Osteochondral Lesions of the Talar Dome: Cartilage Replacement Using Autologous Chondrocyte Implantation and Allografts

CHAPTER 14 Osteochondral Lesions of the Talar Dome


Cartilage Replacement Using Autologous Chondrocyte Implantation and Allografts



Osteochondral lesions of the talus (OLTs) are rare, representing only about 4% of all such lesions in the body.1 This lesion also has been called osteochondritis dissecans, transchondral fracture, talar dome fracture, and osteochondral defect. OLTs consist of a focal cartilage deficit with associated reactive bone edema.


Several staging systems have evolved since Berndt and Harty proposed the first system based on radiographic imaging of the talus in 1959 (Table 14-1).2 Loomer and colleagues3 reviewed computed tomographic (CT) data of 92 patients with OLTs and found a previously unclassified lesion—the radiolucent lesion—in 77% of the patients in their series. In 1999, Hepple and coworkers,4 using magnetic resonance imaging (MRI) added another characteristic to the original classification system—stage 5, subchondral cyst formation.


TABLE 14-1 Staging System Proposed by Berndt and Harty


















Stage Description
Stage 1 Compression of the border of the talus
Stage 2 Incomplete detachment of fragment
Stage 3 Complete detachment, no displacement
Stage 4 Displaced fragment or loose body

From Berndt AL, Harty M. Transchondral fractures (osteochondritis dissecans) of the talus. J Bone Joint Surg Am. 1959;41A:988-1020.


For clarity, most investigators prefer the simplicity of the Berndt and Harty classification system. However, MRI is the imaging modality of choice instead of the plain radiographs used in the original classification description.



NORMAL AND PATHOLOGIC ANATOMY


The talar dome is trapezoidal, and its anterior surface averages 2.5 mm wider than the posterior surface. The medial and lateral articular facets of the talus articulate with the medial and lateral malleoli. The articular surface of these facets is contiguous with the superior articular surface of the talar dome. Approximately 60% of the dome of the talus is covered by the trochlear articular cartilage, which is incapable of supporting intrinsic repair. The cartilage is largely avascular and incapable of healing through the typical inflammatory phase. Because the chondrocytes are contained in a thick extracellular matrix, they are unable to migrate from uninjured matrix to the zone of injury.


The talus has no muscular or tendinous attachments. Most of the blood supply of the talus enters by the neck through the sinus tarsi. The dorsalis pedis artery supplies the head and neck of the talus. The artery of the sinus tarsi is formed from branches of the peroneal and dorsalis pedis arteries. The artery of the tarsal canal branches from the posterior tibial artery. The sinus tarsi artery and the tarsal canal artery join to form an anastomotic sling inferior to the talus, from which branches enter the talar neck.


The articular cartilage of the talus is inconsistent with the posteromedial corner, having a greater depth of cartilage than the anterolateral. This manifests in geographic mechanical properties and may influence the rate and type of articular injury.57



PATIENT EVALUATION




Diagnostic Imaging


Patients with an acute ankle injury with hemarthrosis or substantial tenderness should first undergo weight-bearing plain radiography (i.e., anteroposterior, lateral, and mortise views). Radiographs in various degrees of plantar flexion and dorsiflexion may help in diagnosing posteromedial and anterolateral lesions, respectively.14 Plain radiographs of the contralateral ankle should be obtained, because there is a 10% to 25% incidence of a contralateral lesion.15


MRI can identify occult injuries of the subchondral bone and cartilage that may not be detected with routine radiographs.16,17 Classic MRI findings include areas of low signal intensity on T1-weighted images, which suggests sclerosis of the bed of the talus and indicates a chronic lesion.18,19 T2-weighted images reveal a rim that represents instability of the osteochondral fragment.18,20 After treatment, MRI should reveal a reduction or disappearance of the low signal intensity on T1-weighted images and the rim on T2-weighted images.



TREATMENT




Treatment Options


The goals of cartilage repair are to restore the articular cartilage surface, match the biochemical and biomechanical properties of normal hyaline cartilage, improve the patient’s symptoms and function, and prevent or slow progression of focal chondral injury.


The approach to the OLT can be facilitated through open or arthroscopic approaches. Most primary interventions are performed with the assist of the arthroscope (i.e., microfracture). Open approaches are indicated for lesions unable to be accessed through the arthroscope or when the selected therapy requires direct access to the lesion.



Arthroscopy of the Ankle



Anterior Ankle Arthroscopy.


Arthroscopic surgery of the anterior ankle allows the direct visualization of intra-articular structures of the anterior ankle joint without an arthrotomy or malleolar osteotomy. The congruency of the distal tibia and talar dome makes arthroscopic visualization difficult through a single portal. The distal tibia is concave in the sagittal plane and convex in the coronal plane. The anterior tibial plafond is slightly convex with a medial notch (i.e., notch of Harty) that recedes approximately 4 mm near the junction of the plafond with the medial malleolus. This is an ideal location for introduction of the arthroscopic instruments. The medial malleolus is approximately 2 cm anterior to the lateral malleolus. Anatomic studies have shown that the tibial plafond covers only two thirds of the talar dome in any position.


