Containment versus impingement: finding a compromise for cup placement in total hip arthroplasty

Stem anteversion is not affected by proximal femur geometry in robotic-assisted total hip arthroplasty

BACKGROUND

In the present study, the surgeon aimed to align the stem at 5° to 25° in anteversion. The robotic technology was used to measure stem anteversion with respect to proximal femur anteversion at different levels down the femur.

METHODS

A total of 102 consecutive patients underwent robotic-arm-assisted total hip arthroplasty (RTHA). 3D CT-based preoperative planning was performed to determine femoral neck version (FNV), posterior cortex anteversion (PCA), anterior cortex anteversion (ACA), and femoral metaphyseal axis anteversion (MAA) at 3 different levels: D (10 mm above lesser trochanter), E (the midpoint of the planned neck resection line) and F (head-neck junction). The robotic system was used to define and measure stem anteversion during surgery.

RESULTS

Mean FNV was 6.6° (SD: 8.8°) and the mean MAA was consistently significantly higher than FNV, growing progressively from proximal to distal. Mean SV was 16.4° (SD: 4.7°). There was no statistically significant difference (P = 0.16) between SV and MAA at the most distal measured level. In 96.1% cases, the stem was positioned inside the 5°-25° anteversion range.

CONCLUSIONS

Femoral anteversion progressively increased from neck to proximal metaphysis. Aligning the stem close to femoral anteversion 10 mm above the lesser trochanter often led to the desired component anteversion.

Accuracy of cup placement compared with preoperative surgeon targets in primary total hip arthroplasty using standard instrumentation and techniques: a global, multicenter study

BACKGROUND

Acetabular cup positioning in total hip arthroplasty (THA) is closely related to outcomes. The literature has suggested cup parameters defined by the Lewinnek safe zone; however, the validity of such measures is in question. Several studies have raised concerns about the benefits of using the Lewinnek safe zone as a predictor of success. In this study we elected to use prospective surgeon targets as the basis for comparison to see how successful surgeons are positioning their cup using standard instruments and techniques.

METHODS

A prospective, global, multicenter study was conducted. Cup positioning success was defined as a composite endpoint. Both cup inclination and version needed to be within 10° of the surgeon target to be considered a success. Radiographic analysis was conducted by a third-party reviewer.

RESULTS

In 170 subjects, inclination, target versus actual, was 44.8° [standard deviation (SD 0.9°)] and 43.1° (SD 7.6°), respectively (p = 0.0029). Inclination was considered successful in 84.1% of cases. Mean version, target versus actual, was 19.4° (SD 3.9°) and 27.2° (SD 5.6°), respectively (p < 0.0001). Version was considered successful in 63.4% of cases, and combined position (inclination and version) was considered successful in 53.1%.

CONCLUSION

This study shows that with traditional methods of placing the cup intraoperatively, surgeons are only accurate 53.1% of the time compared with a predicted preoperative plan. This study suggests that the inconsistency in cup positioning based on the surgeon's planned target is potentially another important variable to consider while using a mechanical guide or in freehand techniques for cup placement in THA.

TRIAL REGISTRATION

This study is registered on ClinicalTrials.gov, NCT03189303.

Effect of longer femoral head on leg length, offset, and range of motion in total hip arthroplasty: a simulation study

In this study, we investigated the relationship between head length, leg length, offset, and dislocation resistance using range of motion (ROM) simulations based on computed tomography data to examine if a longer femoral head reduces the risk of dislocation. The femoral components were set to eliminate leg length differences with a + 0 mm head, and variations for + 4-, + 7-, and + 8-mm heads were analyzed. Offset and ROM were assessed when longer heads were used, with the leg length adjusted to be similar to that of the contralateral side. While internal rotation at flexion and external rotation at extension increased with + 4-mm longer heads, the + 7- and + 8-mm heads did not increase dislocation resistance. When adjusting for leg length, the longer heads showed no significant differences in offset and ROM. Enhancing dislocation resistance by solely increasing the offset with a longer head, while simultaneously adjusting the depth of stem insertion, may be a beneficial intraoperative technique. Although a + 4-mm longer head possibly increases ROM without impingement, heads extended by + 7 or + 8 mm may not exhibit the same advantage. Therefore, surgeons should consider this technique based on the implant design.

Measurement of the normal contralateral hip flexion angle and posterior pelvic tilt angle using a pelvic guide pin in total hip arthroplasty

BACKGROUND

We aimed to measure the posterior pelvic tilt angle at maximum hip flexion and hip flexion range of motion at the femoroacetabular joint using a pelvic guide pin and to examine the difference in flexion range of motion when determined by a physical therapist and under anesthesia.

METHODS

Data of 83 consecutive patients undergoing primary unilateral total hip arthroplasty were assessed. Using a pin inserted into the iliac crest to define the cup placement angle under anesthesia before and after total hip arthroplasty, the posterior pelvic tilt angle was determined as the change in pin tilt from the supine position to maximum hip flexion. Flexion range of motion under anesthesia was calculated as the difference in the angle between the trunk and thigh at maximum flexion and the posterior pelvic tilt angle. Flexion range of motion with a fixed pelvis measured preoperatively by a physical therapist was compared to that under anesthesia. A goniometer was used for all measurements and the number of measurements was one.

FINDINGS

Mean posterior pelvic tilt angle of the pin inserted into the pelvis under anesthesia was 15.8° ± 5.3° (3°-26°) preoperatively and 12.1° ± 4.9° (3°-26°) postoperatively. Mean flexion range of motion under anesthesia was 109.4° ± 6.9° (88°-126°) and that measured by a physical therapist was 101.1° ± 8.2° (80°-120°); the difference was significant (9.7°; p < 0.01).

INTERPRETATION

These results highlight the difficulty in accurately determining hip flexion angles without the use of special devices and may help surgeons and physical therapists recognize and address this issue.

A Simple Preoperative Score Predicting Failure Following Decompression Surgery for Degenerative Lumbar Spinal Stenosis

BACKGROUND CONTEXT

Proper patient selection is crucial for the outcome of surgically treated degenerative lumbar spinal stenosis (DLSS). Nevertheless, there is still not a clear consensus regarding the optimal treatment option for patients with DLSS.

PURPOSE

To investigate the treatment failure rate and introduce a simple, preoperative score to aid surgical decision-making.

STUDY DESIGN/SETTING

Retrospective observational study.

PATIENT SAMPLE

Four hundred forty-five patients who underwent surgical decompression for DLSS.

OUTCOME MEASURES

Treatment failure (defined as conversion to a fusion of a previously decompressed level) of lumbar decompression.

MATERIALS AND METHODS

Several risk factors associated with worse outcomes and treatment failures, such as age, body mass index, smoking status, previous surgery, low back pain (LBP), facet joint effusion, disk degeneration, fatty infiltration of the paraspinal muscles, the presence of degenerative spondylolisthesis and the facet angulation, were investigated.

RESULTS

At a mean follow-up of 44±31 months, 6.5% (29/445) of the patients underwent revision surgery with spinal fusion at an average of 3±9 months following the lumbar decompression due to low back or leg pain. The baseline LBP (≥7) [odds ratio (OR)=5.4, P <0.001], the presence of facet joint effusion (>2 mm) in magnetic resonance imaging (OR=4.2, P <0.001), and disk degeneration (Pfirrmann >4) (OR=3.2, P =0.03) were associated with an increased risk for treatment failure following decompression for DLSS. The receiver operating characteristic curve analysis demonstrated that a score≥6 points yielded a sensitivity of 90% and specificity of 64% for predicting a treatment failure following lumbar decompression for DLSS in the present cohort.

CONCLUSIONS

The newly introduced score quantifying amounts of LBP, facet effusions, and disk degeneration, could predict treatment failure and the need for revision surgery for DLSS patients undergoing lumbar decompression without fusion. Patients with scores >6 have a high chance of needing fusion following decompression surgery.

LEVEL OF EVIDENCE

Retrospective observational study, Level III.

