A chipped bone in the knee typically refers to an osteochondral fracture, an injury where a piece of the joint surface breaks away. This fragment includes the smooth, protective articular cartilage and a layer of the underlying subchondral bone. If the fragment completely detaches and floats freely within the joint space, it is often called a “loose body.” These injuries commonly occur due to acute, high-impact trauma, such as a forceful twisting motion during sports activities. Another frequent cause is a sudden kneecap dislocation, where the kneecap strikes the femoral condyle, shearing off a piece of the joint surface. Because this damage affects the joint’s load-bearing surfaces, prompt medical evaluation is required to determine the extent of the injury and establish a treatment plan.
Symptoms and Medical Diagnosis
Patients with an osteochondral fracture often present with immediate, significant knee pain and noticeable swelling, often due to bleeding into the joint space (hemarthrosis). The injury commonly causes mechanical symptoms, which are the most debilitating sign of a loose fragment. These symptoms include the knee “catching,” “giving way,” or locking up, especially when attempting to fully extend or bend the leg. Pain is frequently aggravated by weight-bearing activities, and the patient may have a decreased range of motion.
Diagnosis begins with a thorough physical examination to assess swelling, stability, and tenderness. Initial imaging involves plain X-rays, which clearly reveal the bony component of the fracture, especially if the fragment is large or calcified. X-rays may miss the fracture if the chip is composed primarily of cartilage with only a small piece of bone.
A Magnetic Resonance Imaging (MRI) scan is often necessary to fully evaluate the injury, as it provides detailed images of the soft tissues. The MRI assesses the integrity of the articular cartilage, determines the size and location of the fragment, and checks for associated injuries like ligament tears. A Computed Tomography (CT) scan may also be used to better visualize the precise location and orientation of the bony fragment, aiding in surgical planning. These scans help the physician determine if the fragment is stable (in place) or unstable (loose), guiding the choice between conservative and surgical management.
Conservative Treatment Approaches
Conservative management is typically pursued when the osteochondral fragment is small, stable, non-displaced, or located in a non-weight-bearing area. The initial approach focuses on reducing inflammation and protecting the joint. This often involves the RICE protocol: Rest, Ice, Compression, and Elevation. Rest is achieved by limiting weight-bearing on the injured leg, usually with crutches, to prevent compression forces from displacing the fragment.
Immobilization is used to restrict motion, placing the knee in a brace or cast for a specific period to allow the fragment to heal. During this phase, the patient may be prescribed non-steroidal anti-inflammatory drugs (NSAIDs) to manage pain and swelling. The length of immobilization varies and is determined by follow-up imaging that confirms early signs of healing.
Physical therapy begins during the conservative phase, often starting with exercises to maintain range of motion in the hip and ankle, and isometric exercises for the thigh muscles. Once permitted, therapy progresses to protected weight-bearing and controlled range-of-motion exercises to prevent joint stiffness. The goal of this non-operative route is to allow the bone and cartilage to spontaneously heal without surgery, which is more likely in skeletally immature patients.
Procedures for Surgical Repair
Surgical intervention is generally recommended when the bone chip is large, unstable, or causes recurring mechanical symptoms like locking, to prevent progressive joint degeneration. Most surgical treatments are performed using arthroscopy, a minimally invasive technique involving small incisions and a camera to visualize the joint. The specific procedure chosen depends on the size and condition of the fragment.
For small, detached fragments not suitable for reattachment, the simplest procedure is loose body excision, where the surgeon removes the chip from the joint space. If the fragment is large (greater than one centimeter), relatively fresh, and contains both bone and cartilage, the surgeon may attempt internal fixation. This involves securing the fragment back into its original position using small metal screws, pins, or bioabsorbable devices to promote healing.
If a significant piece of articular cartilage is missing or badly damaged, the surgeon must address the defect to restore a smooth joint surface.
Cartilage Repair Techniques
For smaller defects, microfracture is a common approach, where small holes are drilled into the exposed bone to stimulate bleeding and create a “super-clot.” This clot forms fibrocartilage, a repair tissue that provides a protective coating but is not as durable as the original hyaline cartilage. For larger defects, procedures like the Osteochondral Autograft Transfer System (OATS) may be used. This involves transplanting plugs of healthy bone and cartilage from a less weight-bearing area of the knee to the damaged site.
Recovery and Physical Therapy
The success of the long-term outcome relies heavily on a structured rehabilitation program, regardless of whether treatment involved conservative immobilization or surgical repair. The initial recovery timeline varies substantially; simple arthroscopic loose body removal might allow walking within a week, while fixation or cartilage repair procedures require a much slower progression. Patients undergoing fixation or regenerative procedures are often restricted from weight-bearing for several weeks to months to protect the healing site.
Physical therapy is critical for restoring full joint function, beginning with regaining the knee’s full range of motion without compromising the repair. This early phase includes passive and active assisted range-of-motion exercises, often utilizing continuous passive motion (CPM) machines. As healing progresses, the focus shifts to a strengthening program for the muscles surrounding the knee, including the quadriceps and hamstrings, to stabilize the joint and restore endurance.
The later rehabilitation phase focuses on achieving full knee extension, improving balance through proprioception training, and gradually reintroducing weight-bearing activities like stationary cycling. A safe return to high-impact activities or sports is the final milestone, determined by the physician based on the patient’s demonstrated strength, stability, and lack of symptoms. Potential complications include persistent joint stiffness or the risk of re-injury if activities are resumed too quickly.