Modular femoral stems for total hip arthroplasty (THA) were introduced to allow additional options for surgeons in controlling leg lengths, offset, and implant stability. This option is widely used in Region Emilia Romagna, Italy, where the study was conducted, having a modular neck stem nearly 35% of primary THA in 2013. Great majority of modular neck is made of Titanium alloy.

The study was designed as a retrospective descriptive case series of 67 hips in patients who underwent revision of a THA. All had a Titanium modular neck. In 44 cases revision was due to breakage of the neck, in the remaining 23 it was due to different reasons unrelated to modular neck such as bone fracture, breakage of a ceramic component, cup loosening.

Mean follow up was 3.5 yrs. For all patients excised capsule and surrounding tissue were graded for presence of necrosis, inflammatory exudate, lymphocytes, and wear particles using light microscopy of routine paraffin sections stained with hematoxylin and eosin. The retrieved modular neck-body and head-neck junctions were examined for evidence of fretting and corrosion. For some patient dosage of circulating Titanium was obtained. Approval was obtained from institutional review board.

It resulted that a variable amount of wear was observed in the first group of patients, with no evidence of lymphocytic reaction, but with variable notes of necrosis. Broken necks showed different patterns of damage, with different degree of corrosion, beside the fatigue fracture. In the second group wear was less evident or absent and negativity of lymphocyte reaction was substantially confirmed. Circulating Titanium ions were one order of magnitude higher in first group (mean 35 micrograms /litre).

It can be concluded that fracture of Titanium modular necks occurs progressively, wear does not induce lymphocytic reaction and circulating ions increase.

Good lag screw holding power in trabecular bone of the femoral head is a requisite to achieve stability in the management of proximal femoral fractures. It has been demonstrated that insertion torque and pullout strength of lag screw are linearly correlated. Therefore, insertion torque measurement could be a method to estimate the achieved screw purchase. Manual perception is not reliable [1], but the use of an instrumented screwdriver would make the procedure feasible.

The aim of this study was to assess the accuracy achievable using the insertion torque as predictor of lag screw purchase.

Four different screw designs (two cannulated and two solid-core screws) were investigated in this study. Each screw was inserted into a block of trabecular bone tissue following a standardised procedure designed to maximise the experimental repeatability. The blocks of trabecular tissue were extracted from human as well as bovine femora to increase the range of bone mineral density.

The prediction accuracy was evaluated by plotting pullout strength versus insertion torque, performing a linear regression analysis and calculating the difference (as percentage) between predicted and measured values.

Insertion torque showed a strong linear correlation (coefficient of determination R²: 0.95–0.99) with the pullout strength of lag screw. However the prediction error in pullout strength estimation was greater than 40% for small values of insertion torque, decreasing down to 15% when the lag screw was driven into good quality bone tissue.

Measuring insertion torque can supply quantitative information about the achieved lag screw purchase. Since screw design and insertion procedure have been shown to affect both the insertion torque and the pullout strength [2], the prediction model must be screw-specific and determined, closely simulating the clinical procedure defined by the screw manufacturer. However, the surgeon must be aware that, even under highly repeatable experimental conditions, the prediction error was found to be high when small insertion torque was measured, i.e. when the screw was driven in low quality bone tissue. Therefore, insertion torque is not reliable in evaluating lag screw purchase in the management of proximal femur fracture of osteoporotic patients.

Calcium phosphate cements (CPC) are used as biocompatible and bioactive bone void fillers. Ideally, the mechanical properties of these cements should match those of the surrounding bone. The knowledge of the real mechanical properties of the material is important in the decision-making process regarding possible use of the CPCs in different anatomical sites. Although it is generally recognized that these cements are stiffer and more brittle than desired, there is a limited amount of data about the possible deformation of this class of material before failure. The focus of this study was to determine these properties of injectable CPCs.

Two different types of self-setting CPCs were investigated in this study: i) hydroxyapatite (HA), that historically has been the most widely studied CPC; ii) brushite, that recently has attracted attention due to its faster resorption than that of HA in vivo. Specimens of both cement types were prepared by mixing a powder phase with a liquid phase that were left to harden in phosphate buffered saline at 37°C. Once set, the specimens underwent a quasi-static compressive test to determine the compressive strength, the elastic modulus and the maximum deformation of the two materials. The material testing machine was equipped with a digital image correlation system, which allows accurate measurement of material deformation directly on the specimen surface.

Brushite was found to be significantly more stiff (+80%) and resistant (+84%) than HA. Similar findings were found for the energy needed to create a first crack on the specimen surface. However, the first crack appeared on the specimen surface at the same low deformation level (∼0.15%) independently of the type of material tested. Complete failure of both materials occurred, on average, before reaching 0.25%.

