Table 2.

Comparison of surgical anatomical parameters for HTO in sheep and humans (adapted from (Pape & Madry 2013) with permission)

Congenital anatomical differences	Sheep stifle joint	Human knee	Surgical consequence for the sheep HTO model
Tibial plateau width [mm]	46-56	60-70	Match screw length
			Narrow and strait plate design necessary
Tibia valga [°]	3.5	0	Valgus overcorrection more likely
Normal knee range of motion (transverse axis) [°]	0-35-72	0-0-140	Dorsal plate positioning after open wedge HTO is recommended due to increased loading of the posterior tibial plateau
tibial tuberosity dimension adding to the AP diameter of the tibial head [%]	30-35	10-15	Anterior plate misplacement more likely
Tibial tuberosity height distance in relation to joint line [mm]	10-15 mm	25-30 mm	Anterior plate misplacement more likely
Posterior slope of the posterior articular surface [°]	20 ± 3	0-10	Narrow and straight plate design necessary for posterior placement
Biomechanical properties of tibial head	Brittle cortical bone, together with little spongious bone	Elastic cortical bone with an exuberant amount of spongious bone	Bicortical proximal screw placement mandatory to avoid fracture/dislocation
			Biplanar osteotomy mandatory regardless of the desired direction of correction
Musculature of the hind limb	Voluminous on medial and lateral side of the femur	Remote from bony knee structures	Distal femoral and proximal lateral tibial osteotomy almost impossible to conduct, stay on the medial side of the proximal tibia for any desired correction angle
Trochlea ridge	Medial ridge extending further cranially and dorsally than lateral ridge	Lateral ridge extending further laterally and anteriorly	Higher propensity of patella instability after valgus correction