Radiographic Assessment of Femoral Stem Torsion in Total Hip Arthroplasty-A Comparison of a Caput-Collum-Diaphyseal Angle-Based Technique With the Budin View

BACKGROUND

Correct assessment of femoral stem torsion is crucial in total hip arthroplasty (THA). In this study, we aimed to compare a recently published novel method based on anteroposterior (AP) hip radiographs using the projected caput-collum-diaphyseal (CCD) angle (AP CCD) with the modified posteroanterior Budin view.

METHOD

AP radiographs, modified Budin views, and 3-dimensional computed tomography (3D-CT) images were obtained in 30 patients after minimally invasive, cementless THA. Radiographic measurements performed by 4 observers twice in a 6-week interval were compared with 3D-CT measurements. Furthermore, correlations between the radiographic deviation to 3D-CT and patient specific characteristics were evaluated.

RESULTS

We found a mean difference of 2.2 ± 6.8° between AP CCD and 3D-CT measurements of femoral stem torsion and -0.5 ± 4.2° between the modified Budin view and 3D-CT. We found a high correlation between mean radiographic and 3D-CT stem torsion (r = 0.78, P < .001 for AP CCD and r = 0.84, P < .001 for Budin view). The observers had excellent agreements within (intraclass correlation coefficient, ≥0.88 for AP CCD and intraclass correlation coefficient, ≥0.94 for Budin view) and between (mean concordance correlation coefficient, ≥0.79 for AP CCD and concordance correlation coefficient, ≥0.86 for Budin view) their radiographic measurements.

CONCLUSION

Both radiographic methods enable a simple orientation and a practical conventional radiographic estimation of stem torsion on hip radiographs after THA. However, CT remains the golden standard for exact estimation of stem torsion.

Accuracy of Component Placement in Robotic-Assisted Total Hip Arthroplasty

Robotic-assisted total hip arthroplasty (THA) is a recent platform introduced to decrease the risk of malpositioned components. The goals of this study were to determine whether intraoperative data on robotic-assisted THA acetabular component position accurately predict postoperative radiographic acetabular component position and to determine whether intraoperative data on robotic-assisted THA leg length and offset accurately predict postoperative radiographic leg length and offset data. In 146 patients, pre- and postoperative radiographs and intraoperative component measurements were reported for acetabular inclination, anteversion, leg length change, and offset change. Component position obtained by the robotic system and radiographic data were compared with subgroup analysis for the posterior and direct anterior approaches. The average difference between groups was 3.3°±3.1° for inclination, 2.9°±2.3° for anteversion, 3.0±2.3 mm for leg length change, and 4.0±3.1 mm for change in global offset. Correlation between the robotic system and postoperative radiographs was within 10° for 95.9% of cases for inclination and 99.3% for anteversion. Posterior approach correlation was within 10° for 97.1% of cases for inclination and 100% for anteversion. Anterior approach correlation was within 10° for 92.7% of cases for inclination and 97.6% for anteversion. Intraoperative data on component position obtained from the robotic system compared well with radiographic data on component position. Surgeons must remain vigilant to ensure outliers related to robotic system malfunction do not occur. [Orthopedics. 2016; 39(3):193-199.].

Current standard rules of combined anteversion prevent prosthetic impingement but ignore osseous contact in total hip arthroplasty

PURPOSE

In this prospective study of 135 patients undergoing cementless total hip arthroplasty (THA) we asked whether six current definitions of combined anteversion prevent impingement and increase postoperative patient individual impingement-free range-of-motion (ROM).

METHODS

Implant position was measured by an independent, external institute on 3D-CT performed six weeks post-operatively. Post-operative ROM was calculated using a CT-based algorithm detecting osseous and/or prosthetic impingement by virtual hip movement. Additionally, clinical ROM was evaluated pre-operatively and one-year post-operatively by a blinded observer.

RESULTS

Combined component position of cup and stem according to the definitions of Ranawat, Widmer, Dorr, Hisatome and Yoshimine inhibited prosthetic impingement in over 90 %, while combined osseous and prosthetic impingement still occurred in over 40 % of the cases. The recommendations by Jolles, Widmer, Dorr, Yoshimine and Hisatome enabled higher flexion (p ≤ 0.001) and internal rotation (p ≤ 0.006). Clinically, anteversion rules of Widmer and Yoshimine provided one-year post-operatively statistically but not clinically relevant higher internal rotation (p ≤0.034).

CONCLUSION

Standard rules of combined anteversion detect prosthetic but fail to prevent combined osseous and prosthetic impingement in THA. Future models will have to account for the patient-individual anatomic situation to ensure impingement-free ROM.

[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.

Do post-operative changes of neck-shaft angle and femoral component anteversion have an effect on clinical outcome following uncemented total hip arthroplasty?

The accurate reconstruction of hip anatomy and biomechanics is thought to be important in achieveing good clinical outcomes following total hip arthroplasty (THA). To this end some newer hip designs have introduced further modularity into the design of the femoral component such that neck-shaft angle and anteversion, which can be adjusted intra-operatively. The clinical effect of this increased modularity is unknown. We have investigated the changes in these anatomical parameters following conventional THA with a prosthesis of predetermined neck-shaft angle and assessed the effect of changes in the hip anatomy on clinical outcomes. In total, 44 patients (mean age 65.3 years (standard deviation (SD) 7); 17 male/27 female; mean body mass index 26.9 (kg/m²) (SD 3.1)) underwent a pre- and post-operative three-dimensional CT scanning of the hip. The pre- and post-operative neck-shaft angle, offset, hip centre of rotation, femoral anteversion, and stem alignment were measured. Additionally, a functional assessment and pain score were evaluated before surgery and at one year post-operatively and related to the post-operative anatomical changes. The mean pre-operative neck-shaft angle was significantly increased by 2.8° from 128° (SD 6.2; 119° to 147°) to 131° (SD 2.1; 127° to 136°) (p = 0.009). The mean pre-operative anteversion was 24.9° (SD 8; 7.9 to 39.1) and reduced to 7.4° (SD 7.3; -11.6° to 25.9°) post-operatively (p < 0.001). The post-operative changes had no influence on function and pain. Using a standard uncemented femoral component, high pre- and post-operative variability of femoral anteversion and neck-shaft angles was found with a significant decrease of the post-operative anteversion and slight increase of the neck-shaft angles, but without any impact on clinical outcome.

Acetabular Dysplasia and Surgical Approaches Other Than Direct Anterior Increases Risk for Malpositioning of the Acetabular Component in Total Hip Arthroplasty

BACKGROUND

Persistent acetabular dysplasia (AD) after periacetabular osteotomy has been hypothesized to increase the risk for malpositioning of the acetabular component. In this study, we investigate whether AD is an independent risk factor for cup malpositioning during primary total hip arthroplasty (THA).

