Assessment of cup orientation in hip resurfacing: a comparison of TraumaCad and computed tomography

Purpose

The orientation of the acetabular component in metal-on-metal hip resurfacing arthroplasty affects wear rate and hence failure. This study aimed to establish if interpretation of pelvic radiographs with TraumaCad software can provide a reliable alternative to CT in measuring the acetabular inclination and version.

Methods

TraumaCad was used to measure the acetabular orientation on AP pelvis radiographs of 14 painful hip resurfacings. Four orthopaedic surgeons performed each measurement twice. These were compared with measurements taken from CT reformats. The correlation between TraumaCad and CT was calculated, as was the intra- and inter-observer reliability of TraumaCad.

Results

There is strong correlation between the two techniques for the measurement of inclination and version (p <0.001). Intra- and inter-observer reliability of TraumaCad measurements are good (p <0.001). Mean absolute error for measurement of inclination was 2.1°. TraumaCad underestimated version compared to CT in 93% of cases, by 12.6 degrees on average.

Conclusions

When assessing acetabular orientation in hip resurfacing, the orthopaedic surgeon may use TraumaCad in the knowledge that it correlates well with CT and has good intra- and inter-observer reliability but underestimates version by 12° on average.

Pelvic flexion measurement from lateral projection radiographs is clinically reliable

BACKGROUND

Pelvic flexion affects orientation of the acetabular cup; however, pelvic position is not static in daily activities. During THA it is difficult to know the degree of pelvic flexion with the patient in the lateral position and that position is static. However, surgeons need to appropriately determine pelvic tilt to properly insert the acetabular component.

QUESTIONS/PURPOSES

We investigated the reliability of pelvic flexion angle that was measured by manually identifying the location of the pubic symphysis and bilateral anterior superior iliac spines using synthesized lateral radiographs.

METHODS

We synthesized 49 lateral radiographs based on CT data. Each of the 49 radiographs had a unique position: 7° of varying lateral tilt and rotation in each of seven selected pelvic flexion angles. The pelvic flexion angle was measured three times by three independent observers in each position and determined the accuracy (based on the true value from the reconstructions) and reliability of the measures.

RESULTS

The measurement error was 0.1° (range, -4.8° to 4.0°). There was a tendency for errors when the pelvic flexion angle was 0° or ±5°; the errors were less when the pelvic flexion angle was ±10° or ±20°. Lateral tilt was associated with greater error than rotation. The intraclass correlation coefficient (ICC) of the average value was 0.967. For one observer, more than two measurements are necessary for the ICC to be greater than 0.8, and only one measurement was needed for two of the three observers.

CONCLUSIONS

Our data suggest measurement of pelvic flexion angle using lateral radiographs is reliable. We recommend the measurement be performed once by two observers for better reliability.

In vivo serum titanium ion levels following modular neck total hip arthroplasty--10 year results in 67 patients

The objective of the present cross-sectional study was to determine in vivo titanium ion levels following cementless total hip arthroplasty (THA) using a modular stem system with different shapes for femoral canal fit and multiple neck options. A consecutive series of 173 patients (190 hips) who underwent cementless modular neck THA and a ceramic on polyethylene bearing with a median follow-up of 9 (7-13) years was evaluated retrospectively. According to a standardized protocol, titanium ion measurements were performed on 67 patients using high-resolution inductively coupled plasma-mass spectrometry. Ion levels were compared to a control group comprising patients with non-modular titanium implants (n=11) and to individuals without implants (n=23). Modular neck THA did not result in elevated titanium ion levels compared to non-modular THA. Compared to individuals without implants, both modular THA and non-modular THA showed elevated titanium ion levels. Absolute titanium ion levels, however, were comparatively low for both implants. The data suggest that the present modular stem system does not result in elevated systemic titanium ion levels in the medium term when compared to non-modular stems. Further longitudinal studies are needed to evaluate the use of systemic titanium ion levels as an objective diagnostic tool to identify THA failure and to monitor patients following revision surgery.

Computerized ellipse method for measuring acetabular version after total hip replacement--a precision study using synthetic and real radiographs

BACKGROUND

Previous work by our group to address the problem of acetabular positioning based on 2D methods resulted in the development of a measurement method with better precision--Liaw's version. This method may help the early diagnosis of acetabular loosening. In the present study, we hypothesized that our computerized ellipse method could improve the precision of measuring acetabular version.

METHODS

We developed our Elliversion software to measure acetabular version. Using total hip replacement (THR) Simulator, 96 radiographs were synthesized with random femoral inclination and 5° to 52° version, half with the femoral head included and half without. These synthetic radiographs and 28 real radiographs were measured with both Elliversion and the trigonometric method twice by one of the authors with a one-week interval between measurements. We then calculated the difference in the repeated measurements. Student's t-test was used for statistical analysis of the measuring error and inter-measurement difference.

RESULTS

In the precision study, for synthetic radiographs including the femoral head, the ellipse method was significantly better than the trigonometric method (p < 0.01). For synthetic radiographs without the femoral head, there was no significant difference between the ellipse method and the trigonometric method (p = 0.19). As for the repeated measurements, for synthetic radiographs including the femoral head, the ellipse method was significantly better than the trigonometric method (p = 0.001), whereas for synthetic radiographs without the femoral head, there was no significant difference between the two methods (p = 0.17). For real radiographs, there was no significant difference between the two measuring methods (p = 0.12). However, if we excluded the four poor-quality radiographs, there was a significant difference between the two measuring methods (p = 0.04).

DISCUSSION

We developed a computerized ellipse method for measuring acetabular version on synthetic radiographs and good-quality real radiographs. This method is characterized by its superior precision as compared to the trigonometric method. With the 2D standardized method (Liaw's version), improving the precision of measurement will help earlier diagnosis of acetabular loosening.

Evaluation of the accuracy of femoral component orientation by the CT-based fluoro-matched navigation system

PURPOSE

Accurate orientation of acetabular and femoral components are important during THA. However, no study has assessed the use of the CT-based fluoro-matched navigation system during THA. Therefore, we have evaluated the accuracy of stem orientation by CT-based fluoro-matched navigation.

METHODS

The accuracy of stem orientation by CT-based fluoro-matched navigation was assessed by postoperative CT data. Furthermore, we compared the postoperative stem orientation with the intraoperative registration errors.

RESULTS

The average antetorsion error of the stem (navigation records - postoperative CT) was -0.5° ± 5.2°. The stem valgus error was 0.4° ± 2.7°. The accuracy of the navigation record for the orientation of the stem valgus was dependent on the intraoperative registration errors.

CONCLUSIONS

The clinical accuracy of CT-based fluoro-matched navigation is adequate for stem alignment orientation, and the intraoperative verification of registration errors is valuable for checking the accuracy of stem orientation by navigation.

