Factors affecting the potential for posterior bony impingement after 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.

Influence of stem length on sagittal alignment in total hip arthroplasty: a comparison between short and standard stems

BACKGROUND

Total hip arthroplasty (THA), a critical surgery for hip joint pain relief and mobility restoration, involves careful consideration of various factors, including stem length. Short stems are often chosen for their potential to reduce tissue damage and thigh pain. Precise alignment is necessary to alleviate complications such as stem loosening and fractures. We aimed to compare intramedullary insertion freedom and alignment changes between short and standard stems in THA. This study is based on preoperative planning simulations, highlighting the potential clinical implications.

METHODS

This retrospective study involved 102 hip joints (34 each from Dorr A, B, and C) undergoing initial THA between 2015 and 2017. A preoperative computed tomography scan was used to create three-dimensional bone models for planning virtual surgery, assessing stem insertion in flexion/extension, and measuring the anterior femoral offset. One-way repeated-measures analysis of variance was conducted to compare intramedullary insertion freedom and anterior femoral offset across the three Dorr classifications (A, B, and C). A paired t-test was used to compare intramedullary insertion freedom and anterior femoral offset between short and standard stems for each Dorr classification and between different medullary shapes.

RESULTS

Statistically significant differences were observed between the stem types (p < 0.05). Short stems demonstrated significantly greater intramedullary insertion freedom, with averages of 7.5°, 8.2°, and 9.1° for Dorr A, B, and C, respectively, compared with 4.3°, 5.0°, and 5.8° for standard stems. Additionally, the anterior femoral offset was significantly higher in short stems, with an average increase of 2.5 mm across classifications, compared to 1.2 mm in standard stems (p < 0.05).

CONCLUSION

Short stems offer enhanced intramedullary insertion freedom and improved anterior femoral offset, potentially leading to better alignment outcomes in THA. However, their increased freedom necessitates precise surgical planning, particularly in patients with wider medullary morphologies. These findings emphasize the importance of simulation-based planning in understanding the impact of stem length, while clinical studies are needed to validate these results.

Hip External Rotation Decreases Ischiofemoral Distance: A Positive Correlation Between Cadaveric and Fluoroscopic Studies

PURPOSE

To determine the effect of hip external rotation or extension/adduction on minimizing the ischiofemoral distance (IFD) and assess the correlation between cadaveric and fluoroscopic IFD measurements in different hip positions.

METHODS

This cadaveric study involved 33 hip joints from 17 embalmed cadavers. IFD, the distance between the lesser trochanter and lateral ischium, was measured in different hip positions: neutral, external rotation at 30°, and external rotation at 60° with the hip in both neutral extension and adduction as well as 10° hip extension and 10° hip adduction. Differences in IFD related to positions and correlation between cadaveric and fluoroscopic measurements were analyzed.

RESULTS

IFD measurements showed that the greatest reduction occurred at 60° of external hip rotation, with a significant difference observed only between neutral and 60° external rotation in cadaveric groups (7.60 ± 4.68 vs 5.05 ± 3.48, 95% CI, 0.14-4.96; P = .036). No substantial difference was observed between the extension and adduction positions. Positive correlations were observed between cadaveric and fluoroscopic measurements, especially in the neutral position (r = 0.492, P = .004), external rotation at 30° (r = 0.52, P = .002), external rotation at 60° (r = 0.419, P = .015), and the extension/adduction positions combined with neutral rotation (r = 0.396, P = .023).

CONCLUSIONS

The IFD significantly decreased with increasing degrees of hip external rotation, particularly at 60°. No significant reduction was observed in the extension/adduction positions. In addition, positive correlations were observed between cadaveric and fluoroscopic measurements for specific hip positions: neutral rotation, external rotation at 30° and 60°, and extension/adduction at 10° with neutral rotation.

CLINICAL RELEVANCE

Surgeons can use this knowledge to improve hip impingement assessment through radiography, focusing on positions in which IFD reduction is most notable. Understanding the relationship between hip positions and IFD can enhance the diagnosis of ischiofemoral impingement syndrome and benefit patient care and outcomes.

Analysis of posterior hip joint impingement about developmental dysplasia of the hip after total hip arthroplasty

BACKGROUND

Total hip arthroplasty is the preferred treatment for advanced hip osteoarthritis, yet complications like hip dislocation (0.2 %-10 %) persist due to factors such as implant design, positioning, surgical technique, and patient-specific conditions. Impingement between prosthetic components or the acetabulum and proximal femur is a primary cause of instability.

METHODS

A retrospective analysis of 120 patients (130 hips) undergoing total hip arthroplasty at XX Hospital (2011-2023) categorized patients by lateral center-edge angle: developmental dysplasia of the hip, borderline developmental dysplasia of the hip, and normal hip. ct imaging facilitated virtual 3D bone models for motion analysis, excluding cases with prior hip surgery or spinal fusion. Statistical analyses utilized the Mann-Whitney U test and one-way ANOVA.

FINDINGS

The developmental dysplasia of the hip group showed the highest posterior impingement frequency, significantly affecting range of motion in flexion, adduction, and external rotation compared to borderline developmental dysplasia of the hip and normal hip groups. Variations in femoral neck anteversion, lesser trochanter version, and ischiofemoral space were notable. Posterior impingement commonly occurred between the lesser trochanter and ischial tuberosity.