METHODS

Patient demographics, surgical approach, presence of AD assessed using the lateral center-edge angle, and acetabular cup positioning determined using Martell Hip Analysis Suite were investigated in 836 primary THA patients enrolled in a prospective multicenter study.

RESULTS

We found that presence of AD, defined as the lateral center-edge angle of <25°, is an independent risk factor for malpositioning of the acetabular component during primary THA. Surgical approach other than direct anterior was also independently associated with malpositioned cups.

CONCLUSIONS

Surgeons should therefore take special care during placement of the acetabular component in patients with AD.

Total Hip Arthroplasty Functional Outcomes Are Independent of Acetabular Component Orientation When a Polyethylene Liner Is Used

BACKGROUND

This study evaluated patient-reported outcomes in patients undergoing primary total hip arthroplasty with a polyethylene liner to determine the influence of cup orientation and other variables on patient-reported outcomes.

METHODS

A total of 477 cases were prospectively monitored through average 4.7 years follow-up. Cup position was measured on pelvis radiographs. Patients completed the Western Ontario and McMaster Universities Osteoarthritis Index and Short Form 12 Health Survey questionnaires.

RESULTS

Average cup abduction was 43.1° ± 7.5° and anteversion was 13.3° ± 7.5°. Three hundred cups were within the target zone. All outcomes' improvement from baseline and cup position was not an independent risk factor for the Western Ontario and McMaster Universities Osteoarthritis Index or Short Form 12 Health Survey improvement.

CONCLUSION

Accurate cup orientation may not be critical to maximizing patient-perceived outcomes if the combined anteversion is within a normal range, the hip joint is properly balanced, and a polyethylene liner is coupled with a metal or ceramic femoral head.

Initial Results of an Acetabular Center Axis Registration Technique in Navigated Hip Arthroplasty with Deformed Acetabular Rims

Background

In cementless total hip arthroplasty, imageless computer-assisted navigation is usually used to register the anterior pelvic plane (APP). The accuracy of this method is influenced by the subcutaneous tissues overlying the registration landmarks. On the other hand, the acetabular center axis (ACA) is determined from the acetabular rim. Precise registration of the ACA is possible because of direct palpation using a pointer. Imageless navigation using the ACA usually targets patients with normal acetabular morphology. The aim of this study was to investigate the accuracy of imageless navigation using the ACA instead of the APP in patients with normal or deformed acetabular rims.

Methods

The intraoperative cup position was compared with that obtained from the postoperative computed tomography (CT) images in 18 cases.

Results

The inclination angle derived from the navigation system was 3.4 ± 5.3 degrees smaller and the anteversion angle was 1.4 ± 3.1 degrees larger than those derived from the CT images.

Conclusion

The inclination cup angle of the navigation system was significantly inferior to the true value, particularly in cases with large anterior osteophytes.

Safety in early experience with a direct anterior approach using fluoroscopic guidance with manual leg control for primary total hip arthroplasty: a consecutive one hundred and twenty case series

BACKGROUND AND PURPOSE

An encouraging result with direct anterior approach (DAA) is attractive for both patients and surgeons. However, the risks associated with beginning to use DAA require further analysis of the learning curve and better countermeasures to ensure safety. We ask whether the complication rate in the DAA by the inexperienced surgeon could be decreased with specific countermeasures. Our hypothesis was that the complication rate would be low even in early phase of the learning curve using the DAA with these particular countermeasures.

PATIENTS AND METHODS

We investigated a consecutive series of 120 primary THA using the DAA with four specific countermeasures; 1) defined exclusion criteria for DAA; 2) no positioning table; 3) use of fluoroscopy as much as required; and 4) having an experienced assistant for DAA (one who has performed the procedure in more than 100 cases). The operative time, the time of fluoroscopic use during the operation, intra and post-operative complications, re-operation for any reason, and cup and stem alignment were investigated.

RESULTS

Although the operation times were similar, the duration of fluoroscopy decreased with surgeons' experience. There were no intra-operative complications and no re-operations for any reason. One anterior dislocation was observed in one patient. The mean cup inclination and anteversion angle was 39.7° ± 7.6° and 30.3° ± 7.6°; 43.3 % of stems were positioned in flexion, 55.8 % in the neutral position on the lateral view.

CONCLUSION

We demonstrated a lower complication rate during our early experience with the DAA using four countermeasures. Using these countermeasures for the first 40 cases may be useful for surgeons who are considering DAA.

Standing radiological analysis with a low-dose biplanar imaging system (EOS system) of the position of the components in total hip arthroplasty using an anterior approach

Aims

The primary aim of this study was to analyse the position of the acetabular and femoral components in total hip arthroplasty undertaken using an anterior surgical approach.

Patients and Methods

In a prospective, single centre study, we used the EOS imaging system to analyse the position of components following THA performed via the anterior approach in 102 patients (103 hips) with a mean age of 64.7 years (sd 12.6). Images were taken with patients in the standing position, allowing measurement of both anatomical and functional anteversion of the acetabular component.

Results

The mean inclination of the acetabular component was 39° (standard deviation (sd) 6), the mean anatomical anteversion was 30° (sd 10), and the mean functional anteversion was 31° (sd 8) five days after surgery. The mean anteversion of the femoral component was 20° (sd 11). Anatomical and functional anteversion of the acetabular component differed by >  10° in 23 (22%) cases. Pelvic tilt was the only pre-operative predictive factor of this difference.

Conclusion

Our study showed that anteversion of the acetabular component following THA using the anterior approach was greater than the recommended target value, and that substantial differences were observed in some patients when measured using two different measurement planes. If these results are confirmed by further studies, and considering that the anterior approach is intended to limit the incidence of dislocation, a new correlation study for each reference plane (anatomical and functional) will be necessary to define a ‘safe zone’ for use with the anterior approach. Take home message: EOS imaging system is helpful in the pre-operative and post-operative radiological analysis of total hip arthroplasty. Cite this article: Bone Joint J 2016;98-B:326–333.

Contemporary Surgical Indications and Referral Trends in Revision Total Hip Arthroplasty: A 10-Year Review

BACKGROUND

Revision total hip arthroplasty (THA) represents nearly 15% of all hip arthroplasty procedures in the United States and is projected to increase. The purpose of our study was to summarize the contemporary indications for revision THA surgery at a tertiary referral medical center. We also sought to identify the indications for early and late revision surgery and define the prevalence of outside institution referral for revision THA.