Bone remodelling around uncemented metallic and ceramic acetabular components

Stress shielding–induced bone resorption around cementless acetabular components has been indicated as a potential failure mechanism that may threaten long-term fixation. Using a bone remodelling algorithm in combination with three-dimensional finite element models of intact and implanted pelvises and musculoskeletal loading during normal walking, the objectives of the study were to investigate the deviations in load transfer due to implantation and bone adaptation around cementless metallic and ceramic acetabular components. Variations in implant–bone interfacial condition affected strain shielding and bone remodelling; strain shielding was higher for the bonded condition as compared to the debonded condition. For bonded interfacial condition, severe bone resorption, 20%–50% bone density reduction, was observed within the acetabulum. Considering debonded implant–bone interface, bone density increase of 50%–60% was observed around the supero-posterior part of acetabulum, whereas bone density reductions were low (2%–15%) in other locations. The implant–bone interface appeared less likely to fail, post-operatively and after bone remodelling. Moreover, the implant–bone micromotion was found to be low, less than 100 µm. Strain shielding and bone remodelling were almost similar for the metallic and ceramic components. Based on the results of this study, the ceramic acetabular component appeared to be a viable alternative to metal.

High initial stability in porous titanium acetabular cups: a biomechanical study

Initial stability with limited micromotion in uncemented total hip arthroplasty acetabular components is essential for bony attachment and long-term biomechanical fixation. This study compared porous titanium fixation surfaces to clinically established, plasma-sprayed designs in terms of interface stability and required seating force. Porous plasma-sprayed modular and metal-on-metal (MOM) cups were compared to a modular, porous titanium designs. Cups were implanted into polyurethane blocks with1-mm interference fit and subsequently edge loaded to failure. Porous titanium cups exhibited 23% to 65% improvement in initial stability when compared to plasma-sprayed cup designs (P=.01): a clinically significant increase, based on experience and prior literature. The results of this study indicate increased interface stability in porous titanium-coated cups without significantly increasing the necessary force and energy required for full seating.

The influence of head diameter and wall thickness on deformations of metallic acetabular press-fit cups and UHMWPE liners: a finite element analysis

BACKGROUND

To increase the range of motion of total hip endoprostheses, prosthetic heads need to be enlarged, which implies that the cup and/or liner thickness must decrease. This may have negative effects on the wear rate, because the acetabular cups and liners could deform during press-fit implantation and hip joint loading. We compared the metal cup and polyethylene liner deformations that occurred when different wall thicknesses were used in order to evaluate the resulting changes in the clearance of the articulating region.

METHODS

A parametric finite element model utilized three cup and liner wall thicknesses to analyze cup and liner deformations after press-fit implantation into the pelvic bone. The resultant hip joint force during heel strike was applied while the femur was fixed, accounting for physiological muscle forces. The deformation behavior of the liner under joint loading was therefore assessed as a function of the head diameter and the resulting clearance.

RESULTS

Press-fit implantation showed diametral cup deformations of 0.096, 0.034, and 0.014 mm for cup wall thicknesses of 3, 5, and 7 mm, respectively. The largest deformations (average 0.084 ± 0.003 mm) of liners with thicknesses of 4, 6, and 8 mm occurred with the smallest cup wall thickness (3 mm). The smallest liner deformation (0.011 mm) was obtained with largest cup and liner wall thicknesses. Under joint loading, liner deformations in thin-walled acetabular cups (3 mm) reduced the initial clearance by about 50 %.

CONCLUSION

Acetabular press-fit cups with wall thicknesses of ≤5 mm should only be used in combination with polyethylene liners >6 mm thick in order to minimize the reduction in clearance.

Strict component positioning is necessary in hip resurfacing

BACKGROUND

Hip resurfacing arthroplasty has some advantages, including improved metal-on-metal articulation, a lower dislocation rate and preserved femoral bone. This procedure is a surgical option for younger and more active patients with osteoarthritis and osteonecrosis of the femoral head. Although there have been some reports about the efficacy of this technique, others report serious complications caused by metal debris. Additionally, femoral neck preservation adversely decreases the head-neck ratio and results in postoperative impingement.

METHODS

We evaluated the range of motion after hip resurfacing with various component orientations and optimal component orientations to avoid postoperative impingement using computer simulations in 10 male patients with osteonecrosis.

RESULTS

The mean ranges of motion in flexion, extension, abduction, adduction and internal rotation at 90° of flexion were 92.4° ± 13.8°, 25.7° ± 13.8°, 38.0° ± 11.1°, 29.1° ± 10.0° and 20.9° ± 11.5°, respectively. The oscillation angle in flexion and extension motion was 118.1° ± 10.3°. More than 100° of flexion was acquired in 79 of 240 simulations (32.9 %), and more than 20° extension was acquired in 142 simulations (59.2 %). Combined anteversion was significantly correlated with maximal flexion and extension angles. The component safe zone to fulfill the range of motion criteria varied among patients, and 4 of 10 patients had no safe zone.

CONCLUSIONS

Postoperative impingement occurs relatively frequently in hip resurfacing because of preservation of the femoral neck and component malpositioning. The safe zone of the acetabular component to avoid postoperative impingement is very narrow. Greater care should be taken regarding patient selection, rigorous preoperative planning and accurate component positioning.

Detecting cause of dislocation after total hip arthroplasty by patient-specific four-dimensional motion analysis

BACKGROUND

Dislocation is a major complication after total hip arthroplasty. Prosthesis impingement is considered to be an important cause of dislocation because impingement marks are more frequently found on retrieved cups or liners in patients who have undergone revision surgery because of dislocation (80%-94%) than in those who have undergone reoperation for other reasons (51%-56%). However, it remains a question whether impingement marks are the cause of dislocation or are instead its result. To clarify the issue, it is necessary to confirm noninvasively whether the point of impingement matches the patient's hip position when dislocation occurs.

METHODS

Using four-dimensional patient-specific analysis, we recorded prosthesis impingement in 10 hips with instability after primary total hip arthroplasty when the patients reproduced the dislocation-causing motion.

FINDINGS

We found prosthesis impingement to be related to at least instability in 6 of 10 hips with dislocation after primary total hip arthroplasty and in 4 of 4 hips that underwent revision surgery for recurrent dislocation. All impingements occurred between the anterior wall of the liner and the stem neck in posterior dislocation and between the posterior wall of the liner and the stem neck in anterior dislocation. Revision surgery in 1 of those 4 hips revealed 2 impingement marks on the retrieved liner that closely matched the prosthesis impingement point and the dislocation pathway of the metal head on the liner that were detected earlier during motion analysis.

INTERPRETATION

Prosthesis impingement is an important factor in dislocation after total hip arthroplasty.

Outcomes of minimally invasive anterolateral THA are not superior to those of minimally invasive direct lateral and posterolateral THA

BACKGROUND

There has been considerable interest in minimally invasive surgical (MIS) THA in recent years. The MIS anterolateral approach, or the MIS Watson-Jones approach, is a novel intermuscular abductor-sparing technique. Early reports from case series suggest the potential for superior function and reduced complications; however, the available information from clinical reports is inadequate to suggest surgeons should change from their accepted standard approach.

