Computational modeling of microwave ablation with thermal accelerants.

PURPOSE: To develop a computational model of microwave ablation (MWA) with a thermal accelerant gel and apply the model toward interpreting experimental observations in ex vivo bovine and in vivo porcine liver. METHODS: A 3D coupled electromagnetic-heat transfer model was implemented to characterize thermal profiles within ex vivo bovine and in vivo porcine liver tissue during MWA with the HeatSYNC thermal accelerant. Measured temperature dependent dielectric and thermal properties of the HeatSYNC gel were applied within the model. Simulated extents of MWA zones and transient temperature profiles were compared against experimental measurements in ex vivo bovine liver. Model predictions of thermal profiles under in vivo conditions in porcine liver were used to analyze thermal ablations observed in prior experiments in porcine liver in vivo. RESULTS: Measured electrical conductivity of the HeatSYNC gel was ∼83% higher compared to liver at room temperature, with positive linear temperature dependency, indicating increased microwave absorption within HeatSYNC gel compared to tissue. In ex vivo bovine liver, model predicted ablation zone extents of (31.5 × 36) mm with the HeatSYNC, compared to (32.9 ± 2.6 × 40.2 ± 2.3) mm in experiments (volume differences 4 ± 4.1 cm3). Computational models under in vivo conditions in porcine liver suggest approximating the HeatSYNC gel spreading within liver tissue during ablations as a plausible explanation for larger ablation zones observed in prior in vivo studies. CONCLUSION: Computational models of MWA with thermal accelerants provide insight into the impact of accelerant on MWA, and with further development, could predict ablations with a variety of gel injection sites.

Hip Joint Angles and Moments during Stair Ascent Using Neural Networks and Wearable Sensors.

End-stage hip joint osteoarthritis treatment, known as total hip arthroplasty (THA), improves satisfaction, life quality, and activities of daily living (ADL) function. Postoperatively, evaluating how patients move (i.e., their kinematics/kinetics) during ADL often requires visits to clinics or specialized biomechanics laboratories. Prior work in our lab and others have leveraged wearables and machine learning approaches such as artificial neural networks (ANNs) to quantify hip angles/moments during simple ADL such as walking. Although level-ground ambulation is necessary for patient satisfaction and post-THA function, other tasks such as stair ascent may be more critical for improvement. This study utilized wearable sensors/ANNs to quantify sagittal/frontal plane angles and moments of the hip joint during stair ascent from 17 healthy subjects. Shin/thigh-mounted inertial measurement units and force insole data were inputted to an ANN (2 hidden layers, 10 total nodes). These results were compared to gold-standard optical motion capture and force-measuring insoles. The wearable-ANN approach performed well, achieving rRMSE = 17.7% and R2 = 0.77 (sagittal angle/moment: rRMSE = 17.7 ± 1.2%/14.1 ± 0.80%, R2 = 0.80 ± 0.02/0.77 ± 0.02; frontal angle/moment: rRMSE = 26.4 ± 1.4%/12.7 ± 1.1%, R2 = 0.59 ± 0.02/0.93 ± 0.01). While we only evaluated healthy subjects herein, this approach is simple and human-centered and could provide portable technology for quantifying patient hip biomechanics in future investigations.

A geometric assessment method for estimating dimensional change of retrieved dual mobility liners for total hip arthroplasty.

Despite their emerging use, the current understanding of the in-vivo functional mechanisms of Dual Mobility (DM) Total Hip Replacements (THRs) is poor, and current characterisation methodologies are not suitable for the unique function and design of these types of devices. Therefore, the aim of this study was to develop a geometric characterisation methodology to estimate dimensional change across the articulating surfaces of retrieved DM polyethylene liners so that their invivo function may be better understood. The method involves the acquisition of three-dimensional coordinate data from the internal and external surfaces of DM liners. The data is processed using a bespoke MATLAB script which approximates the unworn reference geometry of each surface, calculates geometric variance at each point and produces surface deviation heatmaps so that areas of wear and/or deformation may be visualised across the implant. One as-manufactured and five retrieved DM liners were assessed, which demonstrated the efficacy, repeatability and sensitivity of the developed method. This study describes an automated and non-destructive approach for assessing retrieved DM liners of any size and from any manufacturer, which may be used in future research to improve our understanding of their in-vivo function and failure mechanisms.