Validation of a Novel Method of Measuring Cup Orientation using BiPlanar Simultaneous Radiographic Images

BACKGROUND

Accurate acetabular component positioning is paramount to the success of total hip arthroplasty. Two-dimensional imaging alone remains a popular tool for implant position assessment despite known limitations. We investigated the accuracy of a novel method for assessing acetabular component position based upon orthogonal simultaneous biplanar Xray images.

METHODS

There were forty consecutive patients who had a pre-existing total hip arthroplasty (THA) on the contralateral side who underwent both computed tomography (CT) and simultaneous orthogonal biplanar radiographic scans for pre-operative planning of THA. The operative inclination (OI) and operative anteversion (OA) of the acetabular cup were calculated by a new measurement method using the biplanar simultaneous scans. Those measurements were compared to measurement of the cup orientation on CT. The measurements were made by two independent observers. Interobserver correlation coefficients were calculated between the two observers to measure reliability.

RESULTS

The mean error in OA measurement of the acetabular cup between simultaneous orthogonal biplanar radiographic and CT imaging was 0.5° (Standard Deviation (SD): 1.9°, minimum -4.0°, maximum 5.0°), the mean error in OI was 0.0° (SD: 1.7°, minimum -5.0°, maximum 4.0°). The average absolute error was 1.5° for OA, and 1.2° for OI. Interobserver correlation coefficient was 0.83 for OA and 0.93 for OI.

CONCLUSION

The novel method of measuring cup orientation using simultaneous biplanar radiographic scans utilized in this study was accurate and reproducible between observers compared to CT measurements.

Model-Based Acetabular Cup Orientation Optimization Based On Minimizing the Risk of Edge-Loading and Implant Impingement Following Total Hip Arthroplasty

In this paper, a computationally-efficient model-based method for determining patient-specific optimal acetabular cup alignment for total hip arthroplasty (THA) is presented. The proposed algorithm minimizes the risk of implant impingement and edge-loading, which are reported as the major causes of hip dislocation following THA. First, by using motion capture data recorded from the patient performing different daily activities, the hip contact force and the relative orientation of the femur and pelvis are calculated by a musculoskeletal model. Then, by defining two quantitative indices i.e., angular impingement distance and angular edge-loading distance, the risk of impingement and edge-loading are assessed for a wide range of cup alignments. And finally, three optimization criteria are introduced to estimate the optimal cup alignment with a tradeoff between the risk of impingement and edge-loading. The results show that patient-specific characteristics such as pelvic tilt could significantly change the optimal cup alignment, especially the value of cup anteversion. Therefore, in some cases, the well-known Lewinnek safe zone may not be optimal, or even safe. Unlike other dynamic model-based methods, in this work, the need for force plate measurements is eliminated by estimating the ground reaction forces and moments, which makes this method more practical and cost-efficient. Furthermore, the low computational complexity due to analytical formulas makes this method suitable for both preoperative and intra-operative planning.

Measurement of safe acetabular medial wall defect size in revision hip arthroplasty with a porous cup

INTRODUCTION

The majority of acetabular revisions can be performed with an uncemented, porous acetabular component with or without bone grafting. These are contained acetabular defects, with an intact acetabular rim (Paprosky type I and II). As defects of the medial wall of the acetabulum are a challenge situation revision surgery, we performed this biomechanical study on a pig pelvis model with contained acetabular defects to determine the size of medial wall defect at which the acetabular cup will have sufficient primary stability.

MATERIALS AND METHODS

In 24 pig pelvis models, different diameter of medial wall defects were created, followed by acetabular component placement. The acetabulum externally loaded, and the force at a level in which the acetabular component remains stable for each diameter of defect, or at which point the acetabular cup moves into the pelvis for >2 mm.

RESULTS

In the models with acetabular medial wall defects of 10 and 20 mm, 2 mm acetabular displacement occurred under a force between 1000 and 1500 N. In those with a medial wall defect of 25 mm, the force that caused acetabular instability was between 700 and 1000 N. In the models with 30 mm of medial wall defect all acetabular components were unstable under a force of 700 N.

CONCLUSIONS

According to our results, acetabular component should be stable if the defect of the medial wall of the acetabulum is less than 68% of the diameter of the acetabular component or if the uncovered surface area of the acetabular component is not greater than 27%, and the force <700 N. For a load of 1000 N, the medial wall defect should not exceed 45% of acetabular component diameter or 18% of uncovered acetabular component surface.

Novel Measure of Acetabular Cup Inclination and Anteversion During Total Hip Arthroplasty

PURPOSE

The purposes of the present research were to assess the accuracy and usability of the inertial navigation system (INS).

MATERIALS AND METHODS

The accuracy of the device navigation subsystem was assessed using benchtop testing. The usability was assessed through simulated use with surgeons. These results were compared to recent cadaveric results for the same system.

RESULTS

The navigation subsystem had an overall mean absolute error of 1.21° and a maximum absolute error across all devices of 4.79°. The device was found to be usable and to add an estimated 7 minutes to surgery time.

CONCLUSION

The INS uses a novel approach to provide the surgeon with accurate and fast acetabular cup inclination and anteversion angles during THA.

The Patient-Specific Combined Target Zone for Morpho-Functional Planning of Total Hip Arthroplasty

Background Relevant criteria for total hip arthroplasty (THA) planning have been introduced in the literature which include the hip range of motion, bony coverage, anterior cup overhang, leg length discrepancy, edge loading risk, and wear. The optimal implant design and alignment depends on the patient’s anatomy and patient-specific functional parameters such as the pelvic tilt. The approaches proposed in literature often consider one or more criteria for THA planning. but to the best of our knowledge none of them follow an integrated approach including all criteria for the definition of a patient-specific combined target zone (PSCTZ). Questions/purposes (1) How can we calculate suitable THA implant and implantation parameters for a specific patient considering all relevant criteria? (2) Are the resulting target zones in the range of conventional safe zones? (3) Do patients who fulfil these combined criteria have a better outcome score? Methods A method is presented that calculates individual target zones based on the morphology, range of motion and load acting on the hip joint and merges them into the PSCTZ. In a retrospective analysis of 198 THA patients, it was calculated whether the patients were inside or outside the Lewinnek safe zone, Dorr combined anteversion range and PSCTZ. The postoperative Harris Hip Scores (HHS) between insiders and outsiders were compared. Results 11 patients were inside the PSCTZ. Patients inside and outside the PSCTZ showed no significant difference in the HHS. However, a significant higher HHS was observed for the insiders of two of the three sub-target zones incorporated in the PSCTZ. By combining the sub-target zones in the PSCTZ, all PSCTZ insiders except one had an HHS higher than 90. Conclusions The results might suggest that, for a prosthesis implanted in the PSCTZ a low outcome score of the patient is less likely than using the conventional safe zones by Lewinnek and Dorr. For future studies, a larger cohort of patients inside the PSCTZ is needed which can only be achieved if the cases are planned prospectively with the method introduced in this paper. Clinical Relevance The method presented in this paper could help the surgeon combining multiple different criteria during THA planning and find the suitable implant design and alignment for a specific patient.

Constrained tripolar liner in patients with high risk of dislocation - Analysis of incidence and risk of failure

Introduction

The aim of this study was to determine number and type of failures and revisions after usage of a constrained tripolar acetabular liner in patients with high risk of dislocation. Potential correlations between these failures and the factors included were analyzed.

Materials and methods

In this retrospective study 55 participants in 68 cases were included after treatment with constrained tripolar acetabular liner. Patient specific data as well as surgery and implant specific data were collected. Radiological images were assessed. Furthermore, the gluteal function was analyzed. The parameters were statistically verified with regard to their influence on the failure of the constrained tripolar liner.

Results

This study included 16 cases (in nine participants) of postoperative failure. This results in a survival rate of 76.5% regarding the number of cases after 17 months. The statistical analysis of the different parameters considered that the number of previous surgeries has a significant (p = 0.027) influence on the failure.

Conclusions

This retrospective study shows that treatment with constrained tripolar acetabular liners is a satisfactory method of treatment in cases with a high risk of dislocation. However, in cases with an increasing number of previous surgeries, an increased risk of failure was found. Therefore, in such cases, this type of supply treatment should be treated critically.

