Positioning of the acetabular component: Key elements
Total hip arthroplasty (THA) aims to return joint function and improve joint stability for patients. If surgeons do not account for the unique biomechanics of each patient, outcomes can be negatively impacted—leg length discrepancy, gait dysfunction, impingement, wear, and loosening are all issues that may arise. Accurate positioning of the acetabular cup is one element of a THA that can alleviate many of these concerns. There are five aspects of cup positioning that influence the success of THA: medialization, depth, height, angular positioning, and pelvic tilt. How do these considerations allow surgeons to accommodate patient-specific characteristics?
It will be of no surprise to AO Recon members to read, that medicine is moving away from a generalized, one-size-fits-all approach towards treatment strategies that take into account an individuals’ unique physiology and/or genetic composition, among other considerations [1, 2]. While customized care based on the unique needs of each patient has been forefront for quite some time, as our understanding of genetics and acknowledgement of physiological differences grows, so too do our treatment options.
Indeed, precision or personalized medicine, the tailoring of health care based on genetics, lifestyle, and environment, is gaining traction around the world—in 2015, US President Obama announced the launch of the National Health Institute’s Precision Medicine Initiative. The Initiative has the stated mission of enabling “a new era of medicine through research, technology, and policies that empower patients, researchers, and providers to work together toward development of individualized care.” 
In OECD countries, THA is expected to grow at a rate of 1.2% per year, with approximately 2.8 million annual hip replacements in 2050 ; another study on THA trends in the US predicts that by 2060, there will be 1.23 million primary THA’s a year in that country alone .
Orthopedic surgeons are seeing the introduction of technology such as 3D printing of device components and instrumentation that facilitate treatment customized to specific patients [6, 7]. While new technology and understanding certainly play a role in improved outcomes, successful THA is increasingly being seen as more reliant on achieving biomechanics optimized for each individual patient and less on achieving generic intraoperative targets.
Goals of THA
For a THA to be considered successful from a surgeon’s perspective, three interdependent elements must be satisfied. Firstly, functionality of the hip joint must be delivered so mobility can be returned to a patient. Secondly, stability within the joint is integral to meeting the goal of mobility and this must be achieved surgically. Thirdly, maximizing the lifespan of the implant is associated with realization of the previous two elements (see Figure 1). Revision THA for any reason brings increased risks to patients such as infection and re-do revisions . Malpositioning of the acetabular cup has been called “the most common cause of THA dislocation” .
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- What we want to avoid: dislocation, pain, revision
- Defining acetabular cup positioning
- Joint reaction force
- Conventional versus anatomic approach
- Angular positioning: anteversion and inclination
- Variability in defining “safe zone” angles
- Different ways to measure and describe the “safe zone”
- Pelvic tilt
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This series of articles was created with the support of the following specialists (in alphabetical order):
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University of British Columbia
Bas A Masri
University of British Columbia
This issue was created by Word+Vision Media Productions, Switzerland
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