Medial unicompartmental knee arthroplasty: does tibial component position influence clinical outcomes and arthroplasty survival?

Impact of the sagittal spinopelvic and coronal lower extremity alignments on clinical outcomes after medial unicompartmental knee arthroplasty

Introduction

We evaluated whether the clinical outcomes, including postoperative knee range of motion (ROM), after unicompartmental knee arthroplasty (UKA) were associated with the sagittal spinopelvic parameters and coronal alignment of the full lower extremity.

Methods

Forty-two patients (50 knees: six men, seven knees; 36 women, 43 knees) who underwent medial UKA between April 2015 and December 2022 were included. Preoperative radiographic examinations of the index for sagittal spinopelvic alignment included the sagittal vertical axis (SVA), lumbar lordosis, sacral slope (SS), pelvic tilt (PT), and pelvic incidence. The anteroposterior hip-knee-ankle angle (HKAA) was calculated. The relationship of clinical outcomes and the risk of knee flexion angle ≤125° and knee flexion contracture ≥10° 1-year post-UKA with radiographic parameters were evaluated.

Results

Preoperative HKA angle affected postoperative knee flexion angle ≤125° (p = 0.017, 95% confidence interval [CI]: 0.473-0.930) in logistic regression analysis. Patients with a knee flexion angle ≤125° had a higher preoperative HKAA (9.8 ± 3.0°), higher SVA (83.8 ± 37.0 mm), and lower SS (23.7 ± 9.0°) than those with a flexion angle >125° (preoperative HKAA: 6.6 ± 4.0°, SVA: 40.3 ± 46.5 mm, SS: 32.0 ± 6.3°) (p = 0.029, 0.012, and 0.004, respectively). PT related to postoperative knee flexion contracture ≥10° (p = 0.010, 95% CI: 0.770-0.965) in the logistic regression analysis. Patients with flexion contracture ≥10° had higher PT (35.0 ± 6.6°) and SVA (82.2 ± 40.5 mm) than those with flexion contracture <10° (PT, 19.3 ± 9.0°; SVA, 42.4 ± 46.5 mm) (p = 0.001 and 0.028, respectively). The postoperative clinical outcome was correlated with the postoperative knee flexion angle and SVA (p = 0.036 and 0.020, respectively).

Conclusions

The preoperative HKAA affected postoperative knee flexion angle, and the knee flexion contracture and clinical outcomes post-UKA were associated with PT and SVA, respectively. To predict outcomes for knee ROM and clinical scores after UKA, radiographic examination, including the sagittal spinopelvic parameters and the coronal view of the full lower extremity, is essential.

Reducing edge loading and alignment outliers with image-free robotic-assisted unicompartmental knee arthroplasty: a case controlled study

BACKGROUND

Survivorship of medial unicompartmental knee arthroplasty (UKA) is technique-dependent. Correct femoral-tibial component positioning associates with improved survivorship. Image-free robotic-assisted unicompartmental knee arthroplasty enables preoperative and intraoperative planning of alignment and assessment of positioning prior to execution. This study aimed to compare the radiological outcomes between robotic-assisted UKA (R-UKA) and conventional UKA (C-UKA).

METHODS

This retrospective case control study involved 140 UKA (82 C-UKA and 58 R-UKA) performed at an academic institution between March 2016 to November 2020, with a mean follow-up of 3 years. Postoperative radiographs were evaluated for mechanical axis and femoral-tibial component position. Component position was measured by two methods: (1) femoral-tibial component contact point with reference to four medial-to-lateral quadrants of the tibial tray and (2) femoral-tibial component contact point deviation from the center of the tibial tray as a percentage of the tibial tray width. Baseline demographics and complications were recorded.

RESULTS

There was a higher mean component deviation in C-UKA compared with R-UKA using method 2 (17.2% vs. 12.8%; P = 0.007), but no difference in proportion of zonal outliers using method 1 (4 outliers in C-UKA, 5.1% vs. 1 outlier in R-UKA, 1.8%; P = 0.403). R-UKA showed no difference in mean mechanical alignment (C-UKA 5° vs. R-UKA 5°; P = 0.250). 2-year survivorship was 99% for C-UKA and 97% for R-UKA. Mean operative time was 18 min longer for R-UKA (P < 0.001).

CONCLUSION

Image-free robotic-assisted UKA had improved component medio-lateral alignment compared with conventional technique.

Methodological Assessment of the 100 Most-Cited Articles in Total Knee Arthroplasty in the Last Decade Compared to the All-Time List

BACKGROUND

Recent advances in total knee arthroplasty (TKA) have been driven by a growing focus on evidence-based medicine. This transition is reflected in the critical appraisal of both, the quality of work and the potential impact on the orthopedic community. The purpose of our study was to (1) identify the top 100 most-cited articles in TKA in the last decade and from all-time, and (2) compare methodological rigor of the most-cited articles in TKA in the last decade to articles all-time by level of evidence.

METHODS

The top 100 cited articles were recorded for manuscripts from the last decade, January 1, 2012 to December 31, 2022, and manuscripts from all-time for TKA. We collected authors, year of publication, journal of the article, country of origin of authors, article type (basic science article, clinical research article), level of evidence, methodological index for non-randomized studies score, physiotherapy evidence database scale, and citation density (total citations/years published).

RESULTS

The largest number of studies for all-time TKA (53.0%) and decade TKA (42.0%) were Level III. The average methodological index for non-randomized studies score for comparative studies was 18.7 for all-time TKA and 20.7 for decade TKA (P < .001). The average physiotherapy evidence database score was 6.1 for all-time TKA and 8.1 for decade TKA (P > .05). The highest citation density for all-time TKA was 111 and for past decade was 63. The number of level II studies in TKA increased from 19.0% from all time to 38.0% from the last decade (P < .05).

CONCLUSIONS

Our findings of improved methodologies over time reflect positive steps toward evidence-based practice in TKA. A continued focus on producing methodologically sound studies may guide evidence-based clinical decision-making.

Robotic-assisted medial unicompartmental knee arthroplasty restored prearthritic alignment and led to superior functional outcomes compared with conventional techniques

PURPOSE

Robotic-assisted medial unicompartmental knee arthroplasty (UKA) can ensure precise preoperative planning, minimise soft tissue damage and restore native coronal alignment. However, few studies have investigated how these advantages translate into differences in early postoperative outcomes. This study aimed to compare differences in early outcomes between conventional UKA (C-UKA) and robotic-assisted UKA (R-UKA).

METHODS

This retrospective study investigated two groups of patients who underwent medial UKA: C-UKA group (n = 35) and R-UKA group (n = 35). We assessed (1) serum indicators (hemoglobin, creatine kinase and C-reactive protein) and pain visual analogue scale (VAS) at postoperative days (PODs) 1, 2, 4 and 6; (2) radiologic parameters including joint line height change and arithmetic and mechanical hip-knee-ankle angle (aHKA and mHKA); (3) patient-reported outcomes including Knee Society Scores, Western Ontario and Mcmaster Universities Arthritis Index (WOMAC) and Forgotten Joint Score-12 (FJS-12) at 1-year follow-up.

RESULTS

Despite similar serum indicator results, pain VAS was lower in the R-UKA group than in the C-UKA group at PODs 2 (2.5 ± 1.3 vs. 3.6 ± 1.2, p = 0.02), 4 (2.4 ± 0.9 vs. 3.3 ± 1.0, p = 0.03) and 6 (1.9 ± 1.1 vs. 3.1 ± 1.1, p < 0.01). The joint line height change was significantly lower in the R-UKA group than in the C-UKA group (0.9 mm ± 0.6 mm vs. 2.0 mm ± 1.3 mm, p = 0.02). The equivalence test for preoperative aHKA and postoperative mHKA revealed equivalence in only the R-UKA group (p < 0.01). The R-UKA group showed better WOMAC and FJS-12 compared to C-UKA group at 1-year follow-up.

CONCLUSION

R-UKA led to lower pain VAS in the early postoperative period compared with C-UKA. Additionally, R-UKA effectively restored the joint line and prearthritic lower limb alignment, resulting in superior functional outcomes at 1-year follow-up compared with C-UKA.

LEVEL OF EVIDENCE

Level III.

Unicompartmental knee replacement: controversies and technical considerations

BACKGROUND

Unicompartmental knee replacement (UKR) is one of the effective interventions for the treatment of symptomatic knee osteoarthritis. Moreover, it has multiple advantages over total knee arthroplasty (TKA), including reduced intraoperative blood loss, decreased risk of transfusion, and faster recovery. This study aimed to discuss critical technical considerations regarding UKR and some of the controversies and updates.

METHODS

We conducted a review to provide an overview of the controversies and technical considerations about UKR in several aspects. Only peer-reviewed articles were included, up to December 2023 using PubMed, Google Scholar, ERIC, and Cochrane database for systematic reviews databases.

RESULT

UKR is associated with superior patient-reported clinical and functional outcomes, as well as shorter hospital stays, fewer postoperative complications, and revealed favorable outcomes in patients' return to sport. The choice between mobile- and fixed-bearing prostheses depends, in part, on the surgeon's preference. The mobile-bearing UKR is a less constrained prosthesis and can potentially result in less wear, but it is more technically demanding. While no significant difference between mobile-bearing versus fixed-bearing prostheses, cementless is superior to cemented design. Furthermore, UKR can be a good alternative for high tibial osteotomy (HTO) and still can be considered after a failed HTO. Lastly, recent reviews have shown a revision rate comparable to that of TKA. This is probably influenced by Improved comprehension of the best indications, patient selection criteria, as well as of the design, materials, and technological advances.

CONCLUSION

UKR treatment for unicompartmental knee osteoarthritis is secure and effective. Based on clinical and functional outcomes, decreased morbidity and mortality, and cost-effectiveness, long-term studies suggest that UKR is superior to TKA. Further investigation in this area is warranted.

Enhancing robotic precision in medial UKA: Image-based robot-assisted system had higher accuracy in implant positioning than imageless robot-assisted system across 292 knees

PURPOSE

The objective of this study was to compare the degree of accuracy in implant positioning and limb alignment offered by two robot-assisted (RA) systems: an image-based robot-assisted (IBRA) versus an imageless robot-assisted (ILRA) system for the treatment of medial knee osteoarthritis with unicompartmental knee arthroplasty (UKA).

