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Failure modes of mechanically aligned versus kinematically aligned total knee arthroplasty
⁎Corresponding author: Whisper Grayson. whisper.grayson@luhs.org
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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
While mechanical alignment (MA) has long been considered the “gold standard” technique when performing total knee arthroplasty (TKA), kinematically aligned (KA) TKA has been gaining recent popularity. This technique aims to restore the pre-arthritic knee anatomy and alignment, with studies demonstrating excellent functional and biomechanical outcomes when compared to MA TKA. The primary aim of this study is to compare reasons for reoperation in MA versus KA primary TKA and understand if the reasons for re-operation differ between the two techniques.
This is a retrospective study including 267 patients who underwent a MA TKA from September 2017 to September 2021, compared to 359 patients who had a KA TKA from October 2021 to December 2024. All procedures were performed by a single arthroplasty-trained surgeon who switched his technique for TKAs in October 2021 from MA to KA. The primary outcome assessed was reoperation, with notes reviewed to assess the reason for reoperation.
While the MA cohort had a higher rate of reoperation (4.1%) compared to the KA cohort (2.2%), it was not significantly different (p = 0.172). Common reasons for reoperation included prosthetic joint infection, extensor mechanism disruption, peroneal nerve injury, and mechanical instability. There was no difference in rates of MUA between the MA and KA cohorts (4.1% versus 2.8%; p = 0.359).
In this study, we found no significant difference in reoperation rates between MA and KA primary TKAs. Prosthetic joint infection was a common cause of reoperation amongst both groups. More MA patients required reoperation for extensor mechanism dysfunction while KA patients experienced more mechanical instability.
Keywords
Total knee arthroplasty
Kinematic alignment
Mechanical alignment
Reoperation
Complications
1 Introduction
Kinematically aligned (KA) total knee arthroplasty (TKA) has been gaining recent popularity over mechanical alignment (MA), which has long been considered the “gold standard” technique for TKA.1–4 Compared to MA, which aims to create a neutral axis of the hip-knee-ankle axis in a two-dimensional plane, the goal of the KA technique is to restore the pre-arthritic anatomy and alignment of the knee.5 Recent studies have demonstrated excellent functional and biomechanical outcomes of KA is comparison with MA TKA.6,7
Prior studies have focused on comparing perioperative and post-operative outcomes between the two techniques, with current literature still divided on whether one technique is superior to the other.5,8,9 Some studies have reported comparable functional outcomes, radiological results, operative time, length of hospital stay, and complication rates between the two techniques.5,9 Contrastingly, other studies have demonstrated superior functional outcomes and patient-reported satisfaction with KA TKA compared to MA.8,10
Despite previous studies reporting similar complication rates between the two groups, there remains a lack of literature evaluating the underlying reasons for reoperation following TKA when comparing MA and KA techniques.9 In this study, we primarily aim to evaluate the reoperation rates and reasons for reoperation following TKA in patients ≥18-years old, comparing MA and KA techniques. Secondary aims include assessing rates of manipulation under anesthesia (MUA) between the two cohorts.
2 Methods
2.1 Patient selection
Following Institutional Review Board (IRB) approval, a retrospective chart review of primary TKAs performed by a single arthroplasty-trained surgeon from September 22nd, 2017 to December 31st, 2024 was performed. Current Procedural Terminology (CPT) code 27447 was used for initial patient extraction, followed by chart review to ensure inclusion and exclusion criteria were met. Inclusion criteria included patients ≥18-years old who had a primary TKA performed by the senior author. This author switched his technique for primary TKA from mechanical alignment to kinematic alignment in October 2021. Thus, all TKAs performed from September 2017 to September 2021 were included in the mechanical alignment cohort and those performed from October 2021 through December 2024 were included in the kinematic cohort. Operative notes were reviewed to further ensure patients received the correct technique for their cohort.
2.2 Variables of interest
Chart review was conducted on the selected patients to collect demographic information including age, sex, race/ethnicity, body mass index (BMI), tobacco use, and follow-up time. Comorbidities were analyzed in the Charlson Comorbidity Index (CCI). The primary post-operative outcome assessed was reoperation, with operative notes reviewed to assess the reason for reoperation. A secondary outcome assessed was manipulation under anesthesia.