Oxidation in Retrieved, Never-Irradiated UHMWPE Bearings: What Can We Learn About in Vivo Oxidation?

BACKGROUND: Published analyses of never-irradiated, ethylene oxide (EtO)-sterilized tibial inserts and EtO- and gas plasma (GP)-sterilized acetabular ultra-high molecular weight polyethylene (UHMWPE) retrievals demonstrated minimal UHMWPE in vivo oxidation, whereas another analysis of EtO-sterilized acetabular liners found elevated oxidation linked with in vivo stresses. This study explored whether never-irradiated UHMWPE bearings are (1) oxidized by the in vivo environment, and (2) more likely to oxidize in higher-stress articulations (knee, ankle, shoulder). METHODS: An institutional review board-approved retrieval archive was queried for never-irradiated, EtO- and GP-sterilized UHMWPE bearings received at revision from 2001 to 2021. A total of 193 EtO-sterilized and 112 GP-sterilized conventional UHMWPE retrievals were analyzed (0 to 25 years in vivo; 133 hip, 144 knee, 18 ankle, and 10 shoulder). Retrieved implants were evaluated for in vivo damage and analyzed for trans-vinylene and ketone content by Fourier transform infrared spectroscopy (FTIR). Twelve never-implanted EtO-sterilized tibial knee inserts, (shelf-aged 5 to 19 years) were non-oxidized controls. Mechanical properties of 3 never-implanted and 3 retrieved tibial inserts were evaluated by ASTM Type-V uniaxial tensile testing. Statistical analyses evaluated correlations between time in vivo and oxidation, and compared mean oxidation rates by articulation. RESULTS: Burnishing was the most common clinical damage for all articulations. Eight retrievals exhibited oxidation-related fatigue damage. All retrievals were validated as never-irradiated (median trans-vinylene index [TVI] = 0.000). Maximum ketone oxidation in retrievals correlated with in vivo time (p < 0.001). Thirty-seven percent of retrievals exhibited UHMWPE (subsurface) oxidation, most frequently ankle, knee, and glenoid inserts. Tensile properties differed between retrieved and never-implanted inserts, changing with oxidation. The oxidation rate differed significantly among the articulations (p < 0.001). CONCLUSIONS: This study cohort confirmed the presence of in vivo oxidation in some non-irradiation-sterilized UHMWPE bearings, with higher-stress articulations (knee, ankle, shoulder) showing evidence of oxidation more frequently and having significantly higher oxidation rates than hips. Mechanical properties degraded by oxidation led to fatigue damage in 8 retrievals after a long duration in vivo. CLINICAL RELEVANCE: Conventional EtO- or GP-sterilized UHMWPE bearings are at minimal risk for fatigue damage secondary to oxidation. However, higher stresses and longer time in vivo (more cycles of use) can lead to increased wear, oxidation, and fatigue damage.

Developing a method for quantifying hip joint angles and moments during walking using neural networks and wearables.

Quantifying hip angles/moments during gait is critical for improving hip pathology diagnostic and treatment methods. Recent work has validated approaches combining wearables with artificial neural networks (ANNs) for cheaper, portable hip joint angle/moment computation. This study developed a Wearable-ANN approach for calculating hip joint angles/moments during walking in the sagittal/frontal planes with data from 17 healthy subjects, leveraging one shin-mounted inertial measurement unit (IMU) and a force-measuring insole for data capture. Compared to the benchmark approach, a two hidden layer ANN (n = 5 nodes per layer) achieved an average rRMSE = 15% and R2=0.85 across outputs, subjects and training rounds.

