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Biomedical subjects

D D Lewis

Publications and source records attributed to D D Lewis.

70 records · Page 4Linked to original sources
PubMed1977

Cell-mediated immunity against particulate and solubilized tumor-associated antigens of murine plasmacytomas detected by macrophage migration inhibition assays.

Cell-mediated immunity (CMI), as detected by the agarose microdroplet macrophage migration inhibition (MMI) assay, was investigated using peritoneal exudate cells (PEC) of BALB/c mice and several crude membrane (CM) and solubilized preparations of murine plasmacytomas. The MMI assay was quite sensitive and detected inhibition of macrophage migration as low as picogram quantities of CM, NP40 detergent- and papainsolubilized preparations (CS) of ADJ-PC5 and LPC-1 plasmacytomas. The data were highly reproducible from one experiment to the next with the same or different lots of the CM or solubilized extracts. Specificity studies demonstrated that ADJ-PC5 and LPC-1 plasmacytomas expressed cross-reactive tumor-associated antigens (TAA) as detected by MMI and confirmed by tumor challenge and Winn neutralization experiments. No cross-reactivity was observed with similar extracts prepared from an unrelated syngeneic simian virus 40 (SV40)-induced sarcoma. The inhibition of macrophage migration observed was mediated by culture supernatants generated from the mixture of plasmacytoma-immune spleen cells with antigens and then assayed in an indirect MMI assay on normal PEC. The agarose microdroplet MMI assay appeared to be a rapid and sensitive method to measure TAA recognition and to monitor TAA isolation and solubilization with minimum numbers of immune cells.

Animals↗
PubMedDate not supplied

A biomechanical comparison of screw and wire fixation with and without polymethylmethacrylate re-enforcement for acetabular osteotomy stabilization in dogs.

OBJECTIVE: Compare the biomechanical characteristics of screw and wire fixation with and without polymethylmethacrylate (PMMA) re-enforcement for acetabular osteotomy stabilization in dogs. ANIMALS: Pelves removed from 8 adult mixed breed dogs weighing between 25 and 30 kg. PROCEDURE: The pubic symphysis of each pelvis was split and a central transverse acetabular osteotomy was performed. One hemipelvis from each dog was stabilized with the composite fixation (interfragmentary Kirschner wire, two screws and a figure-of-eight orthopedic wire with PMMA). The contralateral hemipelves was stabilized with an interfragmentary Kirschner wire, two screws, and a figure-of-eight orthopedic wire without PMMA. All hemipelves were tested in bending by using a materials testing machine at a cross head speed of 5 mm/min. An extensometer was placed on the dorsomedial surface of the hemipelves centered over acetabular osteotomy to record distraction of the osteotomy during loading. A load/deformation curve and a load/distraction curve was produced for each hemipelvis. The slope for the initial linear portion of the load/deformation curve and the load/distraction curve, yield load and maximum load sustained were compared between repair groups using a paired t-test with P < .05 considered significant. RESULTS: The slope of the load/deformation curve was significantly greater (P = .001) for hemipelves stabilized with the composite fixation (mean +/- SD: 69 +/- 18 N/mm) compared with hemipelves stabilized without PMMA (mean +/- SD: 39 +/- 8 N/mm). There was no significant difference (P = .593) between repair groups in the slope of the load/distraction curves as measured on the extensometer. Yield load was significantly greater (P = .0002) for hemipelves stabilized with the composite fixation (mean +/- SD: 184 +/- 25 N) compared to hemipelves stabilized without PMMA (mean +/- SD: 74 +/- 12 N). Maximum load sustained was also significantly greater (P = .013) for hemipelves stabilized with the composite fixation (mean +/- SD: 396 +/- 71 N) compared to hemipelves stabilized without PMMA (mean +/- SD: 265 +/- 94 N). Failure of hemipelves stabilized with the composite fixation occurred primarily by ventrolateral bending of the cranial and caudal pelvic segments at the osteotomy site. Failure of hemipelves stabilized without PMMA occurred by ventrolateral bending of the cranial and caudal pelvic segments at the osteotomy site with pronounced concurrent ventrolateral rotation of the cranial pelvic segment. CONCLUSION: PMMA improves the mechanical characteristics of acetabular fracture fixation, at least in part by neutralization of rotational forces. The results of this study justify use of PMMA as a component of the composite fixation when repairing acetabular fractures.

Acetabulum↗
PubMedDate not supplied

Axial characteristics of circular external skeletal fixator single ring constructs.

