Low dislocation rates with the use of patient specific "Safe zones" in total hip arthroplasty

Are robotic-assisted and computer-navigated total hip arthroplasty associated with superior outcomes in patients who have hip dysplasia?

Introduction

Robotic-assisted (RA) and computer-navigated (CN) total hip arthroplasty (THA) have been demonstrated to improve component placement accuracy compared to manual THA (mTHA) for primary osteoarthritis. As hip dysplasia presents several additional challenges in component placement accuracy and leg length discrepancy (LLD) correction during THA, a systematic review was conducted to evaluate whether utilizing these platforms may be associated with superior outcomes over mTHA in patients who have hip dysplasia.

Methods

PubMed, Medline, EBSCOhost, and Google Scholar were searched on September 13, 2023 to identify comparative studies published after January 1, 2000 that evaluated outcomes of RA-THA or CN-THA in patients who have hip dysplasia. The query yielded 197 unique articles, which were screened for alignment with the study aims. After screening, 10 studies fulfilled all inclusion criteria, comprising 946 patients. Risk of bias was evaluated via the Methodological Index for Nonrandomized Studies tool, and the mean score was 21.2 ± 1.5.

Results

Both RA-THA and CN-THA were not associated with improved acetabular anteversion and inclination when evaluating Crowe I-IV types altogether compared to mTHA, but studies reported improved accuracy for each Crowe I and II cases when assessed individually. While studies reporting acetabular cup placement within the Lewinnek and Callanan safe zones consistently found higher odds of accurate positioning for RA-THA versus mTHA, accuracy in achieving targeted center of rotation was mixed. Also, studies reported no difference in LLD restoration for RA-THA and CN-THA compared to mTHA. While operative time may be increased when utilizing these platforms, they may also expedite specific sequences, offsetting most of the increase in operative time.

Conclusion

This review highlights the advantages of RA-THA and CN-THA for patients who have DDH, particularly when treating Crowe I and II types as superior radiographic outcomes were achieved with these intraoperative technologies. However, there remains a need for studies to investigate whether this results in patient-reported outcome measures.

Fluoroscopy-Assisted Computer Navigation Accurately Determines Cup Position and Leg Length for Anterior Hip Arthroplasty

BACKGROUND

Recently, fluoroscopy-assisted computer navigation has been developed to assess intraoperative cup inclination/anteversion and leg-length discrepancy (LLD) in the operating room. However, there is a relative dearth of studies investigating the accuracy of this software compared with postoperative radiographs.

MATERIALS AND METHODS

We prospectively enrolled 211 navigated anterior total hip arthroplasties using fluoroscopy-assisted computer navigation software. Intraoperative navigated measurements were compared with postoperative anteroposterior radiographs to assess accuracy of cup inclination/anteversion and LLD. Continuous variables were analyzed using the Student's t test, and categorical variables were analyzed using Fisher's exact test.

RESULTS

On postoperative radiographs, 94.3% of cups (199 of 211) were positioned within the Lewinnek "safe zone," compared with 99.1% navigated intraoperatively (P=.01). Eighty-two percent of hips (174 of 211) were navigated intraoperatively to LLDs within ±2 mm; on postoperative radiographs, 65% of hips (138 of 211) had LLDs within ±2 mm (P=.0001). Intraoperatively, 100% of hips (211 of 211) were navigated to LLDs within ±5 mm; similarly, on postoperative radiographs, 98% of hips (207 of 211) had LLDs within ±5 mm (P=.12).

CONCLUSION

A novel fluoroscopy-assisted computer navigation platform accurately assessed intraoperative cup position and LLD during anterior total hip arthroplasty. Careful attention to fluoroscopic technique, positioning of radiographic landmarks, and knowledge of the limitations of fluoroscopy, including parallax effect, are important concepts that surgeons should incorporate into their decision algorithm. [Orthopedics. 2024;47(4):e174-e180.].

The Empty Ischial Fossa Sign: A Visual Representation of Relative Inadequate Anteversion in the Posteriorly Tilted Pelvis

Background

Instability is a known complication following total hip arthroplasty (THA) and is influenced by spinopelvic alignment. Radiographic markers have been investigated to optimize the acetabular cup position. This study evaluated if the empty ischial fossa (EIF) sign and the position of the trans-teardrop line were predictive of postoperative instability.

Methods

All patients who underwent THA from 2011 to 2018 at a single institution were retrospectively reviewed. Pelvic tilt was measured using a trans-teardrop line compared to the superior aspect of the pubic symphysis on standing anteroposterior pelvis radiographs. Postoperative dislocations were identified through chart review and radiographic review. The EIF sign was determined by the presence of uncovered bone below the posterior inferior edge of the acetabular component at the level of the native ischium and posterior wall on standing postoperative anteroposterior radiographs.

