Anterior Cruciate Ligament Reconstruction by Using Bioabsorbable Femoral Cross Pins: MR Imaging Findings at Follow-up and Comparison with Clinical Findings

Purpose: To determine the frequency of imaging findings and complications related to bioabsorbable femoral cross pins at follow-up magnetic resonance (MR) imaging studies after anterior cruciate ligament (ACL) reconstruction and compare these MR imaging findings with clinical evaluation findings. Materials and Methods: The institutional review board approved this retrospective study, and informed consent was waived. Follow-up MR imaging studies (average, 26 months after surgery) in 218 patients with prior ACL reconstruction were retrospectively reviewed. Cross-pin fracture, posterior transcortical breach, migration, resorption, and lateral prominence of cross pins, as well as the cross-pin angle relative to the transepicondylar line, were investigated on MR images. The clinical evaluation included Lachman, anterior drawer, and pivot shift tests, as well as assessment for joint tenderness. Results: Fracture, posterior transcortical breach, migration, and lateral prominence of cross pins were excluded from analysis when at least one cross pin was completely resorbed (n = 16 patients). Forty-five fractured cross pins were seen in 35 (17%) of 202 patients. The posterior femoral cortex was breached in 57 (28%) of 202 patients. Migration of fractured pin fragments occurred in 12 (6%) of 202 patients. There was a significant relationship between fractures and posterior breach of cross pins (P = .001), as well as between cross-pin angles and fractures (P = .002). Both cross pins were completely resorbed in 12 (6%) of 218 patients (average time since surgery, 53 months; range, 8-92 months). No significant association was found between any MR imaging finding related to cross pins and clinical test findings. Conclusion: Fracture and posterior transcortical breach of bioabsorbable femoral cross pins, commonly seen at follow-up MR imaging studies, do not correlate with clinical findings of joint instability or pain. Posteriorly angulated cross pins and posterior transcortical breach are significantly associated with cross-pin fractures. (C) RSNA, 2010