Daniel E. Brooks

Effectiveness of Local Antibiotic Delivery with an Osteoinductive and Osteoconductive Bone-Graft Substitute

BACKGROUND The morbidity associated with open fractures and open fracture treatment is well established. An osteoinductive and osteoconductive bone-graft substitute that prevents infection would decrease the number of procedures required to treat contaminated fractures by eliminating the need for surgical removal of cement beads and perhaps autograft harvest. We hypothesized that the combination of tobramycin-impregnated calcium sulfate pellets and demineralized bone matrix would prevent the establishment of infection in a contaminated fracture model. METHODS A unicortical 12-mm-diameter defect was created in the proximal tibial metaphysis of twenty-nine Spanish goats. After contaminating the wounds with an infective dose of Staphylococcus aureus, we divided the animals into four groups. The negative control group received no treatment, the positive control group received tobramycin-impregnated polymethylmethacrylate beads, the demineralized bone matrix group received 2.5 mL of demineralized bone matrix, and the experimental group received tobramycin-impregnated calcium sulfate pellets with 2.5 mL of demineralized bone matrix. Radiographs were made and intraosseous tissue cultures were performed on postoperative day 21. RESULTS The cultures showed no evidence of intramedullary infection in the experimental or the positive control group, but they were positive for Staphylococcus aureus in six of the seven goats in the negative control group and seven of the eight goats in the demineralized bone matrix group. CONCLUSIONS The combination of tobramycin-impregnated calcium sulfate pellets and demineralized bone matrix was effective in preventing intramedullary Staphylococcus aureus infection in a contaminated goat fracture model.

Antimicrobial efficacy of external fixator pins coated with a lipid stabilized hydroxyapatite/chlorhexidine complex to prevent pin tract infection in a goat model.

BACKGROUND Pin tract infection is a common complication of external fixation. An antiinfective external fixator pin might help to reduce the incidence of pin tract infection and improve pin fixation. METHODS Stainless steel and titanium external fixator pins, with and without a lipid stabilized hydroxyapatite/chlorhexidine coating, were evaluated in a goat model. Two pins contaminated with an identifiable Staphylococcus aureus strain were inserted into each tibia of 12 goats. The pin sites were examined daily. On day 14, the animals were killed, and the pin tips cultured. Insertion and extraction torques were measured. RESULTS Infection developed in 100% of uncoated pins, whereas coated pins demonstrated 4.2% infected, 12.5% colonized, and the remainder, 83.3%, had no growth (p < 0.01). Pin coating decreased the percent loss of fixation torque over uncoated pins (p = 0.04). CONCLUSION These results demonstrate that the lipid stabilized hydroxyapatite/chlorhexidine coating was successful in decreasing infection and improving fixation of external fixator pins.

Viscoelastic characteristics of muscle: passive stretching versus muscular contractions

This study compared the effects of repeated contractions and repeated passive stretches on the viscoelastic properties of muscle. The tibialis anterior (TA) muscles of eight anesthetized male New Zealand white rabbits were studied. In each rabbit, one hindlimb was randomly assigned to the repeated muscular contraction group (CON) and the contralateral hindlimb to the repeated passive stretch group (STRETCH). The passive tension at neutral length was measured in all muscles before and after both repeated muscular contractions or repeated passive stretches. In the CON hindlimb, the peroneal nerve was stimulated with a nerve stimulator for 1 s, and the resulting contractile force was measured. Stimulations were repeated every 10 s for a total of 10 contractions. In the STRETCH hindlimb, the TA was stretched from its shortest in vivo length to its maximum in vivo length 10 times at 20 cm x min-1. The maximum force generated during the first contraction in the CON group averaged 21.74 +/- 1.41 N, with a subsequent reduction with each muscle contraction to 13.66 +/- 0.81 N by the tenth contraction. The average peak tensile force in the STRETCH group was 17.39 +/- 2.61 N for the first passive stretch, decreasing to 13.57 +/- 1.84 by the tenth stretch. After repeated muscular contractions in the CON hindlimbs, the passive tension at neutral length decreased from 0.88 +/- 0.22 N to 0.42 +/- 0.08 N. After repeated passive stretches in the STRETCH hindlimbs, the passive tension at neutral length decreased from 1.16 +/- 0.17 N to 0.67 +/- 0.09 N. The percentage decreases in passive tension between the CON and STRETCH groups were not statistically significant (P = 0.24). The results show that stretching and contracting both result in tissue relaxation of the muscle-tendon unit. This finding may be a result of changes in the viscous elements of the connective tissue secondary to the forces generated by either stretches or contractions. This study suggests that well controlled isometric muscular contractions may result in decreased passive tension in a muscle at neutral length, a finding that one normally associates with passive stretching.

