What could be cause of sudden osteonecrosis in knee?

DEAR DR. ROACH »

I am a 69-year-old Caucasian woman with newly found necrosis of the knee bone, along with a fracture. I do not have diabetes, but I received a month of steroids last November when I had COVID. I also use Adair daily for asthma. I am scheduled for total knee replacement this coming October. My primary care doctor, my orthopedist and my knee surgeon do not know how this occurred. I would like to know so that I might be able to prevent it from happening in the future. I felt fine until after a long walk three months ago. I’ve had to use a cane for walking ever since, and am unable to walk very far, due to pain.

— S.R.

DEAR READER » Osteonecrosis, also called avascular necrosis, literally means “death of bone.” The top of the femur in the hip is the most common bone affected, but many other bones can be affected.

I can’t say for sure what caused your knee bone osteonecrosis, but there are three possibilities I’d consider.

The first is the steroids you took when you had COVID-19. Moderately strong evidence shows that steroids, such as dexamethasone, reduce the risk of dying in hospitalized people with COVID who have low oxygen levels (94% or lower). Unfortunately, the dose of steroids used, although it may have been lifesaving, does put people at higher risk for developing osteonecrosis.

In my opinion, this is the most likely cause.

A second possibility is a rare condition called “spontaneous osteonecrosis of the knee.”

This essentially “unknown cause” tends to affect a specific part of the knee (the medial femoral condyle).

The third possibility I’d consider would be the COVID-19 itself. I found a case series of people with osteonecrosis that occurred in people with COVID-19 infection. Their doses of steroids were not high. However, all these cases were in the hip, not the knee.

This is not a complete list.

Trauma to the knee, excess alcohol use, smoking, radiation treatment and osteoporosis medications (when used for a very long time) all can predispose to osteonecrosis.