The patella (kneecap) is the largest sesamoid bone in the human body. Embedded within the quadriceps tendon, it functions like a pulley to enhance thigh muscle leverage. Its primary role is to protect the front of the knee joint and act as a fulcrum, increasing the efficiency of the extensor mechanism that allows the leg to straighten.
Because of its exposed location, a patellar fracture typically results from high-energy trauma, such as a direct blow from a fall or an impact during a collision. Less commonly, the fracture can occur indirectly from a sudden, forceful contraction of the quadriceps muscle. When a fracture occurs, the integrity of the knee’s extensor mechanism is compromised, requiring recovery focused on restoring the ability to straighten the leg.
Recognizing the Injury and Initial Diagnosis
A broken kneecap causes intense, acute pain felt directly in the front of the knee. The injury site rapidly develops significant swelling and bruising due to bleeding into the joint space (hemarthrosis). A clear sign of a patellar fracture is the inability to actively straighten the leg or perform a straight leg raise against gravity.
During examination, a healthcare provider checks for a gap or defect felt through the skin between the bone fragments. The inability to fully extend the knee strongly indicates the fracture has disrupted the extensor mechanism, guiding treatment decisions.
Standard X-rays are the primary diagnostic tool, taken from multiple angles (anteroposterior, lateral, and “sunrise” views). These images allow the physician to visualize the fracture location and measure the separation and step-off between fragments. In complex cases, or when assessing soft tissue damage, advanced imaging like a Computed Tomography (CT) scan or Magnetic Resonance Imaging (MRI) may be used to fully define the injury.
Understanding Patellar Fracture Types
Fracture patterns are categorized into types that directly influence knee stability and the treatment plan. The simplest is a non-displaced fracture, where the bone is cracked but fragments remain aligned with minimal separation (often less than two millimeters). In this scenario, the surrounding soft tissues (the extensor retinaculum) usually remain intact, preserving the ability to straighten the leg.
A displaced fracture is a more serious injury, occurring when the bone fragments are pulled apart and misaligned. This separation is caused by the powerful pull of the quadriceps muscle attached to the upper fragment, drawing it proximally, while the patellar tendon pulls the lower fragment distally. Displaced fractures inherently compromise the knee’s extensor mechanism, making surgical intervention necessary to restore function.
The most complex pattern is the comminuted fracture, where the patella shatters into three or more pieces. This type often results from a high-impact direct blow that crushes the bone, leading to a loss of the smooth articular surface required for normal joint movement. The presence of multiple small fragments complicates the surgical repair and may necessitate the removal of bone pieces that are too small to fix.
Treatment Pathways: Surgical versus Non-Surgical
The choice of treatment depends on the fracture type and the integrity of the extensor mechanism. Non-surgical management is reserved for non-displaced fractures where the ability to straight-leg raise is preserved and there is minimal displacement or joint surface step-off. This approach involves immobilizing the leg in a cast or specialized hinged brace locked in full extension for approximately six to eight weeks.
Immobilization prevents movement, allowing the bone to heal while minimizing the risk of fragments separating due to muscle pull. Patients are often permitted to bear weight while wearing the brace, though this restriction is determined by the surgeon based on fracture stability. Regular X-rays are taken to confirm that the bone fragments remain correctly positioned as healing progresses.
Surgical treatment, known as open reduction and internal fixation (ORIF), is necessary for all displaced fractures and most comminuted fractures. The primary goals of surgery are to accurately realign the articular surface of the patella and to secure the bone fragments to restore the function of the extensor mechanism. For transverse fractures, the gold standard technique is tension band wiring, which involves using two parallel Kirschner wires (K-wires) and a figure-eight stainless steel wire.
The figure-eight wire is positioned on the anterior surface of the patella, converting the pulling force (tension) exerted by the quadriceps muscle into a compressive force across the fracture site. This compression promotes bone healing and provides stability for early motion. For severely comminuted fractures, especially those affecting the inferior or superior poles, fixation may be impossible due to the small size of the fragments.
In these instances, a partial patellectomy may be performed, involving the removal of small, damaged bone pieces and reattaching the patellar or quadriceps tendon to the remaining fragment. Total patellectomy (complete removal of the kneecap) is rarely performed but may be necessary for extreme comminution, though it significantly reduces quadriceps muscle strength. The decision to pursue surgery is often made promptly, especially for open fractures where the bone has broken through the skin, to prevent infection.
The Recovery and Rehabilitation Process
Following immobilization or surgical fixation, recovery transitions into the lengthy phase of rehabilitation. The initial period after the cast or brace is removed is characterized by significant knee stiffness and rapid atrophy of the quadriceps muscle. Physical therapy is necessary, beginning with gentle exercises focused on regaining the knee’s range of motion.
The therapy program will gradually advance to strengthening exercises, with a particular emphasis on rebuilding the strength of the quadriceps and surrounding musculature that have been weakened from immobilization. Restoring the ability to bend the knee (flexion) and fully straighten it (extension) is a slow process, but it is necessary to restore a normal gait and function. Patients typically require several months to achieve a functional range of motion and strength.
Complications are common, with many patients experiencing residual stiffness or a permanent loss of full range of motion. The metal hardware used in surgical fixation (such as K-wires and tension bands) can cause local irritation, necessitating a second surgery for removal after healing. Furthermore, cartilage damage on the back of the patella can lead to post-traumatic arthritis, causing long-term pain and stiffness. Full recovery and return to pre-injury activities can take anywhere from six to twelve months, depending on the fracture severity and adherence to rehabilitation.