Ten-Year Survivorship and Patient Satisfaction Following Robotic-Arm-Assisted Medial Unicompartmental Knee Arthroplasty: A Prospective Multicenter Study

Patient Satisfaction Following Unicompartmental Knee Arthroplasty: Current Concepts

Unicompartmental knee arthroplasty (UKA) has gained progressive popularity in recent decades, currently comprising approximately 10% of knee arthroplasties in the United States. Nonetheless, UKA has not yet solidified its position as the superior treatment for isolated compartment osteoarthritis, as initial reported implant survivorship was subpar, leading to hesitation in its utilization and stricter patient indications compared to total knee arthroplasty. Patient satisfaction following knee arthroplasty has emerged as a critical metric to gauge patient acceptance and contentment with surgical interventions. Currently, a variety of UKA types exist, differing in bearing design, fixation techniques such as cementless or cemented fixation, and robotic-assisted systems, each with its own merits and drawbacks. Multiple studies have demonstrated the contributions of these innovations to improve clinical outcomes and implant survivorship. However, the abundance of studies has made it challenging to establish a clear overview. This paper provides an overview of the current concepts of UKA, evaluating various aspects of UKA referencing to patient satisfaction and providing a recap of its historical development. Available research demonstrated no significantly universal superior variant of UKA.

Arthroscopy Within Three Months Prior to Unicompartmental Knee Arthroplasty is Associated with an Increased Rate of Periprosthetic Joint Infection

INTRODUCTION

Arthroscopy remains a commonly performed procedure in patients who have meniscal or other osteochondral pathology prior to ultimately being indicated for unicompartmental knee arthroplasty (UKA). The purpose of this study was to examine the timing of knee arthroscopy prior to UKA and its association with 2-year periprosthetic joint infection (PJI) rates and medical and surgical complications.

METHODS

Patients undergoing UKA who had history of ipsilateral arthroscopy within two years prior to the UKA were identified in a national insurance database. A control cohort of propensity matched patients who did not have a history of arthroscopy was identified. Study cohorts were established based on timing of the arthroscopic procedure: 0 to 3, 3 to 6, 6 to12, and 12 to 24 months prior to UKA. Patients were included if they had 2-year postoperative follow-up after UKA. The 90-day rates of postoperative medical and 2-year surgical complications were recorded. Multivariate analysis was conducted to account for confounding variables and covariates.

RESULTS

A final cohort of 3,471 patients met inclusion criteria. Patients undergoing UKA within three months of the arthroscopic procedure demonstrated a higher incidence of PJI when compared to the control cohort (3.30 versus 1.12%, P = 0.012). Additionally, there was an increased rate of periprosthetic fracture observed in those undergoing UKA within three months of arthroscopy when compared to the control (1.10 versus 0.20%, P = 0.010).

CONCLUSION

Patients undergoing ipsilateral arthroscopy within three months of a UKA demonstrated a nearly three-fold increased incidence of PJI when compared to the control. There was no increased incidence of PJI when UKA was staged greater than three months after arthroscopy. These findings provide insight for preoperative considerations for arthroplasty surgeons in this patient population.

High accuracy of component positioning and restoration of lower limb alignment using robotic medial unicompartmental knee arthroplasty

PURPOSE

Unicondylar arthroplasty was performed using robotic medial unicompartmental knee arthroplasty (R-mUKA) and gap-balancing instrumentation. Our hypothesis was that robotic unicondylar knee arthroplasty accurately restores component positioning and lower limb alignment when compared to preoperative planning with actual implantation throughout the range of knee motion due to proper knee balancing.

METHODS

Data were collected prospectively and were analysed for patients undergoing RM-UKA. A cemented UKA was implanted using the MAKO® robotic system. Lower limb alignment at 0°, 30°, 45°, 60° and 90° of flexion was recorded of the native knee, with the trial components in place and finally after component implantation. A spacer according to the femorotibial gap was introduced and the alignment was measured. The position of the final component was planned based on three-dimensional computed tomography images before making the bone cuts. The positioning of the femoral and tibial components was analysed in all three planes.