2.2.1 Operative technique
The MA knees were performed with manual instruments cut at 5° to the intramedullary axis and a neutral extramedullary cut. The KA knees were performed using a manual calipered technique. The operative technique of an unrestricted calipered kinematic total knee arthroplasty has been previously published.11,12 An attempt was made to replicate tibial slope by aligning an angel wing along the medial aspect of the plateau and setting the tibial cut guide such that the cut was parallel to this plane. Implant information is included in Table 1.
| Implant | Mechanical Alignment Cohort (n = 267) | Kinematic Alignment Cohort (n = 359) |
| Depuy Attune | ||
| CR | 34.8% (93) | 83.8% (301) |
| PS | 6.0% (16) | 0% (0) |
| Depuy Sigma | ||
| CR | 32.2% (86) | 1.9% (7) |
| PS | 24.0% (64) | 2.2% (8) |
| Stryker Triathalon | ||
| CR | 0.4% (1) | 0.6% (2) |
| PS | 0.4% (1) | 0% (0) |
| Smith and Nephew Journey | ||
| CR | 1.5% (4) | 0.8% (3) |
| Smith and Nephew Legion | ||
| CR | 0% (0) | 0.6% (2) |
| Zimmer Persona | ||
| CR | 0.7% (2) | 0.3% (1) |
| Medacta | ||
| CR | 0% (0) | 2.2% (8) |
| Microport Evolution | ||
| MP | 0% (0) | 7.2% (26) |
| DJO Enovis Empower Knee | ||
| CR | 0% (0) | 0.3% (1) |
2.3 Data analysis
Means and standard deviations are provided for continuous variables while percentages and sample size provided for categorical variables. Univariate comparisons included chi-square analysis for categorical variables and independent t-tests for continuous variables, with an alpha level set at 0.05.
3 Results
3.1 Patients
A total of 267 patients who underwent a MA TKA from September 2017 to September 2021 were compared to 359 patients who had a KA TKA from October 2021 to December 2024. In the MA group, a majority (63.7%) of the patients were female and the overall average age was 64.8 years (std dev, 9.3) at the time of the primary TKA. The average follow-up for this group was 28.4 (std dev, 22.2) months. The KA cohort was also predominantly female (62.2%), with an average age of 66.6 (std dev, 8.9) years, and average follow-up time of 10.8 (std dev, 8.9) months. There was no significant difference in CCI (3.0 versus 3.2; p = 0.131) or BMI (33.3 versus 34.0; p = 0.200) between the MA and KA cohorts, respectively (Table 2).
| Mechanical Alignment n = 267 | Kinematic Alignment n = 359 | Statistical Analysis | |
| Average Age at TKA (years) | 64.8 (9.3) | 66.6 (8.9) | p=0.015∗ |
| Average Follow-up (months) | 28.4 (22.2) | 10.8 (8.9) | p<0.001∗ |
| Gender | |||
| Female | 63.7% (170) | 62.2% (223) | |
| Male | 36.3% (97) | 37.8% (136) | p = 0.691 |
| Race/Ethnicity | |||
| Caucasian | 47.6% (127) | 61.6% (221) | |
| African American | 22.1% (59) | 13.6% (49) | |
| Hispanic | 25.1% (67) | 16.7% (60) | |
| Asian | 0% (0) | 1.4% (5) | |
| Other/Unknown | 5.2% (14) | 6.7% (24) | p<0.001∗ |
| Average Charlson Comorbidity Index | 3.0 (1.7) | 3.2 (1.6) | p = 0.131 |
| Body Mass Index (kg/m^2) | 33.3 (6.6) | 34.0 (7.2) | p = 0.200 |
| Tobacco Use | |||
| Current | 10.1% (27) | 6.1% (22) | |
| Former | 33.3% (89) | 34.0% (122) | |
| Never | 56.6% (151) | 59.9% (215) | p = 0.181 |
Reoperation Rates Following Total Knee Arthroplasty.
