Knee injury in a 12 year old girl

A 12 year old girl presented to the emergency department with sudden onset of knee pain. Her parents reported that she had twisted her left knee while her foot was fixed on the ground during a game of tennis. She reported hearing a “popping” sound followed by immediate pain and swelling in her left knee. She was initially unable to weight bear. She was otherwise fit and well. She was born at full term and her growth had been normal to date. On examination, her knee was swollen but there was no joint line tenderness or bony deformity. She would not cooperate with range of motion assessment because of the pain. She was distally neurovascularly intact. ### 1. What is the most likely diagnosis and what are the differential diagnoses? #### Answer The most likely diagnosis is acute anterior cruciate ligament (ACL) injury. Differential diagnoses include meniscal tear, osteochondral injury, tibial spine injury, patella dislocation, and collateral ligament injury. #### Discussion The most likely diagnosis is an acute ACL tear. The ACL is one of a pair of intra-articular ligaments (anterior and posterior cruciate) within the knee joint that provide the knee with sagittal (anteroposterior) stability. The tibial attachment of the ACL is just anterior and medial to the interspinous area of the tibial plateau. It runs posterolaterally to its attachment on the medial aspect of the lateral femoral condyle. In younger children, the ACL fibres form a strong connection between the ligament, perichondrium, and epiphyseal cartilage.1 Fibres are stronger than the cancellous bone of the unossified tibial eminence. With age, weaker Sharpey’s fibres link the ligament to …