The impact of standard combined anteversion definitions on gait and clinical outcome within one year after total hip arthroplasty

PURPOSE

Different target areas within the concept of combined cup and stem anteversion have been published for total hip arthroplasty (THA). We asked whether component positioning according to eight standard combined anteversion rules is associated with (1) more physiological gait patterns, (2) higher improvement of gait variables and (3) better clinical outcome after THA.

METHODS

In a prospective clinical study, 60 patients received cementless THA through an anterolateral MIS approach in a lateral decubitus position. Six weeks postoperatively, implant position was analysed using 3D-CT by an independent external institute. Preoperatively, six and 12 months postoperatively range of motion, normalized walking speed and hip flexion symmetry index were measured using 3D motion-capture gait analysis. Patient-related outcome measures (HHS, HOOS, EQ-5D) were obtained by an observer blinded to 3D-CT results. Eight combined anteversion definitions and Lewinnek's "safe zone" were evaluated regarding their impact on gait patterns and clinical outcome.

RESULTS

Combined cup and stem anteversion according to standard combined anteversion definitions as well as cup placement within Lewinnek's "safe zone" did not influence range of motion, normalized walking speed and/or hip flexion symmetry index six and 12 months after THA. Similarly, increase of gait parameters within the first year after THA was comparable between all eight combined anteversion rules. Clinical outcome measures like HHS, HOOS and EQ-5D did not show any benefit for either of the combined anteversion definitions.

CONCLUSIONS

Standard combined cup and stem anteversion rules do not improve postoperative outcome as measured by gait analysis and clinical scores within one year after THA.

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

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

Severe Wear and Pseudotumor Formation Due to Taper Mismatch in a Total Hip Arthroplasty: A Case Report

CASE

We describe the case of a seventy-six-year-old woman who had undergone bilateral total hip arthroplasty with Zweymüller-Metasul prostheses in 1996. After a fall sixteen years after the index procedures, radiographs suggested a taper fracture of the left total hip arthroplasty. However, revision surgery showed pseudotumor formation, with no evidence of taper fracture. Analysis of the prosthesis showed massive wear of the male stem taper caused by a mismatch between the stem taper and the head taper.

CONCLUSION

This case vividly demonstrates how taper size mismatch can cause dramatic metal wear and increased release of metal ions, resulting in pseudotumor formation.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Third-generation alumina-on-alumina total hip arthroplasty: 14 to 16-year follow-up study

Ceramic-on-ceramic articulation has the lowest wear with little osteolysis. However, the wear and osteolysis in long-term follow-up are not known. Another concern is ceramic fracture, which might occur after repeated stress during a long period. Ninety hips (76 patients with a mean age of 47 years) that underwent cementless total hip arthroplasty using third-generation ceramic-on-ceramic articulation were followed for 14-16 years. At final follow-up, there was no measurable ceramic wear and no periprosthetic osteolysis was identified. No ceramic fracture occurred during the follow-up. One hip was revised because of late infection. All prostheses were bone-ingrown. Two patients experienced a grinding sensation. However, no patient had squeak. The mean Harris hip score at the final evaluation was 89 points and the survival rate was 98.9%.

Implication of acetabular width on the anteroposterior pelvic radiograph of patients with developmental dysplasia of the hip

Radiographic parameters that can help acetabular reconstruction during total hip arthroplasty (THA) for patients with developmental dysplasia of the hip (DDH) are few. The radiographs of 138 dysplastic hips that had undergone cementless THA were evaluated regarding the acetabular width above the acetabular component and the coverage of the component by native bone. The acetabular reconstruction process was simulated using 3D models from CT data, and the acetabular component coverage was calculated in 3D space based on the measurement and algorithm we proposed. Significant positive correlation between the acetabular width and the acetabular component coverage was found. Our study introduced a useful parameter, which can mark the superior reference position of the acetabular component for acetabular reconstruction in DDH patients.

Value of computed tomography-based three-dimensional surgical preoperative planning software in total hip arthroplasty with developmental dysplasia of the hip

INTRODUCTION

Preoperative planning with computed tomography (CT)-based three-dimensional templating has been expanded to achieve more precise placement of hip components. However, few reports have addressed the utility of three-dimensional surgical planning software for secondary osteoarthritis cases. This study therefore investigated the value of CT-based three-dimensional templating software for preoperative planning in primary total hip arthroplasty (THA), with an emphasis on developmental dysplasia of the hip.

MATERIALS AND METHODS

We performed a retrospective review of 65 hips in 57 patients who underwent cementless primary THA. The preoperative diagnosis was secondary osteoarthritis in all cases due to developmental dysplasia of the hip. All preoperative planning and postoperative evaluations were completed using CT-based three-dimensional templating software. We analyzed the accuracy of stem size prediction and cup size prediction, the reproducibility of preoperative and postoperative stem anteversion, and the absolute error in preoperative and postoperative stem anteversion using CT-based three-dimensional templating software.

RESULTS

The sizes of 65 % of the femoral stems (42/65) were estimated exactly, and 98 % (63/65) were accurately estimated to within one stem size. The final acetabular cup sizes corresponded exactly to the preoperatively planned size in 92 % of all cases (62/65). 100 % of the cup size estimates were accurate to within one cup size. There was strong reproducibility of preoperative and postoperative stem anteversion (r = 0.88, P < 0.05). The absolute error in stem anteversion was 4.0° ± 3.6°.

CONCLUSIONS

Using CT-based three-dimensional templating software made it possible to achieve reproducible stem anteversion and choose accurate stem and cup sizes in patients with developmental dysplasia of the hip.

