Posterior Inferior Iliac Spine Research Articles

A New Entry Point and Trajectory for Iliac Bolt Fixation in Patients Undergoing Long Fusion to the Sacrum

Introduction Osteotomy of the posterior superior iliac spine for preparation of traditional iliac screw entry point exposes the cancellous bone of the inner ilium and causes loss of circumferential cortical starting point which may compromise biomechanical stability. For this reason, traditional iliac screws may not provide the desired primary stability especially in osteopenic and osteoporotic patients. We describe a new free-hand technique with a starting point located at the posterior inferior iliac spine (PIIS), which does not require any decortication for entry and courses very close to the rigid subcortical bone over sciatic notch while providing a low profile fixation and easier connection with S1 screw. The aim of this study is to evaluate the result of this new iliac bolt fixation technique. Patients and Methods A total of 26 patients (21 F and 5 M) having lumbopelvic fixation with the new technique were reviewed. The new entry point is located at the midpoint of PIIS. Lateral cortex of distal iliac wing is exposed subperiosteally and sciatic notch was palpated for safe trajectory. Screw trajectory is intended to be parallel to the outer cortex of ilium, passing 1 to 1.5 cm above the sciatic notch. PIIS provides a rigid circumferential cortical starting point for entrance and trajectory through thick cortical iliac bone over sciatic notch which provides very strong screw purchase even in osteopenic and osteoporotic spine. New entry point also enables easier connection to S1 screw. Free-hand technique eliminates radiation exposure. Pre-op, post-op, and follow-up X-rays were reviewed for the radiological data. Results Mean age was 63.6 years (range, 19–84 years) and mean follow-up was 14 months (range, 12–18 months). Mean screw length was 93.46 mm (range, 80–110 mm). Screw diameters were 8.5 mm in 22 patients and 7.5 mm in 4 patients. Lumbosacral fusion was achieved in all the cases. There were no neurovascular injuries related to the sciatic nerve and gluteal artery during screw placement. There were no implant failures or screw breakage at end of final follow-up. Conclusion This new technique seems to be a viable option in patients undergoing fusion to the sacrum for iliac bolt fixation. PIIS provides a circumferential cortical starting point and low profile fixation with stronger screw purchase especially in osteoporotic patients.

Sex and side determination of human hip bone by metric parameters of its posterior border

Abstract Background: Identification of sex from skeletal remains is of medico-legal and anthropological importance for forensic experts, anthropologists and anatomists. Hip bone is considered as an ideal bone for sex determination as it provides the highest accuracy levels for sex determination. Aims: To determine the sex and side of the human hip bones by using different metric parameters of posterior border of hip bone. Material and methods: In present study, 200 (100 males and 100 females) dried adult human hip bones of known sex were collected. Two parameters were studied and statistically analysed by paired and unpaired 't' test. Results: In males, distance from the posterior superior iliac spine to the superior border of ischial tuberosity was the discriminant criteria to sex the hip bones while in females, it was distance between the posterior inferior iliac spine (PITS) to ischial tuberosity (IT). Statistically significant difference between the mean related to side were seen in both the variables. Conclusion: These two parameters can be used for sexual dimorphism as well as side determination of human hip bones or its fragments.

Screw placement in percutaneous acetabular surgery: gender differences of anatomical landmarks in a cadaveric study

Percutaneous reduction and periarticular screw implantation techniques have been successfully introduced in acetabular surgery. The advantages of this less invasive approach are attenuated by higher risks of screw misplacement. Anatomical landmarks are strongly needed to prevent malplacement. This cadaver study was designed to identify reliable anatomical osseous landmarks in the pelvic region for screw placement in acetabular surgery. Gender differences were specifically addressed. Twenty-seven embalmed cadaveric hemipelvic specimens (13 male, 14 female) were used. After soft-tissue removal, anterior and posterior column acetabular screw placement was conducted by one orthopaedic trauma surgeon under direct vision. Each column was addressed by antegrade and retrograde screw insertion. Radiographic verification of ideal screw placement was followed by assessment of the distance from the different entry points to adjoining anatomical osseous structures. For anterior column screw positioning, the posterior superior iliac spine (PSIS), posterior inferior iliac spine (PIIS), iliopectineal eminence and centre of the symphysis were most reliable regarding gender differences. For posterior column screw positioning, the distance to the anterior superior iliac spine (ASIS) and the ischial tuberosity showed the lowest deviation between the different gender specimens. Highest gender differences were seen in relation to the cranial rim of the superior pubic ramus in retrograde anterior column screw positioning (p = 0.002). Most landmarks could be targeted within a 2.5-cm range in all specimens. The findings emphasise the relevance of osseous landmarks in acetabular surgery. By adhering to easily identifiable structures, screw placement can be safely performed. Significant gender differences must be taken into consideration during preoperative planning.

