Introduction

Kozinn and Scott have made recommendations about contra-indications for unicompartmental knee replacement (UKR). They suggest that patients younger than 60, weight > 82 kilograms, patients with exposed bone in patella-femoral compartment or patients who are physically active/perform heavy labour should not be offered a UKR. In addition, chondrocalcinosis is a contra-indication. These strict selection criteria are based on the experience with fixed bearing UKAs and are more intuitive than evidence based. The Oxford UKR has a fully congruous mobile bearing and has been shown to have minimal wear. Over the past 25 years, the Oxford Group has followed a standardised protocol for patient selection for UKR. We ignore patella-femoral joint pathology, chondrocalcinosis, patient's age, weight and activity level when deciding the suitability for UKR.

Aim

A case series with functional and radiographic outcomes, of modular endoprosthetic distal femoral replacement in complex cases of periprosthetic fracture.

We obtained pre-operative and six-month post-operative Oxford hip (OHS) and knee scores (OKS) for 1523 patients who underwent total hip replacement and 1784 patients who underwent total knee replacement. They all also completed a six-month satisfaction question.

Scatter plots showed no relationship between pre-operative Oxford scores and six-month satisfaction scores. Spearman’s rank correlation coefficients were -0.04 (95% confidence interval (CI) -0.09 to 0.01) between OHS and satisfaction and 0.04 (95% CI -0.01 to 0.08) between OKS and satisfaction. A receiver operating characteristic (ROC) curve analysis was used to identify a cut-off point for the pre-operative OHS/OKS that identifies whether or not a patient is satisfied with surgery. We obtained an area under the ROC curve of 0.51 (95% CI 0.45 to 0.56) for hip replacement and 0.56 (95% CI 0.51 to 0.60) for knee replacement, indicating that pre-operative Oxford scores have no predictive accuracy in distinguishing satisfied from dissatisfied patients.

In the NHS widespread attempts are being made to use patient-reported outcome measures (PROMs) data for the purpose of prioritising patients for surgery. Oxford hip and knee scores have no predictive accuracy in relation to post-operative patient satisfaction. This evidence does not support their current use in prioritising access to care.

Introduction: Although originally designed to aid the management of primary malignant bone tumours, the indications for modular endoprosthetic replacement (EPR) have expanded to include complex periprosthetic fractures and failed internal fixation. The incidence of these challenging cases is increasing with an aged population. We reviewed retrospectively our experience with the use of EPR in patients who had undergone limb salvage following complex trauma presentations.

Methods: Between 2003 and 2008 twenty one patients presented with complex trauma related problems and underwent EPR at a specialist tertiary referral centre. The mean age was 71 years (range 44–87) and the median number of previous surgical procedures was 3 (range 0–11). Eight patients presented following failed internal fixation of proximal femoral fractures. Nine patients had periprosthetic fractures around joint arthroplasties, seven relating to total knee replacements (TKRs) and two to total hip replacements (THRs). One case of periprosthetic fracture around THR had undergone failed internal fixation. Two patients had distal femoral fractures, of which one was infected and had undergone failed internal fixation, while the other was unrecon-structable. Two patients had proximal tibia fractures which had both undergone failed internal fixation.

Results: The mean Harris Hip Score was 89.5 (range 64–85) at a mean follow up period of 8 months (minimum 4 months). The mean American Knee Society Score was 82 (range 62–100) and the mean functional score was 62 (range 30–75) at a mean follow up period of 6 months (minimum 2 months). Complications included two cases of deep infection; one resulted in a two stage revision procedure, while the other retained the EPR following a washout.

Discussion: Modular EPR in the lower limb is a durable reconstructive option in complex trauma problems, particularly in the elderly and those patients with significant bone loss. Preliminary functional results indicate very satisfactory results.

Introduction: Approximately 20% of unicompartmental knee replacement (UKR) revisions are related to polyethylene wear. The Phase 1 Oxford UKR was introduced as a design against wear, with a fully congruent mobile bearing. The Phase 2 implant was introduced with new instrumentation (femoral mill) and changes to the bearing shape (lower anterior wall) to reduce the incidence of anterior impingement. We have previously shown that the Oxford UKR has a wear rate of 0.02 mm/year at ten years, in well functioning devices, but that higher wear rates can be seen with impingement or if the congruous articulation is lost. The aim of this study was to determine the 20 year in-vivo wear of the Oxford Phase 1 and Phase 2 UKR, using Roentgen Stereophotogrammetric Analysis (RSA).

