In recent years, the incidence of total knee arthroplasty (TKA) has increased worldwide [1,2,3,4]. Some studies have predicted that the number of TKA procedures and the subsequent revision burden may increase further in future, which emphasizes the importance of the successful outcome of revision TKA [5,6,7].
Instability is one of the most frequent causes of knee revision and re-revision along with aseptic loosening and infections [1, 2, 4, 8, 9]. Revision of TKA implants with varying levels of constraint are available to secure knee stability after revision. In the revision or re-revision of TKA patients, the surgeon may confront severe perioperative deformities as well as bony and/or ligament deficiencies. To achieve adequate stability and ideal final outcome, these complex clinical situations may require hinged knee implants. Hinged TKA designs are also used in knees with impaired extensor mechanism, ligamentous laxity producing painful hyperextension of the knee or in patients undergoing oncologic surgery [10,11,12].
Historically, aseptic loosening occurred more often with hinged knee implants that prohibited rotational motion. These models caused much unwanted stress at the prosthesis-bone interface or on the implant itself, leading to implant failure [10, 11]. To prevent such failures, contemporary hinged knee implant designs allow rotational motion. The range of rotation and how weight is transmitted through the knee depends on the type of hinged knee implant [10].
In the literature, recently published rotating hinged knee implant studies are difficult to compare because of their heterogeneity [11, 13]. Indeed, rotating hinged knee studies are often differentiated by indications (aseptic/septic cases), type of implant, or cohort patients (primary/revision). More clinical evidence is therefore needed on the safety and durability of these commonly used knee replacements in revision knee arthroplasties.
The purpose of this study was to determine the mid–term clinical, radiographic, and health-related quality of life (HRQoL) outcomes in patients who underwent revision TKA using the single rotating hinged knee (RHK) design at our institution between January 2004 and December 2013.
Study design and methods
From January 2004 to December 2013, 125 revision TKAs were performed at our institution using the NexGen® RHK implant. The study site is an academic high-volume tertiary referral center with an annual volume of approximately 150 revision TKAs.
This study comprised three phases: first, a prospective follow-up study of all the surviving patients of this cohort was conducted. Second, a retrospective analysis of the prospectively collected outcome data recorded into the electronical joint replacement database at our institution was carried out. Third, information on possible revision surgeries that might have been performed elsewhere, and thus not recorded into our own database, was cross-checked from the Finnish Arthroplasty Register.
All RHK revision knee arthroplasties were performed using the medial parapatellar approach and a tourniquet was also routinely used. TKAs were carried out under spinal anesthesia in combination with intravenous sedation. General anesthesia was only used if there was a contraindication to spinal anesthesia. Immediate, full weight-bearing was allowed, and all patients were mobilized on the first postoperative day. An antithrombotic prophylaxis with low-molecular-weight heparin, enoxaparin, was administered for 4 weeks postoperatively. All details of perioperative care and possible complications were recorded in the hospital’s electronical database in a routine manner. In 48 knees (38%), the patella was resurfaced in the revision TKA. In 25 knees (20%), the patella had already been resurfaced in the primary TKA operation. Cemented femoral and tibial components were used in all operations, and the choice between cemented and uncemented stems was based on surgeon preference. The trabecular metal cones were used in 13 cases (10%). At the baseline of the study, 119 patients (125 knees) were included in the retrospective analysis, where all the demographics, surgery reports, first post-operative visits (at 2–3 months), possible post-operative complications, and adverse events as well as reasons for revisions were obtained from the medical records and the hospital’s electronical clinical database. Information on possible revision surgeries performed on patients elsewhere who were lost to follow-up (18 patients, 18 knees) was cross-checked from the Finnish Arthroplasty Register [4].
