What are the other Names for this Condition? (Also known as/Synonyms)

• Ahlback Disease
• Primary Osteonecrosis of the Knee
• SONK (Spontaneous Osteonecrosis of the Knee)

What is Spontaneous Osteonecrosis of the Knee? (Definition/Background Information)

• Osteonecrosis (or avascular necrosis) is a serious bone disorder characterized by the temporary or permanent disruption of blood supply to the bone, which causes cells and tissues within the affected bone to die. In many, osteonecrosis affects the ends of the long bones in the body and the knee is a common location
• Spontaneous Osteonecrosis of the Knee (SPONK or SONK) is the most common form of knee osteonecrosis. The condition is more often diagnosed in older adults than other age groups. In almost all cases, only one knee is involved. In a vast majority of cases, SPONK involves the medial femoral condyle (the bony prominence of the thigh bone, at the knee end)
• Spontaneous Osteonecrosis of the Knee is said to occur from bone disease causing osteopenia or osteoporosis and insufficiency fractures involving the subchondral bone (the bone layer lying immediately beneath the cartilage). A weak bone from bone density loss is prone to breakage on application of normal stresses; such fractures are termed insufficiency fractures
• Individuals, who develop Spontaneous Osteonecrosis of the Knee, begin to experience sudden pain within the affected bone/joint. This may be accompanied by tenderness, swelling, and reduced range of knee joint movement
• Treatment associated with Spontaneous Osteonecrosis of the Knee includes both nonsurgical and surgical methods. With early diagnosis and appropriate treatment, the prognosis is usually good. However, the prognosis also depends upon the severity of the condition and its early diagnosis

Who gets Spontaneous Osteonecrosis of the Knee? (Age and Sex Distribution)

• Spontaneous Osteonecrosis of the Knee is mostly observed after the age of 55-60 years, in older adults
• Females are affected more than males in a 3:1 ratio
• All racial and ethnic groups are at risk for SPONK and no predilection is observed

What are the Risk Factors for Spontaneous Osteonecrosis of the Knee? (Predisposing Factors)

The risk factors associated with Spontaneous Osteonecrosis of the Knee may include:

• Any bone disease causing reduced bone strength or bone density, which include osteopenia and osteoporosis
• Torn meniscus: A common knee injury that occurs when the cartilage that provides a cushion between the thighbone and shinbone tears

It is important to note that having a risk factor does not mean that one will get the condition. A risk factor increases one’s chances of getting a condition compared to an individual without the risk factors. Some risk factors are more important than others.

Also, not having a risk factor does not mean that an individual will not get the condition. It is always important to discuss the effect of risk factors with your healthcare provider.

What are the Causes of Spontaneous Osteonecrosis of the Knee? (Etiology)

• Spontaneous Osteonecrosis of the Knee is reported to develop as a result of subchondral bone insufficiency fracture, which occurs from weak bones (from osteoporosis). The knee end of the thigh bone is typically affected in SPONK
• Due to such insufficiency fractures, there is a collection of fluid around the bone marrow and consequently, reduced blood supply to the region. This results in cell and tissue death and osteonecrosis

What are the Signs and Symptoms of Spontaneous Osteonecrosis of the Knee?

The signs and symptoms of Spontaneous Osteonecrosis of the Knee may be mild or severe and can vary from one individual to another. Initially, there may not be any noticeable symptoms.

The signs and symptoms of Spontaneous Osteonecrosis of the Knee may include:

• Noticeable pain and tenderness in the affected bone; often, there is a sudden onset of pain
• Initially, the pain does not increase on touch or upon applying pressure to the point
• However, the pain increases when weight/pressure is applied to the bone
• Pain while sleeping
• The pain may be either dull or sharp and shooting pain
• Swelling of tissue around the affected kneecap or knee joint
• Decreased range of motion of the affected joint/bone
• During the later stages, osteophytes or bony projections may form around the affected knee region. These lesions may range in size from 2-5 cm or may even be larger

How is Spontaneous Osteonecrosis of the Knee Diagnosed?

