Acetabular teardrop: Definition, Uses, and Clinical Overview

Acetabular teardrop Introduction (What it is)

Acetabular teardrop is a teardrop-shaped shadow seen on a standard front-view (AP) pelvis X-ray.
It is a radiographic landmark, meaning it is a feature created by overlapping bone contours on imaging.
Clinicians use it as a reference point when assessing hip anatomy, alignment, and certain hip conditions.
It is commonly discussed in orthopedic imaging, trauma evaluations, hip dysplasia workups, and hip replacement planning.

Why Acetabular teardrop used (Purpose / benefits)

Acetabular teardrop helps clinicians “read” pelvic and hip X-rays more consistently by providing a repeatable landmark near the socket of the hip (the acetabulum). Because many hip measurements depend on pelvic positioning and image quality, having a recognizable reference structure can improve how reliably a clinician describes hip anatomy from one visit to the next.

In general terms, Acetabular teardrop is used to:

• Support diagnosis by contributing to the interpretation of hip socket depth, coverage, and medial wall position. This can matter in conditions where the socket is shallow, deep, or displaced.
• Improve measurement consistency on AP pelvis radiographs, especially when comparing the left hip to the right hip or comparing current images to prior images.
• Assist surgical planning and follow-up, most notably in total hip arthroplasty (hip replacement), where radiographic landmarks are used to estimate hip center position, cup placement, and medialization/lateralization on X-ray.
• Provide context in trauma, where pelvic fractures or acetabular fractures may alter normal contours and relationships.

Importantly, Acetabular teardrop is not a disease by itself. It is an imaging feature that can look different depending on anatomy, positioning, age, and pathology.

Indications (When orthopedic clinicians use it)

Orthopedic clinicians and radiologists most often reference Acetabular teardrop in scenarios such as:

• Interpreting an AP pelvis X-ray as part of a hip pain evaluation
• Assessing hip dysplasia or other developmental variations in acetabular shape
• Evaluating suspected protrusio acetabuli (a medially positioned/deep acetabulum)
• Reviewing hip osteoarthritis patterns and joint space relationships
• Evaluating acetabular or pelvic trauma, including fractures affecting the medial wall
• Preoperative templating for total hip arthroplasty (THA) and postoperative comparison
• Comparing side-to-side symmetry in hip alignment or pelvic positioning on X-ray
• Longitudinal follow-up where consistent landmarks improve comparison over time

Contraindications / when it’s NOT ideal

Because Acetabular teardrop is a radiographic landmark rather than a treatment, “contraindications” are mainly situations where it is less reliable or less informative than other approaches.

It may be not ideal or may require caution when:

• The pelvis is significantly rotated or tilted during imaging, changing how the teardrop appears
• The X-ray is underpenetrated/overpenetrated or otherwise low quality, obscuring the contour
• There is prior surgery (hardware, hip replacement components, osteotomies) that alters normal bony outlines
• There are major deformities (advanced dysplasia, severe protrusio, tumor, prior fractures) where typical landmarks are distorted
• The patient is very young, where normal ossification patterns differ and some landmarks may be absent or evolving
• The clinical question requires 3D detail (complex fracture mapping, version assessment, subtle impingement morphology), where CT or MRI may better answer the question
• Precise measurements are needed but pelvic positioning is inconsistent; in those cases, clinicians may prioritize repeat standardized radiographs or alternative imaging

When the landmark is unreliable, clinicians often use additional lines and signs on X-ray, compare with the opposite hip, or select a different imaging modality.

How it works (Mechanism / physiology)

Acetabular teardrop works as a landmark through projection anatomy—the way three-dimensional structures create two-dimensional shadows on an X-ray.

High-level mechanism (what creates the “teardrop”)

On an AP pelvis radiograph, the “teardrop” appearance typically reflects the relationship between:

• The medial wall of the acetabulum (the inner boundary of the hip socket)
• Adjacent pelvic bone surfaces near the quadrilateral plate and pelvic brim region (terminology varies by clinician and radiology tradition)
• The way these cortical margins overlap in the X-ray beam

In simpler terms: the X-ray turns complex pelvic contours into a recognizable teardrop-shaped density near the inner edge of the hip socket.

