Patient-Specific “Safe Zones” Reduce the Rate of Dislocation after Total Hip Arthroplasty

INTRODUCTION: Most dislocations have been shown to occur within Lewinnek’s proposed safe zone (LSZ) for cup inclination (40°±10°) and anteversion (15°±10°). Using a functional and dynamic simulation that accounts for individual patient anatomy and variations in pelvic tilt, we created a patient-specific target orientation for the acetabular cup. The purposes of this study were to: (1) compare pre-operative acetabular cup parameters using this novel dynamic imaging sequence to the LSZ, and (2) describe rates of dislocation in patients whose pre-operative acetabular cup parameters were determined using dynamic imaging sequences.METHODS: We retrospectively reviewed 1,500 consecutive, primary THAs that underwent dynamic sitting and standing pre-operative acetabular cup planning. Using these inputs, we modeled an optimal cup position for each patient. Inclination, anteversion, pelvic tilt, pelvic incidence, lumbar flexion angles, and rates of dislocation were analyzed.RESULTS: Mean age of patients was 63 years. Mean pelvic tilt was 4.7o when supine, -0.3o when standing, and -0.7o when flex-seated. Mean pelvic incidence was 54o and mean lumbar flexion was 43o. Mean inclination was 40° and mean anteversion was 24°. Only 56% of the dynamically planned cups were within the LSZ (p<0.05). Mean inclination and anteversion difference between dynamic and LSZ was 1.3o and 8.9o, respectively. Only 0.5% of dynamically planned cups dislocated post-operatively, all were within LSZ.DISCUSSION: Acetabular cup positioning in patient-specific safe zones reduces the rate of dislocation after THA. Historical target parameters for cup inclination and anteversion significantly differ to target values obtained with the use of functional imaging.

Download Full-text

Effect of pelvic tilt and rotation on cup orientation in standing anteroposterior radiographs

Hip International ◽

10.1177/1120700019831665 ◽

2019 ◽

Vol 30 (1) ◽

pp. 48-55 ◽

Cited By ~ 2

Author(s):

Ho Hyun Yun ◽

William S Murphy ◽

Daniel M Ward ◽

Guoyan Zheng ◽

Brett Hayden ◽

...

Keyword(s):

Computed Tomography ◽

Pelvic Tilt ◽

Patient Specific ◽

Pelvic Rotation ◽

3 Dimensional ◽

Radiographic Measurements ◽

Wide Variability ◽

The Difference ◽

The Right ◽

Cup Positioning

Background: Individual pelvic tilt and rotation have wide variability that can affect the measurement of cup orientation in anteroposterior (AP) radiographs. The purpose of this study was to analyse the effect of pelvic tilt and rotation on radiographic measurements of cup orientation. Methods: A total of 53 patients (63 hips) were included in this study. The patients underwent a computed tomography study with standing AP pelvis radiographs taken both preoperatively and approximately 3 months postoperatively. We used 2-dimensional/3-dimensional matching to measure the pelvic tilt and rotation, and the non-standardised and standardised cup orientation. Results: There was no difference in the pelvic tilt and rotation between the preoperative and postoperative radiographs. The distribution of the differences between the non-standardised and standardised cup anteversion exhibited a change within 5° in only 34/63 (54%) hips. The pelvic tilt correlated with the difference between the non-standardised and standardised cup anteversion, but the pelvic rotation did not. When all 63 hips were separated into the right and left sides, the pelvic rotation inversely correlated with the pelvic tilt-adjusted difference between the non-standardised and standardised cup anteversion of the right side but directly correlated with that of the left side. Conclusions: The current study demonstrated that the measurement of cup anteversion in standing AP radiographs is significantly affected by both the pelvic tilt and pelvic rotation. An improved understanding of the pelvic orientation may eventually allow for desired cup positioning on a patient-specific basis to potentially reduce complications associated with the malposition of the cup.

Download Full-text

A Multiplanar Radiography Method for Assessing Cup Orientation in Total Hip Arthroplasty

Journal of Biomechanical Engineering ◽

10.1115/1.4007664 ◽

2012 ◽

Vol 134 (10) ◽

Cited By ~ 4

Author(s):

Shahram Amiri ◽

Bassam A. Masri ◽

Donald Garbuz ◽

Carolyn Anglin ◽

David R. Wilson

Keyword(s):

