Background Congenital anomalies involving the meniscus and anterior cruciate ligament (ACL) are rare and often discovered incidentally. Discoid meniscus is the most frequently reported congenital variant, whereas medial meniscal hypoplasia and ACL agenesis remain exceptionally uncommon. Case Presentation A 16‐year‐old male presented with right knee pain, swelling, and instability following a noncontact basketball injury. He reported a similar episode weeks earlier. Clinical examination revealed anterior laxity, and magnetic resonance imaging (MRI) demonstrated a nonvisualized ACL consistent with a tear and absent tissue suggestive of a subacute injury. The medial meniscus appeared diminutive without evidence of a tear or displaced fragment. Arthroscopy confirmed a hypoplastic medial meniscus without reparable tissue and complete absence of ACL fibers. The patient underwent ACL reconstruction with internal brace augmentation and anterolateral ligament (ALL) reconstruction. A lateral meniscal tear was also repaired. Postoperative recovery demonstrated progressive improvement in range of motion and quadriceps activation. Conclusion This case highlights a rare presentation of concurrent medial meniscal hypoplasia and congenital absence of the ACL in an otherwise healthy adolescent male. Notably, the patient sustained a pivoting sports‐related injury accompanied by an instability episode, in the absence of any syndromic or systemic congenital anomalies. Recognition of congenital intra‐articular anomalies is essential for accurately interpreting preoperative imaging and understanding that structures such as the ACL and meniscus may not develop in tandem, which can influence surgical planning and clinical decision making.
Paa et al. (Thu,) studied this question.