synonyms: avascular necrosis, knee AVN, osteonecrosis of the medial femoral condyle
Knee Osteonecrosis ICD-9
- 733.43(medial femoral condyle)
Knee Osteonecrosis Etiology / Epidemiology / Natural History
- Spontaneous osteonecrosis of the knee is a common source of debilitating unicompartmental knee pain.
- Generally affects the medial femoral condyle in women >55yrs old. Infrequently affects the tibial plateau
- Secondary osteonecrosis of the knee is related to corticosteriod use, alcohol abuse, sickle cell anemia, systemic lupus erythematosus, generally in patients <45y/o, often bilateral
Knee Osteonecrosis Anatomy
- Mechanical axis of the lower extremity=line drawn from center of femoral head to center of ankle joint, should pass through center of knee. Mechanical axis of the femur = line drawn from center of femoral head to center of the femoral surface of the knee. Mechanical axis of the tibia = line from the center of the tibial plateau to the center of the ankle.
- Anatomic axis=line drawn down center of tibial or femur.
- Tibiofemoral angle=angle between tibial and femoral anatomic axis. Normal = 6° valgus.
- Deformity can be defined as the angle drawn between the mechanical axis of the femur (i.e., the middle of the femoral head to the middle of the femoral surface of the knee) and the mechanical axis of the tibia. or as the deformity defined by the tibiofemoral angle, or the angle created between the anatomic axes of the femur and tibia.
- Medial plateau is larger and concave, lateral plateau is smaller and convex
- Epicondylar axis is @3 degrees externally rotated as compared to posterior condylar line
- Distal femoral condyles are in 9 valgus relative to femoral anatomic axis
- Tibial plateau is in 3 varus relative to tibial axis
- Tibial plateau has @10 posterior slope
- 3 compartments =medial, lateral, patellofemoral
- Medial femoral circumflex artery supplies the femoral head. (anterior humeral circumflex supplies humeral head)
Knee Osteonecrosis Clinical Evaluation
- Spontaneous knee AVN=sudden onset, unilateral severe knee pain generally women >55y/o
- Secondary knee AVN = gradual onset, bilateral poorly localized pain in patients <45y/o.
Knee Osteonecrosis Xray / Diagnositc Tests
- Weight bearing A/P long leg films, Weight-bearing lateral in extension, Tunnel view, Flexion lateral, Merchants view(Merchant, JBJS, 1974), Flexion weight bearing(Rosenburg JBJS, 1988)
- Bone scan: demonstrates increased uptake over affect area.
Knee Osteonecrosis Classification / Treatment
Knee Osteonecrosis Associated Injuries / Differential Diagnosis
- Death: 0.53%
- Periprosthetic Infection: 0.71%
- Pulmonary emboli: 0.41%
- Patella fracture:
- Component Loosening:
- Tibial tray wear:
- Peroneal Nerve Palsy: 0.3% to 2%
- Periprosthetic Femur Fracture:
- Periprosthetic Tibial Fracture:
- Wound Complications / Skin slough: rare
- Patellar Clunk Syndrome: rare
- Patellofemoral Instability: 0.5%-29%
- Popliteal artery injury: 0.05%
- Quadriceps Tendon Rupture: 0.1%
- Patellar Tendon Rupture: <2%
- Fat Embolism
TKA Follow-up care
Knee Osteonecrosis Review References
- Patel DV, Breazeale NM, Behr CT, Warren RF, Wickiewicz TL, O’Brien SJ: Osteonecrosis of the knee: Current clinical concepts. Knee Surg Sports Traumatol Arthrosc 1998;6:2-11
- Ecker ML, JBJS 1995;77A:596