The aim of this study was to define normal, borderline, and abnormal parameters for the morphology of the proximal femur, in the context of the cam deformity, by studying asymptomatic individuals with normal clinical examination and no osteoarthritis from the general population.
Despite the satisfactory short-term implant survivor-ship, there is an increasing concern that the metal-on-metal hip resurfacing arthroplasty (MoMHRA) release large amount of very small wear particles and metal ions. The periprosthetic soft-tissue masses such as pseudotumours are being increasingly reported. These were found be locally destructive, requiring revision surgery in most patients. It has been suggested that either an immune reaction or cytotoxic effect of chromium(Cr) or cobalt(Co) may play a role in its aetiology. However, the effect of the phagocytosis of implant-associated metal nanoparticles on macrophages has not been elucidated. The aim of this study was to investigate the in vitro viability and proliferative response of murine macrophages to clinically relevant metal nanoparticles and ions.
At the end of day 1 and 4, two methods were used to quantify cell proliferation and viability. The AlamarBlue assay(Invitrogen) incorporates a fluorimetric growth indicator and the fluorescence signal correlates with metabolic activity of the cells. LIVE/DEAD stain kit(Molecular Probes) contains two fluorescent dyes to stain living cells green and dead cells red. The viability was calculated by the number of live cells divided by total cell numbers. Inter-group comparisons were performed using one-way ANOVA with Tukey post hoc test. Differences at p<
0.05 were considered to be significant.
Current intervention strategy is focussed on prevention of initial device colonisation and inhibition of genes encoding biofilm formation.
Determine the minimum inhibitory concentration (MIC) of betadine. Investigate the effect of betadine on icaADBC operon encoded staphylococcal biofilm formation. Investigate wether betadine can prevent bacterial adherence and biofilm formation by inhibition of the encoding genes.
Total RNA for cDNA synthesis was isolated from bacterial at different twofold dilutions of betadine concentrations. Real time polymerase chain reaction was used to quantify effects of betadine on gene expression pattern of the icaADBC operon using the constitutively expressed gyrB gene as internal control. Bacterial was cultivated on polystyrene plates coated with different sub-inhibitory and clinical in-use doses of betadine to assess surface adherence.
A step-wise reduction of biofilm was observed at increasing sub-inhibitory doses of betadine (p<
0.0001). IcaA expression correlated with biofilm formation in staphylococcal organisms. Decrease in icaA expression was strongly associated with an increase in expression in the biofilm repressor gene, icaR. The repressive effect of betadine on biofilm formation by Staphylococcal bacteria is by a separate mechanism from its bacteriostatic mechanism of action.
Prevention of bacterial surface attachment as demonstrated by this study is suggestive that these compounds could be developed as a surface coating agents for orthopaedic implants.
Recently, a series of locally destructive soft tissue pseudotumour has been reported in patients following metal-on-metal hip resurfacing arthroplasty (MoMHRA), requiring revision surgery in a high percentage of patients. Based on the histological evidence of lymphocytic infiltration, a delayed hypersensitivity reaction to nickel (Ni), chromium (Cr) or cobalt (Co) has been suggested to play a role in its aetiology. The aim of this study was to investigate the incidence and level of hypersensitivity reaction to metals in patients with pseudotumour.
Group 1: MoMHRA patients with pseudotumours, detected on the ultrasound and confirmed with MRI (n=6, 5 F:1 M, mean age 53 years); Group 2: MoMHRA patients without pseudotumours (n=13, 7 F:6 M, mean age 55 years); and Group 3: age-matched control subjects without metal implants (n=6, 4 F:2 M, mean age 54 years). Lymphocyte transformation tests (LTT) were used to measure lymphocyte proliferation responses to metals. Peripheral blood mononuclear cells were isolated from heparinized blood samples using standard Ficoll–Hypaque® (Pharmacia). The PBMC were cultured at a cell density of 106 cells/mL. Culture was set up in the presence of either:
medium alone; nickel chloride (Sigma; 10-4M-10-6M); cobalt chloride (10-4M-10-6M); and chromium chloride (10-4M-10-6M). After 5 days of culture, cells were pulsed with [3H]-thymidine and proliferation was assessed by scintillation counting. The stimulation index (SI) was calculated by the ratio of mean counts per minute of stimulated to unstimulated cultures. A SI value of greater than 2.0 was interpreted as a positive result.
Tribological studies of hip arthroplasty suggest that larger diameter metal-on-metal (MOM) articulations would produce less wear than smaller diameter articulations. Other advantages using these large femoral heads implants include better stability with lower dislocation rates and improved range of motion. The aim of the present study was to compare chromium (Cr), cobalt (Co) and titanium (Ti) ion concentrations up to 1-year after implantation of different large diameter MOM total hip arthroplasty (THA).
Statistical group comparison revealed significant difference for Cr (p=0.006), Co (p=0.047) and Ti (p=<
0.001). With Biomet implants presenting the best results for Cr and Co and Zimmer the highest Ti level.
Metal on Metal Hip Resurfacing Arthroplasty (MoMHRA) has gained popularity due to its perceived advantages of bone conservation and relative ease of revision to a conventional THR if it fails. Known MoMHRA-associated complications include femoral neck fracture, avascular necrosis/collapse of the femoral head/neck, aseptic loosening and soft tissue responses such as ALVAL and pseudotumours. This study’s aim was to assess the functional outcome of failed MoMHRA revised to THR and compare it with a matched cohort of primary THRs.
