Pre-operative templating in THA. Part II: a CT-based strategy to correct architectural hip deformities

Reliably calibrating X-ray images required for preoperative planning of THA using a device-adapted magnification factor

BACKGROUND AND AIM

Calibrated pelvic X-ray images are needed in the preoperative planning of total hip arthroplasty (THA) to predict component sizes. Errors and mismatch in the size of one or more components are reported, which can lead to clinically relevant complications. Our aim is to investigate whether we can solve the fundamental problem of X-ray calibration and whether traditional X-ray still has a place in preoperative planning despite improved radiological alternatives.

METHODS

Based on geometric and radiographic principles, we estimate that the magnification factor is adapted to the X-ray device and depends strongly on the source-image distance of the device. We analyse the errors of the various calibration methods and investigate which narrow range can be expected to show that the center of rotation is sufficiently accurate. Based on the results of several CT-scans we defined an adapted magnification factor and validated the degree of measurement accuracy.

RESULTS

The true magnification of objects on X-ray images depends mainly on the device settings. Stem size prediction is possible to a limited extent, with an error margin of 4.3%. Components can be predicted with a safety margin of one size up and down as with CT or 3D images. The prerequisite is that the source-image distance is greater than or equal to 120 cm, the table-image distance is known, and the object-image distance is estimated according to the patient's BMI. We defined a device-adapted magnification factor that simplifies the templating routine and can be used to obtain the most reliable preoperative dimensional measurements that can be expected from X-ray images. We found the error margin of the magnification factor with the highest degrees of prediction and precision.

CONCLUSION

Preoperative planning is reliable and reproducible using X-ray images if calibration is performed with the device-adapted magnification factor suggested in this paper.

A simple CT scan protocol for planning of total hip arthroplasty in patients with femoral neck fractures

We describe a method for planning total hip arthroplasty (THA) in patients with a displaced femoral neck fracture based on a simple CT scan protocol of the contralateral hip. This protocol was used on 22 consecutive patients during the inclusion period, followed by reconstruction and 2D templating to predict the implant size and positioning. The exact planned size was achieved in 21/22 (95%) cups, 14/22 (64%) femoral stems and 14/22 (64%) femoral heads. There were no intra- or postoperative fractures. After surgery in which this planning method had been applied, the differences in length and lateral offset were less than 5 mm on average relative to the opposite side (mean postoperative leg length difference of -2 mm (-8 to +3 mm) and lateralization of -4 mm (-14 to +3 mm)). While this technique exposes the patient to additional radiation, it does not require any specific devices or surgical approach and could be used in most hospitals. LEVEL OF EVIDENCE: IV.

Technical note for intraoperative determination of proper acetabular cup size in primary total hip arthroplasty

BACKGROUND

Selecting the optimal size of components is crucial when performing a primary total hip arthroplasty. Implanting the accurate size of the acetabular component can occasionally be exacting, chiefly for surgeons with little experience, whilst the complications of imprecise acetabular sizing or over-reaming can be potentially devastating.

AIM

To assist clinicians intraoperatively with a simple and repeatable tip in elucidating the ambivalence when determining the proper acetabular component size is not straightforwardly achieved, specifically when surgeons are inexperienced or preoperative templating is unavailable.

METHODS

This method was employed in 263 operations in our department from June 2021 to December 2022. All operations were performed by the same team of joint reconstruction surgeons, employing a typical posterior hip approach technique. The types of acetabular shells implanted were: The Dynasty® acetabular cup system (MicroPort Orthopedics, Shanghai, China) and the R3® acetabular system (Smith & Nephew, Watford, United Kingdom), which both feature cementless press-fit design.

RESULTS

The mean value of all cases was calculated and collated with each other. We distinguished as oversized an implanted acetabular shell when its size was > 2 mm larger than the size of the acetabular size indicator reamer (ASIR) or when the implanted shell was larger than 4 mm compared to the preoperative planned cup. The median size of the implanted acetabular shell was 52 (48-54) mm, while the median size of the preoperatively planned cup was 50 (48-56) mm, and the median size of the ASIR was 52 (50-54) mm. The correlation coefficient between ASIR size and implanted acetabular component size exhibited a high positive correlation with r = 0.719 (P < 0.001). Contrariwise, intraoperative ASIR measurements precisely predicted the implanted cups' size or differed by only one size (2 mm) in 245 cases.

