Valgus stress knee radiographs accurately anticipate the bone resection in medial unicompartmental knee arthroplasty: Protocol validation using an image-based robotic system.

PURPOSE: The objective of this study was to describe a planning method for medial unicompartmental knee arthroplasty (UKA) implantation using preoperative stress radiographs to measure the thickness of tibial and femoral bone resections and to validate this method with data from an image-based robotic surgery system. Having such method for preoperative planning would be of interest for surgeons performing UKA in order to anticipate optimal bone resection on both tibia and femoral sides. METHODS: A new planning method for medial UKA based on valgus stress knee radiographs validated it with an image-based robotic surgery system (Restoris MCK, MAKO®, Stryker Corporation) was proposed. This retrospective study involved radiographic measurements of 76 patients who underwent image-based robotic medial UKA between April 2022 and February 2023. Preoperative anteroposterior stress radiographs of the knee were used to simulate UKA implantation. The UKA technique was based on Cartier's angle and aimed at restoring the joint line. The total dimension measured was 14 mm (8 mm for minimal tibial component and polyethylene insert + 4 mm for femoral component + 2 mm for safety laxity). Bone resections were measured in the preoperative valgus stress radiographs and then against the intraoperative bone resection data provided by the robotic system. Inter- and intra-observer reliability was assessed using 25 measurements. RESULTS: The mean planned tibial resection measured in the radiographs was 4.3 ± 0.4 [2.9-5.8], while the mean robotic resection was 4.2 ± 0.5 [2.7-5.8] (mean difference = 0.15 mm, 95% confidence interval [CI] [-0.27 to 0.57]). There was a strong correlation between these two values (Pearson's rank R = 0.79, p < 0.001). Intra- and inter-observer reliability were also very strong (Pearson's rank R = 0.91, p < 0.001, and Pearson's rank R = 0.82, p < 0.001, respectively). The mean planned femoral bone resection measured in the radiographs was 2.7 ± 0.7 mm [1-4.5], while the mean robotic resection was 2.5 ± 0.9 [1-5] (mean difference = 0.21 mm, 95% CI [-0.66 to 1.08]). There was a strong correlation between these two values (Pearson's rank R = 0.82, p < 0.001). Intra- and inter-observer reliability were also strong (Pearson's rank R = 0.88, p < 0.001, and Pearson's rank R = 0.84, p < 0.001, respectively). CONCLUSION: This study describes and validates with robotic information a simple and reproducible preoperative planning method to determine femoral and tibial bone resection for medial UKA implantation using antero-posterior valgus stress knee radiographs, leaving a medial safety laxity of 2 mm. It represents a very valuable contribution to the understanding of UKA principles, which can serve to extend its indications and increase reproducibility of the surgical technique. LEVEL OF EVIDENCE: III. Retrospective cohort study.

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.

[Unicompartmental knee prosthesis]. / Prótesis unicompartimental de rodilla.

In a patient with severe unicompartmental knee osteoarthritis where conservative treatments have been exhausted, with painful symptoms located on the affected side and with a reducible axis, the unicompartmental knee prosthesis (UKP) is the first option for our work group. Within the study to confirm the diagnosis and plan the surgery, weight-bearing knee x-rays, Rosenberg x-rays, and teleradiographs of the lower extremities stand out. The objective of surgery is to replace the affected area, restoring the anatomy with an adequate balance of soft tissues. Regarding alignment, the challenge is not to overload the opposite side or that of the prosthesis. There are mobile and fixed plates and although the clinical and survival results are similar, in recent years with the incorporation of robotic surgery, the balance has tipped towards the use of fixed plates. The clinical and functional results are better and there are fewer complications than when total knee prostheses (TKP) are used in the same type of patients. The survival studied in registries is lower than for TKP, but when used in high-flow centers where the percentage of UKP is close to a third of the total with strict patient selection, the duration is as good as in PTR.