INTERPRETATION

Posterior bony impingement emerged as a predominant factor reducing range of motion and increasing dislocation risk, particularly in developmental dysplasia of the hip patients, challenging the conventional "safe zone" for implant positioning. Personalized surgical strategies tailored to individual bone morphology are crucial for enhancing total hip arthroplasty outcomes and minimizing complications, although limitations include the exclusion of soft tissue influences and focusing solely on range of motion until impingement occurs.

Safe Sex After Total Hip Arthroplasty: Using Computed Tomography-Based Robotics to Evaluate "At-Risk" Sexual Positions

BACKGROUND

Total hip arthroplasty (THA) can improve sexual satisfaction, but fear of dislocation can lead to sexual difficulties following this procedure. Previous kinematic research identified 4 sexual positions in women and 2 in men that were considered at risk for impingement. This study aimed to validate these findings using current robotic THA simulations.

METHODS

The 3-dimensional renderings from 12 patients who received computed tomography (CT)-based robotic THA were used to assess for prosthetic and/or bony impingement among 12 popular sexual positions. There were 9 cup orientations tested for each position (a combination of anteversion [0 °, 15 °, and 30 °] and inclination [40 °, 45 °, and 60 °]). The at-risk positions were tested again using the unique hip positions and cup orientations where previous geometric modeling data found impingement to occur.

RESULTS

Using mean hip positions, impingement occurred in at least 1 patient in 1 of the 12 positions for women (position 5) and 5 of the 12 positions for men (positions 1, 5, 8, 10, and 11). Among the at-risk positions, impingement occurred in none of the 2 at-risk women positions (0 of 17 cup orientations) and in both at-risk men positions (9 of 9 cup orientations for position 8 and 1 of 1 for position 11).

CONCLUSION

Recreating popular and at-risk sexual positions following THA with a CT-based robotics system yielded results that were inconsistent with previous geometric modeling data. Resolving these discrepancies is crucial for surgeons to provide accurate postoperative patient education. The CT-based robotic systems may provide necessary input to feasibly individualize such recommendations, but current limitations in CT-based robotics require continued attention and innovation.

Evaluating computed bony range of motion (BROM) by registering in-vitro cadaver-based functional range of motion (FROM) to a hip motion simulation

BACKGROUND

While modern hip replacement planning relies on hip motion simulation (HMS), it lacks the capability to include soft-tissues and ligaments restraints on computed bony range of motion (BROM), often leading to an overestimation of the in-vivo functional range of motion (FROM). Furthermore, there is a lack of literature on BROM assessment in relation to FROM. Therefore, the study aimed to assess computed BROM using in-vitro cadaver-derived FROM measurements, registered to a CT-based in-house HMS, and to further investigate the effect of functional and anatomical hip joint centres (FHJC and AHJC) on BROM.

METHOD

Seven limiting and three non-limiting circumducted passive FROM of four cadaver hips were measured using optical coordinate measuring machine with reference spheres (RSs) affixed to the pelvis and the femur, following CT-scan of the specimen. The RSs' centres were used to register the measured FROM in HMS, enabling its virtual recreation to compute corresponding BROM by detecting nearest bony impingement. FHJC, estimated from non-limiting FROM, was compared with AHJC to examine their positional differences and effect on BROM.

RESULTS

Differences in BROM and FROM were minimal in deep flexion (3.0° ± 4.1°) and maximum internal rotation (IR) at deep flexion (3.0° ± 2.9°), but substantially greater in extension (53.2° ± 9.5°). Bony impingement was observed during flexion, and IR at deep flexion for two hips. The average positional difference between FHJC and AHJC was 3.1 ± 1.2 mm, resulting in BROM differences of 1°-13° across four motions.

CONCLUSIONS

The study provided greater insight into the applicability and reliability of computed BROM in pre-surgical planning.

A novel method for in vivo measurement of dynamic ischiofemoral space based on MRI and motion capture

Purpose: To use a novel in vivo method to simulate a moving hip model. Then, measure the dynamic bone-to-bone distance, and analyze the ischiofemoral space (IFS) of patients diagnosed with ischiofemoral impingement syndrome (IFI) during dynamic activities. Methods: Nine healthy subjects and 9 patients with IFI were recruited to collect MRI images and motion capture data. The motion trail of the hip during motion capture was matched to a personalized 3D hip model reconstructed from MRI images to get a dynamic bone model. This personalized dynamic in vivo method was then used to simulate the bone motion in dynamic activities. Validation was conducted on a 3D-printed sphere by comparing the calculated data using this novel method with the actual measured moving data using motion capture. Moreover, the novel method was used to analyze the in vivo dynamic IFS between healthy subjects and IFI patients during normal and long stride walking. Results: The validation results show that the root mean square error (RMSE) of slide and rotation was 1.42 mm/1.84° and 1.58 mm/2.19°, respectively. During normal walking, the in vivo dynamic IFS was significantly larger in healthy hips (ranged between 15.09 and 50.24 mm) compared with affected hips (between 10.16 and 39.74 mm) in 40.27%-83.81% of the gait cycle (p = 0.027). During long stride walking, the in vivo dynamic IFS was also significantly larger in healthy hips (ranged between 13.02 and 51.99 mm) than affected hips (between 9.63 and 44.22 mm) in 0%-5.85% of the gait cycle (p = 0.049). Additionally, the IFS of normal walking was significantly smaller than long stride walking during 0%-14.05% and 85.07%-100% of the gait cycle (p = 0.033, 0.033) in healthy hips. However, there was no difference between the two methods of walking among the patients. Conclusions: This study established a novel in vivo method to measure the dynamic bone-to-bone distance and was well validated. This method was used to measure the IFS of patients diagnosed with IFI, and the results showed that the IFS of patients is smaller compared with healthy subjects, whether in normal or long stride walking. Meanwhile, IFI eliminated the difference between normal and long stride walking.

