Introduction. Studies have shown that increased implant conformity in total knee arthroplasty (TKA) has been linked to increased constraint and thus rotational torque at the bone/implant interface. Anterior stabilized (AS) tibial inserts were designed to compensate for excessive AP motion in less-conforming cruciate-retaining (CR) tibial inserts. However, increased constraint may affect implant loading. Therefore, the purpose of this study is to model rotational prosthesis constraint based on implant-specific data and to compare rotational torque and 3D contact forces in implants with CR-lipped and AS tibial inserts during normal gait. Methods. A previously reported knee joint contact model was updated to include rotational torque due to prosthesis constraint (ASTM F1223(14)). Piecewise multiple linear regression with manually selected cutoff points was used to determine estimates of AP force, ML force, and rotation torque as functions of AP displacement, ML displacement, knee external rotation, respectively, and knee flexion angle from standard data. These functions were used to estimate total moment contribution of the prosthesis from measured knee displacement/rotation angles. Estimates were incorporated into the contact model equilibrium equations as needed by the model. As the model parametrically varies muscle activation coefficients to solve for the range of physiologically possible forces at each time point, the reported force/torque values are the mean across all solutions at each time point. Rotational torque and three dimensional contact forces were calculated for 14 informed-consented subjects, five with AS tibial inserts (1/4 m/f, 67±10 years, 29.2±4.4 BMI, 1/4 right/left) and nine with CR-lipped TKRs (2/7 m/f, 64±6 years, 30.6±5.8 BMI, 4/5 right/left). Rotational torque waveforms were compared using statistical nonparametric mapping; 3D contact forces were compared at mean timing of the flexion/extension moment peaks using independent samples t-tests. Results. Waveform analysis of rotational torque found no significant differences between implant types. CR- lipped inserts showed an initial peak internal rotation torque during weight acceptance and continued with a pattern of internal rotation throughout stance. Peak torque for AS inserts also occurred during weight acceptance, but it varied between internal/external rotation torque. Additionally, after weight acceptance, AS subjects showed a pattern of external rotation torque. Mean axial force, medial-lateral shear force, and anterior-posterior shear force waveforms were similarly shaped between implant groups. Flexion and extension moment peaks occurred at 23% and 74% stance on average. There were no significant differences in three-dimensional knee joint contact forces between groups at either time point. Discussion. There were different patterns of rotational torque between groups. Implants with lipped CR inserts tended to undergo internal rotation torques that peaked during weight acceptance. Torque seen in implants with AS inserts was also largest during weight acceptance, but greatly varied between internal and external rotation, before settling in a pattern of external rotation for the remainder of stance. This may be due to constraints added by AS insert geometry. In conclusion, a model of rotational torque due to implant constraints has been developed; increased implant constraint increased the external rotation torque experienced by the implant and may also affect shear forces at the implant surface. For any figures or tables, please contact authors directly

Introduction. Loosening of the baseplate is one of the most common causes of failure in Reverse Shoulder Arthroplasty. To allow osteo-integration to occur and thus provide long-term stability, initial screws fixation plays a pivotal role. In particular, tightening torque and force of nonlocking screws are two parameters that are considered to have a clear impact on implant stability, yet the relation is not fully understood. For this reason, this study aims to define an experimental set-up, to measure force and torque in artificial bone samples of different quality, in order to estimate ranges of optimal surgical values and give guidelines to maximize screw fixation and therefore initial implant stability. Methods. A custom-made torque sensor (Figure 1a) was built and calibrated using a lever deadweight system. To measure the compression force generated by the screw head, three thin FlexiForce sensors (Tekscan, South Boston, US) were enclosed between two 3D printed plates with a central hole to allow screw insertion (Figure 1b). The tightening force, represented by the sum of the three sensors, was calibrated using a uniaxial testing machine (Zwick/Roell, Ulm, Germany). Multiple screw lengths (26mm, 32mm and 47mm) were selected in the protocol. Synthetic bone blocks (Sawbones; Malmö, Sweden) of 20 and 30 PCF were used to account for bone quality variation. To evaluate the effect of a cortical bone layer, for each density three blocks were considered with 0 mm (no layer), 1.5 mm and 3 mm of laminate foam of 50 PCF. The holes for the screws were pre-drilled in the same way as in the operation room. For each combination of screw dimensions and bone quality, ten measurements were performed by acquiring the signal of the insertion torque and tightening force until bone breaking. Results. The typical output signal shows a maximum in the torque and force measurements, corresponding to bone breaking. After failure, a drop in the torque is visible, while a residual force remains present. For the base case (20 PCF), both torque and force show increasing mean values with longer screws, passing from 0.39 Nm (26mm) to 1.12 Nm (47mm) and from 180 N (26mm) to 419 N (47mm) respectively. Similar patterns were observed when the cortical layer was present or the bone quality was increased. Discussion. The findings of this study demonstrate that tightening force and torque are strongly impacted by bone quality and screw length. As main outcome, the maximum torque values could be used in clinical practice as a safety threshold for the surgeon. Compression force could also be used as input parameter in stability predictions of numerical models. Since only bone substitute was used, future research should include the extension to cadaveric bones. For any figures or tables, please contact authors directly

