Comparison of a mechanical acetabular alignment guide with computer placement of the socket

Which one is more affected by navigation-assisted cup positioning in total hip arthroplasty: Anteversion or inclination? A retrospective matched-pair cohort study in Asian physique

INTRODUCTION

The purpose of this study was to compare acetabular cup positioning using an imageless navigation-assisted total hip arthroplasty (THA) to a case-matched control group using the conventional technique in Asian physique.

METHODS

Case matching controlled study using retrospectively collected data for THAs was done. Matching criteria were gender, age ± 5 years, and body mass index ± 5 kg/m². Thirty patients who had navigation THAs were manually matched to a conventional group of 30 patients. After measuring anteversion and inclination on 3-D CT, final cup anteversion was calculated using the mathematical formula (anteversion = arctan [tan (anatomic anteversion) × sin (inclination)]).

RESULTS

No significant difference was observed between mean inclination ( p = 0.420), anteversion ( p = 0.697), and the mean deviation from 15° for anteversion ( p = 0.649). However, there was a statistical significant difference for mean deviation from 40° for inclination ( p = 0.027). There was a significant difference in the percentage of correctly placed acetabular cup in safe zones with inclination ( p = 0.039).

CONCLUSIONS

Although soft tissue overlying the pubic tubercle interfered with registration of the bony landmark and thereby induced inaccuracy of anteversion angles in the navigation group, the use of imageless navigation-assisted technique increases the placement within the safe zone for inclination and enhances the accuracy and the precision of inclination of the acetabular cup relative to the conventional THA rather than anteversion. This finding may be due to the effect of the patient's physique on the anterior pelvic plane (APP)-based reference system of imageless navigation.

Can some early revision total hip arthroplasties be avoided?

Aims

Studying the indications for revision total hip arthroplasty (THA) may enable surgeons to change their practice during the initial procedure, thereby reducing the need for revision surgery. The aim of this study was to identify and describe the potentially avoidable indications for revision THA within five years of the initial procedure.

Patients and Methods

A retrospective review of 117 patients (73 women, 44 men; mean age 61.5 years (27 to 88)) who met the inclusion criteria was conducted. Three adult reconstruction surgeons independently reviewed the radiographs and medical records, and they classified the revision THAs into two categories: potentially avoidable and unavoidable. Baseline demographics, perioperative details, and quality outcomes up to the last follow-up were recorded.

Results

A total of 60 revision THAs (51.3%) were deemed potentially avoidable and 57 (48.7%) were deemed unavoidable. The following were identified as avoidable factors: suboptimal positioning of the acetabular component (29; 48%), intraoperative fracture or a fracture missed on an intraoperative radiograph (20; 33%), early (less than two weeks) aseptic loosening (seven; 11.7%), and symptomatic leg length discrepancy of > 1 cm (four; 6.7%).

Conclusion

A surprisingly large proportion of acute revision THAs are potentially avoidable. Surgeons must carefully evaluate the indications for revision THAs in their practice and identify new methods to address these issues. Cite this article: Bone Joint J 2019;101-B(6 Supple B):97–103.

An Open-Label, Single-Arm Study of a Patient-Specific Femoral Guide for Total Hip Arthroplasty via the Anterolateral Supine Approach, Linked with Three-Dimensional Surgical Support Software: Study Protocol

In total hip arthroplasty (THA), it is generally accepted that the bones of the acetabular cup and femur of hip joint must be accurately cut and components (artificial joint parts) be implanted in exact positions at exact angles to achieve improvement of daily living (ADL) and quality of life (QOL). However, with the conventional surgical method, it is difficult to grasp and measure the acetabular cup and femoral stem precisely during surgery, making some kind of reliable guide necessary. Although it was reported that an accurate angle was achieved in acetabular cup implantation by support instruments for surgical planning, an effective support instrument is now being developed for stem implantation on the out-of-reach femur side. This is the first clinical study to assess the efficacy and safety of anterolateral approach THA using an extracorporeal patient-specific femoral guide (PSG) for stem implantation with three-dimensional (3D) surgical support software in patients with hip joint disease.

Efficacy of Computed Tomography-Based Navigation for Cup Placement in Revision Total Hip Arthroplasty

Background

Navigation systems are an effective tool to improve the installation accuracy of the cup in primary total hip arthroplasty. This study aimed to evaluate the efficacy of a computed tomography-based navigation system in achieving optimal installation accuracy of implants in revision total hip arthroplasty and to clarify the usefulness of the navigation system.

Methods

We conducted a retrospective study of 23 hips in 23 patients who underwent revision total hip arthroplasty using a computed tomography-based navigation system; the control group comprised 33 hips in 33 patients who underwent revision total hip arthroplasty without a navigation system.

Results

The average cup position with the navigation system was 40.0° ± 3.7° in radiographic abduction angle, 18.8° ± 4.8° in radiographic anteversion, and 41.2° ± 8.9° in combined anteversion; without the navigation system, the average cup position was 38.7° ± 6.1°, 19.0° ± 9.1°, and 33.6° ± 20.5°, respectively. The achievement rate of cup positioning within the Lewinnek safe zone was not significantly different between the navigation group (82.6%) and control group (63.6%). In contrast, the achievement rate of cup positioning within the Widmer combined anteversion guidelines was significantly greater in the navigation group (78.3%) than in the control group (48.0%, p = 0.029). Furthermore, outlier cases in the navigation group had a smaller variance of deviation from the optimal cup position than those in the control group did.

Conclusions

The results show that the use of navigation for revision total hip arthroplasty improved cup positioning and reduced the range of outliers. Improvement of cup placement accuracy influenced the installation of the stem and also improved the achievement rate of combined anteversion. Thus, a computed tomography-based navigation system is very useful for surgeons when placing the cup within the target angle in revision total hip arthroplasty.

Variability of Pelvic Orientation in the Lateral Decubitus Position: Are External Alignment Guides Trustworthy?

BACKGROUND

The position of the acetabular component in total hip arthroplasty (THA) is critical for success. However, this remains the most variable aspect of the surgery. We hypothesized that there is wide variation in pelvic orientation in the lateral decubitus position. We sought to determine the variability in pelvic positioning and the frequency of pelvic malposition during THA in lateral decubitus with regard to pelvic tilt and pelvic rotation.

METHODS

We analyzed preoperative standing and intraoperative anteroposterior pelvis X-rays in 248 consecutive THAs performed in lateral decubitus by one surgeon. Pelvic tilt and rotation were determined for preoperative and intraoperative X-rays. Proper intraoperative positioning was defined as less than 10° change in tilt or rotation between preoperative and intraoperative X-rays.

RESULTS

With regard to pelvic tilt, the intraoperative position was proper in 188 (76%) cases. There was a pelvic tilt discrepancy of 10°-20° in 43 (17.5%) cases and greater than 20° in 16 (6.5%) patients. With regard to pelvic rotation, the intraoperative position was proper in 202 (81%) cases. There was a pelvic rotation discrepancy of 10°-20° in 38 (15.4%) cases and greater than 20° in 7 (2.8%) cases. In 248 cases, only 154 (62.1%) had intraoperative positioning within 10° of preoperative tilt and axial rotation. Pelvic malposition occurred in 38% of cases overall.

CONCLUSION

There is wide variation in pelvic orientation in lateral decubitus and frequent discrepancy in pelvic tilt and rotation between preoperative and intraoperative anteroposterior X-rays. Anatomic landmarks should be used to guide acetabular component positioning.

LEVEL OF EVIDENCE III

Diagnostic.