Thickness and tension of the gluteal aponeurosis and the implications for subfascial gluteal augmentation

The aim of this study is to elucidate the thickness and tension of the gluteal aponeurosis (GA) as related to subfascial gluteal augmentation. Twenty buttocks from 10 Korean fresh cadavers (age range: 69-92 years, five men and five women) were dissected. Five radial lines were made from the greater trochanter (GT) to the highest point of origin of the gluteus maximus muscle (GM), the posterior inferior iliac spine (PSIS), the piriformis line (P), the coccyx (Co) and the ischial tuberosity (IT). The upper four lines were intersected by three curvilinear lines that divided them by a quarter, half and three-quarters ratios, and the lowest line was divided by a third ratio and a two-thirds ratio. At the 14 intersecting points, the force needed to break the 6 mm width of the GA was measured. The thickness of the GA was also measured with a digital caliper. The GA was widest at the GT-Co line (161.7±15.8 mm), and it was narrowest at the GT-IT line (106.5±21.2 mm). At most of the points (12 among the 14 points), the breaking strength of the GA was greater than 20 Newtons (N). The breaking strength of the GA did not vary significantly according to the locations (P=0.568, anova). The breaking strength of the males (22.8±6.6 N) was significantly greater than that of the females (20.3±7.5 N, P=0.003, t-test). The thickness of the GA varied according to the locations (0.4±0.2 mm to 0.7±0.3 mm). The thickness of the GA of the upper part (GT-GM line: 0.64±0.24 mm; GT-PSIS line: 0.66±0.23 mm; GT-P line: 0.66±0.24 mm) was significantly greater (P=0.040, 0.017, 0.018, respectively) than that of the lower part (GT-IT line: 0.49±0.18 mm). The GA of the males (0.70±0.23 mm) was significantly thicker than that of the females (0.53±0.21 mm, P<0.001, t-test). We conclude that the GA is capable of holding gluteal implants in the proper position, as the average force to break up the 6 mm width of the GA in females was greater than 20 N.

Surgical anatomy of the superior gluteal nerve and landmarks for its localization during minimally invasive approaches to the hip

The superior gluteal nerve (SGN) is vulnerable to damage during total hip arthroplasty and various pelvic surgeries. Recently introduced minimally invasive approaches to the hip show promise for less muscle trauma compared to conventional approaches. However, the risk of damaging the SGN has not been well documented for such alternative approaches. Therefore, we aimed to investigate the anatomic course of the SGN and to define anatomical landmarks that may be used by surgeons during minimally invasive approaches to the hip. Twenty-eight gluteal regions from 14 formalin-fixed cadavers were dissected and the course and the distances of the SGN and its branches to the tip of the greater trochanter (GT) were measured. The landmarks for standardizing the course of the SGN included the posterior inferior iliac spine (PIIS), GT, and a line (PIIS-GT) connecting these two points. The exit of the SGN was found to be at the medial one third of the PIIS-GT line and 5.4 cm from the GT. Two branching patterns were noted. The branches of the SGN were distributed lateral to the PIIS-GT line. On the basis of our study, the safe zone for the SGN was smaller than previously reported. Posterior, lateral, or anterolateral minimally invasive approaches to the hip should take into account the point of exit of the SGN and the area of distribution of its branches. A minimally invasive anterolateral approach may particularly compromise branches to the tensor fasciae latae muscle. Localization of the SGN and its branches using the anatomic landmarks defined in this study may decrease surgical morbidity.