Prosthetic Hip dislocations remain one of the most common major complications after total hip arthroplasty procedures, which has led to much debate and refinement geared to the optimization of implant and bearing options, surgical approaches, and technique. The implementation of larger femoral heads has afforded patients a larger excursion distance and primary arc range motion before impingement, leading to lowered risk of hip dislocation. However, studies suggest that while the above remains true, the use of larger heads may contribute to increased volumetric wear, trunnion related corrosion, and an overall higher prevalence of loosening, pain, and patient dissatisfaction, which may require revision hip arthroplasty. More novel designs such as the dual mobility hip have been introduced into the United States to optimize stability and range of motion, while possibly lowering the frictional torque and modes of failure associated with larger fixed bearing articulations. Therefore, the aim of this study is to compare the effect of bearing design and anatomic angles on frictional torque using a clinically relevant model8. Two bearing designs at various anatomical angles were used; a fixed and a mobile acetabular component at anatomical angles of 0°,20°,35°,50°, and 65°. The fixed design consisted of a 28/56mm inner diameter/outer diameter acetabular hip insert that articulated against a 28mm CoCr femoral head (n=6). The mobile design consisted of a 28mm CoCr femoral head into a 28/56mm inner diameter/outer diameter polyethylene insert that articulates against a 48mm metal shell (n=6). The study was conducted dynamically following a physiologically relevant frictional model8. A statistical difference was found only between the anatomical angles comparison of 0vs65 degrees in the mobile bearing design. In the fixed bearing design, a statistical difference was found between the anatomical angles comparison of 20vs35 degrees, 20vs50 degrees, and 35vs65 degrees. No anatomical angle effect on frictional torque between each respective angle or bearing design was identified. Frictional torque was found to decrease as a function of anatomical angle for the fixed bearing design (R2=0.7347), while no difference on frictional torque as a function of anatomical angle was identified for the mobile bearing design. (R2=0.0095). These results indicate that frictional torque for a 28mm femoral head is not affected by either anatomical angle or bearing design. This data suggests that mobile design, while similar to the 28mm fixed bearing, may provide lower frictional torque when compared to larger fixed bearings >or= 32mm8. Previous work by some of the authors [8] show that frictional torque increases as a function of femoral head size. Therefore, this option may afford surgeons the ability to achieve optimal hip range of motion and stability, while avoiding the reported complications associated with using larger fixed bearing heads8. It is important to understand that frictional behavior in hip bearings may be highly sensitive to many factors such as bearing clearance, polyethylene thickness/stiffness, polyethylene thickness/design, and host related factors, which may outweigh the effect of bearing design or cup abduction angle. These factors were not considered in this study

Compared to single-incision distal biceps repair (SI), double-incision repair (DI) theoretically allows for reattachment of the tendon to a more anatomically favorable position. We hypothesized that DI repair would result in greater terminal supination torque compared to SI repair for acute distal biceps ruptures. In this retrospective cohort study, patients were included if they sustained an isolated, acute (° supinated position. Secondary outcomes included supination torque in 45° supinated, neutral, and 45° pronated positions, ASES elbow score, DASH, SF-12, and VAS. Power analysis revealed that at least 32 patients were needed to detect a minimum 15% difference in the primary outcome (β = 0.20). Statistical analysis was performed with significance level α = 0.05 using R version 3.4.1 (R Core Team 2017, Vienna, Austria). Of 53 eligible patients, 37 consented to participate. Fifteen were repaired using DI technique and 22 using SI technique. Mean age was 47.3yrs and median follow-up time was 28.1months. The groups did not differ with respect to age, time-to-follow-up, dominance of arm affected, Workers Compensation or smoking status. Mean supination torque, measured as the percentage of the unaffected side, was 60.9% (95%CI 45.1–76.7) for DI repair versus 80.4% (95%CI 69.1–91.7) for SI repair at the 60°supinated position (p=0.036). There were no statistically significant differences in mean supination torque at the 45°supinated position: 67.1% (95%CI 49.4–84.7) for DI versus 81.8% (95%CI 72.2–91.4) for SI (p=0.102), at the neutral position: 88.8% (95%CI 75.2–102.4) for DI versus 97.6% (95%CI 91.6–103.7) for SI (p=0.0.170), and at the 45°pronated position: 104.5% (95%CI 91.1–117.9) for DI versus 103.4 (95%CI 97.2–109.6) for SI (p=0.0.862). No statistically significant differences were detected in the secondary outcomes ASES Pain, ASES Function, DASH scores, SF-12 PCS or MCS, or VAS Pain. A small difference was detected in VAS Function (median 1.3 for DI repair versus 0.5 for SI repair, p=0.023). In a multivariate linear regression model controlling for arm dominance, age, and follow-up time, SI repair was associated with a greater mean supination torque than DI repair by 19.6% at the 60°supinated position (p=0.011). Contrary to our hypothesis, we found approximately a 20% mean improvement in terminal supination torque for acute distal biceps ruptures repaired with the single-incision technique compared to the double-incision technique. Patients uniformly did well with either technique, though we contend that this finding may have clinical significance for the more discerning, high-demand patient

Compared to single-incision distal biceps repair (SI), double-incision repair (DI) theoretically allows for reattachment of the tendon to a more anatomically favorable position. We hypothesized that DI repair would result in greater terminal supination torque compared to SI repair for acute distal biceps ruptures. In this retrospective cohort study, patients were included if they sustained an isolated, acute (° supinated position. Secondary outcomes included supination torque in 45° supinated, neutral, and 45° pronated positions, ASES elbow score, DASH, SF-12, and VAS. Power analysis revealed that at least 32 patients were needed to detect a minimum 15% difference in the primary outcome (β = 0.20). Statistical analysis was performed with significance level α = 0.05 using R version 3.4.1 (R Core Team 2017, Vienna, Austria). Of 53 eligible patients, 37 consented to participate. Fifteen were repaired using DI technique and 22 using SI technique. Mean age was 47.3yrs and median follow-up time was 28.1months. The groups did not differ with respect to age, time-to-follow-up, dominance of arm affected, Workers Compensation or smoking status. Mean supination torque, measured as the percentage of the unaffected side, was 60.9% (95%CI 45.1–76.7) for DI repair versus 80.4% (95%CI 69.1–91.7) for SI repair at the 60°supinated position (p=0.036). There were no statistically significant differences in mean supination torque at the 45°supinated position: 67.1% (95%CI 49.4–84.7) for DI versus 81.8% (95%CI 72.2–91.4) for SI (p=0.102), at the neutral position: 88.8% (95%CI 75.2–102.4) for DI versus 97.6% (95%CI 91.6–103.7) for SI (p=0.0.170), and at the 45°pronated position: 104.5% (95%CI 91.1–117.9) for DI versus 103.4 (95%CI 97.2–109.6) for SI (p=0.0.862). No statistically significant differences were detected in the secondary outcomes ASES Pain, ASES Function, DASH scores, SF-12 PCS or MCS, or VAS Pain. A small difference was detected in VAS Function (median 1.3 for DI repair versus 0.5 for SI repair, p=0.023). In a multivariate linear regression model controlling for arm dominance, age, and follow-up time, SI repair was associated with a greater mean supination torque than DI repair by 19.6% at the 60°supinated position (p=0.011). Contrary to our hypothesis, we found approximately a 20% mean improvement in terminal supination torque for acute distal biceps ruptures repaired with the single-incision technique compared to the double-incision technique. Patients uniformly did well with either technique, though we contend that this finding may have clinical significance for the more discerning, high-demand patient

