Objective—To compare in vitro axial compression, abaxial compression, and torsional stiffnesses of intact and plated radii from small- and large-breed dogs.
Sample—Radii from 18 small-breed and 9 large-breed skeletally mature dogs.
Procedures—3 groups were tested: large-breed dog radii plated with 3.5-mm limited-contact dynamic compression plates (LCDCPs), small-breed dog radii plated with 2.0-mm dynamic compression plates (DCPs), and small-breed dog radii plated with 2.0/2.7-mm cut-to-length plates (CTLPs). The axial compression, abaxial compression, and torsional stiffnesses of each intact radius were determined under loading with a material testing machine. An osteotomy was performed, radii were plated, and testing was repeated. The stiffness values of the plated radii were expressed as absolute and normalized values; the latter was calculated as a percentage of the stiffness of the intact bone. Absolute and normalized stiffness values were compared among groups.
Results—The absolute stiffnesses of plated radii in axial and abaxial compression were 52% to 83% of the intact stiffnesses in all fixation groups. No difference was found in torsion. There was no difference in normalized stiffnesses between small-breed radii stabilized with CTLPs and large-breed radii stabilized with LCDCPs; however, small-breed radii stabilized with DCPs were less stiff than were any other group.
Conclusions and Clinical Relevance—Plated radii of small-breed dogs had normalized stiffnesses equal to or less than plated radii of large-breed dogs. The complications typically associated with plating of radial fractures in small-breed dogs cannot be ascribed to an overly stiff bone-plate construct.
Objective—To determine the influence of stifle joint flexion angle, cranial cruciate ligament (CrCL) integrity, tibial plateau leveling osteotomy (TPLO), and cranial tibial subluxation on the distance between the location of the origin and insertion of the CrCL (CrCLd) in dogs.
Samples—4 pairs of pelvic limbs from adult dog cadavers weighing 23 to 34 kg.
Procedures—Mediolateral projection radiographs of each stifle joint were obtained with the joint flexed at 90°, 105°, 120°, 135°, and 150°. Radiopaque markers were then placed at the sites of origin and insertion of the CrCL. Afterward, radiography was repeated in the same manner, before and after CrCL transection, with and without TPLO. Following CrCL transection, radiographs were obtained before and after inducing overt cranial tibial subluxation. Interobserver variation in measuring the CrCLd without fiduciary markers was assessed. The effect of CrCL integrity, cranial tibial subluxation, flexion angle, and TPLO on CrCLd was also determined.
Results—Interobserver agreement was strong, with an intraclass correlation coefficient of 0.859. The CrCLd was significantly shorter (< 1 mm) at 90° of flexion; otherwise, flexion angle had no effect on CrCLd. Cranial tibial subluxation caused a 25% to 40% increase in CrCLd. No effect of TPLO on CrCLd was found, regardless of CrCL integrity, forced stifle joint subluxation, or flexion angle.
Conclusions and Clinical Relevance—Overt cranial tibial subluxation in CrCL-deficient stifle joints can be detected on mediolateral projection radiographs by comparing CrCLd on neutral and stressed joint radiographs at joint angles between 105° and 150°, regardless of whether a TPLO has been performed.
Objective—To design and manufacture free-form biodegradable polycaprolactone (PCL) bone plates and to compare mechanical properties of femoral constructs with a distal physeal fracture repaired by use of 5 stabilization methods.
Sample Population—40 canine femoral replicas created by use of additive manufacturing and rapid tooling.
Procedures—Surgery duration, mediolateral and craniocaudal bending stiffness, and torsional stiffness of femoral physeal fracture repair constructs made by use of 5 stabilization methods were assessed. The implants included 2 Kirschner wires inserted medially and 2 inserted laterally (4KW), a commercial stainless steel plate (CSP), a custom free-form titanium plate (CTP), thin (2-mm-thick) biodegradable PCL plates (TNP) placed medially and laterally, and thick (4-mm-thick) PCL plates (TKP) placed medially and laterally.
Results—Surgical placement of 4KW was more rapid than placement of other implants The mean caudal cantilever bending stiffness of CTP and CSP constructs was greater than that for TNP TKP and 4KW constructs, and the mean caudal cantilever bending stiffness of TNP and TKP constructs was greater than that for 4KW constructs. The mean lateral cantilever bending stiffness of TKP constructs was greater than that for 4KW constructs. Differences among construct types were not significant in yield strength, ultimate strength, yield torque, and ultimate torque.
Conclusions and Clinical Relevance—The mechanical properties of fracture repair constructs made from free-form PCL biodegradable plates compared favorably with those of constructs made from Kirschner wires. The impact of PCL plates on musculoskeletal soft tissues, bone healing, and bone growth should be evaluated before clinical use.
Objective—To evaluate fluid pressures generated via common wound-flushing techniques.
Sample Population—24 combinations of bottles, needles, a syringe, and a bag.
