Objective-To investigate the influence of varying morphological parameters on canine stifle joint biomechanics by use of a 3-D rigid-body canine pelvic limb computer model that simulated an intact and cranial cruciate ligament (CrCL)–deficient stifle joint across the stance phase of gait at a walk. Sample-Data from computer simulations. Procedures-Computer model morphological parameters, including patellar ligament insertion location, tibial plateau angle (TPA), and femoral condyle diameter (FCD), were incrementally altered to determine their influence on outcome measures (ligament loads, relative tibial translation, and relative tibial rotation) during simulation of the stance phase of gait at a walk. Outcome measures were assessed for each scenario and compared between an intact and CrCL-deficient stifle joint with the sensitivity index (the percentage change in outcome measure divided by the percentage change in input parameter). Results-In a CrCL-intact stifle joint, ligament loads were most sensitive to TPA. In a CrCL-deficient stifle joint, outcome measures were most sensitive to TPA with the exception of caudal cruciate ligament and lateral collateral ligament loads, which were sensitive to FCD and TPA. Relative tibial translation was sensitive to TPA and patellar ligament insertion location, whereas relative tibial rotation was most sensitive to TPA. Conclusions and Clinical Relevance-The computer model sensitivity analyses predicted that individual parameters, particularly TPA and FCD, influence stifle joint biomechanics. Therefore, tibial and femoral morphological parameters may affect the likelihood, prevention, and management of CrCL deficiency.

Objective: To evaluate the role of the semitendinosus muscle in stabilization of the canine stifle joint. Sample: Left stifle joints collected from cadavers of 8 healthy Beagles. Procedures: Left hind limbs, including the pelvis, were collected. To mimic the tensile force of the quadriceps, gastrocnemius, and semitendinosus muscles, wires were placed under strain between the ends of each muscle. A sensor was used to measure the tensile force in each wire. Specimens were tested in the following sequence: cranial cruciate ligament (CrCL) intact, CrCL transected, released (tensile force of semitendinosus muscle was released in the CrCL-transected stifle joint), and readjusted (tensile force of semitendinosus muscle was reapplied in the CrCL-transected stifle joint). Specimens were loaded at 65.3% of body weight, and tensile force in the wires as well as the cranial tibial displacement were measured. Results: Tensile force for the CrCL-transected condition increased significantly, compared with that for the CrCL-intact condition. Mean ± SD cranial tibial displacement for the CrCL-transected condition was 2.1 ± 1.3 mm, which increased to 7.2 ± 2.3 mm after release of the tensile force in the semitendinosus muscle. Conclusions and Clinical Relevance: Results supported the contention that the semitendinosus muscle is an agonist of the CrCL in the stifle joint of dogs. Moreover, the quadriceps and gastrocnemius muscles may be antagonists of the CrCL. These findings suggested that the risk of CrCL rupture may be increased by diseases (such as cauda equina syndrome) associated with a decrease in activity of the semitendinosus muscle.

Objective—To provide a detailed computed tomography (CT) reference of the anatomically normal equine stifle joint. stifle joints. Procedures—CT of the stifle joint was performed on 8 hind limbs. In all limbs, CT was also performed after intra-articular injection of 60 mL of contrast material (150 mg of iodine/mL) in the lateral and medial compartments of the femorotibial joint and 80 mL of contrast material in the femoropatellar joint (CT arthrography). Reformatted CT images in the transverse, parasagittal, and dorsal plane were matched with corresponding anatomic slices of the 8 remaining limbs. Results—The femur, tibia, and patella were clearly visible. The patellar ligaments, common origin of the tendinous portions of the long digital extensor muscle and peroneus tertius muscle, collateral ligaments, tendinous portion of the popliteus muscle, and cranial and caudal cruciate ligaments could also be consistently evaluated. The cruciate ligaments and the meniscotibial ligaments could be completely assessed in the arthrogram sequences. Margins of the meniscofemoral ligament and the lateral and medial femoropatellar ligaments were difficult to visualize on the precontrast and postcontrast images. Conclusions and Clinical Relevance—CT and CT arthrography were used to accurately identify and characterize osseous and soft tissue structures of the equine stifle joint. This technique may be of value when results from other diagnostic imaging techniques are inconclusive. The images provided will serve as a CT reference for the equine stifle joint

