Aims. To identify unanswered questions about the prevention, diagnosis, treatment, and rehabilitation and delivery of care of first-time soft-tissue knee injuries (ligament injuries, patella dislocations, meniscal injuries, and articular cartilage) in children (aged 12 years and older) and adults. Methods. The James Lind Alliance (JLA) methodology for Priority Setting Partnerships was followed. An initial survey invited patients and healthcare professionals from the UK to submit any uncertainties regarding soft-tissue knee injury prevention, diagnosis, treatment, and rehabilitation and delivery of care. Over 1,000 questions were received. From these, 74 questions (identifying common concerns) were formulated and checked against the best available evidence. An interim survey was then conducted and 27 questions were taken forward to the final workshop, held in January 2023, where they were discussed, ranked, and scored in multiple rounds of prioritization. This was conducted by healthcare professionals, patients, and carers. Results. The top ten included questions regarding prevention, diagnosis, treatment, and rehabilitation. The number one question was, ‘How urgently do soft-tissue knee injuries need to be treated for the best outcome?’. This reflects the concerns of patients, carers, and the wider multidisciplinary team. Conclusion. This validated process has generated ten important priorities for future soft-tissue knee injury research. These have been submitted to the National Institute for Health and Care Research. All 27 questions in the final workshop have been published on the JLA website. Cite this article: Bone Joint J 2024;106-B(3):232–239

Aims. To explore key stakeholder views around feasibility and acceptability of trials seeking to prevent post-traumatic osteoarthritis (PTOA) following knee injury, and provide guidance for next steps in PTOA trial design. Methods. Healthcare professionals, clinicians, and/or researchers (HCP/Rs) were surveyed, and the data were presented at a congress workshop. A second and related survey was then developed for people with joint damage caused by knee injury and/or osteoarthritis (PJDs), who were approached by a UK Charity newsletter or Oxford involvement registry. Anonymized data were collected and analyzed in Qualtrics. Results. Survey responses (n = 19 HCP/Rs, 39 PJDs) supported studies testing pharmacological agents preventing PTOA. All HCP/Rs and 30/31 (97%) PJDs supported the development of new treatments that improved or delayed knee symptoms and damage to knee structure. PJDs thought that improving structural knee damage was more important than knee symptoms. Both groups found studies more acceptable as expected future benefit and risk of PTOA increased. All drug delivery routes were acceptable. Workshop participants (around n = 60) reflected survey views. Discussions suggested that stratifying using molecular testing for likely drug response appeared to be more acceptable than using characteristics such as sex, age, and BMI. Conclusion. Our findings supported PTOA drug intervention studies, including situations where there is low risk of disease, no expected benefit of treatment, and frequent treatment administration. PJDs appeared less risk-averse than HCP/Rs. This work reinforces the benefits of consensus and involvement work in the co-creation of PTOA drug trial design. Involvement of key stakeholders, such as PJDs with different risks of OA and regulatory representatives, are critical for trial design success. Cite this article: Bone Joint Res 2024;13(9):513–524

A retrospective survey of 135 posterior dislocations and fracture-dislocations of the hip was carried out in order to define the pattern of associated knee injuries. Thirty-five patients had sustained a significant injury to the knee, of which twenty-five were clearly attributable to a direct blow on the front of the knee (fractured patella, traumatic chondromalacia, fractures of femoral and tibial condyles) and ten were compatible with valgus, yams or rotational forces (medial, lateral and cruciate ligament tears). The second type of injury has not been widely recognised but it is important that it should not be overlooked

Objectives

The aim of the current study was to analyse the effects of posterior cruciate ligament (PCL) deficiency on forces of the posterolateral corner structure and on tibiofemoral (TF) and patellofemoral (PF) contact force under dynamic-loading conditions.

