Sauli Kujala

Effect of porosity on the osteointegration and bone ingrowth of a weight-bearing nickel–titanium bone graft substitute

Porous nickel-titanium (NiTi) alloy is a promising new material for a bone graft substitute with good strength properties and an elastic modulus closer to that of bone than any other metallic material. The purpose of this study was to evaluate the effect of porosity on the osteointegration of NiTi implants in rat bone. The porosities (average void volume) and the mean pore size (MPS) were 66.1% and 259+/-30 microm (group 1, n=14), 59.2% and 272+/-17 microm (group 2, n=4) and 46.6% and 505+/-136 microm (group 3, n=15), respectively. The implants were implanted in the distal femoral metaphysis of the rats for 30 weeks. The proportional bone-implant contact was best in group 1 (51%) without a significant difference compared to group 3 (39%). Group 2 had lower contact values (29%) than group 1 (p=0.038). Fibrotic tissue within the porous implant was found more often in group 1 than in group 3 (p=0.021), in which 12 samples out of 15 showed no signs of fibrosis. In conclusion, porosity of 66.1% (MPS 259+/-30 microm) showed best bone contact (51%) of the porosities tested here. However, the porosity of 46.6% (MPS 505+/-136 microm) with bone contact of 39% was not significantly inferior in this respect and showed lower incidence of fibrosis within the porous implant.

Biocompatibility and strength properties of nitinol shape memory alloy suture in rabbit tendon.

Nitinol (NiTi) is a promising new tendon suture material with good strength, easy handling and good super-elastic properties. NiTi sutures were implanted for biocompatibility testing into the right medial gastrocnemius tendon in 15 rabbits for 2, 6 and 12 weeks. Additional sutures were implanted in subcutaneous tissue for strength measurements in order to determine the effect of implantation on strength properties of NiTi suture material. Braided polyester sutures (Ethibond) of approximately the same diameter were used as control. Encapsulating membrane formation around the sutures was minimal in the case of both materials. The breaking load of NiTi was significantly greater compared to braided polyester. Implantation did not affect the strength properties of either material.

Bone modeling controlled by a nickel-titanium shape memory alloy intramedullary nail

Nitinol (NiTi) shape memory metal alloy makes it possible to prepare functional implants that apply a continuous bending force to the bone. The purpose of this study was to find out if bone modeling can be controlled with a functional intramedullary NiTi nail. Pre-shaped intramedullary NiTi nails (length 26 mm, thickness 1.0-1.4 mm) with a curvature radius of 25-37 mm were implanted in the cooled martensite form in the medullary cavity of the right femur in eight rats, where they restored their austenite form, causing a bending force. After 12 weeks, the operated femurs were compared with their non-operated contralateral counterpairs. Anteroposterior radiographs demonstrated significant bowing, as indicated by the angle between the distal articular surface and the long axis of the femur (p = 0.003). Significant retardation of longitudinal growth and thickening of operated femurs were also seen. Quantitative densitometry showed a significant increase in the average cross-sectional cortical area (p = 0.001) and cortical thickness (p = 0.002), which were most obvious in the mid-diaphyseal area. Cortical bone mineral density increased in the proximal part of the bone and decreased in the distal part. Polarized light microscopy of the histological samples revealed that the new bone induced by the functional intramedullary nail was mainly woven bone. In conclusion, this study showed that bone modeling can be controlled with a functional intramedullary nail made of nickel-titanium shape memory alloy.

Composite Implant of Native Bovine Bone Morphogenetic Protein (BMP) and Biocoral in the Treatment of Scaphoid Nonunions — A Preliminary Study

Background and Aims: Bone morphogenetic protein (BMP) has been shown to induce bone formation and union in long bone defects and nonunions. We report a preliminary study of a composite implant consisting of a biocoral frame, carrier collagen and bovine BMP in the treatment of scaphoid nonunions. Material and Methods: Two proximal and eight waist area scaphoid nonunions were treated using BMP/coral implant combined with either the Matti-Russe procedure (2 cases) or an interpositional bone graft fixed with screws or compression fixation pins (8 cases). In two cases only a one piece BMP/coral implant was used as an interpositional graft and in other cases interpositional autograft was used with granular BMP/coral implant placed between the fragments and the graft. Results and Conclusions: Only two wrists resulted in complete union. These preliminary results suggest that composite implant of BMP, as used in the present study, may not solve the problems encountered in the treatment of scaphoid nonunions. Poor vascular conditions in scaphoid may not provide enough mandatory osteogenic cells for BMP to function properly. In avascular conditions coral does not resorb edequately and implants may also work as a sequester between the bone graft and the scaphoid bone and therefore actually inhibit the healing process.