METHODS

Using our institution's arthroplasty registry, we identified a retrospective cohort of 870 consecutive patients who underwent revision THA at our hospital from 2004 to 2014. Records were reviewed to collect data on patient's primary and revision THA procedures, and the interval between primary THA and revision surgery was determined.

RESULTS

Aseptic loosening (31.3%), osteolysis (21.8%), and instability (21.4%) were the overall most common indications for revision THA and the most common indications for revision surgery within 5 years of primary THA. Aseptic loosening and osteolysis were the most common indications for revision greater than 5 years from primary THA. Only 16.4% of revised hips had their index arthroplasty performed at our hospital, whereas 83.6% were referred to our institution.

CONCLUSIONS

Aseptic loosening, osteolysis, and instability remain the most common contemporary indications for revision THA in an era of alternative bearings and modular components. Most of our revisions were referred from outside institutions, which highlights the transfer of a large portion of the revision THA burden to tertiary referral centers, a pattern that could be exacerbated under future bundled payment models.

The current status and future prospects of computer-assisted hip surgery

The advances in computer assistance technology have allowed detailed three-dimensional preoperative planning and simulation of preoperative plans. The use of a navigation system as an intraoperative assistance tool allows more accurate execution of the preoperative plan, compared to manual operation without assistance of the navigation system. In total hip arthroplasty using CT-based navigation, three-dimensional preoperative planning with computer software allows the surgeon to determine the optimal angle of implant placement at which implant impingement is unlikely to occur in the range of hip joint motion necessary for daily activities of living, and to determine the amount of three-dimensional correction for leg length and offset. With the use of computer navigation for intraoperative assistance, the preoperative plan can be precisely executed. In hip osteotomy using CT-based navigation, the navigation allows three-dimensional preoperative planning, intraoperative confirmation of osteotomy sites, safe performance of osteotomy even under poor visual conditions, and a reduction in exposure doses from intraoperative fluoroscopy. Positions of the tips of chisels can be displayed on the computer monitor during surgery in real time, and staff other than the operator can also be aware of the progress of surgery. Thus, computer navigation also has an educational value. On the other hand, its limitations include the need for placement of trackers, increased radiation exposure from preoperative CT scans, and prolonged operative time. Moreover, because the position of a bone fragment cannot be traced after osteotomy, methods to find its precise position after its movement need to be developed. Despite the need to develop methods for the postoperative evaluation of accuracy for osteotomy, further application and development of these systems are expected in the future.

Abductor Biomechanics Clinically Impact the Total Hip Arthroplasty Dislocation Rate: A Prospective Long-Term Study

BACKGROUND

Factors related to the patient, implant, and surgery have been associated to the rate of dislocation for total hip arthroplasty (THA). We ask if the position of the cup and the reconstruction of the abductor mechanism actually lower the THA dislocation rate.

METHODS

We evaluated 1318 patients (1414 hips) undergoing cementless THA between 1992 and 2012. All THAs had a 28- or a 32-mm femoral head size. Hip reconstruction was radiologically assessed evaluating cup position and the hip rotation center according to Ranawat. The reconstruction of the abductor mechanism was measured using 2 variables: the lever arm distance and the height of the greater trochanter.

RESULTS

There were 38 dislocations (2.7%). After controlling the relevant confounding variables, such as demographic and implant data, multivariate regression analysis showed that the most important factors associated with dislocation were a greater distance to the anatomic hip rotation center and hips outside 2 safe windows for cup position (acetabular inclination and version angles) and abductor mechanism (lever arm distance and height of the greater trochanter).

CONCLUSION

A proper reconstruction of the hip is essential to decrease the risk of dislocation after primary THA. The weakness of the abductor muscles of the hip may be one of the most important causes for dislocation.

Passive Hip Range of Motion Predicts Femoral Torsion and Acetabular Version

BACKGROUND

Orientation abnormalities of the acetabulum and femur have been implicated in early-onset coxarthrosis. The purpose of this study was to identify clinical examination findings predictive of such hip morphologies.

METHODS

A consecutive cohort of 221 patients (442 hips) undergoing hip arthroscopy was included. Demographic characteristics including age, diagnosis, sex, height, weight, body mass index (BMI), and physical activity level were recorded. Passive range of motion was measured for all hips. Preoperative computed tomography scans were utilized to measure femoral torsion and central acetabular version, and a combined femoral torsion-acetabular version (COTAV) index was defined as their sum.

RESULTS

The study cohort comprised 221 patients (sixty-four males, 157 females) with a mean age of 32.5 years and mean BMI of 24.2 kg/m(2). Overall, hips with femoral antetorsion and acetabular anteversion exhibited the greatest internal rotation range of motion at a neutral hip position (mean, 44.2°), whereas hips with femoral retrotorsion and acetabular retroversion demonstrated the lowest corresponding value (20.1°; p < 0.001). Femoral torsion was significantly associated with female sex (p < 0.001), BMI (p < 0.001), and presence of pathology corresponding to cam-type femoroacetabular impingement (FAI) (p = 0.044). Central acetabular version was significantly associated with age (p = 0.021), female sex (p < 0.001), and absence of mixed-type FAI pathology (p = 0.025). Increasing age and internal rotation range of motion at a neutral hip position were the most significant predictors of an increased COTAV index.

CONCLUSIONS

This study confirmed that passive hip range of motion significantly predicts combined femoral torsion and central acetabular version. Accurate clinical assessment of the COTAV index may inform surgical decision-making in hip preservation surgery.

A forty millimetre head significantly improves range of motion compared with a twenty eight millimetre head in total hip arthroplasty using a computed tomography-based navigation system

PURPOSE

Larger-diameter (≥40 mm) femoral heads decrease the incidence of post-operative dislocation in total hip arthroplasty (THA). This study was conducted to discover whether larger-diameter femoral heads result in greater range of motion of the hip with the use of a computed tomography (CT)-based navigation system.

METHODS

Thirty-nine primary THAs were performed via a posterolateral approach using a CT-based navigation system. The stem was inserted in the femur in line with the original femoral neck anteversion. Considering the range of motion during various daily activities which could occur without impingement, the cup anteversion was decided at 10 ° increments according to the stem anteversion. While the cup inclination was set at 40 ° in order to avoid a high inclination angle to prevent the edge roading between the HXLPE liner and ceramic head. After implantation, trial liners and femoral heads were used with either 28 or 40 mm diameter. Maximal hip flexion, extension, abduction, external rotation in extension at 0° and internal rotation angles in flexion at 90 ° were measured. The differences between the ranges of motion with the 40-mm and 28-mm heads were tested. The results were assessed with paired Student t-tests.