Aims. The lack of disease-modifying treatments for osteoarthritis (OA) is linked to a shortage of suitable biomarkers. This study combines multi-molecule synovial fluid analysis with machine learning to produce an accurate diagnostic biomarker model for end-stage knee OA (esOA). Methods. Synovial fluid (SF) from patients with esOA, non-OA knee injury, and inflammatory knee arthritis were analyzed for 35 potential markers using immunoassays. Partial least square discriminant analysis (PLS-DA) was used to derive a biomarker model for cohort classification. The ability of the biomarker model to diagnose esOA was validated by identical wide-spectrum SF analysis of a test cohort of ten patients with esOA. Results. PLS-DA produced a streamlined biomarker model with excellent sensitivity (95%), specificity (98.4%), and reliability (97.4%). The eight-biomarker model produced a fingerprint for esOA comprising type IIA procollagen N-terminal propeptide (PIIANP), tissue inhibitor of metalloproteinase (TIMP)-1, a disintegrin and metalloproteinase with thrombospondin motifs 4 (ADAMTS-4), monocyte chemoattractant protein (MCP)-1, interferon-γ-inducible protein-10 (IP-10), and transforming growth factor (TGF)-β3. Receiver operating characteristic (ROC) analysis demonstrated excellent discriminatory accuracy: area under the curve (AUC) being 0.970 for esOA, 0.957 for knee injury, and 1 for inflammatory arthritis. All ten validation test patients were classified correctly as esOA (accuracy 100%; reliability 100%) by the biomarker model. Conclusion. SF analysis coupled with machine learning produced a partially validated biomarker model with cohort-specific fingerprints that accurately and reliably discriminated esOA from knee injury and inflammatory arthritis with almost 100% efficacy. The presented findings and approach represent a new biomarker concept and potential diagnostic tool to stage disease in therapy trials and monitor the efficacy of such interventions. Cite this article: Bone Joint Res 2020;9(9):623–632

Aims. A substantial fraction of patients undergoing knee arthroplasty (KA) or hip arthroplasty (HA) do not achieve an improvement as high as the minimal clinically important difference (MCID), i.e. do not achieve a meaningful improvement. Using three patient-reported outcome measures (PROMs), our aim was: 1) to assess machine learning (ML), the simple pre-surgery PROM score, and logistic-regression (LR)-derived performance in their prediction of whether patients undergoing HA or KA achieve an improvement as high or higher than a calculated MCID; and 2) to test whether ML is able to outperform LR or pre-surgery PROM scores in predictive performance. Methods. MCIDs were derived using the change difference method in a sample of 1,843 HA and 1,546 KA patients. An artificial neural network, a gradient boosting machine, least absolute shrinkage and selection operator (LASSO) regression, ridge regression, elastic net, random forest, LR, and pre-surgery PROM scores were applied to predict MCID for the following PROMs: EuroQol five-dimension, five-level questionnaire (EQ-5D-5L), EQ visual analogue scale (EQ-VAS), Hip disability and Osteoarthritis Outcome Score-Physical Function Short-form (HOOS-PS), and Knee injury and Osteoarthritis Outcome Score-Physical Function Short-form (KOOS-PS). Results. Predictive performance of the best models per outcome ranged from 0.71 for HOOS-PS to 0.84 for EQ-VAS (HA sample). ML statistically significantly outperformed LR and pre-surgery PROM scores in two out of six cases. Conclusion. MCIDs can be predicted with reasonable performance. ML was able to outperform traditional methods, although only in a minority of cases. Cite this article: Bone Joint Res 2023;12(9):512–521