Comparison of Bulb Syringe and Pulsed Lavage Irrigation with Use of a Bioluminescent Musculoskeletal Wound Model

BACKGROUND Despite the fact that wound irrigation is a common surgical procedure, there are many variables, including delivery device, irrigant type, and fluid volume, that have yet to be optimized. The purpose of this study was to compare, with use of transgenic bioluminescent bacteria and standard quantitative microbiological methods, the efficacy of pulsed lavage and bulb syringe irrigation in reducing wound bacterial counts. METHODS A caprine model of a complex, contaminated musculoskeletal wound was developed with use of a bioluminescent strain of Pseudomonas aeruginosa that can be quantified. Luminescent activity was recorded as relative luminescent units with use of a photon-counting camera six hours after the wound was created and inoculated. Twelve goats were randomly assigned to either the pulsed lavage group or the bulb syringe irrigation group. Each wound was irrigated with normal saline solution in 3-L increments for a total of 9 L and was imaged after each 3-L increment. In addition, quantitative culture samples were obtained from different tissues within the wound before and after irrigation. RESULTS Pulsed lavage decreased the amount of relative luminescent units by 52%, 64%, and 70% at 3, 6, and 9 L, respectively. The bulb syringe irrigation reduced the amount of relative luminescent units by 33%, 44%, and 51% at these same time-points. Significant differences in luminescence were noted between the two groups after both 6 and 9 L of irrigation (p < or = 0.04). The correlation coefficients between relative luminescent units and quantitative cultures for the condition before irrigation and after irrigation were r = 0.96 and 0.83, respectively. CONCLUSIONS Pulsed lavage was more effective than bulb syringe irrigation in reducing bacterial luminescence after both 6 and 9 L of irrigation. Both device and volume effects can be demonstrated with use of this model. Bioluminescent bacteria provide a method to visualize bacterial distribution and to quantify the bacteria in a wound. CLINICAL RELEVANCE Pulsed lavage is a more effective and efficient method of irrigation to remove bacteria in a complex musculoskeletal wound. In the model we used, pulsed lavage irrigation with 3 L of saline solution resulted in a reduction of approximately the same amount of bacteria as did irrigation with 9 L with use of a bulb syringe.

Tobramycin-impregnated calcium sulfate prevents infection in contaminated wounds

Open fractures often are associated with increased rates of infection and nonunion, multiple surgical procedures, and delayed return to preinjury activity. Antimicrobial bone graft substitutes used as an alternative to antibiotic cement beads and/or delayed autologous bone grafting may provide a useful adjunct in patients with open fractures. A stable, unicortical defect was created and contaminated with 30 μL of 5 × 106 colony-forming units/mL of Staphylococcus aureus in the proximal tibial metaphysis of Spanish goats. The negative control group received no treatment, the carrier group received synthetic bone graft alone, the positive control group received tobramycin antibiotic cement, and the treatment group received tobramycin antimicrobial synthetic bone graft (calcium sulfate). After a 3-week evaluation period, intraosseous microbiologic specimens were obtained. The Staphylococcus aureus contaminant was recovered in 11 of 12 animals (mean = 6.9 × 107 colony-forming units/g marrow) in the negative control group and in all animals (mean = 2.2 × 108 colony-forming units/g marrow) in the carrier group. Bacteria were not found in the antibiotic-treated groups. The tobramycin-impregnated calcium sulfate was effective in preventing infection in a contaminated defect. It could be beneficial in reducing the number of surgeries and recovery time because it is bioabsorbable and osteoconductive.

Anabolic-Androgenic Steroid Administration Causes Hypertrophy of Immobilized and Nonimmobilized Skeletal Muscle in a Sedentary Rabbit Model

Although the use of anabolic agents in athletics has generated extensive publicity and controversy, the potential therapeutic benefits of these drugs have not been fully investigated. This randomized, blinded experimental study investigated whether short-term administration of an anabolic-androgenic steroid can limit immobilization-induced muscle atrophy in a rabbit model. We casted one hindlimb each in 48 New Zealand White rabbits and randomly assigned the rabbits to two groups. The treated group received weekly intramuscular injections of the anabolic-androgenic steroid, nandrolone decanoate (15 mg/kg). Immobilization significantly decreased muscle weights in both the treated rabbits and controls. Compared with controls, the body weights of the treated rabbits increased significantly at 2, 4, and 8 weeks. At 4 and 8 weeks, wet weights, dry weights, and contractile forces were significantly greater in both the casted and noncasted tibialis anterior muscle-tendon units of the treated group. Dry weights and casted contractile forces of the extensor digitorum longus muscle unit at 4 weeks and all measures at 8 weeks were greater in the treated rabbits than in controls. These results are contrary to previously accepted views that anabolic-androgenic steroid use leads to muscle hypertrophy only in conjunction with strength training. This study adds to the growing evidence that anabolic-androgenic steroids can produce significant skeletal muscle hypertrophy in sedentary populations.

