Patients’ demographic characteristics
This study was approved by the Institutional Review Board of our hospital, and the requirement for informed consent was waived because of its retrospective design. Between August 2019 and July 2020, we retrospectively reviewed 83 knees (78 patients) of revision TKAs replacing both femoral and tibial components. All operations were performed by a senior surgeon using the same technique at a single center. Inclusion criteria for this study were as follows: (1) revision TKA (replacement of all components) using the cemented VVC Attune® revision knee system (DePuy Synthes, Warsaw, IN, USA) with a fixed-bearing; (2) a minimum follow-up of 2 years after index operation. We excluded 8 knees with other implants during the study period: PFC Sigma TC3® used in 1 knee, legacy constrained condylar knee (NexGen® LCCK®, Zimmer Biomet Warsaw IN, USA) used in 4 knees, and rotating hinge knee prosthesis (NexGen® RHK, Zimmer Biomet, Warsaw, IN, USA) used in 3 knees; thus, 75 cases (72 patients) were enrolled in the final analysis. All cases were followed up for more than 2 years after surgery (Fig. 1).
Subgroup analysis
We divided the modes of failure in primary TKAs into septic mode due to infection and aseptic mode due to other causes. Aseptic mode included loosening, instability, polyethylene (PE) wear, and stiffness.
All patients who underwent revision TKA for infection were diagnosed according to the latest evidence-based criteria from the International Consensus Meeting [8] and received revision surgery using a two-stage revision strategy with a minimum interval of 6 weeks. In the first operation, the implant and all cement remnants were removed. Then, a standardized radical debridement with removal of all macroscopically suspicious soft tissue and bone was performed. Finally, the autoclaved femoral component removed from the patients was reused for temporary articulating antibiotic spacer (132℃, 30 min). In addition, rotating PE liner with antibiotics-impregnated cement was inserted in the tibia that maintained the joint gap (Fig. 2C, D). Antibiotic beads were also inserted in the intramedullary canal or joint cavity, if needed. The second-stage reimplantation was planned only when there was sufficient clinical, radiographic, and laboratory evidence supporting eradication of the infection [9, 10]. The final revision was performed only when fewer than 5 polymorphonuclear leukocytes were observed in the intraoperative frozen biopsy at 400-fold magnification obtained from more than three areas and there was no gross evidence of infection during surgery.
Revision surgeries by aseptic mode were performed as a one-stage strategy [9]. Aseptic loosening was assessed by radiolucent lines (RLLs) on anteroposterior (AP) and lateral radiographs of the knee joint taken in a standardized fashion by the institutional radiology department. RLLs were defined as radiolucent intervals > 2 mm in width between either the implant and the cement or the cement and the underlying bone [11]. Zones around the TKA implants were defined as described by the Modern Knee Society Radiographic Evaluation [12].
We defined instability after TKA as abnormal and excessive displacement of the reticular elements that leads to failure of primary TKA [13]. Traumatic rupture or chronic functional attenuation of ligaments and insufficiency of extensor mechanism may be contributing factors. In the present study, among 4 cases with acute knee dislocation, three cases requiring a hinged implant due to global instability were excluded. PE wear was assessed in vivo by measuring the minimum joint space width in radiographs. Stiffness was defined as a clinical condition with limited range of motion (ROM, < 70 degrees) with or without pain after TKA [14].
In cases with multiple failure modes, two independent investigators who did not participate in surgery classified the patients to minimize any observation bias. In only two cases where consensus could not be reached, the operating surgeon re-classified them as the most fundamental cause. Some cases with PE wear were accompanied by instability, which was determined to be due to instability, the most fundamental cause [13]. Another cases, stiffness caused by septic loosening was classified into the group with septic mode.