Aims. The Coronal Plane Alignment of the Knee (CPAK) classification has been developed to predict individual variations in inherent knee alignment. The impact of preoperative and postoperative CPAK classification phenotype on the postoperative clinical outcomes of total knee arthroplasty (TKA) remains elusive. This study aimed to examine the effect of postoperative CPAK classification phenotypes (I to IX), and their pre- to postoperative changes on patient-reported outcome measures (PROMs). Methods. A questionnaire was administered to 340 patients (422 knees) who underwent primary TKA for osteoarthritis (OA) between September 2013 and June 2019. A total of 231 patients (284 knees) responded. The ­Knee Society Score 2011 (KSS 2011), Knee injury and Osteoarthritis Outcome Score-12 (KOOS-12), and Forgotten Joint Score-12 (FJS-12) were used to assess clinical outcomes. Using preoperative and postoperative anteroposterior full-leg radiographs, the arithmetic hip-knee-ankle angle (aHKA) and joint line obliquity (JLO) were calculated and classified based on the CPAK classification. To investigate the impact on PROMs, multivariable regression analyses using stepwise selection were conducted, considering factors such as age at surgery, time since surgery, BMI, sex, implant use, postoperative aHKA classification, JLO classification, and changes in aHKA and JLO classifications from preoperative to postoperative. Results. The preoperative and postoperative CPAK classifications were predominantly phenotype I (155 knees; 55%) and phenotype V (73 knees; 26%), respectively. The change in the preoperative to postoperative aHKA classification was a significant negative predictive factor for KOOS-12 and FJS-12, while postoperative apex proximal JLO was a significant negative predictive factor for KSS 2011 and KOOS-12. Conclusion. In primary TKA for OA, preoperative and postoperative CPAK phenotypes were associated with PROMs. Alteration in varus/valgus alignment from preoperative to postoperative was recognized as a negative predictive factor for both KOOS-12 and FJS-12. Moreover, the postoperative apex proximal JLO was identified as a negative factor for KSS 2011 and KOOS-12. Determining the target alignment for each preoperative phenotype with reproducibility could improve PROMs. Cite this article: Bone Joint J 2024;106-B(10):1059–1066

Anterior cruciate ligament (ACL) injuries are among the most common and debilitating knee injuries in professional athletes with an incidence in females up to eight-times higher than their male counterparts. ACL injuries can be career-threatening and are associated with increased risk of developing knee osteoarthritis in future life. The increased risk of ACL injury in females has been attributed to various anatomical, developmental, neuromuscular, and hormonal factors. Anatomical and hormonal factors have been identified and investigated as significant contributors including osseous anatomy, ligament laxity, and hamstring muscular recruitment. Postural stability and impact absorption are associated with the stabilizing effort and stress on the ACL during sport activity, increasing the risk of noncontact pivot injury. Female patients have smaller diameter hamstring autografts than males, which may predispose to increased risk of re-rupture following ACL reconstruction and to an increased risk of chondral and meniscal injuries. The addition of an extra-articular tenodesis can reduce the risk of failure; therefore, it should routinely be considered in young elite athletes. Prevention programs target key aspects of training including plyometrics, strengthening, balance, endurance and stability, and neuromuscular training, reducing the risk of ACL injuries in female athletes by up to 90%. Sex disparities in access to training facilities may also play an important role in the risk of ACL injuries between males and females. Similarly, football boots, pitches quality, and football size and weight should be considered and tailored around females’ characteristics. Finally, high levels of personal and sport-related stress have been shown to increase the risk of ACL injury which may be related to alterations in attention and coordination, together with increased muscular tension, and compromise the return to sport after ACL injury. Further investigations are still necessary to better understand and address the risk factors involved in ACL injuries in female athletes. Cite this article: Bone Jt Open 2024;5(2):94–100

The February 2023 Knee Roundup. 360. looks at: Machine-learning models: are all complications predictable?; Positive cultures can be safely ignored in revision arthroplasty patients that do not meet the 2018 International Consensus Meeting Criteria; Spinal versus general anaesthesia in contemporary primary total knee arthroplasty; Preoperative pain and early arthritis are associated with poor outcomes in total knee arthroplasty; Risk factors for infection and revision surgery following patellar tendon and quadriceps tendon repairs; Supervised versus unsupervised rehabilitation following total knee arthroplasty; Kinematic alignment has similar outcomes to mechanical alignment: a systematic review and meta-analysis; Lifetime risk of revision after knee arthroplasty influenced by age, sex, and indication; Risk factors for knee osteoarthritis after traumatic knee injury

