Case Author(s): J. Philip Moyers, MD , 9/30/95 . Rating: #D2, #Q4

Diagnosis: Osteonecrosis, right lateral femoral condyle

Brief history:

Worsening right knee pain.

Images:

Anterior and posterior whole body bone images

View main image(bs) in a separate image viewer

View second image(bs). Lateral and medial views of the right knee

View third image(xr). Current plain films of the knees, AP view

View fourth image(xr). Anterior view of the right knee, approximately 10 months previous

Full history/Diagnosis is available below

Diagnosis: Osteonecrosis, right lateral femoral condyle

Full history:

72-year old woman who had medial and lateral meniscectomy of the right knee by arthroscopic surgery. The patient developed acute onset of pain six months later with increasing difficulty walking since that time. Plain films were obtained for evaluation followed by bone scintigraphy.

Radiopharmaceutical:

21.6 mCi Tc-99m MDP i.v.

Findings:

Bone scintigraphy demonstrates increased activity in both the medial and lateral condyles of the right femur. The activity in the lateral femoral condyle is greater than that in the medial condyle. Otherwise, no abnormal uptake is demonstrated throughout the remainder of the skeleton. Comparison with the bone radiographs obtained the same day, as well as comparison with a prior pre-operative radiograph demonstrates an area of sclerosis and flattening in the lateral femoral condyle with an osteochondral defect. This is a dramatic change from the normal pre-operative radiographs. In this patient population with this history, findings of osteonecrosis are suggested.

Discussion:

This patient had no pre-disposing risk factors for avascular necrosis. Osteonecrosis is usually seen in older patients and is distinct from osteochondritis dissecans, which occurs in adolescence. The vast majority of patients demonstrate changes involving the weight bearing surfaces of the medial femoral condyle with involvement of the lateral femoral condyle seen less frequently. Meniscal tears have been reported in association with this pathologic entity. This patient had a meniscectomy six months earlier.

Reference: Resnick D. Bone and joint imaging. WB Saunders & Co. 1989

Followup:

Plain film correlation of the bone scintigraphy suggests osteonecrosis involving the lateral femoral condyle of the right femur.

Major teaching point(s):

Increased activity in the lateral femoral condyle is demonstrated in the same region as sclerosis on the plain films. However, increased activity also is demonstrated in the medial femoral condyle, which likely represents subradiographic osteonecrosis.

ACR Codes and Keywords:

References and General Discussion of Bone Scintigraphy (Anatomic field:Skeletal System, Category:Effect of Trauma)

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Case number: bs038

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