A three-dimensional parameterized and visually kinematic simulation module for the theoretical range of motion of total hip arthroplasty

A novel preoperative prosthetic position planning algorithm for total hip arthroplasty based on the no-impingement principle: A case study

Most preoperative planning calculations of impingement-free range of motion (IFROM) and impingement-free safe zone (IFSZ) rarely consider non-standard shaped prostheses and bony impingement (BI) for total hip arthroplasty (THA). This research developed a novel algorithm that considers BI, prosthetic impingement, pelvic tilt angle (PT) in the sagittal plane, and non-standard-shaped hip prostheses. This research aimed to investigate the effect of BI and PT on hip IFROM, IFSZ, and the BI rate. Using this algorithm to calculate a case, we found that when considering BI, (1) the upper limit of the hip IFROM was decreased, and the different PT affected the upper limit of the hip IFROM of various movements; (2) the BI rate of the flat-rim liner in standing and sitting postures were 54.6% and 67%; and (3) the maximum IFSZ size of the flat-rim liner was reduced by 12%, the reduction rate of the combined pelvic position with a non-zero IFSZ size was 83.2% for the flat-rim liner. Consideration of BI further reduces the IFROM, the IFSZ size, and the number of the combined position of the pelvis with a non-zero IFSZ size of the hip joint. Importantly, this algorithm provides a reliable tool for personalized prosthesis positioning for THA. This algorithm has excellent applications in personalized surgical planning and surgical robotics.

A novel algorithm to efficiently calculate the impingement-free range of motion of irregularly-shaped total hip arthroplasty components

There is great difficulty in quickly calculating the impingement-free range of motion (IFROM) of hip components with complex shapes after total hip arthroplasty. We have established a new algorithm to investigate the effect of different shapes of hip components on the IFROM and impingement-free safe zone (IFSZ). Then find the best combination of hip prosthesis and the optimal mounting position of the elevated-rim liner under different radiographic anteversion (RA) and radiographic inclination (RI) of the cup. We found the larger the opening angle of the beveled-rim liner and the smaller the cross-sectional area of the stem neck with an inverted teardrop cross-sectional shape, the greater the IFROM of the hip component. The beveled-rim liner in combination with the stem neck with an inverted teardrop-shaped cross-section could provide the greatest IFSZ (excluding the flat-rim liner). The optimal orientation of the elevated-rim liner was the posterior-inferior side (RI ≤ 37°), posterior-superior side (RI ≥ 45°), and posterior side (37° ≤ RI ≤ 45°). Our novel algorithm provides a solution to analyze the IFROM of any hip prosthesis with any complex shape. The shape and size of the cross-section of the stem neck, the orientation of the elevated rim, and the shape and opening angle of the liner are all critical factors for the quantitative calculation of the IFROM and mounting safe zone of the prosthesis. Stem necks with inverted teardrop cross-section and beveled-rim liner improved the IFSZ. The optimal direction of the elevated rim is not constant but varies with RI and RA.

Small Random Angular Variations in Pelvic Tilt and Lower Extremity Can Cause Error in Static Image-based Preoperative Hip Arthroplasty Planning: A Computer Modeling Study

BACKGROUND

Many THA simulation models rely on a limited set of preoperative static radiographs to replicate sagittal pelvic tilt during functional positions and to recommend an implant orientation that minimizes the risk of prosthetic impingement. However, possible random changes in pelvic or lower extremity angular motions and the effect of coronal and axial pelvic tilt are not included in these preoperative models.

QUESTIONS/PURPOSES

(1) Can prosthetic impingement occur if the pelvic tilt or lower extremity alignment randomly varies up to ± 5° from what is measured on a single preoperative static radiographic image? (2) Do changes in coronal and axial pelvic tilt or lower extremity alignment angles have a similar effect on the risk of prosthetic impingement?

METHODS

A de-identified pelvis and lower-body CT image of a male patient without previous THA or lower extremity surgery was used to import the pelvis, femur, and tibia into a verified MATLAB computer model. The motions of standing, pivoting, sitting, sit-to-stand, squatting, and bending forward were simulated. THA implant components included a full hemispherical acetabular cup without an elevated rim, polyethylene liner without an elevated rim, femoral head (diameter: 28 mm, 32 mm, 36 mm, or 40 mm), and a triple-taper cementless stem with three different neck shaft angles (127°, 132°, or 135°) with a trapezoidal neck were used in this model. A static model (cup anatomical abduction 40°, cup anatomical anteversion 20°, stem anatomical anteversion 10°) with a predefined range of sagittal pelvic tilt and hip alignment (0° coronal or axial tilt, without random ± 5° change) was used to simulate each motion. We then randomly varied pelvic tilt in three different pelvic planes and hip alignments (flexion, extension, abduction, adduction, rotation) up to ± 5° and assessed the same motions without changing the implant's anatomical orientation. Prosthetic impingement as the endpoint was defined as mechanical abutment between the prosthetic neck and polyethylene liner. Multiple logistic regression was used to investigate the effect of variation in pelvic tilt and hip alignment (predictors) on prosthetic impingement (primary outcome).

