Young, active patients with end-stage tibiotalar arthritis are most likely to benefit from the allograft procedure. A thor- ough orthopedic history and physical examination must be performed and other sources of hindfoot pain must be excluded. Ligamentous instability, malalignment, and other deformities of the foot and ankle must be evaluated clinically and radiographically. Also, if the ankle cannot be brought to at least neutral position during active-assisted dorsiflexion, then Achilles contracture, posterior capsule contracture, or gastrocnemius contracture must be considered. Ankle align- ment must be checked for any varus or valgus deformity that may need to be corrected at the time of surgery to prevent unnecessary forces across the graft.11Computed tomography
and magnetic resonance imaging can be obtained if necessary to assess the bony architecture and/or subchondral cysts of the tibia or talus. Coexisting foot deformities or malalign- ment must be addressed before ankle allograft replacement and may need corrective osteotomies.
Contraindications for shell allograft ankle reconstruc- tion are an inexperienced surgeon, significant peripheral vas- cular disease, varus or valgus malalignment of the tibiotalar joint greater than 10 degrees, large cystic lesions, instability of the ankle joint, and obesity.
SURGICAL TECHNIQUE:
An external fixator or distraction device is useful during the operation. DePuy Agility (DePuy, Warsaw, IN) ankle arthro- plasty jigs are used to increase the precision of the cuts.
Positioning
Patient is supine on a radiolucent operating table and a soft bolster is placed under the ipsilateral hop. A thigh tourni- quent is placed and the toes are covered with plastic adhesive or Coban wrap.
Approach/Debridement and Distraction of the Ankle Joint
Prior to inflating the tourniquent, a uniplane, unilateral external fixator is placed on the medial side of the ankle for the purposes of distraction during the surgery. Pins are placed medially into the calcaneal body, the talar neck and (two pins) the tibia (Fig. 7–1). The external fixator position is locked in position and then removed from the pins. The leg is exsanguinated and the tourniquet is inflated to 275 mm Hg. The ankle joint is entered through the stan- dard anterior approach between the tibialis anterior and extensor hallucis longus tendon. The extensor retinaculum is incised directly over the extensor hallucis longus tendon.
FIGURE 7–1.Leg with medial external fixator.
57 C H A P T E R 7 Allograft Resurfacing of the Tibiotalar Joint
The neurovascular bundle is revealed with deep dissection and retracted laterally for protection. The tibialis anterior tendon is retracted medially, and the ankle is exposed with subperiosteal dissection. The distal tibia, fibula, and taus are exposed from the medial malleolus to the syndesmosis.
Debridement of the joint osteophytes is performed with rongeurs and osteotomes. Next, an external fixator is replaced to distract the joint symmetrically approximately 1 cm. Distraction is checked with an image intensifier to ensure it is symmetric. In the unlikely event that the ankle was distracted asymmetrically (excessive valgus), the exter- nal fixator can be adjusted to compensate.
Tibial and Talar Cuts
The ankle joint is inspected and the decision made for either bipolar tibiotalar or hemi-joint resurfacing. The ankle radio- graphs are templated preoperatively and the corresponding Agility ankle arthroplasty jig. The jig is placed parallel to the tibial axis with the proxmal end centered just above the tibial tubercle and in line with the tibial crest. Distally, the foot pads now rest on the tibia, and the appropriate-size cutting block is placed in the center of the ankle joint. The foot pads of the alignment jig can now be secured through the tibia with 0.125-inch pins through the jig holes (Fig. 7–2).
Placement and size are confirmed with intraoperative fluo- roscopy (Fig. 7–3). Using an image intensifier in the AP posi- tion, the cutting block can be centered in the medial-lateral direction so that a small portion of the medial malleolus is removed. Because the fibula is left intact during allografting,
the fibula cutting slot is not utilized. In the lateral position, the block is centered in the proximal-distal direction so that sufficient and equal bone is removed from the tibia and talus.
Using a reciprocating saw, the bone cuts of the tibial plafond and talar dome are resected to a depth of approxi- mately 7 mm to 10 mm (Figs. 7–4 and 7–5). An ap- proximately 3- to 4-mm articular portion of the medial malleolus is removed as well. Extreme care is taken because the posterior tibial neurovascular bundle is in close proximity to the posteromedial corner of the ankle joint. On the lateral aspect of the tibial cut, care is taken to avoid contact with the fibula to keep it fully preserved.
Allograft Preparation and Cuts
The Agility ankle cutting block for the donor graft tibial cut is one size larger than the block that was used on the recipient’s native tibia (Figs. 7–6 and 7–7) . The cutting block is manually placed onto the tibial allograft, confirmed with fluoroscopy, and cut with an oscillating saw (Fig. 7–8). The talus graft is then cut free hand using an oscillating saw.
The cut is made at the interface between the anterior neck and cartilage. Both grafts are lavaged to remove immuno- genic marrow elements.
Placement and Fixation of the Grafts
With the ankle in plantarflexion, the grafts are seated into the recipient mortise. Imaging confirms the grafts have com- plete apposition to the host bone and that the anatomy of the tibiotalar joint has been restored. Two parallel 3.0-mm FIGURE 7–2.Cutting jig on native tibia.
FIGURE 7–3.Intraoperative fluoroscopy of jig on native tibia.
cannulated screws are placed into each graft for additional fixation (Fig. 7–9). The screws are placed from the anterior portion of the tibial graft while aiming superiorly and poste- riorly. For the talus allograft, two fixation screws are placed on the the most anterior portion of the articular cartilage
and countersunk into subchondral bone (Fig. 7–10). The external fixator is removed and the ankle is brought through a range of motion to confirm stability. The joint is copiously irrigated with antibiotic solution. Range of motion is tested.
At least 5 degrees of dorsiflexion is needed with the knee straight. If this cannot be achieved, a percutaneous heel cord lengthening and/or a gastrocnemius recession is performed.
The patient must have at least 10 degrees of ankle dorsiflex- ion at the end of the procedure.
FIGURE 7–5.Tibia and talus bone resections articulating surfaces.
FIGURE 7–4.Tibia and talus resected. FIGURE 7–6.Tibia and talus allografts articulating surfaces.
FIGURE 7–7.Tibia and talus allografts articular surfaces.
59 C H A P T E R 7 Allograft Resurfacing of the Tibiotalar Joint
Postoperative Restrictions/Rehabilitation Copious irrigation and routine wound closure are performed, and the patient is placed in a bulky cotton splint with the ankle in neutral dorsiflexion postoperatively. The patient should receive the standard perioperative antibiotics and pain
control. Range-of-motion exercises are started when the wound is healed, around postoperative day 10. Patients are maintained non–weight-bearing for 3 months and then pro- gressed to weight-bearing as tolerated.
Pitfalls
Intraopeative fracture: Extreme care must be taken when making cuts to avoid fracture of the lateral or medial malleolus.
Graft preparation:Use cutting jigs to help improve preci- sion of cuts as improper graft cuts usually result in graft failure.
Neurovascular bundle:Care must be taken not to damage the posterior tibial neurovascular bundle at the postero- medial corner of the ankle joint.
Graft failure:If unsuccessful, the allograft procedure does not prevent repeat allografting, conversion to arthrode- sis, or total ankle arthoplasty.