Successful clinical outcomes following unicompartmental knee arthroplasty (UKA) depend on accurate component alignment, which can be difficult to achieve using manual instrumentation. A new technology has been developed using haptic robotics that replaces traditional UKA instrumentation. This study compares the accuracy of UKA component placement with traditional jig-based instrumentation versus robotic guidance. Forty-four UKAs performed using standard manual instrumentation were compared to 33 performed with a robotically guided implantation system without instrumentation. Each was performed using a minimally invasive surgical approach. The two groups were identical in terms of age (p=0.74), gender (p=0.65) and BMI (p=0.72). The coronal and sagittal alignment of the tibial components were measured on pre- and post-operative AP and lateral radiographs. Postoperative tibial component alignment was compared to the pre-operative plan. For both techniques, the surgical objective was to match the natural tibial posterior slope. The RMS error of the tibial slope was 3.5° manually compared to 1.4° robotically. In addition, the variance using manual instruments was 2.8 times greater than the robotically guided implantations (p< 0.0001). In the coronal plane, the goal of the manual technique was to implant the tibial component perpendicular to the anatomic tibial axis, while the robotic implantations attempted to match the natural varus of the medial compartment. The average error was 3.3 ± 1.8° more varus using manual instruments compared to 0.1 ± 2.4° when implanted robotically (p< 0.0001). Tibial component alignment in UKA is significantly more accurate and less variable using robotic guidance compared to manual, jig-based instrumentation. By enhancing component alignment, this novel technique provides a potential method for improving outcomes in UKA patients

The discussion of outpatient unicompartmental knee arthroplasty (UKA) requires proof that it can be done safely and effectively, and also begs the question of whether it can be performed in an ambulatory surgery center (ASC) rather than a general hospital (which raises costs and is typically less efficient). Successful outpatient UKA requires carefully crafted algorithms/protocols, home support, preoperative planning and preparation, expectation management, risk stratification (not everyone is a candidate), perioperative pain management and buy-in from patients, support networks and the health care team. Relatively little data is available on the feasibility, safety and potential cost savings associated with this shift in care. We evaluated the costs and short term outcomes and complications of 150 consecutive UKAs performed in an ASC compared to those done in a general hospital both on an inpatient and outpatient basis. Determination of the setting of the outpatient surgery was made based on geographic preference by the patients; otherwise choice of inpatient or outpatient surgery in the hospital was left to the discretion of the surgeon and was primarily based on the patients' comorbidity profile and circumstances of home help. Total direct facility costs were calculated, including institutional supplies and services, anesthesia services, implants, additional PACU medications and services required, and costs associated with operating room use. Only total cost was evaluated, as it is the most consistent cost variable amongst the two institutions evaluated. The mean total direct cost of UKA in a general community hospital with an overnight stay was 1.24 and 1.65 times greater than the cost of UKA performed at the same hospital or an ASC on an outpatient basis, respectively. The mean total direct cost of outpatient UKA in a general hospital was 1.33 times greater than the mean total cost of UKA performed in an ASC. Semi-autonomous robotic technology has been introduced to optimise accuracy of implant positioning and soft tissue balance in UKA, with the expectation of resultant improvement in durability and implant survivorship. Currently, nearly 20% of UKA's in the U.S. are being performed with robotic assistance. It is anticipated that there will be substantial growth in market penetration over the next decade, projecting that nearly 37% of UKA's and 23% of TKA's will be performed with robotics in 10 years (Medical Device and Diagnostic Industry, March 5, 2015). First generation robotic technology improved substantially implant position compared to conventional methods; however, high capital costs, uncertainty regarding the value of advanced technologies, and the need for preoperative CT scans were barriers to broader adoption. Newer image-free robotic technology offers an alternative method for further optimizing implant positioning and soft tissue balance without the need for preoperative CT scans and with price points that make it suitable for use in an ASC. Currently, as a result of cost and other practical issues, <1% of first generation robotic technologies are being used in ASC's. Alternatively, more than 35% of second generation robotic systems are in use in ASC's for UKA, due to favorable pricing. In conclusion, UKA can be safely performed in the outpatient setting in select patients. Additionally, we demonstrated a substantial cost savings when UKA is performed in an outpatient setting and care is shifted from a general community hospital to an ASC. Finally, robotics can be utilised to optimise accuracy of implant placement and soft tissue balance in UKA, and newer image-free robotic technology is cost effective for outpatient UKA

