Biomechanical Study Comparing Cut-out Resistance of the X-Bolt® and Dynamic Hip Screw at Various Tip-Apex Distances

BACKGROUND

Bone quality in hip fractures is poor and there is a need to not only correctly position metalwork within the femoral head, but also for implants to resist cut-out. New implant designs may help to reduce metalwork cut-out, leading to fewer failures of fixation. This study compared the cut-out strength of a Dynamic Hip Screw (DHS) to that of an X-Bolt® (X-Bolt Orthopaedics, Dublin, Ireland) implant in an osteoporotic Sawbones® (Sawbones, Vashon Island, WA) model.

METHODS

An unstable fracture model (AO 31-A2) was created using low-density 5 pound per cubic foot (pcf) Sawbones®. The DHS and X-Bolts® were inserted into the Sawbones® femoral head at Tip-Apex Distances (TAD) of 10mm, 15mm, 20mm, 25mm, 30mm and 40mm. A cyclic-loading Instron® machine (Instron Corp., Norwood, MA) pushed the bone at a compression rate of 5mm per minute at a 20-degree angle to the axis of the implant with an upper force limit of 4000N. Maximum force reached and load to failure, defined as movement of the implant by 5mm, were recorded. Four implants were used per group to give a total of 48 tests between the two groups.

RESULTS

The X-Bolt® demonstrated a superior average maximum total load push-out force compared to the DHS group for all of the TAD configurations tested. The maximum force reached in the X-Bolt® group was significantly higher than that in the DHS group at a TAD of 10mm (X-Bolt® 3299.25N vs. DHS 2843.75N, P<0.029) and 30mm (X-Bolt® 2908.25N vs. DHS 2030N, P<0.029). The X-Bolt® also had a higher load to failure than the DHS group at all of the TAD values tested.

CONCLUSIONS

The X-Bolt® implant gave superior performance compared to the standard DHS, as reflected by a greater push-out force in an osteoporotic Sawbones® model.

Delivering a quality-assured fracture liaison service in a UK teaching hospital-is it achievable?

To determine whether new national guidance on the specifications of a fracture liaison service are realistically deliverable, 1 year of data on the performance of such a service were audited. Audit targets were mostly met. This audit demonstrates that these standards are deliverable in a real world setting.

INTRODUCTION

UK service specifications for a fracture liaison service (FLS) have been produced (National Osteoporosis Society, NOS) to promote effective commissioning and delivery of the highest quality care to patients with fragility fractures. How deliverable these standards are has not as yet been methodically reported. Our FLS was modelled on the ten NOS standards; performance was audited after 1 year to determine whether these standards could be delivered and to describe the lessons learnt.

METHODS

Performance was audited against the NOS FLS Service Standards, with management based on the Fracture Risk Assessment Tool (FRAX®), the four-item Falls Risk Assessment Tool (FRAT), National Institute for Health and Care Excellence (NICE) and the National Osteoporosis Guideline Groups (NOGG) guidance. Data were recorded prospectively on a database. The FLS commenced in May 2014, was fully operational in August 2014 and data were captured from 1 September 2014 to 1 September 2015.

RESULTS

The FLS detected 1773 patients and standards were largely achieved. Most, 94 %, patients were seen within 6 weeks, 533 DXA requests were generated, 804 outpatient FRAT assessments were recorded (134 required falls intervention) and 773 patients had bone treatments started. On follow-up at 3 months, between 78-79 % were still taking medication.

CONCLUSIONS

Preliminary evaluation of a FLS implemented according to UK NOS standards demonstrates that the model is practical to apply to a large teaching hospital population. Collection and review of outcome and cost effectiveness data is required to determine the performance of this model in comparison with existing models.

Outcomes of infected revision knee arthroplasty managed by two-stage revision in a tertiary referral centre

BACKGROUND

A two-stage revision remains the gold standard to eradicate deep infection in total knee arthroplasty. Higher failure rates are associated with a number of factors including poly-microbial infections, multiresistant organisms and previous operations. The aims are to investigate [1] the overall success rate of a two-stage revision for infections in TKA, [2] the outcome of repeat two-stage revisions in recurrent infections and [3] the factors affecting the outcomes of such cases.

METHODS

We present the outcomes of a consecutive, retrospective case series of 51 periprosthetic joint infections managed with a two-stage revision knee arthroplasty over a three year period.

