Precision of Pacient-specific Instrumented Open Wedge High Tibial Osteotomy vs Conventional Technicque

Inclusion Criteria: * Informed consent: able to sign informed consent * Clinical: predominantly medial pain/limitation refractory ≥3-6 months * Mobility: flexion ≥90º and flexion contracture ≤10º Stability: varus/valgus and pivot-shift ≤ grade 1. * Radiology: * Medial gonarthrosis Ahlbäck I-III with preserved lateral compartment. * Patellofemoral Iwano 0-2 without disabling patellofemoral pain. * Varus alignment: HKA 4-10°. * Predominantly tibial deformity (decreased MPTA; LDFA close to normal) according to planning. * Anatomy/technical feasibility: proximal tibial morphology suitable for medial opening osteotomy and PSI guide placement. Exclusion criteria: * Comorbidity/clinical situations: * Inflammatory arthritis (e.g., RA, spondyloarthropathies), unresolved previous joint infection or osteomyelitis. * Severe peripheral vasculopathy (ABI \<0.7), advanced peripheral neuropathy or Charcot foot. * Poorly controlled diabetes (HbA1c \>8.5%), advanced renal/hepatic failure (eGFR \<30 ml/min/1.73 m²; Child-Pugh B/C). * Smoking \>20 cigarettes/day without commitment to cessation; active IV drug use or uncontrolled alcoholism. * BMI \>35 kg/m². * Disorder affecting gait (e.g., neurological disease). * Inability to walk at a speed of at least 0.8m/s * Anatomy/radiology * Multiplanar deformities not correctable with isolated medial opening tibial valgus osteotomy (e.g., dominant femoral deformity). * Severe medial subchondral bone defect or extensive necrosis. * Sequelae of proximal tibia fracture or previous ipsilateral HTO that prevent correction or guide use. * Treatments/medication and logistics * Anticoagulation/antiplatelet therapy that cannot be suspended or bridged. * Systemic corticosteroids \>10 mg/day or high-risk immunosuppressants without possibility of adjustment. * Intra-articular infiltration (HA/CS/PRP) within the previous 60 days (respect defined wash-out). * Pregnancy. * Participation in another interfering trial. * Inability to undergo CT (e.g., uncontrollable claustrophobia). * Inability to complete ≥12 months of follow-up.