Although many causes of FAI are described, the vast majority of patients give no history of previous hip disease. The purpose of this study was to investigate the extent to which FAI has an underlying genetic basis, by studying the siblings of patients undergoing surgery for FAI and comparing them with controls.
Patello-femoral instability (PFI) affects 40 individuals per 100,000 population and causes significant morbidity. The causes of patello-femoral instability are multi-factorial, and an isolated anatomical abnormality does not necessarily indicate instability. Patello-femoral subluxation ranges from 0% (stable patella tracking) to 100% (dislocation) and there is an established relationship between the amount of subluxation and anterior knee pain. Traditionally, magnetic resonance (MR) imaging and standard radiographs are used to guide the clinician towards a suitable corrective procedure for PFI. The multi-factorial nature of patello-femoral instability is not addressed with current imaging techniques. This study aims to address which anatomical variables assessed on MR images are most relevant to patello-femoral subluxation. This information will aid surgical decision making, particularly in selecting the most appropriate reconstructive surgery. A retrospective analysis of MR studies of 60 patients with suspected patello-femoral instability was performed. All patients were graded for degree of subluxation using a dynamic MR scan. The patient scans were assessed for the presence of a specific range of anatomical variables:
patella alta, (modified Insall-Salvatti) patella type (Wiberg classification) trochlea sulcus angles for bone and cartilage surfaces the distance of the vastus medialis obliquis (VMO) muscle from the patella trochlea and patella cartilage thickness the horizontal distance between the tibial tubercle and the midpoint of the femoral trochlea (TTD) patella engagement – the percentage of the patella height that is captured in the trochlea groove in full extension. The Wilk’s Lambda test for multi-variate analysis was used to establish whether any relationship was present between the degree of patello-femoral instability and bony or soft tissue anatomical variables. Non-parametric statistical tests were applied across the groups and within the groups to assess their relative significance. The following variables showed a significant relationship with patellofemoral subluxation; distance of the VMO from the patella (<
0.001), TTD (<
0.001), patella engagement (0.001), sulcus angles (0.004) and patella alta (0.005). This study agrees with previous work showing a significant correlation between subluxation and trochlea sulcus angle and TTD. This is the first study to establish a significant correlation between patella engagement and radiological instability. The lower the percentage engagement of the patella in the trochlea, the greater the degree of patello-femoral instability. Patella engagement showed a more significant relationship with subluxation than patella alta. We report a new method of predicting patello-femoral instability by measuring the overlap of the patella in the trochlea groove.
Participants were classified as:
Normal morphology, no clinical features Abnormal morphology, no clinical features Abnormal morphology, clinical signs but no symptoms Abnormal morphology with symptoms and signs Osteoarthritis.
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. 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.
patients’ pre-operative demographics for age, weight, height, BMI, intraoperative variables such as the operating surgeon (n=2), insert and component sizes, and clinical assessment criteria including pre-operative and five-year post-operative Oxford knee (OKS) and Tegner (TS) scores.
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).
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.
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.
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.
revision surgery and poor functional outcome as the end-points.
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.
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.
Knee kinematics were assessed by analysing the movement of the femur relative to the tibia using the PTA.
Finite element (FE) analysis is widely used to calculate stresses and strains within human bone in order to improve implant designs. Although validated FE models of the human femur have been created (Lengsfeld et al., 1998), no equivalent yet exists for the tibia. The aim of this study was to create such an FE model, both with and without the tibial component of a knee replacement, and to validate it against experimental Results: A set of reference axes was marked on a cleaned, fresh frozen cadaveric human tibia. Seventeen triaxial stacked strain rosettes were attached along the bone, which was then subjected to nine axial loading conditions, two four-point bending loading conditions, and a torsional loading condition using a materials testing machine (MTS 858). Deflections and strain readings were recorded. Axial loading was repeated after implantation of a knee replacement (medial tibial component, Biomet Oxford Unicompartmental Phase 3). The intact tibia was CT scanned (GE HiSpeed CT/i) and the images used to create a 3D FE mesh. The CT data was also used to map 600 transversely isotropic material properties (Rho, 1996) to individual elements. All experiments were simulated on the FE model. Measured principal strains and displacements were compared to their corresponding FE values using regression analysis. Experimental results were repeatable (mean coefficients of variation for intact and implanted tibia, 5.3% and 3.9%). They correlated well with those of the FE analysis (R squared = 0.98, 0.97, 0.97, and 0.99 for axial (intact), axial (implanted), bending, torsional loading). For each of the load cases the intersects of the regression lines were small in comparison to the maximum measured strains (<
1.5%). While the model was more rigid than the bone under torsional loading (slope =0.92), the opposite was true for axial (slope = 1.14 (intact) 1.24 (implanted)) and bending (slope = 1.06) loads. This is probably due to a discrepancy in the material properties of the model.
