What do we get from navigation in primary THA?

High variability in pelvic orientation in the lateral decubitus position negatively affects acetabular component placement

Purpose

Determine factors that impart increased risk of acetabular component malposition in the lateral decubitus position.

Methods

A retrospective review of 813 X-rays from posterior THA procedures at a single institution. Pelvic tilt and rotation were measured on preoperative standing AP-pelvis and intraoperative cross-table x-rays. Proper intraoperative pelvic orientation (PPO) was defined as vertical tilt and axial rotation within ± 15° of the preoperative standing pelvis orientation. Acetabular abduction was measured on standing postoperative x-rays with Goal abduction (GA) of 30-50°.

Results

PPO was obtained in 284/413 cases (69 %). Patient sex, weight, BMI, and operative laterality were not significantly associated with PPO. Patients with PPO were shorter (1.68m vs 1.72m, p < 0.01). PPO occurred in 168/221 patients (76 %) with the Capello or Wixson hip positioner, compared to 116/192 (60 %) with the De Mayo positioner (p < 0.01). GA was obtained in 249/284 (88 %) of patients with PPO, as compared to 103/129 (80 %) patients without PPO.

Conclusion

The risk of pelvic malpositioning significantly increases with the use of certain hip positioning systems, and taller patients. Acetabular component abduction is negatively affected by an improperly positioned pelvis.

Superior outcomes of total hip arthroplasty without prior lumbar arthrodesis: a systematic review and meta-analysis

PURPOSE

The number of patients undergoing total hip arthroplasty (THA) surgery after previous lumbar arthrodesis (LA) is rising. Literature suggests that LA may significantly impact pelvic biomechanics and potentially compromise the success of prosthetic hip replacement. This study aims to evaluate complication rates, dislocation rates, and revision rates in patients with prior LA undergoing THA surgery compared to those undergoing THA surgery without prior LA.

METHODS

A systematic review and meta-analysis were conducted following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. A PICOS template was developed to ensure a structured approach. The search for relevant studies was performed across five databases, including Pubmed, Scopus, Embase, Medline, and Cochrane. The selected articles were evaluated based on the Levels of Evidence (LoE) criteria. The Coleman Methodology Score (mCMS) was employed to analyze the retrospective studies. This systematic review and meta-analysis were registered in the International Prospective Register of Systematic Reviews (PROSPERO). For the outcomes that allowed for a meta-analysis performed using R software, a p < 0.05 was considered statistically significant.

RESULTS

The final analysis included seventeen studies comprising a total of 3,139,164 cases of THA. Among these cases, 3,081,137 underwent THA surgery alone, while 58,027 patients underwent THA with a previous LA. The study investigated various factors, including dislocation rates, revision rates, and complication, as well as the surgical approach and type of implant used, for both the THA-only group and the group of patients who underwent THA with prior LA. The analysis revealed a statistically significant difference (p < 0.05) for all variables studied, favoring the group of patients who underwent THA alone without prior LA.

CONCLUSIONS

This systematic review and meta-analysis demonstrated a statistically significant superiority in all analyzed outcomes for patients who underwent THA-only without prior LA. Specifically, patients with isolated THA implants experienced significantly lower incidences of THA dislocation, wound complications, periprosthetic joint infection, revision, and mechanical complications.

LEVEL OF EVIDENCE

Level IV.

Imageless navigation system (Naviswiss) provides accurate component position in total hip arthroplasty with lateral decubitus position for end-stage hip osteoarthritis: a prospective cohort study with CT-validation

AIMS

The Naviswiss system (Naviswiss AG, Brugg, Switzerland) is a handheld imageless navigation device used to improve the accuracy of implant positioning in total hip arthroplasty (THA). However, clinical data for leg length discrepancy and femoral offset is lacking, and the validity of the system has not been reported for patients undergoing THA in the lateral decubitus position. This study aimed to report the accuracy of the device in this patient population.

METHODS

Patients underwent THA in the lateral decubitus position performed by a single surgeon. Component position measured by the device intraoperatively was compared to postoperative measurements on computed tomography (CT) scans. Agreement between the navigation system and postoperative measurements was reported for acetabular cup inclination, acetabular cup version, femoral offset, and leg length discrepancy.

