Aims. Periprosthetic hip fractures (PPFs) after total hip arthroplasty are difficult to treat. Therefore, it is important to identify modifiable risk factors such as stem selection to reduce the occurrence of PPFs. This study aimed to clarify differences in fracture torque, surface strain, and fracture type analysis between three different types of cemented stems. Methods. We conducted biomechanical testing of bone analogues using six cemented stems of three different types: collarless polished tapered (CPT) stem, Versys Advocate (Versys) stem, and Charnley-Marcel-Kerboull (CMK) stem. Experienced surgeons implanted each of these types of stems into six bone analogues, and the analogues were compressed and internally rotated until failure. Torque to fracture and fracture type were recorded. We also measured surface strain distribution using triaxial rosettes. Results. There was a significant difference in fracture torque between the three stem types (p = 0.036). Particularly, the median fracture torque for the CPT stem was significantly lower than that for the CMK stem (CPT vs CMK: 164.5 Nm vs 200.5 Nm; p = 0.046). The strain values for the CPT stem were higher than those for the other two stems at the most proximal site. The fracture pattern of the CPT and Versys stems was Vancouver type B, whereas that of the CMK stem was type C. Conclusion. Our study suggested that the cobalt-chromium alloy material, polished surface finish, acute-square proximal form, and the absence of a collar may be associated with lower fracture torque, which may be related to PPF. Cite this article: Bone Joint Res 2022;11(5):270–277

The aim of this study was to assess the effect of frictional torque and bending moment on fretting corrosion at the taper interface of a modular femoral component and to investigate whether different combinations of material also had an effect. The combinations we examined were 1) cobalt–chromium (CoCr) heads on CoCr stems 2) CoCr heads on titanium alloy (Ti) stems and 3) ceramic heads on CoCr stems. In test 1 increasing torque was imposed by offsetting the stem in the anteroposterior plane in increments of 0 mm, 4 mm, 6 mm and 8 mm when the torque generated was equivalent to 0 Nm, 9 Nm, 14 Nm and 18 Nm. In test 2 we investigated the effect of increasing the bending moment by offsetting the application of axial load from the midline in the mediolateral plane. Increments of offset equivalent to head + 0 mm, head + 7 mm and head + 14 mm were used. Significantly higher currents and amplitudes were seen with increasing torque for all combinations of material. However, Ti stems showed the highest corrosion currents. Increased bending moments associated with using larger offset heads produced more corrosion: Ti stems generally performed worse than CoCr stems. Using ceramic heads did not prevent corrosion, but reduced it significantly in all loading configurations. Cite this article: Bone Joint J 2015;97-B:463–72

The design of the Charnley total hip replacement follows the principle of low frictional torque. It is based on the largest possible difference between the radius of the femoral head and that of the outer aspect of the acetabular component. The aim is to protect the bone-cement interface by movement taking place at the smaller radius, the articulation. This is achieved in clinical practice by a 22.225 mm diameter head articulating with a 40 mm or 43 mm diameter acetabular component of ultra-high molecular weight polyethylene. We compared the incidence of aseptic loosening of acetabular components with an outer diameter of 40 mm and 43 mm at comparable depths of penetration with a mean follow-up of 17 years (1 to 40). In cases with no measurable wear none of the acetabular components were loose. With increasing acetabular penetration there was an increased incidence of aseptic loosening which reflected the difference in the external radii, with 1.5% at 1 mm, 8.8% at 2 mm, 9.7% at 3 mm and 9.6% at 4 mm of penetration in favour of the larger 43 mm acetabular component. Our findings support the Charnley principle of low frictional torque. The level of the benefit is in keeping with the predicted values