As with any revision knee arthroplasty, the first rule of revision is to ensure that the reason for failure has been identified, as revision for pain alone is associated with poor results. This is particularly important when considering revision of a UKA, as surgeons may have a lower threshold for revision than following TKA given the perception that the revision is “easy” and that the pain is “probably from the unresurfaced compartments”. In a multi-center study, we found that many patients undergoing revision of a failed UKA do not have an appropriate evaluation for infection. Evaluation should include a screening ESR and CRP and if abnormal, an aspiration of the knee joint for synovial fluid WBC count, differential and culture. To revise a UKA to a TKA, we perform the revision as we would a primary TKA, ignoring the implanted femoral component and using it to assist with reference of femoral component rotation and for the distal femoral cut; the component is not removed until it must for the final preparation. After finishing the femoral component cuts, the tibia is completely exposed prior to carefully removing the tibial component and re-cutting the tibia. In our experience of 45 consecutive both component revisions of UKA to TKA at Rush, 44 used primary implants (98%), including cruciate retaining implants in 36 of these 44 knees (82%; the balance were PS implants) and tibial stems were utilised in 6 of 44 knees (14%). In order to better understand the outcomes of revision of failed UKA we studied 49 patients revised from UKA to TKA and 43 revised from HTO to TKA and matched them to 43 aseptic, both component revision TKA and 97 primary TKA. At a mean of 4.8 years, the KSS and Function Scores in the UKA to TKA, HTO to TKA and primary TKA cohorts were similar. Total operative times were significantly higher in the HTO to TKA and revision TKA groups. Length of hospital stay was shorter in the primary TKA cohort. The rate of complications and reoperations were higher in the HTO to TKA and revision TKA groups compared to the UKA to TKA and primary TKA groups. Based on these results, we believe that revising an HTO and UKA to a TKA both had functional outcomes more similar to a primary than a revision TKA, however, the complication rate of revising an HTO was more similar to a revision than a primary TKA

Introduction. Persistent pain after medial unicompartmental knee arthroplasty (UKA) is a prevailing reason for revision to total knee arthroplasty (TKA). Many of these pathologies can be addressed arthroscopically. The purpose of this study is to examine the outcomes of patients who undergo an arthroscopy for any reason after medial UKA. Methods. A query of our practice registry revealed 58 patients who had undergone medial UKA between October 2003 and June 2015 with subsequent arthroscopy. Mean interval from UKA to arthroscopy was 22 months (range, 1–101 months). Indications for arthroscopy were acute anterior cruciate ligament tear (1), arthrofibrosis (7), synovitis (12), recurrent hemarthrosis (2), lateral compartment degeneration including isolated lateral meniscus tears (11), and loose cement fragments (25). Results. Mean follow-up after arthroscopy was 37 months (range, 1–134 months). Twelve patients have been revised from UKA to TKA. Relative risk of revision after arthroscopy for lateral compartment degeneration was 4.27 (6 of 11; 55%; p=0.002) and for retrieval of loose cement fragments was 0.05 (0 of 25; 0%; p=0.03). Relative risk for revision after arthroscopy for anterior cruciate ligament tear, arthrofibrosis, synovitis, or recurrent hemarthrosis did not meet clinical significance secondary to the low number of patients in these categories. Conclusions. The results of this study suggest that arthroscopic retrieval of cement fragments does not compromise UKA longevity. However, arthroscopy for lateral compartment degradation after UKA predicts a high risk of revision to TKA regardless of its relative radiographic insignificance

Aims. Robotic-assisted unicompartmental knee arthroplasty (R-UKA) has been proposed as an approach to improve the results of the conventional manual UKA (C-UKA). The aim of this meta-analysis was to analyze the studies comparing R-UKA and C-UKA in terms of clinical outcomes, radiological results, operating time, complications, and revisions. Methods. The literature search was conducted on three databases (PubMed, Cochrane, and Web of Science) on 20 February 2024 according to the guidelines for Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA). Inclusion criteria were comparative studies, written in the English language, with no time limitations, on the comparison of R-UKA and C-UKA. The quality of each article was assessed using the Downs and Black Checklist for Measuring Quality. Results. Among the 3,669 articles retrieved, 21 studies on 19 series of patients were included. A total of 3,074 patients (59.5% female and 40.5% male; mean age 65.2 years (SD 3.9); mean BMI 27.4 kg/m. 2. (SD 2.2)) were analyzed. R-UKA obtained a superior Knee Society Score improvement compared to C-UKA (mean difference (MD) 4.9; p < 0.001) and better Forgotten Joint Score postoperative values (MD 5.5; p = 0.032). The analysis of radiological outcomes did not find a statistically significant difference between the two approaches. R-UKA showed longer operating time (MD 15.6; p < 0.001), but reduced complication and revision rates compared to C-UKA (5.2% vs 10.1% and 4.1% vs 7.2%, respectively). Conclusion. This meta-analysis showed that the robotic approach for UKA provided a significant improvement in functional outcomes compared to the conventional manual technique. R-UKA showed similar radiological results and longer operating time, but reduced complication and revision rates compared to C-UKA. Overall, R-UKA seems to provide relevant benefits over C-UKA in the management of patients undergoing UKA. Cite this article: Bone Jt Open 2024;5(5):374–384

