The patella, commonly known as the kneecap, is a small, flat bone located at the front of the knee joint. The patella is the largest sesamoid bone in the human body, embedded within the quadriceps tendon. It serves two main functional purposes. First, it acts as a bony shield to protect the delicate structures within the knee joint from direct trauma. Second, it enhances the mechanical leverage of the quadriceps muscle, making the extension and straightening of the leg more efficient. A patellar fracture occurs when this bone breaks, compromising the knee’s ability to function properly.
Immediate Signs and Symptoms
A patellar fracture usually produces unmistakable signs immediately following the trauma. The most prominent symptom is the sudden onset of severe, sharp pain directly over the front of the knee. This is often followed quickly by significant swelling and bruising around the joint as blood from the fractured bone collects inside the knee capsule, a condition known as hemarthrosis.
The most telling sign of a serious fracture is the inability to straighten the leg or lift the foot while the heel rests on the floor. This failure indicates that the extensor mechanism has been compromised by the break. In more severe cases, a visible gap or defect in the kneecap may be felt through the skin, confirming that the bone fragments have been pulled apart.
How Doctors Classify and Diagnose the Break
Diagnosis begins with a physical examination where a doctor assesses the knee for swelling, bruising, and the ability to perform a straight leg raise. The physician may also feel the edges of the fractured bone fragments through the skin, especially if the pieces are separated. Imaging studies are then used to confirm the diagnosis and determine the specific pattern of the break.
Standard X-rays taken from multiple angles are the primary diagnostic tool, allowing the doctor to view the alignment and severity of the fracture. In cases where the bone is shattered or the fracture extends into the joint surface, a Computed Tomography (CT) scan may be used to provide a more detailed, three-dimensional view. Patellar fractures are classified based on the alignment of the bone fragments and the pattern of the break:
- Nondisplaced fractures (stable fractures) mean the bone pieces remain closely aligned, typically separated by only a millimeter or two.
- Displaced fractures involve a separation of the fragments by more than a few millimeters, or a step-off in the joint surface.
- Comminuted fractures are complex breaks where the patella is shattered into three or more pieces.
- A transverse fracture runs horizontally across the kneecap, dividing it into two main segments.
Treatment Options for Patellar Fractures
The chosen treatment method depends on the fracture classification and whether the extensor mechanism remains intact. For nondisplaced fractures where the broken pieces are still in contact and the patient can perform a straight leg raise, non-surgical treatment is recommended. This approach involves immobilizing the leg in a cast or brace, usually locked in a straight position, to allow the bone to heal.
Immobilization generally lasts for about four to six weeks, determined by follow-up X-rays showing signs of bone healing. During this period, weight-bearing may be restricted or allowed only with the knee kept straight to prevent forces that could displace the fracture.
Surgical treatment is necessary for displaced fractures, comminuted breaks, or any fracture that disrupts the extensor mechanism. The primary goal of surgery is to precisely realign the bone fragments, restore the smooth articular surface of the knee joint, and securely hold the pieces together. Common surgical techniques include using tension band wiring, where wires and pins are configured to convert the pulling force of the quadriceps muscle into a compressive force.
In cases of highly comminuted fractures, a surgeon may remove fragments too small to be fixed and repair the remaining tendon. Surgical fixation allows for earlier initiation of motion, which is crucial for preventing long-term stiffness. The hardware used in the fixation often needs to be removed in a second procedure months later due to the irritation it can cause under the skin.
Rehabilitation and Return to Function
The recovery process following a patellar fracture relies heavily on a structured physical therapy (PT) program. Immobilization, while necessary for healing, causes the knee joint to become stiff and the quadriceps muscles to weaken rapidly. Rehabilitation is therefore focused on systematically addressing both of these issues.
Physical therapy begins with regaining a functional range of motion (ROM) in the knee, starting with gentle passive and active-assisted exercises. This is quickly followed by strengthening exercises, such as straight leg raises and isometric quadriceps contractions, to rebuild lost muscle power. The timeline for returning to full activity varies, but most patients can expect to resume normal daily activities within three to six months.
Even after successful treatment, some individuals may face long-term issues such as persistent knee stiffness or chronic pain, especially when the quadriceps muscle is activated. Damage to the cartilage covering the back of the patella can also lead to post-traumatic arthritis years later, a common complication after any joint fracture. Strict adherence to the physical therapy regimen is the most important factor for maximizing the chance of a successful recovery and minimizing the likelihood of long-term functional limitations.