QUESTIONS/PURPOSES

We examined the potential superiority of this anterolateral approach, as judged by quality-of-life (QoL) measures, radiographic parameters, and complications, compared to limited-incision MIS direct lateral and MIS posterolateral approaches.

METHODS

We performed a prospective randomized controlled trial involving five surgeons at three centers, recruiting 156 patients undergoing primary THA to receive either the MIS anterolateral or the surgeon's preferred approach (direct lateral or posterolateral). For the 135 patients we report, we collected patient-reported WOMAC, SF-36, Paper Adaptive Test in 5 Domains of Quality of Life in Arthritis Questionnaire [PAT5D], and patient satisfaction scores. We recorded complications and evaluated radiographs for prosthetic component position, subsidence, and fracture. Minimum followup was 24 months (mean, 30 months; range, 24-42 months).

RESULTS

QoL and patient-reported satisfaction were similar between groups. Radiographic evaluation demonstrated no differences in acetabular component positioning; however, mean stem subsidence was 4.6 mm for the MIS anterolateral group and 4.1 mm for the alternate group, with differences observed among the three centers for stem subsidence and fracture. One center had increased rate of fracture requiring treatment and need for revision in the MIS anterolateral group.

CONCLUSIONS

We found no superiority of the MIS anterolateral approach but observed intersite differences in painful stem subsidence and fracture. We have returned to the standard surgical approaches in use before the trial.

LEVEL OF EVIDENCE

Level I, therapeutic study. See Instructions for Authors for a complete description of levels of evidence.

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.

The use of the posterior lesser trochanter line to estimate femoral neck version: an analysis of computed tomography measurements

We hypothesized that the lesser trochanter could be a useful guide for estimating femoral component version during total hip arthroplasty. We conducted a study of 88 patients to evaluate the relationship between the posterior lesser trochanter line (PLTL) and the femoral neck axis (FNA) using computed tomographic scans. The mean angle between the PLTL and the FNA was 17.4° ± 7.1° (range, -1.6° to 36.5°). The PLTL angle correlated (r(2) = 0.67-0.72) with the FNA angle. Intraclass correlation coefficient values showed a high level of intraobserver and interobserver agreement in the angles between the PLTL and the FNA. We found a constant relationship between the lesser trochanter and the FNA, and femoral neck version can be estimated, using the PLTL, with reasonable reliability.

Positioning of the acetabular component in cemented prostheses - radiographic calculation

OBJECTIVE

to assess the reliability of the inclination angle and anteversion of acetabular cup component in patients with idiopatic osteoarthritis of the hip, aseptic necrosis and hip neck fracture using trigonometric formula and plain radiographs.

METHODS

66 patients underwent cemented total arthroplasty of 72 hips. The inclination of acetabular component was measured using plain radiograph. The acetabular component anteversion was measured using trigonometric formula.

RESULTS

it was observed that, in the osteoarthritic hips, hip neck fracture and aseptic necrosis, the degree of agreement was highly significant (p < 0.0001), in the measurements of anteversion and inclination angles, among the three assessments, from intra as well as inter-observers. All the agreement pairs were of excellent degree (ICC > 0.80).

CONCLUSION

using plain radiographs and trigonometric formula, the method resulted to be highly accurate and reliable. Besides being easy to be calculated. No significant variation was found in the anteversion and inclination angles when compared with osteoarthritis of the hip, aseptic necrosis and hip neck fracture.

Evaluation of range of motion restriction within the hip joint

In total hip arthroplasty, determining the impingement free range of motion requirement is a complex task. This is because in the native hip, motion is restricted by both impingement as well as soft tissue restraint. The aim of this study is to determine a range of motion benchmark which can identify motions which are at risk from impingement and those which are constrained due to soft tissue. Two experimental methodologies were used to determine motions which were limited by impingement and those motions which were limited by both impingement and soft tissue restraint. By comparing these two experimental results, motions which were limited by impingement were able to be separated from those motions which were limited by soft tissue restraint. The results show motions in extension as well as flexion combined with adduction are limited by soft tissue restraint. Motions in flexion, flexion combined with abduction and adduction are at risk from osseous impingement. Consequently, these motions represent where the maximum likely damage will occur in femoroacetabular impingement or at most risk of prosthetic impingement in total hip arthroplasty.

Acetabular component positioning using anatomic landmarks of the acetabulum

BACKGROUND

The acetabular cup should be properly oriented to prevent dislocation and to reduce wear. However, achieving proper cup placement is challenging with potentially large variations of cup position. We propose a new technique to position the acetabular cup.

QUESTIONS/PURPOSES

We used this technique, then determined actual cup position and subsequent dislocation rate.

METHODS

We measured acetabular abduction (α°) and anteversion (β°) on preoperative CT scans in 46 patients (50 hips) scheduled for THA. During the operation, we identified the transverse acetabular notch (TAN) and anterior acetabular notch (AAN), a notch at the anterior acetabular margin. We then marked two reference points for 40° abduction at the acetabular rim: the superior point, which is opposite the TAN, and the inferior point at |α - 40| mm inside (when α was > 40°) or outside the TAN (when α was < 40°). We also marked two reference points for 15° anteversion: the posterior point opposite the AAN and the anterior point at |β - 15| mm inside (when β was < 15°) or outside the AAN (when β was > 15°). During cup insertion, we aligned cup abduction to the line between the superior and inferior points and cup anteversion to the line between the anterior and posterior points. We measured cup abduction and anteversion and evaluated the dislocation rate. One patient was lost to followup before 60 months; the minimum followup for the other 45 patients was 60 months (mean, 62.8 months; range, 60-65 months).

RESULTS

The mean cup abduction was 40° (range, 32°-47°) and the mean cup anteversion was 17° (range, 8°-25°). No dislocation occurred postoperatively in 49 hips (45 patients) for a minimum of 5 years followup.

CONCLUSIONS

We obtained adequate cup position with our method and none of 45 patients (49 hips) had dislocation.

LEVEL OF EVIDENCE

Level IV, therapeutic study. See Guidelines for Authors for a complete description of level of evidence.

Effects of design parameters of total hip components on the impingement angle and determination of the preferred liner skirt shape with an adequate oscillation angle

The oscillation angle (OsA), which is the sum of the impingement angles on the two sides when the prosthetic neck sways from the neutral axis of the acetabular cup to the liner rim, is one of the most important factors that can affect the range of motion of an artificial hip joint. The aim of this study was to determine the influence of total hip component design on the impingement angle. Our findings show that an increase in cup depth of the liner restricts the motion of the neck and results in a reduced impingement angle, while an increase in chamfer angle increases the impingement angle until it reaches a critical value when a further increase no longer results in an increase in impingement angle. The impingement angle is not only dependent on the head/neck ratio, but also on the head size itself. For most arbitrarily chosen cup depths and chamfer angles, the neck only impacts at one point on the liner. This study proposes a suitable combination of cup depth and chamfer angle and a preferred impact mode, which, if impingement does occur, enables the neck to impinge on the liner rim over a large area. Cup-neck combinations that have an adequate OsA with maximum femoral head coverage are presented.