En un paciente con artrosis unicompartimental de rodilla grave, donde se agotaron los tratamientos conservadores que tiene clínica dolorosa localizada en el lado afectado y con alteración del eje reductible, la prótesis unicompartimenal de rodilla (PUR) es la primera opción para nuestro grupo de trabajo. Dentro del estudio para confirmar el diagnóstico y planificar la cirugía destacan las radiografías de rodillas con carga, radiografía de Rosenberg y telerradiografías de extremidades inferiores. El objetivo de la cirugía es reemplazar la zona afectada, restituyendo la anatomía con un adecuado balance de partes blandas. Respecto al alineamiento el desafío es no sobrecargar el lado contrario ni tampoco el de la prótesis. Existen de platillo móvil y fijo y aunque los resultados clínicos y de supervivencia son semejantes, en los últimos años con la incorporación de la cirugía robótica, la balanza se ha inclinado para el uso de los platillos fijos. En pacientes con artrosis unicompartimental los resultados clínicos y funcionales son mejores con PUR y tiene menos complicaciones que cuando se usan prótesis totales (PTR). La supervivencia estudiada en registros es menor que para PTR, pero cuando se usa en centros de alto flujo en que el porcentaje de PUR es cercano a un tercio del total con una estricta selección de pacientes, la duración es tan buena como en la PTR.

Prótesis unicompartimental de rodilla / Unicompartmental knee prosthesis

Resumen: En un paciente con artrosis unicompartimental de rodilla grave, donde se agotaron los tratamientos conservadores que tiene clínica dolorosa localizada en el lado afectado y con alteración del eje reductible, la prótesis unicompartimenal de rodilla (PUR) es la primera opción para nuestro grupo de trabajo. Dentro del estudio para confirmar el diagnóstico y planificar la cirugía destacan las radiografías de rodillas con carga, radiografía de Rosenberg y telerradiografías de extremidades inferiores. El objetivo de la cirugía es reemplazar la zona afectada, restituyendo la anatomía con un adecuado balance de partes blandas. Respecto al alineamiento el desafío es no sobrecargar el lado contrario ni tampoco el de la prótesis. Existen de platillo móvil y fijo y aunque los resultados clínicos y de supervivencia son semejantes, en los últimos años con la incorporación de la cirugía robótica, la balanza se ha inclinado para el uso de los platillos fijos. En pacientes con artrosis unicompartimental los resultados clínicos y funcionales son mejores con PUR y tiene menos complicaciones que cuando se usan prótesis totales (PTR). La supervivencia estudiada en registros es menor que para PTR, pero cuando se usa en centros de alto flujo en que el porcentaje de PUR es cercano a un tercio del total con una estricta selección de pacientes, la duración es tan buena como en la PTR.

Abstract: In a patient with severe unicompartmental knee osteoarthritis where conservative treatments have been exhausted, with painful symptoms located on the affected side and with a reducible axis, the unicompartmental knee prosthesis (UKP) is the first option for our work group. Within the study to confirm the diagnosis and plan the surgery, weight-bearing knee x-rays, Rosenberg x-rays, and teleradiographs of the lower extremities stand out. The objective of surgery is to replace the affected area, restoring the anatomy with an adequate balance of soft tissues. Regarding alignment, the challenge is not to overload the opposite side or that of the prosthesis. There are mobile and fixed plates and although the clinical and survival results are similar, in recent years with the incorporation of robotic surgery, the balance has tipped towards the use of fixed plates. The clinical and functional results are better and there are fewer complications than when total knee prostheses (TKP) are used in the same type of patients. The survival studied in registries is lower than for TKP, but when used in high-flow centers where the percentage of UKP is close to a third of the total with strict patient selection, the duration is as good as in PTR.

Short-to Mid-Term Survivorship of a Patient-specific Unicompartmental Knee Arthroplasty Implant Cast from a Three-Dimensional Printed Mold.

The purpose of this study was to determine early survivorship and complication rates associated with the implantation of a new patient-specific unicompartmental knee implant cast from a three-dimensional (3D) printed mold, introduced in 2012. We retrospectively reviewed 92 consecutive patients who underwent unicompartmental knee arthroplasty (UKA) with a patient-specific implant cast from a 3D printed mold between September 2012 and October 2015. The early results of a patient-specific UKA implant were favorable in our cohort, with survivorship free from reoperation of 97% at an average 4.5 years follow-up. Future studies are necessary to investigate the long-term performance of this implant. Survivorship of a patient-specific unicompartmental knee arthroplasty implant cast from a 3D printed mold.

