Chondrocytes are responsible for the mechanical resilience of cartilage by controlling the synthesis/degradation of the extracellular matrix. In osteoarthritis (OA), increased activity of cytokines/degradative enzymes (e.g. IL-1beta, MMP-13) play a key role leading to matrix breakdown/cartilage loss. Studying early events in OA might identify targets for limiting the deleterious changes to cartilage stability. Human chondrocyte shape in situ is normally elipsoidal/spheroidal however abnormal forms within otherwise macroscopically normal cartilage are present. Changes to cell shape can alter ECM metabolism and thus these abnormal forms might be an early event in OA. We have investigated whether levels of IL-1beta and MMP-13 are altered in human chondrocytes of abnormal morphology.

Tibial plateau cartilage was obtained from patients undergoing knee arthroplasty and only areas graded 0 or 0–1 studied. The shape of fluorescently-labelled in situ chondrocytes was classified by confocal scanning laser microscopy with cartilage depth, and cells characterised as normal (no cytoplasmic processes) or abnormal (one/more cytoplasmic process). Within grade 0 cartilage about 40% of the cells demonstrated abnormal morphology with a reduced proportion in deep zones. Fluorescence immunohistochemistry of antibodies for IL-1beta or MMP-13 was studied in the same cells and quantified. There was an increase in IL-1beta fluorescence with abnormal chondrocytes within the superficial (p=0.033; 21 joints > 190 cells) and deep zones (p=0.001; 8 joints > 100 cells). There were no differences between MMP-13 labelling of normal compared to abnormal chondrocytes within either the superficial or deep zones.

Our results suggest that in relatively non-degenerate cartilage, a proportion of the chondrocyte population demonstrated abnormal morphology and that these cells have elevated levels of IL-1beta but not MMP-13. However, we do not know if chondrocyte shape alters cytokine levels, or vice versa. Additionally, the role of cartilage age is unclear, as although the cartilage samples were relatively normal they were obtained from aged individuals. Nevertheless these results show changes to chondrocyte morphology and increased levels of IL-1beta, and thus presumably matrix catabolism - in relatively normal human articular cartilage, raising the possibility that this is an early event in cartilage degeneration.

Supported by the Wellcome Trust (075753).

Introduction: Despite a resurgence in cobalt-chromium metal-on-metal arthroplasty, the potential toxicity of metal ions in the periprosthetic area remains a cause for concern. Studies to date have assessed the acute effect of cobalt ions on osteoblasts over 48 hours. The aim of our study was to determine the response of osteoblasts to cobalt ions over a prolonged period of exposure.

Methods. Primary human osteoblasts were cultured and treated with cobalt (10ppm) over 21 days. Osteoblast function was assessed via alkaline phosphatase activity and calcium deposition. ELISA were used to assess chemokine (IL-8, MCP-1 and TNF-α) secretion. Osteoblast gene expression was assessed using microarray analysis and real time PCR. Immunoflourescent cell staining of actin filaments was used to examine osteoblast morphology.

Results: Chemokine (IL-8) secretion by osteoblasts was significantly increased after 10 days of stimulation with cobalt ions. In parallel with this, osteoblast function was also significantly inhibited as demonstrated by reduced alkaline phosphatase activity and calcium deposition. Regarding osteoblast phenotype, FSP-1, CTGF and TGF-β gene expression were upregulated indicating a transition in osteoblast phenotype. Immunoflourescent staining of actin filaments also showed a change in osteoblast morphology. Taken together, these data show cobalt ions induce a change in the osteoblast phenotype to that of a mesenchymal cell type.

Conclusion: After 10 days of treatment with cobalt ions, osteoblasts no longer function as osteogenic cells. they undergo transition to a mesenchymal cell type. Furthermore, IL-8 secretion is increased which attracts neutrophils to the periprosthetic area thereby contributing to the inflammatory response that characterises osteolysis.

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.

Statement of purpose: Finite element (FE) models of bone can be used to evaluate new and modified knee replacements. Validation of FE models is seldom used, and the quantification of modelling parameters has a considerable effect on the results obtained. The aim of this study is to develop a FE model of a cadaveric tibia and validate it against a comprehensive set of experiments.