The impact of increasing femoral offset and stem anteversion on postoperative dislocation in bipolar hemiarthroplasty

BACKGROUND

Femoral offset and anteversion have been reported to affect the incidence of dislocation following bipolar hemiarthroplasty, although the magnitudes of contributions of the femoral offset and stem anteversion on dislocation, both singly and in combination is not fully understood.

METHODS

Using the CT data of 61 patients (61 hips), including 30 male and 31 female who underwent bipolar hemiarthroplasty, three-dimensional dynamic motion analysis was performed using a modular implant that enabled adjustment of femoral offset and stem anteversion independently. The pattern of impingement and relationship between femoral offset/stem anteversion and range of motion were evaluated using the software.

FINDINGS

We found that a higher femoral offset and stem anteversion correlate with a greater range of motion of flexion and internal rotation. Furthermore, an increased femoral offset has a great effect on increasing range of motion of flexion than stem anteversion, and increased both femoral offset and stem anteversion have fewer effect on the flexion, whereas increasing stem anteversion has a great impact on internal rotation than offset, especially in the case with lower femoral anteversion. However, a higher stem anteversion decrease the range of motion of external rotation, whereas a higher femoral offset leads to an increased range of motion of external rotation.

INTERPRETATION

We demonstrated that both a higher femoral offset and stem anteversion substantially affected the range of motion in flexion, internal rotation and external rotation. However, these are not independent, but rather mutually confounding, the surgeons should consider retaining femoral/anterior offset in bipolar hemiarthroplasty.

Development of bony range of motion (B-ROM) boundary for total hip replacement planning

BACKGROUND AND OBJECTIVE

Pre-operative surgical planning using computer simulation is increasingly standard practice before Total Hip Arthroplasty (THA), in order to determine the optimal implant positions, and thereby minimise post-operative complications such as dislocation, wear and leg length discrepancy. One of the limitations of current methods, however, is the lack of information on the subject-specific reference range of motion (ROM) that could be used as targets for surgical planning. Only a limited number of hip motions are considered, which are neither subject-specific, nor representative of all the hip motions associated with all the activities of daily livings (ADLs). In this paper, therefore, a method was developed to calculate subject-specific representative bony range of motion (B-ROM) that would cover all the possible joint motions and presented in terms of pure joint motions.

METHODS

Only 3D bone geometries of femur and pelvis, constructed from personalised CT scan, were used as inputs for healthy hip joint whereas implant geometries and their positions on native bone geometries were required for planned treatment side or replaced side. Hip joint motion simulation was carried out using six different Tait-Bryan intrinsic rotation sequences of three pure joint motions - flexion-extension, abduction-adduction and internal-external rotation, and B-ROM was then identified for any of these six different sequences which caused earliest feasible impingement. The B-ROM could be used as a list of ROM data points or visualised as multiple 2D surface plots or a 3D envelop. Using the developed method, the B-ROM of a contralateral healthy hip joint of a patient can be used to define the subject-specific target ROM values to inform the surgical planning of the arthritic hip side so that the patient's natural ROM could be restored as closely as possible by the planned implant placements. This was demonstrated with a clinical verification study using 'non-dislocating' and 'dislocating' THA patients.

RESULTS

The results supported the study hypothesis that the percentage of intersected volume of the healthy and replaced side B-ROM was higher for the 'Non-Dislocator' patient (95%) compared to 'Dislocator' (78%). Also, the results showed that the only one sequence (first flexion-extension, then abduction-adduction and finally internal-external rotation) was not adequate to identify all the possible limiting B-ROM, and therefore, all the six rotation sequences should be considered.

CONCLUSIONS

The method encompasses every potential ADL, and as a result, more comprehensive surgical planning is possible, as the implant positions can be optimised in order to maximise impingement-free ROM, and consequently minimise clinical complications.

MRI findings of ischiofemoral impingement after total hip arthroplasty are associated with increased femoral antetorsion

BACKGROUND

Ischiofemoral impingement (IFI) is a known complication after total hip arthroplasty (THA).

PURPOSE

To assess if increased postoperative (FA) is associated with magnetic resonance imaging (MRI) findings of IFI.

MATERIAL AND METHODS

In 221 patients with THA, two independent readers measured FA, ischiofemoral space (IFS), quadratus femoris space (QFS), edema, and fatty infiltration of quadratus femoris muscle. Three sets of IFI-imaging features were defined: acute IFI (set 1): IFS ≤15 mm or QFS ≤10 mm and edema in the quadratus femoris muscle; chronic IFI (set 2): IFS ≤15 mm or QFS ≤10 mm and fatty infiltration of quadratus femoris muscle Goutallier grade ≥2; acute and chronic IFI (set 3) with both criteria applicable. For each set, FA angles were compared between positive findings of IFI and negative findings of IFI. The t-test for independent samples tested statistical significance.

