Comparison of the axial stiffness of carbon composite and aluminium alloy circular external skeletal fixator rings.

OBJECTIVES: The purpose of this study was to compare the axial stiffness of aluminium alloy and carbon composite single-ring constructs. METHODS: Single-ring constructs were made with rings of different material compositions (aluminium alloy and carbon composite), diameters (55 mm, 85 mm, and 115 mm), and thicknesses (6 mm for the single-ring, 12 mm for the double-ring) with all other components remaining constant. Stiffness of each construct was determined under loading in axial compression with a materials testing machine. The axial stiffness of each group was compared using a three-factor factorial analysis of variance investigating all main effects and interactions between ring diameter, ring thickness, and ring material composition; p <0.05 was considered significant. RESULTS: Carbon composite constructs were 16-55% as stiff as corresponding aluminium alloy constructs. Within each combination of ring material composition and ring diameter, stiffness did not significantly increase when the ring thickness was doubled. Within each combination of ring material composition and ring thickness, stiffness significantly decreased with increased ring diameter. CLINICAL SIGNIFICANCE: Aluminium alloy rings were found to be significantly stiffer than carbon composite rings. Although the carbon composite rings were considerably less stiff, clinical recommendations cannot be made from a single-ring in vitro analysis. Further studies are needed to evaluate the behaviour of these rings in vivo.

Evaluation of the dorsal acetabular coverage obtained by a modified triple pelvic osteotomy (2.5 pelvic osteotomy): an ex vivo study on a cadaveric canine codel.

OBJECTIVES: To evaluate the acetabular ventroversion obtained with a modified triple pelvic osteotomy (2.5 PO) compared with that resulting from standard double pelvic osteo-tomy (DPO). STUDY DESIGN: Ex vivo study. ANIMALS: Seven pelves obtained from skeletally mature dogs with a total body weight ranging from 26-41 kg were used. METHODS: Unilateral DPO technique and dorsal ischial mono-cortical osteotomy were performed on every right hemipelvis. Angular ventral rotation was measured by determining the relative orientation of two Kirschner wires placed in the ilial wing and in the dorsal acetabular rim. RESULTS: The mean angle of ventroversion was 9.5 ± 5.2 degrees for the DPO group (range 2.1-18.1) and 10.9 ± 4.8 degrees for the 2.5 PO group (range 4.1-19.5). The mean difference between the 2.5 PO and DPO was 1.5 ± 0.6 degrees (range 0.5-2.1). CONCLUSIONS: The 2.5 PO technique increased acetabular ventroversion versus DPO.

In vitro biomechanical evaluation and comparison of a new prototype locking plate and a limited-contact self compression plate for equine fracture repair.

OBJECTIVE: To determine if the mechanical properties (strength and stiffness) of a new prototype 4.5 mm broad locking plate (NP-LP) are comparable with those of a traditional 4.5 mm broad limited-contact self compression plate (LC-SCP), and to compare the bending and torsional properties of the NP-LP and LC-SCP when used in osteotomized equine third metacarpal bones (MC3). METHODS: The plates alone were tested in four-point bending single cycle to failure. The MC3-plate constructs were created with mid-diaphyseal osteotomies with a 1 cm gap. Constructs were tested in four-point bending single cycle to failure, four-point bending cyclic fatigue, and torsion single cycle to failure. RESULTS: There were not any significant differences in bending strength and stiffness found between the two implants. The MC3-NP-LP construct was significantly stiffer than the MC3-LC-SCP in bending. No other biomechanical differences were found in bending, yield load in torsion, or mean composite rigidity. Mean cycles to failure for bending fatigue testing were similar for both constructs. CLINICAL SIGNIFICANCE: The NP-LP was comparable to the LC-SCP in intrinsic, as well as structural properties. The NP-LP construct was more rigid than the LC-SCP construct under four-point bending, and both constructs behaved similarly under four-point bending cyclic fatigue testing and torsion single cycle to failure. The new NP-LP implant fixation is biomechanically comparable to the LC-SCP in a simulated MC3 fracture.

Extra-articular stabilization of the cranial cruciate deficient stifle with anchor systems.

Complete or partial rupture of the cranial cruciate ligament (CCL) is a common injury of the canine stifle. Most practicing veterinarians would agree that optimal outcome is best achieved with surgical intervention. A popular method of stabilization is an extra-articular suture stabilization. The objective of this manuscript is to describe suture placement in a more isometric position as compared to traditional suture placement. A second objective is to introduce the veterinary surgeon to novel anchor products used for stabilization.