Method: We measured the in-vivo wear of 6 Phase 1 (5 patients, mean age 65.24 years) and 7 Phase 2 (4 patients, mean age 63.43) Oxford UKR bearings. Average time since surgery was 22.37 years and 19.46 years for the Phase 1 and Phase 2 implants respectively. Selection criteria included patients who were mobile, with an exercise tolerance greater than 100m as per the American Knee Society Score (AKSS) functional questionnaire. RSA x-rays were taken with the knee in the normal anatomical position on standing and with the knee flexed to 30o. The Oxford knee score (OKS) and AKSS were gained at the RSA examination. Phase 1 and 2 components were reverse engineered by laser scanning, and converted to CAD models. The CAD models of the tibia and femur were pose-estimated in the RSA software (Medis Specials, Leiden, Netherlands). A sphere was fit to the femoral component and the minimum bearing thickness was determined by measuring the shortest perpendicular distance between the sphere and the plane contained on the tibial tray articular surface. The linear wear for each bearing was calculated by subtracting the measured thickness from the corrected nominal bearing thickness. Non-parametric statistics were used to compare the two Phases.

Results: There was no significant difference in age, OKS and AKSS between the two groups. The median wear rate was 0.078 mm/year for Phase 1 and 0.023 mm/year for Phase 2. This difference was statistically significant (p = 0.027).

Discussion: The difference in wear rate is explained by impingement in Phase 1, which was reduced by design changes with the introduction of Phase 2; the Phase 2 is designed to avoid impingement between the femur and the bearing. This study demonstrates that very low wear rates can be maintained with the Phase 2 implant to the end of the second decade after implantation. This is of particular importance when the device is used in younger patients and demonstrates that the Oxford UKR can be a definitive implant for the treatment of isolated compartmental osteoarthritis.

Introduction: Anteromedial gonarthrosis is a common well described pattern of knee osteoarthritis with cartilage wear beginning in the anteromedial quadrant of the medial tibial plateau in the presence of an intact and functioning ACL. It is well known that mechanical factors such as limb alignment and meniscal integrity affect the progression of arthritis and there is some evidence that the morphology of the tibial plateau may be a risk factor in the development of this disease. The extension facet angle is the angle of the downslope of the anterior portion of the medial tibial plateau joint surface in relation to the middle portion on a sagittal view. If this is an important factor in the development of AMG there may be potential for disease modifying intervention.

This study investigates if there is a significant difference in this angle as measured on MRI between a study cohort with early AMG (partial thickness cartilage damage and intact ACL) and a comparator control cohort of patients (no cartilage damage and ACL rupture).

Methods: 3 Tesla MRI scans of 99 patients; 54 with partial thickness cartilage damage and 44 comparitors with no cartilage damage (acute ACL rupture) were assessed. The extension facet angle was measured (Osirix v3.6) using a validated technique on two consecutive MRI T2 sagittal slices orientated at the mid-coronal point of the medial femoral condyle. (InterClass Correlation 0.95, IntraClass Correlation 0.97, within subject variation of 1.1° and coefficiant of variation 10.7%). The mean of the two extension angle values was used. The results were tabulated and analysed (R v2.9.1).

Results: Of the 99 knees, 38 were female and 61 male; 44 left knees and 55 right. The mean extension facet angle for the partial thickness group was 12.7° (SD 3.35) and for the comparator group 8.7° (SD 3.09). There was a significant difference between these 2 groups (Mann Whitney U, p< 0.001). Although there were significantly more men than women in the comparator group, stratification analysis showed that there was no effect of gender on the mean extension facet angle.