Cohorte histórica de artroplastia unicompartimental de rodilla en un hospital universitario chileno / Historical cohort of unicompartmental knee arthroplasty in a Chilean university hospital

OBJETIVO Describir el resultado funcional informado por el paciente de una cohorte de pacientes sometidos a artroplastia unicompartimental de rodilla (AUR) en un hospital universitario chileno. MÉTODOS Se diseñó un estudio de cohorte histórica. Se incluyeron todos los pacientes que se sometieron a AUR de platillo fijo entre 2003 y 2019. Un evaluador independiente se puso en contacto con los pacientes en junio de 2020. Se utilizó el índice de artritis de las universidades de Western Ontario y McMaster (WOMAC) para comparar los procedimientos de AUR (medial o lateral), la edad (mayor o menor de 70 años), y el seguimiento (más o menos de 5 años). RESULTADOS Se incluyeron 78 pacientes, en un total de 94 AURs. La mediana de edad fue de 64 años (rango: 43 a 85 años). Hubo 72 (76,6%) casos de AUR medial. Un paciente necesitó revisión para artroplastia total de rodilla (ATR). Un total de 60 pacientes (76,9%), correspondientes a 72 AURs (76,7%), fueron contactados con éxito por teléfono para el seguimiento final. La mediana del puntaje en los dominios del WOMAC fue: dolor ­ 1 (rango: 0 a 12); rigidez ­ 0 (rango: 0 a 4); y función física ­ 2 (rango: 0 a 29). La mediana del puntaje total en el WOMAC fue de 4 (rango: 0 a 44). Los pacientes sometidos a AUR lateral lograron mejores puntuaciones funcionales (p » 0,0432), y el puntaje total en el WOMAC fue similar en pacientes mayores o menores de 70 años (p » 0,3706). CONCLUSIONES La AUR es un tratamiento eficaz y reproducible para pacientes con artrosis de rodilla unicompartimental. La edad parece no afectar los resultados funcionales, y la AUR es un tratamiento eficaz en pacientes mayores de 70 años. Estos resultados deberían animar a los cirujanos de rodilla a aprender esta técnica y a los responsables de las políticas de salud pública a considerar la AUR para la osteoartritis de rodilla.

PURPOSE To describe the patient-reported functional outcome of a cohort of patients undergoing unicompartmental knee arthroplasty (UKA) in a Chilean university hospital. METHODS A historical cohort study was designed. All patients who underwent fixedbearing UKA between 2003 and 2019 were included. An independent evaluator contacted the patients in June 2020. The Western Ontario and McMaster Universities Arthritis Index (WOMAC) was used to compare UKA procedures (medial or lateral), age (over or under 70 years), and follow up (longer or shorter than 5 years). RESULTS A total of 78 patients, corresponding to 94 UKAs, were included. The median age was 64 years (range: 43 to 85 years). There were 72 (76.6%) cases of medial UKA. One patient needed revision to total knee arthoplasty (TKA). A total of 60 patients (76.9%), corresponding to 72 UKAs, were successfully contacted by phone for the final follow-up. The median scores on the WOMAC domains were: pain ­ 1 (range: 0 to 12); stiffness ­0 (range: 0 to 4); and physical function ­ 2 (range: 0 to 29). The median total score on the WOMAC was 4 (range: 0 to 44). Patients submitted to lateral UKA had better functional scores (p » 0.0432), and the total WOMAC score was similar among patients older or younger than 70 years of age (p » 0.3706). CONCLUSIONS For patients with unicompartmental knee osteoarthritis, UKA is an effective and reproducible treatment. Age does not seem to affect the functional results, and UKA is an effective treatment in patients over 70 years old. These results should encourage knee surgeons to learn this technique and those responsible for public health policies to consider UKA for knee osteoarthritis

Staged BiCompartmental Knee Arthroplasty has Greater Functional Improvement, but Equivalent Midterm Survivorship, as Revision TKA for Progressive Osteoarthritis After Partial Knee Arthroplasty.

