Sensitive and accurate measures of osteolysis around TKR are needed to enhance clinical management and assist in planning revision surgery. Therefore, our aim was to examine, in a cadaver model of osteolysis around TKR, the sensitivity of detection and the accuracy of measuring osteolysis using Xray, CT and MRI.

Fifty-four simulated osteolytic lesions were created around six cadaver knees implanted with either a cemented or cementless TKR. Twenty-four lesions were created in the femur and thirty in the tibia ranging in size from 0.7 cm3 to 14 cm3. Standard anteroposterior and lateral fluoroscopically guided radiographs, CT and MRI scans with metal reduction protocols were taken of the knees prior to the creation of lesions and at every stage as the lesion sizes were enlarged. The location, number and size of the lesions from images obtained by each method were recorded.

The sensitivity of osteolytic lesion detection was 44% for plain radiographs, 92% for CT and 94% for MRI. On plain radiographs, 54% of lesions in the femur and 37% of lesions in the tibia were detected. None of the six posterior lesions created in the tibia were detected on the AP radiographs; however, three of these six lesions were detected on the lateral radiographs. CT was able to detect lesions of all sizes, except for four lesions in the posterior tibia (mean volume of 1.2 cm3, range 1.06–1.47 cm3). Likewise, MRI was very sensitive in detecting lesions of all sizes, with the exception of three lesions, two of which were in the femur and one was in the medial condyle of the tibia (mean volume of 1.9 cm3, range 1.09–3.14 cm3). Notably, all six posterior tibial lesions, which could not be detected using AP radiographs, were detected by MRI.

This study demonstrates the high sensitivity of both CT and MRI (which uses no ionising radiation) to detect simulated knee osteolysis and can therefore be used to detect and monitor progression of osteolysis around TKR. The study also shows the limitations of plain radiographs to assess osteolysis.

Background and purpose

The two most common complications of femoral impaction bone grafting are femoral fracture and massive implant subsidence. We investigated fracture forces and implant subsidence rates in embalmed human femurs undergoing impaction grafting. The study consisted of two arms, the first examining the force at which femoral fracture occurs in the embalmed human femur, and the second examining whether significant graft implant/subsidence occurs following impaction at a set force at two different impaction frequencies.

The posterior drawer is a commonly used test to diagnose an isolated PCL injury and combined PCL and PLC injury. Our aim was to analyse the effect of tibial internal and external rotation during the posterior drawer in isolated PCL and combined PCL and PLC deficient cadaver knee.

Ten fresh frozen and overnight-thawed cadaver knees with an average age of 76 years and without any signs of previous knee injury were used. A custom made wooden rig with electromagnetic tracking system was used to measure the knee kinematics. Each knee was tested with posterior and anterior drawer forces of 80N and posterior drawer with simultaneous external or internal rotational torque of 5Nm. Each knee was tested in intact condition, after PCL resection and after PLC (lateral collateral ligament and popliteus tendon) resection. Intact condition of each knees served as its own control. One-tailed paired student's t test with Bonferroni correction was used.

The posterior tibial displacement in a PCL deficient knee when a simultaneous external rotation torque was applied during posterior drawer at 90° flexion was not significantly different from the posterior tibial displacement with 80N posterior drawer in intact knee (p=0.22). In a PCL deficient knee posterior tibial displacement with simultaneous internal rotation torque and posterior drawer at 90° flexion was not significantly different from tibial displacement with isolated posterior drawer. In PCL and PLC deficient knee at extension with simultaneous internal rotational torque and posterior drawer force the posterior tibial displacement was not significantly different from an isolated PCL deficient condition (p=0.54).

We conclude that posterior drawer in an isolated PCL deficient knee could result in negative test if tibia is held in external rotation. During a recurvatum test for PCL and PLC deficient knee, tibial internal rotation in extension results in reduced posterior laxity.