Discussion: There is a significance difference in the extension facet angle between patients with AMG with only partial thickness cartilage loss and a comparator group. This has not been shown in a study group of this size before. Since none of the subjects had full thickness cartilage loss it is unlikely that this difference is due to bone attrition changing the angle as part of the disease process but this is an important area for further study. We believe that a higher medial tibial extension facet angle alters the mechanics within the medial compartment, placing these patients at higher risk of developing AMG. This may present an opportunity for risk factor modification, for example osteotomy.

Introduction: Partial Knee Replacement (PKR) is an appealing alternative to Total Knee Replacement (TKR) when the patient has isolated compartment osteoarthritis (OA). In nearly all cases there is a radiolucency observed between the tibial tray wall and the boney interface. The reasons why radiolucencies appear are unknown, but the bone will adapt to its altered mechanical environment by bone remodelling in accordance with ‘Wollf’s Law’. The aim of this study was to investigate the mechanical environment of the tibia bone adjacent to the tray wall, following cemented and cementless PKR, in order to determine whether this region of bone resorbs.

Methods: A validated finite element (FE) model of a cadaver tibia implanted with an Oxford PKR was used in this study. Kinematic data from fluoroscopy measurements during a step-up activity were used to determine the relative tibio-femoral positioning for the Oxford PKR model. Load data were adapted from the in-vivo measured loads using an instrumented implant during a step-up activity. The standard operating protocol was simulated for the Oxford PKR FE models, with the tibial tray implanted in a neutral position. The tibia was sectioned around the tray. Zone 7 was defined as parallel to the vertical tray wall, corresponding to the region on screened x-rays where radiolucencies are observed. It was assumed that the bone in the implanted tibia will attempt to normalise its stress-strain patterns locally to its equilibrium state, the intact tibia, for the same loading conditions. Forty patients (20 cemented, 20 cementless) who had undergone PKR were randomly selected from a database, and their screened x-rays assessed for radiolucency in region 7.

Results: The SED in region 7 was 80% lower in the cemented and cementless tibia, compared to the intact tibia (Figure 2). The maximum tensile stress was 63% lower in the cemented and cementless tibia, compared to the intact tibia. The corresponding maximum compressive stress was 52% lower. Radiolucency was observed in all forty radiographs in region 7.

Discussion: After implantation with a cemented or cementless PKR the bone strains and SED in region 7 are reduced. This reduction may provide the signal for adaptive bone remodelling and bone will be resorbed from this region, decreasing the volume and increasing the SED. Bone resorption will continue until the equilibrium state is reached. If a ‘lazy’ zone between 35% and 50% of the remodelling signal is considered, bone resorption will still occur due to the large decrease in SED for this region. For region 7 to return its SED to the equilibrium state, its volume will need to be reduced by 80%. This is likely to be the reason why a radiolucency is observed clinically in this region in almost every case, whether a cemented or cementless implant is used.

Introduction: Although originally designed to aid the management of primary malignant bone tumours, the indications for modular endoprosthetic replacement (EPR) have expanded to include complex periprosthetic fractures and failed internal fixation. The objective of this study was to evaluate the success of endoprosthetic replacement (EPR) in patients who had undergone limb salvage following complex trauma presentations.

Materials and Methods: Between 2003 and 2008 twenty one patients presented with complex trauma related problems and underwent EPR at a specialist tertiary referral centre. The mean age was 71 years (range 44–87) and the median number of previous surgical procedures was 3 (range 0–11). Eight patients presented following failed internal fixation of proximal femoral fractures. Nine patients had periprosthetic fractures around joint arthroplasties, seven relating to total knee replacements (TKRs) and two to total hip replacements (THRs). One case of periprosthetic fracture around THR had undergone failed internal fixation. Two patients had distal femoral fractures, of which one was infected and had undergone failed internal fixation, while the other was unreconstruc-table. Two patients had proximal tibia fractures which had both undergone failed internal fixation.

Results: The mean Harris Hip Score was 89.5 (range 64–85) at a mean follow up period of 8 months (minimum 4 months). The mean American Knee Society Score was 82 (range 62–100) and the mean functional score was 62 (range 30–75) at a mean follow up period of 6 months (minimum 2 months). Complications included two cases of deep infection; one resulted in a two stage revision procedure, while the other retained the EPR following a washout.