METHODS

This retrospective radiographic study included medial UKAs performed between 2011 and 2023. Radiographic measurements taken preoperatively and at 1-year postoperative control visit focusing on hip-knee-ankle angle (HKA), posterior tibial slope (PTS), tibial component coronal alignment relative to Cartier's angle and restoration of proper joint line (JL) height were analyzed. Outliers for postoperative measurements were defined as follows: HKA <175° or >180°, PTS <2° or >8°, >3° or <-3° alterations in Cartier's angle and ±2 mm changes in the height of the joint line.

RESULTS

The final sample consisted of 292 medial UKAs: 95 (32.5%) with an IBRA system and 197 (67.5%) with an ILRA system. Implant positioning and limb alignment were more accurate in the group of patients treated with IBRA, HKA (77.9% vs. 67.5%, p = 0.07), PTS (93.7% vs. 82.7%, p = 0.01), restoration of tibial varus relative to Cartier's angle (87.4% vs. 65%, p < 0.001) and restoration of JL height (81.1% vs. 69.5%, p = 0.04).

CONCLUSION

Medial UKA surgery using an IBRA system was associated with a higher degree of accuracy in implant positioning and postoperative limb alignment as compared to an ILRA system. This is a valuable contribution to help communicate the advantages of using this surgical technique and improve its reproducibility.

LEVEL OF EVIDENCE

Level III, Retrospective cohort study.

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.

Factors predicting lower limb alignment after Oxford medial unicompartmental knee arthroplasty

This study aimed to identify the factors affecting hip-knee-ankle (HKA) angle following Oxford medial unicompartmental knee arthroplasty (MUKA). A retrospective analysis of 200 patients who underwent Oxford MUKA from June 2018 to October 2020 was conducted. Univariate and multivariate analyses were performed to investigate the impact of surgical and radiographic characteristics on the postoperative HKA angle. The mean HKA angle was 9.5 ± 4.3° before surgery and 3.6 ± 3.7° after surgery (p < 0.001). The postoperative HKA angle significantly correlated with the preoperative HKA angle, bearing size, tibial component alignment angle, and BMI (r = 0.71, p < 0.001; r =  - 0.24, p = 0.001; r = 0.21, p = 0.004; r =  - 0.18, p = 0.011). Multiple linear regression analysis revealed that the preoperative HKA angle (β = 0.68, p < 0.001), bearing size (β =  - 0.31, p < 0.001), tibial component alignment angle (β = 0.14, p = 0.003), and BMI (β =  - 0.09, p = 0.047) significantly affected the postoperative HKA angle. In conclusion, larger preoperative varus deformity, smaller bearing size, greater varus alignment of the tibial component, and lower BMI lead to greater postoperative varus alignment of the lower limb in Oxford MUKA. With this concept, surgeons can more accurately predict postoperative lower limb alignment and avoid malalignment in Oxford MUKA.

Fixed-Bearing Unicompartmental Knee Arthroplasty in Tibia Vara Knees Results in Joint Surface Malalignment and Varus Joint Line Obliquity, but Does Not Affect Functional Outcomes at Greater Than 5 Years Follow-Up

BACKGROUND

This study aimed to investigate the clinical outcomes of fixed-bearing medial unicompartmental knee arthroplasty (UKA) for tibia vara knees and the associated changes in joint space malalignment (JSM) and joint line obliquity (JLO).

METHODS

We retrospectively analyzed a consecutive group of 100 patients who underwent fixed-bearing medial UKA with a preoperative medial proximal tibia angle (MPTA) ≥86° (n = 50) and MPTA <86° (n = 50) and who had a minimum 5-year follow-up. Radiological parameters, including the hip-knee-ankle angle, MPTA, and the postoperative JSM and JLO, were measured. Functional evaluation was performed using the range of motion, visual analog scale, Knee Society Knee Score, Knee Society Function Score, and Western Ontario and McMaster Universities Osteoarthritis Index score.

RESULTS

The MPTA <86° group showed significantly higher postoperative JLO (91.8 versus 90.4°, respectively; P = .002) and JSM (6.1 versus 4.2°, respectively; P = .026) compared to the MPTA ≥86° group. Functional outcomes, including range of motion, visual analog scale, Knee Society Knee Score, Knee Society Function Score, and Western Ontario and McMaster Universities Osteoarthritis Index scores, were not significantly different between the 2 groups.

CONCLUSIONS

Fixed-bearing medial UKA is a safe and effective surgical option for patients who have tibia vara knees, as an increase in JLO and JSM postoperatively does not have a clinically relevant impact, even after a minimum 5-year follow-up.

Computed tomography-based patient-specific cutting guides used for positioning of the femoral component of implants during unicompartmental knee arthroplasty: a cadaver study

BACKGROUND

To investigate whether patient-specific instrumentation (PSI) improves the femoral component positioning of implants during unicompartmental knee arthroplasty (UKA) using cadaver bone models.

METHODS

Fifty adult cadaveric femoral bone specimens collected from February 2016-2018, were randomized to receive medial UKA with a PSI guide (n = 25) or conventional instrumentation (CI) (n = 25). Standard anteroposterior and lateral view radiographs were obtained postoperatively to assess the coronal and sagittal positioning of the femoral prostheses, respectively. The osteotomy time was recorded to assess the convenience of PSI in guiding osteotomy.

RESULTS

Osteotomy time significantly shortened in the PSI group (3.12 ± 0.65 versus 4.33 ± 0.73 min, p < 0.001). There was a significant difference in the postoperative coronal alignment of the femoral component between the PSI and CI groups (varus/valgus angle: 1.43 ± 0.93° vs. 2.65 ± 1.50°, p = 0.001). The prevalence of outliers in coronal alignment was lower in the PSI than the CI group (2/25, 8% vs. 9/25, 36%). Sagittal posterior slope angle of the femoral component was significantly different between the two groups (8.80 ± 0.65° and 6.29 ± 1.88° in the CI and PSI groups, respectively, p < 0.001). The malalignment rate of the femoral component in the sagittal plane was 60% in the CI group, whereas no positioning deviation was observed in the PSI group.

CONCLUSION

This study used a cadaver model to support the fact that CT-based PSI shows an advantage over CI in optimizing implant positioning for UKAs.

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.

The effect of different posterior inclinations of tibial component on tibiofemoral contact pressures after unicompartmental knee arthroplasty

BACKGROUND

Different posterior inclinations of tibial component after unicompartmental knee arthroplasty (UKA) may lead to different biomechanical characteristics of the knee joint. This finite element study was designed to investigate the tibiofemoral contact pressures after UKA with different posterior inclinations of tibial component.

METHODS

Finite element model of a healthy knee joint was constructed, and mobile-bearing (MB) UKA models with 5 different posterior inclinations (3°, 5°, 7°, 9° and 11°) of tibial components were simulated. The maximum contact pressures of tibial plateau cartilage in the lateral compartment and polyethylene insert in the medial compartment were calculated based on the ground reaction force and the angle of the knee flexion obtained by 3D motion capture system.

RESULTS

The loading ratio of medial and lateral compartments during standing stance (medial 54.49%, lateral 45.51%) and tibial anterior displacement (134 N, 3.89 mm) of healthy knee was basically consistent with previous experimental data. The maximum contact pressures of the medial meniscus and lateral tibial plateau cartilage of the healthy knee during standing stance were 2.14 MPa and 1.57 MPa, respectively. At the static standing phase, the maximum contact pressures of the polyethylene insert decreased from 17.90 to 17.29 Mpa, and the maximum contact pressures of the tibial plateau cartilage in the lateral compartment increased from 0.81 to 0.92 Mpa following an increase in the posterior inclination of the tibial component. At the first peak of ground reaction force, the maximum contact pressures of polyethylene insert increased from 22.37 to 25.16 MPa, and the maximum contact pressures of tibial plateau cartilage in the lateral compartment increased from 3.03 to 3.33 MPa, with the increase in the posterior inclination of the tibial component. At the second peak of ground reaction force, the maximum contact pressures of polyethylene insert decreased from 2.34 to 2.22 MPa with the increase in posterior inclination of tibial component.

CONCLUSION

The preoperative and postoperative finite element models of MB UKA were well established. The results showed that the maximum contact pressures of the polyethylene insert did not change significantly with the increase in the posterior inclination of the tibial prosthesis, while the maximum contact pressures of the tibial plateau cartilage of the lateral compartment increased when the posterior inclination of the tibial prosthesis was > 7°. Our results also show that the maximum contact pressures were greater with an excessive inclination angle (11°) of the tibial component, and the pressures of the tibial plateau cartilage in the lateral compartment were more concentrated on the posterior area. This study, therefore, proposes that excessive osteotomy should be avoided.

Robotic arm-assisted unicondylar knee arthroplasty resulted in superior radiological accuracy: a propensity score-matched analysis

INTRODUCTION

Unicompartmental knee arthroplasty (UKA) is an effective surgical treatment for medial compartment arthritis of the knee, yet surgical outcomes are directly related to surgical execution. Robotic arm-assisted surgery aims to address these difficulties by allowing for detailed preoperative planning, real-time intraoperative assessment and haptic-controlled bone removal. This study aimed to compare the clinical and radiological outcomes between conventional manual mobile bearing and robot arm-assisted fixed bearing medial UKA in our local population.

MATERIALS AND METHODS

This is a retrospective case-control study of 148 UKAs performed at an academic institution with a minimum of 1-year follow-up. 74 robotic arm-assisted UKAs were matched to 74 conventional UKAs via propensity score matching. Radiological outcomes included postoperative mechanical axis and individual component alignment. Clinical parameters included a range of motion, Knee Society knee score and functional assessment taken before, 6 and 12 months after the operation.