News and Comments

The Paleoindian burial from the Brazilian rockshelter site of Toca dos Coqueiros was discovered in July 1997 (Guidon et al., 1998). The site is one of several known Paleoindian sites in the immediate region of the Serra da Capivara National Park, located in the northeastern Brazilian state of Piaui (Guidon and Arnaud, 1991). The interred individual, carrying a calibrated date of 11,060 years BP (conventional radiocarbon age of 9,870 50 years BP; beta 109844; Guidon et al., 1998), is significant in being one of the oldest human skeletons recovered in the New World, and was described as female (Lessa and Guidon, 2002). I had the opportunity to examine the Coqueiros individual and reconstruct the skull. I present illustrative data to support the view that the Coqueiros skeleton represents a gracile male. Comparative craniofacial morphometrics suggest as well that Paleoindian groups living in South America at this distant temporal horizon may not have been closely related to later and recent Amerind populations (Neves and Pucciarelli, 1991; Neves et al., 1998, 1999). Our craniometric evaluation of this individual supports that as well (Nelson et al., in press). The cranial vault and much of the enveloping matrix had been stabilized with B72 resin, as these had been subjected to some crushing and fragmentation over the course of time. They did not, however, appear to be particularly deformed, but much of the vault was obscured by soil matrix impregnated with B72. The loose fragment assemblage included a considerable amount of facial material: nasals, maxillary frontal processes, the left malar, and superorbital portions of the frontal, including the glabella. Several basilar fragments were also present, representing the margins of the foramen magnum, sphenoid alae, portions of the occipital squamous, and temporals. In addition to a significant quantity of diagnostic cranial fragments, the assemblage included numerous postcranial fragments. Among this material was the inferior ramus of the right pubis and enough of the posterior inferior iliac spine to reconstruct the posterior margin of the left greater sciatic notch. In addition, both femoral heads and the right humeral and radial heads were available for study. A full reconstruction of the skull was undertaken. Sections of vault bone and matrix embedded in B72 were soaked in acetone, taken apart, cleaned, dried, and reassembled using a plastic-resin DucoTM cement. Loose craniofacial fragments were sorted, sided, and assembled. The bony facial reconstruction was articulated to the vault reconstruction. On the pelvis, the ventral ramus was reconstructed onto the larger portion of the right pubis in order to aid in identification of sex-based morphology. In addition, the posterior inferior iliac spine was reconstructed back to the left innominate, in order to establish the form of the greater sciatic notch. The greater sciatic notch tends to be wider in females and narrower in males, though Fulginiti (1993) demonstrated variability in this tendency. In the dorsal midline, there is sex-based variability in the morphology of the sacrum as well. In males, the centrum of the first sacral vertebra tends to be wider than the alae, by approximately three-fifths vs. onefifth for alar widths, while in females these widths tend to be more evenly apportioned at one-third each of the total sacral width across the top. In the collections at the Fundacao Museu do Homem Americanos (FUMDHAM) is an unambiguous female Paleoindian skeleton dated to within 1,200 years of Coquieros. Lessa and Guidon (2002) mentioned this individual (Toca da Janela da Barro do Antoniao), but stated that they could not use it for comparison. In addition, an unambiguous female os pubis, from a relatively recent burial context (within the past 500 years), was chosen from the collections for purposes of comparison (Fig. 1). Figure 1 is a comparative photograph of the pubic bones from the Coqueiros, Antoniao, and recent female skeletons. The Antoniao individual is in a poor enough state of preservation that visualizing morphology beyond the width of the ventral surface and a hint of the subpubic angle is challenging. In the recent burial (see above), even though the ventral ramus is poorly reconstructed, form is clearly evident, and the width of the ventral surface of the element (with the attendant ventral arc) and subpubic angle are all clearly visible. These stand in stark

Morphometry of iliac anchorage for transiliac screws: a cadaver and CT study of the Eastern population

