Quantitative Effect of Pelvic Position on Radiographic Assessment of Acetabular Component Position

BACKGROUND

Intraoperative fluoroscopy aims to improve component position in total hip arthroplasty. Measurement bias related to image quality, however, has not been quantified. We aim to quantify measurement bias in the interpretation of acetabular component position as a function of pelvis and fluoroscopic beam position in a simulated supine total hip arthroplasty model.

METHODS

Posterior-anterior pelvis and hip images were obtained using a previously described pelvic model with known acetabular component position. Pelvic position was varied in 5° increments of pelvis rotation (iliac-obturator) and tilt (inlet-outlet), and in 1 cm increments from beam center in cranial-caudal and medial-lateral planes. Multiple regression analyses were conducted to evaluate the relationship between the resulting bias in interpretation of component position relative to pelvis position.

RESULTS

Anteversion and abduction measurement bias increased exponentially with increasing deviation in rotation and tilt. Greater bias occurred for anteversion than for abduction. Hip centered images were less affected by pelvis malposition than pelvis centered images. Deviations of beam center within 5 cm in the coronal plane did not introduce measurement bias greater than 5°. An arbitrarily defined acceptable bias of ±5° for both abduction and anteversion was used to identify a range of optimum pelvic positioning each for hip and pelvis centered imaging.

CONCLUSION

Accurate measurement of acetabular component abduction and anteversion, especially anteversion, is sensitive to proper pelvic position relative to the chosen radiographic plane. An acceptable measurement bias of ±5° is achieved when the pelvis is oriented within a newly identified range of optimum pelvic positioning.

Chronological Changes in Axial Alignment of the Ipsilateral Hip and Knee After Total Hip Arthroplasty

BACKGROUND

Internal rotation of the hip and lateral patellar tilt increases after total hip arthroplasty (THA). However, it remains unknown whether these parameters change with time after the index THA.

METHODS

A total of 91 patients undergoing 2-stage bilateral primary THAs between January 2008 and May 2014 were included to assess the association of chronological changes in internal rotation of the hip or lateral patellar tilt with anthropometric and perioperative parameter and changes in alignment after the index THA. Chronological changes were assessed as changes between postoperative computed tomography on the index surgery and the preoperative computed tomography on the contralateral THA. Internal rotation of the hip was defined as the angle between the posterior intercondylar line and a line passing through the posterior inferior iliac spines. Lateral patellar tilt was defined as the angle between the posterior intercondylar line and a line joining the medial and lateral edges of the patella.

RESULTS

Internal rotation of the hip and lateral patellar tilt changed until 2 years after the index surgery by a mean of -2° (range -17.3° to 17.7°) and -2° (range -18.2° to 5.3°), respectively. Adductor tenotomy was associated with increasing internal rotation of the hip with time (adjusted R² 0.076); leg lengthening and larger preoperative femorotibial angle were associated with decreasing lateral patellar tilt with time (adjusted R² 0.159).

CONCLUSION

Both internal rotation of the hip at rest and lateral patellar tilt decreased by approximately 2° until 2 years after surgery and there was a large variation in chronological change.

Interobserver and Intraobserver Reliability of Three-Dimensional Preoperative Planning Software in Total Hip Arthroplasty

BACKGROUND

The purpose of this study is to clarify interobserver and intraobserver reliabilities of the three-dimensional (3D) templating of total hip arthroplasty (THA).

METHODS

We selected preoperative computed tomography from 60 hips in 46 patients (14 men and 32 women) who underwent primary THA. To evaluate interobserver and intraobserver reliability, 6 orthopedic surgeons performed 3D templating twice over a 4-week interval. We investigated intraclass correlation coefficients (ICCs) and percent agreement of component size and alignment, comparing morphological differences in the hip. Reproducibility was also compared between groups with osteoarthritis (OA) and those with osteonecrosis (ON).

RESULTS

The interobserver reliabilities for mean cup size and stem size were excellent, with ICC = 0.907 and 0.944, respectively. The value was significantly higher in the ON group than in the OA group. In the OA group, the reliability of cup size and alignment decreased in hips with severe subluxation. Percent agreement of stem size was significantly different between the shapes of femoral canal. For intraobserver reliability, the mean ICC of cup size was 0.965 overall, while the value in the ON group was significantly higher than in the OA group. The mean ICC of stem size was 0.972 overall.

CONCLUSION

Computed tomography-based 3D templating showed excellent reliability for component size and alignment in THA. Deformity of the affected joint influenced the reliability of preoperative planning.

The Safe Zone Range for Cup Anteversion Is Narrower Than for Inclination in THA

BACKGROUND

Cup malposition is a common cause of impingement, limitation of ROM, acceleration of bearing wear, liner fracture, and instability in THA. Previous studies of the safe zone based on plain radiographs have limitations inherent to measuring angles from two-dimensional projections. The current study uses CT to measure component position in stable and unstable hips to assess the presence of a safe zone for cup position in THA.

QUESTIONS/PURPOSES

(1) Does acetabular component orientation, when measured on CT, differ in stable components and those revised for recurrent instability? (2) Do CT data support historic safe zone definitions for component orientation in THA?

METHODS

We identified 34 hips that had undergone revision of the acetabulum for recurrent instability that also had a CT scan of the pelvis between August 2003 and February 2017. We also identified 175 patients with stable hip replacements who also had a CT study for preoperative planning and intraoperative navigation of the contralateral side. For each CT study, one observer analyzed major factors including acetabular orientation, femoral anteversion, combined anteversion (the sum of femoral and anatomic anteversion), pelvic tilt, total offset difference, head diameter, age, sex, and body mass index. These measures were then compared among stable hips, hips with cup revision for anterior instability, and hips with cup revision for posterior instability. We used a clinically relevant measurement of operative anteversion and inclination as opposed to the historic use of radiographic anteversion and inclination. The percentage of unstable hips in the historic Lewinnek safe zone was calculated, and a new safe zone was proposed based on an area with no unstable hips.

RESULTS

Anteriorly unstable hips compared with stable hips had higher operative anteversion of the cup (44° ± 12° versus 31° ± 11°, respectively; mean difference, 13°; 95% confidence interval [CI], 5°-21°; p = 0.003), tilt-adjusted operative anteversion of the cup (40° ± 6° versus 26° ± 10°, respectively; mean difference, 14°; 95% CI, 10°-18°; p < 0.001), and combined tilt-adjusted anteversion of the cup (64° ± 10° versus 54° ± 19°, respectively; mean difference, 10°; 95% CI, 1°-19°; p = 0.028). Posteriorly unstable hips compared with stable hips had lower operative anteversion of the cup (19° ± 15° versus 31° ± 11°, respectively; mean difference, -12°; 95% CI, -5° to -18°; p = 0.001), tilt-adjusted operative anteversion of the cup (19° ± 13° versus 26° ± 10°, respectively; mean difference, -8°; 95% CI, -14° to -2°; p = 0.014), pelvic tilt (0° ± 6° versus 4° ± 6°, respectively; mean difference, -4°; 95% CI, -7° to -1°; p = 0.007), and anatomic cup anteversion (25° ± 18° versus 34° ± 12°, respectively; mean difference, -9°; 95% CI, -1° to -17°; p = 0.033). Thirty-two percent of the unstable hips were located in the Lewinnek safe zone (11 of 34; 10 posterior dislocations, one anterior dislocation). In addition, a safe zone with no unstable hips was identified within 43° ± 12° of operative inclination and 31° ± 8° of tilt-adjusted operative anteversion.

CONCLUSIONS

The current study supports the notion of a safe zone for acetabular component orientation based on CT. However, the results demonstrate that the historic Lewinnek safe zone is not a reliable predictor of future stability. Analysis of tilt-adjusted operative anteversion and operative inclination demonstrates a new safe zone where no hips were revised for recurrent instability that is narrower for tilt-adjusted operative anteversion than for operative inclination. Tilt-adjusted operative anteversion is significantly different between stable and unstable hips, and surgeons should therefore prioritize assessment of preoperative pelvic tilt and accurate placement in operative anteversion. With improvements in patient-specific cup orientation goals and acetabular component placement, further refinement of a safe zone with CT data may reduce the incidence of cup malposition and its associated complications.

