Minimum Inhibitory Concentration and Postantibiotic Effect of Amikacin for Equine Isolates of Methicillin-Resistant Staphylococcus aureus In Vitro

Objective— To report the minimum inhibitory concentration (MIC) of amikacin sulfate for equine clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA) and characterize the initial kill and duration of the postantibiotic effect (PAE) for selected strains.
Study Design— Experimental study.
Methods— Isolates of MRSA (n=35) had their amikacin MIC determined using the E-test agar diffusion method. Two isolates with MICs>256 μg/mL limit were further characterized using broth macrodilution. Six distinct isolates with amikacin MICs of 32, 48, 128 (2 isolates) and 500 (2 isolates) μg/mL had PAE determinations made over a range of amikacin concentrations from 31.25–1000 μg/mL using standard culture-based techniques.
Results— Median MIC of the 35 isolates was 32 μg/mL (range 2 to >256 μg/mL). Mean PAE of selected MRSA strains had an overall mean (all amikacin doses) of 3.43 hours (range 0.10–9.57 hours). PAE for MRSA exposed to amikacin at 1000 μg/mL was 6.18 hours (range 3.30–9.57 hours), significantly longer than that for all other concentrations ( P <.0001). There was no statistically significant effect of isolate MIC on PAE.
Conclusions— Isolates had a wide range of MIC; however, growth of all 6 selected strains were inhibited within the range of concentrations tested, including 2 strains with MICs of 500 μg/mL. PAE duration was not influenced by the MIC of amikacin but was significantly longer with treatment at 1000 μg/mL than at lower concentrations.
Clinical Relevance— Clinical isolates of MRSA are susceptible to amikacin at concentrations achieved by regional perfusion: however, the modest duration of PAE observed suggest that further laboratory and in vivo evaluation be conducted before recommending the technique for clinical use.     

Medial Plating for the Repair of Middle and Distal Diaphyseal Fractures of the Humerus in Dogs

Six middle and distal humeral shaft fractures in dogs were repaired by the application of a bone plate along the medial shaft of the humerus. In all animals, clinical and radiographic evidence of normal bone healing was observed. The bone plate and ancillary implants were removed from five dogs by 10 months. In none of the six dogs were any untoward effects of placing the bone plate along the medial shaft of the humerus detected nor were there any difficulties encountered with the medial humeral soft tissues.     

Placement of Multiple Full Pins for External Fixation Technique and Results in Four Dogs

A technique using a third bar and guide clamp was developed to permit reduction and stabilization of distal limb fractures with full pins and two connecting bars, one on each side of the bone. The system uses only single Kirschner clamps. Four distal limb fractures were stabilized using this technique. Closed reduction was used in three dogs to avoid devitalization of fragments and avoid contamination of a closed fracture. The fracture site stability achieved with this configuration allowed early return to weight bearing and rapid bone healing.     

Bacterial Culturing for Prediction of Postoperative Complications Following Open Fracture Repair in Small Animals

Swab specimens for bacterial culturing were obtained from 82 consecutive dogs and 13 cats undergoing open reduction and internal fixation of 110 fractures. Bacteria were isolated from 51 wounds. When the data were analyzed by stepwise logistic regression, it was found that bacterial contamination of wounds was associated most often with open fractures and with tibia or radius/ulna fractures. Contaminated wounds were five times more likely to develop complications than those without bacterial contamination. Regardless of results of bacterial culturing, postoperative complications developed significantly more often in animals that were febrile (>39.4° C [103° F]). Postoperative complications did not develop in animals that did not have bacterial contamination of wounds and were not febrile.     

A Comparison of Acute Pull-Out Strength Between Two-Way and One-Way Transfixation Pin Insertion for External Skeletal Fixation in Canine Bone

This study tested the hypothesis that two-way insertion of an external skeletal fixator trans-fixation pin would weaken the pin-bone interface. Smooth and partially threaded (end) trans-fixation pins were placed in tibiae of 32 cadavers by slow speed drilling or hand placement through a predrilled pilot hole. In one bone of each tibial pair, pins were inserted 2 cm beyond the distal cortex and retracted to a predetermined position (two-way). In the contralateral limb, the pins were inserted in one forward motion to the predetermined position (one-way). The peak force (Newtons) required to extract the pins (pull-out strength) axially at a rate of 1 mm/sec was determined by using a universal testing machine. A significant (p < .05) decrease in pull-out strength was found in pins placed by two-way insertion (674 +/- 410) as opposed to one-way insertion (766 +/- 432). The results of this in vitro study suggest that one-way insertion should be used clinically to decrease weakening of the pin-bone interface and prevent possible failure of external fixators. A significantly greater pull-out strength was found for threaded pins placed in the proximal diaphysis (1459 +/- 330 Newtons) compared to the distal metaphysis (873 +/- 297 Newtons).     