The reoperation rates were 4.1% for the MA cohort and 2.2% for the KA cohort (p = 0.172) (Table 3). In the MA cohort, three patients underwent reoperation for prosthetic joint infection (PJI), with one of those patients also having a near complete patellar tendon rupture. Two patients underwent common peroneal nerve decompression and neuroplasty with vascular surgery due to footdrop following their TKA. There were two patients with extensor mechanism dysfunction, one of whom went on to develop a PJI following the procedure to repair their patellar tendon. One patient experienced wound dehiscence, one patient required two operations by vascular surgery for chronic lower extremity edema with deep and superficial reflux, one patient had a patellar dislocation with capsule tear, and the final patient had four operations for arthrofibrosis. The reasons for reoperation and procedures performed for the MA cohort are further outlined in Table 4.
| Mechanical Alignment n = 267 | Kinematic Alignment n = 359 | Statistical Analysis | |
| Reoperation Rate | 4.1% (11) | 2.2% (8) | p = 0.172 |
| Manipulation Under Anesthesia | 4.1% (11) | 2.8% (10) | p = 0.359 |
| Patient | Reason for Reoperation | Procedure Performed |
| 1 | Patella dislocation with capsule tear | Lateral release with medial capsular plication |
| 2 | Prosthetic Joint Infection | Irrigation and debridement with polyethylene exchange |
| 3 | Prosthetic Joint Infection | Irrigation and debridement with revision total knee arthroplasty |
| 4 | Footdrop | Common peroneal nerve decompression and neuroplasty with neurosurgery |
| 5 | Wound dehiscence | Irrigation and debridement with polyethylene exchange |
| 6 | Prosthetic Joint Infection with Near Complete Patellar Tendon Rupture | 1) Arthrotomy, Irrigation and Debridement, and Revision Total Knee Arthroplasty with soft tissue coverage by plastic surgery; 2) Above Knee Amputation with nerve transfers |
| 7 | Chronic lower extremity edema with deep and superficial reflux | Two operations with vascular surgery: 1) Femoral and Iliac venogram with inferior venocavagram and IVUS; 2) Thigh, knee, and calf GSV adhesive closure |
| 8 | Arthrofibrosis | 1) Manipulation under anesthesia; 2) Manipulation under anesthesia; 3) Arthroscopy with lysis of adhesions and manipulation under anesthesia; 4) Scar tissue excision with polyethylene exchange |
| 9 | Patellar tendon tear complicated by Prosthetic Joint Infection | 1) Patellar tendon repair with hamstring autograft; 2) Explant for prosthetic joint infection staged with revision total knee arthroplasty and extensor mechanism reconstruction |
| 10 | Extensor Mechanism Disruption | Extensor Mechanism Repair |
| 11 | Footdrop | Common peroneal decompression and neuroplasty with neurosurgery |
There were eight patients in the KA cohort who required reoperation. The most common source for reoperation in this group was mechanical instability, with two patients having postoperative knee laxity and one with a jumped polyethylene post. There were two PJIs, one with subsequent laxity requiring another operation. One patient had a revision due to stiffness; one had a patelloplasty for a painful patella, and the final patient had a capsule tear. These patients are detailed in Table 5.
| Patient | Reason for Reoperation | Procedure Performed |
| 1 | Painful Patella | Patelloplasty |
| 2 | Knee Laxity | Liner exchange |
| 3 | Knee Stiffness | Revision total knee arthroplasty, polyethylene exchange, and excision of scar tissue |
| 4 | Knee Laxity | Polyethylene Exchange |
| 5 | Prosthetic Joint Infection Followed by Knee Laxity | 1) Irrigation and debridement with polyethylene exchange d/t PJI; 2) Revision total knee arthroplasty d/t laxity |
| 6 | Prosthetic Joint Infection | Revision total knee arthroplasty, irrigation and debridement, and polyethylene exchange |
| 7 | Jumped polyethylene post | Open reduction with polyethylene exchange |
| 8 | Capsule Tear/Patella dislocation | Lateral release with arthrotomy repair |
A secondary outcome assessed was rate of MUA following the primary TKA, with the MA group having a rate of 4.1% compared to the KA group with 2.8% (p = 0.359) (Table 3). The pre-MUA, immediate post-MUA, and one-year post-MUA range of motion values are provided for each patient in Table 6.