Introduction. Recent studies on large diameter femoral head hip replacements have implicated the modular taper junction as one of the significant sources of wear and corrosion products and this has been attributed to increased torque and bending on the taper interface. The aim of this study was to assess the effect of frictional torque and bending moment on fretting corrosion at the taper junction and to investigate whether different material combinations also had an effect. Patients/Materials & Methods. We examined 1) Cobalt Chromium (CoCr) heads on CoCr stems 2) CoCr heads on Titanium alloy (Ti) stems and 3) Ceramic heads on CoCr stems. In test 1 increasing torque was imposed by offsetting the femoral stem in the anterior posterior plane in increments of 0 mm, 4 mm, 6 mm and 8 mm where the force generated was equivalent to 0Nm, 9Nm, 14Nm and 18Nm. In Test 2 we investigated the effect of increasing bending moment by offsetting the application of axial load from the midline in the medial-lateral (ML). Offset increments equivalent to +0, +7 and +14 heads were used. For each test we used n=3 for each different material combination. Results. Significantly higher currents and amplitudes were seen with increasing frictional torque for all material combinations, however titanium alloy stems showed the highest corrosion. Increasing bending moments associated with using larger off-set heads produced more corrosion; with titanium alloy stems generally performing worse than cobalt chrome stems. Using ceramic heads did not prevent corrosion, but this was significantly reduced in all loading configurations. Discussion & Conclusion. This is the first study to quantify corrosion associated with different material combinations and loading conditions. Increasing frictional torque and bending, together with the material combination have a significant effect on the fretting corrosion at the taper modular junction. The best performing material combination was ceramic on CoCr

Of the 11 054 Charnley low-frictional torque arthroplasties carried out at our hospital between 1962 and 1977, 110 (94 patients) had a minimum follow-up of 30 years with a mean of 32.3 years (30.0 to 40.5). The mean age of the patients at operation was 43.3 years (17.0 to 65.0) and 75.7 years (51.0 to 97.0) at follow-up. Overall, 90% of hips (99) were free from pain and activity was reported as normal in 58% of the patients. A total of 13 hips (11.8%) were revised at a mean follow-up of 32.3 years (30.0 to 39.5), with wear and loosening of the acetabular component as the main indications. The clinical results did not reflect the mechanical state of the implant. Follow-up with sequential radiographs of good quality is essential. Revision for radiological changes alone must be accepted if gross loss of bone stock is to be avoided. Improvements in the design, materials and operative technique, based on the long-term outcome, are highlighted

Between November 1962 and December1990 a group of 1092 patients, 668 women and 424 men, under the age of 51 years at the time of surgery, underwent 1434 primary Charnley low-frictional torque arthroplasties and are being followed up indefinitely. Their mean age at operation was 41 years (12 to 51). At the latest review in June 2001 the mean follow-up had been for 15 years 1 month. Of the 1092 patients 54 (66 hips) could not be traced, 124 (169 hips) were known to have died and 220 (248 hips) had had a revision procedure. At a mean follow-up of 17 years and 5 months, 759 patients (951 hips) are still attending. In this group satisfaction with the outcome is 96.2%. The incidence of deep infection for the whole group was 1.67%. It was more common in patients who had had previous surgery (hemi- and total hip arthroplasties excluded), 2.2% compared with 1.5% in those who had not had previous surgery, but this difference was not statistically significant (p = 0.4). There were fewer cases of deep infection if gentamicin-containing cement was used, 0.9% compared with 1.9% in those with plain acrylic cement, but this was not also statistically significant (p = 0.4). There was a significantly higher rate of revision in patients who had had previous hip surgery, 24.8% compared with 14.1% in those who had not had previous surgery (p < 0.001). At the latest review, 1.95% are known to have had at least one dislocation and 0.4% have had a revision for dislocation. The indication for revision was aseptic loosening of the cup (11.7%), aseptic loosening of the stem (4.9%), a fractured stem (1.7%), deep infection (1.5%) and dislocation (0.4%). With revision for any indication as the endpoint the survivorship was 93.7% (92.3 to 95.0) at ten years, 84.7% (82.4 to 87.1) at 15 years, 74.3% (70.5 to 78.0) at 20 years and 55.3% (45.5 to 65.0) at 27 years, when 55 hips remained ‘at risk’

We reviewed 261 patients with 320 Charnley low-friction arthroplasties who had a mean follow-up of 22 years 10 months (20 to 30). Of these, 93.9% considered the operation to be a success; 82.3% were free from pain and 11.6% had occasional discomfort. Satisfactory function was achieved in 59.6% and 62% had an excellent range of movement.

