[Fixed posterior sag position after ACL reconstruction for an apparently "isolated" ACL tear]

We present the case of a paraglider who suffered a valgus external rotation hyperextension injury of the right knee. The incomplete diagnosis of an isolated anterior cruciate ligament (ACL) intrasubstance tear was made and a reconstruction of the ACL with semitendinosus autograft was performed. The associated lesion of the posterior cruciate ligament (PCL) was overlooked and thus the ACL was fixed in a posterior sag position. This led to activity-related pain without any instability. The patient underwent revision surgery with débridement of the ACL and reconstruction of the PCL with quadriceps tendon.