Combined anteversion of the total hip arthroplasty implanted with image-free cup navigation and without stem navigation

In total hip arthroplasty (THA), combined anteversion (CA), the sum of cup anteversion (AV) and stem antetorsion (AT) are used as parameters to assess the appropriateness of overall prosthetic alignment. In this study, we evaluated the CA value based on the post-operative computed tomography (CT) measurements in our patient population who underwent THA using the OrthoPilot™ image-free navigation system (B/BRAUN-Aesculap, Tuttlingen, Germany). During surgery, cup alignment was adjusted with the use of the navigation system while the positioning of the femoral stem was arbitrarily adjusted by the surgeon. Seventy-nine THAs were included in the study. Post-operative CT assessment for the prosthetic alignment showed the average cup inclination and AV values to be 40.5°±4.1° and 20.6°±4.6°, respectively, demonstrating the effectiveness of the navigation system by small values of standard deviation. By contrast, the AT value measured for the stem showed wide variability (mean 23.6°±11.2°). Consequently, the resulting CA was also inconsistent (mean 44.4°±11.2°) and only 61 of the 79 THAs (77.2%) were defined as satisfactory.

Cup press fit in uncemented THA depends on sex, acetabular shape, and surgical technique

BACKGROUND

Uncemented press-fit cups provide bone fixation in primary THA, but the use of screws is sometimes necessary to achieve primary stability of the socket. However, it is unclear whether and when screws should be used.

QUESTION/PURPOSES

We analyzed the factors related to screw use with a press-fit uncemented cup and assessed whether screw use is associated with the same rates of loosening and revision as a press-fit technique.

METHODS

We retrospectively reviewed 248 patients who underwent THA using the same prosthetic design. Eighty-eight hips had screws to achieve primary cup fixation (Group 1), and 189 did not (Group 2). Mean age was 50 years (range, 14-73 years). We analyzed factors related to the patient, acetabular type, and reconstruction of the rotation center of the hip. Minimum followup was 5 years (mean, 8.9 years; range, 5-12 years).

RESULTS

We found higher screw use in women, patients with less physical activity, Acetabular Types A or C, and a distance from the center of the prosthetic femoral head to the normal center of rotation of more than 3 mm. There were four revisions in Group 1 and five in Group 2. Eight hips had radiographic loosening in Group 1 and nine in Group 2. Cups with a postoperative abduction angle of more than 50° had a higher risk for loosening.

CONCLUSIONS

Press fit was achieved less frequently in women and patients with Acetabular Types A or C and less physical activity; a closer distance to the normal center of rotation decreased screw use. Screw use to augment fixation achieved survival similar to that of a press-fit cup.

LEVEL OF EVIDENCE

Level II, prognostic study. See Instructions for Authors for a complete description of levels of evidence.

Does degree of the pelvic deformity affect the accuracy of computed tomography-based hip navigation?

Although some navigation systems have been used for improvement of component positioning, there have been few reports regarding cases of severe pelvic deformity. We performed a retrospective review of 25 cases of total hip arthroplasty with a computed tomography-based navigation system in patients with severe pelvic deformities and estimated acetabular component position and angle between severe deformity group and mild dysplastic group as a control. There were no significant differences in accuracy of navigation system between 2 groups in terms of 3-dimensional component position or angle. Accuracy of computed tomography-based hip navigation does not depend on the degree of pelvic deformity, and this system is also useful to identify acetabular orientation and for precise component implantation in cases of pelvic deformity.

Is the transverse acetabular ligament a reliable cup orientation guide?

BACKGROUND AND PURPOSE

It is controversial whether the transverse acetabular ligament (TAL) is a reliable guide for determining the cup orientation during total hip arthroplasty (THA). We investigated the variations in TAL anatomy and the TAL-guided cup orientation.

METHODS

80 hips with osteoarthritis secondary to hip dysplasia (OA) and 80 hips with osteonecrosis of the femoral head (ON) were examined. We compared the anatomical anteversion of TAL and the TAL-guided cup orientation in relation to both disease and gender using 3D reconstruction of computed tomography (CT) images.

RESULTS

Mean TAL anteversion was 11° (SD 10, range -12 to 35). The OA group (least-square mean 16°, 95% confidence interval (CI): 14-18) had larger anteversion than the ON group (least-square mean 6.2°, CI: 3.8 - 7.5). Females (least-square mean 20°, CI: 17-23) had larger anteversion than males (least-square mean 7.0°, CI: 4.6-9.3) in the OA group, while there were no differences between the sexes in the ON group. When TAL was used for anteversion guidance with the radiographic cup inclination fixed at 40°, 39% of OA hips and 9% of ON hips had more than 10° variance from the target anteversion, which was 15°.

INTERPRETATION

In ON hips, TAL is a good guide for determining cup orientation during THA, although it is not a reliable guide in hips with OA secondary to dysplasia. This is because TAL orientation has large individual variation and is influenced by disease and gender.

Anatomical hip range of motion after implantation during total hip arthroplasty with a large change in pelvic inclination

The supine functional pelvic plane is the recommended reference pelvic plane for acetabular cup planning in navigation-assisted total hip arthroplasty. However, it is unclear whether it can be used in patients with a large preoperative positional change in pelvic inclination (PC) from the supine to the standing position because it is unknown whether these patients have a different hip range of motion (ROM). We measured the anatomical hip ROM after implantation by computed tomography-based navigation in 91 patients and found it to be similar between those with a small PC (<10°) and those with a large PC (≥10°). There was no significant correlation between ROM and preoperative PC. The supine functional pelvic plane is adequate for cup planning whether the PC is small or large.

Effect of BMP-12, TGF-β1 and autologous conditioned serum on growth factor expression in Achilles tendon healing

PURPOSE

Achilles tendon ruptures are devastating and recover slowly and incompletely. There is a great demand for biomolecular therapies to improve recovery, yet little is understood about growth factors in a healing tendon. Here, the role of growth factors during tendon healing in a rat model and their reaction to single and multiple growth factor treatment are explored.

METHODS

Rat tendons were transected surgically and resutured. The expression of bFGF, BMP-12, VEGF and TGF-β1 was assessed by immunohistochemical analysis one to 8 weeks after surgery. Paracrine effects of TGF-β1 or BMP-12 added by adenoviral transfer, as well as the effect of autologous conditioned serum (ACS) on growth factor expression, were evaluated.

RESULTS

bFGF, BMP-12 and VEGF expression was highest 1 week after transection. bFGF and BMP-12 declined during the remaining period whereas VEGF expression persisted. TGF-β1 expression dramatically increased after 8 weeks. ACS treatment increased bFGF (P = 0.007) and BMP-12 (P = 0.004) expression significantly after 8 weeks. Also overall expression of bFGF, BMP-12 and TGF-β1 regardless of time point was significantly greater than controls with ACS treatment (P < 0.05). Both BMP-12 and TGF-β1 treatments had no significant effect. No effect was observed in VEGF with any treatment.