Gravity-Assisted Navigation System for Total Hip Arthroplasty

In this chapter we propose a new system that allows reliable acetabular cup placement in total hip arthroplasty (THA) when the surgery is operated in lateral approach. Conceptually it combines the accuracy of computer-generated patient-specific morphology information with an easy-to-use mechanical guide, which effectively uses natural gravity as the angular reference. The former is achieved by using a statistical shape model-based 2D-3D reconstruction technique that can generate a scaled, patient-specific 3D shape model of the pelvis from a single conventional anteroposterior (AP) pelvic X-ray radiograph. The reconstructed 3D shape model facilitates a reliable and accurate co-registration of the mechanical guide with the patient's anatomy in the operating theater. We validated the accuracy of our system by conducting experiments on placing seven cups to four pelvises with different morphologies. Taking the measurements from an image-free navigation system as the ground truth, our system showed an average accuracy of 2. 1 ± 0. 7^∘ for inclination and an average accuracy of 1. 2 ± 1. 4^∘ for anteversion.

Pelvic positioning in the supine position leads to more consistent orientation of the acetabular component after total hip arthroplasty

Aims

This study aims to: determine the difference in pelvic position that occurs between surgery and radiographic, supine, postoperative assessment; examine how the difference in pelvic position influences subsequent component orientation; and establish whether differences in pelvic position, and thereafter component orientation, exist between total hip arthroplasties (THAs) performed in the supine versus the lateral decubitus positions.

Patients and Methods

The intra- and postoperative anteroposterior pelvic radiographs of 321 THAs were included; 167 were performed with the patient supine using the anterior approach and 154 were performed with the patient in the lateral decubitus using the posterior approach. The inclination and anteversion of the acetabular component was measured and the difference (Δ) between the intra- and postoperative radiographs was determined. The target zone was inclination/anteversion of 40°/20° (± 10°). Changes in the tilt, rotation, and obliquity of the pelvis on the intra- and postoperative radiographs were calculated from Δinclination/anteversion using the Levenberg–Marquardt algorithm.

Results

The mean postoperative inclination/anteversion was 40° (± 8°)/23° (± 9°) with Δinclination and/or Δanteversion > ± 10° in 74 (21%). Intraoperatively, the pelvis was anteriorly tilted by a mean of 4° (± 10°), internally rotated by a mean of 1° (± 10°) and adducted by a mean of 1° (± 5°). Having Δinclination and/or Δanteversion > ± 10° was associated with a 3.5 odds ratio of having the acetabular component outside the target zone. A greater proportion of THAs that were undertaken with the patient in the lateral decubitus position had Δinclination and/or Δanteversion > ± 10° (35.3%, 54/153) compared with those in the supine position (4.8%, 8/167; p < 0.001). A greater number of acetabular components were within the target zone in THAs undertaken with the patient in the supine position (72%, 120/167), compared with those in the lateral decubitus position (44%, 67/153; p < 0.001). Intraoperatively, the pelvis was more anteriorly tilted (p < 0.001) and more internally rotated (p = 0.04) when the patient was in the lateral decubitus position.

Conclusion

The pelvic position is more reliable when the patient is in the supine position, leading to more consistent orientation of the acetabular component. Significant differences in pelvic tilt and rotation are seen with the patient in the lateral decubitus position. Cite this article: Bone Joint J 2018;100-B:1280–8.

Differences in activities of daily living after hip arthroplasty among hip resurfacing, anterolateral THA, and posterolateral THA: a propensity score matched analysis

The aim was to elucidate the differences in activities of daily living (ADL) after hip arthroplasty among hip resurfacing (HRA), anterolateral total hip arthroplasty (AL-THA), and posterolateral THA (PL-THA) patients after age, sex, body mass index, bilateral/unilateral hip arthroplasty, and postoperative duration were matched using propensity scores. A total of 673 hips from 540 consecutive patients who underwent hip arthroplasty were included. A self-completed questionnaire on preoperative and postoperative ADLs was administered during postsurgical visits at least ≥ 4 years postoperatively. Between HRA and PL-THA patients, the numbers of patients who performed heels-down squatting was significantly more in HRA than in PL-THA. Between AL-THA and PL-THA patients, there were significant differences in postoperative ADLs including bathing in a bathtub, riding on a train/bus, cutting toenails, bowing while straight sitting, heels-up/down squatting, riding on a bicycle, driving a car, and domestic travel. There were no significant differences in postoperative ADLs between ≥ 36 mm head and ≤ 32 mm head PL-THA patients, and between AL-THA and HRA patients. This propensity score matched study indicated that AL-THA and HRA patients were more active postoperatively than PL-THA patients.

Standardization of hemipelvis alignment for in vitro biomechanical testing

Although in vitro biomechanical tests are regularly performed, the definition of a suitable reference frame for hemipelvic specimens is still a challenge. The aims of the present study were to: (i) define a reference frame for the human hemipelvis suitable for in vitro applications, based on robust anatomical landmarks; (ii) identify the alignment of a hemipelvis based on the alignment of a whole pelvis (including right/left and male/female differences); (iii) identify the relative alignment of the proposed in vitro reference frame with respect to a reference frame commonly used in gait analysis; (iv) create an in vitro alignment procedure easy, robust and inexpensive; (v) quantify the intra-operator repeatability and inter-operator reproducibility of the procedure. A procedure to univocally identify the anatomical landmarks was created, exploiting the in vitro accessibility of the specimen's surface. Through the analysis on 53 CT scans (106 hemipelvises), the alignment of the hemipelvis based on the alignment of a whole pelvis was analyzed: differences between male/female and right/left hemipelvises were not statistically significant To overcome the uncertainty in the identification of the acetabular rim, a standard acetabular plane was defined. An alignment procedure was developed to implement such anatomical reference frame. The intra-operator repeatability and the inter-operator reproducibility were quantified with four operators, on male and female hemipelvises. The intra-operator repeatability was better than 1.5°. The inter-operator reproducibility was better than 2.0°. Alignment in the transverse plane was the most repeatable. The presented procedure to align hemipelvic specimens is sufficiently robust, standardized, and accessible. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1645-1652, 2018.

A Pilot Study of Augmented Reality Technology Applied to the Acetabular Cup Placement During Total Hip Arthroplasty

BACKGROUND

We developed an acetabular cup placement device, the AR-HIP system, using augmented reality (AR). The AR-HIP system allows the surgeon to view an acetabular cup image superimposed in the surgical field through a smartphone. The smartphone also shows the placement angle of the acetabular cup. This preliminary study was performed to assess the accuracy of the AR-HIP system for acetabular cup placement during total hip arthroplasty (THA).

METHODS

We prospectively measured the placement angles using both a goniometer and AR-HIP system in 56 hips of 54 patients undergoing primary THA. We randomly determined the order of intraoperative measurement using the 2 devices. At 3 months after THA, the placement angle of the acetabular cup was measured on computed tomography images. The primary outcome was the absolute value of the difference between intraoperative and postoperative computed tomography measurements.

RESULTS

The measurement angle using AR-HIP was significantly more accurate in terms of radiographic anteversion than that using a goniometer (2.7° vs 6.8°, respectively; mean difference 4.1°; 95% confidence interval, 3.0-5.2; P < .0001). There was no statistically significant difference in terms of radiographic inclination (2.1° vs 2.6°; mean difference 0.5°; 95% confidence interval, -1.1 to 0.1; P = .13).

CONCLUSION

In this pilot study, the AR-HIP system provided more accurate information regarding acetabular cup placement angle than the conventional method. Further studies are required to confirm the utility of the AR-HIP system as a navigation tool.

A new mini-navigation tool allows accurate component placement during anterior total hip arthroplasty

Introduction

Computer-assisted navigation systems have been explored in total hip arthroplasty (THA) to improve component positioning. While these systems traditionally rely on anterior pelvic plane registration, variances in soft tissue thickness overlying anatomical landmarks can lead to registration error, and the supine coronal plane has instead been proposed. The purpose of this study was to evaluate the accuracy of a novel navigation tool, using registration of the anterior pelvic plane or supine coronal plane during simulated anterior THA.

Methods

Measurements regarding the acetabular component position, and changes in leg length and offset were recorded. Benchtop phantoms and target measurement values commonly seen in surgery were used for analysis. Measurements for anteversion and inclination, and changes in leg length and offset were recorded by the navigation tool and compared with the known target value of the simulation. Pearson's r assessed the relationship between the measurements of the device and the known target values.