To describe the morphometry of iliac columns for transiliac screw and to testify the conformity among the anatomic measurement, two-dimensional (2D) and three-dimensional (3D) computed tomography. We evaluated the length, inner width, and angle of three screw trajectories starting at the iliac tubercle, posterior superior iliac spine, and posterior inferior iliac spine toward the anterior inferior iliac spine. Measurements were made on specimen, two- and 3D computed tomography using 18 embalmed cadaveric pelves. There was no significant difference among three measure methods. The path between the posterior superior iliac spine and anterior inferior iliac spine had the largest iliac column length, with 135 mm in male and 110 mm in female. The canal allowed placement of 8-mm screw in male and 6.5 mm in female with the angle of 25 degrees laterally directed from the midsagittal plane. The line between the posterior inferior iliac spine and anterior inferior iliac spine was below or just located at the top of greater sciatic notch in the majority measurements. The safe section for transiliac screw approximately located above the greater sciatic notch and could be divided into anterior and posterior parts. The measurements among anatomic measurement, 2D and 3D computed tomography are consistent. The screw path from the posterior superior iliac spine toward anterior inferior iliac spine provided the longest anchor site. At the same time, the line between the posterior inferior iliac spine and anterior inferior iliac spine is not available for transiliac screw insertion of eastern population. The posterior of the safe section also can be regarded as another ilium anchorage area for transiliac screws.

Effect of Iliac Screw Insertion Depth on the Stability and Strength of Lumbo-Iliac Fixation Constructs

Comparison of feasibility and safety of the placement of short and long iliac screws by anatomic and biomechanical evaluations as they apply to lumbo-iliac fixation construct. To compare the stability of the short and long iliac screw fixations for lumbo-iliac reconstruction by anatomic and biomechanical evaluations. Spinopelvic reconstruction remains a challenge to spine surgeons. Despite the advent of many fixation methods, the use of iliac screws seems most favorable so far. Various lengths of iliac screws are applied in surgical treatments; however, no biomechanical comparison has been reported based on the screw length. For anatomic observation, CT scan data of 60 Chinese adults were used to measure the details of the iliac spine structures. For biomechanical evaluation, 7 adult human cadavers (L3-pelvis) were observed. L4-S1 pedicle screw fixation was performed with posterior spinal fixation system. On the basis of the lengths of iliac screws, 2 groups were tested (short screw group using 70 mm screws and long screw group using 138 mm screws). In this study, short and long iliac screws were placed in the same specimen. Biomechanical testing was performed on a material testing machine under 800 N compression and 7 Nm torsion loading modes for stiffness evaluations. Finally, pullout testing was performed for all the iliac screws to measure the maximum pullout force. The length of the line between posterior superior iliac spine and anterior inferior iliac spine was 140.6 +/- 1.1 mm, and the distance between this line and the greater sciatic notch was 18.3 +/- 0.8 mm. The length of the line between posterior superior iliac spine and the second narrowest point was 67.1 +/- 0.62 mm in men and 70.1 +/- 1.4 mm in women. Insertion lengths of the short and long iliac screws were 70 +/- 2 mm and 138 +/- 4 mm, respectively. The lumbo-pelvic reconstruction using short and long iliac screws restored 53.3% +/- 13.6% and 57.6% +/- 16.2% of the initial stiffness in compression testing respectively. In torsion testing, the use of short and long iliac screws harvested 55.1% +/- 11.9% and 62.5% +/- 9.2% of the initial stiffness, respectively. No significant difference was detected between the 2 reconstructions in terms of compressive and torsional stiffness (P > 0.05). However, the maximum pullout strength of long iliac screw group was significantly higher than the short screw group (P < 0.05). The local stability is rather difficult to be restored to the original levels regardless the length of iliac screws. Obviously, long iliac screws resisted significantly greater axial pullout force. However, under physiologic, torsional, and compressive loading conditions, the mechanical stability of lumbo-pelvic fixation construct with short iliac screws was comparable with that of the long ones. Therefore, the use of short iliac screws, which are only about half the length of the long iliac screws, could reduce the implantation risk without significantly compromising on the stability of the construct.