Total Hip Arthroplasty ◽

Hip Arthroplasty ◽

Pelvic Tilt ◽

Patient Specific ◽

Systematic Bias ◽

Acetabular Cup ◽

Cadaveric Specimen ◽

Total Hip ◽

Correct Orientation ◽

Bony Landmarks

Correct orientation of the acetabular cup considering patient-specific functional pelvic angles is an important factor for improving outcomes and avoiding complications after total hip arthroplasty. This study introduces a new, noninvasive radiographic tool for accurately determining a patient’s specific pelvic tilt angle preoperatively, as well as accurately assessing acetabular cup orientation with respect to bony landmarks intraoperatively and postoperatively. The method was validated by imaging a bone replica model of the pelvis with implanted hip components, in comparison to digitized references, and verified with a cadaveric specimen. Pelvic tilt was measured with an accuracy of 0.1 deg and SD of 0.4 deg. Operative cup inclination and anteversion showed accuracies of 0.6 deg and 2.5 deg, with SD of 0.4 deg and 0.6 deg, respectively; these could be improved further by subtracting systematic bias. The method shows accuracy advantages over existing radiographic and fluoroscopic methods and exposes the subjects to a lower radiation dose compared to the similar computed tomography methods. These results suggest that the proposed method is feasible for assessing cup placement with reference to the functional and anatomical references. Furthermore, the ability to reference the same bony landmarks preoperatively, intraoperatively, and postoperatively has important research and clinical advantages.

Download Full-text

Relationship between pelvic morphology and functional parameters in standing position for patient-specific cup planning in THA

10.29007/41f9 ◽

2018 ◽

Cited By ~ 1

Author(s):

Maximilian Fischer ◽

Stephanie Schörner ◽

Stefan Rohde ◽

Christian Lüring ◽

Klaus Radermacher

Keyword(s):

Pelvic Tilt ◽

Planning Process ◽

Pelvic Incidence ◽

Pubic Symphysis ◽

Standing Position ◽

Patient Specific ◽

Automatic Process ◽

Sacral Slope ◽

Functional Parameters ◽

Eos Imaging

The sagittal orientation of the pelvis commonly called pelvic tilt has an effect on the orientation of the cup in total hip arthroplasty (THA). Pelvic tilt is different between individuals and changes during activities of daily living. In particular, the pelvic tilt in standing position should be considered during the planning of THA to adapt the target angles of the cup patient-specifically to minimize wear and the risk of dislocation. Methods to measure pelvic tilt require an additional step in the planning process, may be time consuming and additional devices or x-ray imaging are necessary.In this study, the relationship between three functional parameters describing the sagittal pelvic orientation in standing position and seven morphological parameters of the pelvis was investigated. Correlations might be used to estimate the pelvic tilt in standing position by the morphology of the pelvis in order to avoid additional measuring techniques of pelvic tilt in the planning process of THA. For 18 subjects a semi-automatic process was established to match a 3D-reconstruction of the pelvis from CT scans to orthogonal EOS imaging in standing position and to calculate the morphological and functional parameters of the pelvis subsequently.The two strongest correlations of the linear correlation analysis were observed between morphological pelvic incidence and functional sacral slope (r = 0.78; p = 0.0001) and between morphological pubic symphysis-posterior superior iliac spines- ratio and functional tilt of anterior pelvic plane (r = -0.59; p = 0.0098). The results of this study suggest that patient-specific adjustments to the orientation of the cup in planning of THA without additional measurement of the sagittal pelvic orientation in standing position should be based on the correlation between morphological pelvic incidence and functional sacral slope.

Download Full-text

Range of Motion to Impingement Curves Create a New Patient-Specific Impingement-Free Zone for Acetabular Cup Placement

Surgical Technology Online ◽

10.52198/21.sti.38.os1399 ◽

2021 ◽

Author(s):

Thomas McCarthy ◽

Matthew Thompson ◽

Jim Nevelos ◽

Hytham Salem ◽

Brandon Naylor ◽

...

Keyword(s):

