Melissa Kate Ryan

Does cancellous screw insertion torque depend on bone mineral density and/or microarchitecture?

During insertion of a cancellous bone screw, the torque level reaches a plateau, at the engagement of all the screw threads prior to the screw head contact. This plateau torque (T(Plateau)) was found to be a good predictor of the insertion failure torque (stripping) and also exhibited strong positive correlations with areal bone mineral density (aBMD) in ovine bone. However, correlations between T(Plateau) and aBMD, as well as correlations between T(Plateau) and bone microarchitecture, have never been explored in human bone. The aim of this study was to determine whether T(Plateau), a predictor of insertion failure torque, depends on aBMD and/or bone microarchitecture in human femoral heads. Fifty-two excised human femoral heads were obtained. The aBMD and microarchitecture of each specimen were evaluated using dual X-ray Absorptiometry and micro-computed tomography. A cancellous screw was inserted into specimens using an automated micro-mechanical test device, and T(Plateau) was calculated from the insertion profile. T(Plateau) exhibited the strongest correlation with the structure model index (SMI, R=-0.82, p<0.001), followed by bone volume fraction (BV/TV, R=0.80, p<0.01) and aBMD (R=0.76, p<0.01). Stepwise forward regression analysis showed an increase for the prediction of T(Plateau) when aBMD was combined with microarchitectural parameters, i.e., aBMD combined with SMI (R(2) increased from 0.58 to 0.72) and aBMD combined with BV/TV and BS/TV (R(2) increased from 0.58 to 0.74). In conclusion, T(Plateau), a strong predictor for insertion failure torque, is significantly dependent on bone microarchitecture (particularly SMI and BV/TV) and aBMD.

Pullout strength of cancellous screws in human femoral heads depends on applied insertion torque, trabecular bone microarchitecture and areal bone mineral density

For cancellous bone screws, the respective roles of the applied insertion torque (TInsert) and of the quality of the host bone (microarchitecture, areal bone mineral density (aBMD)), in contributing to the mechanical holding strength of the bone-screw construct (FPullout), are still unclear. During orthopaedic surgery screws are tightened, typically manually, until adequate compression is attained, depending on surgeons manual feel. This corresponds to a subjective insertion torque control, and can lead to variable levels of tightening, including screw stripping. The aim of this study, performed on cancellous screws inserted in human femoral heads, was to investigate which, among the measurements of aBMD, bone microarchitecture, and the applied TInsert, has the strongest correlation with FPullout. Forty six femoral heads were obtained, over which microarchitecture and aBMD were evaluated using micro-computed tomography and dual X-ray absorptiometry. Using an automated micro-mechanical test device, a cancellous screw was inserted in the femoral heads at TInsert set to 55% to 99% of the predicted stripping torque beyond screw head contact, after which FPullout was measured. FPullout exhibited strongest correlations with TInsert (R=0.88, p<0.001), followed by structure model index (SMI, R=-0.81, p<0.001), bone volume fraction (BV/TV, R=0.73, p<0.001) and aBMD (R=0.66, p<0.01). Combinations of TInsert with microarchitectural parameters and/or aBMD did not improve the prediction of FPullout. These results indicate that, for cancellous screws, FPullout depends most strongly on the applied TInsert, followed by microarchitecture and aBMD of the host bone. In trabecular bone, screw tightening increases the holding strength of the screw-bone construct.

Time-elapsed screw insertion with microCT imaging

Time-elapsed analysis of bone is an innovative technique that uses sequential image data to analyze bone mechanics under a given loading regime. This paper presents the development of a novel device capable of performing step-wise screw insertion into excised bone specimens, within the microCT environment, whilst simultaneously recording insertion torque, compression under the screw head and rotation angle. The system is computer controlled and screw insertion is performed in incremental steps of insertion torque. A series of screw insertion tests to failure were performed (n=21) to establish a relationship between the torque at head contact and stripping torque (R(2)=0.89). The test-device was then used to perform step-wise screw insertion, stopping at intervals of 20%, 40%, 60% and 80% between screw head contact and screw stripping. Image data-sets were acquired at each of these time-points as well as at head contact and post-failure. Examination of the image data revealed the trabecular deformation as a result of increased insertion torque was restricted to within 1mm of the outer diameter of the screw thread. Minimal deformation occurred prior to the step between the 80% time-point and post-failure. The device presented has allowed, for the first time, visualization of the micro-mechanical response in the peri-implant bone with increased tightening torque. Further testing on more samples is expected to increase our understanding of the effects of increased tightening torque at the micro-structural level, and the failure mechanisms of trabeculae.

