O1084: An Anatomic Study of the Proximal Tibial Epiphysis with Relevance to Percutaneous Epiphysiodesis Usingtransphyseal Screws (PETS)

Background: A potential complication of PETS is development of tibial valgus deformity, which may occur secondary to decreased screw purchase in the thinner medial proximal tibial epiphysis. The thickness of the proximal tibial epiphysis has not yet been well quantified.

Methods: Three-dimensional surface scans of 32 cadaveric proximal tibial epiphyses in specimens aged 3 to 17 years old were obtained and computer modeling software was utilized to measure the thickness of the proximal tibial epiphysis at 20 standardized potential screw insertion points according to a generated 5x4 map. In the sagittal plane, 5 markers were set at 0 (midline), 10%, and 20% of the total physeal length away from midline in the anterior and posterior directions, and in the coronal plane, 4 markers total were set at 25% and 33% of the total physeal width away from the medial and lateral edges (Figure 1).

Results: When normalized to the total width of the proximal tibial epiphysis, the lateral side is thicker compared to the medial side (Figure 2). The positions with the greatest thickness are located at the midline in the sagittal plane and 33% of the total physeal width away from the medial and lateral edges in the coronal plane (0.265 and 0.261 normalized thickness respectively). The proximal tibial epiphysis is particularly thin 25% from the medial edge (normalized thickness range: 0.196-0.221). Multiple regression analysis revealed a significant relationship between increasing age and female sex with thinner normalized medial and lateral heights.

Conclusion: During PETS, screws should be positioned centrally in the sagittal plane and 33% of the total width away from the medial and lateral edges of the proximal tibial epiphysis in the coronal plane to obtain greater screw purchase. Caution should be taken when inserting screws in the medial 25% of the proximal tibial epiphysis as it is thinner relative to the lateral edge, particularly in females.