Results

One thousand seven hundred fifty patients (952 anterior approach and 798 posterior approach) were included. The EIF sign was present in 458 patients (26.2%) and associated with an increased dislocation rate (3.9% vs 0.9%, P < .0001). Patients with spondylosis/instrumented fusion, and positive EIF sign had a dislocation risk of 5.1% vs 1.3% (P = .001). A postoperative outlet pelvis was not significant for increased dislocation risk (odds ratio 2.16, P = .058). Patients with combined spondylosis/fusion, posterior approach, outlet pelvis, and EIF sign had a dislocation rate of 14.5%.

Conclusions

The EIF sign was an independent risk factor for postoperative instability and may represent failure to account for pelvic tilt. Avoidance of the EIF sign during cup positioning may help reduce dislocations following THA.

Point-of-Care Orthopedic Oncology Device Development

BACKGROUND

The triad of 3D design, 3D printing, and xReality technologies is explored and exploited to collaboratively realize patient-specific products in a timely manner with an emphasis on designs with meta-(bio)materials.

METHODS

A case study on pelvic reconstruction after oncological resection (osteosarcoma) was selected and conducted to evaluate the applicability and performance of an inter-epistemic workflow and the feasibility and potential of 3D technologies for modeling, optimizing, and materializing individualized orthopedic devices at the point of care (PoC).

RESULTS

Image-based diagnosis and treatment at the PoC can be readily deployed to develop orthopedic devices for pre-operative planning, training, intra-operative navigation, and bone substitution.

CONCLUSIONS

Inter-epistemic symbiosis between orthopedic surgeons and (bio)mechanical engineers at the PoC, fostered by appropriate quality management systems and end-to-end workflows under suitable scientifically amalgamated synergies, could maximize the potential benefits. However, increased awareness is recommended to explore and exploit the full potential of 3D technologies at the PoC to deliver medical devices with greater customization, innovation in design, cost-effectiveness, and high quality.

Is It Necessary to Obtain Lateral Pelvic Radiographs in Flexed Seated Position for Preoperative Total Hip Arthroplasty Planning?

Background

Many of the current total hip arthroplasty (THA) planning tools only consider sagittal pelvic tilt in the standing and relaxed sitting positions. Considering that the risk of postoperative dislocation is higher when bending forward or in sit-to-stand move, sagittal pelvic tilt in the flexed seated position may be more relevant for preoperative planning. We hypothesized that there was a significant difference in sagittal pelvic tilt between the relaxed sitting and flexed seated positions as measured by the sacral slope in preoperative and postoperative full-body radiographs.

Methods

This was a multicenter retrospective analysis of the preoperative and postoperative simultaneous biplanar full-body radiographs of 93 primary THA patients in standing, relaxed sitting, and flexed seated positions. The sagittal pelvic tilt was measured using the sacral slope relative to the horizontal line.

Results

The mean difference between the preoperative sacral slope in the relaxed sitting position and the flexed seated position was 11.3° (-13° to 43°) (P < .0001). This difference was >10° in 52 patients (56%) and >20° in 18 patients (19.4%). The mean difference between the postoperative sacral slope in a relaxed sitting position and the sacral slope in a flexed seated position was 11.3° (P < .0001). This difference was >10° in 51 patients (54.9%) and >30° in 14 patients (15.1%) postoperatively.

Conclusions

There was a significant difference in sagittal pelvic tilt between the relaxed and flexed seated positions. A flexed seated view provides valuable information that might be more relevant for preoperative THA planning in order to prevent postoperative THA instability.

A Novel Method to Calculate Functional Pelvic Tilt Using a Standing Anteroposterior Pelvis Radiograph

Background

Functional patient-specific acetabular component positioning is important in total hip arthroplasty. We preoperatively evaluate the pelvic tilt (PT) on standing anteroposterior (AP) pelvis radiographs using a novel measurement and then recreate this intraoperatively using imaging. The purpose of this study was to determine if there is a linear correlation between this novel measurement and the actual PT.

Methods

A retrospective study of 200 patients was performed, measuring PT on standing lateral radiographs as the angle between the anterior superior iliac spines and the pubic symphysis. On the AP pelvis radiographs, the trans-teardrop (TT) line was drawn between the teardrops. The vertical distance between the TT line and the top of the pubic symphysis (TTPS) was then measured. A ratio was made between the lengths of both lines to account for the overall size of the pelvis (TTPS/TT). Linear regression analysis was then performed between PT and TTPS/TT.

