Can alendronic acid (bisphosphonate) cause spontaneous osteonecrosis of the knee?

Alendronic Acid and Spontaneous Osteonecrosis of the Knee

Alendronic acid (a bisphosphonate) has not been established as a cause of spontaneous osteonecrosis of the knee (SONK), but may actually be used as a treatment option for this condition.

Understanding SONK and Bisphosphonate Effects

Spontaneous osteonecrosis of the knee (SONK), also referred to more recently as spontaneous insufficiency fracture of the knee (SIFK), is characterized by:

• Subchondral fracture with bone marrow edema visible on MRI
• Primarily affects the medial femoral condyle
• More common in middle-aged and older patients, with higher prevalence in females 1
• Can progress to collapse of the affected bone and subsequent osteoarthritis

Bisphosphonate Relationship with Osteonecrosis

While bisphosphonates have been associated with osteonecrosis of the jaw (ONJ), there is no established causal relationship between alendronic acid and SONK in the medical literature. In fact:

1. Bisphosphonates as treatment: Recent evidence suggests bisphosphonates may be beneficial in treating SONK by reducing bone edema and pain 2, 3

2. Known bisphosphonate adverse effects: Guidelines consistently mention ONJ as a rare complication of bisphosphonate therapy (incidence <1 case per 100,000 person-years) 4, but do not identify SONK as a known adverse effect

3. Atypical fractures: Long-term bisphosphonate use has been associated with atypical subtrochanteric femoral fractures, but not specifically with SONK 4

Treatment Approach for SONK

Current treatment options for SONK include:

Non-surgical Management

• Protected weight-bearing with knee bracing
• NSAIDs and analgesics for pain control
• Bisphosphonates: Zoledronic acid and alendronate have shown efficacy in reducing bone edema and pain in SONK 2, 3

Surgical Management (for advanced cases)

• Arthroscopic debridement
• Core decompression
• Osteochondral autograft
• High tibial osteotomy
• Unicompartmental or total knee arthroplasty for end-stage disease 3

Bisphosphonate Safety Considerations

When using bisphosphonates, clinicians should be aware of established adverse effects:

• Gastrointestinal symptoms with oral formulations 4
• Osteonecrosis of the jaw (rare, <1 case per 100,000 person-years) 4
• Atypical femoral fractures with long-term use 4
• Flu-like symptoms with IV administration 4
• Hypocalcemia with zoledronic acid 4

Clinical Implications

1. For patients with SONK: Bisphosphonates may be considered as part of treatment rather than avoided

2. For patients on long-term bisphosphonate therapy: Regular monitoring for known adverse effects is recommended, but SONK is not an established concern

3. Administration guidelines: When prescribing oral alendronate, patients should take it with a glass of water after an overnight fast, remain upright for 30 minutes, and wait at least 30 minutes before food, drink or other medicines 4

Conclusion

Based on current evidence, alendronic acid has not been established as a cause of spontaneous osteonecrosis of the knee. In fact, bisphosphonates including alendronic acid may be beneficial in treating SONK by reducing bone marrow edema and associated pain. Clinicians should focus on monitoring for established adverse effects of bisphosphonates while considering their potential therapeutic role in SONK management.