| Mechanical Alignment | ||||
| Patient | Timing of MUA Following TKA (months) | Range of Motion:Pre-MUA | Range of Motion:Immediately Post-MUA | Range of Motion:1-year Post-MUA |
| 1 | 2 | 5-70° | 5-100° | 0-95° |
| 2 | 3 | 10-90° | 5-120° | 5-130° |
| 3 | 2 | 5-90° | 5-130° | 0-130° |
| 4 | 2 | 0-75° | 0-130° | 0-95° |
| 5 | 2 and 12 | 2 months: 15-85° 12 months: 5-90° | 2 months: 15-135°12 months: 5-120° | 2 months: 5-90° 12 months: 0-105° |
| 6 | 7 | 0-95° | 0-115° | 0-120° |
| 7 | 2 | 0-90° | 0-125° | 0-110° |
| 8 | 4 | 0-90° | 0-125° | 0-120° |
| 9 | 4 | 0-80° | 0-115° | 0-100° |
| 10 | 3 | 0-90° | 0-125° | 0-110° |
| 11 | 2 | 0-85° | 0-125° | 5-90° |
| Kinematic Alignment | ||||
| 1 | 4 | 5-90° | 5-120° | 5-110° |
| 2 | 2 | 0-85° | 0-120° | 0-115° |
| 3 | 4 | 5-95° | 5-125° | 0-115° |
| 4 | 3 | 0-90° | 0-120° | 0-115° |
| 5 | 17 | 0-115° | 0-115° | 0-110° |
| 6 | 1 | 0-65° | 0-125° | 0-120° |
| 7 | 3 | 5-90° | 5-130° | Not available |
| 8 | 3 | 0-80° | 0-125° | 0-120° |
| 9 | 4 | 0-90° | 0-135° | 0-95° |
| 10 | 3 | 0-60° | 0-130° | Not available |
4 Discussion
KA TKA has been gaining popularity against the long-standing “gold-standard” MA technique.1–4 Previous studies have focused on evaluating the surgical and patient reported outcomes following each technique, with a current divide amongst the literature in terms of superiority between the two techniques.5–9 In this study, we evaluated the reasons for reoperation following primary TKA, comparing MA versus KA. While there was no difference in rates of reoperation between the two groups, there was a higher number of patients undergoing reoperation for extensor mechanism dysfunction in the MA cohort compared to more KA patients experiencing mechanical instability. PJI was a common source of reoperation in both groups.
This study aligns with current literature by seeking to compare two techniques for TKA. A recent meta-analysis conducted by Tian et al. sought to compare the efficacy and imaging parameters of KA versus MA TKAs.5 They included a total of sixteen studies, eleven randomized controlled studies and five cohort studies, with similar results seen between the two techniques.5 The outcome measures assessed included functional scores (including the Knee Society Score, Oxford Knee Score, and the Knee Injury and Osteoarthritis Outcome Score), as well as radiographical measurements, length of operation, and length of hospital stay.5 The authors concluded that there was no difference between the two techniques, with equal benefits seen amongst the patient groups.5 Other studies have found similar results, supporting the notion that there is no significant difference between the two surgical techniques.13,14
Contrastingly, other studies have reported superior benefits following KA TKA compared to the MA technique. A prospective study by Luceri et al. compared the two techniques, with the KA cohort demonstrating significantly higher clinical and functional outcome scores at three months post-operative.10 A study by Elkuluk et al. further supports this stance, with their results demonstrating reduced post-operative pain at six-weeks post-operative as well as higher Forgotten Joint Scores at 1- and 2-years post-operative in patients with a KA TKA when compared to MA.15 All the patients received the same implant and robotic technology.15
In addition to assessing functional outcomes, studies have also focused on surgical results. Prior studies have reported no significant difference in complication rates or reoperation rates between the two techniques.13,16,17 Our study's results support these previous findings, with no significant difference in reoperation witnessed between the two groups. Beyond assessing reoperation rates, however, we sought to identify the reasons for reoperation in an effort to evaluate any potential differences between the MA and KA techniques. While infection was a common source for reoperation amongst both cohorts, more patients in the MA cohort underwent reoperation for extensor mechanism dysfunction compared to more KA patients experiencing mechanical instability.
