Is Combined Anteversion Equally Affected by Acetabular Cup and Femoral Stem Anteversion?

The accuracy of a patient-specific femoral planning and delivery system for total hip arthroplasty

INTRODUCTION

A primary objective when performing a total hip arthroplasty (THA) is to restore hip biomechanics in accordance with a chosen surgical plan. The aim of this study was to assess the accuracy of a 3D-printed patient-specific guide for delivering a planned femoral osteotomy for both a posterior and an anterior approach.

METHODOLOGY

40 patients (20 anterior and 20 posterior) scheduled for THA received a preoperative work-up allowing for patient-specific implant sizing and positioning. Following surgeon confirmation, a patient-specific guide was designed and printed, enabling the desired osteotomy to be executed. Achieved osteotomies were assessed using commercially available software platforms. Planning accuracy was also assessed using both the planning platform as well as more traditional 2D-templating techniques.

RESULTS

The mean deviation between the planned and achieved osteotomy level was -0.6 mm (range -4.1-6.4 mm). 95% of the achieved osteotomy levels were within 3 mm of the plan for both the posterior and anterior approach groups. 70% of the Optimized Positioning System (OPS) planned femoral components were the exact size as planned versus 25% of the 2D-planned components. 98% of the OPS planned femoral components were within 1 size of plan versus 58% for the 2D-planned components. No sizing accuracy difference was observed between planning approaches (p = 0.70).

CONCLUSIONS

A patient-specific osteotomy guide can be a simple and accurate method to reproduce a planned femoral neck resection through an anterior or posterior approach. Further, 3D planning appears to more accurately predict femoral sizing in THA than more conventional 2D methods.

Relating total hip replacement and acetabular cup positioning with outcome: A systematic review

The diverse methodologies employed in assessing cup placement, delineate the recommended target zones for positioning and examine the correlation between cup positioning and occurrences of complications is of interest. We included 51,308 patients and 51,692 hips for this analysis. The overall complication rate was 22.2%. Patients, overall, demonstrated improved outcomes, as evidenced by postoperative hip scores. Two "safe windows" have been defined for surgical procedures: 1) an inclination of 35-50 degrees and an anteversion of 5-25 degrees and 2) an inclination of 35-50 degrees and an anteversion of 15-25 degrees.

How Do Changes in Femoral Anteversion Impact Femoral Rotation and Anterior Offset After Total Hip Arthroplasty?

BACKGROUND

The impact of femoral anteversion changes on femoral rotation and anterior offset following total hip arthroplasty (THA) has not been well studied. This study therefore investigated the relationship among femoral anteversion, anterior offset, and femoral rotation before and after THA.

METHODS

There were 995 patients who had staged primary bilateral THAs who received a preoperative supine computerized axial tomography (CT) scan, following a standardized protocol, for surgical planning prior to each THA. The following measurements were performed for the first operative hip preoperatively and postoperatively on the first and second CT scans, respectively: femoral anatomic anteversion, defined as the angle between the native femoral neck or stem neck axis and the posterior condylar axis; femoral rotation, defined as the angle of the posterior condylar axis relative to the coronal plane of the CT; and femoral anterior offset, defined as the shortest distance between the femoral head center and a femoral plane containing the epicondyles and the piriformis fossa. The mean time between imagings was 11 months (range, 2 to 44). Associations are described using linear regression (β = slope) and Pearson correlation (r) coefficients. A t distribution was used for testing correlation.

RESULTS

Femoral anteversion correlated with femoral anterior offset preoperatively (β = 0.565, r = 0.914, P < 0.001) and postoperatively (β = 0.671, r = 0.958, P < 0.001), and with femoral rotation preoperatively (β = 0.623, r = 0.575, P < 0.001) and postoperatively (β = 0.459, r = 0.517, P < 0.001). Increasing anteversion from preoperatively to postoperatively increased anterior offset (β = 0.621, r = 0.908, P < 0.001) and femoral internal rotation (IR) (β = 0.241, r = 0.273, P < 0.001). Patients who had >20° increase in anteversion (mean increase 26°, range 20 to 40.5°, n = 71) had a mean increase in femoral IR of 9.6 ± 9.8°.

CONCLUSIONS

Increasing femoral anteversion increases anterior offset and IR of the femur, with approximately a 1° increase in IR for every 4° increase in anteversion on average. Surgeons should appreciate the implications of changing anteversion during THA planning.