Anteromedial osteoarthritis is a distinct phenotype of osteoarthritis. The arthritic lesion on the tibia is localised to the anteromedial quadrant with an intact ACL. Deficiency of the ACL leads to a progression to tricompartmental disease. Within the spectrum of intact ACL a varying degree of ligament damage is seen. Our aim was to correlate the progression of ACL damage to the geographical extent of disease and the degree of cartilage loss on the tibial plateau. We systematically digitally mapped 50 tibial plateau resection specimens from clinical photographs of patients undergoing unicompartmental arthroplasty, additionally the damage to their ACL was graded (0: normal, 1:synovium loss, 2:longitudinal splits) These images were imported into image analysis software. Accurate measurements were made of the dimensions of the specimen. Measurements included the AP distance to the anterior and posterior aspect of the lesion, and the distance to the start of the macroscopically non damaged cartilage. The areas of cartilage damage and full thickness loss were also recorded. The results were represented as a % of total area to account for variation in size of the resection specimens. We compared % of full thickness loss in patients with normal to those with damaged, but functionally intact ligaments. All specimens had a similar macroscopic appearance. A significant difference was seen with the progression of ACL damage and area of eburnation of bone. Using an unpaired t test, a significant difference in area of % full thickness cartilage loss (P=0.047) was seen between patients with a normal and longitudinal splits within their ACL. No correlation between the clinical status of the ACL and start or finish point of cartilage loss on the tibial plateau We surmise that the progression from anteromedial to tricompartmental osteoarthritis of the knee may be related to the graduated damage of the ACL.
A sibling risk study that shows a statistically significant increase in risk for anteromedial osteoarthritis of the knee. Anteromedial osteoarthritis is a distinct phenotype of osteoarthritis. Previous studies have shown a genetic aetiology to both hip and knee osteoarthritis. The aim of this study was to determine the sibling risk of antero-medial osteoarthritis of the knee. We conducted a retrospective cohort study of 132 probands with primary anteromedial osteoarthritis, who had undergone unicompartmental arthroplasty. Sibling were identified as having symptomatic knee problems by postal Oxford Knee Score (OKS). A positive OKS was defined as an OKS+/− 2SD of the mean of the proband group. Sibling spouses were used as controls. Those siblings &
spouses that were symptomatic from the OKS were invited to undergo Knee X-rays, to look for radiological signs of osteoarthritis. Osteoarthritis was diagnosed as greater than Grade II on the Kell-gren Lawrence classification. The pattern of disease was noted and it was considered if the sibling were suitable for a unicompartmental knee arthroplasty. The prevalence and sibling risk of anteromedial osteoarthritis was determined using a randomly selected single sibling per proband family. The prevalence was determined in the 103 single proband sibling pairs. There was a statistically significant risk within the sibling group P= 0.024 using the Chi square test. The relative risk of anteromedial osteoarthritis was. 3.21(95% CI 1.08 to 9.17) Genetic factors play a major role in the development of anteromedial osteoarthritis.
Wear debris is a key factor in the pathophysiology of aseptic loosening of orthopaedic endoprostheses. Cobalt-chromium-molybdenum (Co-CrMo) alloys are used for metal-metal hip implants due to their enhanced wear resistance profiles. Whilst these alloys have widespread clinical application, little is known about their direct effect on osteoblast biology. To address this issue, in this study we have investigated particle-mediated inflammation, as a putative mechanism of aseptic loosening. The effects of Co2+ ions on the bone cellular milieu were assessed in vitro by profiling of classical inflammatory mediators. The inflammatory driver PGE2 was quantified and found to be increased, following osteoblast stimulation with metal ions, suggesting the initiation of a local inflammatory response to metal particle exposure. To determine the biological import of this molecular event, the role of metal ions in recruiting inflammatory cells by chemokine production was assessed. These data demonstrated significant induction of the chemokines, IL-8 and MCP-1 following both 12 and 24 hour exposure to 10ppm of Co2+. In this study, we demonstrate that Co2+ particles can rapidly induce chemotactic cytokines, IL-8 and MCP-1 early stress-responsive chemokines that function in activation and chemotaxis of monocytes, and PGE2, which stimulates bone resorption. We have shown that this induction occurs at a transcriptional level with significantly increased mRNA levels. These data lend further weight to the hypothesis that wear mediated osteolysis, is due, at least in part, to underlying chronic inflammation.
There has been controversy about the practice of mixing femoral and acetabular implants from different manufacturers in total hip replacement (THR). We studied the clinical outcomes of over 1500 patients in the Exeter Primary Outcomes Study (EPOS) who underwent primary THR with a cemented Exeter stem (Stryker) but with various acetabular components. This was a prospective non-randomised multicentre study. Patient reported hip scores (Oxford Hip Score (OHS)) were measured before operation and at 1 and 2 years post operatively. The choice of acetabular implant was at the surgeons’ discretion. 982 patients had reached four year follow up. Six types of acetabular component were examined (Exeter, Exeter Contemporary, Duraloc (all Stryker), Charnley (DePuy), Cenator (Corin), and Trilogy (Zimmer)). Patients who received a Charnley cup were found to have worse pre-operative status (significantly higher OHS) than those receiving other cups (especially those receiving Exeter cups) (p<
0.01). Post operatively, this difference continued, with the absolute OHS value remaining greater (i.e. worse clinical result) for the Charnley cup at 1, 2, 3 and 4 years. The association of poor pre-op status with worse post-op result was anticipated. However, when the clinical benefit of surgery (i.e. the improvement in OHS between pre-op and post-op) was assessed, there was no significant difference between the various implants at 1, 2, 3 and 4 years. These results demonstrate that initial clinical benefit of surgery does not differ between patients receiving acetabular implants from varying manufacturers when the Exeter stem is used. These patients will be followed further to determine whether such “mixing and matching” results in differences in longer term outcomes.
