**3.3**

Typically the syndrome appears 4 – 6 month after knee replacement surgery but the cases have been reported almost up to 4 years after surgical intervention. Posterior stabilized Knees are the ones that are commonly affected possibly due to nature of its design. The cases have been reported in cases where patella have been resurfaced and also in the cases where patella has not been resurfaced. The diagnosis is a clinical one, and the impressive clunking and jumping of the involved patella can often be seen or heard across the examining room. The fibrous nodule tends to lodge into the femoral component intercondylar notch during flexion and displaces with an audible and often painful clunk at approximately 30° to 45° from full extension. The diagnosis can be reached based on the history and clinical examination although some surgeons may use a Doppler ultrasound to confirm the diagnosis.

This condition was first described by Insall in 1982 who termed it as "peripatellar nodule" caused by peripatellar soft-tissue impingement against the anterior margin of the intercondylar box of the femoral component". The term "patellar clunk syndrome" however was coined by Hozack in 1989 who described the pathology as a prominent fibrous nodule at the junction of the proximal patellar pole and the quadriceps tendon which wedged into the inter-condylar notch during flexion and dislodged during extension, generating the symptoms. Thorpe and Bocell described a syndrome of similar presentation in 1990. The symptoms they described were "painful and usually visible popping, catching, or locking in the patello-femoral articulation as the knee was brought from flexion to extension." They used the term "tethered patella syndrome" to describe this condition. Condition described by Insall, Hozack, and Thorpe is within the spectrum of the same disease entity. It was caused by peripatellar fibrous hyperplasia, especially prominent in the suprapatellar region and the lateral parapatellar gutter. It was actually a spectrum of disease, which ranged from

The exact cause of patellar clunk syndrome had not been identified. Most authors believed that it was multi-factorial. The design of prosthesis, extent of surgical trauma, change in joint line, patellar height, patellar thickness, and abnormal patellar tracking has been proposed as possible causes. The presence of unilateral patellar clunk syndrome in a patient with bilateral TKA of the same prosthesis provided a good model in examining this complex situation as some of the variables were controlled (i.e. same patient, same disease, and same prosthesis). The presence of excessive peri-patellar fibrosis is a prerequisite of this

Patellofemoral synovial hyperplasia is a less well-described syndrome, characterized by a more diffuse proliferation of tissue proximal to the patella. Symptoms include pain and crepitus, most prominent during active knee extension from a 90° flexed position during stair climbing or rising from a chair. Knee range of motion (ROM) tends not to be affected

Typically the syndrome appears 4 – 6 month after knee replacement surgery but the cases have been reported almost up to 4 years after surgical intervention. Posterior stabilized Knees are the ones that are commonly affected possibly due to nature of its design. The cases have been reported in cases where patella have been resurfaced and also in the cases where patella has not been resurfaced. The diagnosis is a clinical one, and the impressive clunking and jumping of the involved patella can often be seen or heard across the examining room. The fibrous nodule tends to lodge into the femoral component intercondylar notch during flexion and displaces with an audible and often painful clunk at approximately 30° to 45° from full extension. The diagnosis can be reached based on the history and clinical examination although some surgeons may use a Doppler ultrasound to

**3. Patella clunk syndrome** 

**3.1** 

syndrome.

**3.2** 

**3.3** 

confirm the diagnosis.

painful crepitation to full-blown patellar clunk syndrome.

and the lack of a discrete "clunk" is also criterion for this diagnosis.

Fig. 8. Arrow denoting a narrow hair thin lucent line at the superior pole of patella. Also note that patella at the lower pole is thicker than the upper pole

Fig. 9. Arthroscopic image of the nodule at the superior pole of the patella.

## **3.4 Causes of patellar clunk syndrome**


Arthroscopy Following Total Knee Replacement 249

Fig. 10. Arthroscopic sequence of resection of the nodule.

Fig. 11. Appearance after resection of the nodule