Procedures—12 medically trained individuals used the following devices to forcefully expel fluid as for wound flushing: full and half-full 1-L and 500-mL bottles with holes in the cap made with 16-, 18-, 20-, and 22-gauge needles; a 35-mL syringe with the same needle sizes; and a 1-L bag placed in a cuff pressurized to 300 mm Hg, with the same needle sizes. Fluid expulsion pressures were measured and compared.
Results—The highest pressure generated with the bottle was 3.90 — 1.30 psi (mean — SD) with a 16-gauge needle and a full 1-L bottle. The highest pressure generated with the 35-mL syringe was 18.40 — 9.80 psi with a 16-gauge needle. The lowest pressure generated with the 35-mL syringe was 16.70 — 6.50 psi with an 18-gauge needle. The bag under pressure generated a pressure of 7.3 — 0.1 psi with a 16-gauge needle. Needle size did not have a significant effect.
Conclusions and Clinical Relevance—Solution bottles of any size and needle gauge do not meet the requirement for satisfactory flushing pressure of 7 to 8 psi. Use of a 35-mL syringe can produce pressure substantially > 7 to 8 psi, which could damage tissues. The most consistent delivery method to generate 7 to 8 psi was use of a 1-L plastic bag within a cuff pressurized to 300 mm Hg.
Objective—To evaluate the effect of the duration of cold Ischemia on the renin-angiotensin system during renal transplantation In cats and to define the potential Influence of vasoactive factors in renal tissue following cold ischemic storage versus warm ischemic storage
Animals—10 purpose-bred 6-month-old sexually Intact female cats
Procedures—10 cats underwent renal autotransplantation after 30 minutes (n = 5) or 3 hours (5) of simple, ex vivo cold storage of renal autographs. Following autograft reperfusion, direct hemodynamic variables were measured with a telemetric Implant and samples were collected for plasma renin concentration. Activation of vascular-related genes (renin, endothelin, and angiotensin converting enzyme) relative to 2-hour simple cold or warm ischemia was also evaluated.
Results—No significant difference between groups was detected In any of the hemodynamic variables or postreperfusion plasma renin concentrations measured in this study relative to the duration of cold ischemic storage. There was also no difference between warm- and cold-stored kidneys in the expression of vascular-related genes
Conclusions and Clinical Relevance—Prolonged renal Ischemia for clinically relevant durations does not appear to predispose clinically normal cats to altered hemodynamics or high plasma renin concentrations following graft reperfusion. Activation of vasoactive genes does not appear to be Influenced by type of Ischemia over 2 hours. (Am J Vet Res 2010;71:1220-1227)
Objective—To compare an electron beam melting-processed (EBMP) low-modulus titanium alloy mesh stem with a commercial cobalt-chromium (CC) stem in a canine cadaver model.
Sample Population—9 pairs of cadaver femora.
Procedures—EBMP stems of 3 sizes were placed in randomly chosen sides of femora (left or right) and CC stems in opposite sides. Stem impaction distances were recorded. Five strain gauges were attached to the femoral surface to record transverse tensile (hoop) strains in the femur during axial loading. Constructs were axially loaded 4 times to 800 N and 4 times to 1,600 N in a materials testing machine. Axial stiffness of constructs and bone surface strains were compared between EBMP and CC constructs.
Results—Stems were impacted without creating femoral fissures or fractures. Stem impaction distances were larger for EBMP stems than for CC stems. Mean axial stiffness of EBMP constructs was lower than mean axial stiffness of CC constructs. Subsidence did not differ between groups. Bone strains varied among strain gauge positions and were largest at the distal aspect of the stems. At a load of 1,600 N, bones strains were higher in CC constructs than in EBMP constructs for 2 of 4 medial strain gauges.
Conclusions and Clinical Relevance—EBMP stems were successfully impacted and stable and led to a focal decrease in bone strain; this may represent an acceptable option for conventional or custom joint replacement. (Am J Vet Res 2010;71:1089–1095)
Although cemented hip stems have been used successfully as part of total hip replacements in humans, their success rate has been reportedly lower in younger patients than in older patients. The longterm success of hip stems is affected by aseptic implant loosening, implant wear, and stress-mediated bone resorption (stress shielding). Cementless hip stems were originally developed in part because polymethylmethacrylate bone cement was considered to be a contributing factor to aseptic loosening of cemented hip stems. A portion of a cementless stem is textured or coated with porous surfaces for bone ongrowth and ingrowth. Stem stability relies on initial press fit and long-term bone ingrowth into the porous portions of the stems. Cementless stems are large and have a high
Objective—To compare heat generation during insertion, pullout strength, and associated microdamage between a self-tapping positive profile transfixation pin (STTP) and nontapping positive profile transfixation pin (NTTP).
Sample Population—30 pairs of third metacarpal bones (MC3s) from adult equine cadavers.
Procedures—One MC3 of each pair was assigned to the STTP group; the other was assigned to the NTTP group. The assigned pin was inserted into the diaphysis in a lateral to medial direction. Bone temperature increase during pilot-hole drilling and pin insertion was recorded at 1 mm from the final thread position with wire thermocouples at cis and trans cortices. Resistance to axial extraction before and after cyclic loading was measured in a material testing device, and microstructural damage caused by transfixation pin insertion was assessed with scanning electron microscopy.