RESULTS

Thirty-three patients were included in the analysis. The mean difference between intraoperative and postoperative CT measurements was within 2° for angular measurements and 2 mm for leg length. Absolute differences in the two indices were up to 4° and 3 mm. The mean bias was 1°-2° overestimation for cup orientation and up to 2 mm overestimation for leg length change. However, 95% limits of agreement did not exceed absolute thresholds of 10° and 10 mm, especially after correction for bias. One case (3%) was declared intraoperatively for issues with fixation on the greater trochanter.

CONCLUSIONS

The accuracy of the Naviswiss system falls within clinically acceptable recommendations for acetabular cup placement, femoral offset, and leg length for total hip arthroplasty with a anterolateral approach in lateral decubitus position. The system could be further improved with regression-based bias correction.

CT validation of intraoperative imageless navigation (Naviswiss) for component positioning accuracy in primary total hip arthroplasty in supine patient position: a prospective observational cohort study in a single-surgeon practice

BACKGROUND

The aim of this study was to report on the validity of the Naviswiss handheld image-free navigation device for accurate intraoperative measurement of THA component positioning, in comparison with the three-dimensional (3D) reconstruction of computed tomography (CT) images as the gold standard.

METHODS

A series of patients presenting to a single-surgeon clinic with end-stage hip osteoarthritis received primary hip arthroplasty with the anterolateral muscle-sparing surgical approach in the supine position. Imageless navigation was applied during the procedure with bone-mounted trackers applied to the greater trochanter and ASIS. Patients underwent routine CT scans before and after surgery and these were analyzed by using three-dimensional reconstruction to generate cup orientation, offset and leg length changes, which were compared to the intraoperative measurements provided by the navigation system. Estimates of agreement between the intraoperative and image-derived measurements were assessed with and without correction for bias and declared cases with potential measurement issues.

RESULTS

The mean difference between intraoperative and postoperative CT measurements was within 2° for angular measurements and 2 mm for leg length. Absolute differences for the two indices were between 5° and 4 mm. Mean bias was 1.9°-3.6° underestimation for cup orientation and up to 2 mm overestimation for leg length change, but absolute thresholds of 10° and 10 mm were not exceeded by 95% limits of agreement (LOA), especially after correction for bias. Four cases (12%) were declared intraoperatively for issues with fixation on the greater trochanter. Inclusion of these cases generated acceptable accuracy overall and their omission failed to improve between-case variability in accuracy or LOA for both offset and leg length.

CONCLUSIONS

The accuracy of the Naviswiss system applied during primary THA in a supine position and anterolateral surgical approach falls within clinically acceptable recommendations for acetabular cup placement, femoral offset, and length. With refinements to surgical technique to adapt to the navigation hardware, the system could be further improved with regression-based bias correction.

TRIAL REGISTRATION

Registered with the Australian New Zealand Clinical Trials Registry (ACTRN12618000317291).

The walls of the femoral neck as an auxiliary tool for femoral stem positioning

BACKGROUND

Femoral anteversion is a major contributor to functionality of the hip joint and is implicated in many joint pathologies. Accurate determination of component version intraoperatively is a technically challenging process that relies on the visual estimation of the surgeon. The following study aimed to examine whether the walls of the femoral neck can be used as appropriate landmarks to ensure appropriate femoral prosthesis version intraoperatively.

METHODS

We conducted a retrospective study based on 32 patients (64 hips) admitted to our centre between July and September 2020 who had undergone a CT scan of their lower limbs. Through radiological imaging analysis, the following measurements were performed bilaterally for each patient: anterior wall version, posterior wall version, and mid-neck femoral version. Anterior and posterior wall version were compared and evaluated relative to mid-neck version, which represented the true version value.