Results

The device accurately measured cup position and leg length measurements to within 1° and 1 mm of the known target values, respectively. Across all simulations, there was a strong, positive relationship between values obtained by the device and the known target values (r=0.99).

Conclusion

The preliminary findings of this study suggest that the novel navigation tool tested is a potentially viable tool to improve the accuracy of component placement during THA using the anterior approach.

Preoperative Ultrasonographic Assessment of the Anterior Pelvic Plane for Personalized Total Hip Replacement

OBJECTIVES

Correct positioning of the acetabular component is a key factor in minimizing the risk of dislocation after total hip replacement (THR) surgery. A "safe" orientation of the cup is usually defined by 2 angles measured between its geometric axis and the anterior pelvic plane. However, in the current state-of-the-art approach to THR surgery, the intraoperative orientation of the anterior pelvic plane cannot be measured. Even less is known about the functional orientation of the pelvis, which determines the postoperative orientation of the cup during the patient's everyday activities. The aim of this article is to present an original approach to personalized THR surgery, in which the necessary measurements are done preoperatively without interfering with the surgical work flow, and the individual orientation of the cup is obtained without navigation using standard tools that are available in the operating room.

METHODS

To quantify the effect of the anatomic conditions on the final orientation of the cup, we measured the orientation of the anterior pelvic plane in 43 patients scheduled for THR using a newly developed noninvasive method based on ultrasonography and mobile devices.

RESULTS

Our results confirm a large variability of the pelvic orientation in both supine and standing positions. We further show how this variability affects the final position of the cup and discuss its consequences for the patient. Finally, we explore a few practical solutions for individualized cup placement, including our own approach, which is based on tilting of the operating table.

CONCLUSIONS

In this work, we show that the common guidelines used today for cup implantation can only be effectively applied to a small portion of the population. In most cases, it is crucial that the orientation of the cup is readjusted for the particular anatomy of the individual patient.

Inter- and intra-operator reliability in patient-specific template positioning for total hip arthroplasty. A cadaver study

BACKGROUND

The implantation of the acetabular cup essentially determines the clinical outcome of total hip arthroplasty. To address this issue, the aim of this study was to build patient-specific instruments (PSIs) with various reference surfaces, followed by in vitro investigations to examine the inter- and intra-operator reliability as well as the overall precision of these patient-specific templates.

METHODS

Seven human hemi-pelvis specimens were used for this study. After a CT scan, PSIs with different imprint heights were created. The overall precision of the templates and the inter- and intra-operator reliabilities were calculated.

RESULTS

Strong differences in precision between the PSI designs could be observed. The desired orientation of the acetabular cup could be adjusted with a precision of up to 1.55°.

CONCLUSION

Based on our results, we believe that the application of the PSI-based acetabular cup positioning in total hip arthroplasty procedures can potentially increase the precision of cup placement.

The posterior acetabular wall (PAW): an aid to acetabular orientation at primary THA

INTRODUCTION

Incorrect acetabular component positioning during total hip arthroplasty (THA) may lead to dislocation, impingement, wear and revision. Surgeons commonly use the transverse acetabular ligament (TAL) as a landmark for acetabular component orientation. The posterior acetabular wall (PAW) is a structure easily viewed on plain radiography and its position can help guide acetabular component position. In this study, we examine the efficacy of preoperative radiographs in predicting cup position relative to the PAW.

METHODS

Prospective data was recorded on radiographic findings of the posterior wall (prominent, normal, deficient) on a consecutive series of 200 primary THAs utilising a standardised posterior approach. The final cup position relative to the wall was recorded (prominent, flush, deep). Cup inclination and version were then assessed by postoperative radiography and any instances of dislocation recorded.

RESULTS

There were 117 females and 83 males with a mean age of 66.5 years. 154 were recorded as having a normal PAW on radiographs, 152 had the cup positioned in line with the TAL and flush to the PAW. 29 had a deficient PAW and 27 of these had a cup positioned prominently with 17 having a prominent PAW and of these 16 a deep cup position. Postoperative radiographs showed a mean cup version of 20.8° and inclination of 44.7° using this method. There were 21 outliers (10.5%) with no dislocations at a minimum 12-month follow-up.

CONCLUSIONS

The TAL is a continuation of the posterior labrum. As such, the posterior wall is a useful adjunct to and surrogate landmark for the TAL. It has the added advantage that it is visible on radiographs and so aids surgical planning with respect to cup positioning.

Accuracy of Cup Positioning With the Computed Tomography-Based Two-dimensional to Three-Dimensional Matched Navigation System: A Prospective, Randomized Controlled Study

BACKGROUND

The accuracy of various navigation systems used for total hip arthroplasty has been described, but no publications reported the accuracy of cup orientation in computed tomography (CT)-based 2D-3D (two-dimensional to three-dimensional) matched navigation.

METHODS

In a prospective, randomized controlled study, 80 hips including 44 with developmental dysplasia of the hips were divided into a CT-based 2D-3D matched navigation group (2D-3D group) and a paired-point matched navigation group (PPM group). The accuracy of cup orientation (absolute difference between the intraoperative record and the postoperative measurement) was compared between groups. Additionally, multiple logistic regression analysis was performed to evaluate patient factors affecting the accuracy of cup orientation in each navigation.

RESULTS

The accuracy of cup inclination was 2.5° ± 2.2° in the 2D-3D group and 4.6° ± 3.3° in the PPM group (P = .0016). The accuracy of cup anteversion was 2.3° ± 1.7° in the 2D-3D group and 4.4° ± 3.3° in the PPM group (P = .0009). In the PPM group, the presence of roof osteophytes decreased the accuracy of cup inclination (odds ratio 8.27, P = .0140) and the absolute value of pelvic tilt had a negative influence on the accuracy of cup anteversion (odds ratio 1.27, P = .0222). In the 2D-3D group, patient factors had no effect on the accuracy of cup orientation.

CONCLUSION

The accuracy of cup positioning in CT-based 2D-3D matched navigation was better than in paired-point matched navigation, and was not affected by patient factors. It is a useful system for even severely deformed pelvises such as developmental dysplasia of the hips.

Intraoperative fluoroscopy with a direct anterior approach reduces variation in acetabular cup abduction angle

INTRODUCTION

The purpose of this study was to compare acetabular cup position for 2 cohorts of total hip arthroplasty (THA) patients who had a direct anterior approach.

METHODS

100 THA cases were performed with an anterior approach using intraoperative fluoroscopy (IF) to aid in cup positioning. Another group of 100 cases underwent THA with an anterior approach without the use of any fluoroscopy. Postoperative abduction and anteversion angles were measured using Martell's hip analysis software.

RESULTS

Mean abduction angle was 43.2° (standard deviation (SD) = 4.5°) for the IF group versus 37.5°(SD = 7.4°) for cases without IF (p<0.001). 18% more cases with IF fell within the Lewinnek safe zone (p<0.001); however, a similar number of cases had over 50° of abduction. The mean anteversion angles of the two groups were also significantly different (IF 21.8° vs. 24.9°) (p<0.01).

CONCLUSIONS

There was significantly less variation in cup position among the cases using IF with regards to abduction.

Quantifying Pelvic Motion During Total Hip Arthroplasty Using a New Surgical Navigation Device

BACKGROUND

Accurate cup positioning is one of the most challenging aspects of total hip arthroplasty (THA). Undetected movement of the patient during THA surgery can lead to inaccuracies in cup anteversion and inclination, increasing the potential for dislocation and revision surgery. Investigations into the magnitude of patient motion during THA are not well represented in the literature.

METHODS

We analyzed intraoperative pelvic motion using a novel navigation device used to assist surgeons with cup position, leg length, and offset during THA. This device uses an integrated accelerometer to measure motion in 2 orthogonal degrees of freedom. We reviewed the data from 99 cases completed between February and September 2016.