RESULTS

Forty-six (90%) of 51 were referred from other hospitals. Infection was successfully eradicated in 24 (65%) of 37 patients undergoing an initial two-stage procedure. Following a failed two-stage revision, a repeat two-stage revision was performed in 19 patients eradicating infection in 8 (42%). A third two-stage was performed in five of these patients eradicating infection in three with an average follow-up of 43 months. Multidrug resistance was present in 69%, and 47% of the patients were infected with multiple organisms. All unsuccessful outcomes involved at least one multidrug-resistant organism compared to 43% in the successful cohort (P=0.0002). Serological markers prior to a second-stage procedure were not significantly different between successful and unsuccessful outcome groups.

CONCLUSION

Single or multiple two-stage revisions can eradicate infection despite previous failed attempts. In this series, failure is associated with multidrug resistance, previous failed attempts to eradicate infection and a less favourable host response.

In vivo roughening of retrieved total knee arthroplasty femoral components

BACKGROUND

Joint registry data highlights the higher rates of cumulative revision for younger patients undergoing TKR. One of the reasons associated with this higher revision rate may be due to the wear of the UHMWPE leading to loosening. Alternate bearing surfaces have been developed to address this problem; however, roughening of the metal bearing surface has not been demonstrated in vivo.

METHOD

We recorded roughness measurements of retrieved femoral components.

RESULTS

Average lateral condyle roughness was 0.032 μm, compared to control values of 0.020 μm, p=0.002; average medial condyle roughness was 0.028 μm, compared to a control value of 0.019, p<0.001.

CONCLUSION

There was a small but statistically significant roughening of femoral components in vivo compared to controls. This may have important implications for aseptic loosening of knee arthroplasty components and the decision to use scratch resistant components.

Advanced wear of an Oxinium™ femoral head implant following polyethylene liner dislocation

Oxinium™ (Smith & Nephew, Memphis, TN, US) has been used in hip arthroplasty since 2003. The surface coating is hard and provides low wear rates but if this surface coating is damaged, the soft metal core is at risk of accelerated wear. Previous reports have described accelerated wear following intra and postoperative hip dislocation. We report a case of advanced wear of an in situ Oxinium™ femoral head implant following a cracked acetabular liner. The liner had disengaged from the titanium shell, allowing the Oxinium™ head to articulate directly with the shell. The disengaged liner led to dislocation of the Oxinium™ head, with associated pronounced wear of the head and the acetabular cup. The patient had a successful revision procedure. We advise close follow-up of patients with Oxinium™ implants, especially if associated with dislocation and closed reduction.

Advanced wear of an Oxinium™ femoral head implant following polyethylene liner dislocation

Oxinium™ (Smith & Nephew, Memphis, TN, US) has been used in hip arthroplasty since 2003. The surface coating is hard and provides low wear rates but if this surface coating is damaged, the soft metal core is at risk of accelerated wear. Previous reports have described accelerated wear following intra and postoperative hip dislocation. We report a case of advanced wear of an in situ Oxinium™ femoral head implant following a cracked acetabular liner. The liner had disengaged from the titanium shell, allowing the Oxinium™ head to articulate directly with the shell. The disengaged liner led to dislocation of the Oxinium™ head, with associated pronounced wear of the head and the acetabular cup. The patient had a successful revision procedure. We advise close follow-up of patients with Oxinium™ implants, especially if associated with dislocation and closed reduction.

The impact of trauma centre designation on open tibial fracture management

INTRODUCTION

The British Orthopaedic Association/British Association of Plastic, Reconstructive and Aesthetic Surgeons guidelines for the management of open tibial fractures recommend early senior combined orthopaedic and plastic surgical input with appropriate facilities to manage a high caseload. The aim of this study was to assess whether becoming a major trauma centre has affected the management of patients with open tibial fractures.

METHODS

Data were obtained prospectively on consecutive open tibial fractures during two eight-month periods: before and after becoming a trauma centre.

RESULTS

Overall, 29 open tibial fractures were admitted after designation as a major trauma centre compared with 15 previously. Of the 29 patients, 21 came directly or as transfers from another accident and emergency deparment (previously 8 of 15). The time to transfer patients admitted initially to local orthopaedic departments has fallen from 205.7 hours to 37.4 hours (p=0.084). Tertiary transferred patients had a longer hospital stay (16.3 vs 14.9 days) and had more operations (3.7 vs 2.6, p=0.08) than direct admissions. As a trauma centre, there were improvements in time to definitive skeletal stabilisation (4.7 vs 2.2 days, p=0.06), skin coverage (8.3 vs 3.7 days, p=0.06), average number of operations (4.2 vs 2.3, p=0.002) and average length of hospital admission (26.6 vs 15.3 days, p=0.05).