RESULTS

A total of 52 patients were included (mean age 66.3 ± 6.7 years; 34 males, 18 females). The difference in femoral component position after planning and final implantation was 0.04° ± 0.58° more valgus in the coronal plane (p = 0.326) and 0.6° ± 1.4° more flexion relative to the sagittal plane (p = 0.034). The tibial component was placed in the coronal plane in 0.3° ± 0.8° of more varus (p = 0.113) and in the sagittal plane in 0.6° ± 1.2° of more posterior tibial slope (p = 0.001). Lower limb alignment of the native knee in extension was 5.8° ± 2.6° of varus and changed to 3° ± 2.1° varus after UKA (p ≤ 0.01).

CONCLUSION

R-mUKA helps to achieve the target of alignment and component position without any significant differences to the planning. Ligament balancing causes non-significant changes in component position. It allows optimal component position even for off-the-shelf implants respecting the patient's specific anatomy.

LEVEL OF EVIDENCE

II.

Robotic-arm-assisted lateral unicompartmental knee arthroplasty leads to high implant survival and patient satisfaction at mean 10-year follow-up

BACKGROUND

There is a lack of literature reporting on long-term outcomes following robotic-arm-assisted lateral unicompartmental knee arthroplasty (UKA). This study assessed the long-term survivorship, patient-reported satisfaction and pain scores following robotic-arm-assisted lateral UKA for lateral compartment osteoarthritis (OA).

METHODS

A single surgeon's database was reviewed to identify all patients who underwent robotic-arm-assisted lateral UKA with a cemented, fixed-bearing prosthesis prior to May 2015. Patients were contacted to determine implant survivorship, satisfaction and pain. Kaplan-Meier models were applied to analyse survival.

RESULTS

A total of 77 knees (70 patients) with a mean follow-up of 10.2 ± 1.5 years (range: 8.1-13.3) were included. Five knees were revised, corresponding to a 10-year survivorship of 96.1% and estimated survival time of 12.7 ± 0.3 years (95% confidence interval: 12.2-13.2) with all-cause revision as the endpoint. Unexplained pain (40.0%) and progression of OA (40.0%) in contralateral compartments were the most reported reasons for revision. Among patients without revision, 94.4% were either satisfied or very satisfied with their lateral UKA and the average pain score was 1.1.

CONCLUSION

Robotic-arm-assisted lateral UKA led to high implant survivorship and patient satisfaction, and low pain scores at long-term follow-up. Progression of OA in contralateral compartments and unexplained pain were the most frequent reasons for revision. These findings support the continued use of robotic-arm-assisted lateral UKA for lateral compartment OA; however, its clinical value over conventional techniques remains to be established in prospective comparative studies.

LEVEL OF EVIDENCE

Therapeutic Level IV.

Gender does not influence outcomes and complications in medial unicompartmental knee arthroplasty

PURPOSE

The impact of gender on the outcomes of unicompartmental knee arthroplasty (UKA) remains a topic of active discussion with limited exploration thus far. The study aims to elucidate the gender effect on clinical outcomes, complications, pre- and postoperative radiological outcomes following the implantation of a medial UKA at mid-term follow-up in a large section of patients.

METHODS

This was a single-centre, retrospective cohort study encompassing patients undergoing medial UKA between 2011 and 2019. The International Knee Society (IKS) Knee and Function score, patient satisfaction, complications, revisions, pre- and postoperative radiological outcomes (coronal plane alignment, femoral and tibial component positioning, posterior tibial slope) were evaluated. Survival rate at the time of the last follow-up was also recorded.

RESULTS

Of the 366 knees that met the inclusion criteria, 10 were lost to follow-up, accounting for a 2.7% loss. Mean follow-up was 5.2 ± 2 years [2.1-11.3]. Out of the total population, 205 patients were females (57.6%, 205/356) and 151 were males (42.4%, 151/356). Men exhibited superior pre- and postoperative IKS function scores (p = 0.017). However, no significant differences were observed between women and men regarding improvements of IKS Knee and Function scores, radiographic outcomes and implant survivorship.

CONCLUSION

At a mean follow-up of 5 years, this study revealed no significant impact of gender on clinical outcomes and complications in patients undergoing medial UKA. Furthermore, no significant differences were evident in radiographic outcomes, implant positioning and knee phenotype.

LEVEL OF EVIDENCE

Level III.