RESULTS

The mean amount of pitch recorded per patient was 2.7° (standard deviation, 2.2; range, 0.1°-9.9°), whereas mean roll per patient was 7.3° (standard deviation, 5.5; range, 0.3°-31.3°). Twenty-one percent (21 of 99) of patients demonstrated pitch of >4°. Sixty-nine percent (68 of 99) of patients demonstrated >4° of roll, and 25% (25 of 99) of patients demonstrated roll of ≥10°.

CONCLUSION

Our findings indicate that while the majority of intraoperative motion is <4°, many patients experience significant roll, with a large proportion rolling >10°. This degree of movement has implications for acetabular cup position, as failure to compensate for this motion can result in placement of the cup outside the planned safe zone, thus, increasing the potential for dislocation. Further study is warranted to determine the effect of this motion on cup position, leg length, and offset.

Technology in Arthroplasty: Are We Improving Value?

PURPOSE OF REVIEW

Total joint arthroplasty is regarded as a highly successful procedure. Patient outcomes and implant longevity, however, are related to proper alignment and position of the prostehses. In an attempt to reduce outliers and improve accuracy and precision of component position, navigation and robotics have been introduced. These technologies, however, come at a price. The goals of this review are to evaluate these technologies in total joint arthroplasty and determine if they add value.

RECENT FINDINGS

Recent studies have demonstrated that navigation and robotics in total joint arthroplasty can decrease outliers while improving accuracy in component positioning. While some studies have demonstrated improved patient reported outcomes, not all studies have shown this to be true. Most studies cite increased cost of equipment and longer operating room times as the major downsides of the technologies at present. Long-term studies are just becoming available and are promising, as some studies have shown decreased revision rates when navigation is used. Finally, there are relatively few studies evaluating the direct cost and value of these technologies. Navigation and robotics have been shown to improve component position in total joint arthroplasty, which can improve patient outcomes and implant longevity. These technologies offer a promising future for total joint arthroplasty.

WITHDRAWN: Correcting pelvic obliquity in the lateral position to improve acetabular component orientation during total hip arthroplasty

BACKGROUND

Ahead of Print article withdrawn by publisher. The acetabular component orientation during total hip arthroplasty (THA) impacts future hip function and early revision. Correcting pelvic obliquity may improve outcomes.

OBJECTIVE

To correct pelvic obliquity in the lateral position by applying a gradienter and plumb during THA using fluoroscopy.

METHODS

Fifty patients undergoing THA were randomized and divided into 2 groups. In controls, acetabular components were placed using traditional methods. In experimental patients, acetabular components were placed after correcting pelvic obliquity. We measured pelvic obliquity and recorded intra-operative and post-operative abduction angles, comparing abduction angle bias between post-operative measurements and intra-operation estimations.

RESULTS

Before correction, the average pelvic obliquity was -1.647∘± 4.512∘ in experimental patients. The average abduction angle in experimental patients was 42.685∘± 3.355∘ postoperatively, differing by 1.962∘± 1.515∘ from intra-operative estimates, while in control patients, it was 44.534∘± 4.844∘ postoperatively, differing by 4.244∘± 3.042∘ from intra-operative estimates. The bias of the abduction angle was much greater in control than in experimental patients (P< 0.05).

CONCLUSION

The pelvic obliquity in the lateral position affects surgeon judgment during THA. By correcting pelvic obliquity with a gradienter and plumb, the abduction angle bias can be reduced.

Computer navigation of the acetabular component in total hip arthroplasty: a narrative review

Total hip arthroplasty (THA) is a common procedure for primary osteoarthritis, but increasing numbers are also being performed for other pathologies such as secondary arthritis, inflammatory arthropathies and trauma. Estimates suggest that around 8.5 million people in the UK are affected by joint pain secondary to arthritis and a rising ageing population has resulted in an increase in THA operations of around 4% per year over the last six years.

Multiple studies have shown that THA provides improved quality of life scores, but there remains the burden of complications which account for 15% of £1bn NHS liability payouts. DaPalma et al analysed the financial impact of complications following THA and found the additional cost of a dislocation within six weeks of surgery is 342% of the primary cost.

Following primary THA, complications may occur as a result of incorrect component positioning of the femoral stem, the acetabular cup or both. It is known that acetabular malposition may lead to increased rates of dislocation, impingement, edge-loading, polyethylene wear, pelvic osteolysis and prosthesis failure.

Acetabular component positioning has been described as the single most important factor in dictating risk of dislocation following THA. Furthermore, instability and dislocation after primary THA is the most common single reason for revision surgery accounting for 22.5% of all revisions and 33% of acetabular revisions.

We outline the currently available methods of acetabular navigation comparing freehand techniques with computer and robotic-assisted navigation of the acetabular component.

Cite this article: Davenport D, Kavarthapu V. Computer navigation of the acetabular component in total hip arthroplasty: a narrative review. EFORT Open Rev 2016;1:279-285. DOI: 10.1302/2058-5241.1.000050.

Rigid Patient Positioning is Unreliable in Total Hip Arthroplasty

BACKGROUND

To our knowledge, no study has assessed the ability of rigid patient positioning devices to afford arthroplasty surgeons with ideal acetabular orientation throughout surgery. The purpose of this study is to use robotic arm-assisted computer navigation to assess the reliability of pelvic position in total hip arthroplasty performed on patients positioned with rigid positioning devices.

METHODS

A prospective cohort of 100 hips (94 patients) underwent robotic-guided total hip arthroplasty in the lateral decubitus position from the posterior approach, 77 stabilized by universal lateral positioner, and 23 by peg board. Before reaming, computed tomography-templated computer software generated true values of pelvic anteversion and inclination based on the position of the robot arm registered to the patient's preoperative pelvic computed tomography.

RESULTS

Mean alteration in anteversion and inclination values was 1.7° (absolute value, 5.3°; range, -20° to 20°) and 1.6° (absolute value, 2.6°; range, -8° to 10°), respectively. And 22% of anteversion values were altered by >10° and 41% by >5°. There was no difference between hip positioners used (P = .36). Anteversion variability was correlated with body mass index (P = .02).

CONCLUSION

Despite the use of rigid patient positioning devices-a lateral hip positioner or peg board-this study reveals clinically important malposition of the pelvis in many cases, especially with regard to anteversion. These results show a clear need to pay particular attention to anatomic landmarks or computer-assisted techniques to assure accurate acetabular cup positioning. Patient positioning should not be solely trusted.

Revision Total Hip Arthroplasty Using Imageless Navigation With the Concept of Combined Anteversion

BACKGROUND

The purpose of the study was to evaluate the implant positions and clinical results of revision total hip arthroplasty (THA) using an imageless navigation with the concept of combined anteversion.

METHODS

A total of 40 cementless revision THAs (24 men and 16 women) using an imageless navigation with the concept of combined anteversion were retrospectively evaluated. The concept of combined anteversion was applied in cup positioning based on Widmer's equation (cup anteversion + 0.7 × stem anteversion). The mean follow-up period was 80.7 months. Postoperatively, the inclination of the cup was evaluated on standard anteroposterior view of the radiograph, and the anteversion of the cup and femoral stem was evaluated using computed tomography scan. A cup inclination of 40° ± 10° and combined anteversion of the cup and femoral stem of 37° ± 10° based on Widmer's equation were regarded as the "safe zone."

RESULTS

The average anteversion of the revised femoral stems was 15.3° ± 2.9° (range, 9.5°-21.5°), whereas that of the remained femoral stems was 17.4° ± 9.7° (range, 4.2°-29.8°). The inclination, anteversion of the cup, and combined anteversion after revision THA were 42.3° ± 3.1° (range, 32.1°-48.2°), 25.0° ± 2.9° (range, 16.9°-29.5°), and 36.1° ± 3.4° (range, 27.2°-42.9°), respectively. Therefore, the position of the implants, relative to the safe zone, showed no outliers after the revision surgery. Neither dislocation nor osteolysis was observed after the surgery.

