Infections are rare and poorly studied complications of unicompartmental knee athroplasty (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. We present the results of a multicentre retrospective series of UKA PJIs treated with Debridement, Antibiotics and Implant Retention (DAIR). 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.Abstract
Background
Methodology
Gait analysis systems have enjoyed increasing usage and have been validated to provide highly accurate assessments for range of motion. Size, cost, need for marker placement and need for complex data processing have remained limiting factors in uptake outside of what remains predominantly large research institutions. Progress and advances in deep neural networks, trained on millions of clinically labelled datasets, have allowed the development of a computer vision system which enables assessment using a handheld smartphone with no markers and accurate range of motion for knee during flexion and extension. This allows clinicians and therapists to objectively track progress without the need for complex and expensive equipment or time-consuming analysis, which was concluded to be lacking during a recent systematic review of existing applications. A smartphone based computer vision system was assessed for accuracy with a gold standard comparison using a validated ‘traditional’ infra-red motion capture system which had a defined calibrated accuracy of 0.1degrees. A total of 22 subjects were assessed simultaneously using both the computer vision smartphone application and the standard motion capture system. Assessment of the handheld system was made by comparison to the motion capture system for knee flexion and extension angles through a range of motion with a simulated fixed-flexion deformity which prevented full extension to assess the accuracy of the system, repeating movements ten times. The peak extension angles and also numerous discrete angle measurements were compared between the two systems. Repeatability was assessed by comparing several sequential cycles of flexion/extension and comparison of the maximum range of motion in normal knees and in those with a simulated fixed-flexion deformity. In addition, discrete angles were also measured on both legs of three cadavers with both skin and then bone implanted fiducial markers for ground truth reliability accounting for skin movement. Data was processed quickly through an automated secure cloud system.Introduction
Method
Unicompartmental Knee Replacement Arthroplasty (UKA) is a treatment option for early knee OA that appears under-utilised, partly because of a lack of clear guidance on how to best restore lasting knee function using such devices. Computational tools can help consider inherent uncertainty in patient anatomy, implant positioning and loading when predicting the performance of any implant. In the present research an approach for creating patient-specific finite element models (FEM) incorporating joint and muscle loads was developed to assess the response of the underlying bone to UKA implantation. As a basis for future uncertainty modelling of UKA performance, the geometriesof 173 lower limbs weregenerated from clinical CT scans. These were segmented (ScanIP, Simpleware Ltd, UK) to reconstruct the 3D surfaces of the femur, tibia, patella and fibula. The appropriate UKA prosthesis (DePuy, U.S.) size was automatically selected according to tibial plateau size and virtually positioned (Figure 1). Boolean operations and mesh generation were accomplished with ScanIP. A patient-specific musculoskeletal model was generated in open-source software OpenSim (Delp et al. 2007) based on the Gait2392 model. The model was scaled to a specific size and muscle insertion points were modified to corresponding points on lower limb of patient. Hip joint load, muscle forces and lower limb posture during gait cycle were calculated from the musculoskeletal model. The FE meshes of lower limb bones were transformed to the corresponding posture at each time point of a gait cycle and FE analyses were performed (Ansys, Inc. U.S) to evaluate the strain distribution on the tibial plateau in the implanted condition.Introduction
Methods