Total Hip Prostheses in Standing, Sitting and Squatting Positions: An Overview of Our 8 Years Practice Using the EOS Imaging Technology

More total hip arthroplasty (THA) is performed worldwide and especially in younger and more active patients compared to earlier decades. One of the focuses of THA research in the future will be on optimizing the radiological follow-up of these patients using 2D and 3D measurements of implants position while reducing the radiation dose delivered.

Low-dose EOS^® imaging is an innovative slot-scanning radiograph system providing valuable information in patient functional positions (standing, sitting and even squatting positions). EOS has been proven accurate and reliable without significant inconvenience caused by the metallic artifacts of implants. The ability to obtain precise data on implant orientation according to the patient posture opens new perspectives for a comprehensive analysis of the pelvic frontal and sagittal balance and its potential impact on implants function and failures.

We report our 8 years experience on our first 300 THA patients using this technology routinely for pre and post op evaluation. Our results will be compared and confronted with the actual literature about this innovative technology. We shall especially emphasize our experience about patients with abnormal posture and the evolution of the subject over time, because the phenomenon of an aging spine is frequently associated with the process of aging hips.

The 2014 Frank Stinchfield Award: The 'landing zone' for wear and stability in total hip arthroplasty is smaller than we thought: a computational analysis

BACKGROUND

Positioning of total hip bearings involves tradeoffs, because cup orientations most favorable in terms of stability are not necessarily ideal in terms of reduction of contact stress and wear potential. Previous studies and models have not addressed these potentially competing considerations for optimal total hip arthroplasty (THA) function.

QUESTIONS/PURPOSES

We therefore asked if component positioning in total hips could be addressed in terms of balancing bearing surface wear and stability. Specifically, we sought to identify acetabular component inclination and anteversion orientation, which simultaneously resulted in minimal wear while maximizing construct stability, for several permutations of femoral head diameter and femoral stem anteversion.

METHODS

A validated metal-on-metal THA finite element (FE) model was used in this investigation. Five dislocation-prone motions as well as gait were considered as were permutations of femoral anteversion (0°-30°), femoral head diameter (32-48 mm), cup inclination (25°-75°), and cup anteversion (0°-50°), resulting in 4320 distinct FE simulations. A novel metric was developed to identify a range of favorable cup orientations (so-called "landing zone") by considering both surface wear and component stability.

RESULTS

When considering both wear and stability with equal weight, ideal cup position was more restrictive than the historically defined safe zone and was substantially more sensitive to cup anteversion than to inclination. Ideal acetabular positioning varied with both femoral head diameter and femoral version. In general, ideal cup inclination decreased with increased head diameter (approximately 0.5° per millimeter increase in head diameter). Additionally, ideal inclination increased with increased values of femoral anteversion (approximately 0.3° per degree increase in stem anteversion). Conversely, ideal cup anteversion increased with increased femoral head diameter (0.3° per millimeter increase) and decreased with increased femoral stem anteversion (approximately 0.3° per degree increase). Regressions demonstrated strong correlations between optimal cup inclination versus head diameter (Pearson's r=-0.88), between optimal cup inclination versus femoral anteversion (r=0.96), between optimal cup anteversion versus head diameter (r=0.99), and between optimal cup anteversion and femoral anteversion (r=-0.98). For a 36-mm cup with a 20° anteverted stem, the ideal cup orientation was 46°±12° inclination and 15°±4° anteversion.

CONCLUSIONS

The range of cup orientations that maximized stability and minimized wear (so-called "landing zone") was substantially smaller than historical guidelines and specifically did not increase with increased head size, challenging the presumption that larger heads are more forgiving. In particular, when the cup is oriented to improve not only stability, but also wear in the model, there was little or no added stability achieved by the use of larger femoral heads. Additionally, ideal cup positioning was more sensitive to cup anteversion than to inclination.

CLINICAL RELEVANCE

Positioning THA bearings involves tradeoffs regarding stability and long-term bearing wear. Cup positions most favorable to minimization of wear such as low inclination and elevated anteversion were detrimental in terms of construct stability. Orientations were identified that best balanced the competing considerations of wear and stability.

Anterior minimally invasive approach for total hip replacement: five-year survivorship and learning curve

Opponents associate minimally invasive total hip replacement (THR) with additional risks, potentially resulting in increased implant failure rates. The purpose was to document complications, quality of implant positioning and five-year survivorship of THR using the AMIS approach and to test the hypothesis that eventual high complication and revision rates would be limited to an early series and be avoided by junior surgeons who get trained by a senior surgeon. A consecutive series of 150 primary THR implanted during the introduction of the AMIS technique in the department was retrospectively analysed for complications, implant positioning and implant survival after a minimum of five years. Survivorship curves of implants were compared between different surgeons and time periods. Due to implant revision for any reason the five-year survival rate was 94.6%, 78.9% for the first 20 and 96.8% for the following 130 AMIS procedures (p = 0.001). The hazard ratio for implant failure was 0.979 indicating a risk reduction of 2% every further case. The five-year implant survivorship of those procedures performed by two junior surgeons was 97.7%. We conclude that adoption of AMIS temporarily exposed patients to a higher risk of implant revisions, which normalised after the first 20 cases and that experience from a single surgeon's learning curve could effectively be taught to junior surgeons.

Acetabular component orientation in total hip arthroplasty: the impact of obesity

INTRODUCTION

Acetabular component position can be an important determinant of joint stability and bearing surface wear after THA. Nonetheless, the incidence of malpositioning is high. Patient obesity, low surgeon volume, and minimally invasive approaches are known risk factors for malposition. As the incidence of obesity continues to increase, it is important to recognise its effect on intraoperative component positioning in THA.

OBJECTIVES

Our goal was to assess the impact of obesity on component position for a high-volume surgeon using a standard postero-lateral approach.

