“Bone on bone” in the knee describes a condition where the protective cartilage within the joint has significantly worn away, causing direct contact between the ends of the bones. This severe cartilage loss is often associated with advanced osteoarthritis. This article explores the nature of this condition and why it causes pain.
Understanding “Bone on Bone” in the Knee
The knee joint is a complex structure involving three main bones: the femur (thigh bone), the tibia (shin bone), and the patella (kneecap). These bones meet at the knee, forming a hinge-like joint that facilitates movements like walking and squatting. The ends of these bones are covered by articular cartilage, a smooth, flexible, and tough tissue that acts as a natural buffer, reducing friction and absorbing shock during movement.
When someone refers to “bone on bone” in the knee, it signifies a state where this articular cartilage has severely degraded or is completely absent. Without this protective layer, the bony surfaces of the femur and tibia, and sometimes the patella, can rub directly against each other.
The most common cause for this severe cartilage degradation is osteoarthritis (OA), a progressive degenerative joint disease. In OA, the cartilage gradually thins, frays, and roughens over time, eventually leading to its complete erosion. This process can be influenced by factors such as aging, repetitive stress on the joint, obesity, and genetic predisposition.
The Mechanisms Behind Bone-on-Bone Knee Pain
While articular cartilage itself contains no nerve endings, its absence in “bone on bone” knees leads to several pain-generating mechanisms.
Synovitis
One mechanism is the inflammation of the joint lining, known as synovitis. When bones rub together, it irritates the synovial membrane, which produces lubricating fluid for the joint. This irritation can cause the synovium to become inflamed and swollen, leading to persistent pain and stiffness.
Subchondral Bone Changes
Another source of pain arises from changes in the underlying subchondral bone, the bone located just beneath the cartilage. This subchondral bone is richly innervated with sensory nerve endings. When the protective cartilage is lost, increased pressure and abnormal forces are directly transmitted to this nerve-rich bone, activating these pain receptors. Damage to the subchondral bone can also result in conditions like bone marrow edema (fluid buildup) and subchondral cysts, which further contribute to pain.
Bone Spurs (Osteophytes)
The body may also attempt to repair the damaged joint by forming bone spurs, or osteophytes, along the margins of the joint. These bony growths are the bone’s reaction to abnormal movement and excess friction. While bone spurs do not always cause symptoms, they can scrape against surrounding tissues, leading to additional inflammation and pain, or even impinge on nearby nerves.
Muscle Spasms and Weakness
Muscle spasms and weakness can also contribute to the pain experienced with bone-on-bone knees. The body may react to joint instability and discomfort by tensing muscles around the knee, leading to spasms. Over time, this continuous strain can result in muscle fatigue and weakness, further impacting joint function and increasing pain.
Approaches to Managing Bone-on-Bone Knee Pain
Managing bone-on-bone knee pain involves a combination of non-surgical and surgical strategies to alleviate discomfort and improve joint function. Non-surgical approaches are typically the first line of treatment.
Non-Surgical Approaches
Non-surgical options include:
- Lifestyle Modifications: Weight management reduces the load on the knee. Low-impact exercises like walking, bicycling, or water aerobics strengthen muscles and improve flexibility.
- Physical Therapy: Exercises strengthen muscles around the joint, increase flexibility, and reduce pain. Therapists also guide proper movement mechanics.
- Pain Relief Medications: Over-the-counter nonsteroidal anti-inflammatory drugs (NSAIDs) or topical creams are frequently used. Prescription medications may also be recommended.
- Injections: Corticosteroid injections reduce inflammation, and hyaluronic acid injections restore cushioning and lubrication.
- Assistive Devices: Canes or walkers take pressure off the knee. Knee braces provide external stability by shifting weight away from damaged areas.
Surgical Options
When non-surgical treatments do not provide sufficient relief, surgical options may be considered. Knee arthroscopy is a minimally invasive procedure to remove loose fragments of cartilage or bone, or trim irregular cartilage surfaces. For younger individuals with localized damage, an osteotomy may realign the knee joint by shifting weight to a healthier part, potentially delaying total knee replacement. The most definitive solution for severe bone-on-bone knee pain is total knee replacement (arthroplasty), which replaces damaged bone and cartilage with artificial components, eliminating bone-on-bone friction.
When to Seek Professional Medical Advice
It is advisable to consult a healthcare professional if you experience persistent or worsening knee pain that impacts your daily activities or sleep. Seek medical attention if the pain is accompanied by significant swelling, redness, or warmth in the joint. Immediate medical evaluation is necessary if you notice an inability to bear weight on the knee, a sensation of the knee locking or giving way, or if the knee appears bent or deformed. Prompt diagnosis and management can lead to improved outcomes.