RESULTS

In 7.2% (16/221) of patients, findings of IFI (IFS ≤15 mm or QFS ≤10 mm and edema, n = 1; fatty infiltration, n = 9; or both, n = 6) were observed. In women, 11.4% (14/123) exhibited findings of IFI compared to 2.0% (2/98) in men. Comparison in set 1 (n = 7): mean antetorsion of 23.9° ± 9.8° (findings of acute IFI) compared to 14.4° ± 9.7° (P = 0.01). Comparison in set 2 (n = 15): mean antetorsion of 16.2° ± 6.3° (findings of chronic IFI) compared to 14.5° ± 9.9° (P = 0.49). Comparison in set 3 (n = 6): mean antetorsion of 20.4° ± 3.8° (findings of acute and chronic IFI) compared to 14.5° ± 9.9° (P = 0.01).

CONCLUSION

After THA, high postoperative FA is associated with MRI findings of acute as well as acute and chronic IFI. Findings of IFI were commonly seen in women.

Three-Dimensional Functional Impingement in Total Hip Arthroplasty: A Biomechanical Analysis

BACKGROUND

Although component offset can affect impingement after total hip arthroplasty, the exact impact is unclear. Evaluation of offset on an anterior-posterior pelvic radiograph is different than evaluation in functional positions of impingement, namely flexion/internal rotation and extension/external rotation. We quantified the effect of acetabular (cup/liner) vs femoral (head/stem) offsets on changes in range of motion to extra-prosthetic impingement in these 2 impingement-prone functional positions.

METHODS

We retrospectively identified 16 total hip arthroplasty patients (age 61.5 ± 12.1 years, body mass index 28.3 ± 4.9 kg/m²) with preoperative and postoperative computerized tomography scans. To eliminate metal artifact, femoral and pelvic 3-dimensional models were created using preoperative scans aligned with postoperative scans, and 3-dimensional scanned implant models were used to reproduce clinical implantation. We tested ±5 mm acetabular cup, acetabular liner, femoral stem, and femoral head offsets. Maximum range of motion (ROM) to bone-bone impingement was calculated for internal rotation at 90° flexion and external rotation at 10° extension.

RESULTS

In all cases, increased offset increased ROM to impingement, and vice versa. During internal rotation at 90° flexion, ±5 mm liner offset had the greatest impact on ROM (+9°/-10°), followed by cup (+8°/-9°), head (+5°/-7°), and stem (+3°/-5°) offset. During external rotation at 10° extension, ±5 mm cup offset had the greatest impact on ROM (+10°/-10°), followed by liner (+9°/-9°), head (+7°/-8°), and stem (+4°/-4°) offset. However, no statistically significant differences were found in the changes to ROM in flexion obtained through cup and liner offsets, the changes to ROM in extension obtained through liner and head offsets, and the changes to ROM in extension obtained through increasing stem and head offsets.

CONCLUSION

Increasing offset by any method reduces impingement. Center-of-rotation offset changes via acetabular cup or liner have the greatest impact on extra-prosthetic impingement.

Increased Combined Anteversion Is an Independent Predictor of Ischiofemoral Impingement in the Setting of Borderline Dysplasia With Coxa Profunda

PURPOSE

To investigate the differences in radiologic parameters between borderline dysplasia hips (BDDH) +/- coxa profunda and normal hips and to evaluate the correlations between these parameters and the prevalence of ischiofemoral impingement (IFI) in borderline dysplasia.

METHODS

The imaging of patients with BDDH (18° ≤ lateral center edge angle <25°) treated in our hospital from January 2018 to December 2019 was retrospective reviewed. These patients were divided into BDDH with coxa profunda (acetabular fossa touches the ilioischial line, pBDDH) and without coxa profunda (nBDDH) groups. The groups were compared with a control group with normal acetabular coverage. Neck-shaft angle, femoral offset, acetabular versions, acetabular coverage, ischial angle, femoral neck version, and combined anteversion were reviewed and analyzed using computed tomography imaging using one-way analysis of variance.

RESULTS

There were 43 patients (36 female/7 male, 26.13 ± 4.96 years) in the pBDDH group, 22 patients (17 female/5 male, 28.60 ± 5.89 years) in the nBDDH group, and 23 patients (14 female/9 male, 27.67 ± 5.98 years) in the control group. The pBDDH group had increased femoral version, ischial angle, acetabular versions, and decreased ischiofemoral space (IFS)/quadratus femoris space (QFS) than the other 2 groups. The IFS/QFS correlated with neck-shaft angle, femoral offset, femoral neck version, acetabular versions, ischial angle, femoral neck-lesser trochanter angle, posterior acetabular coverage, and combined anteversion in patients with BDDH. Combined anteversion at the 3-o'clock level was an independent predictor of a decreased IFS (beta = -0.348, P = .007) and QFS (beta = -0.255, P = .01, R² = .550). Binary logistic regression demonstrated that patients with BDDH with large combined anteversion at the 3-o'clock level had a greater prevalence of IFI (odds ratio 1.148; P = .001, R² = .505).

CONCLUSIONS

In patients with borderline dysplasia, the QFS/IFS significantly correlated with combined anteversion at the 3-o'clock level on clock face of acetabulum. BDDH with coxa profunda might have a greater prevalence of IFI because of large combined anteversion.

LEVEL OF EVIDENCE

III, retrospective comparative observation study.