The clinical results did not correlate well with the radiological appearance; radiologically loose components did not affect the clinical outcome. The main long-term problem was wear and loosening of the UHMWPE cup. Our findings suggest that the radiological appearance of the arthroplasty is a more reliable indication of the state of the arthroplasty than the clinical results.

Introduction

Cross linked polyethylene (XLPE) has gained popularity as a bearing surface of choice for younger patients despite only medium term results being available for wear rates. Concern remains regarding the long-term stability and durability of these materials. In order to address these issues we present the longest radiological and clinical follow-up of XLPE.

The trend towards more minimal access has led to a series of instruments being developed to enable adequate access for Direct Anterior Approach (DAA) for hip arthroplasty. These include longer levers, hooks attached to the operating table and a series of special attachments to the operating table to position the leg and apply traction where necessary. The forces applied in this way may be transmitted locally, damaging muscle used as a fulcrum, or the knee and ankle joints when torque has to be applied to the femur through a boot. The arthroplasty surgeon's aim is to minimise the forces applied to both bone and soft tissue during surgery. We surmised that the forces needed for adequate access were related to the extent of the capsular and soft tissue releases, and that they could be measured and optimised. with the aim of minimising the forces applied to the tissues around the hip. Eight fresh frozen specimens from pelvis to mid tibia from four cadavers were approached using the DAA. A 6-axis force/torque sensor and 6-axis motion tracking sensor were attached to a threaded rod securely fastened to the tibial and femoral diaphysis. The torque needed to provide first extension, then external rotation, adequate for hip arthroplasty were measured as the capsular structures were divided sequentially. The Zona Orbicularis (ZO) and Ischiofemoral Ligament(IFL) contributed most of the resistance to both extension (4.0 and 3.1Nm) and external rotation torque (5.8 and 3.9Nm). The contributions of the conjoint tendon (1.5 and 2.4Nm) and piriformis (1.2 and 2.3Nm) were substantially smaller. By releasing the Zona Orbicularis and Ischiofemoral Ligament, the torque needed to deliver the femur for hip arthroplasty could be reduced to less than the torque needed to open a jar (2.9–5.5Nm)

Previous studies have highlighted differences in the risk of periprosthetic fracture between tapered slip (TS) and composite beam (CB) stems. This biomechanical study explored periprosthetic fractures around these stems and the effect of adding a 16-gauge calcar or diaphyseal wire to TS stems on their resistance to torque. A power analysis determined a sample size of 7 specimens per group, assuming a standard deviation of 14.8 Nm in peak torque, to provide 90% power to detect a difference of at least 30 Nm between groups. Twenty-one TS stems (eight alone, six with calcar wiring, seven with diaphyseal wiring placed 2 cm distal to the lesser trochanter) and seven CB stems were cemented into standard Sawbones. A servo-hydraulic test machine applied a 1000 N load with a 1-degree rotation per second until failure. The peak torque at failure was measured, and the fracture location recorded. Comparisons were performed using two-sample t-tests. CB stems exhibited a significantly higher peak torque at failure (205.3 Nm) than TS stems (159.5 Nm, p=0.020). Calcar-wire-TS (148.2 Nm, p=0.036) and diaphyseal-wire-TS (164.9 Nm, p=0.036) were both weaker than CB stems. Wired-TS stems showed no significant difference from non-wired-TS stems. Additionally, the study could not conclude that calcar wiring is stronger than diaphyseal wiring. All TS fractures occurred at the mid-stem, simulating a B-type fracture, while the addition of the diaphyseal wire shifted the fracture location more distally in four of seven stems (p=0.0699). This biomechanical study supports the clinical evidence that CB stems have stronger resistance to torque than TS stems and may explain lower risk of periprosthetic fracture. The addition of calcar or diaphyseal wires to TS stems resulted in no significant changes in peak torque to fracture. In patients at high risk of periprosthetic fracture, CB cemented stems should be considered