The course of the inferior gluteal nerve and surgical landmarks for its localization during posterior approaches to hip

The position of the inferior gluteal nerve (IGN) makes it vulnerable to iatrogenic injury during posterior and posterolateral approaches to the hip. Although the posterior approach has been reported to be the most frequently used technique, it is most likely to be associated with damage to the IGN. As there is scant information in the literature regarding the course and the anatomic relationships of the IGN, we aimed to investigate the anatomic course of the IGN and define the anatomical landmarks that can be used by surgeons during posterior approaches to the hip. Thirty-six gluteal regions from adult fixed cadavers were used for this study. A triangular-shaped anatomic area that contains the IGN was defined. This geometric area was formed by connecting the following points: posterior inferior iliac spine (PIIS) (apex), ischial tuberosity (IT) and greater trochanter (GT). This triangle can further be divided into two, the upper triangle being the "danger zone" since it contains the IGN and its branches. The closest mean distance between the point of IGN origin and the PIIS, IT and the GT was 3.2, 4.8 and 5.4 cm, respectively. In all specimens, the nerve entered the deep surface of the gluteus maximus approximately 5.4 cm from the apex of the GT and approached the GT as close as 0.8 cm, on average. Based on our study, dividing the gluteus maximus with standard techniques may damage the IGN. Posterior minimally invasive approaches to the hip should take into account the point of entry of the IGN into the gluteus maximus. Localization of the IGN by using the anatomic triangle defined in this study may decrease surgical morbidity.

Anatomic considerations and the relationship between the piriformis muscle and the sciatic nerve

STATING BACKGROUND: The piriformis syndrome is one of the non-discogenics causes of sciatica. It results from the compression of the sciatic nerve (SN) by the piriformis muscle (PM) in the neutral and piriformis stretch test position. The evidence of the increase in pain in the test position requires a detailed anatomical study addressing the changes that occurred in the SN and PM anatomy during the test position. The aim of this study is to examine this relationship morphometrically. A total of 20 right and left lower limbs of ten adult cadavers were examined. The SN and the PM were made visible. The location of the SN was evaluated with respect to the consistent bony landmarks, including the greater and the lesser trochanter of the femur, the ischial tuberosity, the ischial spine of the hip bone, the posterior inferior iliac spine of the hip bone and the posterior superior iliac spine of the hip bone. The study was done in both neutral and test positions (i.e., 30 degrees adduction 60 degrees flexion and approximately 10 degrees medial rotation position of the hip joint). The width of the greater sciatic notch was 63.09 +/- 13.59 mm. The length of the lower edge of the PM was 95.49 +/- 6.21 mm, and whereas the diameter of the SN where it emerged from the infrapiriforme was 17.00 +/- 3.70 mm, the diameter decreased to 11.03 +/- 2.52 mm at the level of the lesser trochanter of the femur. The SN intersected the PM most commonly in its medial second quarter anatomically. The vertical distance between the medial edge of the SN-PM intersection point and the ischial tuberosity was 85.62 +/- 17.23 and 72.28 +/- 7.56 mm (P < 0.05); the angle between the SN and the transverse plane was 66.36 degrees +/- 6.68 degrees and 71.90 +/- 8.48 degrees (P < 0.05); and the vertical distance between the medial edge of the SN and the apex of the ischial spine of the hip bone was 17.33 +/- 4.89 and 15.84 +/- 4.63 mm (P > 0.05), before and after the test position, respectively. This study provides helpful information regarding the course and the location of the SN. The presented morphometric data also revealed that after stretch test position, the infrapiriforme foramen becomes narrower; the SN becomes closer to the ischial spine of the hip bone, and the angle between the SN and the transverse plane increases. This study confirmed that the SN is prone to be trapped in the test position, and diagnosis of this situation requires dynamic MR and MR neurography study.