A particle filter approach to dynamic kidney pose estimation in robotic surgical exposure.

PURPOSE: Traditional soft tissue registration methods require direct intraoperative visualization of a significant portion of the target anatomy in order to produce acceptable surface alignment. Image guidance is therefore generally not available during the robotic exposure of structures like the kidneys which are not immediately visualized upon entry into the abdomen. This paper proposes guiding surgical exposure with an iterative state estimator that assimilates small visual cues into an a priori anatomical model as exposure progresses, thereby evolving pose estimates for the occluded structures of interest. METHODS: Intraoperative surface observations of a right kidney are simulated using endoscope tracking and preoperative tomography from a representative robotic partial nephrectomy case. Clinically relevant random perturbations of the true kidney pose are corrected using this sequence of observations in a particle filter framework to estimate an optimal similarity transform for fitting a patient-specific kidney model at each step. The temporal response of registration error is compared against that of serial rigid coherent point drift (CPD) in both static and simulated dynamic surgical fields, and for varying levels of observation persistence. RESULTS: In the static case, both particle filtering and persistent CPD achieved sub-5 mm accuracy, with CPD processing observations 75% faster. Particle filtering outperformed CPD in the dynamic case under equivalent computation times due to the former requiring only minimal persistence. CONCLUSION: This proof-of-concept simulation study suggests that Bayesian state estimation may provide a viable pathway to image guidance for surgical exposure in the abdomen, especially in the presence of dynamic intraoperative tissue displacement and deformation.

Use of adhesive cranial bone flap fixation without hardware to improve mechanical strength, resist cerebrospinal fluid leakage, and maintain anatomical alignment: a laboratory study.

OBJECTIVE: Titanium plates and screws (TPS) are the current standard of care for fixation of cranial bone flaps. These materials have been used for decades but have known potential complications, including flap migration, bone resorption/incomplete osseous union, hardware protrusion, cosmetic deformity, wound infection/dehiscence, and cerebrospinal fluid (CSF) leakage. This study evaluated the efficacy of a novel mineral-organic bone adhesive (Tetranite) for cranial bone flap fixation. METHODS: Craniotomy bone flaps created in human cadaveric skulls were tested under quasistatic and impact loading in the following conditions: 1) uncut skull; 2) bone flaps fixated with TPS alone; and 3) bone flaps fixated with bone adhesive alone. All fixative surgical procedures were performed by a group of 16 neurosurgeons in a simulated surgical environment. The position of adhesive-fixated cranial bone flaps was measured using computed tomography and compared with their original native location. The resistance of adhesive-fixated cranial bone flaps to simulated CSF leakage was also evaluated. Because there was a gap around the circumference of the TPS-fixated specimens that was visible to the naked eye, pressurized CSF leak testing was not attempted on them. RESULTS: Adhesive-fixated bone flaps showed significantly stiffer and stronger quasistatic responses than TPS-fixated specimens. The strength and stiffness of the adhesive-fixated specimens were not significantly different from those of the uncut native skulls. Total and plastic deflections under 6-J impact were significantly less for adhesive-fixed bone flaps than TPS. There were no significant differences in any subthreshold impact metrics between the adhesive-fixed and native specimens at both 6-J and 12-J impact levels, with 1 exception. Plastic deflection at 6-J impact was significantly less in adhesive-fixated bone flaps than in native specimens. The energy to failure of the adhesive-fixated specimens was not significantly different from that of the native specimens. Time since fixation (20 minutes vs 10 days) did not significantly affect the impact failure properties of the adhesive-fixated specimens. Of the 16 adhesive-fixated craniotomy specimens tested, 14 did not leak at pressures as high as 40 mm Hg. CONCLUSIONS: The neurosurgeons in this study had no prior exposure or experience with the bone adhesive. Despite this, improved resistance to CSF egress, superior mechanical properties, and better cosmetic outcomes were demonstrated with bone adhesive compared with TPS.