Polymethylmethacrylate (PMMA) bone cement is strong in compression, however it tends to fail under torsion. Sufficient pressurisation and subsequent interdigitation between cement and bone are critical for the mechanical interlock of cemented orthopaedic implants, and an irregular surface on the acetabular cup is necessary for reasonable fixation at the cup-cement interface. There is limited literature investigating discrepancies in the failure mechanisms of cemented all-polyethylene acetabular cups with and without cement spacers, under torsional loading. In vitro experimental comparison of three groups of polyethylene acetabular prosthesis (PAP) cemented into prepared sawbone hemipelvises:. * PAP without PMMA spacers maintaining an equal cement mantle circumferentially. (Group 1 n=3). * PAP without PMMA spacers cemented deliberately ‘bottoming-out’ the implant within the acetabulum. (Group 2 n=3). * PAP with PMMA spacers. (Group 3 n=3). The constructs were tested to torstional failure on a custom designed setup, and statistical analysis done by a one-way ANOVA and Tukey-Welsh test. Group 3 demonstrated superior torsional resistance with a statistically significant torque of 145Nm (SD±12Nm) at failure, compared to group 2 (109Nm, SD±7Nm) and group 1 (99Nm, SD±8Nm). Group 3 experienced failure predominantly at the bone-cement interface, in contrast, Groups 1 and 2 exhibited failure predominantly at the cup-cement interface. There was no significant difference between Group 1 and 2. Qualitative analysis of the failure mode indicates the efficient redistribution of stress throughout the cement mantle, consistent with the greater uniformity of cement. PMMA spacers increase the resistance to torsional failure at the implant-cement interface. Acetabular components without spacers (Groups 1 and 2) failed at the implant-cement interface before the cement-bone interface, at a statistically significantly lower level of torque to failure. Although the PMMA spacers may reduce cement interdigitation at the cement-bone interface the torsional forces required to fail are likely supraphysiological

Aims. It is important to analyze objectively the hammering sound in cup press-fit technique in total hip arthroplasty (THA) in order to better understand the change of the sound during impaction. We hypothesized that a specific characteristic would present in a hammering sound with successful fixation. We designed the study to quantitatively investigate the acoustic characteristics during cementless cup impaction in THA. Methods. In 52 THAs performed between November 2018 and April 2022, the acoustic parameters of the hammering sound of 224 impacts of successful press-fit fixation, and 55 impacts of unsuccessful press-fit fixation, were analyzed. The successful fixation was defined if the following two criteria were met: 1) intraoperatively, the stability of the cup was retained after manual application of the torque test; and 2) at one month postoperatively, the cup showed no translation on radiograph. Each hammering sound was converted to sound pressures in 24 frequency bands by fast Fourier transform analysis. Basic patient characteristics were assessed as potential contributors to the hammering sound. Results. The median sound pressure (SP) of successful fixation at 0.5 to 1.0 kHz was higher than that of unsuccessful fixation (0.0694 (interquartile range (IQR) 0.04721 to 0.09576) vs 0.05425 (IQR 0.03047 to 0.06803), p < 0.001). The median SP of successful fixation at 3.5 to 4.0 kHz and 4.0 to 4.5 kHz was lower than that of unsuccessful fixation (0.0812 (IQR 0.05631 to 0.01161) vs 0.1233 (IQR 0.0730 to 0.1449), p < 0.001; and 0.0891 (IQR 0.0526 to 0.0891) vs 0.0885 (IQR 0.0716 to 0.1048); p < 0.001, respectively). There was a statistically significant positive relationship between body weight and SP at 0.5 to 1.0 kHz (p < 0.001). Multivariate analyses indicated that the SP at 0.5 to 1.0 kHz and 3.5 to 4.0 kHz was independently associated with the successful fixation. Conclusion. The frequency bands of 0.5 to 1.0 and 3.5 to 4.0 kHz were the key to distinguish the sound characteristics between successful and unsuccessful press-fit cup fixation. Cite this article: Bone Jt Open 2024;5(3):154–161