Preoperative factors improving the prediction of the postoperative sagittal orientation of the pelvis in standing position after total hip arthroplasty

The aims of this study were to investigate if the sagittal orientation of the pelvis (SOP) in the standing position changes after total hip arthroplasty (THA) and evaluate what preoperative factors may improve the prediction of the postoperative standing SOP in the context of a patient-specific functional cup orientation. 196 primary THA patients from Japan were retrospectively selected for this study. Computed tomography imaging of the pelvis, EOS imaging of the lower body and lateral radiographs of the lumbar spine in the standing position were taken preoperatively. Common biometrics and preoperative Harris Hip Score were recorded. The EOS imaging in the standing position was repeated three months following THA. A 3D/2.5D registration process was used to determine the standing SOP. Thirty-three preoperative biometric, morphological and functional parameters were measured. Important preoperative parameters were identified that significantly improve the prediction of the postoperative standing SOP by using multiple linear LASSO regression. On average, the SOP changed significantly (p < 0.001) between the preoperative and postoperative standing position three months after THA by 3° ± 4° in the posterior direction. The age, standing lumbar lordosis angle (LLA) and preoperative supine and standing SOP significantly (p < 0.001) improve the prediction of the postoperative standing SOP. The linear regression model for the prediction of the postoperative standing SOP is significantly (p < 0.001) improved by adding the parameters preoperative standing SOP and LLA, in addition to the preoperative supine SOP, reducing the root mean square error derived from a leave-one-out cross-validation by more than 1°. The mean standing SOP in Japanese patients changes already three months after THA in comparison to the preoperative value. The preoperative factors age, LLA, supine and standing SOP can significantly improve the prediction of the postoperative standing SOP and should be considered within the preoperative planning process of a patient-specific functional cup orientation.

The Impingement-free, Prosthesis-specific, and Anatomy-adjusted Combined Target Zone for Component Positioning in THA Depends on Design and Implantation Parameters of both Components

BACKGROUND

Lewinnek's recommendation for orienting the cup in THA is criticized because it involves a static assessment of the safe zone and because it does not consider stem geometry. A revised concept of the safe zone should consider those factors, but to our knowledge, this has not been assessed.

QUESTIONS/PURPOSES

(1) To determine the shape, size, and location of target zones for combined cup and stem orientation for a straight stem/hemispheric cup THA to maximize the impingement-free ROM and (2) To determine whether and how these implant positions change as stem anteversion, neck-shaft angle, prosthetic head size and target range of movements are varied.

METHODS

A three-dimensional computer-assisted design model, in which design geometry was expressed in terms of parameters, of a straight stem/hemispheric cup hip prosthesis was designed, its design parameters modified systematically, and each prosthesis model was implanted virtually at predefined component orientations. Functional component orientation referencing to body planes was used: cups were abducted from 20° to 70°, and anteverted from -10° to 40°. Stems were rotated from -10° to 40° anteversion, neck-shaft angles varied from 115° to 143°, and head sizes varied from 28 to 40 mm. Hip movements up to the point of prosthetic impingement were tested, including simple flexion/extension, internal/external rotation, ab/adduction, combinations of these, and activities of daily living that were known to trigger dislocation. For each combination of parameters, the impingement-free combined target zone was determined. Maximizing the size of the combined target zone was the optimization criterion.

RESULTS

The combined target zones for impingement-free cup orientation had polygonal boundaries. Their size and position in the diagram changed with stem anteversion, neck-shaft angle, head size, and target ROM. The largest target zones were at neck-shaft angles from 125° to 127°, at stem anteversions from 10° to 20°, and at radiographic cup anteversions between 17° and 25°. Cup anteversion and stem anteversion were inverse-linearly correlated supporting the combined-anteversion concept. The range of impingement-free cup inclinations depended on head size, stem anteversion, and neck-shaft angle. For a 127°-neck-shaft angle, the lowest cup inclinations that fell within the target zone were 42° for the 28-mm and 35° for the 40-mm head. Cup anteversion and combined version depended on neck-shaft angle. For head size 32-mm cup, anteversion was 6° for a 115° neck-shaft angle and 25° for a 135°-neck-shaft angle, and combined version was 15° and 34° respectively.

CONCLUSIONS

The shape, size, and location of the combined target zones were dependent on design and implantation parameters of both components. Changing the prosthesis design or changing implantation parameters also changed the combined target zone. A maximized combined target zone was found. It is mandatory to consider both components to determine the accurate impingement-free prosthetic ROM in THA.

CLINICAL RELEVANCE

This study accurately defines the hypothetical impingement-free, design-specific component orientation in THA. Transforming it into clinical precision may be the case for navigation and/or robotics, but this is speculative, and as of now, unproven.

Effect of pelvic tilt and rotation on cup orientation in standing anteroposterior radiographs

BACKGROUND

Individual pelvic tilt and rotation have wide variability that can affect the measurement of cup orientation in anteroposterior (AP) radiographs. The purpose of this study was to analyse the effect of pelvic tilt and rotation on radiographic measurements of cup orientation.

METHODS

A total of 53 patients (63 hips) were included in this study. The patients underwent a computed tomography study with standing AP pelvis radiographs taken both preoperatively and approximately 3 months postoperatively. We used 2-dimensional/3-dimensional matching to measure the pelvic tilt and rotation, and the non-standardised and standardised cup orientation.

RESULTS

There was no difference in the pelvic tilt and rotation between the preoperative and postoperative radiographs. The distribution of the differences between the non-standardised and standardised cup anteversion exhibited a change within 5° in only 34/63 (54%) hips. The pelvic tilt correlated with the difference between the non-standardised and standardised cup anteversion, but the pelvic rotation did not. When all 63 hips were separated into the right and left sides, the pelvic rotation inversely correlated with the pelvic tilt-adjusted difference between the non-standardised and standardised cup anteversion of the right side but directly correlated with that of the left side.

CONCLUSIONS

The current study demonstrated that the measurement of cup anteversion in standing AP radiographs is significantly affected by both the pelvic tilt and pelvic rotation. An improved understanding of the pelvic orientation may eventually allow for desired cup positioning on a patient-specific basis to potentially reduce complications associated with the malposition of the cup.

A Preoperative Analytical Model for Patient-Specific Impingement Analysis in Total Hip Arthroplasty

Prosthetic impingement is important to consider during total hip arthroplasty planning to minimise the risk of joint instability. Modelling impingement preoperatively can assist in defining the required component alignment for each individual. We developed an analytical impingement model utilising a combination of mathematical calculations and an automated computational simulation to determine the risk of prosthetic impingement. The model assesses cup inclination and anteversion angles that are associated with prosthetic impingement using patient-specific inputs, such as stem anteversion, planned implant types, and target Range of Motion (ROM). The analysed results are presented as a range of cup inclination and anteversion angles over which a colour map indicates an impingement-free safe zone in green and impingement risk zones in red. A validation of the model demonstrates accuracy within +/- 1.4° of cup inclination and anteversion. The study further investigated the impact of changes in stem anteversion, femoral head size, and head offset on prosthetic impingement, as an example of the application of the model.

The optimal combined anteversion pattern to achieve a favorable impingement-free angle in total hip arthroplasty

BACKGROUND

There have been no studies on the differences in impingement-free angle that result from different combined anteversion (CA) patterns. The aim of this study was to find the optimal CA pattern for achieving a favorable impingement-free angle, including bony and prosthetic impingement, in total hip arthroplasty.

METHODS

We evaluated 100 patients with no hip arthritis. We investigated the impingement-free angle (flexion, internal rotation with 90° flexion, extension, and external rotation) after changing the stem and cup anteversions to satisfy several CA patterns [cup anteversion + stem anteversion = 30°, 40°, 50°, and 60°; cup anteversion + 0.7 × stem anteversion = 37.3° (:Widmer's theory); and cup anteversion + 0.77 × stem anteversion = 43.3° (:Yoshimine's theory)] using 3-dimensional templating software.

