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Purpose Magnetic resonance imaging (MRI) signal intensity is correlated to structural postoperative changes of the anterior cruciate ligament (ACL) autograft. The purpose of this study was to investigate the ACL autograft maturation process via MRI over 2 years postoperatively, compare it to a native ACL signal and correlate the results with clinical outcome, return to preinjury sports levels, and knee laxity measurements. Methods ACL autograft signal intensity was measured in 17 male patients (age, 28.3 ± 7.0 years) who underwent ACL reconstruction with hamstring autograft at 6 weeks, 3-, 6-, 12-, and 24 months postoperatively by 3 Tesla MRI. Controls with an intact ACL served as control group (22 males, 8 females; age, 26.7 ± 6.8 years). An ACL/PCL ratio (APR) and ACL/muscle ratio (AMR) was calculated to normalize signals to soft tissue signal. APR and AMR were compared across time and to native ACL signal. Clinical outcome scores (IKDC, Lysholm), return to preinjury sports levels (Tegner activity scale), and knee laxity measurement (KT-1000) were obtained and correlated to APR and AMR at the respective time points. Results The APR and AMR of the ACL graft changed significantly from the lowest values at 6 weeks to reach the highest intensity after 6 months (p < 0.001). Then, the APR and AMR were significantly different from a native ACL 6 months after surgery (p < 0.01) but approached the APR and AMR of the native ACL at 1- and 2 years after surgery (p < 0.05). The APR changed significantly during the first 2 years postoperatively in the proximal (p < 0.001), mid-substance (p < 0.001), and distal (p < 0.01) intraarticular portion of the ACL autograft. A hypo-intense ACL MRI signal was associated with return to the preinjury sports level (p < 0.05). No correlation was found between ACL MRI graft signal and clinical outcome scores or KT-1000 measurements. Conclusion ACL grafts undergo a continuous maturation process in the first 2 years after surgery. The ACL graft signals became hyper-intense 6 months postoperatively and approximated the signal of a native intact ACL at 12- and 24 months. Patients with a hypo-intense ACL graft signal at 2 years follow-up were more likely to return to preinjury sports levels. The results of the present study provide a template for monitoring the normal ACL maturation process via MRI in case of prolonged clinical symptoms. However, subjective outcome and clinical examination of knee laxity remain important to assess the treatment success and to allow to return to sports. Level of evidence III.

Background: Patellar sleeve avulsion (PSA) fractures are rare injuries that occur in in skeletally immature patients. Initial diagnosis is key to a successful outcome, as these injuries are easily overlooked on plain radiographs with poor results well documented from delayed management. High index of suspicion from the mechanism of injury, thorough clinical examination and Magnetic Resonance Imaging (MRI) help to avoid misdiagnosis. Case presentation: The case of a 12-year-old male athlete with an acute PSA after a conservative treatment of a SLJ syndrome is described. The patient was referred to our clinic due to severe pain and loss of function after performing a high jump. Plain radiographs (X-ray) and MRI confirmed an inferior pole PSA which was fixed with double trans osseous ultra-high strength tapes. At the 3-month follow-up visit the patient was able to ambulate brace free. At 2-years follow up the patient was able to play soccer and ice hockey. To our knowledge, there are no case reports of inferior pole PSA with prior SLJ syndrome described in literature. Conclusions: Early clinical suspicion and distinguishing this PSA from other enchondral ossification disorders around the knee is critical to avoid misdiagnosis. Whether SLJ syndrome increases the risk of sustaining a PSA is still not clear. Trans osseous fixation with suture tapes leads to good functional results in a young athlete with inferior pole PSA.

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