To resurface or not to resurface the patella remains a controversy in TKA [16]: cost-effectiveness analysis showed superiority of the resurfacing compared to retention of the patella [17]; on the other hand, selectively not resurfacing the patella seemed to provide similar results compared with routine resurfacing [18]. Most previous researches concerning about advantages of the femoral implant design modification only recruited patients who underwent TKA with patella resurfacing [9–11]. To our knowledge, this is the first prospective study to compare the incidence of AKP and patellar crepitus in patients who underwent TKA without patella resurfacing.
Since this study did not resurface the patella and the condition of cartilage of patella correlates with postoperative AKP [15], we also matched patellar cartilage grade between the two groups. The clinical outcomes measured by KSS at one-year follow-up were consistent with Ranawat et al.’s study [10]. However, as Carey et al. suggested better outcomes at six-month follow-up, we did not find the differences at three-month and one-year follow-up, this may due the different measured scores in Carey et al.’ study (WOMAC, Oxford Knee and SF–12 scores), or just a temporary advantage existed at this period but disappeared at one year. Above all, these results may indicate that there was no significant influence of this femoral implant design modification on clinical outcomes of TKA with or without patella resurfacing at short time follow-up.
In this study, the results indicated that the ATTUNE group had a lesser incidence of AKP, as same as Ranawat et al.’s study. However, 3.5% and 13.5% of AKP (ATTUNE and PFC Sigma knee systems, respectively), was obviously lower than 12.5% and 25.8% of AKP in Ranawat et al.’s study. Asian patients tend to have a longer duration of knee osteoarthritis. Prolonged pain results in an increase in pain tolerance, therefore Asian patients may be not as sensitive to pain as those in developed countries. In a previous research studying Japanese patients who underwent TKA, the incidence of AKP was also at a low level (6.5%) [19]. In addition, the incidence of AKP in ATTUNE group was only about one fourth as that in PFC Sigma group (3.5% vs. 13.5%), this ratio was smaller than that of Ranawat et al.’s (12.5% vs. 25.8%). Previous study noted that severe AKP can cause dissatisfaction in patients following primary TKA, and a revision was often needed [20]. In this study, no patient received 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 climbing up and down stairs or squatting. It was rare when the individual was at rest or is walking on flat ground. A sharp increase of pressure on the patella when climbing up and down the stairs or squatting may be the underlying reason for a higher level of AKP. We recorded the degree of the pain using VAS and found that two cases used PFC Sigma knee systems experienced moderate pain which has a certain degree of impact on life, but none used ATTUNE knee systems experienced this. The rest of the cases experienced pain in our study were mild at two-year follow-up, and had little impact on the life quality. These results might indicate that TKA without patella resurfacing benefit from this femoral implant design modification in the aspect of AKP.
In this study, the incidence of patellar crepitus at 1-year (28.9% and 10.6% in PFC Sigma and ATTUNE groups, respectively) was similar than that in Ranawat et al.’s report (30.9% and 17.7%, respectively) [9]. In addition, we found that the noise occurred at three months postoperatively. A previous patellar crepitus analysis of posterior-stabilized TKAs showed that the mean time for the diagnosis of patellar crepitus was approximately at ten months [21], this may suggest that patellar crepitus occurred at an earlier stage in TKA without patella resurfacing. However it does not affect the life quality of patients considering the satisfactions.
We acknowledged this study had several limitations. First, this study was not blinded and randomized, therefore, bias cannot be excluded as a confounding variable. However we managed to match demographic data between cases and controls prospectively. Second, the sample size was calculated by a power analysis, since no published data concerning TKA without patella resurfacing were available for this study. Third, it did not enroll patients underwent TKA with patella resurfacing. Further study should compare AKP and patellar crepitus include both patients underwent TKA with or without patella resurfacing in the same study. In conclusion, TKA without patella resurfacing benefit from this femoral implant design modification in the aspects of AKP and patellar crepitus. This study may provide meaningful information for surgeons who use ATTUNE knee system and selectively not resurfacing the patella in their patients.