INTRODUCTION

Ultra-High Molecular Weight Polyethylene (UHMWPE) wear debris is thought to be a main factor in the development of osteolysis (1). However, the method for the evaluation of the biological response to UHMWPE particles has not yet been standardized.

In this study, four different types of UHMWPE particles were generated using a mechanized pulverizing method and the biological responses of macrophages to the particles were investigated using an inverted cell culturing process (2).

Introduction:

Cone Based CT (CBCT) scanning uses a point source and a planar detector with parallel data acquisition and volumetric coverage of the area of interest. The pedCAT (Curvebeam USA) scanner is marketed as a low radiation dose, compact, faster and inexpensive CT scanner that can be used to obtain both non- weightbearing and true 3 dimensional weightbearing views.

Background

dl-α-Tocopherol (vitamin E) blended ultra-high molecular weight Polyethylene (UHMWPE) was originally developed as a bearing material for use in knee prostheses ⁽¹⁾. The reduced biological response observed for vitamin E (VE) blended UHMWPE wear particles in in vitro experimentation ⁽²⁾ has also demonstrated the materials potential for use in other orthopedic applications, especially total hip arthroplasty (THR). However, due to the excellent results achieved by highly crosslinked UHMWPE in hip simulator testing ⁽³⁾, the use of VE blended UHMWPE in THR would similarly require crosslinking. It was previously reported that VE radicals are formed during radiation crosslinking of VE blended UHMWPE ⁽⁴⁾, and it is hypothesized that these VE radicals may negatively impact the materials biological activity. In this study, ascorbic acid 6-palmitate (lipophilic vitamin C) was applied to electron-beam-irradiated VE blended UHMWPE in an attempt to oxidatively reduce the VE radicals. Electron Spin Resonance (ESR) was used to measure the number of VE radicals within the material and evaluate the regenerating effect of ascorbic acid 6-palmitate.

Introduction

Vitamin-E (VE)-blended UHMWPE has been developed as a bearing-surface material due to the antioxidant ability of VE and has demonstrated a low wear rate in knee simulator [1]. Additionally, in vitro biological response testing has revealed that wear particles from VE blended UHMWPE induce the secretion of inflammatory cytokines at significantly lower levels compared to conventional UHMWPE [2]. However, as the joint kinematics are different between the knee and the hip, it is not guaranteed that these improvements will be repeated in the hip. In this study, the wear resistance of VE-blended UHMWPE was evaluated in knee and hip simulator tests and the effects of VE concentration and electron-beam irradiation were investigated.

Repair of chronic Achilles tendon rupture is technically complex. Flexor jallucis longus (FHL) and peroneus brevis (PB) tendon transfers have been described, but the mechanical properties of these tissues have not been well reported.

The FHL, PB and tendo achilles (TA) tendons were harvested from 17 fresh frozen human cadavers free of gross pathology (mean age 69 years). Samples were tested in uniaxial tension at 100% per minute. Samples were secured using special jigs for the bony aspect or by freezing the tendons in cryogrips using liquid carbon dioxide. The peak load (N), linear stiffness (N/mm) and energy to peak load (N*mm) were determined. Mechanical data was analysed using one way analysis of variance (ANOVA) followed by a Games Howell multiple comparison post-hoc test.

Fifty one tendons were harvested and mechanical testing was successfully completed in all samples apart from one PB that slipped from the grips during testing (sample was omitted from the analysis). The mean ultimate loads differed for each group, with the TA tendons being the strongest (1724.5 N ± 514.3) followed by FHL (511.0 N ± 164.3) and PB (333.1 N ± 137.2) (P< 0.05). Similar results were found with respect to energy, with TA tendons absorbing the most energy followed by FHL and PB (P< 0.05). Stiffness for the TA tendons (175.5 N/mm ± 94.8) was greater than FHL (43.3 N/mm ± 14.1) and PB (43.6 N/mm ± 18.9), which did not differ from each other.

FHL is stronger than PB, but have similar stiffness. The mechanical properties of PB and FHL were both inferior to TA. Graft stiffness appears to be an important variable rather than ultimate load based on the clinical success of both techniques.

Introduction: Repair of chronic Achilles tendon rupture is technically complex. Flexor Hallucis Longus (FHL) and Peroneus Brevis (PB) Tendon transfers have been described, but the mechanical properties of these tissues have not been well reported.