Decreased "Polar Axis Angle" is Associated With Instability After Total Hip Arthroplasty: A New Method to Assess Functional Component Position on Lateral-Seated Radiographs

BACKGROUND

Research on hip instability has focused on establishing "safe" ranges of combined component position in supine posture or functional placement of the acetabular component based on the hip-spine relationship. A new angle, the polar axis angle (PAA), of the total hip arthroplasty (THA) components describes the concentricity of both components and can be evaluated in functional positions that confer a greater risk of instability (ie, sitting). The goal of this study was to compare the PAA in functional positions between patients who experienced a postoperative dislocation and a matched control group who did not have a dislocation.

METHODS

An institutional database was searched for patients experiencing a dislocation after primary THA. Patients who had postoperative full-length standing and lateral-seatedradiographs were included in the dislocator group. A control group of nondislocator patients was matched 2:1 by age, body mass index, sex, and hip-spine classification. Radiographic measurements of the neck angle, acetabular ante-inclination, and PAA were performed by 2 separate blinded, trained reviewers.

RESULTS

The lateral-seated neck angle and lateral-seated PAA measurements were significantly lower in the dislocator groups (n = 37) than the control group (n = 74) (23 versus 33 degrees, P < .001; 74 versus 83 degrees, P = .012, respectively). Significant differences were also observed in changes in the polar axes and neck angles between standing and seated positions (P < .001 and P < .001, respectively). When comparing patients who have mobile spines versus stiff spines within the dislocator group, there were no differences in the acetabular, neck, or PAAs. The effect of neck angle on the PAA showed a linear trend across cohorts.

CONCLUSIONS

Patients who experience postoperative instability have a significantly lower PAA on lateral-seated radiographs when matched for age, sex, body mass index, and hip-spine classification. In addition, the lower seated PAA is driven more strongly by decreased functional femoral anteversion, which emphasizes the role of functional femoral version on stability in THA.

Total Hip Arthroplasty With Subtrochanteric Osteotomy for Crowe IV Dysplasia Using an Extensile Direct Anterior Approach: A Surgical Technique

The direct anterior approach (DAA) has been increasing in popularity for primary total hip arthroplasty (THA). Despite previously documented anatomic limitations to its direct distal extension, alternative exposure methods have been described to safely access the femoral diaphysis and facilitate increasingly complex primary and revision THA scenarios. The DAA has several purported advantages compared to alternative approaches (eg, posterior and lateral-based), including its muscle-sparing nature, use of an internervous plane, and preservation of posterior stabilizing structures. Proponents of the DAA cite decreased postoperative pain, quicker recovery times, potentially lower dislocation rates, ease of intraoperative fluoroscopy, and improved implant placement/restoration of leg lengths. The current literature, however, is sparse when considering the use of this approach in the setting of severely dysplastic hips necessitating a concurrent subtrochanteric shortening osteotomy. When utilizing a posterior approach in this population, previous work from Ollivier and colleagues demonstrated high rates of cementless implant osseointegration and significantly improved clinical outcomes at long-term follow-up. Although relatively few reports of addressing this pathology via the DAA currently exist, initial results are promising. This study seeks to provide a detailed description of a surgical technique for performing primary THA and ipsilateral subtrochanteric shortening osteotomy in this patient population utilizing an extensile DAA.

15-year survivorship of a unique dual-modular femoral stem in primary hip arthroplasty

BACKGROUND

Hip offset, version, and length are interdependent femoral variables which determine stability and leg length. Balancing these competing variables remains a core challenge in hip arthroplasty. The potential benefits of modular femoral stems have been overshadowed by higher rates of failure. The objective of this study was to assess the survivorship of a unique dual-modular femoral stem at an average 15-year follow-up period.

METHODS

The records of all patients with osteoarthritis who underwent primary total hip arthroplasty with this device between 2004-2009 were reviewed. There were no exclusions for BMI or other factors. We examined the data with Kaplan-Meier survival analysis. The primary endpoint for survival was mechanical failure of the modular neck-body junction.

RESULTS

The survivorship of this device in 172 subjects was 100% with none experiencing mechanical failure of the modular junction at an average of 15 years. 60 patients died of causes unrelated to their THA and 9 patients were lost to follow-up. There were three early (≤ 12 months) dislocations (1.7%), and seven total dislocations (4.1%). 16 patients underwent reoperations during the follow-up period, none for any complication of the modular junction. Radiographic results showed well-fixed femoral stems in all cases. There were no leg length discrepancies of greater than 10 mm, and 85% were within 5 mm.