CONCLUSION

In our study, we demonstrated that the size of the first acetabular reamer not entering freely in the acetabular rim corroborates the final acetabular component size to implant. This was also corresponding in the majority of the cases with conventional preoperative templating. It can be featured as a valid tool for avoiding the potentially pernicious complications of acetabular cup over-reaming and over-sizing in primary total hip arthroplasty. It is a simple and reproducible technical note useful for confirming the predicted acetabular cup size preoperatively; thus, its application could be considered routinely, even in cases where preoperative templating is unavailable.

The Value of Computed Tomography Scan in Three-dimensional Planning and Intraoperative Navigation in Primary Total Hip Arthroplasty

Total hip arthroplasty (THA) is a frequently performed procedure; the objective is restoration of native hip biomechanics and achieving functional range of motion (ROM) through precise positioning of the prosthetic components. Advanced three-dimensional (3D) imaging and computed tomography (CT)-based navigation are valuable tools in both the preoperative planning and intraoperative execution. The aim of this study is to provide a thorough overview on the applications of CT scans in both the preoperative and intraoperative settings of primary THA. Preoperative planning using CT-based 3D imaging enables greater accuracy in prediction of implant sizes, leading to enhancement of surgical workflow with optimization of implant inventory. Surgeons can perform a more thorough assessment of posterior and anterior acetabular wall coverage, acetabular osteophytes, anatomical landmarks, and thus achieve more functional implant positioning. Intraoperative CT-based navigation can facilitate precise execution of the preoperative plan, to attain optimal positioning of the prosthetic components to avoid impingement. Medial reaming can be minimized preserving native bone stock, which can enable restoration of femoral, acetabular, and combined offsets. In addition, it is associated with greater accuracy in leg length adjustment, a critical factor in patients' postoperative satisfaction. Despite the higher costs and radiation exposure, which currently limits its widespread adoption, it offers many benefits, and the increasing interest in robotic surgery has facilitated its integration into routine practice. Conducting additional research on ultra-low-dose CT scans and examining the potential for translation of 3D imaging into improved clinical outcomes will be necessary to warrant its expanded application.

Acetabular cup placement and offset control in robotic total hip arthroplasty performed through the modified anterolateral approach

PURPOSE

The modified anterolateral approach (Röttinger) for total hip arthroplasty (THA) offers great advantages over conventional approaches, especially concerning early postoperative symptoms, which are mild and well tolerated by patients. Robotic-assisted implantation might facilitate rapid adoption of the modified anterolateral approach without exposing surgeons to risks encountered during the learning curve. This study posits that the use of robotic assistance in conjunction with the modified anterolateral approach for total hip arthroplasty (THA) can provide a substantial enhancement in the accuracy of cup placement in comparison to manual surgery.

METHODS

Thirty-two robotic-assisted THAs met the inclusion criteria and were matched to 32 conventional cases. Acetabular cup inclination, anteversion, limb-length discrepancy, and acetabular offset were assessed using certified planning software by two independent observers using pre- and postoperative anterior-posterior radiographs. Data was analyzed for normal distribution. Chi2 test was used to determine whether implanted acetabular cups that were within Lewinnek's safe zones were influenced by type of implantation. Effect size estimates and statistical power analysis were also performed to appreciate the appropriateness of the chosen sample size.

RESULTS

Robotic-assisted implantation was found to significantly improve acetabular cup placement in terms of inclination (p < 0.001) but not anteversion (p = 0.783). Although mean postoperative limb-length discrepancy and mean acetabular offset did not differ between groups, a significantly smaller variance was found in the robotic-assisted group (p < 0.001) and (p = 0.04), respectively. There were no significant differences between the two groups in terms of consistently implanting the acetabular cup within the Lewinnek safe zones p = 0.641 for anteversion and p = 0.230 for inclination, respectively.

CONCLUSIONS

Our results show that although robotic-assisted acetabular cup implantation performed through the modified anterolateral approach did not significantly differ from conventional implantation, it did offer increased accuracy in cup positioning, acetabular bone preservation, and limb-length restoration.

Patients With Shorter Stature Exhibit Minimal Hammering Sound Changes During Cementless Stem Insertion in Total Hip Arthroplasty

Background

Listening to the change in the hammering sound is 1 of the elements used to assess the cementless stem stability. This study aimed to quantitatively investigate the change in the acoustic characteristics between the early and late phases of cementless stem insertion in total hip arthroplasty and to identify which patient characteristics contribute to the change in the hammering sound.

