We evaluated the single-cycle structural properties for axial compression, torsion, and 4-point bending with a central load applied to the caudal or lateral surface of a diaphyseal segment from the normal adult equine humerus, radius, third metacarpal bone, femur, tibia, and third metatarsal bone. Stiffness values were determined from load-deformation curves for each bone and test mode. Compressive stiffness ranged from a low of 2,690 N/mm for the humerus to a high of 5,670 N/mm for the femur. Torsional stiffness ranged from 558 N.m/rad for the third metacarpal bone to 2,080 N.m/rad for the femur. Nondestructive 4-point bending stiffness ranged from 3,540 N.m/rad for the radius to 11,500 N.m/rad for the third metatarsal bone. For the humerus, radius, and tibia, there was no significant difference in stiffness between having the central load applied to the caudal or lateral surface. For the third metacarpal and metatarsal bones, stiffness was significantly (P < 0.05) greater with the central load applied to the lateral surface than the palmar or plantar surface. For the femur, bones were significantly (P < 0.05) stiffer with the central load applied to the caudal surface than the lateral surface. Four-point bending to failure load-deformation curves had a bilinear pattern in some instances, consisting of a linear region at lower bending moments that corresponded to stiffness values from the nondestructive tests and a second linear region at higher bending moments that had greater stiffness values. Stiffness values from the second linear region ranged from 4,420 N.m/rad for the humerus to 13,000 N.m/rad for the third metatarsal bone. Differences in stiffness between nondestructive tests and the second linear region of destructive tests were significant (P < 0.05) for the radius, third metacarpal bone, and third metatarsal bone. Difference between stiffness values of paired left and right bones was not detected for any test.

Effects of temperature and storage time on canine bone-transfixation pin specimens were tested by comparing pin pull-out forces. A total of 16 femurs from 8 mature dogs were tested. Five nonthreaded Steinmann pins were placed through both cortices in the diaphysis of each femur. The femurs were then sectioned transversely between each pin, with a bonepin specimen placed evenly into each of 5 groups prior to biomechanical testing. Four bone-pin specimen groups were stored at -20 or -70 C for 14 or 28 days, while 1 specimen group was immediately tested. Pull-out forces for frozen groups were compared with pull-out forces for the fresh group. Using two-way ANOVA, there was no statistical difference in mean axial-extraction forces among bonepin specimen in any of the tested groups. It is concluded that acute pin pull-out forces are not significantly affected by freezing temperature or time. However, specimens stored at -20 C for as few as 14 days had a trend for increased pull-out forces, compared with freshly harvested specimens. Therefore, the authors recommend storage of bone-pin specimens at -70 C when possible.

When Salmonella typhimurium and Clostridium perfringens were tested in conventional chickens, larger numbers of S typhimurium and C perfringens adhered to Eimeria tenella-infected ceca than to uninfected ceca. In germ-free chickens, S typhimurium and C perfringens adhered to the E tenella-infected cecal mucosa more than to the uninfected cecal mucosa, but fewer Bacteroides vulgatus and Bifidobacterium thermophilum adhered to the E tenella-infected ceca than to the uninfected ceca. Many bacteria adhered to the lesions caused by E tenella as observed by scanning electron microscopy. On the basis of our findings, we suggest that infection with E tenella upsets the balance of competitive adherence of bacteria, allowing more colonization of S typhimurium and C perfringens.

OBJECTIVE To determine the effects of 2 augmentation techniques on the mechanical properties of titanium cannulated bone screws. SAMPLE 33 titanium cannulated bone screws (outer diameter, 6.5 mm; guide channel diameter, 3.6 mm). PROCEDURES 11 screws were allocated to each of 3 groups. The guide channel of each screw was filled with polymethyl methacrylate bone cement alone (OCS group) or in combination with a 3.2-mm-diameter orthopedic pin (PCS group) or remained unmodified (control group) before mechanical testing. Each screw underwent a single-cycle 3-point bending test to failure with a monotonic loading rate of 2.5 mm/min. Failure was defined as an acute decrease in resistance to load of ≥ 20% or a bending deformation of 15 mm. Mechanical properties were determined for each screw and compared among the 3 groups. RESULTS All screws in the control and OCS groups and 1 screw in the PCS group broke during testing; a 15-mm bending deformation was achieved for the remaining 10 screws in the PCS group. Maximum load and load at failure differed significantly among the 3 groups. Stiffness and load at yield for the PCS group were significantly greater than those for the control and OCS groups but did not differ between the control and OCS groups. CONCLUSIONS AND CLINICAL RELEVANCE Use of bone cement and an orthopedic pin to fill the guide channel of cannulated screws significantly increased the strength of the construct, but ex vivo and in vivo studies are necessary before this augmentation technique can be recommended for clinical patients.