CONCLUSION

There were no mechanical failures of the modular junction in any of the subjects over the average 15-year period, demonstrating that this dual-modular design is not associated with increased failure rates. We achieved a 1.7% early dislocation rate and a 4.1% total dislocation rate without any clinically significant leg length discrepancies.

How to Estimate Femoral Stem Anteversion During Direct Anterior Approach Total Hip Arthroplasty

Background

There are various traditional landmarks used to estimate the femoral component version, yet none are widely accepted by direct anterior surgeons. The purpose of this study was to compare bony landmarks easily accessible to direct anterior surgeons and to estimate which one provides the best estimate of femoral component anteversion.

Methods

A computed tomography database was used to identify 736 left entire-femur computed tomography scans. Seven visible anatomic landmarks were identified using a computer model in which a 45° virtual neck resection was made at 10 mm above the lesser trochanter. Thirteen axes, to reference the femoral stem position, were created between the 7 landmarks. Means and standard deviations (SDs) of angles between each axis and the transepicondylar axis (TEA) were compared for their precision.

Results

The traditional lesser trochanter predicted anteversion from the TEA was 34.1° (SD 9.7°). Predicted anteversion from the TEA was 3.3° (SD 8.1°) when aligned from the center of the canal to the middle of the medial calcar; 14.0° (SD 8.1°) from the center of the canal to the anterior 1/3 of the medial calcar; and 24.8° (SD 8.5°) from the center of the canal to the most anterior point on the medial calcar.

Conclusions

Compared to the lesser trochanter, 7 axes were more precise (lower SD) when predicting the version. Estimating the femoral component position, via simulated data, using 3 points along the medial calcar is a relatively precise and easily accessible tool for surgeons.

Cemented or uncemented fixation: Which allows a more acceptable prosthetic femoral version in total hip arthroplasty?

BACKGROUND

Three-dimensional computed-tomography (3D-CT) planning for primary Total Hip Arthroplasty (THA) typically uses the external femoral surface; as a result, it is difficult to predict the prosthetic femoral version (PFV) for uncemented femoral stems that press-fit to the internal surface of the bone. Cemented fixation allows the surgeon to adjust the version independent of the internal femoral anatomy. We aimed to better understand the effect of the fixation type on PFV.

METHODS

This was a case series study including a total of 95 consecutive patients (106 hips), who underwent uncemented (n = 81 hips) and cemented (n = 25 hips) primary THA using the posterior approach. The surgeon aimed for a PFV of 20°. Our primary objective was to compare PFV in both groups; our secondary objective was to evaluate the clinical outcomes.

RESULTS

The mean (± SD) PFV was 13° (± 9°) and 23° (± 8°) for the uncemented and cemented THA groups (P < 0.001), respectively. In the uncemented THA group, 36% of the patients had a PFV of < 10°. In the cemented THA group, this clinically important threshold dropped to 8%. Similarly, the Bland-Altman (BA) plots showed wider 95% limits of agreement for the uncemented group. Satisfactory clinical outcomes were recorded.

CONCLUSION

We found that the PFV was more clinically acceptable, for the posterior surgical approach, in the cemented group when compared to the uncemented group. Both THA groups reported high variability indicating the need to develop surgical tools to guide the PFV closer to the surgical target.

Do hip resurfacing and short hip stem arthroplasties differ from conventional hip stem replacement regarding impingement-free range of motion?

Total hip joint replacement (THR) is clinically well-established. In this context, the resulting range of motion (ROM) is crucial for patient satisfaction when performing joint movements. However, the ROM for THR with different bone preserving strategies (short hip stem and hip resurfacing) raises the question of whether the ROM is comparable with conventional hip stems. Therefore, this computer-based study aimed to investigate the ROM and type of impingement for different implant systems. An established framework with computer-aided design 3D models based on magnetic resonance imaging data of 19 patients with hip osteoarthritis was used to analyse the ROM for three different implant systems (conventional hip stem vs. short hip stem vs. hip resurfacing) during typical joint movements. Our results revealed that all three designs led to mean maximum flexion higher than 110°. However, hip resurfacing showed less ROM (-5% against conventional and -6% against short hip stem). No significant differences were observed between the conventional and short hip stem during maximum flexion and internal rotation. Contrarily, a significant difference was detected between the conventional hip stem and hip resurfacing during internal rotation (p = 0.003). The ROM of the hip resurfacing was lower than the conventional and short hip stem during all three movements. Furthermore, hip resurfacing shifted the impingement type to implant-to-bone impingement compared with the other implant designs. The calculated ROMs of the implant systems achieved physiological levels during maximum flexion and internal rotation. However, bone impingement was more likely during internal rotation with increasing bone preservation. Despite the larger head diameter of hip resurfacing, the ROM examined was substantially lower than that of conventional and short hip stem.