Background. The purpose of this study was to assess the overall clinical and radiographic outcomes of unicompartmental knee arthroplasty (UKA) in the 2–10 year postoperative period. The secondary goal was to compare outcomes between fixed- (FB) and mobile-bearing (MB) implant designs. Methods. We performed a retrospective analysis of 237 consecutive primary medial UKAs from a single academic center. All cases were performed by high-volume fellowship-trained arthroplasty surgeons, though UKA comprised <10% of their overall knee arthroplasty practice (<20 medial UKAs per surgeon per year). Clinical outcomes included the Oxford Knee Scores (OKS) and revision rates. Femoral and tibial coronal and sagittal angles (FCA, FSA, TCA, TSA) were radiographically measured. FCA (>±10º deviation from the neutral axis), FSA (>15º flexion), TCA (>±5º deviation from the neutral axis), and TSA (>±5º deviation from 7º) outliers were defined. Far outliers were defined as measurements that fell an additional >±2º outside of these ranges. Outcomes were compared between the FB and MB groups. Results. Overall, OKS scores improved significantly from 18.6 to 34.2 (p<0.0001) following UKA. The overall revision rate at an average 5.5-year follow-up was 14.3%. Only 48.9% and 46.4% of knees simultaneously fell within coronal and sagittal alignment targets for femoral and tibial alignment, respectively. Only 24.1% of all UKAs fell within target alignment in all four measurements. When comparing FB and MB knees, there was no difference in the overall revision rate (12.5% vs. 17.6%, p=0.280), nor were there differences in postoperative OKS (33.6 vs. 35.4, p=0.239) or outlier risk. Conclusions. The proportion of UKA revisions and alignment outliers is greater than expected, even among high-volume surgeons. In general, implant design does not appear to significantly impact clinical outcomes, revision rates, or implant alignment. There was a trend for far outliers to have a higher rate of revision and lower OKS. For figures, tables, or references, please contact authors directly

A majority of patients present with varus alignment and predominantly medial compartment disease. The secret of success in osteoarthritis (OA) treatment is patient selection and patient specific treatment. Different wear patterns have been described and that knowledge should be utilised in modern knee surgery. In case of isolated anteromedial OA, unicompartmental knee arthroplasty (UKA) should be one of the therapeutic options available to the knee surgeon. The discussion not to offer a UKA to patients is based on the fear of the surgeon not being able to identify the right patient and not being able to perform the surgery accurately. The common modes of failure for UKA, which are dislocation or overcorrection leading to disease progression, can be avoided with a fixed bearing implant. Wear can probably be avoided with newer polyethylenes and avoidance of overstuffing in flexion of the knee. Revision for unexplained pain and unknown causes should disappear once surgeons understand persistent pain after surgery much better than they do today. The choice in favor of UKA is a choice of function over survivorship, a choice for reduced comorbidity and lower mortality. Many of the common problems in TKA are not an issue in UKA. Component overhang, decreased posterior offset, changed joint line height, gap mismatch, flexion gap instability, lift off and paradoxical motion hardly exist in UKA if the replacement is performed according to resurfacing principles with respect for the native knee anatomy. New technologies like navigation, PSI and robotics will help with alignment and component positioning. Surgeon education and training should allow over time UKA to be performed by all of us