[Evolving indications for partial knee replacement : New aspects]

BACKGROUND

Partial knee replacement has proven to be an effective therapy for advanced unicompartmental arthrosis of the knee. Despite continuous advancements in implants and surgical techniques over the past decades, the global preference for total knee arthroplasty still persists for historical reasons.

OBJECTIVES

This report aims to illuminate advantages and disadvantages of partial knee replacement considering long-term results, the evolution of indication criteria over recent decades and new aspects in patient selection with potential improvements through emerging technologies.

MATERIAL AND METHODS

The analysis involves the examination of long-term results from clinical studies and registry data, highlighting the risk factors for potential failures and their influence on the development of indication criteria.

RESULTS

Present-day long-term results demonstrate excellent prosthetic survival, aligning with outcomes from total knee arthroplasty. New perspectives for expanding indication criteria are discussed, including the possible application of partial knee replacement in cases of severe varus deformity > 15°, anterior cruciate ligament insufficiency, young active patients, anterior knee pain, and/or patellofemoral arthritis, as well as mild radiographic arthritis with degenerative medial meniscus root tear and meniscal extrusion.

DISCUSSION

Indication criteria have consistently expanded in recent years, taking into account modern insights, and the application of advanced technologies can enhance precision and minimize surgical errors. Furthermore, this report emphasizes that revision rates are not the sole criterion for success and underscores the necessity for a comprehensive examination of clinical results.

The phenotypic diversity of anteromedial osteoarthritis before and after treatment with medial unicompartmental knee arthroplasty: A radiographic analysis of 1000 knees

PURPOSE

This study aimed to assess phenotypic variation in the coronal plane of knees with anteromedial osteoarthritis using the functional knee phenotype classification, before and after treatment with medial unicompartmental knee arthroplasty (UKA).

METHODS

The study comprised 1000 knees of 835 patients (45% females, 55% males, 90% Caucasian) who underwent medial UKA for anteromedial osteoarthritis. Pre and postoperative alignment was evaluated through the hip-knee-ankle angle (HKA), femoral mechanical angle (FMA), and tibial mechanical angle (TMA). Knees were classified according to the functional knee phenotype system which combines limb phenotype (HKA), and femoral and tibial knee phenotypes (FMA and TMA, respectively). Restoration of prearthritic coronal alignment following medial UKA was evaluated by phenotype.

RESULTS

Preoperatively, 76 distinct and 25 relevant (prevalence ≥1%) functional knee phenotypes were identified, of which VARHKA 6°VARFMA 3°NEUTMA 0° was the most common (9.4% of knees). The most prevalent limb phenotype, VARHKA 6°, comprised 15 distinct knee phenotypes (FMA and TMA combinations). Postoperatively, 58 distinct and 17 relevant functional knee phenotypes were observed, of which VARHKA 3°NEUFMA 0°NEUTMA 0° had the highest prevalence at 18.3%. Knees with combined tibial and femoral deformities were associated with a lower probability of restoration of prearthritic coronal alignment following medial UKA, compared to knees without extra-articular deformity, or knees with an isolated tibial or femoral deformity.

CONCLUSION

Phenotype analysis using the functional knee phenotype system demonstrated a wide diversity of coronal alignment phenotypes among knees with anteromedial osteoarthritis in a predominantly Caucasian population. Following medial UKA, a reduction from 25 preoperative to 17 postoperative relevant phenotypes was observed. Consideration of phenotypic variation can be of importance when aiming to restore prearthritic coronal alignment during medial UKA.

LEVEL OF EVIDENCE

Level III, retrospective cohort study.

Image-based robotic-arm assisted unicompartmental knee arthroplasty provides high survival and good-to-excellent clinical outcomes at minimum 10 years follow-up

PURPOSE

The purpose of the present study was to determine the incidence of revision and report on clinical outcomes at a minimum of 10 years follow-up in patients who had received a medial unicompartmental knee arthroplasty (UKA) with an three-dimensional image-based robotic system.

METHODS

A total of 239 patients (247 knees), who underwent medial robotic-arm assisted (RA)-UKA at a single center between April 2011 and June 2013, were assessed. The mean age at surgery was 67.0 years (SD 8.4). Post-operatively, patients were administered the Forgotten Joint Score-12 (FJS-12) and asked about their satisfaction (from 1 to 5). Post-operative complications were recorded. Failure mechanisms, revisions and reoperations were collected. Kaplan-Meier survival curves were calculated, considering revision as the event of interest.