RESULTS

Robot arm-assisted UKA produced a more neutral component coronal alignment in both femoral component (robotic -0.2 ± 2.8, manual 2.6 ± 2.3; P = 0.043) and tibial component (robotic -0.3 ± 4.0, manual 1.7 ± 5.3; P < 0.001). While the postoperative mechanical axis was comparable, robot arm-assisted UKA demonstrated a smaller posterior tibial slope (robotic 5.7 ± 2.7, manual 8.2 ± 3.3; P = 0.02). Clinical outcomes did not show any statistically significant differences.

CONCLUSION

Compared with conventional UKA, robotic arm-assisted UKA demonstrated improved component alignment and comparable clinical outcomes. Improved radiological accuracy with robotic-arm assistance demonstrated promising early results.

Combination of a High Residual Varus and Joint-Line Lowering Strongly Increases the Risk of Early Implant Failure in Medial Unicompartmental Knee Arthroplasty

BACKGROUND

Outliers in implant positioning, malalignment, and joint line height change are risk factors for unicompartmental knee arthroplasty (UKA) failure. However, their relationships and patterns in large datasets remain unexplored. This study assessed medial UKA survival in a large cohort and explored associated risk factors.

METHODS

This was a retrospective cohort study on medial UKA patients (2011 to 2019). Radiological outcomes included tibial implant positioning in the coronal plane, posterior tibial slope, residual knee deformity, and joint line restitution. Survival rate at last follow-up was recorded. Multinomial logistic regression analyzed risk factors, incorporating demographic and univariate analysis data.

RESULTS

Three hundred and sixty-six knees met inclusion criteria, with 10 lost to follow-up (2.7%). Mean follow-up was 61.3 months [24.1 to 135.1]. 5- and 10-year implant survival rates were 92% ± 1.6 and 88.4% ± 3.8, respectively. Multivariate analysis identified post-operative hip-knee-ankle angle (HKA) ≤ 175° (OR = 5.30 [1.64 to 17.13], P = .005) and joint line lowering ≥2 mm (OR = 8.86 [2.06 to 38.06]) as significant risk factors for tibial implant failure. Their combination carried a significantly high risk of failure (OR = 10.3 [3.1 to 34.3]). Post-operative HKA < 175° was common in knees with pre-operative HKA < 172°.

CONCLUSION

This study reports encouraging 5- and 10-year survival outcomes for medial UKA. Tibial loosening was the main reason for revision. Patients with joint line lowering ≥ 2 mm and post-operative HKA ≤ 175° were at high risk of tibial implant failure. Surgeons should carefully restore the joint line in cases of pre-operative HKA < 172°.

Significant correlations between postoperative outcomes and various limb and component alignment strategies in medial unicompartmental knee arthroplasty: a systematic review

PURPOSE

To investigate the correlation between postoperative limb/component alignments and clinical/functional outcomes following medial unicondylar knee arthroplasty (mUKA).

METHODS

Inclusion criteria included peer-reviewed English- or German-language publications assessing postoperative limb or implant alignment and clinical outcomes of mUKA. Methodological Index for Non-Randomized Studies (MINORS) was used to assess article quality.

RESULTS

A total of 2767 knees from 2604 patients were evaluated. Significant correlations were observed between postoperative limb/component alignments and clinical/functional outcomes after mUKA. Inferior outcomes were associated with lower placement and excessive valgus alignment of the tibia component (> 3°). A recommended external rotation of 4°-5° was identified for the tibia component, with specific cut-off values for the femoral and tibia components.

CONCLUSIONS

Optimal outcomes in mUKA were associated with a varus coronal limb alignment. The tibia implant component performed well within a specific alignment range. An exact external rotation value was recommended for the tibia component, while internal rotation correlated negatively with the femoral component.

LEVEL OF EVIDENCE

IV (level IV retrospective case series were included).

Comparison of joint awareness after total knee arthroplasty, medial unicompartmental knee arthroplasty, and high tibial osteotomy: a retrospective study

INTRODUCTION

This study aimed to compare the Forgotten Joint Score-12(FJS) outcomes and the minimum clinically important difference (MCID) of the FJS after high tibial osteotomy (HTO), unicompartmental knee arthroplasty (UKA), and total knee arthroplasty (TKA) with short-term follow-up (at least 2 years). Another objective of the study is to investigate the factors influencing FJS. It is hypothesized that there are differences in FJS outcomes among the three procedures.

METHODS

Patients who underwent HTO, UKA, and TKA from January 2016 to December 2020 and were followed up for a minimum of 2 years were included in the study. The FJS were analyses from a cohort of people who submitted data to two years. The preoperative and postoperative clinical outcomes were compared and evaluated the patient-related factor. The FJS scores were predicted using multiple linear regression analysis. Additionally, Patient's Joint Perception (PJP) questions were used as anchors to determine the achievement of the forgotten joint, and FJS MCID were calculated using the receiver operating characteristic curve (ROC).

RESULTS

Three hundred eighty-nine patients were included in the final study, and there were 111 patients in HTO groups,128patients in UKA groups, and 150 patients in TKA groups. The mean follow-up was 47.0 months. There was a significant difference in the total FJS, between the HTO, UKA, and TKA groups (FJS:59.38 ± 7.25, 66.69 ± 7.44 and 56.90 ± 6.85, p < 0.001. We found the MCID of the FJS of HTO, UKA, and TKA were 63.54, 69.79, and 61.45, respectively. In multiple linear regression, younger age, and higher FS were significant predictors of better FJS.

CONCLUSION

Medial UKA demonstrated lower patient awareness in comparison to HTO and TKA, as assessed by the FJS. Younger age and higher FS were identified as significant predictors of improved FJS, providing valuable guidance for surgical decision-making.

The Reliability of the Divergence Angle for Evaluating Rotational Implant Positioning in Medial Unicompartmental Knee Replacement

Background Unicompartmental knee arthroplasty (UKA) is a highly effective surgical procedure used to treat patients with osteoarthritis affecting a single knee compartment. UKA has gained significant popularity, accompanied by an expansion of its surgical indications. This increasing trend can be attributed to the consistently excellent clinical outcomes associated with UKA, which rival those achieved with total knee arthroplasty (TKA). However, despite these advancements, implant rotation malposition remains a prevalent factor contributing to early failure in UKA cases. The aim of this study is to analyze the rotational positioning of femorotibial implants in UKA and to identify an appropriate angle formed by the femoral component and the tibial component using a newly described angle. Methods This was a retrospective study of patients' data of 40 medial UKA cases of 33 patients who were operated on in our hospital between October 1998 and March 2019. The study introduces a new angle called the "divergence angle." This angle is formed between the lateral portion of the femoral component and the lateral part of the tibial component, as measured on a patellofemoral Merchant view at 30 degrees of knee flexion. The divergence angle was evaluated through radiographic assessment by two independent reviewers. Results According to statistical analysis, the divergence angle was highly reliable with both intra- and inter-observer reproducibility. Intra-observer reproducibility was excellent with an intra-class correlation coefficient (ICC) between 0.901 and 0.933 (p < 0.001). The inter-observer reproducibility was excellent with an ICC of 0.92 (p < 0.001). The Gaussian curve confirmed the normal distribution of the divergence angle values with moderate dispersion of values. The majority of the angles of divergence (85%) measured between the femoral and tibial components were less than 10 degrees (n = 34), with a mean angle of 6.3 ± 4.5°. Conclusion The divergence angle between the femoral and tibial components, measured at 30 degrees of knee flexion using the Merchant view, is an easily accessible, reliable, and reproducible method. This technique enables the assessment of the optimal rotational positioning of implants in medial UKA.

Accuracy of Intraoperative Mechanical Axis Alignment to Long-Leg Radiographs following Robotic-Arm-Assisted Unicompartmental Knee Arthroplasty

Improper alignment and implant positioning following unicompartmental knee arthroplasty (UKA) has been shown to lead to postoperative pain and increase the incidence of revision procedures. The use of robotic-arm assistance for UKA (RAUKA) has become an area of interest to help overcome these challenges. The accuracy of intraoperative alignment compared with standing long-leg X-rays postoperatively following medial RAUKA has been in question. Therefore, the purpose of this study was to (1) determine final mean intraoperative coronal alignment in extension utilizing an image based intraoperative navigation system, and (2) compare final intraoperative alignment to 6-week weight-bearing (WB) long-leg X-rays. Patients who underwent RAUKA for medial compartmental osteoarthritis were identified from January 1, 2018, to August 31, 2019, through our institution's joint registry. The query yielded 136 (72 right and 64 left) patients with a mean age of 72.02 years and mean body mass index (BMI) of 28.65 kg/m2 who underwent RAUKA. Final intraoperative alignment was compared with WB long leg X-rays 6 weeks postoperatively by measuring the mechanical alignment. Statistical analysis was primarily descriptive. Pearson's correlation coefficient was used to determine the relationship between intraoperative alignment to 6-week alignment. A p-value of <0.05 was considered statistically significant. Mean intraoperative coronal alignment after resections and trialing was 4.39 varus ± 2.40 degrees for the right knee, and 4.81 varus ± 2.29 degrees for the left knee. WB long-leg X-rays 6 weeks postoperatively demonstrated mechanical axis alignment for the right and left knees to be 3.01 varus ± 2.10 and 3.7 varus ± 2.38 degrees, respectively. This resulted in a change in alignment of 1.36 ± 1.76 and 1.12 ± 1.84 degrees for the right and left knees, respectively (p < 0.05). Pearson's correlation coefficient demonstrated a correlation of 0.69 between intraoperative to long-leg-X-ray alignment. RAUKA demonstrates excellent consistency when comparing postoperative WB long-leg X-rays to final intraoperative image-based non-WB alignment.