CONCLUSION

Favorable results of this study indicate that imageless navigation helps the surgeon in placing the components of revision THA in the safe zone. This study also shows that when this safe zone is consistently obtained, then no postoperative dislocations were observed in these patients over the 6-year follow-up period.

Patient-specific instrumentation improves the accuracy of acetabular component placement in total hip arthroplasty

Aims

Accurate placement of the acetabular component during total hip arthroplasty (THA) is an important factor in the success of the procedure. However, the reported accuracy varies greatly and is dependent upon whether free hand or navigated techniques are used. The aim of this study was to assess the accuracy of an instrument system that incorporates 3D printed, patient-specific guides designed to optimise the placement of the acetabular component.

Patients and Methods

A total of 100 consecutive patients were prospectively enrolled and the accuracy of placement of the acetabular component was measured using post-operative CT scans.

Results

The mean absolute deviation from the planned inclination and anteversion was 3.9° (0.0° to 13.6°) and 3.6° (0.0° to 12.9°), respectively. In 91% of cases the planned target of +/-10° was achieved for both inclination and anteversion.

Conclusion

Accurate placement of the acetabular component can be achieved using patient-specific guides and is superior to free hand techniques and comparable to navigated and robotic techniques. Cite this article: Bone Joint J 2016;98-B:1342–6.

No Benefit After THA Performed With Computer-assisted Cup Placement: 10-year Results of a Randomized Controlled Study

BACKGROUND

Computer-assisted surgery (CAS) for cup placement has been developed to improve the functional results and to reduce the dislocation rate and wear after total hip arthroplasty (THA). Previously published studies demonstrated radiographic benefits of CAS in terms of implant position, but whether these improvements result in clinically important differences that patients might perceive remains largely unknown.

QUESTIONS/PURPOSES

We hypothesized that THA performed with CAS would improve 10-year patient-reported outcomes measured by validated scoring tools, reduce acetabular polyethylene wear as measured using a validated radiological method, and increase survivorship.

METHODS

Sixty patients operated on for a THA between April 2004 and April 2005 were randomized into two groups using either the CAS technique or a conventional technique for cup placement. All patient candidates for a THA with the diagnosis of primary arthritis or avascular necrosis were eligible for the CAS procedure and randomly assigned to the CAS group by the Hospital Informatics Department with use of a systematic sampling method. The patients assigned to the freehand cup placement group were matched for sex, age within 5 years, pathological condition, operatively treated side, and body mass index within 3 points. All patients were operated on through an anterolateral approach (patient in the supine position) using cementless implants. In the CAS group, a specific surgical procedure using an imageless cup positioning computer-based navigation system was performed. There were 16 men and 14 women in each group; mean age was 62 years (range, 24-80 years), and mean body mass index was 25 ± 3 kg/m(2). No patient was lost to followup at 10 years, but five patients have died (two in the CAS group and three in the control group). At the 10-year followup, an independent observer blinded to the type of technique performed patients' evaluation. Cup positioning was evaluated postoperatively using a CT scan in the two groups with results previously published. At 10 years, we assessed subjective functional outcome and quality of life using validated questionnaires (SF-12, Harris hip score [HHS], Hip injury and Osteoarthritis Outcome Score). Wear rate was then evaluated on standardized radiographs using a previously validated semiautomated computer analogic measurement method (dual circle method). Complications and survivorship were compared between groups. With our available sample size, this study had 80% power to detect a difference of 4 points out of 100 on the HHS at the p < 0.05 level.

RESULTS

With the numbers available, we found we found no differences between groups regarding HSS at last followup 95.3 ± 5.9 points (CAS group) versus 96.2 ± 4.5 points, a mean difference of 0.9 points (95% confidence interval [CI], -4.3 to 4.6; p = 0.6). There was no difference between the groups in terms of the mean (± SD) acetabular linear wear at 10 years. The mean wear was 0.71 ± 0.6 mm in the CAS group versus 0.77 ± 0.52 mm in the control group, a mean difference of 0.06 mm (95% CI, -0.1 to 0.2; p = 0.54). With the numbers available, there was no difference between the CAS group and the conventional THA groups in terms of survivorship free from aseptic loosening (100%; 95% CI, 100%-95%, versus 100%; 95% CI, 100%-94%; p = 0.3).

CONCLUSIONS

Our observations suggest that CAS used for cup placement does not confer any substantial advantage in function, wear rate, or survivorship at 10 years after THA. Because CAS is associated with added costs and surgical time, future studies need to identify what clinically relevant advantages it offers, if any, to justify its continued use in THA.

LEVEL OF EVIDENCE

Level II, therapeutic study.

ACETABULAR COMPONENT ORIENTATION IN TOTAL HIP ARTHROPLASTY: THE ROLE OF ACETABULAR TRANSVERSE LIGAMENT

Objective:

The aim of our study is to present the benefit of using the transvers acetabular ligament for intraoperative determination of the anteversion of acetabular component.

Methods:

Twenty-one total hip arthroplasties were performed. The transverse acetabular ligament was identified and used as a guide to position the acetabular component.

Results:

The mean anteversion angle was 16.9. None of the patients studied sustained a postoperative dislocation during this short follow-up period.

Conclusion:

We conclude from this preliminary study that the transverse acetabular ligament can aid positioning of the acetabular component of a THR. It defines the version of the acetabular component without the need for external instrumentation, and is independent of the position of the patient. Level of Evidence IV; Prospective Study.

Preoperative planning for implant placement with consideration of pelvic tilt in total hip arthroplasty: postoperative efficacy evaluation

Background

In total hip arthroplasty (THA), tilting of the pelvis alters the cup placement angles. Thus, the cup angles need to be planned with consideration of the effects of pelvic tilt. In the present study, we evaluated the efficacy of preoperative planning for implant placement with consideration of pelvic tilt in THA, and the accuracy of a CT-based computer navigation for implant positioning.

Methods

We examined 75 hips of 75 patients who underwent THA and were followed-up for one year postoperatively. The patients were divided into three groups (anterior, intermediate, posterior tilt) according to their preoperative pelvic tilt. Preoperative planning for implant placement was made with consideration of pelvic tilt and a CT-based navigation was used to execute the preoperative planning. Cup inclination, cup anteversion, and combined anteversion (CA) in supine and standing positions were examined 1 year after THA. The accuracy of the computer navigation was also examined.

Results

Mean CA was 35.0 ± 5.8° in supine position and 39.3 ± 5.7° in standing position. CA did not differ among the three subgroups (anterior, intermediate, posterior tilt) in either supine or standing position, indicating implant placements to be equally effective. The desired CA (37.3°) was midway between those in supine and standing positions for each subgroup. Respective mean absolute errors between preoperative planning and postoperative CT measurement was 5.3 ± 5.2° for CA.

Conclusion

We obtained favorable THA results with preoperative planning with consideration of pelvic tilt by demonstrating supine and standing CA to be unaffected by preoperative pelvic tilt one year postoperatively. Mean absolute error of CA between preoperative planning and postoperative measurement was 5° with use of the CT-based navigation.

Visual intraoperative estimation of range of motion is misleading in minimally invasive total hip arthroplasty

INTRODUCTION

Generally range of motion (ROM) in total hip arthroplasty (THA) is intraoperatively assessed by eye. Can we assume that visual estimation of ROM is reliable?

METHODS

60 patients underwent cementless THA in a subgroup analysis of a clinical prospective trial using a minimally invasive anterolateral approach in lateral decubitus position. Four experienced surgeons intraoperatively estimated ROM visually by assessment of the femur relative to the alignment of the patient's pelvis. These estimations were compared with computer navigation measurements.

RESULTS

We found a mean difference between navigation measurements and intraoperative estimations by eye of -5.6° (±10.9°; -17° to 30°) for flexion, respectively, -0.4° (±10.7°; -24° to 30°) for extension, 8.7° (±9.0°; -10° to 34°) for abduction, 5.9° (±18.3°; -58° to 68°) for external rotation and -5.8° (±12.1°; -38° to 22°) for internal rotation. Multivariate analysis showed no association between the visual accuracy of estimation of ROM and patient characteristics, such as BMI, sex, grade of osteoarthritis and treatment side except for a significant correlation of visual accuracy of estimation of extension and the level of professional experience. Otherwise, the level of professional experience had no impact on the accuracy of estimation of ROM by eye.