Aims. Little is known about the risk factors that predispose to a rupture of the posterior cruciate ligament (PCL). Identifying risk factors is the first step in trying to prevent a rupture of the PCL from occurring. The morphology of the knee in patients who rupture their PCL may differ from that of control patients. The purpose of this study was to identify any variations in bone morphology that are related to a PCL. Patients and Methods. We compared the anteroposterior (AP), lateral, and Rosenberg view radiographs of 94 patients with a ruptured PCL to a control group of 168 patients matched by age, sex, and body mass index (BMI), but with an intact PCL after a knee injury. Statistical shape modelling software was used to assess the shape of the knee and determine any difference in anatomical landmarks. Results. We found shape variants on the AP and Rosenberg view radiographs to be significantly different between patients who tore their PCL and those with an intact PCL after a knee injury. Overall, patients who ruptured their PCL have smaller intercondylar notches and smaller tibial eminences than control patients. Conclusion. This study shows that differences in the shape of the knee are associated with the presence of a PCL rupture after injury. A smaller and more sharply angled intercondylar notch and a more flattened tibial eminence are related to PCL rupture. This suggests that the morphology of the knee is a risk factor for sustaining a PCL rupture. Cite this article: Bone Joint J 2019;101-B:1058–1062

Aims. Tibial plateau fractures (TPFs) are complex injuries around the knee caused by high- or low-energy trauma. In the present study, we aimed to define the distribution and frequency of TPF lines using a 3D mapping technique and analyze the rationalization of divisions employed by frequently used classifications. Methods. In total, 759 adult patients with 766 affected knees were retrospectively reviewed. The TPF fragments on CT were multiplanar reconstructed, and virtually reduced to match a 3D model of the proximal tibia. 3D heat mapping was subsequently created by graphically superimposing all fracture lines onto a tibia template. Results. The cohort included 405 (53.4%) cases with left knee injuries, 347 (45.7%) cases with right knee injuries, and seven (0.9%) cases with bilateral injuries. On mapping, the hot zones of the fracture lines were mainly concentrated around the anterior cruciate ligament insertion, posterior cruciate ligament insertion, and the inner part of the lateral condyle that extended to the junctional zone between Gerdy’s tubercle and the tibial tubercle. Moreover, the cold zones were scattered in the posteromedial fragment, superior tibiofibular syndesmosis, Gerdy’s tubercle, and tibial tubercle. TPFs with different Orthopaedic Trauma Association/AO Foundation (OTA/AO) subtypes showed peculiar characteristics. Conclusion. TPFs occurred more frequently in the lateral and intermedial column than in the medial column. Fracture lines of tibial plateau occur frequently in the transition zone with marked changes in cortical thickness. According to 3D mapping, the four-column and nine-segment classification had a high degree of matching as compared to the frequently used classifications. Cite this article: Bone Joint Res 2020;9(6):258–267

Aims. The primary aim of this study was to compare the migration of the femoral and tibial components of the cementless rotating platform Attune and Low Contact Stress (LCS) total knee arthroplasty (TKA) designs, two years postoperatively, using radiostereometric analysis (RSA) in order to assess the risk of the development of aseptic loosening. A secondary aim was to compare clinical and patient-reported outcome measures (PROMs) between the designs. Methods. A total of 61 TKAs were analyzed in this randomized clinical RSA trial. RSA examinations were performed one day and three, six, 12, and 24 months postoperatively. The maximal total point motion (MPTM), translations, and rotations of the components were analyzed. PROMs and clinical data were collected preoperatively and at six weeks and three, six, 12, and 24 months postoperatively. Linear mixed effect modelling was used for statistical analyses. Results. The mean MTPM two years postoperatively (95% confidence interval (CI)) of the Attune femoral component (0.92 mm (0.75 to 1.11)) differed significantly from that of the LCS TKA (1.72 mm (1.47 to 2.00), p < 0.001). The Attune femoral component subsided, tilted (anteroposteriorly), and rotated (internal-external) significantly less. The mean tibial MTPM two years postoperatively did not differ significantly, being 1.11 mm (0.94 to 1.30) and 1.17 mm (0.99 to 1.36, p = 0.447) for the Attune and LCS components, respectively. The rate of migration in the second postoperative year was negligible for the femoral and tibial components of both designs. The mean pain-at-rest (numerical rating scale (NRS)-rest) in the Attune group was significantly less compared with that in the LCS group during the entire follow-up period. At three months postoperatively, the Knee injury and Osteoarthritis Outcome Physical Function Shortform score, the Oxford Knee Score, and the NRS-activity scores were significantly better in the Attune group. Conclusion. The mean MTPM of the femoral components of the cementless rotating platform Attune was significantly less compared with that of the LCS design. This was reflected mainly in significantly less subsidence, posterior tilting, and internal rotation. The mean tibial MTPMs were not significantly different. During the second postoperative year, the components of both designs stabilized and low risks for the development of aseptic loosening are expected. Cite this article: Bone Joint J 2023;105-B(2):148–157

