Background

We switched our antibiotic prophylaxis for elective hip and knee surgery from cefuroxime to flucloxacillin with single dose gentamicin in order to reduce the incidence of C. Diff diarrhoea. More patients subsequently appeared to develop acute kidney injury (AKI).

SIGN guidelines advise the use of flucloxacillin and gentamicin instead of cefuroxime as antibiotic prophylaxis for elective hip and knee arthroplasty. It is our impression that this change in practice has been associated with an increased risk of acute kidney injury (AKI).

During a twelve month period we examined the incidence of AKI sequentially in four groups of patients: cefuroxime prophylaxis (n = 46); high dose flucloxacillin (5-8g) with single shot gentamicin (n = 50); low dose flucloxacillin (1-4 g) with single shot gentamicin (n = 45); and finally cefuroxime again (n = 52).

There were no statistically significant differences by chi-square tests for age, gender, operation (hip or knee), ASA, anaesthesia, baseline serum creatinine, hypertension, diabetes or pre-operative medication. The proportion of patients in each antibiotic group with any form of AKI by RIFLE criteria was: cefuroxime group 1 (9%), high dose flucloxacillin (52%), low dose flucloxacillin (22%), cefuroxime 2 (14%) (p < 0.0001 by chi-square test). Odds ratios (OR) for AKI derived from a multivariate logistic regression model and assigning an OR of 1 to cefuroxime group 1 was: high dose flucloxacillin 14.5 (95% CI, 4.2, 50.2); low dose flucloxacillin 3.0 (0.8-10.9) and cefuroxime group 2 1.9 (0.5, 7.4). Three patients in the high dose flucloxacillin group required temporary haemodialysis.

We have shown a strong association between high dose prophylactic flucloxacillin and subsequent development of AKI. We have no reason to believe that this was confounded by any of the co-variates we measured.

Post-operative regimes involving the use of intra-articular local anaesthetic infiltration may allow early mobilisation in patients undergoing total knee arthroplasty. Few studies have evaluated such regimes outside specialist arthroplasty units. We aimed to determine whether an enhanced recovery programme including the use of local anaesthetic administration could be adapted for use in a district general setting.

Following introduction of this regime to our unit, 100 consecutive patients undergoing primary total knee arthroplasty were reviewed. 56 patients underwent a standard analgesic regime involving a general or spinal anaesthetic and oral analgesics post operatively (group1). 48 patients underwent the newly introduced regime, which included pre-operative counselling, peri-articular local anaesthetic infiltration at operation and intra-articular local anaesthetic top-up administration post-operatively for 24 hours (group 2). Length of stay, post-operative analgesic requirements, and range of knee motion post-operatively were compared.

Median length of stay was less for patients in group 2 compared with those in group 1 (4 days compared to 5 days, p<0.05). Patients in group 2 required lower total doses of opiate analgesia post-operatively. 90% of patients in group 2 were ambulant on the first post operative day, compared with less than 25% of patients in group 1. Mean knee flexion on discharge was greater in patients in group 2 compared with those in group 1 (85 degrees compared with 75 degrees). No infective complications from intra-articular catheter placement were observed. However, technical difficulties were encountered during the introduction period, including loss of catheter placement, leakage of local anaesthetic and adaptation of nursing time for top-up anaesthetic administration.

A rehabilitation regime involving local anaesthetic infiltration for total knee arthroplasty can successfully be adapted for use in a district general setting. Our results suggest if initial technical difficulties are overcome, this regime can provide effective postoperative analgesia, early mobilisation and reduced hospital stay.

Introduction: Bone loss following hip replacement is common. Its role in prosthesis stability and survival is a concern. DXA allows the assessment of adaptive bone remodelling and resorption. We prospectively examined longitudinal bone density changes affecting the Elite Plus [DePuy International Ltd], Leeds, UK), the Ultima Straight Stem (USS) [DePuy], the Exeter [Stryker Howmedica International Ltd, London, UK] and the Ultima Tapered Polished Stem (TPS) [DePuy] to determine whether bone loss was design dependent.