Background. Hip resurfacing has advantages for the young active patient with arthritis; maintaining a large range of motion, preserving bone stock, and reduced dislocation risk. However high serum metal ion levels with metal-on-metal resurfacing, and their clinical implications, has led to a decline in the use of hip resurfacing. Ceramic bearing surfaces display the lowest frictional torque and excellent wear rates. Recent developments have enabled large, strong ceramic materials to be used as resurfacing components. Any wear debris that is generated from these articulations is inert. However an all-ceramic hip resurfacing could be at risk of fracture at the head-stem junction. A new ceramic hip resurfacing system with a titanium-ceramic modular taper junction has been developed. The introduction of a taper introduces the potential for fretting corrosion; we sought to determine the extent of this in an in-vitro model, and compared this prosthesis to the conventional 12/14 titanium-cobalt chrome (Ti6Al4V-CoCr) taper junction. Methods. To simulate the gait cycle, sinusoidal cyclical loads between 300N-2300N, at a frequency of 3Hz, were applied to different head-neck offsets generating different bending moments and torques. The effect of increasing the bending moment and frictional torque were tested separately. Furthermore, the resurfacing head was mounted in a fixture held with just the stem, thus representing complete bone resorption under the head. An electrochemical assessment using potentiostatic tests at an applied potential of 200mV, was used to measure the fretting current (μA) and current amplitude (μA). In a short-term 1000 cycle test, six neck lengths (short to xxx-long) of the Ti6Al4V-CoCr taper were compared to the standard neutral (concentric), and 3mm A/P offset stem options for the resurfacing design. To represent frictional torque, four increments of increasing torque (2-4-6-8Nm) were applied to both tapers. In a long term test with the resurfacing stem, the worst-case scenario of the eccentric offset option and 8Nm of torque were applied, and potentiostatic measurements were taken every million cycles, up to 10 million cycles. Results. For bending moment through the centre of the head, the standard neutral resurfacing taper displayed equivalent fretting current (1.35μA) compared to its conventional taper equivalent, the short 12/14 Ti6Al4V-CoCr taper (Fig. 1a). That was despite the bending moment through the resurfacing taper being higher due to the offset nature of its taper in relation to the centre of the head. For applied torque, the resurfacing taper displayed reduced average fretting current and average maximum fretting current when compared to the conventional taper (Fig. 1b), though this did not reach statistical significance (Kruskal-Wallis test). Under long term testing for worst-case bending and torque, the resurfacing taper displayed low fretting currents (<2μA and <5μA respectively) with no significant variance of the median values across 10 million cycles (Figs. 2 and 3). Conclusion. When compared to the gold-standard taper junction, the LIMA ceramic hip resurfacing displays equivalent fretting corrosion for bending moment and improved fretting corrosion for frictional torque. Across long term testing, stable and low fretting currents at this taper junction highlight its potential in clinical use

In cases of poor bone quality intraoperative torque measurement might be an alternative to preoperative dual energy x-ray absorptiometry (DXA) to assess bone quality in Total Hip Arthroplasty (THA). 14 paired fresh frozen human femurs were included for trabecular peak torque measurement. We evaluated an existing intraoperative torque measurement method to assess bone quality and bone strength. We modified the approach to use this method in total hip arthroplasty (THA), which has not been published before. Since there are several approaches used in THA to exposure the hip joint, we decided to prefer the measurement in the femoral head which allows every surgeon to perform this measurement. Here a 6.5 × 23 mm blade was inserted into the proximal femur without harming the lateral cortical bone (figure 1). Further tests of the proximal femur evaluated the results of this new method: DXA, micro-computed tomography (μCT) and biomechanical load tests. Basic statistical analyses and multiple regressions were done. In the femoral head mean trabecular peak torque was 4.38 ± 1.86 Nm. These values showed a strong correlation with the values of the DXA, the μCT and the biomechanical load test. In comparison to the bone mineral density captured by DXA, the results of the intraoperative torque measurement showed a superior correlation with high sensitive bone quality evaluating methods (mechanical load tests and micro-computed tomography). Hence, the use of this intraoperative torque measurement seems to be more accurate in evaluating bone strength and bone quality than DXA during THA. The torque measurement provides sensitive information about the bone strength, which may affect the choice of implant in cases of poor bone stock and osteoporosis. In clinical use the surgeon may alter the prosthesis if the device indicates poor bone quality. Furthermore, we assume that the disadvantages associated with DXA scans like radiation exposure or errors caused by potential extraosteal sclerosis and interindividual soft-tissue artifacts could be excluded

