Background

Obesity has been linked with increased rates of knee osteoarthritis. Limited information is available on the survival and functional outcome results of rTKR in the obese patients. This registry-based study aimed to identify whether BMI is an independent risk factor for poorer functional outcomes and /or implant survival in rTKA.

Introduction

Periprosthetic fractures of the femur are potentially catastrophic injuries associated with significant morbidity and mortality. Surgical treatment comprises revision arthroplasty or internal fixation. It is well established that a delay in treating patients with hip fracture leads to higher mortality rates, however there is limited evidence regarding mortality rates and the time to surgery in patients with lower limb periprosthetic fractures.

Bone and joint infections of the lower limbs cause significant morbidity for patients. Infection is a devastating complication for prosthetic joint replacements. In this large case series from a single centre in the NE of England, we present our experience of using antibiotic impregnated dissolvable synthetic pure calcium sulphate beads [Stimulan R]1 for local elution of antibiotics at the site of infection.

At our centre, from August 2012 to Jan 2015, antibiotic impregnated dissolvable synthetic pure calcium sulphate beads [Stimulan R]1 was used for local elution of antibiotics in 45 patients with lower limb bone or joint infections. Tailored plans were made by Orthopedic surgeon and Microbiologist MDTs based on bacteria and sensitivities.

Cases included 20 THR, 13 TKR, 5 Hemiarthroplasties, 4 tibial nonunions, 1 infected femoral plate and 2 paediatric osteomyelitis.

Organisms isolated – Coagulase negative Staphs, Staph aureus, MRSA, E coli, Enterococcus, Enterobacter cloacae, Serratia and 1 Salmonella typhimurium!!

In our cases, a combination of Vancomycin and Gentamicin was added to Stimulan beads following manufacturer's mixing guide. In 2 cases, we added Ceftazidime to the beads and Daptomycin in 1 case.

In bone infections, surgical debridement and systemic antibiotics were also needed. All arthroplasty infections underwent explantation with addition of antibiotic impregnated beads either at single stage or both stages of 2 stage revisions and systemic antibiotics.

Follow up (ranging 9months to 2 years) indicates no failure so far. The beads caused no excessive wound drainage. There was no need to remove beads as they dissolve. In the cases where a staged revision was performed, the beads were inserted at first stage and there was microbiological clearance of infection at 2nd stage. Our series includes some experince in paediatric cases too.

As far as we are aware, this is the largest series in the UK from a single centre reporting experience with Stimulan in infected bone and joints of the lower limbs. Our experience suggests use of dissolvable pure Calcium sulphate beads impregnated with carefully selected antibiotics, works as an effective adjunct to current treatments and offers flexibility with choice of antiobiotics that can be added locally.

Objective

To investigate the reasons for revision of Oxford Unicondylar Knee Replacement (UKR). Does insert size used relate to requirement for revision?

Introduction: Staphylococcus aureus is a major cause of chronic infections and causes particular problems in relation to implanted prostheses. Biofilm formation on abiotic surfaces affords bacteria innate protection from opsonophagocytosis and antibiotic agents and complicates the eradication of infection from bone and implanted prostheses. Increased concentrations of sodium, the major extracellular cation, have previously been implicated in increased biofilm formation in Staphylococcus aureus. In this study we demonstrate that increased concentrations of potassium, the major intracellular cation, also causes a significant increase in biofilm formation. Furthermore we also show that halide stress also leads to a primary increase in penicillin resistance in Staphylococcus aureus. Finally we demonstrate that pbp4, a key gene in cell wall synthesis, is down-regulated under sodium and potassium stress.

Methods: Staphylococcus aureus ATCC 9144 was cultured in broth supplemented with variable amounts of potassium chloride and sodium chloride. Biofilm formation was investigated in 96-well microtiter plates using a standard technique. Antibiotic resistance was investigated using graduated E-test strips. Gene transcription was assessed using RT-PCR.

Results: There was a positive correlation between biofilm formation and increased concentrations of sodium and potassium. Biofilm formation was noted to be even greater under potassium stress than under sodium stress. Sodium stress also lead to a five-fold increase in penicillin resistance in naïve Staphylococcus aureus cells. A key gene involved in cell wall production (pbp4) was down-regulated under sodium (p = 0.03) and potassium (p = 0.03) stress.