CONCLUSIONS

Even the experienced surgeon's intraoperative estimation of ROM by eye is not reliable and differs up to 30° compared to objective measurements in minimally invasive THA. For accurate intraoperative assessment of ROM, the use of technical devices is recommended.

TRIAL REGISTRATION

DRKS00000739.

The Transverse Acetabular Ligament as an Intraoperative Guide to Cup Abduction

BACKGROUND

The success of a total hip arthroplasty relies on optimal acetabular cup placement to ensure mating of the femoral head and acetabular cup throughout all positions of the hip joint. Poor cup placement is associated with dislocation, impingement, microseparation, component loosening, and accelerated wear due to rim loading. This study examined a novel method of using the transverse acetabular ligament (TAL) to guide cup inclination during primary total hip arthroplasty.

METHODS

A descriptive study using 16 hips from 9 cadavers. A computer navigation system measured inclination and version of the acetabular component in 3 positions with the lower edge of cup: (1) flush with, (2) 5 mm proximal to, and (3) 5 mm distal to free border of the TAL.

RESULTS

The median inclination angles were 44° in position (1), 30° in position (2), and 64° in position (3). The median anteversion angle for all positions was 19°.

CONCLUSION

Cup inclination was acceptable when the lower edge of the cup was flush or within 5 mm proximal to the TAL.

Late Anterior Dislocation Due to Posterior Pelvic Tilt in Total Hip Arthroplasty

Background:

Excessive pelvic tilt may be one of the factors leading to instability in total hip arthroplasty (THA), even when the acetabular cup is placed properly. To our knowledge, only a few studies have described late anterior dislocation due to posterior pelvic tilt. We present 3 cases with late anterior dislocations possibly due to posterior pelvic tilt.

Cases Presentations:

Case-1: An 84-years-old woman fell and presented with an anterior dislocation 12-years after THA. Her pelvis had tilted to approximately 30° posteriorly in a supine position. After conservative treatment, she presented with 10 recurrent anterior dislocations. She had thoracolumbar kyphosis due to multiple compression fractures. Revision with anterior placement of an elevated liner and a 32-mm head corrected the dislocation, and no further dislocations occurred.

Case-2: A 78-years-old woman fell and presented with an anterior dislocation 4-years after THA. Her posterior pelvic tilt had increased 23° due to a lumbar compression fracture. Revision by decreasing the cup anteversion was performed, but recurrent posterior dislocations occurred. Owing to her worsened general condition, further treatment was abandoned.

Case-3: A 79-years-old woman twisted her body and presented an anterior dislocation 3-years after THA. After manual reduction and conservative treatment, the dislocation recurred. Her posterior pelvic tilt had increased 16°.

Conclusion:

Although minor trauma triggered the anterior instability in these patients, the underlying pathomechanism existed in the progressive pelvic posterior tilt due to thoracolumbar kyphosis. As longer life expectancy as well as implant survivorship is predicted, attention must be paid to the change of pelvic tilt in elderly patients.

EOS-based cup navigation: Randomised controlled trial in 78 total hip arthroplasties

BACKGROUND

Minimising the risk of cup implantation outside the safe zone is among the objectives of navigation during total hip arthroplasty (THA). However, given the technical challenges raised by navigation when the patient is lying on the side, many surgeons still use the freehand technique. We conducted a randomised controlled trial to evaluate the new navigation system NAVEOS in the iliac plane, which is easily identified in the lateral decubitus position, with the objective of determining whether NAVEOS navigation decreased the frequency of cup implantation outside the safe zone compared to freehand cup positioning, without increasing the operative time or the frequency of complications.

HYPOTHESIS

NAVEOS navigation decreases the frequency of cup positioning outside the safe zone compared to freehand positioning.

MATERIAL AND METHODS

This randomised controlled trial compared cup positioning using NAVEOS navigation versus the freehand technique in patients undergoing primary THA. The safe zone was defined according to Lewinnek as 15±10° of radiological anteversion and 40±10° of radiological inclination. Cup position parameters were measured on computed tomography images obtained 3months after THA. The images were read by two independent observers who were blinded to group assignment. The primary evaluation criterion was cup position within the safe zone.

RESULTS

A 1:1 randomisation scheme was used to assign 78 patients (mean age, 68years; age range, 44-91years) to NAVEOS navigation or freehand cup positioning. The two groups were comparable for age, gender distribution, body mass index, and preoperative functional scores. In the NAVEOS group, navigation was discontinued prematurely in 6 patients, because of technical difficulties (n=2) or a marked discrepancy with clinical findings (n=4); however, the intention-to-treat approach was used for the analysis. The proportion of cups in the safe zone was 67% (28/39) in the NAVEOS group and 38% (17/39) in the freehand group (P=0.012). Anteversion was within the 5-25° range for 72% (28/39) cups in the NAVEOS group and 46% (18/39) in the freehand group (P=0.021). Inclination was within the 30-50° range for 95% (37/39) of cups with NAVEOS navigation and 85% (33/39) with freehand positioning (P=0.135). The odds ratio for cup implantation outside the safe zone was significantly lower with NAVEOS compared to freehand positioning (0.54; 95% confidence interval, 0.31-0.91). Mean operative time was 74 (range, 45-115) minutes with NAVEOS navigation and 70 (range, 40-105) minutes with freehand positioning (P=0.382). Complications consisted of 1 case each of anterior dislocation and infection, both in the freehand group.

DISCUSSION

Compared to freehand positioning, NAVEOS navigation significantly lowered the risk of cup positioning outside the safe zone, chiefly via improved achievement of the anteversion target. NAVEOS was not associated with increases in operative time or morbidity.

LEVEL OF EVIDENCE

II, randomised controlled trial with limited statistical power.

Pelvic orientation for total hip arthroplasty in lateral decubitus: can it be accurately measured?

INTRODUCTION

During total hip arthroplasty (THA), accurately predicting acetabular cup orientation remains a key challenge, in great part because of uncertainty about pelvic orientation. This pilot study aimed to develop and validate a technique to measure pelvic orientation; establish its accuracy in the location of anatomical landmarks and subsequently; investigate if limb movement during a simulated surgical procedure alters pelvic orientation.

METHODS

The developed technique measured 3-D orientation of an isolated Sawbone pelvis, it was then implemented to measure pelvic orientation in lateral decubitus with post-THA patients (n = 20) using a motion capture system.

RESULTS

Orientation of the isolated Sawbone pelvis was accurately measured, demonstrated by high correlations with angular data from a coordinate measurement machine; R-squared values close to 1 for all pelvic axes. When applied to volunteer subjects, largest movements occurred about the longitudinal pelvic axis; internal and external pelvic rotation. Rotations about the anteroposterior axis, which directly affect inclination angles, showed &gt;75% of participants had movement within ±5° of neutral, 0°.

CONCLUSIONS

The technique accurately measured orientation of the isolated bony pelvis. This was not the case in a simulated theatre environment. Soft tissue landmarks were difficult to palpate repeatedly. These findings have direct clinical relevance, landmark registration in lateral decubitus is a potential source of error, contributing here to large ranges in measured movement. Surgeons must be aware that present techniques using bony landmarks to reference pelvic orientation for cup implantation, both computer-based and mechanical, may not be sufficiently accurate.

