Reconstruction of focal cartilage defects in the talus with miniarthrotomy and collagen matrix

Surgical principal and objective Treatment of focal cartilage defects (traumatic or osteochondrosis dissecans) of the talus using a collagen matrix. The goal is to stabilize the superclot formed after microfracturing to accommodate cartilage repair. The procedure can be carried out via miniarthrotomy, without medial malleolus osteotomy. Indications International Cartilage Repair Society (ICRS) grade III and IV focal cartilage defects of the talus > 1.5 cm2. Contraindications Generalized osteoarthritis, inflammatory joint disease, gout, neuroarthropathy. Surgical technique Miniarthrotomy to open the ankle joint. Debridement of unstable cartilage and necrotic bone, curettage of cysts. Filling of the bone defects with autologous cancellous bone. Sealing of reconstructed bone with fibrin glue and attachment of a collagen matrix shaped to precisely fit the defect. Postoperative regimen Immobilization for 48 h. Partial weight bearing of 10 kg for 6 weeks, with continuous passive motion. Increasing weight bearing from 7 weeks onwards. Results Follow-up of at least 30 months in 14 patients showed improvement in the Score of the American Orthopedic Foot and Ankle Society (AOFAS) from 50 to 89 points, with equal mobility on both sides of the upper ankle joint.


Introduction
Microfracture is the established procedure for treatment of symptomatic International Cartilage Repair Society (ICRS) grade III-IV cartilage defects of the talus [25]. The purpose of subchondral bone perforation, as in microfracture, is to enhance chondral resurfacing by providing a suitable environment for new tissue formation. The released progenitor cells, mesenchymal stem cells, growth factors and other cytokines form a surgically induced superclot, which provides an enriched environment for fibrous cartilage formation. In defects with subchondral cyst formation, microfracture can be combined with cyst resection and filling of the defect with bone graft from the iliac crest, the tibia or the calcaneus. Compared to all other cartilage repair techniques, the level of evidence for good clinical outcome is highest for microfracture [17]. However, the good initial clinical results are reported to begin to lessen after 5 years [11,19]. Significantly poorer results have been reported for defects exceeding 1.5 cm 2 [4,5].
Autologous chondrocyte implantation (ACI) has increasing gained popularity for the treatment of larger defects during the past few years. ACI is a procedure in which cartilage cells harvested from the patient are expanded in vitro and then implanted into the joint in a second intervention. The superiority of this expensive and time-consuming cartilage reconstruction technique over that of micro-fracture could not be conclusively established so far [9,10,20]. Current research is focused on one-step procedures, e.g. scaffold-enhanced microfracture, with the goal of providing a simple, cost-effective clinical solution that avoids the problems associated with cell culture and a second surgical intervention [8,28].
In larger defects, stabilization of the progenitor cell-containing blood clot formed after microfracture presents a problem [18]. By stabilizing this superclot with a biomaterial, the colonization, proliferation and chondrogenesis of mesenchymal stem cells are facilitated [3,12].
Autologous matrix-induced chondrogenesis (AMIC) is a cartilage repair technique in which, after microfracturing, a collagen type I/III bilayer matrix (Chondro-Gide®, Geistlich Pharma AG, Switzerland) is secured over the cartilage defect using commercially available fibrin glue. Mesenchymal progenitor cells migrate toward and adhere to the porous layer of the matrix; the cell-occlusive compact layer prevents cell loss through leakage into the joint space and protects cells from mechanical stress. In vitro studies have shown that the stability of the collagen matrix form prevents shrinkage of the super clot. Furthermore, its use in combination with fibrin glue (Tissucol or Tisseel from Baxter Healthcare, Deerfield, IL, USA) supports chondrogenic differentiation of human mesenchymal stem cells and significantly enhances proteoglycan deposition [6,22].
The controversial in vitro evidence on the effects of fibrin glue on mesenchymal stem cells and chondrocytes has been a topic of discussion for well over a decade. In rabbit experiments, Brittberg et al. [2] found that the use of Tisseel impaired healing of osteocondral defects and also reported that no cell migration into Tisseel took place, whereas cell migration was observed into blood clots. In contrast, Homminga et al. [13] have shown that chondrocytes in fibrin glue produce extracellular matrix, retain their typical morphology and divide to form colonies. Nowadays, commercially available fibrin glue is routinely used in orthopedics. It is also standard in matrix-induced autologous chondrocyte implantation (MACI) and no negative results have been reported. Its use is supported by the findings of Sage et al. [23], who stated that fibrin glue increases proliferation of and glycosaminoglycan production by cells in cartilage chips. Kirilak et al. [15] found that fibrin sealant promotes migration and proliferation of human articular chondrocytes and that thrombin, an active component of fibrin glue, stimulates these processes.
Alternative techniques for treatment of focal cartilage defects in the talus are the osteochondral autograft transfer system (OATS), allograft or implantation of in vitro cultured autologous chondrocytes in ACI [1,14,24]. The OATS approach is associated with high donor site morbidity. In more than 50% of cases, complaints in the knee joint from where the grafts were harvested were reported [26]. Fur-thermore, an autograft cannot be implanted in the ankle without an osteotomy of the medial or lateral malleolus, which can lead to future complications and late adverse effects. Allograft is hardly available in Europe.

