The anterior part (third space) of the knee appears important in the soft tissue functional outcome following knee replacement surgery. Native patellofemoral kinematics are complex and variable, and further understanding has led to prosthetic redesign. Attention to soft tissue tension anteriorly (balancing the third space) during knee replacement may maximise post-operative function and avoid issues with understuffing and overstuffing. Patellofemoral compression forces may now be measured dynamically during knee replacement, allowing an objective approach to balancing the third space.

Introduction: Balancing the patellofemoral joint (PFJ) in total knee arthroplasty (TKA) involves avoiding over-stuffing. The purpose of this study was to assess how often a strategy of recreating the anterior space of the trochlea (full extension) led to the trochlea depth being recreated in both mid-flexion (30-40 degrees) and deep flexion (80-90 degrees). Methods: One hundred and twenty two consecutive patients undergoing robotic-assisted TKA had femoral components placed according to functional alignment principals and were assessed. The femoral component was sized and positioned in order to ensure that the anterior flange was within 2 mm of the native anatomy, corresponding to a patella position of full extension (0 degrees flexion). Trochlea depth restoration in 3 positions along the floor of the trochlea groove was compared and measured. The trochlea was defined as balanced if the prosthesis was within 2 mm of the native anatomy. Patients were divided into over-stuffed (prosthesis >2 mm above the native anatomy) or under-stuffed (prosthesis >2 mm beneath the native anatomy). Results: All patients 122/122 (100%) had a balanced trochlea in full extension. In total 54 TKA were over or under-stuffed at either mid-flexion or deep flexion. In mid-flexion, 3/122 (2.5%) trochlea were over-stuffed and 39/122 (32%) trochlea were under-stuffed. In deep flexion, 25/122 (20.5%) of trochlea's were overstuffed and 30/122 (24.6%) were under-stuffed. In mid-flexion, balanced trochlea components were more externally rotated relative to the posterior condylar axis compared to unbalanced components (2.35 degrees external rotation vs 1.21 degrees, p=0.004). There were no other significant differences observed between the balanced and unbalanced trochlea groups in mid or deep flexion. Conclusion: Over 40% of TKA over or under-stuff the trochlea in deeper flexion despite the anterior flange being positioned within 2 mm of the native anatomy in full extension. The rate of over or under-stuffing in mid and deep flexion was similar (>40%); however, in mid-flexion, under-stuffing of the native trochlea was more common. The concept of PFJ over or under-stuffing in TKA needs to be redefined to consider the full arc of flexion of the trochlea groove, and the biomechanical and clinical consequences of under-stuffing the trochlea investigated further.

INTRODUCTION:Knee osteoarthritis is a prevalent condition frequently necessitating knee replacement surgery, with demand projected to rise substantially. Partial knee arthroplasty (PKA) offers advantages over total knee arthroplasty (TKA), yet its utilisation remains low despite guidance recommending consideration alongside TKA in shared decision making. Radiographic decision aids exist but are underutilised due to clinician time constraints. MATERIALS AND METHODS:This research develops a novel radiographic artificial intelligence (AI) tool using a dataset of knee radiographs and a panel of expert orthopaedic surgeons' assessments. Six AI models were trained to identify PKA candidacy. RESULTS:1241 labelled four-view radiograph series were included. Models achieved statistically significant accuracies above random assignment, with EfficientNet-ES demonstrating the highest performance (AUC 95%, F1 score 83% and accuracy 80%). CONCLUSIONS:The AI decision tool shows promise in identifying PKA candidates, potentially addressing underutilisation of this procedure. Its integration into clinical practice could enhance shared decision making and improve patient outcomes. Further validation and implementation studies are warranted to assess real-world utility and impact.