Somatosensory evoked potentials in response to tibial nerve stimulation were recorded from the scalp of 31 clinically normal mixed-breed dogs. The latency and amplitude of a main positive potential (P18), recorded with a frontal electrode referenced to the nose, were measured in subjects with body length ranging from 316 to 962 mm. A linear relation to body size explained the variations in latency among dogs (r2 = 0.81); the amplitude variations were explained in part by body size (r2 = 0.44). Bilateral tibial nerve stimulation significantly (P < 0.05) increased the amplitude of P18, but its latency was unaffected, compared with unilateral stimulation. Results of unilateral right and left tibial nerve stimulation were compared and were not different. Replacing acepromazine with xylazine as premedication before thiopental anesthesia did not influence the recordings.

Studies were undertaken to assess the chicken embryo and newly hatched chicken as models for studying the effects of bone-active agents. Initially, 1,25-dihydroxycholecaliferol (1,25[OH]2D3), sodium fluoride (NaF), parathyroid extract, epidermal growth factor, and prostaglandin E2, were tested for lethality over a broad dose range. One or 3 injections of 1,25(OH)2D3 into the yolk sac of chicken embryos resulted in death of embryos given greater than 0.1 ng/injection, whereas 0.01 ng was tolerated by the embryos. Administering 1,25(OH)2D3 intraperitoneally to newly hatched chickens as a single injection or weekly for 3 weeks resulted in no deaths at doses up to 50 ng. One or 3 IV injections of less than 400 micrograms were tolerated by the embryo. Giving chickens feed and water containing 2.4 g of NaF/kg was lethal but no deaths occurred when chickens were given feed containing less than 1.2 g of NaF/kg. Mortality associated with the administration of epidermal growth factor to embryos was inconsistent, in that death occurred in embryos given a single injection of greater than 250 ng, but no deaths occurred in embryos given 3 injections at similar doses. Parathyroid extract and prostaglandin F2 were not lethal when administered to embryos and chickens in a single-injection or multiple-injection regimen. Overall, lethality in chicken embryos given a particular agent reflected the dose of bone-active agent injected, rather than the number of injections. Three of the bone-active agents were selected to characterize their microscopic bone effects in chicken embryos and chickens. Administration of 1,25(OH)2D3 to embryos on day 14 at doses of 100, 10, 1, and 0.1 ng led to subperiosteal hyperosteoidosis in all 5 of the tibiotarsi examined from the high-dose (100 ng) group necropsied on day 18 of incubation. Three of 5 of the tibiotarsi from the 10-ng treatment group were similarly affected. Bone effects were noticed in chickens hatched from the aforementioned treatment groups or in chickens given 1,25(OH)2D3 intraperitoneally and examined at 3 and 6 weeks of age. Administration of NaF to chicken embryos on the 10, 12th, and 14th days of incubation via the IV route at doses of 160, 80, 40 and 20 micrograms/embryo led to subperiosteal hyperosteoidosis in tibiotarsi from 3 of 10 embryos (examined at 18 days of incubation) from the 2 high-dose groups. Tibiotarsi of chickens from this treatment group were microscopically normal at 3 weeks after hatching. When newly hatched chickens were given a diet containing NaF at dosages of 1.2 g/kg, 0.6 g/kg, and 0.3 g/kg, a dose-dependent increase in osteoid was seen at 3 and 6 weeks. In addition, cortical thinning and expansion of the medullary canal were observed only at 3 weeks. In contrast to the effects observed with 1,25(OH)2D3 and NaF, parathyroid extract caused no microscopic bone alterations when given to embryos or chickens. Overall, the bone alterations in the embryo were attributed to increased subperiosteal osteoid formation and defective mineralization. These findings were consistent with known effects of NaF and 1,25(OH)2D3 on bone, and they establish the chicken embryo as a sensitive model for studying bone-active agents.