Surgical principle and objective
The objective of the procedure is treatment of a talar dome osteochondral lesion (OCL) by microfracture in combination with a collagen matrix. The purpose of the collagen matrix is to retain and stabilize the superclot in the defect zone, as well as to protect it from being displaced [3,12]. In most cases, the collagen matrix can be implanted without having to perform an osteotomy of the medial or lateral malleolus [29].

Instruments and implants
F Basic set of surgical instruments for ankle surgery F Self-retaining Kirschner wire (Kwire) distractor (. Fig. 1

Surgical technique
(. Fig. 2, 3, 4, 5, 6, 7, 8, 9) Fig. 4 8 After dissection to the level of the joint capsule, the joint is opened by a longitudinal incision. A 2.0-mm K-wire is drilled into the distal tibia, a second one parallel to the first in the neck of the talus. The talar K-wire is placed at the cartilage-free area ventral to the medial talar shoulder, in order to avoid cartilage damage. Placing the wires using the K-wire distractor as a drill guide facilitates precise positioning of the wires. The joint is then distracted in maximum plantar flexion In the border region, a stable cartilage edge must mark the transition to healthy cartilage. Oval-shaped preparation of the defect facilitates insertion of the collagen matrix. All necrotic bone is removed and cysts curetted. The underlying sclerotic zone is then perforated using multiple small drill holes (1.2-mm K-wire) with adequate cooling or microfracture awls. Particularly in cases with a thick sclerotic wall visible in the preoperative MRI, drilling is preferred to completely perforate the sclerosis. In full-thickness cartilage defects without additional sclerosis, microfracturing is sufficient, avoiding thermal damage to the bone reconstructed to the level of the subchondral bone lamella using autologous cancellous bone. Particular attention must be paid to ensure that the bone graft does not exceed the level of the subchondral bone lamella, which can lead to delamination of the collagen matrix. Cancellous bone harvested from the ipsilateral calcaneus is adequate in most cases. It is also possible to harvest cancellous bone from the tibial head or pelvic crest. Although the content of stem cells in iliac crest bone is higher than in the calcaneus, there is currently no clinical evidence that this has any impact on clinical outcome [7,21]. The bone graft is sealed with fibrin glue, which provides sufficient stability to reconstruct even the talar shoulder