BACKGROUND: Progressive arthritis in the unresurfaced compartments of the knee is one failure mode after partial knee arthroplasty (PKA). While progressive arthritis after PKA is typically treated with revision to TKA (rTKA), staged bicompartmental knee arthroplasty (sBiKA) -the addition of another PKA - is an alternative. This study compared outcomes of sBiKA and rTKA for progressive arthritis after PKA. METHODS: A retrospective comparative study of non-consecutive cases at four institutions were performed in patients with an intact PKA, without loosening or wear, who underwent sBiKA (n = 27) or rTKA (n = 30), for progressive osteoarthritis. Outcomes studied were new Knee Society Function and Objective Scores (KSSF, KSSO), KOOS, Jr., ROM, operative times, length of stay, complication rates and the need for reoperations. RESULTS: Mean time to conversion was 7.4 ± 6 years for sBiKA and 9.7 ± 8 for rTKA, P = .178. Patient demographics and pre-operative outcomes were similar among cohorts. At an average of 5.7 ± 3 (sBiKA) and 3.2 ± 2 years (rTKA), KOOS, Jr. significantly improved, P < .001, by an equivalent amount. Post-operative KSSO and KSSF were significantly higher in the sBiKA cohort, respectively, (90.4 ± 10 vs 72.1 ± 20, P < .001) and (80.3 ± 18 vs 67.1 ± 19, P = .011). sBiKA patients had significantly greater improvement in KSSO (30.7 ± 33 vs 5.2 ± 18, P = .003). One sBiKA patient underwent reoperation for continued pain. CONCLUSION: SBiKA has equivalent survivorship, but greater improvement in functional outcomes as rTKA at short to midterm follow-up. Given the shorter operative times and length of stay, sBiKA is a safe and cost-effective alternative to rTKA for progressive osteoarthritis following PKA. Nevertheless, further follow-up is necessary to determine whether sBiKA is a durable option.

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.

Prior Anterior Cruciate Ligament Reconstruction Does Not Compromise the Functional Outcomes of Medial Unicompartmental Knee Arthroplasty Although Revision for Progressive Arthritis May Occur Earlier.

BACKGROUND: Anterior cruciate ligament (ACL) deficiency is commonly considered a contraindication for unicompartmental knee arthroplasty (UKA). The purpose of this study is to compare the outcomes of UKA after prior ACL reconstruction (rACL cohort) to UKA with an intact native ACL (nACL cohort). METHODS: Forty-five patients from 3 institutions who underwent medial UKA after prior rACL were matched by age, gender, preoperative function scores, and body mass index to 90 patients who underwent UKA with an intact nACL. Primary outcomes were Knee Injury and Osteoarthritis Outcome Score for Joint Replacement, Oxford Knee Scores, Knee Society Functional Scores, and Kellgren-Lawrence scores in the unresurfaced, lateral tibiofemoral compartment. Secondary outcomes were postoperative complications and the need for revision to TKA. RESULTS: At a mean of 3.6 years, all PROMs improved significantly with no differences identified between groups. The incidence of revision TKA was similar between cohorts (P = 1.00); however, the mean time to revision for progressive osteoarthritis was 4.0 years in the nACL group and 2.2 years in the rACL group. Twenty percent of rACL patients had a postoperative complication compared to 8% in the nACL group. Despite presenting with a similar degree of lateral arthritis, a greater percentage of patients developed Kellgren-Lawrence scores of ≥3 in the rACL cohort (9%) than in the nACL cohort (0%). CONCLUSION: A previously reconstructed ACL does not appear to compromise the short-term functional outcomes of UKA; however, there is a higher rate of minor complications and progression of lateral compartment arthritis, which should be considered with patients in the shared decision process.

Two-stage bone and meniscus allograft and autologous chondrocytes implant for unicompartmental osteoarthritis: midterm results.

