Identification of effective elastic modulus using modal analysis; application to canine cancellous bone.

Mechanical properties of cancellous bone is of increasing interest due to its involvement in aging pathologies and oncology. Characterization of fragile bone tissue is challenging and available methodologies include quasi-static compressive tests of small size specimens, ultrasound and indentation techniques. We hypothesized that modal analysis of flexure beams could be a complementary methodology to obtain Young modulus. The sampling methodology was adapted such that the uniqueness of the linear dynamic response was available to determine the elastic modulus from natural frequencies and mode shapes. In a first step, the methodology was validated using a synthetic bone model as control. Then, water-jet cutting allowed collecting fourteen small beam-like specimens in canine distal femurs. X-ray microtomography confirmed the microarchitecture preservation, the homogeneity and the isotropy at the specimen scale to derive effective properties. The first natural frequency in clamped-free boundary conditions was used to obtain mean values of Young modulus, which ranged from 210 MPa to 280 MPa depending on the specimen collection site. Experimental tests were rapid and reproducible and our preliminary results were in good agreement with literature data. In conclusion, beam modal analysis could be considered for exploring mechanical properties of fragile and scarce biological tissues.

Effect of Tibial Plateau Levelling Osteotomy on Cranial Tibial Subluxation in the Feline Cranial Cruciate Deficient Stifle Joint: An Ex Vivo Experimental Study.

OBJECTIVES: This study evaluated the effects of tibial plateau levelling osteotomy on cranial tibial subluxation and tibial rotation angle in a model of feline cranial cruciate ligament deficient stifle joint. METHODS: Quadriceps and gastrocnemius muscles were simulated with cables, turnbuckles and a spring in an ex vivo limb model. Cranial tibial subluxation and tibial rotation angle were measured radiographically before and after cranial cruciate ligament section, and after tibial plateau levelling osteotomy, at postoperative tibial plateau angles of +5°, 0° and -5°. RESULTS: Cranial tibial subluxation and tibial rotation angle were not significantly altered after tibial plateau levelling osteotomy with a tibial plateau angle of +5°. Additional rotation of the tibial plateau to a tibial plateau angle of 0° and -5° had no significant effect on cranial tibial subluxation and tibial rotation angle, although 2 out of 10 specimens were stabilized by a postoperative tibial plateau angle of -5°. No stabilization of the cranial cruciate ligament deficient stifle was observed in this model of the feline stifle, after tibial plateau levelling osteotomy. CLINICAL SIGNIFICANCE: Given that stabilization of the cranial cruciate ligament deficient stifle was not obtained in this model, simple transposition of the tibial plateau levelling osteotomy technique from the dog to the cat may not be appropriate.

Effect of tibial tuberosity advancement on cranial tibial subluxation in the feline cranial cruciate deficient stifle joint: An ex vivo experimental study.

The effects of Tibial Tuberosity Advancement (TTA) on Cranial Tibial Subluxation (CTS) and Tibial Rotation Angle (TRA) were evaluated in a model of feline Cranial Cruciate Ligament (CrCL)-deficient stifle joint. Ten hindlimbs of adult cats were used. Quadriceps and gastrocnemius muscles were simulated using cables, turnbuckles and a spring. An axial load of 30% body weight was applied. The stifle and talocrural joint angles were adjusted to 120°. Patellar tendon angle (PTA), CTS and TRA were measured radiographically before and after CrCL section, after TTA and after additional advancement by 1 and 2mm. CrCL section resulted in a CTS of 8.1±1.5mm and a TRA of 18.4±5.7 °. After TTA, PTA was significantly decreased from 99.1±1.7° to 89.1±0.7°; CTS and TRA did not change significantly (7.8±1.0mm and 15.9±5.7° respectively). Additional advancement of the tibial tuberosity by 1mm did not significantly affect CTS and TRA. Additional advancement of the tibial tuberosity by 2mm significantly reduced the PTA to 82.9±0.9°. A significant decrease of CTS (6.9±1.3mm) and TRA (14.7±3.6°) was also observed. A lack of stabilization of the CrCL deficient stifle was observed after TTA in this model of the feline stifle. Even though the validity of the model can be questioned, simple transposition of the technique of TTA from the cat to the dog appeared hazardous.