METHODS

A consecutive series of 120 obese (BMI >30, mean BMI 34.4) and 120 non-obese patients (mean BMI 25.4), who had undergone primary THA by a single surgeon, were included in our retrospective study. AP pelvis and cross-table radiographs obtained at the first postoperative visit were analysed using EBRA software to determine inclination and anteversion angles. Optimal position was defined as 30-45º of inclination and 5-25º of anteversion.

RESULTS

Mean inclination and anteversion were 40.6 (+/-5.4º) and 16.6 (+/-5.5º) respectively, in the obese group and 39º (+/-5.0º) and 16.2º (+/-7.5º) in the non-obese group. In the obese group 89 (74%) patients were within the desired range for both measurements, 31 (26%) were out of range in at least one, compared to 91 (76%) and 29 (24%) in the non-obese group, respectively. The overall incidence of malpositioning was 25% for both groups. Among outliers, mean deviation from the optimal range was ≤3.8º in both groups.

CONCLUSIONS

The risk of component malpositioning in THA may be reduced when surgery is performed by an experienced, high volume surgeon utilising a standard posterolateral approach. In this setting the deleterious effect of obesity may be overcome.

The learning curve associated with robotic-assisted total hip arthroplasty

There are no reports examining the learning curve during the adoption of robotic assisted THA. The purpose of this study was to examine the learning curve of robotic assisted THA as measured by component position, operative time, and complications. The first 105 robotic-assisted THAs performed by a single surgeon were divided into three groups based on the order of surgery. Component position, operative time, intra-operative technical problems, and intra-operative complications were recorded. There was a decreased risk of acetabular component malpositioning with experience (P<0.05). Operative time appeared to decrease with increasing surgical experience (P<0.05). A learning curve was observed, as a decreased incidence of acetabular component outliers and decreased operative time were noted with increased experience.

A new method of registration in navigated hip arthroplasty without the need to register the anterior pelvic plane

A prospective clinical study of 50 patients was conducted to validate a new method of imageless computer navigated hip arthroplasty. The new method enables the surgeon to acquire all registration points with the patient positioned and draped in lateral decubitus position. The final component orientation was measured from post-operative CT scans. The mean error in component position was -1.1° (SD 3.1°) for inclination and 0.9° (SD 4.3°) for anteversion. This compared favourably with the error of -1.8° (SD 1.8°) for inclination and -4.8° (SD 2.7°) for anteversion when using the traditional APP registration. Results show that one can expect the acetabular component to be within a safe zone of ±10° in 99.8% for inclination and 97.7% for anteversion when using the new lateral registration method. Level of Evidence Level II, Prognostic study.

Results of Primary Total Hip Arthroplasty with 36-mm Femoral Heads on Highly Cross-linked Polyethylene-Minimum Seven-years Follow-up

Purpose

We evaluate the clinical and radiographic midterm results of primary total hip arthroplasty (THA) using a 36 mm diameter femoral head on highly cross-linked polyethylene (minimum 7-year follow-up).

Materials and Methods

We retrospectively reviewed 73 patients (74 hips) that underwent primary THA with a 36 mm diameter femoral head on highly cross-linked polyethylene between July 2004 and February 2007. Clinical follow-ups included specific measurements like modified Harris hip scores (HHS) and Merle d'Aubigne and Postel score. For radiologic evaluations, together with position of acetabular cup at 6 weeks later of post-operation, we separately calculated the penentrations of femoral heads into polyethylene liners during post-operation and one year later check-ups, and during one year later check-ups and final check-ups.

Results

There were no complications except for one case of dislocation. Average modified HHS at final follow-up was 88±7.5 (range, 81-96), and Merle d'Aubigne and Postel scores were more than 15 (range, 15-18). Mean acetabular cup inclination and anteversion were 50.1°(range, 35°-58°) and 23.6°(range, 5°-38°), respectively. Average femoral head penetration during the first postoperative year was 0.071±0.034 mm/year, and steady-state wear rate determined using radiographs taken at one-year postoperatively and at latest follow-up was 0.051±0.022 mm/year. Average femoral head penetration during entire follow-ups was 0.058±0.013 mm/year.

Conclusion

Primary THA with a large diameter femoral head on highly cross-linked polyethylene was found to produce the results comparable to previous in vitro laboratory hip simulation studies. And we also find out good scores in terms of patient's functionality.

A novel non-invasive mechanical technique of cup and stem placement and leg length adjustment in total hip arthroplasty for dysplastic hips

PURPOSE

This study assessed the accuracy of cup and stem positioning and limb length adjustment for developmental dysplasia of the hip (DDH) using our new mechanical technique compared with imageless navigation or a computed tomography (CT)-based navigation system.

METHODS

One hundred thirteen primary total hip arthroplasties (THAs) for DDH were evaluated. At pre-operative positioning, patients were placed in a precise lateral decubitus position by tilting the surgical table using simple ready-made devices (two shot pipe, metal chain, level gauge and goniometer). During surgery, cups were intentionally placed at 45° inclination and 15° anteversion on radiograph by using a level gauge and goniometer.

RESULTS

Cup inclination was 44.2° ± 3.4° (range, 32.0-51.2°), cup anteversion was 19.6° ± 6.1° (range, 3.0-33.1°), stem alignment was 0.04° ± 0.8° valgus (range, 2.1° varus to 1.9° valgus), and leg length discrepancy was -0.37 ± 3.7 mm (range, -12.8 to 8.8 mm) in postoperative radiographs. Outliers (outside ±10° from intentional position) occurred in 15 cases (13.3 %) in inclination or anteversion. Postoperative dislocation did not occur in any cases.

CONCLUSIONS

Cup and stem positioning in THAs with our new mechanical technique yielded satisfactory results compared with previously reported imageless navigation or CT-based navigation. Our results were superior with regard to being non-invasive and low cost and involving minimum radiation exposure.

