the foot to identify occult deformities. In cases of significant malalignment of the ankle or leg, include more proximal leg and comparative views of the opposite side. • A standing AP view that includes the hip, knee, and foot is helpful in difficult cases of malalignment. • Dorsiflexion and plantarflexion standing lateral views. • A Saltzman view for hindfoot and ankle alignment. • An MRI will demonstrate arthritis of the ankle and/or subtalar joint that may not be detected on plain radiographs. Tendon damage should be assessed. • A CAT scan will demonstrate bony voids, cysts, or fracture nonunions that may need to be addressed. • Technetiumand indium-labeled WBC scan to assess for infection.9–13 • Brace immobilization. • Ambulatory aids: cane, crutches, walker. • Activity modification. • Shoe modifications with rocker bottom sole and cushioned heel: orthotic inserts. • Medications: cortisone injections, hyaluronic acid injections, anti-inflammatory medications. • Acute avascular necrosis of the talus. • Charcot arthropathy. • Local/systemic infection. • Severe neurologic or vascular disease affecting the extremity. • Poor lateral skin quality. • Severe osteoporosis or compromised bone stock. • Previous joint infection. • Severe non-reconstructable deltoid insufficiency. • A non-reconstructable nonplantigrade foot. • An absent fibula or medial malleolus. • Body mass index of the patient must be taken into consideration. • The size 1 (smallest) implant is rated for 250 lb. • Age less than 50 years. The goals are to achieve reduced pain, improved range of motion, and better function in patients suffering from ankle arthritis. The implant surfaces are milled after accurately aligning the joint to follow the natural ankle contours. All variables that contribute to malalignment are addressed with this system. Early range of motion and weight bearing at 10 days permit improved motion and less atrophy. The Zimmer Trabecular Metal Total Ankle represents a paradigm shift from existing systems. A utilitarian lateral approach through a fibula osteotomy allows for correction of fibula deformity and clear access to the anterior, posterior, and lateral aspects of the joint.10 Typically, this permits sparing of the deltoid ligament and correction of deformities in all planes: coronal, sagittal, axial, and rotational. A frame is used to achieve an accurate algorithm-driven correction of the alignment. The system uses a coupled resection for optimal positioning and intrinsic stability. The external fixation provides stabilization for an accurate guide-driven milling of the surfaces. The bone-sparing curved shape implant follows the contours of the natural joint and has coronally oriented rails for bone to metal purchase. The implant materials are unique. The bone interface is porous tantalum trabecular metal. The polyethylene insert is bicondylar and is highly crossed linked for maximum durability (FN highly crosslinked poly FAI). The talar dome is cobalt chrome with a bicondylar matching contour (Fig. 52.1).1–5, 14 Key principles are to preserve bone stock and restore anatomic alignment and integrity of bone and soft tissues. The fibular osteotomy permits correction of contributory deformities. Rail orientation in the coronal plane and curve-to-curve stability maintain positioning of the implants. The correction of the deformity is accurately achieved sequentially beginning with soft-tissue release and positioning of the calcaneus, the talus, and finally the tibia in all planes. Coupled bony resections permit geometry precision milling for implant to bone apposition. • The heel should be 6 inches from the end of the table, to allow room for the frame. • Ensure that there is sufficient space to allow the frame to be near the center of the table (Fig. 52.2). • If the leg-rests of the table are not firm, a stiff board is used to prevent the frame from shifting. • A bump or bean bag under the ipsilateral hip to lift up the hemipelvis 15 to 20 degrees which places the femoral bicondylar axis 15 to 20 degrees of internal rotation and the fibular–medial malleolus axis parallel to the floor. • An arm rest placed at the side of the end of the table allows the contralateral leg to be stable on the table while providing more room for the affected ankle. • Secure the opposite leg so that it is not inadvertently pushed off the operating room (OR) table during the case. Fig. 52.1 Trabecular Metal components—note the semiconstraint bicondylar shape and porous tantalum–bone interface. Fig. 52.2 Positioning and incision: The leg is elevated 4 to 6 inches off the table and the sole of the foot is 6 inches distance to the end of table. 