Quantification of pelvic tilt in total hip arthroplasty

Pelvic flexion measurement from lateral projection radiographs is clinically reliable

BACKGROUND

Pelvic flexion affects orientation of the acetabular cup; however, pelvic position is not static in daily activities. During THA it is difficult to know the degree of pelvic flexion with the patient in the lateral position and that position is static. However, surgeons need to appropriately determine pelvic tilt to properly insert the acetabular component.

QUESTIONS/PURPOSES

We investigated the reliability of pelvic flexion angle that was measured by manually identifying the location of the pubic symphysis and bilateral anterior superior iliac spines using synthesized lateral radiographs.

METHODS

We synthesized 49 lateral radiographs based on CT data. Each of the 49 radiographs had a unique position: 7° of varying lateral tilt and rotation in each of seven selected pelvic flexion angles. The pelvic flexion angle was measured three times by three independent observers in each position and determined the accuracy (based on the true value from the reconstructions) and reliability of the measures.

RESULTS

The measurement error was 0.1° (range, -4.8° to 4.0°). There was a tendency for errors when the pelvic flexion angle was 0° or ±5°; the errors were less when the pelvic flexion angle was ±10° or ±20°. Lateral tilt was associated with greater error than rotation. The intraclass correlation coefficient (ICC) of the average value was 0.967. For one observer, more than two measurements are necessary for the ICC to be greater than 0.8, and only one measurement was needed for two of the three observers.

CONCLUSIONS

Our data suggest measurement of pelvic flexion angle using lateral radiographs is reliable. We recommend the measurement be performed once by two observers for better reliability.

Research status and application prospects of digital technology in orthopaedics

In the last 10 years, basic and clinical research in orthopaedics has developed rapidly. Understanding of orthopaedic disorders involves not only routine diagnosis, but also the pursuit of highly efficient and accurate three-dimensional imaging of the intra- and extra-medullary distribution, form and structure of orthopaedic disorders, thus allowing scientific evaluation of the indications for surgery, drawing up of the best surgical plan, minimization of operative trauma and the earliest possible restoration of limb function. Meanwhile, the most important type of basic research, which was previously biomechanical research, has gradually become computational biomechanics based on in vitro cadaver experiments. This review aims to summarize the research status and application prospects of digital technology in orthopaedics, including virtual reality technology, reverse engineering and rapid prototyping techniques, computational biomechanics, computer navigation technology and management of digitization of medical records.

Anatomical relationships of human pelvises and their application to registration techniques

Knowledge of consistent anatomical relationships is an important criterion for establishing registration procedures for orthopedic navigation systems. Based on an analysis of 420 CT data sets, we investigated whether a robust registration of the pelvis in a lateral decubitus position could be achieved based on anatomical relationships. For this purpose, we assessed basic statistics and variation in anatomical parameters. It was found that inter-teardrop and inter-fossa distances exhibit a high degree of consistency in pelvises of the same gender. Additionally, stable relationships were found between the anterior pelvic plane (APP) and other reference planes that rely on acetabular points instead of pubic points. Based on these results, a registration procedure for the pelvis was developed which uses only landmarks that are accessible intra-operatively from the ipsilateral side. The deviation between a standard APP registration and this new registration method was assessed. For a standard cup position (40° inclination, 15° anteversion), the resulting deviations were found to be 0.15 ± 2.86° for inclination and 0.27 ± 3.46° for anteversion. Of the registrations, 99% had cup positions within the Lewinnek safe zone. This shows that accurate lateral pelvis registration based on anatomical relationships is achievable.

Does standing affect acetabular component inclination and version after THA?

BACKGROUND

Avoiding complications after hip arthroplasty with hard-on-hard bearings, especially metal-on-metal, correlates with the position of the acetabular component. Supine imaging with conventional radiography has traditionally been utilized to assess component inclination (abduction), as well as anteversion, after THA and surface replacement arthroplasty (SRA). However, most adverse events with hard bearings (excessive wear and squeaking) have occurred with loading. Standing imaging, therefore, should provide more appropriate measurements.