The Effect of Circumferential Taping on Flexor Tendon Pulley Failure in Rock Climbers

The purpose of this study was to determine whether circumferential taping of the base of the finger increases the A2 pulleys load to failure in a model simulating a rock climbers grip. Nine pairs of fresh-frozen cadaveric hands, 20 to 47 years of age, were rigidly mounted in a specialized jig that maintained the finger in the climbers “crimp” position. Two of the four fingers of each hand were reinforced over the A2 pulley with three wraps of cloth adhesive tape. The flexor digitorum profundus and superficialis tendons were distracted until pulley or tendon failure. Overall, A2 pulley strength was greater in male specimens than in female specimens, and the A2 pulley of the small finger was the weakest tested. The A2 pulley failed simultaneously with the A3 and A4 pulleys in 55% of the tests. In the remaining trials, a single pulley failed initially followed by the remainder of the sheath. Of the 72 fingers studied, complete data were available for comparison of 22 pairs of fingers. No statistically significant difference in load to A2 pulley failure was noted between the taped and untaped finger pairs. Based on our findings we do not support taping the base of the fingers as a prophylactic measure against flexor tendon sheath injury in the climbing athlete.

Evaluation of Commercially Available Fluid-Warming Devices for Use in Forward Surgical and Combat Areas

The fluid-warming capabilities of four individual fluid warmers, i.e., Level 1, FMS 2000, Thermal Angel, and Ranger, were compared to evaluate their potential for medical use in forward military echelons of care. Lactated Ringers solution (LR) and Hextend at room temperature (20 degrees C) or refrigerated temperature (4-7 degrees C) and packed red blood cells at 4 degrees C to 7 degrees C were used with each warmer at two different flow rates. The FMS 2000 consistently warmed all fluids to approximately 37 degrees C, regardless of the starting temperature or flow rate. The Level 1 and Ranger also efficiently warmed all fluids except cold LR to approximately 37 degrees C. The Thermal Angel generally warmed room temperature fluid, cold Hextend, and packed red blood cells to at least 33 degrees C to 34 degrees C but could not warm cold LR. The clinical standard is to have fluids warmed to 32 degrees C at a minimum and more preferably to 34 degrees C to 35 degrees C. Of the fluid warmers tested, only the Thermal Angel failed to achieve such a temperature in warming cold LR. Data from the present study suggest the Ranger and FMS 2000 to be operationally adaptable to at least echelons 1 and 2, respectively, whereas far-forward use of the Thermal Angel has limitations.

Comparison of the Split Stacked Versus the Split Achilles Allograft for Dual Femoral Tunnel Posterior Cruciate Ligament Reconstruction

Background Cadaveric testing has shown that double-bundle reconstruction better replicates the native anatomy of the posterior cruciate ligament. With the current trend toward allograft Achilles posterior cruciate ligament reconstructions, the need to determine a graft configuration with the highest tensile and pull-out strength has become paramount. Hypothesis The split stacked Achilles allograft construct provides greater graft material to traverse the notch and provides increased load to failure at the tibial point of fixation compared with a standard monoblock Achilles allograft construct. Study Design Controlled laboratory study. Methods Eight matched pairs of Achilles allograft tendons were secured to 8 matched pairs of fresh-frozen human cadaveric tibiae. Group 1 consisted of single-block grafts (n = 8), and group 2 included the split stacked grafts (n = 8). The cross-sectional area of each grafts 2 collagenous bundles was measured with a micrometer. The graft constructs were pulled to ultimate failure at a rate of 50 mm/min on a materials testing machine. Results The mean cross-sectional area of the group 2 split stacked grafts (76.6 ± 3.1 mm2) was significantly greater than that of the group 1 single-block grafts (48.2 ± 3.0 mm2; P = .00006). The maximum load to failure of the group 2 construct was significantly greater (1383 ± 102 N) than that of the group 1 single-block configuration (1020 ± 136 N; P = .01). Conclusion These results indicate that the novel split stacked configuration of an Achilles tendon allograft provides a greater cross-sectional area of graft material across the joint as well as a significant increase in the overall load to failure strength compared with a standard monoblock Achilles allograft construct. Clinical Relevance The split stacked Achilles graft is an efficient method for using the entire allograft. With maintenance and use of all collagen fibers, the split stacked Achilles construct provides essentially 2 grafts in 1 while only using a single tibial tunnel.