Introduction:. High failure rates with large diameter, metal on metal hip replacements have highlighted a potential issue with the head/stem taper junction as one of the significant sources of metal ion release. Postulated reasons as to why this may be such a problem with large head metal on metal hip replacements is due to the increased torque achieved by the larger head size. This may be responsible for applying greater micromotion between the head and stem taper and consequently greater amounts of fretting corrosion. The aim of this study was to perform short term in vitro electrochemical tests to assess the effect of increasing head diameter and torque on the fretting corrosion susceptibility of the head/stem taper interface and to investigate its effect on different material combinations. Methods:. 36 mm Cobalt Chrome (CoCr) femoral heads were coupled with either a CoCr or Titanium (Ti) stem with 12/14 tapers, all with a smooth surface finish. Increasing perpendicular horizontal offsets in the sagittal plane created incremental increases in torque. Offset increments of 0 mm, 5.4 mm and 7.5 mm were selected (Figure 1) to simulate the torque force equivalent to 9 Nm, 12 Nm and 17 Nm. An inverted hip replacement setup was used (ASTM F1875-98) (Figure 2). Components were statically loaded at 0 kN and 2.3 kN prior to sinusoidal cyclic loading and electrochemical testing. Mean & fretting currents were calculated every 50 cycles up to a maximum of 1000 cycles of sinusoidal cyclic loading at 3 Hz along with the Overall Mean Current (OMC), Overall Mean Fretting Current (OMFC) and Overall Current change (OCC). Results:. There was a significant increase in the mean current (R = 0.992, p = 0.008) and fretting current (R = 0.929, p = 0.071) for CoCr-CoCr and in the mean current (R = 0.780, p = 0.005) and fretting current (R = 0.810, p = 0.006) for CoCr-Ti material combinations, with increasing femoral offsets. The highest currents (mean and fretting) were produced at 7.5 mm and the lowest at 0 mm offsets. The proportional relationship between torque and corrosion was observed for both CoCr-CoCr and CoCr-Ti material combinations. With low torques we saw higher OMC and OMFC with the Co-Ti material combination however with higher torques we saw higher OMC and OMFC with the CoCr-CoCr combination (Figure 3). Conclusion:. Increasing torque leads to increased susceptibility to fretting corrosion at the modular head/stem taper interface of total hip replacements for both head stem material combinations. This study highlights the risk of high frictional torque, independent of material combination, on the head/ stem with the use of large heads. This is particularly relevant with the increasing use of larger diameter femoral heads across all bearing material combinations, in current hip arthroplasty practice

Introduction. It has been speculated that impact deformation of thin 1-piece cups used for modern metal-on-metal hip replacement may contribute to early failure. The purpose of this study was to reproduce typical impact deformation and quantify the effect of this on the frictional torque generated at the hip. Methods. We tested nine hip couples of three designs (the ASR, BHR and Durom) and three sizes (42mm, 46mm and 50mm). A custom compression device was designed to replicate the in vivo forces and impact deformation of 1-piece metal cups reported in the literature. Each cup was mounted in the device, which itself was mounted on a mechanical testing machine. The cups were compressed with incremental loads up to a maximum of 2000N. At each increment we measured cup deformation, and then the head component was seated into the cup. The hip was lubricated and the head component rotated 60 degrees axially within the cup and the axial torque was measured. Results. Maximum deformation occurred at the rim for all cups, and was not associated with cup diameter (p = 0.42). However, at all applied loads the BHR cups were deformed significantly less than both the ASR and Durom cups (all p < 0.05). We observed deformation that exceeded the diametric clearance for both the ASR and Durom. Deformation resulted in increased axial torque up to eight times higher than those measured at zero deformation. The maximum torques generated for the BHR cups were significantly lower than those observed for both the ASR and Durom cups. Discussion. Deformation of 1-piece cups, equatorial bearing and subsequent increased frictional torque is likely to have widespread consequences for the performance of metal-on-metal hip replacement. This may include loosening of the cup, mechanical damage at the taper junction and increased early wear of the bearing surface

Burroughs et al showed that frictional torque increases with increasing head size in a simple in vitro model and showed differences in frictional torque with different polyethylene materials [1]. Therefore, the purpose of this study was to evaluate the influence of bearing material and bearing size on the frictional torque of hip bearings utilizing a more physiologically relevant hip simulator model. A total of four hip bearing combinations (Crosslinked PE/CoCr, Conventional PE/CoCr, Crosslinked PE/Delta and Alumina /Alumina) with various bearing sizes were evaluated. The sizes tested in this study range from 22 mm to 44 mm; it is important to note that the study only evaluated bearing combinations (size and material combination) currently commercially available. A total of three samples per bearing combination were tested, with the exception of conventional PE, which included a total of 4 samples. A MTS hip joint simulator was used. All components were oriented anatomically with the femoral head mounted below on a rotating angled block which imparts a 23° biaxial rocking motion onto the head. Loading was held constant at each load level (500N, 1000N, 1500N, 2000N, 2450N) for at least two rotational cycles while all 3 axes of load and all 3 axes of moments were measured at 10 khz. Fresh Alpha Calf Fraction serum was utilized as a lubricant. Results show that frictional torque increases with the increase of head size regardless of head material for all polyethylene combinations (p > 0.05), as shown in Figure 1 and 2. However, results showed no change in frictional behavior for the Alumina/Alumina combination regardless of the bearing size. The results of this test did not show any significant difference between crosslinked PE and conventional PE materials for sizes 28 mm and 32 mm when paired against a CoCr head (p > 0.05) (Figure 3). The Alumina/Alumina bearing combination had the lowest frictional torque among all the bearing material combinations evaluated in this study. This data suggests that there is a strong correlation between increased head size and increased frictional torque (R. 2. = 0.6906, 0.8847) for the polyethylenes evaluated here regardless of head material. No correlation can be concluded for the Alumina /Alumina bearing combination (R. 2. = 0.0217). The combination of Alumina /Alumina seems to have the most favorable frictional properties. This data also suggests no effect on frictional properties regardless of the polyethylene material (crosslinked and conventional) for sizes 28 mm and 32 mm. The frictional torque values recorded in this study are different than those published by Burroughs et al [1]. This difference may be attributed to the testing methodology. The current study utilizes a hip simulator, which closely mimics the natural joint providing a more physiologically relevant model whereas the Burroughs et al study utilizes a single axis machine. It is important to understand that frictional behavior in hip bearings may be highly sensitive to bearing clearance, cup thickness, and stiffness, which may outweight the effect of head diameter. Further evaluation is necessary to isolate and investigate those parameters