QUESTIONS/PURPOSES

We determined whether standing changed standard measurements of acetabular component position using a novel biplanar imaging system compared to traditional supine imaging.

METHODS

We performed simultaneous biplanar standing imaging of the lower extremity with a novel imaging system using low radiation collimated beam on 46 patients who underwent THA (23) or SRA (23). Patients who had previously undergone THA had standard CT scans performed. For patients who underwent SRA, we compared acetabular inclination in the supine versus double-limb and single-limb standing.

RESULTS

Standing anteversion differed from supine anteversion by greater than 5° for 12 of 23 patients who underwent THA (range, 5°-16°). For patients who underwent SRA, 13 of 23 patients exhibited a difference of greater than 3° in inclination between supine and double-limb standing images, and six of 23 patients exhibited a difference of greater than 3° in inclination between supine and single-limb standing images.

CONCLUSIONS

Standing changed the acetabular inclination and version in a substantial percentage of patients undergoing hip arthroplasty.

Computed tomography assessment of image-free navigation-assisted cup placement in THA in an Asian population

The authors hypothesized that an image-free navigation system would be more accurate than postoperative 3-dimensional (3-D) reconstructed computed tomography (CT) for acetabular cup inclination and anteversion during total hip arthroplasty (THA) in an Asian population. Eighty-one THAs were performed in 72 patients using the OrthoPilot image-free navigation system (B. Braun Aesculap, Tuttlingen, Germany). Cup placement position was measured by postoperative 3-D CT and compared with intraoperative navigation data. The discrepancies between the navigation data and the 3-D CT data were analyzed, as well as the correlation factors that affected the discrepancies. The discrepancies between the navigation data and the 3-D CT data were -1.5° ± 7.1° (P=.04) for anteversion and -1.1° ± 7.6° (P=.02) for inclination. The accuracy and precision of the anteversion discrepancies were 5.6° ± 4.4° and 3.2°, respectively. The accuracy and precision of the inclination discrepancies were 4.5° ± 4.4° and 2.8°, respectively. Five (6%) outliers existed in terms of the safe zones of anteversion and inclination. The main correlated factor among the pelvic geometry was tilt rather than rotation and obliquity of the bony anterior pelvic plane.In an Asian population, the calculated accuracy and precision of acetabular cup inclination and anteversion during THA were more reliable and the outliers were reduced using the OrthoPilot navigation system. However, discrepancies existed between intraoperative navigation data and postoperative 3-D CT data. The pelvic geometry of biometrical factors influenced the discrepancies in the navigation data.

Early functional results after hemiarthroplasty for femoral neck fracture: a randomized comparison between a minimal invasive and a conventional approach

BACKGROUND

A minimal invasive approach for elective hip surgery has been implemented in our institution in the past. It is widely hypothesized that implanting artificial hips in a minimal invasive fashion decreases surgical trauma and is helpful in the rehabilitation process in elective hip surgery. Thereby geriatric patients requiring emergency hip surgery also could theoretically benefit from a procedure that involves less tissue trauma.

METHODS

Sixty patients who sustained a fractured neck of femur were randomly assigned into two groups. In the minimal invasive arm, the so called "direct anterior approach" (DAA) was chosen, in the conventional arm the Watson-Jones-Approach was used for implantation of a bipolar hemi-arthroplasty.Primary outcome parameter was the mobility as measured by the four-item-Barthel index. Secondary outcome parameters included pain, haemoglobin-levels, complications, duration of surgery, administration of blood transfusion and external length of incision. Radiographs were evaluated.

RESULTS

A statistically significant difference (p = 0,009) regarding the mobility as measured with the four-item Barthel index was found at the 5th postoperative day, favouring the DAA. Evaluation of the intensity of pain with a visual analogue scale (VAS) showed a statistically significant difference (p = 0,035) at day 16. No difference was evident in the comparison of radiographic results.

CONCLUSIONS

Comparing two different approaches to the hip joint for the implantation of a bipolar hemi-arthroplasty after fractured neck of femur, it can be stated that mobilization status is improved for the DAA compared to the WJA when measured by the four-item Barthel index, there is less pain as measured using the VAS. There is no radiographic evidence that a minimal invasive technique leads to inferior implant position.