Accuracy of Component Placement in Robotic-Assisted Total Hip Arthroplasty

Robotic-assisted total hip arthroplasty (THA) is a recent platform introduced to decrease the risk of malpositioned components. The goals of this study were to determine whether intraoperative data on robotic-assisted THA acetabular component position accurately predict postoperative radiographic acetabular component position and to determine whether intraoperative data on robotic-assisted THA leg length and offset accurately predict postoperative radiographic leg length and offset data. In 146 patients, pre- and postoperative radiographs and intraoperative component measurements were reported for acetabular inclination, anteversion, leg length change, and offset change. Component position obtained by the robotic system and radiographic data were compared with subgroup analysis for the posterior and direct anterior approaches. The average difference between groups was 3.3°±3.1° for inclination, 2.9°±2.3° for anteversion, 3.0±2.3 mm for leg length change, and 4.0±3.1 mm for change in global offset. Correlation between the robotic system and postoperative radiographs was within 10° for 95.9% of cases for inclination and 99.3% for anteversion. Posterior approach correlation was within 10° for 97.1% of cases for inclination and 100% for anteversion. Anterior approach correlation was within 10° for 92.7% of cases for inclination and 97.6% for anteversion. Intraoperative data on component position obtained from the robotic system compared well with radiographic data on component position. Surgeons must remain vigilant to ensure outliers related to robotic system malfunction do not occur. [Orthopedics. 2016; 39(3):193-199.].

Initial Results of an Acetabular Center Axis Registration Technique in Navigated Hip Arthroplasty with Deformed Acetabular Rims

Background

In cementless total hip arthroplasty, imageless computer-assisted navigation is usually used to register the anterior pelvic plane (APP). The accuracy of this method is influenced by the subcutaneous tissues overlying the registration landmarks. On the other hand, the acetabular center axis (ACA) is determined from the acetabular rim. Precise registration of the ACA is possible because of direct palpation using a pointer. Imageless navigation using the ACA usually targets patients with normal acetabular morphology. The aim of this study was to investigate the accuracy of imageless navigation using the ACA instead of the APP in patients with normal or deformed acetabular rims.

Methods

The intraoperative cup position was compared with that obtained from the postoperative computed tomography (CT) images in 18 cases.

Results

The inclination angle derived from the navigation system was 3.4 ± 5.3 degrees smaller and the anteversion angle was 1.4 ± 3.1 degrees larger than those derived from the CT images.

Conclusion

The inclination cup angle of the navigation system was significantly inferior to the true value, particularly in cases with large anterior osteophytes.

The current status and future prospects of computer-assisted hip surgery

The advances in computer assistance technology have allowed detailed three-dimensional preoperative planning and simulation of preoperative plans. The use of a navigation system as an intraoperative assistance tool allows more accurate execution of the preoperative plan, compared to manual operation without assistance of the navigation system. In total hip arthroplasty using CT-based navigation, three-dimensional preoperative planning with computer software allows the surgeon to determine the optimal angle of implant placement at which implant impingement is unlikely to occur in the range of hip joint motion necessary for daily activities of living, and to determine the amount of three-dimensional correction for leg length and offset. With the use of computer navigation for intraoperative assistance, the preoperative plan can be precisely executed. In hip osteotomy using CT-based navigation, the navigation allows three-dimensional preoperative planning, intraoperative confirmation of osteotomy sites, safe performance of osteotomy even under poor visual conditions, and a reduction in exposure doses from intraoperative fluoroscopy. Positions of the tips of chisels can be displayed on the computer monitor during surgery in real time, and staff other than the operator can also be aware of the progress of surgery. Thus, computer navigation also has an educational value. On the other hand, its limitations include the need for placement of trackers, increased radiation exposure from preoperative CT scans, and prolonged operative time. Moreover, because the position of a bone fragment cannot be traced after osteotomy, methods to find its precise position after its movement need to be developed. Despite the need to develop methods for the postoperative evaluation of accuracy for osteotomy, further application and development of these systems are expected in the future.

Computer-Assisted Orthopedic Surgery: Current State and Future Perspective

Introduced about two decades ago, computer-assisted orthopedic surgery (CAOS) has emerged as a new and independent area, due to the importance of treatment of musculoskeletal diseases in orthopedics and traumatology, increasing availability of different imaging modalities, and advances in analytics and navigation tools. The aim of this paper is to present the basic elements of CAOS devices and to review state-of-the-art examples of different imaging modalities used to create the virtual representations, of different position tracking devices for navigation systems, of different surgical robots, of different methods for registration and referencing, and of CAOS modules that have been realized for different surgical procedures. Future perspectives will also be outlined.

Accuracy of Component Positioning in 1980 Total Hip Arthroplasties: A Comparative Analysis by Surgical Technique and Mode of Guidance

The purpose of this multi-surgeon study was to assess and compare the accuracy of acetabular component placement, leg length discrepancy (LLD), and global offset difference (GOD) between six different surgical techniques and modes of guidance in total hip arthroplasty (THA). A total of 1980 THAs met inclusion criteria. Robotic- and navigation-guided techniques were more consistent than other techniques in placing the acetabular cup into Lewinnek's safe zone (P<0.005 and P<0.05, respectively). Robotic-guided surgery was more consistent than other techniques in placing the acetabular component within Callanan's safe zone (P<0.005). No statistically significant differences were found between groups in the frequency of patients with excessive LLD. Clinically significant differences between groups were not found in the frequency of patients with excessive GOD. Level of Evidence: IV.

Pelvic tilt and movement during total hip arthroplasty in the lateral decubitus position

OBJECTIVES

Total hip arthroplasty (THA) is often performed in the lateral decubitus (lateral) position. In this position, the pelvis may have various degrees of tilt leading to implant malposition. We sought to quantify the pelvic tilt in lateral position and further pelvic movement during surgery.

METHODS

In 95 cases with primary THA, three-dimensional pelvic tilts were quantified by superimposing images reconstructed from CT data onto antero-posterior radiographs taken in lateral position at set-up and after cup placement. Pelvises were fixed with a device compressing anterior superior iliac spines and sacrum.

RESULTS

Various degrees of pelvic tilt occurred compared to the supine position; sagittal: -3.1° (-25.5° to 10.2°), axial: 3.9° (-8.4° to 17°), coronal: 0.9° (-11.9° to 13.2°). Absolute changes more than 5° were observed 43%, 47%, and 12% in the sagittal, axial, and coronal planes, respectively. The more preoperative posterior pelvic tilt resulted in the more change in the sagittal plane. Further pelvic movement of about 3° in three planes were observed ranging from -11° to 20° after cup placement.

CONCLUSION

This study showed various pelvic tilt and movement during THA. As pelvic tilt directly alters the cup orientation, its changes should be well understood. Improved tools for positioning and holding the pelvis are required.

Fluctuation of Cup Orientation During Press-Fit Insertion: A Possible Cause of Malpositioning

We evaluated real-time angular changes during press-fit cup insertion in 70 total hip arthroplasties. Inclination and anteversion cup angles on navigation system were recorded after each procedure of five hammer blows during cup insertion, and maximum deviated inclination (MDI) and anteversion (MDA) angles until the cup was fully seated were measured. We found 1 (1%) and 29 (41%) hips with increases and decreases in MDI of 5° or more, and 13 (19%) and 6 (8%) hips with increases and decreases in MDA of 5° or more, respectively. The MDI in men was significantly lower and the MDA for left-side surgery was significantly higher. Surgeons should pay attention to fluctuation in angular changes during cup insertion and may consider countermeasures to minimize cup malpositioning.

The Accuracy of a Mechanical Cup Alignment Guide in Total Hip Arthroplasty (THA) Through Direct Anterior and Posterior Approaches Measured with CT-Based Navigation

The purpose of this study was to compare the accuracy of a mechanical cup alignment guide using CT-based navigation between a direct anterior approach (DAA) in both supine and lateral positions and a posterior approach (PA) in the lateral position. A trial cup was placed with a mechanical guide that aimed at 47° of radiographic inclination and 14° of anteversion. The average cup inclination and anteversion were measured using CT-based navigation. The average radiographic anteversion in the DAA supine and lateral group was larger, and that in the PA group was smaller than the target angle. In conclusion, there are no differences in the accuracy or precision of cup angles among the DAA supine, DAA lateral position, and PA groups using a mechanical guide.