Impingement in total hip arthroplasty: A geometric model

Total Hip Arthroplasty (THA) is one of the most common and successful surgical interventions. The survivorship at 10 years for the most commonly used systems is over 95%. However, the incidence of revision is usually much higher in the 0-1 year time period following the intervention. The most common reason for revision in this early time period is dislocation and subluxation, which may be defined as complete or permanent, and partial or temporary loss of contact between the bearing surfaces respectively. This study comprises the development of a geometric model of bone and an in situ total hip replacement, to predict the occurrence and location of bone and component impingement for a wide range of acetabular cup positions and for a series of frequently practiced activities of daily living. The model developed predicts that anterior-superior component impingement is associated with activities that result in posterior dislocation. The incidence may be reduced by increased cup anteversion and inclination. Posterior-inferior component impingement is associated with anterior dislocation activities. Its incidence may be reduced by decreased cup anteversion and inclination. A component impingement-free range was identified, running from when the cup was positioned with 45° inclination and 25° anteversion to 70° inclination and 15°-20° anteversion.

Effects of additional neck cut of the femur on the range of motion in total hip arthroplasty for hip dislocation: a computer simulation study

BACKGROUND

Subtrochanteric shortening osteotomy (SSO) is commonly performed in total hip arthroplasty (THA) for high hip dislocation. However, this procedure is technically difficult and includes complications. Additional neck cut (ANC) of the femur is a procedure that involves femoral shortening by possibly eliminating the need for SSO in THA for high hip dislocation. Herein, we evaluated the effect and the depth limit of ANC of the femur on the range of motion (ROM) in THA for high hip dislocation.

METHODS

ROM was measured in 26 patients with high hip dislocation using computer software. The stem was deeply positioned at 5-mm intervals from 0 mm to 30 mm (7 groups). The ROM before impingement was measured during flexion, internal rotation (IR) at 90° flexion, external rotation (ER) and abduction. Receiver operator coefficient (ROC) curves for abduction were generated. The cut-off value of ANC where the required ROM was achieved was also determined.

RESULTS

Deeper ANCs increased the ROM values during flexion and IR, but they decreased the ROM values during ER and abduction. The ROM values during ER were also limited in 0-mm ANCs. According to the result of the ROC curve for abduction, 15 mm was considered as the permissible range of ANC.

CONCLUSIONS

In THA for high hip dislocation additional neck cut should be taken into consideration for hips requiring less than 15-mm shortening. For more extended corrections a subtrochanteric shortening osteotomy should be performed.

A novel efficient and precise technique for removing acetabular osteophytes in patients undergoing total hip arthroplasty: the SH-9Hospital acetabular edge file

Background

Total hip arthroplasty (THA) is frequently performed in patients with end-stage hip disease. Periacetabular osteophytes are common during THA; however, these osteophytes should be removed intraoperatively to avoid potential impingement between osteophytes and femoral prostheses and decrease dislocation risk. There are no current standard procedures or surgical technique criteria to remove these osteophytes. Osteophytes around the acetabulum are usually removed with an osteotome, yet this presents certain disadvantages. Hence, this study aimed to introduce a novel and more efficient technique than the aforementioned one, the SH-9Hospital acetabular edge file.

Methods

Fifty-four patients (54 hips) who underwent primary THA using osteotome and the SH-9Hospital acetabular edge file to remove periacetabular osteophytes intraoperatively were retrospectively studied. Clinical and radiographic data were obtained for all patients intra- and postoperatively.

Results

The mean osteophyte removal time was 274.6±102.7 s and 51.3±21.1 s in the osteotome and SH-9Hospital acetabular edge file groups, respectively. Intraoperative images and postoperative radiographs showed that acetabular osteophytes were removed thoroughly and precisely by the acetabular edge file and that there was no iatrogenic injury and prostheses malposition in both groups.

Conclusions

The SH-9Hospital acetabular edge file was a novel, efficient, highly precise, and repeatable method for removing periacetabular osteophytes in patients undergoing total hip arthroplasty.

The Patient-Specific Combined Target Zone for Morpho-Functional Planning of Total Hip Arthroplasty

Background Relevant criteria for total hip arthroplasty (THA) planning have been introduced in the literature which include the hip range of motion, bony coverage, anterior cup overhang, leg length discrepancy, edge loading risk, and wear. The optimal implant design and alignment depends on the patient’s anatomy and patient-specific functional parameters such as the pelvic tilt. The approaches proposed in literature often consider one or more criteria for THA planning. but to the best of our knowledge none of them follow an integrated approach including all criteria for the definition of a patient-specific combined target zone (PSCTZ). Questions/purposes (1) How can we calculate suitable THA implant and implantation parameters for a specific patient considering all relevant criteria? (2) Are the resulting target zones in the range of conventional safe zones? (3) Do patients who fulfil these combined criteria have a better outcome score? Methods A method is presented that calculates individual target zones based on the morphology, range of motion and load acting on the hip joint and merges them into the PSCTZ. In a retrospective analysis of 198 THA patients, it was calculated whether the patients were inside or outside the Lewinnek safe zone, Dorr combined anteversion range and PSCTZ. The postoperative Harris Hip Scores (HHS) between insiders and outsiders were compared. Results 11 patients were inside the PSCTZ. Patients inside and outside the PSCTZ showed no significant difference in the HHS. However, a significant higher HHS was observed for the insiders of two of the three sub-target zones incorporated in the PSCTZ. By combining the sub-target zones in the PSCTZ, all PSCTZ insiders except one had an HHS higher than 90. Conclusions The results might suggest that, for a prosthesis implanted in the PSCTZ a low outcome score of the patient is less likely than using the conventional safe zones by Lewinnek and Dorr. For future studies, a larger cohort of patients inside the PSCTZ is needed which can only be achieved if the cases are planned prospectively with the method introduced in this paper. Clinical Relevance The method presented in this paper could help the surgeon combining multiple different criteria during THA planning and find the suitable implant design and alignment for a specific patient.