Standing or supine x-rays after total hip replacement - when is the safe zone not safe?

An acetabular prosthesis orientated outside the 'safe zone' is one of the key contributing factors in increasing complications after total hip replacement (THR). Although acetabular orientation is routinely assessed using supine x-rays, standing x-rays have been proposed because a change in body position alters pelvic tilt and therefore acetabular orientation. This study aimed to assess whether acetabular components orientated within the 'safe zone' in supine can also be outside the 'safe zone' in standing. Thirty patients (12M, 18F) had lateral and antero-posterior pelvic x-rays taken in standing and supine positions six weeks post THR. Pelvic tilt and acetabular orientation (anteversion and inclination) were measured and compared with respect to the limits of the 'safe zone'. In standing, the pelvis was relatively posteriorly tilted and both acetabular anteversion and inclination increased (p<0.0001). In 16 patients the acetabulum was orientated within the 'safe zone' in supine but outside the 'safe zone' in standing. Patients were significantly more likely to be outside the 'safe zone' in standing than when supine (p<0.0001).

Midterm results of large diameter Biolox forte ceramic head on delta ceramic liner articulation in total hip arthroplasty

Seventy-nine patients (94 hips), who underwent cementless alumina-on-alumina total hip arthroplasty (THA) with the use of a 36-mm delta ceramic liner-on-alumina ceramic femoral head, were followed for an average of 6.5years (range, 5-7.7years). All acetabular and femoral components were bone-ingrown and neither pelvic nor femoral osteolysis was identified until the latest follow-up. The survivorship with revision surgery as an endpoint was 97.9% (95% confidence interval=100%-95%). Ceramic related complications such as fracture and squeaking did not occur in any patient. The mid-term results of cementless THA with this type of ceramic articulation are encouraging.

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

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

Optimal acetabular component orientation estimated using edge-loading and impingement risk in patients with metal-on-metal hip resurfacing arthroplasty

Edge-loading in patients with metal-on-metal resurfaced hips can cause high serum metal ion levels, the development of soft-tissue reactions local to the joint called pseudotumours and ultimately, failure of the implant. Primary edge-loading is where contact between the femoral and acetabular components occurs at the edge/rim of the acetabular component whereas impingement of the femoral neck on the acetabular component's edge causes secondary or contrecoup edge-loading. Although the relationship between the orientation of the acetabular component and primary edge-loading has been identified, the contribution of acetabular component orientation to impingement and secondary edge-loading is less clear. Our aim was to estimate the optimal acetabular component orientation for 16 metal-on-metal hip resurfacing arthroplasty (MoMHRA) subjects with known serum metal ion levels. Data from motion analysis, subject-specific musculoskeletal modelling and Computed Tomography (CT) measurements were used to calculate the dynamic contact patch to rim (CPR) distance and impingement risk for 3416 different acetabular component orientations during gait, sit-to-stand, stair descent and static standing. For each subject, safe zones free from impingement and edge-loading (CPR <10%) were defined and, consequently, an optimal acetabular component orientation was determined (mean inclination 39.7° (SD 6.6°) mean anteversion 14.9° (SD 9.0°)). The results of this study suggest that the optimal acetabular component orientation can be determined from a patient's motion and anatomy. However, 'safe' zones of acetabular component orientation associated with reduced risk of dislocation and pseudotumour are also associated with a reduced risk of edge-loading and impingement.

Validation of patient specific surgical guides in total hip arthroplasty

BACKGROUND

The validation of patient-specific surgical guides (PSGs) by their design and the comparison of planned and actual PSG setting in total hip arthroplasty (THA) have not previously been reported.

METHODS

The errors between preoperative planning and computed tomography (CT)-based PSG setting (E1), and between preoperative planning and implantation (E2) were evaluated using CT in 16 fresh cadaveric hips.

RESULTS

E2 was significantly smaller with the wide-base-contact resurfacing-THA PSG than with the narrow-base-contact type (P<0.05). E1/E2 of the wide-base-contact neck-cut PSG was 1.6±0.7°/2.4±1.1° for the coronal plane and 1.2±0.8 mm/0.7±0.5mm for the medial neck-cut height. E1/E2 of the wide-base-contact cup-impaction PSG was 1.0±0.9°/3.4±1.9° for inclination and 1.7±1.1°/6.6±4.4° for anteversion.

CONCLUSIONS

The wide-base-contact PSG in resurfacing-THA and the PSG for neck-cut in THA could be applied clinically. Although cup-impaction PSG setting was acceptable, errors were made due to the impaction process during cup implantation.

A titanium plasma-sprayed cup with and without hydroxyapatite-coating: a randomised radiostereometric study of stability and osseointegration

We present a prospective, two-centre radiostereometric analysis (RSA) regarding the stability of a flattened pole titanium press-fit cup (EP-FIT PLUS), and whether additional hydroxyapatite coating leads to faster bone ingrowth into the porous coating. Forty-two postmenopausal female patients (44 hips) undergoing total hip arthroplasty for primary osteoarthritis, selected to avoid hormonal factors influencing bone metabolism, were randomised to receive this cup with a titanium-plasma-sprayed surface with or without an additional hydroxyapatite coating. RSA was used to measure cup translation and rotation along three cardinal axes with respect to the host bone at the following time points: immediately postoperatively, at 6 weeks, and at 3, 6, 12, and 24 months. The most pronounced translation was proximal (0.11 mm) and posterior tilt (-0.27°). No difference in translation and rotation could be detected between the two groups. With the exception of one cup with an isolated radiolucent line <2 mm in zone 1, all cups showed complete osseointegration on conventional radiographs. The flattened pole cup provided excellent early stability and no advantage could be detected with additional hydroxyapatite coating.