Summary of Methods: Seventeen tri-axial rosettes were attached to a cleaned, fresh frozen cadaveric human tibia and the tibia was subjected to 13 loading conditions. Deflection and strain data were used for comparison with the FE model. A geometric model was created on the basis of computed tomography (CT) scans. The CT data was used to map 600 orthotropic material properties to the tibia. All experiments were simulated on the FE model. Measured principal strains were compared to their corresponding FE values using regression analysis. The validated tibia model was reduced in size (75mm to the proximal) and then re-modelled to represent only the proximal tibia. This re-modelled tibia was validated against the reduced size FE model. Virtual surgery was performed on the validated proximal model to implant a UKR.

Summary of Results: For the whole tibia model, the regression line for all axial loads combined had a slope of 0.999, an intercept of −6.24 micro-strain, and an R2 value of 0.962. The root mean square error as a percentage was 5%. For the proximal tibia model, correlation coefficients of 0.989 and 0.976 were obtained for the maximum and minimum principal strains respectively.

Statement of Conclusions: An FE model of an implanted proximal tibia has been validated against experimental data. This model is able to accurately predict the deflection and stresses in a replaced knee joint to obtain clinically relevant information. This will provide a virtual model of unicompartmental arthroplasty, where variables such as fixation method and bearing mechanics can be assessed.

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.

Purpose: To compare the site of lesions in medial and lateral unicompartmental osteoarthritis (OA) of the knee.

Methods: Patients with medial (n=35) and lateral (n=15) OA, having unicompartmental knee arthroplasty, were recruited. Intra-operatively, the distance between the anterior, posterior, medial and lateral margins of the full-thickness lesion and reference lines dividing the condyles was measured. The midpoints of lesions were calculated and groups were compared. Lateral radiographs were used to determine the relationship between the lesion site and knee flexion angle (KFA).

Results: Femoral lesion: In lateral OA, the midpoint of lesions was 25.0mm (SD:8.8) posterior to the reference line passing transversely through the apex of the inter-condylar notch. This was significantly different (p< 0.001) from midpoint in medial OA, which was 10.7mm (SD:9.4) posterior to the reference line.

Tibial lesion: In lateral OA, the midpoint of lesions was 2.0mm (SD:6.5) posterior to the reference line passing through the mid-coronal plane of the resected tibia. This was located significantly more posterior (p=0.038) than midpoint in medial OA, which was 2.2mm (SD:5.7) anterior to the reference line.

Knee Flexion Angle: In lateral OA, the midpoint of lesions was on average at 40° flexion and sites of smaller lesions were very variable. The lesion expanded both anteriorly and posteriorly. In medial OA, smaller femoral lesions occurred in full extension and extended further posteriorly with disease progression.

No significant difference was demonstrated in medial and lateral localisation of the lesions.

Conclusion: Medial OA begins near full extension, progresses in a predictable manner and is perhaps initiated by events occurring at heel strike. Lateral OA begins in flexion in a less predictable manner, at KFA above that seen during the gait cycle. The different sites of lesions in medial and lateral OA suggest different aetiology and pathophysiology. Therefore, prevention and treatment strategies should be different.

We report on a group of 20 metal-on-metal resurfaced hips (17 patients) presenting with a soft tissue mass associated with various symptoms. We describe these masses as pseudotumours.

All patients underwent plain radiography and fuller investigation with CT, MRI and ultrasound. Where samples were available, histology was performed. All patients in this series were female. Presentation was variable; the most common symptom was pain or discomfort in the hip region. Other symptoms included spontaneous dislocation, nerve palsy, an enlarging mass or a rash. The common histological features were extensive necrosis and lymphocytic infiltration. Fourteen of the 20 cases (70%) have so far required revision to a conventional hip replacement and their symptoms have either settled completely or improved substantially since the revision surgery. Two of the three bilateral cases have asymptomatic pseudotumours on the opposite side.

We estimate that about 1% of patients develop a pseudotumour in the first five postoperative years after a hip resurfacing. The cause of these pseudotumours is unknown and is probably multi-factorial, further work is required to define this; they may be manifestations of a metal sensitivity response. We are concerned that with time the incidence of these pseudotumours will increase.

The purpose of this study was to determine if a single physiotherapy intervention would enable patients to kneel following Unicompartmental knee arthroplasty (UKA).

Kneeling is an important functional activity that is frequently not performed after knee arthroplasty, thus affecting a patient’s ability to carry out basic tasks of everyday life. There is however no clinical reason why patients should not kneel and many with proposed knee surgery ask about the possibility of kneeling after their operation.