CONCLUSIONS

The volume and management of open tibial fractures, independent of fracture grade, has been directly affected by the introduction of a trauma centre enabling early combined senior orthopaedic and plastic surgical input. Our data strongly support the benefits of trauma centres and the continuing development of trauma networks in the management of open tibial fractures.

Gluteal necrosis following pelvic fracture and bilateral internal iliac embolization: Reconstruction using a transposition flap based on the lumbar artery perforators

INTRODUCTION

The use of bilateral internal iliac artery embolization to control hemorrhage associated with pelvic fractures is a life saving intervention. Gluteal necrosis is a rare but potentially fatal complication of this procedure. Following debridement, reconstruction can present a considerable challenge due to the compromised vascularity of local tissue.

PRESENTATION OF CASE

A 17 year old girl suffered an open book pelvic fracture following a road traffic accident. In order to stop profuse bleeding, bilateral internal iliac artery embolization was performed. This procedure was complicated by the development of right sided gluteal necrosis. Following extensive debridement, a transposition flap based on the lumbar artery perforators was performed to cover the soft tissue defect.

DISCUSSION

Gluteal necrosis occurs in approximately 3% of cases following internal iliac artery embolization. Following complete excision of the devitalised tissue reconstructive surgery is necessary. Local flaps are suboptimal options when the integument supplied by branches of the internal iliac arteries has been compromised following embolization. Furthermore, the use of a free flap is restricted by the lack of a readily accessible undamaged recipient vessel. In the present case a transposition flap based on the lumbar artery perforators facilitated robust reconstruction of the buttock region.

CONCLUSION

To avoid sepsis, it is imperative that gluteal necrosis following internal iliac artery embolization is recognized and promptly debrided. A transposition flap based on the lumbar artery perforators is a good option for subsequent soft tissue coverage, which avoids use of tissue supplied by the branches of the internal iliac arteries.

Delayed diagnosis of pseudoaneurysm formation in a patient with diaphyseal aclasis

A 15 year old boy, with known diaphyseal aclasis, presented with a swollen left leg. The diagnosis of popliteal pseudoaneurysm, a known and well understood vascular complication, was delayed due to presentation suggestive of a chondrosarcoma. In this age group, sarcomatous change is more common and a potentially sinister complication of diaphyseal aclasis. Following a sarcoma MDT referral, the correct diagnosis was confirmed by ultrasound and CT angiogram. This case identifies one of the largest, non-ruptured popliteal pseudoaneurysms reported and illustrates an unusual complication of a rare orthopaedic genetic condition, which is potentially limb threatening.

The knee in full flexion: an anatomical study

There has been only one limited report dating from 1941 using dissection which has described the tibiofemoral joint between 120 degrees and 160 degrees of flexion despite the relevance of this arc to total knee replacement. We now provide a full description having examined one living and eight cadaver knees using MRI, dissection and previously published cryosections in one knee. In the range of flexion from 120 degrees to 160 degrees the flexion facet centre of the medial femoral condyle moves back 5 mm and rises up on to the posterior horn of the medial meniscus. At 160 degrees the posterior horn is compressed in a synovial recess between the femoral cortex and the tibia. This limits flexion. The lateral femoral condyle also rolls back with the posterior horn of the lateral meniscus moving with the condyle. Both move down over the posterior tibia at 160 degrees of flexion. Neither the events between 120 degrees and 160 degrees nor the anatomy at 160 degrees could result from a continuation of the kinematics up to 120 degrees . Therefore hyperflexion is a separate arc. The anatomical and functional features of this arc suggest that it would be difficult to design an implant for total knee replacement giving physiological movement from 0 degrees to 160 degrees .

Fatty acid balance studies in preterm infants fed formula milk containing long-chain polyunsaturated fatty acids (LCP) II

A milk formula (Prematil-LCP) containing long-chain polyunsaturated fatty acids (LCP) and with a fatty acid profile closely resembling breast milk has recently been introduced for preterm infants. A double-blind randomized controlled trial was performed comparing fatty acid absorption from Prematil-LCP (n=10) and standard Prematil (n=10). Formula-fed preterm infants underwent 3 d fat balances (once full enteral feeds were established) along with a parallel human milk fed group (n=11). Plasma samples were taken on the last day. Median total fat excretion (absorption, %) was 2.34g kg(-1) (82.0), 2.64g kg(-1) (82.9) and 1.65g kg(-1) (87.8) with Prematil, Prematil-LCP and human milk feeding, respectively. This reflected differences in the excretion and absorption of long-chain saturated fatty acids. All groups excreted detectable LCP. LCP disappearance was higher in infants fed human milk than in those fed Prematil-LCP, particularly for n-6 LCP (p < 0.01). Nevertheless, excreted LCP equated to < 30% dietary intake, with Prematil-LCP feeding. Plasma lipid fatty acid composition reflected differences in dietary LCP intake.