OBJECTIVE To investigate the effect of an excessive tibial plateau angle (TPA) and change in compressive load on tensile forces experienced by the cranial cruciate, medial collateral, and lateral collateral ligaments (CCL, MCL, and LCL, respectively) of canine stifle joints. SAMPLE 16 cadaveric stifle joints from 16 orthopedically normal Beagles. PROCEDURES Stifle joints were categorized into unchanged (mean TPA, 30.4°) and excessive (mean TPA before and after modification, 31.2° and 41.1°, respectively) TPA groups. The excessive TPA group underwent a TPA-increasing procedure (curvilinear osteotomy of the proximal aspect of the tibia) to achieve the desired TPA. A robotic system was used to apply a 30- and 60-N compressive load to specimens. The craniomedial band of the CCL, caudolateral band of the CCL, MCL, and LCL were sequentially transected; load application was repeated after each transection. Orthogonal force components were measured in situ. Forces on ligaments were calculated after repeated output force measurements as the contribution of each component was eliminated. RESULTS Increasing the compressive load increased tensile forces on the craniomedial and caudolateral bands of the CCL, but not on the MCL or LCL, in specimens of both groups. At the 60-N load, tensile force on the craniomedial band, but not other ligaments, was greater for the excessive TPA group than for the unchanged TPA group. CONCLUSIONS AND CLINICAL RELEVANCE Results indicated that stress on the CCL may increase when the compressive load increases. The TPA-increasing procedure resulted in increased tensile force on the CCL at a 60-N compressive load without affecting forces on the MCL or LCL.

OBJECTIVE To determine values of F-wave parameters for the tibial nerve in clinically normal Miniature Dachshunds and those with thoracolumbar intervertebral disk herniation (IVDH). ANIMALS 53 Miniature Dachshunds (10 clinically normal and 43 with various clinical grades of thoracolumbar IVDH). PROCEDURES F-waves were elicited in the interosseous muscles of 1 hind limb in each dog by stimulation of the tibial nerve. F-wave parameters were measured for 32 stimuli/dog, and mean values were calculated. Linear regression was performed to assess correlations between F-wave parameters and clinical severity of IVDH. RESULTS For clinically normal dogs, mean ± SD values of shortest F-wave latency, mean F-wave conduction velocity, mean F-wave duration, and ratio of the mean F-wave amplitude to M response amplitude were 8.6 ± 0.6 milliseconds, 83.7 ± 6.1 m/s, 6.6 ± 1.5 milliseconds, and 9.8 ± 8.5%, respectively. F-wave persistence was 100%. Mean F-wave duration was positively correlated with clinical grade of IVDH. Linear regression yielded the following regression equation: F-wave duration (milliseconds) = 6.0 + 2.7 × IVDH grade. One dog with grade 2 IVDH had a mean F-wave duration shorter than that of all 5 dogs with grade 1 IVDH; 1 dog with grade 3 IVDH had a longer duration than that of all 10 dogs with grade 4 IVDH. CONCLUSIONS AND CLINICAL RELEVANCE Mean F-wave duration was correlated with the severity of inhibitory motor tract dysfunction in the spinal cord of dogs. F-wave examination may be useful for objective functional evaluation of upper motor neurons in the spinal cord.

