Acute Interpositional Fat Autograft Does Not Protect Against Bar Formation in Physeal Fractures.

BACKGROUND Long-bone fractures in children can lead to premature physeal bar formation and growth disturbance. Bar excision has been studied, but data on prophylactic tissue interposition into physeal fractures are limited. This study used an established animal model to evaluate acute placement of fat autograft. The number of animals was selected to give 80% power on the basis of pilot data on induction of radiographic bars in physeal fractures. METHODS Proximal tibial fractures were created in 30 rabbits by placing pins in the epiphysis and levering the distal tibia, propagating the fracture through the physis. Twenty fracture sites had interposed fat autograft (fat group), and 10 did not (fracture group). The 30 untreated contralateral limbs were the control group. Radiographs were assessed preoperatively and immediately, 10 days, and 6 weeks following fracture. Radiographic measurements were compared using repeated-measures analysis of variance. Micro-computed tomography (microCT) 3D reconstructions and histologic analysis further characterized the healing and control tibial physes. RESULTS Fat and fracture groups were similar (age, weight, body length, surgical duration, and weight and body length increases over 6 weeks). No difference was observed in the probability of radiographic bar formation between the fat (12 of 20) and fracture (7 of 10) groups (p = 0.702). On the basis of the medial-lateral side difference, fat (0.66 ± 1.64 mm) and fracture (0.53 ± 1.36 mm) groups demonstrated increased valgus growth compared with controls (-0.74 ± 1.16 mm) (p = 0.002 and p = 0.04). Six weeks following fracture, tibial length was less in the fat group compared with the control group (fat: 101.4 ± 3.1 mm, control: 103.7 ± 2.6 mm, p = 0.02). MicroCT 3D reconstructions demonstrated no difference in bone bridging between fat and fracture groups, and the fat group having more bone bridging than controls (83 ± 102 versus 11 ± 49, p = 0.004). Histologic analysis showed disorganized tissue without evidence of physeal cartilage preservation for most limbs in both treatment groups. CONCLUSIONS Fat autograft interposition did not reliably prevent radiographic bar formation or angular deformity when placed during physeal fracture reduction. 3D reconstructions and histology indicated that the fat was converted to bone just as readily as if a disrupted physis had no interposition, yet with a reduction in the surface area of bone bar formation that did not reach significance. CLINICAL RELEVANCE Given these findings, we do not necessarily advocate for acute prophylactic fat interposition into physeal fractures for bar prevention in pediatric fractures.