Aims. The aim of this study was to report patient and clinical outcomes following robotic-assisted total knee arthroplasty (RA-TKA) at multiple institutions with a minimum two-year follow-up. Methods. This was a multicentre registry study from October 2016 to June 2021 that included 861 primary RA-TKA patients who completed at least one pre- and postoperative patient-reported outcome measure (PROM) questionnaire, including Forgotten Joint Score (FJS), Knee Injury and Osteoarthritis Outcomes Score for Joint Replacement (KOOS JR), and pain out of 100 points. The mean age was 67 years (35 to 86), 452 were male (53%), mean BMI was 31.5 kg/m. 2. (19 to 58), and 553 (64%) cemented and 308 (36%) cementless implants. Results. There were significant improvements in PROMs over time between preoperative, one- to two-year, and > two-year follow-up, with a mean FJS of 17.5 (SD 18.2), 70.2 (SD 27.8), and 76.7 (SD 25.8; p < 0.001); mean KOOS JR of 51.6 (SD 11.5), 85.1 (SD 13.8), and 87.9 (SD 13.0; p < 0.001); and mean pain scores of 65.7 (SD 20.4), 13.0 (SD 19.1), and 11.3 (SD 19.9; p < 0.001), respectively. There were eight superficial infections (0.9%) and four revisions (0.5%). Conclusion. RA-TKA demonstrated consistent clinical results across multiple institutions with excellent PROMs that continued to improve over time. With the ability to achieve target alignment in the coronal, axial, and sagittal planes and provide intraoperative real-time data to obtain balanced gaps, RA-TKA demonstrated excellent clinical outcomes and PROMs in this patient population. Cite this article: Bone Jt Open 2022;3(7):589–595

Patient-reported outcome measures (PROMs) are being used increasingly in total knee arthroplasty (TKA). We conducted a systematic review aimed at identifying psychometrically sound PROMs by appraising their measurement properties. Studies concerning the development and/or evaluation of the measurement properties of PROMs used in a TKA population were systematically retrieved via PubMed, Web of Science, Embase, and Scopus. Ratings for methodological quality and measurement properties were conducted according to updated COnsensus-based Standards for the selection of health Measurement INstruments (COSMIN) methodology. Of the 155 articles on 34 instruments included, nine PROMs met the minimum requirements for psychometric validation and can be recommended to use as measures of TKA outcome: Oxford Knee Score (OKS); OKS–Activity and Participation Questionnaire (OKS-APQ); 12-item short form Knee Injury and Osteoarthritis Outcome (KOOS-12); KOOS Physical function Short form (KOOS-PS); Western Ontario and McMaster Universities Arthritis Index-Total Knee Replacement function short form (WOMAC-TKR); Lower Extremity Functional Scale (LEFS); Forgotten Joint Score (FJS); Patient’s Knee Implant Performance (PKIP); and University of California Los Angeles (UCLA) activity score. The pain and function subscales in WOMAC, as well as the pain, function, and quality of life subscales in KOOS, were validated psychometrically as standalone subscales instead of as whole instruments. However, none of the included PROMs have been validated for all measurement properties. Thus, further studies are still warranted to evaluate those PROMs. Use of the other 25 scales and subscales should be tempered until further studies validate their measurement properties. Cite this article: Bone Joint Res 2021;10(3):203–217