RESULTS

The impingement-free angle changed dramatically among the various CA patterns. The optimal CA was changed by various stem anteversion. Only CA: Widmer with stem anteversion of 20° satisfied daily-life range of motion (ROM) requirements (flexion ≥130°, internal rotation with 90° flexion ≥ 45°, extension ≥ 40°, external rotation ≥ 40°).

CONCLUSION

Good impingement-free angle cannot be obtained with single fixed CA. Different CA patterns should be used, depending on the differences in the stem anteversion. A CA of 30° with 0° ≤ stem anteversion ≤10°; a CA:Widmer with 20° of stem anteversion; a CA of 40° or Widmer with 30° of stem anteversion. When stem anteversion is ≥40°, CA should be decided by each patient's state. Among them, a stem anteversion of 20° with cup anteversion of 23.3° was found to be the best CA pattern.

Restoration of center of rotation and balance of THR

Improvements in early hip arthroplasties focused on surgical techniques with subsequent studies emphasizing restoration of the hip center of rotation for longevity of the implant. Current literature suggests femoral stem anteversion of 10-20°, cup anteversion of 20-25° and a combined anteversion of 25-40° in males, 30-45° in females. Inclination goal appears to be 45° precisely to balance between impingement & dislocation versus edge loading & accelerated wear. Restoration of the acetabular center of rotation will improve joint reactive forces and reduce wear. Here we describe techniques to achieve a well balanced total hip with restoration of the center of rotation.

Effect of changing femoral head diameter on bony and prosthetic jumping angles

BACKGROUND

In THA, using a larger femoral head can increase the oscillation angle and jumping distance. However, there have been no reports which indicate precisely how increasing the jumping distance leads to an increase in the angle from impingement to dislocation (jumping angle). In this study, we clarified the jumping angle of various head diameters and its relationship with pelvic morphology.

METHODS

Using a three-dimensional templating system, virtual THA and ROM simulations were performed in 82 patients. We investigated the distance between bony and prosthetic impingement points and the head centre and calculated the jumping angle for various head diameters. We measured various pelvic shapes and length to clarify the relationship between pelvic morphology and impingement distance.

RESULTS

Jumping angles were 7.7° ± 3.2°, 12.1° ± 1.6°, 15.4° ± 2.5° and 10.0° ± 3.0° with flexion, internal rotation with 90° flexion (IR), extension and external rotation (ER), respectively, when we used a 22-mm head diameter. Bony jumping angle increased about 0.5°, 0.8°, 1.0° and 0.7° per 2-mm increase in head diameter with flexion, IR, extension and ER. On the other hand, prosthetic jumping angle remained almost stable at about 31°. Impingement distance was related to pelvic morphology in all directions. Bony jumping angles differed with ROM; the biggest was seen with extension, followed by IR, ER and flexion. On the other hand, bony jumping angle was less than prosthetic jumping angle in all cases.

CONCLUSION

Bony jumping angles differed with ROM; the biggest was seen with extension, followed by IR, ER and flexion. Prosthetic impingement angles were stable. In addition, the bony jumping angle was less than the prosthetic jumping angle in all cases.

Hip malformation is a very common finding in young patients scheduled for total hip arthroplasty

INTRODUCTION

In Denmark, 20% of all registered total hip arthroplasties (THA) from 1995 to 2014 has been patients younger than 60 years with primary idiopathic osteoarthritis (OA). It is speculated that hip malformations may be a major contributor to early OA development. It has been shown that hip malformation may compromise implant position and, therefore, identifying and knowing the incidence of malformations is important. Our aim was to assess the prevalence and type of hip malformations in a cohort of younger patients undergoing THA.

MATERIALS AND METHODS

In this prospective two center cohort study, 95 consecutive patients (106 hips) met the inclusion criteria. One observer performed radiographic measurements for malformations and radiographic OA. Inter- and intraobserver variability was assessed.

RESULTS

From 95 patients (male n = 52 and female n = 43) age ranged from 35 to 59 years and prevalences of hip malformations were; CAM-deformity 50.9 and 25.5%, coxa profunda 33 and 27.4%, acetabular retroversion 33 and 29.2%, and acetabular dysplasia 10.4 and 3.8%. All patients showed minimum of one malformation. Prevalences of Tönnis grade 0-1 were 22.6% and 2-3 were 77.4%.

CONCLUSION

All patients showed malformations, especially high prevalences were found for CAM-deformity, coxa profunda and acetabular retroversion. Identifying these malformations is fairly simple and recognizing the high prevalence may help surgeons avoid pitfalls during implant positioning in THA surgery. Further, focus on hip malformations may facilitate correct referral to joint-preserving surgery before OA develops.

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

INTRODUCTION

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Biomechanical model based evaluation of Total Hip Arthroplasty therapy outcome

OBJECTIVE

Total-hip-arthroplasties are performed to treat patients with osteoarthritis. Surgical planning is usually based on specific radiographs. These information could also be used as data for biomechanical modelling.

METHODS

Models are rarely used during clinical practice. Our aim was to analyze model-based the pre- and postoperatively hip-biomechanic. Pre- and postoperative X-rays of 30 patients were examined by using 4 biomechanical-models.

RESULTS

The received results showed variations e.g. an increase and decrease of hip-load pre- and postoperative.

CONCLUSION

With the data of these models it would be possible to integrate the amplitude and orientation of the hip-joint-resultant-force into the therapeutical approach.

Radiographic cup anteversion measurement corrected from pelvic tilt

The purpose of this study was to develop a novel technique to improve the accuracy of radiographic cup anteversion measurement by correcting the influence of pelvic tilt. Ninety virtual total hip arthroplasties were simulated from computed tomography data of 6 patients with 15 predetermined cup orientations. For each simulated implantation, anteroposterior (AP) virtual pelvic radiographs were generated for 11 predetermined pelvic tilts. A linear regression model was created to capture the relationship between radiographic cup anteversion angle error measured on AP pelvic radiographs and pelvic tilt. Overall, nine hundred and ninety virtual AP pelvic radiographs were measured, and 90 linear regression models were created. Pearson's correlation analyses confirmed a strong correlation between the errors of conventional radiographic cup anteversion angle measured on AP pelvic radiographs and the magnitude of pelvic tilt (P < 0.001). The mean of 90 slopes and y-intercepts of the regression lines were -0.8 and -2.5°, which were applied as the general correction parameters for the proposed tool to correct conventional cup anteversion angle from the influence of pelvic tilt. The current method proposes to measure the pelvic tilt on a lateral radiograph, and to use it as a correction for the radiographic cup anteversion measurement on an AP pelvic radiograph. Thus, both AP and lateral pelvic radiographs are required for the measurement of pelvic posture-integrated cup anteversion. Compared with conventional radiographic cup anteversion, the errors of pelvic posture-integrated radiographic cup anteversion were reduced from 10.03 (SD = 5.13) degrees to 2.53 (SD = 1.33) degrees. Pelvic posture-integrated cup anteversion measurement improves the accuracy of radiographic cup anteversion measurement, which shows the potential of further clarifying the etiology of postoperative instability based on planar radiographs.

How to address ischiofemoral impingement? Treatment algorithm and review of the literature

Ischiofemoral impingement (IFI) is a rare cause of hip pain defined by a narrowing of the space between the lateral aspect of the os ischium and the lesser trochanter of the femur. Several underlying anatomic, functional and iatrogenic pathologies have been identified for symptomatic IFI in native hip joints and after total hip arthroplasty. Clinical symptoms vary but most commonly consist of pain of the lower buttock and groin including the inner thigh, and a snapping or clunking phenomenon is often reported. Symptoms may be provoked by a combined extension, adduction and external rotation during physical examination and during long-stride walking. Radiographs of the pelvis and an axial or false-profile-view of the hip as well as magnetic resonance imaging (MRI)-scans should be obtained to strengthen the diagnosis. On MRI, the quadratus femoris muscle signal and the space confined by the anatomic structures surrounding the muscle, the quadratus femoris space, are to be assessed. Targeted infiltration of the muscle can be helpful both diagnostically and therapeutically. The literature on differential diagnoses and treatment options for IFI is limited; therapeutic suggestions are offered only in case reports and series. With this work, we aim to give a systematic approach to the non-surgical and surgical treatment options for IFI based upon the current literature and the authors' personal experience.

