Acetabular anatomy and the relationship with pelvic vascular structures. Implications in hip surgery

Determination of a Safe Zone for Ischial Screw Placement in Total Hip Arthroplasty

BACKGROUND

Implantation of acetabular components with supplemental screw fixation is commonly performed to improve osteointegration and long-term stability in total hip arthroplasty (THA). Placement of ischial screws improves stability in biomechanical studies, but can be technically challenging. The study aimed to provide a safe zone for ischial screw placement with reference to easily identifiable intra-operative landmarks.

METHODS

A retrospective review of patients was performed and 27 preoperative pelvis computed tomography scans were collected. After converting these images to 3-dimensional reconstructions of the pelvis, a safe zone for ischial screw placement was established with reference to the anterior superior iliac spine (ASIS) and the acetabular center and rim.

RESULTS

The safe zone of an ischial screw in the en face sagittal plane was a median of 17 degrees (interquartile range [IQR]: 11,23) anterior to 13 degrees (IQR: 10,18) posterior to the reference line from the ASIS through the center of the acetabulum. The safe zone in the coronal plane was 34 degrees (IQR: 18,68) medial to 13 degrees (IQR: 8,19) lateral from a start point 1 centimeter medial to the inferior acetabular rim with a screw length of 25 millimeters. An ischial screw optimized for length directed down the center of the ischium was qualitatively demonstrated to have a start point unobtainable intraoperatively, originating within the cotyloid fossa.

CONCLUSION

The ASIS, center of the acetabulum, and acetabular rim provide identifiable intraoperative landmarks for guiding ischial screw placement in hip arthroplasty.

Vascular Injuries During Hip and Knee Replacement

Vascular injuries associated with hip and knee arthroplasty are rare but can result in devastating outcomes for the patient. A sound knowledge of vascular anatomy, potential mechanisms of injury, and diagnosis and management of vascular injuries are vital to an arthroplasty surgeon. Identifying high-risk patients and procedures allows careful preoperative planning, which combined with meticulous intraoperative technique, may help avoid vascular complications. When vascular injuries do occur, early recognition and intervention are critical to an improved outcome.

Intraoperative Radiographic Detection of Intrapelvic Acetabular Screw Penetration: Lessons Learned From Our Trauma Colleagues

BACKGROUND

Intraoperative vascular injury during total hip arthroplasty represents a catastrophic complication. Acetabular screw placement represents one possible mode of injury. The purpose of this study was to evaluate the utility of various fluoroscopic views in the detection of intrapelvic screw penetration.

METHODS

A radiopaque pelvis Sawbones model was instrumented with a hemispherical acetabular component. Four intrapelvic quadrants were defined. Screws were placed, 3 in each quadrant, and imaged sequentially at 3 depths: 0 mm, 5 mm, and 10 mm penetrated. Eight fluoroscopic images were used: anteroposterior, inlet, outlet, iliac oblique, obturator oblique, "down the wing," obturator outlet, and a "quad" view. Three blinded, independent surgeons evaluated the images for intrapelvic screw penetration. Images were analyzed in isolation and as a "triple-shot series" consisting of the "quad," obturator outlet, and iliac oblique views. Sensitivity and specificity values were then calculated.

RESULTS

In isolation, the "quad" view had the highest sensitivity for screw penetration (62%). The triple-shot series was found to be 100% sensitive in all 4 quadrants for detecting 10 mm of screw penetration. The specificity of the series was found to be 100% in all quadrants except for the posterior superior quadrant where it was 67%. Interobserver agreement approached perfection (Kappa ≥0.947) between all surgeons (P < .001) when using the 3-view series.

CONCLUSIONS

This study is the first to assess the use of fluoroscopy in the detection of intrapelvic penetration of transacetabular screws. We found that a 3-radiograph series provided a sensitive and specific metric for the detection of intrapelvic screw penetration.

Anthropometric Measurement About the Safe Zone for Transacetabular Screw Placement in Total Hip Arthroplasty in Asian Middle-Aged Women: In Vivo Three-Dimensional Model Analysis

BACKGROUND

Although the pelvic vascular injury caused by a transacetabular screw is rare, it is a major local complication of total hip arthroplasty. We aimed to obtain anthropometric data about the safe zone for the placement of transacetabular screws by analyzing the three-dimensional (3D) reconstruction model and determine the safe length of transacetabular screws by performing the 3D simulated surgery.