Introduction. Over the past several decades, numerous surgical procedures have been perfected in the inpatient hospital setting and then evolved into outpatient procedures. This has been shown to be a safe and economical transition for many orthopedic procedures. A prime example is ACL reconstruction. We report here our early experience with our initial consecutive series of outpatient UKA's done in a free standing ASC (ambulatory surgery center). Materials and Methods. From 8/26/2008 to 5/20/12 there were 60 UKA's performed as outpatient procedures at a free standing ASC. Average patient age was 57.7 years (range of 46–69). Medical comorbidities included 22 patients with HTN and 7 with diabetes. All patients had general anesthesia with periarticular injection of the involved knee (25 cc's of Marcaine with epinephrine 1:100,000) and an intraarticular injection after closure of the capsule with 25 cc of Marcaine with epinephrine mixed with 5 cc of morphine sulfate. Patients without allergy to sulfa were given 200mg of Celebrex bid for three days and hydrocodone/acetaminophin 10/325 1–2 tabs q4 hours prn pain. Patients were discharged home when stable, ambulating with aids as needed, with length of stay ranging from 60–180 minutes (average of 85 minutes). Results. No patients required admission to the hospital for any reason. There was one hemarthrosis in a medial UKA which developed on postoperative day 4. There was uneventful resolution of this event with conservative management and an excellent result was achieved. The vast majority of patients were ambulating well and without walking aids at the 2 week postoperative evaluation. The total number of UKAs performed by the author in the ASC since 8/26/2008 is now 282, still without any complications requiring admission to the hospital. Conclusion. Outpatient UKA performed in an ambulatory surgery center was found to be a safe, efficient, and effective method for the management of unicompartmental osteoarthritis of the knee in this relatively healthy cohort of patients. It is now our routine approach for patients undergoing UKA, with inpatient hospitalization being reserved for those patients who are at higher postoperative risk due to multiple medical comorbidities

Converting UKA to TKA can be difficult, and specialised techniques are needed. Issues include bone loss, joint line approximation, sizing, and rotation. Determining the complexity of conversion pre-operatively helps predict the need for augmentation, grafting, stems, or constraint. In a 2009 study from our center, 50 UKA revised to TKA (1997–2007) were reviewed: 9 implants (18%) were modular fixed-bearing, 4 (8%) were metal-backed nonmodular fixed-bearing, 8 (16%) were resurfacing onlay, 10 (20%) were all-polyethylene step-cut, and 19 (38%) were mobile bearing designs; 5 knees (10%) failed due to infection, 5 (10%) due to wear and/or instability, 10 (20%) for pain or progression of arthritis, 8 (16%) for tibial fracture or severe subsidence, and 22 (44%) due to loosening of either one or both components. Insert thickness was no different between implants (P=0.23) or failure modes (P=0.27). Stemmed component use was most frequent with nonmodular components (50%), all-polyethylene step-cut implants (44%), and modular fixed-bearing implants (33%; P=0.40). Stem use was highest in tibial fracture (86%; P=0.002). Augment use was highest among all-polyethylene step-cut implants (all-polyethylene, 56%; metal-backed, 50%; modular fixed-bearing, 33%; P=0.01). Augmentation use was highest in fracture (86%) and infection (67%), with a significant difference noted between failure modes (P=0.003). Failure of nonmodular all-polyethylene step-cut devices was more complex than resurfacing or mobile bearing. Failure mode was predictive of complexity. Reestablishing the joint line, ligamentous balance, and durable fixation are critical to assuring a primary outcome. In a 2013 multicenter study of 3 institutions including ours, a total of 175 revisions of medial UKA in 168 patients (81 males, 87 females; average age of 66 years) performed from 1995 to 2009 with a minimum of 2-year clinical follow-up were reviewed. The average time from UKA to revision TKA was 71.5 months (range 2 months to 262 months). The four most common reasons for failure of the UKA were femoral or tibial loosening (55%), progressive arthritis of the lateral or patellofemoral joints (34%), polyethylene failure (4%) and infection (3%). Mean follow-up after revision was 75 months. Nine of 175 knees (4.5%) were subsequently revised at an average of 48 months (range 6 months to 123 months). The rate of revision was 1.23 revisions per 100 observed component years. The average Knee Society pain and function score increased to 75 and 66, respectively. In the present series, the re-revision rate after revision TKA from UKA was 4.5% at an average of 75 months or 1.2 revisions per 100 observed component years. Compared to published individual institution and national registry data, re-revision of a failed UKA is equivalent to revision rates of primary TKA and substantially better than re-revision rates of revision TKA. These data should be used to counsel patients undergoing revision UKA to TKA

