Hydroxyapatite-coated external-fixation pins. The effect on pin loosening and pin-track infection in leg lengthening for short stature.

Pin loosening and infection are inherent complications of external fixation. This study deals with their effects of using either hydroxyapatite (HA)-coated or uncoated external fixation pins in leg-lengthening procedures on patients of short stature. We used HA-coated pins on one side and uncoated pins on the other (randomly determined) in 28 bilateral lengthenings undertaken in 23 patients. A total of 322 pins was used. The mean implantation time was 530 days and the mean lengthening achieved was 78% of initial bone length. Mean extraction torque was 7611.6 Nmm degree(-1) for HA-coated and 85.4 Nmm degree(-1) for uncoated pins (p < 0.001). The rate of pin loosening was 4% (7/161) for HA-coated and 80% (129/161) for uncoated pins (p < 0.001). There was no statistically significant difference in the incidence of pin-track infection between the two groups. The use of HA coating appears to be an effective method of reducing the incidence of pin loosening in external fixation with a long implantation time and for mechanically highly stressed procedures such as leg lengthening for short stature.

Effect of early axial dynamization on tibial bone healing: a study in dogs.

Early axial dynamization and its effect on experimental tibial bone healing was compared with healing under rigid fixation in a time-sequenced manner using dogs. An external fixator that could be rigidly locked or set to allow free axial movement while preventing bending and shear was used. Both tibias were osteotomized and externally fixed, leaving a gap between bone ends of 2 mm. At 1 week, one side was dynamized, whereas the other side was kept rigidly locked as a control. Dogs were euthanized at 1 day and 1, 3, 5, 8, and 11 weeks after dynamization. The outcome measures were static and dynamic load-bearing, periosteal callus development, new bone formation, callus tissue composition, and mechanical strength. Load bearing was higher on the dynamized limbs during standing for the first 5 weeks and during gait for the first 3 weeks after dynamization compared with the controls. Maximum periosteal callus size was reached faster and was distributed more symmetrically on the dynamized side. The periosteal callus area decreased at 12 weeks on the dynamized sides, but there was no significant change in the area on the control sides. Endosteal new bone formation and bone density decreased between 9 and 12 weeks only on the dynamized sides. The dynamized side showed a significantly higher torsional stiffness at 6 weeks than did the controls. There were no significant differences between dynamized and control tibias at other times. Maximum torque also tended to be higher on the dynamized sides at the same time. Early axial dynamization appeared to accelerate callus formation and remodeling and to provide higher mechanical stiffness during early stages of bone healing.

Biomechanical, scanning electron microscopy, and microhardness analyses of the bone-pin interface in hydroxyapatite coated versus uncoated pins.

OBJECTIVE: To evaluate the bone-pin interface in hydroxyapatite coated versus uncoated pins. DESIGN: Eighty-four bicylindrical stainless steel external fixation pins were implanted in a test group of 14 sheep. One-half of the pins were coated with hydroxyapatite and the rest remained uncoated. INTERVENTION: Six coated pins were implanted in the left tibia of seven sheep, and six uncoated pins were implanted in the left tibia of the other seven sheep. In all sheep, the right tibia was left intact. During pin implantation, the final insertion torque was measured, and a linear external fixator was mounted on the pins. Then the medial tibial mid-diaphysis was exposed and a 5-mm resection osteotomy was performed. The sheep were killed six weeks after surgery. MAIN OUTCOME MEASURES: The extraction torque was measured on four pins removed from each sheep. Radiographic pin tract rarefaction was measured on all the pins. Two pins from each sheep were used for histologic, scanning electron microscopy (SEM), and microhardness analysis. Histomorphometric analysis was carried out on the SEM specimens at x 36 magnification. RESULTS: Radiographic pin tract rarefaction was significantly lower in the hydroxyapatite coated pins than in the uncoated pins (P < 0.001). Group average insertion torque was 960 +/- 959 N/mm in the hydroxyapatite coated pins, and 709 +/- 585 N/mm in the uncoated pins (p = not significant). Group average extraction torque was 1485 +/- 1308 N/mm and 298 +/- 373 N/mm, respectively (p = 0.0001). Histomorphometric analysis showed that the group average bone-pin contact was 50.7 +/- 16.9% in the hydroxyapatite coated pins and 27.6 +/- 7.1% in the uncoated pins (p < 0.01). Microhardness analysis showed that bone tissue close to the pins was softer than bone tissue far from them. CONCLUSION: Hydroxyapatite coating is an effective method of refining the bone-pin interface and may improve the clinical results of the external fixation technique.

Hydroxyapatite coated external fixation pins: an experimental study.

A sheep model was developed for the implantation of 84 bicylindrical stainless steel external fixation pins. One-half of the pins were coated with hydroxyapatite, and the rest remained uncoated. A set of 6 pins with the same coating was implanted in the lateral side of the left tibias of 14 sheep, the final insertion torque was measured, and a monolateral external fixator was assembled on the pins. The medial tibial middiaphysis then was exposed and a 5-mm resection osteotomy was done. Sheep were euthanized 6 weeks after surgery, radiographs were taken, and the initial extraction torque was measured on 4 pins from each sheep. Undecalcified sectioning and histologic and histomorphometric analyses were done on the remaining 2 pins. Radiographic pin tract rarefaction was significantly lower in the hydroxyapatite coated pins compared with the uncoated pins. Group average insertion torque was 960 +/- 959 Nmm in the hydroxyapatite coated pins and 709 +/- 585 Nmm in the uncoated pins. Group average initial extraction torque was 1485 +/- 1308 Nmm and 298 +/- 373 Nmm, respectively. Bone pin contact was 85.7% +/- 8.9% and 50.3% +/- 20.4%, respectively, in hydroxyapatite coated and uncoated pins. Bone between the threads was 95.6% +/- 5.7% and 80% +/- 8.7%, respectively, in hydroxyapatite coated and uncoated pins. Hydroxyapatite coating was effective for improving the bone-to-pin interface.