Background Periprosthetic fracture is a rare complication of arthroplasty but can have devastating consequences for the patient and presents a complex surgical challenge. Locking compression plate and retrograde intramedullary nail are both widely accepted surgical fixation techniques for distal femoral periprosthetic fractures around a total knee arthroplasty. Although there is still a need for further high-quality research into both techniques, there is even less literature concerning the use of distal femoral replacement to treat distal femoral periprosthetic fractures. Interest has been piqued in distal femoral replacements for the treatment of distal femoral periprosthetic fractures due to the theoretical advantages of immediate post-operative weight-bearing and lack of dependence on fracture union, but there are still understandably reservations about performing such an extensive and invasive procedure when an accepted alternative is available. This meta-analysis aims to evaluate the current literature to compare the complication rates and return to pre-operative ambulatory status of distal femoral replacement and locking compression plate. Method A literature search was performed to identify articles related to the management of distal femoral periprosthetic fractures around a total knee arthroplasty in adherence to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) checklist. Methodological quality was assessed using the methodological index for non-randomized studies (MINORS) criteria. Articles were reviewed, and data extracted for analysis. Results Five articles met the inclusion criteria, reporting on 345 periprosthetic fractures. The overall rates of complications for distal femoral replacement and locking compression plate were: re-operation (6.1% vs 12.1%), infection (3.0% vs 5.3%), mortality (19.7% vs 19.3%), and return to pre-operative ambulatory status (60.9% vs 71.8%) (respectively). Conclusion This meta-analysis shows no statistically significant difference in the rates of re-operation, infection, mortality or return to pre-operative ambulatory status when comparing distal femoral replacement to locking compression plate.

Purpose: This work developed a novel preclinical test of total knee replacements (TKRs) in order to explain TKR instability linked to patient dissatisfaction. It was hypothesized that stability tests on the isolated moving prostheses would provide novel comparative data on the stability and kinematics among TKR designs. Methods: Three TKR designs, DePuy Synthes Attune MS, Stryker Triathlon and Zimmer Biomet Persona MC, were assessed using a robotic arm while flexing-extending 0-140 degrees. Tests imposed 710 N body weight combined with three tibial loads: no anterior-posterior (AP) force, 90 N anterior or 90 N posterior force. Other load effects were minimized and the kinematics was recorded. Each implant was tested six times to investigate the repeatability of the method. Data were analysed using statistical parametric mapping with one-way analysis of variance (ANOVA). If significance was found (p < 0.05), post hoc t tests with Bonferroni correction were used to contrast groups. Results: Significant differences were found throughout flexion-extension. Femoral rollback, AP stability, coupled internal-external rotation and AP position (roll-back) were all influenced by implant design. AP stability of the TKRs reduced with flexion reaching Attune 15 mm, Persona 13 mm and Triathlon 21 mm at 140 degrees flexion. Tractive rolling significantly affected kinematics in the less congruent Triathlon design, with 6 mm different paths between flexion and extension motion (p < 0.05 across 5-100 degrees). Paradoxical anterior femoral sliding in early flexion (0-40 degrees) occurred in Persona and Triathlon designs. Conclusions: The novel testing technique provides, for the first time, comparative data on the inherent stability and kinematics of the TKR implants themselves across the arc of flexion-extension, independent of variables including soft tissue behaviour and surgical technique. The data show how much each prosthesis can contribute to the stability and motion of the implanted knee. Similar data from a wider range of designs will enable more informed decisions regarding implant design choice, aiming to reduce the prevalence of TKR instability in patients.

Background Infections are rare and poorly studied complications of unicompartmental knee arthroplasty (UKA) surgery. They are significantly less common compared to infections after total knee arthroplasties (TKAs). Optimal management of periprosthetic joint infections (PJIs) after a UKA is not clearly defined in the literature. This article presents the results of the largest multicentre clinical study of UKA PJIs treated with Debridement, Antibiotics and Implant Retention (DAIR). Materials and Methods In this retrospective case series, patients presenting between January 2016 and December 2019 with early UKA infection were identified at three specialist centres using the Musculoskeletal Infection Society (MSIS) criteria. All patients underwent a standardized treatment protocol consisting of the DAIR procedure and antibiotic therapy comprising two weeks of intravenous (IV) antibiotics followed by six weeks of oral therapy. The main outcome measure was overall survivorship free from reoperation for infection. Results A total of 3225 UKAs (2793 (86.2%) medial and 432 (13.8%) lateral UKAs) were performed between January 2016 and December 2019. Nineteen patients had early infections necessitating DAIR. The mean follow-up period was 32.5 months. DAIR showed an overall survivorship free from septic reoperation of 84.2%, with overall survivorship free from all-cause reoperation of 78.95%. The most common bacteria were Coagulase-negative Staphylococci, Staphylococcus aureus and Group B Streptococci. Three patients required a second DAIR procedure but remained free from re-infection at follow-up obviating the need for more demanding, staged revision surgery. Conclusions In infected UKAs, the DAIR procedure produces a high rate of success, with a high survivorship of the implant. Key messages Debridement, Antibiotics and Implant Retention (DAIR) is a successful and minimally invasive surgical option for the management of periprosthetic joint infections (PJIs) after UKA. The surface area available for bacteria to colonise is much smaller in UKAs compared to total knee arthroplasties (TKAs), and this may account for the higher success rates of the DAIR procedure in infected UKAs versus infected TKAs. A second DAIR procedure can be considered in the management of the early recurrence of PJIs with a well-fixed UKA.