RESULTS

A total of 188 patients (196 knees) were assessed at a mean follow-up of 11.1 years (SD 0.5, range 10.0-11.9), resulting in a 79.4% follow-up rate. Seven RA-UKA underwent revision, resulting in a survivorship rate of 96.4% (CI 94.6%-99.2%). Causes of revision included aseptic loosening (2 cases), infection (1 case), post-traumatic (1 case), and unexplained pain (3 cases). The mean FJS-12 and satisfaction were 82.2 (SD 23.9) and 4.4 (SD 0.9), respectively. Majority of cases (174/196, 88.8%) attained the Patient Acceptable Symptoms State (PASS, FJS-12 > 40.63). Male subjects had a higher probability of attaining a "forgotten joint" (p < 0.001) and high satisfaction (equal to 5, p < 0.05), when compared to females.

CONCLUSIONS

Three-dimensional image-based RA-UKA demonstrated high implant survivorship and good-to-excellent clinical outcomes at minimum 10 years follow-up. Pain of unknown origin represented the most common reason for RA-UKA revision.

LEVEL OF EVIDENCE

III.

Knees with anteromedial osteoarthritis show a substantial phenotypic variation prior and following medial unicompartmental knee arthroplasty

PURPOSE

The primary aim of this study was to evaluate the phenotypic variation using the Coronal Plane Alignment of the Knee (CPAK) classification among 1000 knees with anteromedial osteoarthritis (OA) both prior to and following medial unicompartmental knee arthroplasty (UKA). The secondary aim of this study was to investigate whether knees maintained their preoperative CPAK phenotype and to evaluate the phenotypic alterations following medial UKA.

METHODS

The CPAK classification was used to analyze 1000 knees that underwent medial UKA as treatment for anteromedial OA. Knees were categorized into nine distinct CPAK phenotypes based on their arithmetic hip-knee-ankle angle (aHKA), which estimates the pre-arthritic alignment, and joint line obliquity (JLO), both pre- and postoperatively. Phenotypic variation was analyzed by sex and age, and the phenotypic alterations following medial UKA were evaluated by phenotype.

RESULTS

Preoperatively, CPAK phenotype I had the highest prevalence (45.0%). Among males, the preoperative prevalence of CPAK phenotype I was significantly higher compared to females (53.2% vs. 35.0%, respectively; p ≤ .001), whereas females exhibited a significantly higher occurrence of CPAK phenotype V compared to males (9.8% vs. 4.4%, respectively; p ≤ .015). Following medial UKA, CPAK phenotype II had the highest prevalence (53.3%). Overall, 45.1% of knees maintained their preoperative CPAK phenotype following medial UKA, which was most frequently observed among CPAK phenotype II (67.7%) and III (65.8%).

CONCLUSION

There is a substantial variation in CPAK phenotypes among knees with anteromedial OA, as well as following treatment with medial UKA. This variability challenges the assumption of uniform characteristics among knees with an identical wear pattern associated with anteromedial OA and emphasizes the complexity and variability of this specific form of OA.

LEVEL OF EVIDENCE

III, Retrospective cohort study.

Higher incidence of patellar incongruence after under correction of pre-arthritic coronal alignment following medial unicompartmental knee arthroplasty

PURPOSE

This study aimed to compare patellofemoral joint alignment of knees with restored pre-arthritic coronal alignment versus knees with under- or overcorrection from their pre-arthritic coronal alignment following medial unicompartmental knee arthroplasty (UKA) and evaluate the effect of patellofemoral joint alignment on patient-reported outcomes.

METHODS

A retrospective analysis of 517 knees following robotic-arm assisted medial UKA was conducted. Postoperative mechanical hip-knee-ankle angle (mHKA) was compared to estimated pre-arthritic coronal alignment, using the arithmetic hip-knee-ankle angle (aHKA). Knees were considered restored to the pre-arthritic coronal alignment if mHKA was within 2.0° of aHKA (Group 1). Non-restored knees were subdivided into > 2.0° over correction (Group 2), or > 2.0° under correction (Group 3) from the pre-arthritic coronal alignment. Patellar congruence and patellar tilt angles were compared between groups. The Kujala score and Knee Injury and Osteoarthritic Outcome Score for Joint Replacement (KOOS, JR) were analyzed by group. Continuous data was compared using analysis of variance or Kruskal-Wallis tests. Chi-squared tests were used to compare discrete variables. Logistic regressions were conducted to estimate the probability of postoperative patellofemoral malalignment.