The optimal surgical approach for total hip replacement (THR) remains controversial. We report the clinical outcomes of over 1000 patients in the Exeter primary outcomes study (epos) who underwent primary THR with a cemented Exeter stem (Stryker) but with various acetabular components. This was a prospective non randomised multi centre study. Patient reported hip scores (oxford hip score (OHS)) were measured before operation and at 3 months (n= 1312), 1 (n=1276), 2 (n= 1225), 3 (n=1205) and 4 (n=975) years post operatively. Physician reported scores (Merle d’Aubigne / Postel, MDAP) were measured before operation and at 12 months. All of the operations were carried out using either the anterolateral (Hardinge or modification) or posterior approach. The posterior approach gave better absolute OHS scores at 3 months and 1 year compared with the anterolateral approach. The improvement in OHS between the pre-op and relevant post-op score was better for the posterior than the Hardinge approach, and this extended to 4 years (all p<
0.05). Early dislocation rates were low in both groups. There was significantly more likely to be heterotopic ossification in the Hardinge group, while stem alignment into varus was more common in the posterior approach group. There was no significant difference between the two approaches as measured using the MDAP score at pre-op or at 12 months after surgery. These results demonstrate that initial patient perceived clinical benefit of surgery is greater using a posterior than with an anterolateral approach. This should be considered when assessing the best approach for a particular patient. The current results emphasise the value of using patient based outcome measures, as the MDAP score did not detect a difference in outcomes between the two groups.
This study assesses the functional in vivo kinematics of Advanced Medial Pivot (AMP) TKR and compares it to kinematics of the normal knee.
There has been controversy about whether limb length discrepancy (LLD) affects outcome after total hip replacement (THR). We examined input variables and outcomes of over 1200 patients who received primary THR with the Exeter stem and a variety of acetabular components in the Exeter Primary Outcomes Study. This was a non randomized prospective multi centre study. We examined whether specific groups of patients or surgeons were more likely to have LLD at one year after surgery. Data for leg length measured on clinical assessment were available for 1207 patients at 1 year. 237 patients were recorded as having a leg length difference of 1 cm or more, and 73 a difference of 2 cm or more. 138 were longer on the operated side and 99 were shorter. The likelihood of having LLD of 2 cm or more was not significantly affected by the grade of surgeon (consultant or trainee), BMI, age of patient, position of patient during surgery or surgical approach, or the use of regional or general anaesthetic. We examined the effect of LLD on outcomes at 3 months and 1,2,3 and 4 years. Patients with LLD >
1cm had significantly worse Oxford Hip Scores (OHS) at 1, 2, 3 and 4 years (p<
0.01), with the OHS generally being an average 2 points worse in those with LLD. The most consistent difference between those with and without LLD was a patient reported limp on the Oxford Hip Questionnaire. We conclude that LLD is a common problem after THR and that all patient groups may be affected. It is associated with a significantly worse functional outcome as measured by a validated hip score. Systematic adoption of accurate intra-operative measures of leg length might pay dividends in minimizing this complication.
Hip resurfacing arthroplasty (HRA) is increasingly carried out as an alternative to total hip arthroplasty (THA) in young patients. During the procedure, a metal stem on the retrosurface of the HRA is inserted into the femoral head to ensure the implant is located centrally with respect to the femoral neck. It has been suggested that the stem may interfere with bone loading. In light of this, the current study employed finite element (FE) models to investigate the change in the HRA-implanted bone mechanics as a result of removing the stem. FE models of a cadaveric femur pre- and post-HRA surgery were analysed to determine changes in bone stress/ strain. The implanted models simulated geometry for a cemented HRA with and without a non-cemented stem (HRA-Stem and HRA-NoStem, respectively) and included more accurate multiple material parameters to simulate the non-homogeneous material distribution in the femoral bone. The models included loading conditions simulating an instant at 10% of the gait cycle. Bone stresses/strains in the femoral head and neck of the implanted models were compared with the intact condition to assess the change in bone mechanics. Changes in cement mantle stresses between the HRA-Stem and HRA-NoStem models were also compared. When comparing similar volumes of bone in the femoral neck, both HRA models showed a similar variation in stress from the intact condition and bone stresses were low in comparison to the ultimate strength of cortical bone. There was less change in peak strain energy in the femoral head of the HRA-NoStem model than the HRA-Stem model. Cement mantle stresses in the HRA-NoStem model were slightly higher than for the HRA-Stem model and the peak compressive stress was close to the fatigue limit for bone cement. These preliminary results suggest that the bone loading is more normal without the stem. However, there are increased cement mantle stresses.