Range Of Motion ◽

Internal Rotation ◽

Pelvic Tilt ◽

External Rotation ◽

Objective Assessment ◽

Safe Zone ◽

Patient Specific ◽

Acetabular Cup ◽

High Flexion ◽

Free Zone

Introduction: The acetabular “safe zone” has recently been questioned as a reliable reference for predicting total hip arthroplasty impingement and instability as many dislocations occur within the described parameters. Recently, an improved understanding of spino-pelvic mechanics has provided surgeons useful information to both identify those at a higher risk of dislocation and, in some cases, allows altering component positioning to accommodate the patient’s individual “functional” range of motion. The purpose of this study was to create a new patient-specific impingement-free zone by considering range of motion (ROM) to prosthetic impingement for both high flexion and extension poses, thus demarcating a zone that avoids both anterior and posterior impingement, thereby creating an objective approach to identifying a patient’s ideal functional safe zone. Materials and Methods: A validated hip ROM three-dimensional simulator was utilized to create ROM-to-impingement curves for both high flexion as well as pivot and turn poses. The user imported a computerized tomography (CT) with a supine pelvic tilt (PT) value of zero and implant models (tapered wedge stem, 132° neck angle, 15° stem version, 36mm femoral head). Femur-to-pelvis relative motions were determined for three upright seated poses (femur flexed at 90° and 40° internal rotation, with 0°, 10°, and 20° posterior PT), one chair rise pose (femur flexed at 90° and 0° internal rotation, with the pelvis flexed anteriorly until the pelvis made contact with the femur), and three standing pivot and turn poses (femur set at 5° extension, and 35° external rotation, with 5° posterior PT, 0°, and 5° anterior PT). ROM-to-impingement curves for cup inclination versus anteversion were graphed and compared against the Lewinnek safe zone. Results: The ROM-to-impingement curves provide an objective assessment of potential impingement sites as they relate to femoral rotation and pelvic tilt. The area between the stand and sit curves is the impingement-free area. A sitting erect pose with a simulated stiff spine (0° PT) yielded less impingement-free combinations of cup inclination and version than poses with greater than 0° posterior pelvic tilt. Conclusion: The results demonstrate that the acetabular target zone has a relatively small margin for error between the sitting and standing ROM curves to impingement. Importantly, anterior and posterior pelvic tilt can markedly increase the risk of impingement, potentially leading to posterior or anterior dislocations, respectively. This study highlights the importance of correctly identifying the patient-specific functional range of motion to execute optimal component positioning.

Download Full-text

Measuring Pelvic Tilt with the Use of a Navigated Smart-Devices Based Ultrasound System

10.29007/8ch6 ◽

2018 ◽

Author(s):

Tobias Martin ◽

Andreas Alk ◽

Josef Kozak

Keyword(s):

Pelvic Tilt ◽

Reference Model ◽

Symphysis Pubis ◽

Patient Specific ◽

Smart Devices ◽

Smart Device ◽

Anatomical Landmarks ◽

Acetabular Cup ◽

Correct Alignment ◽

Ultrasound System

The key for a successful total hip replacement (THR) and the longevity of the implant is the correct alignment of the acetabular cup which is to be considered as the most critical component. The alignment of the cup is defined with respect to anterior pelvic plane (APP). The APP defines the reference for the anteversion and inclination angles which sets the basis for the correct alignment of the implant. The angle of the plane is created by three distinct anatomical landmarks which are represented by two anterior superior iliac spines (ASIS) and the symphysis pubis. The angle of the APP in respect to the coronal plane defines the pelvic tilt (PT) which can be anterior or posterior. The rotation of the pelvis highly depends on the individual anatomy of the subject. This means that a neutral pelvic tilt (PT) in supine position is rarely observed and also may be dissimilar in standing position. In this paper we present a non-invasiveness and cost-effective prototype for measuring the patient-specific PT under the use of a navigated smart-device based ultrasound system for supporting surgery planning. In view of the non-invasiveness method the system can be used to measure pre- and postoperative pelvic orientation. With the use of an artificial hip reference model different cases were measured. The computed results look very promising with a standard deviation of ±1°.

Download Full-text

The impact of hip-spine relations on the results of total hip arthroplasty (literature review)

ORTHOPAEDICS TRAUMATOLOGY and PROSTHETICS ◽

10.15674/0030-59872021173-79 ◽

2021 ◽

pp. 73-79

Author(s):

Mykola Korzh ◽

Volodymyr Radchenko ◽

Volodymyr Filipenko ◽

Kostiantyn Popsuishapka ◽

Olga Pidgaiska

Keyword(s):

