Biomechanical evaluation of a novel nucleus pulposus prosthesis in canine cadaveric spines

Partial disc replacement is a new surgical technique aimed at restoring functionality to degenerated intervertebral discs (IVDs). The aim of the present study was to assess biomechanically the behaviour of a novel nucleus pulposus prosthesis (NPP) in situ and its ability to restore functionality to the canine IVD after nuclectomy alone or after combined dorsal laminectomy and nuclectomy. Nine canine T13-L5 specimens (L2L3 group) and 10 L5-Cd1 specimens (LS group) were tested biomechanically in the native state, after nuclectomy (L2L3 group) or after combined dorsal laminectomy and nuclectomy (LS group), and after insertion of the NPP. Range of motion (ROM), neutral zone (NZ), and neutral zone stiffness (NZS) were determined in flexion/extension, lateral bending, and axial rotation. Nuclectomy alone and combined dorsal laminectomy and nuclectomy caused significant instability in all motion directions. Implantation of the NPP resulted in significant restoration of the parameters (ROM, NZ, and NZS) towards the native state; however, fragmentation/herniation of the NPP occurred in 47% of the cases. In conclusion, the NPP has the ability to improve functionality of the nuclectomized canine IVD. The high rate of NPP failure requires modifications directed at the integrity of the NPP and its confinement to the nuclear cavity.     

Morphologic and functional features of the canine cruciate ligaments

OBJECTIVE: To review the gross, microscopic, and functional anatomy of the cranial cruciate ligament (CCL) in dogs. STUDY DESIGN: Literature review. METHODS: Reports of the anatomy and function of the cruciate ligaments in dogs were retrieved by search of the 1975-2005 PubMed database. RESULTS: The CCL has an important biomechanical function resisting cranial drawer, hyperextension, and internal rotation and acts to fine tune and guide the stifle through its rolling and sliding motion. It has a complex architecture, and distinct geographic regions within the ligament have different functional roles depending on the angle and loading conditions. Collagen type I is the main component of the extracellular matrix; the fibrils have a crimped structure. The cruciate ligaments are almost completely covered by synovium, protecting them from synovial fluid. Cruciate blood supply is mainly of soft tissue origin. The intraligamentous network is relatively limited whereas the core of the middle third of the CCL is even less well vascularized. Neurohistologic studies are very limited in the dog. Various mechanoreceptors and proprioceptive receptors have been identified within the substance of the cruciate ligaments. CONCLUSIONS: CCL structural characteristics play an important part in its complex behaviour with the crimped pattern of the collagen fibrils being an important determinant of its biomechanical properties. In contrast to reports of managing CCL rupture, there are few reports describing the microanatomy and neurovascular morphology of the cruciate ligaments. CLINICAL RELEVANCE: Cruciate disease is likely multi-factorial. Improved understanding of CCL degradation leading to CCL rupture is critical to development of new diagnostic tests for cruciate disease in dogs. Appropriate intervention during the early stages of disease process might preserve CCL structural properties by preventing further collagen degradation. Accurate knowledge of functional and fiber bundle anatomy is imperative for reconstruction and restoration of normal stifle joint physiology. Reconstructive goals should alleviate existing instability and mimic normal kinematics. Knowledge of the exact function of the CCL in the neuromuscular control around the stifle joint could possibly explain osteoarthritis progression after CCL damage.     

Signalment differences in bone mineral content and bone mineral density in canine appendicular bones. A cadaveric study.

The objective was to determine signalment-related differences in bone mineral content (BMC) and bone mineral density (BMD) in dogs. Unilateral appendicular bones were harvested from 62 canine cadavers. Mid-diaphyseal regions of interest (ROIs) were scanned using a Hologic DXA device Braincon, Vienna, Austria). BMC and BMD were calculated within this region. Middle-aged dogs (3-10 years) revealed the highest BMC and BMD levels. Mean BMC and BMD were higher in males compared to females. Furthermore, body-weight of the male dogs was significantly higher compared to the females (P < 0.0001). Body weight and bone length were significantly associated with BMC and BMD (P < or = 0.023) in all bones but the radius. These data suggest that BMC and BMD appear to be highest in male large-breed dogs with a body weight greater than 30 kg. These results may help determine risk factors in fracture development and healing.     

