However, how other radiological leg alignment parameters change after THR and how these changes work out on the kinematics and kinetics of gait are not well documented. As mentioned, this change in leg alignment might increase the risk for medial knee OA since a varus alignment increases the knee joint load. showed that besides the larger FO, the leg also appeared to be more varus after THR. found that patients with a restored FO after THR walk with more hip adduction and walk faster. showed that a reduced FO increases abductor muscle force to maintain normal gait, which in turn increases the joint reaction force. A recent simulation study of Rüdiger et al. A reduced FO creates an asymmetrical gait pattern with a reduced knee RoM on the affected side. A slightly increased femoral offset (FO) is currently standard practice after THR, as a larger FO provides more stability, reduces wear and gives a better functional outcome. By performing a THR, the positioning of the prosthesis has an influence on the natural alignment of the leg. a varus alignment increases the medial knee joint load. It is also known that leg alignment has an influence on the knee joint load: i.e. The decreased hip range of motion (RoM) in the sagittal plane was found to relate to the decreased knee adduction moment whereas the increased hip adduction angle was related to the increased hip adduction moment. For the external hip adduction moments the literature is not unambiguous as some studies found increased hip loading, whereas other studies did not find an overload for patients after THR.ĭifferences in gait kinematics between hip OA patients after THR and healthy controls can partly explain the differences in the joint moments in the frontal plane. Due to this lateralization of the knee joint load, patients likely have an increased risk for lateral knee osteoarthritis (OA) after THR. Patients still show a reduced external knee adduction moment in the second half of stance in both the operated leg and the non-operated leg compared to a healthy control group. It is known that the joint loads, expressed as net joint moments, do not return to normal up to 2 years after total hip replacement (THR). This study was retrospectively registered with DRKS (German Clinical Trials Register) under the number DRKS00015053. For surgeons it is important not to create too much of a structural varus alignment by implanting the new hip joint as varus alignment can increase the knee adduction moment and the risk for osteoarthritis of the medial knee compartment. A combination of these radiological leg parameters, especially the varus alignment, and the deviating kinematics explain the joint moments in the frontal plane during gait after total hip replacement surgery.

In our patient group the joint moments after total hip replacement did not differ from healthy controls, whereas radiological leg alignment parameters changed significantly after the total hip replacement. The combination with a kinematic parameter (knee range of motion, foot progression angle) increased the predictive value for the knee moments. The hip moment (first half of stance) and the knee moments (first and second half of stance) were mostly determined by the varus/valgus alignment (29% and respectively 36% and 35%). The operated leg showed significantly ( P < 0.05) more varus (1.1°) as well as a larger femoral offset (+ 8 mm) and a larger Hip-Knee-Shaft-Angle (+ 1.3°) after total hip replacement however no significant differences in the joint moments in the frontal plane compared to healthy controls were found. Preoperatively and 1 year postoperatively all patients had biplanar radiographic examinations and 3D gait analysis. MethodsĢ2 unilateral hip osteoarthritis patients who were scheduled for total hip replacement were included in the study. The goal of this study was to determine if total hip replacement surgery affects radiological leg alignment (Hip-Knee-Shaft-Angle, femoral offset, Neck-Shaft-Angle and varus/valgus alignment) and which of these parameters can explain the joint moments, additionally to the gait kinematics. Gait kinematics after total hip replacement only partly explain the differences in the joint moments in the frontal plane between hip osteoarthritis patients after hip replacement and healthy controls.

Xray of normal hip replacement