Abstract
A role for use of bulk fresh allografts in ankle surgery has been well established. Although the enthusiasm for large fresh allograft osteoarticular ankle replacement has diminished over the past several years, this technique remains an effective approach to reconstruction in the appropriate patient. In our own clinical experience in numerous patients, large bulk osteoarticular replacement grafts of the ankle have lasted more than 12 years with no complications. Such cases, however, constitute the exception rather than the rule, because many of these grafts have failed over time. The decision to use a fresh graft in reconstruction for a massive osteochondral lesion is far easier, because few realistic alternatives are available, and the results with this procedure have been excellent over the years. While the osteoarticular replacement procedure is indicated for patients with arthritis and for whom either an arthrodesis or total ankle replacement is not ideal, one has to follow stringent inclusion criteria.
Key Words
Osteoarticular allograft, osteochondral, arthritis, bulk allograft, cartilage, bipolar allograft
Osteoarticular Fresh Allograft Ankle Replacement
A role for use of bulk fresh allografts in ankle surgery has been well established. Although the enthusiasm for large fresh allograft osteoarticular ankle replacement has diminished over the past several years, this technique remains an effective approach to reconstruction in the appropriate patient. Furthermore, the options for treating sizable cystic lesions in either the distal tibia or the talus are very limited without the use of fresh osteoarticular grafts. In general, the smaller the size of the graft used, the less likely it is that failure will occur, whether from necrosis, collapse, graft fracture, or development of arthritis. The evidence to date suggests some critical volume of graft material or immunogenic load that the ankle can tolerate before rejection or failure occurs. In our own clinical experience in numerous patients, large bulk osteoarticular replacement grafts of the ankle have lasted more than 12 years with no complications. Such cases, however, constitute the exception rather than the rule, because many of these grafts have failed over time. The decision to use a fresh graft in reconstruction for a massive osteochondral lesion is far easier, because few realistic alternatives are available, and the results with this procedure have been excellent over the years. Indeed, there was a period approximately 8 years ago when we stopped performing these procedures because of the high complication rate, and at that time we received call from one of our patients for whom we had performed the procedure 5 years previously, and she had returned to running long distances. This encouraged us to review our cases again and to discuss the procedure with the few other surgeons in the country who were performing the osteoarticular allograft joint replacement. The consensus was that the procedure is indicated for a narrow scope of indications. Previously we had been performing the procedure for many patients, young and old, those with limited range of motion, and those with posttraumatic and idiopathic arthritis. We decided to begin to limit the indications for the procedure such that if failure occurred, then conversion of the procedure to an ankle joint replacement would be a reasonable decision. This limited the age range for these patients to those above 35 years, and preferably above 40 years, those with good range of motion of the ankle, where the tissues surrounding the ankle were pliant and softer than in those with severe posttraumatic arthritis, and in those patients with excellent anatomy of the ankle joint remaining. So, while the osteoarticular replacement procedure is indicated for patients with arthritis and for whom either an arthrodesis or total ankle replacement is not ideal, one has to follow stringent inclusion criteria.
Considerations in selection of suitable candidates for this procedure include the patient’s age, activity level, weight, and desire for continued mobility of the ankle. The most significant aspect of surgical planning involves assessing the potential for failure. Certainly, a primary ankle arthrodesis has a recognized success rate and, from a technical standpoint, should be greater than 95%. If an ankle arthrodesis becomes necessary after failure of an osteoarticular allograft replacement, this success rate is much lower, with failure attributed to graft collapse, sclerosis, or avascular necrosis. The other options after failure are to repeat the graft procedure or to perform a total ankle replacement. The latter procedure is fairly straightforward, provided the appropriate criteria for an ankle replacement are met and there is sufficient bone stock available. Additional changes to the protocol were very strict preoperative size matching of the graft and host, careful removal of all soft tissue attachments to the bone, pulsatile lavage to remove all vascular elements from the graft, and sizing the height of the graft carefully. Rigid fixation of the graft using compression screws is also now advocated as opposed to absorbable pins. Bone incorporation occurs at the margins of the graft up to approximately 3 mm, and it is therefore not relevant if a thicker graft is used on either the talus or tibia, but in particular the tibia may benefit from increased thickness. The thinner grafts were subject to fracture and necrosis, and increasing the thickness in addition to the aforementioned parameters improved the more recent outcomes.