Methods

The acoustic parameters of the hammering sounds in the early and late phases of cementless taper-wedged stem insertion for 51 hips in 45 patients who underwent total hip arthroplasty (mean age = 68 years, height = 1.56 m, weight = 55.0 kg) were analyzed. Parameters including patient's basic characteristics, radiographical femoral morphology, and canal fill ratio were assessed as potential contributors to the change in the hammering sound.

Results

The low-frequency bands (0.5-1.0 kHz and 1.0-1.5 kHz) showed the largest changes during stem insertion and were therefore considered key bands for the analysis of sound alterations. Multivariate linear regression analysis showed that height (β = 8.312, P = .013) and proximal canal fill ratio (β = -3.8568, P = .038) were independently associated with the sound alterations. The decision tree analysis identified height (≥1.66 m or <1.66 m) as the best single discriminator for the sound alteration.

Conclusions

Patients with smaller stature showed the least change in the hammering sound during stem insertion. Understanding the acoustic characteristics of hammering sound alteration during cementless stem insertion may aid in the achievement of optimal stem insertion.

Acetabular Diameter Assessment and Three-Dimensional Simulation for Acetabular Reconstruction in Dysplastic Hips

BACKGROUND

This study aimed to investigate the relationship between acetabular width, three-dimensional (3D) simulation, and surgical results in total hip arthroplasty patients who have developmental dysplasia of the hip (DDH).

METHODS

This retrospective study included 216 DDH cases. Inner and outer acetabular width (OAW) was measured at the plane passing through the center of acetabular fossa. 3D simulation and 2D standard templating were performed. The actual cup size and the use of augments during surgery were recorded. Association among the indices and their distribution in different types of DDH were analyzed.

RESULTS

A difference of 13 to 14 millimeters (mm) was found between the inner acetabular width and actual cup size used in type II, III, and IV cases, while the difference was 0.2 to 3.6 mm for OAW. The accuracy of 2D templating and 3D simulation in predicting cup size was comparable in Crowe type I (86.5 versus 76%, P = .075), type II (72.7 versus 51.5%, P = .127), and type III (93.3 versus 66.7%, P = .169). The 3D simulation was significantly more accurate in Crowe type IV (89.1% versus 60.9%, P = .001). Augments and bone grafts were significantly more commonly used in type II (25%) than in the other types (0 to 6.5%).

CONCLUSION

OAW more accurately predicted actual cup size than inner acetabular width. The supero-lateral acetabular bone defects in type II cases require additional attention. Compared with 2D templating, 3D simulation is more accurate in predicting actual cup size in dysplastic hips with severe deformity and may be recommended in these selected cases, especially for Crowe IV patients.

Segmental Acetabular Defects Managed by Augments in Conjunction with CT During Robotic Total Hip Arthroplasty: A Report of 2 Cases

CASES

We present 2 robotic-assisted hip arthroplasty cases with significant segmental acetabular defects that could compromise cup fixation. We outline an algorithmic planning approach on a computed tomography (CT)-based platform to address these defects by predicting augmentation needs, when component adjustments alone are inadequate, and describe the novel combination of augments in conjunction with robotic-assisted hip arthroplasty.

CONCLUSION

CT-based robotic-assisted hip arthroplasty is a powerful tool to assess and address acetabular deficiencies. Rudimentary augment planning extracts additional value out of the preoperative CT. However, there remains room for intelligent assessment of hip centers and for deliberate augment planning and execution.

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.

Validation of CT-Based Three-Dimensional Preoperative Planning in Comparison with Acetate Templating for Primary Total Hip Arthroplasty

OBJECTIVE

This study aims to compare the accuracy of CT-based preoperative planning with that of acetate templating in predicting implant size, neck length, and neck cut length, and to evaluate the reproducibility of the two methods.

METHODS

This prospective study was conducted between August 2020 and March 2021. Patients who underwent elective primary total hip arthroplasty by a single surgeon were assessed for eligibility. The included patients underwent both acetate templating and CT-based planning by two observers after the operation. Each observer conducted both acetate templating and CT-based planning twice for each case. The outcome measures included the following: (1) the accuracy of surgical planning in predicting implant size, calcar length, and neck length, which was defined as the difference between the planned size and length and the actual size and length; (2) reproducibility of the two planning techniques, which were assessed by inter-observer and intra-observer reliability analysis; (3) the influence of potential confounding factors on planning accuracy, which was evaluated using generalized estimating equations.