What factors drive polyethylene wear in total knee arthroplasty? : results of a large retrieval series.

AIMS: Wear of the polyethylene (PE) tibial insert of total knee arthroplasty (TKA) increases the risk of revision surgery with a significant cost burden on the healthcare system. This study quantifies wear performance of tibial inserts in a large and diverse series of retrieved TKAs to evaluate the effect of factors related to the patient, knee design, and bearing material on tibial insert wear performance. METHODS: An institutional review board-approved retrieval archive was surveyed for modular PE tibial inserts over a range of in vivo duration (mean 58 months (0 to 290)). Five knee designs, totalling 1,585 devices, were studied. Insert wear was estimated from measured thickness change using a previously published method. Linear regression statistical analyses were used to test association of 12 patient and implant design variables with calculated wear rate. RESULTS: Five patient-specific variables and seven implant-specific variables were evaluated for significant association with lower insert wear rate. Six were significant when controlling for other factors: greater patient age, female sex, shorter duration in vivo, polished tray, highly cross-linked PE (HXLPE), and constrained knee design. CONCLUSION: This study confirmed that knee wear rate increased with duration in vivo. Older patients and females had significantly lower wear rates. Polished modular tibial tray surfaces, HXLPE, and constrained TKA designs were device design factors associated with significantly reduced wear rate. Cite this article: Bone Joint J 2021;103-B(11):1695-1701.

Effect of head size and rotation on taper corrosion in a hip simulator.

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.

Oxidized Zirconium Components Maintain a Smooth Articular Surface Except Following Hip Dislocation.

BACKGROUND: Oxidized zirconium (OxZr) offers theoretical advantages in total hip and knee arthroplasty (THA and TKA, respectively) relative to other biomaterials by combining the tribological benefits of ceramics with the fracture toughness of metals. Yet, some studies have found that OxZr does not improve outcomes or wear rates relative to traditional bearing materials such as cobalt-chromium (CoCr). Separately, effacement of the thin ceramic surface layer has been reported for OxZr components, though the prevalence and sequelae are unclear. METHODS: To elucidate the in vivo behavior of OxZr implants, the articular surfaces of 94 retrieved THA and TKA femoral components (43 OxZr TKA, 21 OxZr THA, 30 CoCr THA) were analyzed using optical microscopy, non-contact profilometry, and scanning electron microscopy. RESULTS: We found that OxZr components maintain a smooth articular surface except following hip dislocation. Three of four OxZr femoral heads revised following dislocation exhibited severe damage to the articular surface, including macroscopic regions of ceramic-layer effacement and exposure of the underlying metal substrate; these components were 23-32 times rougher than pristine OxZr controls. When revised for dislocation, OxZr femoral heads were substantially rougher than CoCr femoral heads (median Sa = 0.431 v. 0.020 µm, P = .03). In contrast, CoCr femoral heads exhibited low overall roughness values regardless of whether they dislocated (median Sa = 0.020 v. 0.008 µm, P = .09, CoCr dislocators v. non-dislocators). CONCLUSIONS: Effacement of the ceramic surface layer and substantial articular surface roughening is not atypical following dislocation of OxZr femoral heads, making OxZr much less tolerant than CoCr to hip dislocation.

Damage patterns in polyethylene fixed bearings of retrieved total ankle replacements.

INTRODUCTION: Poor long-term outcomes continue to hinder the universal adoption of total ankle replacements (TAR) for end stage arthritis. In the present study, polyethylene inserts of TARs retrieved at revision surgery were analyzed for burnishing, scratching, mechanical damage, pitting, and embedded particles. METHODS: Fourteen retrieved polyethylene inserts from a fixed bearing total ankle replacement design currently in clinical use were analyzed. Duration of time in vivo was between 11.5 months and 120.1 months. Three investigators independently graded each articular surface in quadrants for five features of damage: burnishing, scratching, mechanical damage, pitting, and embedded particles. RESULTS: No correlation was found for burnishing between the anterior and posterior aspects (p = 0.47); however, scratching and pitting were significantly higher on the posterior aspect compared to the anterior aspect (p < 0.03). There was a high correlation between burnishing and in vivo duration of the implant (anterior: R = 0.67, p = 0.01, posterior: R = 0.68, p = 0.01). CONCLUSION: The higher concentration of posterior damage on these polyethylene inserts suggested that prosthesis-related (design) or surgeon-related (technique) factors might restrict the articulation of the implant. The resulting higher stresses in the posterior articular surfaces may have contributed to the failure of retrieved implants Keywords: Retrieval, Polyethylene Damage, Total Ankle Replacement.