Equilibrative nucleoside transporter 1 (ENT1) transfers nucleosides, such as adenosine, across plasma membranes. We reported previously that mice lacking ENT1 (ENT1-KO) exhibit progressive ectopic calcification of spinal tissues, including the annulus fibrosus (AF) of intervertebral discs (J Bone Miner Res 28:1135–49, 2013, Bone 90:37–49, 2016). Our purpose was twofold: (1) to compare ectopic calcifications in ENT1-KO mice with those in human DISH, and (2) to investigate the molecular pathways underlying pathological calcification in ENT1-KO mice. Studies were performed with age-matched wild-type (WT) and ENT1-KO mice, as well as human cadaveric vertebral columns meeting radiographic criteria for DISH. Mouse and human specimens were scanned using high-resolution, micro-computed tomography (micro-CT). As well, some samples were decalcified and processed for histological assessment. Calcified lesions in selected specimens were examined using energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD). To investigate molecular changes associated with ectopic calcification, we isolated AF tissue from thoracic intervertebral discs of WT and ENT1-KO mice. Tissues were then subjected to transcriptomic and proteomic analyses. Micro-CT of ENT1-KO mice revealed ectopic calcification of spinal tissues, first appearing in the cervical-thoracic region and extending caudally with advancing age. Histological examination of calcified lesions in mice revealed accumulations of amorphous, eosinophilic, acellular material in paraspinal ligaments and entheses, intervertebral discs, mandibular symphysis, and sternocostal articulations. There was no evidence of inflammation associated with these lesions. EDX of calcified lesions revealed a high content of calcium and phosphorus in a molar ratio of ∼1.6, with hydroxyapatite detected by micro-XRD. Ten human cadaveric spines (three females and seven males, mean age 81 years) that met radiographic criteria for DISH were analysed in detail by micro-CT. Remarkable heterogeneity in the density and morphology of ectopic calcifications was observed. Analyses of calcifications by EDX and XRD again yielded a calcium/phosphorus ratio of ∼1.6 and a crystalline diffraction pattern matching hydroxyapatite. Histological examination of human lesions revealed regions of mature ossification and other areas of irregular amorphous calcification that resembled lesions in ENT1-KO mice. Microarray analysis of AF tissue from WT and ENT1-KO mice showed extensive dysregulation of transcription in affected tissues. Cell cycle-associated transcripts were the most affected, including the E2f family of transcription factors and proliferating cell nuclear antigen. In addition, expression of genes involved in the regulation of mineralization and bone development were dysregulated. Proteomic analyses confirmed transcriptomic changes and revealed alterations in known modulators of biomineralization such as matrix Gla-protein. Many of the characteristics of ectopic calcification in ENT1-KO mice resemble those of DISH in humans. Human lesions were found to be heterogeneous with regions of pathological ossification and amorphous calcification, the latter resembling lesions in the mouse model. Our studies of the molecular events associated with ectopic calcification in ENT1-KO mice may provide insights into the pathogenesis of DISH in humans. ENT1-KO mice may also be useful for evaluating therapeutics for the prevention of ectopic calcification in DISH and related disorders

Introduction. For nearly 58% of total knee arthroplasty (TKA) revisions, the reason for revision is exacerbated by component malalignment. Proper TKA component alignment is critical to functional outcomes/device longevity. Several methods exist for orthopedic surgeons to validate their cuts, however, each has its limitations. This study developed/validated an accurate, low-cost, easy to implement first-principles method for calculating 2D (sagittal/frontal plane) tibial tray orientation using a triaxial gyroscope rigidly affixed to the tibial plateau of a simulated leg jig and validated 2D tibial tray orientation in a human cadaveric model. Methods. An initial simulation assessed error in the sagittal/frontal planes associated with all geometric assumptions over a range of positions (±10°, ±10°, and −3°/0°/+3° in the sagittal, frontal, and transverse planes, respectively). Benchtop experiments (total positions - TP, clinically relevant repeated measures - RM, novice user - NU) were completed using a triaxial gyroscope rigidly affixed to and aligned with the tibial tray of the fully adjustable leg-simulation jig. Finally, two human cadaveric experiments were completed. A similar triaxial gyroscope was mounted to the tibial tray of a fresh frozen human cadaver to validate sagittal and frontal plane tibial tray orientation. In cadaveric experiment one, three unique frontal plane shims were utilized to measure changes in frontal plane angle. In cadaveric experiment two, measurements using the proprosed gyroscopic method were compared with computer navigation at a series of positions. For all experiments, one rotation of the leg was completed and gyroscopic data was processed through a custom analysis algorithm. Results. Mathematical simulations showed that over the range of tested orientations, error from our geometric assumptions would be less than 1° and 0.2° in the sagittal and frontal planes, respectively. Results of all bench-top experiments are shown in Figure 1. The average angular error during the TP experiment (black bars) was 1.09°±0.80° and 0.60°±0.46° in the sagittal/frontal planes. The average angular error during the RM experiment (white bars) in the sagittal/frontal planes was 0.27°±0.25° and 0.30°±0.23°. The average angular error from the NU experiment (grey bars) in the sagittal/frontal planes was 1.50°±1.57° and 0.82°±0.77°. During cadaveric experiment one (Figure 2), computed frontal plane angles were 2.83°±0.98°, −1.67°±1.99°, and −4.33°±0.53° after placing distinct 2° lateral, 2° medial, and 4° medial shims. Finally, the average angular error from cadaveric experiment two (Figure 3) over all positions was 1.73°±1.12° and 1.56°±1.45° in the sagittal and frontal planes, respectively. Discussion. Despite the high frequency of TKA procedures, a significant number fail and need to be revised for improper component alignment. This study showed through a first-principles approach that surgeons can assess 2D orientation of the tibial component intraoperatively with 1° of accuracy with a single triaxial gyroscope rigidly affixed to the tibial plateau. Moreover, this study showed through the use of a cadaveric model that surgeons could assess 2D alignment of the tibial component with a gyroscope rigidly affixed to the tibial plateau. To our knowledge, this is first method to offer true 2D tibial tray orientation assessment using only a single triaxial gyroscope

