Patients with Spontaneous Osteonecrosis of the Knee are Not Characterized By Elevated Levels of Thrombophilia-Associated Factors

Purpose: Spontaneous Osteonecrosis of the Knee (SONK) is considered the most prevalent type of knee osteonecrosis but the pathophysiology of SONK is unclear. The purpose of this study was to test whether patients with SONK are characterized by abnormal levels of thrombophilia-associated factors.

Methods: 21 Patients were recruited from a tertiary sports and knee clinic. Inclusion criteria were: (1) Age > 40 years; (2) acute onset knee pain which was not precipitated by trauma; (3) physical examination demonstrating localized tenderness and pain elicited by percussion over one of the knee condyles (either medial or lateral); and (4) MRI findings consistent with SONK. Exclusion criteria were Factors described as possibly associated with secondary osteonecrosis. All patients underwent blood tests for thrombophilia-associated factors. Thrombophilic profile was based on published recommendations for laboratory tests screening related to thrombophilia, and included: (1) Functional antithrombin; (2) functional protein C; (3) free protein S; (4) activated protein C resistance; (5) factor V Leiden; and (6) mutation G-20210-A of the prothrombin gene; (7) Levels of Lupus anticoagulant (LA) - Russell viper venom test (RVVT) and a Silica Clotting Time (SCT); (8) anticardiolipin antibodies (aCL) - IgG and IgM; (9) beta-2 glycoprotein I antibodies - IgG and IgM; (10) Prothrombin time/INR (PT); (11) activated partial thromboplastin time (aPTT), and (12) plasma Fibrinogen levels.

Results: There were 13 (62%) men and 8 (38%) women. Patient age was median 66 years (range, 44-77 years). Thrombophilia-associated factor levels fell within norm limits with the exception of very minimally elevated Fibrinogen level in one patient who had 579 mg/dL and another 5 patients who had up to 421 mg/dL compared to normal upper limit defined as 400 mg/dL.

Conclusion: Patients with SONK are not characterized by abnormal pro-thrombotic profile as indicated by a battery of genetic and acquired thrombophilia-associated factors. Therefore, thrombophilia screening is not justified in this debilitating illness, and future research should explore alternative associated factors which may assist in planning prevention and treatment strategies.