13-cm-long lateral incision along the posterior border of the fibula with 3-cm horizontal distal extension over the sinus tarsi. • A pile of folded blankets 4 to 6 inches thick and large enough in length and width to support the frame is placed from the end of the table to the level of the knee. Secure it with circumferential tape to the table. This elevates the operative leg to facilitate the lateral C arm images without the obstruction from the contralateral limb (Fig. 52.2). • A thigh tourniquet is placed and secured. Typically, it is not inflated. • Set up the large C-arm. Multiple AP and lateral images will be required during the case. • Lead gowns must be worn before scrubbing as the large C-arm is used. The leg is not yet in the alignment stand: • Along the posterior border of the fibula, make the incision approximately 13 cm proximal to the ankle joint. Extend it distally, just distal to the tip of the fibula over the sinus tarsi for 3 to 5 cm (Fig. 52.2). This permits more anterior exposure of the ankle joint and allows for less aggressive soft-tissue retraction anteriorly. • Open the peroneal sheath along the fibula just over the posterior edge of the bone and elevate the periosteal flap to the anterior aspect of the fibula (Fig. 52.3a, b). • Distally, at the tip of the fibula, leave the superior retinaculum intact by preserving the inferior and posterior aspect of the periosteum on the bone (Fig. 52.3a). • Elevate the anterior periosteum and then in the same flap transect the anterior talofibular ligament off the fibula. • Elevate the anterior capsule and periosteum off the distal 3-4 cm of the tibia, staying below the peroneal artery. • Continuing the periosteal flap anterior to the ankle joint to allow exposure to the medial joint line. • Place a suture tag on the edge of the anterior talofibular ligament and the capsular periosteal flap to facilitate identification and closure. • If there is no fibula deformity, a five-hole fibular reconstruction plate is applied. A screw is placed proximally above the level of the osteotomy to anticipate the contour of the bone. Three holes are predrilled and measured distally (Fig. 52.3e). Note: If the tissues laterally are thin, a semi tubular or lower profile plate should be used. • An oblique osteotomy in the sagittal plane or coronal plane will be made in the fibula. • The distal-most aspect of the cut should be 1.5 to 2 cm proximal to the ankle joint, to allow adequate room for milling and placement of the tibial implant. • Place a 0.45 K-wire obliquely across the fibula first, and evaluate under C-arm to plan the position of the osteotomy (Fig. 52.3d). • If there is sagittal malalignment or in cases of no deformity, make an oblique cut with a thin micro-sagittal saw from proximal–lateral to distal medially, angled about 45 degrees to the long axis, under cool water irrigation (Fig. 52.3f). • An alternative osteotomy is made obliquely in the coronal plane like a Weber B fracture. This osteotomy allows for lengthening or shortening of the fibula as well as correction of varus or valgus deformity. • Incise the lower syndesmotic ligaments sharply anteriorly and posteriorly to mobilize the fibula. • Use a medium-size elevator to free up the fibula from the syndesmosis, so that it can be hinged distally (Fig. 52.3f, g). If there is a partial synostosis of the syndesmosis, use a chisel to take it down. • Leave intact the calcaneofibular and posterior talofibular ligaments. • Pin the fibula against the foot into the calcaneus under oscillation mode with a 1.6-mm K-wire so that it does not obstruct the sweep of the router along the posterior talus. Bend, cut, and cover the wire with a pin cap. • Place a periosteal elevator in the joint and twist it between the tibia and talus to release contractures (Fig. 52.3h). The elevator should be used to release the posterior capsule by placing it deeply between the tibia and talus and sliding