Conclusion: Modular EPR in the lower limb is a durable reconstructive option in complex trauma problems, particularly in the elderly and those patients with significant bone loss. Preliminary functional results indicate very satisfactory results.

The results of mobile bearing Oxford unicompartmental knee replacement (UKR) in the lateral compartment have been disappointing (five-year survival: 82%). Therefore, it is recommended that mobile bearings should not be used for lateral UKR. This low survivorship is primarily due to a high dislocation rate. A detailed analysis confirmed the elevated lateral tibial joint line to be a contributory factor to bearing dislocation. A new surgical technique was therefore introduced in which care was taken neither to remove too much bone from the distal femur nor to over tighten the knee and therefore ensure that the tibial joint line was not elevated. Other modifications included use of a domed tibial component.

The aim of this study is to compare the outcome of these iterations: the original series (series I), those with improved surgical technique (series II) and the domed tibial component (series III). The primary outcome measure was bearing dislocation at one year. One year was chosen as all the dislocations in the first series occurred within a year. In the original series (n=53), implanted using a standard open approach, there were six dislocations in the first year, the average flexion 110°, and 95% had no/mild pain on activity. In the second series (n=65), there were 3 dislocations, the average flexion was 117°, and 80% had no/mild pain on activity.

In the third series with the modified technique and a convex domed tibial plateau, there was one dislocation, average flexion was 125° and 94% had no/mild pain on activity. At four years the cumulative primary dislocation rates were 10%, 5% and 0% respectively, and were significantly different (p=0.04).

The improved surgical technique and implant design has reduced dislocation rate to an acceptable level so a mobile bearing can now be recommended for lateral UKR.

About ten years ago we introduced sophisticated instrumentation and an increased range of component sizes for the Oxford unicompartmental knee replacement (UKR) to facilitate a minimally invasive surgical (MIS) approach. The device is now routinely implanted through an incision from the medial pole of the patella to the tibial tuberosity. This has resulted in a more rapid recovery and an improved functional result. As the access to the knee is limited there is a concern that the long term results may be compromised. The aim of this study was to determine the 10 year survival.

A prospective follow up of all Phase 3 minimally invasive Oxford UKR implanted by two senior authors (DWM & CAFD) has been undertaken. So far 1015 UKRs have been implanted for anteromedial osteoarthritis. All patients received a cemented implant through a MIS approach and were followed up prospectively by an independent observer. The data was collected prospectively regarding pre-operative status, complications and clinical as well as functional outcome at predetermined intervals.

The average age of patients was 66.4 years (range: 33 – 88) with mean Oxford Knee Score 41 (SD: 7.9) at the time of last follow up, Knee Society Score (objective) of 84 (SD: 13) and Knee Society Score (functional) of 83 (SD: 21). At ten years the survival of this cohort is 96%. There were 22 revisions including 7 for progression of arthritis, 5 for infection, 5 for bearing dislocation, 4 for unexplained pain and one for rupture of ACL secondary to trauma.

We conclude that the Oxford Knee can be implanted reliably through a minimally invasive approach, giving excellent long term results.

Our aim was to investigate the molecular features of progressive severities of cartilage damage, within the phenotype of Anteromedial Gonarthrosis (AMG).

Ten medial tibial plateau specimens were collected from patients undergoing unicompartmental knee replacements. The cartilage within the area of macroscopic damage was divided into equal thirds: T1(most damaged), to T3 (least damaged). The area of macroscopically undamaged cartilage was taken as a 4th sample, N. The specimens were prepared for histological (Safranin-O and H& E staining) and immunohistochemical analysis (Type I and II Collagen, proliferation and apoptosis). Immunoassays were undertaken for Collagens I and II and GAG content. Real time PCR compared gene expression between areas T and N.

There was a decrease in OARSI grade across the four areas, with progressively less fibrillation between areas T1, T2 and T3. Area N had an OARSI grade of 0 (normal). The GAG immunoassay showed decreased levels with increasing severity of cartilage damage (p< 0.0001). There was no significant difference in the Collagen II content or gene expression between areas. The Collagen I immunohistochemistry showed increased staining within chondrocyte pericellular areas in the undamaged region (N) and immunoassays showed that the Collagen I content of this macroscopically and histologically normal cartilage, was significantly higher than the damaged areas (p< 0.0001). Furthermore, real time PCR showed a significant increase in Collagen I expression in the macroscopically normal areas compared to the damaged areas (p=0.04).