Contralateral Lower-Limb Functional Status Before Total Hip Arthroplasty: An Important Indicator for Postoperative Gait Speed

BACKGROUND

Postoperative gait speed, especially comfortable gait speed, is an important factor for predicting function after total hip arthroplasty (THA). In this study, we examined factors related to gait speed, including preoperative lower and upper-limb functional parameters and postoperative lower-limb alignment. In addition, we examined factors related to postoperative good comfortable gait speed (≥1.34 m/s: one indicator of a good clinical outcome). The purpose of this study was to determine if better preoperative functional parameters had a positive effect on postoperative gait speed.

METHODS

This prospective case-control study included 91 patients with hip osteoarthritis who underwent unilateral THA. Patients who had undergone a prior hip surgical procedure or had Crowe type-3 and 4 hips, complications after THA, knee osteoarthritis-related pain, and severe lumbar conditions were excluded. The 1-leg standing time (OLST) and knee extensor strength of the operatively treated side and the contralateral side and the functional reach test were examined preoperatively and at 1 year postoperatively. The leg-length discrepancy and global offset compared with the contralateral side and leg lengthening were examined using 3-dimensional models captured through computed tomographic scans.

RESULTS

The preoperative contralateral side OLST was a significant factor (p < 0.001) for postoperative comfortable gait speed, and the preoperative contralateral-side knee extensor strength was a significant factor (p = 0.018) for postoperative maximum gait speed. Leg-length discrepancy and differences in global offset after THA were not significant factors for postoperative gait speed. The preoperative comfortable gait speed with a cutoff value of 1.115 m/s (area under the receiver operating characteristic curve, 0.690 [95% confidence interval, 0.569 to 0.810]; p = 0.003; sensitivity of 65.5% and specificity of 74.2%) was an independent factor associated with a good postoperative comfortable gait speed. Preoperative contralateral-side OLST was a significant factor (p = 0.027) for preoperative comfortable gait speed.

CONCLUSIONS

The preoperative contralateral-side, lower-limb functional status is a significant factor for postoperative gait speed. Early surgical intervention before the contralateral-side function declines or a preoperative rehabilitation intervention on the contralateral side may improve THA outcome.

LEVEL OF EVIDENCE

Prognostic Level II. See Instructions for Authors for a complete description of levels of evidence.

Factors affecting impingement and dislocation after total hip arthroplasty - Computer simulation analysis

BACKGROUND

Studies on the causes and factors affecting dislocation after total hip arthroplasty have revealed conflicting results. The purpose of this study was to evaluate the factors affecting impingement and dislocation after total hip arthroplasty, using a 3-dimensional dynamic motion analysis.

METHODS

The CT data of 53 patients (53 hips: anterior dislocation; 11 cases, and posterior dislocation; 42 cases) who experienced hip dislocation after total hip arthroplasty with posterior approach, and 120 control patients (120 hips) without dislocation were analyzed. Parameters related to implant alignment, offset and leg length were evaluated. The impingement type was also analyzed using a software.

FINDINGS

Considering implant settings affecting dislocation, patients at risk for posterior dislocation had decreased stem anteversion, combined anteversion, femoral offset, and leg length. Nevertheless, patients at risk for anterior dislocation had only lower leg length, and these patients may also be at risk for a higher incidence of recurrent dislocation. Bony impingement occurred in almost half of the cases with posterior dislocation, while implant impingement was associated with anterior dislocation. Importantly, anterior dislocation was not as common as posterior dislocation even in cases with occurrence of posterior impingement.

INTERPRETATION

Bony impingement substantially affects dislocation even in the situation where the implant position and alignment are determined by the so-called "safe zone", especially on the anterior side, while implant impingement affects anterior dislocation. The restoration of anterior offset (i.e., prescribed by the stem anteversion and femoral offset) and combined anteversion is critical for avoidance of posterior dislocation after total hip arthroplasty.

Bone-to-Bone and Implant-to-Bone Impingement: A Novel Graphical Representation for Hip Replacement Planning

Bone-to-bone impingement (BTBI) and implant-to-bone impingement (ITBI) risk assessment is generally performed intra-operatively by surgeons, which is entirely subjective and qualitative, and therefore, lead to sub-optimal results and recurrent dislocation in some cases. Therefore, a method was developed for identifying subject-specific BTBI and ITBI, and subsequently, visualising the impingement area on native bone anatomy to highlight where prominent bone should be resected. Activity definitions and subject-specific bone geometries, with planned implants were used as inputs for the method. The ITBI and BTBI boundary and area were automatically identified using ray intersection and region growing algorithm respectively to retain the same ‘conical clearance angle’ obtained to avoid prosthetic impingement (PI). The ITBI and BTBI area was then presented with different colours to highlight the risk of impingement, and importance of resection. A clinical study with five patients after 2 years of THA was performed to validate the method. The results supported the study hypothesis, in that the predicted highest risk area (red coloured zone) was completely/majorly resected during the surgery. Therefore, this method could potentially be used to examine the effect of different pre-operative plans and hip motions on BTBI, ITBI, and PI, and to guide bony resection during THA surgery.