Imageless navigation versus traditional method in total hip arthroplasty: A meta-analysis

PURPOSE

Accuracy of acetabular component orientation is improved with computer navigation in THA. In recent years, imageless navigation has become more commonplace, whereas there still exist different arguments about this technique.

METHODS

We conducted a meta-analysis to assess the accuracy of imageless navigation for acetabular implantation in total hip arthroplasty. The computer based online search strategy covered the major medical databases (Cochrane Library, Medline, Pubmed, and EmbaseI) from January 2004 to December 2014. Data of selected clinical trials were analysed using Revman 5.1 software.

RESULTS

7 clinical trials enrolling 485 patients were included. Mean cup inclination and anteversion were not statistically significantly different between the conventional groups and the imageless computer navigated groups (P = 0.83 and P = 0.89 respectively). Deviation from the desired position of inclination shows no significant differences (P = 0.06), whereas deviation from the desired position of anteversion was smaller in computer navigated group (P<0.0001). Only one study gave useful information about operation time which is significantly increased (MD = 23.00, P = 0.001).

CONCLUSIONS

Current literature generally hold the opinion that navigation is a reliable tool to optimize cup placement, but still there are some different voices about imageless navigation system. This meta-analysis emphasizing more on the accuracy of cup-positioning with imageless navigation reveals that imageless navigation is preferable compared with traditional method.

The difference between the radiographic and the operative angle of inclination of the acetabular component in total hip arthroplasty: use of a digital protractor and the circumference of the hip to improve orientation

A high radiographic inclination angle (RI) contributes to accelerated wear and has been associated with dislocation after total hip arthroplasty (THA). With freehand positioning of the acetabular component there is a lack of accuracy, with a trend towards a high radiographic inclination angle. The aim of this study was to investigate whether the use of a digital protractor to measure the operative inclination angle (OI) could improve the positioning of the acetabular component in relation to a 'safe zone'. We measured the radiographic inclination angles of 200 consecutive uncemented primary THAs. In the first 100 the component was introduced freehand and in the second 100 a digital protractor was used to measure the operative inclination angle. The mean difference between the operative and the radiographic inclination angles (∆RI-OI) in the second cohort was 12.3° (3.8° to 19.8°). There was a strong correlation between the circumference of the hip and ∆RI-OI. The number of RI outliers was significantly reduced in the protractor group (p = 0.002). Adjusting the OI, using a digital protractor and taking into account the circumference of the patient's hip, improves the RI significantly (p < 0.001) and does not require additional operating time.

Utility of Preoperative Femoral Neck Geometry in Predicting Femoral Stem Anteversion

This study investigated the relationships between the preoperative femoral anteversions and the femoral stem anteversion using CT scans and CT-based 3D models to determine whether any preoperative anteversion measurement correlates with the postoperative stem anteversion. Pre-operative and post-operative CT scans of 19 hips with THAs were evaluated. Five preoperative anatomical femoral anteversion measurements (CT-Head, CT-Below Head, CT-Neck, 3D-Head, and 3D-Neck) were compared with the postoperative femoral stem anteversion. The preoperative CT-Neck anteversion measurement was most correlated with the postoperative stem anteversion (r=0.761, P=0.002) with the narrowest ranges of the differences (-10.2° to 11.0°). The preoperative anteversions using the femoral neck geometry from CT scans can be used for the estimation of the postoperative femoral stem anteversion in THA.

Acetabular component navigation in lateral decubitus based on EOS imaging: A preliminary study of 13 cases

INTRODUCTION

Acetabular component navigation classically requires palpation of the bone landmarks defining the anterior pelvic plane (APP) (anterior superior iliac spine [ASIS] and pubis), the recording of which is not very reliable when performed in lateral decubitus. The objectives of the current experimental study were: (1) to assess the clinical feasibility of NAVEOS navigation (based on EOS imaging) in lateral decubitus; and (2) to compare precision versus classical APP-based navigation (NAVAPP).

HYPOTHESIS

Iliac plane navigation using EOS is as reliable as APP navigation.

PATIENTS AND METHODS

A continuous prospective series of 13 total hip replacements were implanted in lateral decubitus under APP-guided navigation (NAVAPP). Planning used preoperative EOS measurement. The ASIS, pubis and ipsilateral posterior superior iliac spine (PSIS) were located and exported to the navigator. Intra-operatively, NAVEOS landmarks (acetabular center, ASIS and PSIS on the operated side) were palpated. Postoperatively, cup inclination and anteversion with respect to the APP were measured on EOS imaging (SterEOS3D software). The SterEOS3D measurements were compared to those of the performed NAVAPP and simulated NAVEOS navigations.

RESULTS

Three patients were excluded for technical reasons. In the remaining 10, inclination on NAVAPP and SterEOS3D differed by a median 4° (range, 0-12°), and on NAVEOS versus SteEOS3D by 5° (range, 2-10°); anteversion on NAVAPP and SterEOS3D differed by a median 4.5° (range, 0-12°), and on NAVEOS versus SteEOS3D by 4° (range, 0-14°).

CONCLUSION

Precision was comparable between NAVEOS and classical navigation. NAVEOS simplifies cup navigation in lateral decubitus on initial acquisition. These results require validation on a larger sample.

The impact of standard combined anteversion definitions on gait and clinical outcome within one year after total hip arthroplasty

PURPOSE

Different target areas within the concept of combined cup and stem anteversion have been published for total hip arthroplasty (THA). We asked whether component positioning according to eight standard combined anteversion rules is associated with (1) more physiological gait patterns, (2) higher improvement of gait variables and (3) better clinical outcome after THA.

METHODS

In a prospective clinical study, 60 patients received cementless THA through an anterolateral MIS approach in a lateral decubitus position. Six weeks postoperatively, implant position was analysed using 3D-CT by an independent external institute. Preoperatively, six and 12 months postoperatively range of motion, normalized walking speed and hip flexion symmetry index were measured using 3D motion-capture gait analysis. Patient-related outcome measures (HHS, HOOS, EQ-5D) were obtained by an observer blinded to 3D-CT results. Eight combined anteversion definitions and Lewinnek's "safe zone" were evaluated regarding their impact on gait patterns and clinical outcome.

RESULTS

Combined cup and stem anteversion according to standard combined anteversion definitions as well as cup placement within Lewinnek's "safe zone" did not influence range of motion, normalized walking speed and/or hip flexion symmetry index six and 12 months after THA. Similarly, increase of gait parameters within the first year after THA was comparable between all eight combined anteversion rules. Clinical outcome measures like HHS, HOOS and EQ-5D did not show any benefit for either of the combined anteversion definitions.

CONCLUSIONS

Standard combined cup and stem anteversion rules do not improve postoperative outcome as measured by gait analysis and clinical scores within one year after THA.

Does haptic robot-assisted total hip arthroplasty better restore native acetabular and femoral anatomy?

BACKGROUND

The objective was to evaluate whether total hip arthroplasty (THA) using haptic robot assistance restores hip geometry better than the free-hand technique.

METHODS

Twelve robot-assisted and 14 free-hand unilateral THA patients underwent CT scan for three-dimensional (3D) hip models. The anteversion, inclination and hip joint centre locations of the native and implanted hips in each patient were quantified and compared.

RESULTS

Significant increase of combined anteversion by 19.1 ± 11.7° and 23.5 ± 23.6° and decrease of cup inclination by 16.5 ± 6.0° and 10.2 ± 6.8° were observed in the robot-assisted and the free-hand THAs, respectively. Less variation in the difference of the component orientations (max 11.1 vs 18.3°) and the femoral head centre (max 4.5 vs 6.3 mm) were found in the robot-assisted group.

CONCLUSION

This study demonstrated that neither robot-assisted nor free-hand THAs had fully restored native hip geometry. However, the higher precision of the robot-assisted THA suggested that it has potential utility in restoring the native hip geometry. Copyright © 2015 John Wiley & Sons, Ltd.