Curvature of the greater sciatic notch in sexing the human pelvis

The maximum curvature of the greater sciatic notch and two standardized indices were calculated for use in the sexing of human hip bones. This was done by means of quadratic regression of the contour points of the greater sciatic notch. The new variables are not directly affected by the osteometric landmarks (e.g. ischial spine, tubercle of the piriformis, and posterior inferior iliac spine) which determine the greatest width of the notch. These landmarks are, however, known to be ill-defined on occasion, but nevertheless have been used to derive the conventional depth-to-width index and angles of the sciatic notch. The curvature parameter and its new indices were applied to the sciatic notch of 164 Japanese hip bones of known sex (104 males and 61 females). The accuracy of the new variables in the determination of sex was assessed and compared with that of the conventional indices and angles of the sciatic notch. The best discriminating variable was found to be the posterior angle with an accuracy of 91%. The new parameters of the present study that represent localized shape of the sharply curved edge of the notch diagnosed sex with an accuracy of 88%. In paleoanthropological or forensic cases, using the maximum curvature of the sciatic notch and its indices may be applicable to sexing the hip bones of specimens with postmortem damage.

Intrapelvic pin migration after periacetabular reconstruction and arthroplasty of the hip in metastatic pelvic disease—a case report

In January 1997, a 62-year-old man was diagnosed with a hypernephroma of the right kidney and bilat-eral pulmonary metastases. He underwent a right nephrectomy as initial surgery. Histology showed a 16-mm granular cell renal carcinoma of the lower part of the right kidney. He received chemotherapy with α-interferon for the following 11 months. In November 1999, CT showed a 4-cm osteolytic lesion from the right posterior inferior iliac spine to the roof of the acetabulum. The medial and lat-eral bony borders were partially destroyed and the lesion was therefore classified as class III accord-ing to Harrington (1981).The patient underwent local radiation therapy in December 1999, and a second course of chemo-therapy with vinblastine. Immune modulation ther-apy with α-interferon showed a partial remission of the pulmonary metastases. In addition, he received intravenous treatment with bisphosphonates. In February 2000, the patient sustained a patho-logical fracture of the right iliac wing with medial and cranial dislocation of the entire acetabulum.A second course of radiation therapy was given in August 2000. In April 2001, the patient presented with an advanced right periacetabular fracture (Figure 1). A periacetabular reconstruction and a total hip arthroplasty was performed. A reinforcement cage (Burch-Schneider, Protek, Switzerland) was com-bined with a cemented standard stem with a 28-mm metal ball head and cemented polyethylene inlay. After reduction of the fracture, structural continu-ity was achieved and reinforced with 3 Steinmann pins using the compound osteosynthesis tech-nique, i.e. the pins were entirely covered with bone cement, which filled the gap. 1 pin was inserted from the superior iliac crest to the cranial part of the acetabulum, and 2 pins through the center of the acetabulum. One of these pins was unthreaded (Figure 2). The pins were cut off flush with the iliac crest.The patient quickly regained pain-free walking using 2 crutches. At routine follow-up (6 months), he was satisfied with the functional result (Figure 3).In November 2001, the patient suffered an epi-sode of transient hematuria and was treated under the suspicion of urinary tract infection. An abdomi-nal sonography showed mild hepatic steatosis but no other abnormalities. 9 months after surgery, a routine pelvic radiograph (Figure 4) showed migration of one of the Steinmann pins. A CT scan was performed, which showed the dislocation of the pin into the pelvic cavity very close to the blad-der, the anterior side of the rectum and the prostate (Figure 5). There was no sign of any penetration of the neighbouring organs. The dislocated pin was removed under general anesthesia by a modified ilio-inguinal approach without difficulty. The his-tological findings showed no signs of local tumor

Effects of Salter innominate osteotomy on the sacroiliac joint in patients with developmental hip dysplasia.

The pressure effects of Salter innominate osteotomy (SIO), a surgical treatment for developmental hip dysplasia (DHD), on the sacroiliac joint were investigated in a retrospective study. Pre- and post-operative direct anteroposterior pelvic radiographs of 60 cases with unilateral DHD treated by SIO were examined. The mean age at surgery was 27.7 months (range 18-48 months). The distance from the posterior inferior iliac spine to the midline (from the middle of the first sacral vertebra to the symphysis pubis) was measured. No difference was found between pre- and post-operative distances on the normal, non-operated side. On the operated side, no change was observed in 10 cases (16.7%), but the distance increased by 2 mm or 3 mm in 50 cases (83.3%) post-operatively. This increase was statistically significant, but not related to age at surgery. These findings indicate that SIO creates pressure on the inferior part of the sacroiliac joint, resulting in some displacement. Such irreversible changes may eventually lead to joint degeneration and pain.