Single cycle to failure in torsion of three standard and five locking plate constructs.

OBJECTIVES: The biomechanical properties of standard plates and recently designed locking plates were compared in torsion. We hypothesized that titanium (Ti) constructs would have the greatest deformation, and String of Pearls (SOP) constructs the greatest strength and stiffness. METHODS: Dynamic compression plates (DCP), stainless steel (SS) limited contact (LC)-DCP, Ti LC-DCP, locking compression plate (LCP), 10 mm and 11 mm Advanced Locking Plate System (ALPS) 10 and 11, SOP and Fixin plates were applied to a validated bone model simulating a bridging osteosynthesis. Yield torque (strength), yield angle (deformation) and stiffness were compared using one-way ANOVA with post hoc Tukey (p <0.05). RESULTS: The ALPS 11 constructs had significantly greater elastic deformation than all constructs except for the ALPS 10. There were not any differences in strength observed except for the ALPS 10 constructs, which was less than that for the SOP, LCP, DCP and ALPS 11 constructs. No differences in construct torsional stiffness were observed with the SS LC-DCP, DCP, LCP and SOP constructs; however all had greater stiffness than all remaining constructs. The ALPS 10 construct had lower stiffness than all constructs. CLINICAL SIGNIFICANCE: Modulus of elasticity of Ti explains the higher deformation and lower stiffness of these systems, with similar results for the Fixin due to its lower section modulus compared to all other plates. The SOP and standard constructs had surprisingly similar biomechanical properties in torsion. The rationale for selecting these implants for fracture repair likely needs to be based upon their differing biomechanical properties inherent to the diverse implant systems.

Single cycle to failure in bending of three standard and five locking plates and plate constructs.

OBJECTIVE: To evaluate the biomechanical properties of standard and locking plates in bending. We hypothesised that titanium (Ti) constructs would have the greatest deformation and that String of Pearl (SOP) constructs would have the greatest strength and stiffness, and would behave differently compared to plates alone. METHODS: Dynamic compression plates (DCP), stainless steel (SS) limited contact (LC)-DCP®, Ti LC-DCP, locking compression plates (LCP), 10 mm and 11 mm advanced locking plate system (ALPS 10 / 11), SOP and Fixin plates were evaluated individually and as constructs applied to a validated bone model simulating a bridging osteosynthesis. Bending stiffness and strength were compared using one-way ANOVA with post hoc Tukey, and unpaired t-test (p <0.05). RESULTS: The SOP plates had significantly greater stiffness than all other plates; Ti LC-DCP, ALPS 10 and Fixin plates had significantly lower stiffness than all other plates. The SOP constructs had the highest mean bending stiffness, and strength that was significantly different from only the Ti LC-DCP, ALPS 10 and Fixin constructs. The ALPS 10 constructs had the lowest mean bending stiffness, and strength that was significantly different from only ALPS 11 and SOP constructs. Comparison of bending structural stiffness of plates versus constructs showed a significant difference in all plate pairs except for the DCP and ALPS 10. CLINICAL RELEVANCE: Due to differing plate construct properties inherent to these diverse implant systems, identical approaches to fracture management and plate application cannot be applied.

Tibial tuberosity transposition-advancement for treatment of medial patellar luxation and concomitant cranial cruciate ligament disease in the dog. Surgical technique, radiographic and clinical outcomes.

OBJECTIVE: To report surgical technique, morphometric effects and clinical outcomes for tibial tuberosity transposition-advancement (TTTA), sulcoplasty and para-patellar fascial imbrication for management of concomitant medial patellar luxation (MPL) and cranial cruciate ligament (CCL) disease in 32 dogs. STUDY DESIGN: Case series. METHODS: A previous technique for tibial tuberosity advancement was modified to incorporate lateral and distal tibial tuberosity transposition. Preoperative, immediate, and six to eight week postoperative radiographs were reviewed with morphometry of a range of tibial and stifle anatomic parameters. Findings of sequential clinical examinations to six to 20 months postoperatively were recorded. RESULTS: Thirty-nine stifles were treated by surgery. Medial patellar luxation grade ranged from II to IV/IV. The CCL rupture was complete in 17/39 stifles, and incomplete in 22/39. Complications occurred in 11/39 stifles including MPL recurrence (n=4). Resolution of subjectively-assessed lameness occurred in 29/39 stifles at the six to eight week assessment. Resolution of lameness was eventually documented in 35/39 stifles (4/39 lost to follow-up), and was maintained at the six to 20 month reassessment where available. The TTTA induced relative patella baja in 31/39 stifles. Magnitude of actual tibial tuberosity advancement was lower than that predicted by cage size. CLINICAL SIGNIFICANCE: Tibial tuberosity transposition-advancement is a potential treatment modality for concomitant CCL disease and MPL in the dog, but refinement of planning is required, while biomechanical and kinematic effects remain unknown.