OBJECTIVE: Evaluate the effects of varying ring diameter, wire tension, and wire-divergence angle on the axial stiffness characteristics of circular external skeletal fixator single-ring constructs. Study Design-Biomechanical evaluation using circular fixator components and a Delrin cylinder bone model. METHODS: Single ring constructs using two 1.6 mm diameter Kirschner wires to secure a 19 mm Delrin cylinder centered within the ring were examined. Component variables evaluated were ring diameter (50 mm, 66 mm, 84 mm, and 118 mm), wire-divergence angle (30 degrees, 60 degrees, and 90 degrees ), and wire tension (0 kg, 30 kg, 60 kg, and 90 kg). A total of 48 constructs were examined. Rings were rigidly mounted on a universal testing system and the cylinder loaded in axial compression (7.4 N/s) to 220 N. Load/displacement curves were analyzed to determine the following: the displacement (mm) that occurred before the slope of each load/displacement curve became linear, the stiffness (N/mm) of the linear portion of each load/deformation curve, and the total displacement (mm) produced at maximal load. Least-squares linear regression was used to model response variables as linear functions of ring diameter, wire divergence angle, and wire tension. Three-way interactions and 2-way interactions among independent component variables were evaluated first in the modeling process and included in a best model if response variables were found to have statistically significant regression coefficients. The regression coefficients and corresponding standard errors and covariances were used to estimate the maximal effect and standard error attributable to wire divergency angle (change from 30 degrees to 90 degrees ) and wire tension (change from 0 to 90 kg) for each ring diameter. RESULTS: All load/deformation curves had an initial exponential increase in stiffness, with the slope becoming linear at higher loads. The exponential phase was more pronounced in larger-diameter ring constructs and was mitigated by tensioning the wires. Ring diameter had the greatest influence on displacement that occurred before the curve became linear (semipartial r(2) [sp-r2] = .89), stiffness (sp-r2 = .94), and total displacement (sp-r2 = .93). Wire tension exerted a smaller influence on displacement that occurred before the curve became linear (sp-r2 =.06), stiffness (sp-r2 = .03), and total displacement (sp-r2 = .05). Wire divergence angle had a nominal effect on displacement that occurred before the curve became linear (sp-r2 = .0001), on stiffness (sp-r2 = .004), and on total displacement (sp-r2 =.003). CONCLUSIONS: Ring diameter had a profound effect on the axial stiffness characteristic of single ring constructs. Tensioning of the fixation wires can improve the axial stiffness characteristics of these constructs, particularly in larger diameter ring constructs, by mitigating the initial exponential phase of the load/deformation curve. Wire divergence angle had only a nominal differential effect on axial stability. CLINICAL RELEVANCE: Understanding how individual component variables and their interactions influence bone segment stability should help surgeons to optimize interfragmentary strain. Tensioning fixation wires is probably unnecessary in 50 mm diameter ring constructs, but assumes greater importance as ring diameter increases.

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PubMedDate not supplied

Postoperative examination of the biceps femoris muscle sling used in excision of the femoral head and neck in dogs.

Twenty-four dogs underwent unilateral excision of the femoral head and neck. An adjunctive biceps femoris muscle sling procedure was done in 16 dogs. In eight dogs (controls), the flap was dissected and returned to its original position. Four dogs with muscle slings were euthanatized on days 2, 5, 30, and 60, respectively. Four control dogs were euthanatized on day 2 and four dogs on day 5. Limb function did not differ consistently between dogs with muscle slings and control dogs. There was marked swelling and edema of the affected limb in half the dogs with muscle slings but not in the controls. Postoperative temperature elevations were significantly higher in dogs with muscle slings on days 1 and 2 (p less than 0.05). Infection was documented in four dogs with muscle slings. Flaps from control dogs had only minor gross and histologic abnormalities. On days 2 and 5, flaps from dogs with muscle slings appeared congested and swollen beneath and distal to the ostectomy site, with infarction involving 50 to 90% of the muscle mass. On days 30 and 60, the muscle slings were atrophic and fibrous, and by day 60 a synovial membrane covered the surfaces of all slings within the pseudarthrosis. Muscle fiber loss was attributed to infarction, necrosis, and disuse atrophy.

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Hepatic lobectomy in the dog. A comparison of stapling and ligation techniques.

The left lateral hepatic lobe was removed in six dogs with a stapling instrument and in six dogs by blunt dissection and ligation. Both techniques were safe and effective. Lobectomy by dissection and ligation was slower and less complete than by stapling. Major intraoperative or postoperative hemorrhage did not occur with either method. Serum chemistry values were elevated after surgery in all dogs but did not differ significantly between treatment groups. Microscopic hemorrhage, necrosis, and inflammation of the lobectomy site were more pronounced after dissection and ligation than stapling.

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Deep-frozen allogeneic cancellous bone grafts in 10 dogs: a case series.