CONCLUSION

bFGF, BMP-12, VEGF and TGF-β1 are differentially expressed during tendon healing. Additional BMP-12 or TGF-β1 has no significant influence, whereas ACS generally increases expression of all factors except VEGF. Staged application of multiple growth factors may be the most promising biomolecular treatment.

Development and evaluation of an image-free computer-assisted impingement detection technique for total hip arthroplasty

Periprosthetic or bony impingement in total hip arthroplasty (THA) has been correlated to dislocation, increased wear, reduced postoperative functionality with pain and/or decreased range of motion (ROM). We sought to study the accuracy and assess the reliability of measuring bony and periprosthetic impingement on a virtual bone model prior to the implantation of the acetabular cup with the help of image-free navigation technology in an experimental cadaver study. Impingement-free ROM measurements were recorded during minimally invasive, computer-assisted THA on 14 hips of 7 cadaveric donors. Preoperatively and postoperatively the donors were scanned using computed tomography (CT). Impingement-free ROM on three-dimensional CT-based models was then compared with corresponding, intraoperative navigation models. Bony/periprosthetic impingement can be detected with a mean accuracy limit of below 5° for motion angles, which should be reached after THA for activities of daily living with the help of image-free navigation technology.

New method for measuring acetabular component positioning with EOS imaging: feasibility study on dry bone

PURPOSE

Malposition of the acetabular cup is the most common cause of total hip arthroplasty (THA) dislocation. The position of a total hip implant is usually analysed on computed tomography (CT) scan. We aim to prove it is possible to measure, with good accuracy, the position of an acetabular cup using the low-dose irradiation (EOS) imaging.

MATERIAL AND METHODS

We implanted an acetabular cup in a pelvic dry bone and measured cup anteversion and inclination with scanography. We performed 14 series of EOS acquisitions with different inclination, rotation and pelvic tilt, which were analysed by five observers. Two observers repeated angle measurements. We then calculated measurement inter- and intrareproducibility and accuracy.

RESULTS

Using a confidence interval (CI) of 95 %, inter- and intra-observer reproducibility were ±1.6, and ±1.4°, respectively, for cup inclination; accuracy in comparison with CT was ±2.6°. Using a 95 % CI, inter- and intra-observer reproducibility for cup anteversion were ±2.5° and ±2.3°, respectively. Measurement accuracy compared with CT was ±3.9°.

CONCLUSION

EOS imaging system is superior to standard radiography in terms of measuring acetabular anteversion and inclination.

Two-incision minimally invasive vs standard total hip arthroplasty: comparison of component position and hospital costs

Forty-nine patients undergoing 2-incision total hip arthroplasty were matched by age, gender, body mass index, and comorbidity to patients undergoing a standard lateral Hardinge approach. Hospital costs and charges were compared along with length of stay, component position, and complication rates. Component position and complication rates were identical for the 2 groups. However, hospital costs and charges were significantly lower for the 2-incision group, as was length of stay.

Dynamic measurements of hip movement in deep bending activities after total hip arthroplasty using a 4-dimensional motion analysis system

Although deep hip bending activities are often required in Asian populations because of traditional lifestyles and religious practices, few have examined the required hip range of motion (ROM) in these activities after total hip arthroplasty (THA). We performed postoperative motion analysis to evaluate the differences in required ROMs between Japanese-style and Western-style deep hip bending activities, to investigate whether prosthetic impingement would occur during these activities and to clarify the necessity for precautions in these activities after THA. Japanese-style activities did not require larger hip ROMs than Western-style ones, and all required hip flexion angles were less than 120°. Prosthetic impingement was not observed, with a safety margin 10° or higher until impingement in any directions of flexion, adduction, or internal rotation for any activities. Thus, particular postoperative precautions for Japanese-style activities are not required.

[Handling modern imaging procedures in a high-tech operating room]

Operating rooms are the central unit in the hospital network in trauma centers. In this area, high costs but also high revenues are generated. Modern operating theater concepts as an integrated model have been offered by different companies since the early 2000s. Our hypothesis is that integrative concepts for operating rooms, in addition to improved operating room ergonomics, have the potential for measurable time and cost savings. In our clinic, an integrated operating room concept (I-Suite, Stryker, Duisburg) was implemented after analysis of the problems. In addition to the ceiling-mounted arrangement, the system includes an endoscopy unit, a navigation system, and a voice control system. In the first 6 months (9/2005 to 2/2006), 112 procedures were performed in the integrated operating room: 34 total knee arthroplasties, 12 endoscopic spine surgeries, and 66 inpatient arthroscopic procedures (28 shoulder and 38 knee reconstructions). The analysis showed a daily saving of 22-45 min, corresponding to 15-30% of the daily changeover times, calculated to account for potential savings in the internal cost allocation of 225-450 EUR. A commercial operating room concept was evaluated in a pilot phase in terms of hard data, including time and cost factors. Besides the described effects further savings might be achieved through the effective use of voice control and the benefit of the sterile handle on the navigation camera, since waiting times for an additional nurse are minimized. The time of the procedure of intraoperative imaging is also reduced due to the ceiling-mounted concept, as the C-arm can be moved freely in the operating theater without hindering cables. By these measures and ensuing improved efficiency, the initial high costs for the implementation of the system may be cushioned over time.

Multi-color palette of fluorescent proteins for imaging the tumor microenvironment of orthotopic tumorgraft mouse models of clinical pancreatic cancer specimens

Pancreatic-cancer-patient tumor specimens were initially established subcutaneously in NOD/SCID mice immediately after surgery. The patient tumors were then harvested from NOD/SCID mice and passaged orthotopically in transgenic nude mice ubiquitously expressing red fluorescent protein (RFP). The primary patient tumors acquired RFP-expressing stroma. The RFP-expressing stroma included cancer-associated fibroblasts (CAFs) and tumor-associated macrophages (TAMs). Further passage to transgenic nude mice ubiquitously expressing green fluorescent protein (GFP) resulted in tumors that acquired GFP stroma in addition to their RFP stroma, including CAFs and TAMs as well as blood vessels. The RFP stroma persisted in the tumors growing in the GFP mice. Further passage to transgenic nude mice ubiquitously expressing cyan fluorescent protein (CFP) resulted in tumors acquiring CFP stroma in addition to persisting RFP and GFP stroma, including RFP- and GFP-expressing CAFs, TAMs and blood vessels. This model can be used to image progression of patient pancreatic tumors and to visually target stroma as well as cancer cells and to individualize patient therapy.

Genomic characterization of explant tumorgraft models derived from fresh patient tumor tissue

Background

There is resurgence within drug and biomarker development communities for the use of primary tumorgraft models as improved predictors of patient tumor response to novel therapeutic strategies. Despite perceived advantages over cell line derived xenograft models, there is limited data comparing the genotype and phenotype of tumorgrafts to the donor patient tumor, limiting the determination of molecular relevance of the tumorgraft model. This report directly compares the genomic characteristics of patient tumors and the derived tumorgraft models, including gene expression, and oncogenic mutation status.

