Success of total hip replacement (THR) is closely linked to positioning of the acetabular component. Malalignment increases complication rates. Our aim was to describe the anteversion and inclination of the inherent acetabulum in arthritic hips and identify the number that fall out with the ‘safe zone’ of acetabular position described by Lewinnek et al. (anteversion 15±10 degrees; inclination 40±10 degrees). A series of 65 hips undergoing non-image based computer navigated THR for Osteoarthritis were investigated. Anteversion and inclination was measured with the help of cup trials fixed with computer trackers aligned in orientation of the natural acetabulum. The acetabular inclination in all hips was measured on pre-operative digital radiographs.Introduction
Materials/Methods
Soft tissue balancing is an important aspect of total knee replacement surgery. Traditionally sequential medial soft tissue release is performed for balancing in varus deformity. Its effects on kinematics and dynamic Femoro-Tibial-Mechanical-Angle (FTMA) have been described in extension and 90° flexion in coronal plane. However most studies have missed what happens when the knee flexes from 0 to 90 degrees This study is one of the first to describe its effects on knee kinematics throughout flexion. The aim was to look at deviation of FTMA in coronal plane with traditional sequential medial release with and without measured stress applied in varus and valgus at each point of measurement through the range of flexion. 12 cadaveric knees were studied using a computer navigation system. Rigid bodies were fixed to femur and tibia. The knee was exposed as per doing TKR surgery with medial parapatellar approach with no disturbance to the collateral ligaments. The anatomy was registered using a infra red waves based passive tracker navigation system. FTMA was studied in extension, 0°, 5°, 30°,45°,60°,90° and maximum flexion. Sequential medial release was performed in 7 steps as described by Luring et al. The sequential steps were Step 1: 2 cm release (antero medial tibial sleeve), Step 2: Postero-medial release, Step 3: 4 cm medial sleeve release, Step 4: 6 cm medial sleeve release, Step 5: Deep medial collateral ligament, Step 6: posterior cruciate ligament (PCL) medial half only, Step 7: entire PCL. At each step FTMA was measured with and without stressing at each point of flexion. A 10 Newton Meter moment arm was applied for varus and valgus stress force.Introduction
Methods
Traditionally sequential medial soft tissue release is performed for balancing in total knee arthroplasty for varus knees. Its effects on kinematics have been described in extension and 90° flexion in coronal plane. This is the first study to describe its effects on kinematics throughout flexion. 12 cadaveric knees were studied using a computer navigation system to assess kinematics. Femoro-Tibial-Mechanical-Angle(FTMA) was studied in extension, 0°, 5°, 30°,45°,60°,90° and maximum flexion. Sequential medial release was performed in 7 steps, described by Luring et al(Ref). At each step FTMA was measured without and with stressing. A 10 Newton Meter moment arm was applied for varus and valgus stress. Most of the initial release steps had little effect on FTMA without force applied, especially in the initial 60° of flexion. Application of varus force demonstrated very small changes. Application of valgus force demonstrated little change in initial arc of flexion until step 5 was reached (Table 1). Our study concludes the present sequence of medial release may not be correct and should be further investigated to modify the sequence for soft tissue balancing in TKR surgery.