Methods: The FHL, PB and tendo Achilles (TA) tendons were harvested from 17 fresh frozen human cadavers free of gross pathology (mean age 69 years). Samples were tested in uniaxial tension at 100% per minute. Samples were secured using special jigs for the bony aspect or by freezing the tendons in cryogrips using liquid carbon dioxide. The peak load (N), linear stiffness (N/mm) and energy to peak load (N*mm) were determined. Mechanical data was analysed using one way analysis of variance (ANOVA) followed by a Games Howell multiple comparison post-hoc test.

Results: 51 tendons were harvested. Mechanical testing was successfully completed in all samples apart from one PB that slipped from the grips during testing (sample was omitted from the analysis). The mean ultimate loads differed for each group, with the TA tendons being the strongest (1724.5 N ± 514.3) followed by FHL (511.0 N ± 164.3) and PB (333.1 N ± 137.2) (P< 0.05). Similar results were found with respect to energy, with TA tendons absorbing the most energy followed by FHL and PB (P< 0.05). Stiffness for the TA tendons (175.5 N/mm ± 94.8) was greater than FHL (43.3 N/mm ± 14.1) and PB (43.6 N/mm ± 18.9), which did not differ from each other.

Conclusions: FHL is stronger than PB, but have similar stiffness. The mechanical properties of PB and FHL were both inferior to TA. Graft stiffness appears to be an important variable rather than ultimate load based on the clinical success of both techniques.

The use of intramedullary column screws in the treatment of acetabular fractures is becoming more widely utilized. The development of percutaneous methods to insert these screws under image intensifier guidance is one of the main reasons for their increased use. Few groups are navigating insertion of these screws. The available screws are cannulated 6.5–8 mm screws. Most surgeons prefer using 3.2 mm guide wires to reduce deflection. With a shank diameter of 4.5 mm, 3.2 mm cannulation significantly weakens the screws. We postulated that both columns, specially the posterior column can accommodate larger screw diameters which will increase the stability of fixation allowing earlier full weight bearing. The currently used screws were designed for fixation of femoral neck fractures. As percutaneous fixation of acetabular fractures is a growing area of interest, this warrants designing suitable screws with larger diameters.

Eight CT scans of the adult pelvis –performed for non fracture related indications-, were studied (7 females, 1 male). We found that the anatomical cross-section of the columns is irregular but approximately triangular. The method we used to determine the largest diameter of a screw to fit each column was fitting cylinders in the columns. Robin’s 3D software was used to segment acetabula and convert the CT data into polygon mesh (stereolithography STL format) bone surfaces at an appropriate Hounsfield value. The resulting STL files were imported in Robin’s Cloud software, where polygon mesh cylinders of 10 mm diameter were fitted in each column. These cylinders were then manipulated to achieve best fit and their diameters were gradually increased to the biggest diameter which still fitted in the column.

The mean diameters of the fitted cylinders were 10.8 mm (range: 10–13mm) and 15.2 mm (range 14–16.5mm) for the anterior and posterior columns respectively.

To our knowledge, this is the first investigation to study the cross sectional dimensions of the anterior and posterior columns of the acetabulum. Our small sample shows that both columns can safely accommodate larger screws than those currently used. We plan to investigate this further using cadavers.

Acetabular and pelvic fractures are amongst the most challenging to treat, still requiring major open surgery. The operations to reduce and fix them entail lengthy operative time, significant blood loss and use of ionising radiation.

We report on the initial stages of developement of a minimally invasive method for navigated reduction and percutaneous fixation of acetabular fractures (NRFA). A commercial navigation platform (Acrobot Ltd.) will be adapted for use with this technique. CT based planning will be used to identify the correct realignment of the the bone fragments, which will then be reduced percutaneously with the aid of two tracked arms attached to the navigation system. Schanz pins, which are inserted in pre-operatively planned sites in each fragment using safe trajectories, are handled as joysticks to manipulate the fracture under computer assistance. Registration of the fragments after insertion of the joysticks will be carried out by means of fluoroscopic images of the AP and Judet views of the fractured acetabulum. Once reduction is achieved by following on-screen instructions, the joysticks are held in place by a custom clamping system connected to one of the arms, while the other is used for percutaneous insertion of column screws.

