[Clinical examination of the hip joint in adults]

Inaccurate offset restoration in total hip arthroplasty results in reduced range of motion

Offset restoration in total hip arthroplasty (THA) is associated with postoperative range of motion (ROM) and gait kinematics. We aimed to research into the impact of high offset (HO) and standard stems on postoperative ROM. 121 patients received cementless THA through a minimally-invasive anterolateral approach. A 360° hip ROM analysis software calculated impingement-free hip movement based on postoperative 3D-CTs compared to ROM values necessary for activities of daily living (ADL). The same model was then run a second time after changing the stem geometry between standard and HO configuration with the implants in the same position. HO stems showed higher ROM for all directions between 4.6 and 8.9° (p < 0.001) compared with standard stems but with high interindividual variability. In the subgroup with HO stems for intraoperative offset restoration, the increase in ROM was even higher for all ROM directions with values between 6.1 and 14.4° (p < 0.001) compared to offset underrestoration with standard stems. Avoiding offset underrestoration resulted in a higher amount of patients of over 20% for each ROM direction that fulfilled the criteria for ADL (p < 0.001). In contrast, in patients with standard stems for offset restoration ROM did increase but not clinically relevant by offset overcorrection for all directions between 3.1 and 6.1° (p < 0.001). Offset overcorrection by replacing standard with HO stems improved ROM for ADL in a low number of patients below 10% (p > 0.03). Patient-individual restoration of offset is crucial for free ROM in THA. Both over and underrestoration of offset should be avoided.

Risk Factors and Cup Protrusion Thresholds for Symptomatic Iliopsoas Impingement After Total Hip Arthroplasty: A Retrospective Case-Control Study

BACKGROUND

Groin pain and functional limitations may occur after total hip arthroplasty (THA) due to iliopsoas impingement (IPI). We aimed to determine the risk factors and thresholds of cup protrusion for symptomatic IPI.

METHODS

This retrospective case-control study evaluated 569 primary THAs performed by a single surgeon in a single center. In all THAs, the cup was inserted with the assistance of the computed tomography-based navigation system. Twenty-two THAs (3.9%) were identified to have symptoms of IPI and included in the IPI group. Control group 1 comprised 547 THAs. Control group 2 (66 THAs) was formed by recruiting 3 data-matched controls per patient in control group 1. Risk factors for IPI were assessed in the IPI group and control group 1. Further analysis was performed in the IPI group and control group 2 to evaluate cup protrusion parameters measured on computed tomography images and radiographs.

RESULTS

Multivariate logistic regression analysis confirmed that the anterolateral approach was associated with a higher risk of IPI (odds ratio [OR], 4.20); however, its goodness of fit was low. Axial protrusion length ≥12 mm (OR, 23.29; sensitivity = 72.7; specificity = 91.0) and sagittal protrusion length ≥4 mm (OR, 61.60; sensitivity = 86.4; specificity = 78.8) were determined as independent predictors of symptomatic IPI. In the linear regression analyses, higher native acetabular version and lower cup anteversion and inclination were related to cup protrusion.

CONCLUSIONS

This study determined the thresholds of cup protrusion length for IPI and identified associated factors increasing cup protrusion, which are useful for surgeons in determining cup position and alignment.

Navigation is Equal to Estimation by Eye and Palpation in Preventing Psoas Impingement in THA

BACKGROUND

Iliopsoas tendon impingement is one possible reason for persistent groin pain and diminished functional outcome after THA. So far, estimation by eye and palpation is the standard procedure to intraoperatively assess the distance of the cup to the anterior rim. However, novel technologies such as imageless navigation enable intraoperative measurements of the cup in relation to the psoas tendon and bony landmarks.

QUESTIONS/PURPOSES

We asked whether psoas impingement (1) can be reduced using imageless navigation compared with the standard technique and (2) is associated with specific patient characteristics. Furthermore, we investigated (3) if anterior cup protrusion (overhang) is associated with lower outcome scores for pain and function.

METHODS

The current study is a reanalysis of data from a randomized controlled trial evaluating navigation for THA; 135 patients were randomized for surgery with or without the use of imageless navigation. The risk for anterior protrusion of the cup above the acetabular rim and thus potential psoas impingement, defined as an overhang of the cup above the anterior acetabular rim as measured on postoperative CT, was either controlled with the help of navigation or standard control by eye and palpation intraoperatively. Postoperatively, the anterior protrusion of the cup above the acetabular rim was measured on three-dimensional (3-D) CT by a blinded, external institute. In addition to patient-related outcome measures, the Harris hip score, Hip disability and Osteoarthritis Outcome Score, and EuroQol were obtained 1 year postoperatively. Altogether 123 data sets were available for primary analysis and 115 were available for 1-year followup.

RESULTS

There was no difference, with the numbers available, between the navigated and the control groups in terms of the mean distance of the cup below the anterosuperior acetabular rim (3.9 mm; -5.3 to 12.6 mm versus 4.4 mm; -7.9 to 13.7 mm; p = 0.72) or the anteroinferior acetabular rim (4.7 mm; -6.2 to 14.8 mm versus 4.2 mm; -7.1 to 16.3 mm; p = 0.29). There was no difference, with the numbers available, in terms of the proportion of cups with anterior overhang (7%, four of 57 versus, 15%, 10 of 66; p = 0.16), respectively. After controlling for potential confounding variables such as cup inclination, cup size, patient age, BMI, stage of arthritis, and length of skin incision, we found cup anteversion (hazard ratio [HR], 0.87; 95% CI, 0.81-0.93; p < 0.001) and female sex (HR, 3.88; 95% CI, 1.01-14.93; p = 0.049) were associated with a propensity to potential psoas impingement. With the numbers available, there were no differences observed in clinical scores between groups with and without anterior cup protrusion.