Aims. It is important to analyze objectively the hammering sound in cup press-fit technique in total hip arthroplasty (THA) in order to better understand the change of the sound during impaction. We hypothesized that a specific characteristic would present in a hammering sound with successful fixation. We designed the study to quantitatively investigate the acoustic characteristics during cementless cup impaction in THA. Methods. In 52 THAs performed between November 2018 and April 2022, the acoustic parameters of the hammering sound of 224 impacts of successful press-fit fixation, and 55 impacts of unsuccessful press-fit fixation, were analyzed. The successful fixation was defined if the following two criteria were met: 1) intraoperatively, the stability of the cup was retained after manual application of the torque test; and 2) at one month postoperatively, the cup showed no translation on radiograph. Each hammering sound was converted to sound pressures in 24 frequency bands by fast Fourier transform analysis. Basic patient characteristics were assessed as potential contributors to the hammering sound. Results. The median sound pressure (SP) of successful fixation at 0.5 to 1.0 kHz was higher than that of unsuccessful fixation (0.0694 (interquartile range (IQR) 0.04721 to 0.09576) vs 0.05425 (IQR 0.03047 to 0.06803), p < 0.001). The median SP of successful fixation at 3.5 to 4.0 kHz and 4.0 to 4.5 kHz was lower than that of unsuccessful fixation (0.0812 (IQR 0.05631 to 0.01161) vs 0.1233 (IQR 0.0730 to 0.1449), p < 0.001; and 0.0891 (IQR 0.0526 to 0.0891) vs 0.0885 (IQR 0.0716 to 0.1048); p < 0.001, respectively). There was a statistically significant positive relationship between body weight and SP at 0.5 to 1.0 kHz (p < 0.001). Multivariate analyses indicated that the SP at 0.5 to 1.0 kHz and 3.5 to 4.0 kHz was independently associated with the successful fixation. Conclusion. The frequency bands of 0.5 to 1.0 and 3.5 to 4.0 kHz were the key to distinguish the sound characteristics between successful and unsuccessful press-fit cup fixation. Cite this article: Bone Jt Open 2024;4(3):154–161

Aims. This study investigates head-neck taper corrosion with varying head size in a novel hip simulator instrumented to measure corrosion related electrical activity under torsional loads. Methods. In all, six 28 mm and six 36 mm titanium stem-cobalt chrome head pairs with polyethylene sockets were tested in a novel instrumented hip simulator. Samples were tested using simulated gait data with incremental increasing loads to determine corrosion onset load and electrochemical activity. Half of each head size group were then cycled with simulated gait and the other half with gait compression only. Damage was measured by area and maximum linear wear depth. Results. Overall, 36 mm heads had lower corrosion onset load (p = 0.009) and change in open circuit potential (OCP) during simulated gait with (p = 0.006) and without joint movement (p = 0.004). Discontinuing gait’s joint movement decreased corrosion currents (p = 0.042); however, wear testing showed no significant effect of joint movement on taper damage. In addition, 36 mm heads had greater corrosion area (p = 0.050), but no significant difference was found for maximum linear wear depth (p = 0.155). Conclusion. Larger heads are more susceptible to taper corrosion; however, not due to frictional torque as hypothesized. An alternative hypothesis of taper flexural rigidity differential is proposed. Further studies are necessary to investigate the clinical significance and underlying mechanism of this finding. Cite this article: Bone Jt Open 2021;2(11):1004–1016

There is a strong association between the presence of a calcar collar on a cementless stem and a reduced risk of revision surgery for periprosthetic fracture of the femur (PFF). A medial calcar collar may act to reduce relative movement between the implant and femur during PFF, through calcar-collar contact (CCC). The aims were:. Estimate the effect of CCC on periprosthetic fracture mechanics. Estimate the effect of initial calcar-collar separation on the likelihood of CCC. Three groups of six composite femurs were implanted with a fully coated collared cementless femoral stem. Neck resection differed between groups (group 1 = no additional resection, group 2 = 3mm additional resection, group 3 = 6mm additional resection). PFF were simulated using a previously published technique. Fracture torque and rotational displacement were measured and torsional stiffness and rotational work prior to fracture were estimated. Results between trials where CCC did and did not occur where compared using Mann-Whitney U tests. Logistic regression estimated the odds (OR) of failing with 95% confidence interval (CI) to achieve CCC for a given initial separation. Where CCC occurred fracture torque was greater (47.33 [41.03 to 50.45] Nm versus 38.26 [33.70 to 43.60] Nm, p= 0.05) and torsional stiffness was greater (151.38 [123.04 to 160.42] rad.Nm. −1. versus 96.86 [84.65 to 112.98] rad.Nm. −1. , p <0.01). CCC was occurred in all cases in group one, 50% in group two and 0% in group three. OR of failure to obtain CCC increased 3.8 fold (95% CI 1.6 to 30.2, p <0.05) for each millimetre of separation. Resistance to fracture and construct stiffness increased when a the collar made contact with the calcar prior to fracture and the chances of contact decrease with increasing initial separation at the time of implantation. Surgeons should aim to achieve a calcar-collar distance of less than 1mm following implantation to ensure CCC and to reduce the risk of fracture