Comparing inter- and intraobserver reliability between two-dimensional and three-dimensional measurements in the tibial component position of unicompartmental knee arthroplasty

In unicompartmental knee arthroplasty (UKA), the tibial component has a small coronal plane width, the tibia and tibial component rotations are mismatched, and the large tibial component posterior tilt may make accurate measurements of component positions difficult in radiography. The study aimed to assess the intra- and interobserver reliabilities of radiographic (2D) and 3D computed tomography (3D-CT) measurements and to determine the minimum detectable change (95% confidence level, MDC95) in the tibial component position measurements in UKA. The study included 23 females and 7 males. Two surgeons measured the tibial component position. Intraclass and interclass correlation coefficients (ICC) were calculated to obtain reliability, and Bland-Altman analysis was performed to assess systematic errors. The MDC95 was calculated according to MDC95 = standard error of measurement × 1.96 × √2. In the 2D and 3D- CT measurements, intraobserver reliability for coronal and sagittal positions of the tibial component were sufficiently reliable, where ICCs were >0.8. In the coronal plane, the ICCs for interobserver reliability were lower in 2D (ICC, 0.5-0.7) than in 3D-CT (ICC > 0.9). Bland-Altman plots showed systematic bias in sagittal alignment in the 2D assessment. In the 3D assessment of intra- and interobserver reliability, the MDC95 of the coronal, sagittal, and axial planes was <2°. In the 2D intra- and interobserver reliability, the MDC95 of the coronal and sagittal planes was >2°. The 2D measurement had a risk of misidentifying the tibial component position in UKA.

Setting the Tibial Component Rotation Based on Femoral Landmarks Allows Congruent Knee Kinematics in Robotic-Assisted Medial Unicompartmental Knee Replacement

The accurate positioning of the prosthetic components is essential for achieving successful results in medial unicompartmental knee arthroplasty (mUKA). The tibial component rotation in image-based robotic-assisted UKA is usually based on tibial bony landmarks matched to the pre-operative CT model. The study aimed to evaluate whether setting the tibial rotation on femoral CT-based landmarks allows congruent knee kinematics. We retrospectively analyzed data from 210 consecutive image-based robotic-assisted mUKA cases. In every case, we set the tibia rotation landmark parallel to the posterior condylar axis and centered it on the trochlea groove defined on the preoperative CT scan. The implant positioning was primarily set parallel to this rotation landmark and then adjusted based on tibial sizes avoiding component over- or under-hang. During surgery, we recorded the knee kinematics under valgus stress to reduce the arthritic deformity. A femoral-tibial contact point was recorded over the entire range of motion and displayed as a tracking profile on the tibia implant. The femoro-tibial tracking angle (FTTA) was then calculated based on a tangent line to the femoro-tibial tracking-points and the difference to the femur-based rotation landmark. In 48% of the cases, we could position the tibia component exactly to the femoral rotation landmark, whereas in 52% of cases, minimal adjustments were made to avoid component’s under- or over-hang. The mean tibia component rotation (TRA) with reference to our femur-based landmark was +0.24° (SD ± 2.9°). The femur-based tibia rotation landmark showed a high correspondence to the FTTA with 60% of the cases having less than 1° of deviation. Mean FTTA was +0.7° (SD ± 2.2°). The mean difference between the absolute value of the TRA and the FTTA (|TRA| − |FTTA|) was −0.18° (SD ± 2°). Setting the tibial component rotation based on CT scan femoral landmarks and not on tibial anatomical landmarks is a reliable method to obtain congruent knee kinematics during image-based robotic-assisted medial UKA with less the 2° deviations on average.

Preoperative Bone Marrow Edema Negatively Impacts 10-Year Outcomes After Unicompartmental Knee Arthroplasty

BACKGROUND

The purpose of this study was to investigate the association between the extent of subchondral bone marrow edema (BME), as classified by magnetic resonance imaging, and intermediate to long-term outcomes after unicompartmental knee arthroplasty (UKA) for medial compartment osteoarthritis.

METHODS

We enrolled 150 knees (144 patients) that underwent fixed-bearing UKA between April 2003 and December 2014 with a minimum follow-up of 5 years; the mean overall follow-up duration was 10 years (range, 5-18 years). We divided the patients into 2 groups based on the presence or absence of preoperative BME. Patients were also subdivided into 4 groups according to their BME scores determined by the magnetic resonance imaging Osteoarthritis Knee Score method. Clinical outcomes were assessed using the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) and the Forgotten Joint Score. Furthermore, survival rates and relevant risk factors that affect joint survivorship were analyzed.

RESULTS

The groups with BME demonstrated significantly worse postoperative WOMAC pain and Forgotten Joint Scores at the final follow-up than the group without BME (all P < .05). We also found significant differences among the scores of groups with different BME grades (all P < .05). Post hoc analysis demonstrated differences between groups 1 and 2, 1 and 3, 1 and 4, and 2 and 4 (all P < .05) with a significant correlation between postoperative clinical outcomes and the extent of BME (r = 0.430 [WOMAC pain], r = -0.342 [Forgotten Joint Score]; P < .05). The survival rate was 95.4% for a mean period of 10 years for the UKAs, and the UKA survival was not associated with the presence of BME (P = .232; log-rank test).

CONCLUSION

At a mean of 10 years, preoperative BME negatively impacted the clinical outcomes, especially pain, after UKA. However, UKA contributed to excellent survival rates for the same duration of follow-up, regardless of BME severity. Although this study does not provide any evidence that preoperative BME should be identified as a contraindication, evaluation of BME can provide crucial information about the expected outcomes.

Better accuracy and implant survival in medial imageless robotic-assisted unicompartmental knee arthroplasty compared to conventional unicompartmental knee arthroplasty: two- to eleven-year follow-up of three hundred fifty-six consecutive knees

PURPOSE

Implant malpositioning, joint line (JL) lowering, and malalignment have been identified as risk factors for implant failure in unicompartmental knee arthroplasty (UKA). The aims of this study were to compare the accuracy of implant positioning in robotic-assisted UKA versus conventional UKA in a large cohort and examine the correlation with implant survival at mid-term follow-up.

METHODS

This retrospective study included 356 medial UKAs from 2011 to 2019. The radiological measurements performed were coronal positioning of tibial implant according to Cartier angle (Δ Cartier), posterior tibial slope (PTS), residual hip-knee-ankle (HKA), and JL restoration. Outliers were defined as follows: post-operative HKA < 175° or > 180°, Δ Cartier > 3° or <  - 3°, JL change ≥ 2 mm, and PTS < 2° or > 8°. The survival probability was reported at the last follow-up.

RESULTS

Out of the 356 knees included, 159 underwent conventional UKA (44.5%) and 197 (55.5%) robotic-assisted UKA. The mean follow-up was 61.3 months ± 24.0. Robotic UKA was associated with better accuracy compared to conventional UKA in relation to HKA (67% vs 56%, p = 0.023), JL restoration (70% vs 44%, p < 0.0001), PTS (83% vs 55%, p < 0.0001), and tibial varus restoration (65% vs 55%, p = 0.049). Implant survival in the robotic group was found to be superior at the last follow-up (96.4% versus 87.3% at 9 years, p = 0.004).

CONCLUSION

Robotic assistance in patients undergoing medial UKA was associated with better accuracy compared to conventional UKA with respect to tibial implant positioning, post-operative limb alignment, and JL restoration. This was translated in improved survival at mid-term follow-up favouring the robotic group.

Pre-operative predictive factors of residual varus on the mechanical axis after Oxford unicompartmental knee arthroplasty

Background

Residual varus after Oxford unicompartmental knee arthroplasty (UKA) happens frequently. This study aims to evaluate the pre-operative contributing factors of residual varus.

Methods

A total of 1,002 knees (880 patients, 201 patients were male, and 679 were female) underwent Oxford UKA in the Orthopedic Surgery Department of the Beijing Jishuitan Hospital from March 2018 to April 2021. The mean age of the patient was 64.7 ± 7.7 years. To assess residual varus, the full-length lower extremity is placed upright for EOS imaging, with the knee fully extended. The angle of post-operative residual varus was measured as described by Noyes et al. Of the knees studied, they were either categorized into an under-corrected group (post-operative Noyes angle >5°) or a corrected group (post-operative Noyes angle ≤5°). Age, gender, body mass index (BMI), range of motion (ROM), Clinical American Knee Society Score (Clinical AKSS), and Function American Knee Society Score (Function AKSS) were compared. The following additional parameters were measured: pre-operative Noyes angle, lateral distal femoral angle (LDFA), medial proximal tibial angle (MPTA), the posterior slope of the proximal tibia angle (PPTA), joint line converge angle (JLCA), and fixed flexion deformity (FFD).

Results

There was no statistically significant difference between the two groups in regards to gender (p = 0.428), surgical leg (p = 0.937), age (p = 0.851), BMI (p = 0.064), pre-operative Clinical AKSS (p = 0.206) and Function AKSS (p = 0.100). However, pre-operative ROM statistically differed between the two groups (p < 0.001). The contributing factors of post-operative residual varus were determined to be the following parameters: pre-operative MPTA (p < 0.001, OR = 4.522, 95% CI: 2.927-6.984), pre-operative Noyes (p < 0.001, OR = 3.262, 95% CI: 1.802-5.907) and pre-operative FFD (p = 0.007, OR = 1.862, 95% CI: 1.182-2.934). The effects of pre-operative LDFA (p = 0.146), JLCA (p = 0.942), and pre-operative PPTA (p = 0.899) on the post-operative mechanical axis did not show statistical significance.

Conclusions

Patients with severe pre-operative varus, particularly varus deformity mainly from the tibial side or pre-operative FFD, are more prone to get extremity mechanical axis residual varus after UKA with Oxford.

Robotic-Assisted Unicompartmental Knee Arthroplasty Reduces Components' Positioning Differences among High- and Low-Volume Surgeons

Robotic-assisted medial unicompartmental knee arthroplasty (mUKA) has been introduced to improve accuracy in implant positioning and limb alignment, overcoming the reported high failure rates of conventional UKA. Indeed, mUKA is a technically challenging procedure strongly related to surgeons' skills and expertise. The purpose of this study was to evaluate the likelihood of robotic-assisted surgery in reducing the variability of coronal and sagittal component positioning between high- and low-volume surgeons. We evaluated a prospective cohort of 161 robotic mUKA implanted between May 2018 and December 2019 at two high-volume robotic centers. Patients were divided into two groups: patients operated by "high-volume" (group A) or "low-volume" (group B) surgeons. We recorded intraoperative lower-limb alignment, component positioning, and surgical timing. Postoperatively, every patient underwent a radiographical protocol to assess coronal and sagittal femoral/tibial component alignment. Range of motion and other clinical outcomes were assessed pre- and 12 months postoperatively by using oxford knee score, forgotten joint score, and visual analog scale. Of 161 recruited knees, 149 (A: 101; B: 48) were available for radiographic analysis at 1 month, and clinical evaluation at 12 months. No clinical difference neither difference in mechanical alignment nor coronal/sagittal component positioning were found (p > 0.05). A significant difference was recorded in surgical timing (A: 57 minutes; B: 86 minutes; p < 0.05). No superficial or deep infections or other major complications have been developed during the follow-up. Robotics surgery in mUKA confirmed its value in improving the reproducibility of such technical procedure, with satisfactory clinical outcomes. Moreover, it almost eliminates any possible differences in component positioning, and lower limb alignment among low-and high- volume knee surgeons.