RESULTS

Mean anterior wall anteversion was 20° (95% CI, 17.6-22.8°) and mean posterior wall anteversion was -12° (95% CI, -15 to -9.7°). The anterior walls of the femoral neck had a constant of -7 and a coefficient of 0.9 (95% CI, -9.8 to -4.2; p < 0.0001; R² 0.77).The posterior walls of the femoral neck had a constant of 20 and a coefficient of 0.7 (95% CI, 17.8-22.5; p < 0.0001; R² 0.60).

CONCLUSIONS

Surgeons can accurately obtain femoral anteversion by subtracting 7° from the angle taken between the anterior wall and the posterior femoral condyles or by adding 20° to the angle taken between the posterior wall and the posterior femoral condyles.

Robot-assisted knee arthroplasty improves component positioning and alignment, but results are inconclusive on whether it improves clinical scores or reduces complications and revisions: a systematic overview of meta-analyses

PURPOSE

The purpose of this systematic overview was to identify, synthesise and critically appraise findings of meta-analyses on robot-assisted versus conventional unicompartmental knee arthroplasty (UKA) and total knee arthroplasty (TKA). The hypothesis was that robotic assistance would reduce complications and revision rates, yield better clinical scores, and improve component positioning and alignment.

METHODS

Two researchers independently conducted a literature search using Embase^®, MEDLINE^®, Web of Science, Allied and Complementary Medicine™ and Cochrane Database of Systematic Reviews on 2 November 2020 for meta-analyses (Level I-IV) on robotic assistance in UKA and/or TKA. Outcomes were tabulated and reported as weighted mean difference (WMD), risk ratio (RR) or weighted odds ratio (WOR), and were considered statistically significant when p < 0.05.

RESULTS

A total of ten meta-analyses were identified; four on robot-assisted UKA (n, 1880 robot-assisted vs. 2352 conventional UKA; follow-up, 0 to 60 months), seven on robot-assisted TKA (n, 4567 robot-assisted vs. 5966 conventional TKA; follow-up, 0 to 132 months). Of the meta-analyses on UKA, one found that robotic assistance reduced complication rates (relative risk (RR), 0.62), one found that it improved clinical scores (weighted mean difference (WMD), 19.67), three found that it extended operation times (WMD, 15.7 to 17.1 min), and three found that it improved component positioning and alignment (WMD, - 1.30 to - 3.02 degrees). Of the meta-analyses on TKA, two found that robotic assistance improved clinical scores (WMD, 1.62-1.71), two found that that it extended surgery times (WMD, 21.5-24.26 min), and five found that it improved component positioning and alignment (WMD, - 0.50 to - 10.07 degrees). None of the meta-analyses reported differences in survivorship between robot-assisted versus conventional knee arthroplasty.

CONCLUSION

Robot-assisted knee arthroplasty enabled more accurate component positioning and placement within target zones, but extended operation time considerably. Although robotic assistance improved component positioning, its benefits regarding clinical scores, patient satisfaction and implant survivorship remains to be confirmed. Finally, this overview revealed that six of the ten meta-analyses were of 'critically low quality', calling for caution when interpreting results.

LEVEL OF EVIDENCE

IV.

Orthopedic Surgeons' Accuracy When Orienting an Acetabular Cup. A Comparison with Untrained Individuals

Background and Objectives: Previous studies demonstrated a huge variability among surgeons when it comes to reproducing the position of an acetabular cup in total hip arthroplasty. Our main objective is to determine if orthopedic surgeons can replicate a given orientation on a pelvic model better than untrained individuals. Our secondary objective is to determine if experience has any influence on their ability for this task. Materials and Methods: A group of specialist orthopedic hip surgeons and a group of volunteers with no medical training were asked to reproduce three given (randomly generated) acetabular cup orientations (inclination and anteversion) on a pelvic model. Error was measured by means of a hip navigation system and comparisons between groups were made using the appropriate statistical methods. Results: The study included 107 individuals, 36 orthopedic surgeons and 71 untrained volunteers. The mean error among surgeons was slightly greater as regards both inclination (7.84 ± 5.53 vs. 6.70 ± 4.03) and anteversion (5.85 ± 4.52 vs. 5.48 ± 3.44), although statistical significance was not reached (p = 0.226 and p = 0.639, respectively). Similarly, although surgeons with more than 100 procedures a year obtained better results than those with less surgical experience (8.01 vs. 7.67 degrees of error in inclination and 5.83 vs. 5.87 in anteversion), this difference was not statistically significant, either (p = 0.852 and p = 0.981). Conclusions: No differences were found in the average error made by orthopedic surgeons and untrained individuals. Furthermore, the surgeons' cup orientation accuracy was not seen to improve significantly with experience.

