Arthroscopic Internal Fixation of Osteochondritis Dissecans

Christian N. Anderson

Allen F. Anderson

Background

• Osteochondritis dissecans (OCD) is an idiopathic lesion of the subchondral bone that can compromise the articular cartilage if healing fails to occur.¹,²

• While the etiology remains controversial, clinical³ and basic science⁴ studies in the older literature support trauma as a pathogenesis of OCD.

• More recently, evidence from animal studies indicates that OCD in the classic location of the medial femoral condyle is caused by occlusion of the epiphyseal vascular arcade.⁵,⁶,⁷

• OCD lesions can be reliably classified into six arthroscopic categories—three immobile types and three mobile types, based on the Research in Osteochondritis of the Knee (ROCK) study group classification system (Fig. 55-1).¹

• Treatment for OCD is dictated by skeletal maturity of the patient and stage of the lesion at the time of presentation.

• The goal of treatment is to preserve the articular cartilage through healing of the OCD fragment.

Preoperative Planning

Radiographic Evaluation

• Plain radiographs: anteroposterior (AP), 45-degree posteroanterior (PA) flexed, lateral, and sunrise weight-bearing views.

• Long-leg radiograph to determine the mechanical axis of the extremity.

• Magnetic resonance imaging (MRI) can determine the integrity of the articular cartilage and lesion stability. The MRI criteria for OCD instability include high T2 signal behind the fragment, surrounding cysts, a cartilage fracture line, and a fluid-filled defect.

Treatment Algorithm

• Skeletally immature patients with immobile lesions and healthy articular cartilage

• Non-weight bearing for 6 weeks, followed by activity restriction until radiographic healing is achieved

• If noncompliant, immobilization for 6 weeks

• If patient is within 6 months of skeletal maturity or OCD lesion has failed to heal despite 6 months of conservative treatment, antegrade or retrograde drilling is indicated.

• Patients with unstable or loose fragments are candidates for operative fixation with or without bone grafting.

• Patients who have OCD lesions that have failed to heal despite operative fixation or who have irreparable lesions are candidates for a resurfacing procedure.

Figure 55-1 | The ROCK study group classification for OCD lesions.⁴

Surgical Technique: Antegrade Drilling

Setup (Fig. 55-2)

• The patient is positioned supine on the operating table.

• The operative leg is placed in an arthroscopic leg holder one handbreadth above the patella.

• The leg holder is raised to elevate the operative knee above the contralateral extremity for viewing in the lateral plane while using fluoroscopy.

Figure 55-2 | Operating room setup. The C-arm and video monitor are placed on the contralateral side of the injured knee, while the C-arm monitor is placed on the ipsilateral side.

• The leg holder should be set up to allow the surgeon to remove the leg if needed so that the lesion can be accessed through an arthrotomy with the knee in flexion.

• The C-arm is placed on the opposite side of the injured extremity, and the monitor is placed on the same side as the operative extremity (Fig. 55-2).

• Before preparing and draping the extremity, fluoroscopic images of the knee in the AP and lateral planes are obtained, and the location of the lesion is identified, if possible (Fig. 55-3A).

Drilling

• Standard arthroscopic portals are established, and a diagnostic arthroscopy is completed.

• In stable lesions (cue ball), the articular surface may have good subchondral support and may look and feel completely normal. The articular cartilage over the lesion also may be softer than the surrounding cartilage.

• When the lesion cannot be identified arthroscopically (Fig. 55-3B), a 0.045-in smooth Kirschner wire (K-wire) is inserted into the suspected location of the lesion (Fig. 55-3C). Fluoroscopic imaging in the AP and lateral planes is then used to confirm that the K-wire is in the lesion (Fig. 55-3D).

• Once the lesion is identified, a 0.062-in or 0.045-in smooth K-wire is placed in a Jacob drill chuck so that it is 1.5 cm longer than a standard 5-mm arthroscopic cannula.

• The 0.045-in K-wire damages less of the articular cartilage and is just as efficacious as the 0.062-in K-wire (Fig. 55-3E and F).

• The cannula is inserted into the knee adjacent to the lesion and is used to prevent iatrogenic articular cartilage damage and overpenetration of the K-wire into the physis.

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