Understanding the Hip–Spine Relationship in Total Hip Replacement: Insights from the Hip-Spine Workgroup

When planning a total hip replacement, most patients concentrate on the damaged hip joint. However, surgeons need to think about a bigger picture: how the hip and spine work together as a single unit. This connection, called the hip–spine relationship, is important for deciding the best position of the acetabular component (hip socket) during total hip arthroplasty (THA).

For years, research in this area has been complex and sometimes confusing because different studies used different terminology to describe the same concepts. Recognising this problem, a group of experienced hip and spine surgeons, including Associate Professor Andrew Shimmin, formed the Hip-Spine Workgroup. Their goal was simple but important: to create clarity, consistency, and a common language in the science of spinopelvic mechanics.

Their 2019 consensus review offers a clearer, standardised method. This helps surgeons use spinopelvic principles more effectively when planning hip replacements.

Why the Hip–Spine Relationship Matters

The pelvis sits between the spine and the hip. When you stand, sit, walk, or bend, your spine and pelvis move together. These movements influence how the hip socket works.

This matters because:

• Even a perfectly placed cup in the operating theatre can become maloriented during daily activities if the pelvis rotates differently than expected.
• Spine stiffness, spinal deformity, and abnormal pelvic tilt patterns can change the way a hip implant behaves.
• Without understanding this relationship, the risk of impingement, edge-loading, instability, and dislocation may increase.

Because of this, modern hip replacement is shifting from generic “safe zones” toward patient-specific functional planning.

The Challenge: Confusing Terminology Across the Literature

Before the Hip-Spine Workgroup formed, research on spinopelvic motion was filled with:

• Overlapping definitions
• Conflicting descriptions
• New terminology that was not universally accepted
• Difficulty comparing studies due to inconsistent language

This made it hard for surgeons to interpret research consistently, and even harder to apply findings to real patients.

The 2019 consensus review addressed this gap head-on.

The Hip-Spine Workgroup: A Unified Approach

Origins of the Workgroup

• Concept created in 2017
• First meeting held at the American Academy of Orthopaedic Surgeons (AAOS) Meeting, 2018
• Members included hip surgeons, spine surgeons, and researchers committed to improving clarity in the field

Goals of the Workgroup

• Standardise terminology for describing hip–spine interactions
• Provide a clear, simplified explanation of spinopelvic mechanics
• Create a foundation for future research that uses consistent, widely accepted language
• Help surgeons understand which spinopelvic factors truly matter in planning THA
• Promote collaboration between hip and spine specialists

Key Contributions of the Consensus Review

1. A Clear Framework for Understanding Spinopelvic Mechanics

The review breaks down the complex hip–spine relationship into simple, clinically meaningful concepts. This includes:

• What happens to the pelvis when the spine bends
• How posture changes affect acetabular orientation
• Which patients are most at risk of abnormal pelvic motion

This clarity helps surgeons plan cup position with greater precision.

2. Agreed Terminology for Future Research

The Workgroup selected and defined commonly accepted terms that both hip and spine surgeons can use. This consistency is important for:

• Improving research quality
• Allowing studies to be compared directly
• Helping clinical guidelines evolve
• Ensuring that what surgeons read in the literature is truly usable in practice

3. A Simplified Guide for Surgeons

Rather than overwhelming surgeons with conflicting theories or mathematical models, the review provides:

• A concise summary of essential concepts
• Practical guidance on how to apply spinopelvic understanding during THA
• Recommendations that apply across a wide range of patient types

This practical approach makes the subject more accessible to everyday clinical practice.

What This Means for Patients Undergoing Hip Replacement

For patients, this research matters because it supports a more personalised approach to hip replacement. Instead of relying solely on standard angles or “safe zones,” surgeons who apply these principles:

• Evaluate how your spine and pelvis move together
• Tailor the cup position to your functional movement patterns
• Consider the impact of spinal stiffness, degenerative changes, or previous spine surgery
• Reduce risks of dislocation and improve long-term implant stability

The result is a hip replacement that is designed not just for X-ray alignment, but for how you sit, stand, walk, and move in everyday life.

Key Takeaways from the Consensus Review

• The hip–spine relationship is essential for accurate cup positioning in THA.
• Historical confusion in terminology made research difficult to interpret.
• The Hip-Spine Workgroup was formed to unify language and simplify concepts.
• The 2019 consensus review provides clear definitions and practical guidance to help surgeons worldwide.
• Using this standardised framework leads to safer, more predictable hip replacement outcomes.

1. What is the hip–spine relationship in hip replacement?

The hip–spine relationship describes how the spine, pelvis and hip move together. These movements influence the functional position of the acetabular cup during daily activities, making it an important factor in planning hip replacement surgery.

2. Why was the Hip-Spine Workgroup created?

The Workgroup was formed to standardise terminology related to spinopelvic mechanics. Before this, conflicting definitions across studies made the topic confusing and difficult for surgeons to apply in practice.

3. What does the 2019 consensus review aim to achieve?

The review simplifies the hip–spine relationship, provides clear definitions, summarises key literature and establishes common terminology that can be used consistently worldwide in research and clinical practice.

4. How does understanding the hip–spine relationship help improve hip replacement outcomes?

A clearer understanding allows surgeons to predict changes in pelvic tilt and acetabular orientation during real-life movements. This leads to better cup positioning, improved stability and a lower risk of impingement or dislocation.

5. Why was inconsistent terminology a problem in spinopelvic research?

Different studies used different names for the same concepts or introduced new terms without consensus. This made comparisons difficult, slowed scientific progress and complicated clinical decision-making.

6. How does this research benefit patients?

Patients benefit from more accurate, personalised implant positioning based on their functional spinal and pelvic mechanics. This results in improved stability, function and long-term satisfaction after total hip arthroplasty.

7. Does this approach change how surgeons plan a hip replacement?

Yes. Instead of relying only on static imaging or traditional “safe zones,” surgeons consider functional imaging, spinopelvic balance and individual movement patterns to optimise acetabular component placement.

Reference:

A systematic approach to the hip-spine relationship and its applications to total hip arthroplasty N Eftekhary, A Shimmin, JY Lazennec, A Buckland, R Schwarzkopf, LD Dorr, D Mayman, D Padgett, J Vigdorchik The Bone & Joint Journal 101 (7), 808–816