RESULTS

Group 1 included 357 knees (69.1%), Group 2 included 57 knees (11.0%), and Group 3 included 57 knees (11.0%). The prevalence of postoperative abnormal patellar congruence (i.e. ≥ 17°) was higher in Group 3 at 40.4% (p = 0.009), with a higher odds ratio of having an abnormal patellar congruence angle (2.3, p = 0.01) compared to Group 1. The prevalence of postoperative abnormal patellar tilt (i.e. ≥ 14°) was comparable between groups (n.s.). At mean follow up of 4.4 ± 1.6 years, Kujala was worse in Group 3 (76.6 ± 17.4 compared to 84.0 ± 14.9 and 85.0 ± 14.4 in Groups 1 and 2, respectively; p = 0.006). Mean KOOS, JR outcomes were comparable among groups. No significantly inferior Kujala or KOOS, JR outcomes were observed in patients across all groups with abnormal patellar congruence or tilt angles.

CONCLUSION

Knees with under correction from their pre-arthritic coronal alignment following medial UKA were associated with a two-fold higher probability of having postoperative patellofemoral incongruence, as well as inferior mid-term Kujala scores compared to knees with restored pre-arthritic coronal alignment and knees with overcorrection from their pre-arthritic coronal alignment. Patellofemoral incongruence alone did not negatively impact functional outcome scores.

LEVEL OF EVIDENCE

IV, case series.

Cost-utility analysis of robotic arm-assisted medial compartment knee arthroplasty

Aims

To perform an incremental cost-utility analysis and assess the impact of differential costs and case volume on the cost-effectiveness of robotic arm-assisted unicompartmental knee arthroplasty (rUKA) compared to manual (mUKA).

Methods

This was a five-year follow-up study of patients who were randomized to rUKA (n = 64) or mUKA (n = 65). Patients completed the EuroQol five-dimension questionnaire (EQ-5D) preoperatively, and at three months and one, two, and five years postoperatively, which was used to calculate quality-adjusted life years (QALYs) gained. Costs for the primary and additional surgery and healthcare costs were calculated.

Results

rUKA was associated with a relative 0.012 QALY gain at five years, which was associated with an incremental cost per QALY of £13,078 for a unit undertaking 400 cases per year. A cost per QALY of less than £20,000 was achieved when ≥ 300 cases were performed per year. However, on removal of the cost for a revision for presumed infection (mUKA group, n = 1) the cost per QALY was greater than £38,000, which was in part due to the increased intraoperative consumable costs associated with rUKA (£626 per patient). When the absolute cost difference (operative and revision costs) was less than £240, a cost per QALY of less than £20,000 was achieved. On removing the cost of the revision for infection, rUKA was cost-neutral when more than 900 cases per year were undertaken and when the consumable costs were zero.

Conclusion

rUKA was a cost-effective intervention with an incremental cost per QALY of £13,078 at five years, however when removing the revision for presumed infection, which was arguably a random event, this was no longer the case. The absolute cost difference had to be less than £240 to be cost-effective, which could be achieved by reducing the perioperative costs of rUKA or if there were increased revision costs associated with mUKA with longer follow-up.

Robotic-assisted unicompartmental knee arthroplasty: historical perspectives and current innovations

Robotic assisted unicompartmental knee arthroplasty (RAUKA) has emerged as a successful approach for optimizing implant positioning accuracy, minimizing soft tissue injury, and improving patient-reported outcomes. The application of RAUKA is expected to increase because of its advantages over conventional unicompartmental knee arthroplasty. This review article provides an overview of RAUKA, encompassing the historical development of the procedure, the features of the robotic arm and navigation systems, and the characteristics of contemporary RAUKA. The article also includes a comparison between conventional unicompartmental arthroplasty and RAUKA, as well as a discussion of current challenges and future advancements in the field of RAUKA.