Aims. The patient-acceptable symptom state (PASS) is a level of wellbeing, which is measured by the patient. The aim of this study was to determine if the proportion of patients who achieved an acceptable level of function (PASS) after medial unicompartmental knee arthroplasty (UKA) was different based on the status of the anterior cruciate ligament (ACL) at the time of surgery. Methods. A total of 114 patients who underwent UKA for isolated medial osteoarthritis (OA) of the knee were included in the study. Their mean age was 65 years (SD 10). No patient underwent a bilateral procedure. Those who had undergone ACL reconstruction during the previous five years were excluded. The Knee injury Osteoarthritis Outcome Score Activities of Daily Living (KOOS ADL) function score was used as the primary outcome measure with a PASS of 87.5, as described for total knee arthroplasty (TKA). Patients completed all other KOOS subscales, Lysholm score, the Western Ontario and McMaster Universities Osteoarthritis Index, and the Veterans Rand 12-item health survey score. Failure was defined as conversion to TKA. Results. Survivorship at ten years was 97% in both the ACL-deficient and ACL-intact groups. The mean survival was 16.1 years (95% confidence interval (CI) 15.3 to 16.8) for the ACL-deficient group and 15.6 years (95% CI 14.8 to 16.361) for the ACL-intact group (p = 0.878). At a mean of nine years (SD 3.5) in the ACL-deficient group, 32 patients (87%) reached the PASS for the KOOS ADL. In the ACL-intact group, at a mean of 8.6 years (SD 3) follow-up, 63 patients (85%) reached PASS for the KOOS ADL. There was no significant difference in the percentage of patients who reached PASS for all KOOS subscales and Lysholm between the two groups. Conclusion. PASS was achieved in 85% of all UKAs for KOOS ADL, similar to reports for TKA. Fixed-bearing, medial, non-robotically-assisted UKA resulted in 97% survival at ten years in both the ACL-deficient and ACL-intact groups. There was no significant difference in all outcomes between the two groups. Understanding PASS will allow better communication between surgeons and patients to improve the surgical management of patients with single compartment OA of the knee. This study provides mid- to long-term data supporting the use of PASS to document outcomes following UKA. PASS was met in more than 85% of patients with no differences between ACL-deficient and ACL-intact knees at a mean follow-up of nine years. Cite this article: Bone Joint J 2021;103-B(8):1367–1372

Aims. A significant percentage of patients remain dissatisfied after total knee arthroplasty (TKA). The aim of this study was to determine whether the sequential addition of accelerometer-based navigation for femoral component preparation and sensor-guided ligament balancing improved complication rates, radiological alignment, or patient-reported outcomes (PROMs) compared with a historical control group using conventional instrumentation. Methods. This retrospective cohort study included 371 TKAs performed by a single surgeon sequentially. A historical control group, with the use of intramedullary guides for distal femoral resection and surgeon-guided ligament balancing, was compared with a group using accelerometer-based navigation for distal femoral resection and surgeon-guided balancing (group 1), and one using navigated femoral resection and sensor-guided balancing (group 2). Primary outcome measures were Patient-Reported Outcomes Measurement Information System (PROMIS) and Knee injury and Osteoarthritis Outcome (KOOS) scores measured preoperatively and at six weeks and 12 months postoperatively. The position of the components and the mechanical axis of the limb were measured postoperatively. The postoperative range of motion (ROM), haematocrit change, and complications were also recorded. Results. There were 194 patients in the control group, 103 in group 1, and 74 in group 2. There were no significant differences in baseline demographics between the groups. Patients in group 2 had significantly higher baseline mental health subscores than control and group 1 patients (53.2 vs 50.2 vs 50.2, p = 0.041). There were no significant differences in any PROMs at six weeks or 12 months postoperatively (p > 0.05). There was no difference in the rate of manipulation under anaesthesia (MUA), complication rates, postoperative ROM, or blood loss. There were fewer mechanical axis outliers in groups 1 and 2 (25.2%, 14.9% respectively) versus control (28.4%), but this was not statistically significant (p = 0.10). Conclusion. The sequential addition of navigation of the distal femoral cut and sensor-guided ligament balancing did not improve short-term PROMs, radiological outcomes, or complication rates compared with conventional techniques. The costs of these added technologies may not be justified. Cite this article: Bone Joint J 2020;102-B(6 Supple A):24–30