Tissue typing is not necessary for this procedure. The most important aspect of preoperative planning is correct sizing of the graft, because it must fit perfectly. If the graft is a few millimeters too small, the ankle will still function well, because the “fit” occurs between the articular surfaces of the tibia and the talus. If the graft is too large, however, it will not fit at all, and although the tibia can be cut medially or laterally, the talus will abut against the malleoli, and failure will occur. This requires a careful plan with the graft procurement companies for accurate sizing off the radiograph, since the size of the graft is measured by technicians in the field with calipers at a given location on the talus, which one can specify. A preoperative computed tomography scan is encouraged to ensure accuracy of measurement.
The incision is identical to that for total ankle replacement: an anterior central midline incision over the ankle. Once the joint has been exposed and denuded of all juxta-articular osteophytes, the anterior aspect of the distal tibia is resected so that the plafond can be completely visualized. This clear view helps with planning the tibial cut correctly. A cutting block for the tibial cut is far easier and more precise than free-hand cuts, which should be avoided. The sizing of the cutting block is important, and 7 mm of distal tibia is removed. Judging the position of the cutting block relative to the lateral aspect of the ankle, which is not cut, is unimportant. The position of the block must be verified carefully by fluoroscopic examination, and minor adjustments must be made until the block is positioned to remove approximately 7 mm of the distal tibial surface. In cutting the tibia, it is important to protect the articular surface of the fibula and the medial malleolus. One consideration is to use the original technique of cutting the tibia using the Agility joint replacement cutting guide for the tibia and cutting the lateral third of the medial malleolus. It is not clear whether this is necessary, or whether the tibia and talus alone without the medial malleolus are sufficient. Certainly, current prosthetic design in ankle joint replacement does not include the medial malleolus at all, and it is likely that the same applies to the allograft. Sometimes the fibular articular surface is abnormal because of articular wear or deformity, such as shortening or external rotation. However, we do not normally disturb the fibula, although clearly for some cases, an osteotomy of the fibula may be required to restore length and correct rotational deformity simultaneously. The bone is then carefully pried off the tibia, and the remaining lateral tibia is then removed in segments with a small osteotome until the entire joint is visible ( Fig. 16.1 ). The talar cut is made freehand, with removal of approximately 6 mm of bone in the center of the dome of the talus ( Fig. 16.2 ). The tibial graft is then sized, and the cutting block is applied to the tibia under fluoroscopic guidance so that an identically sized matching graft can be harvested ( Fig. 16.3 ). If necessary, one can remove a larger-size graft from the distal tibia and then shave this to a perfect cut once the size match is confirmed on the patient, but this then implies a free-hand cut of the graft, which does not ensure a perfect fit. The tibial graft rarely fits perfectly because of the anatomic constraints of the fibula posterolaterally. In this case, the graft must be narrowed posteriorly, or the fibula cut with a reciprocating saw until the graft slides into place. The cut on the talar allograft is made freehand, again to the size of the ankle. The talus is held in a vice grip, and guide pins are inserted in two planes under fluoroscopy to ensure that the cut will be uniplanar. Cutting sufficient width to the talus to prevent fracture is important.
Once the two grafts have been cut, they are assembled outside of the ankle and then inserted as a single unit. The talus needs to be centered under the tibia, and the graft tends to position itself perfectly with forced passive dorsiflexion of the ankle as the talus finds its resting position under the tibial articular surface. The tibial graft is then secured with the two 4.0 mm compression screws, and the talus is fixed with 3.0 mm compression screws buried under the articular cartilage or headless compression screw, which is inserted through the anterior aspect of the articular surface of the talus ( Fig. 16.4 ). Alternatively, if more talus is cut from the graft, then some of the neck of the talus may be present, through which screws can be inserted ( Fig. 16.5 ).