METHODS

We reviewed 50 hips of 25 patients who underwent lower extremity angiographic computed tomography scans retrospectively. We reconstructed the 3D models of 50 hips with normal pelvic bone and vascular status using the customized computer software. We measured the central angle and safe depth of the safe zone of the transacetabular screws on the 3D models. We also performed the 3D simulated surgery to confirm the safe length of screws in each hole of the customized cup implant.

RESULTS

The measured central angle of the posterior-superior area was 79.5°. And we determined a mean safe depth of 49.8 mm in the safe zone, with a central angle of 47.7°. During the 3D simulated surgery, we determined a mean safe length of the transacetabular screw of 43.3 mm when applied to a lateral hole on a line bisecting the posterior-superior area.

CONCLUSION

Although our study was limited by the use of a virtual computer program, the quantitative measurements obtained can help reduce the incidence of pelvic vascular injury during transacetabular screw fixation in total hip arthroplasty.

Revision Hip Arthroplasty in Patient with Acetabulum Migration into Subperitoneal Space-A Case Report

Revision hip arthroplasty procedures have been extensively discussed in the literature. At the same time, discussions of the management of acetabular component protrusion into the pelvic cavity, and, more specifically, the subperitoneal space, necessitating an additional abdominal approach for the revision arthroplasty, have only been published as case reports and descriptions of transperitoneal approaches have been even rarer. This paper presents the case of a 63-year-old female patient in whom a peritoneal approach was necessary to access a migrated acetabular component. The outcome of the treatment, which represented a complex orthopedic and general surgical problem, was good. We believe that the complexity of revision hip arthroplasty in patients with protrusion of the acetabular component together with the head and proximal part of the stem of the implant into subperitoneal space calls for a careful re-analysis of the category of Type III bony acetabulum defects according to Paprosky, where the recognition of two subtypes would facilitate analysis of such cases.

Acute Surgical Management of Vascular Injuries in Hip and Knee Arthroplasties

With an increasing number of total hip and knee arthroplasties being done at surgical centers and vascular surgeons often not immediately available in this setting, it is critical for orthopaedic surgeons to be comfortable with the acute surgical management of vascular injuries. Although they are fortunately uncommon in primary total hip and knee arthroplasties, damage to a major artery or vein can have potentially devastating consequences. Surgeons operating both in a hospital and an ambulatory surgical setting should be familiar with techniques to gain proximal control of massive bleeding because the principles can be helpful in primary and revision arthroplasties. In this study, we review the vascular anatomy around the hip and knee and the surgical management of these potentially catastrophic complications.

Long-term total hip arthroplasty rates in patients with acetabular and pelvic fractures after surgery: A population-based cohort study

BACKGROUND/OBJECTIVE

Osteoarthritis typically develops after surgery for traumatic fractures of the acetabulum and may result in total hip arthroplasty (THA). We conducted a population-based retrospective study to investigate the incidence of THA after treatment of acetabular, pelvic, and combined acetabular and pelvic fractures with open reduction-internal fixation surgery compared with that in the control group.

DESIGN

A retrospective population-based cohort study.

SETTING

Data were gathered from the Taiwan National Health Insurance Research Database.

PARTICIPANTS

We enrolled 3041 patients with acetabular fractures, 5618 with pelvic fractures, and 733 with combined pelvic and acetabular fractures between January 1, 1997, and December 31, 2013, totaling 9392 individuals. The control group comprised 664,349 individuals. Study participants were followed up for the occurrence of THA until death or the end of the study period.

RESULTS

The THA rates after surgical intervention were 17.82%, 7.28%, and 18.01% in patients with acetabular, pelvic, and combined acetabular and pelvic fractures, respectively. Moreover, they were significantly higher for the acetabular fracture, pelvic fracture, and combined-fracture groups (adjusted hazard ratios [aHRs] = 58.42, 21.68, and 62.04, respectively) than for the control group (p < 0.0001) and significantly higher for the acetabular fracture and combined-fracture groups than for the pelvic fracture group (aHRs = 2.59 and 2.68, respectively; p < 0.0001).

CONCLUSION

The incidence rates of THA after surgical intervention in the pelvic fracture, acetabular fracture, and combined-fracture groups were significantly higher than that of the control group.