Three-Dimensional Evaluation of Innominate Bone Rotation in Female Patients with Developmental Dysplasia of the Hip

Background

Patients with developmental dysplasia of the hip (DDH) are known to have abnormal pelvic morphologies; however, rotation of innominate bone features remains unclear. Thus, we investigated innominate bone rotation in patients with DDH by measuring the associated angles and distances using three-dimensional (3D) computed tomography.

Methods

We defined four straight lines in pelvic 3D models: from the anterior superior iliac spine to the posterior superior iliac spine, from the anterior inferior iliac spine to the posterior inferior iliac spine, from the pubic tubercle to the ischial spine, and from the pubic tubercle to the ischial tuberosity. Similarly, we measured the angles formed by these lines using the vertical axis of the anterior pelvic plane on the horizontal plane and the horizontal axis on the sagittal plane. Additionally, we measured the distances between the femoral head centers and the acetabular centers in the coronal plane.

Results

The difference in internal rotation angle between the superior and inferior parts of the iliac bone was significantly lower, by approximately 1.7°, in the DDH group than in the control group (p = 0.007); the difference between the inferior and superior parts of the ischiopubic bone was significantly higher, by approximately 1.5°, in the DDH group (p < 0.001). In the sagittal plane, the sum of the superior aspect of the iliac bone and the inferior aspect of the ischium was significantly lower in the DDH group (p = 0.001) than in the control group. The distances between the femoral heads and the acetabula were significantly greater in the DDH group than in the control group (p = 0.03, p < 0.01, respectively).

Conclusions

Patients with DDH had a more internally rotated ilium and ischiopubic bone than normal individuals; however, it should be emphasized that internal rotation was reduced near the acetabulum, and the acetabulum was shifted laterally. Similarly, it was shown that patients with DDH had different rotations of the ilium and ischiopubic bone in the sagittal plane.

Clinical and surgical outcomes of robot-assisted versus conventional total hip arthroplasty: a systematic overview of meta-analyses

Robot-assisted total hip arthroplasty (THA), in comparison to conventional THA, improves radiographic outcomes, but it remains unclear whether it alters complication rates, clinical and functional outcomes, and implant survival.

The purpose of this systematic overview was to summarize the findings of the most recent meta-analyses that compare clinical and surgical outcomes of robot-assisted versus conventional THA.

Two readers independently conducted an electronic literature search, screening and data extraction from five electronic databases. Inclusion criteria were: meta-analyses evaluating robot-assisted versus conventional THA in terms of radiographic outcomes, clinical and functional scores, and complications and revision rates. The literature search returned 67 records, of which 14 were duplicates and 49 were excluded, leaving three meta-analyses published within the past two years for data extraction and analysis.

The present overview of meta-analyses suggests that, compared to conventional THA (n = 3011), robot-assisted THA (n = 1813) improves component placement and reduces intraoperative complications. The overview also affirms that robot-assisted THA could extend surgery by 20 minutes, and increases risks of postoperative heterotopic ossification, dislocation, and revision. None of the meta-analyses found significant differences in clinical or functional scores between robot-assisted and conventional THA.

Future studies and reviews should make a clear distinction between active and semi-active robotic assistance, address technology matureness, and describe the experience of surgeons with robotic assistance.

Cite this article: EFORT Open Rev 2021;6:1157-1165. DOI: 10.1302/2058-5241.6.200121

Effects of lower limb and pelvic pin positions on leg length and offset measurement errors in experimental total hip arthroplasty

Background

Leg length (LL) and offset (OS) are important factors in total hip arthroplasty (THA). Because most LL and OS callipers used in THA depend on fixed points on the pelvis and the femur, limb position could affect measurement error. This study was conducted on a THA simulator to clarify the effects of lower limb position and iliac pin position on LL and OS errors and to determine the permissible range of limb position for accurate LL and OS measurement.