A novel method for evaluating combined component anteversion in total hip arthroplasty on cross-table lateral hip radiographs

INTRODUCTION

Accurate measurement of combined component anteversion (CA) is important in evaluating the radiographic outcomes following total hip arthroplasty (THA). The aim of the present study was to evaluate the accuracy and reliability of a novel radiographic method in estimating CA in THA.

MATERIALS AND METHODS

The radiographs and computer tomography of patients who underwent a primary THA were retrospectively reviewed, to measure the radiographic CA (CAr), defined as the angle between a line connecting the center of the femoral head to the most anterior rim of the acetabular cup and a line connecting the center of the femoral head to the base of the femoral head to allow a comparison with the CA measured on the CT (CACT). Subsequently, a computational simulation was performed to evaluate the effect of cup anteversion, inclination, stem anteversion, and leg rotation on the CAr and develop a formula that would correct the CAr according to the acetabular cup inclination based on the best-fit equation.

RESULTS

In the retrospective analysis of 154 THA, the average CAr_cor, and CACT were 53 ± 11° and 54 ± 11° (p > 0.05), respectively. A strong correlation was found between CAr and CACT (r = 0.96, p < 0.001), with an average bias of - 0.5° between CAr_cor and CACT. In the computational simulation, the CAr was strongly affected by the cup anteversion, inclination, stem anteversion, and leg rotation. The formula to convert the CAr to CA_cor was: CA-cor = 1.3*Car - (17* In (Cup Inclination) - 31.

CONCLUSION

The combined anteversion measurement of THA components on the lateral hip radiograph is accurate and reliable, implying that it could be routinely used postoperatively but also in patients with persistent complaints following a THA.

LEVEL OF EVIDENCE

Cross-sectional study, Level III.

Simulating movements of daily living in robot-assisted total hip arthroplasty with 3D modelling

Aims

Computer-assisted 3D preoperative planning software has the potential to improve postoperative stability in total hip arthroplasty (THA). Commonly, preoperative protocols simulate two functional positions (standing and relaxed sitting) but do not consider other common positions that may increase postoperative impingement and possible dislocation. This study investigates the feasibility of simulating commonly encountered positions, and positions with an increased risk of impingement, to lower postoperative impingement risk in a CT-based 3D model.

Methods

A robotic arm-assisted arthroplasty planning platform was used to investigate 11 patient positions. Data from 43 primary THAs were used for simulation. Sacral slope was retrieved from patient preoperative imaging, while angles of hip flexion/extension, hip external/internal rotation, and hip abduction/adduction for tested positions were derived from literature or estimated with a biomechanical model. The hip was placed in the described positions, and if impingement was detected by the software, inspection of the impingement type was performed.

Results

In flexion, an overall impingement rate of 2.3% was detected for flexed-seated, squatting, forward-bending, and criss-cross-sitting positions, and 4.7% for the ankle-over-knee position. In extension, most hips (60.5%) were found to impinge at or prior to 50° of external rotation (pivoting). Many of these impingement events were due to a prominent ischium. The mean maximum external rotation prior to impingement was 45.9° (15° to 80°) and 57.9° (20° to 90°) prior to prosthetic impingement. No impingement was found in standing, sitting, crossing ankles, seiza, and downward dog.

Conclusion

This study demonstrated that positions of daily living tested in a CT-based 3D model show high rates of impingement. Simulating additional positions through 3D modelling is a low-cost method of potentially improving outcomes without compromising patient safety. By incorporating CT-based 3D modelling of positions of daily living into routine preoperative protocols for THA, there is the potential to lower the risk of postoperative impingement events.

The Current Proposed Total Hip Arthroplasty Surgical Planning Guidelines Based on Classification of Spine Stiffness May be Flawed Due to Incorrect Assumptions

BACKGROUND

The available classifications and preoperative planning tools for total hip arthroplasty assume that: 1) there is no variation in the sagittal pelvic tilt (SPT) if the radiographs are repeated, and 2) there is no significant change in the postoperative SPT postoperatively. We hypothesized that there would be significant differences in postoperative SPT tilt as measured by the sacral slope, thus rendering the current classifications and tools flawed.

