Osteonecrosis of the Knee - Knee & Sports

Introduction

Two distinct entities including
- secondary osteonecrosis of the knee (this topic)
- spontaneous osteonecrosis of the knee (SONK)
Epidemiology
- demographic
  - women:men 3:1
  - more common in women <55 years with risk factors
  - reported to be found after knee arthroscopy in middle-aged women
- location
  - typically involves more than one compartment of the knee or even the metaphysis
  - 80% are bilateral
  - multifocal lesions are not uncommon
- risk factors
  - alcoholism
  - dysbaric disorders (decompression sickness, "the bends")
  - marrow-replacing diseases (e.g. Gaucher's disease)
  - sickle cell disease
  - hypercoagulable states
  - steroids (either endogenous or exogenous)
  - SLE
  - inflammatory bowel disease
  - transplant patient
  - virus (CMV, hepatitis, HIV, rubella, rubeola, varicella)
  - protease inhibitors (type of HIV medication)
  - trauma
Pathophysiology
- spontaneous osteonecrosis
  - appears to represent a subchondral insufficiency fracture
  - another hypothesis is an association with a meniscal root tear
Prognosis
- self-limiting condition

Physical Exam

Symptoms
- pain with weightbearing, especially sitting to standing

Imaging

Radiographs
- first line imaging studies
  - AP knee
  - lateral knee
  - merchant view knee
- findings
  - wedge-shaped lesion on imaging
MRI
- most useful study
- findings
  - highest sensitivity and specificity
  - T1: dark
  - T2: bright (marrow edema)

Differential

Osteochondritis dissecans (OCD)
- more commonly found at lateral aspect of medial femoral condyle of 15 to 20-year-old males
Transient osteoporosis
- more common in young to middle-aged men
- multiple joint involvement found in 40% of patients (transient migratory osteoporosis)
Occult fractures and bone bruises
- associated with trauma, weak bones, or overuse

Treatment

Nonoperative
- NSAIDs, limited weightbearing, quadriceps strengthening, activity modification
  - indications
    - first-line of treatment
  - outcomes
    - favorable, but less so than nonoperative management for SONK
Operative
- diagnostic arthroscopy
  - indications
    - remove small, unstable fragments from the joint
- core decompression
  - indications
    - extra-articular lesions
- osteochondral allograft
  - indications
    - large symptomatic lesions in younger patients that failed nonoperative management
- total knee arthroplasty (TKA)
  - indications
    - large area of involvement
    - collapse
    - osteonecrosis in multiple compartments

(SAE07PE.30) A 12½-year-old boy reports intermittent knee pain and limping that interferes with his ability to participate in sports. He actively participates in football, basketball, and baseball. He denies any history of injury. Examination shows full range of motion without effusion. Radiographs reveal an osteochondritis dissecans (OCD) lesion on the lateral aspect of the medial femoral condyle. MRI scans are shown in Figures 14a and 14b. Initial treatment should consist of Review Topic

QID: 6090

FIGURES:

activity modification

82%

(94/115)

arthroscopic evaluation of fragment stability.

11%

(13/115)

transarticular drilling of the lesion with 0.045 Kirschner wire.

(2/115)

arthroscopic excision of the fragment and microfracture of underlying cancellous bone.

(3/115)

excision of the fragment and mosaicplasty.

(2/115)

ML 1

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