Abstract and Introduction
Abstract
Preoperative templating provides several benefits to the patient, surgeon, and hospital. Appropriate implant selection and sizing optimizes surgical workflow and leads to efficient care-delivery systems. Accurate templating establishes intraoperative targets for component position and reduces complications such as leg length inequality, impingement, wear, dislocation, and fracture, all of which lead to decreased patient satisfaction. Recent technological advances in preoperative imaging include a better understanding of patient-specific pelvic motion allowing the surgeon to preoperatively address the risk of lumbar pathology with adjustments in component placement and bearing choice. The introduction of two-dimensional to three-dimensional (3D) radiographs, biplanar low-dose radiographs, and computed tomography scans with 3D reconstructions have all allowed for a more comprehensive preoperative planning in 3D. This article will review the fundamentals of templating before total hip arthroplasty with an emphasis on how to incorporate and implement patient-specific pelvic motion and 3D templating into practice.
Introduction
The primary goal of preoperative planning is to create a surgical plan that includes expected implant sizes and position that will restore hip length and offset, address patient-specific bone abnormalities, and assess for alternations in pelvic mobility that may increase the risk for fracture or dislocation. Careful preoperative templating can reduce the risk of dislocation with restoration of hip length and offset in addition to accommodating for abnormal pelvic motion with component position adjustments or alternative bearing selection. In addition, periprosthetic fracture risk can be reduced by matching the stem design with proximal femoral anatomy and identifying poor bone quality that may require femoral stem cementation, and leg length inequalities can be minimized by establishing intraoperative targets for neck resection and planned leg lengthening.
As with any procedure, a thorough medical and surgical history, evaluation of patient comorbidities, and physical examination should be obtained as part of the preoperative workup and relevant factors incorporated into the preoperative template. Certain patient factors can increase risk for instability, such as developmental dysplasia of the hip, osteonecrosis, neuromuscular conditions, and history of spinal fusions. Surgeons should plan accordingly with consideration of the use of larger femoral heads, high offset stems, or dual mobility components to optimize hip stability.[1–3]
In addition, evaluation of patient gait and leg length measurements should be done to determine actual/true leg length discrepancy (LLD) versus apparent/functional discrepancy on preoperative radiographs. In the clinic, the true leg length can be measured from the anterior superior iliac spines to medial malleolus, whereas the apparent LLD is based on the patient's perception while standing and can be determined with the placement of the Coleman blocks under the shorter limb until the patient subjectively feels as if the limbs are of equal length.[1] Apparent leg length could also be measured from the xiphisternum, umbilicus, or pubic symphysis to the medial malleolus when the patient is lying supine. Angular and torsional deformities such as flexion contractures of the knee and hip (shortening) or adduction/abduction contractures of the hip (shortening/lengthening, respectively) can also affect functional limb length. These periarticular contractures can notably influence changes in the standing and sitting pelvic positions and should be incorporated when planning target acetabular implant position. In addition, if a pelvic obliquity is present, it is important to determine whether the source of the LLD is suprapelvic, pelvic, or infrapelvic.[4] A pelvic obliquity may be flexible (and often secondary to true limb length differences) or fixed (secondary to spine fusion or rigid degenerative scoliosis), and this information can be incorporated into target leg length intraoperatively.
J Am Acad Orthop Surg. 2021;29(5):e208-e216. © 2021 American Academy of Orthopaedic Surgeons