simultaneous bilateral knee arthroplasty.Patients were assessed (i) immediately prior to surgery, (ii) 12 months following surgery, and (iii) 6-7 years following surgery.At the pre-operative and 12 months post-operative assessments, patients were assessed on the Oxford-12 Knee Score, the Knee Society Knee Score, the SF-12, the presence or absence of contralateral knee pain and body mass index.At 6-7 years post-operative assessment, patients were asked about any surgery or pain in each knee since their total knee arthroplasty.A Classification and Regression Tree was developed to identify factors associated with a higher likelihood of progression to bilateral total knee arthroplasty.Seven hundred and fourteen patients were included; 69% of these were assessed at 6-7 years.Of these patients 31.6%progressed to bilateral total knee arthroplasty within 7 years of the index surgery.The strongest prediction model of who progressed to bilateral knee arthroplasty included three classification levelspain in the contralateral knee prior to the index surgery, body mass index, and Mental Component Score on SF12 measure prior to the index surgery.None of the measures from the 12 month assessment improved the prediction model.Patients who reported an absence of pain in the contralateral knee prior to the index surgery had a 20% chance of progressing to bilateral total knee arthroplasty within 7 years.Patients who reported the presence of pain in the contralateral knee prior to the index surgery, and had a body mass index greater than 30.7 had a 70% chance of progressing to bilateral knee arthroplasty.Patients with pain in the contralateral knee but with a body mass index of less than 30.7 were just as likely to progress to bilateral knee surgery as those with high body mass index if they had a Mental Component Score of greater than 55.In this cohort, one in three total knee arthroplasty patients progressed to bilateral total knee arthroplasty within 7 years of the index surgery.Progression to bilateral knee arthroplasty was predicted by 3 key outcomesthe presence of pain in the contralateral knee, body mass index and SF12.These outcomes were measured prior to the index surgery, and can therefore help to inform expectations of outcome, and planning for multiple surgeries.

simultaneous bilateral knee arthroplasty.Patients were assessed (i) immediately prior to surgery, (ii) 12 months following surgery, and (iii) 6-7 years following surgery.At the pre-operative and 12 months post-operative assessments, patients were assessed on the Oxford-12 Knee Score, the Knee Society Knee Score, the SF-12, the presence or absence of contralateral knee pain and body mass index.At 6-7 years post-operative assessment, patients were asked about any surgery or pain in each knee since their total knee arthroplasty.A Classification and Regression Tree was developed to identify factors associated with a higher likelihood of progression to bilateral total knee arthroplasty.Seven hundred and fourteen patients were included; 69% of these were assessed at 6-7 years.Of these patients 31.6%progressed to bilateral total knee arthroplasty within 7 years of the index surgery.The strongest prediction model of who progressed to bilateral knee arthroplasty included three classification levelspain in the contralateral knee prior to the index surgery, body mass index, and Mental Component Score on SF12 measure prior to the index surgery.None of the measures from the 12 month assessment improved the prediction model.Patients who reported an absence of pain in the contralateral knee prior to the index surgery had a 20% chance of progressing to bilateral total knee arthroplasty within 7 years.Patients who reported the presence of pain in the contralateral knee prior to the index surgery, and had a body mass index greater than 30.7 had a 70% chance of progressing to bilateral knee arthroplasty.Patients with pain in the contralateral knee but with a body mass index of less than 30.7 were just as likely to progress to bilateral knee surgery as those with high body mass index if they had a Mental Component Score of greater than 55.In this cohort, one in three total knee arthroplasty patients progressed to bilateral total knee arthroplasty within 7 years of the index surgery.Progression to bilateral knee arthroplasty was predicted by 3 key outcomesthe presence of pain in the contralateral knee, body mass index and SF12.These outcomes were measured prior to the index surgery, and can therefore help to inform expectations of outcome, and planning for multiple surgeries.