Introduction. It has been hypothesized that a unicompartmental knee arthroplasty (UKA) is more likely to be revised than a total knee (TKA) because conversion surgery to a primary TKA is available. The purpose of this study was to determine if there is a lower threshold for UKA revisions compared to TKA revisions based on Oxford Knee Scores and range of motion (ROM). Methods. We retrospectively reviewed 636 aseptic revision cases performed between 1998 and 2018. This included 137 UKAs that underwent conversion to TKA and 499 TKA revisions. Pre-revision age, body mass index (BMI), time in situ, Oxford Knee Scores, and ROM were available for all patients. T-tests were performed to determine if significant differences existed between the two groups. The minimal clinically important difference (MCID) when comparing Oxford scores between cohorts has been reported as 5 points. Results. There were no differences between the two groups based on gender, BMI, age, or time to revision. The top three reasons for revision are different. TKR revision diagnoses were loosening 43%, instability 18% and wear 13%. UKA revision diagnoses are progression of OA 37%, loosening 36%, and wear 12%. All UKA were converted to TKA while there were 440 partial and 59 all component TKR revisions. Out of a maximum 48 points, the mean Oxford score of the UKAs before revision was 23±9.5, which was significantly higher than the TKAs at 19.3±9.7 (p<0.001). UKA patients scored statistically better on nine of the twelve Oxford questions with no difference in pain, walking, and sit to stand questions. Revised UKA had greater pre-revision ROM (1140) than TKR (990, p<0.001). Conclusion. The mean UKA Oxford scores prior to revision were significantly better than pre-revision TKA scores and better on 9 of 12 individual Oxford questions. However, the 3.7 point mean difference is less than the 5 point MCID for the Oxford Knee Score. This study suggests that at our institution there may not be a difference in patient reported Oxford preoperative scores between UKA and TKR revisions implying that we are not more likely to revise a UKA than a TKA. This is not surprising since our center does a high volume of UKA. We have also performed sub analyses comparing UKA revision scores to partial and both component TKA revision scores. For figures, tables, or references, please contact authors directly

One of the arguments in favor of unicompartmental knee arthroplasty (UKA) is the possibility of an easier revision. Especially if UKA is considered as an early intervention allowing bridging until total knee arthroplasty (TKA) is necessary at later age. If indeed primary TKA results can be obtained at time of revision, UKA becomes a real indication to postpone TKA until a later age. For obtaining primary TKA results, a primary knee should be indicated for the revision. This is possible if the UKA cuts were conservative and within the resection level of a primary TKA. Furthermore bone loss should be contained and either be resected or easily solved with substituting techniques compatible with a primary TKA. Finally, the primary implant utilised should allow a full interchangeability of the tibial and femoral sizes. This allows a lower tibial cut during the revision, often leading to a smaller size but interchangeability avoids downsizing the femur and creating flexion gap instability. If the UKA to TKA revision asks for stems, bone substitutions, joint line changes and more constraint, the primary result will not be obtained. Therefore it is important to select a bone preserving UKA system that allows for conservative bone cuts and avoids deep keel preparations. UKA to TKA with primary components and without gap mismatches or joint line changes leads to excellent outcome

Introduction. Unicompartmental Knee Arthroplasty (UKA) has been offered as a tissue sparing alternative to total knee arthroplasty (TKA) for treatment of early to mid-stage osteoarthritis (OA). While the spared tissue and retention of cruciate ligaments may result in faster recovery, smaller incision, less bone resection, decreased pain and blood loss and more normal kinematics and function, UKA has shown unpredictable results in practice, which may be due to variations in surgical techniques. 1. Recently a robotic-assisted technique has been introduced as a means to provide more consistent and reproducible surgical results. In this study, the early return to function was measured to determine proposed benefits between UKA and TKA. Methods. Patients requiring either UKA or TKA were prospectively enrolled in this IRB approved study. Each patient received pre-operative education regarding their expected physical therapy (PT) regimen, which was uniform for all patients. PT was determined to be concluded when each patient reached an achievable functional endpoint with each of the following 5 criteria: range of motion from 5 to 115 degrees, recovery of flexion and extension strength to 4/5 of pre-operative strength, gait with minimal limp and without an assistive device for 250 feet and ability to ascend and descend a flight of stairs with step over gait and good control. The number of PT visits to reach each functional goal was recorded. Results. 18 patients (19 knees) were enrolled in the study, with 8 females and 10 males. 13 knees received a TKA and 6 received a UKA. Average age was 65.6 ± 6.4 (range: 54–79) and average body mass index (BMI) was 27.62± 4.9 (range: 20.1–36.6). Age and BMI did not differ between the two groups. Average number of PT visits to reach each functional endpoint is listed in table 1 below. While the UKA group required less visits to reach each criteria, a significant difference (P<0.05) was seen in gait with minimal limp, flexion to 115 degrees, and extension of 5 degrees. Table 1. Number of Physical Therapy visits required to reach Functional Endpoint for TKA and UKA patients. Discussion. Early results show less physical therapy is required for UKA patients than TKA patients to reach the same functional goals. As physical therapy accounts for a significant portion of the episode of care for knee arthroplasty, this quicker recovery may result in a decreased economic burden. More patients and longer follow-up are required to determine full clinical and economic benefit of UKA procedure