Intra-abdominal and intra-pelvic complications following operations around the hip: causes and management-a review of the literature

Although successful and well-established procedures, hip operations whether elective or trauma are coupled with a variety of complications. Among the most uncommon complications are injuries to intra-abdominal or intra-pelvic organs which could prove potentially life-threatening. While there are various reports of such injuries in the literature, we aimed to perform a systematic review in order to examine the causes and relationships between intra-abdominal and intra-pelvic complications and the mechanism of injury, the pattern of presentation, identification, the course of management and outcomes. We identified 69 reports describing a total of 84 complications in intra-pelvic and intra-abdominal contents in 75 patients. These involved six major categories, including the intestinal tract, the urinary tract, the genital tract, the vascular system, the viscera and peripheral nerves. The most commonly injured system was the urinary (33.33%), followed by the vascular (29.76%) and the intestinal (22.62%). Among these systems, the most prevalent complications involved injury to the urinary bladder (32.14%), the large intestine (68.42%) and the external iliac artery (44%). The majority of recorded complications were postoperative with 71 incidents in 63 cases (84.52%). In intra-operative complications the most prevalent injury was due to hardware penetration (53.85%), while in postoperative it was due to hardware migration (92.06%). The management of injuries varied widely, with the most common approach being open exploration and direct repair (77.33%). The reported management outcomes included death (8%) and Girdlestone resection (2.67%), while the majority of the patients healed uneventfully (82.67%) owing mostly to immediate intervention. Despite being rare, such complications may still occur in a variety of settings and may subsequently lead to potential life-threatening situations. Thus, in order to avoid catastrophic outcomes we emphasize the need for prompt identification, immediate intervention and a multidisciplinary approach when necessary.

Surgical anatomy of the pelvic vasculature, with particular reference to acetabular screw fixation in cementless total hip arthroplasty in Asian population

PURPOSE

Pelvic vascular injury is a serious complication associated with acetabular component setting with screw fixation in cementless total hip arthroplasty (THA). In this study, we investigated the safety zone for acetabular component setting with screw fixation in cementless THA as a means to prevent pelvic vascular injury.

METHODS

Thirty left hip joints of Japanese cadavers (11 males and 19 females) were analyzed. We used a hemispherical measuring cup with 52 guide holes designed to allow vertical insertion of a Kirschner wire. After the measuring cup was placed on the acetabulum, the Kirschner wire was inserted from each guide hole to examine the anatomical relationship between the acetabulum and the pelvic vessels. We calculated the frequency of pelvic vessel punctures and measured the distance from the acetabular surface to the pelvic vessels at each guide hole.

RESULTS

Our findings revealed that pelvic vessels do not exist in certain parts of the posterior area of the acetabulum. Furthermore, in this area, intrapelvic vessels are either lacking or located at a distance ≥31 mm from the surface of the acetabulum.

CONCLUSION

The posterior area of the acetabulum, excluding its central portion, appeared to be the safety zone for acetabular screw fixation in Japanese cadavers.

How to avoid injuries of the superior gluteal nerve

BACKGROUND

Injuries to the superior gluteal nerve are a common complication in hip replacement surgery. They can be avoided with a good anatomical knowledge of the course of the superior gluteal nerve.

METHODS

We dissected 29 half pelvises of adult cadavers. The distance and the angle from the entry points of branches of the superior gluteal nerve into the deep surface of the gluteus medium and minimus muscles to the midpoint of the superior border of the greater trochanter were measured.

RESULTS

The dissections revealed that the nerve divided into 2 branches (86.20%) or 3 branches (13.8%). The more caudal branch was responsible for innervation of the tensor fascia latae.

CONCLUSIONS

A 2-3-cm safe area above the greater trochanter is appropriate to prevent nerve damage.

Location of intrapelvic vessels around the acetabulum assessed by three-dimensional computed tomographic angiography: prevention of vascular-related complications in total hip arthroplasty

BACKGROUND

During total hip arthroplasty (THA), the external iliac, femoral, and obturator vessels are at risk of vascular injury when penetrating the inner cortex of the pelvis. The purpose of this study was to clarify the location of these vessels using three-dimensional computed tomographic angiography (3DCT-A).

METHODS

We enrolled 100 subjects (200 hips) without hip disease and performed examinations on the following. (1) External iliac-femoral vessels: we measured the shortest distance from these vessels to the pelvis on axial CT images and investigated the factors affecting distance. The anatomical course of the iliac artery was classified as straight, curved, or tortuous, and the correlation between course and age was established. (2) Obturator vessels: we measured the shortest distance from the obturator vessels to the quadrilateral surface on axial CT images. (3) Visualization of pelvic vessels was through the pelvis by dual-phase 3DCT-A.