In AMG there are distinct areas, demonstrating progressive cartilage loss. We conclude that in this phenotype the Collagen I increase, in areas of macroscopically and histologically normal cartilage, may represent very early changes of the cartilage matrix within the osteoarthritic disease process. This may be able to be used as an assay of early disease and as a therapeutic target for disease modification or treatment.

Introduction: This study explores whether modern magnetic resonance imaging (MRI) with improved cartilage sequencing is able to show a more detailed view of antero-medial osteoarthritis of the knee (AMOA) than previously, so enabling a radiographic description of this common phenotype of disease. Modern MRI technology allows us to visualize in great detail the structures and cartilage within the knee, providing a better understanding of the pathoanatomy of AMOA. This description of the end stage of disease is useful as a baseline when investigating the progression of arthritis through the knee. Preoperative assessment of patients and selection of intervention is very important and preoperative imaging forms an integral part of this. This will also be useful in preoperative assessment and surgical management of patients.

Methods: 50 patients with a radiographic diagnosis of anteromedial osteoarthritis of the knee and had been listed for unicompartmental knee arthroplasty (UKA) had MRI as part of their pre-op workup. At operation all were deemed suitable for UKA using the current Oxford indications. The image sequences were coronal, axial and sagittal with a predetermined cartilage protocol. The state of the ACL, cartilage wear degree and location, presence and pattern of osteophytes, meniscal anatomy and subchondral high signal were assessed.

Results: All the ACLs were visualized and in continuity, however 40% showed intrasubstance high signal. 100% of medial compartments showed full thickness anteromedial loss with preservation of the posteromedial cartilage. When present, the meniscus was extruded in 75% of cases.

90% of lateral compartments were normal and none had full thickness cartilage loss. However 10% showed high signal in the tibial plateau. There was a highly reproducible pattern of osteophyte formation; 94% posteromedial and posterolateral aspect of medial femoral condyle; 90% medial tibial; 80% medial femoral and 84% lateral intercondylar notch.

Discussion: This study maps the pattern of anteromedial osteoarthritis using modern MRI techniques. This creates a baseline description of disease which is useful when investigating disease progression. This also has importance in determining preoperative indications (preservation of ACL and posteromedial cartilage); surgical technique (determine pattern of osteophytes requiring resection) and potentially important for long-term outcome (early lateral compartment changes).

Introduction: Anteromedial gonarthrosis (AMG) is a distinct phenotype of osteoarthritis (OA), with a specific pattern of disease. There is full thickness cartilage loss anteromedially, progressing to an area of damaged cartilage, and then to an area of macroscopically and histologically normal cartilage posteriorly. It can be considered to be a spatial model of OA progression. Apoptosis, or chondrocyte cell death, has been shown to be a feature of OA cartilage, however the triggers are poorly understood; similarly, reactive oxygen species (ROS) have been implicated in OA. They have never been studied in a replicable topographical model of OA. This study characterises the regional levels of cell death and implicated ROS in AMG using a number of immunohistochemical studies.

Method: Ten tibial resection specimens were obtained from patients undergoing unicompartmental knee arthroplasty. Eight above knee amputations (from patients with peripheral vascular disease) were used as age matched controls. Cross sections taken through all regions were paraffin embedded. Routine histology was performed and immunohistochemical studies were conducted for Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL), Active Caspase 3, Cytochrome C, Active Bax, Bim, 3-Nitrotyrosine and Forkhead Box O3A (FOXO 3A).

