• Unicompartmental knee arthroplasty (UKA) is associated with improved functional outcomes but reduced implant survivorship compared to total knee arthroplasty (TKA).

• Surgeon-controlled errors in component positioning are the most common reason for implant failure in UKA, and low UKA case-volume is associated with poor implant survivorship and earlier time to revision surgery.

• Robotic UKA is associated with improved accuracy of achieving the planned femoral and tibial component positioning compared to conventional manual UKA.

• Robotic UKA has a learning curve of six operative cases for achieving operative times and surgical team comfort levels comparable to conventional manual UKA, but there is no learning curve effect for accuracy of implant positioning or limb alignment.

• Robotic UKA is associated with reduced postoperative pain, decreased opiate analgesia requirements, faster inpatient rehabilitation, and earlier time to hospital discharge compared to conventional manual UKA.

• Limitations of robotic UKA include high installation costs, additional radiation exposure with image-based systems, and paucity of studies showing any long-term differences in functional outcomes or implant survivorship compared to conventional manual UKA.

• Further clinical studies are required to establish how statistical differences in accuracy of implant positioning between conventional manual UKA and robotic UKA translate to long-term differences in functional outcomes, implant survivorship, complications, and cost-effectiveness.

Cite this article: EFORT Open Rev 2020;5:312-318. DOI: 10.1302/2058-5241.5.190089

• Optimal implant selection is a major component of high-quality arthroplasty care, and revision risk is an important parameter characterizing knee arthroplasty implant clinical performance.

• National and regional arthroplasty registries are essential sources of revision risk data, but these data are often difficult to find because they are buried within extensive annual reports. Summarizing total knee arthroplasty (TKA) implant revision risks as presented in registry reports can maximize the usefulness of registry data for orthopaedic surgeons.

• The findings summarize the revision risk data found in national arthroplasty reports from the Australian, Danish, Finnish, and the England, Wales, Northern Ireland and the Isle of Man registries, and in regional arthroplasty reports from the Emilia-Romagna Region (Italty), and the Michigan Arthroplasty Registry Collaborative Quality Initiative (MARCQI) registries.

• The six supplemental summary tables present revision risk data for TKA implants by cemented, uncemented, hybrid, and unreported fixation types. Additional summary tables are presented for revision risk of unicondylar (UKA) and patellofemoral joint (PFJ) revisions. Within TKA fixation categories, revision risks at 10 years ranged from 2.4% to 35.7% (cemented), 2.8% to 25.0% (uncemented), 2.0% to 9.2% (hybrid), and 0.0% to 39.7% (unreported). Unicondylar 10-year revision risk ranged from 4.9% to 17.2%. Patellofemoral joint 10-year revision risk ranged from 15.2% to 21.7%.

• There is substantial variation in one, three, five, and 10-year revision risk across implants, which suggests surgeons should choose implants carefully.

Cite this article: EFORT Open Rev 2020;5:268-272. DOI: 10.1302/2058-5241.5.190053

• Some authors have reported that outpatient total knee arthroplasty (TKA) is a successful, safe and cost-effective treatment in the management of advanced osteoarthritis.

• The success obtained has been attributed to the coordination of the multidisciplinary team, standardized perioperative protocols, optimal hospital discharge planning and careful selection of patients.

• One study has demonstrated a higher risk of perioperative surgical and medical outcomes in outpatient TKA than inpatient TKA, including component failure, surgical site infection, knee stiffness and deep vein thrombosis.

• There remains a lack of universal criteria for patient selection. Outpatient TKA has thus far been performed in relatively young patients with few comorbidities.

• It is not yet clear whether outpatient TKA is worth considering, except in very exceptional cases (young patients without associated comorbidities).

• Outpatient TKA should not be generally recommended at the present time.

Cite this article: EFORT Open Rev 2020;5:172-179. DOI: 10.1302/2058-5241.5.180101

• It is clear that the stiff total knee arthroplasty (TKA) is a multifactorial entity associated with preoperative, intraoperative and postoperative factors.

• Management of the stiff TKA is best achieved by preventing its occurrence using strategies to control preoperative factors, avoid intraoperative technical errors and perform aggressive, painless postoperative physical medicine and rehabilitation; adequate pain control is paramount in non-invasive management.

• Careful attention to surgical exposure, restoring gap balance, minimizing surgical trauma to the patellar ligament/extensor mechanism, appropriate implant selection, pain control and adequate physical medicine and rehabilitation (physiotherapy, Astym therapy) all serve to reduce its incidence.

• For established stiff TKA, there are multiple treatment options available including mobilization under anaesthesia (MUA), arthroscopic arthrolysis, revision TKA, and combined procedures.

Cite this article: EFORT Open Rev 2019;4:602-610. DOI: 10.1302/2058-5241.4.180105

• Robotic total knee arthroplasty (TKA) improves the accuracy of implant positioning and reduces outliers in achieving the planned limb alignment compared to conventional jig-based TKA.

• Robotic TKA does not have a learning curve effect for achieving the planned implant positioning. The learning curve for achieving operative times comparable to conventional jig-based TKA is 7–20 robotic TKA cases.

• Cadaveric studies have shown robotic TKA is associated with reduced iatrogenic injury to the periarticular soft tissue envelope compared to conventional jig-based TKA.

• Robotic TKA is associated with decreased postoperative pain, enhanced early functional rehabilitation, and decreased time to hospital discharge compared to conventional jig-based TKA. However, there are no differences in medium- to long-term functional outcomes between conventional jig-based TKA and robotic TKA.

• Limitations of robotic TKA include high installation costs, additional radiation exposure, learning curves for gaining surgical proficiency, and compatibility of the robotic technology with a limited number of implant designs.

