Histopathological and Radiographic Features of Osteolysis After Fixation of Osteochondral Fragments Using Poly-L-Lactic Acid Pins for Osteochondral Lesions of the Talus

Background: Fixation of osteochondral fragments is a potential option for treating an osteochondral lesion of the talus (OLT) involving large lesions in the remaining articular cartilage surface. Bioabsorbable devices, especially those made of poly-L-lactic acid (PLLA), can be used for the fixation of an OLT. Postoperative osteolysis surrounding the PLLA pins is occasionally observed; however, the significance of osteolysis remains unknown. Purpose: To elucidate the association between osteolysis surrounding the PLLA pins, histopathological findings in subchondral bone, and preoperative Hounsfield unit (HU) values at the pin fixation site. Study Design: Case Series; Level of evidence, 4. Methods: This retrospective analysis included 20 patients with OLT (11 men and 9 women; mean age, 20.9 years; 1 bilateral case). Tissue from the osteochondral fragment was collected intraoperatively using a bone biopsy needle for histological evaluation. The fragment was fixed through the biopsy hole using a PLLA pin. Osteolysis surrounding the PLLA pin was assessed at 1 year postoperatively using magnetic resonance imaging (MRI). Histopathological scores were assigned based on trabecular bone loss, empty lacunae, inflammatory granulation tissue, cartilage-like tissue, and the presence of osteoclasts. The HU values around the pin insertion site, detected on the postoperative MRI scans, were measured using the region of interest based on the preoperative coronal and sagittal computed tomography (CT) images. Results: Osteolysis was observed postoperatively in 9 ankles (42.9%). Histopathological evaluation revealed that the osteolysis group had a significantly higher pathological score than the nonosteolysis group (10.2 vs 6.3; P < .001). Lower HU values were identified in the osteolysis group on preoperative coronal and sagittal CT images ( P < .05). The histopathological score negatively correlated with preoperative HU values (Pearson r = −0.46; P = .037). Conclusion: Intraoperative biopsy of the OLT allowed for histopathological evaluation of the same site as that of the PLLA pin fixation. Our findings suggest that preoperative subchondral trabecular deterioration is associated with the incidence of postoperative osteolysis surrounding the PLLA pin. Additionally, low preoperative HU values in subchondral bone under OLT may serve as a predictor of osteolysis surrounding the PLLA pin.