Table 3. Characteristics of ON after SARS-CoV-2 infection.
| Variables | ON after SARS-CoV-2 infection | Spontaneous ON | Secondary ON |
|---|---|---|---|
| Age | 60.4 years | >55 years | <45 years |
| Gender | M:F = 4:3 | M:F = 1:3 | F > M with SLE |
| M > F with alcohol as associated factor | |||
| Onset of pain | Mainly sudden, 11 weeks after COVID infection | Sudden | Gradual |
| Bilaterality | No | <5% | >80% |
| Location on bone | Epiphysis metaphysis | Epiphysis | Multiple |
| Condylar involvement | One or more, diffuse | One condyle | Epiphysis, metaphysis and diaphysis |
| Femur and tibia affected | 2 of 7 | No | 20% |
| Other joint involvement | Not at the same time | No | >90% (hip, shoulder, ankle) |
| Associate factors | CCS in 4 out of 7 cases | None | CCS, alcohol, tobacco, other |
| Associated disease | COVID | None | SLE, Gaucher’s disease, thrombophilia, sickle cell, Caisson disease |
| MRI features | Diffuse bone marrow edema (mostly in STIR) | Bone marrow edema (STIR, PD, T1) | Signs of AVN, hypointense serpentine line with a well-defined border and a rim or double halo sign, adjacent to the proximal border of the osteonecrotic bone |
| Soft tissue edema | Semi-lunar shaped lesion | ||
| No subchondral bone thickening | Subchondral bone thickening | ||
| Signs of AVN | Peripheral sclerosis |
ON, osteonecrosis; SARS-CoV-2, severe acute respiratory syndrome coronavirus 2; F, female; M, male; SLE, systemic lupus erythematosus; COVID, coronavirus disease; CCS, corticosteroids; MRI, magnetic resonance imaging; STIR, short tau inversion recovery; PD, proton density; AVN, avascular necrosis.