RESULTS

The ranges of motion in flexion, extension, abduction and internal rotation angles improved significantly with the 40-mm heads compared with the 28-mm heads. The ranges of motion of cases where maximal flexion angle was 90° or less were excluded, improved significantly with the 40 mm heads.

CONCLUSIONS

We concluded that the larger-diameter 40-mm femoral prosthetic heads result in greater ranges of motion in flexion, extension, abduction and internal rotation.

Postural and Chronological Change in Pelvic Tilt Five Years After Total Hip Arthroplasty in Patients With Developmental Dysplasia of the Hip: A Three-Dimensional Analysis

The pelvis generally tilts to the posterior with movement from the supine to standing position, and with time after total hip arthroplasty (THA). This study aimed to investigate changes in pelvic tilt from the preoperative supine position to the standing position at 5 years after THA (pelvic change, PC). We measured pelvic tilt using a 2D-3D matching technique in 77 unilaterally affected patients who underwent primary THA. PC in 8% of all patients was ≤-20°, and the greatest PC was -25°. In these patients, posterior pelvic tilt continued up to 5 years after THA. These patients were older, and their lumbo-lordotic angle was small. For such cases, cup orientation should be planned to account for continuous posterior change in pelvic tilt after THA.

The Validity of Using the Posterior Condylar Line as a Rotational Reference for the Femur

Rotation of the femur is usually measured by the posterior condylar line (PCL). However, the functional position of the PCL has not been studied well. The angles between the PCL and the horizontal body line (HBL) were measured on preoperative computed tomographic (CT) images of 324 hips with osteoarthritis and compared with the CT images taken after hip arthroplasty. The PCL rotated 0.4° (±10.9° SD) internally from the HBL on preoperative CT images and was significantly correlated with femoral anteversion, Kellgren-Lawrence grade, and sex. On postoperative CT images, the PCL rotated 10.1° (interquartile range, 1.7°-15.5°) internally from the HBL. There was individual variance in the position of the PCL, and caution may be needed when using it as a rotational reference.

A Novel Approach for Dynamic Testing of Total Hip Dislocation under Physiological Conditions

Constant high rates of dislocation-related complications of total hip replacements (THRs) show that contributing factors like implant position and design, soft tissue condition and dynamics of physiological motions have not yet been fully understood. As in vivo measurements of excessive motions are not possible due to ethical objections, a comprehensive approach is proposed which is capable of testing THR stability under dynamic, reproducible and physiological conditions. The approach is based on a hardware-in-the-loop (HiL) simulation where a robotic physical setup interacts with a computational musculoskeletal model based on inverse dynamics. A major objective of this work was the validation of the HiL test system against in vivo data derived from patients with instrumented THRs. Moreover, the impact of certain test conditions, such as joint lubrication, implant position, load level in terms of body mass and removal of muscle structures, was evaluated within several HiL simulations. The outcomes for a normal sitting down and standing up maneuver revealed good agreement in trend and magnitude compared with in vivo measured hip joint forces. For a deep maneuver with femoral adduction, lubrication was shown to cause less friction torques than under dry conditions. Similarly, it could be demonstrated that less cup anteversion and inclination lead to earlier impingement in flexion motion including pelvic tilt for selected combinations of cup and stem positions. Reducing body mass did not influence impingement-free range of motion and dislocation behavior; however, higher resisting torques were observed under higher loads. Muscle removal emulating a posterior surgical approach indicated alterations in THR loading and the instability process in contrast to a reference case with intact musculature. Based on the presented data, it can be concluded that the HiL test system is able to reproduce comparable joint dynamics as present in THR patients.

Computer-Assisted Orthopedic Surgery: Current State and Future Perspective

Introduced about two decades ago, computer-assisted orthopedic surgery (CAOS) has emerged as a new and independent area, due to the importance of treatment of musculoskeletal diseases in orthopedics and traumatology, increasing availability of different imaging modalities, and advances in analytics and navigation tools. The aim of this paper is to present the basic elements of CAOS devices and to review state-of-the-art examples of different imaging modalities used to create the virtual representations, of different position tracking devices for navigation systems, of different surgical robots, of different methods for registration and referencing, and of CAOS modules that have been realized for different surgical procedures. Future perspectives will also be outlined.

Double mobility cup total hip arthroplasty in patients at high risk for dislocation: a single-center analysis

INTRODUCTION

Double mobility cup systems (DMCS) have gained increasing acceptance, especially in patients at high risk for dislocation. The aim of this investigation was to analyze the frequency and indications of the DMCS use in our praxis and to evaluate dislocation and cup revision rates after a minimum follow-up of 2 years.

MATERIALS AND METHODS

All patients implanted with a DMCS from May 2008 to August 2011 were identified from our institutional database of primary and revision THA procedures. Patient demographics, including ASA score, were recorded, along with details of the surgical procedures, indications for DMCS use, and post-operative clinical course and any complications. Radiographs were analyzed for implant positioning and radiological signs of loosening.

RESULTS

1046 primary THA were implanted, of these 39 (4 %) primary DMCS. Indications were severe neuromuscular disease (SND) (14), hip abductor degeneration (HAD) (9), cognitive dysfunction (CD) (8) and others. 345 revision THA were performed, of these 50 (14 %) revision DMCS. Indications were recurrent dislocations (27), multiple prior hip surgeries (13), HAD (5), CD (3) and others. Overall dislocation rate was 2/89 (2 %); both in revision THA. Overall cup revision rate was 5/89 (6 %): 3 septic, 1 periprosthetic acetabular fracture, 1 "intraprosthetic dissociation". 67 patients were available for the standardized questionnaire at a median follow-up of 43 months (range 25-78). 19 patients were not available for two-year follow-up: 17 died and two were lost to follow-up.

CONCLUSIONS

This study supports the use of DMCS constructs in primary and revision hip arthroplasty for specific high-risk patients. We continue to indicate DMCS in this patient group. We do caution against extending indications for DMCS to lower risk patient groups due to unknown issues surrounding wear and component longevity.

Range of Hip Joint Motion in Developmental Dysplasia of the Hip Patients Following Total Hip Arthroplasty With the Surgical Technique Using the Concept of Combined Anteversion: A Study of Crowe I and II Patients

The combined anteversion surgical technique has been proposed and used in clinical practice. To more objectively evaluate the feasibility of this surgical technique using combined anteversion concept for DDH patients, we studied 34 DDH patients (40 hips) in this research. Every patient underwent pelvic CT scans before and after surgery and the HHSs were recorded. Optimal range of joint motion was measured using a three-dimensional reconstruction technique and a dynamic measurement technique. The results revealed that joint function met the requirements of daily life and the range of motion was not over-limited by impingement between the prosthesis and the skeleton. Moreover, the combined anteversion was found to be the most critical parameter in this study.