Sixty adults participated in a prospective randomised controlled trial with blinded assessments. At 6 weeks post-operatively UKA patients were randomised to either the Routine care group where no advice on kneeling was given or to the Kneeling intervention group where participants were taught and given advice on how to kneel and were encouraged to do so. They were re-assessed at 1 year. The primary outcome measure was Question 7 of the Oxford Knee Score which asks the question “Could you kneel down and get up again afterwards?”

Pre-operatively there was no difference in the kneeling ability of the two groups. At 1 year the difference in kneeling ability between the two groups was highly significant (p< 0.05). Spearman’s correlation coefficient showed no significant association between a change in score of Question 7 at 1 year and the following factors; scar position, numbness, range of flexion, arthritic involvement of other joints and pain. Linear regression analysis also confirmed that these factors were not successful in predicting a change in kneeling ability.

This study showed that the single factor predictive of kneeling ability was the physiotherapy intervention provided at 6 weeks post-operatively and it is suggested that kneeling should be incorporated into patient’s post-operative rehabilitation programmes.

Introduction: Treatment options for the young active patient with isolated symptomatic medial compartment OA and pre-existing ACL deficiency are limited. Implant longevity and activity levels may preclude TKA, whilst HTO and unicompartmentasl knee arythroplasty (UKA) are unreliable due to ligamentous instability. UKAs tend to fail because of wear or tibial loosening resulting from eccentric loading. Combined UKA and ACL reconstruction may therefore be a solution.

Method: Fifteen patients with combined ACL reconstruction and Oxford UKA (ACLR group), were matched (age, gender and follow-up period) with 15 patients with Oxford UKA with intact ACL (ACLI group). Prospectively collected clinical and x-ray data from the last follow-up (minimum 3 years, range: 3 – 5) were compared. Ten patients from each group also underwent in-vivo kinematic assessment using a standardised protocol.

Results: At the last follow-up, the clinical outcome for the two groups were similar. One ACLR patient needed revision due to infection. Radiological assessment did not show any significant difference between relative component positions and none of the patients had pathological radiolucencies suggestive of component loosening. Kinematic assessment showed posterior placement of the femur on tibia in extension for the ACLR group, which corrected with further flexion.

Conclusions: The short-term clinical results of combined ACL reconstruction and UKA are excellent. Lack of pathological radiolucencies and near normal knee kinematics suggest that early tibial loosening due to eccentric loading is unlikely.

Aim: The aim of this study was to asses the accuracy of skyline radiographs in the assessment of the patellofemoral joint, when compared to open intraoperative assessment.

Methods: Eighty nine patients undergoing knee replacement surgery were included in the study. Skyline radiographs were obtained preoperatively. These radiographs were assessed and graded by an experienced musculoskeletal radiologist using the Altman and Ahlbäck classifications. The grades were calculated for both the medial and lateral facets of the PFJ. Intraoperative assessment of the Patellofemoral joint was undertaken at the time of surgery. The damage was graded using the modified Collins classification (0: Normal, 1: Superficial damage, 2: Partial thickness cartilage loss, 3: Focal Full thickness cartilage loss < 2cm2, 4: Extensive full thickness cartilage loss < 2cm2). Data was obtained for the Medial Facet, Lateral Facet and Trochlea.

Results: Spearman’s rank correlation coefficient between the radiographic and macroscopic changes within the lateral PFJ were poor with both the Altman 0.22 (p=0.0350) and Ahlbäck 0.24 (p=0.018). The correlation of the medial PFJ was slightly better with a coefficient for Altman 0.42 (P< 0.0001) and Ahlbäck 0.34 (P> 0.001).

Conclusion: In conclusion skyline radiographs provide a poor to moderate preoperative assessment of the degree of osteoarthritis within the patella-femoral joint. This has significant implications for establishing radiographic criteria for planning patella-femoral joint replacement.

Purpose: The aim of this study is to compare the long-term survival results of TKA in patients under the age of 60, using

revision surgery and

Method: From our knee database we identified a cohort of 60 total knee replacements that had been performed over 15 years previously. We identified those who had died, those who had been revised and established the Oxford Knee Score (OKS) for all those still surviving.

Results Using the following endpoint criteria the cumulative 15-year survival was (A) revision surgery alone = 78% (CI 12), (B) revision surgery or an OKS less than or equal to 24 (50% of total OKS) = 63% (CI 13), and (C) revision surgery or moderate pain = 48% (CI 14).