and turning it as it moves from the inside to the outside of the joint posteriorly. Later during the milling, this permits placement of the posterior retractor and protection of the posterior medial structures. Fig. 52.3 Lateral approach: (a) Incise the periosteum along with skin and subcutaneous incision along the posterior edge of fibula preserving 1 cm most distal attachment of superior peroneal retinaculum. (b) Peel off the periosteum anteriorly. (c) Cut the anterior talo fibular and anterior inferior tibio fibular ligaments. (d) Place a K-wire in line with proposed osteotomy and check with fluoroscopy to determine that the cut will be 1.5 cm above the joint line. (e) Apply and (if needed) contour the fibular plate before osteotomy. Drill one hole above the osteotomy and insert a screw to finalize the apposition to the bone. Then drill and measure three distal hole sizes. (f) Fibular osteotomy. (g) Turning down the distal fragment with gradual cutting of connecting ligaments of syndesmosis. Preserve the calcaneofibular ligament and posterior talofibular ligament. (h) Freeing the posterior and anterior capsule off the tibia using a periosteal elevator. • An arthrotomy of the medial ankle may be required to remove bony impingement, especially in the medial gutter along the anterior or distal aspect of the medial malleolus or medial neck of the talus. • A severe varus deformity can be more readily corrected with a medial arthrotomy. This releases the superficial deltoid and allows for placement of a medial laminar spreader or pin distraction spreader (Hintermann’s distractor; Fig. 52.4). • The deep deltoid is rarely, if ever, released in this system. • With the leg still out of the frame, measure the width of the talus with the Zimmer depth gauge. Go all the way to the medial border of the talus. Confirm proper placement with fluoroscopy (Fig. 52.9). Determine the largest implant that can be used, without any medial-lateral overhang. Use the smaller measurement in between sizes to preserve more medial malleolar bone stock. • Confirm the size with the AP sizer or silhouette, although this rarely effects the decision. • Once the size is determined, remove any large anterior spurs with a rongeur, and assess the need for a percutaneous Achilles lengthening or Gastrocnemius recession. • If there is still a contracture, the foot can be placed in the frame in 5, 10, or 15 degrees. • Place the leg in the frame, as outlined in the Zimmer instruction manual in the middle and parallel to the long bars of the frame (Fig. 52.5a, b). • Make sure the proper internal rotation is set with the medial edge of the foot parallel to the oblique medial border of the foot plate (Fig. 52.5c). • To check that the talar internal rotation is correct, place the wide and flat end of the probe inside the router guide and against the anterior half of the lateral body of the talus. It should be flush to the surface. Make sure the milling tower is tight to maximize accuracy of this step. • Use Coban to hold the forefoot to the plate. Ensure that the foot posts are not pressing into the foot. • Make sure the leg is positioned high enough (superiorly) in the frame so that a clear lateral fluoroscopic image can be obtained without the other leg being in the way. The folded blankets should have facilitated this (Fig. 52.5d). • The heel should be in the heel rest, but 1 to 2 cm off the foot plate to facilitate distraction of the joint with the calcaneal pins (Fig. 52.5a). • The surgeon can place the calcaneal pin, parallel to the talar joint surface, prior to placement in the frame or once in the frame (Fig. 52.6a, b). • As the calcaneal pin is tightened, take a few C-arm images. Eccentric tightening of the pin may be needed to bring the talus into a neutral positon. The heel now should be resting against the foot plate.
52.1 Indications
52.1.1 Clinical Evaluation
52.1.2 Radiographic Evaluation
52.1.3 Nonoperative Options
52.1.4 Contraindications
Relative Contraindications
52.1.5 Indication Controversies
52.2 Goals of Surgical Procedure
52.3 Advantages of Surgical Procedure
52.4 Key Principles
52.5 Preoperative Preparation and Patient Positioning
52.6 Operative Technique
52.6.1 Implant Sizing
52.6.2 Guide Frame Application
Musculoskeletal Key
Fastest Musculoskeletal Insight Engine