Fatty acid balance studies in term infants fed formula milk containing long-chain polyunsaturated fatty acids

Long-chain polyunsaturated fatty acids (LCP) are thought to be required for optimal nervous system development in the newborn. A commercial milk formula containing LCP (Aptamil-LCP) with a fatty acid profile closely resembling breast milk, has recently been introduced for term infants. The absorption of fatty acids in term infants was examined in a double-blind randomized controlled trial comparing Aptamil-LCP (n = 20) and standard Aptamil (n = 20). Formula-fed newborn infants were studied from birth for 14 d. Fat balances (3 d) were performed from d 10. A 3-d stool collection was performed from d 10 in a parallel breastfed group (n = 21). Plasma samples were taken on d 6. Median fat excretion (mg kg[-1]) was 897.1, 615.0 and 355.2 with Aptamil, Aptamil-LCP and breastfeeding, respectively. The median total fat absorption coefficient in Aptamil-LCP-fed infants was higher than in those fed standard Aptamil (p < 0.01). These findings were accounted for by differences in the excretion and absorption of long-chain saturated fatty acids (C14:0, C16:0 and C18:0). Higher fat excretion was associated with bulkier and firmer stools. Only trace amounts of LCP were detected in the stools of all groups. This accounted for less than 4% of dietary intake in Aptamil-LCP-fed infants. No differences in the utilization of LCP from Aptamil-LCP and breast milk feeding were apparent. Plasma phospholipid fatty acid composition data reflected differences in dietary LCP intake. Thus, PL LCP levels were highest in the breastfed infants and lowest in the Aptamil-fed infants, with values for the Aptamil-LCP-fed group falling in between.

Effect on placental transfer of exogenous lipid administered to the pregnant rabbit

The transfer of lipids across the placenta was measured after infusion of an emulsion of triacylglycerol and phospholipid (intralipid) into 10 anesthetized rabbits. Maternal and umbilical venous and arterial samples were collected at 10-min intervals. All samples were analyzed for concentration and fatty acid composition of FFA, triacylglycerol, and phospholipid fractions. At the end of the infusion period of intralipid, there was a significant increase in the maternal concentrations of total triacylglycerol (p < 0.01) and of total phospholipid (p = 0.01) but not of total FFA (p > 0.05). Maternal plasma triacylglycerol and phospholipid altered in composition to match that of the infused Intralipid by the end of the infusion. Despite the significant rise in maternal triacylglycerol and phospholipid concentrations, the umbilical vein-artery difference for these lipid fractions remained unchanged and very low. In contrast, the umbilical vein-artery difference for FFA (p < 0.02) rose gradually throughout the experiments. There was no significant change in the fatty acid composition of the maternal FFA, but the fatty acid composition of the umbilical vein-artery difference for FFA changed to reflect the composition of Intralipid. These experiments show that exogenous triacylglycerol and phospholipid dramatically alter the lipid fractions presented to the placenta in the maternal plasma but do not cross the placenta intact. However, the composition of the FFA crossing the placenta is modulated to become more similar to that of the exogenous lipid.

Placental transfer of free fatty acids: importance of fetal albumin concentration and acid-base status

Free fatty acids (FFA) are the main class of naturally occurring lipids transferred across the placenta, irrespective of species. In order to study the importance of fetal plasma albumin concentration and pH on placental transfer of FFA, in situ perfusion of the rabbit placenta in late gestation was used as an experimental model. Increasing albumin concentration on the fetal side of the placenta from 1 to 6% significantly increased transfer of FFA across the placenta. However, alteration of the umbilical perfusate pH in the range 7.0-7.5 had no significant effect.