Total Hip Arthroplasty ◽

Literature Review ◽

Hip Arthroplasty ◽

Pelvic Tilt ◽

Pelvic Incidence ◽

Patient Specific ◽

Spinal Diseases ◽

Stable Range ◽

Total Hip ◽

The Impact

Spine balance can alter THA outcomes, but the exact mechanism is not yet well recognized. We aimed at bridging the gap between hip and spine surgeons with an up-to-date analysis of the best available literature review concerning to data as for total hip arthroplasty results of those patient with concomitant spine disorders. In total hip arthroplasty accurate acetabular cup placement is essential for impingement free and stable range of motion. For decades, hip surgeons have relied on traditional safe acetabular zones to reduce prosthetic instability. Nevertheless, hip dislocation is one of the most common complications following total hip arthroplasty. Numerous studies have shown that patients with abnormal spinopelvic mobility due to degenerative spinal diseases and after spinal fusion surgery had an increased rate of dislocations after THA. In our review we described the main spine-pelvic parameters, such as pelvic tilt, sacral slope, pelvic incidence, lumbar lordosis etc. and spino-pelvic motions and how they can change in standing and sitting postures. Measurements of these parameters are necessary for presurgical planning before hip arthroplasty especially those patients who had previously made spine fusion. A review of literature shows that sagittal pelvic kinematics, but not the pelvic incidence, influences the risk of prosthetic impingement or dislocation. Pelvic position is dynamic during gait and other daily living activities. Variations in anteroposterior pelvic tilt affects the resulting spatial orientation of the acetabulum. Recommendations for cup positioning are switching from a classic Lewinneck safe zone to a patient-specific approach, with the standing cup orientation giving way to a new parameter of interest: the functional orientation of the cup. Thus, functional cup anterversion should be taken into consideration. Abnormal spinopelvic mobility is a risk factor for THA dislocation. Thus patients with combined spine and hip pathology are at higher risk for further complications and they should be identified and screened more carefully. Key words. Spine-pelvic relations, sagittal alingement, hip arthroplasty, dislocation

Download Full-text

The Level of Conus Medullaris in 629 Healthy Japanese Individuals

Journal of Clinical Medicine ◽

10.3390/jcm10143182 ◽

2021 ◽

Vol 10 (14) ◽

pp. 3182

Author(s):

Hiroaki Nakashima ◽

Keigo Ito ◽

Yoshito Katayama ◽

Mikito Tsushima ◽

Kei Ando ◽

...

Keyword(s):

Regression Analysis ◽

Magnetic Resonance ◽

Pelvic Tilt ◽

Pelvic Incidence ◽

Multivariate Regression Analysis ◽

Conus Medullaris ◽

Magnetic Resonance Images ◽

Factors Affecting ◽

Adult Volunteers ◽

Significant Factors

The conus medullaris typically terminates at the L1 level; however, variations in its level and the factors associated with the conus medullaris level are unclear. We investigated the level of conus medullaris on magnetic resonance imaging in healthy volunteers. In total, 629 healthy adult volunteers (≥50 individuals of each sex and in each decade of age from 20 to 70) were enrolled. The level of the conus medullaris was assessed based on the T2-weighted sagittal magnetic resonance images, and factors affecting its level were investigated employing multivariate regression analysis including the participants’ background and radiographical parameters. L1 was the most common conus medullaris level. Participant height was significantly shorter in the caudally placed conus medullaris (p = 0.013). With respect to the radiographical parameters, pelvic incidence (p = 0.003), and pelvic tilt (p = 0.03) were significantly smaller in participants with a caudally placed conus medullaris. Multiple regression analysis showed that the pelvic incidence (p < 0.0001) and height (p < 0.0001) were significant factors affecting the conus medullaris level. These results indicated that the length of the spinal cord varies little among individuals and that skeletal differences affect the level of the conus medullaris.

Download Full-text

Accuracy of cup placement in total hip arthroplasty by means of a mechanical positioning device: a comprehensive cadaveric 3d analysis of 16 specimens

Hip International ◽

10.1177/1120700019874822 ◽

2019 ◽

pp. 112070001987482

Author(s):

Arthur J Kievit ◽

Johannes G G Dobbe ◽

Wouter H Mallee ◽

Leendert Blankevoort ◽

Geert J Streekstra ◽

...

Keyword(s):

3D Models ◽

Safe Zone ◽

3D Analysis ◽

Anterior Pelvic Plane ◽

Mechanical Device ◽

Acetabular Cup ◽

Anteversion Angle ◽

Positioning Device ◽

The Mean ◽

Safe Zones

Introduction: We tested whether a mechanical device (such as Hipsecure) to pinpoint the anterior pelvic plane (APP) as a guide can improve acetabular cup placement. To assess accuracy we asked: (1) is the APP an effective guide to position acetabular cup placement within acceptable ° of divergence from the optimal 40° inclination and 15° anteversion; (2) could a mechanical device increase the number of acetabular cup placements within Lewinnek’s safe zone (i.e. inclination 30° to 50°; anteversion 5° to 25°)? Methods: 16 cadaveric specimens were used to assess the 3D surgical success of using a mechanical device APP to guide acetabular cup placement along the APP. We used the Hipsecure mechanical device to implant acetabular cups at 40° inclination and 15° anteversion. Subequently, all cadaveric specimens with implants were scanned with a CT and 3D models were created of the pelvis and acetabular cups to assess the outcome in terms of Lewinnek’s safe zones. Results: The mean inclination of the 16 implants was 40.6° (95% CI, 37.7–43.4) and the mean anteversion angle was 13.4° (95% CI, 10.7–16.1). All 16 cup placements were within Lewinnek’s safe zone for inclination (between 30° and 50°) and all but 2 were within Lewinnek’s safe zone for anteversion (between 5° and 25°). Conclusion: In cadaveric specimens, the use of a mechanical device and the APP as a guide for acetabular cup placement resulted in good positioning with respect to both of Lewinnek’s safe zones.