Biomechanical analysis of the canine hind limb: calculation of forces during three-legged stance

This paper presents a three-dimensional biomechanical model of the canine hind limb, and describes the process of determining the muscle forces and joint reaction forces and moments occurring in the hind limb during three-legged stance. The model was based on anatomical and morphometric data presented in a previous paper. Equations of equilibrium were formulated for the different components of the hind limb. Since the number of unknowns exceeded the number of equations, the problem was statically indeterminate.Two optimization techniques were applied to solve this statically indeterminate problem. The resultant hip-joint reaction force (acting on the acetabulum) predicted by these optimization methods ranged between 0.73 and 1.04 times body weight, and was directed dorsally, medially and caudally. The resultant knee-joint reaction force (acting on the femur) ranged between 1.05 and 1.08 times body weight, and was directed dorsally, laterally and cranially. The largest muscle forces predicted by the minimization of maximal muscle stress (MMMS) criterion were in the biceps femoris (0.24 times body weight), rectus femoris (0.15 times body weight), medial gluteal (0.18 times body weight), semi-membranosus (0.09 times body weight), the lateral and intermediate vastus (0.18 times body weight) and the medial vastus (0.17 times body weight). The largest muscle forces predicted by the minimization of the sum of muscle forces (MSMF) criterion were in the biceps femoris (0.29 times body weight), lateral and intermediate vastus (0.45 times body weight)), and the deep gluteal (0.16 times body weight).The magnitudes and directions of the forces in the joints of the canine hind limb, as well as in the muscles that surround these joints, provide a database needed for future biomechanical analyses of the physiology and pathophysiology of the canine hind limb.     

Mechanoreceptors in the medial and lateral glenohumeral ligaments of the canine shoulder joint.

In order to have a better understanding of the role of ligaments in canine shoulder joint stability, the presence of mechanoreceptors in the medial (MGHL) and lateral (LGHL) glenohumeral ligaments was detected by means of a modified gold chloride stain. Three morphologically distinct mechanoreceptors were identified: Ruffini receptors (type I endings), Pacinian corpuscles (type II endings) and Golgi tendon organ-like receptors (type III endings). These receptors are mainly localized at each end of the ligaments and are prevalently in their glenoid portion. In particular, in the MGHL the highest density was at the cranial arm of the insertion into the scapula. The variety of mechanoreceptors in canine shoulder ligaments might indicate an afferent function in providing the CNS with joint proprioceptive information. Therefore, besides acting as passive mechanical stabilizers, the MGHL and the LGHL may serve as sensory structures, contributing actively to joint stability. Ligamentous injuries which occur in shoulders not only affect mechanical restraint but also alter the proprioceptive input to the CNS by means of disruption of the mechanoreceptors.     

Biomechanical properties of canine cortical bone allografts: effects of preparation and storage