Diagnostic methods that a physician may use to help diagnose Spontaneous Osteonecrosis of the Knee include:

• Physical examination and evaluation of medical history
• Assessment of the signs and symptoms
• Functional evaluation of the affected knee joint
• Tests and procedures to diagnose any underlying condition, if any
• X-ray of the knee: X-rays can help the physician rule-out other possible causes of knee discomfort. During the early stages of osteonecrosis, it is difficult to locate the appearance of any abnormal bone changes. However, X-rays can usually identify the presence of osteonecrosis during the later stages
• Magnetic resonance imaging (MRI) of the knee joint: An MRI is an imaging technique that creates images of soft tissues and bones, which helps detect any bone abnormalities during the early stages of osteonecrosis
• Bone scan: A bone scan is a diagnostic method used to identify any bone abnormalities by injecting tiny amounts of radioactive material into the bloodstream
• Computerized tomography (CT) of the knee joint: A CT scan takes a series of X-ray images from several different angles, which are then merged to create cross-sectional images of bones and soft tissues of the body. This allows a physician to examine the bone or joint and its surrounding structures

Many clinical conditions may have similar signs and symptoms. Your healthcare provider may perform additional tests to rule out other clinical conditions to arrive at a definitive diagnosis.

What are the possible Complications of Spontaneous Osteonecrosis of the Knee?

The complications associated with Spontaneous Osteonecrosis of the Knee may include:

• Further deterioration of the involved bone; if left untreated, the bone or joint may collapse
• Immobility of the affected knee
• Walking difficulties, walking with a limp
• Chronic disability
• Recurrence of the condition
• Complications that may arise from surgery to the knee

How is Spontaneous Osteonecrosis of the Knee Treated?

The treatment of Spontaneous Osteonecrosis of the Knee includes non-surgical and surgical methods and may depend on the severity of the condition (mild or severe). A healthcare provider may start with non-surgical treatment methods before adopting surgical procedures and techniques. These include:

• Applying ice to the region can help with pain and reduce swelling
• Avoiding further stress/weight on the involved knee, such as by using a pair of crutches; preventing further bone damage
• Non-steroidal anti-inflammatory oral medications, such as ibuprofen and naproxen, may be used to help decrease pain and swelling
• Use of bisphosphonate medications help in slowing or preventing progression of the condition
• Medications for osteonecrosis may decrease the progression of this condition
• Corticosteroid injections help provide temporary relief of symptoms and in improving the range of motion. It is important to note that corticosteroid injections may only give temporary relief. Prolonged episodes of such injections can injure the joints in the long-run
• Electrical stimulation therapy to aid in the growth of the affected bone
• After the symptoms has decreased, it is important to begin some light motion exercises.  Physical therapy may help restore strength, as well as provide flexibility to the muscles

Surgical treatment measures include:

• High tibial osteotomy: The affected bone is surgically removed/cut and reshaped or realigned; usually, in younger patients
• Core decompression: Core decompression is used to treat early-stage osteonecrosis. In this surgical procedure, the pressure within the bone is decreased by removing a part of the bone causing the abnormal pressure
• Partial or total replacement of the involved joint: The involved joint is replaced through a surgical procedure using a prosthetic implant. A physician will recommend this surgical procedure, if the condition is limited to a certain portion of the joint
• Total knee arthroplasty: In total knee arthroplasty, the involved joint cartilage is completely removed. It is then replaced by a metal and plastic prosthetic implant. This surgical procedure is recommended if the entire joint is acutely affected
• Cartilage grafting: Cartilage grafting is a surgical procedure to replace the damaged cartilage, which may be damaged due to osteonecrosis, or any traumatic injury
• Bone grafting or osteochondral autografting: It is a technique that involves removing a healthy bone from within the body and replacing the affected bone
• Knee arthroscopy: Arthroscopic surgery is a minimally invasive surgical procedure that is used to visualize, diagnose, and repair the knee joint using small instruments
• Meniscus repair: Meniscus repair is a minimally invasive surgical technique that uses suturing (stitching) to repair torn meniscus

How can Spontaneous Osteonecrosis of the Knee be Prevented?

A few recommendations to help prevent Spontaneous Osteonecrosis of the Knee include:

• Preventing osteoporosis through regular exercise and a balanced diet
• Increased dietary intake of calcium and vitamin D
• Avoid excessive intake of alcoholic beverages
• Monitor long-term consumption of steroidal medications
• Individuals, who participate in any high-risk sports, such as football or hockey, should wear appropriate safety equipment to help prevent a serious injury

What is the Prognosis of Spontaneous Osteonecrosis of the Knee? (Outcomes/Resolutions)

• If treated early, a high percentage of individuals who develop Spontaneous Osteonecrosis of the Knee may show an improvement and experience favorable outcomes; the bone may rebuild itself
• In general, the amount of bone damaged by this condition significantly affects its prognosis. A delay in treatment or an absence of treatment can severely affect the prognosis and cause functional loss of the involved bone

Additional and Relevant Useful Information for Spontaneous Osteonecrosis of the Knee:

The following DoveMed website link is a useful resource for additional information:

https://www.dovemed.com/health-topics/orthopedc-disorders/