Proximal hamstring tendon avulsion from the ischial tuberosity is a significant injury, with surgical repair shown to have superior functional outcomes compared to non-surgical treatment. However, limited data exists regarding the optimal rehabilitation regime following surgical repair. The aim of this study was to investigate patient outcomes following repair of proximal hamstring tendon avulsions between a conservative (CR) versus an accelerated rehabilitation (AR) regimen. This prospective randomized controlled trial (RCT) randomised 50 patients undergoing proximal hamstring tendon repair to either a braced, partial weight-bearing rehabilitation regime (CR=25) or an accelerated, unbraced regime, that permitted full weight-bearing as tolerated (AR=25). Patients were evaluated pre-operatively and at 3 and 6 months post-surgery, via patient-reported outcome measures (PROMs) including the Lower Extremity Functional Scale (LEFS), Perth Hamstring Assessment Tool (PHAT) and 12-item Short Form Health Survey (SF-12). Primary analysis was per protocol and based on linear mixed models. Both groups were matched at baseline with respect to patient characteristics. All PROMs improved (p>0.05) and, while the AR group reported a significantly better Physical Component Score for the SF-12 at 3 months (p=0.022), there were no other group differences. Peak isometric hamstrings strength and peak isokinetic quadriceps and hamstrings torque symmetry were all comparable between groups (p>0.05). Three re-injuries have been observed (CR=2, AR=1). After proximal hamstring repair surgery, post-operative outcomes following an accelerated rehabilitation regimen demonstrate comparable outcomes to a traditionally conservative rehabilitation pathway, albeit demonstrating better early physical health-related quality of life scores, without an increased incidence of early re-injury

Post-operative peri-prosthetic femoral fracture (PO-PPFF) is one of the most relevant complications in primary Total Hip Arthroplasty (pTHA), accountable for a significant clinical and socio-economic burden both in revision and fixation settings. We retrospectively reviewed of our series of 1586 cementless total hip arthroplasty performed between 1999 and 2019 (achieving a minimum of 5-years follow-up) with different short stems. We have observed a cumulative low incidence of PO-PPFF of 0,33% (5 cases): we divided Po-PPFF in two groups: fracture occurred around a short stem (A) and around a standard shortened stem (B), according to French Hip & Knee Classification of Short Stems. Despite the length of observed period (mean follow-up 12 years, min 5 years max 24 years) a total of 1512 cases (mean age at surgery 61 years, max 74, min 40 years) were available to clinical and radiographic follow-up, being this population enrolled in elective surgery clinical protocols. Our data exceed the low incidence of post-operative femoral fracture around bone -preserving previously reported by Kim in 2018 (12 fracture out of 1089 cases:1.1%). No correlation have been observed among occurrence of PO-PPF age of the patient and no fracture occurred around cemented short stems despite patient's characteristics were unfavourable in term of age and bone quality. This result is not unexpected, giving the lower incidence of peri-prosthetic fracture even cemented conventional stems, as reported in all registry and systematic reviews. A similar behaviour was reported in 2020 Australian Joint Registry, where Post-operative periprosthetic femoral fracture showed a steep curve in early period, but remaining firmly below 1% during the following 12 years. Our clinical data seems to confirm previous studies by Jones (conducted on synthetic bone and fresh-frozen cadaveric femurs) where higher fracture angles and higher fracture torque were detected in short hips compared to standard stems