The effects of various preparation and storage procedures and of different storage times on structural properties of canine cortical bone allografts were determined by evaluation of the compressive load to failure of a whole diaphyseal segment, the ability of a screw to resist being pulled from a cortical segment, and the torque required to strip the threads of a screw hole in a cortical segment. Preparation and storage procedures evaluated were sterile collection and storage at -20 C; ethylene oxide sterilization and storage at room temperature (22 C); chemical sterilization (methanol and chloroform, then iodoacetic acid) and storage at -20 C; and chemical sterilization, partial decalcification, and storage at -20 C. Storage times were 1, 16, and 32 weeks for each procedure. After 1 week of storage, aseptically collected frozen bone and ethylene oxide-sterilized bone had an increase, compared with matched controls, in load to failure in compression, but pullout load or screw-stripping torque did not change. Chemically sterilized bone had not changed after 1 week of storage, whereas chemically sterilized and partially decalcified bone had a 40% to 60% decrease in compressive load to failure, pullout load, and screw-stripping torque. Chemically sterilized and partially decalcified bone remained weak after 16 and 32 weeks of storage. Significant structural alterations were not detected in aseptically collected bone after 16 or 32 weeks of storage. Ethylene oxide-sterilized bone had a reduced pullout load after 32 weeks of storage. Chemically sterilized bone had significantly reduced compressive load to failure and pullout load after 16 and 32 weeks of storage.(ABSTRACT TRUNCATED AT 250 WORDS)     

A retrospective study of canine pancytopenia

To better define the incidence and causes of canine pancytopenia, we retrospectively evaluated the results of complete blood counts submitted to the University of Minnesota Veterinary Teaching Hospital during a 1-year period. Pancytopenia was defined as packed cell volume < 36%, total leukocyte count < 6,000/microliter or total segmented neutrophil count < 3,000/microliter, and platelet count < 200,000/microliter. Of 4,560 complete blood counts, 110 (2.4%) samples from 51 dogs met the criteria for pancytopenia. Eleven different disease processes were identified. These included chemotherapy-associated pancytopenia (n=22), parvovirus infection (n=5), malignant histiocytosis (n=5), idiopathic aplastic anemia (n=3), sepsis (n=3), myelodysplastic syndrome (n=3), immune-mediated hematologic disease (n=3), lymphoblastic leukemia (n=2), ehrlichiosis (n=2), estrogen toxicity (n=2), and multiple myeloma (n=1). Malignant histiocytosis and idiopathic aplastic anemia occurred more frequently than was expected. Doxoruicin was the chemotherapeutic agent associated with pancytopenia. Hematologic recovery and patient survival time varied with the cause of pancytopenia; therefore, a specific diagnosis was essential for establishing prognosis. Differentiation among causes of pancytopenia requires a systemic approach that includes elimination of infectious and drug-induced causes, and examination of bone marrow aspiration and core biopsy specimens.     

Biomechanical analysis of suture anchors and suture materials in the canine femur

Objective— Biomechanical analysis of acute load to failure (ALF) of 3 veterinary and 1 human suture anchor and cyclic load to failure with two suture material/suture anchor constructs in canine femoral condyles.
Study Design— Biomechanical in vitro study.
Sample Population— Cadaveric femora from 20–30 kg dogs.
Methods— Three veterinary and 1 human suture anchor were placed in the cranial and caudal aspects of the femoral condyle and subjected to 0° ALF. Anchors were loaded with 5 USP Fiberwire or 27 kg test nylon leader line (NLL) and subjected to 90° cyclic testing for 10,000 cycles followed by ALF at 90°.
Results— No significant difference in ALF for any anchor type was detected in the cranial aspect of the femoral condyle; however all veterinary anchors had higher ALF in the caudal aspect of the femoral condyle. In cyclic testing, the constructs in descending order (most cycles to least) were: (1) FlexiTwist/NLL, (2) Securos/Fiberwire, Securos/NLL, (3) IMEX/Fiberwire, IMEX/NLL, and (4) FlexiTwist/Fiberwire, Fastin/Fiberwire. Fiberwire was significantly stronger than NLL in post-cycling ALF testing.
Conclusions— Veterinary anchors had higher ALF in the caudal versus cranial aspect of the femoral condyle. Except for the FlexiTwist in which NLL performed better, Fiberwire and NLL both had similar cyclic performance with each veterinary anchor type. The veterinary anchors exceeded the human anchor in ALF and cycles to failure.
Clinical Relevance— The tested veterinary suture anchors with Fiberwire or NLL may be used in the femoral condyle, preferably in the caudal aspect, and should withstand estimated loading conditions in appropriately confined postoperative canine patients.     