LEVEL OF EVIDENCE

Level III, diagnostic study.

Intraoperative Complications and Mid-Term Follow-Up of Large-Diameter Head Metal-on-Metal Total Hip Arthroplasty and Hip Resurfacing Arthroplasty

BACKGROUND AND AIMS

Large-diameter head total hip arthroplasty and hip resurfacing arthroplasty were popular in Finland from 2000 to 2012 for the treatment of hip osteoarthritis. The aim of this retrospective study was to investigate the mid-term survival of large-diameter head total hip arthroplasty patients operated on in three university hospitals and to compare these results to the survival of hip resurfacing arthroplasty patients.

MATERIAL AND METHODS

A total of 3860 hip arthroplasties (3029 large-diameter head total hip arthroplasties in 2734 patients and 831 hip resurfacing arthroplasties in 757 patients) were operated on between January 2004 and December 2009. The mean follow-up was 4.3 years (range: 0.3-8.0 years) in the total hip arthroplasty group and 5.1 years (range: 1.7-7.9 years) in the hip resurfacing arthroplasty group. Cox multiple regression model and Kaplan-Meier survival analysis were used to study the survival of the total hip arthroplasties and the hip resurfacing arthroplasties. Intraoperative complications and reasons for revisions were also evaluated.

RESULTS

In Cox regression analysis, the hazard ratio for revision of hip resurfacing arthroplasty was 1.5 compared with large-diameter head total hip arthroplasty (95% confidence interval: 1.0-2.2) ( p = 0.029). The cumulative Kaplan-Meier survival rate was 90.7% at 7.7 years for the large-diameter head total hip arthroplasty (95% confidence interval: 86.8-94.6) and 92.2% at 7.6 years for hip resurfacing arthroplasty (95% confidence interval: 89.9-94.6). There were a total of 166/3029 (5.5%) intraoperative complications in the large-diameter head total hip arthroplasty group and 20/831 (2.4%) in the hip resurfacing arthroplasty group ( p = 0.001). Revision for any reason was performed on 137/3029 (4.5%) of the arthroplasties in the large-diameter head total hip arthroplasty group and 52/831 (6.3%) in the hip resurfacing arthroplasty group ( p = 0.04).

CONCLUSION

The mid-term survival of both of these devices was poor, and revisions due to adverse reactions to metal debris will most likely rise at longer follow-up. There were more intraoperative complications in the large-diameter head total hip arthroplasty group than in the hip resurfacing arthroplasty group.

Intra-operative digital imaging: assuring the alignment of components when undertaking total hip arthroplasty

Aims

The aims of this study were to examine the rate at which the positioning of the acetabular component, leg length discrepancy and femoral offset are outside an acceptable range in total hip arthroplasties (THAs) which either do or do not involve the use of intra-operative digital imaging.

Patients and Methods

A retrospective case-control study was undertaken with 50 patients before and 50 patients after the integration of an intra-operative digital imaging system in THA. The demographics of the two groups were comparable for body mass index, age, laterality and the indication for surgery. The digital imaging group had more men than the group without. Surgical data and radiographic parameters, including the inclination and anteversion of the acetabular component, leg length discrepancy, and the difference in femoral offset compared with the contralateral hip were collected and compared, as well as the incidence of altering the position of a component based on the intra-operative image.

Results

Digital imaging took a mean of five minutes (2.3 to 14.6) to perform. Intra-operative changes with the use of digital imaging were made for 43 patients (86%), most commonly to adjust leg length and femoral offset. There was a decrease in the incidence of outliers when using intra-operative imaging compared with not using it in regard to leg length discrepancy (20% versus 52%, p = 0.001) and femoral offset inequality (18% versus 44%, p = 0.004). There was also a difference in the incidence of outliers in acetabular inclination (0% versus 7%, p = 0.023) and version (0% versus 4%, p = 0.114) compared with historical results of a high-volume surgeon at the same centre.

Conclusion

The use of intra-operative digital imaging in THA improves the accuracy of the positioning of the components at THA without adding a substantial amount of time to the operation.

Cite this article: Bone Joint J 2018;100B(1 Supple A):36–43.

Plan in 2-D, execute in 3-D: an augmented reality solution for cup placement in total hip arthroplasty

Reproducibly achieving proper implant alignment is a critical step in total hip arthroplasty procedures that has been shown to substantially affect patient outcome. In current practice, correct alignment of the acetabular cup is verified in C-arm x-ray images that are acquired in an anterior-posterior (AP) view. Favorable surgical outcome is, therefore, heavily dependent on the surgeon's experience in understanding the 3-D orientation of a hemispheric implant from 2-D AP projection images. This work proposes an easy to use intraoperative component planning system based on two C-arm x-ray images that are combined with 3-D augmented reality (AR) visualization that simplifies impactor and cup placement according to the planning by providing a real-time RGBD data overlay. We evaluate the feasibility of our system in a user study comprising four orthopedic surgeons at the Johns Hopkins Hospital and report errors in translation, anteversion, and abduction as low as 1.98 mm, 1.10 deg, and 0.53 deg, respectively. The promising performance of this AR solution shows that deploying this system could eliminate the need for excessive radiation, simplify the intervention, and enable reproducibly accurate placement of acetabular implants.

Midterm Results of Conversion from Failed Bipolar Hemiarthroplasty to Total Hip Arthroplasty

BACKGROUND

Conversion from failed bipolar hemiarthroplasty (HA) to total hip arthroplasty (THA) presents a great challenge to orthopedic surgeons for bipolar head removal and cup placement with or without change of femoral stem. Conversion THA after failed bipolar arthroplasty is known to offer both symptomatic and functional improvement. This study evaluates the midterm functional outcome and complications, especially dislocation associated with femoral head diameter, after conversion THA.

MATERIALS AND METHODS

Forty eight hips with the conversion of bipolar HA to THA were followed up for an average 6.2 years (range 2.0-11.5 years). Twenty one hips had conversion surgery to THA using metal-on-metal articulation (28 or 32 mm head). Nine hips used ceramic-on-ceramic (28-40 mm) and eighteen hips used large head metal-on-metal bearing (>40 mm). Outcome was evaluated using Harris Hip Score (HHS) and Western Ontario McMaster Universities Osteoarthritis Index (WOMAC) score. The radiographs were analyzed for evidence of osteolysis and/or loosening. The complications were evaluated, especially dislocation with different femoral head diameter.

RESULTS

Average HHS significantly improved from 42 preoperatively to 86 postoperatively and the average WOMAC score also significantly improved from 47 to 22 postoperatively. Radiological evaluation showed all the femoral components were stable. There was one acetabular component loosening, which required revision 9 years after conversion to THA. One dislocation and one recurrent dislocation were recorded in isolated acetabular revision hip; whereas one dislocation, one recurrent dislocation, and one trochanteric nonunion occurred in the hips with revision of both components. All dislocations occurred in hips with a femoral head size of 28 mm (P = 0.052). The cup and femoral head interval length was the most significant factor contributing to dislocation (P = 0.013).

CONCLUSIONS

Conversion THA after failed bipolar HA offers a reliable pain relief and functional improvement. To prevent dislocation, it is highly recommended to use a larger diameter femoral head, especially where the cup size is big.

Accuracy of Cup Positioning With the Computed Tomography-Based Two-dimensional to Three-Dimensional Matched Navigation System: A Prospective, Randomized Controlled Study

BACKGROUND

The accuracy of various navigation systems used for total hip arthroplasty has been described, but no publications reported the accuracy of cup orientation in computed tomography (CT)-based 2D-3D (two-dimensional to three-dimensional) matched navigation.

METHODS

In a prospective, randomized controlled study, 80 hips including 44 with developmental dysplasia of the hips were divided into a CT-based 2D-3D matched navigation group (2D-3D group) and a paired-point matched navigation group (PPM group). The accuracy of cup orientation (absolute difference between the intraoperative record and the postoperative measurement) was compared between groups. Additionally, multiple logistic regression analysis was performed to evaluate patient factors affecting the accuracy of cup orientation in each navigation.