Results—The STTP group developed a significant increase in bone temperature, compared with the NTTP group. No significant difference was found between the mean maximal pullout strength of the STTP and the NTTP in both non–cyclic-loaded and cyclic-loaded groups. Microdamage to the bone-pin interface was lower when the STTP versus the NTTP was used, but more bone debris was apparent after inserting the STTP.
Conclusion and Clinical Relevance—Because of the significant increase in temperature generation and debris accumulation despite similar pullout strengths and lesser microfracture formation, the STTP likely poses a higher risk of bone necrosis and potential loosening than the NTTP. This might be corrected by redesign of the tapping aspect of the STTP.
Objective—To evaluate effectiveness of allogeneic bone screws and pins for internal fixation of midbody transverse fractures of equine proximal sesamoid bones (PSBs) in vitro.
Sample Population—14 forelimbs from cadavers of 3-year-old Thoroughbreds.
Procedures—Allogeneic cortical bone fragments were collected from the limbs of a male Thoroughbred, and cortical bone screws were prepared from the tissue by use of a precision desktop microlathe programmed with the dimensions of a metal cortical bone screw. A midbody transverse osteotomy of each PSB was performed by use of a bone-shaping oscillating saw and repaired via 1 of 3 internal fixation techniques: 1 allogeneic bone screw with 1 allogeneic bone pin (type I; n = 6 PSBs), 2 allogeneic bone screws (type II; 8), or 1 stainless steel cortical bone screw (control repair; 6). Mechanical tension measurements were obtained by use of a commercially available materials testing system.
Results—Mean ± SD tensile strength (TS) was 668.3 ± 216.6 N for type I repairs, 854.4 ± 253.2 N for type II repairs, and 1,150.0 ± 451.7 N for control repairs.
Conclusions and Clinical Relevance—Internal fixation of PSB fractures by the use of allogeneic bone screws and bone pins was successful. Although mean TS of control repairs with stainless steel cortical bone screws was greater than the mean TS of type I and type II repairs, the difference between type II and control repairs was not significant. Allogeneic screws may advance healing and result in fewer complications in a clinical setting.
Objective—To compare bursting pressures in canine jejunum, measured by use of an in vitro and an in situ bursting pressure technique.
Study Population—Cadavers of 3 healthy adult dogs.
Procedures—54 enterotomies were performed on 3 canine cadavers immediately after euthanasia. After completion of enterotomy closure, bursting pressure was measured on 9 jejunal segments by use of an in situ technique and on 9 jejunal segments by use of an in vitro technique for each canine cadaver. Bursting pressure testing time was recorded for both in situ and in vitro techniques. Techniques were compared by means of randomized block ANOVA.
Results—The mean ± SE in vitro and in situ bursting pressures were 93.63 ± 24.10 mm Hg and 141.19 ± 38.10 mm Hg and were not significantly different. Mean in situ testing time was 40.7 min/cadaver; mean in vitro testing time was 50.3 min/cadaver.
Conclusions and Clinical Relevance—The in situ bursting pressure testing technique yielded results similar to those of the in vitro method, was somewhat less labor-intensive, and may be applicable to future studies of live dogs.
Objective—To determine elution characteristics of bone morphogenetic protein (BMP)-2 from a polycaprolactone coating applied to orthopedic implants and determine effects of this coating on osseointegration.
Procedures—An in vitro study was conducted to determine BMP-2 elution from polycaprolactone-coated implants. An in vivo study was conducted to determine the effects on osseointegration when the polycaprolactone with BMP-2 coating was applied to bone screws. Osseointegration was assessed via radiography, measurement of peak removal torque and bone mineral density, and histomorphometric analysis. Physiologic response was assessed by measuring serum bone-specific alkaline phosphatase activity and uptake of bone markers.
Results—Mean ± SD elution on day 1 of the in vitro study was 263 ± 152 pg/d, which then maintained a plateau at 59.8 ± 29.1 pg/d. Mean peak removal torque for screws coated with polycalprolactone and BMP-2 (0.91 ± 0.65 dN·m) and screws coated with polycaprolactone alone (0.97 ± 1.30 dN·m) did not differ significantly from that for the control screws (2.34 ± 1.62 dN·m). Mean bone mineral densities were 0.535 ± 0.060 g/cm2, 0.596 ± 0.093 g/cm2, and 0.524 ± 0.142 g/cm2 for the polycaprolactone–BMP-2–coated, polycaprolactone-coated, and control screws, respectively, and did not differ significantly among groups. Histologically, bone was in closer apposition to the implant with the control screws than with either of the coated screws.
Conclusions and Clinical Relevance—BMP-2 within the polycaprolactone coating did not stimulate osteogenesis. The polycaprolactone coating appeared to cause a barrier effect that prevented formation of new bone. A longer period or use of another carrier polymer may result in increased osseointegration.