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Patients undergoing staged bilateral knee arthroplasty are less aware of their kinematic aligned knee compared to their mechanical knee
∗Corresponding author: Tomer Keidan. tomerkeidan@gmail.com
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Received: ,
Accepted: ,
This article was originally published by Reed Elsevier India Pvt. Ltd. and was migrated to Scientific Scholar after the change of Publisher.
Abstract
Abstract
To compare knee joint awareness following kinematic alignment (KA) TKA in patients who had previously undergone mechanical alignment (MA) on their contralateral knee.
We performed a retrospective study of all consecutive patients who underwent staged bilateral TKA, the first using MA technique and the second utilizing the KA technique, without patient specific instrumentations. Primary outcome was assessed by the Forgotten Joint Score (FJS) with a minimum 1-year follow-up. Differences between knees were also assessed by three predefined key questions. Secondary outcome were differences in knee alignment assessed by long standing x-rays.
Overall, 38 patients (76 knees) met inclusion criteria and were included in the analysis. The mean time for follow up was significantly shorter (P < 0.01) in the KA knees (1.8 years, SD 0.3) compared to the MA knees (3.1 years, SD 0.8). Nonetheless, patients were significantly less aware of their KA knees compared to their MA knees; median FJS scores were 74.0 for the KA group (IQR¼ 54.5–92.0) and 67.0 for the MA group (IQR¼ 43.7–88.0) (p = 0.01). Overall, 31 patients (81.6%) preferred their KA knee over their MA knee 6 (15.8%) (p < 0.001). KA bone cuts resulted in net varus of the medial proximal tibia (86.9, SD 2.0) and valgus of the distal femur (86.6, SD 2.8). However, the overall alignment was similar (femorotibial angle 5.4 ± 2.3 vs. 4.7 ± 2.4, p = 0.45).
Patients who underwent staged bilateral knee arthroplasty were less aware of the knee that was kinematically aligned compared to the knee that was mechanically aligned. Future studies should focus on the long-term survivorship of KA TKA.
Keywords
Kinematic alignment
Mechanical alignment
Total knee arthroplasty
1 Introduction
Total knee arthroplasty (TKA) with mechanical alignment (MA) has been a standard procedure for knee replacement for over three decades.2,7,10 A MA aligns the hip-knee-ankle angle of the leg to a neutral position when weight bearing by positioning the femur and tibia perpendicular to the mechanical axis of the bone. With restored neutral alignment, the mechanical axis is in line with the knee's center and historically has good results with low rates of implant failure.10
Although a successful MA TKA places the femur in a neutral position, this anatomical position is rarely found in healthy native knee anatomy.5,24 International arthroplasty registries have reported rates of 20–25% of patient dissatisfaction with a MA1,11 with some authors reporting only 70% of patients satisfied with MA function and 72–86% satisfied with pain relief7 Rates of dissatisfaction are notably higher in younger patients undergoing MA TKA.18 From a mechanical perspective, this high rate of patient dissatisfaction has been attributed to elevated collateral ligament tension, unnatural limb realignment and a distorted joint line angle, to name a few. Bellemans et al. have shown that 32% of males and 17% of females have constitutional varus knees, with a natural alignment of 3° or more upon skeletal maturity.6 Given this large variability in knee alignment, alternative techniques that seek to replicate native knee anatomy are being pursued.
A kinematic alignment (KA) aims to replicate the anatomical alignment of the previously healthy articular surface via bone resection with minimal ligament release.11 The native soft tissue is conserved by replicating the native position of the femoral and tibial components. Natural positioning minimizes ligament release and results in rotation of the femur and tibia, which maintains the native soft-tissue envelope.11,17 Although comparative studies between KA and MA are lacking, recent studies have reported improved rates of patient satisfaction1,8,11 This may be due to natural weight bearing stance and minimal soft tissue and ligament release.
The most desirable outcome following TKA would be to forget completely that the knee had been replaced.2,6 The forgotten joint score (FJS-12) has been proposed as a tool for capturing subtle improvements, and differentiating patients with good and excellent outcomes.21,22 Furthermore, the FJS-12 may be more discerning than scores that evaluate pain and function alone with a less noticeable “ceiling effect”.12,13 The FJS-12 has been validated in multiple languages and between different populations.9,14,16,19 In this study, we compared knee joint awareness following KA surgery in patients who had previously undergone MA surgery on their contralateral knee.