Relationship of the biceps-brachialis complex to the medial coronoid process of the canine ulna.

OBJECTIVE: To describe the anatomic relationship of the biceps brachii-brachialis muscle complex and the medial compartment of the canine elbow. STUDY DESIGN: Anatomical cadaveric study. METHODS: Cadaveric forelimbs, and radius and ulna bones were examined to study the anatomy of the biceps brachii-brachialis complex and its relationship to the medial compartment of the elbow. RESULTS: The biceps brachii and brachialis muscles comprise a large muscular complex. The biceps brachii is a pennate fibred muscle which plays a major role in stabilising the elbow joint during the stance phase and facilitating limb acceleration during the swing phase. Additionally, the insertion of the muscular complex onto the ulnar tuberosity is such that a moment is generated which the authors hypothesise rotates the medial coronoid process against the radial head. The result is a compressive force which generates internal shear stress oblique to the long axis of the medial coronoid process. The authors further hypothesise that this may result in the microdamage or fragmentation of the medial coronoid process. CONCLUSION: The authors' conclude that contraction of the biceps brachii and brachialis complex may explain an aetiopathogenesis for fragmented medial coronoid process not associated with elbow dysplasia.

The effects of wire diameter and an additional lateral wire on pin and tension-band fixation subjected to cyclic loads.

Despite reports of frequent complications, pin and tension- band wire remains the most common repair of simple olecranon fractures and osteotomies. A recent mechanical study found wire diameter to be the key determinant of pin and tension-band construct strength; models with 1.25-mm wire were much stronger than those with standard 1.0-mm wire exposed to single loads to failure. Additionally, fixation strength was also increased when a lateral wire was used in combination with a standard figure-of-eight wire. The purpose of the present study was to assess any advantages provided by 1.25-mm wire or an additional lateral wire over 1.0-mm wire for pin and tension-band fixation subjected to cyclic loading. Pin and tension-band fixation was applied to plastic olecranon osteotomy models with three wire configurations: 1.0-mm figure-of-eight, 1.25-mm figure-of-eight, and combined 1.0-mm figure-of-eight and lateral. Cyclic load was applied while caudal osteotomy displacement was measured with an extensometer. The three groups were compared in terms of cycles to failure, mean minimum displacement, mean maximum displacement, and mean displacement per cycle. Models with an additional lateral wire survived significantly more cycles than those with a solitary 1.0-mm figure-of-eight wire, although caudal osteotomy displacements were not significantly different. Conversely, models with 1.25-mm wire allowed significantly smaller minimum and maximum displacements than those with 1.0-mm wire, but did not survive significantly more cycles. It therefore appears that clinical use of 1.25-mm wire may improve stability, while use of an additional lateral wire may improve durability.

Mutagenesis of ribosomal protein S8 from Escherichia coli: defects in regulation of the spc operon.

The structural features of Escherichia coli ribosomal protein S8 that are involved in translational regulation of spc operon expression and, therefore, in its interaction with RNA have been investigated by use of a genetic approach. The rpsH gene, which encodes protein S8, was first inserted into an expression vector under the control of the lac promoter and subsequently mutagenized with methoxylamine or nitrous acid. A screening procedure based on the regulatory role of S8 was used to identify mutants that were potentially defective in their ability to associate with spc operon mRNA and, by inference, 16S mRNA. In this way, we isolated 39 variants of the S8 gene containing alterations at 34 different sites, including 37 that led to single amino acid substitutions and 2 that generated premature termination codons. As the mutations were distributed throughout the polypeptide chain, our results indicate that amino acid residues important for the structural integrity of the RNA-binding domain are not localized to a single segment. Nonetheless, the majority were located within three short sequences at the N terminus, middle, and C terminus that are phylogenetically conserved among all known eubacterial and chloroplast versions of this protein. We conclude that these sites encompass the main structural determinants required for the interaction of protein S8 with RNA.