Methods

An LL and OS measurement instrument was used. Two pin positions were tested: the iliac tubercle and the top of the iliac crest intersecting with the extension of the femoral axis. First, the limb was moved in one direction (flexion-extension, abduction-adduction, or internal-external rotation), and LL and OS were measured for each pin position. Next, the limb was moved in combinations of the three directions. Then, the permissible range of combined limb position, which resulted in LL and OS measurement error within ±2 mm, was determined for each pin position.

Results

Only 4° of abduction/adduction caused 5–7 mm error in LL and 2–4 mm error in OS, irrespective of pin position. The effects of flexion–extension and internal–external rotation on LL error were smaller for the top of the iliac crest than for the iliac tubercle, though OS error was similar for both pin positions. For LL, the permissible range of the combined limb position was wider for the top of the iliac crest than for the iliac tubercle.

Conclusion

To minimize LL and OS measurement errors in THA, adduction–abduction must be maintained. The iliac pin position in the top of the iliac crest is preferred because it provides less LL measurement error and a wider permissible range of combined limb position for accurate LL measurement.

Anterior pelvic plane registration accuracy and cup position measurement using ultrasound- and pointer-based navigation in primary total hip arthroplasty

BACKGROUND

Incorrect cup positioning in primary total hip arthroplasty is known as a risk factor for early implant failure. The use of navigation systems leads to more accurate cup positioning.

OBJECTIVE

The aim of this study was to compare the registration accuracy of the anterior pelvic plane and the measurement accuracy of the definite cup position for a pointer computer-assisted orthopaedic navigation system (P-CAOS) and an ultrasound-based navigation tool (US-CAOS) in an intra-individual study design.

METHODS

Anterior pelvic plane registration was performed in 44 patients receiving a primary total hip arthroplasty with P-CAOS and US-CAOS. The cup implantation was performed using US-CAOS. Intraoperatively, the cup position was assessed using P-CAOS and US-CAOS. The postoperative cup position was determined via CT scan. Inclination and anteversion errors were calculated using intraoperative values and CT data. All operations were performed by a single, high-volume surgeon using a minimally invasive anterolateral approach.

RESULTS

The mean inclination error was 0.9∘ in the US-CAOS group and -1.1∘ in the P-CAOS group. This was not statistically significant. The mean anteversion error was significantly reduced (p< 0.001) in the US-CAOS group (1.4∘) compared to the P-CAOS group (-8.0∘). Significantly more cups (23 of 44; 52%) in the P-CAOS group were outliers regarding to the defined anteversion error range of 15∘± 10∘. Outliers in the US-CAOS group amounted to two (of 44; 5%) (p< 0.001). The number of outliers regarding the inclination error range of 40∘± 10∘, did not differ significantly between the P-CAOS (2; 5%) and US-CAOS (1; 2%) group.

CONCLUSION

We were able to show a systematic anterior pelvic plane registration error in this intraindividual study design. US-CAOS based APP landmark registration showed to be significantly more precise compared to P-CAOS registration. The anteversion error of the cup using US-CAOS showed to be significantly reduced compared to the P-CAOS method.

3D Printed Guides and Preoperative Planning for Uncemented Stem Anteversion Reconstruction during Hip Arthroplasty: A Pilot Study

Objective

To investigate if 3D printed guides and preoperative planning can accurately control femoral stem anteversion.

Methods

A prospective comparative study was carried out from 2018 to 2020, including 53 patients who underwent hip arthroplasty for femoral neck fracture. The target rotation center of the femoral head is determined by three-dimensional planning. In group A, planning was made by 2D templates. In group B, preoperative 3D planning and 3D printed osteotomy/positioning guides were performed. After the operation, 3D model registration was performed to calculate the accuracy of anteversion restoration.