BACKGROUND: We analyzed the clinical and radiographic evolution of patients with knee unicompartmental osteoarthritis and axis alteration and osteochondral lesions in the femoral condyle, treated with tibial plateau and meniscus allograft and cultured autologous chondrocyte implantation in the femur in two steps. PURPOSE: To analyze the clinical results with the first patients treated with this two-stage technique to avoid knee prosthesis in patients with unicompartmental osteoarthritis. MATERIAL AND METHODOLOGY: Sixteen patients, average age 56 years, were included in a cohort study. We performed an osteotomy with tibia plateau allograft, including the meniscus. In a second surgery, the chondrocyte fibrin scaffold was placed in the femur. Clinical symptoms and function were measured using KSSR and KOOS scores. Wilcoxon's test was performed to compare the results over the 2-year follow-up period. RESULTS: Mean KSSR before surgery was 35.69 (SD: 3.75) points, rising to 67 (SD: 15.42) at 3 months, 95.88 at 12 months (SD: 2.68) and 96.31 at 24 months (SD: 2.24). The KOOS before surgery was 65.14 (SD: 16.34), rising to 72.68 after 3 months (SD: 19.15), 76.68 at 12 months (SD: 18.92) and 64.28 at 24 months (SD: 11.79). Four of 5 patients returned to engaging in the activity that they had stopped practicing. Three patients experienced collapse of the tibia allograft, and they needed later a prosthesis. CONCLUSIONS: Simultaneous tibia plateau allograft and autologous chondrocyte implantation in the femur, after correction of the angular deformity, were performed, restoring the anatomy of the medial compartment and knee function in 82% of the patients 2 years after the operation. LEVEL OF EVIDENCE: IV.

Octogenarians Undergoing Medial Unicompartmental Knee Arthroplasty Have Similar Patient-Reported Outcomes as Their Younger Counterparts.

BACKGROUND: As a procedure with lower surgical morbidity, unicompartmental knee arthroplasty (UKA) may present a practical solution for elderly patients with unicompartmental arthritis. However, few studies have analyzed the results of UKA in the extreme elderly. This study compared the functional and perioperative outcomes between octogenarians and age-appropriate controls undergoing UKA. METHODS: Prospectively collected data of 44 patients aged ≥80 years who underwent unilateral UKA were analyzed. Each octogenarian was matched 1:3 with 132 patients aged 65-74 years using propensity scores adjusting for gender, body mass index, Charlson comorbidity index, and preoperative scores. Knee Injury and Osteoarthritis Outcome Score for Joint Replacement and Short Form-12 were collected preoperatively and 2 years postoperatively. Complications, reoperations, readmissions, and unplanned visits were recorded up to 1 year postoperatively. RESULTS: The mean age was 70.0 ± 2.7 years in the control group and 83.0 ± 3.0 years in the octogenarian group (P < .001). The percentage of outpatient procedures was comparable (control 50.0%; octogenarian 45.5%; P = .601). With the exception of poorer Short Form-12 physical scores in octogenarians at 2 years (39.4 ± 14.1 vs 44.9 ± 9.2, P = .028), there was no difference in final postoperative scores or improvement in scores between the groups. The rate of complications, reoperations, readmissions, and emergency room visits was also similar. The five-year survivorship was 97% in the control group and 93% in the octogenarian group (P = .148). CONCLUSION: Octogenarians undergoing UKA can experience clinical outcomes that are similar to those of their younger counterparts. The clinical trajectory outlined may help clinicians provide valuable prognostic information to elderly patients and guide preoperative counseling.

Robotic-assisted vs conventional surgery in medial unicompartmental knee arthroplasty: a clinical and radiological study.

BACKGROUND: The use of unicompartmental knee arthroplasty (UKA) has increased and new technologies have been developed to improve patient survival and satisfaction, soft tissue balance, alignment, and component size. Robot-assisted systems offer an increase in surgical precision and accuracy. The purpose of this study is to evaluate the precision of component position using five radiological parameters in conventional and robotic-assisted medial UKA using the NAVIO system. METHODS: A cohort study was designed for patients who underwent medial UKA between April 2017 and March 2019 in a single center. Patients were allocated in the conventional (UKA-C) or robotic-assisted (UKA-R) group. The variables analyzed were age, gender, affected knee side, length of hospital stay, surgical time, and radiological measurements such as anatomical medial distal femoral angle (aMDFA), anatomical medial proximal tibial angle (aMPTA), tibial slope, the sagittal femoral angle, and the component size. A target was defined for each measurement, and a successful UKA was defined if at least four radiological measures were on target after surgery. Also, patients' reported outcomes were evaluated using the Oxford Knee Score (OKS) and a numeric rating scale (NRS) for pain. RESULTS: Thirty-four patients were included, 18 of them underwent UKA-R. The success rate for UKA in the UKA-R group was 87%; meanwhile, in the UKA-C group this was 28%, this difference was significant and powered (Fisher's exact test, p = 0.001; 1 - ß = 0.95). Also, a 5-point difference in favor of the UKA-R group in the median OKS (p = 0.01), and a significantly lower median NRS for pain (p < 0.000) were found after surgery. CONCLUSIONS: UKA-R achieved more precision in the radiological parameters' measure in this study. Also, UKA-R has a trend towards a better OKS and a lower NRS for pain at short-term follow-up.

