Views: 0 Author: Site Editor Publish Time: 2026-09-04 Origin: Site
Acetabular screw fixation is widely used in cementless total hip arthroplasty (THA) to improve initial cup stability. However, screw placement carries a risk of injury to the pelvic vessels, particularly when screws penetrate beyond the acetabular bone.
Pelvic vascular injury is an uncommon but potentially catastrophic complication. Because major vessels are located outside the direct surgical field, bleeding may occur in the retroperitoneal space without obvious blood loss at the acetabular site. Delayed recognition can result in substantial morbidity and, in severe cases, death.
The anatomical relationship between the acetabulum and pelvic vessels has been investigated in Western populations. However, differences in body size, pelvic morphology, and vascular anatomy may influence the applicability of these findings to Asian patients.
A Japanese cadaveric study examined the relationship between the acetabular surface and pelvic vessels to identify regions that may offer a lower risk of vascular injury during cementless THA. The findings provide useful anatomical guidance, but they should be interpreted as risk-reduction evidence rather than a guarantee of surgical safety.
During cementless THA, acetabular screws may be inserted to improve cup fixation. The depth and direction of screw penetration are important because the inner surface of the acetabulum is closely related to major pelvic vessels.
Potentially vulnerable structures include:
External iliac artery and vein
Obturator artery
Superior gluteal artery
Inferior gluteal artery
Other pelvic vascular branches
The risk is not distributed evenly around the acetabulum. Some regions are closer to major vessels, while others have a greater distance between the acetabular surface and the vascular structures.
This anatomical variation makes it important to consider both screw position and screw length rather than relying solely on a generalized “safe zone.”
The study analyzed 30 left hip joints from Japanese cadavers, including 11 males and 19 females. The mean age was 84.5 years, with a range of 58 to 98 years. The mean height was 154 cm, and the mean body weight was 36.8 kg.
Specimens with a history of hip surgery or pelvic visceral surgery were excluded because previous procedures may alter the anatomical relationship between the acetabulum and pelvic vessels.
The study used a hemispherical measuring cup with 52 guide holes to assess the relationship between the acetabular surface and pelvic vessels. Kirschner wires were inserted through the guide holes, and the researchers observed whether the wires intersected the vessels.
The vessels evaluated included:
External iliac artery
External iliac vein
Obturator artery
Superior gluteal artery
Inferior gluteal artery
The study did not include certain pelvic veins because their positions were difficult to identify reliably in the cadaveric specimens.
The acetabulum was divided into four quadrants using two reference lines passing through the acetabular center:
A zone: Anterior quadrant
B zone: Superior quadrant
C zone: Posterior quadrant
D zone: Inferior quadrant
This division allowed the researchers to compare the distribution of pelvic vessels and the minimum distance from the acetabular surface to the vessels.
The anterior region, particularly the anterior part of A zone, demonstrated a high frequency of vascular penetration.
In some areas, the observed penetration rate exceeded 50%, and in the central anterior region it exceeded 75%.
These findings suggest that the anterior acetabulum should be approached with particular caution when considering screw fixation.
Parts of D zone demonstrated penetration rates exceeding 50%.
The obturator artery was identified in much of the inferior region, as well as in areas extending toward the acetabular center.
This supports the importance of avoiding unnecessary screw penetration in the inferior acetabular region.
The study found that some areas of B and C zones had no major pelvic vessels directly adjacent to the acetabular surface.
However, the absence of a vessel in a particular region does not automatically mean that the region is universally safe. Vascular anatomy varies between individuals, and some vessels were still present in parts of the posterior acetabulum.
The important finding was that, in certain posterior regions, the minimum distance from the acetabular surface to the identified vessels was approximately 31 mm or greater.
This greater distance may provide a useful anatomical margin when selecting screw length.
The posterior acetabulum is generally considered a lower-risk region for screw fixation because major pelvic vessels are often located farther from the acetabular surface than in the anterior and inferior regions.
However, the study emphasized that the posterior acetabulum is not uniformly free of vascular structures.
The researchers identified the following general pattern:
| Acetabular region | Main vascular structures identified | General anatomical implication |
|---|---|---|
| Anterior region | External iliac artery and vein | Higher vascular risk |
| Inferior region | Obturator artery | Higher vascular risk |
| Superior region | Superior gluteal artery | Greater vessel-to-surface distance in some areas |
| Posterior region | Superior and inferior gluteal vessels in selected areas | Lower risk in selected regions, but not universally vessel-free |
The clinical implication is that posterior placement may reduce vascular risk, but it does not eliminate the need for individualized planning.