Methods: 164 patients were randomised to one of 4 stem designs. Patients received DXA peri-prosthetic examinations using the LUNAR EXPERT-XL at 7 days, then at

6, 12, 18 and 24 months. Custom analysis software was used to improve precision. Zones were excluded if identified as affected by heterotopic ossification post surgery. For each group the mean and standard error was determined for each follow up. 137 had follow up data to 24 months.

Results: Considering the whole peri-prosthetic region, all stems lost 5–9% BMD in the first 6 Months. The USS lost the most bone and the tapered stems, the Exeter and the TPS the least. Over the next 18 months changes were no more than 2%. The greatest losses were in the proximal zones, ranging between 8 and 20%. The USS lost significantly more (p < 0.05) than the others at 24 months. In zone 5 the TPS exhibited significantly higher recovery than the other designs at 24 months.

Discussion: Whilst the bone remodelling of the two tapered designs was largely equivalent, they exhibited a significant difference in the distal medial region. This study shows evidence that non-subsiding stems lose more bone than tapered subsiding designs.

Introduction: Heterotopic ossification (HO) is common post total hip replacement. Dual energy x-ray absorptiometery (DXA) is an established technique used to assess peri-prosthetic, bone mineral density (BMD) changes in the femur following surgery. The effect of HO on these measurements has not previously been reported. In this study we investigated the incidence and distribution of HO and the extent to which it affected peri-prosthetic DXA results.

Methods: As part of a two-year, prospective, primary cemented THR trial, 137 patients were assessed at six month intervals with DXA as well as anterior-posterior and lateral radiographs. HO was identified from radiographs and then further localised to the seven femoral Gruen zones using DXA subtraction imaging.

Results: HO affected at least one Gruen zone in 46% of study patients. The mean BMD in zone 1 dropped to 89% of the postoperative value in unaffected patients by six months whereas it actually increased to 102% in the HO patients (p< 0.001). This 12% difference persisted throughout the duration of the trial. Zone two was affected in 17 patients and a significant gain of 5% was noted in these patients at 12 months (p< 0.05). From observation of AP x-rays alone, 12% of the HO cases would have been missed.

HO was found to be significantly associated with male gender and increasing age at time of operation. Surgical approach to the hip also had an effect, osteotomies producing a greater incidence of HO formation.

Discussion: HO has a dramatic effect on BMD values determined by DXA. This has not previously been reported and may have affected other peri-prosthetic studies. We recommend careful screening for HO when reporting femoral peri-prosthetic BMD changes.

Introduction: Dual Energy x-ray absorptiometery (DXA) is a useful tool for the assessment of peri-prosthetic bone mineral changes following total joint replacement. In order to assess these changes the precision of the DXA technique must be optimised. While patient positioning is an important factor, the role of the analysis software should also be considered. We developed and applied a new image analysis method to data from the EXPERT-XL fan beam densitometer (LUNAR GE, USA) aiming to improve reproducibility of bone region and tissue type determination by the analysis software.

Methods: 60 patients with cemented THR received repeat same day DXA examinations. These were initially analysed strictly according to the manufacturer’s femoral peri-prosthetic protocol. A modification of this protocol was attempted allowing further small corrections to the tissue typing by the operator. The scans were then reanalysed using locally developed image analysis to accurately determine the bone, prosthesis and Gruen zone boundaries. The coefficient of variation (CV) was calculated from the differences of the repeat examinations for each of the seven Gruen zones and for the whole peri-prosthetic region.

Results: The average zone CV was 5%. The poorest was zone 1 (10%) and best zone 4 (2%). With the operator corrections there was an overall 4% improvement. With our method there was an overall 40% reduction in variation (average CV 3%, maximum 4%, minimum 2%). The whole region CV was 3.1% for the standard method 2.7% modified and 1.3% for our method.

Discussion: Our method significantly improved the reproducibility of EXPERT analysis. This study demonstrates the high dependency of DXA precision on robust regional analysis.