LEVEL OF EVIDENCE

Level II therapeutic study.

Reliability of cup position in navigated THA in the lateral decubitus position using the 'flip technique'

Malpositioning of the acetabular component in total hip arthroplasty (THA) increases the risk of dislocation, reduces the range of motion and may contribute to bearing surface wear. During computer assisted navigation, the anterior pelvic plane is registered intraoperatively by percutaneous palpation, but this may be unreliable. The aim of our study was to evaluate the reliability of imageless navigation in acetabular positioning employing data acquisition in the supine position and surgery in the lateral position ('flip technique'). We report 24 patients affected by primary osteoarthritis undergoing THA in which implants were placed with a conventional free-hand technique using the acetabular transverse ligament for cup orientation. For imageless navigation we used Orthopilot-Aesculap software. All patients had a postoperative computed tomography (CT) scan at three months, using previously validated dedicated software for cup orientation. Data collected using navigation software were compared with CT measurements. The mean acetabular inclination and anteversion recorded intra-operatively using navigation software were respectively 41°5' (SD: 9.61) and 9°5' (SD: 4.01) respectively. The mean inclination and anteversion calculated post-operatively by the CT based image software were 44°2' (SD 5.83) and 14°4' (SD 6.42) respectively. There was a statistically significant difference between the anteversion values (p=0.04). Therefore, the acquisition of parameters in the supine position with surgery performed in the lateral decubitus position creates unreliable data concerning cup anteversion using an imageless navigation system, and therefore the 'flip technique' cannot be recommended.

Understanding acetabular cup orientation: the importance of convention and defining the safe zone

Understanding acetabular cup orientation is important in all aspects of total hip arthroplasty including preoperative planning, intraoperative positioning, and postoperative analysis. New concepts in ideal cup orientation such as 'combined anteversion' have emerged. Using computer navigation and three-dimensional imaging, the potential for accuracy and precision of implantation have improved. Nevertheless, the varying manner in which the terms "anteversion" and "abduction" are often used in the literature is indicative of a nebulous understanding of the complex spatial anatomy of acetabular cup orientation.

Cup positioning in total hip arthoplasty: spatial alignment of the acetabular entry plane

PURPOSE

Correct cup positioning is one of the keys for successful total hip replacement. There are mechanical and computer assistant guides for correct cup positioning in the market. To optimize the cup positioning, the use of navigation systems is recommended. The aim of this study was to compare spatial orientation of the acetabulary entry plane in relation to tables plane which is used by mechanical guides as well as anterior pelvic plane used for cup orientation by navigation systems.

METHODS

CT raw data of 80 Caucasians (160 acetabuli) (done in supine position) with osteoartritic hips were collected. 3-D pelvic reconstruction was generated using Amira software (Visage Imaging Berlin, Germany). Anterior pelvic plane and acetabulary entry plane were defined by reliable anatomical landmarks. Spatial orientation were calculated by a custom made program code for the Amira software.

RESULTS

There were no differences between anterior pelvic plane and table's plane as well as spatial orientation of acetabulary entry plane of both acetabuli in relation to anterior pelvic plane or table's plane. Furthermore, there was no correlation between age, sex or body mass index and spatial orientation of the acetabulary entry plane as well.

CONCLUSIONS

The use of mechanical alignment guides for cup orientation during total hip arthroplasty based on table's plane in patient's supine position is a successful method to achieve proper cup orientation.

Robotic assisted total hip arthroplasty using the MAKO platform

Surgeons want to perform a perfect total hip replacement (THR) with every operation. Human performance has limitations, especially when performing a mechanical operation in a biological environment. Recent suggested changes to improve outcomes have been large femoral heads and anterior incisions, but unfortunately neither has resulted in any scientific data that change has been effected. The scientific data does tell us that poor component positions and impingement are the source of increasing mechanical complications. Therefore, attempts to improve the surgeon's performance by precise quantitative knowledge in the operating room have been used. We discuss robotic guided navigation as a solution. This technology provides predictable and reproducible results.