Results

There was a strong linear correlation between the TTPS/TT ratio on AP pelvis radiographs and PT on lateral radiographs (r = 0.785, r² = 0.616, P < .001). On subanalysis of the female cohort, the correlation became even stronger (r = 0.864, r² = 0.747, P < .001). Using regression analysis, a linear equation was created (PT = 97.32 [TTPS/TT] - 5.51), to calculate the PT using the TTPS/TT ratio.

Conclusions

There is a strong linear correlation between the TTPS/TT ratio and PT. Using this information, a surgeon can reliably use the distance between the TT line and the superior pubic symphysis on an AP radiograph to recreate the patient's functional PT intraoperatively, allowing for a more accurate patient-specific placement of the acetabular component.

Does Individualization of Cup Position Affect Prosthetic or Bone Impingement Following THA?

INTRODUCTION

Spinopelvic (SP) mobility patterns during postural changes affect three-dimensional acetabular component position, the incidence of prosthetic impingement, and total hip arthroplasty (THA) instability. Surgeons have commonly placed the acetabular component in a similar "safe zone" for most patients. Our purpose was to determine the incidence of bone and prosthetic impingement with various cup orientations and determine if a preoperative SP analysis with individualized cup orientation lessens impingement.

METHODS

A preoperative SP evaluation of 78 THA subjects was performed. Data was analyzed using a software program to determine the prevalence of prosthetic and bone impingement with a patient individualized cup orientation versus six commonly selected cup orientations. Impingement was correlated with known SP risk factors for dislocation.

RESULTS

Prosthetic impingement was least with the individualized choice of cup position (9%) vs. preselected cup positions (18 to 61%). The presence of bone impingement (33%) was similar in all groups and not affected by cup position. Factors associated with impingement in flexion were age, lumbar flexion, pelvic tilt (stand to flexed seated), and functional femoral stem anteversion. Risk factors in extension included standing pelvic tilt, standing SP tilt, lumbar flexion, pelvic rotation (supine to stand and stand to flexed seated), and functional femoral stem anteversion.

CONCLUSION

Prosthetic impingement is reduced with individualized cup positioning based on SP mobility patterns. Bone impingement occurred in one-third of patients and is a noteworthy consideration in preoperative THA planning. Known SP risk factors for THA instability correlated with the It dependspresence of prosthetic impingement in both flexion and extension.

Image-based robotic-assisted total hip arthroplasty through direct anterior approach allows a better orientation of the acetabular cup and a better restitution of the centre of rotation than a conventional procedure

PURPOSE

The aim was to investigate the contribution of robotics assisted total hip arthroplasty (THA) through direct anterior approach (DAA) in improving radiographic precision, functional results and complications.

METHODS

This retrospective study compared 100 primary conventional THA (cTHA) to 50 primary robotic THA (rTHA) through DAA. All cups were placed with the objective of having no anterior overhang while respecting the safe zones (SZ). Radiographic analysis included cup inclination and anteversion, vertical and horizontal changes of the rotation centre (ΔVCOR, ΔHCOR), acetabular and femoral offset. SZ were 30-50° of inclination and 10-30° of anteversion. Outliers were defined as medial displacement of the COR > 5 mm, vertical displacement of the COR > 3 mm superiorly. Harris hip score (HHS) and complications were compared at one year of follow-up.

RESULTS

The robotic cups were better oriented with 98% in the global SZ versus 68% in the cTHA group (p = 0.0002). The COR was on average better restored in the robotic group in both the horizontal and vertical planes (Δ HCOR =  - 5.0 ± 5.0 vs - 3.4 ± 4.9, p = 0.03; Δ VCOR = 1.6 ± 3.3 vs 0.2 ± 2.7, p = 0.04). There were fewer outliers in the rTHA group concerning VCOR (28% versus 10%, p = 0.03). There was no significant difference in HHS and complication rate at one year.

CONCLUSION

The use of robotics for THA by DAA provided an advantage in controlling the orientation of the cup and the restoration of its rotation centre. Thanks to the 3D planning on CT scan, it allowed to respect the thresholds while avoiding the anterior overhangs.

Functional implant positioning in total hip arthroplasty and the role of robotic-arm assistance

INTRODUCTION

Accurate implant positioning, tailored to the phenotype and unique biomechanics of each patient is the single most important objective in achieving stability in THA and maximise range of motion. The spine-pelvis-hip construct functions as a single unit adapting to postural changes. It is widely accepted in the literature that no universaltarget exists and variations in spinopelvic mobility mandate adjustments to the surgical plan; thus bringing to the fore the concept of personalised, functional component positioning.