Conclusion The functional survival of TKA in patients under the age of 60 decreases in the second decade following implantation with a significant number of prostheses failing the patient due to knee pain

Introduction: The information in the literature about the relative merits of cemented and cementless unicompartmental knee replacement (UKR) is contradictory, with some favouring cementless fixation while others favouring cemented fixation. Cemented fixations give good survivorship but there is concern about the radiolucency which frequently develops around the tibial component. The exact cause of the occurrence of radiolucency is unknown but according to some, it may suggest suboptimal fixation.

Method: Sixty-two knees (31 in each group) were randomised to receive either cemented or cementless UKR components. The components were similar except that the cementless had a porous titanium and hydroxyappatite (HA) coating. Patients were prospectively assessed by an independent observer pre-operatively and annually thereafter. The clinical assessment included Oxford Knee Score, Knee Society Scores and Tegner activity score. Fluoroscopically aligned radiographs were assessed for thickness and extent of radiolucency under the tibial implant.

Results: At one year there were no differences in the clinical outcome between the groups and there were no loose components. No radiolucencies thicker than 1mm were seen. At one year none of the cementless tibias and 30% of the cemented tibias had complete radiolucencies. One out of 31 cementless (3%) and 12 out of 31 cemented (39%) had partial radiolucencies. This difference between these two groups was high significant (p< 0 0001).

Conclusions: This study clearly demonstrates that the incidence of radiolucency beneath the tibial component is influenced by component design and method of fixation. With identical designs of tibial component none of the cementless components developed complete radiolucences whereas 30% of the cemented components did. We conclude that HA achieves better bone integration than cement.

Introduction: We report on a group of 20 metal-on-metal resurfaced hips (17 patients) presenting with a soft tissue mass associated with various symptoms; these masses we termed pseudotumours. All patients underwent plane radiography; CT, MRI and ultrasound investigations were also performed for some patients. Where samples were available histology was performed.

Methods: All patients in this series were female. Presentation was variable; the most common symptom was pain or discomfort in the hip region. Other symptoms included spontaneous dislocation, nerve palsy, a noticeable mass or a rash. The common histological features were extensive necrosis and lymphocytic infiltration. Fourteen of the 20 cases (70%) have so far required revision to a conventional hip replacement and their symptoms have either settled completely or improved substantially since the revision surgery. Two of the three bilateral cases have asymptomatic pseudotumours on the opposite side.

Conclusions: We estimate that about 1% of patients develop a pseudotumour in the first five postoperative years after a hip resurfacing. The cause of these pseudotumours is unknown and is probably multi-factorial, further work is required to define this; they may be manifestations of a metal sensitivity response. We are concerned that with time the incidence of these pseudotumours will increase.

The aim of this study was to investigate the molecular features of progressive severities of cartilage damage, within the phenotype of Anteromedial Osteoarthritis of the Knee (AMOA).

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). 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 (ANOVA 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 territorial 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 (ANOVA P< 0.0001). Furthermore, real time PCR showed that there was a significant increase in Collagen I expression in the macroscopically normal areas (p=0.04).

In AMOA 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: Avascular necrosis of the femoral head after resurfacing hip replacement is an important complication which may lead to fracture or failure. We compared the changes in femoral head oxygenation resulting from the posterior approach to those resulting from the anterolateral approach and the trochanteric flip approach.

Methods: In 37 patients undergoing hip resurfacing surgery, a calibrated gas-sensitive electrode was inserted superolaterally in the femoral head via the femoral neck following division of the fascia lata. Inter-operative X-ray confirmed correct electrode placement. Baseline oxygen concentration levels were recorded immediately after electrode insertion. All results were expressed relative to this baseline, which was considered as 100% relative oxygen concentration. Oxygen levels were monitored continuously throughout the operation. 10 patients underwent surgery through the posterior approach, 12 patients through the anterolateral approach and 15 through the trochanteric flip approach.

Results: A similar pattern of intra-operative reduction in femoral oxygen concentration was observed for all reviewed approaches. The average change in oxygen concentration during surgery through the trochanteric flip approach was found to be significantly less than through posterior (p< 0.02) and anterolateral (p< 0.02) approaches. Oxygen concentration following joint relocation and soft tissue reconstruction recovered significantly in the anterolateral and trochanteric flip group only. The posterior approach resulted in significantly lower oxygen concentration at the end of the procedure (22%, SD 31) than the anterolateral approach (123%, SD 99; p< 0.05) and the trochanteric flip approach (89%, SD 62, p< 0.02).

