L. Orienti

A Comparison of Hydroxyapatite-Coated, Titanium-Coated, and Uncoated Tapered External-Fixation Pins. An in Vivo Study in Sheep*

Three types of surfaces for external fixation pins were compared. One hundred and eight stainless-steel tapered 5/6-millimeter pins were divided into three groups: thirty-six pins remained uncoated (Group A), thirty-six were plasma-sprayed with hydroxyapatite (Group B), and thirty-six were plasma-sprayed with titanium (Group C). The pins were implanted in the left tibia of eighteen sheep, with each sheep receiving six pins from the same group. A unilateral fixator then was assembled on the pins. The medial aspect of the mid-part of the tibial diaphysis was exposed, and a five-millimeter-long cylinder of bone was removed so that load would be borne by the bone-pin interfaces. Six weeks after the procedure, radiographs demonstrated rarefaction of twenty-nine pin tracks in Group A, fifteen in Group B, and thirty in Group C (p = 0.021 for Group A compared with Group B and p = 0.016 for Group B compared with Group C). The mean final insertion torque (and standard deviation) was 4360 ± 1050 newton-millimeters in Group A, 3420 ± 676 newton-millimeters in Group B, and 3740 ± 643 newton-millimeters in Group C. With the numbers available, no significant differences could be detected among these values. The mean extraction torque was 253 ± 175 newton-millimeters in Group A, 3360 ± 1260 newton-millimeters in Group B, and 1720 ± 1030 newton-millimeters in Group C (p = 0.002 for Group A compared with Group B, p = 0.017 for Group A compared with Group C, and p = 0.03 for Group B compared with Group C). The extraction torque was significantly lower than the corresponding insertion torque in both Group A (p < 0.001) and Group C (p = 0.003); no significant difference could be found, with the numbers available, in Group B (hydroxyapatite-coated pins). At sixty times magnification, direct contact was seen along a mean of 16 ± 9 per cent of the bone-pin interface in Group A, 30 ± 12 per cent of the interface in Group B, and 28 ± 15 per cent of the interface in Group C (p = 0.042 for Group A compared with Group C). However, at 10,000 times magnification, direct bone-pin contact was found only in Group B. CLINICAL RELEVANCE: The better fixation and greater interface strength of the hydroxyapatite-coated tapered pins should lead to a substantial decrease in the frequency of loosening and infection and consequently to a remarkable improvement in the clinical results of external fixation.

Improvement of the bone-pin interface with hydroxyapatite coating: an in vivo long-term experimental study.

The present study was designed to comparatively evaluate the bone-pin interface in a long-term unloaded experimental study in two groups of pins, uncoated and coated with hydroxyapatite. Forty pins made of stainless steel were used. Half of the pins were plasma-sprayed with hydroxyapatite, and the other half remained uncoated. Four adult sheep were selected. Each sheep tibia was implanted with five pins. Two sheep were euthanized 4 months after surgery and the remaining two 12 months after surgery. Extraction torque was higher in the hydroxyapatite-coated pins compared with the uncoated ones at both 4 (p < or = 0.0005) and 12 months (p < or = 0.0005) after implantation. The histological patterns observed in the sheep euthanized 4 and 12 months after implantation were very similar. An extensive bony coverage of the hydroxyapatite-coated pins without any coating resorption and delamination from the metallic substrate was observed. Fibrous tissue encapsulation was found in the uncoated pins. These results demonstrate that the hydroxyapatite coating significantly improved the bone-pin interface. A similar improvement of bone-pin interface rigidity in many clinical situations is likewise possible.

Muscular Trauma Treated with a Ga-Al-As Diode Laser: In Vivo Experimental Study

The aim of the study was to verify in an experimental model the effects of laser therapy performed with Ga-Al-As diode lasers (780 nm, 2500 mW) on traumatised muscles. Forty adult New Zealand male rabbits were divided into four groups (A, B, C and D) of ten animals each. Each group of animals was further divided into two subgroups of five animals each. The animals were submitted to muscular trauma for 7 min by clamping the posterior muscles of the left thigh under general anaesthesia. Four days later, the rabbits in the B1, B2, C1, C2, D1 and D2 subgroups started daily laser therapy. The parameters utilised were: 150 J/cm2 energy density, 3 W, 50 Hz in group B; 250 J/cm2, 3 W, 100 Hz in group C; and 800 J/cm2, 3 W, 0 Hz (continuous output) in group D. The animals in subgroups A1 and A2 were used as untreated controls and allowed to heal spontaneously. In order to prepare samples for histological, histochemical and histomorphometrical studies, dissection of the posterior muscle of the thigh was performed under general anaesthesia and before sacrifice, after five days of laser therapy in the subgroups B1, C1 and D1 and after ten days of laser therapy in subgroups B2, C2 and D2. The samples of untreated subgroups A1 and A2 were subjected to the same procedure and at the same times as the corresponding laser-treated groups. The following parameters were analysed on muscular samples: qualitative histological aspect (lactate dehydrogenase (LDH), cytochrome oxidase, acid phosphatase and alkaline phosphatase concentration with histoenzymatic methods) and quantitative histomorphometric evaluation of muscular damage and tissue repair. Blood samples were drawn from each subgroup before the trauma and again before sacrifice to measure the creatine phosphokinase (CK) and LDH levels. The results obtained in the tables are shown. Analysis of the results showed a better qualitative and quantitative healing process in traumatised muscles treated with Ga-Al-As diode laser therapy than in spontaneously healed ones. The results obtained with laser therapy were confirmed as haematic, histoenzymatic and histomorphometric values. According to these results, there is a positive relationship between the biostimulation properties of the laser and the healing of traumatised muscular tissue.

Resorbable device for fracture fixation: in vivo degradation and mechanical behaviour.