[Diagnostics and therapy of luxation after total hip arthroplasty]

BACKGROUND

Luxation following endoprosthetic hip replacement represents a frequent and severe complication and is the reason for a relevant number of hip arthroplasty revision interventions. The probability of occurrence of luxation of a total hip arthroplasty is associated with the indications, patient and operation-specific risk factors. Approximately 50 % of luxations after total hip arthroplasty occur within 3 months of the operation (early luxation).

DIAGNOSTICS

The diagnostics of luxation of total hip arthroplasty are carried out by clinical and radiological methods. The causative assignment is made by assessment of joint stability, the bony situation (e.g. loosening, periprosthetic fracture and defects) and the soft tissue (e.g. pelvitrochanterian musculature). In cases of clinical and paraclinical signs of infection and of late luxations, a joint puncture is indicated.

THERAPY

Therapy decisions are made depending on the cause (e.g. implant malpositioning, pelvitrochanterian insufficiency, impingement, incongruence between head and inlay and combinations of causes). Therapy of acute total hip prosthesis luxation begins with imaging controlled repositioning carried out with the patient under adequate analgesia and sedation. Conservative therapy is carried out by immobilization with a hip joint orthesis or pelvis-leg cast for 6 weeks. Operative therapy strategies for recurrent luxation are restoration of the correct implant position and sufficient soft tissue tension. Larger hip heads, bipolar heads and tripolar cups are more commonly used due to the geometrically lower probability of dislocation (higher jumping distance). Luxation of total hip prostheses due to infection is treated according to the principles of periprosthetic infection therapy. The rate of recurrence of luxation of 30 % is high so that in cases of unsuccessful therapy treatment should best be carried out in a center for revision arthroplasty.

CONCLUSIONS

The search for the exact cause of total hip prosthesis luxation is extremely important. A classification is only possible when the exact cause is known and together with patient and implant-specific details the therapeutic approach can be ascertained. In revision operations the intraoperative functional diagnostics must be exactly documented. The reasons for delayed luxations could be prosthesis infections, abrasion and loosening.

Robotic total hip arthroplasty

Modern total hip replacement is typically effective and durable, but early failures do occur. Component position influences functional outcome, durability, and risk of complications. Surgical robotics provides the detail-oriented surgeon with a robust tool to optimize the accuracy and precision of total hip arthroplasty, with the potential to minimize risk of mechanical failure. This article describes efficient workflows for using surgical robotics to optimize surgical precision without increasing surgical complexity.

Navigated Acetabular Cup Fixation for Acetabular Deformity or Revision Total Hip Arthroplasty

Purpose

To evaluate the usefulness of navigated acetabular cup fixation for total hip arthroplasty in patients with acetabular deformity or revision total hip arthroplasty.

Materials and Methods

This study enrolled 28 patients with at least 12 months' follow-up. The safe zone of the acetabular cup was defined as 40°±10°in inclination and 15°±10°in anteversion. The authors used the navigation and radiographic data to determine whether the acetabular cup was located within the safe zone or not. To evaluate the clinical outcomes, preoperative and last follow-up Harris hip scores were checked, and the occurrence of complications was evaluated.

Results

According to the navigation data, the mean inclination and anteversion were 38.5°±4.7°(range, 32°-50°) and 16.6°±4.0°(range, 8°-23°), respectively. According to the radiographic data the mean inclination and anteversion were 40.5°±4.6°(range, 32°-50°) and 19.4°±4.2°(range, 8°-25°), respectively. In both cases, all values were within the safe zone. Harris hip score was improved in all patients from preoperative 52.3±14.4 points (range, 29-87 points) to 88.0±9.0 points (range, 65-99 points) at the last follow-up. There was no dislocation or loosening of both cases.

Conclusion

Navigated acetabular cup fixation is a useful technique for total hip arthroplasty in patients with acetabular deformity or revision total hip arthroplasty because it prevents the malposition and related complications.

A complete-pelvis segmentation framework for image-free total hip arthroplasty (THA): methodology and clinical study

BACKGROUND

Complete-pelvis segmentation in antero-posterior pelvic radiographs is required to create a patient-specific three-dimensional pelvis model for surgical planning and postoperative assessment in image-free navigation of total hip arthroplasty.

METHODS

A fast and robust framework for accurately segmenting the complete pelvis is presented, consisting of two consecutive modules. In the first module, a three-stage method was developed to delineate the left hemi-pelvis based on statistical appearance and shape models. To handle complex pelvic structures, anatomy-specific information processing techniques were employed. As the input to the second module, the delineated left hemi-pelvis was then reflected about an estimated symmetry line of the radiograph to initialize the right hemi-pelvis segmentation. The right hemi-pelvis was segmented by the same three-stage method,

RESULTS

Two experiments conducted on respectively 143 and 40 AP radiographs demonstrated a mean segmentation accuracy of 1.61±0.68 mm. A clinical study to investigate the postoperative assessment of acetabular cup orientations based on the proposed framework revealed an average accuracy of 1.2°±0.9° and 1.6°±1.4° for anteversion and inclination, respectively. Delineation of each radiograph costs less than one minute.

CONCLUSIONS

Despite further validation needed, the preliminary results implied the underlying clinical applicability of the proposed framework for image-free THA.

Optimal anterior femoral offset for functional range of motion in total hip arthroplasty--a computer simulation study

PURPOSE

Compared to medial femoral offset (MFO), the role of anterior femoral offset (AFO) on range of motion (ROM) in total hip arthroplasty (THA) has not been fully examined. We therefore defined AFO as the anterior distance from the centre of the femoral head to the proximal femoral axis in the sagittal plane and determined the optimal AFO required for ROM needed for activities of daily living using a computer-simulated THA model.