Results

We screened 60 patients and randomized a total of 53 to 2 parallel study arms: 30 patients to the group A (traditional operation) and 23 patients to the group B (3D preoperative planning and 3D printed guide). There were no significant differences in demographic or perioperative data between study groups. The restoration accuracy of group A was 5.42° ± 3.65° and of group B was 2.32° ± 1.89°. The number and rate of abnormal cases was 15 (50%) and 2 (8.7%), respectively. Significant statistical differences were found in angle change, restoration accuracy, and number of abnormal cases.

Conclusion

Three-dimensional preoperative planning and 3D printed guides can improve the accuracy of the restoration of femoral anteversion during hip arthroplasty.

Comparable dislocation and revision rates for patients undergoing total hip arthroplasty with subsequent or prior lumbar spinal fusion: a meta-analysis and systematic review

BACKGROUND

There is a known correlation between the procedures of lumbar spinal fusion (LSF), total hip arthroplasty (THA) and the complication of hip dislocation and revision occurring in patients. However there is no consensus as to whether the risk of this complication is higher if THA is performed before or after LSF. This meta-analysis aims to determine the influence of surgical sequence of lumbar spinal fusion and total hip arthroplasty on the rates of hip dislocation and revisions.

METHODS

A meta-analysis was conducted with a multi-database search (PubMed, OVID, EMBASE, Medline) according to PRISMA guidelines on 27th May 2020. Data from all published literature meeting inclusion criteria were extracted and analyzed with an inverse variance statistical model.

FINDINGS

A total of 25,558 subsequent LSF and 43,880 prior LSF THA patients were included in this study. There was no statistically significant difference in all-cause revisions (OR = 0.86, 95%CI: 0.48-1.54, p = 0.61), dislocation (OR = 0.82, 95%CI: 0.25-2.72, p = 0.75) or aseptic loosening (OR = 1.14, 95%CI: 0.94-1.38, p = 0.17) when comparing patients receiving LSF subsequent versus prior to THA.

CONCLUSION

Lumbar spinal fusion remains a risk factor for dislocation and revision of total hip arthroplasties regardless of whether it is performed prior to or after THA. Further preoperative assessment and altered surgical technique may be required in patients having THA who have previously undergone or are likely to undergo LSF in the future.

EVIDENCE LEVEL

Level II, Meta-analysis of homogeneous studies.

WITHDRAWN: Comparison of the accuracy between imageless navigation and manual freehand approaches for total hip arthroplasty: a systematic review and meta-analysis

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Clinical outcomes and complication profile of total hip arthroplasty after lumbar spine fusion: a meta-analysis and systematic review

BACKGROUND

Hip and spine pathology can alter the biomechanics of spino-pelvic mobility. Lumbar spine fusions can reduce the mobility of the lumbar spine and therefore result in compensatory femoral motion, contributing towards dislocations of THA.

PURPOSE

This meta-analysis aims to determine the effect of pre-existing spine fusions on THA outcomes, and complication profile including hip dislocations, all-cause revisions and all complications.

METHODS

A multi-database search was performed according to PRISMA guidelines. All studies that compared patients who underwent THA with and without prior SF were included in the analysis.

RESULTS

Ten studies were included in this review, consisting of 28,396 SF THA patients and 1,550,291 non-SF THA patients. There were statistically significant higher rates of hip dislocation (OR 2.20, 95% CI 1.71-2.85, p < 0.001), all-cause revision (OR 3.43, 95% CI 1.96-6.00, p < 0.001) and all complications (OR 2.83, 95% CI 1.28-6.24, p = 0.01) in SF than in non-SF THA patients. When registry data were excluded, these rates were approximately doubled. Subgroup analysis of revisions for dislocations was not statistically significant (OR 5.28, 95% CI 0.76-36.87, p = 0.09). While no meta-analysis was performed on clinical outcomes due to heterogeneous parameter reporting, individual studies reported significantly poorer outcomes in SF patients than in non-SF patients.