Analysis of hip range of motion in everyday life: a pilot study

Patients undergoing total hip arthroplasty are increasingly younger and have a higher demand concerning hip range of motion. To date, there is no clear consensus as to the amplitude of the "normal hip" in everyday life. It is also unknown if the physical examination is an accurate test for setting the values of true hip motion. The purpose of this study was: 1) to precisely determine the necessary hip joint mobility for everyday tasks in young active subjects to be used in computer simulations of prosthetic models in order to evaluate impingement and instability during their practice; 2) to assess the accuracy of passive hip range of motion measurements during clinical examination. A total of 4 healthy volunteers underwent Magnetic Resonance Imaging and 2 motion capture experiments. During experiment 1, routine activities were recorded and applied to prosthetic hip 3D models including nine cup configurations. During experiment 2, a clinical examination was performed, while the motion of the subjects was simultaneously captured. Important hip flexion (mean range 95°-107°) was measured during daily activities that could expose the prosthetic hip to impingement and instability. The error made by the clinicians during physical examination varied in the range of ±10°, except for flexion and abduction where the error was higher. This study provides useful information for the surgical planning to help restore hip mobility and stability, when dealing with young active patients. The physical examination seems to be a precise method for determining passive hip motion, if care is taken to stabilise the pelvis during hip flexion and abduction.

Outcomes of polyethylene liner cementation into a fixed metal acetabular shell with minimum follow-up of 7 years

Cementation of a polyethylene liner into the well-fixed shell is a convenient option for revision total hip arthroplasty. We retrospectively reviewed 45 patients who had liner cementation to investigate the risk factors which gave rise to major complications and reoperation. Patients were observed for a minimum of 7 years (range 7.8-14 years). Relevant risk factors (age, BMI, surgical approach, previous cup size and position, types of coated surface) were assessed with Cox regression analysis. The mean Harris Hip Score was improved from 62.5 (range 57-68) preoperatively to 87.1 (range 70-97). A total of 7 hips (15.5%) had acetabular component loosening that was treated with reoperation. Prevalence of acetabular component loosening was statistically significantly higher in hydroxyapatite-coated group (5 of 13) than in the Ti-coated group (2 of 32, p = 0.015). All recurrent dislocations occurred in patients treated with a posterior approach. Diameter of the previous metal shell of below 54 mm showed a lower 10-year survival rate than those greater than 54 mm in diameter. PE liner cementation in stable metal cup is a useful alternative option for carefully selected patients. Pre-existing HA-coated cups as well as small sized cups were indicative of poor outcomes.

Intraoperative Fluoroscopy Improves Component Position During Anterior Hip Arthroplasty

The goal of this retrospective review was to determine whether fluoroscopic guidance improves acetabular cup abduction and anteversion alignment during anterior total hip arthroplasty. The authors retrospectively reviewed 199 patients (fluoroscopy group, 98; nonfluoroscopy group, 101) who underwent anterior total hip arthroplasty at a single center with and without C-arm fluoroscopy guidance. Included in the study were patients of any age who underwent primary anterior approach total hip arthroplasty performed by a single surgeon, with 6-month postoperative anteroposterior pelvis radiographs. Acetabular cup abduction and anteversion angles were measured and compared between groups. Mean acetabular cup abduction and anteversion angles were 43.4° (range, 26.0°-57.4°) and 23.1° (range, 17°-28°), respectively, in the fluoroscopy group. Mean abduction and anteversion angles were 45.9° (range, 29.7°-61.3°) and 23.1° (range, 17°-28°), respectively, after anterior total hip arthroplasty without the use of C-arm guidance (nonfluoroscopy group). The use of fluoroscopy was associated with a statistically significant difference in cup abduction (P=.002) but no statistically significant difference in anteversion angles. In the fluoroscopy group, 80% of implants were within the combined safe zone compared with 63% in the nonfluoroscopy group. A significantly higher percentage of both acetabular cup abduction angles and combined anteversion and abduction angles were in the safe zone in the fluoroscopy group. Fluoroscopy is not required for proper anteversion placement of acetabular components, but it may increase ideal safe zone placement of components.

A critical analysis of radiographic factors in patients who develop dislocation after elective primary total hip arthroplasty

PURPOSE

In order to diminish total hip arthroplasty (THA) dislocation rate, surgeons strive to achieve adequate component orientation, offset and limb length. In addition, dislocation rate can theoretically be reduced by increasing head diameter and by choosing implants with favorable head-to-neck and cup-to head ratios. We assessed nine radiographic and implant-related parameters associated with an increased risk of dislocation in patients who sustained a dislocation and in those with a stable arthroplasty.

METHODS

A total of 1,487 consecutive elective primary THAs performed by a single surgeon, using a posterolateral approach were reviewed at an average follow-up of 18 months (range, 1-112). Fixation was hybrid in 85 % of hips and non-cemented in 15 %. Thirty-eight patients (38 hips, 2.5 %) sustained at least one dislocation. Thirty-seven patients with good quality, standardized anteroposterior radiographs were selected as a "study group". The study group was matched-paired (1:3) with patients who had a stable arthroplasty based on gender, age, BMI, diagnosis and follow-up. Variables compared between the groups included: head size, cup size, head-to-neck ratio, cup-to-head ratio, leg-length discrepancy, offset, cup inclination, cup version and cup orientation based on the safe zone defined by Lewinnek et al.

RESULTS

None of the nine parameters showed a statistically significant difference between the groups.

DISCUSSION

In this study, 90 % of patients who developed a dislocation had properly positioned acetabular components. In addition, the vast majority of patients in the study group had adequate restoration of limb length and offset. The results of our study may be useful for the orthopedic surgeons who discuss instability following THA surgery, particularly in patients with radiographically sound reconstructions.

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.

Pelvic tilt and movement during total hip arthroplasty in the lateral decubitus position

OBJECTIVES

Total hip arthroplasty (THA) is often performed in the lateral decubitus (lateral) position. In this position, the pelvis may have various degrees of tilt leading to implant malposition. We sought to quantify the pelvic tilt in lateral position and further pelvic movement during surgery.

METHODS

In 95 cases with primary THA, three-dimensional pelvic tilts were quantified by superimposing images reconstructed from CT data onto antero-posterior radiographs taken in lateral position at set-up and after cup placement. Pelvises were fixed with a device compressing anterior superior iliac spines and sacrum.