METHODS

Various AFOs were obtained by changing stem anteversion (stem-AV) and stem tilt in the sagittal plane (stem-tilt) using a CT-based simulation software. The required ROM was defined as: flexion ≥ 110°, internal rotation at 90° flexion (IR) ≥ 30°, external rotation (ER) ≥ 30°, and extension ≥ 30°, and we determined AFO and MFO to satisfy required ROM.

RESULTS

AFO was positively correlated with stem-AV and anterior stem-tilt. MFO was negatively correlated with stem-AV and not influenced by stem-tilt. Flexion and IR increased with both increased AFO and MFO, whereas extension and ER decreased with increased AFO. A smoothing spline curve showed the optimal AFO and MFO for required ROM to be from 15 mm to 25 mm on average and more than 32.1 mm, respectively.

CONCLUSIONS

This is the first study to show that AFO directly influenced ROM in THA. Optimal AFO as well as MFO should be reconstructed to achieve sufficient ROM.

Partial greater trochanter osteotomy for hip reduction in total hip arthroplasty for high dislocated hip: a preliminary report

Background

Hip reduction in total hip arthroplasty for high dislocated hips is difficult. Various femur osteotomy procedures have been used for hip reduction, but these methods increase operative time and risk of nonunion. We investigated the efficacy of a novel partial greater trochanter osteotomy technique for hip reduction in total hip arthroplasty for patients with high hip dislocation.

Methods

Twenty-one patients (23 hips) with high dislocated hip were treated with total hip arthroplasty that included partial greater trochanter osteotomy, i.e., the upper 2/3 greater trochanter was resected, and the gluteus medius muscle attachment was spared. The clinical outcome was evaluated by comparing the Harris hip scores and radiographic exam results, obtained before surgery and at follow-ups.

Results

Follow-ups of 21 patients ranged from 13 to 56 months. The mean Harris hip score increased from preoperative 55.0 (36–69) to postoperative 86.1 (71–93; P = 0.00). The average preoperative leg length discrepancy in patients with unilateral high hip dislocation was 46 mm (28–65 mm); postoperatively leg length discrepancy was less than 1 cm in 11 patients, between 1 and 2 cm in 8 patients, and more than 2 cm in 2 patients. The average leg lengthening at the time of surgery was 36 mm (24–54 mm). Trendelenburg’s gait changed from positive to negative in 20 hips by the last follow-up. No nerve injury occurred postoperative.

Conclusion

Partial greater trochanter osteotomy is an effective method to render hip reduction in total hip arthroplasty for patients with high dislocation of the hip.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2474-15-293) contains supplementary material, which is available to authorized users.

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

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

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

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

[Risk factors for total hip arthroplasty dislocation and its functional outcomes]

OBJECTIVES

To evaluate risk factors for dislocation after primary total hip arthroplasty (THA), and its functional outcomes.

MATERIAL AND METHODS

A retrospective study was conducted on 22 cases with dislocation and 431 controls without dislocation, all performed with lateral access. The data were collected prospectively with a minimum follow-up of 5 years. Patient related factors, from primary surgery, and position of components on simple radiographs were analyzed. Harris and Merle D'Aubigné hip scores, and short Womac questionnaire were used.

RESULTS

Demographic, patient-related or surgical technique factors were not risk predictors of dislocation. With regard to position of components, an acetabular abduction >50° (p = 0.003) and anteversion lower or higher than 10°- 20° (p = 0.044) were risk factors. Controls and dislocation treated conservatively had similar outcomes, and in both were better than in those treated with surgical revision (p = 0.03).

DISCUSSION

Factors relating to the patient and soft tissues status may influence the stability of the arthroplasty, but malposition of the acetabular component seems to be the most important and common risk factor for dislocation.

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

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

Predictability of Acetabular Component Angular Change with Postural Shift from Standing to Sitting Position

BACKGROUND

The angles of the acetabular component of a total hip replacement change with body postural changes, and this change can affect stability and wear. We sought to correlate the intraoperative angles of inclination and anteversion of the cup with the changes in these angles when patients moved from standing to sitting and determine if these changes were predictable.

METHODS

Eighty-five patients (eighty-five hips) had sagittal (lateral) spinopelvic radiographs made while they were standing and while they were sitting before and after undergoing total hip replacement. The spinosacral tilt and the pelvic tilt were measured on these radiographs. The angles of acetabular inclination and anteversion achieved at surgery changed during sitting. Each patient was classified according to the stiffness of the spine/pelvis as measured by the change in posterior sacral or pelvic tilt between the standing and sitting positions. The magnitude of change of the sagittal cup position (termed ante-inclination) was correlated to the stiffness classification of the pelvis. An experimental phantom model reproduced possible combinations of intraoperative inclination and anteversion and correlated them to sagittal ante-inclination according to pelvic tilt.

RESULTS

The pelves with normal stiffness tilted posteriorly 20° to 35° with the postural change from standing to sitting. Ante-inclination of the acetabular cup averaged 29.6° ± 8.4° (95% confidence interval [CI] = 13.1° to 46°) with standing and 54.6° ± 10.2° (95% CI = 44.4° to 64.8°) with sitting. The stiff pelves had a mean of 4° less tilt than those with normal stiffness and 13° less than the hypermobile pelves with the postoperative sitting position. The phantom model showed ante-inclination could be predicted by measuring the preoperative degrees of change in sacral/pelvic tilt from standing to sitting.

CONCLUSIONS

Ante-inclination during sitting results in a more vertical acetabular cup, which can result in hip instability, especially drop-out dislocation, and edge-loading wear. Patients with supine coronal cup inclination of ≥50° and anteversion of ≥25° and those with a hypermobile pelvis are at risk. It is the pelvic spatial position during postural change that creates the postoperative consequences of the surgical cup placement.

