Tibia Multiplanar Deformities and Growth Disturbance Following Expandable Endoprosthetic Distal Femur Replacement

Background: Expandable distal femur endoprosthesis (EDFE) is commonly used to compensate for the loss of the distal femoral epiphyseal plate in skeletally immature children who have undergone surgical resection of bone malignancies. However, the effect of the passive tibial component of the EDFE on tibial growth has not been extensively studied in the literature. This study aims to delineate the type, frequency, and associated risk factors of multiplanar proximal tibial deformities in skeletally immature children following the use of the expandable distal femur endoprosthesis (EDFE). Moreover, we plan to detect how these deformities influence the long-term functionality of the endoprosthesis in defining the need for subsequent implant revision or further surgical management. Patients and Methods: A total of 20 patients aged (7−12) years underwent expandable distal femur replacement. Two types of implants were used: Juvenile Tumor System (JTS) non-invasive prosthesis in 14 patients, and Modular Universal Tumor and Revision System (MUTARS)® Xpand Growing Prostheses in six patients. A scanogram and CT scan documented the measurements of longitudinal and multiplanar growth as leg length discrepancy (LLD), femur length discrepancy (FLD), tibia length discrepancy (TLD), and the yield values of rotational, sagittal, and coronal deformities of the tibia. The patients were followed up to assess the need for further management. Sex, age, size of tibial plate perforation, and type of implant used were studied for possible correlation with deformities or growth disturbance. Results: The patients were followed up for a mean of 3 (2−7) years. A total of 14 patients, (10 JTS, 4 implant cast) had a tibial deformity and/or growth disturbance. A single patient was found to have all deformities (growth, rotational, coronal, and sagittal). Fourteen patients were found to have an LLD ranging from 5.3 to 59 mm (median 21 mm), 12 had a TLD from 3 to 30 mm, (median 10 mm), and 11 patients showed evidence of malrotation from 6 to 32 degrees (median 11 degrees). TLD was found to contribute entirely to LLD in three patients, and >50% of LLDs in seven patients. All LLDs were treated conservatively, except in three patients; two received contralateral tibia epiphysiodesis and one received revision with a new implant. A single patient had a posterior tibia slope angle (PTSA) of −2.8 degrees, and three patients had a coronal deformity with a mean medial proximal tibia angle (MPTA) of 80.3 (77−83 degrees). Conclusions: Tibial growth disturbance and multiplanar deformities occur in the majority of patients following EDFE replacement, exacerbating LLD. Yet, these disturbances may be well tolerated, managed conservatively, and rarely mandate endoprosthetic revision or subsequent corrective surgery. Age at the time of surgery was found to be the only significant contributor to the development of tibia growth disturbance.