Turn-of-the-Nut Method Is Not Appropriate for Use in Cancellous Bone.

Objective: The level to which bone screws are tightened is determined subjectively by the operating surgeon. It is likely that the tactile feedback that surgeons rely on is based on localized tissue yielding, which may predispose the screw–bone interface to failure. A limited number of studies have investigated the ratio between clinical tightening torque and stripping torque. The purpose of this study was to measure, for the first time, the ratio between yield torque (Tyield) and stripping torque (Tmax) during screw insertion into the cancellous bone and to compare these torques with clinical levels of tightening reported in the literature. Additionally, a rotational limit was investigated as a potential end point for screw insertion in cancellous bone. Methods: A 6.5-mm outer diameter commercial cancellous bone screw was inserted into human femoral head specimens (n = 89). Screws were inserted to failure, while recording insertion torque, compression under the screw head, and rotation angle. Results: The median, interquartile ranges, and coefficient of variation were calculated for each of the following parameters: Tyield, Tmax, Tyield/Tmax, slope, Tplateau, and rotation angle. The median ratio of Tyield/Tmax and rotation angle was 85.45% and 96.5 degrees, respectively. The coefficient of variation was greatest for the rotation angle compared with the ratio of Tyield/Tmax (0.37 vs. 0.12). Conclusions: The detection of yield may be a more precise method than the rotation angle in cancellous bone; however, bone–screw constructs that exhibit a Tyield close to Tmax may be more susceptible to stripping during insertion. Future work can identify factors that influence the ratio of Tyield/Tmax may help to reduce the incidence of screw stripping.

Protocol for a randomised crossover trial to evaluate patient and nurse satisfaction with electronic and elastomeric portable infusion pumps for the continuous administration of antibiotic therapy in the home: the Comparing Home Infusion Devices (CHID) study

Introduction Previous studies comparing satisfaction with electronic and elastomeric infusion pumps are limited, and improvements in size and usability of electronic pumps have since occurred. The Comparing Home Infusion Devices (CHID) study plans to assess patient and nurse satisfaction with an elastomeric and electronic pump for delivering intravenous antibiotic treatment in the home. Secondary objectives are to determine pump-related complications and actual antibiotic dose administered, evaluate temperature variation and compare pump operating costs. Methods and analysis The CHID study will be a randomised, crossover trial. A trained research nurse will recruit patients with infectious disease aged ≥18 years and prescribed ≥8 days of continuous intravenous antibiotic therapy from the Royal Adelaide Hospital (RAH) (Adelaide, Australia). Patients will be randomised to receive treatment at home via an elastomeric (Baxter Infusor) or an electronic (ambIT Continuous) infusion pump for 4–7 days, followed by the other for a further 4–7 days. Patient satisfaction will be assessed by a 10-item survey to be completed at the end of each arm. Nurse satisfaction will be assessed by a single 24-item survey. Patient logbooks and case notes from clinic visits will be screened to identify complications. Pumps/infusion bags will be weighed to estimate the volume of solution delivered. Temperature sensors will record skin and ambient temperatures during storage and use of the pumps throughout the infusion period. Costs relating to pumps, consumables, antibiotics and servicing will be determined. Descriptive statistics will summarise study data. Ethics and dissemination This study has been approved by the RAH Human Research Ethics Committee (HREC/16/RAH/133u2009R20160420, version 6.0, 5 September 2016). Study results will be disseminated through peer-reviewed publications and conference presentations. The CHID study will provide key insights into patient and provider satisfaction with elastomeric and electronic infusion pumps and inform future device selection. Trial registration number ACTRN12617000251325; Pre-results.

Safety and effectiveness of ‘hospital in the home’ and ‘outpatient parenteral antimicrobial therapy’ in different age groups: A systematic review of observational studies

The aim of this study was .to systematically review the published literature of observational studies evaluating the safety and effectiveness of hospital in the home (HITH) and outpatient parenteral antimicrobial therapy (OPAT) in the general population, older people and children.