There is concern that patients undergoing total hip replacement by trainee surgeons may do worse than those operated on by consultants. We examined the clinical outcomes of over patients in the Exeter Primary Outcomes Study who underwent primary THR with a cemented Exeter stem (Stryker) with various acetabular components. Over 1400 patients entered the prospective non-randomised multi centre study. Patient reported hip scores (Oxford Hip Score (OHS)) were measured pre operation and at 3 months, 1,2,3 and 4 years post operatively. The number of patients assessed at 4 years was 982. Trainees operated on patients with worse pre-operative OHS (p<
0.05; t test)) and on significantly less patients under 60 years (p<
0.05 chi square). There was no significant difference in the improvement in OHS (i.e. pre-op OHS – post-op OHS) at any post-operative time point between consultants and trainees. However, patients operated upon by consultants had consistently better postoperative absolute OHS scores (p<
0.05 at 3 months and 1, 2, 3 and 4 years; t test). Complications were low in both groups. Operations performed by trainees lasted longer (mean of 104 vs. 85 minutes). There was also no difference in OHS scores of patients operated by trainees whether they were assisted by an SHO (n=132) or by a consultant (n=249). In this large cohort of patients there was no difference in the improvement in OHS between patients operated by registrars and consultants. The difference in the absolute OHS values is likely explained by the difference in pre-operative status. We conclude that THRs performed by consultants and by trainees under appropriate supervision give similar initial clinical results. Given current changes to shorten surgical training, it is important that outcomes of THRs performed by future trainees are reviewed to ensure that outcomes are maintained.
The design philosophy of polished tapered total hip replacements (THR), such as the Exeter, intends for them to migrate distally within the cement mantle. As well as migration, dynamically induced micromotion (DIMM) occurs as a result of functional activity between the implant and the cement. The aim of the current study was to develop and validate a finite element (FE) model of the Exeter/cement/bone system which can be used to predict DIMM and investigate the stresses induced in the cement mantle during functional activity. In the context of the current study, DIMM is defined as the displacement of the implant component relative to the bone when moving from double leg stance to single leg stance on the operated limb. Using Roentgen Stereo-photogrammetric Analysis (RSA), DIMM was measured in 21 patients implanted with Exeter stems 3 months post-operatively. A previous study, using a reduced FE model of the Exeter stem and the surrounding cement mantle focused on the solution of the contact problem at the stem-cement interface. It was demonstrated that sliding contact combined with Coulomb friction and an appropriate parameter setting could be used to predict DIMM of a polished tapered stem. For the purposes of the current study, the previous simple model was incorporated into the FE model of the Muscle Standardised Femur and validated against the RSA measurements for DIMM. For the current extended model, loading included muscle forces representing all active muscles acting on the femur. The effect of initial cement stresses and interdigitation was also considered. The Exeter stem demonstrated significant DIMM (p<
0.017). The FE model, accounting for sliding contact at the cement–implant interface was able to predict similar distal migration of the head and the tip. The results of both the calculations and the measurements showed that the femoral head moves medially, distally and posteriorly relative to the bone. In the cement mantle, maximum principal stresses were oriented circumferentially, minimum principal stresses were oriented radially. When the taper got engaged, submicroscopic movements which did not recover following unloading still took place and accumulated. The results of the present study showed that it is possible to measure DIMM in the Exeter stem and combine this with FE modelling of the contact mechanism. Future studies will include various activities, such as walking or stair climbing. Based on accumulated submicroscopic movements, short-, mid- or long-term migration patterns will be predicted.
The long-term survival of total knee arthroplasty (TKA) has been well established; however, functional outcome remains inconsistent. More normal postoperative TKA kinematics have been shown to produce better knee function. Improved kinematics can be obtained by using implants with optimised surface geometry. Hence a TKA with an appropriate surface geometryis likely to provide superior long-term functional outcome. The Advance-Medial Pivot TKA (Wright Medical) is a fixed bearing prosthesis with a conforming medial compartment and a non-conforming (flat on flat) lateral compartment. This surface geometry is designed with the intention of replicating the normal knee motion of sliding or pivoting medially and rolling back laterally. Aim: To investigate the sagittal plane kinematics of Advanced Medial Pivot Knee and compare with those of “flat on flat” fixed bearing TKA and normal knees 18 patients who had undergone primary TKA for osteoarthritis were recruited at an average of 18 months post operation. These patients performed flexion and extension exercises against gravity and a step up exercise. Video fluoroscopy of these activities was used to obtain the patellar tendon angle (PTA). This is a previously validated method for assessing sagittal plane kinematics of a knee joint. The kinematic profile of the Advance Medial Pivot Knee was compared to the profile of 14 normal knees and 30 flat on flat, fixed bearing TKA’s. The sagittal plane kinematics of the Advance TKA differed from the normal knees. However, similarly to normal knees, a linear relationship was observed between PTA and knee flexion angle throughout knee flexion range. The kinematics of the Medial Pivot Knee were similar to normal when the knee was in a highly flexed position. Functional plane kinematics of the Advance Medial Pivot TKA appear to meet the design criteria in that a linear relationship between PTA and flexion angle is maintained. Further work is required to establish if these improved sagittal plane kinematics translate into improved functional outcome.
Medial unicompartmental replacement (UKR) has been shown to have superior functional results to total knee replacement (TKR) in appropriately selected patients, and this has been associated with a resurgence of interest in the procedure. This may relate to evidence showing that the kinematic profile of UKR is similar to the normal knee, in comparison to TKR, which has abnormal kinematics. Concerns remain over the survivorship of UKR and work has suggested the anterior cruciate ligament (ACL) may become dysfunctional over time. Cruciate mechanism dysfunction would produce poor kinematics and instability providing a potential mechanism of failure for the UKR.
