Does Computer-Assisted Femur First THR Improve Musculoskeletal Loading Conditions?

Functional assessment in patients undergoing total hip arthroplasty

Aims

Conventional patient-reported surveys, used for patients undergoing total hip arthroplasty (THA), are limited by subjectivity and recall bias. Objective functional evaluation, such as gait analysis, to delineate a patient's functional capacity and customize surgical interventions, may address these shortcomings. This systematic review endeavours to investigate the application of objective functional assessments in appraising individuals undergoing THA.

Methods

The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines were applied. Eligible studies of THA patients that conducted at least one type of objective functional assessment both pre- and postoperatively were identified through Embase, Medline/PubMed, and Cochrane Central database-searching from inception to 15 September 2023. The assessments included were subgrouped for analysis: gait analysis, motion analysis, wearables, and strength tests.

Results

A total of 130 studies using 15 distinct objective functional assessment methods (FAMs) were identified. The most frequently used method was instrumented gait/motion analysis, followed by the Timed-Up-and-Go test (TUG), 6 minute walk test, timed stair climbing test, and various strength tests. These assessments were characterized by their diagnostic precision and applicability to daily activities. Wearables were frequently used, offering cost-effectiveness and remote monitoring benefits. However, their accuracy and potential discomfort for patients must be considered.

Conclusion

The integration of objective functional assessments in THA presents promise as a progress-tracking modality for improving patient outcomes. Gait analysis and the TUG, along with advancing wearable sensor technology, have the potential to enhance patient care, surgical planning, and rehabilitation.

A Workflow Change in Anterior Approach Total Hip Arthroplasty Leads to Improved Accuracy of Biomechanical Reconstruction Without Increased Risk of Complications

Background

During anterior approach total hip arthroplasty (THA), the femur may be an impediment for acetabular access, pushing reamers proximally and consequently altering the hip center. In an effort to address this, the senior author changed the surgical workflow from acetabulum first (AF) to femur first (FF). The objective of this study was to compare the precision of biomechanical hip reconstruction and clinical outcomes between the FF and AF techniques.

Methods

This is a retrospective, case-control study of 267 anterior THAs (132 AF and 135 FF). A normal, contralateral hip was used to determine the native biomechanical parameters. Using a calibrated software program, radiographic measurements were performed to calculate the hip center position, femoral offset, global offset, and leg length of the operative and native hips using 2-week postoperative anteroposterior pelvis radiographs. Demographics, operative information, hemoglobin change, and complication data were obtained. Functional outcomes were assessed with the Hip Dysfunction and Osteoarthritis Outcome Score for Joint Replacement survey at 1 year postoperatively.

Results

The groups exhibited similar demographic characteristics. The FF group demonstrated significantly more accurate and more precise reconstruction of horizontal and vertical hip centers, femoral offset, and leg length. There was no significant difference in operative time, hemoglobin change, complication rate, or Hip Disability and Osteoarthritis Outcome Score, Joint Replacement scores between groups.

Conclusions

The FF technique allowed for more accurate and precise reconstruction of the hip center, leg length, and offset in THA than the AF workflow. Furthermore, the FF approach demonstrated no significant differences in complication rate or blood loss, nor in clinical outcomes.

Level of Evidence

Therapeutic Study Level III.

Effect of the underlying cadaver data and patient-specific adaptation of the femur and pelvis on the prediction of the hip joint force estimated using static models

The prediction of the hip joint force (HJF) is a fundamental factor for the prevention of edge loading in total hip arthroplasty. Naturally, the loading of the liner of the acetabular component depends on the HJF acting on the artificial joint. In contrast to dynamic musculoskeletal models, static models for HJF prediction do not require motion analysis of the patient. However, patient-specific adaptability and validity of static models have to be scrutinized. In this study, a modular framework for HJF prediction using static models is introduced to compare the results of different cadaver templates that are the basis of most static and dynamic models, and different scaling laws for the patient-specific adaptation with in vivo HJF of ten patients for one-leg stance and level walking. The results revealed the significant effect of the underlying cadaver template used for the prediction of the HJF (p < 0.01). A higher degree of patient-specific scaling of the cadaver template often did not significantly reduce the prediction error. Three static models with the lowest prediction errors were compared to results of dynamic models from literature. The prediction error of the peak HJF of the static models (median absolute errors below 15% body weight in magnitude and below 5° in direction) was similar in magnitude and even smaller in direction compared to dynamic models. The necessary reduction of a load-based target zone for the prevention of edge loading due to the uncertainty of the HJF prediction has to be considered in the preoperative planning. The framework for HJF prediction is openly accessible at https://github.com/RWTHmediTEC/HipJointForceModel.

