Introduction:
When performing hip arthroplasty to manage femoral neck fracture (FNF) in the elderly patients, the optimal choice between total hip arthroplasty (THA) or hemiarthroplasty (HA) is still controversial. In addition, dual mobility cups (DM) have been shown to prevent instability that remains a concern in these patients with conventional THA. This study compared the outcomes of HA, DM and conventional THA to manage FNF across a nationwide observation issued from the Swiss National Joint Registry (SIRIS).

Method:
From 2012 and 2022 in Switzerland, 37,169 patients who were managed with hip arthroplasty for FNF were exhaustively and prospectively included in the SIRIS registry. There were 22,053 HA, 3,263 DM THA and 11,853 conventional THA included. The revision rates and survivorship for septic and aseptic failures were compared between HA, DM and conventional THA. Hazard ratios (HR) for revisions were used to compare HA, DM and conventional THA. Subgroups analyses with adjustments for age, gender, BMI and ASA score were performed.

Results:
At 10-year follow-up, the cumulative revision rates for HA were 7.8% [6.4-9,4], for DM THA 8.1% [7.6-10] and conventional THA 8.7% [7,7-9,9]. HA tended towards a lower revision risk than DM and conventional THA (HR=0.86 [95%-CI: 0.72-1.02]) without reaching significance. However, in patients < 65 years, the revision rate after HA was as high as 20.7% [13.5-31.1] with 56,1% of the revisions being for conversion to THA. In addition, HA performed with cementless femoral stem were characterized by significantly higher revision rate than HA performed with cemented femoral stem regarding the risk of femoral periprosthetic fracture (HR=1.81 [95%- CI: 1.39 to 2.38]). Moreover, the revision rate due to dislocation was significantly higher for HA performed through a posterior approach compared to anterior approaches (Hueter or Hardinge) (HR=1.64 [95%-CI: 1.268 – 2.113]).

Conclusions:
When considering arthroplasty options to manage FNF, no significant difference was observed in terms of revision rate and survivorship between HA, DM THA and conventional THA. However, a 20% revision rate at 10 years follow-up was observed after HA in patients < 65 years. Therefore, THA is recommended in younger patients and/or when life expectancy is > 10 years. Importantly for HA, a cemented femoral stem should be considered to limit the risk of femoral periprosthetic fracture as well as anterior approaches to avoid dislocation.

Background:
Despite many advantages, the direct anterior approach (DAA) is associated with a risk of lateral cutaneous femoral nerve (LCFN) injury. This may lead to numbness of the antero-lateral thigh, which is only temporary in most cases, but can sometimes cause persistent neuropathic symptoms with pain, numbness, and tingling, impairing mobility and daily activities. This study aims to evaluate the effect of LCFN lesions after primary THA using the DAA on long-term clinical outcome and function.
Methods:
Our institutional database of primary THA patients (2015-2022) was searched for patients with LCFN lesions after DAA. Only patients with a consultation by a neurologist for LCFN symptoms were included. Prospective clinical assessment (Ethical approval 2023-01287) included Visual Analog Scale (VAS), incision length, distance to anterior superior iliac spine (ASIS), size of the area of symptoms, Tinel sign, range of motion (ROM). Patient-reported outcomes (OHS, COMI Hip, UCLA) were obtained.
Results:
Out of 1418 patients screened, only 29/2.0% (female: 19, 65.6%) met the criteria (7 surgeons). Mean age 64y±12, BMI 26.8kg/m²±4.3, surgical time 77min±25, 20.7% smokers (n=6), 55.2% bikini incision (n=16). 22 patients (75.9%) had ultrasound, 18 (62.1%) received nerve infiltration (13/ 18 (72.2%) showed long-term LCFN symptom improvement), and 2 (6.9%) had surgical neurolysis. Preliminary clinical data of 12 patients with a mean f-up of 4.8±2.0 (2.3 – 8.6) years. Mean VAS 1.9±2.2, incision length 9.2cm±1.1, distance to ASIS 4.3cm±1.3. 10 hypesthesia, 5 dysesthesia, 2 tingling, area size 287cm²±269. Tinel sign positive (n=2, 16.6%). Mean hip flexion 100°±6, internal 23.8°±6.8/external 37.9°±3.3 rotation. Mean OHS 38.5±7.2, COMI Hip 3.03±2.24, UCLA 5.9±2.2.
Conclusion:
Painful LCFN lesions after primary THA using DAA are rare in a high-volume orthopedic setting (>200 THA/surgeon/year), with an overall higher occurrence in women. However, persistent LCFN symptoms after intraoperative nerve injury appear to have a relevant impact on long-term clinical outcomes. The bikini incision did not increase the risk for LCFN symptoms. Ultrasound-guided nerve infiltration led to favorable long-term therapeutic results.