Biomechanical and clinical evaluation of a modified 3-loop pulley suture pattern for reattachment of canine tendons to bone

OBJECTIVE: To describe a modified 3-loop pulley suture pattern for the reattachment of canine tendons to bone along with a biomechanical comparison with the locking-loop suture. STUDY DESIGN: In vitro biomechanical study and clinical case report. ANIMALS OR SAMPLE POPULATION: Biomechanical study: 10 paired gastrocnemius tendons and calcaneii harvested from 5 canine cadavers. Case report: a Doberman with avulsion of the gastrocnemius tendon of insertion. METHODS: Biomechanical study: paired tendons were reattached to the calcaneus with either a modified 3-loop pulley pattern or a locking-loop pattern. Tensile loading to failure was performed. A direct, non-contact, method of gap measurement, using digital video, was used to measure gap formation. Load required to initiate gap formation (defined as load at a 1 mm gap) and to produce a 3 mm gap was evaluated in addition to maximum load and gap at failure. RESULTS: Mean (+/-SEM) 1 mm gap loads were 31.0+/-4.2 and 17.2+/-2.5 N, mean 3 mm gap loads were 49.1+/-2.4 and 28.9+/-3.2 N, and mean maximum loads were 72.9+/-4.3 and 55.8+/-2.2 N for the modified 3-loop pulley suture and the locking-loop suture, respectively. These differences were statistically significant (P<.05). The gap at failure was similar for both repairs. The clinical case remained sound 7 months postoperatively. CONCLUSIONS: A modified 3-loop pulley pattern is biomechanically superior to a locking-loop pattern for reattachment of the canine gastrocnemius tendon to bone and may be suitable for clinical use. CLINICAL RELEVANCE: Tendon repairs with a gap >3 mm are reported to be at increased risk of rupture during the first 6 weeks postoperatively. A modified 3-loop pulley pattern resists gap formation better than a locking-loop pattern.     

Dorsal cross pinning of the atlantoaxial joint: New surgical technique for atlantoaxial subluxation

The subluxated atlantoaxial joint of a tetraplegic Yorkshire terrier was reduced and secured in position by means of cross pinning applied via a dorsal approach. The dog made a very satisfactory recovery. The surgical technique for this new procedure is described. Further investigations into the biomechanics of such fixation, and long term follow-up of treated cases, will be required to evaluate accurately the value of this technique.     

Initial evaluation of canine urinary cystatin C as a marker of renal tubular function

Objectives : To evaluate the performance of a particle‐enhanced turbidimetric assay for measuring canine urinary cystatin C and to investigate if the urinary cystatin C to creatinine ratio is higher in dogs with renal disease than in non‐renal disease dogs. Methods : Urinary cystatin C was measured by particle‐enhanced turbidimetric assay using an avian antihuman cystatin C antibody and the performance of this assay was evaluated. Clinical relevance was tested in 46 dogs that were divided into three groups: healthy dogs (n=14), non‐renal disease dogs (n=17) and dogs with renal disease (n=15). Results : The assay was linear (R2=0·99) and precise (mean intra‐ and inter‐assay coefficients of variation were 2·3 and 2·9%, respectively). The recovery was 111·5% and the limit of blank was 0·02 mg/L. Urinary cystatin C and urinary cystatin C to creatinine ratio differed significantly (P<0·001) between the three cohorts of dogs. Clinical Significance : Measurement of cystatin C by particle‐enhanced turbidimetric assay performed with high precision and linearity. This assay can be processed on automated clinical chemistry analysers making it widely available to commercial laboratories. Urinary cystatin C to creatinine ratio can differentiate dogs with renal disease from dogs without renal disease. These preliminary results suggest that urinary cystatin C to creatinine ratio is a promising marker for evaluating renal tubular function.