2 Methods
Starting August 1st, 2017, we started performing KA at our institution. Following IRB approval, we retrospectively collected data on all consecutive primary KA TKA up to November 1st, 2018 to allow a minimum 1-year follow-up (n = 281). Only patients who had a previous MA TKA performed at our institution on their contralateral knee were included in this study (n = 56). Those who had their MA TKA performed more than 5 years prior to final follow up were excluded to minimize recall bias (n = 13). Five patients were not available for follow-up and were excluded as well.
All surgeries (on both legs) were performed by three senior orthopaedic surgeons with over 10 years of surgical experience each in joint arthroplasty. In all cases, spinal anesthesia was performed and periarticular lidocaine and steroids were injected into the posterior capsule. Two grams of 1st generation cephalosporin were given prior to surgery. Surgeries were performed without a tourniquet. A midline approach and medial parapatellar arthrotomy were utilized for both MA and KA techniques.
2.1 KA surgical technique
The non-restricted KA technique has been previously described.3 In short, it combines several methods for knee replacement (kinematical alignment/measured resection/gap balancing) into one technique through 3 key surgical steps: 1) Kinematically aligning the femoral component. The distal femur cut is based on the erosion pattern and the correct offset reference block. 2) Recreating individualized limb alignment by soft tissue guidance throughout knee range of motion using special shims. 3) Linking the tibia cut to the kinematically aligned femur using a specific instrument to serve as a guide for the tibia cut. This balancing technique avoids any need to release or manipulate soft tissue structures. No navigation or patient specific instrumentation were used.
2.2 MA surgical technique
MA was performed by utilizing a standard measured resection technique. Following arthrotomy and slight medial release (for varus knees), the distal femur cut was based on an intramedullary referencing system guided by the medullary canal (anatomic axis). The valgus cut was set to 5° to be perpendicular to the mechanical axis. The tibial cut was set at 90° relative to the anatomic axis based on an extramedullary guide. A spacer block was then used to examine the extension gap. If the gaps were not symmetric after the bony cuts were made, soft tissue tension was altered (in a stepwise manner) to achieve a balanced knee in extension. The posterior femoral cut was then made using a posterior reference system. Femoral rotation was determined intraoperatively (ranging between 3 and 7°) by assessing the medial and lateral flexion gaps. If more tension was felt on the medial side compared to the lateral side, higher degrees of external rotation were set hence compensating soft tissue imbalance by bone cuts. Spacer block was used once again to examine the flexion gap.
2.3 Data collection
Basic demographic and comorbidity information were documented, including patient age, sex, and Charlson comorbidity index (CCI). Patients were followed up for a minimum of 2 years after the most recent TKA. The primary outcome that was assessed was the awareness of the knee by using the FJS-12. The FJS-12 uses a 5-point Likert response format, consisting of 12 equally weighted questions with the raw score transformed to range from 0 to 100 points, with high scores indicating less joint awareness (i.e. good satisfaction).
All patients were phone interviewed by a medical student (TK) blinded to the clinical scenario and were asked to fill out the FJS-12. They were also asked the following three key questions: (1) with which knee was the rehab less painful? (2) After which surgery was the return to normal activity faster? and (3) Which knee do you prefer overall? Information on range of motion was obtained from medical records at the last follow up. Complications were documented through patient interview and query of their medical records. Secondary outcomes assessed were radiographic assessment based on preoperative and postoperative long standing x-rays. Overall alignment as well as medial proximal tibial angle and lateral distal femoral angle, were calculated by an orthopedic resident.
2.4 Statistical analysis
The mean, standard deviation (SD) and 95% confidence intervals (CIs) were determined for the FJS-12. Shapiro-Wilk test was used to determine normal distribution. A Wilcoxon signed-rank test determined whether the FJS was different between the KA and MA TKA. T-test was used to compare between demographic continuous variables. Categorical variables (including the three questions) were compared using the chi square test. Statistical analysis was conducted with SPSS 23 Statistical Software (SPSS Inc, Chicago, IL, USA), and significance was set at p < 0.05.