Introduction
Effective perioperative pain management and early mobilization after surgery are crucial to optimize recovery. In addition to routine pain medication, peripheral anaesthetic blocks are reportedly effective. The aim of this study was to determine the effect of the the PEricapsular Nerve Group (PENG) block on postoperative (1) patient-reported pain, (2) total consumption of morphine and (3) length of stay (LOS) after surgical hip dislocation (SHD).

Methods
IRB-approved, single-center, multidisciplinary, prospective, randomized, double-blind controlled trial of patients undergoing SHD for femoro-acetabular impingement between June 2022 and November 2023. Preoperatively, patients were randomly assigned to either the study group (39 patients) or the control group (33 patients). Both groups underwent an ultrasound-guided injection of a 20 mL solution, the study group received 0.5% ropivacaine and the control group 0.9% NaCl. Each patient, anesthesiologist and surgeon were blinded to the solution injected. Nine patients who required additional procedures or did not receive the standard analgesia protocol were excluded from the study, resulting in a total of 71 patients (72 hips). The demographics of the two groups did not significantly differ. Overall the study population was 38% female, mean age was 29 ± 6 (19 to 46) years and mean body-mass-index was 23 ± 3 (19 to 30) kg/m2. We assessed (1) postoperative pain at 1h, 6h, 12h and 24h postoperatively via the Visual Analogue Scale (VAS) ranging from 0 (no pain) to 10 (maximal pain), (2) total morphine consumption in Morphine Equivalent Dose (MED) during the first 24 hours after surgery and (3) the LOS in days. Differences between the study group and the control group were analyzed using the Mann-Whitney test. The significance level was set at α < .05.

Results
VAS differs slightly and significantly at 1hour in the study group (4 ± 2 [0 to 8] VAS) compared to the control group (5 ± 2 [1 to 10] VAS) (P < .05). There were no significant difference at any of the three other time points, for the 24-hour morphine consumption and the LOS between the two groups (all P > .05). No femoral motor nerve block or injection site infection were observed in either group.

Conclusion
In this prospective randomized controlled trial, the PENG block showed a slight difference in terms of reported VAS at 1 hour postoperatively only, but no difference in morphine consumption and LOS after SHD when compared to a placebo.

Background
Previous studies have indicated poor outcomes in patients having revision of metal-on-metal (MoM) total hip arthroplasty (THA) resulting from Adverse Local Tissue Reaction (ALTR). We reviewed all patients who had a MoM THA revision to determine (1) the rate of complications; (2) the clinical and radiological outcomes; and (3) the influence of the index revision on the serum metal ions levels; and to compare the results (1) to (3) in cases with isolated revision of the acetabular component to those after revision of both acetabular and femoral components.

Methods
We identified 79 patients who underwent a revision of a MoM THA and did not show any sign of loosening of the femoral stem. Among these, 62 had an isolated revision of the acetabular component (Gp1) and 17 had a revision of both components (Gp2). Mean age at revision surgery was 61.8 years. The mean time from the index MoM THA was 93.1 months and mean followup after revision was 57.7 months. Major complications (instability, infection, aseptic loosening, and periprothetic fracture within one year) were documented and included in the analyses. The PMA and the Harris Hip score (HHS) were determined, and Patient-reported outcome measures (PROMs) were collected. Serum samples were analyzed to assess serum Cobalt (Co) and Chromium (Cr), before and within 12 months of revision.

Results
Revision diagnoses were ALTR (66%), aseptic loosening of the cup (7.6%), iliopsoas impingement (3.8%), recurrent dislocation (2.5%), chronic pain (1.3%) and heterotopic ossification (1.3%). Five major complications occurred in five different patients (6.3%). There were two acetabular component loosenings (both in Gp1)) and three dislocations (2 in Gp1 and 1 in Gp2). Smoking appeared as a statistically significant predictive factor of complication (p=0.027). Intraoperative blood loss and operation time were significantly lower in Gp1. Similar improvements in PMA, HHS, SF-12 and Womac scores were observed in both groups. Metal ion levels decreased after revision and this difference was not significant between Gp1 and 2.

Conclusion
In comparison to the current literature, our study shows a low complication rate after MoM revision THA. Our data suggest that isolated revision of the acetabular component of failed MoM THA can be performed without revising a stable femoral component and results in similar complication rate, clinical improvement, and metal ion decrease as compared to both components revision.