Objectives. Percutaneous iliosacral screw placement is a standard, stabilization technique for pelvic fractures. The purpose of this study was to assess the effectiveness of a novel biplanar robot navigation aiming system for percutaneous iliosacral screw placement in a human cadaver model. Methods. A novel biplanar robot navigation aiming system was used in 16 intact human cadaveric pelvises for percutaneous iliosacral screw insertion. The number of successful screw placements and mean time for this insertion and intra-operative fluoroscopy per screw-pair were recorded respectively to evaluate the procedure. The accuracy of the aiming process was evaluated by computed tomography. Results. Sixteen intact human cadaveric pelvises were treated with percutaneous bilateral iliosacral S1 screw placement (32 cannulated screws, diameter-7.3mm, Synthes, Switzerland). All screws were placed under fluoroscopy-guided control using the biplanar robot navigation aiming system (TINAV, GD2000, China). There was no failed targeting for screw-pair placements. Computed tomography revealed high accuracy of the insertion process. 32 iliosacral screws were inserted (mean operation time per screw-pair 56 ± 3 minutes, mean fluoroscopy time per screw-pair 11.7 ± 9 seconds). In post-operative CT-scans the screw position was assessed and graded as follows: I. secure positioning, completely inserted in the cancellous bone (86%); II. secure positioning, but contacting cortical bone structures (9%); III. malplaced positioning, penetrating the cortical bone (5%). Conclusion. This cadaver study indicated that an aiming device–based biplanar robot navigation system is highly reliable and accurate. The promising results suggest that it has the advantages of high positioning accuracy, decreased radiation exposure, operational stability and safety. It can be used not only for the percutaneous iliosacral screw placement but also for other orthopedic surgeries that require precise positioning

OSSTEC is a pre-spin-out venture at Imperial College London seeking industry feedback on our orthopaedic implants which maintain bone quality in the long term. Existing orthopaedic implants provide successful treatment for knee osteoarthritis, however, they cause loss of bone quality over time, leading to more dangerous and expensive revision surgeries and high implant failure rates in young patients. OSSTEC tibial implants stimulate healthy bone growth allowing simple primary revision surgery which will provide value for all stakeholders. This could allow existing orthopaedics manufacturers to capture high growth in existing and emerging markets while offering hospitals and surgeons a safer revision treatment for patients and a 35% annual saving on lifetime costs. For patients, our implant technology could mean additional years of quality life by revising patients to a primary TKA before full revision surgery. Our implants use patent-filed additive manufacturing technology to restore a healthy mechanical environment in the proximal tibia; stimulating long term bone growth. Proven benefits of this technology include increased bone formation and osseointegration, shown in an animal model, and restoration of native load transfer, shown in a human cadaveric model. This technology could help capture the large annual growth (24%) currently seen in the cementless knee reconstruction market, worth $1.2B. Furthermore, analysis suggests an additional market of currently untreated younger patients exists, worth £0.8B and growing by 18% annually. Making revision surgery and therefore treatment of younger patients easier would enable access to this market. We aim to offer improved patient treatment via B2B sales of implants to existing orthopaedic manufacturer partners, who would then provide them with instrumentation to hospitals and surgeons. Existing implant materials provide good options for patient treatments, however OSSTEC's porous titanium structures offer unique competitive advantages; combining options for modular design, cementless fixation, initial bone fixation and crucially long term bone maintenance. Speaking to surgeons across global markets shows that many surgeons are keen to pursue bone preserving surgeries and the use of porous implants. Furthermore, there is a growing demand to treat young patients (with 25% growth in patients younger than 65 over the past 10 years) and to use cementless knee treatments, where patient volume has doubled in the past 4 years and is following trends in hip treatments. Our team includes engineers and consultant surgeons who have experience developing multiple orthopaedic implants which have treated over 200,000 patients. To date we have raised £175,000 for the research and development of these implants and we hope to gain insight from industry professionals before further development towards our aim to begin trials for regulatory approval in 2026. OSSTEC implants provide a way to stimulate bone growth after surgery to reduce revision risk. We hope this could allow orthopaedic manufactures to explore high growth markets while meaning surgeons can treat younger patients in a cost effective way and add quality years to patients' lives