Unicompartmental Knee Arthroplasty Has Lower Infection, Conversion, and Complication Rates Compared to High Tibial Osteotomy

INTRODUCTION

 Isolated medial knee osteoarthritis can be surgically treated with either unicompartmental knee arthroplasty (UKA) or high tibial osteotomy (HTO). Proponents of UKA suggest superior survivorship, while HTO offers theoretically improved alignment and joint preservation delaying total knee arthroplasty (TKA). Therefore, we compared complications in a large population of patients undergoing UKAs or HTOs. We specifically assessed 90 days, 1 year, and 2 years: (1) periprosthetic joint infection (PJI) rates, (2) conversion to TKA rates, as well as (3) complication rates.

METHODS

 A review of an administrative claims database was used to identify patients undergoing primary UKA (n = 13,674) or HTO (n = 1,096) from January 1, 2010 to December 31, 2019. Complication rates at 90 days, 1 year, and 2 years were compared between groups using unadjusted odds ratios (ORs) with 95% confidence intervals. Subsequently, multivariate logistic regressions were performed for PJI and conversion to TKA rates.

RESULTS

 At all time points, patients who underwent UKA were associated with lower rates of infection compared with those who underwent HTOs (all OR ≤ 0.51, all p ≤ 0.010). After 1 year, patients who received UKAs were found to have lower risk of requiring a conversion to a TKA versus those who received HTOs (all OR ≤ 0.55, all p < 0.001). Complications such as dislocations, periprosthetic fractures, and surgical site infections were found at lower odds in UKA compared with HTO patients.

CONCLUSION

 This study provides large-scale analyses demonstrating that UKA is associated with lower infection rates and fewer conversions to TKA compared with patients who have undergone HTO. Dislocations, periprosthetic fractures, and surgical site infections were also found to be lower among UKA patients. However, with careful patient selection, good results and preservation of the native knee are achieved with HTOs. Therefore, UKA versus HTO may be an important discussion to have with patients in an effort to lower the incidence of postoperative infections and complications.

Referencing the Tibial Plateau With a Probe Improves the Accuracy of the Posterior Slope in Medial Unicompartmental Knee Arthroplasty

Background

There is currently no consensus on intraoperative references for determining the posterior tibial slope (PTS) in medial unicompartmental knee arthroplasty (UKA). The medial tibial plateau could serve as a direct reference for determining the native PTS through the placement of a hook probe in the anteroposterior direction of the medial tibial plateau. This study aimed to examine the accuracy of this new referencing method.

Methods

We consecutively performed 55 medial UKAs using our new method (study group), and the preoperative and postoperative PTS on lateral knee radiographs were examined. These outcomes were then compared with those of consecutive 50 medial UKAs performed using the conventional method (control group), which immediately preceded the start of the use of the new method.

Results

The correlation coefficient between the preoperative and postoperative PTS of the study group was larger than that of the control group (0.887 and 0.482, respectively). The mean implantation error of the PTS in the study group was smaller than that of the control group (-1.1° ± 1.3° and -3.0° ± 3.2°, respectively; P < .0001). The percentages of knees within 2° of implantation error were 73% and 34% in the study and control groups, respectively (P < .0001). The root mean square errors in the study and control groups were 1.7° and 4.3°, respectively.

Conclusions

The direct referencing method with a probe can significantly improve the accuracy of tibial sagittal alignment.

Improved accuracy and reproducibility of a novel CT-free robotic surgical assistant for medial unicompartmental knee arthroplasty compared to conventional instrumentation: a cadaveric study

PURPOSE

Alignment errors in medial unicompartmental knee arthroplasty (UKA) predispose to premature implant loosening and polyethylene wear. The purpose of this study was to determine whether a novel CT-free robotic surgical assistant improves the accuracy and reproducibility of bone resections in UKA compared to conventional manual instrumentation.

METHODS

Sixty matched cadaveric limbs received medial UKA with either the ROSA^® Partial Knee System or conventional instrumentation. Fifteen board-certified orthopaedic surgeons with no prior experience with this robotic application performed the procedures with the same implant system. Bone resection angles in the coronal, sagittal and transverse planes were determined using optical navigation while resection depth was obtained using calliper measurements. Group comparison was performed using Student's t test (mean absolute error), F test (variance) and Fisher's exact test (% within a value), with significance at p < 0.05.

RESULTS

Compared to conventional instrumentation, the accuracy of bone resections with CT-free robotic assistance was significantly improved for all bone resection parameters (p < 0.05), other than distal femoral resection depth, which did not differ significantly. Moreover, the variance was significantly lower (i.e. fewer chances of outliers) for five of seven parameters in the robotic group (p < 0.05). All values in the robotic group had a higher percentage of cases within 2° and 3° of the intraoperative plan. No re-cuts of the proximal tibia were required in the robotic group compared with 40% of cases in the conventional group.

CONCLUSION

The ROSA^® Partial Knee System was significantly more accurate, with fewer outliers, compared to conventional instrumentation. The data reported in our current study are comparable to other semiautonomous robotic devices and support the use of this robotic technology for medial UKA.

LEVEL OF EVIDENCE

Cadaveric study, Level V.

Predictors of a forgotten joint after medial fixed-bearing unicompartmental knee arthroplasty

BACKGROUND

A forgotten joint is considered the ultimate goal of joint replacement. We aim to explore the predictive factors of a forgotten joint after fixed-bearing unicompartmental knee arthroplasty (UKA).

METHODS

This retrospective cohort study used prospectively collected data from 302 cases of medial-compartment UKA with a minimum of 2-year follow-up. The primary outcome was the achievement of a forgotten joint after UKA, according to the Forgotten Joint Score (FJS-12) at the last follow-up. Patients with FJS-12 > 84 were considered to have forgotten UKA. Univariate and multivariate logistic regression analyses were conducted with preoperative patient characteristics and surgery-related factors as potential predictors.

RESULTS

Of patients, 94 (31.1%) achieved a forgotten joint post-surgery. Multivariate logistic regression analysis revealed that preoperative hip-knee-ankle angle (HKAA), anatomic lateral distal femoral angle (aLDFA), and postoperative HKAA and HKAA changes were independent predictors of a forgotten joint. The probability of achieving a forgotten joint increased by 29% (OR = 1.29, 95% CI: 1.12-1.51) with a 1° increase in aLDFA. Preoperative HKAA, postoperative HKAA, HKAA changes (ΔHKAA), and outcomes exhibited a non-linear relationship. The probability of achieving a forgotten joint was the highest with preoperative HKAA > 172.0°, postoperative HKAA of 176.0-178.5°, and ΔHKAA < 5.5°.

CONCLUSION

To achieve the forgotten joint state, the ideal HKAA range after medial fixed-bearing UKA is 176.0-178.5° and ΔHKAA should be <5.5°. Patients with smaller preoperative aLDFA and HKAA have a lower probability of achieving a forgotten joint after UKA.

Proximal tibial morphology is associated with risk of trauma to the posteromedial structures during tibial bone resection reproducing the anatomical posterior tibial slope in bicruciate-retaining total knee arthroplasty

BACKGROUND

A tibial cut with the native posterior tibial slope (PTS) is a theoretical prerequisite in bicruciate-retaining total knee arthroplasty (BCRTKA) to regain physiological knee kinematics. The present study reveals tibial morphological risk factors of trauma to the posteromedial structures of the knee during tibial bone resection in BCRTKA.

METHODS

Fifty patients undergoing BCRTKA for varus knee osteoarthritis were analyzed. A three-dimensional tibial bone model was reconstructed using a computed tomography-based preoperative planning system, and the coronal tibial slope (CTS) and medial PTS (MPTS) were measured. Then, we set the simulated tibial cutting plane neutral on the coronal plane, posteriorly inclined in accordance with the MPTS on the sagittal plane, and 9 mm below the surface of the subchondral cortical bone (i.e., 11 mm below the surface of the cartilage) of the lateral tibial plateau. The association between the tibial morphology and the distance from the simulated cutting plane to the semimembranosus (SM) insertion (Dsm) was analyzed.

RESULTS

Of the 50 patients, 19 (38%) had negative Dsm values, indicating a cut into the SM (namely, below the posterior oblique ligament) insertion. The MPTS was negatively correlated with Dsm (r = -0.396, p = 0.004), whereas the CTS was positively correlated with Dsm (r = 0.619, p < 0.001). On multivariate linear regression analysis, the MPTS and CTS were independent predictors of Dsm.

CONCLUSION

In the setting of tibial cuts reproducing the native MPTS in BCRTKA, patients with larger PTS and smaller CTS had more risk of trauma to the posteromedial structures.

Robotic-Assisted Versus Manual Unicompartmental Knee Arthroplasty: A Time-Driven Activity-Based Cost Analysis

BACKGROUND

The cost-effectiveness of robotic-assisted unicompartmental knee arthroplasty (RA-UKA) remains unclear. Time-driven activity-based costing (TDABC) has been shown to accurately reflect true resource utilization. This study aimed to compare true facility costs between RA-UKA and conventional UKA.

METHODS

We identified 265 consecutive UKAs (133 RA, 132 conventional) performed at a specialty hospital in 2016-2020. Itemized facility costs were calculated using TDABC. Separate analyses including and excluding implant costs were performed. Multiple regression was performed to determine the independent effect of robotic assistance on facility costs.