Introduction: Malpositioned cups with an uncovered anterolateral rim can irritate the iliopsoas tendon causing pain. However, early revision of a stable implant with slight protrusion should be avoided. Iliopsoas (IP) tenotomy has demonstrated effectiveness in alleviating pain even in these cases. This study assesses the clinical outcome, the impact on hip flexion strength and the morphological changes of the IP muscle in magnetic resonance imaging (MRI) following labral-level tenotomy.

Methods: All patients undergoing arthroscopic labral-level IP tenotomy for tendinopathy after hip arthroplasty between 2013 and 2020 with at least 12 months follow-up were included. Pre- and post-operative cross-sectional areas of the iliopsoas muscle were measured at 2 different levels in the MRI. Muscle atrophy according to Goutallier, tendon irregularities, muscle edema and compensatory hypertrophy were assessed. Hip flexion strength was measured in seated and supine position using a dynamometer. Analysis was performed using Mann-Whitney U and Kruskal-Wallis tests.

Results: The study evaluated 22 patients of whom 17 met the inclusion criteria. Median follow-up was 51 months (range 12 - 105). Post-operative MRIs revealed a reduction of the iliopsoas cross-sectional area by 36% (±33.85%) at the anterior superior iliac spine (ASIS) and 31% (±30.02%) at the anterior inferior iliac spine (AIIS) as compared to the unaffected side. When comparing pre- and post-operative MRIs of the affected side, a reduction of 34% (±27.53%) at the ASIS and of 25 % (±15.69%) at the AIIS was observed. Using the Goutallier classification, we observed atrophy (psoas/iliacus) as followed: grade 0 (1/4), grade 1 (6/7), grade 2 (9/5), grade 3 (1/1) and grade 4 (0/0). Hip flexion showed a reduction of strength of 12% in seated and 18% in supine position when comparing the affected with the non-affected side. All patients reported a complete reduction of their symptoms and were satisfied with the procedure.

Conclusion: The study confirms that IP muscle atrophy occurs in most patients after IP tenotomy, on average reducing the cross-sectional area of the IP muscle by about one-third. Despite this reduction, hip flexion strength remains virtually unaffected. These findings align with existing research, highlighting the absence of severe atrophy after labral-level tenotomies compared to lesser trochanteric ones. In this study all patients reported satisfaction after tenotomy.

Introduction: Previous studies have shown that dexamethasone has a positive effect on postoperative pain control, opioid consumption, postoperative nausea, vomiting and length of hospital stay after arthroplasty surgery. The study assessed if adding perioperative dexamethasone to our current pain regimen after hip arthroscopy is more effective than a placebo. It was hypothesized that dexamethasone can reduce postoperative pain, reduce opioid consumption, improve subjective pain and nausea scores and reduce the number of vomiting events.
Study Design: Double-blinded randomized controlled trial; level of evidence 1.
Methods: Fifty patients requiring an unilateral elective hip arthroscopy were randomized to receive perioperative intravenous dexamethasone (2x12mg) or a placebo (NaCl 0.9%). The patient, the surgeons, the treating anesthesiologist as well as the involved nursing and physiotherapy personnel were blinded. Primary outcome included postoperative pain, secondary outcomes opioid consumption and nausea scores as assessed with a translated revised American Pain Society Patient Outcome Questionnaire (APS-POQ-R) six hours postoperatively, on day 1 and 2 and vomiting events. A clinical follow-up was performed 12 weeks postoperatively to assess for adverse events.
Results: The mean age at inclusion was 29 years in both groups. Postoperative pain levels did not differ significantly in the majority of instances. The opioid requirements during the hospitalisation in the dexamethasone group were significantly lower than in the placebo group 31.96 ±20.56 mg vs. 51.43 ±38.00mg (P=0.0139). Significantly fewer vomiting events were noted in the dexamethasone group 0.15 ±0.59 vs 0.65 ±0.91 (P=0.034). Demographics and surgical parameters did not differ significantly.
Conclusion: Perioperative intravenous dexamethasone significantly reduced postoperative opioid consumption by 40% without compromising pain level and safety, as no corticosteroid-related side effects were observed. Dexamethasone may be a valuable adjuvant to a multimodal systemic pain regimen after hip arthroscopy.