In Vivo Corrosion of Sleeved Ceramic Femoral Heads: A Retrieval Study.

BACKGROUND: The purpose of this study was to evaluate a series of retrieved sleeved ceramic femoral heads used in total hip arthroplasty (THA) and determine qualitative and quantitative damage and corrosion patterns. METHODS: An IRB-approved implant retrieval database was utilized to identify all sleeved ceramic femoral heads collected from 1995 to 2004. There were 16 implants with an average duration of in situ of 70 months (range, 13-241 months). The femoral stem was known in 14 cases and was titanium alloy in each of those cases. None were revised for metal-related complications. Ten implants (63%) were from primary THAs, and 6 (38%) were from revision THAs. Damage and corrosion were qualitatively graded using a modified Goldberg method. A quantitative assessment was performed with a coordinate measurement machine (CMM). RESULTS: Among the 16 retrieved implants, 1 (6%) demonstrated severe Grade 4 corrosion, 5 (31%) had moderate Grade 3 corrosion, 5 (31%) had mild Grade 2 corrosion, and 5 (31%) had no visible corrosion at the inner sleeve that interfaces with the stem trunnion. The only case of grade 4 corrosion occurred in the only head-sleeve in the study that was not factory assembled and was mated with a titanium molybdenum zirconium ferrous (TMZF) alloy stem. The mean maximum linear corrosion depth at the taper interface, as measured by the CMM, was 7.7 microns (range, 0.9-32.9 microns). CONCLUSION: This study is the first to quantify corrosion at the titanium interface of sleeved ceramic femoral heads. Potentially clinically significant damage and corrosion patterns were observed in a few failed retrievals; however, the majority of cases demonstrated minimal or no damage.

Bilateral Femoral Component Fractures After Primary Total Knee Arthroplasty With Cruciate-Retaining Femoral Component.

A 69-year-old male presented with atraumatic bilateral femoral component fractures at different time intervals after simultaneous bilateral total knee arthroplasty using the cemented Biomet Ascent Knee System. The right and left knee implant fractures occurred 12 and 17 years after primary arthroplasty, respectively. This patient was notably tall (190.5 cm, 98th percentile) and maintained an active lifestyle before implant fractures. Sequential, bilateral knee implant fractures in a system with a previously acceptable track record suggest that biomechanics, patient characteristics, and surgical factors can significantly influence the risks for fracture of an implant.

An Anatomic Predisposition to Mandibular Angle Fractures.