Results: Cell death, as detected by TUNEL appeared predominantly in the surface layer of chondrocytes of damaged cartilage (p< 0.001). Median values were 23% in superficial cartilage (range 0 – 51) compared to 0% in deeper cartilage (range 0 – 15). There was a significant difference in TUNEL staining between regions (p=0.001). This ranged from 26% (most damaged) to 4% (undamaged). There was a good correlation with degree of cartilage damage (ρ=0.66, p< 0.001) asdefined by histological grade and TUNEL was significantly higher (p< 0.001) in AMG compared to the control samples which showed an average of 2% TUNEL overall. Upstream markers of apoptosis (Active Caspase 3, Cytochrome C, Active Bax), assessed qualitatively, were present in a similar distribution to that of TUNEL staining. 3-Nitrotyrosine was also shown to be a predominantly surface phenomenon. There was a significant difference (p< 0.001) between regions, ranging from 58% (most damaged) to 10% (undamaged). Again, this was significantly higher that the control samples (p< 0.001). In line with indicators of ROS mediated damage, Bim and FOXO3A were also detected.

Discussion: The mechanism of apoptosis in OA cartilage has not been studied in depth, and understanding the biochemical and molecular responses of ‘stressed’ chondrocytes may provide invaluable information about the specific causes of cell death. Such cellular responses may provide targets for disease modification, thus delaying or preventing the need for joint arthroplasty. We conclude that AMG is a phenotype demonstrating cartilage at progressive stages of disease. Apoptosis involves the intrinsic mitochondrial pathway and ROS appear to be implicated. Further work is needed to provide evidence of what lies further upstream of markers demonstrated in this study.

Introduction: Most unicompartmental knee replacements (UKRs) employ cement for fixation of the prosthetic components to the bone. The information in the literature about the relative merits of cemented and cementless UKR is contradictory, with some favouring cementless fixation while others favouring cemented fixation. There is concern about the radiolucency which frequently develops around the tibial component with cemented fixations. The exact cause of the occurrence of radiolucency is unknown but according to some, it may suggest suboptimal fixation.

Method: Following ethical approval, 62 patients with medial OA were randomised to receive either cemented (n=31) or cementless components (n=31). All patients underwent identical surgical procedure with either a cemented or cementless Oxford UKR. Patients were assessed clinically and radiologically. The x-rays were taken with an image intensifier (I.I.). The position of the I.I. was adjusted until it was perfectly aligned with the tibial bone-implant interface thereby allowing accurate assessment of presence and extent of the radiolucency.

Results: The patients in the two groups were well matched. There was no significant difference in the clinical scores between the two groups. The mean OKS for the cemented group was 40 (± 8.3) and 42 (± 4.6) for cementless group. Narrow radiolucent lines were seen at the bone-implant interfaces of 75% of the cemented tibial components; partial in 43% and complete in 32%. In the cementless implants, partial radiolucencies were seen in 7% and complete radiolucencies in none. The differences are statistically highly significant (p< 0.0001) and imply satisfactory bone ingrowth into the cementless implants.

Conclusions: The method of fixation influences the incidence of radiolucency. With identical designs, no patient with cementless components developed any complete radiolucency. The observation raises the question as to whether cementless rather than cemented components should be routinely used for UKR.

Purpose: The purpose of this study was to report the mid-term survival results of Oxford UKAs in patients of 50 years of age or less, using (1) revision surgery and (2) Oxford Knee Scores (OKS) as outcome measures.

Method: A literature review identified studies of Oxford mobile bearing UKAs containing individuals 1) 50 years old or less with 2) medial osteoarthritis and 3) 2 years or longer follow-up. Authors were approached to participate in a multi-centre survival analysis by submitting all their patients, 50 years of age or less, who received a medial UKA for osteoarthritis. Patients who had died, been lost to follow-up or who underwent revision were identified. OKS were established for all patients with surviving implants.

Results: Seven centres submitted 107 patients. The mean age was 47 years (range 32–50). The average follow-up was 4 years (range 1–25). Forty-seven patients had follow-up into their fifth year or longer. The cumulative 7-year survival using revision as the endpoint was 96% (CI 8). The mean post-operative OKS for surviving implants was 38 (CI 2) out of a possible 48.

Conclusion: While early survival rates and function are encouraging, long-term follow-up is required before concluding UKA is a viable treatment option in young patients with unicompartmental knee arthritis.

Inflammatory changes in synovial tissues occur commonly in knee osteoarthritis (OA) and are termed “inflammatory OA”. The pathogenic significance of this inflammatory OA is uncertain. It is also not known whether inflammatory changes in the synovial membrane are reflected in the synovial fluid (SF) and whether the SF contains a similar inflammatory cell infiltrate.