Methods

Fresh tumor tissues from 182 cancer patients were implanted subcutaneously into immune-compromised mice for the development of primary patient tumorgraft models. Histological assessment was performed on both patient tumors and the resulting tumorgraft models. Somatic mutations in key oncogenes and gene expression levels of resulting tumorgrafts were compared to the matched patient tumors using the OncoCarta (Sequenom, San Diego, CA) and human gene microarray (Affymetrix, Santa Clara, CA) platforms respectively. The genomic stability of the established tumorgrafts was assessed across serial in vivo generations in a representative subset of models. The genomes of patient tumors that formed tumorgrafts were compared to those that did not to identify the possible molecular basis to successful engraftment or rejection.

Results

Fresh tumor tissues from 182 cancer patients were implanted into immune-compromised mice with forty-nine tumorgraft models that have been successfully established, exhibiting strong histological and genomic fidelity to the originating patient tumors. Comparison of the transcriptomes and oncogenic mutations between the tumorgrafts and the matched patient tumors were found to be stable across four tumorgraft generations. Not only did the various tumors retain the differentiation pattern, but supporting stromal elements were preserved. Those genes down-regulated specifically in tumorgrafts were enriched in biological pathways involved in host immune response, consistent with the immune deficiency status of the host. Patient tumors that successfully formed tumorgrafts were enriched for cell signaling, cell cycle, and cytoskeleton pathways and exhibited evidence of reduced immunogenicity.

Conclusions

The preservation of the patient’s tumor genomic profile and tumor microenvironment supports the view that primary patient tumorgrafts provide a relevant model to support the translation of new therapeutic strategies and personalized medicine approaches in oncology.

Validation of the femoral anteversion measurement method used in imageless navigation

Total hip arthroplasty restores lost mobility to patients suffering from osteoarthritis and acute trauma. In recent years, navigated surgery has been used to control prosthetic component placement. Furthermore, there has been increasing research on what constitutes correct placement. This has resulted in the definition of a safe-zone for acetabular cup orientation. However, there is less definition with regard to femoral anteversion and how it should be measured. This study assesses the validity of the femoral anteversion measurement method used in imageless navigation, with particular attention to how the neutral rotation of the femur is defined. CT and gait analysis methodologies are used to validate the reference which defines this neutral rotation, i.e., the ankle epicondyle piriformis (AEP) plane. The findings of this study indicate that the posterior condylar axis is a reliable reference for defining the neutral rotation of the femur. In imageless navigation, when these landmarks are not accessible, the AEP plane provides a useful surrogate to the condylar axis, providing a reliable baseline for femoral anteversion measurement.

Anteversion of the acetabular component aligned with the transverse acetabular ligament in total hip arthroplasty

In total hip arthroplasty (THA), accurately positioning the cup is crucial for achieving an adequate postoperative range of motion and stability. For 47 THA cases in which the inferomedial rim of the cup had been positioned parallel to the transverse acetabular ligament, we retrospectively performed the measurements of the radiographic cup anteversion angle relative to the anterior pelvic plane using 3-dimensional reconstruction computed tomography. The mean anteversion angle was 21.2°, with no significant difference detected in mean cup anteversion between the dysplastic hip group (15 hips) and the control group (15 hips). We suggest that the transverse acetabular ligament is a practical anatomical landmark for determining cup anteversion in THA for both dysplastic and nondysplastic hip cases.

A new method of measuring acetabular cup anteversion on simulated radiographs

PURPOSE

Optimal positioning of acetabular components is crucial for maintaining stability of THA. Postoperative assessment of acetabular anteversion is a vital but difficult task. Various methods have been devised with good results for measuring anteversion on plain radiographs but these methods are either too complicated or require special objects like scientific calculators, special protectors, tables, etc. A new simplified method of measuring anteversion on plain radiographs was created based on basic geometry.

METHODS

Anteversion of acetabular components was estimated on computer generated images of the acetabular cup by our method and compared with two previously established methods of Liaw and Pradhan. Measurement was done at 400 different positions of acetabular cup and compared with actual values. Another analysis was done after adding the femoral head to the acetabular component, thus obscuring some of the acetabular rim.

RESULTS

Mean and standard deviation of error for our method was 0.77° ± 0.75° as compared to 0.93° ± 0.86° and 0.72° ± 0.68° for the methods of Liaw and Pardhan, respectively, with no significant differences from actual values. Maximal errors for our method, Liaw's and Pradhan's method were 3°, 4°, and 2.91°, respectively. On analysis, after the adding femoral head, there was a significant error of measurement with Liaw's method, while our method as well as Pardhan's remained accurate. All methods showed high inter- and intraobserver reliability.

CONCLUSION

Our new simplified method of measuring acetabular anteversion on plain radiographs is acceptable in comparision to other established methods and requires only routinely used goniometer and calliper.

Theoretical relationships between component design, patient bone geometry and range-of-motion post hip resurfacing

Clinical studies indicate that range of motion until prosthetic impingement is important in understanding unexplained failures of hip resurfacings, yet the underlying biomechanical principles have received little attention. This study investigates the mathematical relationships between component design, position, patient bone geometry and range of motion in hip resurfaced prostheses. Variations in range of motion and impingement-free safe-zones for cup position were calculated using an established method of vector analysis that facilitated parametric analysis in a time efficient manner. The alpha angle, defined as the angle between the centreline of the femoral neck and the waist of the femoral head/neck junction, was used to represent the natural femoral neck. Range of motion and impingement-free safe-zones were inversely proportional to the alpha angle and cup inclusion angle. The size of the safe-zone was most sensitive to the alpha angle with a 6 degrees reduction, decreasing the range of cup positions without impingement by 80-100%. Lowering the upper limit of cup inclination from 55 degrees to 45 degrees reduced the range of cup positions that allow impingement-free motion by 47-94%. No common safe-zone was observed for the range of component sizes and positions investigated. This offers an explanation to why clinic studies have failed to associate outcome with standardised positioning criteria.

The association between Femoral Tilt and impingement-free range-of-motion in total hip arthroplasty

Background

There is a complex interaction among acetabular component position and antetorsion of the femoral stem in determining the maximum, impingement-free prosthetic range-of-motion (ROM) in total hip arthroplasty (THA). By insertion into the femoral canal, stems of any geometry follow the natural anterior bow of the proximal femur, creating a sagittal Femoral Tilt (FT). We sought to study the incidence of FT as measured on postoperative computed tomography scans and its influence on impingement-free ROM in THA.

Methods

The incidence of the postoperative FT was evaluated on 40 computed tomography scans after cementless THA. With the help of a three-dimensional computer model of the hip, we then systematically analyzed the effects of FT on femoral antetorsion and its influence on calculations for a ROM maximized and impingement-free compliant stem/cup orientation.

Results

The mean postoperative FT on CT scans was 5.7° ± 1.8°. In all tests, FT significantly influenced the antetorsion values. Re-calculating the compliant component positions according to the concept of combined anteversion with and without the influence of FT revealed that the zone of compliance could differ by more than 200%. For a 7° change in FT, the impingement-free cup position differed by 4° for inclination when the same antetorsion was used.