Aims. Unicompartmental knee arthroplasty (UKA) is a bone-preserving treatment option for osteoarthritis localized to a single compartment in the knee. The success of the procedure is sensitive to patient selection and alignment errors. Robotic arm-assisted UKA provides technological assistance to intraoperative bony resection accuracy, which is thought to improve ligament balancing. This paper presents the five-year outcomes of a comparison between manual and robotically assisted UKAs. Methods. The trial design was a prospective, randomized, parallel, single-centre study comparing surgical alignment in patients undergoing UKA for the treatment of medial compartment osteoarthritis (ISRCTN77119437). Participants underwent surgery using either robotic arm-assisted surgery or conventional manual instrumentation. The primary outcome measure (surgical accuracy) has previously been reported, and, along with secondary outcomes, were collected at one-, two-, and five-year timepoints. Analysis of five-year results and longitudinal analysis for all timepoints was performed to compare the two groups. Results. Overall, 104 (80%) patients of the original 130 who received surgery were available at five years (55 robotic, 49 manual). Both procedures reported successful results over all outcomes. At five years, there were no statistical differences between the groups in any of the patient reported or clinical outcomes. There was a lower reintervention rate in the robotic arm-assisted group with 0% requiring further surgery compared with six (9%) of the manual group requiring additional surgical intervention (p < 0.001). Conclusion. This study has shown excellent clinical outcomes in both groups with no statistical or clinical differences in the patient-reported outcome measures. The notable difference was the lower reintervention rate at five years for roboticarm-assisted UKA when compared with a manual approach. Cite this article: Bone Joint J 2021;103-B(6):1088–1095

In unicompartmental knee arthroplasty (UKA), extension gap commonly decreases after inserting the trial components. As most of UKA technique incorporates the fixture of implants using bone cement, it is likely that the gap decreases further when inserting the actual implants. We performed a new additional procedure that enables a precise adjustment of the extension gap. Thirty-two patients who had undergone UKA (ZIMMER Unicompartmental High-Flex Knee System, Zimmer®, Warsaw) using the spacer block technique at our hospital in 2013 were reviewed. Ten cases had difficulties in achieving full extension after the trial implants were inserted, and hence, a new procedure of longitudinal incision between the medial collateral ligament and the posterior capsule was performed. This additional method created a mean increase of 3mm of the extension gap, and facilitated the knee to extend completely. There were no cases that had an increase in the flexion gap. Previously, a tibial osteotomy was added in such cases, but this had a risk of increasing not just the extension gap but also the flexion gap. This method is a valid technique for precise adjustments, and could also be applied to patients with severe flexion contracture to treat by UKA

Aims. It remains controversial whether patellofemoral joint pathology is a contraindication to lateral unicompartmental knee arthroplasty (UKA). This study aimed to evaluate the effect of preoperative radiological degenerative changes and alignment on patient-reported outcome scores (PROMs) after lateral UKA. Secondarily, the influence of lateral UKA on the alignment of the patellofemoral joint was studied. Methods. A consecutive series of patients who underwent robotic arm-assisted fixed-bearing lateral UKA with at least two-year follow-up were retrospectively reviewed. Radiological evaluation was conducted to obtain a Kellgren Lawrence (KL) grade, an Altman score, and alignment measurements for each knee. Postoperative PROMs were assessed using the Kujala (Anterior Knee Pain Scale) score, Knee Injury and Osteoarthritis Outcome Score Joint Replacement (KOOS JR), and satisfaction levels. Results. A total of 140 knees (130 patients) were identified for analysis. At mean 4.1 years (2.0 to 8.5) follow-up, good to excellent Kujala scores were reported. The presence of mild to moderate preoperative patellofemoral joint osteoarthritis had no impact on these scores (KL grade 0 vs 1 to 3, p = 0.203; grade 0 to 1 vs 2 to 3, p = 0.674). Comparable scores were reported by patients with osteoarthritis (Altman score of ≥ 2) evident on either the medial or lateral patellofemoral joint facet (medial, p = 0.600 and lateral, p = 0.950). Patients with abnormal patellar congruence and tilt angles (≥ 17° and ≥ 14°, respectively) reported good to excellent Kujala scores. Furthermore, lateral UKA resulted in improvements to patellofemoral alignment. Conclusion. This is the first study demonstrating that mild to moderate preoperative radiological degenerative changes and malalignment of the patellofemoral joint are not associated with poor patient-reported outcomes at mid-term follow-up after lateral fixed-bearing UKA. Our data suggest that this may be explained by realignment of the patella and thereby redistribution of loads across the patellofemoral joint. Cite this article: Bone Joint J 2020;102-B(6):727–735