A cross sectional study was designed in which 24 patients who had undergone successful UKR were recruited and divided into early (2–5 years) and late (>
9 years) groups according to time since surgery. Patients performed flexion/extension against gravity, and a step up. Video fluoroscopy of these activities was used to obtain the Patellar Tendon Angle (PTA), the angle between the long axis of the tibia and the patella tendon, as a function of knee flexion. This is a previously validated method of assessing sagittal plane kinematics of a knee joint. This work suggests the sagittal plane kinematics of a fixed bearing UKR is maintained in the long term. There is no evidence that the cruciate mechanism has failed at ten years. However, increased tibial bearing conformity from ‘dishing’, and adequate muscle control, cannot be ruled out as possible mechanisms for the satisfactory kinematics observed in the long term for this UKA.
Bone stock loss secondary to debris and mechanic alin-stability presents a challenge in revision hip arthroplasty. The aim of our study is to evaluate the clinical outcome of revision hip arthroplasty using the Oxford hip prosthesis combined with impaction allografting. Between 1999 and 2002, we revised 72 hips in 69 patients using this technique (mean age 65years). Indications were aseptic loosening (56), infection (8), peri-prosthetic fracture (7) and a broken stem (1). The mean time to revision was 8.5 years (1–21years). Patients were assessed clinically and with the Oxford Hip Score (OHS) pre- and post-operatively. Fifty-seven patients also had acetabular revision. Four patients required femoral osteotomy to remove the old prosthesis. We used a mean of 1.8 (1–4) femoral heads per operation. Patients were mobilised partially weight bearing (8weeks) followed by a gradual return to full loading. Complications included peri-operative femoral fracture (6), infection (6), dislocation (10), DVT (1)and PE (2). The average blood transfusion was 1.8 units (0–9). The OHS improved from 45 (26–58) pre-operatively to 24.3 post-operatively (12–43). No hip has been re-revised for aseptic loosening at a mean follow-up of 32.7months (16–51). The Oxford hip is a trimodular prosthesis with a polished tapered metaphyseal section that is free to slide and rotate on the stem. The stem is first inserted uncemented into the diaphysis. Bone graft is impacted proximally, with mesh if necessary, and then the proximal wedge is cemented in. The wedge allows for some subsidence in the cement and creates optimal radial force transmission, which is essential for bone-remodelling stimulation and preventing proximal stress shielding. Although this is a short-term experience, we believe that the use of the tri-modular Oxford stem combined with minimal proximal impaction allografting is a reliable method of dealing with difficult revision femoral surgery. The results were comparable with a primary arthroplasty in terms of pain relief and functional results.
Background: In anteromedial osteoarthritis, only the medial compartment of the knee is affected and the collateral ligaments as well as the cruciate mechanism are intact. These preconditions make the knee suitable for UKA. The operative technique of the Oxford UKA theoretically allows the surge on to replicate the natural kinematics of the knee, due to accurate ligament balancing and fully congruent meniscal bearing design of the prosthesis. Our hypothesis was that no difference in tibiofemoral kinematics is observed after UKA. In addition we also hypothesised that the results of the image guided surgery would be the same as the normal surgical procedure.
The purpose of the study: to determine if Patient height-and gender could be used to predict component size With a minimally invasiveapproach for unicompartmental knee replacement. Material and methods: One hundred x-rays of patients (44 men, 56 women), who had undergone Oxford UKR, were reviewed. The preoperative radiographs were assessed for component size using the standard template. The postoperative x-rays were reviewed to determine-whether the ideal component size had been used or if not what could be the most appropriate. Patient’s height was recorded. The proportion of patients for whom an appropriate size could be selected by either template or height measurements was calculated. Current templating system accurately predicted the ideal size in 67%. In no case was the size incorrect by more than one size. The following size bands were set according to height. For men: size small in patients less than160 cm, medium less than 170 cm and large less than 180cm. For women: size small in patients less than 165 cm, medium less than 175cm and large less than 185 cm. Height accurately predicted the ideal size in75%. In no case was the assessment of component size incorrect by more than one size. As the Oxford femoral component is spherical, its size is not critical and it is acceptable to use one size too large or too small. Both height and templating safely predicted an acceptable size in all cases and predicted the ideal size in about 70% >
Conclusion: Gender specific height should be used to predict the component size in situations were templating is difficult as in digital x-rays orsuperimposition of the two femoral condyles, and non-standardised x-raymagnification.
The indications for unicompartmental knee arthroplasty (UKA) remain controversial; in particular the threshold of disease in the patellofemoral compartment is debated. Whilst some authorities ignore the condition of the patellofemoral joint, others consider pre-existing patellofemoral osteoarthritis (PFOA) a contra-indication to UKA. The aim of this study was to determine the influence of PFOA on the outcome of medial UKA. This prospective study involved one hundred consecutive patients who had undergone cemented medial Oxford UKA (phase 3), via a minimally invasive approach, at least one year previously. Patients were divided into two groups according to the presence or absence of full thickness cartilage loss (FTCL) on the patella or trochlea at operation. A pre-operative skyline radiograph was graded using the Altman score, by an independent Musculoskeletal Radiologist. Outcome was evaluated with the Knee Society Score (AKSS) and the Oxford Knee Score (OKS, maximum 48). Groups were compared for differences in knee score and Altman grade using a one way ANOVA. Repeat analysis was performed using the presence of anterior knee pain (AKP) as the group defining variable. There were 28 patients with FTCL, and both groups were well matched for age, gender and activity levels. Analysis showed no significant difference in post operative knee scores between groups with either the presence of FTCL or the presence of AKP pre-operatively as a factor. There was no significant difference in Altman grade between groups. Intra-operative evidence of PFOA in patients with medial compartment osteoarthritis does not prejudice the outcome of UKA. Even the inclusion of patients with symptomatic AKP, without necessarily having PFOA, does not affect the outcome after UKA. These short results are encouraging, but longer follow up is required.