RESULTS

A total of 57 cases were included in the study. CT-based planning was more accurate than acetate templating for predicting cup size (93% vs 79%, p < 0.001) and stem size (93% vs 75%, p < 0.001). When assessed by mean absolute difference, the comparison between acetate templating and CT-based planning was 4.28 mm vs 3.74 mm (p = 0.122) in predicting neck length and 3.05 mm vs 2.93 mm (p = 0.731) in predicting neck cut length. In the inter-observer reliability analysis, an intraclass correlation coefficient (ICC) of 0.790 was achieved for predicting cup size, and an ICC of 0.966 was achieved for predicting stem size using CT-based planning. In terms of intra-observer reliability, Observer 1 achieved an ICC of 0.803 for predicting cup size and 0.965 for predicting stem size in CT-based planning. Observer 2 achieved ICC values of 0.727 and 0.959 for predicting cup and stem sizes, respectively. The average planning time was 6.48 ± 1.55 min for CT-based planning and 6.12 ± 1.40 min for acetate templating (p = 0.015).

CONCLUSION

The CT-based planning system is more accurate than acetate templating for predicting implant size and has good reproducibility in total hip arthroplasty.

Outcomes of primary total hip arthroplasty using 3D image-based custom stems in unselected patients: a systematic review

To report clinical and radiographic outcomes of primary THA using three-dimensional (3D) image-based custom stems.

This systematic review was performed according to PRISMA guidelines and registered with PROSPERO (CRD42020216079). A search was conducted using MEDLINE, Embase and Cochrane. Clinical studies were included if they reported clinical or radiographic outcomes of primary THA using 3D image-based custom stems. Studies were excluded if specific to patients with major hip anatomical deformities, or if not written in English.

Fourteen studies were eligible for inclusion (n = 1936 hips). There was considerable heterogeneity in terms of manufacturer, proximal geometry, coating and length of custom stems. Revision rates ranged from 0% to 1% in the short-term, 0% to 20% in the mid-term, and 4% to 10% in the long-term, while complication rates ranged from 3% in the short-term, 0% to 11% in the mid-term and 0% to 4% in the long-term. Post-operative Harris hip scores ranged from 95 to 96 in the short-term, 80 to 99 in the mid-term, and 87 to 94 in the long-term. Radiographic outcomes were reported in eleven studies, although none reported 3D implant sizing or positioning, nor compared planned and postoperative hip architecture.

Primary THA using 3D image-based custom stems in unselected patients provides limited but promising clinical and radiographic outcomes. Despite excellent survival, the evidence available in the literature remains insufficient to recommend their routine use. Future studies should specify proximal geometry, length, fixation, material and coating, as well as management of femoral offset and anteversion. The authors propose a classification system to help distinguish between custom stem designs based primarily on their proximal geometry and length.

Cite this article: EFORT Open Rev 2021;6:1166-1180. DOI: 10.1302/2058-5241.6.210053

Quantitative and individualized assessment of the learning curve in preoperative planning of the acetabular cup size in primary total hip arthroplasty

INTRODUCTION

The aim of the present study was to investigate the learning curves of 2 trainees with different experience levels to reach proficiency in preoperative planning of the cup size based on learning curve cumulative summation (LC-CUSUM) statistics and a cumulative summation (CUSUM) test.

MATERIALS AND METHODS

One-hundred-twenty patients who had undergone primary total hip arthroplasty with a cementless cup were selected. Preoperative planning was performed by an experienced orthopedic surgeon. Trainee 1 (student) and trainee 2 (resident) planned the cup size. The trainees were blinded to the preoperative plan and the definitive cup size. Only after a cup size was chosen, the trainees were unblinded to the preoperative plan of the surgeon. LC-CUSUM was applied to both trainees to determine when proficiency in determining the appropriate cup size was reached. A CUSUM test was applied to ensure retention of proficiency.

RESULTS

With reference to the preoperative plan of the surgeon, LC-CUSUM indicated proficiency after 94 planning attempts for trainee 1 and proficiency after 66 attempts for trainee 2, respectively. Trainee 1 and 2 maintained proficiency thereafter. With reference to the definitive cup size, LC-CUSUM did not signal competency within the first 120 planning attempts for trainee 1. Trainee 2 was declared competent after 103 attempts and retained competency thereafter.

CONCLUSIONS

LC-CUSUM/CUSUM allow for an individualized, quantitative and continuous assessment of planning quality. Based on LC-CUSUM statistics, the two trainees of this study gain proficiency in planning of the acetabular cup size after 50-100 attempts when an immediate feedback is provided. Previous experience positively influences the performance. The study serves as basis for the medical education of students and residents in joint replacement procedures.