Frequent complications of deficient patellae after component removal in 1.5-stage exchange arthroplasty for...

To compare the complication rates between deficient patellae (remnant patellae after component removal) and non-resurfaced patellae after 1.5-stage exchange arthroplasty for periprosthetic joint infection and identify risk factors for complications of deficient patellae.

Complications in 76 deficient patellae (group D) and 41 non-resurfaced patellae (group N), with a minimum follow-up of 2 years after 1.5-stage exchange arthroplasty were retrospectively analyzed. Demographic characteristics and mean follow-up period did not differ between the groups. The incidences of patellar maltracking, erosion, and fractures were investigated. Factors affecting each patellar complication in group D were investigated in terms of age, sex, body mass index, postoperative hip-knee-ankle angle (HKA), remnant patellar thickness, and change in joint line height.

The incidence of patellar maltracking and erosion was significantly higher in group D than in group N [maltracking: 16 (21.1%) vs. 0 cases (0%), p = 0.001; erosion: 30 (39.5%) vs. 2 cases (4.9%), p < 0.001]. The incidence of patellar fractures tended to be higher in group D [6 (7.8%) vs. 0 cases, p = 0.090]. In group D, postoperative valgus limb alignment and younger age were identified as significant factors that affected patellar maltracking (odds ratio of postoperative HKA = 1.628, p = 0.005) and erosion (odds ratio of age = 0.909, p = 0.009), respectively.

Close observation of the complications of deficient patellae is required after 1.5-stage exchange arthroplasty. Valgus limb alignment should be avoided to reduce the risk of complications. Early second-stage revision with patellar reconstruction can be considered in younger patients with deficient patellae.

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