Experimental Induction of Physeal Injuries by Fracture, Drill, and Ablation Techniques: Analyses of Immunohistochemical Findings.

BACKGROUND: Although physeal fractures and physeal bars can result in significant clinical consequences to growth and development of the injured physis, little orthopaedic research has focused upon this topic. Our objective was to extend a previously developed rat model to examine the immunohistochemical features following surgical application of techniques disrupting the physis. METHODS: Physes were surgically disrupted using fracture (control), epiphyseal scrape (ES), or epiphyseal drill (ED). After 1, 3, 6, 10, or 21 days, animals were euthanized, sites processed for histology and immunohistochemical localization of vascular endothelial growth factor (VEGF), Factor VIII, Sox-9, PTHrP (parathyroid hormone-related protein) and PTHrP-R (parathyroid hormone-related protein receptor) in resting, proliferative, and hypertrophic physeal zones. Incidence of physeal bars, vertical septa and islands within the metaphysis was quantified. Semiquantitative analysis of immunohistochemistry was performed. RESULTS: Physeal bars, vertical septa, and displaced cartilage islands were present each of the surgical treatments. Fisher's exact test showed a statistically significant increase in the presence of physeal bars (P=0.002) and vertical septa (P=0.012) in the ED group at 10 and 21 days. Analysis of VEGF showed significant differences among the surgical treatments involving the resting zone, and the proliferative zone for days 1, 6, and 21 (P≤0.02) with greater mean scores present in the fracture (control) group, followed by the ED group; the lowest scores were present in the ES group. PTHrP-R immunolocalization showed significant differences among treatments in the hypertrophic zone at days 6 and 21 (P=0.022 and 0.044, respectively). CONCLUSIONS: On the basis of the type of surgical treatment, results show significant differences in the presence of VEGF (reflecting the vascular bed) in the resting and proliferating zones at days 1, 6, and 21. VEGF localization was less abundant in the ED group (which had more physeal bars), suggesting that lack of vascular ingrowth plays a role in physeal bar formation. CLINICAL RELEVANCE: Basic science data presented here provide insight into the importance of the various regions of the physis and its repair and continued growth after physeal fracture. We suggest that a better understanding of the cellular basis of physeal arrest following physeal fracture may have future relevance for the development of treatments to prevent or correct arrest.

The Role of the Basement Plate in Physeal Bar Formation.

BACKGROUND: Physeal fractures and resultant physeal bars can pose significant problems in skeletal development for the injured growing child. Although now well-recognized, only a small body of experimental literature covering this problem is available. The goal of this study was to help further develop an understanding of the different regions of the physis and the way in which each region responds to injury/fracture. METHODS: This Institutional Animal Care and Use Committee (IACUC)-approved study assessed bar formation using radiologic and histologic methods and measured leg lengths of skeletally immature rats. The right tibia was used as the control to measure leg length discrepancy (LLD), and the left tibia received either a fracture only (F), an epiphyseal scrape (ES), an epiphyseal drilling procedure (ED), or metaphyseal drilling (MD). Radiographs and LLD measurements were obtained at postoperative days 0, 21, and 56. RESULTS: A significant LLD was present at day 56 in the ED group (P=0.01). Radiographic identification of bars showed significant evidence of bar formation for the ES and ED groups at 21 days and the ED group at 56 days (P<0.05). Histologic examination showed a high incidence of histologic physeal bar formation in the ES, ED, and MD groups at 21 and 56 days. CONCLUSIONS: Findings showed that the physis was able to continue to grow following an injury to the physis' hypertrophic region. MD produced little effects with few physeal bars and little LLD. By postoperative day 56, ED animals showed greater LLD than ES animals. Penetration of the basement plate was more likely to lead to bar formation/growth retardation than was ablation of the epiphyseal region of the physis (including resting cells). CLINICAL RELEVANCE: Data presented here provides insight into the importance of different regions of the physis and its repair/continued growth after physeal fracture. We suggest that a better understanding of the physiological cause of physeal arrest after physeal fracture will be important for the development of treatments to prevent physeal arrest or to treat physeal arrest after it occurs.