Whether to resurface the patella in TKA remains controversial [19]. A cost-effectiveness analysis demonstrated the superiority of resurfacing over retention of the patella [20]. On the other hand, selectively not resurfacing the patella appeared to yield similar results compared with routine resurfacing [21]. The main feature of the modern prosthesis is the modification of the femoral component, which includes a deeper and more extensive femoral trochlear groove and a smoother intercondylar box transition zone. The new design aims―at least theoretically―to reduce the incidence of patellar crepitus and AKP. Most previous research investigating the advantages of the femoral implant design modification only recruited patients who underwent TKA with patellar resurfacing [10-12]. To our knowledge, the present investigation was the first prospective study to compare the incidence of AKP and patellar crepitus in patients who underwent TKA without patellar resurfacing.
A meta-analysis showed that there was no relationship between cartilage condition and AKP [22]. Because this study did not resurface the patella and Vahur Metsna et al. [18] found that the cartilage damage to the patella may be correlated with postoperative AKP, we also matched patellar cartilage grade between our two groups. The clinical outcomes measured according to KSS at the 1-year follow-up were consistent with the outcomes reported by Ranawat et al. [11]. Carey et al. [12] suggested better outcomes at the 6-month follow-up; however, we did not find differences at the 3-month and 1-year follow-ups, which may have been due the different measured scores in the study by Carey et al. (i.e., Western Ontario and McMaster Universities Osteoarthritis Index, Oxford Knee, and Short-form-12 scores), or simply a temporary advantage existed at this period but disappeared at 1 year. Nevertheless, these results may indicate that this femoral implant design modification had no significant influence on clinical outcomes of TKA with or without patellar resurfacing at the short-term follow-up.
Results of this study indicated that the ATTUNE group had a lower incidence of AKP, similar to the study by Ranawat et al. [11]. However, AKP incidences of 3.5% and 13.5% (ATTUNE and P.F.C. Sigma Knee Systems, respectively) were obviously lower than the incidences of AKP reported by Ranawat et al. (12.5% and 25.8%, respectively). Asian patients tend to exhibit a longer duration of knee osteoarthritis. Prolonged pain often results in an increase in pain tolerance; therefore, Asian patients may be not as sensitive to pain as those in developed countries. In previous research involving Japanese patients who underwent TKA, the incidence of AKP was also low (6.5%) [23]. In addition, the incidence of AKP in the ATTUNE group was only approximately one-quarter of that in P.F.C. Sigma group (3.5% vs 13.5%), this ratio was lower than in the study by Ranawat et al. (12.5% vs 25.8%) [11]. A previous study noted that severe AKP can lead to patient dissatisfaction following primary TKA, and revision was often required [24]. In the present study, no patient underwent secondary patellar replacement. Furthermore, we recorded the state of movement when pain occurred for the assessment of AKP and found that it mainly occurred when ascending and/or descending stairs or squatting; it was rare that an individual reported pain while at rest or walking on flat ground. A sharp increase in pressure on the patella when ascending or descending stairs or squatting may be the underlying reason for a higher level of AKP. We assessed the degree of the pain using a VAS and found that two knees that underwent TKA using the PFC Sigma Knee Systems experienced moderate pain, which had a certain degree of impact on quality of life. In contrast, no patients using the ATTUNE Knee System experienced pain. The remainder of patients who experienced pain in our study reported it to be mild at the 2-year follow-up and it had little impact on the quality of life. These results may indicate that TKA without patellar resurfacing benefits from this femoral implant design modification with regard to AKP.
In the present study, the incidence of patellar crepitus at 1 year (10.6% and 28.9% in ATTUNE and P.F.C. Sigma groups, respectively) was similar to the incidences reported by Ranawat et al. (17.7% and 30.9%, respectively) [11]. In addition, we found that the patellar creptius occurred at 3 months postoperatively. A previous analysis of posterior-stabilized TKAs revealed that the mean time to the diagnosis of patellar crepitus was approximately 10 months [25], which may suggest that patellar crepitus occurred at an earlier stage in TKA without patellar resurfacing. However, it does not affect the quality of life of patients given the level of reported satisfaction.
We acknowledge that the present study had several limitations. First, it was not blinded and randomized; therefore, bias cannot be excluded as a confounding variable. However, we managed to prospectively match demographic data between cases and controls. Second, the sample size was calculated using a power analysis because no published data regarding TKA without patellar resurfacing were available for this study. Third, we did not enrol patients who underwent TKA with patellar resurfacing. Future studies should compare AKP and patellar crepitus and include both patients who undergo TKA with or without patellar resurfacing in the same study. Some have suggested that surgical technique, more size options, and rotation of the femoral component may also lead to these differences. As such, further research investigating these factors should be performed [26].
In conclusion, patients who underwent TKA without patellar resurfacing benefited from this femoral implant design modification with regard to AKP and patellar crepitus. This study may provide meaningful information to surgeons who use the ATTUNE Knee System and selectively omit resurfacing the patella in their patients.