Background
Intraarticular hip pain is a significant clinical challenge, with recent literature implicating lesions in the ligamentum teres (LT) as potential contributors. Damage to the LT is prevalent among young patients undergoing joint-preserving surgery. There is a significant lack of research examining LT biomechanics specifically within the relevant patient cohort—individuals who qualify for joint-preserving surgical interventions. Aims: to determine (1) the biomechanical properties (ultimate load to failure, tensile strength, stiffness, and elastic modulus) of fresh frozen ligaments from patients undergoing surgical hip dislocation and (2) to identify patient-specific factors that are associated with them.
Methods
IRB-approved study on intraoperatively harvested LTs of 74 consecutive patients undergoing surgical hip dislocation for joint preservation (August 2021 to September 2022). After exclusion of patients with previous surgery, posttraumatic deformities, avascular necrosis, slipped capital femoral epiphysis and Perthes disease, 31 ligaments analyzed. Main indication for surgery was femoroacetabular impingement. Standardized AP pelvic- and axial radiographs and CT scans performed to identify associated radiological factors. Thorough transection of the LT at its origin and insertion area. Documentation of intraarticular damage to the ligamentous-fossa-foveolar complex. Storage at -20° C. Specimens were mounted to a materials testing machine (Instron Electropuls 10,000, Norwood, MA, USA) via custom clamps. Ultimate failure load, tensile strength, stiffness and elastic modulus were determined.
Results
Ultimate load to failure was 126 ± 92 N while tensile strength was 1 ± 0.8 MPa. Stiffness was 24 ± 15 N/mm, the elastic modulus 7 ± 5 MPa. Multiple regression showed that age < 20 years old, female sex and excessive femoral torsion were associated with higher values, while underlying lesions of the acetabular fossa and fovea seen intraoperatively were predictors for decreased structural properties.
Conclusion
In comparison to other stabilizing ligaments in the body such as the anterior cruciate ligament (ACL) of the knee, the LT seems to be substantially weaker. It is therefore questionable if the LT provides considerable stability to the hip joint. Younger, female patients with high femoral torsion exhibited higher ligament properties.

Background: Stair climbing is important for maintaining mobility, high quality of life, and independence. Although healthy persons can climb stairs quite easily, this strenuous task might be quite demanding when motor functions are reduced. A detailed biomechanical analysis of stair climbing in patients with muscle weakness could provide insight into the diverse and complicated processes involved in human locomotion and may be useful in the field of rehabilitation
Purpose: To investigate the effects of an experimentally induced weakness of the gluteal muscles, through sequential nerve blocks of the superior gluteal nerve to the fascia lata (SGNtfl), superior (SGN), and inferior gluteal nerve (IGN), on joint kinematics, reactions forces (JRFs), and dynamic balance performance during stair climbing in healthy young adults.

Methods: Ten healthy adult volunteers received sequential blocks of the SGNtfl, SGN, and IGN on their dominant right leg. At the control condition and following each block, the participants were instructed to perform stair-ascent and descent activities. A full-body movement analysis was then performed and joint kinematics, JRFs, and dynamic balance performance were recorded. 

Results: Following the SGN block, five out of ten of the healthy participants couldn’t complete the task. In participants who completed the task, their joint kinematics were significantly different compared to the control condition, demonstrating more hip flexion and internal rotation during both stair-ascent and descent activity under the SGN block. Significantly lower JRFs were observed following SGN and IGN blocks at the hip, knee, and ankle compared to the control condition. The participants demonstrated also an increased center of mass (CoM) mean and standard deviation in the mediolateral direction during both stair-ascent and descent under the SGN and IGN block.

Conclusion: Stair climbing was mostly affected by a weakness of the hip abductors, with 50% of the healthy volunteers not being able to complete the task. In patients who did complete the task, the compensation was insufficient as reflected in the abnormal joint kinematics, reduced JRFs, and worst dynamic balance performance.

Introduction: Accurate component placement plays a critical role in the outcome of total hip arthroplasty (THA). Robotic-assisted THA (R-THA) has emerged as an option to optimize this aspect compared to the conventional manual THA (C-THA). The aim of this meta-analysis was to analyse the studies comparing R-THA and C-THA in terms of radiological results, clinical outcomes, perioperative parameters, complications, and revisions.
Methods: The literature search was conducted on three databases (PubMed, Cochrane Library, and Web of Science) on January 25, 2024 according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Inclusion criteria were: comparative studies, written in English language, with no time limitation, focusing on the comparison of R-THA and C-THA. The quality of each article was assessed using the “Downs and Black’s Checklist for Measuring Quality”.
Results: Among the 1883 articles retrieved, 38 studies (9537 patients) were included. R-THA provided superior radiological results compared to C-THA in terms of acetabular cup placement within the Lewinnek safe zone (p < 0.01) and horizontal change of the rotation centre (p = 0.05). No statistically significant difference was obtained in terms of clinical scores between the two approaches, including Harris Hip Score, Western Ontario and McMaster Universities Arthritis Index, Forgotten Joint Score, and Merle d’Aubigné Hip Score. R-THA showed longer operative time (p < 0.01) compared to C-THA but shorter length of hospital stay (p = 0.05) and lower complication rates (p = 0.04). No difference was obtained in terms of intra-operative bleeding and revision rates.
Conclusion: The results of this meta-analysis suggest that R-THA could provide more precise cup placement and better restoration of the native hip anatomy while reducing complication rates and hospital stay compared to C-THA. However, these benefits did not translate into clinical differences in terms of patient-reported outcome measures between the two approaches and R-THA required longer operative time compared to C-THA. While the overall results do not suggest decisive benefits from the use of robotic technology, future studies should investigate if further technical improvements will translate into clinically relevant benefits for patients undergoing THA.