Aims. The purpose of this multicentre observational study was to investigate the association between intraoperative component positioning and soft-tissue balancing on short-term clinical outcomes in patients undergoing robotic-arm assisted unicompartmental knee arthroplasty (UKA). Patients and Methods. Between 2013 and 2016, 363 patients (395 knees) underwent robotic-arm assisted UKAs at two centres. Pre- and postoperatively, patients were administered Knee Injury and Osteoarthritis Score (KOOS) and Forgotten Joint Score-12 (FJS-12). Results were stratified as “good” and “bad” if KOOS/FJS-12 were more than or equal to 80. Intraoperative, post-implantation robotic data relative to CT-based components placement were collected and classified. Postoperative complications were recorded. Results. Following exclusions and losses to follow-up, 334 medial robotic-arm assisted UKAs were assessed at a mean follow-up of 30.0 months (8.0 to 54.9). None of the measured parameters were associated with overall KOOS outcome. Correlations were described between specific KOOS subscales and intraoperative, post-implantation robotic data, and between FJS-12 and femoral component sagittal alignment. Three UKAs were revised, resulting in 99.0% survival at two years (95% confidence interval (CI) 97.9 to 100.0). Conclusion. Although little correlation was found between intraoperative robotic data and overall clinical outcome, surgeons should consider information regarding 3D component placement and soft-tissue balancing to improve patient satisfaction. Reproducible and precise placement of components has been confirmed as essential for satisfactory clinical outcome. Cite this article: Bone Joint J 2019;101-B:435–442

Aims. Limited evidence is available on mid-term outcomes of robotic-arm assisted (RA) partial knee arthroplasty (PKA). Therefore, the purpose of this study was to evaluate mid-term survivorship, modes of failure, and patient-reported outcomes of RA PKA. Methods. A retrospective review of patients who underwent RA PKA between June 2007 and August 2016 was performed. Patients received a fixed-bearing medial or lateral unicompartmental knee arthroplasty (UKA), patellofemoral arthroplasty (PFA), or bicompartmental knee arthroplasty (BiKA; PFA plus medial UKA). All patients completed a questionnaire regarding revision surgery, reoperations, and level of satisfaction. Knee Injury and Osteoarthritis Outcome Scores (KOOS) were assessed using the KOOS for Joint Replacement Junior survey. Results. Mean follow-up was 4.7 years (2.0 to 10.8). Five-year survivorship of medial UKA (n = 802), lateral UKA (n = 171), and PFA/BiKA (n = 35/10) was 97.8%, 97.7%, and 93.3%, respectively. Component loosening and progression of osteoarthritis (OA) were the most common reasons for revision. Mean KOOS scores after medial UKA, lateral UKA, and PFA/BiKA were 84.3 (SD 15.9), 85.6 (SD 14.3), and 78.2 (SD 14.2), respectively. The vast majority of the patients reported high satisfaction levels after RA PKA. Subgroup analyses suggested tibial component design, body mass index (BMI), and age affects RA PKA outcomes. Five-year survivorship was 98.4% (95% confidence interval (CI) 97.2 to 99.5) for onlay medial UKA (n = 742) and 99.1% (95% CI 97.9 to 100) for onlay medial UKA in patients with a BMI < 30 kg/m. 2. (n = 479). Conclusion. This large single-surgeon study showed high mid-term survivorship, satisfaction levels, and functional outcomes in RA UKA using metal-backed tibial onlay components. In addition, favourable results were reported in RA PFA and BiKA. Cite this article: Bone Joint J 2020;102-B(1):108–116