• Further higher quality studies are required to compare differences in conventional TKA versus robotic TKA in relation to long-term functional outcomes, implant survivorship, time to revision surgery, and cost-effectiveness.

Cite this article: EFORT Open Rev 2019;4:611-617. DOI: 10.1302/2058-5241.4.190022

• Multi radius (MR) total knee arthroplasty (TKA) has been associated with mid-flexion instability.

• Single radius (SR) TKA may provide better anteroposterior stability through single flexion axis and biomechanical advantage for quadriceps function.

• Medial pivot (MP) TKA and gradually reducing (GR) radius TKA produce better knee kinematics.

• Clinical outcomes are equivalent for SR, MR and MP TKA.

• Short-term studies have shown better clinical outcomes and kinematics for GR TKA.

• Thinner and narrow anterior flange, deeper trochlea groove and more anatomical trochlea design reduces patellofemoral complications in TKA

• Ultracongruent inserts provide comparable clinical outcomes to posterior-stabilized TKA and cruciate retaining TKA.

Cite this article: EFORT Open Rev 2019;4:519-524. DOI: 10.1302/2058-5241.4.180083

• Total knee arthroplasty (TKA) has evolved into a successful, cost-effective treatment for end-stage knee arthrosis.

• The patellofemoral articulation in TKA has largely been ignored during its development despite being an important determinant of outcome.

• New technologies still need further development to incorporate the patella in TKA surgical planning and operative technique.

• Alternative approaches to alignment in TKA will have a secondary impact on patellofemoral mechanics and possibly future implant designs.

• Technologies that assist with precise implant positioning may alter our understanding and overall practice of TKA.

Cite this article: EFORT Open Rev 2019;4:503-512. DOI: 10.1302/2058-5241.4.180094

• The gold standard for treating chronic periprosthetic joint infection is still considered to be double-stage exchange revision. The purpose of this review is to analyse the difference in terms of eradication rates and functional outcome after single- and double-stage prosthetic exchange for chronic periprosthetic joint infection around the knee.

• We reviewed full text articles written in English from 1992 to 2018 reporting the success rates and functional outcomes of either single-stage exchange or double-stage exchange for knee arthroplasty revision performed for chronic infection. In the case of double-stage exchange, particular attention was paid to the type of spacer: articulating or static.

• In all, 32 articles were analysed: 14 articles for single-stage including 687 patients and 18 articles for double-stage including 1086 patients. The average eradication rate was 87.1% for the one-stage procedure and 84.8% for the two-stage procedure. The functional outcomes were similar in both groups: the average Knee Society Knee Score was 80.0 in the single-stage exchange group and 77.8 in the double-stage exchange. The average range of motion was 91.4° in the single-stage exchange group and 97.8° in the double-stage exchange group.

• Single-stage exchange appears to be a viable alternative to two -stage exchange in cases of chronic periprosthetic joint infection around the knee, provided there are no contra-indications, producing similar results in terms of eradication rates and functional outcomes, and offering the advantage of a unique surgical procedure, lower morbidity and reduced costs.

Cite this article: EFORT Open Rev 2019;4:495-502. DOI: 10.1302/2058-5241.4.190003

• Kneeling ability is consistently the poorest patient-rated outcome after total knee replacement (TKR), with 60–80% of patients reporting difficulty kneeling or an inability to kneel.

• Difficulty kneeling impacts on many activities and areas of life, including activities of daily living, self-care, leisure and social activities, religious activities, employment and getting up after a fall. Given the wide range of activities that involve kneeling, and the expectation that this will be improved with surgery, problems kneeling after TKR are a source of dissatisfaction and disappointment for many patients.

• Research has found that there is no association between range of motion and self-reported kneeling ability. More research is needed to understand if and how surgical factors contribute to difficulty kneeling after TKR.

• Discrepancies between patients’ self-reported ability to kneel and observed ability suggests that patients can kneel but elect not to. Reasons for this are multifactorial, including knee pain/discomfort, numbness, fear of harming the prosthesis, co-morbidities and recommendations from health professionals. There is currently no evidence that there is any clinical reason why patients should not kneel on their replaced knee, and reasons for not kneeling could be addressed through education and rehabilitation.

• There has been little research to evaluate the provision of healthcare services and interventions for patients who find kneeling problematic after TKR. Increased clinical awareness of this poor outcome and research to inform the provision of services is needed to improve patient care and allow patients to return to this important activity.

Cite this article: EFORT Open Rev 2019;4:460-467. DOI: 10.1302/2058-5241.4.180085

• Hinged implants are the most constrained knee replacement prostheses. They are very useful in complex cases of total knee arthroplasty (TKA) revision.

• Hinged implants have evolved with rotating bearings and modularity that allows local joint reconstruction or segmental bone replacement.

• They are required when significant instability persists in cases with inadequate collateral ligaments and significant flexion laxity.

• They are now used when a large bone defect is reconstructed, or when bone fixation of the implant is questionable especially in the metaphyseal zone.

• The use of hinged implants in TKA revision is associated with high complication rates. Published outcomes differ based on the patients’ aetiology.

• The outcomes of rotating-hinged implants used in septic revisions or salvage situations are poorer than other types of revision and have a higher complication rate.

• The poor general health of these patients is often a limitation.

• Despite these relatively poor results, hinged implants continue to have a place in revision surgery to solve major instability or to obtain stable bone fixation of an implant when the metaphysis is filled with bone grafts or porous devices.

Cite this article: EFORT Open Rev 2019;4 DOI: 10.1302/2058-5241.4.180070