Femur first surgical technique: a smart non-computer-based procedure to achieve the combined anteversion in primary total hip arthroplasty

Background

The relevance of prosthetic component orientation to prevent dislocation and impingement following total hip arthroplasty (THA) has been widely accepted. We investigated the use of a non-computer-based surgery to address the reciprocal orientation of the acetabular and femoral components.

Methods

In the femur first technique, the cup is positioned relative to the stem. When the definitive antetorsion of femoral component is fixed, the cup is positioned in a compliant anteversion to the stem. Clinical and radiographic assessments were performed before and 3 months after THA. Radiographic assessment was performed in standing position with the EOS 2D/3D radiography system. 3D images were used to preoperative anterior pelvic plane (APP) angle, postoperative acetabular inclination (AI) and anteversion (AA), and postoperative stem antetorsion. Clinical assessment was performed with Harris Hip Score (HHS).

Results

Forty patients (40 hips) underwent primary THA with an average age of 61 years (range, 36–84). Average HHS increased from 43 ± 5 (range, 37–52) preoperatively to 97 ± 6 (range, 86–100) at the last follow-up (P < 0.0001). Average combined anteversion value of cup with liner and stem was 38° ± 9° (range, 12°-55°). Average AI value of cup with liner was 39° ± 6° (range, 30°-55°) in the group with standard stem and 45° ± 7° (range, 39°-58°) in the group with varized stem (P = 0.007). Relationship analysis showed no correlation between the combined anteversion values of the cup with liner and stem with APP angle values (r = 0.26, P = 0.87).

Conclusions

Femur first technique allows the surgeon to achieve a combined anteversion ranging from 25° to 50° with a cup inclination ranging from 30° to 50°. The cup is positioned according to the functional plane of the patient regardless the preoperative pelvic tilt.

Sagittal spinopelvic alignment predicts hip function after total hip arthroplasty

The aim of this study was to investigate the association between preoperative sagittal spinopelvic alignment and postoperative clinical outcomes after total hip arthroplasty (THA). This retrospective study included 92 patients with hip osteoarthritis who underwent primary THA between May 2013 and October 2015. Patients' characteristics, radiographic sagittal spinopelvic parameters and modified Harris Hip Scores, including function scores (gait scores and functional activities scores), were investigated. Multivariate linear regression analysis was performed to determine the associations between each preoperative sagittal spinopelvic parameter and postoperative hip function The preoperative sagittal spinopelvic parameters that were associated with postoperative gait scores were sagittal vertical axis (adjusted β-coefficient=-0.28, P=0.02), lumbar lordosis angle (adjusted β-coefficient=0.29, P=0.0089), pelvic tilt (adjusted β-coefficient=-0.25, P=0.045), sacral slope (adjusted β-coefficient=0.27, P=0.017) and pelvic incidence minus lumbar lordosis angle (adjusted β-coefficient=-0.31, P=0.01). The preoperative sagittal spinopelvic parameters that were related to the postoperative functional activities scores were sagittal vertical axis (adjusted β-coefficient=-0.38, P=0.0051) and pelvic incidence minus lumbar lordosis angle (adjusted β-coefficient=-0.39, P=0.0033). Patients with preoperative imbalanced sagittal alignment such as larger sagittal vertical axis, larger pelvic incidence minus lumbar lordosis and retroversion of pelvis had poorer clinical outcomes than others after THA. While, those preoperative imbalanced patients with anteversion of pelvis may have a compensatory ability which could correct the abnormal sagittal alignment after THA. Preoperative sagittal spinopelvic alignment affected postoperative clinical outcomes after THA.

Current Concepts in Acetabular Positioning in Total Hip Arthroplasty

Being one of the most successful surgeries in the history of medicine, the indications for total hip arthroplasty have widened and are increasingly being offered to younger and fitter patients. This has also led to high expectations for longevity and outcomes. Acetabular cup position has a significant impact on the results of hip arthroplasty as it affects dislocation, abductor muscle strength, gait, limb lengths, impingement, noise generation, range of motion (ROM), wear, loosening, and cup failure. The variables in cup position are depth, height, and angular position (anteversion and inclination). The implications of change in depth of center of rotation (COR) are medialized versus anatomical positioning. As opposed to traditional medialization with beneficial effects on joint reaction force, the advantages of an anatomical position are increasingly recognized. The maintained acetabular offset offers advantages in terms of ROM, impingement, cortical rim press fit, and maintaining medial bone stock. The height of COR influences muscle activity and limb lengths and available bone stock for cup support. On the other hand, ideal angular position remains a matter of much debate and reliably achieving a target angular position remains elusive. This is not helped by variations in the way we describe angular position, with operative, radiologic, or anatomic definitions being used variably to describe anteversion and inclination. Furthermore, pelvic tilt plays a major role in functional positions of the acetabulum. In addition, commonly used techniques of positioning often do not inform us of the real orientation of the pelvis on operating table, with possibility of significant adduction, flexion, and external rotation of the pelvis being possibilities. This review article brings together the evidence on cup positioning and aims to provide a systematic and pragmatic approach in achieving the best position in individual cases.

Patient-specific hip geometry has greater effect on THA wear than femoral head size

In vivo linear penetration in total hip arthroplasty (THA) exhibits similar values for 28mm and 32mm femoral head diameter with considerable variations between and within the studies. It indicates factors other than femoral head diameter influence polyethylene wear. This study is intended to test the effect of patient׳s individual geometry of musculoskeletal system, acetabular cup orientation, and radius of femoral head on wear. Variation in patient׳s musculoskeletal geometry and acetabular cup placement is evaluated in two groups of patients implanted with 28mm and 32mm THA heads. Linear wear rate estimated by mathematical model is 0.165-0.185mm/year and 0.157-0.205mm/year for 28 and 32mm THA heads, respectively. Simulations show little influence femoral head size has on the estimated annual wear rate. Predicted annual linear wear depends mostly on the abduction angle of the acetabular cup and individual geometry of the musculoskeletal system of the hip, with the latter having the greatest affect on variation in linear wear rate.

Gait six month and one-year after computer assisted Femur First THR vs. conventional THR. Results of a patient- and observer- blinded randomized controlled trial

A prospective randomized controlled trial is presented that is used to compare gait performance between the computer assisted Femur First (CAS FF) operation method and conventional THR (CON). 60 patients underwent a 3D gait analysis of the lower extremity at pre-operative, 6 months post-operative and twelve months post-operative. Detailed verification experiments were facilitated to ensure the quality of data as well as to avoid over-interpreting of the data. The results confirm a similar data-quality as reported in the literature. Walking speed, range of motion and symmetry thereof improved over the follow-up period, without significant differences between the groups. While all parameters do significantly increase over the follow-up period for both groups, there were no significant differences between them at any given time-point. Patients undergoing CAS FF showed a trend to improved hip flexion angle indicating a possible long-term benefit.

Cup implantation accuracy using the HipCOMPASS mechanical intraoperative support device

Background

While navigation systems have been developed to increase implantation accuracy in total hip arthroplasty (THA), they are not yet sufficiently versatile or commonly used. Therefore, to elevate the appeal of such systems, we have developed HipCOMPASS, a simple and effective mechanical angle indicator for use in supine THA.

Questions/purposes

How accurate is the mean cup orientation [in terms of errors in radiographic anteversion (RA) and inclination (RI)] in cases where HipCOMPASS is used for intraoperative support? Does HipCOMPASS increase this cup orientation accuracy compared to THA cases without it? Does HipCOMPASS increase mean operation time?

Methods

We measured cup orientation in 97 THA cases with HipCOMPASS and in 80 cases without it. Then we compared the angles determined in preoperative planning with the angles revealed by postoperative computed tomography (CT) for both groups. The discrepancy between them was defined as an error. Errors greater than 10° were considered outliers. Additionally, mean operative time with and without the Hip COMPASS were compared.