Prediction and Visualisation of Bony Impingement for Subject Specific Total Hip Arthroplasty

Bony impingement (BI) may contribute to restricted hip joint motion, and recurrent dislocation after total hip arthroplasty (THA), and therefore, should be avoided where possible. However, BI risk assessment is generally performed intra-operatively by surgeons, which is partially subjective and qualitative. Therefore, the aim of the study was to develop a method for identifying subject-specific BI, and subsequently, visualising BI area on native bone anatomy to highlight the amount of bone should be resected. Activity definitions and subject-specific bone geometries, constructed from CT scans, with planned implants were used as inputs for the method. For each activity, a conical clearance angle (CCA) was checked between femur and pelvis through simulation. Simultaneously, BI boundary and area were automatically calculated using ray intersection and region growing algorithm respectively. The potential use of the developed method was explained through a case study using an anonymised pre-THA patient data. Two pure (flexion, and extension) and two combined hip joint motions (internal and external rotation at flexion and extension respectively) were considered as activities. BI area were represented in two ways: (a) CCA specific where BI area for each activity with different CCAs was highlighted, (b) activity specific where BI area for all activities with a particular CCA was presented. Result showed that BI area between the femoral and pelvic parts was clearly identified so that the pre-operative surgical plan could be adjusted to minimise impingement. Therefore, this method could potentially be used to examine the effect of different preoperative plans and hip motion on BI, and to guide bony resection during THA surgery.

Impact of stem design and cementation on postoperative femoral antetorsion in 227 patients with total hip arthroplasty (THA)

OBJECTIVE

In total hip arthroplasty (THA), surgeons attempt to achieve a physiological antetorsion. However, postoperative antetorsion of the femoral stem is known to show large variabilities. The purpose of this study was to assess whether postoperative antetorsion is influenced by stem design or cementation.

MATERIALS AND METHODS

This retrospective study included 227 patients with a hip prosthesis with five different stem designs (S1: short curved, S2 and S3: standard straight, S4: standard straight collared, S5: cemented straight), who had metal suppressed 1.5T-MRI of the hip between February 2015 and October 2019. Measurement of femoral antetorsion was done independently by two fellowship-trained radiologists on axial images by measuring the angle between the long axis of the femoral neck and the posterior condylar tangent of the knee. Measured angles in the different groups were compared using the t test for independent samples.

RESULTS

The cementless collared stem S4 showed the highest antetorsion with 18.1° (± 10.5°; range -10°-45°), which was significantly higher than the antetorsion of the collarless S3 with 13.3° (± 8.4°; - 4°-29°) and the cemented S5 with 12.7° (± 7.7°; - 3°-27°) with p = 0.012 and p = 0.007, respectively. S1 and S2 showed an antetorsion of 14.8° (± 10.0°; 1°-37°) and 14.1° (± 12.2°; - 20°-41°). The torsional variability of the cementless stems (S1-4) was significantly higher compared with that of the cemented S5 with a combined standard deviation of 10.5° and 7.7° (p = 0.019).

CONCLUSION

Prosthesis design impacts the postoperative femoral antetorsion, with the cementless collared stem showing the highest antetorsion. Cemented stems demonstrated significantly lower variability, suggesting the lowest rate of inadvertent malrotation.

Is the ischiofemoral space value of Japanese hip joints equal to that of Western populations?

Ischiofemoral space (IFS) is a radiological parameter employed for diagnosing ischiofemoral impingement (IFI). The mean IFS value measured with the leg in natural resting position has been reported as 23.0 mm in males and 18.6 mm in females in a patients-based Western population. The normal value of IFS for an Asian population is unknown. This study therefore aimed to investigate whether the IFS value in Japanese hip joints equals that of the Western population. We retrospectively examined 89 consecutive Japanese individuals (178 hips) (46 male subjects with 92 hips, 43 female subjects with 86 hips; mean age 58.7 ± 15.7 years, range 17-84 years) who had undergone computed tomography (CT) for conditions unrelated to hip disorders and ordered by other departments at our institution. All CT scans were performed in a standardized fashion: patient in a flat spine position, hips and knees in extension, and the leg in its natural resting position. IFS was evaluated on axial images as the shortest distance between the ischium and the lesser trochanter. The mean IFSs of this Japanese patient-based population were 20.5 ± 7.3 mm [95% confidence interval (CI) 19.0-22.0] in the male cohort and 13.9 ± 6.5 mm (95% CI 12.6-15.3) in the female cohort. The IFS value was significantly smaller in female subjects than in male subjects. Taking the lower limit of 95% CI into consideration, the IFSs measured in natural leg-resting position in the Japanese male and female groups were significantly smaller than those of the Western populations.

Anatomic stem inserted according to native anteversion could reproduce the native anterior distance of the femoral head and decrease bony impingement in total hip arthroplasty

PURPOSE

To investigate whether anatomic and straight stems could reproduce the anteroposterior distance (AD) of the native femoral head and evaluate the effect of AD of the femoral head on range of motion (ROM) and bony impingement.

METHODS

This retrospective simulation study included 64 patients who had undergone primary total hip arthroplasty between 2012 and 2014. Using computed tomography (CT)-based templating software, anatomic and straight stems were inserted with same alignment. AD of the head centre was compared between the two stems and native anatomy. Furthermore, post-operative ROM was calculated, and correlation between AD and ROM was assessed.