OBJECTIVE To use high-field and low-field MRI to describe the anatomy of the proximal portion of the tarsal region (proximal tarsal region) of nonlame horses. SAMPLE 25 cadaveric equine tarsi. PROCEDURES The proximal portion of 1 tarsus from each of 25 nonlame horses with no history of tarsal lameness underwent high-field (1.5-T) and low-field (0.27-T) MRI. Resulting images were used to subjectively describe the anatomy of that region and obtain measurements of the collateral ligaments of the tarsocrural joint. RESULTS Long and short components of the lateral and medial collateral ligaments of the tarsocrural joint were identified. Various bundles of the short collateral ligaments were difficult to delineate on low-field images. Ligaments typically had low signal intensity in all sequences; however, multiple areas of increased signal intensity were identified at specific locations in most tarsi. This signal intensity was attributed to focal magic angle effect associated with orientation of collagen fibers within the ligaments at those locations. Subchondral bone of the distal aspect of the tibia was uniform in thickness, whereas that of the medial trochlear ridge of the talus was generally thicker than that of the lateral trochlear ridge. In most tarsi, subchondral bone of the talocalcaneal joint decreased in thickness from proximal to distal. CONCLUSIONS AND CLINICAL RELEVANCE Results generated in this study can be used as a reference for interpretation of MRI images of the proximal tarsal region in horses.

OBJECTIVE To quantitatively measure the amount of pressure induced at the calcaneus and cranial tibial surface of dogs by use of 2 cast configurations. ANIMALS 13 client- or student-owned dogs. PROCEDURES Pressure sensors were placed over the calcaneus and cranial tibial surface. Dogs then were fitted with a fiberglass cast on a pelvic limb extending from the digits to the stifle joint (tall cast). Pressure induced over the calcaneus and proximal edge of the cast at the level of the cranial tibial surface was simultaneously recorded during ambulation. Subsequently, the cast was shortened to end immediately proximal to the calcaneus (short cast), and data acquisition was repeated. Pressure at the level of the calcaneus and cranial tibial surface for both cast configurations was compared by use of paired t tests. RESULTS The short cast created significantly greater peak pressure at the level of the calcaneus (mean ± SD, 0.2 ± 0.07 MPa), compared with peak pressure created by the tall cast (0.1 ± 0.06 MPa). Mean pressure at the proximal cranial edge of the cast was significantly greater for the short cast (0.2 ± 0.06 MPa) than for the tall cast (0.04 ± 0.03 MPa). CONCLUSIONS AND CLINICAL RELEVANCE A cast extended to the level of the proximal portion of the tibia caused less pressure at the level of the calcaneus and the proximal cranial edge of the cast. Reducing the amount of pressure at these locations may minimize the potential for pressure sores and other soft tissue injuries.

OBJECTIVE To determine accuracy for a technique of needle redirection at a single craniolateral site for injection of 3 compartments of the equine stifle joint, describe the external needle position, and identify the location of the needle tip within each joint compartment. SAMPLE 24 equine cadaver stifle joints. PROCEDURES Stifle joints were placed in a customized stand. After the needle was placed, external needle position was measured and recorded. Each joint compartment (medial and lateral compartments of the femorotibial joint and the femoropatellar joint) was injected with a solution containing iodinated contrast medium, water, and dye. Radiography, assessment of intra-articular location of the needle tip, and gross dissection were performed to determine success of entering each joint compartment. Student t tests and an ANOVA were used to compare mean values. RESULTS Overall accuracy was 19 of 24 (79.1%), and accuracy for individual joint compartments was at least 21 of 24 (87.5%). Mean depth of needle insertion to access each compartment of the stifle joint was 5.71 cm. Mean angle of insertion (relative to the long axis of the tibia) was 82.1°, 80.3°, and 18.5° for the medial compartment of the femorotibial joint, lateral compartment of the femorotibial joint, and femoropatellar joint, respectively, and 28° medial, 7.3° lateral, and 1.3° lateral for the medial compartment of the femorotibial joint, lateral compartment of the femorotibial joint, and femoropatellar joint, respectively. CONCLUSIONS AND CLINICAL RELEVANCE Results supported that this was an accurate technique for successful injection of the 3 equine stifle joint compartments.