Introduction. Cementless total knee arthroplasty (TKA) implants use an interference fit to achieve fixation, which depends on the difference between the inner dimensions of the implant and outer dimensions of the bone. However, the most optimal interference fit is still unclear. A higher interference fit could lead to a superior fixation, but it could also cause bone abrasion and permanent deformation during implantation. Therefore, this study aims to investigate the effect of increasing the interference fit from 350 µm to 700 µm on the primary stability of cementless tibial implants by measuring micromotions and gaps at the bone-implant interface when subjected to two loading conditions. Methods. Two cementless e.motion® tibial components (Total Knee System, B. Braun) with different interference fit and surface coating were implanted in six pairs of relatively young human cadaver tibias (47–60 years). The Orthoload peak loads of gait (1960N) and squat (1935N) were applied to the specimens with a custom made load applicator (Figure 1A). The micromotions (shear displacement) and opening/closing gaps (normal displacement) were measured with Digital Image Correlation (DIC) in 6 different regions of interest (ROIs - Figure 1B). Two General Linear Mixed Models (GLMMs) were created with micromotions and interfacial gaps as dependent variables, bone quality, loading conditions, ROIs, and interference fit implants as independent variables, and the cadaver specimens as subject variables. Results. No significant difference was found for the micromotions between the two interference fit implants (gait p=0.755, squat p=0.232), nor for interfacial gaps (gait p=0.474, squat p=0.269). In contrast, significant differences were found for the ROIs in the two dependent variables (p < 0.001). The micromotions in the anterior ROIs (AM and AL) showed fewer micromotions for the low interference fit implant (Figure 2). More closing gaps (negative values) were seen for all ROIs (Figure 3), except in AM ROI during squat, which showed opening gaps (positive values). The posterior ROIs (PM and PL) showed more closing than seen in the anterior ROIs (AM and AL) for both loading configurations. Discussion. The results presented here demonstrate that increasing the interference fit from 350 µm to 700 µm does not affect the micromotions at the implant-bone interface of tibial TKA. While micromotions values were all below the threshold for bone ingrowth (40 µm), closing gaps were quite substantial (∼−150 µm). Since cementless e.motion® TKA components with an interference fit of 350 µm had shown a survival rate of 96.2% after 8.3 years postoperatively, interfacial gaps can be expected to be within a threshold value that can guarantee good primary stability. Moreover, increasing the interference fit to 700 µm can be considered a good range for an interference fit. For any figures or tables, please contact the authors directly

