Excising the soft tissues may help avoid the nodular formation of patellar clunk

Arthroscopic debridement may not be successful in all cases of this mostly design-related problem.

Issue: February 2009

Research has indicated that patellar clunk syndrome most commonly occurs with earlier posterior-stabilized designs which can result in fibrous nodules in the suprapatellar region of the knee.

At the 25th Annual Current Concepts in Joint Replacement Winter 2008 Meeting, Thomas P. Sculco, MD, said that excision of all synovial, fibrous and fatty tissue in the suprapatellar region may help prevent the nodular formation and noted that arthroscopic debridement may not be successful in all cases.

Thomas P. Sculco

“This is mainly a design-related problem,” Sculco said. “There is a significant reduction in the incidence of this problem with a change in the design of the implant — there have been less lateral releases, less anterior crepitus, less arthroscopic surgery — and this has helped tremendously. If you have the problem, arthroscopic management is the way to go. Although, advise your patients that not everyone does well when this occurs.”

Design

Earlier posterior-stabilized total knee arthroplasty (TKA) designs could cause quadriceps tendon irritation above the patella which could lead to the development of nodules in the suprapatellar portion of the knee, Sculco said. With the knee extended, these nodules sit in the suprapatellar region. But, when the knee is flexed, the nodules can extend into the patellofemoral joint. In the most severe cases, the patella can dislocate.

“Now, there is no question that it is an implant design-related problem, and this has been demonstrated in a number of studies,” Sculco said. “But, the biggest offender in terms of the development of patellar clunk was the original IB (Insall-Burstein, Zimmer) posterior-stabilized knee.”

He noted that the implant had a nonanatomic design and was not amenable to the patella or the soft tissues above the patella. However, design modifications made the current posterior-stabilized designs more anatomic. These designs feature deeper patellar grooves that extend to the intercondylar notch which give the patella a better tracking surface, he said.

In a study comparing TKAs using the older, Insall-Burstein II posterior-stabilized design and a newer posterior-stabilized design, Sculco and his colleagues found an 18% incidence of anterior crepitus with the older design and a 5% rate with the newer, anatomic design.

“Additionally, the need for arthroscopic debridement for patellar clunk in the IB series was 4% and 0.3% with the newer design demonstrating that a modification of design, looking at patella kinematics, essentially eliminated the problem,” he said.

Sculco also cited a study conducted by David Ip, MD, which compared the results of 238 total knees performed with either the NexGen Legacy (Zimmer) or the Insall-Burstein II systems. The 2-year follow-up revealed no cases of patellar clunk with the NexGen Legacy system and a 7.5% rate with the older device.

Prevention

“In terms of prevention, I think that it is important to debride the soft tissues and fat, particularly the in the suprapatellar area,” Sculco said. While the nodules can be large, they can be easily removed in a 15- to 20-minute procedure using a shaver.

Sculco noted that researchers investigating arthroscopic debridement in 18 cases of patellar clunk reported an 82% success rate, while a study examining the treatment in all comers found a 42% success rate.

“When you advise your patients, [tell them that] if you have this problem, not everybody is successfully treated and sometimes they will reoccur,” he said. Sculco also cited research by John L. Beight, MD, and colleagues which found four recurrences out of 11 arthroscopic debridements for the problem.

For more information:

Thomas P. Sculco, MD, can be reached at the Hospital for Special Surgery, 5535 E. 70th St., New York, NY 10021; 212-774-2478; e-mail: tpstkr@aol.com. His institution receives research support from Exactech Inc., Smith & Nephew and Zimmer.

References:

Beight JL, Yao B, Hozack WJ, et al. The patellar “clunk” syndrome after posterior stabilized total knee arthroplasty. Clin Orthop Rel Res. 1994;299:139-142.

Ip D, Wu W, Tsang W. Composition of two total knee prostheses on the incidence of patella clunk syndrome. Int Ortho. 2002;26:48-51.

Maloney WJ, Schmidt R, Sculco TP. Femoral component design and patellar clunk syndrome. Clin Orthop Rel Res. 2003;410:199-202.

Sculco TP. Avoiding patellar clunk & crepitus: How loud the sound. Paper #121. Presented at the 25th Annual Current Concepts in Joint Replacement Winter Meeting. Dec. 10-13, 2008. Orlando, Fla.