Knee Osteochondritis Dissecans

Osteochondritis dissecans (OCD), by definition, is a disorder of one or more ossification centers, characterized by sequential degeneration or aseptic necrosis and recalcification. OCD lesions involve both bone and cartilage. These lesions differ from acute traumatic osteochondral fractures; however, they may manifest in a similar fashion. OCD lesions also must be differentiated from meniscal pathology. OCD causes 50% of loose bodies in the knee. The etiology of these lesions is multifactorial, including trauma, ischemia, abnormal ossification centers, genetic predisposition, or some combination of these factors. Little agreement exists among researchers regarding the etiology of OCD.

Images of osteochondritis dissecans of the knee are provided below:

In 1558, Ambroïse Paré removed loose bodies from a knee joint. In 1870, Paget described quiet necrosis within the knee. In 1888, König coined the term "osteochondritis dissecans." He proposed this condition was caused by spontaneous necrosis due to trauma.

With the advent of roentgenography, osteochondrotic conditions in other joints, primarily the hip, were recognized. In 1910, Legg, Calvé, and Perthes independently identified a condition of the hip joint in children, which is now known as Legg-Calvé-Perthes disease. In 1921, Waldenström introduced the term coxa plana (ie, disintegration of capital femoral epiphysis.)

Since the introduction of radiography, 50 additional anatomic sites within the body where OCD can occur have been identified.

Recent studies

Tabaddor et al evaluated the efficacy and safety of poly 96L/4D-lactide bioabsorbable copolymer fixation for unstable OCD in 24 adolescents (mean age, 14.4 y). Plain films at an average of 19.2 months after surgery showed interval healing in 9 patients, no significant change in 1, complete healing in 13, and loose bodies with no interval healing in 1. MRIs showed interval healing in 16 of 17 knees at a mean follow-up of 22.4 months.[1]

Pascual-Garrido et al examined the outcomes of surgical procedures for osteochondritis dissecans in 46 adult patients (48 knees), with patients ranging in age from 20 to 49 years. Patients who were treated with surgical cartilage procedures showed durable function and symptomatic improvement at a mean of 4 years follow-up. Patients treated with arthroscopic reduction and internal fixation and loose-body removal had greater improvement in outcome scores than those treated with an osteochondral allograft. Seven knees required revision procedures at a mean follow-up of 14 months.[2]

Adachi et al evaluated the functional and radiographic outcome of retroarticular drilling without bone grafting in 12 patients with juvenile osteochondritis dissecans after 6 months of unsuccessful nonoperative treatment. The mean Lysholm score significantly improved postoperatively (from 72.3 to 95.8). All lesions except 1 healed after retroarticular drilling, and healing was achieved at a mean of 4.4 months on plain radiographs and 7.6 months on magnetic resonance imaging.[3]

Kijowski et al retrospectively compared the sensitivity and specificity of previously described magnetic resonance imaging criteria for the detection of instability in patients with juvenile or adult osteochondritis dissecans of the knee, with arthroscopic findings as the reference standard. Separately, previously described MR imaging criteria for detection of OCD instability were 0-88% sensitive and 21-100% specific for juvenile OCD lesions and 27-54% sensitive and 100% specific for adult OCD lesions. When used together, the criteria were 100% sensitive and 11% specific for instability in juvenile OCD lesions and 100% sensitive and 100% specific for instability in adult OCD lesions. The authors concluded from their findings that previously described MR imaging criteria for OCD instability have high specificity for adult but not juvenile lesions of the knee.[4]

The 2 distinctive subsets of patients are skeletally immature patients and skeletally mature patients.

Little agreement exists among researchers regarding the etiology of OCD. Possible etiologies include the following:

• Trauma

• Skeletal maturation (accessory centers of ossification)

• Vascular causes/ischemia

• Genetic conditions (eg, multiple epiphyseal dysplasia)

• Metabolic factors

• Hereditary factors

• Anatomic variation

United States statistics

The average age at presentation is 10-20 years, but osteochondritis dissecans may occur in persons of any age group. The male-to-female ratio is 2-3:1.

Bilateral involvement is noted in 30-40% of cases. In 85% of cases, lesions are observed on the medial femoral condyle (MFC) of the knee; 15% of cases are observed on the lateral femoral condyle. Of the MFC lesions, 70% occur in the posterolateral aspect.

Of patients with OCD, 21-40% have some history of trauma.

International statistics

In Sweden, prevalence is reported at the following levels:

• In skeletally immature patients, 150 cases per 250,000 people are reported.

• In skeletally immature female patients, 18 cases per 100,000 people are reported.

• In skeletally immature male patients, 29 cases per 100,000 people are reported.