Introduction
Questions remain concerning the long-term surveillance needs of MoM THAs. Objectives were to assess blood cobalt levels over time in MoM THA and the relation with clinical outcomes in small heads.

Methods
We included all primary MoM THAs with postoperative blood cobalt concentrations. These THAs were performed between 11/1998 and 03/2011. We stratified the MoM THAs in 2 groups, small (≤ 36mm) vs. large (> 36mm) head. To assess the pattern of blood cobalt levels over time only unilateral MoM THAs with at least two cobalt measurements were included. Linear mixed effects models were used for analysis.

Results
Overall, 526 MoM THAs were included, 427 with small heads (199 females) and 99 with large heads (31 females). Mean time of serologies for metal ion levels was 10.5 years. Revision for any reason was performed in 51 of these patients. Considering patients with at least two serologies before revision (n = 205), cobalt ion levels were higher for patients with large compared to small heads (median ±interquartile range: 3.5 ±5.3 vs. 1.3 ±1.4, p < 0.001). We did not find any effect of time on cobalt ion levels (ps > 0.42).
Cobalt levels before and after MoM prosthesis removal for large (medians 7.8 vs. 1.8) and small heads (medians 1.9 vs. 0.9) indicated a reduction to values in the normal range for large heads.
We did not find any significant correlation between cobalt ion levels and clinical outcomes (WOMAC pain and function scores, and Harris hip and limp scores; Spearman’s rs < 0.8, ps > 0.15).

Conclusion
We observed stable cobalt levels over time. Repeat laboratory workups seem unnecessary given that cobalt values remained stable. Removal of the MoM prosthesis largely reduced cobalt blood concentrations to normal levels in the months after the intervention. Clinical outcomes in small head MoM THAs were not associated with cobalt levels.

Introduction
One-stage bilateral total hip arthroplasty (bTHA) in selected patients with bilateral hip OA may expedite rehabilitation particularly when using a direct anterior approach (DAA). While previous studies using other approaches indicate that bTHA may have increased complication rates, advancements in surgical and anesthetic techniques have improved outcomes of bTHA. Postulated benefits of bTHA include a single anesthesia, reduced total hospital stay, and shorter overall rehab. However, data on long-term patient-reported outcomes (PROMs) following bTHA/DAA is scarce. This study aims to compare long-term PROMs between bTHA and unilateral THA (uTHA), both through a DAA.

Methods
In this retrospective case series, patients were selected from our THA registry. PROMs: OHS, COMI, UCLA, EQ5D, Global treatment outcome (GTO) were completed at home before surgery, and at 6, 12, 24, 48, and 60 months postoperatively. To minimize selection bias, propensity score-matching distributed patient characteristics evenly between two treatment groups. Of 11’031 cases in the registry, 357 bilateral cases were matched 1:2 within 4’098 cases having complete 2-year data. The final groups comprised 357 bTHAs and 714 uTHAs.

Results
The baseline characteristics of the two groups, including sex, age, BMI, ASA classification, smoking status, and other sociodemographic factors, were comparable. As expected, bTHA showed longer surgical time (but 4 min less than double that of uTHA), more blood loss, and longer hospital stay (p < 0.01). Intra-operative complications were more frequent in the bTHA group (27% vs 16%, p < 0.05), e.g. calcar cracks occurred in 12 and 10 hips, respectively, ie. below 1.7% for both groups once adjusted for the number of hips operated. Regarding PROMs, there was no significant difference between the two groups for COMI, OHS, or EQ5D at any follow-up interval. Interestingly, the UCLA activity score was higher in the bTHA group at 6, 12, and 24 months and GTO were also rated more favorably in bTHA at 2-year postoperative (p < 0.05).

Conclusion
This retrospective comparative matched cohort study suggests that bTHA yields equivalent or superior mid-term PROMs compared to uTHA, with comparable complication rates when adjusted for the number of hips. One-stage bilateral approach might offer significant economic benefits, warranting a detailed cost analysis against staged THA/DAA procedures.