Introduction. Frictional torque is generated at the hip joint during normal gait loading and motion [1]. This study investigated the effect of shell deformation due to press-fit on frictional torque generated at the articulating surfaces of cementless acetabular shells that incorporated fixed and dual mobility bearing designs. Materials and Methods. Figure 1 lists the study groups (minimum of n = 5). All groups were tested with a 50 mm Trident PSL shell (Stryker Orthopaedics, NJ) and a Ti6Al4V trunnion. Metal-on-Metal specimens were custom designed and manufactured, and are not approved for clinical use. The remaining groups consisted of commercially available products (Stryker Orthopaedics, NJ). All groups were tested with the shells in deformed and undeformed states. Deformed Setup: A two-point relief configuration was created in a polyurethane foam block (Figure 2) with a density of 30 lb/ft. 3. to replicate shell deformation due to press-fit [2]. The blocks were machined to replicate the press-fit prescribed in the shell's surgical protocol. Each shell was assembled into the foam block by applying an axial force at 5 mm/min until it was completely seated. Undeformed Setup: Each shell was assembled in a stainless steel block with a hemispherical cavity that resulted in a line-to-line fit with the shell OD. Frictional torque was measured using a physiologically relevant test model [3]. In this model, the specimen block was placed in a fixture to simulate 50° abduction and 130° neck angle (Figure 2). A 2450N side load was applied and the femoral head underwent angular displacement of ± 20° for 100 cycles at 0.75 Hz. The articulating surfaces were lubricated with 25% Alpha Calf Fraction Serum. Peak torque was observed towards the end or the beginning of each cycle where the velocity of the femoral head approaches 0 and the head changes direction. This torque is referred as maximum static frictional torque. Specimen groups were statistically compared with a single-factor ANOVA test and a Tukey post-hoc test at 95% confidence level. Paired t-tests were performed to compare individual groups in deformed and undeformed states. Results. Figure 3 contains the results. In both deformed and undeformed states, the MoM group exhibited the highest frictional torque whereas the MDM group had the lowest frictional torque. In both states, the difference in frictional torque between MoM vs. 28 mm–Fixed Bearing and MoM vs. MDM was statistically significant whereas the difference between 28 mm-Fixed Bearing and MDM was not statistically significant. Shell deformation due to press-fit did not have a significant effect on any of the groups. Discussion. This study evaluated the effect of press-fit on the frictional torque generated in various cementless acetabular systems using a physiologically relevant in-vitro test model. Results from this test suggest a trend towards lower frictional torque for dual mobility bearings, which is worthy of further investigation

Introduction. Ilizarov fixators are reliant on tensioned fine wires for stability. The tension in the wires is generated using specific tensioning devices. Loss of wire tension over time may lead of loss a stability and complications. A series of in vitro experiments were undertaken to explore wire tensioner accuracy, the impact of fixation bolt torque and initial tension on loss of tension in ilizarov constructs under static and dynamic loads. Materials & Methods. Medical grade materials were applied to a synthetic bone analogue using surgical instruments in all experiments. Bolt torque was fixed at 6, 10 or 14 Nm using a torque limiting wrench. Wire tension was assessed using a strain measurement bridge. Wires were tensioned to 90, 110 and 130kg as measured by a commercial dynamometric tensioner. Static and dynamic testing was undertaken using an instron testing machine. Cyclical loads from 50–750N were applied for 5000 cycles. Results. Actual wire tension was approximately 15% less than indicated by the tensioner device. Using fixation bolt torques of 10Nm and 14Nm achieved final wire tensions of around 60% and 80% of that applied at 90 and 130kg of applied tension. Static load testing demonstrated self stiffening to similar levels in all pre-tensions. Dynamic testing demonstrated significant loss of tension, most of which occured in the first 3 cycles, inversely proportional to the tension initially applied. Conclusions. These experiments provides insight into the effect of initially applied wire tension on Illizarov mechanical performance. It is important surgeons understand how the different ways that these devices are applied affects mechanical performance. Further research examining what factors affect performance across different manufacturers equipment would therefore be relevant, alongside the development of novel fixation methods to reduce wire slippage and the further development of equipment for clinical use