Discussion: Cellular injury or insult can lead to cell necrosis and lysis. The intracellular concentration of potassium is 30 times higher than that of the surrounding extracellular fluid. Hence, cell necrosis leads to markedly increased local concentrations of potassium. These experiments show that an increase in potassium concentration leads to an increase in biofilm formation. This suggests that biofilm formation and hence infection of implanted prostheses may be more likely in areas of major tissue trauma such as large resections and revisions. Furthermore, cellular stress leads to increased resistance to penicillin, a cell wall active antibiotic, in naïve cells which may nullify prophylaxis and complicate bacterial eradication in vivo. Finally we postulate a link between the experimental rise in penicillin resistance and the down-regulation of pbp4 demonstrated by RT-PCR under the same halide stresses.

While hidden blood loss has been shown to occur in hip fractures the timing and cause have not yet been demonstrated. This study investigated the degree of pre-operative blood loss within the first 24hrs after intertrochanteric hip fracture.

188 patients with extracapsular hip fractures had their full blood count taken on admission and after 24 hours. The haemoglobin (Hb) and haematocrit (Hct) were noted at each time. Fractures were grouped as undisplaced or displaced. Those who were operated on prior to the 24hr blood sample were excluded. All patients with intracapsular or sub-trochanteric fractures were excluded, as were any who received a blood transfusion prior to their 24hr blood sample being taken. The tests for differences between blood samples and the existence of displacement were performed using paired and independent Student’s t-test. The level of significance was set at P< 0.05. All data was analysed using SPSS statistical software version 11.

The overall fall in the Hb within 24hr was significant (1.6 g/dl, P< 0.001), as was the fall in the haematocrit (0.05, P< 0.05). Displaced fractures had a significantly lower Hb at 24hrs than undisplaced (10.6g/dl vs 11.8 g/dl, P=0.001). The fall in Hb was significantly greater in displaced fractures compared to undisplaced (1.7g/dl vs 1.2g/dl, P< 0.05). Changes in the Hct mirrored those of the Hb.

This study identified a significant blood loss that occurs within the first 24hrs after an intertrochanteric hip fracture, prior to theatre. The cause is unlikely to be secondary to dehydration as the Hct fell with the Hb. Thus the most likely cause is the trauma itself. The admission Hb is possibly an inaccurate measure of the true value and patients may be more shocked than first thought. A more liberal resuscitation policy may be warranted.

Introduction: Staphylococcus aureus is a major cause of chronic infections and causes particular problems in relation to implanted prostheses. Biofilm formation on abiotic surfaces affords bacteria innate protection from opsonophagocytosis and antibiotic agents and complicates the eradication of infection from bone and implanted prostheses. Increased concentrations of sodium, the major extracellular cation, have previously been implicated in increased biofilm formation in Staphylococcus aureus. In this study we demonstrate that increased concentrations of potassium, the major intracellular cation, also causes a significant increase in biofilm formation. Furthermore we also show that halide stress also leads to a primary increase in penicillin resistance in Staphylococcus aureus.

Methods: Staphylococcus aureus ATCC 9144 was cultured in broth supplemented with variable amounts of potassium chloride and sodium chloride. Biofilm formation was investigated in 96-well microtiter plates using a standard technique. Antibiotic resistance was investigated using graduated E-test strips.

Results: There was a positive correlation between bio-film formation and increased concentrations of sodium and potassium. Biofilm formation was noted to be even greater under potassium stress than under sodium stress. Sodium stress also lead to a five-fold increase in penicillin resistance in naïve Staphylococcus aureus cells.

Discussion: Cellular injury or insult can lead to cell necrosis and lysis. The intracellular concentration of potassium is 30 times higher than that of the surrounding extracellular fluid. Hence, cell necrosis leads to markedly increased local concentrations of potassium. These experiments show that an increase in potassium concentration leads to an increase in biofilm formation. This suggests that biofilm formation and hence infection of implanted pros-theses may be more likely in areas of major tissue trauma such as large resections and revisions. Furthermore, cellular stress leads to increased antibiotic resistance in naïve cells which may nullify prophylaxis and complicate bacterial eradication in vivo.

Introduction: The Oxford Knee Score (OKS) is commonly used in the assessment of outcome for knee arthroplasty. All patients having knee arthroplasty at our institution undergo OKS at both nurse led pre-assessment and admission physiotherapy visit, a period of 10 to 30 days pre-operatively. At both instances, the scoring form is left with the patient and collected at the end of the visit.

Anecdotal evidence from our centre suggested that patients attending for arthroplasty surgery were scoring differently at each visit.

The aim of this study is to establish if there is a significant difference OKS at pre-assessment visit and on admission to the ward.