CONCLUSION

THA patients with SF are at higher risks of hip dislocations, all-cause revisions and all complications, which may adversely affect patient-reported outcomes. Surgeons should be aware of these risks and appropriately plan to account for altered spino-pelvic biomechanics, in order to reduce the risks of hip dislocations and other complications.

LEVEL OF EVIDENCE

II (Meta-analysis of non-homogeneous studies). These slides can be retrieved under Electronic Supplementary Material.

Clinical efficacy of OrthoPilot navigation system versus conventional manual total hip arthroplasty: A systematic review and meta-analysis

Objective

This study was performed to compare the clinical efficacy between the OrthoPilot navigation system and conventional manual surgery in patients undergoing total hip arthroplasty.

Methods

The Embase, PubMed, CINAHL, and Cochrane databases were searched for clinical trials. The outcome measurements were the anteversion angle, inclination angle, and complications. Review Manager 5.3 statistical software was used for the data analysis.

Results

Significant differences were found in the femoral offset and overall complication rate between the conventional and navigation groups. Additionally, the conventional group had significantly less anteversion than the navigation group. However, the navigation group had significantly better inclination. The operation time was significantly shorter in the conventional than navigation group.

Conclusion

Both the OrthoPilot navigation system and conventional total hip arthroplasty result in significant improvements in patient function with similar overall complication rates and have their own advantages in achieving good cup position. The conventional procedure has a shorter operation time than does use of a navigation system.

Virtual trial to evaluate the robustness of cementless femoral stems to patient and surgical variation

Primary stability is essential for the success of cementless femoral stems. In this study, patient specific finite element (FE) models were used to assess changes in primary stability due to variability in patient anatomy, bone properties and stem alignment for two commonly used cementless femoral stems, Corail® and Summit® (DePuy Synthes, Warsaw, USA). Computed-tomography images of the femur were obtained for 8 males and 8 females. An automated algorithm was used to determine the stem position and size which minimized the endo-cortical space, and then span the plausible surgical envelope of implant positions constrained by the endo-cortical boundary. A total of 1952 models were generated and ran, each with a unique alignment scenario. Peak hip contact and muscle forces for stair climbing were scaled to the donor's body weight and applied to the model. The primary stability was assessed by comparing the implant micromotion and peri-prosthetic strains to thresholds (150 μm and 7000 µε, respectively) above which fibrous tissue differentiation and bone damage are expected to prevail. Despite the wide range of implant positions included, FE prediction were mostly below the thresholds (medians: Corail®: 20-74 µm and 1150-2884 µε, Summit®: 25-111 µm and 860-3010 µε), but sensitivity of micromotion and interfacial strains varied across femora, with the majority being sensitive (p < 0.0029) to average bone mineral density, cranio-caudal angle, post-implantation anteversion angle and lateral offset of the femur. The results confirm the relationship between implant position and primary stability was highly dependent on the patient and the stem design used.

Evaluating the primary stability of standard vs lateralised cementless femoral stems - A finite element study using a diverse patient cohort

BACKGROUND

Restoring the original femoral offset is desirable for total hip replacements as it preserves the original muscle lever arm and soft tissue tensions. This can be achieved through lateralised stems, however, the effect of variation in the hip centre offset on the primary stability remains unclear.

METHODS

Finite element analysis was used to compare the primary stability of lateralised and standard designs for a cementless femoral stem (Corail®) across a representative cohort of male and female femora (N = 31 femora; age from 50 to 80 years old). Each femur model was implanted with three designs of the Corail® stem, each designed to achieve a different degree of lateralisation. An automated algorithm was used to select the size and position that achieve maximum metaphyseal fit for each of the designs. Joint contact and muscle forces simulating the peak forces during level gait and stair climbing were scaled to the body mass of each subject.

FINDINGS

The study found that differences in restoring the native femoral offset introduce marginal differences in micromotion (differences in peak micromotion <21 μm), for most cases. Nonetheless, significant reduction in the interfacial strains (>3000 με) was achieved for some subjects when lateralized stems were used.

INTERPRETATION

Findings of this study suggest that, with the appropriate size and alignment, the standard offset design is likely to be sufficient for primary stability, in most cases. Nonetheless, appropriate use of lateralised stems has the potential reduce the risk of peri-prosthetic bone damage. This highlights the importance of appropriate implant selection during the surgical planning stage.