Inter-subject variability is inherently present in patient anatomy and is apparent in differences in shape, size and relative alignment of the bony structures. Understanding the variability in patient anatomy is useful for distinguishing between pathologies and to assist in surgical planning. With the aim of supporting the development of stratified orthopaedic interventions, this work introduces an Articulated Statistical Shape Model (ASSM) of the lower limb. The model captures inter-subject variability and allows reconstructing ‘virtual’ knee joints of the lower limb shape while considering pose. A training dataset consisting of 173 lower limbs from CT scans of 110 subjects (77 male, 33 female) was used to construct the ASSM of the lower limb. Each bone of the lower limb was segmented using ScanIP (Simpleware Ltd., UK), reconstructed into 3D surface meshes, and a SSM of each bone was created. A series of sizing and positioning procedures were carried out to ensure all the lower limbs were in full extension, had the same femoral length and that the femora were aligned with a coincident centre. All articulated lower limbs were represented as: (femur scale factor) × (full extension articulated lower limb + relative transformation of tibia, fibula and patella to femur). Articulated lower limbs were in full extension were used to construct a statistical shape model, representing the variance of lower limb morphology. Relative transformations of the tibia, fibula and patella versus the femur were used to form a statistical pose model. Principal component analysis (PCA) was used to extract the modes of changes in the model. The first 30 modes of the shape model covered 90% of the variance in shape and the first 10 modes of the pose model covered 90% of the pose variance. The first mode captures changes of the femoral CCD angle and the varus/valgus alignment of the knee. The second mode represents the changes in the ratio of femur to tibia length. The third mode reflects change of femoral shaft diameter and patella size. The first mode characterising pose captures the medial/lateral translation between femur and tibia. The second mode represents variation in knee flexion. The third mode reflects variation in tibio-femoral joint space. An articulated statistical modelling approach was developed to characterize inter-subject variability in lower limb morphology for a set of training specimens. This model can generate large sets of lower limbs to systematically study the effect of anatomical variability on joint replacement performance. Moreover, if a series of images of the lower limb during a dynamic activity are used as training data, this method can be applied to analyse variance of lower limb motion across a population.
Increased incidence of obesity and longer life expectancies will place increased demands on load bearing joints. In the present work, a method of pre-clinical evaluation to assess the condition of the joint and potentially inform on cases of joint deterioration, is described. Acoustic emission (AE) is a non-destructive test methodology that has been used extensively in engineering for condition monitoring of machinery and structures. It is a passive technique that uses piezoelectric sensors to detect energy released from internal structural defects as they deform and grow. The technique has been used with some success in the past to identify characteristic signals generated from the knee joint during activities such as standing and sitting, in candidate arthroplasty patients (1,2). In this study, 40 asymptomatic subjects had AE data generated from their knee joints analysed. Subject characteristics such as age, gender, and lifestyle were disclosed and evaluated against the AE data. Each subject was invited to take a seated position and a piezoelectric AE sensor (Pancom P15, 150kHz resonance, 19mm diameter) was attached to the subject's knee using a wax couplant and tape as close to the articulating surface and on a bony prominence to avoid signal attenuation in the soft tissue. Subjects were invited to sit and stand 3 times. AE data were collected and processed using an AMSY5 AE processor (Vallen, Germany). Tests were repeated on a separate occasion and selected subjects were invited to participate on a third occasion. The AE data of particular interest were the peak amplitudes and the frequency power spectrum of the waveform. Post-test inspection of subject characteristics allowed them to be separated into three broad categories: no previous history (group A), some instances of pain in the knee (group B), and those who have had previous minor surgery on the knee (group C). The corresponding AE results were grouped separately. It was found that groups A and B demonstrated similar signal amplitude characteristics while group C produced much higher, significantly different (p<0.05) amplitudes and amplitude distributions. Typical results are shown in figure 1. At present, broad trends could be identified and relationships emerged between the data and subject history (prior surgery, typical daily activity). Further work will continue with asymptomatic subjects and the work will be extended to pre-operative patients to identify whether certain trends are amplified in this population.
