THA Templating - Recon - Orthobullets

Introduction

Definition
- the process of anticipating the size and position of implants prior to surgery
Importance
- allows surgeon to anticipate potential difficulties
- to reproduce hip biomechanics
- minimizes leg length inequality
Accuracy
- 52-98% accurate +/- one size
- related to experience and practice
Steps
- obtain appropriate radiographs
- record vital patient information on template (age, height, weight, etc)
- establish radiographic landmarks
- establish limb length discrepancy
- template acetabular component
  - do this first to determining center of rotation of new hip
- template femoral component
Tips
- best to achieve a good template with sizes in the middle range of the component system
- different system may be a better choice if this cannot be achieved

Radiographic Analysis

Necessary radiographs
- AP pelvis
  - centered over pubic symphysis
- AP hip
  - taken with 10-15 degrees of internal rotation
    - places femoral neck parallel to cassette
    - external rotation on radiographs will
      - falsely decrease offset
      - create valgus appearing femoral neck
      - falsely decrease femoral canal diameter
- frog lateral hip
Magnification
- 20% is standard
  - most templates account for this
- magnification markers are helpful
Secondary assessment of radiographs
- pelvic obliquity
  - may be secondary to spinal deformity
  - may cause leg-length issues
- acetabular retroversion
  - makes appropriate positioning of acetabular component more difficult intraoperatively

Radiographic Landmarks

Femoral side
- medullary canal
- greater trochanter
- lesser trochanter
- saddle point
  - most distal part of the junction between the superior aspect of the femoral neck and the greater trochanter
Acetabular side
- acetabular roof
- tear drop
  - created by superposition of the most distal part of the medial wall of the acetabulum and the tip of the anterior/posterior horn of acetabulum
Pelvis
- ischial tuberosities
  - important to determine limb length discrepancy

Establish Limb Length Discrepancy

Steps
- on AP pelvis, draw horizontal line connecting the ischial tuberosities
  - ensure the line extends beyond the medial femoral cortices bilaterally
- mark the top (proximal-most point) of both lesser trochanters on the AP pelvis radiograph
- measure the distance between the inter-tuberosity line and the line drawn at the most proximal aspect of the lesser trochanters
Alternatives
- a line connecting the teardrops may be used instead of the ischial tuberosity line
  - this may be more accurate

Template the Acetabulum

Template the Femur