Relevant hip anatomy and structures

To understand why the landmark matters, it helps to know the surrounding anatomy:

• Acetabulum: the socket portion of the hip joint
• Femoral head: the “ball” of the hip joint
• Joint space on X-ray: a radiographic representation of cartilage thickness (cartilage itself is not directly visible on plain radiographs)
• Medial acetabular wall: the inner boundary of the socket toward the pelvis
• Pelvic orientation: tilt and rotation can change apparent distances and angles on an AP pelvis view

Onset, duration, and reversibility (as applicable)

Acetabular teardrop is not a treatment and has no “onset” or “duration.” It is a feature seen at the moment of imaging. Its appearance can change over time due to growth, degeneration, fractures, reconstruction, or differences in pelvic positioning from one X-ray to the next.

Acetabular teardrop Procedure overview (How it’s applied)

Acetabular teardrop is not a procedure. It is a reference point used during imaging interpretation. A typical clinical workflow looks like this:

1. Evaluation / exam
   A clinician assesses symptoms, function, and history, then determines whether imaging is needed.

2. Preparation
   A standard pelvis or hip X-ray is obtained. Proper positioning (as feasible) helps produce a reliable AP pelvis view for measurements and comparisons.

3. Intervention / testing (the imaging review)
   The clinician or radiologist identifies Acetabular teardrop on each side and uses it alongside other landmarks to:

• Compare symmetry between hips
• Estimate hip center and socket position
• Consider whether the acetabulum appears shallow, deep, or medially displaced
• Support fracture or arthritis assessment when relevant

4. Immediate checks
   The image is reviewed for quality (rotation, tilt, visibility). If needed, repeat imaging may be obtained to better answer the clinical question.

5. Follow-up
   Findings are integrated with the patient’s presentation. If serial X-rays are used (for arthritis progression or after hip surgery), the teardrop may be one of several points used for comparison across time.

Types / variations

Acetabular teardrop is often discussed as a single landmark, but there are practical variations in how it appears and how it is used.

Common variations include:

• Normal vs altered teardrop morphology
  The teardrop can appear more prominent, less distinct, asymmetric, or displaced depending on pelvic positioning and acetabular anatomy.

• Age-related differences
  In children, pelvic ossification patterns differ from adults. Certain radiographic landmarks (including teardrop-related features) may be less consistent or interpreted differently depending on age and skeletal maturity.

• Positioning-dependent variation
  Pelvic rotation and tilt can change:

• The apparent width of the teardrop

• The spacing between the teardrop and the femoral head

• Side-to-side symmetry
  This is one reason standardized radiographs matter for comparison.

• Pathology-associated patterns (examples)

• In protrusio acetabuli, the medial socket relationship can appear shifted inward on radiographs, and teardrop relationships may be part of the overall interpretation.
• In hip dysplasia, the socket may be shallow with altered coverage; the teardrop is considered alongside other measurements and signs (not as a stand-alone diagnostic test).

• In fractures or postsurgical states, the teardrop may be disrupted, obscured, or less reliable.

• Measurement use cases
  In practice, clinicians may use the teardrop as a reference when describing:

• Medialization/lateralization of the hip center

• Relative cup position after THA on plain films
  The exact measurement approach varies by clinician and case.

Pros and cons

Pros:

• Helps provide a repeatable landmark on AP pelvis X-rays
• Useful for side-to-side comparison of hip anatomy on the same film
• Can support preoperative planning and postoperative review in hip arthroplasty imaging
• Contributes to the overall assessment of socket position and medial wall relationships
• Quick to identify for trained readers on standard radiographs
• Works as part of a broader set of lines/signs, improving communication in reports and consults

Cons:

• Not a true stand-alone “structure”; it is a projection that depends on technique
• Pelvic rotation/tilt can significantly change its appearance and measurements
• Can be hard to see on suboptimal films or in complex anatomy
• Less reliable in major deformity, fracture disruption, or after certain surgeries
• Interpretation can differ across readers; terminology and emphasis vary by clinician and case
• Provides limited information compared with CT/MRI for 3D questions

Aftercare & longevity

Because Acetabular teardrop is an imaging landmark, there is no direct “aftercare.” Instead, the practical focus is on what influences the usefulness and consistency of the landmark over time.

Factors that can affect how meaningful the teardrop is in follow-up imaging include:

• Consistency of radiograph technique
  Similar pelvic positioning across visits improves comparison. Differences in rotation or tilt can mimic changes that are not truly anatomical.

• Progression of underlying conditions
  Degenerative changes, fractures, or remodeling can alter pelvic and acetabular contours, changing how the teardrop appears.

• Surgical changes
  After procedures like THA, radiographs may use the teardrop as one of several reference points. Long-term usefulness depends on implant type, positioning, and imaging quality (details vary by material and manufacturer, and by clinician and case).

