DVC allowed measurements of displacement and strain distribution in bone through the comparison of two, or more, 3D images. Hence, it has a potential as a diagnostic tool in combination with clinical CT. Currently, traditional computed tomography (CT) allows for a detailed 3D analysis of hard tissues, but imaging in a weight-bearing condition is still limited. PedCAT-CT (Curvebeam, USA) emerged as a novel technology allowing, for the first time, 3D imaging under full-weight bearing (Richter, Zech et al. 2015). Specifically, a PedCAT-CT based DVC was employed to establish its reliability through the strain uncertainties produced on bone structure targets, preliminarily to any further clinical studies. In addition, a reverse engineering FE modeling was used to predict possible force associated to displacement errors from DVC.

Three porcine thoracic vertebrae were used as bone benchmark for the DVC (Palanca, Tozzi et al. 2016, Tozzi, Dall'Ara et al. 2016). The choice of using porcine vertebrae (in a CT designed for foot/ankle) was driven by availability, as well as similar dimensions to the calcaneus. Each vertebra was immersed in saline solution and scanned twice without any repositioning (zero-strain-test) with a pedCAT-CT (Curvebeam, USA) obtaining an isotropic voxel size of 370 micrometers. Volumes of interest of 35 voxel were cropped inside the vertebrae. Displacement and strains were evaluated using DVC (DaVis-DC, LaVision, Germany), with different spatial resolution. The displacement maps were used to predict the force uncertainties via FE (Ansys Mechanical v.14, Ansys Inc, Canonsburg, PA). Each element was assigned a linear elastic isotropic constitutive law (Young modulus: 8 GPa, Poisson's ratio: 0.3, as in (Follet, Peyrin et al. 2007)). Overall, the precision error of strain measurement was evaluated as the average of the standard deviation of the absolute value of the different component of strain (Liu and Morgan 2007).

The force uncertainties obtained with the FE analysis produced magnitudes ranging from 231 to 2376 N. No clear trend on the force was observed in relation to the spatial resolution. Precision errors were smaller than 1000 microstrain in all cases, with the lowest ranging from 83 microstrain for the largest spatial resolution. Full-field strain on the bone tissue did not seem to highlight a preferential distribution of error in the volume.

The precision errors showed that the pedCAT-CT based DVC can be sufficient to investigate the bone tissue failure (7000–10000 microstrain) or, physiological deformation if well-optimized. FE analysis produced important force uncertainties up to 2376 N. However, this is a preliminary investigation. Further investigation will give a clearer indication on DVC based PedCAT-CT, as well as force uncertainties predicted. So far, the DVC showed its ability to measure displacement and strain with reasonable reliability with clinical-CT as well.

The treatment of acute full thickness chondral damage within the knee is a surgical challenge. Frequently used surgical techniques include chondroplasty, micro-fracture and chondrocyte implantation. These procedures give unpredictable functional outcomes and if the formation of neocartilage is achieved it is predominantly composed of type 1 collagen.

The TruFit osteochondral plug was designed to provide a scaffold for cell proliferation into full thickness chondral defects. It is a composite polymer composed of polylactide co-glycolide, calcium sulphate and poly-glycolide fibres. It is composed of 2 layers, one with a similar trabecular network to cancellous bone and a superficial layer designed to simulate articular lining.

The TruFit bone plug was analysed using micro-computed tomography. Its morphology characteristics, granulometry, mechanical performance and image guided failure were tested as well as numerical modelling to assess the permeability of TruFit.

Morphological parameters of the TruFit bone plug compared favourably with those of human tissue. Under load the scaffold exhibited shear bands throughout the composite leading to a failure mechanism similar to cancellous bone. Stress relaxation rates of the scaffolds were greatly decreased under wet conditions, likely due to plasticisation of the scaffold by water.