Statistical Method: A pilot study was carried out. A power calculation revealed a requirement for 44 patients to enter the study. The resultant probability was 90 percent that the study would detect a difference at a two sided 5.0 percent significance level, if the minimum clinical difference is 3 points. This is based on the standard deviation of the difference in the response variables of 6. A clinical difference of 3 is drawn from previous studies investigating the use of the OKS.

44 patients undergoing arthroplasty surgery had their OKS for both visits retrospectively analysed.

The mean of the totals of both visits was analysed and found to conform to normality and hence was further investigated by a paired samples t test.

Comparison of individual scoring revealed a violation of normality and hence was further analysed using a Wilcoxon Signed Ranks Test.

Results: A statistically significant result at the 5% level was observed t= 2.197 (44df), p= 0.03. OKS at pre-assessment was lower than at admission to the ward by 1.1 point. (−2.1 – 0.9 95% CI).

Analysis of the individual scoring at both intervals revealed only three of the pairs achieved statistical significance and in each case, the difference was less than 3 scoring units. No significant difference was seen when time between assessments was analysed.

Conclusion: This study demonstrates that although there is a difference in total scoring using the OKS between two patient episodes prior to arthroplasty, a clinically relevant difference is not detected, and neither is a statistically significant difference detected when all scoring steps are analysed.

This work supports earlier studies that pre-operative assessment using the OKS is robust to variance in the pre-operative scoring window.

All patients undergoing knee arthroplasty at our institution complete Oxford Knee Scoring (OKS) at nurse-led pre-assessment and again at an admission physiotherapy visit on the ward which may be up to 2 months later.

The aim of this study is to establish the extended reproducibility of the OKS by statistical analysis of scores taken at these intervals.

44 patients were required to achieve a 90 % probability to detect a difference at a two-sided 5 % significance level with a minimum clinical difference of 3 points, a cut off used in previous works regarding the use of OKS.

Both the overall population means and the differences between individual questions were analysed by a paired samples t test and a Wilcoxon Signed Ranks Test respectively.

Mean interval between attendance for pre-assessment and admission visit was 16 days (7–60).

A statistically significant result at the 5% level was observed for the t test t= 2.197 (44df), p= 0.03. OKS at pre-assessment was lower than at admission to the ward by 1.1 point. (−2.1 – 0.9 95% CI).

Analysis of difference between individual questions revealed only three of the pairs achieved statistical significance and in each case, the difference was less than 3 scoring units.

This study demonstrates that although there is a difference in total scoring using the OKS between two patient episodes prior to arthroplasty, a clinically relevant difference is not detected, and neither is a statistically significant difference detected when all scoring steps are analysed.

The original validation of the OKS was obtained using test-retest reproducibility over a 24 hour period. This work shows that the OKS is robust to violations in reproducibility at duration much greater than this and for practical purposes is valid if taken at any point during the pre-admission phase of care.

Background: In a recent publication from the National Joint Registry it was suggested that prosthesis type influenced patient satisfaction at one year following knee arthroplasty. In this report Unicondylar Replacement (UKR) was associated with lower levels of patient satisfaction when compared to cemented TKR. The unicondylar group did however have a significantly lower Oxford Knee Score (OKS) than the TKR group and this occurred irrespective of patient age.

A common perception is that UKR is only offered to patients with lesser disease, with a decreased clinical profile. This may explain their higher levels of dissatisfaction as the overall change in their OKS from pre to post operation would be relatively smaller than for TKR.

Aim: We hypothesised that patients listed for UKR have less severe disease and therefore a lower preoperative OKS when compared to TKR.

Methods: After sample size calculation we retrospectively analysed 76 patients who underwent either UKR or TKR under the care of a single surgeon. OKS was recorded at a dedicated pre-assessment clinic. The decision to offer UKR was based on clinical and radiological criteria as outlined by the Oxford group.

Results: There were 38 patients in either group. The mean pre-operative OKS was 39.5 (26–56, SD 7.6) in the UKR group and 41.6 (31–51, SD 5.7) in the TKR group. There was no statistical difference between these two groups (p=0.18).

Discussion: Patients listed for knee replacement have significant pain and functional impairment. In our population those suitable for UKR have similarly severe symptoms to those who do not meet the criteria for UKR and are only eligible for TKR. It remains unclear why patients undergoing UKR should be less satisfied when they have better post operative patient reported outcome scores. It emphasizes the need for careful patient selection and counselling in patient undergoing UKR.