Results

With the use of HipCOMPASS, the mean absolute error values in radiographic anteversion and inclination were 2.9° ± 2.3° (range 0°–12.8°) and 2.9° ± 2.1° (0.1°–7.7°), respectively. In contrast, without the use of HipCOMPASS, radiographic anteversion and inclination error values were 8.8° ± 5.8° (0.1°–25.4°) and 6.1° ± 4.5° (0.2°–21.0°), respectively. Outlier occurrence rates were 1.0 % with HipCOMPASS and 48.8 % without it. Mean operative times with and without HipCOMPASS use were 109.2 ± 23.8 min (74–199 min) and 137.6 ± 40.6 min (71–298 min), respectively.

Conclusions

The study has found that HipCOMPASS dramatically increases implantation accuracy and it is also a simple and highly versatile tool that can be implemented quickly. Given its low cost in addition to its favourable accuracy, simple implementation, and short operative time, HipCOMPASS can be regarded as a very useful and effective THA support device.

Level of evidence

Retrospective comparative study, Level 3.

Accuracy of measuring acetabular cup position after total hip arthroplasty: comparison between a radiographic planning software and three-dimensional computed tomography

PURPOSE

Various methods are available for measuring acetabular cup position after total hip arthroplasty (THA) on standard anterior-posterior (AP) radiographs. We compared the accuracy of a commercial radiographic planning software program with that of three-dimensional computed tomography (3D-CT) scans.

METHODS

We obtained plain AP radiographs and 3D-CTs from 65 patients after THA. In addition to calculating cup anteversion and inclination with 3D-CT, we determined the cup position using the radiographic planning software program mediCAD® 2.5 (Hectec, Niederviehbach, Germany). Furthermore, we compared the measurements using the inter-teardrop and bi-ischial lines as pelvic landmarks.

RESULTS

The mean difference in anteversion between 3D-CT and mediCAD® software was 0.1° using the inter-teardrop line (standard deviation [SD], 8.8°; range, -21° to 23°; p = 0.97) and 0.4° using the bi-ischial line (SD, 8.8°; range, -23° to 21°; p = 0.72). Inclination showed a mean difference of 0.6° using the inter-teardrop line (SD, 4.4°; range, -9° to 21°; p = 0.24) and 0.5° using bi-ischial line (SD, 4.6°; range, -9° to 22°; p = 0.35). The means for absolute differences were 7.2° for anteversion and 3.1° for inclination. With regard to using the bi-ischial or inter-teardrop line, no significant difference was found between the two pelvic landmarks. The intra-class correlation coefficient (ICC) was analysed for anteversion and inclination using either the inter-teardrop line or the bi-ischial line as radiographic baseline.

CONCLUSIONS

A radiographic planning software program (mediCAD®) is a helpful tool for measuring cup inclination on AP radiographs. With respect to anteversion, measurements are rather susceptible to mistakes with mean inaccuracies of over 7°. Thus, 3D-CT remains the "gold standard" if a lower tolerance limit (±3°) is required for more complex biomechanical evaluations. As a pelvic landmark, the interteardrop line is preferential to the bi-ischial line because of its lower impact on the position of the pelvis.

[Total hip arthroplasty in overweight osteoarthritis patients]

BACKGROUND

An increasing number of patients scheduled for total hip arthroplasty (THA) are obese and exhibit a different risk profile from that of patients of normal weight.

OBJECTIVES

To provide an overview of the impact of obesity on the outcome of primary THA.

MATERIALS AND METHODS

Literature review and discussion of own epidemiological data.

RESULTS

Obese patients can expect as much functional improvement as non-obese patients after THA. However, peri- and postoperative complication (e.g., periprosthetic infection and dislocation) rates are reported to be increased in obese THA patients.

CONCLUSIONS

The knowledge of obesity-associated risks is the prerequiste for successful THA in obese patients.

Does Computer-Assisted Femur First THR Improve Musculoskeletal Loading Conditions?

We have developed a novel, computer-assisted operation method for minimal-invasive total hip replacement (THR) following the concept of “femur first/combined anteversion,” which incorporates various aspects of performing a functional optimization of the prosthetic stem and cup position (CAS FF). The purpose of this study is to assess whether the hip joint reaction forces and patient's gait parameters are being improved by CAS FF in relation to conventional THR (CON). We enrolled 60 patients (28 CAS FF/32 CON) and invited them for gait analysis at three time points (preoperatively, postop six months, and postop 12 months). Data retrieved from gait analysis was processed using patient-specific musculoskeletal models. The target parameters were hip reaction force magnitude (hrf), symmetries, and orientation with respect to the cup. Hrf in the CAS FF group were closer to a young healthy normal. Phase-shift symmetry showed an increase in the CAS FF group. Hrf orientation in the CAS FF group was closer to optimum, though no edge or rim-loading occurred in the CON group as well. The CAS FF group showed an improved hrf orientation in an early stage and a trend to an improved long-term outcome.

Importance of the spinopelvic factors on the pelvic inclination from standing to sitting before total hip arthroplasty

PURPOSE

Dislocation after total hip arthroplasty (THA) is a major postoperative complication. Even if the cup is in the safe zone, dislocation caused by implant impingement may occur during postural changes. The aim of the present study was to investigate the spinopelvic factors that influence pelvic inclination changes from standing to sitting in patients with hip diseases who were candidates for THA.

METHODS

74 patients who underwent primary THA were included according to our criteria. The analysis of the sagittal balance of the spinopelvic complex was performed on standing and sitting lateral radiographs. Pelvic incidence (PI), sacral slope (SS), pelvic tilt (PT), lumbar lordosis angle (LLA), thoracic kyphosis angle (TK), and sagittal vertical axis (SVA) were measured. The differences between the standing and sitting positions regarding the spinal and pelvic parameters were analyzed. Correlations between the variables of the spinopelvic parameters were examined using Spearman's rank correlation coefficient.

RESULTS

The changes in SVA, TK, LLA, SS, PT, and PI from the standing to sitting positions, respectively, were -3.9 ± 48.2 mm, -0.1° ± 6.4°, 21.4° ± 17.7°, 22.2° ± 12.2°, -22.3° ± 13.2°, and 0.4° ± 6.9°. The lumbar lordosis was reduced and pelvic rotation was extended from the standing to the sitting position. The correlation coefficient between the change in the SS and that in the LLA was 0.72 (p < 0.0001). The correlation coefficient between the change in PT and that in the LLA was -0.68 (p < 0.0001).

CONCLUSIONS

The change in pelvic inclination from standing to sitting is strongly related to the mobility of the lumbar spine in patients with hip diseases.

Impingement-free range of movement, acetabular component cover and early clinical results comparing ‘femur-first’ navigation and ‘conventional’ minimally invasive total hip arthroplasty

We report the kinematic and early clinical results of a patient- and observer-blinded randomised controlled trial in which CT scans were used to compare potential impingement-free range of movement (ROM) and acetabular component cover between patients treated with either the navigated ‘femur-first’ total hip arthroplasty (THA) method (n = 66; male/female 29/37, mean age 62.5 years; 50 to 74) or conventional THA (n = 69; male/female 35/34, mean age 62.9 years; 50 to 75). The Hip Osteoarthritis Outcome Score, the Harris hip score, the Euro-Qol-5D and the Mancuso THA patient expectations score were assessed at six weeks, six months and one year after surgery. A total of 48 of the patients (84%) in the navigated ‘femur-first’ group and 43 (65%) in the conventional group reached all the desirable potential ROM boundaries without prosthetic impingement for activities of daily living (ADL) in flexion, extension, abduction, adduction and rotation (p = 0.016). Acetabular component cover and surface contact with the host bone were > 87% in both groups. There was a significant difference between the navigated and the conventional groups’ Harris hip scores six weeks after surgery (p = 0.010). There were no significant differences with respect to any clinical outcome at six months and one year of follow-up. The navigated ‘femur-first’ technique improves the potential ROM for ADL without prosthetic impingement, although there was no observed clinical difference between the two treatment groups.