Changes in pelvic tilt following total hip arthroplasty

BACKGROUND

It is important to understand chronological changes in pelvic tilt after total hip arthroplasty (THA). In this study, we first investigated changes in pelvic tilt after THA. Second, we determined the correlation between preoperative pelvic tilt and the extent of postoperative changes in the pelvic tilt. Third, we evaluated the effects of changes in pelvic tilt on postoperative function and disability.

METHODS

We examined 149 patients who received primary THA over a follow-up period of 1 year. We compared postoperative changes with the preoperative pelvic tilt on the basis of the anterior pelvic plane (APP) defined by DiGioia and patient demographics.

RESULTS

A significant correlation was observed between preoperative APP and the amount of postoperative change in APP, suggesting that patients with severe preoperative pelvic tilt generally experience greater postoperative changes in pelvic tilt. Our data showed that patients with preoperative anterior pelvic tilt generally exhibit posterior changes in pelvic tilt after operation, while patients with preoperative posterior pelvic tilts did not experience significant postoperative changes in pelvic tilt. The 1-year postoperative function scores in patients with preoperative anterior pelvic tilt were lower than those in patients with preoperative posterior pelvic tilt.

CONCLUSIONS

Pelvic tilt changed by varying degrees following THA. Special attention must be paid when positioning the acetabular component, particularly in patients with severe pelvic tilt prior to surgery. A greater understanding of the postoperative changes in pelvic tilt may improve the outcome of THA.

Preoperative fluoroscopic imaging reduces variability of acetabular component positioning

We evaluated the preoperative errors in the pelvic tilt of 249 hips before total hip arthroplasty using fluoroscopic imaging while the patients were in the lateral decubitus position. The mean absolute value errors of the pelvic tilt were 2.94° (SD, 2.92°), 2.49° (SD, 2.68°), and 5.92° (SD, 5.20°) in the coronal, transverse, and sagittal planes, respectively. Such preoperative errors in the pelvic tilt contribute to malpositioning of the acetabular component, as is frequently observed on postoperative radiographs. We reduced the incidence of malpositioning by correcting the errors in the pelvic tilt through repositioning of the operating table using fluoroscopic imaging before surgery. The new technique using fluoroscopic imaging described in this article can be performed within a short time without a navigation system.

Robotic guidance in total hip arthroplasty: the shape of things to come

Surgeons want to perform a perfect total hip arthroplasty (THA) with every operation. Human performance has limitations, especially when performing a mechanical operation in a biological environment. Recent suggested changes to improve outcomes have been large femoral heads and anterior incisions, but unfortunately, neither has resulted in any scientific data that change has been effected. The scientific data tell us that poor component positions and impingement are the source of increasing mechanical complications. Therefore, attempts have been made to improve the surgeon's performance by precise quantitative knowledge in the operating room. Robotic-guided navigation provides numerical data for cup inclination plus anteversion and center of rotation; femoral leg length and offset; and combined anteversion of the cup and stem. The acetabular bone preparation is done with a reamer connected to a robotic arm, which prevents human error by the surgeon of reaming off line or too deep. This technology provides predictable and reproducible results.

The relationship between the angle of version and rate of wear of retrieved metal-on-metal resurfacings: a prospective, CT-based study

We measured the orientation of the acetabular and femoral components in 45 patients (33 men, 12 women) with a mean age of 53.4 years (30 to 74) who had undergone revision of metal-on-metal hip resurfacings. Three-dimensional CT was used to measure the inclination and version of the acetabular component, femoral version and the horizontal femoral offset, and the linear wear of the removed acetabular components was measured using a roundness machine. We found that acetabular version and combined version of the acetabular and femoral components were weakly positively correlated with the rate of wear. The acetabular inclination angle was strongly positively correlated with the rate of wear. Femoral version was weakly negatively correlated with the rate of wear. Application of a threshold of > 5 μm/year for the rate of wear in order to separate the revisions into low or high wearing groups showed that more high wearing components were implanted outside Lewinnek's safe zone, but that this was mainly due to the inclination of the acetabular component, which was the only parameter that significantly differed between the groups. We were unable to show that excess version of the acetabular component alone or combined with femoral version was associated with an increase in the rate of wear based on our assessment of version using CT.