A phenomenon of methicillin resistance in methicillin sensitive Staphylococcus aureus has been noted in organisms living in biofilm induced by the state of cell wall deficiency. The rate and the amount of biofilm formed by the cell wall deficient organisms far exceeds that of cell wall patent organisms. Once removed from the biofilm the S. aureus had the same sensitivities of the original organism. Cell wall deficient organisms outside the biofilm did not demonstrate the methicillin resistance. A known laboratory strain (ATCC 9144) was induced into a cell wall deficient state and allowed to form biofilm. The rate of formation and amount formed was compared with that formed by cell wall patent organisms. Before inducing cell wall deficiency sensitivity to methicillin was demonstrated using standard microbiological technique. Using an oxacillin containing plate as a culture medium: the biofilm, cell wall deficient organisms and the cell wall competent organisms were inoculated onto separate media. Organisms from the biofilm were isolated and grown free of the biofilm on blood agar. Any growth on the oxacillin containing plate would demonstrate methicillin resistance. There was no growth on the plates containing the cell wall competent or cell wall deficient organisms. There was however growth on the plate inoculated with bio-film, however when organisms were isolated from the biofilm, there was no growth on the media. Antibiotic sensitivities of the original inoculant and the organisms isolated from the biofilm were the same. The biofilm, induced as a result of cell wall deficiency, offers a form of structural protection to the Staphylococcus aureus without altering the resistance pattern of organism. Standard microbiological techniques would therefore report the organism as methicillin sensitive, however clinically the organism may behave as a methicillin resistant organism. The state of cell wall deficiency encourages the formation of biofilm in S. aureus. In-vitro the state of cell wall deficiency is induced using high osmolality media or sub-lethal doses of cell wall active antibiotics. Both these states are found in clinical practice.

The use of sub-lethal doses of cell wall active antibiotics to induce cell wall deficiency in S aureus has been described. Cell Wall Deficient S aureus show an increased in-vitro ability to form biofilm. Cephalosporins(cell wall active antibiotics.) are commonly used at time of arthroplasty surgery as antimicrobial prophylaxis. Adherence is fundamental step in biofilm formation.

The adherence of cell wall deficient S aureus versus ‘wild type’ S aureus to glass was investigated. Slides comparing the two types of organisms were analysed using fluoroscopy and J-image software. The ability to adhere to plastic was investigated using a micro-titre based absorption test. In a third investigation a centrifugal force was used to quantify the adherence ability of the cell wall deficient organisms to the glass slides.

The cell wall deficient organisms demonstrated an increased ability to adhere to glass compared to the ‘wild type’. After exposure, there was on average twenty times more cell wall deficient organisms per unit area compared to the ‘wild-type’. The micro-titre plates were similar. After incubation, the absorption of each well was measured. Compared to the ‘wild type’ there was a significantly increased absorption in wells containing the cell wall deficient organisms. Showing an increased ability to adhere to plastic. The third technique quantified the ability to adhere using a centrifugal force. The slides were exposed to ‘wild type’ and cell wall deficient organisms, however before staining they were placed in a centrifuge. On analysis there were five cell wall deficient S aureus per field of view, compared to 0.5 ‘wild-type’.

An increased ability of cell wall deficient S aureus to adhere to surfaces has been shown. Adherence is fundamental to biofilm formation. The significance to orthopaedics is that the inadequate use of Cephalosporins at time of operation may be facilitating chronic infections.

This study set out to determine the incidence of avulsion of the posterior horn of the lateral meniscus in isolated Anterior cruciate ligament injuries.

Anterior cruciate injuries are often associated with meniscal injuries and a number of different patterns of injuries are described. Although avulsion of the posterior horn of the lateral meniscus has been reported in combined ACL/MCL injuries this has not been reported in isolated ACL injuries. We examined 25 consecutive patients who had ACL ruptures and recorded the presence or absence of an avulsed posterior horn of the lateral meniscus. The mechanism of injury was also recorded. We found 6 patients (24%) with avulsion of the posterior horn of the lateral meniscus from its tibial attachment. All these patients had an external rotation injury rather than a valgus type injury.

Avulsion of the posterior horn of the lateral meniscus is a relatively common finding in ACL injury. If this injury occurs the normal load sharing function of the meniscus may not be present and this may be part of the explanation for the development of degenerative change in the ACL injured knee.

There are various methods of measuring proprioception at the knee. Beard et al (1993) have described a delay in reflex hamstring contraction in anterior cruciate deficient knees. We have repeated their experiment and were unable to detect any significant difference in reflex hamstring contraction between the injured and uninjured legs. We discuss possible neurophysiological and biomechanical causes for the conflicting results and conclude that this method may not be a valid measure of proprioception.