Functional outcome after patellofemoral joint replacement (PFA) for osteoarthritis remains inconsistent. It is believed that functional outcome for joint replacement is dependent upon postoperative joint kinematics. Minimal disruption of the native joint, as in PFA, should produce more normal kinematics and improved outcome. No previous studies have examined joint kinematics after isolated PFA.
Twelve patients who had undergone successful PFA at least two years previously were recruited. Patients performed flexion/extension against gravity, and a step up. Video fluoroscopy of these activities was used to obtain the Patellar Tendon Angle (PTA), the angle between the long axis of the tibia and the patella tendon, as a function of knee flexion. This is a previously validated method of assessing sagittal plane kinematics of a knee joint. The kinematic profile of the PFA joints was compared to the profiles for fourteen normal knees. Overall, the kinematic plot obtained for PFA reflected similar trends to that for normal knees; but the PTA was slightly but significantly increased throughout the entire range of flexion (two degrees). This is equivalent to an average displacement of the lower pole of the patella of 1.5mm. Sagittal plane knee kinematics after PFA are much more normal than after TKR and this should give improved functional outcome. The observed increase in PTA through range may result from increased patella thickness or a shallow trochlear groove and may influence patellofemoral contact forces.
Oxford Unicompartmental knee arthroplasty (UKA) is now performed using a minimally invasive surgical (MIS) technique. Although early results are encouraging, the studies assessing outcome could be criticised for the restricted number of patients and limited follow-up. Aim of this study was to assess clinical outcome and prosthetic survival rate inpatients with minimally invasive Oxford medial UKA. This prospective study assessed 500 consecutive patients, who underwent cemented Oxford UKA for medial OA using MIS technique. Patients were assessed using objective and functional Knee Society Score (KSS). This study has confirmed preliminary findings that Oxford UKA using a minimally invasive approach is safe, reliable and effective.
Proprioception protects joints against injurious movements and is critical for joint stability maintenance under dynamic conditions. Knee replacement effect on proprioception in general remains elusive. This study aimed to evaluate the changes in proprioceptive performance after knee replacement; comparing Total (TKA) to Unicompartmental Knee Arthroplasty (UKA). Thirty-four patients with osteoarthritis were recruited; 15 patients underwent TKA using the AGC prosthesis and 19patients underwent UKA using the Oxford prosthesis. Both cruciate ligaments were preserved in the UKA group, while only the PCL was preserved in TKA patients. Patients’ age was similar in both groups.>
Joint Position Sense (JPS) and postural sway were used as measures of proprioception. Both groups were assessed pre- and 6 months post-operatively in both limbs. JPS was measured as the error in actively and passively reproducing five randomly ordered knee flexion angles between 30 and 70°using an isokinetic dynamometer. Postural sway (area and path) was measured during single leg stance using a Balance Performance Monitor. Functional outcome was assessed using the Oxford Knee Score (OKS). Pre-operatively, no differences in JPS or sway were found between limbs in either group. No differences existed between the two groups. Post-operatively, both groups had significant improvement of JPS in the operated limb (UKA mean4.64°, SD1.44° and TKA mean5.18°, SD1.35°). No changes in JPS were seen in the control side. A significant improvement (P<
0.0001) in sway area and path was found in the UKA group only in both limbs. No significant changes in sway occurred in either limb of TKA patients. The OKS improved from 21.4 to 35.5 for TKA patients and from 23.9 to 38for UKA patients. Both UKA and TKA improve proprioception as assessed by JPS. However, UKA alone improves postural sway in both limbs. This may impart explain why UKA patients function better than TKA patients
The Charnley Elite femoral component was first introduced in 1992 as a new design variant of the original Charnley femoral component (De Puy, Leeds, UK) with modified neck and stem geometry. The original component had undergone few changes in nearly forty years and has excellent long-term results. Early migration of the new stem design was determined by Roentgen Stereophotogrammetric Analysis (RSA)1. Rapid early migration of a component relative to the bone, measured by RSA, is predictive of subsequent aseptic loosening for a number of femoral stems. As there was rapid early migration and rotation of the Charnley Elite stem, we predicted that the long-term results would be poor. An outcome assessment is indicated as stems of this type are still being implanted. One hundred Charnley Elite stems, implanted in our centre between 1994 and 1997 were included in a prospective, cross-sectional follow-up study. Outcome measures include validated clinical scores (Charnley hip score, Harris hip score and Oxford hip score) and radiological scores (Gruen classification) as well as revision rates over the past 10 years. The clinical follow-up supports the RSA predictions of early failure of the Charnley Elite femoral stem.
Early migration of the new stem design was determined by Roentgen Stereophotogrammetric Analysis (RSA). Rapid early migration of a component relative to the bone, measured by RSA, is predictive of subsequent aseptic loosening for a number of femoral stems. As there was rapid early migration and rotation of the Charnley Elite stem, we predicted that the long-term results would be poor. An outcome assessment is required as stems of this type are still being implanted.
Preliminary clinical scores in the patients who had not undergone any subsequent surgery were adequate (Oxford Hip Score mean average of 23.9). Thirteen percent of radiographs analysed had evidence of loosening, giving an overall loosening rate of 14% at 8 years.
