Patellofemoral Complications Associated With Total Knee Arthroplasty

Patellofemoral complications once accounted for as much as 50% of complications after total knee arthroplasty (TKA). These statistics come from arthroplasties performed in the 1980s and early 1990s. With improvements in surgical technique and prosthetic design, the incidence has decreased, but it is still significant. Problems include pain after an unresurfaced patella, maltracking, fracture, prosthetic loosening, osteonecrosis, and prosthetic wear.

One of the persistent controversies in TKA is whether the patella requires resurfacing. I had more than 40 years of experience working with this question. In 1973, most prosthetic designs did not provide for even the possibility of patellar resurfacing of either the trochlea or patella. In 1974, a prosthesis we used in the form of the duopatellar design provided a femoral component with a trochlear flange and an optional polyethylene button for the patellar side of the patellofemoral joint. At that time, 80% of our patients had rheumatoid arthritis. In 1974, we resurfaced only 5% of the patellae in both patients who had rheumatoid arthritis and those with osteoarthritis. The patellae that were resurfaced were the ones having severe degenerative changes with exposed patellar bone at the time of arthrotomy. A 5-year review showed that 10% of the patients with rheumatoid arthritis had secondary degeneration of the patella with cystic changes, pain, swelling, and sometimes the recurrence of rheumatoid synovitis ( Fig. 5.1 ). By the end of the 1970s agreement was uniform within our group to resurface the patella in all patients with rheumatoid arthritis regardless of the operative findings.

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Secondary degeneration of an unresurfaced patella in rheumatoid arthritis.

Even in retrospect, we could not predict which patients with rheumatoid arthritis would have problems. I do not mean to say that an unresurfaced patella in these patients will always encounter difficulty. I have some patients with rheumatoid arthritis without a resurfaced patella who still functioned well without patellofemoral symptoms more than 30 years after surgery.

Patients with osteoarthritis fared better than those with rheumatoid arthritis ( Fig. 5.2 ). Patients who did have secondary degeneration of the patella after TKA usually had a slight maltracking problem. The result would be areas of focal wear causing pain and possibly leading to progressive degeneration of the bone and progressive subluxation ( Fig. 5.3 ). From this experience I developed certain selection criteria in the 1980s that led to selective patellar resurfacing in approximately 80% of patients with osteoarthritis and left 20% of patellae unresurfaced. The indications for not resurfacing included noninflammatory osteoarthritis, which meant that patients with gout, pseudogout, or an inflamed knee synovium were always resurfaced. In addition, patients not resurfaced would need to have congruent tracking of the patella on the preoperative skyline with maintenance of a joint space. No areas of exposed eburnated bone would be present at surgery. The unresurfaced patella would also have to track congruently with the trochlear flange of the prosthesis. Using these selection criteria, the 10-year survivorship of unresurfaced patellae was 97%. On the other hand, resurfaced patellae from that era were experiencing a higher incidence of complications, including accelerated wear of a metal-backed patella, potential wear and deformation of an all-polyethylene patella, patella stress fracture, and prosthetic loosening.

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Twenty-year follow-up of an unresurfaced patella in osteoarthritis.

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Subluxation of an unresurfaced patella with point contact and wear (arrow).

Second-decade evaluation of results showed that some patients with unresurfaced patellae could develop significant symptoms as late as 15 years after their arthroplasty and require secondary resurfacing. At the same time, improvements in prosthetic design and surgical technique were diminishing the complications seen with resurfacing. In a personal review of 4993 consecutive posterior cruciate ligament (PCL)-retaining primary knee arthroplasties at mean follow-up of 15 years, I found that 7 of 178 knees (4%) that had not been resurfaced required secondary resurfacing. In contrast, only 9 of 4815 resurfaced patellae required reoperation. Further, four had the fixation lugs shear off, three had loosened, one had fractured, and one suffered clunk syndrome (see the following section).

Another potential issue when the patella has not been resurfaced is that pain occurring in an unresurfaced knee might be wrongfully attributed to the patellofemoral compartment. Unnecessary and unhelpful repeat surgery to resurface the patella could occur. This potential scenario prompted me to eliminate older patients and those with very low pain thresholds from the group that I might have previously left unresurfaced. For this reason, my incidence of not resurfacing the patella diminished to less than 2% of cases. If I did not resurface the patella, it was after a careful preoperative discussion with the individual patient about the pros and cons of this decision.

The advantages of not resurfacing are the conservation of patellar bone, avoiding resurfacing complications, easy salvage, and permitting high patellofemoral forces to be placed on this articulation without concern for prosthetic wear in active patients. The disadvantages are the possibility of incomplete pain relief and that updated long-term comparative reoperation rates for resurfacing favor resurfacing in most patients.

The ideal candidate for nonresurfacing is probably the young, heavy, active male patient ( Fig. 5.4 ). When considering not resurfacing the patella, always remember that the prosthetic geometry of the trochlear flange of the prosthesis can make a difference. Obviously a flange that is not anatomic or is flat will not tolerate an unresurfaced patella as easily as one that is anatomic in shape. The reported results of nonresurfacing must also be considered to be prosthesis specific and not necessarily generic.

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Preoperative skyline view of an ideal candidate for nonresurfacing.

Excessive Valgus Placement of the Femoral Component

Even if the surgeon counteracts valgus placement of the femoral component with some varus placement of the tibial component, correcting overall limb alignment, a valgus femoral component can compromise patellar tracking. The valgus placement shifts the most proximal portion of the trochlear flange medially so that the patella may not even be centered on the groove in full extension ( Fig. 5.5 ).

Patella Alta

Patella alta can affect tracking in a similar manner. In this situation, the patella is positioned higher than the top of the prosthetic trochlear flange in full extension and may not be funneled properly into the groove of the trochlea. The predicament of patellar tracking is accentuated when the trochlear flange of the prosthesis is both narrow and shallow ( Fig. 5.6 ).

Component Malrotation

Internal rotation of either the femoral or the tibial component can promote maltracking. On the femoral side this is caused because with internal rotation of the femoral component the trochlear groove is moved medially away from the natural mediolateral position of the patella. I believe the effect of internal rotation of the femoral component on patellar maltracking may be overestimated. Depending on prosthetic geometry, it takes approximately 4 degrees of rotation of the femur to move the trochlear groove 2 mm. The amount of internal rotation required to have a significant effect on patellar tracking therefore will have to be quite excessive ( Fig. 5.7 ).

In addition, the effect of internal femoral component rotation can be counteracted by undersizing the patellar component and shifting it medially and by moving the femoral component as far laterally on the distal femur as possible (as long as prosthetic overhang is not created). The major importance of femoral component rotation is to assist in the establishment of flexion gap symmetry. The technical details of determining femoral component rotation are discussed in detail in Chapter 2 .