3 Results
A total of 38 patients (76 knees) were included in this study, with an average age of 71.7 years (SD = 6.7) at the time of last follow-up. Their average BMI was 31.8 (SD = 2.6) and average CCI was 0.7 (SD = 0.8). The average time to follow-up was 2.3 years (SD = 0.3) in the KA group and 3.0 (SD = 0.8) in the MA group. Demographics, preoperative ROM and radiographic alignment are summarized in Table 1.
| Kinematic Alignment (n = 38) | Mechanical Alignment (n = 38) | p-value | |
| Age, yr | 71.7 (6.7) | ||
| Sex, male | 11 (21.5%) | ||
| Body Mass Index (Kg/m 2 ) | 31.4 (2.5) | ||
| Charlson Comorbidity Index | 0.6 (0.8) | ||
| Side, right | 17 (44.7%) | 21 (55.3%) | 0.49 |
| Time to Follow-up, yr | 1.76 (0.3) | 3.1 (0.8) | <0.01 |
Patients were significantly less aware of their KA TKA compared to their MA TKA (p = 0.01)); the median FJS-12 score was 74.0 for the KA group (IQR¼ 54.5–92.0) and 67.0 for the MA group (IQR¼ 43.7–88.0) (Fig. 1). One patient (2.6%) in the KA group scored under 40 as compared to 7 patients (18.4%) in the MA group, and 12 patients (31.6%) in the KA group scored above 90 as compared to 7 patients (18.4%) in the MA group (Fig. 2).
In both groups, ROM improved compared to the preoperative state with no significant differences between the two groups postoperatively; postoperative mean extension was 0.8 (SD = 2.2) in the KA group compared to 0.6 (SD = 2.3) in the MA group (p = 0.52), and mean flexion was 116.6 (SD = 12.0) in the KA group compared to 112.6 (SD = 12.2) in the MA group (p = 0.25). While there were significant differences in the MPTA (p < 0.01) and LDFA (p < 0.01) postoperatively, overall alignment (tibiofemoral angle) was not different (p = 0.45) between the two groups (Table 2).
| Preoperative | Postoperative | |||||
| Kinematic Alignment (n = 38) | Mechanical Alignment (n = 38) | p-value | Kinematic Alignment (n = 38) | Mechanical Alignment (n = 38) | p-value | |
| Range of Motion | ||||||
| Extension | 1.6 (2.7) | 1.7 (3.8) | 0.94 | 0.8 (2.2) | 0.6 (2.3) | 0.52 |
| Flexion | 103.9 (14.8) | 102.1 (13.7) | 0.54 | 116.6 (12.0) | 112.6 (12.2) | 0.25 |
| Limb Alignment | ||||||
| TFA | 2.6 (2.0) | 1.2 (2.1) | 0.68 | 5.4 (2.3) | 4.7 (2.4) | 0.45 |
| MPTA | 86.0 (2.8) | 86.9 (2.9) | 0.30 | 86.9 (2.0) | 89.9 (2.7) | <0.001 |
| LDFA | 87.8 (2.1) | 88.3 (2.7) | 0.34 | 86.6 (2.8) | 89.8 (2.1) | <0.001 |
In all 3 key questions, significant advantage was seen for the KA side (p's < 0.001); Patients felt that rehab was less painful (68.4% versus 15.8%) and return to normal activity was quicker (63.2%). Overall, 31 patients (81.6%) prefer their KA knee compared to 6 patients (15.8%) who prefer their MA knee (Table 3).
| Kinematic Alignment | Mechanical Alignment | No Difference | p value | |
| With which knee was the rehab less painful? | 26 (68.4%) | 6 (15.8%) | 6 (15.8%) | <0.001 |
| After which surgery was the return to normal activity faster? | 24 (63.2%) | 6 (15.8%) | 8 (21.1%) | <0.001 |
| Which knee do you prefer overall? | 31 (81.6%) | 6 (15.8%) | 1 (2.6%) | <0.001 |
4 Discussion
In this study, we compared knee joint awareness following KA TKA in patients who had undergone MA TKA in their contralateral knee in the past. The main finding of this study was that differences in the recorded Forgotten Joint Score (FJS), were statistically significant and superior for the KA side in comparison with the MA side. The fact that only one patient (2.6%) in the KA group scored under 40 as compared to 7 patients (18.4%) in the MA group supports the notion that KA may play a role in reducing the dissatisfaction from unknown reason seen following TKA.