Anteromedial and anterolateral portals are the standard approach for anterior ankle arthroscopy. The anteromedial portal is located at the level of the joint line just medial to the anterior tibialis tendon. The notch of Harty allows passage of the arthroscope posteriorly. The saphenous vein and nerve run along the anterior border of the medial malleolus. The saphenous nerve and its branches are usually located lateral to the vein and are at risk with this approach. Staying close to the tibialis anterior tendon minimizes the risk of damage to the saphenous structures.


The anterolateral portal is found just lateral to the peroneus tertius, entering the joint between the fibula and the talus just distal to the joint line. In this location, the lateral and medial branches of the superficial peroneal nerve may be injured if their locations are not carefully identified before a skin incision is made.


Distraction techniques facilitate the placement of the arthroscope and instruments into the tightly configured ankle joint (Fig. 14-1). Noninvasive techniques involving straps, harnesses, and outriggers are distraction methods used most commonly. These techniques minimize the risk of neurovascular injury and other complications.22





Arthroscopic Débridement with Microfracture.


Arthroscopic treatment of OLTs involves three principles: removing loose bodies, securing the OLT to the talar dome (i.e., open reduction with internal fixation), and stimulating development of fibrocartilage. Open reduction with internal fixation is reserved for large, acute OLTs. More often, the lesion is débrided to a stable articular rim, and marrow stimulation techniques are used to create the healing cartilage.


The microfracture technique for OLTs is based on the success of similar techniques in the knee (Fig. 14-2).24,25 Using awls, microfractures (i.e., perforations) are made approximately 3 to 4 mm apart in the subchondral bone while maintaining the integrity of the bone plate. The microfracture technique promotes new tissue formation by releasing substances such as mesenchymal stem cells, growth factors, and healing proteins.24 Ultimately, cartilage-like cells (i.e., fibrocartilage) form and fill the original defect.



Tol and associates26 reviewed 32 studies that reported the results of treatment for OTL. Nonoperative treatment had an average success rate of 45%, whereas the best success rate of 85% was achieved with excision, curettage, and drilling. Posteromedial lesions are difficult to access with this technique. The size of the lesion also plays a role in the success or failure of this procedure. In the meta-analysis by Tol and colleagues,26 the lesion size averaged 0.7 cm; currently, lesions larger than 1 cm are thought to have a less predictable outcome with microfracture.


The limitation of microfracture is that fibrocartilage is created to fill the defect. This is predominantly type I cartilage, which lacks the organized structure of normal hyaline cartilage and therefore has inferior wear characteristics (Fig. 14-3).



We retrospectively reviewed the results of arthroscopy and microfracture in 189 patients; MRI was used to determine the size of the lesion.27 Good results were achieved in 132 patients with an average lesion size of 0.67 cm2; 22 patients with an average lesion size of 0.76 cm2 had fair results; and 36 patients with an average lesion size of 1.09 cm2 had poor results (Fig. 14-4).




Open Approaches to the Ankle: Malleolar Osteotomies


The tibiotalar articular surface can be accessed through arthrotomies and arthroscopically. For techniques in which an articular graft must be delivered to the articular defect, an open approach is often favored. Muir and colleagues28 studied nine cadavers to evaluate the accessibility of the talar dome by various approaches about the ankle. They used four arthrotomies and three osteotomies and characterized the percentage of the talar dome that could be accessed in a perpendicular fashion with respect to the articular surface. They found that without an osteotomy, up to 24% of the medial talar dome (average, 17%) and 25% of the lateral talar dome (average, 20%) could not be accessed. Osteotomies add an average of 22% exposure, although there remains a central 15% that is inaccessible in a perpendicular manner.28



Chevron Medial Malleolar Osteotomy.


The chevron medial malleolar osteotomy is advantageous for many reasons. It is a reproducible technique that is familiar to most orthopedic surgeons, it provides good perpendicular access to the medial talar dome, it can be adjusted for the location of the lesions, it is vertically stable, and it is performed in the metaphyseal bone, which provides reliable healing.


When planning a medial malleolar osteotomy, careful preoperative identification of the exact location of the lesion on CT or MRI is important to ensure that the osteotomy cut will allow access to the lesion. The location of the osteotomy cut can be confirmed intraoperatively through a small arthrotomy before making the definitive bone cut.


The patient is placed in a supine position, and a thigh tourniquet is applied. A central incision is created over the medial malleolus, and careful dissection is performed to identify and protect the posterior tibial tendon. The anteromedial aspect of the joint is identified, and a small arthrotomy is performed to assist in visualizing the angle of the osteotomy.


Drill holes for two 4.5-mm screws are placed across the planned osteotomy site before making the cut. The holes are drilled and tapped to ensure anatomic reduction of the osteotomy. The chevron is oriented with the apex proximal, which facilitates a perpendicular approach to the medial talus. The periosteum is divided sharply along the proposed osteotomy.

Jun 19, 2016 | Posted by in MUSCULOSKELETAL MEDICINE | Comments Off on Osteochondral Lesions of the Talar Dome: Cartilage Replacement Using Autologous Chondrocyte Implantation and Allografts
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