PURPOSE: To investigate a predisposition to mandibular angle fractures, a retrospective study was performed in which fractured mandibles were compared with healthy mandibles with no history of fracture. Other investigations of angle fracture risk have exclusively studied patients with existing fractures. In addition, the risk has not been comprehensively explained in conjunction with the specific features of mandibular anatomy. We sought to characterize any anatomic variations between the jaws that had fractured and those that had never fractured. MATERIALS AND METHODS: Healthy mandibles with no history of fracture were physically measured at the William M. Bass Skeletal Collection at the University of Tennessee, Knoxville and compared with fractured mandibles from computed tomography (CT) scans at the Dartmouth Hitchcock Medical Center. A total of 52 healthy mandibles and 44 CT scans were evaluated. MATLAB machine learning algorithms (MathWorks, Natick, MA) were used to compare the study populations and isolate those anatomic features that differed between healthy and fractured mandibles. RESULTS: Machine learning classifiers were able to differentiate between male and female jaws, with the condylion-gnathion distance the most distinguishing feature. The 6 most common anatomic features that differed between healthy and fractured mandibles were the 1) retromolar space, 2) perimeter of the cross-section just proximal to the second molar, 3) breadth of the ramal cross-section, 4) thickness of the oblique ridge, 5) transgonial angle, and 6) location of the ipsilateral mental foramen. The presence of third molars was also related to fracture risk, with third molars present in 72.7% of the fractured mandibles versus 26.9% of unfractured mandibles. Of the fractured mandibles with third molars present, 87.5% had the fracture running directly through the tooth or its socket. CONCLUSIONS: The results from the present study have provided evidence that anatomic differences exist between mandibles that sustain angle fractures and those that do not. Although much of the morphology was found to be interdependent, the fracture risk could be accurately predicted using 6 anatomic features. Understanding these mandibular variations and identifying patients vulnerable to mandibular fracture could provide clinicians with additional objective information. Furthermore, using the methods demonstrated in our study, future research could focus on developing an algorithm that includes these unique anatomic features in the hope of assisting surgeons in providing tailored treatment for mandibular angle fractures according to patient-specific morphology.

In Vivo Corrosion of Modular Dual-Mobility Implants: A Retrieval Study.

BACKGROUND: Modular dual-mobility (MDM) total hip arthroplasty (THA) implants have an additional metal-metal interface between the metal liner and outer metal shell that poses a risk of corrosion. The purpose of this study is to evaluate retrieved MDM liners to evaluate qualitative and quantitative damage and corrosion patterns at this interface. METHODS: Twelve MDM implants of one design with a mean in situ duration of 26 months (range, 1-57 months) were evaluated. Six implants (50%) were from primary THAs and 6 (50%) from revision THAs. The taper region of the liner at risk of damage was qualitatively graded using modified Goldberg criteria while quantitative dimensional assessment was performed with a validated coordinate measurement machine. RESULTS: Among the retrieved implants, 2 (17%) demonstrated severe grade 4 corrosion, 5 (42%) moderate grade 3 corrosion, 4 (33%) mild grade 2 corrosion, and 1 (8%) grade 1 (no visible corrosion). Mean maximum linear corrosion depth at the taper interface measured 35.5 microns (range, 8.4-176.2 microns). All implants had a maximum linear corrosion depth >7 microns, a threshold suggestive of potentially clinically significant material loss. Three corrosion patterns were identified: generalized corrosion, a stripe of corrosion about the middle of the taper region, and focal areas of corrosion at the portion of the taper closest to the joint surface. CONCLUSION: Visual and dimensional analysis of all 12 retrieved MDM implants demonstrated identifiable corrosion/wear of the cobalt-chromium metal liner taper of varying severity. These implants should be used judiciously until larger series with clinical correlation can be completed.

Identification of a calcium phosphoserine coordination network in an adhesive organo-apatitic bone cement system.

Calcium phosphate-based bone cements have been widely adopted in both orthopedic and dental applications. Phosphoserine (pSer), which has a natural role in biomineralization, has been identified to possess the functionality to react with calcium phosphate phases, such as tetracalcium phosphate (TTCP) and α-tricalcium phosphate (α-TCP), and form a uniquely adhesive cement. This study investigated the chemical composition and phase evolution of a heterogeneous calcium phosphate (56% TTCP and 15% α-TCP) and pSer cement system with respect to pH. The coordination network of calcium phosphoserine monohydrate was discovered as the predominant crystalline phase of this adhesive apatitic cement system. Furthermore, it was determined that pH has a significant effect on the reaction kinetics of the system, whereby a lower pH tends to accelerate the reaction rate and favor products with lower Ca/P ratios. These findings provide a better understanding of the reaction and products of this adhesive organo-ceramic cement, which can be compositionally tuned for broad applications in the orthopedic and dental spaces. STATEMENT OF SIGNIFICANCE: The application of self-setting calcium phosphate cements (CPCs) in hard tissue regeneration has been a topic of significant research since their introduction to the field 30 years ago. Traditional CPCs, however, are limited by their suboptimal mechanical properties due to their solely inorganic composition. Recently, it was discovered that monomeric phosphoserine (pSer) is capable of serving as a setting reagent for a subset of CPC systems, resulting in an adhesive organo-ceramic composite. Despite its adhesive functionality and biomedical potential, its reaction chemistry and product composition were not well characterized. The present study identifies a calcium phosphoserine coordination network as the primary crystalline phase of this apatitic cement system and further characterizes compositional tunability of the products with respect to pH.