During total hip arthroplasty (THA), surgeons have control over the structure of the operated limb, specifically on femoral, acetabular and global offsets. The literature suggests that decreasing the femoral offset (FO) and/or the global offset (GO) leads to decreased function [2] and pain [3] and recommends to restore GO by increasing FO and reducing acetabular offset (AO) [2]. Still, the literature presents discrepancies in definitions of post-surgery change in offsets and lacks assessment of the effect of change in AO [2]. This study evaluated the independent effect of increasing, restoring, or decreasing the femoral, acetabular and global offsets on pain and function.

All patients undergoing primary THA between 2018 and 2020 in our institution (n=766) were retrospectively selected based on the following criteria: surgery for end-stage coxarthrosis, no other arthroplasty of the lower limb or spine, bi-plane X-rays (to assess offsets [5,6]) before and after surgery, and WOMAC pain and function scores before and one year after surgery. The change in offsets (dO) was classified in three groups based on the Smallest Detectable Changes (SDC) [4], assessed on a similar population (4.8mm, 6.3mm and 6.2mm respectively for the femoral, acetabular, and global offset) [5,6]: increased (I, dO > SDC), restored (R, -SDC < dO < SDC) and decreased (D, dO < SDC). Differences were assessed with Kruskall-Wallis tests or Chi2 test (p < 0.05).

A total of 166 patients were included (sex: 58% F, age: 68.3+/-11.4 years old, BMI: 26.8+/-5.0kg/m2). Group populations were as follows: FO (11D, 111R, 44I), AO (67D, 98R, 1I), GO (46D, 111R, 9I). No differences in terms of age, BMI or sex were found. The decreased FO group had more pain (median [interquartile range] WOMAC pain: 80 [45]) than the increased FO group (100 [10]), and lower function (WOMAC function: 75 [52]) than increased (95 [12]) and restored (93 [21]) FO groups. The decreased GO group had more pain (WOMAC pain: 90 [24]) than the restored group (100 [15]). No differences were found between AO groups.

These results support recommendations to avoid decreasing the femoral and global offsets for optimal function and pain scores one year post-surgery. No isolated effect of the acetabular offset was found.

[1] Ferguson, The Lancet, 2018
[2] DiGiovanni, EFORT Open Reviews, 2023
[3] Bullen, Journal of Arthroplasty, 2023
[4] de Vet, Cambrige University Press, 2011
[5,6] Gasparutto, Scientific Reports, 2023, 2022

Introduction: Cobalt-chromium (CoCr) wear and corrosion products from total hip arthroplasty (THA) have been linked to adverse local tissue reactions (ALTR). Widespread use of large diameter (>40 mm, LD), third-generation metal-on-metal (MoM) THA lead to awareness regarding this issue. However, second-generation, small-diameter (28/32 mm, SD) MoM THA performed well, with excellent long-term survival. This study aimed to characterize the wear behavior of SD MoM THA.
Methods: Thirty-nine cases with revised SD MoM THA were analyzed. Median (range) time in situ was 18.2 years (0.6-27.9). Inclination and anteversion angles were measured from pre-revision radiographs. Adverse events and demographic data were recorded. Bearing surfaces were measured with an optical coordinate-measuring-machine to quantify material loss.
Results: Median (range) inclination and radiographic anteversion angles were 44° (32 - 61) and 22° (0 - 47), respectively. Reasons for revision included ALTR, periprosthetic fracture, and malposition. Median (range) volumetric material loss of the heads and metal liners were 3.71 mm3 (0.17-82.32) and 11.72 mm3 (0.2 – 126.25), respectively, with a combined median bearing surface material loss of 15.75 mm3 (1.08-165.17). There was no correlation between total bearing wear and any patient demographics or cup orientation. Head wear volume had a trending correlation with patient age (p=0.076), which was significant (coef=-0.46, p=0.03) when controlled for time in situ (coef=0.59, p=0.17). Local tissue responses were mild to moderate, with marked particle-laden macrophages but little to no lymphocytic responses. Co and Cr ion whole blood ion levels were 2.1 ug/L (0.5, 73.5) and 2.2 ug/L (0.3, 29.10), respectively, significantly correlated only with the occurrence of secondary cup dislocation (p=0.016 and p=0.05) and showed a trend of a positive correlation with inclination angle (p=0.12 and p=0.068).
Conclusion: This relatively large cohort of SD MoM retrievals exhibited remarkably low wear, especially compared to later generations of LD MoM bearings. Wear was independent from time in situ and implant positioning indicating unknown factors, such as patient activity levels, probably had a large impact. The theoretical wear rate of 0.97 mm3/year was lower than predictions from simulators, and ~66% of bearings exhibited no wear beyond the running-in period.

