الفهرس 
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Abstract
Background: Varus deformity of the knee is a predisposing factor for osteoarthritis of the medial femoro-tibial compartment. High tibial osteotomy is the surgery of choice for such patients. Patients with varus deformity generally have asymmetrical wear of the knee joint. This is due to the concentration of axial force in the medial compartment, which causes greater impact on the subchondral bone of this compartment, intravenous hypertension and microfractures of the subchondral bone. Over time, this overload results in the deformity and pain that characterize arthrosis. The idea of high tibial osteotomy (HTO) is to unload an overloaded compartment, to slow down the progress of osteoarthritis and to allow healing of articular cartilage. High tibial osteotomy is used to correct coronal alignment of the proximal tibia but also causes changes in posterior tibial slope (PTS) unintentionally. Numerous studies reported that posterior tibial slope increases after high tibial osteotomy. This unintentional increase may influence knee kinematics and stability in the sagittal plane. Several recommendations have been suggested for preventing this unintentional increase in posterior tibial slope. This unintended increase in tibial slope was found to be due to the unique anatomical configuration of the proximal tibial cross-section, such that an opening wedge with equal anterior and posterior gap heights can increase the sagittal tibial slope. Therefore, to dampen any increase in tibial slope, it has been recommended that the anterior opening gap should be about 1/2 to 2/3 of the posterior opening gap The aim of the work: to assess effect of open wedge high tibial osteotomy for varus knee osteoarthritis on posterior tibial slope and its effects on knee functions. Materials and Methods: This work involved the study of a prospective case series treated since 1/2018 and followed up for a minimum of 1 year to assess the effect of open wedge valgus high tibial osteotomy on tibial slope and knee functions. It included 29 patients (30 knees) admitted to Mansoura University Hospital and kafr El Sheikh university Hospital with mainly medial compartment knee osteoarthritis who were treated using medial open wedge high tibial osteotomy fixed with a puddu or T- plate. Knee arthroscopy was done for each case prior to osteotomy to interfere with intra-articular lesions. The operative technique involved following Noyes et al recommendations for making the gap ratio between anterior and posteromedial gap of the osteotomy = 1/2 to minimize the unintended increase in tibial slope. Follow up of the cases for a minimum of 1 year was done using modified hospital for special surgery knee score Results: After measurement of the posterior tibial slope and assessment of knee function using modified HSS scoring scale, an increase in the tibial slope angle after valgus HTO with a mean change of 1.2 degrees was found. This increase had no effect on the final score of knee function as there was no correlation between slope changes and degree of score changes before and after surgery. There was no correlation between degree of correction and slope changes. There was a positive correlation between slope changes and results of anterior drawer test.Conclusion: The medial opening wedge technique causes significant change in the posterior tibial slope of the proximal tibial joint surface .The change in posterior tibial slope with a mean of 1.2° does not affect the postoperative knee functions at short term follow up. The change in tibial slope after valgus HTO affects the anterior drawer test results and may put a risk on the ACL functions. Following noyes et al recommendations for Posteromedial placement of the wedge plate and maintenance of the antero-posterior gap ratio to be 1/2 helps to minimize the changes in posterior tibial slope after HTO.