RESULTS

The accuracy of cup inclination was 2.5° ± 2.2° in the 2D-3D group and 4.6° ± 3.3° in the PPM group (P = .0016). The accuracy of cup anteversion was 2.3° ± 1.7° in the 2D-3D group and 4.4° ± 3.3° in the PPM group (P = .0009). In the PPM group, the presence of roof osteophytes decreased the accuracy of cup inclination (odds ratio 8.27, P = .0140) and the absolute value of pelvic tilt had a negative influence on the accuracy of cup anteversion (odds ratio 1.27, P = .0222). In the 2D-3D group, patient factors had no effect on the accuracy of cup orientation.

CONCLUSION

The accuracy of cup positioning in CT-based 2D-3D matched navigation was better than in paired-point matched navigation, and was not affected by patient factors. It is a useful system for even severely deformed pelvises such as developmental dysplasia of the hips.

Influence of femoral bowing on range of motion after total hip arthroplasty

PURPOSE

The influence of physiologic femoral bowing on range of motion (ROM) after total hip arthroplasty (THA) remains unknown. The purpose of this study was to investigate the morphology of the femur in patients who underwent THA, and to analyze the influence of femoral bowing on ROM due to implant impingement after THA.

METHODS

The ROM was calculated from 100 hips in 90 patients who underwent THA using computed tomography data with a 3D dynamic analysis software. Lateral and anterior bowing angles of the femur were measured. A modular implant (Modulus system, Lima Corporate, Villanova di San Daniele del Friuli, Italy) was used for simulation. In all subjects, cup inclination, anteversion, and stem anteversion were set to 40°, 15°, and 30°, respectively. Multiple linear regression analyses were performed to assess the relationship between the morphology of the femur and ROM.

RESULTS

Lateral bowing of the femur was demonstrated to be significantly correlated with age (r = 0.361, p < 0.001) and female sex (r = 0.315, p = 0.001). Lateral bowing of the femur was significantly positively correlated with flexion and internal rotation (Int-R) with 90° flexion. Anterior bowing was significantly associated with decreasing flexion, decreasing Int-R with 90° flexion and increasing Int-R with 45° flexion and 15° adduction.

CONCLUSIONS

A ROM-optimized cup position cannot be calculated from femoral stem anteversion values alone; therefore, when surgeons position the cup in relation to the femoral stem anteversion, the influence of femoral bowing may also require consideration.

Highly Cross-Linked Polyethylene Reduces Osteolysis Incidence and Wear-Related Reoperation Rate in Cementless Total Hip Arthroplasty Compared With Conventional Polyethylene at a Mean 12-Year Follow-Up

BACKGROUND

A number of studies on total hip arthroplasty have compared highly cross-linked polyethylene (HXLPE) with conventional polyethylene (CPE) liners beyond 10 years. However, the impact of HXLPE on the wear-related reoperation rate is unclear. The purpose of this study was to evaluate the clinical advantage of using a single manufacturer's HXLPE in terms of reducing the reoperation rate.

METHODS

The study was a follow-up retrospective cohort study over a mean of 12 years that examined patients aged 45-70 years with cementless total hip arthroplasty using a 26-mm-diameter cobalt-chromium head. Sixty-seven patients (79 hips; HXLPE group = 41 hips, CPE group = 38 hips) were evaluated for a minimum 10-year follow-up. Kaplan-Meier survival analysis was performed, with wear-related reoperations and radiographic osteolysis serving as the end points. The polyethylene wear rate was also assessed.

RESULTS

The mean 12-year follow-up rates of survivorship that were evaluated using wear-related reoperations as the end point were 100% and 91.4% in the HXLPE and CPE groups, respectively (P = .007), and the mean 12-year follow-up rates of survivorship with osteolysis as the end point were 100% and 36.2%, respectively (P < .001). Compared with the CPE group, the HXLPE group presented a significantly reduced wear rate (HXLPE group, 0.035 mm/y; CPE group, 0.118 mm/y).

CONCLUSION

A unique strength of this study is that we assessed a single manufacturer's HXLPE while keeping most other implant parameters uniform. This study reveals the clinical advantage of using a single manufacturer's HXLPE in terms of a reduced wear-related reoperation rate at a mean 12-year follow-up.

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

INTRODUCTION

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Calcar Femorale in Patients with Osteoarthritis of the Hip Secondary to Developmental Dysplasia

Background

We investigated whether the calcar femorale, a cortical septum in the region of the lesser trochanter of the femur, correlates with results of femoral stem implantation in patients with osteoarthritis of the hip secondary to developmental dysplasia using computed tomography.

Methods

This retrospective study included 277 hips (41 males and 236 females; age, 37 to 92 years) of patients who had presented to Okayama Medical Center with hip pain. Of these, a total of 219 hips (31 males and 188 females) had previously undergone total hip arthroplasty. According to the Crowe classification, 147 hips were classified as Crowe grade I, 72 hips as Crowe grade II–IV, and 58 hips as normal.

Results

The calcar femorale was identified in 267 hips (96.4%). The calcar femorale was significantly shorter and more anteverted in Crowe grade II–IV hips than in Crowe grade I or normal hips. Significant differences in the shape of the calcar femorale were found according to the severity of hip deformity. Three stem designs were analyzed: single-wedge (59 hips), double-wedge metaphyseal filling (147 hips), and modular (13 hips). Single-wedge stems were inserted more parallel to the calcar femorale rather than femoral neck anteversion, while other types of stems scraped the calcar femorale.

Conclusions

The angle of the calcar femorale differs according to the severity of hip deformity, and the calcar femorale might thus serve as a more useful reference for stem insertion than femoral neck anteversion in total hip arthroplasty using a single-wedge stem.

Geometric analysis and clinical outcome of two cemented stems for primary total hip replacement with and without modular necks

INTRODUCTION

Restoration of the physiological biomechanical principles of the hip is crucial in total hip replacement. The aim of this study was to compare an arthroplasty system with different offset options (a: Exeter^®) with a dual-modular stem (b: Profemur Xm^®).

MATERIALS AND METHODS

A local and an inertial coordinate system were used to assist the description of the components' assembly in the prosthesis. A resection line of the femoral head in standard position was added to the arthroplasties and geometric parameters were measured. The outcomes of 93 patients were clinically evaluated (a: n = 50, b: n = 43). Preoperative planning was compared to postoperative radiographs (femoral offset, leg-length), and clinical scores (HHS, WOMAC, total range of motion) were assessed preoperatively, and then 1 and 2 years after surgery.

RESULTS

The Exeter^® offers an offset range from 32.1 to 56.9 mm and the Profemur Xm^® a range from 29.3 to 55.3 mm. The leg-length variability of the Profemur Xm^® has a range of 25.9 mm, the Exeter^® a range of 13.7 mm. The Profemur Xm^® offers more possible combinations of offset and leg-length reconstruction. The neck-stem angles of the Exeter^® range from 125.2° to 126.3°, of the Profemur Xm^® from 127.2° to 142.6°. There was no statistically significant difference in clinical outcome and radiological parameters.

CONCLUSIONS

We conclude that both stems offer a wide range of options for anatomical reconstruction of the hip resulting in similarly good clinical results. The Profemur Xm^® stem has advantages for the reconstruction of hips that deviate from standard anatomy but has the drawback of additional corrosive wear at the stem/neck interface.