Uncemented femoral stem orientation and position in total hip arthroplasty: A CT study

In total hip arthroplasty (THA), accurate positioning of components is important for the functionality and long life of the implant. Femoral component version has been underinvestigated when compared with the acetabular cup. Accurate prediction of the femoral version on the preoperative plan is particularly important because a well-fitting uncemented stem will, by definition, press-fit into a version that is dictated by the anatomy of the proximal femur. A better understanding of this has recently become an unmet need because of the increased use of uncemented stems and of preoperative image-based planning. We present the first, three-dimensional (3D) comparison between the planned and achieved orientation and position of the femoral components in THA. We propose a comparison method that uses the 3D models of a, computed tomography-generated (CT-generated), preoperative plan and a postoperative CT to obtain the discrepancy in the six possible degrees of freedom. We ran a prospective study (level 2 evidence) of 30 patients undergoing uncemented THA to quantify the discrepancy between planned and achieved femoral stem orientation and position. The discrepancy was low for femoral stem vertical position and leg length, and varus-valgus and anterior-posterior orientation. The discrepancy was higher for femoral version with a mean (±SD) of -1.5 ± 7.8 deg. Surgeons should be aware of the variability of the eventual position of uncemented stems in THA and acknowledge the risk of achieving a less-than-optimal femoral version, different from the preoperative 3D CT plan.

The impact of hip implant alignment on muscle and joint loading during dynamic activities

BACKGROUND

Component alignment is an important consideration in total hip arthroplasty. The impact of changes in alignment on muscle forces and joint contact forces during dynamic tasks are not well understood, and have the potential to influence surgical decision making. The objectives of this study were to assess the impact of femoral head/stem and cup component placement on hip muscle and joint contact forces during tasks of daily living and to identify which alignment parameters have the greatest impact on joint loading.

METHODS

Using a series of strength-calibrated, subject-specific musculoskeletal models of patients performing gait, sit-to-stand and step down tasks, component alignments were perturbed and joint contact and muscle forces evaluated.

FINDINGS

Based on the range of alignments reported clinically, variation in head/stem anteversion-retroversion had the largest impact of any degree of freedom throughout all three tasks; average contact forces 413.5 (319.1) N during gait, 262.7 (256.4) N during sit to stand, and 572.7 (228.1) N during the step down task. The sensitivity of contact force to anteversion-retroversion of the head/stem was 31.5 N/° for gait, which was similar in magnitude to anterior-posterior position of the cup (34.6 N/m for gait). Additionally, superior-inferior cup alignment resulted in 16.4 (4.9)° of variation in the direction of the hip joint contact force across the three tasks, with the most inferior cup placements moving the force vector towards the cup equator at the point of peak joint contact force.

INTERPRETATION

A quantitative understanding of the impact and potential tradeoffs when altering component alignment is valuable in supporting surgical decision making.

Leg length and offset differences above 5mm after total hip arthroplasty are associated with altered gait kinematics

We aimed to investigate the relationship between postoperative leg length/offset (LL/OS) reconstruction and gait performance after total hip arthroplasty (THA). In the course of a prospective randomized controlled trial, 60 patients with unilateral hip arthrosis received cementless THA through a minimally-invasive anterolateral surgical approach. One year post-operatively, LL and global OS restoration were analyzed and compared to the contralateral hip on AP pelvic radiographs. The combined postoperative limb length/OS reconstruction of the operated hip was categorized as restored (within 5mm) or non-restored (more than 5mm reduction or more than 5mm increment). The acetabular component inclination, anteversion and femoral component anteversion were evaluated using CT scans of the pelvis and the femur. 3D gait analysis of the lower extremity and patient related outcome measures (HHS, HOOS, EQ-5D) were obtained pre-operatively, six months and twelve months post-operatively by an observer blinded to radiographic results. Component position of cup and stem was comparable between the restored and non-restored group. Combined LL and OS restoration within 5mm resulted in higher Froude number (p<0.001), normalized walking speed (p<0.001) and hip range-of-motion (ROM) (p=0.004) during gait twelve months postoperatively, whereas gait symmetry was comparable regardless of LL and OS reconstruction at both examinations. Clinical scores did not show any relevant association between the accuracy of LL or OS reconstruction and gait six/twelve months after THA. In summary, postoperative LL/OS discrepancies larger than 5mm relate to unphysiological gait kinematics within the first year after THA. DRKS00000739, German Clinical Trials Register.