While controversy remains as to the relative benefit of operative (OM) versus non-operative management (NOM) of Achilles tendon ruptures (ATR), few studies have examined the effect on high impact maneuvers such as jumping and hopping. The purpose of this study is to compare functional performance and musculotendinous morphology in patients following OM or NOM for acute ATR. Eligible patients were aged 18-65 years old with an ATR who underwent OM or NOM within three weeks of injury and were at least one-year post injury. Gastrocnemius muscle thickness and Achilles tendon length and thickness were assessed with ultrasound. Functional performance was examined with single-leg hop tests and isokinetic plantar strength at 60o/s and 120o/s. 24 participants completed testing (12/ group). Medial (OM: 2.2 ± 0.4 cm vs 1.9 ± 0.3 cm, NOM 2.15 ± 0.5 cm vs 1.7 ± 0.5 cm; p = 0.002) and lateral (OM 1.8 ± 0.3 cm vs 1.5 ± 0.4 cm, NOM 1.6 ± 0.4 cm vs 1.3 ± 0.5 cm; p = 0.008) gastrocnemius thickness were reduced on the affected limb. The Achilles tendon was longer (OM: 19.9 ± 2.2 cm vs 21.9 ± 1.6 cm; NOM: 19.0 ± 3.7 cm vs 21.4 ± 2.9 cm; p = 0.009) and thicker (OM: 0.48 ± 0.16 cm vs 1.24 ± 0.20 cm; NOM: 0.54 ± 0.08 cm vs 1.13 ± 0.23 cm; p < 0.001) on the affected limb with no differences between groups. Affected limb plantar flexion torque at 20o plantar flexion was reduced at 60o/s (OM: 55.6 ± 20.2 nm vs 47.8 ± 18.3 nm; NOM: 59.5 ± 27.5 nm vs 44.7 ± 21.0 nm; p = 0.06) and 120o/s (OM: 44.6 ± 17.9 nm vs 36.6 ± 15.0 nm; NOM: 48.6 ± 16.9 nm vs 35.8 ± 10.7 nm; p = 0.028) with no group effect. There was no difference in single leg hop performance. Achilles tendon length explained 31.6% (p = 0.003) and 18.0% (p = 0.025) of the variance in plantar flexion peak torque limb symmetry index (LSI) at 60o/s and 120o/s respectively. Tendon length explained 28.6% (p=0.006) and 9.5% (p = 0.087) of LSI when torque was measured at 20o plantar flexion at 60o/s and 120o/s respectively. Conversely, tendon length did not predict affected limb plantar flexion peak torque (nm), angle-specific torque at 20o plantar flexion (nm) and affected limb single leg hop distance (cm) or LSI (%). There was no difference in tendon length between treatment groups and deficits in gastrocnemius thickness and strength are persistent. Deficits in the plantar flexion strength LSI are partially explained by increased tendon length following Achilles tendon rupture, regardless of treatment strategy. Hop test performance is maintained and may be the result of compensatory movements at other joints despite persistent plantarflexion weakness

Nearly a quarter of screws cause damage during insertion by stripping the bone, reducing pullout strength by over 80%. Studies assessing surgically achieved tightness have predominately shown that variations between individual surgeons can lead to underpowered investigations. Further to the variables that have been previously explored, several basic aspects related to tightening screws have not been evaluated with regards to how they affect screw insertion. This study aims to identify the achieved tightness for several variables, firstly to better understand factors related to achieving optimal intraoperative screw purchase and secondly to establish improved methodologies for future studies. Two torque screwdrivers were used consecutively by two orthopaedic surgeons to insert 60 cortical, non-locking, stainless-steel screws of 3.5 mm diameter through a 3.5 mm plate, into custom-made 4 mm thick 20 PCF sheets of Sawbone, mounted on a custom-made jig. Screws were inserted to optimal tightness subjectively chosen by each surgeon. The jig was attached to a bench for vertical screw insertion, before a further 60 screws were inserted using the first torque screwdriver with the jig mounted vertically, enabling horizontal screw insertion. Following the decision to use the first screwdriver to insert the remaining screws in the vertical position for the other variables, the following test parameters were assessed with 60 screws inserted per surgeon: without gloves, double surgical gloves, single surgical gloves, non-sterile nitrile gloves and, with and then without augmented feedback (using digitally displayed real-time achieved torque). For all tests, except when augmented feedback was used, the surgeon was blinded to the insertion torque. Once the stopping torque was reached, screws were tightened until the stripping torque was found, this being used to calculate tightness (stopping/stripping torque ratio). Screws were recorded to have stripped the material if the stopping torque was greater than the stripping torque. Following tests of normality, Mann-Whitney-U comparisons were performed between and combining both surgeons for each variable, with Bonferroni corrections for multiple comparisons. There was no significant (p=0.29) difference in the achieved tightness between different torque screw drivers nor different jig positions (p=0.53). The use of any gloves led to significant (p < 0 .001) increases in achieved tightness compared to not using gloves for one surgeon but made no difference for the other (p=0.38–0.74). Using augmented feedback was found to virtually eliminate stripping. For one surgeon average tightness increased significantly (p < 0 .001) when torque values were displayed from 55 to 75%, whilst for the other, this was associated with significantly decreases (p < 0 .001), 72 to 57%, both surgeons returned to their pre-augmentation tightness when it was removed. Individual techniques make a considerable difference to the impact from some variables involved when inserting screws. However, the orientation of screws insertion and the type of screwdriver did not affect achieved screw tightness. Using visual feedback reduces rates of stripping and investigating ways to incorporate this into clinical use are recommended. Further work is underway into the effect of other variables such as bone density and cortical thickness

Introduction. In my paediatric Orthopaedic practice I use Kirchner wires for the fixation of the TSF on bone. I noted a significant percentage of wire loosening during the post-operative period. The aim of this project was to establish the effectiveness of the wire clamping mechanism and find ways to reduce the incidence of wire loosening when using the TSF. Materials and Methods. In the first instance wire slippage was measured intra-operatively after the tensioner was removed using an intra-operative professional camera. Following this study mechanical tests were performed in the lab measuring the pull out properties of Kirchner wires using different bolts and different torque levels in order to tighten the wire on the fixator. Results. Our clinical study confirmed wire slippage intra-operatively immediately after the tensioner was removed. Wire slippage after the tensioner was removed was found to vary from 0.01 mm to 0.51 mm (mean 0.19 mm). Our mechanical tests showed that the ideal torque for tightening the wire on the frame using a bolt was around 15 N.m. A comparison between cannulated and slotted bolts suggested that cannulated bolts are more effective as a clamping mechanism. A comparison between aluminium made Taylor Spatial frame rings and stainless steel made Ilizarov rings suggested that the Taylor Spatial frame rings are more effective as part of a clamping mechanism. Conclusions. It is important that clinicians routinely measure the torque they use to clamp wires on circular external fixators. Clinicians and manufacturers are informed that the type of bolt used is important in maintaining wire tension. Manufacturers should design the ideal bolt which effectively grips the wire without the risk of fracture. The Ilizarov frame clamping mechanism can be effectively used with the Taylor Spatial frame