Cruciate-retaining and posterior-stabilised implant designs are available for primary total knee arthroplasty. However, whether the implant design is associated with a difference in the level of activity still remains unclear. This clinical trial compared posterior-stabilised and cruciate-retaining implants in sport-related patient-reported outcome measures, range of motion, rate of return to sport, and weekly time dedicated to sport in active adults. It was also hypothesised that in young and active patients both implants lead to a similar rate of return to sport in terms of hours per week, type of sport, and joint mobility. All patients were evaluated preoperatively and for a minimum of 36 months follow-up. The University of California Los Angeles activity scores, High-Activity Arthroplasty Score, and Visual Analogue Scale were administered preoperatively and at the last follow-up. The range of motion was investigated at admission and the last follow-up. Data concerning the hours per week dedicated to sports and the type of sport practiced were also collected at admission and at the last follow-up. The Kaplan–Meier Curve was performed to compare implant survivorship. Data from 227 procedures (cruciate-retaining: 109, posterior-stabilised: 118) were prospectively collected. At the last follow-up, no difference was reported in The University of California Los Angeles activity scores (p = 0.6), High-Activity Arthroplasty Score (p = 0.1), Visual Analogue Scale (p = 0.9), flexion (p = 0.7) and extension (p = 0.4). No difference was found in the rate of return (p = 0.1) and weekly hours dedicated to sport (p = 0.3). The Kaplan–Meier curve evidenced no statistically significant difference in implant survivorship (p = 0.6). At approximately five years of follow-up, no difference was reported between cruciate-retaining and posterior-stabilised implants in active adults in sport-related patient-reported outcomes measures, range of motion, pain, weekly time dedicated to sport, rate of return to sport, and implant survivorship. Level II, prospective study.

Functional dissatisfaction following total knee replacement (TKR) is recorded as high as 20%. The majority of these patients report anterior knee pain (AKP) as the main source of dissatisfaction. Elevated patellofemoral compression forces and soft tissue extensor hood strain have been implicated in the generation of significant AKP. A novel method of assessing and measuring patellofemoral compression forces dynamically in the native and resurfaced patella for TKR in four different quadrants of the patella is described. Results are reported from an in vitro model and cadaveric studies in the native and resurfaced knee. Patellofemoral compression forces are shown to be characteristic and consistent over repeated assessments in the native knee. Placement of a TKR significantly alters this pattern. Furthermore, over-stuffing or under-stuffing the resurfaced patella also significantly alters the nature and magnitude of patellofemoral compression forces. These studies may lead to an improved understanding of the nature of AKP following TKR, and using this assessment tool presents an opportunity to more effectively balance the third space, reproduce the native patellofemoral forces, and subsequently reduce AKP following TKR.

Background Instability is one of the most common reasons for revision after a total knee replacement. It accounts for 17.4% of all single-stage revision procedures performed in the UK National Joint Registry. Through a careful patient evaluation, physical assessment and review of investigations one can identify the likely type of instability. Aims To critically examine the different types of instability, their presentation and evidence-based management options. Method A comprehensive literature search was conducted to identify articles relevant to the aetiology and management of instability in total knee replacements. Results Instability should be categorised as isolated or global and then, as flexion, mid-flexion, extension or recurvatum types. By identifying the aetiology of instability one can correctly restore balance and stability. Conclusion With careful judgement and meticulous surgical planning, instability can be addressed and revision surgery can provide patients with successful outcomes.

Background Instability is one of the most common reasons for revision after a total knee replacement. It accounts for 17.4% of all single-stage revision procedures performed in the UK National Joint Registry. Through a careful patient evaluation, physical assessment and review of investigations one can identify the likely type of instability. Aims To critically examine the different types of instability, their presentation and evidence-based management options. Method A comprehensive literature search was conducted to identify articles relevant to the aetiology and management of instability in total knee replacements. Results Instability should be categorised as isolated or global and then, as flexion, mid-flexion, extension or recurvatum types. By identifying the aetiology of instability one can correctly restore balance and stability. Conclusion With careful judgement and meticulous surgical planning, instability can be addressed and revision surgery can provide patients with successful outcomes.