Background

Tourniquets are routinely used in total knee arthroplasty (TKA) with an estimated use by up to 93% of surgeons. Advantages include the ability to provide a bloodless field of view to facilitate cement application and increase the success of the procedure. Overall reduction in blood loss is another perceived advantage, however recent research has demonstrated no measurable reduction and conversely a substantial increase in complications such as deep vein thrombosis and systemic emboli. Given the significant complications of tourniquet use we aim to identify patients’ views on tourniquets and of emphasis their awareness of the possible risks involved prior to the procedure.

Background

Traditionally, a Surgical Tourniquet (ST) is used during Total Knee Replacement Surgery (TKRS) to prevent blood flow to the leg and improve the surgical field of view. The use of a ST is known to increase the risk of venous thromboembolism. Echogenic material, suggestive of emboli has been observed in the brain following ST deflation in TKRS despite the absence of a patent foramen ovale, likely through pulmonary shunts. The aim of this study was to assess whether cerebral emboli result from tourniquet use in TKRS and the sequelae of any emboli.

Background

Tourniquets are routinely used in total knee arthroplasty (TKA) with an estimated use by up to 93% of surgeons. Advantages include the ability to provide a bloodless field of view to facilitate cement application and increase the success of the procedure. Overall reduction in blood loss is another perceived advantage, however recent research has demonstrated no measurable reduction and conversely a substantial increase in complications such as deep vein thrombosis and systemic emboli. Given the significant complications of tourniquet use we aim to identify patients' views on tourniquets and of emphasis their awareness of the possible risks involved prior to the procedure.

The cement used for hemiarthroplasties by the authors and many other surgeons in the UK is Palacos® (containing 0.5g Gentamicin). Similar cement, Copal® (containing 1g Gentamicin and 1g Clindamycin) has been used in revision arthroplasties. We aim to investigate the effect on SSI rates of doubling the gentamicin dose and adding a second antibiotic (clindamycin) to the bone cement in hip hemiarthroplasty.

We randomised 848 consecutive patients undergoing cemented hip hemiarthroplasty for fractured NOF into two groups: Group I, 464 patients, received standard cement (Palacos®) and Group II, 384 patients, received high dose, double antibiotic-impregnated cement (Copal®). We calculated the SSI rate for each group at 30 days post-surgery. The patients, reviewers and statistician were blinded as to treatment group.

The demographics and co-morbid conditions were statistically similar between the groups. The combined superficial and deep SSI rates were 5 % (20/394) and 1.7% (6/344) for groups I and II respectively (p=0.01). Group I had a deep infection rate 3.3 %(13/394) compared to 1.16% (4/344) in group II (p=0.082). Group I had a superficial infection rate 1.7 % (7/394) compared to 0.58% (2/344) in group II (p=0.1861). 33(4%) patients were lost to follow up, and 77 (9%) patients were deceased at the 30 day end point.

Using high dose double antibiotic-impregnated cement rather than standard low dose antibiotic-impregnated cement significantly reduced the SSI rate (1.7% vs 5%; p=0.01) after hip hemiarthroplasty for fractured neck of femur in this prospective randomised controlled trial.

Currently, the cement being used for hemiarthroplasties and total hip replacements by the authors and many other surgeons in the UK is Palacos® (containing 0.5g Gentamicin). Similar cement, Copal® (containing 1g Gentamicin and 1g Clindamycin) has been used in revision arthroplasties, and has shown to be better at inhibiting bacterial growth and biofilm formation. We aim to investigate the effect on SSI rates of doubling the gentamicin dose and adding a second antibiotic (clindamycin) to the bone cement in hip hemiarthroplasty.

We randomised 848 consecutive patients undergoing cemented hip hemiarthroplasty for fractured NOF at one NHS trust (two sites) into two groups: Group I, 464 patients, received standard cement (Palacos®) and Group II, 384 patients, received high dose, double antibiotic-impregnated cement (Copal®). We calculated the SSI rate for each group at 30 days post-surgery. The patients, reviewers and statistician were blinded as to treatment group.

The demographics and co-morbid conditions (known to increase risk of infection) were statistically similar between the groups. The combined superficial and deep SSI rates were 5 % (20/394) and 1.7% (6/344) for groups I and II respectively (p=0.01). Group I had a deep infection rate 3.3 %(13/394) compared to 1.16% (4/344) in group II (p=0.082). Group I had a superficial infection rate 1.7 % (7/394) compared to 0.58% (2/344) in group II (p=0.1861). 33(4%) patients were lost to follow up, and 77 (9%) patients were deceased at the 30 day end point. There was no statistical difference in the 30 day mortality, C. difficile infection, or the renal failure rates between the two groups.