The debate among surgeons on whether KA produces superior satisfaction compared to MA continues, as evident by 3 recent systematic reviews.10,15,23 These studies assessed various patient reported outcomes with a specific focus on the Knee function score (KFS), oxford knee score (OKS) and Western Ontario and McMaster Universities Arthritis Index (WOMAC), knee society score (KSS) and a slight functional benefit for KA was seen. Young et al.23 assessed FJS-12 scores in a randomized control trial by comparison between KA (PSI based) and MA in 50 patients and 49 patients respectively. They found a mean FJS score of 69 (SD = 26) and 66 (SD = 26) respectively and this difference was not statistically significant (p = 0.4). The main outcome that we were interested in the present study was patient awareness of their replaced knees using the FJS-12 questionnaire. As opposed to Young et al. we found that patients undergoing staged bilateral TKA were significantly less aware of their KA knee compared to their MA knee. There are several explanations to the different results; Young et al. reported a SD of 26 in the FJS scores, yet compared mean and not the median without examining normal distribution. Moreover, in their study KA was based on patient specific instrumentation (PSI) which is substantially different then the calipered non restricted KA technique that we used in the present study. Finally, the fact that patients in our study had undergone both MA and KA procedures, may have affected these results as patients had a direct comparison.
The fact that our cohort was comprised of patients who had already undergone surgery in their contralateral knee, allowed us to directly compare satisfaction using three key questions. A significant advantage was seen for the KA side in all key questions. The fact that 81.6% of patients preferred their KA knee over their MA knee should encourage orthopaedic surgeons to perform KA TKAs on their patients. Importantly, a recent systematic review reported significantly inferior functional outcomes for the second-operated knee compared with the first-operated knee in five out of seven studies examining staged bilateral TKA.15 Differences in outcomes with different intervals between the first and second operated knee were not significant. The fact that the KA TKA was the second–operated knee in all our patients and they were still more satisfied compared to the first (MA) operated knee, emphasizes even further the functional benefit of KA.
Constitutional varus is common and relative to the mechanical axis in a native knee, the tibia's articular surface averages 3° varus and the femur averages 2–3° valgus.6,23 Bellemans et al.6 reviewed 250 healthy adults and determined that 32% of men and 17% of women have a natural varus angle greater than 3°. If patients with these natural deviations undergo a MA, more soft tissue releases will be necessary with a subsequent decrease in patient satisfaction.4,6 The pre and postoperative measurements performed in this study suggest that while the tibial and femoral cuts replicate the native anatomy and are not perpendicular to the mechanical axis, the overall knee alignment remains similar between the MA and KA techniques. These findings support previous studies on the subject.11,23
Early KA methods utilized PSIs created using a preoperative computed tomography of the patient's knee proved to be a time consuming and expensive process.20 Additionally, studies have reported that PSIs do not result in increased patient satisfaction or component realignment.4 The “linked technique” used in the KA group in this study compensates for the positions of the femur and tibia, is guided by soft tissue, and replicates native knee anatomy.3 The patients that were included in this study were operated during the first 6 month after transition to the KA technique after at least 10 years of practicing MA technique. The fact that the KA knees were more successful compared to the MA suggests that the calipered unrestricted KA is easy to learn and that surgeons should feel safe switching from a perpendicular cut to the mechanical access to the kinematic technique, with an insignificant learning curve.
The main limitation of this study was its retrospective design that has imposed several points to take into account. The KA and MA knees were not always performed by the same surgeon. Nevertheless, all 3 surgeons are well experienced in the field of knee arthroplasty working in the same institution and using similar protocols. Patients follow up time period differed based on the procedure and may introduced a recall bias that could have affected the answers to the 3 key questions and FJS. However we tried to reduce this bias by including patients undergoing staged TKA within a relatively short time period. Finally, The time of follow up in this study does not allow us to make any conclusions on the survivorship of the 2 techniques which is still a major issue and concern for surgeons in their dilemma whether to perform KA TKA and future studies should investigate long term follow-up.
With consideration of these limitations, our findings suggest that kinematic aligned TKA results in less knee awareness compared to traditional mechanical alignment. This was true even though the KA was performed as the second operation and soon after the transition of well experienced joint arthroplasty surgeons to performing KA TKA. Our results should reassure and encourage experienced and non-experienced surgeons who are interested on performing KA in patients with a previous MA TKA. However future studies should investigate long term survivorship of the implants following KA TKA.
CRediT authorship contribution statement
Yaron Bar Ziv: Conceptualization. Ilan Small: Writing - original draft. Tomer Keidan: Data curation. Eran Beit Ner: Writing - original draft. Gabriel Agar: Conceptualization. Noam Shohat: Writing - original draft.
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