Revision knee arthroplasty is increasing and in 2010 constituted 6% of knee replacements done in the UK according to the National Joint Registry1. Infection was the 2nd most common cause accounting for 23% of the revision burden1. Two-stage revisions are considered the gold standard with success rates from 80–100%2. Single-stage revisions are becoming increasingly popular at certain centers with reported benefits of reduced “down-time” for the patient and a decreased financial burden. The senior author (DSB) has been performing single-stage revisions for infections for over 10 years. We were interested in seeing the success rate for this method and possibly identify factors that would portend a poorer result.INTRODUCTION
OBJECTIVES
The aim of this study was to perform a comprehensive evaluation of the changes in function from pre- to post-surgery in total and unilateral knee arthroplasty (UKA/TKA) patients. Twenty healthy (age 62.4 ±5.9, 11 male), 14 UKA (age 60.9 ±10.1, 8 male) and 17 TKA (age 67.2 ±8.1, 9 male) patients were studied. KA patients were assessed four weeks pre- and six months post-operation. Measures of perceived pain and function were collected using Oxford Knee Score (OKS) questionnaire. Tests of objective function included joint range of motion (RoM), ultrasound imaging, and 3-D motion analysis/inverse modelling from gait and sit-stand. An optimal set of variables was used to classify KA function using the Cardiff DST method. Pre-KA and healthy individuals were accurately classified (96%). Post-operation questionnaire measures of function improved for both UKA and TKA groups. However, observed measures of RoM, muscle atrophy and gait had only limited gains. This resulted in 57% of UKA and only 27% of TKA patients being classified as healthy post-operation. The results of this study show that 6 months post-surgery UKA patients had higher function than TKA. Using statistical approaches to combine functional assessments has provided an accurate platform to classify function and estimate changes from pre- to post-surgery. The clinical application of this tool requires further investigation and comparison to commonly used clinical techniques.
Both the RANK/RANKL system and the endocannabinoid system have roles in bone remodelling. Activation of CB1 receptors on sympathetic nerve terminals in trabecular bone modulates bone remodelling by attenuating adrenergic inhibition over bone formation. CB2 receptors are involved in the local control of bone cell differentiation and function. Osteoblastic CB2 receptor activation negatively regulates RANKL mRNA expression indicating an interaction between the two systems and that efficient bone remodelling requires a balance between these two systems. The aim of the study was to establish the presence of the different components of the endocannabinoid system and the RANK/RANKL signalling pathway in human bone and osteoclast culture. Levels of endocannabinoids (AEA, 2-AG) and their related compounds (OEA, PEA) in human trabecular bone, obtained from patients undergoing elective orthopaedic surgery, were measured using Liquid Chromatography Mass Spectrometry (LC-MS-MS). mRNA for the endocannabinoid synthetic and catabolic enzymes (NAPE-PLD, DAGLa, FAAH, MAGL), cannabinoid-activated receptors (CB1, CB2, PPARs, TRPV1), and RANK, RANKL and NFkB were determined using Taqman Real-Time PCR. Osteoclasts were differentiated from U-937 cells (Human leukaemic monocyte lymphoma cell line), following the sequential treatment using TPA (0.1μg/ml) followed by either TNF-a (3ng/ml) or calcitriol (10−8M), cultured for up to 30 days. Osteoclasts were identified by positive staining with tartrate resistant acid phosphatase (TRAP), multinucleation and the ability to form resorption pits on calcium phosphate coated discs. Taqman Real-Time PCR was performed to detect the expression of the osteoc! last marker genes TRAP and cathepsin K, together with genes of the endocannabinoid and RANK/RANKL signalling pathways.Introduction
Methods
We performed an advancement and medial transfer of the tibial tuberosity based on Fulkerson's principle to treat intractable anterior knee pain associated with patellofemoral maltracking diagnosed by dynamic MRI. Between January 1998 and July 2000 twenty-two patients had 28 knees operated for anterior knee pain. There were 4 men and 18 women with a mean age of 28 years (range 18-41). Indications for surgery were [a] failure to improve after six months of physiotherapy and [b] patellofemoral maltracking evident in dynamic MRI. Mean follow-up was for 37 months (23 – 42). Knee instability score modified by Fulkerson was employed for objective and subjective assessment. Objectively 22 (79%) knees achieved good to excellent results. Four knees (14%) had fair, and two (7%) had poor results. Excellent and very good results were seen in 20 knees. These patients were a younger age group (mean age 21 years) and had minimal degeneration (grade I-II) of the patellofemoral joints. Two patients achieved good results. One of them had moderate (grade III) and one minimal (II) arthritis. Three knees with fair results had advanced (grade IV or V) and one had moderate (grade III) arthritis. Out of two patients who had a poor result, one had advanced degeneration (grade V) that later required a patellofemoral joint resurfacing. The other was a 24 year old woman with grade II changes. She was treated by the pain therapy team. Anterior displacement of the tuberosity in the presented study was kept to 5 mm to avoid the possible complications of wound break down. The overall length and depth of the osteotomy was also reduced to minimise risk of fracture and commence early mobilisation. Based on our results there is a strong case of justification for Anteromedialisation of tibial tuberosity using a smaller length of osteotomy and lesser degree of anteriorisation in carefully selected patients with Patellofemoral arthralgia associated with maltracking patella.