Using high dose double antibiotic-impregnated cement rather than standard low dose antibiotic-impregnated cement significantly reduced the SSI rate (1.7% vs 5%; p=0.01) after hip hemiarthroplasty for fractured neck of femur in this prospective randomised controlled trial.

Background: There are no large comparative metal ion studies of commercially available hip resurfacing devices which have taken into account the effects of femoral size and cup inclination and anteversion.

Patients and methods: Metal ion analysis is carried out routinely at our independent centre. We present the metal ion results of 95 unilateral ASR patients and 70 unilateral BHR patients. For all patients, acetabular cup orientation was assessed using EBRA software. Patients with other metallic implants and those within 12 months of surgery were excluded.

Results: Whole blood/serum chromium (Cr) and cobalt (Co) concentrations were inversely related to femoral component size in both the ASR and BHR group (p< 0.05). Cr and Co levels were only seen to increase in the BHR group when the cup was implanted with an inclination greater than 55°. A significant relationship was identifed between the anteversion of the BHR cup and Cr and Co (p< 0.05 for Co, Spearman Rank correlation), with an increase in ions observed at anteversion angles > 17°. Cr and Co were more strongly influenced by cup position in the case of the ASR, with an increase in metal ions observed at inclinations greater than 45° and anteversion angles of < 10° and > 20°.

Discussion: The increased tolerance of the BHR cup to inclinations between 45–55° is likely due to the larger BHR cup providing greater protection against edge loading. When the cohort was divided by gender, the median Cr concentrations of the male ASR patients were significantly lower than those of the BHR males (p< 0.001). This suggests that in larger components positioned at more satisfactory angles of inclination and anteversion, the lower clearance of the ASR proves more significant than the extra coverage provided by the BHR cup. The BHR appears to be more sensitive to changes in anteversion than inclination.

Introduction: MEPE was identified in patients with tumors and oncogenic hypophosphatemic osteomalacia (OHO), and therefore thought to inhibit osteoblast differentiation and proliferation. However when looking at the structure of MEPE in detail a number of important domains are observed, including a glycosamino-glycan-attachment site, and a RGD cell-attachment motif. The RGD motif is by far the best characterized peptide sequence for stimulating cell adhesion on synthetic surfaces. Glycosaminoglycan attached to MEPE also has the potential to interact with numerous growth factors, proteases and cell surface receptors. MEPE shares molecular similarities with several dentin-bone phosphoglycoproteins which exhibit an ASARM motif shown to potently inhibit calcium crystallization and crystal growth in the salivary duct system. More recently the ASARM peptide sequence has been shown to be a inhibitor of osteoblast mineralization.

Method: To test the hypothesis that MEPE has multiple functional sites, PCR Primers were designed to provide a truncated MEPE protein, which contained pro-osteogenic motifs and had the anti-osteogenic ASARM motif removed. PCR products were cloned using the pBAD TOPO® TA Expression Kit. MEPE was than expressed in E. coli and purified by HIS column chromatography. Expression of truncated MEPE was confirmed by coomassie staining, Western blot with an antibody to an epitope tag and sequence analysis. Truncated MEPE was passively absorbed overnight at 4 oC in a 96 well plate (0.3–50 micrograms) and Fibronectin was laid down (30 micrograms) as a positive control. Primary rat osteoblasts in serum free medium were seeded into the wells (10,000 cells/well) in triplicate and incubated at 37oC for 24 hours. MTT assay was used to estimate cell number, the coloured product absorbance was then determined at 490nm and adhesion was expressed relative to fibronectin. In addition we laid down truncated MEPE into three 8 well chamber slides as above. This was left overnight at 4 oC. Primary rat osteoblasts were then seeded into the wells (10,000 cells/well) in triplicate and incubated at 37oC for 4 hours in serum free medium. Cells were viewed and images captured with a phase contrast microscope.

Results: We have successfully expressed MEPE in E. Coli and devised a purification strategy for obtaining protein. This has been confirmed by coomassie, silver stain and Western blot analysis. The MTT assay showed a significant increase in cell adhesion and proliferation within wells coated with 50 micrograms (70% +/− 0.67(relative to fibronectin)), 30 micrograms (63% +/− 0.81), 3 micrograms (54% +/− 2.4) of MEPE when compared with TCP (32% +/− 0.56). Furthermore we have shown increased osteoblast spreading with increasing dose when compared to tissue culture plastic alone.

Conclusion: The data shows a dose dependent response of osteoblast to increasing concentrations of the novel MEPE protein. This provides evidence that MEPE without the ASARM domain increases osteoblast adhesion, cell anchorage and spreading. Further studies are currently been undertaken to establish its long term effects on osteoblast function and suitability for incorporation into orthopaedic biomaterials.