Introduction. Conventional screws achieve sufficient insertion torque in healthy bone. In poor bone screw stripping can occur prior to sufficient torque generation. It was hypothesized that a screw with a larger major/minor diameter ratio would provide improved purchase in poor bone as compared to conventional screws. We evaluated the mechanical characteristics of such a screw using multiple poor bone quality models. Methods. Testing groups included: conventional screws, osteopenia screws used in bail-out manner (ie, larger major/minor diameter screws inserted into a hole stripped by a conventional screw), and osteopenia screws used in a preemptive manner (ie, no screw stripping occurrence). Stripping Torque: Screws were inserted through standard straight plates into a low density block of foam with a predrilled hole. Stripping torque was defined as maximum insertion torque reached by the screw before the screw began to spin freely in the foam. Pullout. Pullout tests were conducted on screws inserted into the same test media. Axial pull-out testing was then conducted by applying a tensile load to the screws. Compression. Screws were inserted through standard straight plates by hand while the amount of compression achieved between plate and bone was measured using a pressure sensor. The same foam test media was utilized in addition to osteoporotic fresh-frozen femoral diaphyseal cadaver (bone mineral density<0.60 g/cm2). The screws were tightened across a range of possible insertion torques with pressure measurements taken at multiple intervals. Results. The osteopenia bone screws showed a 67% increase in torque before stripping occurred (p<0.01) when compared to the conventional screw. The osteopenia screw used in a bail-out manner showed a 57% increase in stripping torque (p<0.01) and a 76% increase in pullout strength (p<0.01) when compared to the conventional screw. Additionally, the bail-out screw showed a minimal decrease in both stripping torque (6%, p = 0.45) and pullout strength (11%, p<0.01) when compared to the osteopenia screw tested in preemptive manner. There was a linear relationship between applied torque and compressive force generation for both osteopenia and conventional screws. The osteopenia screws were able to gain greater compression against bone across a range of insertion values as compared to conventional bone screws. Discussion. The osteopenia screw achieved superior stripping torque, pullout strength, and compressive forces when compared to conventional screws in simulated poor quality bone and osteoporotic cadaver bone. When used as a bail-out screw, it also achieved superior stripping torque and pullout strength. The results of this study indicate that a screw of larger major/minor diameter ratio could be an effective bail-out option for screw stripping associated with osteopenic fracture fixation

Introduction. Short-segment posterior instrumentation for spine fractures is threatened by unacceptable failure rates. Two important design objectives of pedicle screws, bending and pullout strength, may conflict with each other. Hypothesis. Multiobjective optimization study with artificial neural network (ANN) algorithm and genetic algorithm (GA). Materials & Methods. Three-dimensional finite element (FE) methods were applied to investigate the optimal designs of pedicle screws with an outer diameter of 7 mm using a multiobjective approach for these two objectives. Based on the FE results on an L25 orthogonal array, two objective functions were developed by an ANN algorithm. Then, the trade-off solutions known as Pareto optima were explored by a GA. The optimal design was validated by mechanical tests. Results. The knee solutions of the Pareto fronts had simultaneous high bending and pullout strength ranging from 92 to 94 percent of their maxima. The corresponding range of the design parameters was 3.8 to 4.06 mm for inner diameter and 3.21 to 3.3 mm for pitch; 0 mm for beginning position of conical angle, 0.4 mm for proximal root radius, 5 degrees for proximal half angle, and 0.1 mm for thread width. The optimal design was well validated by mechanical tests, comparing with commercially available pedicle screws. Discussion & Conclusions. The optimal design of pedicle screws obtained could achieve an ideal with high mechanical performance in both bending and pullout tests