Comparison of the bone modeling effects caused by curved and straight nickel-titanium intramedullary nails.

Nitinol (NiTi) shape memory metal alloy makes it possible to prepare functional implants. A curved intramedullary NiTi nail has been shown to cause bending of the bone, bone thickening, increase in cortical area, and reduction in bone longitudinal growth. The purpose of the present study was to find out whether these changes are caused by the bending force of the curved nail or by the intramedullary nailing itself. Pre-shaped intramedullary NiTi nails were implanted in the cooled martensitic form into the medullary cavity of the right femur in 12 rats, where they started to restore their austenitic form, causing a bending force. Straight nails were used as controls in another 12 rats. After 12 weeks, the operated femurs were compared with their non-operated contralateral counterparts and the differences were compared between the groups. Anteroposterior radiographs demonstrated bone bowing only in the curved nail group. Retardation of longitudinal growth was observed in both groups, showing that the growth effect seems to be due to the intramedullary nailing itself. Increase in bone cross-sectional area and cortical thickness were found in both groups. However, this increase was more evident with the curved nail, indicating that the bending force of the functional nail seems to induce these changes.

Wireless Infrared Thermometer in the Follow-Up of Finger Temperatures

After replantation surgery it is helpful to use temperature monitoring in order to detect vascular problems early. One of the methods currently employed is to use a thermometer with a wired probe attached to the tissue being monitored. An infrared wireless thermometer, commonly used in industry, measures temperatures of surfaces without actually touching them. The purpose of this study was to evaluate the efficacy of infrared wireless thermometer technology for monitoring finger temperature. Finger temperatures of 38 volunteers were measured using the infrared wireless thermometer. A traditional wired thermometer was used as control. The measurements of both thermometers were similar when the temperature was 31.5° and over, with no statistical differences (mean difference 0.06°, P=0.521). At lower temperatures, however, the wireless infrared thermometer showed slightly lower temperature values (mean difference 1.01°, P<0.001). There was no difference between the finger temperatures of smokers and non-smokers. There is potential for the wireless infrared thermometer to be used as an easier alternative to the traditional wired thermometer in monitoring temperatures of revascularised or replanted parts including digital replants. Further clinical studies would be warranted.

Intraosseous schwannoma of the middle phalanx

Intraosseous schwannoma is an extremely rare, benign neoplasm. Only a few cases involving the bones of the hand have been reported, and none of these cases has involved middle phalanx. We present a case of intraosseous schwannoma of the middle phalanx of the right ring finger.

Pyrolytic carbon MCP arthroplasty: a report of seven prostheses implanted in two patients

Rheumatoid arthritis most commonly affects the metacarpophalangeal (MCP) joints of the hand. Pyrolytic carbon MCP arthroplasty has lately provided a new alternative in the treatment of these patients, but reports in the literature are still few. Here, we report the mid-term results of seven such prostheses implanted in two elderly patients with rheumatoid arthritis. Pyrolytic carbon MCP arthroplasty was performed on three MCP joints in one patient and on four MCP joints in another patient. A specific postoperative mobilization protocol was applied. Range of motion, grip strength, and pinch strength were recorded, and radiographs were taken at three, six, and ten months postoperatively. Ten months after the operation, the operated joints were pain-free, and grip and pinch strengths had improved. On average, the passive range of motion had improved and the active range of motion had remained about the same. The joints were clinically stable. No adverse remodeling or bone resorption was observed radiographically. Ulnar deviation recurred in one of the two cases. These results suggest pyrolytic carbon MCP arthroplasty to be a noteworthy alternative in the treatment of MCP joints affected by rheumatoid arthritis. Early treatment, before the development of severe soft tissue destruction, seems to yield better results.