Morphological study of the newly designed cementless femoral stem

A morphology study was essential to the development of the cementless femoral stem because accurate dimensions for both the periosteal and endosteal canal ensure primary fixation stability for the stem, bone interface, and prevent stress shielding at the calcar region. This paper focused on a three-dimensional femoral model for Asian patients that applied preoperative planning and femoral stem design. We measured various femoral parameters such as the femoral head offset, collodiaphyseal angle, bowing angle, anteversion, and medullary canal diameters from the osteotomy level to 150 mm below the osteotomy level to determine the position of the isthmus. Other indices and ratios for the endosteal canal, metaphyseal, and flares were computed and examined. The results showed that Asian femurs are smaller than Western femurs, except in the metaphyseal region. The canal flare index (CFI) was poorly correlated (r < 0.50) to the metaphyseal canal flare index (MCFI), but correlated well (r = 0.66) with the corticomedullary index (CMI). The diversity of the femoral size, particularly in the metaphyseal region, allows for proper femoral stem design for Asian patients, improves osseointegration, and prolongs the life of the implant.

Risk of edge-loading and prosthesis impingement due to posterior pelvic tilting after total hip arthroplasty

BACKGROUND

Proper implant orientation is essential for avoiding edge-loading and prosthesis impingement in total hip arthroplasty. Although cup orientation is affected by a change in pelvic tilt after surgery, it has been unclear whether surgeons can prevent impingement and edge-loading by proper positioning by taking into account any change in pelvic alignment associated with alteration of hip range of motion.

METHODS

We simulated implant orientation without edge-loading and prosthesis impingement, even with a change in pelvic tilt and associated change in hip range of motion after surgery, by collision detection using implant models created with computer-aided design.

FINDINGS

If posterior pelvic tilting with a corresponding hyperextension change in hip range of motion after surgery remains within 10°, as occurs in 90% of cases, surgeons can avoid edge-loading and impingement by correctly orienting the implant, even when using a conventional prosthesis. However, if a 20° change occurs after surgery, it may be difficult to avoid those risks.

INTERPRETATION

Although edge-loading and impingement can be prevented by performing appropriate surgery in most cases, even when taking into account postoperative changes in pelvic tilt, it may also be important to pay attention to spinal conditions to ensure that pelvic tilting is not extreme because of increasing kyphosis.

The T-line as an intraoperative landmark for reproducing the native femoral anteversion during hip arthroplasty

INTRODUCTION

Three-dimensional computed tomographic (CT)-based preoperative planning for total hip arthroplasty (THA) enabled us to evaluate the cut surface of the femoral neck osteotomy. When we planned the stem placement in 20° of anteversion, we noticed that the line connecting the trochanteric fossa and the middle of the medial cortex of the femoral neck (T line) was coincident with the component torsion in many cases. We attempted to evaluate the accuracy of the T line for reproducing the native femoral anteversion during THA comparing it with the midcortical line, the reference guide previously reported by Suh.

MATERIALS AND METHODS

The institutional review board allowed a retrospective review of CT images of 100 normal hip joints. We performed virtual THA using the non-anatomic straight stem at three different cutting heights of 5, 10, or 15 mm above the lesser trochanter. The anteversion of the stem implanted parallel to the T line or midcortical line was measured.

RESULTS

The mean difference of the stem anteversion using the T line and the native femoral anteversion was -0.77º (95 % CI: -1.92º to 0.38º), 0.69º (95 % CI: -0.42º to 1.79º) and 3.38º (95 % CI: 2.29º-4.46º) at cutting heights of 5, 10 and 15 mm, respectively. Using the midcortical line, stems tended to retroversion.

CONCLUSIONS

Aligning the stem parallel to the T line on the cut surface provides a good reproduction of the femoral anteversion. The T line can be an useful intraoperative reference guide for the anteversion of the femoral component in THA for patients without severe hip deformity.

Correlation of Structural Bony Abnormalities and Mechanical Symptoms of Hip Joints

PURPOSE

The purpose of this study is to determine structural bony abnormalities predisposing for femoroacetabular impingement by comparison of patients with and without mechanical symptoms.

MATERIALS AND METHODS

We conducted this comparative study on 151 patients (151 hips; mean age 44.8 years; range 16-73 years) with mechanical symptoms with results of multi-detector computed tomography (MDCT) arthrography (the symptomatic group). Each patient was matched with a control who underwent MDCT due to ureter stone (the asymptomatic group) in terms of age, gender, site (right or left), and time at diagnosis. Acetabular evaluations, which included cranial and central anteversion and anterior and lateral center edge angles and femoral measurements, were performed. In addition, we evaluated the prevalence and characteristics of structural bone abnormalities between the two groups.

RESULTS

The prevalence for patients who had at least one structural bony abnormality in the symptomatic and asymptomatic groups was 80.1% (121/151) and 54.3% (82/151), respectively (odds ratio: 3.39, 95% confidence interval: 2.30-5.66; P<0.001). The most common osseous abnormality was the isolated Pincer type in both groups: 89 (73.6%) of 121 hips with an osseous abnormality in the symptomatic group and 57 (69.5%) of 82 hips with an osseous abnormality in the asymptomatic group. By analysis of CT arthrography in symptomatic patients, a labral tear was found in 107 hips (70.9%), and 86 (80%) of these hips had a structural bony abnormality.

CONCLUSION

A significantly greater prevalence rate of structural bony abnormality was observed for the symptomatic group than for the asymptomatic group. These findings are helpful for development of appropriate treatment plans.

