Targeted transarterial embolization of the femoral head: development of a minimally invasive approach to model Legg-Calvé-Perthes disease in piglets

Abstract

Clinical management of children with Legg-Calvé-Perthes Disease (LCPD) is hampered by incomplete understanding of how the extent of ischemic injury and the duration and quality of subsequent repair determine patient outcome. The traditional piglet model of LCPD is limited to capturing global femoral head ischemia; thus, a new model is needed in which the extent of ischemia can be varied to replicate the spectrum of disease seen in children. In this exploratory study, we used an iterative approach to test and refine methods to bilaterally occlude vessels supplying the femoral heads in n = 8 young piglets under angiographic control. The deep and/or acetabular medial femoral circumflex arteries (DMFCA and AMFCA) were identified and embolized using either embolic particles or liquid embolic agents. The extent of ischemia was assessed immediately post-embolization (4 piglets) and/or 7 days following embolization (7 piglets) using contrast-enhanced magnetic resonance imaging (CE-MRI). After the final CE-MRI, piglets were euthanized, and their femora were harvested for histologic evaluation. Embolization of the DMFCA alone caused transient ischemia that largely resolved by 7 days with small regions of fibrovascular repair of ischemic injury remaining on histology. Embolization of both the DMFCA and AMFCA resulted in a greater degree of pathologic changes at 7 days post-operatively, but also with nearly complete restoration of femoral head perfusion. We found that combining injection of embolic particles with subsequent placement of an embolic micro-coil was the most effective approach to induce ischemic injury, which may be aided in larger piglets. While our findings should be interpreted cautiously due to the wide range in the age and size of animals investigated, they demonstrate that transarterial embolization of the vascular supply of the femoral head results in transient ischemia and histological changes consistent with partial ischemic injury. These results will inform further development of a minimally invasive piglet model of LCPD that offers a unique representation of the spectrum of pathophysiology of LCPD compared to the traditional model.

Fig 1. Two-dimensional angiography of the piglet hip pre- and post-embolization.

(A) Normal vascular anatomy of the porcine hip, Piglet 1. (B) Sub-selection of the DMFCA demonstrating ascending flow of a contrast agent toward the femoral head, Piglet 4. (C) Absence of perfusion within the DMFCA following its embolization after injection of a contrast agent into the deep femoral artery, Piglet 4. (D) Enhancement of the femoral head after sub-selection of the AMFCA prior to embolization, Piglet 8. (E) Absence of femoral head perfusion after sub-selective injection of a contrast agent into the embolized AMFCA, Piglet 8. Femoral head (*); femoral head and femur (dotted red line); DMFCA (white arrowheads); AMFCA (blue arrows).

Fig 2. Histologically defined regions of interest.

Four distinct patterns were present in the examined sections, including (A) normal marrow and bone, (B) reduced cellularity of marrow without other changes, (C) fibrovascular repair tissue, and (D) necrosis of marrow and/or bone without evidence of repair. H&E, scale bars = 100 µm.

Fig 3. Three-dimensional reconstruction of hip vascular anatomy.

(A), (B), and (C) depict the lateral, anterior (cranial), and medial aspects of the hip joint and its vasculature, respectively in a 6-week-old piglet on CT angiography with intra-arterial contrast injection. Femoral head (*); greater trochanter (GT); femoral neck (FN); DMFCA (white arrowheads); AMFCA (blue arrows).

Fig 4. CE-MRI and histology of the hip joints following bilateral embolization of the DMFCA alone in Piglet 1.

Subtracted CE-MRI of T1-weighted TSE images acquired either (A) immediately after post-embolization, or (B) 7-days post embolization. Regions of ischemia appear black (*) and regions with perfusion appear either gray or white (arrow). Corresponding histology at 0.5$\times$ of the (C) right and (D) left hip obtained after euthanasia at 7-days postoperatively. Areas of fibrovascular repair (black dotted line); areas of necrosis (green line). Scale bars = 5 mm.

Fig 5. CE-MRI and histology of the right hip following embolization of both the DMFCA and AMFCA in Piglet 8.

(A) Subtracted CE-MRI of T1-weighted TSE images acquired 7-days post embolization. (B) Corresponding H&E-stained histology at 0.5$\times$. Secondary center of ossification of the femoral head (yellow line); regions of increased signal on CE-MRI that correspond to regions of fibrovascular repair on histology (dotted line); regions of ischemia on CE-MRI that correspond to acute necrosis without repair on histology (green lines); histologically normal regions of the femoral head (++). Scale bar = 5 mm.