Aims

Total hip arthroplasty (THA) patients undergoing or having a prior lumbar spine fusion (LSF) have an increased risk of mechanical complications. The aim of this registry-based, retrospective comparative cohort study is to assess the longer term survival of THA in patients who have undergone a LSF during a 17-year period (2000 to 2017).

DVC is a novel full-field and contactless measurement technique for calculating displacements and strains inside bones (Grassi and Isaksson 2015) through the comparison of 3D reconstructions (CT, micro-CT, MRI, etc.) from unloaded and loaded samples. Recent in zero-strain tests to estimate the measurement precision by applying a known state of strain (Palanca, Tozzi et al. 2015) suggested that DVC is suitable to identify regions where bone tissue is yielded (i.e. subjected to high strains). Conversely to reliably measure strain in the physiological range a severe compromise with spatial resolution is necessary (Dall'Ara, Barber et al. 2014, Palanca, Tozzi et al. 2015). In order to use DVC to explore the relationship between the local physiological strain and bone microarchitecture, an error lower than 200 microstrain (an order of magnitude lower than the mean strain) and a spatial resolution of the strain measurement lower than 100 μm is required. The aim of this work is to define if, and to what extend, high-quality images obtained by synchrotron radiation micro computed tomography (SR-μCT) improve the precision of a global DVC approach.

Cylindrical specimens of cortical and trabecular bone were extracted from a fresh bovine femur and embedded in acrylic resin. Both samples were scanned twice without any repositioning (‘repeated scantest’) at beamline l13–2 of Diamond Light Source (Oxford, UK). 4000 projections of 53 ms exposure were collected via fly-scanning with a CdWO₄scintillator-coupled pco.edge 5.5 detector with 4× magnification and an effective pixel size of 1.6μm. Strains were evaluated using a global DVC approach (ShIRT-FE) in two cubic volumes of interest (VOI) of 1,000 voxels in side length, for each specimen, exploring a DVC spatial resolution from 16 to 498 μm. The precision of measurements was evaluated extracting a similar indicator to (Liu and Morgan 2007).

Precision improved with decreasing spatial resolution, confirming a trend similar to that obtained with ‘laboratory source’ μCT on similar specimens (Palanca, Tozzi et al. 2015). To obtain a precision of better than 200 microstrains the cortical and trabecular samples required spatial resolutions of 41 and 80 μm respectively. Comparing these results to those of previous studies, where similar specimens were scanned with ‘laboratory source’ μCT (effective voxel size of the order of ten μm) the errors were vastly reduced (approximately one order of magnitude). In fact, in order to obtain a precision of better than 200 microstrain, spatial resolutions of 550 (cortical) and 480 (trabecular) μm were needed (Dall'Ara, Barber et al. 2014).

This work showed that using high-quality tomograms obtained by synchrotron radiation μCT decreases the measurement uncertainties of a global DVC approach with respect to those obtained with laboratory source μCT. DVC could therefore be used with μCT data to evaluate displacement and strain in the physiological range with remarkable spatial resolution.

Summary

A retrospective study on 98 patients shows that FE-based bone strength from CT data (using validated FE models) is a suitable candidate to discriminate fractured versus controls within a clinical cohort.

Summary Statement

In a retrospective study, FE-based bone strength from CT data showed a greater ability than aBMD to discriminate proximal femur fractures versus controls.

We investigated the effect of pre-heating a femoral component on the porosity and strength of bone cement, with or without vacuum mixing used for total hip replacement.

Cement mantles were moulded in a manner simulating clinical practice for cemented hip replacement. During polymerisation, the temperature was monitored. Specimens of cement extracted from the mantles underwent bending or fatigue tests, and were examined for porosity.

Pre-heating the stem alone significantly increased the mean temperature values measured within the mantle (+14.2°C) (p < 0.001) and reduced the mean curing time (−1.5 min) (p < 0.001). The addition of vacuum mixing modulated the mean rise in the temperature of polymerisation to 11°C and reduced the mean duration of the process by one minute and 50 seconds (p = 0.01 and p < 0.001, respectively). In all cases, the maximum temperature values measured in the mould simulating the femur were < 50°C. The mixing technique and pre-heating the stem slightly increased the static mechanical strength of bone cement. However, the fatigue life of the cement was improved by both vacuum mixing and pre-heating the stem, but was most marked (+ 280°C) when these methods were combined.

Pre-heating the stem appears to be an effective way of improving the quality of the cement mantle, which might enhance the long-term performance of bone cement, especially when combined with vacuum mixing.

Bone reconstruction in pediatric oncology always has to face two major problems: the frequent unavailability of small prosthetic tools and the difficulty in finding bone allografts of adequate size.