The biomechanical properties of the TruFit bone plugs are a cause for concern. The Scaffolds mechanical performance under load rapidly deteriorates in wet conditions at body temperature (the natural knee environment). This early failure will lead to defects in the articular surface where the plug has been inserted. Clinical data is sparse. This study correlates with work performed by Dockery et al & Spalding et al. These clinical studies have shown that the TruFit implant shows no evidence of bone ingrowth or osteoconductivity. It provides no subchondral support to neocartilage or tissue that was stimulated to form around the defects and surgical sites.

Introduction

Novel hydrogel implants, TRUFIT® bone plugs, have been developed by Smith & Nephew to replace worn-out cartilage surfaces, restoring mobility and relieving joint pain. There is limited information, however, on the biomechanical properties of the implants. Therefore, appropriate mechanical testing and modelling must be carried out to assess their mechanical properties for load bearing applications.

In this study, compressive properties of TRUFIT® bone and dual layer implants were examined under selected physiological loading conditions. The bone layer of the implant was also modelled using a biphasic poroviscoelastic (BPVE) material constitutive law and the results from the model are compared with those from the experiments.

Purpose of the study: To compare the DHS plate fixation with the Targon PF nail for the treatment of intratro-chanteric fractures.

Material and methods: This was a prospective randomized study including 60 patients hospitalized in the emergency setting between December 2003 and June 2004for intratrochanteric fractures. The AO classification was used. We analyzed: patient status (ASA), operative time (type of implant, duration), the postoperative period (blood loss, radiologic findings, duration of hospital stay, early postoperative complications) and at last follow-up, Harris hip score, date of resumed walking, mortality. Patients were assessed at three months postop. This study included 60 patients, 34 with a Targon PF nail and 26 with a DHS. Mean patient age for nailing was 81 years (SD 12.8, range 23–86); for DHS it was 82 years (SD 9.8; range 47–97).

Results: Mean blood loss was 410 ml with the Targon PF nail and 325 ml with the DHS, a nearly significant difference (p=0.07). The other results did not demonstrate any significant difference. At three months five cases of screw cut out were noted. Bone healing was achieved in all cases. The Trargon PF nail and the DHS provide equivalent results, with less bleeding an lesser cost for the DHS.

Purpose: Classically reported, degenerative femorotibial remodelling after meniscectomy results from different biomechanical mechanisms depending on the compartment considered. Occurring in the medial compartment, the most frequent situation, the lesions result from punctual contact compression of the cartilage. In the lateral compartment the mechanism involves increased relative instability of the structures controlling mobility. Lateral meniscectomy disrupts femorotibial kinetics of the meniscotibial gliding articulation leading to horizontal instability and subsequent generation of osteoarthritic degeneration which explains the development of lateral decompensations without genu valgum. Based on work by Grammont and Rudy, we proposed a method to limit this horizontal instability and transfer part of the stress to the medial compartment by medial translocation of the tibial tubercle.

Material and methods: Eighteen patients, mean age 44 years, underwent treatment for disabling degeneration without major misalignment (mean HKA 181°) a mean ten years after lateral meniscetomy. Degenerative remodelling of the lateral compartment was observed on the AP views in 30% of the knees and on the tangent views in 57% Five patients had early-stage lesions of the medial compartment and femoropatellar degradation was observed in 53%. Involvement of the lateral compartment was confirmed by systematic articular exploration and patellofemoral chondropathy was observed in eight knees. Translocation of the anterior tibial tubercle was associated with section of the lateral patellar wing in all knees associated with tension plasty medially.

Results: In 88% of the knees, the postoperative period was uneventful. Weight-bearing supported with a Zimmer cast was maintained for 21 days. Functional outcome was assessed at mean 28 months. Eleven patients had a new clinical and radiographic work-up (mean 34 months). Pain was improved in 88% of the knees, allowing sustained resumption of occupational activities at three months (four knees completely forgotten). Radiographically, at mean 34 months, the lateral cartilage lesions had stabilised with no impact on the medial compartment.

Discussion: In light of these results, we have decided to continue this therapeutic approach, reserving the technique for cases of symptomatic lateral decompensation in young subjects without major valgus malalignment.