Deep-frozen, aseptically collected and processed allogeneic cancellous bone was implanted in eight dogs during the surgical repair of diaphyseal long bone fractures and in two dogs during arthrodeses. A combined allogeneic and autogeneic cancellous bone graft was used in two fractures with a segmental bone loss of more than 5 cm. Bone union occurred in five fractures and in both arthrodeses. Failure of fixation occurred in two dogs with nonunion fractures and in a third dog with an open, infected fracture. Biopsies from the fracture sites were obtained from these dogs following failure of their fracture fixation. The cancellous bone graft appeared to be in the process of normal incorporation in each case. Failure of fixation was attributed to technical or case management errors or both, in each of the three fractures that failed to achieve bony union. Frozen allogeneic cancellous bone grafts were effectively incorporated when used in the primary repair of fractures and arthrodeses. Combined autogenous and allogeneic cancellous bone grafts may be particularly useful in the repair of fractures with large segmental diaphyseal bone defects. The use of allogeneic cancellous bone grafts in nonunion fractures requires further investigation before it can be recommended.

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Results of screw/wire/polymethylmethacrylate composite fixation for acetabular fracture repair in 14 dogs.

OBJECTIVE: To assess the clinical results in dogs with acetabular fractures stabilized using a screw-wire-polymethylmethacrylate (SWP) composite fixation. STUDY DESIGN: A retrospective study of client-owned dogs with acetabular fractures. ANIMALS: Fourteen dogs ranging in age from 4 to 95 months (mean, 34 +/- 25 months; median, 25 months) and body weight from 8 to 39 kg (mean, 25 +/- 6 kg; median, 27 kg). METHODS: Medical records and radiographs were retrospectively evaluated to determine location of the fracture, presence of preexisting degenerative joint disease, accuracy of fracture reduction and complications associated with surgery. Long-term results were evaluated by subjective assessment of lameness, elicitation of pain and/or crepitus on manipulation of the coxofemoral joint, measurements of pelvic limb circumference, coxofemoral joint goniometric measurements, and radiographic evaluation. RESULTS: Fracture reduction was considered anatomic in 13 dogs. At the time of the last follow-up evaluation (mean, 347 +/- 261 days; median, 380 days) 10 dogs were sound on the affected limb, three dogs had a subtle weight-bearing lameness of the affected limb, and the remaining dog had a consistent non-weight-bearing lameness of the affected limb. Mild (n = 10) or moderate (n = 1) degenerative changes of the affected coxofemoral joint attributed to the acetabular fracture and its repair were noted on the follow-up radiographs in 11 dogs. Limb circumference of the affected limb ranged from -8.2% to +10.8% (mean, -0.8 +/- 4.2%; median, -0.7%) of the contralateral limb. CONCLUSIONS: The SWP composite fixation consistently maintained anatomic reduction, was associated with few complications, and yielded satisfactory clinical results. CLINICAL RELEVANCE: The SWP composite fixation technique would seem to be an acceptable means of stabilizing acetabular fractures in dogs.

Acetabulum↗
PubMedDate not supplied

A biomechanical evaluation and assessment of the accuracy of reduction of two methods of acetabular osteotomy fixation in dogs.

OBJECTIVE: To compare the accuracy of reduction, biomechanical characteristics, and mode of failure of two methods of acetabular osteotomy repair. STUDY DESIGN: Acetabular osteotomies were created in 16 paired hemipelves and stabilized with a screw/wire/polymethylmethacrylate composite fixation technique (SWP) or a 2-mm veterinary acetabular plate (VAP). Eight intact hemipelves were used as controls. SAMPLE POPULATION: Twelve canine cadavers. METHODS: Accuracy of osteotomy reduction was evaluated grossly and by measurement of articular incongruencies formed in polyvinylsiloxane impression casts. Acetabula were loaded in modified bending until failure using a universal testing machine. Data from load-deformation curves were used to determine the biomechanical characteristics of the repaired and intact acetabula. Mode of failure was evaluated grossly and radiographically. RESULTS: Osteotomy reduction was superior in acetabula stabilized with SWP. Mean values +/- standard deviation for load at failure and stiffness of the intact acetabula were 2,796 +/- 152.9 N and 267.5 +/- 61.9 N/mm. Corresponding values for SWP and VAP were 1,192 +/- 202.7 N and 136.3 +/- 76.5 N/mm, and 1.100.5 +/- 331.6 N and 110.0 +/- 51.3 N/mm, respectively. The mean load at failure and stiffness of intact acetabula was significantly greater than acetabula stabilized with SWP or VAP. There was no significant difference between SWP and VAP for load at failure or stiffness. Failure of acetabula stabilized with SWP occurred by fracture of the polymethylmethacrylate and ventrolateral bending of the wires. Acetabula stabilized with VAP failed by ventrolateral twisting of the plate and bending of the caudal screws. CONCLUSIONS: SWP and VAP provide comparable rigidity, however, the SWP facilitates more accurate osteotomy reduction. CLINICAL RELEVANCE: These findings support the use of the SWP technique as an alternative method of acetabular fracture repair.

