Correlation between the acetabular diameter and thickness in Thais

Journal of Orthopaedic Surgery, Jun 2002 by Varodompun, Namchai, Thinley, Tshewang, Visutipol, Boonyarak, Ketmalasiri, Bunyat, Pattarabunjerd, Narongchai

ABSTRACT

We conducted a study on dried cadaveric pelvic bones to determine the relation between acetabular diameter and thickness of the acetabular wall.

The acetabulum was divided into four quadrants: antero-superior, postero-superior, postero-inferior, and antero-inferior. The diameters of the acetabulum were measured for 152 pelvic bones. The thickness of the center of the acetabulum was measured with the use of a caliper at four quadrants of the acetabulum. The average acetabular diameter was found to be 51.8224 mm for all the acetabuli. The average thickness in the posterior quadrant has been calculated to be about 50% of the acetabular diameter, which is about 26 mm. The acetabular diameter and the thickness of the acetabulum correlated very well though there was very little significance statistically (0.099) due to the lack of full data for all the individual bones.

Linear correlation between the thickness and the diameter is definitely collinear but the correlation is not statistically significant. Some additional factors such as bone density, body mass, etc, are required to correlate the thickness and the diameter. Further study is required in this field.

Key words: acetabulum, acetabular diameter, acetabular thickness, screw length

INTRODUCTION

During surgery of the acetabular fractures or during the placement of acetabular cups in arthroplasty, placement of the screws in the acetabulum is very critical because of the neurovascular structures that surround it. It is very important to know the anatomical landmarks as well as the average length of the screws that can be placed safely at various quadrants of the acetabulum.

OBJECTIVE

The objective of the study was to find the correlation between the acetabular diameter and the thickness of the acetabulum at various quadrants in Thais.

MATERIALS AND METHODS

152 dry pelvic bones were used to measure the diameter and the thickness of the acetabulum: 18 female acetabuli (age 17 to 70 years), 118 male acetabuli (age 20 to 86 years). The ages of 16 were not recorded, and 80 were right-sided and 72 left-sided. A caliper with pointed ends measuring to 0.01 mm determination was used to measure the thickness of the acetabulum. The diameters of all 152 acetabulums were measured.

The acetabuli were divided into four quadrants as described by Wasielewski et al.4 by bisecting them by a line from the anterior superior iliac spine and another line passing through the center of the acetabulum perpendicular to the first line. This division divided the acetabulum into the thickest part, which was at the posterior-superior part, followed by the posteriorinferior part, then the anterior-superior part and the thinnest part, anterior-inferior.

DISCUSSION

From our study we found the thicknesses of the postero-superior and the postero-inferior rim were 85% and 72% of the acetabular diameters . They can accommodate more than 37 mm and less than 44 mm of screw length.

Our findings are almost the same as that of PC Noble 1'2 , who found that the thickness of the acetabulum was more than 50% of the acetabular diameter at the posterior rim, 40% to 50% around it and 30% to 40% over the dome of the acetabulum and less than 30% in the centre. SK Stranne et al.,3 in their mechanical model study about the screw-augmented fixation of acetabular components, reported that the bicortical screw fixation over the superior ilium, posterior column and the ischium was strongest, indicating that these areas are the thickest parts.

Reviewing the articles, there is no mention of the acetabular diameter in males and females. We found the acetabular diameter in males was larger than in females.

The most important thing in acetabular surgery is the operative technique, and using these safe quadrants may be important to avoid injuring the neurovascular structures. Even drilling and using the depth gauge can injure them. By just knowing the acetabular diameter,the screw lengths can be approximated at various quadrants of the acetabulum and inserted safely without damaging the neurovascular structures.

We have found that the linear correlation between the thickness and the diameter of the acetabulum is collinear though it is not statistically significant. More data, such as bone density, body mass etc. is required.

CONCLUSION

There is definite correlation between the diameter and the thickness of the acetabulum although it is statistically not significant. Additional information with regard to bone density, bone mass, etc. is needed. Further study is required in this field.

REFERENCES

1. Noble PC. Biomechanical advances in total hip replacement. In: Niwa S and Hattori, ed, Biomechanics in Orthopedics. Tokyo: Springer-Verlag 1992, 46-75.

2. Noble PC. Instructional Course Lecture: Contributions of Basic and Applied Sciences to Hip Replacement in the Older Patient. St.Louis: Mosby 1994, 381-92.

3. Stranne SK, Callaghan JJ, Elder SH, Gilisson RR, Seaber AV. Screw-augmented fixation of acetabular components: A Biomechanical model to determine optional screw placement. J Arthroplasty 1991, 6: 301-5.