Biomechanical comparison of two locking plate constructs under cyclic torsional loading in a fracture gap model. Two screws versus three screws per fragment.

OBJECTIVES: The number of locking screws required per fragment during bridging osteosynthesis in the dog has not been determined. The purpose of this study was to assess the survival of two constructs, with either two or three screws per fragment, under cyclic torsion. METHODS: Ten-hole 3.5 mm stainless steel locking compression plates (LCP) were fixed 1 mm away from bone surrogates with a fracture gap of 47 mm using two bicortical locking screws (10 constructs) or three bicortical locking screws (10 constructs) per fragment, placed at the extremities of each LCP. Constructs were tested in cyclic torsion (range: 0 to +0.218 rad) until failure. RESULTS: The 3-screws constructs (29.65 ± 1.89 N.m/rad) were stiffer than the 2-screws constructs (23.73 ± 0.87 N.m/rad), and therefore, were subjected to a greater torque during cycling (6.05 ± 1.33 N.m and 4.88 ± 1.14 N.m respectively). The 3-screws constructs sustained a significantly greater number of cycles (20,700 ± 5,735 cycles) than the 2-screws constructs (15,600 ± 5,272 cycles). In most constructs, failure was due to screw damage at the junction of the shaft and head. The remaining constructs failed because of screw head unlocking, sometimes due to incomplete seating of the screw head prior to testing. CLINICAL SIGNIFICANCE: Omitting the third innermost locking screw during bridging osteosynthesis led to a reduction in fatigue life of 25% and construct stiffness by 20%. Fracture of the screws is believed to occur sequentially, starting with the innermost screw that initially shields the other screws.

Ex vivo cyclic mechanical behaviour of 2.4 mm locking plates compared with 2.4 mm limited contact plates in a cadaveric diaphyseal gap model.

OBJECTIVES: To compare the mechanical properties of locking compression plate (LCP) and limited contact dynamic compression plate (LC-DCP) constructs in an experimental model of comminuted fracture of the canine femur during eccentric cyclic loading. METHODS: A 20 mm mid-diaphyseal gap was created in eighteen canine femora. A 10-hole, 2.4 mm stainless steel plate (LCP or LC-DCP) was applied with three bicortical screws in each bone fragment. Eccentric cyclic loadings were applied at 10 Hertz for 610,000 cycles. Quasistatic loading / unloading cycles were applied at 0 and 10,000 cycles, and then every 50,000 cycles. Structural stiffness was calculated as the slope of the linear portion of the load-displacement curves during quasistatic loading / unloading cycles. RESULTS: No bone failure or screw loosening occurred. Two of the nine LCP constructs failed by plate breakage during fatigue testing, whereas no gross failure occurred with the LC-DCP constructs. The mean first stiffness of the LCP constructs over the course of testing was 24.0% lower than that of constructs stabilized by LC-DCP. Construct stiffness increased in some specimens during testing, presumably due to changes in bone-plate contact. The first stiffness of LC-DCP constructs decreased by 19.4% and that of locked constructs by 34.3% during the cycling period. A biphasic stiffness profile was observed: the second stiffness was significantly greater than the first stiffness in both groups, which allowed progressive stabilization at elevated load levels. CLINICAL SIGNIFICANCE: Because LCP are not compressed to the bone, they may have a longer working length across a fracture, and thus be less stiff. However, this may cause them to be more susceptible to fatigue failure if healing is delayed.

Dual mobility canine total hip prosthesis: implant characteristics and surgical procedure.

Prosthetic dislocation is one of the most common complications after canine hip replacement. The use of dual mobility acetabular components has been shown to reduce the rate of dislocation in first intent hip replacement in human patients who are at high risk for dislocation. In such implants, a mobile polyethylene liner articulates on one side with a metallic acetabular component and on the other side with a metallic prosthetic head. A dual mobility cemented acetabular component has been designed for use in dogs, and is available for use in association with a previously designed modular femoral component. This report describes the characteristics and the procedure for implantation of this implant combination.

