Comparison of histomorphometric and radiographic effects of growth guidance with tension-band devices (eight-Plate and FlexTack) in a pig model.

Background and purpose - Temporary hemiepiphysiodesis for growth modulation in skeletally immature patients is a long-known technique. Recently the use of tension-band devices has become popular. This study compares 2 tension-band implants (eight-Plate and FlexTack) regarding their effects on the growth plate.Animals and methods - 12 pigs in 2 equally sized groups (A and B) were investigated. The right proximal medial tibia was treated with either eight-Plate or FlexTack. The left tibia of the same pig was treated with the opposite implant. After 9 weeks all implants were removed. Animals in group B were then hosted for another 5 weeks. Histomorphometric analysis of the growth plate was carried out after 9 and 14 weeks, respectively. Radiographs were taken at implantation, removal, and after 14 weeks.Results - Both tension-band devices achieved a statistically significant and clinically relevant growth inhibition, whereas the effect appeared to be more distinct after the use of FlexTack. Implant-related complications or physeal damage was not observed. After implant removal, rebound phenomenon was radiologically observed in all cases. The growth plates treated with eight-Plate showed a paradox reversal of the zonal distributions, with an increase of the proliferative zones at the previously arrested medial aspect of the physis and a decrease laterally.Interpretation - Both eight-Plate and FlexTack proved to be appropriate devices for growth-guiding treatment. The radiographic evaluation showed a change in angular axes after treatment with each implant, while the correction appeared to be faster with FlexTack. The paradox cartilaginous reaction observed after removal of the eight-Plate might be a histopathological correlate for rebound phenomenon.

Comparison of Temporary Epiphysiodesis With RigidTacks™ and Blount-Staples in a Porcine Animal Model Using Magnetic Resonance Imaging.

RigidTack™ is a newly developed implant for total temporary epiphyseodesis. The implant combines the technical advantages of the traditionally used rigid Blount-staples and the newer flexible eight-plates™. Thus, the implant is rigid like the Blount-staples, which may be a biomechanical advantage in temporary epiphyseodesis, and has an easy and guided implantation technique like the eight-plate™. As in eight-plates™, supposedly only two RigidTacks™ are sufficient for temporary epiphyseodesis compared to six Blount-staples in traditional treatment. The goal of this study was to compare Blount-staples and RigidTacks™ in regard to the total potential of growth arrest, the occurrence of postoperative implant-associated complications, secondary angular deformities, and central joint deformations. Twelve pigs were allocated in two groups (n = 6) for treatment of the proximal tibia. Total temporary epiphysiodesis was performed with either four Blount-staples or two RigidTacks™. Magnetic resonance imaging (MRI)-scans were performed before and 14 weeks after surgery, and the amount and distribution of growth arrest were evaluated by measuring the interphyseal distance in nine defined zones. Total temporary epiphysiodesis with two RigidTacks™ resulted in a similar amount of growth arrest as that of four Blount-staples. No significant coronal or sagittal angular deformities or joint deformities were observed in either group; however, one secondary loosening of a Blount-staple occurred. The study concluded that Blount-staples and RigidTacks™ are adequate implants for total temporary epiphysiodesis. Whether or not the precise implant-placement through the guided implantation technique of RigidTacks™ and a reduced number of implants indeed lead to a reduction of secondary angular deformities has to be investigated in further clinical trials. © 2019 The Authors. Journal of Orthopaedic Research® published by Wiley Periodicals, Inc. on behalf of Orthopaedic Research Society. J Orthop Res 38:946-953, 2020.