Despite Equivalent Medicare Reimbursement, Facility Costs for Outpatient Total Knee Arthroplasty Are Higher Than Unicompartmental Knee Arthroplasty.

BACKGROUND: With the recent removal of total knee arthroplasty (TKA) from the Centers for Medicare and Medicaid Services (CMS) Inpatient Only list, facility reimbursement for outpatient TKA now falls under the Outpatient Prospective Payment System at the same rate as unicompartmental knee arthroplasty (UKA). The purpose of this study was to compare true facility costs of patients undergoing outpatient TKA with those undergoing UKA. METHODS: We reviewed a consecutive series of 2310 outpatient TKA and 231 UKA patients from 2018 to 2019. Outpatient status was defined as a hospital stay of less than 2 midnights. Facility costs were calculated using a time-driven, activity-based costing algorithm. Implants, supplies, medications, and personnel costs were compared between outpatient TKA and UKA patients. A multivariate analysis was performed to control for confounding medical and demographic variables. RESULTS: When compared with patients undergoing UKA, outpatient TKA patients had higher implant costs ($3403 vs $3081; P < .001) and overall hospital costs ($6350 vs $5594; P < .001). Outpatient TKA patients had a greater length of stay (1.2 vs 0.5 days; P < .001) and greater postoperative personnel costs ($783 vs $166; P < .001) than UKA patients. When controlling for comorbidities, outpatient TKA was associated with a $803 (P < .001) increase in overall facility costs compared with UKA. CONCLUSION: Despite equivalent reimbursement from CMS as UKA, outpatient TKA has increased facility costs to the hospital. Although implant costs can vary greatly by institution, CMS should consider appropriately reimbursing outpatient TKA for the additional personnel costs when compared with UKA.

Robotic-assisted surgery in medial unicompartmental knee arthroplasty: does it improve the precision of the surgery and its clinical outcomes? Systematic review.

There is a high prevalence of knee osteoarthritis that affects only the medial tibiofemoral compartment. In this group of patients with severe disease, the medial unicompartmental knee arthroplasty (UKA) is an excellent choice. However, this technique has a great learning curve due to the lower tolerance of improper positioning and alignment. In this context, the robotic-assisted surgery (RAS) arises as an option to improve the accuracy and secondarily enhance the clinical outcomes related to the UKA. The objective in this study is to determine if there are significant advantages with the use of RAS over conventional surgery (CS). In the systematic review of the literature, classification of the results in three main subjects: (A) precision and alignment; (B) functional results and clinical parameters; (C) survivorship. We found 272 studies, of which 15 meet the inclusion and exclusion criteria. There is mostly described that RAS significantly improves the accuracy in position (80-100% of planned versus performed P < 0.05), alignment (2-3 times less error variance P < 0.05) and selection of the proper size of the implants (69.23% of correct size femoral implants versus 16.67% using CS P < 0.0154). Recently, there is mild evidence about benefits in the early rehabilitation and post-operative pain, but in all studies reviewed, there is no advantages of RAS in the long-term functional evaluation. There is no strong literature that supports a longer survival of the prothesis with RAS, being the longest mean follow-up reported of 29.6 months. RAS is a useful tool in increasing the precision of the medial UKA implant placement. However, there is still a lack of evidence that properly correlates this improvement in accuracy with better clinical, functional and survival results.

Robotic-assisted Unicompartmental knee Arthroplasty optimizes joint line restitution better than conventional surgery.

