Dr. Kevin Yip

Dr Kevin Yip
Orthopaedic Surgeon
MBBS(UK), FRCS(EDIN), FAM(SING), FHKCOS(ORTHO)

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Osteochondritis Dissecans of the Knee

Basics
Description
  • A pathologic joint entity of localized bone necrosis with overlying cartilage injury
  • Osteochondritis dissecans primarily affects the knee, but it is also seen in the hip (in late Legg-Calve-Perthes disease), elbow, and ankle.
  • Osteochondritis dissecans occurs primarily in the 2nd decade of life, but it also is seen in children and older adults.
  • Older adolescents, after physeal closure, have less ability to heal these lesions with nonoperative treatment.
  • Several forms of Little League elbow are types of osteochondritis dissecans of the radial head and capitellum.
  • Also called osteochondral fracture
  • Most common locations:
    • Posterolateral medial femoral condyle: 70%
    • Inferocentral lateral femoral condyle: 20%
    • Patella: 10%
    • Trochlea: 1%
Epidemiology
  • Juvenile and adult forms
  • More common in males
  • 25% bilateral
Incidence
More frequent in active sports participants
 
Risk Factors
Patients susceptible to trauma (i.e., those with increased joint laxity, genu valgum, obesity, or intraosseous vascular anomalies)
 
Genetics
  • Increased predilection in some families
  • No known Mendelian pattern
Etiology
  • Unknown and controversial
  • Repetitive trauma versus inflammatory versus ischemic cause
Diagnosis
Signs and Symptoms
History
  • Knee pain: Insidious and activity related
  • Occasionally locking or catching of the knee if the fragment becomes loose
Physical Exam
  • Check knee ROM.
  • Tenderness over the lesion
  • Knee effusion:
    • Graded as mild, moderate, large
    • Mostly seen in unstable lesions
  • McMurray test (for meniscal pathology)
  • Lachman test (for ACL pathology)
  • Antalgic gait
  • Thigh atrophy
  • Examine the contralateral knee: 25% of these injuries are bilateral
Tests
Imaging
  • Radiography:
    • AP, lateral, and tunnel needed
    • Radiographs may be negative.
    • Bilateral views often obtained for comparison and to look for contralateral lesions
    • Tunnel radiographs are taken with knee in 45° of flexion, which allows improved visualization of areas of the femoral condyle commonly involved in osteochondritis dissecans
  • MRI:
    • Often required for diagnosis if radiographs are negative
    • Look for:
      • Bone marrow edema
      • Lesion size
      • Loose bodies
    • MRI classification of lesions:
      • Stage I: Small signal change, no clear margins
      • Stage II: Osteochondritis dissecans fragment with clear margins without fluid between fragment and bone
      • Stage III: Fluid partially visible between fragment and bone
      • Stage IV: Fluid completely surrounds fragment
      • Stage V: Fragment displaced
    • Unstable lesion: 4 criteria on T2-weighted images:
      • Line of high signal intensity >5 mm in length between the osteochondritis dissecans lesion and underlying bone
      • Area of increased homogenous signal >5 mm in diameter beneath the lesion
      • Focal defect >5 mm in articular surface
      • High signal line traversing the subchondral plate into the lesion
    • Lesion size may be main determinant of healing
    • High signal line behind the fragment is most predictive of unstable lesions:
      • Found in 72% of unstable lesions
      • Most common sign in patients for whom nonoperative management fails
  • Bone scans:
    • Outdated
    • Can be used to predict potential for healing of osteochondral lesions
    • Increased uptake = More likely to heal
Pediatric Considerations
In children <7 years old, irregularities of the distal femoral epiphyseal ossification center may mimic osteochondritis dissecans.
 
Pathological Findings
A separated articular fragment with attached necrotic bone is noted.
 
Differential Diagnosis
  • Stress fracture: Pain is of acute onset.
  • ACL injury: Positive Lachman test
  • Physiologic ossification abnormalities in children <7 years old (see earlier)
  • Meniscal injury: Patients have mechanical symptoms of locking and clicking and may have a positive McMurray test
  • Spontaneous osteonecrosis of the knee:
    • History of steroid use
Treatment
General Measures
  • Treatment principles:
    • Small, stable lesions with intact cartilage in skeletally immature patients are most likely to heal with nonoperative management.
    • Unstable lesions warrant arthroscopic evaluation.
    • Treatment is based on:
      • Patient’s age
      • Lesion size and location
      • Lesion’s radiographic stage
      • Whether the lesion is unstable
  • Nonoperative treatment:
    • Best for lesions presenting before physeal closure (best prognosis)
    • Lesions <5 mm often can be managed with observation alone (no surgery, just follow-up).
    • Recent recommendations: 3-phase nonoperative management protocol
      • Phase 1: 6 weeks of knee immobilizer and crutch-protected gait; child should be pain free at the end; repeat radiographs at the end.
      • Phase 2 (weeks 6-12): Weightbearing as tolerated without immobilization; physical therapy for knee ROM; quadriceps strengthening
      • Phase 3 (begins at 3 months): Supervised increase in activities, high-impact and shear activities restricted until patient is pain free for several months; consider repeat MRI; repeat immobilization for lesion progression.
Surgery
  • Consider for:
    • All patients with detached or unstable lesions
    • Symptomatic patients approaching physeal closure and unresponsive to nonoperative treatment
    • Stable lesions that have not healed in 6-9 months
    • Large lesions (>5 mm)
  • Techniques:
    • Arthroscopic drilling:
      • Stable lesions with intact articular surfaces
      • Creates channels for revascularization
      • Can be transarticular or through epiphysis (very difficult)
      • Transarticular drilling is effective for osteochondritis dissecans lesions in skeletally immature patients.
      • Curative in 85% with open physes and 75% with closed physes
      • Factors associated with failure of treatment include nonclassic lesion location, multiple lesions, and underlying medical problems.
    • Reduction and fixation of fragment:
      • For unstable and partially unstable lesions
      • Can pack autogenous bone graft into crater if subchondral bone loss is present
      • Headless screws
      • Titanium screws are MRI compatible.
      • Long-established loose fragments are difficult to stabilize and have poor healing potential.
    • Large, unsalvageable fragments:
      • Drilling
      • Abrasion arthroplasty
      • Microfracture
      • Recruited cells form fibrocartilage.
      • Autologous osteochondral plug transplantation for lesions <2 mm in diameter
      • Autologous chondrocyte implantation for large defects and skeletally mature patients
Follow-up
Prognosis
  • Small nondisplaced fragments or those occurring before physeal closure usually heal.
  • Large, unstable lesions may lead to early osteoarthritis.
Complications
  • Nonunion of the reduced fragment
  • Displacement of a nondisplaced lesion, creating a loose body
Patient Monitoring
  • Nondisplaced fragments treated nonoperatively should be followed closely for evidence of displacement.
  • Serial radiographs or MRI every 3-6 months to follow healing or lack thereof
Miscellaneous
Codes
ICD9-CM
732.7 Osteochondritis dissecans
 
Patient Teaching
Stress the importance of avoiding the offending activities to allow time for the lesion to heal.
 
FAQ
Q: What is the best initial treatment of a large, unstable osteochondritis dissecans lesion in a skeletally mature patient?
A: This lesion has a poor prognosis with nonoperative management. Therefore, the best treatment is debridement of the dead bone on the fragment and in the crater, subchondral drilling with or without bone grafting, and fragment fixation with a headless titanium screw to allow MRI follow-up studies. Postoperatively, the patient is treated nonweightbearing for 6-8 weeks with early motion.

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