Effective mechanical properties of diaphyseal cortical bone in the canine femur.

The effective elastic modulus, yield strength, yield strain, ultimate strength, ultimate strain, strain energy density at yield and strain energy density at ultimate failure of femoral diaphyseal cortical bone were investigated on canine femurs. Four femurs representative of the canine population were selected from four statistically-determined clusters based on increasing size and weight comprising the Toy poodle (5 kg), Poodle (12 kg), German shorthaired pointer (25 kg) and Doberman (50 kg). The zones of interest were the lateral, medial, cranial, and caudal quadrants of the mid-diaphysis. Effective mechanical properties were measured using quasi-static three-point bending tests on strips. The averages ± SD were 15.6 ± 2.6 GPa for effective elastic modulus, 174.3 ± 32.1 MPa for yield strength, 0.012 ± 0.003 for yield strain, 251.0 ± 49.1 MPa for ultimate strength, 0.021 ± 0.005 for ultimate strain, 10.7 ± 4.0J m(-3) × 10(5) for strain energy density at Yield and 33.0 ± 14.1 Jm(-3)× 10(5) for strain energy density at ultimate failure. Significant differences were found between dogs and the effective elastic modulus increased with breed weight and size (13.9 GPa for the Toy poodle to 17.2 GPa for the Doberman). The ultimate strength σ(u) and strain energy density at ultimate failure U(u) were significantly lower in the Toy poodle than in the Poodle and German shorthaired pointer indicating that the cortical bone material in the Toy poodle differed from that of the other dogs. Examination of the zones of interest revealed that the cranial quadrant showed the greatest stiffness, whereas strength was highest at the medial site. The caudal cortex was less stiff and strong than the cranial cortex.

A case of stifle osteochondrosis treated by osteochondral autogenous grafting. One month morphological follow-up.

OBJECTIVE: To describe the one-month morphological appearance of autogenous osteochondral grafting in a dog with stifle osteochondrosis. METHOD: Osteochondral autografting was performed in one stifle of an eight-month-old dog with spontaneously occurring bilateral osteochondrosis. RESULT: Histopathological analysis performed one month after surgery confirmed partial integration of the grafts and osteochondral survival. CLINICAL SIGNIFICANCE: Autogenous osteochondral grafting in stifle osteochondrosis results in acceptable graft survival postoperatively and is worthy of further evaluation.

A case of bilateral patellar osteochondrosis and fracture in a cat. Clinical and histological findings.

Fracture of the patella associated with bilateral osteochondrosis of the superior pole of the patella in a 14-week-old cat is reported with histological findings. Patellar osteochondrosis has been described in humans, horses, pigs, and dogs and is characterised by incomplete union of the ossification centres related to an abnormal process of endochondral ossification. However this disease has not yet been described in cats. Macroscopically, two main fragments separated by interposed tissue were identified on the left patella. In contrast, no fracture but only a fissuration of the articular cartilage was observed on the right patella. Bilateral partial patellectomy was performed. Histological examination of the excised fragments from the left patella revealed two main areas of trabecular bone separated by a wide irregular band of hyaline cartilage. The microscopic aspect of the right patella was similar to that of the left. Serial sections showed the initial appearance of an area of necrosis in the central band of hyaline cartilage, and that this hyaline cartilage was subsequently replaced by fibrovascular connective tissue. These findings indicate that some patellar fractures may be due to patellar osteochondrosis.

A case of dorso-medial luxation of the radial carpal bone in a dog.

Luxation of the radial carpal bone is an uncommon injury in the dog and cat. Previous clinical cases have reported palmaro-medial luxation with injury to the short radial collateral ligament. In this study a case of dorsomedial luxation of the radial carpal bone in a 10-year-old female Gordon Setter is described. A closed reduction of the luxation was performed and a conservative treatment was carried out. Thirteen months after the reduction, the dog had a satisfactory limb function, despite the presence of degenerative joint disease of the carpus. A pathogenic hypothesis for this dorso-medial luxation of the radial carpal bone is proposed reproducing the luxation on canine cadavers.