Table 4.

Medial joint space opening assessment of all included applicable imaging studies

References	Imaging modality	Measurement method	Medial joint space opening
De Flaviis et al. 1988 (PS) [43]	Ultrasonography	With and without valgus stress Gap width measurement: width of intraarticular space along the anterior third, the middle, and the posterior third of the internal face of the joint	Grade I rupture: 7.0–10.0 mm Grade II rupture: 9.0–18.0 mm Grade III rupture: 12.0–23.0 mm
Friedl et al. 1991 (PS) [42]	Ultrasonography	In 20° of flexion, with and without valgus stress Gap width measurement: distance between the end of the femoral condyle and tibia	No rupture: 2.9 ± 1.4 mm Partial rupture: 5.2 ± 1.3 mm Complete rupture: 6.6 ± 1.6 mm
Slane et al. 2017 (CS) [52]	Ultrasonography	Without MCL injury, in 20° of flexion, with and without valgus stress (loaded) Gap width measurement: distance between distal femur and proximal tibia relative to the skin	Unloaded: 8.7 ± 2.4 mm Loaded (10 Nm valgus): 10.7 ± 2.2 mm
Lutz et al. 2020 (PS) [44]	Ultrasonography	In 0° and 30° of flexion, unloaded and loaded valgus stress (15 daN) Gap width measurement: distance between the most medial corresponding points on the femoral condyle and tibial plateau	Unloaded 0°: 5.7 ± 1.2 mm Loaded 0° (15daN): 7.4 ± 1.4 mm Unloaded 30°: 6.1 ± 1.1 mm Loaded 30° (15daN): 7.8 ± 1.2 mm
Sawant et al. 2004 (PS) [37]	Radiography	In 10–15° of flexion, with valgus stress Gap width measurement: most medial distance between femoral condyle and corresponding medial tibial plateau	Mean only isolated MCL injury: 15 mm, range: 10–18 mm Mean combined MCL with ACL and/or PCL injury: 17 mm, range: 10–29 mm
LaPrade et al. 2010 (CS) [26]	Radiography	In 0° and 20° of flexion, with valgus stress (clinical and loaded), before and after sectioning Gap width measurement: shortest distance between the subchondral bone surface of the most distal aspect of the medial femoral condyle and the corresponding medial tibial plateau	Increase of MG in clinical examination 20° knee FL Sectioning of proximal sMCL: by 3.2 mm to 10.6 ± 1.9 mm Sectioning of distal sMCL: by 3.1 mm to 10.6 ± 1.4 mm Complete meniscofemoral injury: by 6.7 mm to 14.1 ± 2.1 mm Complete meniscotibial injury: by 5.4 mm to 12.9 ± 2.2 mm
Studler et al. 2011 (PS) [30]	dynamic MRI	Clinical examination with valgus stress Gap width measurement: distance between medial tibial margin and the cortex of the medial femoral condyles	Grade I rupture: 2.3 mm Grade II rupture: 2.9 mm (1.9–4.9 mm)

ACL anterior cruciate ligament, CS cadaveric study, daN dekanewton, FL flexion, MCL medial collateral ligament, MF meniscofemoral attachment of deep MCL, MG medial gap, MT meniscotibial attachment of deep MCL, n.r. not reported, PCL posterior cruciate ligament, POL posterior oblique ligament, PS prospective study