In skeletally immature individuals, the vascularity to epiphyseal bone is very good, supporting both osteogenesis and chondrogenesis. With disruption of the epiphyseal vessels, varying degrees and depth of necrosis occur, resulting in a cessation of growth to both osteocytes and chondrocytes. In turn, this pattern leads to nonspecific changes that produce disordered enchondral ossification, resulting in subchondral avascular necrosis or OCD.

Four stages of OCD have been identified, including revascularization and formation of granulation tissue, osteoclasis of necrotic fragments, intertrabecular osteoid deposition, and remodeling of new bone. With delay in the revascularization stage, an osteochondritis dissecans lesion develops. OCD lesions may lead to articular-surface irregularities, which can cause degenerative arthritic changes.

A proposed cause of OCD is an anatomic variation allowing the lateral aspect of the femoral condyle to abut the tibial spine, leading to repetitive localized epiphyseal microtrauma with osteochondral separation and subsequent OCD. This pattern may lead the patient to walk with the tibia externally rotated to avoid this abutment.

The general rule for the prognosis of OCD is the younger the patient, the better the prognosis. The prognosis also depends on the size and severity of the lesion.

A study by Nakayama et al examined 37 patients to understand factors affecting the prognosis of conservative treatment for stable juvenile osteochondritis dissecans of the lateral femoral condyle. The study found that 32.6% of the 43 knees studied had no signs of radiologic healing at 6 month follow-up. A discoid meniscus was identified in all of these knees with no healing. Another risk factor for poor non-opertative healing was a time period ≥ 6 months from onset to consultation.[5]

In another study of conservative treatment for knee OCD, Andriolo et al identified the size of the lesion as a prognostic factor; larger lesions are associated with worse outcomes and a slower healing rate. In addition, unstable lesions tend to have worse outcomes. Other negative prognostic factors include older patient age and skeletal maturity, as well as swelling and mechanical symptoms (eg, locking).[6]

Complications

A nonunion of the OCD fragment may occur and progress to dissociation, leading to intra-articular loose body symptoms. This, in turn, may lead to a type of reconstructive procedure such as OATS or ACI (see Surgical Intervention in Acute Phase). Regardless of treatment, degenerative articular changes may develop over time.

Symptoms are usually vague and poorly localized. A vague ache within the knee, with possible clicking or popping, may be reported. Varying degrees of pain, swelling, and stiffness are reported.

Symptoms may be associated with activities (eg, sports, activities of daily living).

With complete fragment separation, locking symptoms may occur.

Prolonged symptoms lead to progressive degenerative arthritis.

Giving way of the knee may occur secondary to quadriceps weakness.

Effusion may be present.

Quadriceps atrophy and weakness may be evident.

Occasionally, a loose body may be palpable.

The patient may lack full knee extension compared with the contralateral knee.

Tenderness is noted over the lesion.

Evaluate gait for external rotation of the tibia.

Perform the Wilson test to check for OCD. The examiner flexes the knee to 90° while internally rotating the tibia. A positive Wilson sign occurs when pain is elicited at 30° of flexion and is relieved with external rotation.

Images of osteochondritis dissecans of the knee are depicted below:

Plain radiography (anteroposterior, lateral, and tunnel views) shows OCD lesions as well-circumscribed crescent-shaped areas of radiolucency above an area of subchondral bone, separated from the femoral condyle. In 75% of cases, the lesion is located on the posterolateral aspect of the MFC.

Arthrography, which is not used routinely, may be helpful but is invasive; MRI can obtain similar data.

Bone scanning may be helpful with a high index of suspicion or in patients with occult bilateral involvement; however, it cannot determine the age of the lesion.

With gadolinium enhancement, MRI is helpful for determining the vascularity of the lesion, for determining whether involvement is bilateral, and for determining if smaller lesions are present. MRI also helps determine the degree of loosening of the lesion. However, to determine lesion instability in young patients, MRI should not be used in isolation; it should be used in conjunction with clinical symptoms (eg, locking, catching, and swelling) and physical examination to determine if the lesion is unstable and may require surgical fixation.[7] In this setting, MRI can be helpful in determining appropriate treatment and tracking the extent of healing.

CT scanning may helpful in determining the appropriate treatment and is used when MRI is unavailable or contraindicated.

Knee arthroscopy can be used as a diagnostic tool and a therapeutic tool. Results of arthroscopic evaluation allow determination of the size and stability of the lesion and allow tracking the lesion for evidence of healing. In addition, arthroscopic treatment of OCD, by whatever means, is possible and avoids formal knee arthrotomy.

Medical Issues/Complications

Important variables affect the choice of treatment. The general rule is the younger the patient, the better the prognosis. Guidelines for treatment are outlined by the following categories:

• Category 1 (ie, girls younger than 11 y, boys younger than 13 y): These patients usually do well with nonoperative treatment.

• Category 2 (girls aged 11-15 y, boys aged 13-17 y): These patients are near skeletal maturity. Treatment depends on the looseness of the lesions.