Leg length correction in computer assisted primary total hip arthroplasty: A collective review of the literature

AIM

The aim of this study was to determine whether computer assisted surgery (CAS) can provide a more accurate, reproducible technique to achieve equal leg lengths in total hip arthroplasty (THA) and to compare the clinical outcome with conventional on table judgement of leg lengths in unilateral total hip replacement.

METHODS

A collective review of the literature was undertaken utilizing applicable databases. Research criteria were the following: (1) Developing and developed country studies, (2) level II, III, IV and V studies, (3) human subjects only, (4) period of study from 1996 to 2017 - English text only. The identified publications were assessed for their relevance and methodology and 20 articles were selected.

RESULTS

The overall evaluation of the results demonstrates that CAS provides a more accurate reproduction of limb length in THA compared to conventional freehand THA. Short to medium-term studies have demonstrated no benefit in clinical outcome scores. There is a high degree of correlation between measurements provided by CAS intraoperatively and radiographic measurements postoperatively.

CONCLUSION

CAS provides a more accurate, reproducible technique to achieve limb length equality in THA compared to conventional freehand THA, however more intensive long-term studies are required to establish the effect on implant longevity and revision surgery rates in the two groups.

Biomechanical Robustness of a Contemporary Cementless Stem to Surgical Variation in Stem Size and Position

Successful designs of total hip replacement (THR) need to be robust to surgical variation in sizing and positioning of the femoral stem. This study presents an automated method for comprehensive evaluation of the potential impact of surgical variability in sizing and positioning on the primary stability of a contemporary cementless femoral stem (Corail®, DePuy Synthes). A patient-specific finite element (FE) model of a femur was generated from computed tomography (CT) images from a female donor. An automated algorithm was developed to span the plausible surgical envelope of implant positions constrained by the inner cortical boundary. The analysis was performed on four stem sizes: oversized, ideal (nominal) sized, and undersized by up to two stem sizes. For each size, Latin hypercube sampling was used to generate models for 100 unique alignment scenarios. For each scenario, peak hip contact and muscle forces published for stair climbing were scaled to the donor's body weight and applied to the model. The risk of implant loosening was assessed by comparing the bone–implant micromotion/strains to thresholds (150 μm and 7000 με) above which fibrous tissue is expected to prevail and the periprosthetic bone to yield, respectively. The risk of long-term loosening due to adverse bone resorption was assessed using bone adaptation theory. The range of implant positions generated effectively spanned the available intracortical space. The Corail stem was found stable and robust to changes in size and position, with the majority of the bone–implant interface undergoing micromotion and interfacial strains that are well below 150 μm and 7000 με, respectively. Nevertheless, the range of implant positions generated caused an increase of up to 50% in peak micromotion and up to 25% in interfacial strains, particularly for retroverted stems placed in a medial position.

Advances in hip arthroplasty surgery: what is justified?

Total hip arthroplasty (THA) surgery has shown dramatic changes in terms of increased number of procedures and of technical development in recent years. It has been described as “the operation of the 20^th century” for the excellent results, the high satisfaction of the patients and the improvement of the quality of life.

A lot of variations have been introduced over the last few decades in THA especially in terms of indications (both in younger and older patients), techniques and devices (approaches, tissue preservation, biomaterials and industrial finishing), per-operative management (blood loss and pain control) and post-operative protocols (the so called “fast track” surgery). Looking at all these advances the emerging question is: have all of them been justified both in terms of improvement of the results for the patients and of the cost/benefit ratio from an economical point of view?

The purpose of this paper is to critically analyse the advantages and the disadvantages of the theoretically proposed “advances in hip arthroplasty” and attempt to understand which are justified of such “advances” nowadays, based on the international and the European perspective with a focus on the author’s personal clinical experience.

Cite this article: EFORT Open Rev 2017;2. DOI: 10.1302/2058-5241.2.170008. Originally published online at www.efortopenreviews.org