RESULTS

(1) The external iliac vein was located significantly closer to the pelvis than the artery, especially on the left side and in aged and female subjects. The single-curved and tortuous double-curved vessel types were found in aged subjects, and external iliac vessels of these types were closer to the pelvis than vessels of the straight type. In 36 subjects, the external iliac veins lay directly on the osseous surface of the pelvis (right 16, left 36). Of these 36 subjects, only one had straight-type vessels. (2) Obturator vessels were located just behind the acetabulum near the obturator foramen. (3) Reconstructed 3DCT images enabled us to visualize the pelvic vessels and demonstrated the danger area for penetrating the inner cortex of the pelvis.

CONCLUSION

Understanding the anatomical orientation of the pelvic vessels around the acetabulum using 3DCT-A could be helpful for preventing vascular injury during THA.

Total hip arthroplasty revision in case of intra-pelvic cup migration: designing a surgical strategy

Intrapelvic acetabular cup migration is a rare but serious complication, which can occur after cup loosening following total hip arthroplasty. To make safe intrapelvic implant removal, several principles must be respected: identification of potential risks with a thorough preoperative workup, preoperative planing of a surgical strategy for removing protruding hardware without injuring noble anatomical structures, preserving muscle and bone stock, pelvic anatomy reconstruction (including, as needed, osteosynthesis of the pelvis), and prosthetic components selection correcting any length discrepancy. Preoperative assessment is based on a complete radiological workup, angio-CT, as well as studies searching for signs of inflammation (blood workup and joint aspiration). All cases of intrapelvic migration of an acetabular component do not systematically command a subperitoneal approach. The presence of some residual bone shell, an intrapelvic foreign body, or a path deviation from normal in a vascular bundle or an ureter must be analyzed before deciding on the approach. The potential problems managing this mode of loosening event are a reminder for the need of periodical total hip arthroplasty follow-up. This regular monitoring helps preventing complications sometimes life threatening.

Anatomical considerations of the internal iliac artery in association with the ilioinguinal approach for anterior acetabular fracture fixation

INTRODUCTION

Vascular injury may be encountered during an anterior approach to the pelvis or acetabulum-be it due to hematoma decompression, clot dislodgement during fracture manipulation, or iatrogenic. This can be associated with significant bleeding, hemodynamic instability, and subsequent morbidity. If the exact source of bleeding cannot be easily identified, compression of the internal iliac artery may be a lifesaving procedure.

MATERIALS AND METHODS

We describe an extension of the lateral window of the ilioinguinal (or Olerud) approach elaborated on cadavers.

RESULTS

The approach allows emergent access the internal iliac artery and intraoperative cross-clamping of the internal iliac vessels to control bleeding.

CONCLUSION

The approach allows rapid access to the internal iliac artery. The surgeon should be familiar, however, with the surgical anatomy of this region to avoid potential injury to the ureter, peritoneum, lymphatics, and sympathetic nerves overlying the vessels when using the approach described.

Safe zone for transacetabular screw fixation in prosthetic acetabular reconstruction of high developmental dysplasia of the hip

BACKGROUND

Prosthetic reconstruction of hips with Crowe type-IV developmental dysplasia (a high complete dislocation) is technically demanding. Insufficient osseous coverage and osteopenic bone stock frequently necessitate transacetabular screw fixation to augment primary stability of the metal acetabular shell. We sought to determine whether a previously reported quadrant system for screw fixation of the acetabular cup can be applied in patients with high dislocation of the hip and to define a specialized safe zone for screw fixation in these hips, if needed.

METHODS

Using volumetric computed tomographic data and image-processing software, we made three-dimensional reconstructions of the osseous and vascular structures in eighteen hips in twelve patients. We virtually reconstructed a cup in the true acetabulum and dynamically simulated transacetabular screw fixation. We mapped the hemispheric cup into several areas and, for each, measured the distance between the virtual screw and the external iliac (femoral) and obturator blood vessels. In the six patients with unilateral high dislocation of the hip and a relatively normal, contralateral hip, the six relatively normal hips served as controls.

RESULTS

Reconstruction of the cup at the level of the true acetabulum shifted the center of rotation anteroinferiorly in the hips with a high, complete dislocation. Screws guided by the quadrant system frequently injured the obturator blood vessels in the hips with a high dislocation. In these patients, the safe zone shifted as a result of moving the prosthetic cup.

