To compare between kinematic and mechanichal alignment after High Tibial Osteotomy (clinically and radiologically)

High tibial osteotomy (HTO) is a well-established joint-preserving procedure for younger and active patients with medial compartment osteoarthritis associated with varus malalignment. By laterally shifting the mechanical axis of the lower limb, HTO unloads the diseased medial compartment, alleviates pain, and delays the need for knee arthroplasty.

Traditionally, HTO planning has relied on a Mechanical alignment strategy, aiming to shift the weight-bearing line toward the lateral compartment. Fujisawa et al. described targeting a point located at approximately 62-65% of the tibial plateau width, which has been shown to optimize medial compartment unloading and improve long-term survivorship following HTO.

However, mechanical alignment applies a uniform correction target without accounting for individual anatomical variability. This is commonly achieved by correcting varus alignment to a slight valgus position (approximately 3-5°) through increasing the medial proximal tibial angle (MPTA). Such standardized correction may result in overcorrection, increased joint-line obliquity, altered soft-tissue balance, and excessive loading of the lateral compartment. These biomechanical changes may accelerate lateral cartilage degeneration and contribute to postoperative complications, potentially compromising long-term outcomes.

In contrast, Kinematic alignment (KA) is based on restoring the patient's native anatomical alignment and physiological joint-line orientation, rather than forcing all patients toward a fixed valgus target. By correcting only the pathological varus deformity and restoring the MPTA toward physiological values without overcorrection, kinematic alignment aims to preserve normal knee biomechanics and balanced soft-tissue tension.

Accordingly, the present study aims to make HTO not a temporary relief evaluate whether a kinematic alignment strategy in HTO can achieve comparable or superior clinical and radiological outcomes compared with mechanical alignment, while potentially reducing complications and delaying the need for total knee replacement.

Inclusion Criteria:

• Clinical: 1. Age : Adult with symptomatic osteoarthritic varus knee 2-Medial knee pain with functional limitation ≥6 months despite optimized non-operative care.

Radiological: 1- Medial compartment OA in Xray AP-Lateral view 2-Degree of varus ≥3 and ≤15 degree in long film(full-length, standing hip-to-ankle radiographs) 3-•Varus knee (mpta ≤85 degree and ldfa ≤93 and jlca ≤5)

Physical : 1-Range of motion: Flexion ≥110°, flexion contracture ≤10°, extension lag ≤5°.

2-Gait testing: Able to walk unaided (or with standard aid) for instrumented gait analysis.

Exclusion Criteria:

• 1- Predominantly lateral compartment OA 2- severe patellofemoral arthritis 3- Prior high tibial osteotomy, knee arthroplasty, or complex fracture around the knee 4-Inflammatory arthropathies (eg, rheumatoid arthritis) 5- end stage medial compartment osteoarthritis with bone erosions 6-chondrocalcinosis