Jess H. Lonner, MD

Am J Orthop. 2001;30(9):713-714

Abstract

Figure 1. Postoperative axial radiograph in a patient who underwent successful total knee arthroplasty, but continued to have anterior knee pain and crepitus. Note the articulation between the lateral edge of the patella and the femoral prosthesis. This patient was successfully treated with patellar revision with a larger prosthesis and patellar chamfering.

Derangement of the anterior compartment of the knee can cause patellofemoral dysfunction in up to 50% of secondary surgeries after total knee arthroplasty. A technique of patellar chamfering is described that can minimize the risk of anterior knee pain from lateral patellar impingement without compromising bone stock for future operations.

Patellofemoral dysfunction continues to be a relatively common complication after total knee arthroplasty despite design modifications and technical advancements. Derangement of the anterior compartment of the knee is the culprit in up to 50% of secondary surgeries after total knee arthroplasty.^1,2

Patellar implants vary in sizes and shapes. Arguments are available to support use of differing designs, whether onlayed or inset. It is well recognized that medialization of the patellar component in total knee arthroplasty may facilitate proper patellar tracking. At times, the medial-lateral dimension of the native patella may be considerably larger than the dimensions of the prosthetic patellar button.³ This mismatch may result in bony impingement of the uncovered lateral portion of the resurfaced patella on the femoral trochlea, causing anterior knee pain with routine activities (Figure 1).

This problem may be avoided by chamfering of the uncovered portion of the lateral patella. The patellar bed is prepared in a standard fashion if one chooses the onlay method of patellar resurfacing rather than the inset method of resurfacing. A transverse cut is made from the medial facet to the lateral facet, removing approximately 10 mm of articular surface.

An appropriately sized patellar template is applied to the prepared bone bed and lug holes are made, securing the trial button, in a slightly medialized position. The lateral edge of the trial component is then traced and patellar tracking assessed (Figure 2). The exposed lateral bony edge can then be obliquely chamfered with a saw or rasp to ensure that impingement of the uncapped lateral bed is avoided (Figure 3).

Figure 2. (A through D) Technique of "patellar chamfering." The lateral edge of the patellar button trial is traced to demarcate the extent of uncapped bone. Chamfering is performed with a saw or a rasp.

Figure 3. Postoperative axial radiograph showing a chamfered patella with cemented button.

This technique is an effective prophylactic measure that can easily be used during the time of total knee arthroplasty to minimize the risk of anterior knee pain from lateral patellar impingement without compromising bone stock for future potential operations.

Acknowledgment

The author wishes to note that he is a paid consultant for DePuy Orthopaedics, Inc.

References

1.	Brick GW, Scott RD. The patellofemoral component in total knee arthroplasty. Clin Orthop. 1988;231:163-178.
2.	Lynch AF, Rorabeck CH, Bourne RB. Extensor mechanism complications following total knee arthroplasty. J Arthroplasty. 1987;2:135-140.
3.	Sato T, Lew WD, Gustilo RB. The incidence, cause, and long term course of anterior knee pain after cemented total knee arthroplasty. Proceedings of the Annual Meeting of the American Academy of Orthopaedic Surgeons, Orlando, Florida, March, 2000.

Dr. Lonner is Assistant Professor of Orthopaedic Surgery, University of Pennsylvania School of Medicine, Pennsylvania Hospital, Philadelphia, Pennsylvania.