Discussion and Conclusion: The anterolateral and trochanteric flip approaches disrupt the femoral head blood supply significantly less than the posterior approach in patients undergoing resurfacing. The most consistent intra-operative oxygen levels were observed during surgery through the trochanteric flip approach. Oxygen concentration during the anterolateral approach was found to be highly dependent upon leg position. The incidence of complications related to avascular necrosis might be decreased by adopting blood supply conserving surgical approaches.

Introduction: A major concern with cemented hip resurfacing arthroplasty (HRA) femoral components is the thermal damage to femoral head during cement curing; this maybe linked to fracture (reported incidence ~2%) and early failure. We investigated the effect of a modifid surgical technique using pulse lavage, lesser trochanter suction and early reduction on the maximum temperature recorded in the femoral head during HRA, compared to manual lavage and reduction after cement curing.

Methods: Patients undergoing total hip replacement (THR) were given a dummy HRA procedure, during which a temperature probe was inserted into the femoral head and the measuring tip placed close to the reamed surface; the position of the probe was confirmed by inter-operative xray. Four subjects received a dummy HRA femoral component using manual lavage and Simplex cement. The implanted femur was kept dislocated until the cement cured. The implanted heads were then removed and sectioned to locate the temperature probes, the THR surgery was then performed. Five patients receiving a definitive HRA were also measured; for these subjects suction on the lesser trochanter was used, pulse lavage given for 30 seconds prior to cementing with Simplex, and pulse lavage of the femoral head for 2 minutes, applied 1 minute after cementing the femoral component. The implanted joint was then immediately reduced and a further two minutes of pulse lavage applied to the reduced joint. Temperatures were recorded until the cement finally cured. In every case the cement was hand mixed for 1 minute and the component implanted at 2 minutes 30 seconds after mixing began.

Results: Sectioning showed that probe tips were < 0.5mm from cement mantle. The maximum temperature recorded in the femoral head was significantly (p=0.014) greater for the manual technique, median value of 47.2°C (37.0 to 67.9°C), than for the pulse lavage technique, median value of 32.7°C (31.7 to 35.6°C).

Discussion: The results show that excessive bone temperatures can occur during hip resurfacing. Temperatures above 45°C kill bone cells, the manual technique may lead to substantial thermal necrosis. Technique modification, with the use of suction on the lesser trochanter, generous use of pulse-lavage and joint reduction prior to cement curing, significantly reduced the temperatures recorded. With the modified technique, the maximum temperatures were well below the threshold of thermal damage. This modified technique is recommended as the potential for thermal bone necrosis is significantly reduced.

Introduction: Avascular necrosis of the femoral head after resurfacing hip replacement is an important complication which may lead to fracture or failure. We compared the changes in femoral head oxygenation resulting from the anterolateral approach to those resulting from the posterior approach.

Methods: In 22 patients undergoing hip resurfacing surgery, a calibrated gas-sensitive electrode was inserted supero-laterally in the femoral head via the femoral neck following division of the fascia lata. Inter-operative X-ray confirmed correct electrode placement. Baseline oxygen concentration levels were recorded immediately after electrode insertion. All results were expressed relative to this baseline, which was considered as 100% relative oxygen concentration. Oxygen levels were monitored continuously throughout the operation. 10 patients underwent surgery through the posterior approach, 12 patients through the antero-lateral approach.

Results: During the operation patterns were similar for both groups, except following joint relocation and soft tissue reconstruction; oxygen concentration recovered significantly in the anterolateral group only. The posterior approach resulted in significantly lower (p< 0.01) oxygen concentration at the end of the procedure (22%, SD 31) than the antero-lateral approach (123%, SD 99).

Discussion and Conclusion: The anterolateral approach disrupts the femoral head blood supply significantly less than the posterior approach in patients undergoing resurfacing. The incidence of complications related to avascular necrosis might be decreased by adopting blood supply conserving surgical approaches.

Introduction: Treatment options for the young active patient with isolated symptomatic medial compartment osteoarthritis and pre-existing anterior cruciate ligament (ACL) deficiency are limited. Implant longevity and activity levels may preclude total knee arthroplasty (TKA), whilst high tibial osteotomy HTO and unicompartmental arthroplasty (UKA) are unreliable due to ligamentous instability. UKA’s tend to fail because of wear or tibial loosening resulting from eccentric loading. Combined UKA and ACL reconstruction may therefore be a solution.