METHODS

This study was a multicenter, retrospective analysis of preoperative and postoperative (1.5-6 months) full-body imaging of 237 primary total hip arthroplasty (standing and sitting positions). Patients were categorized as 1) stiff spine (standing sacral slope sitting sacral slope < 10°) and 2) normal spine (standing sacral slope-sitting sacral slope ≥ 10°). Results were compared using the paired t-test. The posthoc power analysis showed a power of 0.99.

RESULTS

The difference in mean standing and sitting sacral slope between the preoperative and postoperative measurements was 1°. However, in standing position, this difference was more than 10° in 14.4% of patients. In the sitting position, this difference was more than 10° in 34.2% of patients and more than 20° in 9.8% of patients. Postoperatively, 32.5% of patients switched groups based on the classification, which rendered the preoperative planning suggested by the current classifications flawed.

CONCLUSION

Current preoperative planning and classifications are based on a single acquisition of preoperative radiographs without the incorporation of possible postoperative changes in SPT. Validated classifications and planning tools should incorporate repeated measurements to determine the mean and variance in SPT and consider the significant postoperative changes in SPT.

A Comparison of Radiographic Outcomes after Total Hip Arthroplasty between the Direct Lateral Approach and Posterior Lateral Approach with EOS 2D/3D X-Ray Imaging System

OBJECTIVE

The classical approaches for total hip arthroplasty (THA) are the direct lateral approach (DLA) and posterior lateral approach (PLA). There are few studies comparing implant orientation with these two approaches, and the impact of surgical approaches on implant orientation remains controversial. With the rise of the EOS imaging system, we aimed to use it to identify the differences between and factors associated with implant orientation after THA using DLA and PLA.

METHODS

In our department from January 2019 to December 2021, 321 primary unilateral THAs that used PLA and DLA were enrolled. A total of 201 patients who received PLA and 120 patients who received DLA were included in this study. Two blinded observers measured each case using EOS imaging data. Postoperative imaging metrics and other relevant influencing factors of the two surgical approaches were compared. Postoperative imaging metrics, including the anteversion and inclination of the cup, anteversion of the stem, and combined anteversion were measured based on EOS. Other relevant influencing factors included age, approach, gender, laterality, BMI, anterior pelvic plane inclination, femoral head diameter, femoral offset, lateral pelvic tilt, pelvic incidence, pelvis axial rotation, sacral slope, sagittal pelvic tilt, and surgery time. Multiple linear regression analyses were performed to identify the predictors of acceptability for each imaging data point.

RESULTS

No dislocation was found in the 321 patients who underwent primary THA during this period. The mean anteversion and combined anteversion of the cups using the DLA were 21.33° ± 17.31° (-51.7°-60.8°) and 33.71° ± 20.85° (-38.8°-77.6°) and PLA were 25.34° ± 12.76° (-5.5°-57.0°) and 42.37° ± 18.85° (-8.7°-84.7°), respectively. The DLA group had smaller anteversion (p = 0.038) and combined anteversion (p < 0.001). We found that surgical approach (p < 0.05), anterior pelvic plane inclination (p < 0.001), gender (p < 0.001), and femoral head diameter (p < 0.001) were important factors affecting acetabular cup anteversion (R2  = 0.375) and combined anteversion (R2  = 0.525).

CONCLUSIONS

In total hip arthroplasty, different prosthesis installation directions should be made according to different surgical approaches. Compared with the direct lateral approach, the acetabular anteversion can be intentionally enlarged when using the posterolateral approach. Surgical approach, anterior pelvic plane inclination (APPI), gender, and femoral head diameter were significant predictors of prosthesis orientation. The anterior pelvic plane inclination may be a useful standard for assessing the position of the prosthesis using EOS.

Imaging in Hip Arthroplasty Management-Part 1: Templating: Past, Present and Future

Hip arthroplasty is a frequently used procedure with high success rates. Its main indications are primary or secondary advanced osteoarthritis, due to acute fracture, osteonecrosis of the femoral head, and hip dysplasia. The goals of HA are to reduce pain and restore normal hip biomechanics, allowing a return to the patient’s normal activities. To reach those goals, the size of implants must suit, and their positioning must meet, quality criteria, which can be determined by preoperative imaging. Moreover, mechanical complications can be influenced by implant size and position, and could be avoided by precise preoperative templating. Templating used to rely on standard radiographs, but recently the use of EOS^® imaging and CT has been growing, given the 3D approach provided by these methods. However, there is no consensus on the optimal imaging work-up, which may have an impact on the outcomes of the procedure. This article reviews the current principles of templating, the various imaging techniques used for it, as well as their advantages and drawbacks, and their expected results.