Cite this article: Bone Joint J 2015; 97-B:890–8.

Accuracy of an adjustable patient-specific guide for acetabular alignment in hip replacement surgery (Optihip)

Implant malalignment in hip arthroplasty increases the risk of revision surgery due to problems such as hip instability, wear, and impingement. Traditional instrumentation lacks accuracy and does not individualize the goal. Computer-assisted surgery (CAS) and patient-specific solutions improve accuracy but add considerably to the cost, amongst other drawbacks. We developed an adjustable mechanical device, called Optihip, which is set to a patient-specific goal preoperatively and is independent of pelvis position intraoperatively. The purpose of the present study was to evaluate Optihip's accuracy ex vivo. Acetabular components were implanted into six cadaveric specimens, 12 hips, by two surgeons, with the device individually adjusted according to preoperative templating on computed tomography (CT) images relative to defined acetabular rim landmarks; options also exist for templating on single or biplanar X-rays. Intraoperatively, the device was positioned on the corresponding anatomical landmarks allowing the insertion of a guide pin, which then defined the desired orientation of the acetabular cup during impaction. Mean absolute difference between the preoperatively planned cup alignment and final acetabular cup orientation, measured from postoperative CT images, was 2.5±1.2° for inclination and 2.5±2.2° for version with maximum values of 4.7° and 6.8°, respectively. Compared with previous in vivo reports, Optihip guided the acetabular cup orientation more accurately than conventional hip arthroplasty, and comparably to CAS or patient-specific systems, while fitting into the normal surgical workflow. Although clinical testing is required to confirm these experimental results, the positive ex vivo accuracy suggests good potential for improving revision rates and patient functional outcome.

The effect of femoral neck osteotomy on femoral component position of a primary cementless total hip arthroplasty

PURPOSE

The aim of this study was to quantify the femoral canal diameter and version at different femoral neck osteotomy locations, and to investigate the effect of the osteotomy plane on femoral component position in total hip arthroplasty (THA).

METHODS

Preoperative and postoperative three-dimensional models were reconstructed in 15 patients (19 hips) who underwent primary cementless THA with tapered non-anatomical femoral stem. On the pre-operative models, the osteotomy plane was simulated at different levels (-5, 0, 5, and 10 mm from the femoral saddle [piriformis fossa]) and angles (30, 40, 50, and 60° from the femoral anatomical axis). Medullary canal version and mediolateral diameter were measured on the osteotomy surfaces. On the postoperative models, the femoral neck osteotomy plane, stem anteversion and alignment were measured.

RESULTS

The average canal diameter ranged from 22.8 to 26.3 mm at different osteotomy levels and from 20.8 to 29.0 mm at different osteotomy angles. The average canal version ranged from 11.4 to 23.2° at different resection levels and from 12.8 to 21° at different resection angles. The femoral stem anteversion was correlated with neck osteotomy angle (R = 0.72), whereas stem alignment in frontal plane (varus/valgus) was correlated with neck osteotomy level (R = 0.87).

CONCLUSIONS

The femoral neck osteotomy plane in THA affects the postoperative stem position due to the complex morphology of the proximal femoral medullary canal, suggesting that both femoral neck resection level and angle should be considered in optimizing femoral component alignment in THA patients.

Spinal factors influencing change in pelvic sagittal inclination from supine position to standing position in patients before total hip arthroplasty

In some atypical patients, pelvic sagittal inclination (PSI) changes posteriorly by >10° from supine to standing position before total hip arthroplasty (THA). Several studies have suggested PSI in standing position is related to lumbar degeneration. The purpose of this study was to investigate spinal factors influencing changes in PSI from supine to standing position before THA. Participants comprised 163 consecutive patients who had undergone THA. Presence of compression fractures, presence of lumbar spondylolisthesis, thoracic kyphosis angle, lumbar lordosis angle, S1 anterior tilt angle and T4 plumb line position were investigated as spinal factors. Presence of compression fractures, age, presence of lumbar spondylolisthesis and small S1 anterior tilt angle were independently associated with posterior change in PSI from supine to standing position in patients before THA.

Navigating the reaming of the acetabular cavity in total hip arthroplasty: does it improve implantation accuracy?

Computer navigation in total hip arthroplasty is used to improve accuracy of component implantation. Reaming of the acetabular cavity during total hip arthroplasty (THA) can be navigated although this is not done routinely. We hypothesised that navigating the reaming of the acetabular cavity will improve implantation accuracy. A single surgeon series of 100 navigated THAs were analysed retrospectively. In 49 the reaming of the acetabular cavity was done using navigation and in 51 this was done freehand. The verified cup position and the error from the planned position were recorded. The mean error from planned to verified inclination was 2.20 degrees (SD 1.59°) in the navigated group versus 2.33 degrees (SD 1.96°) in the freehand group. The mean anteversion error was 1.92 degrees (SD 1.51°) for the navigated group and 1.45 degrees (SD 1.38°) for the freehand group. This was not statistically significant. This rejects our hypothesis. Navigating the reaming of the acetabular cavity did not improve the accuracy of the implantation against the set inclination and anteversion target during computer navigated THA.

Computed tomography for preoperative planning in total hip arthroplasty: what radiologists need to know

The number of total hip arthroplasties is continuously rising. Although less invasive surgical techniques, sophisticated component design, and intraoperative navigation techniques have been introduced, the rate of peri- and postoperative complications, including dislocations, fractures, nerve palsies, and infections, is still a major clinical problem. Better patient outcome, faster recovery and rehabilitation, and shorter operation times therefore remain to be accomplished. A promising strategy is to use minimally invasive techniques in conjunction with modular implants, aimed at independently reconstructing femoral offset and leg length on the basis of highly accurate preoperative planning. Plain radiographs have clear limitations for the correct estimation of hip joint geometry and bone quality. Three-dimensional assessment based on computed tomography (CT) allows optimizing the choice and positions of implants and anticipating difficulties to be encountered during surgery. Postoperative CT is used to monitor operative translation and plays a role in arthroplastic quality management. Radiologists should be familiar with the needs of orthopedic surgeons in terms of CT acquisition, post-processing, and data transfer. The CT protocol should be optimized to enhance image quality and reduce radiation exposure. When dedicated orthopedic CT protocols and state-of-the-art scanner hardware are used, radiation exposure can be decreased to a level just marginally higher than that of conventional preoperative radiography. Surgeons and radiologists should use similar terminology to avoid misunderstanding and inaccuracies in the transfer of preoperative planning.

Effect of femoral neck modularity upon the prosthetic range of motion in total hip arthroplasty

In total hip arthroplasty, aseptic loosening and dislocation are associated with not being able to achieve the correct prosthetic component orientation. Femoral neck modularity has been proposed as a solution to this problem by allowing the surgeon to alter either the neck-shaft or version angle of the prosthetic femoral component intra-operatively. A single replicate full factorial design was used to evaluate how effective a modular femoral neck cementless stem was in restoring a healthy prosthetic range of motion in comparison with a leading fixed-neck cementless stem with the standard modular parameters. It was found that, if altered to a large enough degree, femoral neck modularity can increase the amount of prosthetic motion as well as alter its position to where it is required physiologically. However, there is a functional limit to the amount that can be corrected and there is a risk with regard to the surgeon having to select the optimum modular neck before any benefit is realised.

Is cup positioning challenged in hips previously treated with periacetabular osteotomy?

After periacetabular osteotomy (PAO), some patients develop osteoarthritis with need of a total hip arthroplasty (THA). We evaluated the outcome of THA following PAO and explored factors associated with inferior cup position and increased polyethylene wear. Follow-up were performed 4 to 10 years after THA in 34 patients (38 hips) with previous PAO. Computer analysis evaluated cup position and wear rates. No patient had dislocations or revision surgery. Median scores were: Harris hip 96, Oxford hip 38 and WOMAC 78. Mean cup anteversion and abduction angles were 22° (range 7°-43°) and 45° (range 28°-65°). Outliers of cup abduction were associated with persisting dysplasia (CE <25°). THA after PAO can produce excellent clinical results. Persisting acetabular dysplasia following PAO may lead surgeons to place the acetabular component in excessive cup abduction, and this tendency should be recognized at the time of the PAO.