This study examined 34 cases of knee joint OA and cytologically and immunohistochemically characterised inflammatory cells in the synovial membrane and SF. Specimens of SF and synovial membrane were taken at the time of knee arthroplasty.

All cases of inflammatory OA synovium contained (CD68+) macrophages; several cases also contained a scattered, focally heavy (CD3+) lymphocytic infiltrate and occasional lymphoid aggregates. Inflammatory changes in OA SF reflected this cell composition with numerous CD68+ macrophages and CD3+ lymphocytes being noted in inflammatory OA cases. The SF volume was greater (> 5ml) in cases of inflammatory OA. Non-inflammatory OA knee joints contained very few inflammatory cells, which were mainly macrophages, in both the synovial membrane and SF.

Our findings indicate that inflammatory changes in the synovial membrane of OA knee joints are reflected in the SF and that the volume of SF is commonly increased in cases of inflammatory OA. Both macrophages and lymphocytes in the inflammatory infiltrate of knee joint SF may contribute to joint destruction in OA by providing mononuclear phagocyte osteoclast precursors and the production of inflammatory cytokines and growth factors that promote osteoclastogenesis.

In conclusion, the cytology of SF and synovitic membrane are similar in inflammatory OA. With knee effusions of greater than 5mls and inflammatory synovitic membrane consideration of total knee arthoplasty in the presence of single compartment disease should be considered because of the risk of further joint destruction.

Introduction: This study explores whether modern magnetic resonance imaging (MRI) with improved cartilage sequencing is able to show a more detailed view of anteromedial osteoarthritis of the knee (AMOA). Preoperative assessment of patients and selection of intervention is very important and preoperative imaging forms an integral part of this. Modern MRI technology may allow us to visualize in great detail the structures and cartilage within the knee, providing a better understanding of the pathoanatomy of AMOA. This will be useful in preoperative assessment and surgical management of patients.

Methods: 50 patients with a radiographic diagnosis of anteromedial osteoarthritis of the knee and had been listed for unicompartmental knee arthroplasty (UKA) had MRI as part of their pre-op workup. At operation all were deemed suitable for UKA using the current Oxford indications. The image sequences were coronal, axial and sagittal with a predetermined cartilage protocol. The state of the ACL, cartilage wear location and pattern, presence of osteophytes and subchondral high signal were assessed.

Results: All the ACLs were visualized and in continuity, however 40% showed intrasubstance high signal.

100% of medial compartments showed full thickness anteromedial loss with preservation of the posteromedial cartilage. When present, the meniscus was extruded in 96% of cases.

Discussion: This study maps the pattern of anteromedial osteoarthritis using modern MRI techniques. This has importance in determining preoperative indications (preservation of ACL and posteromedial cartilage); surgical technique (determine pattern of osteophytes requiring resection) and potentially important for long-term outcome (early lateral compartment changes).

Introduction: Viscosupplementation is an effective treatment for patients suffering from knee osteoarthritis (OA). Most available products use 3 or 5 injection regimens. The objective of this study was to compare the safety and efficacy of a single 6 mL intra-articular administration of hylan G-F 20 with placebo.

Methods: In this prospective, multicenter, randomized, double-blind study, patients diagnosed with knee OA were randomized to one 6-mL injection of hylan G-F 20 or saline. The primary efficacy analysis (WOMAC A) was performed on the intent-to-treat population and was based on a repeated-measures model over the 26 weeks of the study. The incidence of adverse events (AEs) was collected over the study duration