Acetabulum↗
PubMedDate not supplied

Gracilis or semitendinosus myopathy in 18 dogs.

The clinical findings in 18 dogs with gracilis (n = 17) or semitendinosus (n = 1) myopathy are described. Each dog had a similar hind-limb gait abnormality characterized by a shortened stride with a rapid, elastic medial rotation of the paw, internal rotation of the hock and external rotation of the calcaneus [corrected] and internal rotation of the stifle during the mid-to-late swing phase of the stride. Medical management prior to or in lieu of surgery was attempted (n = 8) with no apparent response. Fifteen dogs had one or multiple surgical procedures. Although transection, partial excision, or complete resection of the affected muscle resulted in resolution of lameness following surgery, lameness recurred six weeks to five months (mean, 2.5 months; median, two months) following surgery. Adjunctive medical treatment did not prevent recurrence. Variable replacement of the affected muscle with fibrous connective tissue (predominantly along the caudolateral border of the muscle) was evident grossly, and replacement of myofibers with fibrous connective tissue was confirmed histologically. A definitive etiology could not be established.

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Arthroscopic examination and treatment of osteochondritis dissecans of the femoral condyle of six dogs.

Arthroscopy was used to diagnose and treat osteochondritis dissecans (OCD) of the femoral condyle in six dogs. Bilateral lesions were seen in two dogs. The medial condyle was affected in five stifles, and the lateral condyle was affected in three stifles. Subchondral bone defects were identified on radiographs in six of eight affected stifles. Resolution of the lameness associated with the arthroscopic procedure occurred one-to-14 days (mean, three days) following arthroscopy. Lameness resolved completely in four cases within two weeks and in one case six weeks following arthroscopy. Mild lameness persisted in one case. Arthroscopy is an effective means of diagnosis and treatment of OCD of the femoral condyle, and it is associated with minimal postoperative morbidity when compared to arthrotomy.

Animals↗
PubMedDate not supplied

Evaluation of four interfragmentary Kirschner wire configurations as a component of screw/wire/polymethylmethacrylate fixation for acetabular fractures in dogs.

The biomechanical contribution of the interfragmentary Kirschner wire as a component of composite fixation for acetabular fracture repair was subjectively and objectively evaluated. Acetabular osteotomies were repaired using the screw/wire/polymethylmethacrylate (SWP) composite fixation with or without one of three configurations of Kirschner wire in 32 hemipelves obtained from 16 dogs. Reduction, assessed objectively and subjectively, was unaffected by Kirschner wire placement. Hemipelves repaired with Kirschner wire(s) were subjectively more stable prior to application of polymethylmethacrylate when manually assessed in multiple planes. Consistent incremental increases in stiffness, yield load, and maximum load sustained that were observed during biomechanical testing were not significant, with the exception that hemipelves repaired with two Kirschner wires had significantly greater yield loads than hemipelves repaired without Kirschner wires. The subjective results of this study support the use of at least one interfragmentary Kirschner wire to maintain reduction prior to polymethylmethacrylate application; however, fracture configuration and location may dictate the number and pattern of interfragmentary Kirschner wires used to maintain reduction prior to application of the polymethylmethacrylate. The objective results and observations made during biomechanical testing suggest that use of one or more interfragmentary Kirschner wires may enhance stability after polymethylmethacrylate application.

Acetabulum↗
PubMedDate not supplied

Electrocardiographic findings in dogs with motor vehicle-related trauma.

Motor vehicle-related injury is the most common form of trauma incurred by dogs, and cardiac arrhythmias are a well-recognized complication. Although posttraumatic arrhythmias are often observed, little is known regarding their frequency. This study utilized continuous ambulatory electrocardiography (i.e., Holter monitoring) to describe the cardiac rhythm disturbances in 30 dogs sustaining trauma in motor vehicle accidents. Ventricular ectopy was identified by Holter monitoring in 29 of 30 dogs, although the initial electrocardiogram (EKG) only documented ventricular ectopic complexes (VECs) in four dogs. Ventricular ectopy was infrequent in most dogs (i.e., 62% of the dogs had less than 100 VECs per day for the entire study), but 16% developed frequent arrhythmias (greater than 4,000 VECs per day). In all cases, the VECs were observed within 24 hours of injury. Forty-three percent of dogs had at least one episode of ventricular tachycardia, including several dogs that had an overall infrequent rate of VECs (i.e., less than 100 or 100 to 1,000 VECs per day). Although baseline EKGs are useful in identifying arrhythmias in most dogs, the length of the recording should be increased to improve the likelihood of observing an abnormal EKG event. Most importantly, additional EKGs should be obtained or continuous EKG monitoring should be performed in dogs that display clinical signs that could be attributed to ventricular arrhythmias.

Accidents, Traffic↗