PURPOSE: To compare joint line restoration after unicompartmental knee arthroplasty (UKA) between conventional and robotic-assisted surgery. Previous studies have shown that joint line distalization can lead to higher failure rates. The hypothesis was that robotic-assisted UKA is associated with less femoral component distalization and a precise tibial cut, which allows a more anatomical restitution of the knee joint line. METHODS: Retrospective cohort study of patients undergoing medial or lateral UKA between May 2018 and March 2020. Preoperative and postoperative radiologic assessment of the joint line was performed by two observers, using three different methods, one for tibial slope and one for tibial resection. Robotic assisted UKA and conventional UKA groups were compared. RESULTS: Sixty UKA were included, of which 48 (77.42%) were medial. Robotic-assisted UKA were 40 (64.52%) and 22(35.48%) were conventional The distalization of the femoral component was higher in the conventional group despite the method of measurement used In both Weber methods, the difference was statistically different: Conventional 2.3 (0.9 to 5.6) v/s Robotic 1.5 (- 1.1 to 4.1) (p =0.0025*). A higher proportion of patients achieved a femoral component position ≤ two millimeters from the joint line using robotic-assisted UKA compared to the conventional technique . No statistical difference between robotic-assisted and conventional UKA was found in tibial resection and slope. CONCLUSION: Robotic-assisted UKA shows a better rate of joint line restoration due to less femoral component distalization than conventional UKA. No difference was found in the amount of tibial resection between groups in this study. LEVEL OF EVIDENCE: III.

Unicompartmental Knee Arthroplasty Provides Significantly Greater Improvement in Function than Total Knee Arthroplasty Despite Equivalent Satisfaction for Isolated Medial Compartment Osteoarthritis.

BACKGROUND: While some advocate for unicompartmental knee arthroplasty (UKA) for isolated medial compartment osteoarthritis (OA), others favor total knee arthroplasty (TKA). The purpose of this study was to compare the functional outcomes of UKA and TKA performed for patients with unicompartmental arthritis (OA). METHODS: A study was performed on 133 patients that met strict criteria for UKA, but who underwent either medial UKA or TKA for isolated medial compartment OA based upon physician equipoise. The primary outcome-New Knee Society Score (KSS)-was assessed preoperatively and at 2 years postoperatively. A propensity score weighted regression was used to balance the groups on several key covariates, including age, gender, body mass index, and baseline KSS. RESULTS: After propensity weighting, there were no significant differences between UKA and TKA in overall baseline KSS or KSS after 2 years postoperatively. While TKA patients had demonstrated a significantly greater improvement in the symptoms KSS subscale, UKA patients had a significantly greater improvement in the function subscale. Expectations were significantly more likely to be met after UKA, but there were no differences in patient satisfaction. CONCLUSION: UKA and TKA are both highly successful options for treating patients with medial compartment OA, although functionality increased more, and expectations were more likely to be met, after UKA in this study. Given equivalent patient satisfaction after both TKA and UKA, surgeons should consider factors such as clinical experience, individual preference, cost of care, surgical risk, and recovery needs, when making treatment decisions regarding this clinical entity.

Pros and Cons: A Balanced View of Robotics in Knee Arthroplasty.

In both unicompartmental knee arthroplasty (UKA) and total knee arthroplasty (TKA), compared with conventional techniques robotic technology has been shown to optimize the precision of bone preparation and component alignment, reducing outliers and increasing the percentage of components aligned within 2° or 3° of the target goal. In addition, soft tissue balance can be quantified through a range of motion in UKA and TKA using the various robotic technologies available. Although the presumption has been that the improved alignment associated with robotics will improve function and implant durability, there are limited data to support that notion. Based on recent and emerging data, it may be unreasonable to presume that robotics is necessary for both UKA and TKA. In fact, despite improvements in various proxy measures, the precision of robotics may be more important for UKA than TKA, although if system costs and surgical efficiencies continue to improve, streamlining perioperative processes, reducing instrument inventory, and achieving comparable outcomes in TKA may be a reasonable goal of robotic surgery.

The Valgus Stress Radiograph Does Not Determine the Full Extent of Correction of Deformity Prior to Medial Unicompartmental Knee Arthroplasty.

Routine preoperative stress radiographs have been advocated, in part, to determine "full correctability" of deformities before proceeding with unicompartmental knee arthroplasty (UKA) despite limited data supporting their utility. Fifty consecutive patients undergoing medial UKA with robotic navigation were studied. In 20° of flexion, significantly greater correctability was achieved after removal of osteophytes by an additional 1.8°, with a mean corrected alignment of 2.5° varus. Seventy-four percent of knees were not correctable to neutral alignment or more. In conclusion, preoperative stress radiographs have overstated value in patients undergoing medial UKA since the full extent of correctability of varus deformity cannot be determined until after removal of osteophytes and since most deformities are not fully correctable to neutral in UKA.