RESULTS

There was a strong positive correlation between native anteversion (mean 21.9°) and anatomic stem anteversion (mean 22.5°) (R = 0.975, P < 0.001). There was no significant difference in AD between the native and anatomic stems (mean 37.7 and 38.8 mm, respectively), but AD of the straight stem was significantly lower than that of the native and anatomic stems. The straight stem showed a significantly lower ROM in flexion and internal rotation angles with 90° flexion (IR) than the anatomic stem (P < 0.05 and P < 0.001, respectively). AD showed a stronger correlation with ROM of IR than with stem anteversion.

CONCLUSIONS

The anatomic stem could reproduce AD of the native femoral head centre, but the head centre of the straight stem in the same anteversion with anatomic stem translated significantly posterior, significantly decreasing the ROM of flexion and IR and increasing bony impingement of IR. To avoid bony impingement and acquire sufficient ROM, reproducing AD was important.

The optimal combined anteversion pattern to achieve a favorable impingement-free angle in total hip arthroplasty

BACKGROUND

There have been no studies on the differences in impingement-free angle that result from different combined anteversion (CA) patterns. The aim of this study was to find the optimal CA pattern for achieving a favorable impingement-free angle, including bony and prosthetic impingement, in total hip arthroplasty.

METHODS

We evaluated 100 patients with no hip arthritis. We investigated the impingement-free angle (flexion, internal rotation with 90° flexion, extension, and external rotation) after changing the stem and cup anteversions to satisfy several CA patterns [cup anteversion + stem anteversion = 30°, 40°, 50°, and 60°; cup anteversion + 0.7 × stem anteversion = 37.3° (:Widmer's theory); and cup anteversion + 0.77 × stem anteversion = 43.3° (:Yoshimine's theory)] using 3-dimensional templating software.

RESULTS

The impingement-free angle changed dramatically among the various CA patterns. The optimal CA was changed by various stem anteversion. Only CA: Widmer with stem anteversion of 20° satisfied daily-life range of motion (ROM) requirements (flexion ≥130°, internal rotation with 90° flexion ≥ 45°, extension ≥ 40°, external rotation ≥ 40°).

CONCLUSION

Good impingement-free angle cannot be obtained with single fixed CA. Different CA patterns should be used, depending on the differences in the stem anteversion. A CA of 30° with 0° ≤ stem anteversion ≤10°; a CA:Widmer with 20° of stem anteversion; a CA of 40° or Widmer with 30° of stem anteversion. When stem anteversion is ≥40°, CA should be decided by each patient's state. Among them, a stem anteversion of 20° with cup anteversion of 23.3° was found to be the best CA pattern.

Effect of changing femoral head diameter on bony and prosthetic jumping angles

BACKGROUND

In THA, using a larger femoral head can increase the oscillation angle and jumping distance. However, there have been no reports which indicate precisely how increasing the jumping distance leads to an increase in the angle from impingement to dislocation (jumping angle). In this study, we clarified the jumping angle of various head diameters and its relationship with pelvic morphology.

METHODS

Using a three-dimensional templating system, virtual THA and ROM simulations were performed in 82 patients. We investigated the distance between bony and prosthetic impingement points and the head centre and calculated the jumping angle for various head diameters. We measured various pelvic shapes and length to clarify the relationship between pelvic morphology and impingement distance.

RESULTS

Jumping angles were 7.7° ± 3.2°, 12.1° ± 1.6°, 15.4° ± 2.5° and 10.0° ± 3.0° with flexion, internal rotation with 90° flexion (IR), extension and external rotation (ER), respectively, when we used a 22-mm head diameter. Bony jumping angle increased about 0.5°, 0.8°, 1.0° and 0.7° per 2-mm increase in head diameter with flexion, IR, extension and ER. On the other hand, prosthetic jumping angle remained almost stable at about 31°. Impingement distance was related to pelvic morphology in all directions. Bony jumping angles differed with ROM; the biggest was seen with extension, followed by IR, ER and flexion. On the other hand, bony jumping angle was less than prosthetic jumping angle in all cases.

CONCLUSION

Bony jumping angles differed with ROM; the biggest was seen with extension, followed by IR, ER and flexion. Prosthetic impingement angles were stable. In addition, the bony jumping angle was less than the prosthetic jumping angle in all cases.

Prevention of Dislocation After Total Hip Arthroplasty

BACKGROUND

Prevention of dislocation after primary total hip arthroplasty (THA) begins with patient preoperative assessment and planning.

METHODS

We performed a literature search to assess historical perspectives and current strategies to prevent dislocation after primary THA. The search yielded 3458 articles, and 154 articles are presented.

RESULTS

Extremes of age, body mass index >30 kg/m2, lumbosacral pathology, surgeon experience, and femoral head size influence dislocation rates after THA. There is mixed evidence regarding the effect of neuromuscular disease, sequelae of pediatric hip conditions, and surgical approach on THA instability. Sex, simultaneous bilateral THA, and restrictive postoperative precautions do not influence the dislocation rates of THA. Navigation, robotics, lipped liners, and dual-mobility acetabular components may improve dislocation rates.

CONCLUSIONS

Risks for dislocation should be identified, and measures should be taken to mitigate the risk. Reliance on safe zones of acetabular component positioning is historical. We are in an era of bespoke THA surgery.