A retrieval analysis perspective on revision for infection.

BACKGROUND: Retrieval analysis has long served the orthopaedic community as a tool for understanding implant failure modes; however, what retrieval studies can reveal about the nature of prosthetic joint infection (PJI) remains unknown. We hypothesize that records from a comprehensive joint retrieval program should corroborate clinically-reported temporal characteristics of prosthesis-related infection. METHODS: We examined 2527 records documenting a decade of explanted hip and knee components to quantify the following: (1) the relative contribution of infection to revision arthroplasty; (2) the effects of joint type, revision status, and reason for retrieval on indwelling time; and (3) whether the temporal distribution of infected explants reflects clinical experience. RESULTS: In this series, 20% (507/2527) of explants were performed for infection, with PJI being more commonly implicated in the retrieval of revision implants than of primaries. Infected prostheses were explanted 23.2 months sooner on average than those retrieved for other causes. Within the subset of infected devices, revision components were explanted 11.2 months sooner than primaries, with no appreciable difference observed between hips and knees. Retrieval-based temporal distributions were most similar to PJI studies with endpoint enrollment or long duration follow-up, suggesting a later average onset of infection than reported in comparable clinical studies with short (<10-year) follow-up. CONCLUSIONS: Infection represents a major cause of revision arthroplasty, and is associated with shorter indwelling times in revision components than in primaries. Studies with less than 10 years of follow-up are likely to under-report late PJI.

Continuously monitoring shoulder motion after total shoulder arthroplasty: maximum elevation and time spent above 90° of elevation are critical metrics to monitor.

BACKGROUND: Traditional clinical shoulder range-of-motion (ROM) measurement methods (ie, goniometry) have limitations assessing ROM in total shoulder arthroplasty (TSA) patients. Inertial measurement units (IMUs) are superior; however, further work is needed using IMUs to longitudinally assess shoulder ROM before TSA and throughout post-TSA rehabilitation. Accordingly, the study aims were to prospectively capture shoulder elevation in TSA patients and to compare the results with healthy controls. We hypothesized that patients would have reduced maximum elevation before TSA compared with controls but would have improved ROM after TSA. METHODS: A validated IMU-based shoulder elevation quantification method was used to continuously monitor 10 healthy individuals (4 men and 6 women; mean age, 69 ± 20 years) without shoulder pathology and 10 TSA patients (6 men and 4 women; mean age, 70 ± 8 years). Controls wore IMUs for 1 week. Patients wore IMUs for 1 week before TSA, for 6 weeks at 3 months after TSA, and for 1 week at 1 year after TSA. Shoulder elevation was calculated continuously, broken into 5° angle "bins" (0°-5°, 5°-10°, and so on), and converted to percentages. The main outcome measures were binned movement percentage, maximum elevation, and average elevation. Patient-reported outcome measures and goniometric ROM were also captured. RESULTS: No demographic differences were noted between the cohorts. Average elevation was not different between the cohorts at any time. Control maximum elevation was greater than pre-TSA and post-TSA week 1 and week 2 values. Time under 30° and time above 90° were equal between the cohorts before TSA. After TSA, patients showed decreased time under 30° and increased time above 90°. DISCUSSION: This study demonstrates that acute and chronic recovery after TSA can be assessed via maximum elevation and time above 90°, respectively. These results inform how healthy individuals and patients use their shoulders before and after TSA.