OBJECTIVE To evaluate biomechanical properties of intact feline mandibles, compared with those for mandibles with an experimentally created osteotomy that was stabilized with 1 of 2 internal fixation configurations. SAMPLE 20 mandibles from 10 adult feline cadavers. PROCEDURES An incomplete block study design was used to assign the mandibles of each cadaver to 2 of 3 groups (locking plate with locking screws [locking construct], locking plate with nonlocking screws [nonlocking construct], or intact). Within each cadaver, mandibles were randomly assigned to the assigned treatments. For mandibles assigned to the locking and nonlocking constructs, a simple transverse osteotomy was created caudal to the mandibular first molar tooth after plate application. All mandibles were loaded in cantilever bending in a single-load-to-failure test while simultaneously recording load and actuator displacement. Mode of failure (bone or plate failure) was recorded, and radiographic evidence of tooth root and mandibular canal damage was evaluated. Mechanical properties were compared among the 3 groups. RESULTS Stiffness, bending moments, and most post-yield energies for mandibles with the locking and nonlocking constructs were significantly lower than those for intact mandibles. Peak bending moment and stiffness for mandibles with the locking construct were significantly greater than those for mandibles with the nonlocking construct. Mode of failure and frequency of screw damage to tooth roots and the mandibular canal did not differ between the locking and nonlocking constructs. CONCLUSIONS AND CLINICAL RELEVANCE Results indicated that both fixation constructs were mechanically inferior to intact mandibles. The locking construct was mechanically stronger than the nonlocking construct.

OBJECTIVE To determine the effects of racetrack surface and shoe characteristics on formation of wear grooves in the horseshoes of racehorses. SAMPLES 1,121 horseshoes from 242 Thoroughbred racehorses collected during routine horseshoeing procedures at 4 racetracks with dirt or synthetic surfaces. PROCEDURES Data for 1,014 horseshoes from 233 racehorses were analyzed. Horseshoes were photographed, and length and width of grooves formed at the heels of the solar surface of horseshoes were measured on the photographs. Effects of racetrack, racetrack surface, and shoe characteristics (eg, shoe size, clips, and nails) on length and width of grooves were assessed by use of a mixed-model anova. RESULTS Length and width of wear grooves differed significantly on the basis of racetrack, nail placement, and limb side (left vs right). Differences in groove dimensions between types of racetrack surface (dirt vs synthetic) were less apparent than differences among racetracks. CONCLUSIONS AND CLINICAL RELEVANCE Measurements of the length and width of wear grooves in the horseshoes of racehorses may be useful for understanding some aspects of hoof interactions with various racetrack surfaces. Interpretation of differences in wear grooves for various racetrack surfaces will likely require quantitation of the mechanical behavior of the surfaces.

Objective- To compare the mechanical properties of laryngeal tie-forward (LTF) surrogate constructs prepared with steel fixtures and No. 5 braided polyester or braided polyethylene by use of a standard or a modified suture placement technique. Sample- 32 LTF surrogate constructs. Procedures- Surrogate constructs were prepared with steel fixtures and sutures (polyester or polyethylene) by use of a standard or modified suture placement technique. Constructs underwent single-load-to-failure testing. Maximal load at failure, elongation at failure, stiffness, and suture breakage sites were compared among constructs prepared with polyester sutures by means of the standard (n = 10) or modified (10) technique and those prepared with polyethylene sutures with the standard (6) or modified (6) technique. Results- Polyethylene suture constructs had higher stiffness, higher load at failure, and lower elongation at failure than did polyester suture constructs. Constructs prepared with the modified technique had higher load at failure than did those prepared with the standard technique for both suture materials. All sutures broke at the knot in constructs prepared with the standard technique. Sutures broke at a location away from the knot in 13 of 16 constructs prepared with the modified technique (3 such constructs with polyethylene sutures broke at the knot). Conclusions and Clinical Relevance- Results suggested LTF surrogate constructs prepared with polyethylene sutures or the modified technique were stronger than those prepared with polyester sutures or the standard technique.

Objective-To design and fabricate fiberglass-reinforced composite (FRC) replicas of a canine radius and compare their mechanical properties with those of radii from dog cadavers. Sample-Replicas based on 3 FRC formulations with 33%, 50%, or 60% short-length discontinuous fiberglass by weight (7 replicas/group) and 5 radii from large (> 30-kg) dog cadavers. Procedures-Bones and FRC replicas underwent nondestructive mechanical testing including 4-point bending, axial loading, and torsion and destructive testing to failure during 4-point bending. Axial, internal and external torsional, and bending stiffnesses were calculated. Axial pullout loads for bone screws placed in the replicas and cadaveric radii were also assessed. Results-Axial, internal and external torsional, and 4-point bending stiffnesses of FRC replicas increased significantly with increasing fiberglass content. The 4-point bending stiffness of 33% and 50% FRC replicas and axial and internal torsional stiffnesses of 33% FRC replicas were equivalent to the cadaveric bone stiffnesses. Ultimate 4-point bending loads did not differ significantly between FRC replicas and bones. Ultimate screw pullout loads did not differ significantly between 33% or 50% FRC replicas and bones. Mechanical property variability (coefficient of variation) of cadaveric radii was approximately 2 to 19 times that of FRC replicas, depending on loading protocols. Conclusions and Clinical Relevance-Within the range of properties tested, FRC replicas had mechanical properties equivalent to and mechanical property variability less than those of radii from dog cadavers. Results indicated that FRC replicas may be a useful alternative to cadaveric bones for biomechanical testing of canine bone constructs.