CONCLUSIONS

We found no differences between imageless navigation and estimation by eye and palpation in preventing potential psoas impingement. Despite the comparable clinical outcome for patients with and without cup protrusion, the orthopaedic surgeon should be especially aware of propensity for psoas impingement in women.

LEVEL OF EVIDENCE

Level II, therapeutic study.

Even the Intraoperative Knowledge of Femoral Stem Anteversion Cannot Prevent Impingement in Total Hip Arthroplasty

BACKGROUND

In this prospective study of 66 patients undergoing cementless total hip arthroplasty through a minimally invasive anterolateral approach, we evaluated the impact of an intraoperative hybrid combined anteversion technique on postoperative range of motion (ROM).

METHODS

After navigation of femoral stem anteversion, trial acetabular components were positioned manually, and their position recorded with navigation. Then, final components were implanted with navigation at the goals prescribed by the femur-first impingement detection algorithm. Postoperatively, three-dimensional computed tomographies were performed to determine achieved component position and model impingement-free ROM by virtual hip movement, which was compared with published values necessary for activities of daily living. This model was run a second time with the implants in the position selected by the surgeon rather than the navigation program. In addition, we researched into risk factors for ROM differences between the freehand and navigated cup position.

RESULTS

We found a lower flexion of 8.3° (8.8°, P < .001) and lower internal rotation of 9.2° (9.5°, P < .001) for the freehand implanted cups in contrast to a higher extension of 9.8° (11.8°, P < .001) compared with the navigation-guided technique. For activities of daily living, 58.9% (33/56) in the freehand group compared with 85.7% (48/56) in the navigation group showed free flexion (P < .001) and similarly 50.0% (28/56) compared with 76.8% (43/56) free internal rotation (P < .001). Body mass index, incision length, and cup size were identified as independent risk factors for reduced flexion and internal rotation in the freehand group.

CONCLUSION

For implementation of a combined anteversion algorithm, intraoperative alignment guides for accurate cup positioning are required using a minimally invasive anterolateral approach. Obese patients are especially at risk of cup malpositioning.

Novel measurement method on plain radiographs to predict postoperative stem anteversion in cementless THA

Preoperative knowledge of femoral stem anteversion can reduce instability and impingement especially using the standard "cup first" technique in cementless total hip arthroplasty (THA). In this study, we asked whether stems at risk of retroversion or high anteversion (>20°) can be detected preoperatively using hip radiographs in two planes (anteroposterior and Lauenstein). In 123 patients undergoing cementless THA using a non-anatomic, non-modular, straight stem, low centered hip radiographs in two planes were obtained preoperatively and three-dimensional computed tomography (3D-CT) 6 week postoperatively. The novel developed Isthmus Ratio (iRatio) as the relation between canal isthmus and calcar isthmus in the anteroposterior and Lauenstein view was calculated by two observers twice in a 6-week interval. iRatio was compared to postoperative 3D-CT stem version measured by an independent and blinded, external institute. We found a correlation between mean radiographic iRatio and 3D-CT stem torsion of r = 0.578 (p < 0.0001). The observers had excellent agreements within (ICC ≥0.918) and between (mean CCC = 0.967) radiographic iRatio measurements. Eighty-one percent (21/26) of the retroverted cementless stems had a preoperative iRatio below 0.35 and 91% (10/11) of stems with an anteversion exceeding 20° an iRatio above 0.55, respectively. The novel iRatio represents a feasible and reliable method for analyzing anteversion of the final stem on plain radiographs before cementless THA with a straight, tapered stem. iRatios below 0.35 and above 0.55 represent a warning of retroversion and anteversion more than 20° of the final stem, respectively. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:2025-2030, 2016.

Visual intraoperative estimation of range of motion is misleading in minimally invasive total hip arthroplasty

INTRODUCTION

Generally range of motion (ROM) in total hip arthroplasty (THA) is intraoperatively assessed by eye. Can we assume that visual estimation of ROM is reliable?

METHODS

60 patients underwent cementless THA in a subgroup analysis of a clinical prospective trial using a minimally invasive anterolateral approach in lateral decubitus position. Four experienced surgeons intraoperatively estimated ROM visually by assessment of the femur relative to the alignment of the patient's pelvis. These estimations were compared with computer navigation measurements.

RESULTS

We found a mean difference between navigation measurements and intraoperative estimations by eye of -5.6° (±10.9°; -17° to 30°) for flexion, respectively, -0.4° (±10.7°; -24° to 30°) for extension, 8.7° (±9.0°; -10° to 34°) for abduction, 5.9° (±18.3°; -58° to 68°) for external rotation and -5.8° (±12.1°; -38° to 22°) for internal rotation. Multivariate analysis showed no association between the visual accuracy of estimation of ROM and patient characteristics, such as BMI, sex, grade of osteoarthritis and treatment side except for a significant correlation of visual accuracy of estimation of extension and the level of professional experience. Otherwise, the level of professional experience had no impact on the accuracy of estimation of ROM by eye.

CONCLUSIONS

Even the experienced surgeon's intraoperative estimation of ROM by eye is not reliable and differs up to 30° compared to objective measurements in minimally invasive THA. For accurate intraoperative assessment of ROM, the use of technical devices is recommended.

TRIAL REGISTRATION

DRKS00000739.

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

BACKGROUND

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

METHOD

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

RESULTS

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

CONCLUSION

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