Conclusions

A range-of-motion optimized cup position in THA cannot be calculated based on antetorsion values alone. The FT has a significant impact on recommended cup positions within the concept of “femur first” or “combined anteversion”. Ignoring FT may pose an increased risk of impingement as well as dislocation.

Understanding acetabular cup orientation: the importance of convention and defining the safe zone

Understanding acetabular cup orientation is important in all aspects of total hip arthroplasty including preoperative planning, intraoperative positioning, and postoperative analysis. New concepts in ideal cup orientation such as 'combined anteversion' have emerged. Using computer navigation and three-dimensional imaging, the potential for accuracy and precision of implantation have improved. Nevertheless, the varying manner in which the terms "anteversion" and "abduction" are often used in the literature is indicative of a nebulous understanding of the complex spatial anatomy of acetabular cup orientation.

[Principles and new concepts in computer-navigated total hip arthroplasty]

Combined component placement of cup and stem is closely correlated to stability, functionality and wear in total hip replacement (THA). Computer-navigated orthopedic surgery offers a reliable control method for a complex three-dimensional situation. Imageless navigation systems without the need of preoperative or intraoperative image acquisition and exposure to radiation have been proven to increase the accuracy of positioning the acetabular component and measure intraoperative leg length and offset changes precisely. A new development in this field is the noninvasive external femoral reference marker array system in conjunction with an imageless measurement technique. The future generation of imageless navigation systems will switch from simple measurement tasks to an integral part of the surgical process in navigated THA. The aim will be to find an optimized complementary component orientation with improved postoperative functionality and optimized range of motion without impingement.

Ultrasound-based computer navigation of the acetabular component: a feasibility study

INTRODUCTION

This feasibility study investigated the accuracy of anterior pelvic reference plane (APP) registration and acetabular cup orientation in two cadavers with different BMIs.

METHOD

Five observers each registered the APP five times in the 2 cadavers (BMIs: 32 kg/m(2) and 25 kg/m(2)) using an ultrasound-based navigation system. By comparison against the CT-derived reference landmarks, the errors in determining the individual landmarks defining the APP, as well as the resulting errors in the orientation of the APP and the acetabular cup orientation were determined.

RESULTS

Across all measurements obtained with the ultrasound navigation system, the errors in rotation and version in determining the APP were 0.5° ± 1.0° and -0.4° ± 2.0°, respectively. The cup abduction and anteversion errors determined from all measurements of the five investigators for both cadavers together were -0.1° ± 1.0° and -0.4° ± 2.7°, respectively. The data further demonstrated a high reproducibility of the measurements for the resulting cup adduction and anteversion angle.

CONCLUSION

Our preliminary results confirm that ultrasound navigation is a highly accurate tool that allows a reproducible registration of the APP and thereby enables accurate and precise intraoperative determination of the acetabular cup orientation also in patients with increased BMI.

A prospective randomised controlled trial comparing three alternative bearing surfaces in primary total hip replacement

The ideal bearing surface for young patients undergoing total hip replacement (THR) remains controversial. We report the five-year results of a randomised controlled trial comparing the clinical and radiological outcomes of 102 THRs in 91 patients who were < 65 years of age. These patients were randomised to receive a cobalt-chrome on ultra-high-molecular-weight polyethylene, cobalt-chrome on highly cross-linked polyethylene, or a ceramic-on-ceramic bearing. In all, 97 hip replacements in 87 patients were available for review at five years. Two hips had been revised, one for infection and one for peri-prosthetic fracture. At the final follow-up there were no significant differences between the groups for the mean Western Ontario and McMaster Universities osteoarthritis index (pain, p = 0.543; function, p = 0.10; stiffness, p = 0.99), Short Form-12 (physical component, p = 0.878; mental component, p = 0.818) or Harris hip scores (p = 0.22). Radiological outcomes revealed no significant wear in the ceramic group. Comparison of standard and highly cross-linked polyethylene, however, revealed an almost threefold difference in the mean annual linear wear rates (0.151 mm/year versus 0.059 mm/year, respectively) (p < 0.001).

Reliability and validity of measuring version of the acetabular component

A variety of radiological methods of measuring version of the acetabular component after total hip replacement (THR) have been described. The aim of this study was to evaluate the reliability and validity of six methods (those of Lewinnek; Widmer; Hassan et al; Ackland, Bourne and Uhthoff; Liaw et al; and Woo and Morrey) that are currently in use. In 36 consecutive patients who underwent THR, version of the acetabular component was measured by three independent examiners on plain radiographs using these six methods and compared with measurements using CT scans. The intra- and interobserver reliabilities of each measurement were estimated. All measurements on both radiographs and CT scans had excellent intra- and interobserver reliability and the results from each of the six methods correlated well with the CT measurements. However, measurements made using the methods of Widmer and of Ackland, Bourne and Uhthoff were significantly different from the CT measurements (both p < 0.001), whereas measurements made using the remaining four methods were similar to the CT measurements. With regard to reliability and convergent validity, we recommend the use of the methods described by Lewinnek, Hassan et al, Liaw et al and Woo and Morrey for measurement of version of the acetabular component.

Dislocation after total hip arthroplasty: a randomized clinical trial of a posterior approach and a modified lateral approach

We compared the dislocation rate of total hip arthroplasty between posterior approach and lateral approach in a prospective randomized trial. One hundred ninety-six hips were randomly chosen for a posterior approach with a posterior soft tissue repair (99 hips) or a lateral approach (97 hips). The average duration of follow-up was 37.9 months. Three hips (3%) dislocated in the lateral group, whereas none from the posterior group dislocated. At the final follow-up, the Harris hip score and limping were similar in the 2 groups. The joint stability obtained by the posterior soft tissue repair in the posterior approach group seemed to produce more favorable result when compared to the stability obtained from the lateral approach group.

Improvement of tendon repair using muscle grafts transduced with TGF-β1 cDNA

Tendon rupture is a common injury. Inadequate endogenous repair often leaves patients symptomatic, with tendons susceptible to re-rupture. Administration of certain growth factors improves tendon healing in animal models, but their delivery remains a challenge. Here we evaluated the delivery of TGF-β1 to tendon defects by the implantation of genetically modified muscle grafts. Rat muscle biopsies were transduced with recombinant adenovirus encoding TGF-β1 and grafted onto surgically transected Achilles tendons in recipient animals. Tissue regenerates were compared to those of controls by biomechanical testing as well as histochemical and immunohistochemical analyses. Healing was greatly accelerated when genetically modified grafts were implanted into tendon defects, with the resulting repair tissue gaining nearly normal histological appearance as early as 2 weeks postoperatively. This was associated with decreased deposition of type III collagen in favour of large fibre bundles indicative of type I collagen. These differences in tendon composition coincided with accelerated restoration of mechanical strength. Tendon thickness increased in gene-treated animals at weeks 1 and 2, but by week 8 became significantly lower than that of controls suggesting accelerated remodelling. Thus localised TGF-β1 delivery via adenovirus-modified muscle grafts improved tendon healing in this rat model and holds promise for clinical application.