• Rehabilitation and loading context (when surgery or injury is involved)
  In post-injury or post-surgical scenarios, clinicians correlate imaging landmarks with the broader clinical plan (weight-bearing status, function, symptoms). The teardrop itself does not determine activity; it is one piece of the overall interpretation.

Alternatives / comparisons

Acetabular teardrop is one landmark among many. Clinicians often compare or complement it with other tools depending on the question.

Other plain-film (X-ray) landmarks and signs

On AP pelvis or dedicated hip radiographs, clinicians may also rely on:

• Shenton’s line (helps assess hip alignment and certain displacement patterns)
• Ilioischial line (Köhler line) (used in assessing medial acetabular migration and pelvic relationships)
• Acetabular sourcil and roof (used when considering coverage and degenerative change patterns)
• Joint space evaluation (a radiographic proxy for cartilage health)
• Additional signs and angles used for dysplasia or impingement assessments (selection varies by clinician and case)

Compared with these, Acetabular teardrop is often valued for its repeatability on many AP pelvis films, but it is rarely interpreted in isolation.

CT vs X-ray (when more detail is needed)

• CT provides clearer 3D detail for complex acetabular and pelvic fractures, version, and bony morphology. It can be preferred when surgical planning needs precise anatomy beyond a 2D projection.
• X-ray is faster and commonly used as a first-line imaging study. The teardrop is primarily an X-ray-based concept and is most useful within that context.

MRI vs X-ray (when soft tissue matters)

• MRI is better for soft tissues (labrum, cartilage, tendons) and certain bone stress injuries.
• X-ray is better for overall bony structure and alignment, where landmarks like the teardrop can be applied.

Ultrasound (more limited for this landmark)

Ultrasound is used in some hip evaluations (often pediatric or soft tissue-focused), but it does not replicate the same bony projection landmarks used on AP pelvis radiographs.

Acetabular teardrop Common questions (FAQ)

Q: Is Acetabular teardrop an actual “tear” or injury in the hip?
No. Acetabular teardrop is a normal radiographic appearance created by overlapping bony contours on an X-ray. It is a landmark used to interpret hip and pelvic images, not an injury itself.

Q: Does a finding related to the teardrop explain hip pain by itself?
Usually not by itself. The teardrop is a reference point; clinicians interpret it alongside symptoms, exam findings, and other imaging signs (such as joint space narrowing, fracture lines, or alignment changes). Pain causes and imaging findings do not always match perfectly.

Q: What does it mean if the teardrop looks different on one side?
Asymmetry can occur from pelvic positioning during the X-ray, natural anatomical differences, or underlying conditions that change the acetabular wall or socket position. A clinician typically checks image quality and other landmarks before concluding that asymmetry represents pathology.

Q: Can Acetabular teardrop be used to diagnose hip dysplasia or protrusio acetabuli?
It can contribute to the overall assessment, but it is not typically a single definitive test. Hip dysplasia and protrusio are usually evaluated using a combination of radiographic measures, landmarks, and clinical context. The exact diagnostic approach varies by clinician and case.

Q: How is it used in hip replacement (total hip arthroplasty) imaging?
On plain radiographs, surgeons and radiologists may use the teardrop region as a reference when describing cup position, hip center estimates, and side-to-side comparisons. It is one of several landmarks used to communicate implant position and follow-up changes over time.

Q: Is identifying the teardrop painful or invasive?
No. It is identified on standard X-rays. The process is noninvasive; any discomfort is usually related to positioning for imaging if the hip is already painful.

Q: What is the cost range for imaging where the teardrop is assessed?
Costs vary widely by region, facility type, insurance coverage, and whether additional imaging (like CT or MRI) is required. For pricing, clinics typically provide an estimate based on the ordered study and billing setup.

Q: Can I drive or return to work after an X-ray that includes Acetabular teardrop assessment?
An X-ray itself usually does not limit driving or work. Restrictions, if any, are typically related to the underlying injury or condition being evaluated rather than the imaging landmark. Activity guidance varies by clinician and case.

Q: Does the teardrop determine weight-bearing status after injury or surgery?
No. Weight-bearing decisions are based on the diagnosis (for example, fracture stability, surgical repair, or implant considerations) and the clinician’s plan. The teardrop is simply one imaging reference that may be considered in the broader evaluation.

Q: If the teardrop is “not visible,” is that always abnormal?
Not always. Visibility can be affected by age, ossification patterns, image quality, pelvic rotation/tilt, or altered anatomy from prior injury or surgery. When it is unclear, clinicians typically rely on additional landmarks or different imaging to answer the clinical question.