RESULTS

Various degrees of pelvic tilt occurred compared to the supine position; sagittal: -3.1° (-25.5° to 10.2°), axial: 3.9° (-8.4° to 17°), coronal: 0.9° (-11.9° to 13.2°). Absolute changes more than 5° were observed 43%, 47%, and 12% in the sagittal, axial, and coronal planes, respectively. The more preoperative posterior pelvic tilt resulted in the more change in the sagittal plane. Further pelvic movement of about 3° in three planes were observed ranging from -11° to 20° after cup placement.

CONCLUSION

This study showed various pelvic tilt and movement during THA. As pelvic tilt directly alters the cup orientation, its changes should be well understood. Improved tools for positioning and holding the pelvis are required.

The influence of sagittal spinal deformity on anteversion of the acetabular component in total hip arthroplasty

The interaction between the lumbosacral spine and the pelvis is dynamically related to positional change, and may be complicated by co-existing pathology. This review summarises the current literature examining the effect of sagittal spinal deformity on pelvic and acetabular orientation during total hip arthroplasty (THA) and provides recommendations to aid in placement of the acetabular component for patients with co-existing spinal pathology or long spinal fusions. Pre-operatively, patients can be divided into four categories based on the flexibility and sagittal balance of the spine. Using this information as a guide, placement of the acetabular component can be optimal based on the type and significance of co-existing spinal deformity.

Serum Metal Ions with a Titanium Modular Neck Total Hip Replacement System

The goal of this study is to evaluate serum levels of chromium (Cr), cobalt (Co), and titanium (Ti) within the first two years following total hip arthroplasty using a Ti modular neck system. Twenty-five patients were randomized to a metal-on-metal (MoM) bearing with an all CoCr shell, and the remaining 25 received a metal-on-polyethylene (MoP) with a Ti shell. Serum levels demonstrated increases for Cr, Co, and Ti at 1 year (P < .001). MoM had similar Ti levels to MoP hips at 1 year (P=0.11) but lower at 2 years (P=0.03). Results suggest that the passive corrosion (i.e., chemical, pitting, and crevice corrosion) of exposed non-articular metal surfaces may be a greater source of ions than the neck-stem or head-neck interfaces.

Fluctuation of Cup Orientation During Press-Fit Insertion: A Possible Cause of Malpositioning

We evaluated real-time angular changes during press-fit cup insertion in 70 total hip arthroplasties. Inclination and anteversion cup angles on navigation system were recorded after each procedure of five hammer blows during cup insertion, and maximum deviated inclination (MDI) and anteversion (MDA) angles until the cup was fully seated were measured. We found 1 (1%) and 29 (41%) hips with increases and decreases in MDI of 5° or more, and 13 (19%) and 6 (8%) hips with increases and decreases in MDA of 5° or more, respectively. The MDI in men was significantly lower and the MDA for left-side surgery was significantly higher. Surgeons should pay attention to fluctuation in angular changes during cup insertion and may consider countermeasures to minimize cup malpositioning.

Difference in Stem Alignment Between the Direct Anterior Approach and the Posterolateral Approach in Total Hip Arthroplasty

The purpose of this study was to investigate the effects of different surgical approaches, the posterolateral approach (PLA) and the direct anterior approach (DAA), on postoperative femoral anteversion and stem coronal and sagittal alignment in total hip arthroplasty (THA), and to identify the factors related to postoperative femoral anteversion and stem alignment. A total of 209 hips of 181 patients were evaluated. THA was performed through the PLA in 80 hips and through the DAA in 129 hips. Femoral anteversion and stem alignment were measured on postoperative computed tomography images. The factor related to postoperative anteversion change was preoperative femoral anteversion, and the surgical approaches did not affect the postoperative anteversion change, while surgical approach did have an effect on stem sagittal alignment.

Supercapsular percutaneously-assisted total hip arthroplasty: radiographic outcomes and surgical technique

BACKGROUND

The supercapsular percutaneously-assisted total hip (SuperPATH(®)) approach for total hip arthroplasty (THA) was developed to promote early mobilization and greater range of motion, physiologic gait kinematics and improved pain control. The superpath approach is a hybrid of the Superior Capsulotomy (SuperCap(®)) approach and the percutaneously assisted total hip (PATH(®)) technique.

METHODS

Postoperative radiographs of 66 consecutive patients from the first 100 patients who underwent the SuperPATH approach were analysed by an independent third party for component position and seating, femoral offset and leg length. A detailed description of preoperative and postoperative preparation, soft tissue dissection, preparation of the femoral canal and acetabulum, and implant positioning is also provided with figures to illustrate.

RESULTS

All components in this case series were well seated and position deemed optimal. Leg lengths were measured to within 5 mm of the contralateral side and mean acetabular abduction angle was 40.13° (SD 6.30°).

CONCLUSIONS

Through preservation of the external rotators, hip capsule, and abductor integrity, the SuperPATH approach for THA maximally preserves the surrounding soft tissue envelope. Implant position was optimal within the 'learning curve' of the first 100 cases for described THA safe zones. Long term outcome data for the SuperPATH approach are being collected as part of an ongoing study to compare to favourable short and mid-term results.

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.

Midterm Results of Delta Ceramic-on-Ceramic Total Hip Arthroplasty

This study reports mid-term results of Delta ceramic on ceramic (COC) in total hip arthroplasty (THA). Subjects received Delta COC THA in a prospective multi-center study with either 28 mm (n=177) or 36 mm (n=168) articulations. Annual clinical and radiographic evaluations were performed, and patients were asked about hip noises. At mean 5.3-year follow-up there were 3 (0.9%) post-operative liner fractures. Nine revisions were performed (2 liner fracture, 4 stem loosening, 3 deep infection). Kaplan-Meier survivorship at 6 years was 96.9% (94.0-98.4). Twenty-six (7.5%) subjects reported squeaking, of whom none were revised. One (0.3%) subject could reproduce a sound in clinic. More patients reported squeaking with a 36 mm bearing (28 mm: 7/177, 36 mm: 19/168, P=0.013).

Does warming up improve surgical outcome in total hip arthroplasty?

PURPOSE

Warming up prior to surgery has been shown to enhance surgeons' performance during laparoscopic procedures. It is unknown whether or not warming up prior to total hip arthroplasty (THA) will have a similar effect on surgical outcome.

METHODS

We retrospectively evaluated the effect of warming up on the intraoperative outcome of 82 patients who underwent a primary THA with identical implants. The patients were divided equally into two groups. Group 1 (first case of the day) served as "warm-up procedure," while Group 2 (second case of the day) was the "post-warm-up procedure."