RESULTS

Due to longer operative time, RA-UKA patients had higher personnel costs and total facility costs ($2,270 vs $1,854, P < .001). Controlling for demographics and comorbidities, robotic assistance was associated with an increase in personnel costs of $399.25 (95% confidence interval [CI] $343.75-$454.74, P < .001), reduction in supply costs of $55.03 (95% CI $0.56-$109.50, P = .048), and increase in total facility costs of $344.27 (95% CI $265.24-$423.31, P < .001) per case. However, after factoring in implant costs, robotic assistance was associated with a reduction in total facility costs of $235.87 (95% CI $40.88-$430.85, P < .001) per case.

CONCLUSION

Using TDABC, overall facility costs were lower in RA-UKA despite a longer operative time. To facilitate wider adoption of this technology, implant manufacturers may negotiate lower implant costs based on volume commitments when robotic assistance is used. These supply cost savings appear to offset a portion of the increased costs. Nonetheless, further research is needed to determine if RA-UKA can improve clinical outcomes and create value in arthroplasty.

St Georg Sled medial unicompartmental arthroplasty: survivorship analysis and function at 20 years follow up

PURPOSE

The peri-operative and short-term benefits of unicompartmental knee arthroplasty (UKA) are well supported in the literature. However, there remains concern regarding the higher revision rate when compared with total knee replacement. This manuscript reports the functional outcome and survivorship of a large series of fixed bearing, medial unicompartmental replacements (St Georg Sled), with a minimum of 20 years follow-up.

METHODS

Between 1974 and 1994, 399 patients (496 knees) underwent a medial fixed-bearing UKA. Prospective data were collected pre-operatively and at regular intervals post-operatively using the Bristol Knee Score (BKS), Oxford Knee (OKS) and Western Ontario MacMaster (WOMAC) scores. Kaplan-Meier survival analysis was used to determine survivorship, with revision or need for revision as end point, and differences assessed using Mantel-Cox log rank test.

RESULTS

Functional knee scores improved post-operatively, but demonstrated a slight decline from 10 years of follow-up onwards. Survivorship is estimated as 86% at 10 years, 80% at 15 years, and 78% at 20 years. Sixty knees were revised, with progression of disease in another compartment the commonest reason. Eighty eight percent were revised using a primary prosthesis. For patients over the age of 65 years at the time of index procedure, 93% died with a functioning prosthesis in situ.

CONCLUSION

Medial UKA demonstrates good long-term function and survivorship, and represents an excellent surgical option for patients aged over 65 years of age, where few patients will require a revision procedure.

LEVEL OF EVIDENCE

IV.

Patient-specific instruments do not show advantage over conventional instruments in unicompartmental knee arthroplasty at 2 year follow-up: a prospective, two-centre, randomised, double-blind, controlled trial

PURPOSE

The aim of this two-centre RCT was to compare pre- and post-operative radiological, clinical and functional outcomes between patient-specific instrumentation (PSI) and conventional instrumented (CI) unicompartmental knee arthroplasty (UKA). It was hypothesised that both alignment methods would have comparable post-operative radiological, clinical and functional outcomes.

METHODS

One hundred and twenty patients were included, and randomly allocated to the PSI or the CI group. Outcome measures were peri-operative outcomes (operation time, length of hospital stay and intra-operative changes of implant size) and post-operative radiological outcomes including the alignment of the tibial and femoral component in the sagittal and frontal plane and the hip-knee-ankle-axis (HKA-axis), rate of adverse events (AEs) and patient-reported outcome measures (PROMs) pre-operatively and at 3, 12 and 24 months post-operatively.

RESULTS

There was a statistically significant difference (p < 0.05) in alignment of the femoral component in the frontal plane in favour of the CI method. No statistically significant differences were found for the peri-operative data or in the functional outcome at 2-year follow-up. In the PSI group, the approved implant size of the femoral component was correct in 98.2% of the cases and the tibial component was correct in 60.7% of the cases. There was a comparable rate of AEs: 5.1% in the CI and 5.4% in the PSI group.

CONCLUSION

The PSI method did not show an advantage over CI in regard of positioning of the components, nor did it show an improvement in clinical or functional outcome. We conclude that the possible advantages of PSI do not outweigh the costs of the MRI scan and the manufacturing of the PSI.

LEVEL OF EVIDENCE

Randomised controlled trial, level I.

Kinematic alignment of medial UKA is safe: a systematic review

PURPOSE

Owing to the improved understanding of knee kinematics and the successful introduction of the kinematic alignment (KA) technique for implanting total knee arthroplasty (TKA), it was recently understood that the "Cartier angle technique" corresponds to a kinematic implantation of the uni-compartmental knee arthroplasty (UKA) components. When compared to the universally spread mechanical alignment (MA) technique for implanting UKA, the KA method generates a more anatomic prosthetic knee that may be clinically advantageous. The aims of this study are to determine if KA UKAs are associated with acceptable functional performance and patient satisfaction (question 1), rates of residual pain and tibia plateau fracture (question 2), and rates of reoperation and revision (question 3), and to define the component orientation and limb alignment as measured on radiograph (question 4), and the stress shielding related bone loss in the proximal tibia (question 5) with KA UKA, and where possible to compare with MA UKA.

STUDY HYPOTHESIS

KA UKA generates good clinical outcomes, similar or superior to the ones of MA UKA.

METHOD

Systematic review of literature databases were primarily searched using Healthcare Databases Advanced Search (HDAS). Two primary searches were conducted using the electronic databases MEDLINE, EMBASE, and PubMed, and a secondary search was conducted using review articles and bibliography of obtained papers in order to ascertain more material.

RESULTS

Nine eligible non-comparative prospective (3) or retrospective (6) cohort studies, which cumulated 593 KA UKAs with follow-up between 3.2 and 12 years, fulfilled the inclusion criteria for this systematic review. The findings demonstrated high Knee Society Score (KSS) (from 87 to 95) and function scores (from 81 to above 91) in addition to patient satisfaction scores of 88%. There was no revision for tibia plateau fracture, 0.8% (5 cases) for unexplained pain tibia, 2.0% (12 cases) for component loosening, and 5.6% (33 cases) for any causes of aseptic failures reported for KA UKA. The prosthetic lower limb and tibia implant alignments were both found to be in slight varus (means between 3 and 5°), and the postoperative joint line and tibia component was shown to be parallel to the floor when standing. The KA UKA components migration, as measured on radiostereometry, was acceptable.

DISCUSSION/CONCLUSION

The KA technique is an alternative, personalised, more physiological method for implanting UKA, which could be clinically advantageous when compared to the MA technique. The literature supports the good mid- to long-term clinical safety and good efficacy of KA UKA; however, comparison between KA and MA techniques for UKA was not performed due to limited literature. Further investigations are needed to better define the clinical impact of KA UKA, and the acceptable limits for KA of the UKA tibial component.

LEVEL OF EVIDENCE

Level 4; systematic review of level 4 studies.

Revision indications for medial unicompartmental knee arthroplasty: a systematic review

INTRODUCTION

Unicompartmental knee arthroplasty (UKA) has advantages over total knee arthroplasty including fewer complications and faster recovery; however, UKAs also have higher revision rates. Understanding reasons for UKA failure may, therefore, allow for optimized clinical outcomes. We aimed to identify failure modes for medial UKAs, and to examine differences by implant bearing, cement use and time.

MATERIALS AND METHODS

A systematic review was conducted by searching MedLine, EMBASE, CINAHL and Cochrane databases from 2000 to 2020. Studies were selected if they included ≥ 250 participants, ≥ 10 failures and reported all failure modes of medial UKA performed for osteoarthritis (OA).

RESULTS

A total of 24 cohort and 2 registry-based studies (levels II and III) were selected. The most common failure modes were aseptic loosening (24%) and OA progression (30%). Earliest failures (< 6 months) were due to infection (40%), bearing dislocation (20%), and fracture (20%); mid-term failures (> 2 years to 5 years) were due to OA progression (33%), aseptic loosening (17%) and pain (21%); and late-term (> 10 years) failures were mostly due to OA progression (56%). Rates of failure from wear were higher with fixed-bearing prostheses (5% cf. 0.3%), whereas rates of bearing dislocations were higher with mobile-bearing prostheses (14% cf. 0%). With cemented components, there was a high rate of failure due to aseptic loosening (27%), which was reduced with uncemented components (4%).

CONCLUSIONS

UKA failure modes differ depending on implant design, cement use and time from surgery. There should be careful consideration of implant options and patient selection for UKA.

Makoplasty medial unicondylar knee replacement: Correction or postoperative angle matters?

INTRODUCTION

Various considerations prevail around optimal postoperative varus deformity, correction angle and physiological constitutional varus deformity. The goal of our present study was to understand correlation between these parameters and their influence over Western Ontario McMaster University Osteoarthritis Index scale (WOMAC).

MATERIALS AND METHODS

Consecutive robotic-arm-assisted medial onlay fixed bearing unicompartmental knee arthroplasty (UKA) in 143 knees studied. WOMAC score was recorded preoperatively and at specific intervals after surgery for consecutive 2 years.

RESULTS

Mean preoperative and postoperative varus deformities were 10.2° and 4.8°, respectively, and mean correction angle was 5.4°. The preoperative varus and correction angles were found well correlated (r = 0.815). The amount of improvement in the WOMAC total score was not influenced by the postoperative varus angle.

CONCLUSION

The correction angle has a stronger correlation with preoperative varus deformity, and postoperative varus deformity does not imply favourable clinical outcomes.