Anatomic and Radiographic Considerations for Placement of Transiliac Screws in Lumbopelvic Fixations

Lumbopelvic fixation in spinal and pelvic surgery relies on rods or screws as an iliac anchor. Secure placement of screws with maximum diameter and length for the greatest pullout strength requires knowledge of the iliac structure and of intraoperative fluoroscopic landmarks for secure placement. Therefore, the authors evaluated the intrailiac length, inner width, and cortical thickness of three different transiliac screw anchor paths aimed toward the anterior inferior iliac spine and initiated at the iliac tubercle, posterior superior iliac spine, or posterior inferior iliac spine. Measurements were made using two- and three-dimensional computed tomographic reformations in 40 consecutive trauma patients (27 measurements in 21 males, 16 to 75 years old; 28 measurements in 19 females, 16 to 78 years old). In addition, fresh and dry human cadaveric specimens were marked with metal wires at the previously determined optimal screw path to determine fluoroscopic landmarks for easiest and best controlled transiliac screw placement. The posterior superior iliac spine-anterior inferior iliac spine path had the largest bony canal lengths, with 141 mm in male and 129 mm in female patients. Two stereotypic iliac constrictions allowed placement of 8-mm implants in male and 6- to 7-mm implants in female patients. Cortical thickness at that optimal extraarticular path was 5.2 mm in the male and 4.7 mm in the female patients. Transiliac screws can be placed during operation under fluoroscopic control using standard lateral and obturator oblique-outlet views, the latter presenting a stereotypical teardrop figure above the acetabulum.

The projection of the lateral sacral mass on the outer table of the posterior ilium.

This study was designed to construct the projection of the lateral sacral mass on the posterior ilium using cadaveric pelves and to measure the dimensions of the projection. The present study was undertaken to determine quantitatively the location of the lateral sacral mass on the outer table of the ilium. Anatomic studies relative to instrumentation of the posterior iliosacral region are few. No previous anatomic studies with regard to the projection of the lateral sacral mass have been reported. Twelve cadaveric pelves were used for this study. To determine the projection of the lateral sacral mass on the outer table of the posterior ilium, several Kirschner wires were drilled along the outermost peripheral edge of the lateral sacral mass from the inner table of the ilium through the outer table. A triangle projection on the outer table of the posterior ilium was then constructed according to the placed Kirschner wires. The widths and height of the projection, and the distances from the axis of the projection to posterior superior iliac spine and posterior inferior iliac spine were measured bilaterally. The average height of the projection of the lateral sacral mass was 61.4 mm. The average base width of the projection was 56.8 mm. The average distances from posterior superior iliac spine and posterior interior iliac spine to the longitudinal axis of the projection of the lateral mass were 30 mm and 27.4 mm, respectively. This study reported the average location of the lateral sacral mass on the outer table of the ilium. The superior area of the projection may be an ideal zone for transiliosacral screw placement.

The location of the sacroiliac joint on the outer table of the posterior ilium.

Ten cadaveric sacroiliac joints were cleaned of soft tissue and analyzed to determine the average location of the sacroiliac joint on the outer table of the posterior ilium. The superior and inferior limbs of the joint were characterized according to length and width. The longitudinal axis for each limb was determined and located on the outer table of the posterior ilium. The location of the sacroiliac joint was then characterized with respect to established anatomic landmarks. The average lengths of the superior and inferior limbs were 4.4 and 5.6 cm, respectively. The width of each limb averaged 2.0 cm. The average distance from the longitudinal axis of the superior limb to the posterior superior iliac spine was 5.5 cm. The average longitudinal axis of the inferior limb was 1.2 cm superior to the inferior margin of the posterior inferior iliac spine. The angle between the two axes averaged 93 degrees.