RESULTS

The static-based model without the random variation did not result in any prosthetic impingement under any conditions. However, with up to ± 5° of random variation in the pelvic tilt and hip alignment angles, prosthetic impingement occurred in pivoting (18 possible combinations), sit-to-stand (106 possible combinations), and squatting (one possible combination) when a 28-mm or a 32-mm head was used. Variation in sagittal tilt (odds ratio 4.09 [95% CI 3.11 to 5.37]; p < 0.001), axial tilt (OR 3.87 [95% CI 2.96 to 5.07]; p < 0.001), and coronal tilt (OR 2.39 [95% CI 2.03 to 2.83]; p < 0.001) affected the risk of prosthetic impingement. Variation in hip flexion had a strong impact on the risk of prosthetic impingement (OR 4.11 [95% CI 3.38 to 4.99]; p < 0.001).

CONCLUSION

The combined effect of 2° to 3° of change in multiple pelvic tilt or hip alignment angles relative to what is measured on a single static radiographic image can result in prosthetic impingement. Relying on a few preoperative static radiographic images to minimize the risk of prosthetic impingement, without including femoral implant orientation, axial and coronal pelvic tilt, and random angular variation in pelvis and lower extremity alignment, may not be adequate and may fail to predict prosthetic impingement-free ROM.

CLINICAL RELEVANCE

Determining a safe zone for THA implant positioning with respect to impingement may require a dynamic computer simulation model to fully capture the range of possible impingement conditions. Future work should concentrate on devising simple and easily available methods for dynamic motion analysis instead of using a few static radiographs for preoperative planning.

Influencing factors for the increased stem version compared to the native femur in cementless total hip arthroplasty

PURPOSE

Stem version is not always equivalent to femoral neck version (native version) in cementless total hip arthroplasty (THA). We therefore examined the discrepancy of version between the native femoral neck and stem using pre- and postoperative computed tomography (CT), the level of the femur where the canal version most closely fit the stem version, and the factors influencing version discrepancy between the native femoral neck and stem.

METHODS

A total of 122 hips in 122 patients who underwent primary THA using a metaphyseal-fit stem through the postero-lateral approach were included. Pre- and postoperative CT images were utilized to measure native and stem version, and the version of the femoral canal at four levels relative to the lesser trochanter.

RESULTS

The mean native and stem versions were 28.1 ± 11.0° and 38.0 ± 11.2°, respectively, revealing increased stem version with a mean difference of 9.8° (p < 0.0001). A total of 84 hips (68.9 %) revealed an increase in version greater than 5°. Femoral canal version at the level of the lesser trochanter most closely approximated that of stem version. Among the factors analysed, both univariate and multivariate analysis showed that greater degrees of native version and anterior stem tilt significantly reduced the version discrepancy between the native femoral neck and stem version.

CONCLUSIONS

Since a cementless stem has little version adjustability in the femoral canal, these findings are useful for surgeons in preoperative planning and to achieve proper component placement in THA.

Surgeon error in performing intraoperative estimation of stem anteversion in cementless total hip arthroplasty

To examine the accuracy of intraoperative estimation of stem anteversion in total hip arthroplasty (THA), we compared the intraoperatively estimated stem anteversion (estimated prosthetic anteversion) to stem anteversion measured by postoperative computed tomography (true anteversion) in 73 hips in 73 patients. Estimated prosthetic anteversion was significantly greater than true anteversion by 5.8°, and the mean absolute value of surgeon error was 7.3° ranging from 11° underestimation to 25° overestimation. Surgeons tended to overestimate when the true anteversion was smaller. A multivariate analysis showed that advanced knee osteoarthritis significantly increased surgeon error. These results indicated that estimated prosthetic anteversion was generally larger than true anteversion and that the grade of knee osteoarthritis affected the degree of surgeon error.

Mathematical formulae to calculate the theoretical range of motion of prosthetic hip implants with non-circular neck geometry

Component design and position are major factors in achieving adequate range of motion post hip replacement. It is therefore important to understand how implant design and positioning impact the motion available before impingement. The Yoshimine-Ginbayashi equations allow the theoretical range of motion of total hip replacements to be calculated accurately and quickly. However, a significant limitation of these equations is that they can only be applied to femoral neck geometry with a circular cross section. The objective of the present study was to reformulate the equations to allow fast and accurate calculation of the range of motion for prostheses with any femoral neck geometry. Using vector analysis, formulae were derived such that the range of motion could be calculated from the cross section of the neck at the point of impingement, cup radius at the point of impingement, cup inclination angle, cup anteversion angle, neck angle of the femoral component from the transverse plane and neck anteversion. The range of motion was calculated for circular, truncated circle and free-form femoral neck geometry under a range of component positions. These values were successfully compared with those measured from analysis of solid models in three-dimensional computer-aided design software. The method of analysis presented offers a powerful new technique enabling hip prostheses to be analysed in an accurate and efficient manner, therefore facilitating optimisation of the design geometry, assessment of existing pre-clinical designs and clinical pre- or postoperative evaluation.