Introduction. Patient Specific Guides (PSGs) are used to increase the accuracy of arthroplasty. PSGs achieve this by incorporating geometry that fits in one unique position and orientation on a patient's bone. Sufficient docking rigidity ensures PSGs do not shift before being fixed by pins. Despite the importance of PSG docking rigidity, minimal research has been conducted on this issue. This study aims to determine whether commercially available PSGs, in their equilibrium position, provide sufficient stability for reliable surgical use. Materials and Methods. A commercially available PSG (Glenoid PSG, BLUEPRINT™, Wright Medical) was analyzed and tested in this study; the mechanical performance of this guide was assessed using a custom testing apparatus mounted to a universal testing machine (UTM) (MTI-10k, Materials Testing Inc), assembled with a high-precision load cell (MiniDyn Type 9256C, Kistler). The apparatus accepts an additively manufactured glenoid surrogate and was designed to transform vertical crosshead forces from the UTM into PSG-applied forces transverse to the glenoid plane along anterior-posterior and superior-inferior axes and PSG-applied torques about lateral, anterior, and superior axes. Three trials were recorded for each force and torque application. Prior to each test, the glenoid surrogate and PSG were articulated together with a constant 27N compressive force — equivalent to the normal force exerted by a surgeon using the guide — applied using springs. Forces were recorded when the guide was displaced 2mm by transverse loads or 5° by torque application; if the guide visibly dislodged from the glenoid surrogate before either criterion was met, force was recorded at the time of dislodgement. If no PSG movement occurred, testing ceased at 75N or 1.19N⋅m, depending on the test type. Results. The lowest and highest torques to displace the PSG by 5° were around the lateral (−0.08±0.02 N⋅m) and superior axes (0.87±0.23 N⋅m), respectively. The lowest and highest forces to displace the PSG by 2mm were along the inferior (31.77± 6.30N) and posterior axes (64.80±0.79N), respectively. Although it yielded at a higher torque than about the lateral axis, CCW rotation about the posterior axis produced the earliest PSG dislodgement at 3.76° while the PSG dislodged after only 1.05mm in the anterior direction. Discussion. The above results demonstrate that the tested PSG design produces similar docking rigidity for all tested rotations except rotations about the lateral axis, which provided 4 times less stability than the next lowest result. This indicates that the PSG may not provide sufficient resistance in this direction to prevent inadvertent mal-rotation. The relatively low rigidity in anterior and superior translation indicate that this PSG design may be prone to mal-positioning errors in these directions. With these data in mind, PSG docking rigidity is not equal in all loading directions which could play a role in the clinical accuracy. Furthermore, this indicates that a systematic, objective method for PSG design optimization may be warranted. For any figures or tables, please contact authors directly

Introduction. A search of the literature indicates several constrained total knee arthroplasty (TKA) systems are at risk for articular surface lockdown bolts backing out. The backing out of a lockdown bolt may lead to an unstable and/or painful knee and may necessitate revision. Upon backing out, the bolt may damage implant components and surrounding tissues. To date, studies in the literature have not simulated or replicated loosening of bolts in TKA. Therefore, the objectives of this study were to 1) develop a set of physiological loading parameters that challenge bolted articular surfaces; 2) evaluate whether significant bolt torque is lost during application of this loading to a CCK device with a bolt as a secondary locking mechanism. Materials and Methods. Physical test parameters to loosen lockdown bolts were developed based on loading experienced during activities of daily living. Sinusoidal waveforms and timing were used to simulate worst case walking gait conditions. Compared to data from everyday activities in instrumented TKR patients, anterior posterior loads and internal/external torques exceeding the absolute maximums observed were selected. To transfer more shear and torsion to the joint interface, compressive load lower than typically reported for walking gait was used. Frequency was representative of walking gait motion. The offset in torsional waveform enables a ratcheting motion to drive a loose bolt out of the joint: during external femoral rotation of a left knee, reduced compressive load and posterior directed femoral loading on a CCK spine creates a potential articular surface lift-off. The lift-off may grab the underside of the front bolt shoulder while external (CCW) rotation loosens the bolt. These loading conditions exist during toe-off of walking gait. Two CCK devices were evaluated to capture potential difference in performance: a medium articular surface combination and a smaller articular surface combination. Testing was performed on a load frame capable of rotation and vertical / horizontal translation. Results. No bolts completely loosened when fully tightened. However, average loss in bolt torque of 39.3% on the medium and 21.5% on the smaller articular surface was observed. Loading led to reorientation of the articular surfaces verified by markings on the components. Additional constructs that were under-tightened intentionally to one-quarter of target torque value lost all bolt torque and completely backed out. Discussion and Significance. The backing out of lockdown bolts in TKA has been reported in the literature but not replicated in-vitro. A challenging, physiologically relevant set of loading parameters was developed and applied to a CCK device with an articular surface lockdown bolt. Upon loading, the bolts experienced statistically significant loss of bolt torque which may be attributed to articular surface reorientation. Selected loading parameters led to complete bolt back-out in under-tightened constructs