Surgical treatment of both-column fractures by staged combined ilioinguinal and Kocher-Langenbeck approaches.

Between 1981 and 1989, 18 patients affected by both-column acetabular fractures were operated on by staged combined ilioinguinal and Kocher-Langenbeck approaches. Postoperative reduction quality and long-term radiographic results were evaluated according to the Matta radiological systems. The Harris hip scoring system was used for the functional results. Average follow-up was 53.2 months, ranging from 24 to 132 months. Reduction was anatomical in five cases (27.8 per cent), satisfactory in 11 (67.1 per cent), and non-anatomical in two cases (11.1 per cent). Radiographic long-term results were excellent in nine cases (50 per cent), good in five (27.8 per cent), fair in two (11.1 per cent) and poor in two (11.1 per cent). The Harris score was more than 90 in eight patients (44.4 per cent), between 80 and 90 in seven (38.8 per cent), between 80 and 70 in one (5.5 per cent), and less than 70 in two (11.1 per cent).

Composite bone grafting and plate fixation for the treatment of nonunions of the forearm with segmental bone loss: a report of eight cases.

Between June 1986 and December 1991, eight aseptic isolated severe forearm segmental bone losses were treated. The average age of the patients was 26 years. Three cases involved the radius and five the ulna. The average time between the onset of trauma and the final surgical intervention was 9 months. The surgical technique consisted of complete removal of necrotic bone, filling of the bone defect with an intercalary autogenous bone graft, and stable internal fixation, which required combining a plate and an opposite cortical bone allograft. The average bone loss length after freshening the bone ends was 7 cm (range 4-11). The average follow-up was 48 months (range 24-80). In all eight cases union and recovery of forearm function was achieved. The proposed surgical technique proved to be effective in obtaining results with no major complications.

Mechanical performance of the Monticelli-Spinelli external fixation system.

Six configurations of the Monticelli-Spinelli external fixator were tested for axial compression, bending, and torsion. The ring wire clamp unit was separately tested under repeated cyclic loading and retightening of the clampnuts. The configurations studied were the following: 3 standard (4-ring and 3-ring with 5-mm between the wires and 3-ring with 40 mm between the wires); and 3 hybrid (3-ring and 1 pin, and 2-ring and 2 pins with the rings either placed closer or distant to the fracture). For each configuration, 5 frames were constructed. Axial stiffness was nonlinear for both fixator types. Four-ring fixators and 2-ring 2-pin fixators had similar stiffness, yet were stiffer than 3-ring configurations. Anteroposterior bending stiffness was highest in the 4-ring configurations, whereas oblique bending for standard fixators was similar to lateral bending stiffness for the hybrid configurations. Torsion was higher in the 4-ring construction and in hybrid frames compared to the standard 3-ring frames. For the ring wire clamp unit, stiffness increased and hysteresis diminished after each retightening of the clampnuts because of the increase of contact between clamps and ring. The hybrid configurations provide an alternative that enables more simple configurations with less transfixing elements and sufficient stiffness.

Surgical treatment of bicondylar fractures of the distal humerus.

Between 1981 and 1989 22 bicondylar fractures of the distal humerus were operated on. Fractures were classified according to the AO system. Fixation consisted of medial and lateral plates combined to articular screws in 14 cases, one articular screw associated to one medial screw and a lateral plate in four cases, three lag screws in three cases, and in one case the articular screw was associated to one medial screw and one 'Y' plate. Osteotomy of the olecranon was fixed by one intramedullary screw and one wire in 15 cases, other simpler methods (wire or screw alone) were used in seven cases. A scoring system that included pain, range of motion, radiological results and postoperative activity level, was developed to study the results. Two fractures went to nonunion. Results were quoted as excellent in six cases, good in five cases, fair in eight patients and poor in three cases. Younger patients achieved a better range of motion (P = 0.039) and better functional level (P = 0.015), and differences in radiological score (P = 0.029), activity level score (P = 0.048) and total score (P = 0.0031) were observed depending on the anatomical fracture type.

Histomorphometry of hydroxyapatite coated and uncoated porous titanium bone implants.

Two different groups of hydroxyapatite (HA) coated and uncoated porous titanium implants, 250-350 microns and 500-700 microns diameter beads, were press-fitted into femoral canine cancellous bone. After 12 wks, the dogs were killed and histomorphometric backscattered electron microscopy studies were carried out. Comparing HA coated versus uncoated implants in the 250-350 microns bead diameter group, the percentage of bone (P = 0.01) and bone index (P = 0.01) were higher in the HA coated implants. Comparing HA coated versus uncoated implants in the 500-700 microns bead diameter group, bone ingrowth (P = 0.01) and bone depth penetration (P = 0.008) were higher in HA coated samples. It can be concluded that the HA coating was an effective method for improving bone formation and ingrowth in the porous implants.