The increased torque required to dislocate dual mobility (DM) components may increase peri-prosthetic femoral fracture (PPF) risk. Current literature often relies on revision as an endpoint and may underestimate PPF. This study aims to review PPF rate, risks and treatment following primary DM implantation. Prospective cohort study of 549 patients following primary DM total hip arthroplasty (THA) between 2013 and 2021. Collected data included demographics, indication for surgery, cortical index and PPF. 549 patients were identified with primary DM THA. Mean age was 73 years (26–96). 446 (81.2%) patients had their index surgery following hip fracture. 18 patients (3.27%) sustained a PPF. Cumulative PPF rate was 1.5% at 1-year, 2.2% at 5-years and 3.27% overall. PPF was higher in patients undergoing surgery following hip fracture (4%) vs. other indications (1%). OR 4.04 (95% CI:0.53, 30.72), p=0.219. Mean cortical index was lower in patients with PPF 0.4 (95% CI:0.36, 0.45) compared to those without 0.46 (95% CI:0.45, 0.46) p=0.029. Treatment for PPF included 10 (55.6%) open reduction internal fixation (ORIF), 7 (38.9%) revision THA and 1 conservatively managed. PPF rate following DM use is higher in our cohort than published rates. Our rates are comparable to some papers when subgroup analysis of older patients and cemented taper slip stems are considered. PPF risk with DM may be increased in patients undergoing surgery after hip fracture or with a lower cortical index preoperatively. Over half of PPF were managed with ORIF and may mask PPF risk studies that report using revision as an endpoint

Introduction. Gluteus medius is disrupted during lateral approach total hip arthroplasty (THA) which may impact its function and ability to control the pelvis. The objective was to compare gluteus medius activation and joint mechanics associated with a Trendelenburg sign (pelvic drop, trunk lean) during gait and hip abductor strength between patients that underwent lateral or posterior THA approaches one year post-surgery and healthy adults. Methods. Participants that underwent primary THA for hip osteoarthritis using lateral (n=21) or posterior (n=21) approaches, and healthy adults (n=21) were recruited for this cross-sectional study. Participants completed five walking trials. Surface electromyography captured gluteus medius activation. A 3-dimensional optical motion capture system measured frontal plane pelvic obliquity and lateral trunk lean angles. Participants performed maximum voluntary isometric contractions (MVIC) on a dynamometer to measure hip abductor torque. Characteristics from gait waveforms were identified using principal component analysis, and participant waveforms were scored against these characteristics to produce principal component scores. One-way analysis of variance and effect sizes (d) compared gait principal component scores and isometric hip abductor torque between groups. Results. Lateral THA group had statistically significant higher gluteus medius PC-scores indicating higher overall amplitudes during gait (p<0.01, d=0.97) and prolonged midstance activation (p=0.01, d=0.95) compared to the healthy group (Figure). There were no statistically significant (p>0.05) differences in pelvis or trunk angles. Isometric hip abductor torque was significantly (p=0.03, d=0.74) lower in the lateral THA than healthy group. There were no statistically significant differences between THA groups (d=0.27–0.50). Conclusions. Although the lateral THA group had lower abductor torque, there were no Trendelenburg signs during gait. Elevated gluteus medius activation in this group was a compensation for the weakness, and the muscle produced sufficient force to control the pelvis. Also, 1 year post-THA there were no statistically significant gait differences between lateral and posterior approaches. For any tables or figures, please contact the authors directly

In this in vitro study of the hip joint we examined which soft tissues act as primary and secondary passive rotational restraints when the hip joint is functionally loaded. A total of nine cadaveric left hips were mounted in a testing rig that allowed the application of forces, torques and rotations in all six degrees of freedom. The hip was rotated throughout a complete range of movement (ROM) and the contributions of the iliofemoral (medial and lateral arms), pubofemoral and ischiofemoral ligaments and the ligamentum teres to rotational restraint was determined by resecting a ligament and measuring the reduced torque required to achieve the same angular position as before resection. The contribution from the acetabular labrum was also measured. Each of the capsular ligaments acted as the primary hip rotation restraint somewhere within the complete ROM, and the ligamentum teres acted as a secondary restraint in high flexion, adduction and external rotation. The iliofemoral lateral arm and the ischiofemoral ligaments were primary restraints in two-thirds of the positions tested. Appreciation of the importance of these structures in preventing excessive hip rotation and subsequent impingement/instability may be relevant for surgeons undertaking both hip joint preserving surgery and hip arthroplasty. Cite this article: Bone Joint J 2015; 97-B:484–91