Bony impingement limits design-related increases in hip range of motion

BACKGROUND

Factors affecting risk for impingement and dislocation can be related to the patient, implant design, or surgeon. While these have been studied independently, the impact of each factor relative to the others is not known.

QUESTIONS/PURPOSES

We determined the effect of three implant design factors, prosthetic placement, and patient anatomy on subject-specific ROM.

METHODS

We virtually implanted hip geometry obtained from 16 CT scans using computer models of hip components with differences in head size, neck diameter, and neck-shaft angle. A contact detection model computed ROM before prosthetic or bony impingement. We correlated anatomic measurements from pelvic radiographs with ROM.

RESULTS

When we implanted the components for best fit to the subject's anatomy or in the recommended orientation of 45° abduction and 20° anteversion, ROM was greater than 110° of flexion, 30° of extension, 45° of adduction-abduction, and 40° of external rotation. Changes in head size, neck diameter, and neck-shaft angle generated small gains (3.6°-6°) in ROM when analyzed individually, but collectively, we noted a more substantial increase (10°-17°). Radiographic measurements correlated only moderately with hip flexion and abduction.

CONCLUSIONS

It is feasible to tailor implant placement to each patient to maximize bony coverage without compromising ROM. Once bony impingement becomes the restricting factor, further changes in implant design may not improve ROM. Radiographic measurements do not appear to have value in predicting ROM.

HiL simulation in biomechanics: a new approach for testing total joint replacements

Instability of artificial joints is still one of the most prevalent reasons for revision surgery caused by various influencing factors. In order to investigate instability mechanisms such as dislocation under reproducible, physiologically realistic boundary conditions, a novel test approach is introduced by means of a hardware-in-the-loop (HiL) simulation involving a highly flexible mechatronic test system. In this work, the underlying concept and implementation of all required units is presented enabling comparable investigations of different total hip and knee replacements, respectively. The HiL joint simulator consists of two units: a physical setup composed of a six-axes industrial robot and a numerical multibody model running in real-time. Within the multibody model, the anatomical environment of the considered joint is represented such that the soft tissue response is accounted for during an instability event. Hence, the robot loads and moves the real implant components according to the information provided by the multibody model while transferring back the position and resisting moment recorded. Functionality of the simulator is proved by testing the underlying control principles, and verified by reproducing the dislocation process of a standard total hip replacement. HiL simulations provide a new biomechanical testing tool for analyzing different joint replacement systems with respect to their instability behavior under realistic movements and physiological load conditions.

Increased anteversion of press-fit femoral stems compared with anatomic femur

BACKGROUND

With contemporary canal-filling press-fit stems, there is no adjustability of stem position in the canal and therefore the canal anatomy determines stem version. Stem version will affect head/neck impingement, polyethylene wear from edge loading, and hip stability, but despite this, the postoperative version of a canal-filling press-fit stem is unclear.

QUESTIONS/PURPOSES

Is there a difference between the version of the nonoperated femur and the final version of a canal-filling press-fit femoral component? Could a difference create an alignment problem for the hip replacement?

METHODS

Sixty-four hips were studied with fluoroscopy and 46 nonarthritic and 41 arthritic hips were studied with MRI. A standardized fluoroscopic technique for determining preoperative and postoperative femoral version was developed with the patient supine on a fracture table undergoing supine total hip arthroplasty. To validate the methods, the results were compared with two selected series of axial MRI views of the hip comparing the version of the head with the version of the canal at the base of the neck.

RESULTS

For the operated hips, the mean anatomic hip version was less than the stem version: 18.9° versus 27.0°. The difference on average was 8.1° of increased anteversion (SD, 7.4°). Both MRI series showed the femoral neck was more anteverted on average than the femoral head, thereby explaining the operative findings.

CONCLUSION

With a canal-filling press-fit femoral component there is wide variation of postoperative component anteversion with most stems placed in increased anteversion compared with the anatomic head. The surgical technique may need to adjust for this if causing intraoperative impingement or instability.

Wear degradation of long-term in vivo exposed alumina-on-alumina hip joints: linking nanometer-scale phenomena to macroscopic joint design

The wear behavior of alumina femoral heads was examined at follow-up periods between 7.7 and 10.7 years. Four head retrievals of the same size (28 mm in diameter) were divided into two groups with different design characteristics. Systematically using scanning electron and atomic force microscopy procedures, wear characteristics could be classified on the entire heads according to five zones with increasing degrees of wear damage (Grade 1-5), in addition to one zone of stripe wear (Grade SW). The stripe wear zone showed quite different topographical features as compared to frictionally worn zones. Furthermore, hip implants designed with different clearances are shown to lead to different wear patterns on the femoral head surface, the smaller the clearance the wider the worn surface area. Cathodoluminescence piezo-spectroscopy provided information about the residual stress state in surfaces worn to different degrees and helped clarifying the wear mechanisms on the microscopic scale.

Clinical evaluation of hip joint rotation range of motion in adults

INTRODUCTION

Data on hip joint rotation range of motion (ROM) are rare; the methods of measurement vary and reproducibility has not been evaluated, in particular in relation to the subject's position (prone or supine, seated).

HYPOTHESIS

Hip joint rotation ROM is symmetrical, and ROM is not modified by the patient's position when data is obtained.

PATIENTS AND METHODS

This series included 120 adults between 20 and 60 years old (71 women, 49 men), who had no hip, spine or lower extremity disorders. External (ER) and internal (IR) rotation ROM was obtained using a photographic method by two observers. Measurements were obtained with the patient in three positions: the dorsal decubitus (supine) (P1), and ventral decubitus (prone) (P2) with the hip in extension and seated with the hip in flexion (P3).

RESULTS

Hip rotation ROM was P1: 68.1° (ER=38.5°; IR=29.6°); P2: 77.1°(ER=41.8°; IR=35.2°); P3: 78.5° (ER=78.5°; IR=37.9°) with no significant difference among the three positions. Interobserver reproducibility was satisfactory (concordance correlation coefficient (ccc) 0.7) and was comparable in the three positions with a ccc of 0.7072 (P1), 0.7426 (P2) and 0.7332 (P3), respectively. Hip rotation ROM balance was ER predominant in 47.5%, neutral in 39.5% and IR predominant in 13%. Hip rotation ROM balance was symmetric in both hips in 73 subjects (61%). Hip rotation ROM was reduced with age (P<0.0001), and was 4.7° less in men (P=0.0078), and in overweight subjects (P<0.0006).

DISCUSSION

Our values are probably lower than those in the literature because of the difference in study population. In our series, age, BMI and gender seemed to be determining factors. Hip rotation ROM balance is usually ER predominant or neutral. Hip rotation ROM can be measured in the three positions with no significant difference, with satisfactory interobserver reproducibility for each.

TYPE OF STUDY

Diagnostic prospective study: level III.