Sexual activity after total hip arthroplasty: a motion capture study

Relative risk of impingement and joint instability during sexual activities after total hip arthroplasty (THA) has never been objectively investigated. Hip range of motion necessary to perform sexual positions is unknown. A motion capture study with two volunteers was performed. 12 common sexual positions were captured and relevant hip joint kinematics calculated. The recorded data were applied to prosthetic hip 3D models to evaluate impingement and joint instability during motion. To explore the effect of acetabular component positioning, nine acetabular cup positions were tested. Four sexual positions for women requiring intensive flexion (> 95°) caused prosthetic impingements (associated with posterior instability) at 6 cup positions. Bony impingements (associated with anterior instability) occurred during one sexual position for men requiring high degree of external rotation (> 40°) combined with extension and adduction at all cup positions. This study hence indicates that some sexual positions could be potentially at risk after THA, particularly for women.

Risk of impingement and third-body abrasion with 28-mm metal-on-metal bearings

BACKGROUND

Concerns have been raised about the sequelae of metal-on-metal (MoM) bearings in total hip arthroplasty (THA). However, retrieval studies, which offer the best insight into the clinically relevant mechanisms of MoM wear, have followed predictable trends to date such as indicting cobalt-chromium (CoCr) metallurgy, cup design, high conformity between the head and cup, "steep cups," "microseparation," and "edge wear."

QUESTIONS/PURPOSES

We wished to evaluate a set of retrieved 28-mm MoM THA for signs of (1) cup-to-stem impingement; (2) normal wear pattern and concomitant stripe damage on femoral heads that would signify adverse wear mechanics; and (3) well-defined evidence of third-body scratches on bearings that would indicate large abrasive particles had circulated the joint space.

METHODS

Ten 28-mm MOM retrievals were selected on the basis that femoral stems were included. Revision surgeries at 3 to 8 years were for pain, osteolysis, and cup loosening. CoCr stems and the MoM bearings were produced by one vendor and Ti6Al4V stems by a second vendor. All but two cases had been fixed with bone cement. We looked for patterns of normal wear and impingement signs on femoral necks and cup rims. We looked for adverse wear defined as stripe damage that was visually apparent on each bearing. Wear patterns were examined microscopically to determine the nature of abrasions and signs of metal transfer. Graphical models recreated femoral neck and cup designs to precisely correlate impingement sites on femoral necks to cup positions and head stripe patterns.

RESULTS

The evidence revealed that all CoCr cup liners had impinged on either anterior or posterior facets of femoral necks. Liner impingement at the most proximal neck notch occurred with the head well located and impingement at the distal notch occurred with the head rotated 5 mm out of the cup. The hip gained 20° motion by such a subluxation maneuver with this THA design. All heads had stripe wear, the basal and polar stripes coinciding with cup impingement sites. Analysis of stripe damage revealed 40 to 100-μm wide scratches created by large particles ploughing across bearing surfaces. The association of stripe wear with evidence of neck notching implicated impingement as the root cause, the outcome being the aggressive third-body wear.

CONCLUSIONS

We found consistent evidence of impingement, abnormal stripe damage, and evidence of third-body abrasive wear in a small sample of one type of 28-mm MoM design. Impingement models demonstrated that 28-mm heads could lever 20° out of the liners. Although other studies continue to show good success with 28-mm MoM bearings, their use has been discontinued at La Pitie Hospital.

Acetabular component anteversion in primary and revision total hip arthroplasty: an observational study

PURPOSE

In a prospective manner to evaluate the range of acetabular component anteversion actually achieved by the use of a cup positioner in cementless revision and primary THA.

METHODS

We operated 71 patients with cementless primary THA, and 26 patients with cementless acetabular revision surgery. We aimed to obtain cup anteversion of 10 to 30° with an impactor-positioner. In all cases we used elevated liners and a ceramic head with diameter 28. At 3 months postoperatively the component versions were measured using CT with the patient in supine position.

RESULTS

The acetabular component version in the primary hips ranged from 28° of retroversion to 42° of anteversion with a mean of 17.4 ± 14.0°, while the cup version in the revision hips ranged from 4° of retroversion to 32° of anteversion with a mean of 15.0 ± 9.6°(p=0.427). The anteversion of 40 (56%) of the primary acetabular components were within the target zone of 10 to 30°, while 19 (27%) were below the target zone and and 12 (17%) were above the target range. The anteversion of 19 (73%) of the revision acetabular components were within the target zone, while 6 (23%) were below the target zone and 1 (4%) were above the target range. The differences in distribution between the primary and revision operations were not significant (p=0.183).

CONCLUSIONS

The intraoperative estimation of acetabular anteversion by free hand technique in many cases was not within the intended range of 10 to 30° in either primary or revision THA and with no differences between the two series.

Using the transverse acetabular ligament as a landmark for acetabular anteversion: an intra-operative measurement

PURPOSE. To measure the transverse acetabular ligament (TAL) anteversion in hips with severe deformity, using fluoroscopy-computed tomographic navigation. METHODS. 31 hips in 10 men and 19 women aged 40 to 78 (mean, 58.7) years who underwent total hip arthroplasty for primary osteoarthritis (n=6) or osteoarthritis secondary to developmental hip dysplasia (n=19) or congenital hip dislocation (n=6) were included. The severity of hip dislocation was classified according to the Crowe classification; 15 hips were grade 1, 7 were grade 2, 3 were grade 3, and 6 were grade 4. The TAL anteversion was measured using fluoroscopy-computed tomographic navigation. The difference in TAL anteversion between non-dislocated hips (Crowe grade 1, n=15) and dislocated hips (Crowe grades 2-4, n=16) was compared. RESULTS. In all 31 hips, the TAL could be visualised intra-operatively. No patient reported severe pain, early wear, loosening, or dislocation after 2 years. The mean TAL anteversion and inclination angles measured by the navigation system were 26.5 (SD, 8.9; range, 8-42) degrees and 41.5 (SD, 4.6; range, 32-49) degrees, respectively. 22 of the 31 hips were in the safe zone. TAL anteversion in non-dislocated and dislocated hips was not significantly different. Inter- and intra-observer mean absolute differences in TAL anteversion were 0.3 and 0.4 degree, respectively. CONCLUSION. The TAL is a useful anatomic landmark for total hip arthroplasty in dislocated hips.

Pelvic tilt is minimally changed by total hip arthroplasty

BACKGROUND

While surgical navigation offers the opportunity to accurately place an acetabular component, questions remain as to the best goal for acetabular component positioning in individual patients. Overall functional orientation of the pelvis after surgery is one of the most important variables for the surgeon to consider when determining the proper goal for acetabular component orientation.

QUESTIONS/PURPOSES

We measured the variation in pelvic tilt in 30 patients before THA and the effect of THA on pelvic tilt in the same patients more than a year after THA.

METHODS

Each patient had a CT study for CT-based surgical navigation and standing and supine radiographs before and after surgery. Pelvic tilt was calculated for each of the radiographs using a novel and validated two-dimensional/three-dimensional matching technique.

RESULTS

Mean supine pelvic tilt changed less than 2°, from 4.4° ± 6.4° (range, -7.7° to 20.8°) before THA to 6.3° ± 6.6° (range, -5.7° to 19.6°) after THA. Mean standing pelvic tilt changed less than 1°, from 1.5° ± 7.2° (range, -13.1° to 12.8°) before THA to 2.0° ± 8.3° (range, -12.3° to 16.8°) after THA. Preoperative pelvic tilt correlated with postoperative tilt in both the supine (r(2) = 0.75) and standing (r(2) = 0.87) positions.

CONCLUSIONS

In this population, pelvic tilt had a small and predictable change after surgery. However, intersubject variability of pelvic tilt was high, suggesting preoperative pelvic tilt should be considered when determining desired acetabular component positioning on a patient-specific basis.