Biomechanical Study of Canine Spinal Fracture Fixation Using Pins or Bone Screws With Polymethylmethacrylate

Five configurations of pins or screws interconnected with polymethylmethacrylate (PMMA) were applied to isolated canine lumbar spines (L2 to L5) in which a complete fracture-luxation had been produced at L3 to L4. Twenty-five repaired spines and five intact control spines were subjected to four-point bending and tested once to failure in ventral flexion. The purpose of this study was to determine the effects of pin number, pin angle, and use of 3.5-mm cortical bone screws instead of smooth 3.2-mm diameter pins on rigidity and ultimate strength of spinal fractures repaired by the implant-PMMA fixation technique. Bending moment versus the angular deformation curves were recorded. Rigidity, bending moment at 10° angular deformation, moment at failure, and deformation at failure of each type of fixation were compared using analysis of variance. Spinal segments stabilized with eight pin-PMMA fixation had significantly greater rigidity and strength at failure than four pin-PMMA fixations ( P < .05). Furthermore, spinal segments stabilized with eight pins angled away from the fracture failed at significantly greater bending moment than those with eight pins angled toward the fracture ( P < .05). However, for four-pin fixation, greater strength was achieved by angling pins in the bone toward the fracture site ( P < .05). Screw-PMMA fixations failed by screw bending and were less rigid and weaker at failure than the corresponding configuration of pin-PMMA fixation ( P < .05).     

Arthrodesis for Congenital Flexural Deformity of the Metacarpophalangeal and Metatarsophalangeal Joints

A llama, a miniature horse, and a miniature donkey with severe bilateral congenital flexural deformities of the metacarpophalangeal and metatarsophalangeal joints were treated successfully by arthrodesis with dynamic compression plating or external skeletal fixation. The flexor tendons were more taut than the suspensory ligaments and were transected. In the llama, the suspensory ligament was transected, and overcorrection caused ischemic necrosis of one distal limb and subluxation of the other fetlock joint. In the horse and donkey, the suspensory ligament was preserved and wedge osteotomy was performed to correct the deformity.     

Results of Craniotomy for the Treatment of Cerebral Meningioma in 42 Cats

Forty-two cats underwent craniotomy for removal of a meningioma between 1985 and 1991. Median duration of clinical signs before examination was 1.25 months. All cats had inappropriate demeanor: 48% were dull and 38% were lethargic. Neurological deficits included impaired vision in 93%, paresis in 83%, and seizures in 19%. Computed tomography (CT) showed solitary masses in 86% and multiple masses in 14%. Intraoperative complications included hemorrhage and difficulty excising deep or adherent masses. Anemia in 13 of 42 cats was the most common immediate postoperative complication. Ten of 42 cats had no improvement or a more severe neurological status after surgery. Eight of 42 cats died immediately after surgery; 6 of these were anemic. Of the cats that survived the immediate postoperative period, evaluation 10 to 14 days after surgery showed that 97% (33 of 34) were alert and 79% (27 of 34) had returned to normal behavior. Neurological deficits, except for vision impairment, had resolved in most cats. The duration of follow-up varied from 1.3 months to 55.1 months. Ten cats developed neurological abnormalities from 1 month to 44.2 months after surgery; of these, 6 had tumor recurrence or new growth confirmed by CT scan or necropsy. Overall survival was 71% at 6 months, 66% at 1 year, and 50% at 2 years. Age of cat and location of tumor did not significantly affect survival ( P = . 1034 and .1851, respectively). There were too few precise measurements of tumor size to make a valid statistical comparison of the effect of size on survival. Location or presence of multiple tumors did not affect final outcome. Results of this study indicate that surgical excision is a beneficial method of treatment of cranial meningioma in cats.