The distance between the acetabular surface and pelvic vessels is only one part of the safety calculation.
The surgeon must also consider:
The thickness of the acetabular bone
The direction of the drill
The depth of the drill trajectory
The length of the screw
The position of the acetabular cup
Individual pelvic morphology
A screw that is safe in one direction may become hazardous if the trajectory changes.
The study suggested that, in selected posterior regions, the greater vessel-to-surface distance may allow the use of 15–25 mm screws while maintaining a lower risk of vascular injury.
However, this should not be interpreted as a universal recommendation for every patient. Screw length must still be determined according to the patient's anatomy and the actual depth of the available bone.
The study provides evidence that certain posterior regions may have a greater distance from pelvic vessels.
However, the term “safe zone” should be interpreted carefully.
A more accurate clinical description is:
A lower-risk region for acetabular screw placement, based on the observed anatomical relationship between the acetabular surface and pelvic vessels.
This distinction is important because the study was based on cadaveric anatomy rather than clinical outcomes.
The study included Japanese cadavers without known hip abnormalities. Patients undergoing THA may have:
Osteoarthritis-related anatomical changes
Developmental dysplasia of the hip
Acetabular deformity
Osteophytes
Pelvic bone loss
Vascular tortuosity
Atherosclerotic changes
These factors may alter the distance between the acetabular surface and pelvic vessels.
Therefore, the study findings should not be applied without considering the patient's individual anatomy.
The acetabular cup is not always positioned exactly as planned.
The study considered a potential cup positioning error of approximately 15° when evaluating the practical safety of screw placement.
This is clinically relevant because even a small change in screw direction can alter the relationship between the screw tip and the pelvic vessels.
The implication is that a screw trajectory should not be considered safe solely because it is located in a theoretically favorable region.
The goal of acetabular screw fixation is to achieve sufficient initial stability while minimizing the risk of penetration beyond the acetabular bone.
A longer screw is not automatically a better screw.
The surgeon should balance:
Initial cup stability
Available bone stock
Screw purchase
Risk of vascular penetration
Risk of intraoperative and postoperative complications
The study's findings support the concept that screw length should be selected according to anatomical requirements rather than using a uniform length for every patient.
The study provides valuable anatomical information, but several limitations should be considered.
First, the sample consisted of 30 Japanese cadaveric hips, which limits the generalizability of the findings to other populations.
Second, the specimens were predominantly elderly, with a mean age of 84.5 years. Their anatomy may differ from that of younger patients undergoing THA.
Third, the study did not directly evaluate patients with hip osteoarthritis, developmental dysplasia, or other acetabular deformities.
Fourth, the study assessed the anatomical relationship between the acetabulum and pelvic vessels, but it did not establish that a particular screw position or length is clinically risk-free.
Finally, the study did not directly compare different screw lengths or trajectories in a clinical trial.
The Japanese cadaveric study provides important anatomical evidence for acetabular screw placement during cementless THA.
The main findings are:
Anterior and inferior acetabular regions are associated with a higher risk of pelvic vascular injury.
Selected posterior regions generally have a greater distance from major pelvic vessels.
The posterior acetabulum may represent a lower-risk region for screw fixation, but it is not universally vessel-free.
Screw length and trajectory must be considered together.
Individual anatomy and cup positioning remain essential to surgical planning.
The study supports a risk-reduction approach to acetabular screw fixation rather than the concept of an absolute anatomical safe zone.
Acetabular screw fixation is an important technique in cementless total hip arthroplasty, but it must be performed with careful attention to pelvic vascular anatomy.
The Japanese cadaveric study suggests that selected posterior acetabular regions may offer a greater distance from major pelvic vessels than the anterior and inferior regions. This may help surgeons select screw positions and lengths that reduce the risk of vascular injury.
However, the findings should be interpreted as anatomical guidance, not as a substitute for individualized surgical planning.
For clinical practice, the most appropriate approach is to combine anatomical knowledge, preoperative imaging, careful cup positioning, and conservative screw-length selection to achieve stable fixation while minimizing the risk of pelvic vascular injury.