This technique is potentially suitable for a number of acetabular fractures which include transverse, anterior column, posterior column, T-fractures and some associated both columns fractures. These constitute over 50% of Letournel’s and 60% of Matta’s original series of acetabular fractures. Furthermore, this percutaneous technique could reduce bleeding, wound complications, hospital stay and cost of treatment. Intra operative ionising radiation would be greatly reduced for both patients and the surgeons.

Adequate training with the use of this software may provide a greater number of surgeons the capability to surgically treat these complex fractures.

Introduction Zone 2 flexor tendon repairs can require ‘venting’ or partial resection of the A2 and/or A4 pulleys. We test a new technique where the pulley is divided and repaired with a V-Y plasty, increasing the pulley circumference. This allows access to perform the repair and/or permits free tendon gliding post-repair.

Methods Two groups of A2 and A4 pulleys from cadaveric fingers were divided and repaired in a V-Y fashion such that the circumference of the pulley tunnel was increased. The fingers were then mounted onto custom-made jigs and tested using a materials testing machine. One group had the A2 pulley assessed for changes in work of flexion by testing both before and after V-Y plasty. The second group had both the A2 and A4 pulleys tested for load to failure during functional loading. Biomechanical testing was performed.

Results There was a significant reduction in work of flexion after V-Y pulley expansion procedures were performed. Loads to failure for the A2 and A4 pulleys were in excess of 400% and 200% greater than one would expect in-vivo during a post-operative active mobilisation protocol. V-Y tendon pulley expansion increases the tunnel size while providing a mechanically sound pulley. It also maintains the pulley length and its coverage of the underlying tendon.

Conclusions This technique provides surgeons with an attractive alternative to simply ‘venting’ or resecting an otherwise troublesome pulley.

Introduction: Various plating devices and screw systems are available for single and multi-level cervical fusions. Recent reports regarding screw migration under torsional load and a “windshield wiper effect” has brought to light the importance of plate and screw design as well as the choice of graft.

Aim: This study examined the relative stability of cervical plating systems under pure bending and axial-torsional fatigue using the Cloward type graft.

Methods: Five fresh-frozen human cervical and 10 porcine spines assessed by dual-energy x-ray absorptiometry (DEXA) scanning and then reconstructed at the C_2–3 and levels using the anterior Cloward technique. C_4–5 Two different plating systems (a solid plate and a hollow plate) were used and alternated between the C2–3 and C4–5 levels. Strain gauges placed on the plates themselves. The systems were subjected to pure bending and torsional loading.. Five kilogram loads were used to apply bending moments to the spine and did not differ between the two systems evaluated. Bending moments and displacement angles were recorded for the pure bending loading regime and torque versus time was recorded for the torsional fatigue loading.

Results: Strain gauge analysis revealed minimal strains on the plates under the loading conditions. Torque versus time was measured, and the decay constant was calculated from the decay curves. The hollow plating system decayed quicker than the solid plating system. Angular displacement under pure bending was minimal. The hollow system plate system resisted greater torque compared with the solid system. The decay curves eventually reached an asymptote for the both systems. This implied that the systems become stable under fatigue loading. The X-rays illustrated no failure at the screw/ bone interface (i.e. No “wiper” effect) after torsional fatigue.

Introduction: Proximal bone resorption is a common problem after total hip arthroplasty. This has been attributed to stress shielding and has been reported to be more pronounced for cemented than for uncemented implants.

Aim: To investigate the cortical strain distribution of a new proximal “fit and fill” cementless, titanium, femoral, hip prosthesis based on the SROM design.

Methods: Strain gauges were mounted on five fresh-frozen cadaveric and five saw-bone femora and checked against a template for the prosthesis. The strain gauges were placed at four levels on the anterior, posterior, medial and lateral cortices corresponding to the Gruen zones. Two extra strain gauges were placed on the proximal posteromedial cortex. Loading was applied to the intact and reconstructed femora in the ISO 7206–4 orientation and single legged stance in an MTS servo-hydraulic testing machine. Data were analysed using analysis of variance.

Results: The strain distributions following reconstruction and multi-axis loading (ISO 7206–4 orientation) approximated the strains in an intact femur in the diaphysis. The proximal posteromedial cortical strains were approximately 50% of those of the intact femur.

Conclusions: The strains observed in the proximal femur following reconstruction in the present study are considerably higher than most others reported in the literature. A number of factors may contribute to the high proximal strains observed. This study has illustrated that geometric design and material selection along with surgical technique may allow for greater loading to proximal bone and enhance the long term integrity of this type of implant.