The study protocol was approved by the Institutional Review Board of our institution (GCIRB2019-301) prior to the study. All patients presenting to one level I trauma center (as determined by the Korean central government) with an orthopaedic trauma in at least 1 body region and treated between 2007 and 2021. A total of 100 patients (115 knees) with MLKIs and/or dislocations were identified. Inclusion criteria were as follows: (1) skeletally mature patients, (2) diagnosis of MLKI, (3) surgical treatment by a knee surgeon with experience in MLKIs, and (4) MRI report of the knee before surgery by an experienced musculoskeletal radiologist. Exclusion criteria were as follows: (1) previous lesion of the knee, (2) previous surgery of the knee, and (4) patients with incomplete data.

Data were retrospectively extracted from the hospital notes and a dedicated patient database. All patients provided informed consent before participation. All patients underwent full trauma evaluation in the trauma resuscitation unit. This included an initial assessment by a trauma team, which consisted of traumatologists trained in both surgical and emergency medicine. The affected extremities underwent standard radiographic evaluation, and computed tomography (CT) scans of the head, chest, abdomen, and pelvis were obtained as part of the standard evaluation protocol at our institution. KDs were classified based on the direction of the tibial displacement relative to the femur, degree of injury force, mechanism of injury, and accompanying damaged structures. Multiligamentous knee injuries and knee dislocations were identified using the International Classification of Diseases, Ninth Revision codes, and defined as injuries to two or more ligaments of the knee. Multiligamentous knee injuries have been classified according to the position, energy of the injury, causes of injury, and injured anatomic structures. In our evaluation of ligamentous injury patterns, it was meticulously considered a range of factors including the extent of ligamentous injuries, specific patterns of fractures, and any abnormalities in the meniscus associated with these injuries.

In all enrolled cases, Magnetic resonance imaging (MRI) was routinely performed to evaluate injured structures and degree of injury once the patient’s overall condition was confirmed [1, 18, 22]. Intera-Achieva 3.0T MRI scanner (Philips Healthcare, Andover, MA, USA) was used. The knee was kept in extension during scanning. Coronal images using a 3D fast-spin echo technique (echo time, 35 ms; repetition time, 1800 ms; echo train length, 46; bandwidth, ± 101.5 kHz over entire frequency range; acquisition matrix, 320 × 318; number of excitations, 1; field to view, 160 mm; slice thickness, 0.5 mm with no gap; scan time, 6 min 49 s) were taken for this study. Using the Centricity RA-1000 (GE Medical Systems, Milwaukee, WI, USA), a type of Picture Archiving and Communication System (PACS) called DICOM (Digital Imaging and Communications in Medicine) was exported and used for analysis.

All MRI studies were reviewed and confirmed by a single fellowship-trained sports medicine orthopaedic surgeon and experienced musculoskeletal radiologist. MRI is very useful for the diagnosis and treatment of KDs when used in combination with radiographs and a thorough physical examination. Injured structures as well as the degree of injury were evaluated by MRI [1, 18, 22]. Detailed data on knee injuries were gathered from MRI reports and surgical records. Data on the injured knee structures were recorded—ACL, PCL, MCL, LCL, popliteus tendon, iliotibial band (ITB), and biceps tendon—and classified as normal, partial tear, complete tear, or avulsion. Based on MRI findings, the disrupted ligaments were divided into complete and partial ruptures. The arthroscopic procedures were reviewed to determine the presence of concomitant meniscal lesions. The medial and lateral menisci were classified as normal or torn, and tears were described in regard to their location (anterior horn, midthird, or posterior horn). If discrepancies were noted when both MRI and surgical findings were reported, the functional integrity of these structures was assessed under anesthesia at the time of surgery [20, 21].

The anatomic structures of the knee were categorized into four groups: ACL, PCL, medial structures, and posterolateral structures. All knees were classified according to the modified Schenck classification [13, 17]. This anatomical classification divides the knee into the anterior cruciate ligament (ACL), posterior cruciate ligament (PCL), medial collateral ligament (MCL), lateral collateral ligament (LCL), and the posterolateral structure, and uses combination of these for more precise injury categorization. Posterolateral corner injuries included the disruption of the lateral collateral ligament, popliteus, and/or biceps femoris. This classification system has provided a basis for comparing reports of multiple-ligament knee injuries in the literature based on the severity of the knee injury. MLKIs were considered as injuries of at least 2 of the 4 main ligaments of the knee: ACL, PCL, MCL, and PLC. MLKIs were divided into two subgroups; (1) MLKI with dislocation which was defined as a case exhibiting complete disruption of at least three of the four major knee ligaments, or case who visited the emergency room with dislocated but unreduced knee joints, 40 knees were included in this study (2) MLKI without dislocation as a case exhibiting complete disruption of at 1–2 of the 4 main ligaments, 75 knees were enrolled.