Dynamical analysis of dislocation-associated factors in total hip replacements by hardware-in-the-loop simulation

Since dislocation of total hip replacements (THR) remains a clinical problem, its mechanisms are still in the focus of research. Previous studies ignored the impact of soft tissue structures and dynamic processes or relied on simplified joint contact mechanics, thus, hindered a thorough understanding. Therefore, the purpose of the present study was to use hardware-in-the-loop (HiL) simulation to analyze systematically the impact of varying implant positions and designs as well as gluteal and posterior muscle function on THR instability under physiological-like loading conditions during dynamic movements. A musculoskeletal multibody model emulated the in situ environment of the lower extremity during deep sit-to-stand with femoral adduction maneuver while a six-axis robot moved and loaded a THR accordingly to feed physical measurements back to the multibody model. Commercial THRs with hard-soft bearings were used in the simulation with three different head diameters (28, 36, 44 mm) and two offsets (M, XL). Cup inclination of 45°, cup anteversion of 20°, and stem anteversion of 10° revealed to be outstandingly robust against any instability-related parameter variation. For the flexion motion, higher combined anteversion angles of cup and stem seemed generally favorable. Total hip instability was either deferred or even avoided even in the presence of higher cup inclination. Larger head diameters (>36 mm) and femoral head offsets (8 mm) deferred occurrence of prosthetic and bone impingement associated with increasing resisting torques. In summary, implant positioning had a much higher impact on total hip stability than gluteal insufficiency and impaired muscle function. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:2557-2566, 2017.

[Biomechanical study of different suture methods in repairing tendon rupture]

Objective

To evaluate the biomechanical property of tendons repaired with the modified Kessler suture combined with " 8" suture, and to provide evidence for the clinical application of this suture methods in repairing acute Achilles tendon rupture.

Methods

Forty frozen flexor digitorum longus tendons from fresh pork hind leg were randomly assigned into 4 groups, 10 specimens each group. In group A, the tendons were dissected transversely at the midpoint to forming the model of tendon with transversely cutting injury. The tendons in groups B, C, and D were dissected transversely at the midpoint, then a 2 cm segment of tendon from the incision in each side was dissected longitudinally with 1 mm internal to forming " frayed tendon" model. All the tendons were sutured with2-0 non-absorbable suture material with different suturing methods: in group A, the tendons with transversely cutting injury model with Krackow suture, and in the groups B, C, and D with Krackow suture, Kessler suture, and the modified Kessler suture combined with " 8" suture separately. All repaired tendons were fixed onto the biomechanical testing machine. The length, width, and thickness of each side and midpoint of the tendons were recorded, and the cross-sectional area was calculated. The tendons were stretched at a speed of 15 mm/minutes until failure (suture avulsion or rupture). The computer automatically recorded the maximum load, stress, strain, the failure displacement, and the stiffness. These biomechanical parameters of tendons in different groups were analyzed and compared.

Results

There was no significant difference in the length and cross-sectional area of each tendon among 4 groups ( F=0.245, P=0.863; F=0.094, P=0.963). Two tendons in group B, 1 in group C, and 1 in group D were excluded because of tendon slipping; all tendons in group A and 8 tendons in group B failured due to suture rupture, 9 tendons in group C due to suture slipping, and 9 tendons in group D due to 3 sutures slipping from tendon tissue together. The maximum load, the maximum stress, the maximum strain, the failure displacement, and the stiffness of the tendons between groups A and B showed no significant difference ( P>0.05). The maximum load, the maximum stress, and the stiffness of the tendons in group D were larger than those in both groups B and C ( P<0.05), but no significant difference was found in the maximum strain and the failure displacement between groups B, C, and D ( P>0.05). The maximum load, the maximum stress, the failure displacement, and the stiffness of the tendons in group B were larger than those in group C ( P<0.05), but the difference of maximum strain between groups B and C was not significant ( P>0.05).

Conclusion

The modified Kessler suture combined with " 8" suture can provide better biomechanical property of the repaired tendon compared with other suture approaches.

What is the Impact of a Spinal Fusion on Acetabular Implant Orientation in Functional Standing and Sitting Positions?

BACKGROUND

This study used EOS imaging of primary total hip arthroplasty (THA) patients, with and without predating spinal fusion, to investigate (1) the impact of spinal fusion on acetabular implant anteversion and inclination, and (2) whether more extensive spinal fusion (fusion starting above the thoracolumbar junction or extension of fusion to the sacrum) affects acetabular implant orientation differently than lumbar only spinal fusion.

METHODS

Ninety-three patients had spinal fusion (case group), and 150 patients were without spinal fusion (controls). None of the patients experienced dislocation. The change in sacral slope (SS) and cup orientation from standing to sitting was measured.

RESULTS

Mean SS change from the standing to sitting positions was -7.9°in the fusion group vs -18.4°in controls (P = .0001). Mean change in cup inclination from the standing to sitting positions was 4.9°in the fusion group vs 10.2°in controls (P = .0001). Mean change in cup anteversion from standing to sitting positions was 7.1°in the fusion group vs 12.1°in controls (P = .0001). For each additional level of spinal fusion, the change in SS from standing to sitting positions decreased by 1.6(95% confidence interval [CI], 2.2073-1.0741), the change in cup inclination decreased by 0.8(95% CI, 0.380-1.203), and the change in cup anteversion decreased by 0.9(95% CI, 0.518-1.352; P < .001 in all cases).

CONCLUSION

Patients with spinal fusion demonstrated less adaptability of the lumbosacral junction. Longer spinal fusion or inclusion of the pelvis in the fusion critically impacts hip-spine biomechanics and significantly affects the ability to compensate in the standing-to-sitting transition.

Biomechanical model based evaluation of Total Hip Arthroplasty therapy outcome

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Novel cemented cup-holding technique while performing total hip arthroplasty with navigation system

Recently, navigation systems have been more widely utilized in total hip arthroplasty. However, almost all of these systems have been developed for cementless cups. In the case of cemented total hip arthroplasty using a navigation system, a special-ordered cemented holder is needed. We propose a novel cemented cup-holding technique for navigation systems using readily available articles. We combine a cementless cup holder with an inverted cementless trial cup. The resulting apparatus is used as a cemented cup holder. The upside-down cup-holding technique is useful and permits cemented cup users to utilize a navigation system for placement of the acetabular component.

Multi-modal imaging, model-based tracking, and mixed reality visualisation for orthopaedic surgery

Orthopaedic surgeons are still following the decades old workflow of using dozens of two-dimensional fluoroscopic images to drill through complex 3D structures, e.g. pelvis. This Letter presents a mixed reality support system, which incorporates multi-modal data fusion and model-based surgical tool tracking for creating a mixed reality environment supporting screw placement in orthopaedic surgery. A red–green–blue–depth camera is rigidly attached to a mobile C-arm and is calibrated to the cone-beam computed tomography (CBCT) imaging space via iterative closest point algorithm. This allows real-time automatic fusion of reconstructed surface and/or 3D point clouds and synthetic fluoroscopic images obtained through CBCT imaging. An adapted 3D model-based tracking algorithm with automatic tool segmentation allows for tracking of the surgical tools occluded by hand. This proposed interactive 3D mixed reality environment provides an intuitive understanding of the surgical site and supports surgeons in quickly localising the entry point and orienting the surgical tool during screw placement. The authors validate the augmentation by measuring target registration error and also evaluate the tracking accuracy in the presence of partial occlusion.

Radiographic cup anteversion measurement corrected from pelvic tilt

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

The Results of Total Hip Arthroplasty After Sugioka Transtrochanteric Anterior Rotational Osteotomy for Osteonecrosis

BACKGROUND

Since Sugioka transtrochanteric anterior rotational osteotomy (ARO) for osteonecrosis of the femoral head (ONFH) changes the morphology of the proximal femur, total hip arthroplasty (THA) after previous ARO is considered a technically demanding procedure. The purpose of this study was to compare the clinicoradiologic outcomes of THA after ARO with those of THA without any antecedent surgery for ONFH.

METHODS

Twenty-four hips in 20 patients who underwent cementless THA after ARO (postosteotomy group) were retrospectively reviewed and compared with patients who underwent cementless THA without any antecedent surgery for ONFH during the same period (primary group). In the postosteotomy group, the mean duration from ARO to THA was 19.7 years. All patients were followed for at least 5 years (mean, 8.3 years; follow-up rate, 78.5%). A clinical assessment was performed preoperatively and at the latest follow-up using the Harris Hip Score. A radiographic examination was performed at 3 months after THA and at the latest follow-up.