Purpose. the purpose of this study was to compare the rollback ratio in the bi-cruciate substituting BCS-TKA and the Oxford UKA. Methods. 20 subjects (28 knees) who were performed the BCS-TKA (Journey II: Smith and Nephew) and 24 subjects (29 knees) who were performed the Oxford UKA, were included in this study. Approximately 6 months after surgery, and when the subjects recovered their range of knee motion, following the Laidlow's method (The knee 2010), lateral radiographic imaging of the knee was performed with active full knee flexion. The most posterior tibiofemoral contact point was measured for evaluation of femoral rollback (Rollback ratio). Flexion angle was also measured using the same radiograph and the correlation of rollback and flexion angle was analyzed. As a control, radiographs of the contralateral knees of who were performed Oxford UKA were evaluated (29 knees). Results. The rollback ratios of the BCS-TKA, Oxford UKA, and the control knees were 37.9±4.9%, 35.7±4.2%, and 35.3±4.8% respectively from the posterior edge of the tibia. No significant difference in rollback ratio was observed. The flexion angles of the BCS-TKA, Oxford UKA, and the control knees were 121.8±8.4°, 125.4±7.5°, and 127±10.3°, respectively. No significant difference in knee flexion angle was observed. Significant correlation between rollback ratio and knee flexion angle was observed (p=0.002: Pearson's correlation coefficient =−0.384). Conclusion. In conclusion, BCS-TKA showed no significant difference of rollback ratio when compared with the control knees and the Oxford UKA knees. There is the possibility that the design of BCS-TKA could reproduce the native ACL and PCL function

Introduction: The purpose of this study is to determine in vivo femorotibial axial rotation magnitudes and patterns in mobile-bearing posterior stabilized total knee arthroplasty (PS-TKA) and unicondylar knee arthroplasty (UKA) in deep flexion. Material and Methods: Using video fluoroscopy, 12 subjects having a mobile-bearing PS-TKA (NexGen LPS Flex) and 12 subjects having a mobile-bearing UKA (Oxford UNI) were analyzed to determine their in vivo kinematic patterns under both weight bearing and non weight bearing. All implants were implanted by the same surgeon and were judged successful clinically with no pain and ligament laxity. The femoral and tibial components were overlaid onto the fluoroscopic images using a three-dimensional automated model-fitting technique to determine joint mobility. Results: The average range of motion was 124 degrees of flexion for the PS-TKA and 137 degrees of flexion for the UKA. Although subjects in this study exhibited variable motion pattern, the common is anterior movement in extension to 45 degrees of flexion and posterior movement in 60 degrees of flexion to full flexion. The average internal rotation of the tibia was 18 degrees in UKA and 6 degrees in PS-TKA at 100 degrees of flexion to full. Incidence of lateral condylar lift off greater than 2mm was 5 in the PS-TKA and 1 in the UKA. Discussion: A medial pivot kinematic pattern was observed in deep flexion in UKA. However in extension to 45 or 60 degrees of flexion, anterior condylar movement was observed in both groups. The motion pattern of UKA in 60 degree of flexion to full was close to the natural knee motion

Renewed interest in UKA necessitates further investigation into the ramifications of conversion to TKA due to either implant failure or progressive joint disease. The purpose of this study was to compare the depth of tibial resection at UKA and the resulting implications for conversion to TKA using two different UKA techniques and implant designs. A radiographic review of 42 UKA’s from a single surgeon was performed. Sixteen cases utilized a standard all-polyethylene tibial onlay UKA marketed as a minimally invasive resurfacing implant. The other 26 employed a novel robotically assisted technique and a tibial inlay implant design. Measurement techniques were developed to determine the depth of medial tibial plateau resection at initial UKA as well as potential tibial cuts and implant components required at conversion. Average depth of bony medial plateau resection was significantly greater in the standard technique onlay design group (8.5 ± 2.26 mm) compared to the robotically assisted inlay group (4.4 ± 0.93 mm) (p< .0001). At conversion to a standard TKA, the proposed tibial osteotomy would require medial augmentation/revision components in 75% of the onlay group as compared to 4% of the robotically assisted inlay group (p< .0001). Robotically assisted UKA using a tibial inlay design appears to be a truly resurfacing procedure with respect to the tibia, resulting in significantly less tibial bone resection at UKA as well as simpler conversion to TKA when compared to conventional onlay techniques