CONCLUSIONS

The quadrant system, although helpful in determining screw placement in hips with a normal center of rotation, can be misleading and of less value in guiding screw insertion to augment acetabular shells for hips with a high dislocation. We believe that a safe zone specific to hips with a high dislocation should be used to guide transacetabular screw fixation.

Operative treatment of transverse acetabular fractures: is it really necessary to fix both columns?

OBJECTIVE

we prospectively evaluated clinical and radiographic outcomes in patients with displaced combined transverse-posterior wall acetabular fractures managed at our Institution over a period of seven years by posterolateral single approach, direct posterior wall and posterior column reduction and plating, and indirect reduction of anterior column controlled by fluoroscopic images with or without lag-screw fixation. The aim was to identify if the obtained immediate postoperative Matta radiographic roof-arc angles after fracture reduction and fixation alters in the postoperative period when comparing posterior plating alone versus posterior plate and anterior column lag-screw fixation.

PATIENTS AND METHODS

35 skeletally mature patients (31 male and four female, with mean age of 39.9 years old [range, 23.3 to 66.7 y/o]) with combined transverse-posterior wall acetabular fractures surgically treated by a posterolateral single approach were enrolled in this prospective investigation. Nineteen patients had associated orthopaedic injuries. The first part of the acetabular fracture management was similar to all patients and consisted in anatomical reduction and fixation of the transverse posterior component followed by anatomical reduction and fixation of the posterior wall component. The transverse anterior component reduction was controlled by fluoroscopic images (anteroposterior (AP), iliac oblique, and obturator oblique views) and digital palpation through the greater sciatic notch. Fifteen of the 35 patients had an additional lag-screw fixation from the posterior to the anterior columns with an extra-long small-fragment cortical screw. AP and Judet oblique radiographic views were taken at the end of the procedure and roof-arc angles were measured. Clinical results were assigned according to the grading system of Merle D'Aubigne and Postel as modified by Matta et al. Radiographic roof-arc angles were checked and compared between the two groups of patients to the same data collected both at the time of the surgical procedure and at three months postoperatively. Statistical analysis was done by either using chi-square (clinical outcome) and Mann-Whitney (roentgenographic outcome) tests, with a level of significance of alpha = 5%.

RESULTS

at final follow-up examination 18 to 84 months postoperatively (mean, 46.8 months), the clinical results were considered satisfactory in 31 (88.6%) patients (excellent in nine (25.7%) and good in 22 (62.9%) patients). There was no difference between patients with (n = 15) and without (n = 20) fixation of the transverse anterior component of the acetabular fracture (p = 0.67). Radiographic roof-arc angles measured at discharge, at three months postoperatively and at the last follow-up consultation didn't changed significantly (p > 0.05). There was no statistically significant difference between patients treated with (n = 15) and without (n = 20) fixation of the anterior component of the transverse acetabular fracture in terms of medial displacement of the femoral head.

CONCLUSION

the authors suggest that associated transverse-posterior wall acetabular fractures can be managed by a single posterior approach. Direct reduction and fixation of the posterior wall and column components is an adequate option for these injuries. If there is adequate indirect reduction of the anterior column, as checked by digital palpation and fluoroscopy, we feel that it is not necessary to fix the anterior column component of the transverse acetabular fracture.

Morphologic features of the acetabulum

INTRODUCTION

The embryology and development of the hip joint are complex. The acetabulum is not always of the same shape, width, or depth. Minor anatomical abnormalities in the acetabular shape, joint congruences are frequent. Controversies still exist on the importance of these variations and help to prevent problems following in surgical procedures such as acetabular reconstruction and femoracetabular impingement.

MATERIAL AND METHODS

The aim of this study is to provide the location of the unusual facets, the acetabular point, and the anterior ridge of the acetabulum based on a morphological study of human pelvic bones. Morphologic features of the acetabulum, particularly determination of unusual facets, were studied in 226 human coxal bones.

RESULTS

In adult coxal bones the acetabular fossa has an irregular clover-leaf shape, the superior lobe being smaller than the anterior and the posterior lobes. Measured lunate surface area varied between 14.5 and 30.5 cm2. A smooth unusual facet was found anteroinferior to the lunate surface in 62 acetabulums. Measured along the long axis, its size varied between 11 and 17 mm. Three different shapes of the unusual facet were as follows: oval (32.26%), piriform (45.16%), and elongated (22.58%). The prevalence of the piriform facet shape was higher in males. In 59.68% of the bones it extended to the superior ramus of the pubis, and in the remaining 40.32% it was limited within the acetabular margin. It is postulated that this facet could be a consequence of a particular posture, which results in traction of the ligaments attached to this area. Four distinct configurations were identified relative to the anterior acetabular ridge. The majority 98 (43.36%) were curved; 64 (28.33%) were angular; 37 (16.37%) were irregular; and 27 (11.94%) were straight.