Introduction
The hip abductors are one of, if not the most important muscle group of the hip. They play a relevant role in everyday activities, not least because they are essential for efficient ambulation. Weakness of the hip abductors leads to pain and limping. Treatment of a relevant weakness can be frustrating and surgical treatment in particular must be carefully considered. In order to understand abductor weakness in detail, it is important to know which muscles are involved and to what extent. The aim of this study was to investigate the effects of an experimentally induced weakness of the gluteal muscles on abduction power of the hip.

Methods
Ten healthy adults received a sequential nerve block of the supplying branch of the tensor fasciae latae (branch of the superior gluteal nerve), the gluteus maximus (inferior gluteal nerve) and the supplying branch of the gluteus medius and minimus (branch of the superior gluteal nerve). Subsequently, the maximal abduction force (Newton) was measured in the lateral decubitus position in three positions of the hip (30° flexion, neutral position, 30° extension in the hip joint).

Results
In 30° flexion average abduction force was 220 newton without block, 187 newton with block of the tensor fasciae latae, 97 newton with block of the gluteus maximus and 83 newton with block of the gluteus medius and minimus, respectively. In neutral position average abduction force was 213 newton without block, 200 newton with block of the tensor fasciae latae, 115 newton with block of the gluteus maximus and 82 newton with block of the gluteus medius and minimus, respectively. In 30° extension average abduction force was 116 newton without block, 146 newton with block of the tensor fasciae latae, 94 newton with block of the gluteus maximus and 61 newton with block of the gluteus medius and minimus, respectively.

Conclusion
An experimentally induced weakness of the tensor fasciae latae only reduces the abduction force by a maximum of 15% in all positions and is most involved when the hip is flexed. It is therefore overestimated as an abductor.
An experimentally induced weakness of the gluteus maximus reduces the abduction force in neutral position by 46%, in extension of the hip by 43% and in flexion by 56%. It is therefore not as important as the gluteus medius and minimus muscles, but is underestimated as an abductor.

Background: ETO offers excellent exposure of the femoral canal and the acetabulum in revision arthroplasty while being a true intermuscular and internervous approach. While initially described by Wagner with a split of the gluteus medius tendon (“transgluteal”) and later by Younger et al as an extension of a posterior approach, Lakstein et al described an approach similar to a surgical hip dislocation with preservation of the posterior soft tissues and an anterior dislocation of the hip. We have applied this technique routinely with reconstruction with a primary stem, which has not been described before. The aim of this study is to describe the technique, the safety and outcome of this approach in our series.
Patients and Methods: Patients undergoing total hip revision surgery between 01.01.2018 until 31.12.2021 at our clinic using an ETO and reconstruction with primary implants have been included. The decision to perform an ETO was taken prior to the operation. The ETO was performed without detaching the short external rotators or posterior capsule in all cases. The length of the ETO was 60-90mm distal of the vastus ridge (inominatum). Similar to a surgical hip dislocation, the anterior capsule was exposed and opened, followed by an anterior dislocation. Reconstruction was performed using a primary stem. The ETO fragment was fixed with 2 standard cerclages and a monocortical 8-plate or 2 trochanteric screws. All patients were invited for a clinical review (including PROMS) and x-ray.
Results: 19 patients (age 66+8; 39% male) have been included. ASA score was 2 in 11(61%) and 3 in 7 (39%) cases. No patients were lost to follow-up. 14 were available for clinical exam, 4 patients were interviewed by phone and 1 patient died of an unrelated cause, with the implant still in place. Average F-up was 30+7 months (range 20-40 months). No re-revisions were necessary with no evidence of radiological loosening. ETOs fully consolidated in all cases. At the latest f-up, all PROMs improved compared to the preoperative score: COMI from 7.3+1.3 to 1.3+1.7, OHS from 23+6 to 44+6 UCLA score from 3.1+0.8 to 6.3+1.4.
Summary/Conclusions: ETO with anterior joint dislocation and reconstruction with primary implants is safe in selected cases and may lead to good clinical results, while being cost effective, and avoiding the downsides of long revision stems or unnecessary stem modularity.

Introduction:
Early aseptic loosening is caused by deficient osteointegration of the femoral stem due to increased micromotions and represents a common mode of failure in uncemented total hip arthroplasty. This study hypothesized that a higher femoral offset, a smaller stem size and obesity increase femoral micromotion, potentially resulting in early aseptic loosening.

Methods:
A Finite-Element-Analysis was conducted based on computed tomography segmented model of four patients who received a total hip arthroplasty with a triple-tapered straight stem (size 1, 3, 6). The influence of femoral stem offset (short neck, standard, lateral), head length (S to XXL), femoral anteversion and obesity during daily activities of fast walking and stair climbing was analyzed. The micromotions for the femoral stem zones were compared to a threshold representing a value above which only partial osseointegration is expected.