The Medial Tibial Plateau Can Be Used as a Direct Anatomical Reference for the Posterior Tibial Slope in Medial Unicompartmental Knee Arthroplasty

There has been no consensus about how to determine the individual posterior tibial slope (PTS) intraoperatively. The purpose of this study was to investigate whether the tibial plateau could be used as a reference for reproducing individual PTS during medial unicompartmental knee arthroplasty (UKA). Preoperative computed tomography (CT) data from 48 lower limbs for medial UKA were imported into a three-dimensional planning software. Digitally reconstructed radiographs were created from the CT data as the lateral knee plain radiographs and the radiographic PTS angle was measured. Then, the PTS angles on the medial one-quarter and the center of the MTP (¼ and ½ MTP, respectively), and that on the medial tibial eminence (TE) were measured on the sagittal multiplanar reconstruction image. Finally, 20 lateral knee radiographs with an arthroscopic probe placed on the ¼ and the ½ MTP were obtained intraoperatively, and the angle between the axis of the probe and the tangent line of the plateau was measured. The mean radiographic PTS angle was 7.9 ± 3.0 degrees (range: 1.7-13.6 degrees). The mean PTS angles on the ¼ MTP, the ½ MTP, and the TE were 8.1 ± 3.0 degrees (1.2-13.4 degrees), 9.1 ± 3.0 degrees (1.4-14.7 degrees), and 9.9 ± 3.1 degrees (3.1-15.7 degrees), respectively. The PTS angles on the ¼ MTP and the ½ MTP were strongly correlated with the radiographic PTS angle (r =0.87 and 0.80, respectively, p < 0.001). A statistically significant difference was observed between the mean angle of the radiographic PTS and the PTS on the TE (p < 0.01). The mean angle between the axis of the probe and the tangent line of the tibial plateau was -0.4 ± 0.9 degrees (-2.3-1.3 degrees) on the ¼ MTP and -0.1 ± 0.7 degrees (-1.5-1.2 degrees) on the ½ MTP, respectively. An area from the medial one-quarter to the center of the MTP could be used as an anatomical reference for the individual PTS.

The MAKO robotic-arm knee arthroplasty system

INTRODUCTION

The Mako robotic arm knee arthroplasty system was initially indicated in unicompartmental knee arthroplasty followed by bicompartmental and total knee arthroplasty techniques. The system utilizes three elements: (1) Pre-op 3D CT based planning and image based intra-op navigation. (2) Pre-resection implant modifications with integrated alignment, implant position and gap data, and (3) A semi-constrained robotic arm assisted execution of bone resection with "haptic" boundaries, and cemented implants.

MATERIALS AND METHODS

This paper evaluates variable pre-op implant placement, and anatomic reference positioning; data entry with incorporation of alignment, implant congruency through range of motion, and gaps; bone resection with "haptic" boundaries, and final implant evaluation with kinetic sensors.

RESULTS

The Mako system allowed for improved implant placement utilizing CT guidance, bone resection accuracy, flexibility for functional implant placement with gap balancing. When combined with kinetic sensors, there was improved rotation and soft tissue balance.

CONCLUSION

The MAKO robotic system can assist the surgeon with anatomic landmarks, provides the flexibility for independent gap balance through implant and alignment refinement, and three-dimensional soft tissue balancing data to achieve functional stability. Registry data has shown improved outcome survivorship irrespective of the surgeons' volumes and learning curves.

Alignment in Medial Fixed-Bearing Unicompartmental Knee Arthroplasty: The Limb Has a Leg Up on the Component

BACKGROUND

To assess how implant alignment affects unicompartmental knee arthroplasty (UKA) outcome, we compared tibial component alignment of well-functioning UKAs against 2 groups of failed UKAs, revised for progression of lateral compartment arthritis ("Progression") and aseptic loosening ("Loosening").

METHODS

We identified 37 revisions for Progression and 61 revisions for Loosening from our prospective institutional database of 3351 medial fixed-bearing UKAs performed since 2000. Revision cohorts were matched on age, gender, body mass index, and postoperative range of motion with "Successful" unrevised UKAs with minimum 10-year follow-up and Knee Society Score ≥70. Tibial component coronal (TCA) and sagittal (TSA) plane alignment was measured on postoperative radiographs. Limb alignment was quantified by hip-knee-ankle (HKA) angle on long-leg radiographs. In addition to directly comparing groups, a multivariate logistic regression examined how limb and component alignments were associated with UKA revision.

RESULTS

In the Progression group, component alignment was similar to the matched successes (TCA 3.6° ± 3.5° varus vs 5.1° ± 3.5° varus, P = .07; TSA 8.4° ± 4.4° vs 8.8° ± 3.6°, P = .67), whereas HKA angle was significantly more valgus (0.3° ± 3.6° valgus vs 4.4° ± 2.6° varus, P < .001). Loosening group component alignment was also similar to the matched successes (TCA 6.1° ± 3.7° varus vs 5.9° ± 3.1° varus, P = .72; TSA 8.4° ± 4.6° vs 8.1° ± 3.9°, P = .68), and HKA was significantly more varus (6.1° ± 3.1° varus vs 4.0° ± 2.7° varus, P < .001). Using a multivariate logistic regression, HKA angle was the most significant factor associated with revision (P < .001).

CONCLUSION

In this population of revised UKAs and long-term successes, limb alignment was a more important determinant of outcome than tibial component alignment.

LEVEL OF EVIDENCE

Level III case-control study.

Implant Alignment and Patient Factors Affecting the Short-Term Patient-Reported Clinical Outcomes after Oxford Unicompartmental Knee Arthroplasty

This study aims at clarifying implant alignment and other patient factors' influence on clinical outcomes, particularly on patient-reported outcomes (PRO), following Oxford unicompartmental knee arthroplasty (OUKA). A total of 142 patients after OUKA were divided into two groups according to the validated Japanese version of the knee injury and osteoarthritis outcome score (KOOS) for each subscale of pain, symptoms, and activities of daily living (ADL) at postoperative year 1 and 2: group 1 had ≥80 scores and group 2 had <80 scores. Postoperative clinical and radiographical findings were then compared among groups in each subscale. Using postoperative year 1 and 2 data, a multivariable logistic regression analysis was conducted to clarify factors for clinical outcomes' improvement. In the analysis of KOOS subscale of symptoms at postoperative year 1, gender distribution, preoperative body mass index, and postoperative maximum knee flexion angles differed significantly among groups. In the analysis for KOOS subscale of ADL, significant differences were observed in postoperative tibial component varus angles. Multivariable logistic regression analysis revealed that all of these parameters significantly related to ≥80 KOOS scores of each subscale at postoperative year 1. Additionally, at postoperative year 2, larger postoperative knee flexion angles and tibial component varus angles related to ≥80 KOOS subscale of symptoms and ADL were observed. In conclusion, tibial component's larger varus alignment was associated with the better PRO at both 1 and 2 years after OUKA. Importantly, larger postoperative knee flexion angle helped achieve good short-term PRO after OUKA.

All-Polyethylene Tibial Component Does Not Affect Survivorship of Medial Unicompartmental Knee Arthroplasty at Mid-Term Follow-Up

The present study's primary aim was to determine the survivorship of a large cohort of patients implanted with a single design all-polyethylene tibial component medial unicompartmental knee arthroplasty (UKA). Its secondary purpose was to investigate the reasons underlying implant failure, with specific attention to component positioning and limb alignment. Between 2007 and 2013, 166 patients underwent medial UKA with a single design all-polyethylene tibial component at two centers. Preoperatively and postoperatively, patients were administered clinical outcome scores and radiographic information were collected. Postoperative complications and causes of revision were recorded. A total of 140 patients (80 in Center A and 60 in Center B) who underwent all-polyethylene tibial component medial UKA (82 cases in Center A and 60 in Center B) were taken into account. Kaplan-Meier cumulative survivorship of implants was 96.5% (confidence interval [CI]: 91.7-98.6%) at an average follow-up of 61.1 months. Tibial aseptic loosening was accounted for failure in one case, while no correlation was found between implant positioning and failure. Two revisions were performed in Center A and three in Center B. Slight correction of the preoperative varus deformity was performed at both centers. All-polyethylene tibial component UKA provided satisfactory clinical and functional outcome, with excellent survival rate in the early and mid-term follow-up. Continued patient follow-up is needed to determine long-term survivorship of the examined UKA model.

Cementless unicompartmental knee replacement achieves better ten-year clinical outcomes than cemented: a systematic review

PURPOSE

The aim of this study was to report and compare the long-term revision rate, revision indications and patient reported outcome measures of cemented and cementless unicompartmental knee replacements (UKR).

METHODS

Databases Medline, Embase and Cochrane Central of Controlled Trials were searched to identify all UKR studies reporting the ≥ 10 year clinical outcomes. Revision rates per 100 component years [% per annum (% pa)] were calculated by fixation type and then, subgroup analyses for fixed and mobile bearing UKRs were performed. Mechanisms of failure and patient reported outcome measures are reported.

RESULTS

25 studies were eligible for inclusion with a total of 10,736 UKRs, in which there were 8790 cemented and 1946 cementless knee replacements. The revision rate was 0.73% pa (CI 0.66-0.80) and 0.45% pa (CI 0.34-0.58) per 100 component years, respectively, with the cementless having a significantly (p < 0.001) lower overall revision rate. Therefore, based on these studies, the expected 10-year survival of cementless UKR would be 95.5% and cemented 92.7%. Subgroup analysis revealed this difference remained significant for the Oxford UKR (0.37% pa vs 0.77% pa, p < 0.001), but for non-Oxford UKRs there were no significant differences in revision rates of cemented and cementless UKRs (0.57% pa vs 0.69% pa, p = 0.41). Mobile bearing UKRs had significantly lower revision rates than fixed bearing UKRs in cementless (p = 0.001), but not cemented groups (p = 0.13). Overall the revision rates for aseptic loosening and disease progression were significantly lower (p = 0.02 and p = 0.009 respectively) in the cementless group compared to the cemented group (0.06 vs 0.13% pa and 0.10 vs 0.21% pa respectively).

CONCLUSIONS

Cementless fixation had reduced long-term revision rates compared to cemented for the Oxford UKR. For the non-Oxford UKRs, the revision rates of cementless and cemented fixation types were equivalent. Therefore, cementless UKRs offer at least equivalent if not lower revision rates compared to cemented UKRs.

LEVEL OF EVIDENCE

III.