Download Full-text

The utility of supine radiographs in the assessment of thoracic flexibility and risk of proximal junctional kyphosis

Journal of Neurosurgery Spine ◽

10.3171/2020.11.spine201565 ◽

2021 ◽

pp. 1-7

Author(s):

Francis Lovecchio ◽

Renaud Lafage ◽

Jonathan Charles Elysee ◽

Alex Huang ◽

Bryan Ang ◽

...

Keyword(s):

Thoracic Spine ◽

Lumbar Lordosis ◽

Pelvic Tilt ◽

Pelvic Incidence ◽

Vertical Axis ◽

Control Analysis ◽

Proximal Junctional Kyphosis ◽

Sagittal Vertical Axis ◽

Significant Difference ◽

Junctional Kyphosis

OBJECTIVE Supine radiographs have successfully been used for preoperative planning of lumbar deformity corrections. However, they have not been used to assess thoracic flexibility, which has recently garnered attention as a potential contributor to proximal junctional kyphosis (PJK). The purpose of this study was to compare supine to standing radiographs to assess thoracic flexibility and to determine whether thoracic flexibility is associated with PJK. METHODS A retrospective study was conducted of a single-institution database of patients with adult spinal deformity (ASD). Sagittal alignment parameters were compared between standing and supine and between pre- and postoperative radiographs. Thoracic flexibility was determined as the change between preoperative standing thoracic kyphosis (TK) and preoperative supine TK, and these changes were measured over the overall thoracic spine and the fused portion of the thoracic spine (i.e., TK fused). A case-control analysis was performed to compare thoracic flexibility between patients with PJK and those without (no PJK). The cohort was also stratified into three groups based on thoracic flexibility: kyphotic change (increased TK), lordotic change (decreased TK), and no change. The PJK rate was compared between the cohorts. RESULTS A total of 101 patients (mean 63 years old, 82.2% female, mean BMI 27.4 kg/m2) were included. Preoperative Scoliosis Research Society–Schwab ASD classification showed moderate preoperative deformity (pelvic tilt 27.7% [score ++]; pelvic incidence–lumbar lordosis mismatch 44.6% [score ++]; sagittal vertical axis 42.6% [score ++]). Postoperatively, the average offset from age-adjusted alignment goals demonstrated slight overcorrection in the study sample (−8.5° ± 15.6° pelvic incidence–lumbar lordosis mismatch, −29.2 ± 53.1 mm sagittal vertical axis, −5.4 ± 10.8 pelvic tilt, and −7.6 ± 11.7 T1 pelvic angle). TK decreased between standing and supine radiographs and increased postoperatively (TK fused: −25.3° vs −19.6° vs −29.9°; all p < 0.001). The overall rate of radiographic PJK was 23.8%. Comparisons between PJK and no PJK demonstrated that offsets from age-adjusted alignment goals were similar (p > 0.05 for all). There was a significant difference in the PJK rate when stratified by thoracic flexibility cohorts (kyphotic: 0.0% vs no change: 18.4% vs lordotic: 35.0%; p = 0.049). Logistic regression revealed thoracic flexibility (p = 0.045) as the only independent correlate of PJK. CONCLUSIONS Half of patients with ASD experienced significant changes in TK during supine positioning, a quality that may influence surgical strategy. Increased thoracic flexibility is associated with PJK, possibly secondary to fusing the patient’s spine in a flattened position intraoperatively.

Download Full-text

Erratum to: The Effect of Postural Pelvic Dynamics on the Three-dimensional Orientation of the Acetabular Cup in THA Is Patient Specific

Clinical Orthopaedics and Related Research ◽

10.1097/corr.0000000000001887 ◽

2021 ◽

Vol Publish Ahead of Print ◽

Author(s):

Thom E. Snijders ◽

Tom P. C. Schlösser ◽

Marijn van Straalen ◽

René M. Castelein ◽

Rob P. Stevenson ◽

...

Keyword(s):

Three Dimensional ◽

Patient Specific ◽

Acetabular Cup

Download Full-text