Patellar clunk syndrome is a relatively unusual postoperative complication of resurfaced patella total knee arthroplasty (TKA). It is found that this problem happens more often with the posteriorly stabilized total knee replacement. Patellar Clunk Syndrome is caused by a fibrous nodule at the proximal patella and distal quadriceps tendon. With flexion, this nodule slides into the intercondylar notch, and extension causes it to clunk out.
When the knee is bent and straightened, the patella can be heard and felt to clunk painfully in people with this condition. It is a clunk, like a car stumbling into gear after a long ride, and it is caused by an issue with the patella (kneecap). In certain circumstances, the audible clunk can be heard.
Patellar Clunk Syndrome Symptoms
The patella prosthesis may clunk or catch when the knee is aggressively stretched from a flexed posture, which can be uncomfortable or painful.
Typically, when a patient extends their knee from a fully flexed position, they will have anterior knee pain. As the knee extends, it may clunk painfully or audibly. This clunk can typically be felt and/or heard 30–60 degrees after the complete extension of the joint.
It is possible to have a less severe variant of this disease, which manifests itself as crepitus that may or may not be painful when the knee is stretched from a flexed posture.
The anatomy of the patient and/or the surgical approach and/or materials used by the surgeon to perform the TKA account for the vast majority of the risks involved. These are some of the risk factors:
- Intercondylar box-sized femoral implants.
- TKA with posterior stabilization.
- Components of the femur that are reduced in size and flexed.
- Tibial polyethylene implants that are thicker.
- Insertion of the tibial implant anteriorly.
- Patellar composite thickness reduction.
- Increased post-surgical knee flexion.
- A history of knee surgery.
Although certain risk variables have been established, it is unclear and probably complicated how exactly they affect the disease.
Patellar Clunk Syndrome Causes
The development of a fibrous lump or scar tissue on the back of the quadriceps tendon is the etiology of PCS. In most cases, the nodule will be located just proximal to the base of the patella (the superior pole), and the symptomatic “clunk” is mostly felt when the nodule becomes trapped in the intercondylar gap of the femoral prosthesis during vigorous knee extension.
Although the precise etiology that led to the formation of the nodule is unknown, it is believed that it occurred either as a result of the location of a patellar button when the patella is resurfaced or as a result of the layout and geometry of the intercondylar cut of the femoral prosthesis. Both of these factors are thought to contribute to the development of the nodule.
Patellar Clunk Syndrome Diagnosis
The majority of the diagnosis is made based on a clinical examination. Patellar clunk syndrome radiographic abnormalities comprise patella Baja, a proximally located patellar button, or subluxation or outright displaced patellar component. The soft tissue lesion cannot be accurately defined by conventional radiography.
MRI is the best way to look at native joints because it can look at things from different angles and shows soft tissues better than other methods. Artifacts from the metallic parts of a TKA make traditional MRI imaging problematic. Recent changes to protocols show that MRI is useful for figuring out what’s wrong with painful joints like the hip and knee.
Patellar Clunk Syndrome Treatment
The best course of action is to use a contemporary, well-positioned implant to prevent the development of the clunk in the first place. PCS can be treated by revising (or “fixing”) the knee replacement procedure that was originally performed. In cases where the clunk only sometimes or mildly bothers the patient, surgery is regarded as an unnecessary risk because the discomfort isn’t severe enough.
Surgical excision of the fibrous tissue is typically recommended as the first line of treatment for patellar clunk syndrome. The excision of fibrous tissue is mostly accomplished via open incision or arthroscope.
The deployment of extremely small instruments is required for arthroscopic removal. The keyhole incisions are made by the surgeon, who then places a miniature camera and light source. A sizable screen outside shows the camera feed. The fibrous tissue is subsequently removed through a second keyhole incision using little devices.
The fibrous tissue is cut away during the open removal, which allows the surgeon to closely monitor the process. To access the underside of the quadriceps muscle, the surgeon makes a small incision in the skin and then cuts and separates the tissues. After that, the fibrous tissue is removed. The results of surgery are good, and patients usually say that their symptoms go away.