Results: 253 patients were randomized to hylan G-F 20 (n=124) or placebo (n=129). Mean age was 63 years (42–84), BMI 29.4 (19.5–52.4 kg/m2), 71% were female, and all had primary knee OA of Kellgren Lawrence grade 2 (45%) or 3 (55%). Patients in the hylan G-F 20 group experienced a mean change from baseline in their WOMAC A Likert pain score (0–4 scale) over 26 weeks (primary efficacy criteria) of −0.84, which was statistically significantly different from the change reported in the placebo group (−0.69, p=0.047). Statistically significant differences favoring hylan G-F 20 were also reported for most of the secondary efficacy criteria: WOMAC A1 (estimate Odds Ratio over 26 weeks placebo/hylan G-F 20, 0.64, p=0.013), patient global assessment (0.69, p=0.029), and clinical observer global assessment (0.71, p=0.041); WOMAC B and C changes were not statistically significant between groups. There was no statistically significant difference in the use of rescue medication between the 2 groups. There were no serious AEs related to treatment. In the target knee, injection-related AEs occurred in 4.9% and 3.1% of patients for hylan G-F 20 and placebo, respectively, and treatment-related AEs occurred in 3.3% and 0.8% of patients, respectively. All target knee AEs were local pain, with or without joint swelling or effusion, and were of mild or moderate intensity.

Conclusion: This double-blind placebo-controlled study showed one injection of hylan G-F 20, possibly repeated 6 months later, was safe and provided symptomatic relief lasting up to 6 months in patients with knee OA.

Statement of purpose: The aim of this study is to evaluate different designs of unicompartmental knee replacement (UKR) by comparing the peak von Mises and contact stresses in polyethylene (PE) bearings over a step-up activity.

Summary of Methods: A validated finite element (FE) model was used in this study. Three UKR designs were modelled: a spherical femoral component with a spherical PE bearing (fully-congruent), a poly-radial femoral component with a concave PE bearing (semi-congruent), and a spherical femoral component with a flat bearing (non-congruent).

Kinematic data from in-vivo fluoroscopy measurements during a step-up activity was used to determine the relative tibial-femoral position as a function of knee flexion angle for each model. Medial and lateral force distribution was adapted from loads measured in-vivo with an instrumented implant during a step-up activity. The affect that varying the bearing thickness has on the stresses in the bearing was investigated. In addition, varus-valgus mal-alignment was investigated by rotating the femoral component through 10 degrees.

Summary of Results: Only the fully congruent bearing experienced peak von Mises and contact stresses below the PE lower fatigue limit (17MPa) for the step-up activity (fully congruent PE peak contact stress, 5MPa). The highest PE contact stresses were observed for the semi-congruent and non-congruent designs, which experienced approximately 3 times the PE lower fatigue limit. Peak PE von Mises stresses for the semi-congruent and non-congruent designs were similar, peaking at approximately 25MPa. Peak PE von Mises stresses were ameliorated with increased bearing thickness. Varus-valgus mal-alignment had little effect on the peak stresses in the three UKR designs.

Statement of Conclusions: Fully congruent articulating surfaces significantly reduce the peak contact stresses and von Mises stresses in the bearing. The FE model demonstrates that fully congruent bearings as thin as 2.5mm can be used without increasing the contact stresses significantly. Fully congruent designs can use thinner bearings and enable greater bone preservation.

Introduction: The results of the mobile bearing Oxford unicompartmental knee replacement (UKR) in the lateral compartment have been disappointing with a five year survival of 82%. Therefore, it is recommended that mobile bearings should not be used for lateral UKR. This low survivorship is primarily due to high dislocation rate, all occurring in the first year. A detailed analysis of the causes of bearing dislocation confirmed the elevated lateral tibial joint line to be a contributory factor. A new surgical technique was therefore introduced in which care was taken neither to remove too much bone from the distal femur nor to over tighten the knee and therefore ensure that the tibial joint line was not elevated. Other modifications to the technique were also introduced including use of a domed tibial component.

Aim: The aim of this study is to compare the outcome of these iterations: the original series [series I], Series II with improved surgical technique and the domed tibial component [Series III].

Method: The primary assessment of outcome was bearing dislocation at one year. One year was chosen as all the dislocations in the first series occurred within a year. In series I, there were 53 knees, in series II 65 knees and in series III 60 knees, all with a minimum of one year follow up.

Results: In series I, there were 6 bearing dislocations (11%) and the average range of movement (ROM) was 110°. In the second series, there were 2 dislocations (3%) and the average ROM was 118°. In the third series, there were no primary dislocations and the average ROM was 125°.

Conclusions: The improved surgical technique and implant design has reduced the dislocation rate to an acceptable level so a mobile bearing can now be recommended for lateral UKR.