Where Are We Now?
The surgical options for treating the patella in TKA include routine resurfacing, routine nonresurfacing, and selective resurfacing. A recent meta-analysis  of resurfacing versus nonresurfacing found that resurfacing is associated with less anterior knee pain than non-resurfacing. However, resurfacing requires the surgeon to remove a substantial amount of patellar bone. During revision TKA, loss of patellar bone stock can result in inability to perform patellar component revision and require leaving the remaining patellar bone unresurfaced, patellectomy, or may result in extensor mechanism disruption, which are often associated with considerable functional impairment . While revision implants and techniques for the femur and tibia are readily available, revision options to treat a loose or worn resurfaced patella are more limited.
Patellar nonresurfacing retains viable patellar bone stock and subsequent secondary resurfacing is relatively straightforward and easily performed in symptomatic patients. Nonresurfacing also is appealing in younger patients who may anticipate more than one revision TKA in their lifetimes. Other indications not to resurface that are used by surgeons who perform selective resurfacing may include the absence of patellar arthritis and thin patellae . Since nonresurfacing has been associated with more-frequent anterior knee pain than resurfacing, circumferential electrocautery to denervate the patella may improve anterior knee pain after TKA. However, the current study  indicates patellar cauterization resulted in no difference in pain and functional scores in patients with simultaneous, bilateral, primary TKA who had patellar non resurfacing with electrocautery treatment on one knee but not the contralateral side. The indications for selective patellar resurfacing or nonresurfacing have not been well established, and the rates of patellar resurfacing or nonresurfacing vary widely among surgeons .
Where Do We Need To Go?
Selective resurfacing or selective non-resurfacing implies that specific patients are better suited for one treatment or the other. What is missing on this topic is a clear understanding of which patient demographic and anatomical characteristics are associated with favorable and unfavorable long-term extensor mechanism function, amount of anterior knee pain, and need for additional patellar or extensor mechanism surgery after resurfacing or nonresurfacing.
Treatment of the patella in TKA should be based on a risk-benefit ratio. However, there are a number of gaps in our knowledge that make it difficult to know with precision exactly how to calculate that ratio. The benefits of resurfacing and non-resurfacing have been better established than the risks of each treatment. Which patients develop catastrophic problems such as patella fracture and extensor mechanism disruption that can occur many years after resurfacing? Which patients require secondary resurfacing due to persistent anterior knee pain after non resurfacing? Since the indications for selective resurfacing or nonresurfacing are often based on patient age, bone quality, patellar size, and patellar arthritis these characteristics should be included in studies of extensor mechanism function and complications after TKA.
How Do We Get There?
Patellar complications, particularly after resurfacing, may develop many years after TKA. Therefore, long-term studies of patellar resurfacing and nonresurfacing that include specific demographics and anatomical considerations which may potentially influence the long-term outcome of treatment of the patella should be analyzed. Large tertiary care centers which have joint registries and treat patients for both primary and subsequent revision TKA may be best equipped to provide information about how the treatment of the patella during primary TKA affects the integrity of the extensor mechanism and results of revision TKA. Single institution databases should be able to provide data on patellar size, severity of patellar arthritis, patellar bone quality, gender, age and BMI which may influence the long-term survivorship of the extensor mechanism after resurfacing or non-resurfacing.
Many single cohort TKA studies with non-resurfaced patella as well as comparative studies of patellar resurfacing to nonresurfacing have been reported. Specific anatomic patellar characteristics such as severity of patellar arthritis, patellar size, and bone quality could provide additional important information to determine the risk factors associated with need for secondary resurfacing.
1. Budhiparama NC, Hidayat H, Novito K, Utomo ND, Lumban-Gaol I, Nelissen R. Does circumferential patellar denervation result in decreased knee pain and improved patient-reported outcomes in patients undergoing non-resurfaced, simultaneous, bilateral total knee arthroplasty? Clin Orthop Relat Res. [Published online ahead of print]. DOI: 10.1097/CORR.0000000000001035
2. Maney AJ, Koh CK, Frampton CM, Young SW. Usually, selectively, or rarely resurfacing the patella during primary total knee arthroplasty: Determining the best strategy. J Bone Joint Surg Am.
3. Maradit-Kremers H, Haque OJ, Kremers WK, Berry DJ, Lewallen DG, Trousdale RT, Sierra RJ. Is selectively not resurfacing the patella an acceptable practice in primary total knee arthroplasty? J Arthroplasty. 2017;32:1143-1147.
4. Tang XB, Wang J, Dong PL, Zhou R. A Meta-analysis of patellar replacement in total knee arthroplasty for patients with knee osteoarthritis. J Arthroplasty. 2018;33:960-967.
5. Tetreault MW, Gross CE, Yi PH, Bohl DD, Sporer SM,4, Della Valle CJ. A classification-based approach to the patella in revision total knee arthroplasty. Arthroplast Today. 2017;3:264-268.