Special surgical considerations
F Depending on the location of the cartilage defect, other approaches can be used to facilitate access to the diseased cartilage area. With a central approach, the entire ankle joint can be well visualized. This approach is particularly useful for treating defects of the medial and lateral talar shoulder, as well as for centrally located defects. The ventrocentral access approach uses the space between the anterior tibial and the extensor hallucis longus tendons (. Fig. 10). The neurovascular bundle is retracted laterally using a blunt Hohmann retractor. F The ventrolateral approach (Ollier approach) is carried out lateral to the peroneus tertius tendon, ventral to the lateral malleolus (. Fig. 11). Lesions of the lateral talar shoulder can be addressed well with this approach. The closure of the capsule can be combined with an external ligaments stabilization procedure. F Dorsal approaches are seldom necessary, since with adequate distraction of the joint using the K-wire distractor (. Fig. 1), more dorsally located defects can also be accessed. If such an approach is planned, the patient is positioned on the contralateral side in the case of a dorsolateral defect. The affected leg is positioned free, in order to be able to flex the knee to allow for adequate dorsal extension of the ankle joint. The dorsolateral approach runs dorsal to the lateral malleolus and enables medial or lateral retraction of the peroneal tendons (. Fig. 12). F For a dorsomedial approach between the medial malleolus and the posterior tibial tendon (. Fig. 13), the patient is positioned on the affected side. The contralateral leg is well-padded and the affected leg is positioned in a freely moveable manner. The use of a short vacuum mattress considerably facilitates the procedure. Adequate flexion of the knee is necessary to allow free dorsiflexion of the ankle joint. F Any axial deformities or instabilities present should be addressed within the context of this intervention. Hindfoot deformity corrections, as well as capsule and ligament reconstructions can be carried out according to standard surgical techniques. . Fig. 14 shows a patient with hindfoot varus undergoing a concurrently performed closing wedge osteotomy of the calcaneus.

Postoperative management
F Complete immobilization of the ankle at 90° for 48 h. If inserted, remove drain after 48 h. Begin with continuous passive motion limited to 20-0-20°, to provide continuous containment of the defect by the tibia dur- help of an aluminum foil, which is pressed into the defect with forceps such that the borders of the cartilage are clearly depicted. It is then cut to size and its exact fit is checked once again. The collagen matrix, hydrated in a physiological saline solution, is cut to shape with the help of the template. When hydrated, the matrix expands by 10-15%. The collagen matrix has a rough side that should face the bone; the smooth side faces the joint with commercially available fibrin glue and the collagen matrix is glued on top. Additional suturing is not required. To decrease the risk of delamination when the joint is moved, care should be taken not to overlap the matrix with the edges of the adjacent cartilage. After hardening of the glue, the distractor is removed and the joint moved throughout the range of motion several times. If delamination occurs, possible matrix protrusion with the adjacent cartilage should be assessed and eliminated by shaving off excess matrix. Bone graft exceeding the level of the subchondral bone can also lead to delamination of the matrix. In this case, excess graft should be reduced before reattaching the matrix Fig. 9 8 Finally, the joint is closed in layers with resorbable suture material. A drain without suction can be inserted if necessary. After applying an elastic compression bandage, the tourniquet is released. The ankle is immobilized with a dorsal plaster splint for the first 48 h after surgery ing the healing period and to minimize the risk of delamination. In defects located very ventral or dorsal to the joint surface, the recommended range of motion is modified accordingly. F Dorsal splint for 2 weeks until wound healing is complete. F Weeks 1-6: partial weight bearing of 10 kg. F Weeks 7-12: stepwise increase in weight bearing (increasing by 20 kg every 2 weeks).
F From week 13 onward, daily activities including cycling and swimming are permitted. F Sports involving impact load or a rapid change of direction should be avoided for at least 12 months. F Whether or not a return to professional sports is possible after cartilage reconstruction has not yet been conclusively established. F There is no indication for routine MRI follow-up. However, if the patient complains of persistent pain, MRI is indicated.    [27]. Repetition of the intervention is possible.
However, after failure of initial surgery, it is important to reassess axial malalignment or instability as possible causes.

Results
Postoperative  Fig. 15). Further sufficiently powered, randomized clinical trials with uniform methodology and validated outcome measures are needed to compare the results of surgical strategies for treating OCLs of the talus. The results suggest that AMIC may be an effective way to treat full-thickness lesions of the talus without harvesting chondrocytes from the talus in patients who do not respond to initial curettage.