Last updated on 15 May 2025
Description
Total hip arthroplasty, commonly referred to as hip replacement surgery, involves the surgical replacement of the hip joint with an artificial implant. This complex procedure requires careful consideration of several critical parameters to ensure optimal outcomes:
- Limb Length Discrepancy: The Hilgenreiner’s line serves as a valuable tool for assessing any discrepancies in limb length. It is important to note that variations in limb length of up to 1 cm are generally well tolerated by patients.
- Center of rotation: The center of rotation is vital for successful hip replacement surgery. Accurately positioning the acetabular component to replicate the anatomical center of rotation of the femoral head is essential. Both acetabular and femoral components must align with normal anatomical structures, and the distance from the femoral head to a landmark, such as the teardrop, should be consistent bilaterally. Excessive lateral positioning of the acetabular component should be avoided to reduce the risk of dislocation and limping.
- Femoral Offset: The femoral offset is a critical measurement in total hip replacement surgery, defined as the distance from the center of rotation of the femoral head to the longitudinal axis of the femur or femoral stem. Proper alignment of this offset is essential for optimal hip joint biomechanics post-surgery, with normal values typically ranging from 30 mm to 60 mm.
Requirements
This procedure is applicable to both conventional radiography (CR) and computed tomography (CT) imaging, with a requirement for clear representation of the hip bones to ensure accurate assessment and planning.
Measurements
The measurements made by the procedure are displayed in the image:
2D
- Femoral Offset (FO): The distance measured from the Anatomical Axis of the Femur (AAF) to a Hilgenreiner parallel line that runs through the center of the femoral head;
- Limb Length Discrepancy (LLD): The variation in length measured between the Lesser Trochanters’ Lines (LTL) on both sides..
- Centrum-Collum-Diaphyseal (CCD): The angle formed between the axis of the femoral shaft and the axis of the femoral neck.
3D
Pelvis
- Femoral Offset (FO): The distance measured from the Anatomical Axis of the Femur (AAF) to a Hilgenreiner parallel line that runs through the center of the femoral head;
- Limb Length Discrepancy (LLD): The variation in length measured between the Lesser Trochanters’ Lines (LTL) on both sides..
- Centrum-Collum-Diaphyseal (CCD): The angle formed between the axis of the femoral shaft and the axis of the femoral neck.
- Pelvic Tilt (PT): The measurement taken from the midpoint of the proximal edge of the interpubic disc to a line that connects the centers of both femoral heads.
- Femoral Center of Rotation (COR): The distance is measured from the tip of the teardrop to the center of rotation of the femoral head. This measurement is taken as the length from the teardrop to a perpendicular line that intersects with the center of rotation (COR).
- Acetabular Center-Edge (CEA): The angle formed by a vertical line drawn to Hilgenreiner’s line at the midpoint of the femoral head and a line extending from the midpoint of the femoral head to the lateral acetabular rim.
Femur
- Femoral Head Diameter (FHD): The measurement taken from the most lateral edge to the most medial edge of the femoral head.
- Distances Between Trochanters (DT): The measurement of the distance from the tip of the greater trochanter to the lesser trochanter.
- T-score: The T-score represents the difference between an individual's bone mineral density and the established baseline of 0, which corresponds to the bone mineral density of a healthy young adult.
- Cup Implant Coverage (IC): The percentage of the acetabulum surface that is covered with the cup template (the representation can be shown/hidden.
- Dorr Classification
Auxiliary references
- Anatomical Axis of Femur (AAF): An axis that extends from the center of the proximal femur to the distal femur.
- Lesser Trochanters’ Line (LTL): A line that is perpendicular to Hilgenreiner’s line (HilL), originating from HilL and extending to the proximal edge of each lesser trochanter.
- Intramedullary canal: The intricate structure of the femoral intramedullary canal.
How to perform
Pre-op stage
- Validate landmarks and consult measurements
Upon creating the case and uploading the image, the system will automatically place all relevant landmarks, allowing you to view the pre-operative values of each measurement.
If necessary, you can refine the position of these landmarks. Simply click on "Edit landmarks," make the required adjustments, and then save your changes by selecting "Save." The measurements will be updated accordingly, enabling you to continue to the next step by clicking “Approve.”
To reposition the landmarks, simply hover your cursor over the desired landmark and use the left mouse button to adjust each handle to the most appropriate location.
Plan stage
- Template selection and positioning
Upon the approval of the procedure, you will proceed to the templating stage. Here, you can select the manufacturer of your choice. If only one manufacturer is available, it will be automatically selected for you.
During the template configuration phase, you have the flexibility to adjust the properties of the selected template(s) and reposition them as needed.
To finalize the plan, it is essential to click on "Approve plan" and confirm the action in the dialog box that appears.
Export stage
The final stage of the planning process involves the Export step. At this point, you can download a comprehensive PDF report that encapsulates all the planning information, ensuring you have a thorough record of the procedures and measurements taken.