Removal of solidly fixed implants is a challenge in revision knee arthroplasty. It is fraught with the risk of intraoperative fractures and bone stock vital for the success of subsequent revision surgery. We describe the double extraction technique for extraction of solidly fixed implants. This technique was first tested in laboratory setting and then replicated in the operation theatre with successful results. In this retrospective study we analysed all our patients in which we used the double extraction technique for the removal of solidly fixed implants. In this procedure, the surgeon and the assistant each place an osteotome on the cement metal interface at symmetric positions, directly opposite each other on the medial and lateral sides. They deliver synchronous blows with a mallet at positions around the interface until the cement fractures. The femoral component can then be easily removed. The technique was tested in a laboratory before it was used clinically. Polyurethane mouldings, representing a suitable substrate for cementing metal components were fixed on to a steel rod of similar weight and length as the lower leg. Stainless steel discs (40mm diameter x 4mm thickness) were cemented on to the polyurethane substrate to form a model of a cemented implant. The discs were instrumented to allow recording of the mechanical processes caused by the double extraction technique and to allow comparison with the single osteotome extraction technique. The methodology successfully demonstrated that the double osteotome technique increases the contact force of the second blow. When the synchronous blows are delivered, less energy is expended in the movement of tibia and more is contributed to the removal of the component. In this study we looked at a total of 206 patients were the solidly fixed tibial and femoral components were removed using the double extraction technique. There were 86 men and 126 women. The mean age of the patients was 66.8 years (range 37–87 years). Only patients with solidly fixed implants were included in this study. Stability of implants was assessed with preoperative radiographs and then confirmed intraoperatively. Patients with loose implants intraoperatively were excluded from this study. We present our results with use of this technique in 206 patients with follow up of 1 to 5 years.
Removal of solidly fixed implants is a challenge in revision knee arthroplasty. It is fraught with the risk of intraoperative fractures and bone stock vital for the success of subsequent revision surgery. We describe the double extraction technique for extraction of solidly fixed implants. This technique was first tested in laboratory setting and then replicated in the operation theatre with successful results. In this retrospective study we analysed all our patients in which we used the double extraction technique for the removal of solidly fixed implants. In this procedure, the surgeon and the assistant each place an osteotome on the cement metal interface at symmetric positions, directly opposite each other on the medial and lateral sides. They deliver synchronous blows with a mallet at positions around the interface until the cement fractures. The femoral component can then be easily removed. The technique was tested in a laboratory before it was used clinically. Polyurethane mouldings, representing a suitable substrate for cementing metal components were fixed on to a steel rod of similar weight and length as the lower leg. Stainless steel discs (40mm diameter × 4mm thickness) were cemented on to the polyurethane substrate to form a model of a cemented implant. The discs were instrumented to allow recording of the mechanical processes caused by the double extraction technique and to allow comparison with the single osteotome extraction technique. The methodology successfully demonstrated that the double osteotome technique increases the contact force of the second blow. When the synchronous blows are delivered, less energy is expended in the movement of tibia and more is contributed to the removal of the component. In this study we looked at a total of 206 patients were the solidly fixed tibial and femoral components were removed using the double extraction technique. There were 86 men and 126 women. The mean age of the patients was 66.8 years (range 37–87 years). Only patients with solidly fixed implants were included in this study. Stability of implants was assessed with preopera-tive radiographs and then confirmed intraoperatively. Patients with loose implants intraoperatively were excluded from this study. We present our results with use of this technique in 206 patients with follow up of 1 to 5 years.