METHODS

This manuscript aims to outline the challenges posed by spinopelvic imbalance and present a reproducible, stepwise approach to achieve functional-component positioning. We also present the one-year functional outcomes and Patient Reported Outcome Measures of a prospective cohort operated with this technique.

RESULTS AND CONCLUSION

Robotic-arm assisted Total Hip Arthroplasty has facilitated enhanced planning based on the patient's phenotype and evidence suggests it results in more reproducible and accurate implant positioning. Preservation of offset, avoiding leg-length discrepancy, accurate restoration of the centre of rotation and accomplishing the combinedversion target are very important parameters in Total Hip Arthroplasty that affect post-operative implant longevity, patient satisfaction and clinical outcomes.

Does the Dual Mobility Cup Reduce Dislocation After Primary Total Hip Arthroplasty in Elderly Patients at High Risk of Dislocation?

OBJECTIVE

The dual mobility cup (DMC) is designed to extend the longevity of the prosthesis by improving stability, enhancing the range of motion, and decreasing impingement without increasing wear. We hypothesized that DMC would reduce the risk of dislocation in elderly patients. This study aimed to investigate the clinical and radiographic outcomes of DMC-total hip arthroplasty (THA) in elderly patients at high risk of dislocation.

METHODS

From June 2016 to March 2020, 94 patients with a mean age of 77.7 years (97 hips) who underwent a posterolateral approach for DMC-THA in our department were followed up for at least one year. Preoperative and postoperative pelvic tilt angles (PTA) and DMC orientation were prospectively collected for all patients. Intraoperative and postoperative complications were recorded. A parametric test was used for normal distribution, and a non-parametric test was used for non-normal distribution.

RESULTS

Abduction and anteversion angles of the cup were 42.4 and 18.0° in the supine position immediately postoperative. The average PTA for patients in the supine and standing positions were 26.5 and 34.5°, respectively. When moving from the supine to the standing position, patients experienced a mean posterior pelvic tilt of 9°. No intraoperative acetabular-related complications were recorded. Postoperative complications included early infection in one patient (1.0%) and dislocation in one patient (1.0%).

CONCLUSION

Our study demonstrates that DMC-THA provides satisfactory short-term outcomes in elderly patients at a high risk of dislocation, regardless of the change in PTA resulting from postural transition.

The length of distal skin incision of the postero-lateral approach affects the cup inclination during the total hip arthroplasty

Aim: The primary aim of the study was to determine whether the length of the distal skin incision of the posterolateral approach affects the cup inclination during total hip arthroplasty (THA). Material and Method: In this study, a cohort of 71 consecutive patients who performed between January 2017 and December 2021 with unilateral THA using a posterolateral approach was retrospectively assessed. Two groups were formed according to acetabular cup inclination with normal anteversion angle. There were 56 hips in the inside group and 17 in the outside group. A curvilinear skin incision of around 13 cm was performed. Component position evaluation was carried out through a radiographic assessment of the acetabular component on an anteroposterior pelvis radiograph. The rate of an outlier was compared between groups according to the safe zone defined as 30° to 50° of inclination and 5° to 25° of anteversion, which was described by Lewinnek et al. Results: No significant difference in the average total incision length was found between the two groups (p=0.207). While the average distal incision length was 7.91±0.62 cm (range, 6.8-9 cm) in the inside group and 6.37±0.21 cm (range, 6-6.7 cm) in the outside group. According to ROC analysis, a patient with ≤6.7 cm of the distal length of incision (DLI) was 5.71 times more likely to be outside than a patient with >6.7 cm of DLI. Seventeen hips (23.3%) were found outside the safe range. Substantial differences were observed regarding radiographic cup inclination between the two groups (p=0.0001). In the inside group, the average cup inclination was 44.11°±3.44° (range, 37°-50°), whereas, in the outside group, it was 55.41°±2.5° (range, 52°-59°). However, there were no significant differences in the average radiographic cup anteversion between the two groups (p=0.960). Although 11 of 17 (64.5%) patients were classified as obese (BMI ≥30) in the outside group experienced higher rates of inaccurate cup orientation, logistic regression analysis showed that the individual effects of obesity on the occurrence of the inaccurate cup position were not observed (p=0.884). One posterior hip dislocation occurred after one month postoperative in the outside group. Conclusions: Longer distal portion of the skin incision of the posterolateral approach should be performed to achieve optimal operative inclination angles of the acetabular cup during THA. The surgeon must have no hesitation in extending the distal skin incision when adopting the posterolateral approach.