What is an Insufficiency Fracture of the Knee?
Insufficiency fracture of the knee, also referred to as subchondral insufficiency fracture of the knee (SIFK), is a type of stress fracture that occurs when excessive and repetitive stress is applied to the femoral condyles or tibial plateau of the knee. Insufficiency fractures of the knee are non-traumatic fractures that occur immediately below the cartilage of a joint (subchondral bone). These fractures are seen more frequently in women and affect older patients, usually over the age of 55. If left untreated, insufficiency fracture of the knee can potentially be a devastating condition that may advance rapidly to acute osteoarthritis with articular surface collapse.
Anatomy of the Knee
The knee is made up of the femur (thighbone), tibia (shinbone), and patella (kneecap). The lower end of the femur meets the upper end of the tibia to form the knee joint. A small disc of bone called the patella rests on a groove on the front side of the femoral end. The fibula, another bone of the lower leg, forms a joint with the shinbone. The bones are held together by protective tissues, ligaments, tendons, and muscles. Synovial fluid within the joint aids in the smooth movement of the bones over one another. The meniscus, a soft crescent-shaped area of cartilage between the femur and tibia, serves as a cushion and helps absorb shock during motion.
Causes and Risk Factors for Insufficiency Fracture of the Knee
Some of the common causes and risk factors for developing insufficiency fracture of the knee include:
- Repetitive stress or overuse
- Meniscal tears
- Bone weakness due to osteoporosis
- Knee osteoarthritis
- Osteopenia or low bone mineral density
- Regular cortisone use
- Older adults, specifically postmenopausal and osteoporotic women
Signs and Symptoms of Insufficiency Fracture of the Knee
Signs and symptoms associated with insufficiency fracture of the knee include:
- Acute onset of severe pain in the absence of trauma or following minor trauma
- Accumulation of fluid (edema) within the subchondral bone
- Difficulty walking even short distances as the disease progresses
- Rest typically makes the pain better, but the pain comes back if walking is resumed
- Pain at night
- Joint movement restriction
Diagnosis of Insufficiency Fracture of the Knee
As part of a routine examination, your doctor will review your medical history and symptoms and perform a thorough physical examination. In order to confirm the diagnosis, your physician will order a plain X-ray imaging. In early cases, the X-ray may appear normal. However, in advanced cases, we see a breakdown of the bone with flattening of the knee condyle. If the X-ray appears normal, MRI can identify early changes of swelling or marrow edema within the knee. In more advanced cases, focal areas of osteonecrosis (bone death) can sometimes be seen just underneath the cartilage. Additionally, we might also detect meniscal extrusions, meniscal tears, and knee arthritis. Once diagnosed, your physician will order bone density with a DEXA scan and blood tests to exclude low calcium or vitamin D.
Treatment for Insufficiency Fracture of the Knee
Treatment for insufficiency fracture of the knee can either be surgical or non-surgical, with conservative treatment often being the mainstay of treatment and consisting of pain-relieving medications, rest from weight-bearing activity, and protected weight-bearing with crutches followed by 6 weeks of weight-bearing rest to improve symptoms and promote fracture healing. In the second stage, quadriceps and hamstring exercises are recommended, initially non-weight bearing on machines (side-lying hip abduction, knee curls, and knee extensions), followed by weight-bearing weight training, including Pilates and Yoga. Other conservative treatments may include hyaluronic acid or PRP injections to decrease pain and improve healing.
Surgery is only recommended if symptoms fail to improve with conservative treatment or a late diagnosis or in more advanced cases. Surgical options may include subchondroplasty (where a bone substitute is injected), keyhole surgery with core decompression, or knee replacement.