The mechanical technique involves making a femoral cut at 5° for all patients, rather than aiming to restore their pre-arthritic distal femoral angle as seen with the kinematic technique.18 The mechanical technique may therefore lead to a relative under-resection of the distal lateral femoral condyle in many patients.18 This can then place the extensor mechanism under stress during knee flexion and may contribute to the larger incidence of patients requiring reoperation for extensor mechanism dysfunction in the MA versus KA group in our study.19 Contrastingly, while the KA technique aims to restore native soft tissue tension rather than balancing the knee in all four quadrants, this likely leads to a higher probability of error.18 This may explain why the patients in our KA cohort experienced feelings of instability at a higher rate than the MA patients. Of note, however, all of the patients who experienced instability were effectively treated with upsizing of the polyethylene insert. A final concern with KA knees, particularly in the valgus phenotype, is the risk of patellar dislocation.20 The more valgus the femur is placed, the more medial the trochlea is aimed.20 Howell et al. published his results on a consecutive series of 1117 knees and found his primary complication to be patellofemoral issues, which occurred in the more valgus phenotypes.20 In this study there was one patellar dislocation in each cohort.20 However, the majority of knees were performed using prosthesis with a high trochlear angle (12-14 deg) which may have been protective of this complication.20 Avoiding over flexion of the femoral component is also a strategy to theoretically reduce the incidence of patellofemoral subluxation/dislocation in KA knees.20
The results of this study must be considered within its limitations, including the inherent potential for bias connected to the retrospective design. Next, all of the procedures were performed by a single surgeon, limiting the generalizability of the study. Furthermore, the study lacks the strength of a randomized control trial. Since the senior author switched his technique from MA to KA, there is the potential for bias associated with the reasoning that a surgeon's skills strengthen throughout their career. While unlikely, the variation in implants used between the two groups may have contributed to any differences in results, thus posing a potential limitation. Lastly, while both groups had adequate follow-up time, the KA cohort has had significantly shorter time for follow-up given the timeline of the study. We acknowledge the large discrepancy in follow-up time; however, the main purpose of the study was not trying to prove a higher or lower complication rate between the two techniques, but rather to understand if the types of complications are different between the two groups. Additionally, the vast majority of complications occurred within the first 90 days. Nonetheless, without long term follow-up outcomes such as loosening or poly wear cannot be assessed. However, notably there were no cases of aseptic tibial loosening despite no restrictions on coronal varus alignment.
To our knowledge, this paper is the largest study evaluating the reasons for reoperation between MA and KA TKAs. The results demonstrate no significant difference in reoperation rates with the most common reason for reoperation being PJI. Despite this, the MA cohort did have more instances of reoperation for extensor mechanism disruption compared to mechanical instability being a common cause in the KA group. Future studies are needed to further investigate these two techniques for TKA.
5 Conclusion
In this study, we found no significant difference in reoperation rates between MA and KA primary TKAs. Prosthetic joint infection was a common cause of reoperation amongst both groups. More MA patients required reoperation for extensor mechanism dysfunction while KA patients experienced more mechanical instability.
Percentages and Sample size provided for categorical variables.
Consent
Institutional Review Board approval was submitted and received for this study, and the manuscript is not submitted elsewhere for publication consideration. Patient gave consent for this case report to be written and published.
Ethical review committee statement
The study has been performed in accordance with the ethical standards in the 1964 Declaration of Helsinki and has been carried out in accordance with relevant regulations of the US Health Insurance Portability and Accountability Act (HIPAA).
Funding statement
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
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