RESULTS

The Harris Hip Score at the latest follow-up in the postosteotomy group was equivalent to that in the primary group, but longer operation time and greater intraoperative blood loss were observed in the postosteotomy group. There were no significant differences in postoperative complications, including dislocation (2 hips in each group). The leg lengthening in the postosteotomy group tended to be longer. No hips showed implant malpositioning, loosening, or required any revision surgery.

CONCLUSION

The clinicoradiologic outcomes of THA after ARO are considered to be comparable with those of THA without any antecedent surgery for ONFH.

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

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

Surgical Approach May Influence Survival of Large-Diameter Head Metal-on-Metal Total Hip Arthroplasty: A 6- to 10-Year Follow-Up Study

Large-diameter head (LDH) metal-on-metal (MoM) total hip arthroplasty (THA) has lost popularity because of metal allergy or ALTRs (adverse local tissue reactions) in the past decade. Whether the surgical approach may influence the survival of LDH-MoM-THA has not been reported. From 2006 to 2009, we performed 96 LDH-MoM-THAs on 80 patients using an in situ head-neck assembly technique through a modified Watson-Jones approach. With a mean follow-up of 8.4 years (range, 6.3–10.1 years), the implant survival rate was 100%. All patients were satisfied with the results and the Harris Hip Score improved from 52 points to 98 points. No ALTRs were found, but 17.7% of the 96 hips (17 adverse events) experienced adverse events related to the cup, including 5 cases of outlier cup malposition, 11 cases of inadequate cup seating, and 1 acetabular fracture. The tissue tension that was improved by a muscle-sparing approach might lessen the chance of microseparation or edge-loading that is taken as the major risk for early implant failure. Further investigation of whether these LDH-MoM-THAs would fail or not would require a longer follow-up or even retrieval analysis in the future.

The mechanical effects of cup inclination and anteversion angle on the bearing surface

BACKGROUND

Regarding the cup setting in total hip arthroplasty, range of motion and prevention of dislocation are important. From past reports, the wear of the bearing surface may affect long-term results. This study evaluated the stress applied to the bearing surface by the combined use of the three-dimensional rigid spring model and the finite-element analysis.

METHODS

For contact pressure distribution of the bearing surface, interference analysis was performed using a three-dimensional rigid body spring model. Furthermore, stress was applied to the inner surface of the cup installed in the bone so that the same stress distribution obtained from the interference analysis was achieved. The finite-element analysis was then performed at each condition, which changed the inclination and anteversion angles of the cup to examine the relationship of maximum equivalent stress.

RESULTS AND DISCUSSION

The maximum equivalent stresses on the bearing surface under the condition with fixation of an anteversion angle of 0° were 0.78, 0.85, and 1.15 MPa at inclination angles of 25°, 40°, and 55°, respectively. The stress value at 55° was approximately 1.5 times greater than that at 25°. The maximum equivalent stresses on the bearing surface under the condition with fixation of an inclination angle of 40° were 0.85, 0.9, and 1.02 MPa at anteversion angles of 0°, 15°, and 30°, respectively. The stress value at 30° was approximately 1.2 times greater than that at 0°. This study suggests that large inclination and anteversion angles may enhance the stress on the bearing surface and affect long-term results.

Femur First navigation can reduce impingement severity compared to traditional free hand total hip arthroplasty

Impingement is a major source of dislocation and aseptic loosening in total hip arthroplasty (THA). We compared impingement free range of motion (ROM) using a novel computer navigated femur first approach to conventional THA. In addition, impingement between genders was also explored. In a retrospective analysis of 121 THA patients, subject-specific post-operative ROM was simulated using post-operative 3D-CT data, and compared with the benchmark ROM, essential for activities of daily living. Three parameters were defined to express both implant-to-implant (ITI) and bone-to-bone (BTB) impingement - coverage percentage, third angle, and impingement severity. Although coverage percentage was similar between the navigated and conventional group for both ITI (p = 0.69) and BTB (p = 0.82) impingement, third angle was significantly reduced in the navigation group for both ITI (p = 0.02) and BTB (p = 0.05) impingement. Impingement severity for both ITI (p = 0.01) and BTB (p = 0.05) was significantly decreased in the navigation group compared to the conventional. Impingement severity in men was considerably higher compared to women for both ITI (p = 0.002) and BTB (p = 0.02). Navigation guided femur first THA is able to improve alignment of ROM axis, and consequently, to reduce impingement in THA. Men seem to be more prone to impingement than women.

Segmental acetabular rim defects, bone loss, oversizing, and press fit cup in total hip arthroplasty evaluated with a probabilistic finite element analysis

PURPOSE

Management of segmental rim defects and bone mineral density (BMD) loss in the elderly prior to total hip replacement is unclear within classification systems for acetabular bone loss. In this study, our objectives were (1) to understand how a reduction in BMD in the elderly affects the oversizing of a press-fit cup for primary fixation and (2) to evaluate whether the location of the segmental defect affected cup fixation.

METHODS

A finite element (FE) model was used to simulate and evaluate cup insertion and fixation in the context of segmental rim defects. We focused on the distribution of patients over age 70 and used BMD (estimated from CT) as a proxy for aging's implications on THR and used probabilistic FE analysis to understand how BMD loss affects oversizing of a press-fit cup.

RESULTS

A cup oversized by 1.10 ± 0.28 mm provides sufficient fixation and lower stresses at the cup-bone interface for elderly patients. Defects in the anterior column and posterior column both required the same mean insertion force for cup seating of 84% (taken as an average of 2 anterior column and 2 posterior column defects) compared to the control configuration, which was 5% greater than the insertion force for a superior rim defect and 12% greater than the insertion force for an inferior rim defect.

CONCLUSIONS

A defect along the superior or inferior rim had a minimal effect on cup fixation, while a defect in the columns created cup instability and increased stress at the defect location.

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

Background

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

Methods

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

Results

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

Conclusions

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

The validity and reproducibility of cross table radiographs compared with CT scans for the measurement of anteversion of the acetabular component after total hip arthroplasty

Aims

The aim of this study was to assess the reproducibility and validity of cross table radiographs for measuring the anteversion of the acetabular component after total hip arthroplasty (THA) and to compare it with measurements using CT scans.

Patients and Methods

A total of 29 patients who underwent THA between June 2010 and January 2016 were included. There were 17 men and 12 women. Their mean age was 43 years (26 to 65). Seven patients underwent a bilateral procedure. Thus, 36 THAs were included in the study. Lateral radiographs and CT scans were obtained post-operatively and radiographs repeated three weeks later. The anteversion of the acetabular component was measured using the method described by Woo and Morrey and the ischiolateral method described by Pulos et al and these were compared with the results obtained from CT scans.

Results

The mean anteversion was 18.35° (3° to 38°) using Woo and Morrey’s method, 51.45° (30° to 85°) using the ischiolateral method and 21.22° (2° to 48°) using CT scans. The Pearson correlation coefficient was 0.754 for Woo and Morrey’s method and 0.925 for the ischiolateral method. There was a linear correlation between the measurements using the ischiolateral method and those using CT scans. We derived a simple linear equation between the value of the CT scan and that of ischiolateral method to deduce the CT scan value from that of ischiolateral method and vice versa.

Conclusion

The anteversion of the acetabular component measured using both plain radiographic methods was consistently valid with good interobserver reproducibility, but the ischiolateral method which is independent of pelvic tilt was more accurate. As CT is costly, associated with a high dose of radiation and not readily available, the ischiolateral method can be used for assessing the anteversion of the acetabular component. Cite this article: Bone Joint J 2017;99-B:1006–11.

Biomechanical research on contour cage with transacetabular screws fixation in revision total hip arthroplasty

BACKGROUND

Use biomechanical technique to access the strain distribution and stability of Contour anti-protrusion cage with or without the whole circumference acetabular cup fixation by the transacetabular screws.

METHODS

Pelvic specimens from 10 male cadavers were used for the biomechanical test. The models of type C bone defect were copied according to the AAOS classification. Group 1: the contour reconstruction ring was fixed only by flange screws; Group 2: the contour reconstruction ring was fixed both by flange screws and transacetabular screws in dome. Under load in Heel Strike, Midstance, and Toe off phase, the transverse and longitudinal strains were measured in both the superior measure site near the root of the iliac wing and the inferior measure site near the root of the ischium. The relative displacement between the anterior inferior spine and the root of ischium below acetabular component was also measured.