Abstract. Extended Trochanteric Osteotomy (ETO) improves surgical exposure and aids femoral stem and bone cement removal in Revision Total Hip Replacement (RTHR) surgery. The aim of this study was to identify healing rates and complications of ETO in RTHR. Methods. From 2012 to 2019 we identified patients who underwent ETO for RTHR. Data collected demographics, BMI, diabetes, anticoagulants, indication for ETO, surgical approach, length of ETO and complications. Descriptive analysis of patient demographics, multiple linear regression analysis was performed to assess ETO complications. Results. There were 63 patients with an average age of 69 years. Indications for ETO were aseptic loosening (30), infection (15), periprosthetic fracture (9), recurrent dislocation (5), broken implant (4). There were 44 cemented and 19 uncemented femoral stem that underwent ETO. Average time from index surgery was 12 years (less than a year to 38 years). All procedures were through posterolateral approach and all ETO were stabilised with cables. Average length of ETO was 12.5cm. BMI varied from 18 to 37. There were 5 diabetics and 16 on anticoagulants. All but one ETO went on to unite. Other complications included infection, dislocations, lateral thigh pain and significant limp. Discussion. Fixation of ETO can be with either wires or cables or plate with cables/screws. Advantages of cables are no irritation over greater trochanter, no disruption of gluteus medius/vastus lateralis continuity, reproducible tension in cables and use of torque limiter minimises loss of tension in cables

Total knee arthroplasty with a rotating hinge knee with carbon-fibre-reinforced (CFR)-PEEK as an alternative bushing material with enhanced creep, wear and fatigue behaviour has been clinically established [1-4]. The objective of our study was to compare results from in vitro biotribological characterisation to ex vivo findings on a retrievals. A modified in vitro wear simulation based on ISO 14243-1 was performed for 5 million cycles on rotating hinge knee (RHK) designs (EnduRo®) out of cobalt-chromium and ZrN-multilayer ceramic coating. The rotational & flexion axles-bushings and the flanges are made of CFR-PEEK with 30% polyacrylonitrile fibre content. Analysis of 12 retrieved EnduRo® RHK systems in cobalt-chromium and ZrN-multilayer in regard to loosening torques, microscopic surface analysis, distinction between different wear modes and classification with a modified HOOD-score has been performed. For the RHK design with the polyethylene gliding surface and bushings and flanges made out of CFR-PEEK, a cumulative volumetric wear was measured to be 12.9±3.95 mm. 3. in articulation to cobalt-chromium and 1.3±0.21 mm. 3. to ZrN-multilayer coating - a significant 9.9-fold decrease (p=0.0072). For the CFR-PEEK flexion bushing and flanges the volumetric wear rates were 2.3±0.48 mm. 3. /million cycles (cobalt-chromium) and 0.21±0.02 mm. 3. /million cycles (ZrN-multilayer) (p=0.0016). The 5 million cycles of in vitro wear testing reflect a mean in vivo service life of 2.9 years, which is in accordance to the time in vivo of 12–60 months of the retrieved RHK components [5]. The main wear modes were comparable between retrievals and in vitro specimens, whereby the size of affected area on the retrieved components showed a higher variation. For the EnduRo® RHK design the findings on retrieved implants demonstrate the high suitability of CFR-PEEK as a biomaterial for highly loaded bearings, such as RHK bushings and flanges in articulation to cobalt-chromium and to a ZrN-multilayer coating

Background. Complications of metal-on-metal hip resurfacing, leading to implant failure, include femoral notching, neck fracture, and avascular necrosis. Revision arthroplasty options include femoral-only revision with a head, however mis-matching radial clearance could accelerate metal ion release. Alternatively, revision of a well-fixed acetabular component could lead to further bone loss, complicating revision surgery. We have developed a ceramic hip resurfacing system with a titanium-ceramic taper junction; taking advantage of the low frictional torque and wear rates that ceramic affords. Taking a revision scenario into account, the ceramic head has a deep female taper for the resurfacing stem, but also a superficial tapered rim. Should revision to this resurfacing be required, any femoral stem with a 12/14 taper can be implanted, onto which a dual taper adaptor is attached. The outer diameter of the taper adaptor then becomes the male taper for the superficial taper of the ceramic head; ultimately allowing retention of the acetabular component. In an in-vitro model, we have compared the fretting corrosion of this taper adaptor to existing revision taper options: a titanium-cobalt chrome (Ti-CoCr) taper junction, and a titanium-titanium sleeve-ceramic (Ti-Ti-Cer) taper junction. Methods. To simulate gait, sinusoidal cyclical loads between 300N-2300N, at a frequency of 3Hz was applied to different neck offsets generating different bending moments and torques. Bending moment and frictional torque were tested separately. An electrochemical assessment using potentiostatic tests at an applied potential of 200mV, was used to measure the fretting current (μA) and current amplitude (μA). In a short term 1000 cycle test with bending moment, four neck lengths (short to x-long) were applied. For frictional torque, four increments of increasing torque (2-4-6-8Nm) were applied. In a long-term test using the taper adaptor, the combination of worst-case scenario of bending and torque were applied, and fretting currents measured every million cycles, up to 10 million cycles. Results. Short-term test: When adjusting bending moment the taper adaptor displayed equivalent fretting currents for the short and medium neck lengths. Using the long neck the taper adaptor displayed a higher fretting current, though this was not significant (Kruskal-Wallis test). However, using the X-Long adaptor the fretting current was significantly higher than the other tapers (Fig. 1). Across the range of frictional torques, the taper adaptor displayed equivalent fretting currents to the Ti-CoCr single taper. The Ti-Ti-Cer displayed the lowest fretting currents but this was not significant when compared to the other combinations (Fig. 2). Long-term test: combining the worst case bending (X-Long) and torque (8Nm) showed consistent fretting currents and current amplitudes across 10 million cycles, with no significant variance of the median values (Fig. 3). Conclusion. Electro-chemical testing has highlighted caution if revision arthroplasty is performed using the X-Long taper adaptor. However for shorter neck lengths, fretting corrosion is comparable to existing revision tapers. The LIMA ceramic resurfacing arthroplasty is an integrated system and can be safely revised to a conventional hip system using a dual taper head, and taper adaptor