Aim of this work is to present the research lines in this field, currently active in our institution to improve the planning and the results of reconstructive tumor surgery in children. Starting from patient’s CT data sets, subject-specific 3D models of bone segments can be created and compared with the similar models obtained by the CT analysis of massive allografts stored in the Rizzoli Bone Bank.

In the same time the computer modelling technologies allow the development of three-dimensional environment, where the surgeon can navigate and exploit both artificial (prostheses, metallic plates and screws) or biological tools (bone allografts or autografts).

The presented method has been utilized with success in 10 children (mean age 8, range 4–13) that underwent a skeletal reconstruction of the limbs in the last year (proximal humerus 1, diaphyseal humerus 1, total humerus 1, distal radius 1, proximal femur 3, diaphyseal femur 1, proximal tibia 1, diaphyseal tibia

Aims: The aim of this study is to report the pre-clinical validation and clinical experience with modular neck primary prosthesis.

Introduction: Modular acetabular designs are widespread used in primary THA for their versatility while little experience is reported with modular femoral designs. Stem modularity could be useful when the anatomy is overthrown and for mini-incision approaches, providing an increased adaptability without any need for a large inventory or expensive custom made prostheses.

Methods: The fretting-corrosion behavior of the neck-stem coupling and the amount of particulate released under simulated physiological activities were investigated. In vitro tests were performed in Ringer’s solution loading the stem up to 20 millions cycles (i.e. 20 yrs) according to ISO 7206. From January 1995 to December 2001, 864 primary surgeries were performed with a modular stem. There were 458 women and 406 men; the mean age was 55 years (16–81 years). The main pre-operative diagnosis was primary arthritis (58.1%), the second CHD (22.2%). The stem survival was estimated by the Kaplan-Meier method.

Results: Evidence of primary corrosion was not found, conversely areas showing fretting damage were seen. The amount of fretted material was estimated in less than 1mg/year. Clinically 3 stems were revised, 2 for recurrent dislocation, 1 for stem subsidence, none for mechanical failure. At 6 years the estimated stem survival is 99.4%.

Conclusions: Modular stems have shown excellent clinical and mechanical behavior. The amount of fretting debris product is negligible taking that a stable prosthesis is likely to produce more than 10mg/year of metal debris.

Aims: Aim of this study is to review the role of biomechanical modelling in computer aided orthopaedic surgery (CAOS), and to identify the issues that prevent a wider adoption of biomechanical modelling in the clinical practice.

Methods: we reviewed the experience we cumulated over the years in the use of biomechanical models to answer clinically relevant questions in the domains of joint prosthetics design and of skeletal strength under pathological conditions. also summarised the studies done in the past few years on the use of computer aided systems in the pre-operative planning, with particular reference to the Hip-OpA9 surgical planner for total hip replacement. Last, we analyse the improvements that the introduction of new technologies such as the Multimod Application Framework is likely to allow in a near future. All this information was combined in order to establish two possible scenarios for the next generation of computer aided orthopaedic surgery solutions: the use of biomechanics models as pre-operative and intra-operative decision-support instruments, and the role of multisensorial interfaces in CAOS applications.

Results: With this review we found that various technology limitation still limit a wider introduction of biomechanics modelling in CAOS. Specific research activities must be focused on the generation of patient-specific models of the musculo-skeletal apparatus that are not only anatomically but also functionally correct and accurate.

Conclusions: While multimodal imaging (CT+MRI+ SPECT) may provide the best results, solutions are being developed which are compatible with the logistics of the clinical practice.

Most of the approaches to computer aided surgery currently in use share the need for an accurate pre-operative surgical planning to establish the optimal conditions that the surgeon should achieve using such specialised instrumentation.

The penetration of these computer-aided planning tools in the clinical practice is still limited. The systems that replicate such 2D planning are user-friendly, but lack the full three-dimensional definition of the implant position. On the contrary, systems based on CT data, which allow a fully 3D planning, usually have cumbersome interfaces. Last but not least all programs currently available are only aimed to visualise the position and orientation of the prosthetic components, presuming that the anatomical referencing is sufficient for the surgeon to decide the correctness of the planning.

The Hip-Op research project was aimed to the development of a complete surgical simulation software environment for the pre-operative planning of total hip replacement surgery. The software had to fulfil the following basic requirements: a CT-based three-dimensional planning environment; a user-friendly graphic user interface based on the Multimodal Display approach; the possibility to integrate analysis modules aimed to provide the surgeon with additional functional data; complete independence from the type of hip prosthesis or from the intra-operative instrumentation.

The graphical interface of Hip-Op is based on an innovative visualisation paradigm, which is called Multimodal display. Hip-Op represents the anatomical objects by means of multiple views, each of which simulates a different medical imaging modality familiar to the medical professional. Two analysis modules are currently integrated in Hip-Op to provide clinically relevant 3D indicators of the implant fit and fill in the host femur.