FINDINGS

Compared with Group 1, the transverse and longitudinal pressure strain of Group 2 on the superior measure site decreased, and measure sites also showed reductions on the inferior under load under three different gait phases. The result of mean relative displacement showed transacetabular screws fixation couldn't provide significant improvement of displacement prevention.

INTERPRETATION

Biomechanical test showed that under the premise of a satisfied bone allograft and well-fixed flange screws in iliac and ischium, the satisfactory initial stability of the reconstruction cup can be achieved, but could not be improved by transacetabular screw technique. However, the max strain in root part of the flange will be reduced using transacetabular screws in ilium, pubis and ischium together, and the strain distribution will also be improved.

What are the six degree-of-freedom errors of a robotically-machined femoral cavity in total hip arthroplasty and are they clinically important? An in-vitro study

Errors during a robot-assisted THA may result in a femoral cavity with position and orientation different than planned. This can lead to a femoral component placement that inaccurately sets a patient's femoral anteversion (FA), femoral offset (FO), and vertical offset (VO). The objectives of this study were to determine the position and orientation errors of robotically-machined femoral cavities in six degrees of freedom and to determine how position and orientation errors translate into errors in the setting of FA, FO, and VO. After creating preoperative plans, robot-assisted THAs were performed on twelve cadaveric specimens. The position and orientation of the machined cavities were compared to those of the planned cavities to determine the errors in six degrees of freedom. Placement of femoral components into the machined cavities was simulated, and the differences in FA, FO, and VO between the simulated and planned component placement were computed. While bias (i.e. mean error) occurred for three of six degrees of freedom in femoral cavities machined by a robotic system, the root mean squared errors (RMSEs) when the placement of femoral component was simulated were limited to 1.9° for FA, 1.0mm for FO, and 2.1mm for VO and were clinically unimportant.

WITHDRAWN: Correcting pelvic obliquity in the lateral position to improve acetabular component orientation during total hip arthroplasty

BACKGROUND

Ahead of Print article withdrawn by publisher. The acetabular component orientation during total hip arthroplasty (THA) impacts future hip function and early revision. Correcting pelvic obliquity may improve outcomes.

OBJECTIVE

To correct pelvic obliquity in the lateral position by applying a gradienter and plumb during THA using fluoroscopy.

METHODS

Fifty patients undergoing THA were randomized and divided into 2 groups. In controls, acetabular components were placed using traditional methods. In experimental patients, acetabular components were placed after correcting pelvic obliquity. We measured pelvic obliquity and recorded intra-operative and post-operative abduction angles, comparing abduction angle bias between post-operative measurements and intra-operation estimations.

RESULTS

Before correction, the average pelvic obliquity was -1.647∘± 4.512∘ in experimental patients. The average abduction angle in experimental patients was 42.685∘± 3.355∘ postoperatively, differing by 1.962∘± 1.515∘ from intra-operative estimates, while in control patients, it was 44.534∘± 4.844∘ postoperatively, differing by 4.244∘± 3.042∘ from intra-operative estimates. The bias of the abduction angle was much greater in control than in experimental patients (P< 0.05).

CONCLUSION

The pelvic obliquity in the lateral position affects surgeon judgment during THA. By correcting pelvic obliquity with a gradienter and plumb, the abduction angle bias can be reduced.

[Comparative study on differences in acetabular position during total hip arthroplasty between by direct anterior approach and by posterolateral approach]

Objective

To compare the differences in acetabular position during total hip arthroplasty (THA) between by direct anterior approach and by posterolateral approach.

Methods

Between December 2008 and December 2015, 102 patients undergoing THA were included in the study. THA was performed by anterior approach in 51 cases (anterior group) and by posterolateral approach in 51 cases (posterolateral group). There was no significant difference in gender, age, body mass index, side, and cause of illness between 2 groups ( P>0.05), with comparability. The acetabular abduction angle and anteversion angel were measured on the X-ray film at 1 day after operation to evaluate whether the acetabular prosthesis was displaced in the safe zone.

Results

The acetabular abduction angle was (42.28±5.77)° in the anterior group and was (43.93±7.44)° in the posterolateral group, showing no significant difference ( t=1.30, P=0.19). The acetabular anteversion angle was (21.14±5.17)° in the anterior group and was (21.05±4.10)° in the posterolateral group, showing no significant difference ( t=0.05, P=0.96). The ratio in the target safe zone of the acetabular abduction angle in the anterior group and the posterolateral group were 88.2% (45/51) and 84.3% (43/51) respectively, showing no significant difference ( χ²=0.33, P=0.56). The ratio in the target safe zone of the acetabular anteversion was 80.4% (41/51) in the anterior group and was 82.4% (42/51) in the posterolateral group, showing no significant difference between 2 groups ( χ²=0.06, P=0.79). The ratio in the target safe zone of both the abduction and anteversion angel was 70.6% (36/51) in the anterior group and was 68.6% (35/51) in the posterolateral group, showing no significant difference ( χ²=0.05, P=0.82).

Conclusion

There is no differences in the acetabulum position during THA between by direct anterior approach and posterolateral approach.

The History of Biomechanics in Total Hip Arthroplasty

Biomechanics of the hip joint describes how the complex combination of osseous, ligamentous, and muscular structures transfers the weight of the body from the axial skeleton into the appendicular skeleton of the lower limbs. Throughout history, several biomechanical studies based on theoretical mathematics, in vitro, in vivo as well as in silico models have been successfully performed. The insights gained from these studies have improved our understanding of the development of mechanical hip pathologies such as osteoarthritis, hip fractures, and developmental dysplasia of the hip. The main treatment of end-stage degeneration of the hip is total hip arthroplasty (THA). The increasing number of patients undergoing this surgical procedure, as well as their demand for more than just pain relief and leading an active lifestyle, has challenged surgeons and implant manufacturers to deliver higher function as well as longevity with the prosthesis. The science of biomechanics has played and will continue to play a crucial and integral role in achieving these goals. The aim of this article, therefore, is to present to the readers the key concepts in biomechanics of the hip and their application to THA.

Translatory hip kinematics measured with optoelectronic surgical navigation

PURPOSE

An optoelectronic surgical navigation system was used to detect small but measurable translational motion of human hip cadavers in high-range passive motions. Kinematic data were also examined to demonstrate the role of soft tissues in constraining hip translation.

METHODS

Twelve cadaver hips were scanned using CT, instrumented for navigation, and passively taken through motion assessment. Center of the femoral head was tracked in the acetabular coordinates. Maximum non-impinging translation of the femoral head for each specimen hip was reported. This was repeated for 5 tissue states: whole, exposed to the capsule, partially or fully incised capsule, resection of the ligamentum teres and labrectomy. Femoral motions were compared to the reported value for ideal ball and socket model.

RESULTS

Whole and exposed hips underwent maximal translations of [Formula: see text] and [Formula: see text] mm, respectively. These translational motions were statistically significantly different from reported value for a purely spherical joint, [Formula: see text]. Further tissue removal almost always significantly increased maximum non-impingement translational motion with [Formula: see text].

CONCLUSION

We found subtle but definite translations in every cadaver hip. There was no consistent pattern of translation. It is possible to use the surgical navigation systems for the assessment of human hip kinematics intra-operatively and improve the treatment of total hip arthroplasty patients by the knowledge of the fact that their hips translate. Better procedure selection and implantation optimization may arise from improved understanding of the motion of this critically important human joint.

Surgical accuracy, function, and quality of life of simultaneous versus staged bilateral Total hip Arthroplasty in patients with Osteonecrosis of the femoral head

BACKGROUND

The optimal surgical option for patients requiring bilateral hip replacement remains controversial. The purpose of this study was to compare surgical accuracy; functional outcome and health-related quality of life; and prosthetic-related complications and revision surgery of a simultaneous bilateral total hip arthroplasty (THA) with those of a staged bilateral THA with an interval between procedures <12 months.

