Histologic evaluation of the depth of necrosis produced by argon beam coagulation: implications for use as adjuvant treatment of bone tumors.

Argon beam coagulation (ABC) has been advocated as adjuvant treatment after curettage of aggressive benign bone tumors. This study was done to evaluate the depth of necrosis in cancellous bone treated with ABC. A 6-month-old pig was sacrificed and 20 1.5-cm cortical windows were created in the metaphyseal areas of the humeri, femora, and tibiae, exposing the underlying cancellous bone. The defects were randomly assigned to four groups: A, control; B, ABC at 50 W; C, 100 W; and D, 150 W. Histologic evaluation determined the depth of necrosis at each setting: A, 0.1 +/- 0.1 mm; B, 1.0 +/- 0.5 mm; C, 2.9 +/- 1.0 mm; and D, 4.2 +/- 0.7 mm. There were statistically significant differences between each of the experimental groups and the control (p < .0001), between groups B and C (p < .0001), and groups C and D (p = .0002).

Transphyseal anterior cruciate ligament reconstruction using mesenchymal stem cells.

BACKGROUND: Conventional techniques for reconstruction of the anterior cruciate ligament in skeletally immature patients risk potential iatrogenic growth disturbance because of drilling across the physis. Animal models have demonstrated mixed results regarding growth disturbances from soft tissue grafts across the physis. HYPOTHESIS: Mesenchymal stem cells derived from bone marrow may be effective in preventing growth arrest after intra-articular anterior cruciate ligament reconstruction. STUDY DESIGN: Controlled laboratory study. MATERIAL AND METHODS: The anterior cruciate ligament was removed from 15 skeletally immature rabbits, which were divided into 3 groups: 5 rabbits (group 1) had only drilling of tunnels through the distal femoral and proximal tibial physes 5 (group 2) underwent drilling of the tunnels and reconstruction with an extensor digitorum communis autograft; and 5 (group 3) had drilling and reconstruction with an extensor digitorum communis autograft that had been seeded with mesenchymal stem cells. Radiographs were obtained every 3 weeks, and the animals were sacrificed 3 to 20 weeks after surgery. The surgically treated and contralateral control knees were salvaged, and each knee was examined grossly, radiographically, and histologically. RESULTS: A bone bridge spanned the physis in all nongrafted knees (group 1) by 3 weeks after surgery. In group 2, the extensor digitorum communis autograft seemed to slow but not prevent the development of bony bridges and angular deformities. In contrast, the mesenchymal stem cell-seeded grafts (group 3) appeared to provide a marked protective effect against growth arrest and angular deformity. CONCLUSION: The results of this study suggest that angular deformity and growth arrest that occur after drilling across the physis during anterior cruciate ligament reconstruction can be prevented or minimized by implanting mesenchymal stem cells onto the transphyseal soft tissue graft. CLINICAL RELEVANCE: These results may facilitate the development of strategies to prevent growth disturbances of the physis with intra-articular reconstructive procedures in pediatric patients.

Chondrocyte injection in distraction epiphysiolysis (rabbit model).

The purpose of this study was to determine if cultured chondrocytes could prevent premature closure of the physis after physeal distraction in a rabbit model. Epiphyseal distraction at the proximal tibial epiphysis was performed in 24 immature rabbits. Chondrocytes were harvested from the iliac apophysis. The animals were divided into three groups: A, epiphyseal distraction alone; B, injection of phosphate buffered saline (PBS) after epiphyseal distraction; and C, injection of cultured chondrocytes after epiphyseal distraction. After epiphyseal separation was noted radiographically, each animal was evaluated at routine intervals. At 2 to 4 weeks, significant tibial lengthening as compared to the contralateral tibia was noted in all three groups. At 10 weeks, lengthening was apparent only in group C; in groups A and B, the operated tibia was shorter than the unoperated one. Histologic examination at 4 weeks revealed partial bony bridge formation with cell clustering in the fibrocartilaginous matrix in groups A and B. In group C, the matrix showed a typical hyaline aspect with cells organized in columns at the injection site. The zone of hypertrophic chondrocytes was enlarged. It appears that the injected cells differentiated into hypertrophic chondrocytes and delayed premature physeal closure. At 10 weeks after distraction of the physis, the width of the physis was restored to 75% of normal, but disordered chondrocyte growth with cell clustering was present in the cell-injected group.

Stem cell repair of physeal cartilage.

To evaluate the ability of cultured mesenchymal stem cells (MSC) to repair physeal defects, MSC-matrix constructs with 5% gelatin (group A), 10% gelatin/Gelfoam (Pharmacia, Peapack, NJ) (group B), and MSC grown in the presence of TGF-beta3 with Gelfoam (group C) were implanted in proximal tibial physeal defects created in 20 immature rabbits. Control groups (untreated partial defect and partial defect treated with Gelfoam) showed bony bar formation with varus deformities of 30 degrees and 28 degrees, respectively. Group A had an average 23 degrees varus deformity with bony bridge formation, and group B had mild varus angulation (average 14 degrees) of the proximal tibia. In group C, there was no significant varus deformity (average 9 degrees), and histologic examination showed that some of the columnation areas interspersed with chondrocytes were irregularly arranged in the matrix. These findings suggest that repair of physeal defects can be enhanced by the implantation of MSC cultured with TGF-beta3.