Objectives. Proximal tibial fracture is one of the most common postoperative complications of unilateral knee arthroplasty (UKA). The objective of the present study is to investigate the risk factors of these fractures, occurred after UKA in our facility. Method. We performed 314 UKAs between May 2006 and December 2013. All cases were done using Oxford UKA. Proximal tibial fractures were observed in 5 cases. 4 cases were female and 1 case was male, and the age at the operation ranged from 73 to 90. All cases were osteoarthritis. 4 cases were diagnosed as stress fracture with minimum displacement, and 1 case was fracture with displacement. We investigated the risk factors of the tibial fracture among those 5 cases. Low bone mineral density(BMD), the presence of medial tibial cortex pinhole, excessive vertical cut, and adjacence of keel and posterior tibia cortex were estimated as risk factors. Results. The loss in BMD was seen in all cases. Medial tibial cortex pinhole was recognized in 2 cases. Excessive vertical cut was recognized in 3 cases. Adjacence of keel and posterior tibia bone cortex was recognized in 3 cases, and the distance between keel and posterior tibia bone cortex was less than 3mm in all of these 3 cases. 4 cases those diagnosed as stress fractures, healed spontaneously with conservative treatment, but the case with displaced fragment needed ORIF. Discussion. Loss in BMD was seen in all cases as predicted, and this is one of the highest risk factors in UKA patient. Preoperative PTH use is recommended when low BMD was seen. Other risk factors are, medial tibial cortex pinhole, excessive vertical cut, and adjacence of keel and posterior tibial cortex. These risk factors are preventable if some cares are taken during the operation. Medial inclination of the tibial plateau should be checked preoperatively to avoid excessive vertical cut. If the distance between keel and posterior tibial cortex is less than 3mm at the preoperative planning, we should consider converting the implant. Furthermore, it is important to pay attention to intraoperative procedures. We should not use heavy hammer and avoid excessive varus force during cementing. For the prevention of tibial fractures after UKA, both strict preoperative planning and prevention of intraoperative errors are important

Total knee arthroplasty (TKA) provides good results even for severe knee osteoarthritis (OA) patients. However, patients often suffer from post-operative pain and have long rehabilitation periods. In recent years, utilization of unicompartmental knee arthroplasty (UKA) has increased in an effort to decrease pain and shorten recovery compared to TKA. Moreover, the long-term results of the UKA have improved. Many surgeons now wonder whether TKA or UKA is better for patients with isolated medial knee OA. In Japan, the government has public insurance system and patients are able to receive the joint replacement surgery inexpensively. This study was conducted to compare the cost the public insurance and the patients co-payment for TKA and UKA. We investigated a series of thirty TKAs and fifteen UKAs performed in Fussa Hospital (Tokyo, Japan) from July 2012 to April 2013. Data from two TKAs' were excluded since the patients had comorbidities (asthma and severe DM) that extended their hospitalizations. Patients were discharged from the hospital if they were able to go up and down the stairs or were able to conduct routine activities of daily living. Total payments the hospital received averaged $19600 (S.D. $1600) for a TKA and $15200 (S.D. $1300) for a UKA. Patients paied averaged of $690 (S.D. $370) for a TKA and $470 (S.D. $170) for a UKA (Figure 1). The surgical fee was $3769 for both TKA and UKA, and was uniform thoughout Japan. The implant price averaged $6200 (S.D. $300) for TKA and $3900 (S.D. $200) for UKA, where prices were also determined by the government. Hospitalization averaged 28 days (S.D. 7 days) for TKA and 21 days (S.D. 6 days) for UKA. For both TKA and UKA, the total cost and the number of days in hospital were highly correlated (R = 0.92 and R = 0.96, respectively). A linear cost model suggests the TKA cost was $210 times days of hospitalization plus $13100 and the UKA cost was $220 times days of hospitalization plus $10000. Patients' payments were not correlated to the days of hospitalization (R = 0.22 and R = 0.45, respectively). TKA and UKA are performed all over the world now and the number of the surgeries increases each year. Althouth each country has a different insurance system, many countries face an increasing and problematic economic burden for both patients and insurance organization (either public or private company). This study showed UKA is less expensive than TKA by $4400, an advantage that might complement the traditional view that UKA is less invasive and often has fewer complications for treating isolating medical compartment OA. For Japanese system, patients pay relatively little out-of pocket despite long hospitalization, and length of stay has a direct and significant effect on total cost for TKA and UKA