METHODS

A total of 123 unselected consecutive patients (mean age, 43.3 years) who underwent bilateral THAs for osteonecrosis of the femoral head (ONFH) with a minimum follow-up of two years (mean, 60.2 months) were studied retrospectively; 63 simultaneous procedures served as a test group and 60 staged procedures served as a control group.

RESULTS

The mean postoperative leg-length discrepancy (LLD) and the percentage of patients who had an LLD >3 mm were significantly lower in the simultaneous group (P < 0.001 and P = 0.001, respectively). A higher number of cups within the safe zones, a higher correction rate, and a lower failure rate for the cup placement in the second-operated hip were also identified in the simultaneous group. The mean Harris hip score, EuroQol-5D index, and EuroQol-visual analogue scale score were all better in the simultaneous group at the latest follow-up (P < 0.001, in all comparisons). We found that the simultaneous procedure was associated with a lower incidence of postoperative prosthetic-related complications and revision surgery.

CONCLUSIONS

We suggest that bilateral ONFH could be treated with a simultaneous THA rather than a staged THA to achieve a better surgical outcome.

Mid-term results of the BIOLOX delta ceramic-on-ceramic total hip arthroplasty

Aims

We conducted a prospective study of a delta ceramic total hip arthroplasty (THA) to determine the rate of ceramic fracture, to characterise post-operative noise, and to evaluate the mid-term results and survivorship.

Patients and Methods

Between March 2009 and March 2011, 274 patients (310 hips) underwent cementless THA using a delta ceramic femoral head and liner. At each follow-up, clinical and radiological outcomes were recorded. A Kaplan-Meier analysis was undertaken to estimate survival.

Results

Four patients (four hips) died and 18 patients (20 hips) were lost to follow-up within five years. The remaining 252 patients (286 hips) were followed for a mean of 66.5 months (60 to 84). There were 144 men (166 hips) and 108 women (120 hips) with a mean age of 49.7 years (16 to 83) at surgery. The mean pre-operative Harris Hip Score of 47.1 points improved to 93.8 points at final follow-up. Six patients reported squeaking in seven hips; however, none were audible. Radiolucent lines involving Gruen zones one and/or seven were seen in 52 hips (18.2%). No hip had detectable wear, focal osteolysis or signs of loosening. One hip was revised because of fracture of the ceramic liner, which occurred due to an undetected malseating of the ceramic liner at the time of surgery. One hip was revised for a periprosthetic fracture of the femur, and one hip was treated for periprosthetic joint infection. The six-year survivorship with re-operation for any reason as the endpoint was 99.0% (95% confidence interval 97.8% to 100%).

Discussion

The rate of delta ceramic fracture was 0.3% (one of 286). While ceramic head fracture was dominant in previous ceramic-on-ceramic THA, fracture of the delta ceramic liner due to malseating is a concern. Cite this article: Bone Joint J 2017;99-B:741–8.

Tapered stems one-third proximally coated have higher complication rates than cylindrical two-third coated stems in patients with high hip dislocation undergoing total hip arthroplasty with step-cut shortening osteotomy

BACKGROUND

The results of cementless stems in total hip arthroplasty (THA) done because of congenital dislocation with step-cut osteotomy is not well known, particularly the influence of the design and the role of extent of porous coating. Therefore we performed a retrospective study to evaluate the mid to long-term results THA performed with a single type acetabular component and different geometry and fixation type stems with ceramic bearings in the setting of step-cut subtrochanteric osteotomy in high hip dislocated (HHD) patients. We asked if the stem type affect the outcomes in terms of (1) intra and postoperative complication rates (2) radiographic outcomes (3) prosthesis survival in step-cut subtrochanteric shortening osteotomy.

HYPOTHESIS

The type of the stem, whether cylindrical or tapered does not affect the outcome if the femoral canal fit and fill is obtained and the step-cut femoral shortening osteotomy is primarily fixed.

MATERIALS AND METHODS

Forty-five hips in 35 patients with a mean follow up of 10 years (range, 7-14 years) were evaluated. The single type cementless cup was placed at the level of the true acetabulum, a step-cut shortening femoral osteotomy was performed and reconstruction was performed with two different types of tapered stem in twenty-two hips (Synergy™ and Image™ proximally coated, Smith and Nephew, Menphis, TN, USA) and one type of cylindrical stem (Echelon™ with 2/3 coated, Smith and Nephew, Menphis, TN, USA) in twenty-three hips. Harris hip scores (HHS) and a University of California Los Angeles (UCLA) activity scores were calculated for all patients and successive X-rays were evaluated regarding component loosening and osteolysis, along with complications related to bearing, step-cut osteotomy and stem types.

RESULTS

Forty-one hips (91%) had good and excellent clinical outcome according to HHS. The mean UCLA activity scores improved from 3.2±0.6 points (range, 2-4) preoperatively to 6.3 points±0.5 (range, 5-7) at the latest follow-up. The mean femoral shortening was 36±10mm (range, 20-65mm). Four (9%) dislocations were observed. There were five (11%) intra-operative femoral fractures and three (7%) cases of non-union, which were observed in tapered stems. Cylindrical stems had superior neutral alignment primarily. With any stem revision as the end point, cylindrical stems had a higher survival rate (100%) than all tapered stems (82%; 95% confident interval [CI] 77-97%) at ten years. With any revision as the end point, the 10-year survival rate for acetabular component (Reflection-Ceramic Interfit) and for femoral components were 98% (95% CI, 85-99%) and 91% (95% CI, 78-97%), respectively.

CONCLUSIONS

There were more implant related complications in HHD patients undergoing THA when tapered stems with 1/3 proximal coating were used to reconstruct a step cut osteotomized femur, compared to cylindrical stems 2/3 coated.

LEVEL OF EVIDENCE

IV, retrospective study.

The evolution of an uncemented acetabular component in alumina-on-alumina total hip arthroplasty has improved clinical outcome

Aims

To determine the effect of a change in design of a cementless ceramic acetabular component in fixation and clinical outcome after total hip arthroplasty

Patients and Methods

We compared 342 hips (302 patients) operated between 1999 and 2005 with a relatively smooth hydroxyapatite coated acetabular component (group 1), and 337 hips (310 patients) operated between 2006 and 2011 using a similar acetabular component with a macrotexture on the entire outer surface of the component (group 2). The mean age of the patients was 53.5 (14 to 70) in group 1 and 53.0 (15 to 70) in group 2. The mean follow-up was 12.7 years (10 to 17) for group 1 and 7.2 years (4 to 10) for group 2.

Results

No hips were revised due to complications related to bearing fracture or to stem loosening. A total of 15 acetabular components were revised for aseptic loosening in group 1 and two in group 2. The survival rate for acetabular component aseptic loosening at eight years was 96.8% (95% confidence interval (CI) 94.8 to 98.7) for group 1 and 99.2% (95% CI 98.0 to 100) for group 2. The risk for aseptic loosening of the acetabular component was higher in group 1 (p = 0.04, Hazard Ratio (HR) 4.99), dysplastic acetabula (p = 0.01, HR 4.12), components outside Lewinnek´s zone (p < 0.001, HR 6.13) and in those with a hip rotation centre distance greater than 5 mm (p = 0.005, HR 4.09).

Conclusion

Alumina ceramic-on-ceramic THA is an excellent option for young patients. Although newer components appeared to improve fixation, acetabular reconstruction is essential to obtain a satisfactory outcome. Cite this article: Bone Joint J 2017;99-B:749–58.

Level of surgical experience is associated with change in hip center of rotation following cementless total hip arthroplasty: A radiographic assessment

Objectives

After total hip arthroplasty (THA), restoration of hip center of rotation (COR) is essential to ensure stability of the prosthetic hip and longevity of the prosthesis. Our aim was to determine whether, and how, the COR changed postoperatively compared to the native COR following implantation of a cementless acetabular component in anatomical position and to compare the accuracy of cup placement between two surgeons with different levels of surgical experience.