Introduction. Pedicle screw pullout or loosening is increased in the osteoporotic spine. Recent studies showed a significant increase of pullout forces especially for PMMA-augmentation. With application of conventional viscosity PMMA the risk of cement extravasation is associated. This risk can be reduced by using radiofrequency-responsive, ultrahigh viscosity bone cement. Method. 11 fresh-frozen lumbar vertebral bodies (VB) from 5 cadavers were collected and freed from soft-tissue and ligaments. By DEXA scan (Siemens QDR 2000) 8 VB were identified as severely osteoporotic (BMD 0.8 g/cm3), 3 VB were above this level. Two screws (6×45 mm, WSI-Expertise Inject, Peter Brehm, Weisendorf, Germany) were placed in the pedicles. Through the right screw 3ml of radiofrequency-responsive bone cement (StabiliT® ER2 Bone Cement, DFine, Germany) were injected via hydraulic cement delivery system (StabiliT® Vertebral Augmentation System, DFine, Germany). As control group, left pedicle screws remained uncemented. After potting the whole VB in technical PMMA (Technovit 4004, Heraeus Kulzer, Germany) axial pullout test was performed by a material testing device (Zwick-Roell, Zmart-Pro, Ulm, Germany). Results. The mean BMD of all specimen was 0.771 g/cm3 (min./max. 0.615/1.116, SD ± 0.170). Due to the definition of osteoporosis 8 specimens had a BMD lower than 0.8 g/cm3 (mean 0.677, min./max. 0.615/0,730, SD ±0.045). The non-osteoporotic group consisted of 3 specimens with a mean BMD of 1.020 g/cm3 (min/max 0.928/1.116, SD ±0.094). Overall we observed an increase in the mean axial pullout strength of 284% when using cement augmentated screws (non-cemented 385 N vs. cemented 1029 N, p 0,001). In the osteoporotic group the mean pullout force of the non-cemented screws was 407 N vs. 1022 N for the cemented screws (p 0.001). Similarly the pullout force rose in the non-osteoporotic group from 325 N for the non-cemented screws to 1048 N for the cemented screws p 0,001). All surgical procedures could be performed without technical problems. Conclusion. This cadaver study demonstrates the efficacy and effectiveness of pedicle-screw augmentation with ultra-high viscosity cement. Pullout forces are significantly increased, especially in osteoporotic bone. No complications like clogged in cannulated pedicle-screws or extravasation of bone cement were observed. In daily clinical routine radiation exposure to operator during cement delivery is reduced due to remote-controlled, automated delivery of radiofrequency-responsive bone cement. Furthermore availability of longer time to work with the cement (up to 30 min) is achieved; hectically injection or multiple-cement-mixing is not necessary anymore. The WSI-Expertise cannulated pedicle screws can be inserted and also augmented in a minimal-invasive technique. The PMMA then is injected through an extension adapter. PMMA augmentation of pedicle screws is already well established in spine surgery. With the combination of radiofrequency-responsive, ultra-high viscosity bone cement and cannulated pedicle screws this established procedure could become more controlled and safer for both patient and physician

Antegrade nailing of proximal humeral fractures using a straight nail can damage the bony insertion of the supraspinatus tendon and may lead to varus failure of the construct. In order to establish the ideal anatomical landmarks for insertion of the nail and their clinical relevance we analysed CT scans of bilateral proximal humeri in 200 patients (mean age 45.1 years (sd 19.6; 18 to 97) without humeral fractures. The entry point of the nail was defined by the point of intersection of the anteroposterior and lateral vertical axes with the cortex of the humeral head. The critical point was defined as the intersection of the sagittal axis with the medial limit of the insertion of the supraspinatus tendon on the greater tuberosity. The region of interest, i.e. the biggest entry hole that would not encroach on the insertion of the supraspinatus tendon, was calculated setting a 3 mm minimal distance from the critical point. This identified that 38.5% of the humeral heads were categorised as ‘critical types’, due to morphology in which the predicted offset of the entry point would encroach on the insertion of the supraspinatus tendon that may damage the tendon and reduce the stability of fixation.

We therefore emphasise the need for ‘fastidious’ pre-operative planning to minimise this risk.

Cite this article: Bone Joint J 2014;96-B:249–53.

In Neer type II (Robinson type 3B) fractures of the distal clavicle the medial fragment is detached from the coracoclavicular ligaments and displaced upwards, whereas the lateral fragment, which is usually small, maintains its position. Several fixation techniques have been suggested to treat this fracture. The aim of this study was to assess the outcome of patients with type II distal clavicle fractures treated with coracoclavicular suture fixation using three loops of Ethibond. This prospective study included 14 patients with Neer type II fractures treated with open reduction and coracoclavicular fixation. Ethibond sutures were passed under the coracoid and around the clavicle (UCAC loop) without making any drill holes in the proximal or distal fragments. There were 11 men and three women with a mean age of 34.57 years (29 to 41). Patients were followed for a mean of 24.64 months (14 to 31) and evaluated radiologically and clinically using the Constant score. Fracture union was obtained in 13 patients at a mean of 18.23 weeks (13 to 23) and the mean Constant score was 96.07 (91 to 100). One patient developed an asymptomatic fibrous nonunion at one year. This study suggests that open reduction and internal fixation of unstable distal clavicle fractures using UCAC loops can provide rigid fixation and lead to bony union. This technique avoids using metal hardware, preserves the acromioclavicular joint and provides adequate stability with excellent results.

Cite this article: Bone Joint J 2013;95-B:983–7.

Introduction

The objective of this study was to determine if a synthetic bone substitute would provide results similar to bone from osteoporotic femoral heads during in vitro testing with orthopaedic implants. If the synthetic material could produce results similar to those of the osteoporotic bone, it could reduce or eliminate the need for testing of implants on bone.