Results:
The minimum femoral offset configuration compared to the maximum offset configuration (short neck stem, S head vs lateral stem, XXL head) leads to a relative mean micromotion increase of 24% for the upper stem zone. Increasing the body weight (BMI 30 to 35 kg/m2) increases the micromotion by 20% for all stem zones. The obese population recorded threshold-exceeding micromotions for stem sizes 1 and 3 for all offset configurations during stair climbing.

Conclusion:
Higher femoral offset, a smaller stem size, and higher loading due to obesity lead to an increase in micromotion between the prosthesis and proximal femur and represent a risk configuration for impaired osseointegration of a triple-tapered straight stem, especially when these three factors are present simultaneously.

Background: Identifying hip instability in symptomatic patients with borderline dysplasia of the hip (BDH) is of paramount importance as it can influence both surgical decision-making and surgical outcomes. The femoroepiphyseal acetabular (FEAR) index is strongly affected by the hip add-/abduction angle during pelvic radiograph, which until now has not been considered in the recommended threshold values.
Purpose: The aim of the present study was to report the optimal threshold of the corrected FEAR index in detecting hip instability in patients with BDH.
Methods: Patients with oligosymptomatic BDH treated conservatively (n = 25), patients treated with a periacetabular pelvic osteotomy (PAO) due to hip instability (n = 42) or hip arthroscopy due to symptomatic femoroacetabular impingement (FAI) (n = 50) with good patient-reported outcomes at the final follow-up were identified. The FEAR index was measured on the pelvic radiograph at the initial hip add-/abduction angle (uncorrected FEAR index) and 0° of hip add-/abduction angle (corrected FEAR index).
Results: The corrected FEAR index varied significantly from the uncorrected FEAR index in all groups with an average deference of 9 ± 9° in the oligosymptomatic BDH group, 6 ± 4° in the BDH group with instability, and 5 ± 5° in the BDH with FAI. The optimal threshold for the corrected FEAR index was - 13° (OR = 7.8 ; 95% CI = 2.6 to 23.1, p < .001), which yielded a sensitivity of 86% and specificity of 52% for detecting hip instability in the current cohort.
Conclusion: The corrected FEAR index might vary significantly from the uncorrected FEAR index, which is highly dependent on the hip add-/abduction angle during the pelvic radiograph. The optimal threshold of the corrected FEAR index to predict hip instability in a painful hip with a BDH was ≥ -13°.

Introduction: Highly cross-linked polyethylene (XLPE) is an important progress in total hip arthroplasty (THA), greatly reducing wear, compared to conventional polyethylene (CPE). Crosslinking is commonly achieved by irradiation. Irradiation dose and thermal treatment are the main material determinants of revision after THA identified so far. How the degree of crosslinking varies between products and how this impacts tribological behaviour is unclear so far. This study compares the degree of crosslinking and in vitro wear rates across a cohort of retrieved and unused polyethylene (PE) cups/liners from various manufacturers.
Methods: PE acetabular cups/liners were collected from one centre from April 2021 to April 2022. The trans-vinylene index (TVI) and the oxidation index (OI) were determined by Fourier-transformed infrared spectrometry. Wear was measured using a pin-on-disc test.
Results: 47 PE specimens from 8 manufacturers were included. The TVI was stable within each group and independent of time in situ. A linear correlation (r2=0.995) could be observed between the old and the current TVI standard, except for vitamin E infused PE. No excessive oxidation interfered. The absorbed irradiation dose calculated from the TVI corresponded to product specifications for all but two products. For one, an equivalent mean irradiation dose of 241% was observed, likely explained by higher crosslinking from electron, compared to gamma irradiation. For another XLPE, much lower than expected (mean 41% ± 13%) doses were measured than indicated by the manufacturer. Lower wear was observed for higher TVI. The one XLPE with unexpectedly low TVI showed wear more comparable to CPE. Despite adequate TVI, another vitamin E infused XLPE showed slightly higher in vitro wear than the other ones.
Conclusion: The TVI is a reliable measure of the absorbed dose of irradiation of PE and does not alter over time. Conversion from the old to the current standard is linear, except for vitamin E infused PE. Various brands differ by manufacturing details and consequently characteristics. Absorption and penetration of electron irradiation and gamma irradiation differ, potentially leading to different degrees of cross-linking. There is a non-linear, inverse correlation between TVI and in vitro wear. Irradiation doses calculated from the measured TVI deviated from specifications for one XLPE, which correlated with an inferior in vitro wear rate, comparable to CPE rather than the other XLPE.