Materials and methods

We evaluated 145 patients (145 hips) who underwent unilateral primary THA, who had no distorted acetabulum on the affected hip and a normal contralateral hip. Hip reconstruction was radiologically and clinically assessed at a minimum 2-year follow-up. Perioperative change in COR, initial cup position, offset, leg-length discrepancy (LLD), radiographic cup orientation, Harris Hip Score (HHS), component loosening, and dislocations were compared between the highly experienced surgeon and less-experienced surgeon groups.

Results

The COR was significantly displaced in the superior and medial directions postoperatively. Significant differences were identified in the vertical COR change, initial cup position, LLD, cup inclination, and cups within safe zones, but not in the horizontal COR change, offset parameters, cup anteversion, or HHS. There were no radiographic evidence of component loosening in both groups, but three dislocations (7%) only in the group operated on by the less-experienced surgeon (p = 0.027).

Conclusions

We found that the postoperative COR tended to be displaced in the superior and medial directions, and that the level of surgical experience strongly affected the accuracy and consistency of cup placement, particularly in COR position and cup inclination.

Screws are not needed when secure interference fit of uncemented acetabular components is adequate: a 5- to 15-year follow-up with clinical and radiological analysis

PURPOSE

Even with good surgical preparation, adequate primary stability of the acetabular component is not always achieved after primary total hip replacement (THR). We hypothesise that adequate bone preparation for appropriate cortical loading would allow us to avoid screw use.

METHODS

A total of 791 uncemented cups were analysed to compare the need for screws to obtain primary fixation in 5 different designs. Arthritic hips with inflammatory arthritis or severe congenital hip disease were excluded. A press-fit technique was first tried in all hips and screws were only used when strictly needed. Radiological acetabular shape and postoperative cup position were assessed in all hips. The mean follow-up was 9.6 (5-15) years.

RESULTS

Screws were required in 155 hips (19.6%). We could not detect any difference in the percentage of screw use between designs. We found that female patients (odds ratio [OR] 2.06; 95% confidence interval [CI], 1.41-3.02) and cups with a greater distance to the hip rotation centre on the postoperative radiograph (OR 1.69; 95% CI, 1.17-2.45) had a higher risk for screw use. A greater anteversion of the cup had a lower risk for screw use (OR 0.96; 95% CI, 0.94-0.99). At latest follow-up no hips had needed revision for aseptic loosening.

CONCLUSIONS

Good intraoperative technique is not enough to avoid screw use since more accurate cup position and reconstruction of the hip rotation centre are required for an adequate interference fit. A press-fit technique can provide similar mid-term results to screw use in hips without severe deformities.

New cross-table lateral radiography method for measuring acetabular component anteversion in total hip arthroplasty: a prospective study of 93 primary THA

INTRODUCTION

Various methods have been described for measuring acetabular component anteversion. However, accurate measurement of anteversion is difficult. We herein propose a new method using cross-table lateral (CL) radiography performed with the contralateral hip flexed to 45° (45° flexed CL radiography). The main purpose of this study was to evaluate the reliability and validity of this new method.

METHODS

The study group included 93 patients who underwent total hip arthroplasty (THA). All hips were evaluated with computed tomography (CT) and both standard and 45° flexed CL radiographs to measure acetabular component anteversion the week after THA. The intraobserver and interobserver reliability of each measurement was assessed. Plain radiography measurements were compared with reference CT measurements to evaluate their validity.

RESULTS

All measurements had excellent intraobserver and interobserver reliability, and plain radiography measurements correlated well with CT measurements. The mean measurements were 21.9° (3°-39°) with CT, 24.9° (7°-47°; p<0.001) with standard CL radiographs, and 22.5° (7°-43°; p = 0.112) with 45° flexed CL radiographs.

DISCUSSION

The anteversion values measured with our new method were closer to the CT values used as a reference standard than those with standard CL radiographs. Our new method appears to be reliable and valid for measuring acetabular component anteversion.

Effect of Acetabular Position on Polyethylene Liner Wear Measured Using Simultaneous Biplanar Acquisition

BACKGROUND

Studies that have previously examined the relationship between acetabular component inclination angle and polyethylene wear have shown increased wear of conventional polyethylene with high inclination angles. To date, there are no long-term in vivo studies examining the correlation between cup position and polyethylene wear with highly crosslinked polyethylene.

METHODS

An institutional arthroplasty database was used to identify patients who had metal-on-highly crosslinked polyethylene primary total hip arthroplasty using the same component design with a minimum follow-up of 10 years. A modified radiostereometric analysis examination setup was utilized, recreating standard anteroposterior and cross-table lateral examinations in a single stereo radiostereometric analysis acquisition. The same radiographs were used to measure inclination angle and anteversion.

RESULTS

A total of 43 hips were included for analysis in this study. Average follow-up was 12.3 ± 1.2 years. The average linear wear rate was calculated to be 0.066 ± 0.066 mm/y. Inclination angle was not correlated with polyethylene wear rate (P = .82). Anteversion was also not correlated with polyethylene wear rate (P = .11).

CONCLUSION

At long-term follow-up of >10 years, highly crosslinked polyethylene has a very low wear rate. This excellent tribology is independent of acetabular position. The low wear rate highlights the excellent results of metal on highly crosslinked polyethylene, and supports its use in total hip arthroplasty.

Cementless Hip Stem Anteversion in the Dysplastic Hip: A Comparison of Tapered Wedge vs Metaphyseal Filling

BACKGROUND

Appropriate stem anteversion is important for achieving stability of the prosthetic joint in total hip arthroplasty. Anteversion of a cementless femoral stem is affected by the femoral canal morphology and varies according to stem geometry. We investigated the difference and variation of the increase in anteversion between 2 types of cementless stems, and the correlation between each stem and the preoperative femoral anteversion.

METHODS

We retrospectively compared 2 groups of hips that underwent total hip arthroplasty using a metaphyseal filling stem (78 hips) or a tapered wedge stem (83 hips). All the patients had osteoarthritis due to hip dysplasia. Computed tomography was used to measure preoperative femoral anteversion at 5 levels and postoperative stem anteversion.

RESULTS

The increase in anteversion of the tapered wedge stem group (22.7° ± 11.6°) was more than that of the metaphyseal filling stem group (17.2° ± 8.3°; P = .0007). The variation of the increase in the tapered wedge stem group was significantly larger than that in the metaphyseal filling stem group (P = .0016). The metaphyseal filling stem group was more highly and positively correlated with femoral anteversion than the tapered wedge stem group.

CONCLUSION

Femoral anteversion affects stem anteversion differently according to stem geometry. The tapered wedge stems had greater variation of the increase in anteversion than did the metaphyseal filling stems. Based on the results of this study, it is difficult to preoperatively estimate the increase in stem anteversion for tapered wedge stems.

Conversion Hip Arthroplasty in Failed Fixation of Intertrochanteric Fracture: A Propensity Score Matching Study

BACKGROUND

Conversion hip arthroplasty is a salvage procedure for failed internal fixation of intertrochanteric fractures. However, the technical difficulties and perioperative morbidity of conversion arthroplasty are uncertain.

METHODS

We compared the type of arthroplasty (total hip arthroplasty or hemiarthroplasty), operative parameters, perioperative morbidity, 1-year mortality, implant stability, and clinical results of 33 conversion hip arthroplasties due to a failed internal fixation of intertrochanteric fracture with those of a matched control group of 33 primary hip arthroplasties due to the same fracture. Propensity score was used for the control matching of gender, age, and body mass index.

RESULTS

Total hip arthroplasty was more frequently performed in the conversion group (10/33) compared to the primary group (3/33) (P = .016). The operation time, perioperative blood loss, amount of transfusion, and risk of femoral fracture during the operation were increased in the conversion group. The overall 1-year mortality was 3% (1 patient) in the conversion group and 9% (3 patients) in the primary group (P = .307). At a mean of 3-year follow-up, there was no significant difference in clinical results and none of the implants were loose in both groups.

CONCLUSION

In patients with failed internal fixation of intertrochanteric fracture, conversion hip arthroplasty should be planned and executed, bearing in mind the increased operative morbidities corresponding to operation time, perioperative blood loss, requirement of transfusion, and intraoperative femoral fracture.