Method: Fifteen patients with combined ACL reconstruction and Oxford UKA (ACLR group), were matched (age, gender and follow-up period) with 15 patients with Oxford UKA with intact ACL (ACLI group). Prospectively collected clinical and x-ray data from the last follow-up (minimum 3 years, range: 3–5) were compared. Ten patients from each group also underwent in-vivo kinematic assessment using a standardised protocol.

Results: At the last follow-up, the clinical outcome for the two groups were similar (ACLR: OKS 46, KSS (objective): 99, ACLI: OKS 43, KSS (objective): 94). One ACLR patient needed revision due to infection. Radiological assessment did not show any significant difference between relative component positions and none of the patients had pathological radiolucencies suggestive of component loosening. Kinematic assessment showed posterior placement of the femur on tibia in extension for the ACLR group, which corrected with further flexion.

Conclusions: The short-term clinical results of combined ACL reconstruction and UKA are excellent. Lack of pathological radiolucencies and near normal knee kinematics suggest that early tibial loosening due to eccentric loading is unlikely. Similarly, wear is unlikely to be a problem because of the wear resistance of mobile bearing devices.

Introduction: The Oxford unicompartmental knee replacement (UKR) use in the lateral compartment has been associated with a reduced flexion range and increased medial compartment pain than seen with its medial counterpart due to, in part, the inadequacy of a flat tibial tray replacing the domed anatomy of the lateral tibia. A new design incorporating a domed tibial component and a biconcave meniscal bearing has been developed to overcome these problems.

This study reports a clinical comparison of new and old establishing whether this modified implant has maintained the established normal kinematic profile of the Oxford UKR.

Method: Patients undergoing lateral UKR for OA were recruited for the study. Fifty one patients who underwent UKR with the domed design were compared to 60 patients who had lateral UKR with a flat inferior bearing surface. Kinematic evaluation was performed on 3 equal subgroups (n = 20); Group 1-Normal volunteer knees, Group 2-Flat Oxford Lateral UKR’s and Group 3-Domed Oxford Lateral UKR’s. The sagittal plane kinematics of each knee was assessed using videofluoroscopic analysis whilst performing a step up and deep knee bend activity. The fluoroscopic images were recorded digitally, corrected for distortion using a global correction method and analysed using specially developed software to identify the anatomical landmarks needed to determine the Patella Tendon Angle (PTA) (the angle the patella tendon and the tibial axis).

Knee kinematics were assessed by analysing the movement of the femur relative to the tibia using the PTA.

Results: PTA/KFA values, for both devices, from extension to flexion did not show any significant difference in PTA values in comparison to the normals as measured by a 3-way ANOVA. The Domed implant achieved higher maximal active flexion during the lunge exercise than those with a flat implant. Only 33% of the flat UKR’s achieved KFA of 130° or more under load whilst performing a lunge, compared with 75% of domed UKR’s and 90% of normal knees. No flat UKR achieved a KFA of 140° or more, yet 50% of all domed UKR’s did, as did 60% of all normal knees.

Conclusions: There was no significant difference in sagittal plane kinematics of the domed and flat Oxford UKR’s. Both designs had favorable kinematic profiles closely resembling that of the normal knee, suggesting normal function of the cruciate mechanism. The domed knees had a greater range of motion under load compared to the flats, approaching levels seen with the normal knee, suggesting that limited flexion for the flat plateau results from over tightening in high flexion and that this is corrected with the domed plateau. Problems with the second generation of lateral Oxford UKA have been rectified by a new bi-concave bearing without losing bearing stability and normal kinematics.

Introduction: Interest in hip resurfacing has recently been renewed by the introduction of metal-on-metal designs; it is being increasingly used for young patients, with over 30,000 implanted worldwide. The 5 year clinical results appear promising, but there are no long term data available. Radiostereometry (RSA) measures of implant migration have been able to predict implant failure; specifically large and continuous migration predicts aseptic loosening. We present the results of a five year RSA study examining the migration of the Birmingham Hip Resurfacing (BHR).

Methods: Twenty-four subjects with primary OA were implanted with the BHR device and with bone markers for RSA. RSA measurements were taken at 3, 6, 12, 24 and 60 months. The migration of the head and the tip of femoral component were measured in 3D.

Results: Preliminary analysis showed that the total 3D migration of the head and tip over five years was 0.32mm and 0.23mm respectively.

Discussion: A distal migration of more than 0.4mm over 2 years increases the likelihood of failure in conventional stems. The total migration of the BHR was approximately 0.3mm over a five year period, significantly less than cemented THR devices. The device is stable and this is promising for long-term survival.