• Category 3: Physeal closure and skeletal maturity have occurred. Treatment is based on the size and stability of the lesion.

  • Grade 1 - Positive radiography findings and an intact articular surface

  • Grade 2 - Articular injury noted at arthroscopy

  • Grade 3 - Loose lesion (stays within crater)

  • Grade 4 - Loose fragment within joint

Surgical Intervention

Arthroscopy versus open treatment

Arthroscopy is preferred so that arthrotomy can be avoided.

Drilling of the defect may be performed, with the hope that revascularization will occur.

Pinning may be performed to stabilize the fragment. Stainless-steel pins usually require removal to avoid additional chondral injury. Resorbable pins can be used to avoid the need for removal; however, they may not be rigid enough or may not last long enough to allow healing.

Excision of the fragment and removal of loose bodies may be necessary.

Screw fixation may be performed for fragment stabilization. In this method, usually a specialized screw or Herbert-type screw, as shown in the images below, is used.

One study on children with symptomatic osteochondritis dissecans lesions in the knee found significant improvement in knee function scores after simple arthroscopic fixation using polylactide biodegradable lag screws.[8]

Abouassaly et al studied common techniques for surgically managing osteochondritis dissecans, including transarticular drilling for stable lesions and bioabsorbable pin fixation for unstable lesions. The researchers concluded that most lesions healed postoperatively, regardless of technique and that further high-quality trials are required to more appropriately compare the effectiveness of techniques.[9]

In another study of surgical procedures, Schulz et al found that thinking is shifting toward greater popularity for surgical treatment to encourage vascular ingrowth and healing. However, unstable and displaced lesions are still difficult to treat. Although various salvage procedures have shown promise, the potential for long-term morbidity remains.[10]

Osteochondral autograft transplantation (OATS) involves harvesting cylindrical osteochondral grafts from other areas of the knee to reconstruct a weight-bearing surface. A maximum 1-cm lesion (crater) depth is allowed for use of this treatment method.

Osteochondral allograft transplantation is similar to OATS except that a freshly harvested allograft condyle is used. The advantages are that the exact condyle curvature can be reconstructed and no further defect is created during autograft harvest.

Autologous chondrocyte implantation (ACI), by Carticel, requires a diagnostic arthroscopy, harvesting of a small amount of cartilage cells for cloning, and subsequent arthrotomy for reimplantation. Bone grafting of the OCD crater is often necessary prior to implantation.

Newer surgical treatments, including single-stage cell-based procedures, use mesenchymal stem cells and matrix augmentation. Any decision about appropriate surgery requires evaluation of both lesional (size, depth, stability) and patient (age, athletic level) characteristics.[11]

Other Treatment

In children with nondisplaced fragments, initial treatment includes limitation of activity with the use of crutches and restricted range of motion (eg, knee immobilizer, range-of-motion brace).

Recommend a trial of nonoperative treatment for 6-12 months.[12] If symptoms persist or failure to unite is observed, proceed with surgical treatment.

Return to play is allowed once the OCD lesion has healed and quadriceps strength has returned to within normal limits. If the athlete was treated surgically, he or she may return to play when the OCD lesion has healed and any obstructive retained hardware has been removed.

Treat with pain medication and nonsteroidal anti-inflammatory drugs (NSAIDs) of choice, as indicated, to control pain, inflammation, and swelling.

Class Summary

Pain control is essential to quality patient care. Analgesics ensure patient comfort and have sedating properties, which are beneficial for patients who experience pain.

Acetaminophen and Codeine (Tylenol #3)

Indicated for the treatment of mild to moderate pain. Use for postoperative pain control.

Hydrocodone and acetaminophen (Vicodin, Lorcet-HD, Norcet)

Drug combination indicated for moderate to severe pain.

Class Summary

Have analgesic, anti-inflammatory, and antipyretic activities. Their mechanism of action is not known, but they may inhibit cyclooxygenase activity and prostaglandin synthesis. Other mechanisms also may exist, such as inhibition of leukotriene synthesis, lysosomal enzyme release, lipoxygenase activity, neutrophil aggregation, and various cell membrane functions.

Ibuprofen (Motrin, Ibuprin)

DOC for patients with mild to moderate pain. Inhibits inflammatory reactions and pain by decreasing prostaglandin synthesis.

Naproxen (Naprosyn, Anaprox, Naprelan, Aleve)

For relief of mild to moderate pain. Inhibits inflammatory reactions and pain by decreasing activity of cyclooxygenase, which results in a decrease of prostaglandin synthesis.

Ketoprofen (Oruvail, Actron, Orudis)

For relief of mild to moderate pain. Inhibits inflammatory reactions and pain by decreasing activity of cyclooxygenase, which results in a decrease of prostaglandin synthesis.