Assessing Shoulder Biomechanics of Healthy Elderly Individuals During Activities of Daily Living Using Inertial Measurement Units: High Maximum Elevation Is Achievable but Rarely Used.

Current shoulder clinical range of motion (ROM) assessments (e.g., goniometric ROM) may not adequately represent shoulder function beyond controlled clinical settings. Relative inertial measurement unit (IMU) motion quantifies ROM precisely and can be used outside of clinic settings capturing "real-world" shoulder function. A novel IMU-based shoulder elevation quantification method was developed via IMUs affixed to the sternum/humerus, respectively. This system was then compared to in-laboratory motion capture (MOCAP) during prescribed motions (flexion, abduction, scaption, and internal/external rotation). MOCAP/IMU elevation were equivalent during flexion (R2 = 0.96, µError = 1.7 deg), abduction (R2 = 0.96, µError = 2.9 deg), scaption (R2 = 0.98, µError = -0.3 deg), and internal/external rotation (R2 = 0.90, µError = 0.4 deg). When combined across movements, MOCAP/IMU elevation were equal (R2 = 0.98, µError = 1.4 deg). Following validation, the IMU-based system was deployed prospectively capturing continuous shoulder elevation in 10 healthy individuals (4 M, 69 ± 20 years) without shoulder pathology for seven consecutive days (13.5 ± 2.9 h/day). Elevation was calculated continuously daily and outcome metrics included percent spent in discrete ROM (e.g., 0-5 deg and 5-10 deg), repeated maximum elevation (i.e., >10 occurrences), and maximum/average elevation. Average elevation was 40 ± 6 deg. Maximum with >10 occurrences and maximum were on average 145-150 deg and 169 ± 8 deg, respectively. Subjects spent the vast majority of the day (97%) below 90 deg of elevation, with the most time spent in the 25-30 deg range (9.7%). This study demonstrates that individuals have the ability to achieve large ROMs but do not frequently do so. These results are consistent with the previously established lab-based measures. Moreover, they further inform how healthy individuals utilize their shoulders and may provide clinicians a reference for postsurgical ROM.

Stance and swing phase knee flexion recover at different rates following total knee arthroplasty: An inertial measurement unit study.

Total knee arthroplasty (TKA) is the most common joint replacement in the United States. Range of motion (ROM) monitoring includes idealized clinic measures (e.g. goniometry during passive ROM) that may not accurately represent knee function. Accordingly, a novel, portable, inertial measurement unit (IMU) based ROM measurement method was developed, validated, and implemented. Knee flexion was computed via relative motion between two IMUs and validated via optical motion capture (p > 0.05). Prospective analyses of 10 healthy individuals (5M, 50 ±â€¯19 years) and 20 patients undergoing TKA (3 lost to follow up, 10M, 65 ±â€¯6 years) were completed. Controls wore IMUs for 1-week. Patients wore IMUs for 1-week pre-TKA, 6-weeks immediately post-TKA, and 1-week at 1-year post-TKA. Flexion was computed continuously each day (8-12 h). Metrics included daily maximum flexion and flexion during stance/swing phases of gait. Maximum flexion was equal between cohorts at all time points. Contrastingly, patient stance and swing flexion were reduced pre-TKA, yet improved post-TKA. Specifically, patient stance and swing flexion were reduced below control/pre-TKA values during post-TKA week 1. Stance flexion exceeded pre-TKA and equaled control levels after week 2. However, swing flexion only exceeded pre-TKA and equaled control levels at 1-year post-TKA. This novel method improves upon the accuracy/portability of current methods (e.g. goniometry). Interestingly, surgery did not impact maximum ROM, yet improved the ability to flex during gait allowing more efficient and safe ambulation. This is the first study continuously monitoring long-term flexion before/after TKA. The results offer richer information than clinical measures about expected TKA rehabilitation.