Surgical techniques
The rectus snip approach was performed only in 4 patients who had difficulty in joint exposure due to severe patellar baja [15]. All other revision TKAs were underwent through a medial parapatellar approach along the existing scar. The failed implants, bone cement, and debris were carefully removed being paid to minimizing bone loss. The original joint line was restored by applying distal metal augments to the femoral bone defect. We tried to confirm the accurate rotation of an appropriately sized femoral component with respect to the trans-epicondylar axis. Sequential intramedullary reaming of the femur and tibia was performed according to the planned length and thickness of the stems. Both femoral and tibial stems were used in all patients. Since this new revision system had an offset option compared to the predecessor, if it was eccentric to the canal, an offset stem was used [16]. In particular, in a revision situation where the flexion gap was large, posterior shifting of the femoral component by the posterior offset stem and additional posterior femoral augments were used to optimize the flexion gap [17]. The Anderson Orthopedic Research Institute (AORI) grade was performed intraoperatively by the operating surgeon after removal of the primary prosthesis [18]. Depending on the size and grade of the defect, autologous or allogenic structured bone grafts or trabecular metal cones were used [19]. After that, the host bone was fine-tuned and metal augmentation was applied to achieve press-fit fixation considering the level of the joint line. Finally, knee stability, patella tracking, lower limb alignment, and ROM were checked. We applied a cementing technique for all revision TKAs. In revision TKAs due to infection, a total cementation technique using susceptible antibiotics was used (Fig. 2), whereas for revision TKAs due to aseptic complications, a modified hybrid cementation technique with press-fit stem was used. The cement was applied around the implant distal to the modular junction of the stem and was also applied at the tip of both stems (Fig. 3) [17, 20].
When the total cementation technique was performed, an intramedullary bone plug was inserted considering the length of the stem. Antioxidant fixed-bearing PE inserts were used in all cases. Patellar resurfacing was not performed on all patients due to concern for infection [21].
A closed suction drain was inserted and was removed 24‒48 h after surgery. All patients applied the same perioperative pain control protocol, including multimodal drug regimen and postoperative patient-controlled analgesia. Active ROM exercise was started on the day of surgery. If normal quadriceps femoris strength was recovered on the 2nd or 3rd postoperative day, partial weight bearing with a crutch was allowed. Full weight bearing was permitted 3 weeks after surgery.
Outcome assessments
The demographic characteristics were investigated before surgery. Clinical assessments were performed in all patients preoperatively and at last follow-up. The clinical questionnaires were assessed based on the Knee Injury and Osteoarthritis Outcome Score for Joint Replacement (KOOS-JR) [22] and the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) for pain and function [23]. They were recorded by an independent researcher in outpatient clinic. ROM of the knee joint (including flexion contracture and further flexion angle) was measured using a long-armed goniometer by an independent physical therapist. The values at the final follow-up were compared with the preoperative values. For subgroup analysis, patients were divided into group A (septic mode) and B (aseptic mode).
Bilateral standing AP and lateral radiography of the knee joint, Merchant view, and lower-extremity scanography were performed preoperatively; at 3, 6, 12, and 24 months postoperatively; and then every year until the last follow-up. All radiographic measurements were digitally acquired using a picture archiving and communication system (Maroview®, version 5.4; Marotech, Seoul, Korea) in the format of DICOM (Digital Imaging and Communicating in Medicine). Radiographic outcomes included the hip–knee–ankle (HKA) angle (with varus alignment as a negative value) and posterior tibial slope angle (PTSA, the angle between the tangent to the medial tibial plateau and the perpendicular line to the proximal tibial anatomic axis) [24]. The positions of femoral and tibial components were measured using the α, β, γ, and δ angles according to the Knee Society Radiographic Evaluation method [25]. Moreover, RLLs were investigated through AP and lateral radiographs [11]. Changes of femoral joint line after index operation were assessed. The femoral joint line position was defined as the distance from the adductor tubercle to the joint line in an AP radiography (Fig. 4) [26].
The incidence of postoperative complications was documented via chart review. In addition to surgery-related complications, systemic complications were also investigated. Systemic complications were defined as exacerbation of underlying systemic disease or development of a new medical problem [25].
Statistical analysis
Statistical evaluation was performed using IBM SPSS software (Version 28; IBM Co., Chicago, IL, USA), and continuous data were expressed as means with SDs. All dependent variables were tested for normality of distribution and equality of variances using the Kolmogorov–Smirnov test and analyzed using parametric or nonparametric tests based on normality. According to normality test, the paired t test was used to compare the preoperative and postoperative clinical and radiographic outcomes. Intergroup comparisons were made using independent sample t test. The Fisher exact test was used to compare ratios between the groups. For all tests, p < 0.05 was considered statistically significant.