It has been demonstrated that the compressive behaviour of CPCs depends on their composition and porosity [1]. One of the main reasons for the high strength and stiffness of the brushite studied here was its low porosity (∼12%). However, the maximum deformation is not positively affected by this decrease in porosity. In fact, both materials show the same brittle behaviour, i.e. they undergo comparably little deformation before they break. Under these conditions, increasing the compressive strength may not always be beneficial clinically, e.g. in the treatment of vertebral compression fractures, where the high stiffness of the bone cements used has been identified as a risk factor for adjacent-level fractures [2]. However, it is not clear whether a 20-fold higher stiffness than the trabecular bone would give a different clinical outcome than a 10-fold higher stiffness. These high-strength, high-stiffness cements may also be used as a basis for further biomaterial development, e.g. in the creation of macro-porous scaffolds, which is usually challenging due to the commonly low mechanical properties of the base CPC material.

In clinical orthopedics suitable materials that induce and restore biological functions together with the right mechanical properties are particularly needed for the regeneration of musculoskeletal tissue. An innovative solution to answer this need is represented by tissue engineering. This technique could overcome the limits of traditional approaches involving the use of homologous, autologous or allogenetic tissue (e.g. tissue availability, immune rejection and pathogen transfer). In this field, rapid prototyping techniques are emerging as the most promising tool to realize three-dimensional tissue constructs with highly complex geometries.

Based on CAD/CAM technology, rapid prototyping allows development of patient-specific 3D scaffolds from digital data obtained with latest generation imaging tools. These structures can be realized in different materials, tailoring their mechanical properties and architectural features. Most rapid prototyping techniques allow the creation of acellular 3D scaffolds, which must be subsequently seeded with cells. Conversely, 3D bioprinting can deposit bio-ink containing molecules/cells, providing desired spatial distribution of growth factors/cells within the scaffold. The need of printable materials suitable for processing with inkjet, dispensing, or laser-print technologies, forces the use of matrices within a specific range of viscosity. However, these materials have low mechanical features. To overcome this problem and to obtain a final construct with good mechanical properties, bioprinting tissue fabrication can rely on the alternate deposition of thermoplastic materials and cell-laden hydrogels. Since mechanical performance is determined not only by the material properties but also by the geometry (microarchitecture) of the structure, printing parameters can be modified to obtain the desired features.

The new 3D platform available at Rizzoli Orthopaedic Institute, consisting of a Computer Tomography (GE Medical Systems, Milano, Italia) and a 3D Bio-Printer (RegenHU, Villaz-St-Pierre, Switzerland) is used to address the above-mentioned issues. Preliminary results showed that it is possible to modify the microarchitecture of the printed structures adjusting their apparent density and stiffness in the range of the trabecular bone tissue. Additionally, it has been proven that the calcium phosphate based paste, used as bioink, allows cell attachment and proliferation. Therefore, the platform allows to print scaffolds with open and interconnected porosities and suitable mechanical properties. They can be filled with different components such as cells or soluble growth factors at specific locations.

Modular femoral stems for total hip arthroplasty (THA) were introduced to allow additional options for surgeons in controlling leg lengths, offset and implant stability. This option is widely used in our Region, where the study was conducted, having a modular neck stem nearly 35% of primary THA in 2013. Great majority of modular neck is made of Titanium alloy.

The study was designed as a retrospective descriptive case series of 67 hips in patients who underwent revision of a THA. All had a Titanium modular neck. In 44 cases revision was due to breakage of the neck, in the remaining 23 it was due to different reasons unrelated to modular neck such as bone fracture, breakage of a ceramic component, cup loosening.

Mean follow up was 3.5 yrs. For all patients excised capsule and surrounding tissue were graded for presence of necrosis, inflammatory exudate, lymphocytes, and wear particles using light microscopy of routine paraffin sections stained with hematoxylin and eosin. The retrieved modular neck-body and head-neck junctions were examined for evidence of fretting and corrosion. For some patient dosage of circulating Titanium was obtained. Approval was obtained from institutional review board.

It resulted that a variable amount of wear was observed in the first group of patients, with no evidence of lymphocytic reaction, but with variable notes of necrosis. Broken necks showed different patterns of damage, with different degree of corrosion, beside the fatigue fracture. In the second group wear was less evident or absent and negativity of lymphocyte reaction was substantially confirmed. Circulating Titanium ions were one order of magnitude higher in first group (mean 35 micrograms /liter).

It can be concluded that fracture of Titanium modular necks occurs progressively, wear does not induce lymphocytic reaction and circulating ions increase.

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.