RESULTS

We found no statistically significant difference when we compared cup abduction and anteversion angles, femoral offset, postoperative LLD, stem alignment, hip center of rotation and femoral stem canal fill between the two groups (p > 0.05).

CONCLUSION

Warming up prior to performing surgery does not make a difference for primary THA when performed by an experienced surgeon. However, these results may not reflect its effect on procedures that require fine motor skills or done by an orthopedic trainee or less experienced surgeons.

Effects of coordinate-system construction methods on postoperative computed tomography evaluation of implant orientation after total hip arthroplasty

OBJECTIVE

In total hip arthroplasty, it is important to assess postoperative implant orientation. The computed tomography-based (CT-based) three-dimensional (3D) templating method using 3D preoperative planning software is generally recommended. In this method, postoperative implant orientation within a bony coordinate system can be measured by overlaying a 3D computerized model of the implant on a real postoperative CT image of the implant. The bony coordinate system consists of several reference points (RPs) marked on a CT image of the bone surface. Therefore, preoperative and postoperative coordinate systems do not always match. We investigated how the difference between coordinate systems constructed from RPs chosen by manual methods (M1 and M2) and those constructed by the computer matching method influences the results of measurement validation.

METHODS

In M1, postoperative RPs were chosen without a specific tool in a single planning module. In M2, postoperative RPs were chosen with as little deviation as possible from preoperative RPs, verifying preoperative RPs on another monitor.

RESULTS

M1 and M2 produced mean errors in acetabular cup inclination of 0.7° ± 0.5° and 0.5° ± 0.3°, respectively, and mean errors in cup anteversion of 1.3° ± 1.2° and 0.5° ± 0.4°, respectively, which were statistically significant differences. M1 and M2 produced mean errors in femoral stem anteversion of 2.4° ± 2.0° and 2.7° ± 2.1°, respectively, not a significant difference, but these errors were larger than errors in cup orientation.

DISCUSSION

We recommend referring to preoperative RPs when choosing postoperative RPs. Surgeons must be aware that for evaluation of postoperative stem anteversion, manual methods may produce considerable error.

Influence of surgical approach on component positioning in primary total hip arthroplasty

Background

Minimal invasive surgery (MIS) has gained growing popularity in total hip arthroplasty (THA) but concerns exist regarding component malpositioning. The aim of the present study was to evaluate femoral and acetabular component positioning in primary cementless THA comparing a lateral to a MIS anterolateral approach.

Methods

We evaluated 6 week postoperative radiographs of 52 hips with a minimal invasive anterolateral approach compared to 54 hips with a standard lateral approach. All hips had received the same type of implant for primary cementless unilateral THA and had a healthy hip contralaterally.

Results

Hip offset was equally restored comparing both approaches. No influence of the approach was observed with regard to reconstruction of acetabular offset, femoral offset, vertical placement of the center of rotation, stem alignment and leg length discrepancy. However, with the MIS approach, a significantly higher percentage of cups (38.5 %) was malpositioned compared to the standard approach (16.7 %) (p = 0.022).

Conclusions

The MIS anterolateral approach allows for comparable reconstruction of stem position, offset and center of rotation compared to the lateral approach. However, surgeons must be aware of a higher risk of cup malpositioning for inclination and anteversion using the MIS anterolateral approach.

A Useful Anatomical Reference Guide for Stem Anteversion during Total Hip Arthroplasty in the Dysplastic Hip

Computed tomography scans of 50 dysplastic hips were obtained and reconstructed using preoperative planning software for total hip arthroplasty. The anteversion of the stem implanted parallel to the line connecting the trochanteric fossa and the middle of the medial cortex of the femoral neck (T line) was measured. The cutting heights of 5mm and 10mm above the lesser trochanter were simulated. The mean difference of the anteversion of the stem using the T line and the native femoral anteversion was 2.7° (95% CI: 1.0°-4.5°) and 3.5° (95% CI: 1.5°-5.5°) at cutting heights of 5mm and 10mm respectively. An anteversion using a T line is compatible with native femoral anteversion even in developmental dysplasia of the hip.

The influence of stem offset and neck shaft angles on the range of motion in total hip arthroplasty

PURPOSE

To evaluate the influence of stem offset and neck shaft angles on the range of motion before component impingement (ROMCI) and bony impingement (ROMBI), and the types of impingement in total hip arthroplasty (THA).

METHODS

Using the computed tomography data of 101 patients who underwent THA, three-dimensional dynamic motion analysis was performed using a modular implant (Kinectiv(®) stem) that enabled adjustment of offset and leg length independently. We defined offset as horizontal offset (HO) and leg length as vertical offset (VO), and measured the ROMCI and ROMBI in flexion (Flex), internal rotation (Int-R) and external rotation (Ext-R) with the configuration of each horizontal/vertical offset.

RESULTS

We found that HO lengthening increased the ROMCI and ROMBI in Flex and Int-R by delaying bony impingement, although excessive lengthening had minimal effect. On the contrary, VO lengthening decreased the ROMCI and ROMBI in Flex and ROMCI in Int-R. As for Ext-R, VO lengthening had positive effects on the ROMCI and ROMBI, whereas lengthening of HO had negative effects on the ROMCI and ROMBI.

CONCLUSIONS

We demonstrated that the appropriate long offset with a low shaft angle increased the ROM in Flex and Int-R, and a high neck shaft angle increased the ROM in Ext-R. We should use implants properly in accordance with the types of impingement for avoiding dislocations in THA.

Low femoral antetorsion as a risk factor for bony impingement after bipolar hemiarthroplasty

Introduction

Reports of dislocation after bipolar hemiarthroplasty (BHA) abound in literature, and several studies have mentioned the factors that are associated with an increased risk of dislocation. However, there is no report detailing the pattern of impingement in BHA and how femoral antetorsion can affect the range of motion (ROM) after BHA.

Purpose

The purpose of this study was to evaluate the pattern of impingement in BHA and whether femoral antetorsion affects the ROM after BHA using three-dimensional (3D) dynamic motion analysis.

Methods

Using the computed tomography (CT) data of 60 patients (60 hips), including 31 men and 29 women who underwent BHA for the treatment of idiopathic osteonecrosis (ION) of the femoral head, we calculated the antetorsion of the femoral neck, ROM of flexion (Flex), internal rotation (Int-R), and external rotation (Ext-R) using a CT-based 3D simulation software. We evaluated the pattern of impingement and the relationship between femoral antetorsion and ROM in BHA. As for the implant position in the 3D simulation software, the anteversion of the femoral implant was set to be the same as the natural antetorsion of the femoral neck and neck length was set to be the standard neck in all cases.

