The Centers for Advanced Orthopaedics
Maryland Orthopedic Specialists
A Division of The Centers for Advanced Orthopaedics
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Knee

Osteonecrosis of the Knee

Osteonecrosis of the knee occurs when bone tissue in the knee loses its blood supply and begins to die. If undetected and untreated, the overlying articular cartilage collapses along with the necrotic bone, producing a permanent arthritic lesion. Early diagnosis — often by MRI before any X-ray changes appear — is the key to maximally effective treatment. Maryland Orthopedic Specialists diagnoses and manages osteonecrosis of the knee across the full spectrum of disease, from early-stage preservation to partial or total knee arthroplasty for end-stage collapse.

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What is osteonecrosis of the knee?

Spontaneous osteonecrosis of the knee (SONK) — also called SPONK — is the most common form. It typically involves the medial femoral condyle of older women (median age ~65), presenting as sudden-onset medial knee pain without a preceding traumatic event.

Spontaneous osteonecrosis of the knee (SONK) — also called SPONK — is the most common form. It typically involves the medial femoral condyle of older women (median age ~65), presenting as sudden-onset medial knee pain without a preceding traumatic event. SONK is now understood to represent insufficiency-type subchondral stress fractures in bone made fragile by osteoporosis, rather than true avascular necrosis with vascular disruption.

Secondary osteonecrosis is related to identifiable risk factors — corticosteroid use, alcohol abuse, sickle cell disease, lupus, or prior meniscal surgery — and can affect any condyle. It tends to affect younger patients and is more often multifocal.

Both forms progress through stages:

  • Early (Stage I–II): MRI shows bone marrow edema and a necrotic lesion; X-rays are normal or subtly abnormal.
  • Advanced (Stage III): Subchondral collapse (crescent sign or flattening visible on X-ray).
  • End-stage (Stage IV): Full-thickness articular cartilage collapse and secondary osteoarthritis.

Treatment options

Early Stage (I–II): Bone-Preservation Strategies

When osteonecrosis is caught before subchondral collapse, joint-preserving treatment offers the best chance of halting progression. Core decompression — drilling one or more channels through the femoral neck into the necrotic zone — reduces intraosseous pressure, improves blood flow, and stimulates healing. Bisphosphonates such as alendronate (Fosamax) should be discontinued, as they impair the bone remodeling necessary for recovery; other medications associated with osteonecrosis, including chronic corticosteroids, should be reduced or eliminated in coordination with the prescribing physician. Protected weight-bearing during the healing phase is essential to prevent collapse of the softened subchondral bone.

Surgical Procedure

Total Knee Replacement

Complete resurfacing of the knee joint — femur, tibia, and patella — with metal and polyethylene implants to eliminate arthritis pain and restore mechanical alignment. Performed at a hospital facility with full inpatient support services.

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Partial Knee Replacement (Unicompartmental)

Resurfacing of only the damaged compartment of the knee — medial, lateral, or patellofemoral — while preserving the intact ligaments and articular cartilage in the remaining healthy compartments.

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Frequently Asked Questions

Is SONK related to AVN of the hip?
Not directly. While both involve subchondral bone death, SONK is now understood to primarily represent subchondral insufficiency fractures rather than the ischemic osteonecrosis seen in the femoral head. The treatment principles overlap for advanced disease (arthroplasty) but differ early.
How quickly does osteonecrosis of the knee progress?
Prognosis depends on lesion size. Small lesions (< 40% of condylar width) often resolve or stabilize with protected weight-bearing. Large lesions frequently progress to collapse within months, making prompt diagnosis and treatment critical.
What are the treatment options for osteonecrosis of the knee, and do I need surgery?
Treatment depends on the stage and size of the lesion. In early or small lesions, non-surgical management — including protected weight-bearing with crutches, pain medication, and monitoring with serial MRIs — can allow the bone to heal. If the lesion is larger, involves a significant portion of the weight-bearing surface, or has progressed to collapse, surgical options such as core decompression, osteotomy, or partial/total knee replacement may be necessary. Your MOS surgeon will stage the disease on imaging and match the treatment plan to your specific situation.
Can osteonecrosis of the knee be caused by medications or other medical conditions?
Yes. Secondary osteonecrosis of the knee can be triggered by corticosteroid use (even short courses at high doses), excessive alcohol consumption, blood clotting disorders, sickle cell disease, and certain autoimmune conditions. Spontaneous osteonecrosis of the knee (SONK), which typically affects older women, is now thought to be related to an underlying insufficiency fracture rather than true vascular compromise. Understanding the cause helps guide treatment and reduces the risk of the condition developing in the opposite knee.
What is the long-term outlook for my knee after osteonecrosis?
Long-term outcomes depend heavily on the stage at diagnosis and the size of the affected area. Small lesions detected early, particularly those in SONK, often stabilize and allow patients to maintain good knee function for many years. Larger lesions that have progressed to joint surface collapse carry a higher risk of developing secondary arthritis, which may eventually require knee replacement. At MOS we use close imaging follow-up to detect any progression early, giving us the best opportunity to intervene before significant joint damage occurs.

Meet the specialists

Christopher S. Raffo, MD

Christopher S. Raffo, MD

Orthopedic Surgery · Sports Medicine

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James S. Gardiner, MD

James S. Gardiner, MD

Orthopedic Surgery · Sports Medicine

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John J. Christoforetti, MD

John J. Christoforetti, MD

Orthopedic Surgery · Sports Medicine · Hip Preservation Surgery

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Brian McCormick, MD

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Medically reviewed by Christopher S. Raffo, MD
Last reviewed June 15, 2026

References

  1. Ahlbäck S, Bauer GC, Bohne WH. Spontaneous osteonecrosis of the knee. Arthritis Rheum. 1968;11(6):705–733. https://doi.org/10.1002/art.1780110606
  2. Yamamoto T, Bullough PG. Spontaneous osteonecrosis of the knee: the result of subchondral insufficiency fracture. J Bone Joint Surg Am. 2000;82(6):858–866. https://doi.org/10.2106/00004623-200006000-00009
  3. Lotke PA, Abend JA, Ecker ML. The treatment of osteonecrosis of the medial femoral condyle. Clin Orthop Relat Res. 1982;171:109–116. https://doi.org/10.1097/00003086-198211000-00020
  4. Breer S, Oheim R, Krause M, et al. Spontaneous osteonecrosis of the knee (SPONK). Semin Arthritis Rheum. 2013;42(4):420–427. https://doi.org/10.1016/j.semarthrit.2012.07.004
  5. American Academy of Orthopaedic Surgeons. Osteonecrosis of the Knee. OrthoInfo. https://orthoinfo.aaos.org/en/diseases--conditions/osteonecrosis-of-the-knee/