Intraoperative validation of navigated limb measurements in THA using a pinless femoral array

Appropriate limb length (LL) and femoral offset (OS) after total hip arthroplasty (THA) are crucial for a successful and lasting outcome. However, intraoperative assessment is difficult. Computed navigation is effective but the use of radiation and of invasive bone references is cause of concern. Imageless, pinless navigation systems have been shown to be accurate in experimental studies. However, almost no clinical validation has been performed. We used a minimally-invasive computer-navigated system (MICNS) in conjunction with an imageless measurement technique for implanting 60 consecutive THAs. Head/neck trial components of different size were applied, and the differences in LL and femoral OS measurements were recorded and compared to the implant manufacturer's specifications, corrected for the anatomical variations of each patient. The imageless MICNS revealed a valid and accurate intra-operative tool for measuring LL and femoral OS in vivo.

An analysis of the best method for evaluating anteversion of the acetabular component after total hip replacement on plain radiographs

Several radiological methods of measuring anteversion of the acetabular component after total hip replacement (THR) have been described. These studies used different definitions and reference planes to compare methods, allowing for misinterpretation of the results. We compared the reliability and accuracy of five current methods using plain radiographs (those of Lewinnek, Widmer, Liaw, Pradhan, and Woo and Morrey) with CT measurements, using the same definition and reference plane. We retrospectively studied the plain radiographs and CT scans in 84 hips of 84 patients who underwent primary THR. Intra- and inter-observer reliability were high for the measurement of inclination and anteversion with all methods on plain radiographs and CT scans. The measurements of inclination on plain radiographs were similar to the measurements using CT (p = 0.043). The mean difference between CT measurements was 0.6° (-5.9° to 6.8°).

Measurements using Widmer’s method were the most similar to those using CT (p = 0.088), with a mean difference between CT measurements of -0.9° (-10.4° to 9.1°), whereas the other four methods differed significantly from those using CT (p < 0.001).

This study has shown that Widmer’s method is the best for evaluating the anteversion of the acetabular component on plain radiographs.

Cite this article: Bone Joint J 2014; 96-B:597–603.

Conversion total hip arthroplasty after previous transtrochanteric rotational osteotomy for osteonecrosis of the femoral head

The results of conversion total hip arthroplasty (THA) after failed transtrochanteric rotational osteotomy (TRO) are still controversial. We retrospectively reviewed 18 patients with ONFHs who had been treated previously by TRO and were later converted to THAs (conversion group). We made a matched control group of 18 primary THAs for ONFH done by same hip surgeon (PTHA group). There was an improvement in the Harris hip score and WOMAC score at the final follow-up but the improvement was not statistically significant between the two groups. Only internal rotation was significantly better in the PTHA group than in the conversion group. THA after TRO provides satisfactory clinical and radiological outcomes with no significant increase in perioperative morbidity in comparison with that in the primary THA.

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

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

Total hip arthroplasty using imageless computer-assisted hip navigation: a prospective randomized study

In a prospective randomized study of two groups of 65 patients each, we compared the acetabular component position when using the imageless navigation system compared to the freehand conventional technique for cementless total hip arthroplasty. The position of the component was determined postoperatively on computed tomographic scans of the pelvis. There was no significant difference for postoperative mean inclination (P = 0.29), but a significant difference for mean postoperative acetabular component anteversion (P = 0.007), for mean deviation of the postoperative anteversion from the target position of 15° (P = 0.02) and for the outliers regarding inclination (P = 0.02) and anteversion (P < 0.05) between the computer-assisted and the freehand-placement group. Our results demonstrate the importance of imageless navigation for the accurate positioning of the acetabular component.

Total hip arthroplasty using large-diameter metal-on-metal articulation in patients with neuromuscular weakness

The purpose of this prospective study was to evaluate the clinical and functional outcomes of THA using large-diameter metal-on-metal articulation in patients with neuromuscular weakness. Nineteen consecutive patients (19 hips) with neuromuscular weakness and displaced femoral neck fractures were enrolled. Functional improvement and recovery, radiological evaluation of THA and surgical morbidity were assessed. Mean Harris hip and WOMAC scores at final follow-up were 81.0 and 42.9, respectively. At final follow-up, no dislocation, metal hypersensitivity, or osteolysis was observed and no patient required revision of THA. The findings of this study indicate that the functional results of THA using large-diameter metal-on-metal articulation in patients with neuromuscular weakness can produce satisfactory outcomes with early functional recovery and a low dislocation rate.

Risk factors for poor hip flexion after total hip arthroplasty for the treatment of ankylosing spondylitis a multivariate analysis

The purpose of this study is to investigate the clinical and radiographic results of total hip arthroplasty (THA) for the treatment of ankylosing spondylitis (AS) and to evaluate the effects of patient, prosthesis design, and surgical technique-related risk factors on postoperative functional results. We retrospectively reviewed the clinical and radiographic results of THA performed in 167 hips for 100 patients with AS. The average follow-up period was 54.8 months (range, 32-129 months). The hip passive-flexion arc averaged only 0 ° (0-40.0 °) before surgery, compared with 100.0 ° (85.0-110.0 °) at the most recent follow-up examination (P < 0.001). Multivariate regression demonstrated that significant variables for postoperative hip flexion were degree of preoperative flexion contracture, preoperative level of C-reactive protein, use of a 32-mm femoral head, and postoperative heterotopic ossification. In patients with AS with severe pain, limited motion and posture, as well as deformity, the overall outcomes after THA were found to be favorable with an encouraging midterm prosthetic survivorship, a low complication rate and a high level of patients' satisfaction. It seemed these patients were particularly predisposed to relative poor range of motion of the involved hips after THA which was closely related to patients' satisfaction. The surgeons should pay careful attention to all possible risk factors perioperatively and develop a comprehensive treatment regimen.