Robotic arm-assisted unicompartmental knee arthroplasty: high survivorship and good patient-related outcomes at a minimum five years of follow-up

PURPOSE

Robotic arm-assisted unicompartmental knee arthroplasty (RA-UKA) has been shown to improve component placement, reduce intraoperative variability, increase patient satisfaction and improve short-term survivorship results. The aim of this retrospective study was to determine the incidence of revision and the clinical performance at a minimum of 5-year follow-up for a cohort of patients who received a medial RA-UKA.

METHODS

Between April 2011 and July 2013, a total of 254 patients underwent medial RA-UKA at a single centre. Clinical performance was investigated using the Forgotten Joint Score-12 (FJS-12) and a 5-level Likert scale made of five items to assess joint perception and patient satisfaction. Kaplan-Meier implant survivorship was calculated and reasons for revision were collected. The effect of age, gender and body mass index (BMI) on the probability of reporting high FJS-12 and satisfaction were assessed.

RESULTS

After considering exclusion criteria and loss to follow-up, a total of 216 patients (224 medial RA-UKAs) were assessed at a mean 5.9 years of follow-up. Five RA-UKAs underwent implant revision, resulting in an overall Kaplan-Meier survivorship of 97.8%. Unexplained knee pain (0.9%) was the most common reason for RA-UKA revision. Good-to-excellent FJS-12 scores and high satisfaction levels were reported at mid-term follow-up. Male patients had higher probability of having FJS-12 > 90 (p < 0.05) and high satisfaction levels (p < 0.05).

CONCLUSIONS

RA-UKAs demonstrated high survivorship and good-to-excellent patient-reported outcome measures and satisfaction levels at minimum 5-year follow-up. Results for male patients had improved clinical performance when compared to female subjects.

LEVEL OF EVIDENCE

IV.

Total and unicondylar knee arthroplasty are equivalent treatment options in end-stage spontaneous osteonecrosis of the knee, and the size of the lesion has no influence on the results

PURPOSE

The purpose of the present study was to compare total (TKA) and unicondylar (UKA) knee arthroplasty for spontaneous osteonecrosis of the knee (SONK), and to investigate potential correlations to radiographic parameters.

METHODS

All consecutive patients with a magnetic resonance imaging (MRI) proven SONK treated with either TKA or UKA between 2002 and 2018 were analysed. The primary outcomes were postoperative complications and failure rates. Functional assessment included Knee Society Score (KSS), WOMAC Score, and range of motion. A novel three-dimensional measurement method was established to determine the size of the osteonecrotic lesion. All outcome parameters were correlated to the size of the necrotic lesion using Spearman's rank correlation.

RESULTS

The two treatment groups (34 TKAs, 37 UKAs) did not differ regarding age, body mass index, and ratio of the volume of the necrotic lesion to the volume of the femoral condyle (n.s.). At a mean follow-up of 6.6 years, patients with UKA had better functional outcomes compared to patients with a TKA (WOMAC Score 1.0 vs. 1.6, p = 0.04; KSS pain 86 vs. 83, n.s), with a similar complication rate. No correlation was found between necrotic lesion size and failure rate (n.s.).

CONCLUSION

UKA is a valuable treatment option for SONK leading to good functional results and a low failure rate. In case of a surgeon's concern regarding implant anchorage, TKA represents an equivalent solution. The MR-tomographic size of the osteonecrotic lesions seems to have no influence on the results.

LEVEL OF EVIDENCE

III.

Relevance of the Tibial Slope on Functional Outcomes in ACL-Deficient and ACL Intact Fixed-Bearing Medial Unicompartmental Knee Arthroplasty

BACKGROUND

Excessive posterior tibial slope in medial unicompartmental knee arthroplasty (UKA) has been implicated in early failure. The purpose of this study was to evaluate the relationship between preoperative posterior tibial slope and postoperative slope of the implant (PSI) on outcomes in patients with anterior cruciate ligament (ACL) intact and ACL-deficient knees after fixed-bearing medial UKA.

METHODS

Patients who underwent a medial UKA between 2002 and 2017 with a minimum 3-year follow-up were included. Preoperative posterior tibial slope and postoperative PSI were measured. Outcomes measures included Knee Injury and Osteoarthritis Outcomes Score (KOOS) subscales, Lysholm, and VR-12. Failure was defined as conversion to total knee arthroplasty.

RESULTS

Of 241 knees undergoing UKA, 131 patients (70 women, 61 men; average age of 65 ± 10 years (average BMI of 27.9 ± 4) were included. For all patients, survivorship was 98% at 5 years and 96% at 10 years with a mean survival time for UKA was 15.2 years [95% CI: 14.6-15.7]. No failure had a PSI >7°. There were no superficial or deep infections. There were no significant differences in outcome scores between the ACL intact and the ACL-deficient group; therefore, the data were combined for analysis. At mean 8-year follow-up, KOOS pain scores were better in patients with PSI ≤7° (87 ± 16) than those with PSI >7° (81 ± 15). 76% of patients with PSI ≤7° reached the Patient Acceptable Symptom State for KOOS pain; whereas, 59% of patients with PSI >7° reached PASS for KOOS pain (P = .015).

CONCLUSION

Patients with postoperative posterior slope of the tibial implant >7° had significantly worse postoperative pain, without conversion to TKA, and with maintenance of high function. In ACL deficient and intact knees, nonrobotically-assisted, fixed-bearing medial UKA had a 96% survivorship at 10 years.

Postoperative clinical outcomes of unicompartmental knee arthroplasty in patients with isolated medial compartmental osteoarthritis following medial meniscus posterior root tear

Background

Cartilage degradation progresses rapidly following medial meniscus posterior root tear (MMPRT). Unicompartmental knee arthroplasty (UKA) has been performed for medial compartmental osteoarthritis following MMPRT. We evaluated the clinical and radiographic outcomes of UKA for medial compartmental osteoarthritis after an untreated MMPRT.

Methods

Twenty-one patients who underwent UKA for isolated medial compartment osteoarthritis following MMPRT were retrospectively investigated. Clinical outcomes were assessed using the Knee Injury and Osteoarthritis Outcome Score and knee range of motion. The posterior tibial slope and tibial component inclination were evaluated using plain radiographs.

Results

The mean follow-up periods were 25.5 ± 13.8 months. Clinical outcomes improved significantly postoperatively. The mean postoperative knee extension angle was −1.1° ± 2.1°, and the knee flexion angle was 134.3° ± 4.9°. The posterior tibial slope angle decreased from 9.0° ± 2.0° preoperatively to 5.4° ± 1.8° postoperatively, and postoperative tibial component inclination at the final follow-up was 2.9° ± 1.1° varus. No aseptic loosening or deep infections were observed.

Conclusion

UKA significantly improved clinical outcomes and could be a viable surgical option for treating isolated medial compartmental osteoarthritis accompanied by untreated MMPRT.

Does robotic-assisted unicompartmental knee arthroplasty have lower complication and revision rates than the conventional procedure? A systematic review and meta-analysis

OBJECTIVE

We conducted this systematic review and meta-analysis of studies on patients who underwent unicompartmental knee arthroplasty (UKA) to compare the complication rates, revision rates and non-implant-specific complications between robotic-assisted and conventional UKA.

DESIGN

Systematic review and meta-analysis.

DATA SOURCES

The PubMed, Embase, Web of Science and Cochrane databases were searched up to 30 June 2020.

ELIGIBILITY CRITERIA

Case-control studies comparing robotic-assisted and conventional UKA.

DATA EXTRACTION AND SYNTHESIS

Data from all eligible articles were independently extracted by two authors. We analysed the differences in outcomes between robotic-assisted and conventional UKA by calculating the corresponding 95% CIs and pooled relative risks (RRs). Heterogeneity was assessed using the χ² and I² tests. All analyses were performed using the 'metafor' package of R V.3.6.2 software.

RESULTS

A total of 16 studies involving 50 024 patients were included in the final meta-analysis. We found that robotic-assisted UKA had fewer complications (RR: 0.52, 95% CI: 0.28 to 0.96, p=0.036) and lower revision rates (RR: 0.42, 95% CI: 0.20 to 0.86, p=0.017) than conventional UKA. We observed no significant differences in non-implant-specific complications between the two surgical techniques (RR: 0.80, 95% CI: 0.61 to 1.04, p=0.96). No publication bias was found in this meta-analysis.

CONCLUSIONS

This study provides evidence that robotic-assisted UKA has fewer complications and lower revision rates than conventional UKA; however, owing to important limitations, the results lack reliability, and more studies are required.

PROSPERO REGISTRATION NUMBER

CRD42021246927.

Robotic Assistance in Unicompartmental Knee Arthroplasty Results in Superior Early Functional Recovery and Is More Likely to Meet Patient Expectations

Robotic technology has reduced the errors of implant alignment in unicompartmental knee arthroplasty (UKA), but its impact on functional recovery after UKA is poorly defined. The purpose of this study was to compare early functional recovery, pain levels, and satisfaction in UKA performed with either robotic assistance or conventional methods. A retrospective analysis was performed on 89 matched consecutive patients who underwent outpatient UKA by a single physician using either conventional instruments (n = 39) or robotic methods (n = 50), with otherwise identical perioperative protocols. Outcomes studied included Lower Extremity Functional Score (LEFS), new Knee Society Score (KSS), Knee Injury and Osteoarthritis Outcome Score for Joint Replacement (KOOS-JR.), VR/SF-12, Visual Analog Scale (VAS) pain scores, and perioperative opioid consumption. Patients in the robotic cohort had superior early functional outcomes, with greater LEFS (conventional = 23; robotic = 31) at 1 week post-op (p=0.015) and KOOS-JR (conventional = 74; robotic = 81) at up to 6 months post-op (p=0.037); these two values remained statistically significant after mixed-model regression analysis (p=0.010; p=0.023), respectively. At 1 year post-op, expectations were more likely to be met in those who received robotic assistance (p=0.06). No differences were reported with respect to postoperative opioid usage (p=0.320), reoperations (p=1.00), and complications (p=0.628). Robotic-assisted UKA resulted in more rapid recovery and less early postoperative pain and were more likely to meet expectations than conventional UKA, although functional differences equilibrated by 1 year postoperatively. Further follow-up is necessary to determine if implant durability is impacted by robotics.