In the prospective study phase, an extra follow-up visit was scheduled between 4 and 14 years post-operatively, depending on the year of the index operation. All of the 59 living and unrevised patients (61 knees) were recruited by telephone for an extra follow-up visit at our outpatient clinic (Fig. 1). In total, 39 patients (41 knees) agreed to participate in the follow-up phase of this study. Those patients who were unable to attend the extra follow-up visit received a set of PROM questionnaires by surface mail and were asked to visit their nearest health care provider for plain radiographs to be taken. The extra follow-up visit included plain radiographs of the operated joint, clinical assessment by a physiotherapist, and the use of PROMs, i.e., the Oxford Knee Score (OKS), the Knee Injury and Osteoarthritis Outcome Score (KOOS), the 15D (generic measure of health-related quality of life), and the Forgotten Joint Score (FJS).
Radiographic evaluation
Preoperative
Radiographic findings, such as osteolytic defects and stability of the patella, were evaluated from the pre-operative radiographs. Pre-revision bone defects were classified according to Anderson Orthopaedic Research Institute (AORI) classification [14] and these classifications were compared to peroperative findings for final assessment. The stability of the patella was examined from the skyline patellar radiographs. All patient records and pre-operative radiographs were examined by the first author who had not been involved in the revision surgeries and had not met the patients during the follow-up visits. To estimate the reliability of the measurements, a sample (n = 20) of the pre-operative radiographs was later reviewed by an experienced orthopaedic surgeon who was blinded to the original measurements.
Postoperative
All postoperative plain radiographs from the extra follow-up were evaluated by two senior orthopaedic surgeons (co-authors JN and AE). Radiographic evaluation was performed from standardized weight-bearing antero-posterior (AP), lateral, and skyline patellar views. Radiographs were assessed for the presence of radiolucent lines or osteolytic defects.
Patient-reported outcome measures
Health-related quality of life (HRQoL) was measured using the comprehensive generic 15D instrument. The instrument combines the advantages of a profile and a preference-based single index measure. The 15D instrument includes the following 15 dimensions: mobility, vision, hearing, breathing, sleeping, eating, speech, excretion, usual activities, mental function, discomfort and symptoms, depression, distress, vitality, and sexual activity. For each dimension, the respondent chooses one of the five ordinal levels that best describe their state of health at the time (best =1; worst =5). The single index score (15D score) represents the overall HRQoL on a 0–1 scale (1 = full health, 0 = being dead). The dimension level values reflect the goodness of the levels relative to no problems on the dimension (=1) and to being dead (=0). These values are then calculated from the health state descriptive system (questionnaire) by using a set of population-based preference or utility weights. Mean dimension level values are used to draw 15D profiles for groups [15]. The minimum clinically important change or difference in the 15D score has been estimated to be ±0.015 on the basis that people can, on average, feel such a difference [16].
We compared our study population’s 15D results to those of an age- and gender-standardized sample of the general Finnish population (n = 4052) taken from the Health 2011 Survey carried out by the National Institute for Health and Welfare of Finland [17].
The OKS and the KOOS have been widely used to assess the outcomes of knee replacements [18, 19]. In this study, the OKS was categorized into four different grades: poor (0–26), fair (27–33), good (34–41), and excellent (42–48) [18]. The KOOS is an extension to the WOMAC Osteoarthritis index and includes five separately scored subscales. The subscales are Pain, other Symptoms, Function in daily living (ADL), Function in sport and recreation, and knee-related quality of life [20]. Forgotten Joint Score (FJS) assesses the patient’s ability to forget the replaced joint while performing recreational activities and in daily life. A higher degree of ¨forgetting¨ the joint indicates a better outcome of surgery [20].
The Kaplan-Meier (K-M) analysis was performed to assess the survival rate of the RHK implant. Both survival rates and 95% confidence intervals (CI) were derived from K-M models. The independent samples t-test was used to test the statistical significance of the differences in the mean 15D results between the groups. Statistical significance was set at p < 0.05. The statistical analysis was performed with SPSS Statistics for Mac (version 25.0). Competing risk analysis was performed with R (version 4.0.2). The study was funded by an institutional grant from Zimmer Biomet Inc. (Warsaw, IN, USA). The study was approved by the local ethical committee (R17010).