Results

This study revealed the mechanism of impingement in BHA: (1) bone to bone impingement and (2) implant to bone impingement. We found a significant decrease in the ROM of Flex and Int-R inversely proportional to the femoral antetorsion. In patients with lower femoral antetorsion, the ROM of Flex and Int-R decreased due to bony impingement (the anterior great trochanteric region of the femur impinges on the anteroinferior edge of the anteroinferior iliac spine). Whereas, high anteversion of the femoral implant may decrease the ROM of Ext-R; however, our results also showed that even the lowest ROM of Ext-R with 10° hip extension was over 40°.

Conclusions

We demonstrated that lower femoral antetorsion substantially affects the ROM of Flex and Int-R due to bony impingement. For these patients, there should be consideration given to retaining femoral “anterior offset” in BHA.

The reliability and accuracy of measuring anteversion of the acetabular component on plain anteroposterior and lateral radiographs after total hip arthroplasty

There is no single standardised method of measuring the orientation of the acetabular component on plain radiographs after total hip arthroplasty. We assessed the reliability and accuracy of three methods of assessing anteversion of the acetabular component for 551 THAs using the PolyWare software and the methods of Liaw et al, and of Woo and Morrey. All measurements of the three methods had excellent intra- and inter-observer reliability. The values of the PolyWare software, which determines version of the acetabular component by edge detection were regarded as the reference standard. Although the PolyWare software and the method of Liaw et al were similarly precise, the method of Woo and Morrey was significantly less accurate (p < 0.001). The method of Liaw et al seemed to be more accurate than that of Woo and Morrey when compared with the measurements using the PolyWare software. If the qualified lateral radiograph was selected, anteversion measured using the method of Woo and Morrey was considered to be relatively reliable.

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.

Bone ingrowth around porous-coated acetabular implant: a three-dimensional finite element study using mechanoregulatory algorithm

Fixation of uncemented implant is influenced by peri-prosthetic bone ingrowth, which is dependent on the mechanical environment of the implant-bone structure. The objective of the study is to gain an insight into the tissue differentiation around an acetabular component. A mapping framework has been developed to simulate appropriate mechanical environment in the three-dimensional microscale model, implement the mechanoregulatory tissue differentiation algorithm and subsequently assess spatial distribution of bone ingrowth around an acetabular component, quantitatively. The FE model of implanted pelvis subjected to eight static load cases during a normal walking cycle was first solved. Thereafter, a mapping algorithm has been employed to include the variations in implant-bone relative displacement and host bone material properties from the macroscale FE model of implanted pelvis to the microscale FE model of the beaded implant-bone interface. The evolutionary tissue differentiation was observed in each of the 13 microscale models corresponding to 13 acetabular regions. The total implant-bone relative displacements, averaged over each region of the acetabulum, were found to vary between 10 and 60 μm. Both the linear elastic and biphasic poroelastic models predicted similar mechanoregulatory peri-prosthetic tissue differentiation. Considerable variations in bone ingrowth (13-88%), interdigitation depth (0.2-0.82 mm) and average tissue Young's modulus (970-3430 MPa) were predicted around the acetabular cup. A progressive increase in the average Young's modulus, interdigitation depth and decrease in average radial strains of newly formed tissue layer were also observed. This scheme can be extended to investigate tissue differentiation for different surface texture designs on the implants.

Cup Implant Planning Based on 2-D/3-D Radiographic Pelvis Reconstruction-First Clinical Results

GOAL

In the following, we will present a newly developed X-ray calibration phantom and its integration for 2-D/3-D pelvis reconstruction and subsequent automatic cup planning. Two different planning strategies were applied and evaluated with clinical data.

METHODS

Two different cup planning methods were investigated: The first planning strategy is based on a combined pelvis and cup statistical atlas. Thereby, the pelvis part of the combined atlas is matched to the reconstructed pelvis model, resulting in an optimized cup planning. The second planning strategy analyzes the morphology of the reconstructed pelvis model to determine the best fitting cup implant.

RESULTS

The first planning strategy was compared to 3-D CT-based planning. Digitally reconstructed radiographs of THA patients with differently severe pathologies were used to evaluate the accuracy of predicting the cup size and position. Within a discrepancy of one cup size, the size was correctly identified in 100% of the cases for Crowe type I datasets and in 77.8% of the cases for Crowe type II, III, and IV datasets. The second planning strategy was analyzed with respect to the eventually implanted cup size. In seven patients, the estimated cup diameter was correct within one cup size, while the estimation for the remaining five patients differed by two cup sizes.

CONCLUSION

While both planning strategies showed the same prediction rate with a discrepancy of one cup size (87.5%), the prediction of the exact cup size was increased for the statistical atlas-based strategy (56%) in contrast to the anatomically driven approach (37.5%).

SIGNIFICANCE

The proposed approach demonstrated the clinical validity of using 2-D/3-D reconstruction technique for cup planning.

Cup version can be accurately measured on the false profile view radiograph

INTRODUCTION

Accurate measurement of cup version on plain radiographs remains difficult due to the two-dimensional projection of an ellipse and difficulty obtaining reproducible radiographs.

PURPOSE

Determine: 1) if the cup angle measured on the false profile view (FPV) could be used to determine radiographic cup version; 2) how patient positioning would affect cup angle measurement on the FPV; 3) if implant cup design affects cup angle measurement.

MATERIALS AND METHODS

Three cup version positions were assessed in a sawbone: 13° (normal); 28° (excessive anteversion) and -2° (retroversion). Cup angle was measured on the FPV at five different degrees of pelvic rotation within each cup version group. Pelvic rotation was quantified using the ratio of the inter-femoral head distance measured on the FPV versus the anteroposterior radiographs (FP/AP ratio). Eighty patients (40 metal-on-polyethylene, 40 metal-on-metal) post-total hip were also assessed. Cup version was assessed with Einzel-Bild-Roentgen-Analysis software (EBRA). R2 was calculated to assess correlation between both measurement methods.

RESULTS

For the sawbone model, an R2 of 0.95 was obtained. For patients, overall R2 was 0.56 with an FP/AP ratio of 0.3-0.49 having an R2 of 0.72. The EBRA anteversion versus cup angle scatterplot had an R2 of 0.72 (95%CI: +/-7.8°). Subgroup analysis revealed no differences between the metal-on-poly and metal-on-metal for cup angle measurements. The intra-class coefficient for intra- and inter-observer reliability for all cases (individual and combined FP/AP groups) was 0.98 to 0.99.

CONCLUSION

The FPV cup angle measurement value provides an accurate measurement of radiographic cup anteversion with well-defined patient position parameters.