Two different low birth weight formulae compared

The performance of two different, commercially available, low birth weight formulae feeds was compared in preterm infants. The aim of the study was to determine the effect of compositional differences on tolerance, stool frequency and consistency, fat balance and weight gain. Inborn infants with birth weight less than 1500 g were randomised at birth to receive Prematil or Osterprem. Thirty infants received more than 900 ml/kg per week of designated formula alone during a total of 70 weeks of study. Three day fat balance was performed on 23 infants. Osterprem contains 40% more fat than Prematil. The composition of this fat is different in that Osterprem contains no medium chain triglycerides (MCT) compared to 30% in Prematil. Clinical evaluation demonstrated that Osterprem is associated with a significantly higher mean energy intake compared to Prematil (3442 and 3127 kJ/kg per week) but mean weight gain is not significantly different (123 and 112 g/kg per week). Mean stool frequency is higher on Osterprem (20.5 and 14.5 stool/week) and the consistency of stools firmer. This is attributable to a higher mean fat output (2.3 and 0.9 g/kg per day) secondary to the higher fat content of the feed and lower mean absorption (71.6 and 83.5%). Both feeds are well tolerated. The study also confirms that absorption of unsaturated fatty acids is inversely proportional to chain length.

New aerosol delivery system for neonatal ventilator circuits

There is mounting evidence that a variety of drugs delivered as aerosols are likely to be of benefit in neonatal units. To avoid many of the problems associated with the use of jet nebulisers in ventilator circuits, a chamber was designed to be used in conjunction with a metered dose inhaler (MDI). The dimensions (4 cm x 11 cm) were chosen in an attempt to maximise drug delivery. In vitro studies were subsequently performed in order to determine the optimum operating conditions. Sodium cromoglycate delivered via this system was collected on a filter placed between the tip of an endotracheal tube and a model lung. The dose delivered was determined by means of an ultraviolet spectrophotometric assay. Using a Draeger Babylog 8000 ventilator it was found that drug delivery as maximised by actuating the device just before the inspiratory cycle when the chamber was placed adjacent to the endotracheal tube and by using a long (one second) inspiratory time. Under these conditions 1.5-2% of the original dose was deposited upon the filter at tidal volumes of 11-22 ml. When considered in terms of body weight this is many times the equivalent dose delivered to adults from an MDI. Effective drug delivery to the filter was confirmed using a radiolabelled aerosol. Radiolabelled studies delivering aerosol to the lungs of intubated rabbits demonstrated that deposition aerosol was distributed uniformly between lobes when corrected for the weight of each lobe. In conclusion, the device appears likely to deliver significant, reproducible quantities of drug to the lower respiratory tract while being simple to use.

Evaluation of techniques for delivery of steroids to lungs of neonates using a rabbit model

Little is known about delivery of aerosolised steroids to neonatal patients undergoing assisted positive pressure ventilation and after extubation. A rabbit model has been established to investigate factors influencing drug delivery. Beclomethasone dipropionate, in a metered dose inhaler, was radiolabelled with technetium 99m. The mass median aerodynamic diameter of the aerosol was 3.3 (2.0) microns and the impactor measurements confirmed that the technetium distribution corresponded with that of the drug particles. The metered dose inhaler was actuated into a collapsible spacer that was used to ventilate and deliver aerosol to anaesthetised rabbits by a tracheostomy. From each actuation of the drug 2.9 (0.4)% of the aerosol deposited in the trachea and main bronchi and 1.2 (0.4)% in the lung. When the drug was delivered by a spacer device, with face-mask attachment, to rabbits breathing freely through a tracheostomy, aerosol deposition increased to 4.4 (2.1)% in the trachea and main bronchi and 1.9 (0.9)% in the lung lobes. The maximum change in systolic blood pressure after administration of aerosol by the collapsible spacer was a decrease of 13%. The methods described may prove useful for the delivery of inhaled steroids to neonatal patients likely to develop bronchopulmonary dysplasia.

The effects of dietary supplementation with fish oil in patients with psoriasis

Ten patients with psoriasis resistant to conventional topical treatment were given dietary supplements of fish oil, providing approximately 12 g of eicosapentaenoic acid daily for a period of at least 6 weeks. In eight patients there was a modest improvement in their psoriasis, the principal effects being a diminution of erythema and scaling. The dietary treatment resulted in a substantial inhibition of leukotriene B4 production by the peripheral blood polymorphonuclear leukocytes in vitro. The discrepancy between the high degree of inhibition of leukotriene B4 synthesis and the modest therapeutic effect suggests that leukotriene B4 is not the only mediator involved in the development of the psoriatic lesion. Furthermore, the in vivo cutaneous levels of leukotriene B4 might not have been inhibited to the same extent as the polymorphonuclear leukocyte levels in vitro. Further studies on the use of fish oil supplements, both on their own and in conjunction with other forms of treatment in psoriasis are warranted. It will also be important to determine whether the altered profile of 5-lipoxygenase products found in the blood is also seen in the skin.