This study presents the 2 year migration results of the BHR femoral component using Roentgen Stereophoto-grammteric Analysis (RSA).
Joint Position Sense (JPS) &
sway were used as measures of proprioception performance. Both groups were assessed pre- and 6 months post-op. JPS was measured using an isokinetic dynamometer (KinCom, Chatanooga Ltd) as the error in actively and passively reproducing fi ve randomly ordered knee fl exion angles (30°, 40°, 50°, 60° and 70°). Sway (area, path and velocity) was measured during single leg stance using a Balance Performance Monitor (SMS Medical) for 30-second interval. Functional outcome was assessed using the Oxford Knee Score (OKS). Pre-operatively, no differences in JPS or sway were found between limbs in either group. No differences existed between the two groups. Post-operatively, both groups had signifi cant improvement of JPS in the operated limb only (Mean ± standard deviation for UKA 4.64±1.44° and for TKA 5.18±1.35°). No changes in JPS were seen in the control side. Group 2 patients showed signifi cant improvement in both sway area and path (p<
.0001) for both limbs post-operatively. No signifi cant post-operative changes in sway occurred in either limb of Group 1 patients. The OKS improved post-operatively in both groups, rising from 21.4 to 35.5 for Group 1 patients and from 23.9 to 38 for Group 2 patients.
Between 1999 and 2002, we revised 72 hips in 69 patients using this technique (mean age 65years, 28 to 88). Fifty-six cases had aseptic loosening, 8 had infection (2 stages), 7 had peri-prosthetic fractures and 1 had a broken stem. The mean time to revision was 8.5years (1 to 21). Patients were assessed clinically and with the Oxford Hip Score (OHS) pre- and post-operatively. Fifty-seven patients also had acetabular revision. Four patients required femoral osteotomy to remove the old prosthesis. We used a mean of 1.8 (1 to 4) femoral heads per operation. Complications included 6 peri-operative femoral fractures diagnosed at operation and fixed successfully, 6 infections, 10 dislocations (2 were recurrent), one deep vein thrombosis, 2 pulmonary embolism and one gastrointestinal haemorrhage. The average blood transfusion was 1.8 units (0 to 9). The OHS improved from 45 (26 to 58) pre-operatively to 24.3 post-operatively (12 to 43). No hip has been re-revised for aseptic loosening at a mean follow-up of 32.7 months (16 to 51).
There is an increasing interest amongst surgeons and demand from patients for hip resurfacing. One concern regarding resurfacing is the incidence of femoral neck fracture post operatively. McMinn and Treacy report an incidence of 0.4% in their series, our finding was of an incidence of over four times as high (1.9%). We looked at our database of hip resurfacings and tried to identify the risk factors for fracture. We identified 11 fractures and compared these with 22 controls selected by choosing the cases performed by the surgeon immediately before and after the fracture case. We analysed their medical notes and x-rays. Statistical analysis was performed using a package in ™Excel. The implants were either Birmingham Hip (Midland Medical Technologies) or Cormet (Corin) resurfacings. No statistically significant correlation was found for sex, age or body mass index. We found that fracture was twice as likely in the presence of possible or probable osteopenia. We did not find that fracture was more likely to occur in patients with a previous diagnosis of Perthes, DDH, SUFE and avascular necrosis (AVN). We found patients with a superior overhang of the femoral component on the neck did not risk fracture, however we could not demonstrate that notching in itself increased the risk of fracture. There was no correlation with neck-shaft and stem-shaft angle or neck lengthening and offset and subsequent neck fracture. In 13 bilateral cases there was fracture in 3 (incidence 23%). Apart from one fracture that occurred at 18 weeks post-operatively all the others occurred before eight weeks. Five fractures occurred in patients who subsequently on histological analysis were found to have avascular necrosis. We conclude that bilateral surgery is probably unwise. That a superior overhang seems to protect against fracture as long as this is not at the expense of creating an inferior notch. Finally, we find AVN in a number of retrieved heads, what is the true incidence of AVN and does the approach adopted cause the avascular process and if so why do we see so few fractures?
Polyethylene wear remains an important cause of failure in knee replacements. Retrieval studies, simulators and simple X-ray methods produce wear data that may be inaccurate or unrealistic. We have developed an accurate RSA system for measuring wear in-vivo. Using this system we have found wear rate in a fixed bearing TKR to be about 0.1mm/yr[ Four Oxford uni-compartmental knee replacements, with excellent clinical results were studied ten years after implantation. RSA X-rays were taken in double leg stance with the knee in full extension and 15 and 30 degrees flexion. Following RSA calibration, silhouettes of the components on the stereo X-rays were extracted using a Canny edge detector and were matched to silhouettes projected using CAD models to determine the 3D component position. The average minimum thickness of the bearing was determined and was compared with the measured minimum thickness of 14 unused bearings to calculate linear penetration. The average linear penetration after average 10 years implantation (range 8.5 to 10.25 years) was 0.16 mm (SD 0.13 mm). The average penetration rate was 0.017 mm/year (SD 0.011 mm/year). The maximum linear penetration rate was 0.027 mm/year. The penetration rate is similar to that obtained in a retrieval study [
The kinematic profile of single axis design TKR was closer to normal especially near extension. During mid-flexion, abnormal anterior femoral translation was noticed with the polyradial design. No significant difference was noted between CR and CS designs.