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Table 4 Surgical anatomical parameters relevant for HTO in humans and sheep
| Human knee | Sheep stifle joint | Surgical consequences for the sheep HTO model | |
|---|---|---|---|
| Tibial plateau width [mm] | 60-70 | 46-56 | match screw length, narrow and strait plate design necessary |
| Tibia valga [°] | 0 | 3.5 | valgus overcorrection more likely |
| Knee range of motion [°] | 0-0-140 | 0-35-72 | dorsal plate positioning after open wedge HTO suggested due to increased loading of the posterior tibial plateau |
| Tibial tuberosity dimension adding to the anterio-posterior diameter of the tibial head [%] | 10-15 | 30-35 | anterior plate misplacement more likely |
| Tibial tuberosity height distance in relation to the joint line [mm] | 25-30 | 10-15 | anterior plate misplacement more likely |
| Posterior slope of the posterior articular surface [°] | 0-10 | 20 ± 3 | narrow and straight plate design necessary for posterior placement |
| Biomechanical properties of the tibial head | elastic cortical bone, exuberant amount of spongious bone | brittle cortical bone, few spongious bone | bicortical proximal screw placement mandatory to avoid fracture and dislocation, biplanar osteotomy mandatory regardless of the desired direction of correction |
| Musculature of the hind limb | remote from bony knee structures | voluminous on medial and lateral side of the femur | distal femoral and proximal lateral tibial osteotomy almost impossible, stay on the medial side of the proximal tibia for any desired correction angle |
| Trochlea ridge | lateral ridge extending further laterally and anteriorly | medial ridge extending further cranially and dorsally than lateral ridge | higher propensity of patella instability after valgus correction |
