When a joint is described as “bone on bone,” it means that the cartilage protecting the ends of the bones has worn away almost entirely, a condition medically defined as severe osteoarthritis (OA) or Kellgren-Lawrence Grade 4. This advanced stage of joint degeneration typically results in intense pain and significantly limited mobility. In seeking relief, many individuals encounter “gel injections,” which is the common term for viscosupplementation, a medical procedure involving the injection of hyaluronic acid into the joint space. This treatment is often explored as a way to manage symptoms before considering a major surgical procedure.
Understanding Viscosupplementation Injections
Viscosupplementation involves introducing a gel-like substance, hyaluronic acid (HA), directly into the joint cavity. HA is a naturally occurring component of synovial fluid, where it acts as a lubricant and shock absorber. In an osteoarthritic joint, the concentration and quality of natural HA decline, reducing the fluid’s ability to protect joint structures.
The injected HA aims to restore the natural viscoelastic properties of the joint fluid, providing better lubrication and cushioning. Beyond mechanical action, the substance is also thought to have biological effects, including anti-inflammatory properties that reduce swelling and pain. Some evidence suggests that exogenous HA may stimulate the body’s native joint cells, called synoviocytes, to produce more of their own hyaluronic acid.
This treatment differs from corticosteroid injections, often called “steroid shots.” Corticosteroids deliver an anti-inflammatory agent to rapidly reduce localized swelling and pain, with effects lasting weeks to a couple of months. Viscosupplementation is a non-steroidal treatment that takes longer to achieve its full effect (often several weeks), but its benefits can last for up to six months or more.
Assessing Efficacy for Severe Joint Damage
The core question regarding viscosupplementation is its effectiveness in joints with severe, bone-on-bone damage. Clinical evidence suggests that the efficacy of these injections decreases significantly as the severity of osteoarthritis increases. The treatment is most effective in patients with mild-to-moderate OA, where substantial cartilage remains.
In a severely degenerated joint, the mechanical environment is altered, and the injected fluid has little remaining tissue to protect. The structural defects and high friction of bone-on-bone contact are a challenge that lubrication alone cannot overcome. This lack of cartilage space limits the fluid’s ability to provide meaningful cushioning or properly distribute the load across the joint.
Despite diminished returns, some patients with severe osteoarthritis (Kellgren-Lawrence Grade 4) may still experience clinically relevant pain relief and improved function. However, the magnitude of improvement is lower compared to patients with less advanced disease. For these individuals, the treatment temporarily manages pain and delays the need for a more invasive procedure.
Determining Patient Suitability
Viscosupplementation is positioned in the treatment hierarchy after conservative measures have failed but before surgical intervention is necessary. The ideal candidate has symptomatic mild-to-moderate OA and has not found adequate relief from first-line treatments, such as physical therapy, weight management, and nonsteroidal anti-inflammatory drugs (NSAIDs). The goal is to provide a safe, non-surgical option that improves quality of life and delays progression to end-stage treatments.
Patient suitability also depends on factors like age, activity level, and health. For younger, active individuals with earlier-stage OA, the treatment may maintain function and mobility. Conversely, patients with severe joint instability or significant joint effusions may not be suitable candidates, as mechanical issues or inflammation could compromise the injection’s effectiveness.
Treatment Alternatives When Injections Are Ineffective
When viscosupplementation fails to provide lasting relief for bone-on-bone pain, the strategy must pivot to options designed for end-stage joint disease. For most patients with severe, chronic pain and functional limitation, the most definitive treatment is total joint replacement, or arthroplasty. This surgery removes the damaged joint surfaces and replaces them with prosthetic components, successfully eliminating bone-on-bone friction and restoring function.
Advanced Non-Surgical Options
Advanced non-surgical and minimally invasive alternatives may be considered before or in place of total joint replacement. These include pain management techniques like radiofrequency ablation, which temporarily deactivates the nerves transmitting pain signals from the joint. Some patients also explore regenerative medicine therapies, such as platelet-rich plasma (PRP) or stem cell injections, although their long-term effectiveness for severe OA remains under research.