CONCLUSION

There have been no reports on details such as unusual facets, acetabular point, and anterior ridge of the acetabulum in a single research. These findings will be of help in planning reorientation procedures, using spikes, screws, and press-fitting for fixation.

Acetabular anatomy and transacetabular screw fixation at the high hip center

A quadrant system that defines the safe acetabular locations for screw placement exists for the anatomic hip center. We wanted to develop a similar system for the high hip center. The purposes of our study were to identify the anatomic structures at risk during placement of transacetabular screws in the high hip center, to identify maximum bone depth for screw purchase, and to determine if a high hip center quadrant system could be validated to guide placement of screws during acetabular arthroplasty. For this cadaver study of nine pelves, an acetabulum was reamed superiorly into the high hip center a distance equal to (1/2) of the native acetabular diameter. Screws exiting the acetabular bone by 15 mm were inserted before a computed tomography scan and a precise anatomic dissection were done. Structures at risk of penetration by screws include the external iliac vessels, the obturator nerve and vessels, the superior gluteal nerve and vessels, and the sciatic nerve. We found that a quadrant system at the high hip center can demarcate safe zones for screw placement. At the high hip center, only the peripheral (1/2) of the posterior quadrants are safe for screw placement.

Radiographic evaluation of screw position in revision total hip arthroplasty

Injury to intrapelvic structures during removal of screws in revision acetabular arthroplasty is an uncommon, yet potentially serious complication. Bicortical screws are at greatest risk for causing injury during removal, especially if directed toward intrapelvic vessels and nerves. Complications can be minimized with thorough evaluation of screw position before revision surgery. A study of seven cadaveric pelves was done to determine if plain radiographic views provide useful information regarding screw position. In each pelvis, bicortical transacetabular screws were fixed in all acetabular quadrants 15 mm longer than the measured depth. Afterward, anteroposterior, inlet, Judet, and cross-table lateral radiographic views were obtained and intrapelvic dissections were done. Radiographs and intrapelvic dissections were compared to determine screw position. We found that the obturator and iliac oblique (Judet) views were most useful in defining screw position. The iliac oblique view clearly revealed screws that violated the quadrilateral surface and therefore were directed toward the obturator vessels and nerve. The obturator oblique view revealed screws that violated the anterior column and therefore were directed toward the external iliac vessels. The lateral view additionally clarified such screws by determining general anterior or posterior direction.

Malformation of the acetabular fossa as a cause of intrapelvic injury in total hip arthroplasty: a report of 2 cases

We report 2 cases of bone defects of the acetabulum. The first case was a patient who underwent a total hip arthroplasty. An intraoperative bleeding occurred because of an injury of an intrapelvic artery. Preoperative radiographs did not show this bone defect. A similar abnormality of the acetabulum was found in a series of 30 pelves that were dissected for a cadaver study. In this case, the bone defect was located in the center of the right acetabulum.

Safe screw placement in acetabular revision surgery

Revision of an acetabular component with extensive bone loss is a procedure that sometimes includes allografting or the placement of an unusually sized or positioned uncemented acetabular component. We evaluated the quadrant system used to guide screw placement in primary uncemented total hip surgery in the high hip center, jumbo component, and 3 designs of reinforcement rings. We used 14 pairs of cadaver hemipelves, which were prepared by removing all soft tissues except the medial neurovascular structures. With each implant, all screw holes were tested to determine if they followed the safe quadrant recommendations. In the high hip center, the center and anterior of the superoposterior quadrant was dangerous. All of the other implants met the quadrant recommendations.

Safe removal of massive intrapelvic cement using ultrasonic instruments

The extraction of massive intrapelvic deposits of cement in revision total hip arthroplasty presents the surgeon with a philosophical dilemma and a technical challenge. The cement is difficult to remove because of the disparity between the size of the cement mass and the defect in the acetabulum. In addition, the cement mass lies close to major intrapelvic organs, and the use of force applied with sharp cement-removing instruments poses a danger to these structures. We report on the ultrasonic technique of cement removal used to extract a massive intrapelvic cement deposit safely.