The availability of a high molecular weight poly(L-lactide), with supposed good mechanical properties, encouraged us to carry out an in vivo experimental study to evaluate the degradation rate and accompanying loss of strength during interaction with bone. Small cylindrical PLLA rods were manufactured by compression moulding. Thirty-six male New Zealand rabbits (b.w. 3 kg), randomly divided into six groups of six animals each, were submitted to implantation of the rods under general anaesthesia (0 3x7 mm rods in the lateral condylic region of the right femur and 0 3x50 mm rods in the intracondylic channel of the left femur). The animals were then sacrificed at the end of each experimental time (4, 8, 12, 24, 52, 64 weeks), hence the femurs were explanted. Histology showed no inflammatory cells with fragmentation or resorption of bone trabeculae. Mechanical studies showed a decrease in mechanical properties and flexional stiffness, and the absence of evident material resorption. Finally, the properties of this newly developed resorbable device, when confirmed, seem to justify future clinical introduction of this synthetic material.

COMPARISON AMONG THREE DIFFERENT BIOCOATINGS FOR ORTHOPAEDIC PROSTHESES. AN EXPERIMENTAL ANIMAL STUDY

One-hundred-eighty cylindrical monocortical titanium implants, 4mm diameter and 12mm long, with three different coatings: fluorohydroxyapatite (group A), hydroxyapatite (group B), and titanium oxide (group C), all applied by vacuum plasma spray were bilaterally, randomly implanted into the femurs and tibiae of twelve adult mongrel sheep. The sheep were divided into four groups (1, 2, 3 and 4) numbering three sheep each. Sheep of groups 1, 2, 3 and 4 were euthanized at two weeks, one month, three and nine months after implantation, respectively. Biomechanical and histomorphological analysis were performed. Extraction torque increased over time in all groups until the nine months period. At all the studied periods, the bone-implant contact was higher in Groups A and B compared to Group C. However, only at nine months did this difference reach statistical significance (p<0.005 comparing Groups A and B to C). The results of this study show that all the three coatings could be recommended for clinical applications.

Experimental evaluation of a resorbable intramedullary plug for cemented total hip replacement

In order to evaluate degradation kinetics and biocompatibility of a resorbable poly(D,L-lactic acid) (PDLLA) plug for total cemented hip prostheses, an experimental in vitro and in vivo study was carried out. Degradation rate studies were performed in Ringer solution and after in vivo plug implantation in the femoral medullar cavity of rabbits. In vitro biocompatibility was evaluated in murine fibroblast cell cultures. PDLLA plugs showed faster degradation kinetics in vivo than in vitro. Histological evaluations showed that PDLLA completely disappeared in vivo 26 weeks after implantation. Fibrous tissue in the medullar cavity was observed at 13 weeks, but no histological changes were observed after 26 weeks. Also, the in vitro tests showed good biocompatibility of the biomaterial. Our results show the possibility of considering this resorbable plug for clinical situations instead of the traditionally used plugs [polyethylene, poly(methyl methacrylate) or cancellous bone] due to its biocompatibility, degradation properties and simplicity of use.

Measurement of insertion torque of tapered external fixation pins: A comparison between two experimental models.

The aim of this study was to compare an in vitro versus an ex vivo experimental model to test the insertion torque of two different types of external fixation pins. A torque measuring machine was developed in order to perform accurate measurements. Forty tapered pins made of stainless steel were utilized. Half of the pins were plasma-spray coated with hydroxyapatite (HA) and the other half remained uncoated. For the in vitro model 20 cylinders were used that were made of synthetic polymer according to ASTM standards. For the ex vivo model 10 fresh femora harvested from adult sheep were used. All the pins were implanted after predrilling, and insertion torque was measured. Statistical analysis of the in vitro versus the ex vivo model showed significant differences in both coated (p < 0. 0005) and uncoated (p = 0.002) external fixation pins. These results may be due to the surface roughness that caused significant friction between the HA coating and the polyvinylchloride in the in vitro model. The significant difference between the in vitro and ex vivo results lead us to state that the in vitro model does not realistically simulate the behavior of external fixation pins implanted in bone.

Laser Doppler Evaluation of Microcirculation Behaviour during an Ischaemia-Reperfusion Injury

Laser Doppler flowmetry (LDF) was tested in an experimental ischaemic model on rat limbs to evaluate the degree of ischaemia and to find a possible correlation with values obtained with this device and prognosis. Under general anaesthesia, 40 Wistar rats were submitted to 4 h and 30 min of ischaemia of the left hind limb. Ten rats formed the control group (group 1). Two enzymes, native superoxide dismutase (SOD) and SOD modified with polyethylene glycol, were employed in 15 rats each (groups 2 and 3). Data were collected by means of LDF both in the sole and muscles before ischaemia (steady state), during ischaemia and at the beginning of reperfusion, and only in the sole after 1 h of reperfusion. A range of predictive (95%) perfusion values (PU) for limb healing or necrosis was identified at the beginning of reperfusion. During ischaemia, PU changed from 0 to 10, both in the sole and in the muscle. A three-factor ANOVA (site, group, time) did not show interaction of these factors with PU (F = 1.655; p = 0.195), even if every single effect was significant (p < 0.0005). A two-factor ANOVA (group, time) showed a significant interaction of these factors with PU (F = 4.079; p = 0.019). The logistic regression between the reperfusion PU of each site and the survival of the limb was observed at the beginning and after 1 h of reperfusion in the sole only. Furthermore, a correlation between sole and muscle PU at the steady state and at the beginning of the reperfusion period was observed. The results showed the effectiveness of LDF, which can be considered a quite reliable tool to evaluate the degree of ischaemia and to have a good correlation with prognosis in this kind of experiments.