Intervertebral disc (IVD) degeneration plays a major role in low back pain which is the leading cause of disability. Current treatments in severe cases require surgical intervention often leading to adjacent segment degeneration. Injectable hydrogels have received much attention in recent years as scaffolds for seeding cells to replenish disc cellularity and restore disc properties and function. However, they generally present poor mechanical properties. In this study, we investigated several novel thermosensitive chitosan hydrogels for their ability to mimic the mechanical properties of the nucleus pulposus (NP) while being able to sustain the viability of NP cells, and retain proteoglycans. CH hydrogels were prepared by mixing the acidic chitosan solution (2% w/v) with various combinations of three gelling agents: sodium hydrogen carbonate (SHC) and/or beta-glycerophosphate (BGP) and/or phosphate buffer (PB) (either BGP0.4M, SHC0.075M-BGP0.1M, SHC0.075M-PB0.02M or SHC0.075M-PB0.04M). The gelation speed was assessed by following rheological properties within 1h at 37°C (strain 5% and 1Hz). The mechanical properties were characterized and compared with that of human NP tissues. Elastic properties of the hydrogels were studied by evaluating the secant modulus in unconfined compression. Equilibrium modulus was also measured, using an incremental stress-relaxation test 24h after gelation in unconfined compression (5% strain at 5%/s followed by 5min relaxation, five steps). Cells from bovine IVD were encapsulated in CH-based gels and maintained in culture for 14 days. Cytocompatibility was assessed by measuring cell viability, metabolism and DNA content. Glycosaminoglycan (GAG) synthesis (retained in the gel and released) was determined using DMMB assay. Finally injectability was tested using human cadaveric discs. Unconfined compression confirmed drastically enhanced mechanical properties compared to conventional CH-BGP hydrogels (secant Young modulus of 105 kPa for SHC0.075PB0.02 versus 3–6 kPa for BGP0.04). More importantly, SHC0.075PB0.02 and SHC0.075BGP0.1 hydrogels exhibited mechanical properties very similar to NP tissue. For instance, equilibrium modulus was 5.2±0.6 KPa for SHC0.075PB0.02 and 8±0.8 KPa for SHC0.075BGP0.1 compared to 6.1±1.7 KPa for human NP tissue. Rheological properties and gelation time (G′=G″ after less than 15 s at 37°C, and rapid increase of G') of these hydrogels also appear to be adapted to this application. Cell survival was greater than 80% in SHC0.075BGP0.1 and SHC0.075PB0.02 hydrogels. Cells encapsulated in the new formulations also showed significantly higher metabolic activity and DNA content after 14 days of incubation compared to cells encapsulated in BGP0.4 hydrogel. Cells encapsulated in SHC0.075BGP0.1 and SHC0.075PB0.02 produced significantly higher amounts of glycosaminoglycans (GAG) compared to cells encapsulated in SHC0.075PB0.04 and BGP0.4 hydrogels. The total amount of GAG was higher in SHC0.075BGP0.1 hydrogel compared to SHC0.075PB0.02. Interestingly, both the SHC0.075BGP0.1 and SHC0.075PB0.02 hydrogels retained similar amounts of GAG. Injectability through a 25G syringe, filling of nuclear clefts and good retention in human degenerated discs was demonstrated for SHC0.075PB0.02 hydrogel. SHC0.075BGP0.1 appears to be a particularly promising injectable scaffold for IVD repair by providing suitable structural environment for cell survival, ECM production and mechanical properties very similar to that of NP tissue

Traditional procedures for orthopedic total joint replacements have relied upon bone cement to achieve long-term implant fixation. This remains the gold standard in number of procedures including TKR and PKR. In many cases however, implants fixed with cement have proven susceptible to aseptic loosening and 3. rd. body wear concerns. These issues have led to a shift away from cement fixation and towards devices that rely on the natural osteoconductive properties of bone and the ability of porous-coated implants to initiate on-growth and in-growth at the bone interface, leading to more reliable fixation. To facilitate long-term fixation through osseointegration, several mechanical means have been utilized as supplemental mechanism to aid in stabilizing the prostheses. These methods have included integrated keels and bone screws. The intent of these components is to limit implant movement and provide a stable environment for bone ingrowth to occur. Both methods have demonstrated limitations on safety and performance including bone fracture due keel induced stresses, loosening due to inconsistent pressfit of the keel, screw-thread stripping in cancellous bone, head-stripping, screw fracture, screw loosening, and screw pullout. An alternative method of fixation utilizing blade-based anchoring has been developed to overcome these limitations. The bladed-based fixation concept consists of a titanium alloy anchor with a “T-shaped” cross-section and sharped-leading end that can be impacted directly into bone. The profile is configured to have a bladed region on the horizontal crossbar of the “T” for engagement into bone and a solid rail at the other end to mates with a conforming slot on the primary body of the prosthesis. A biased chisel tip is added to the surface of the leading blade edge to draw the bone between the anchor's horizontal surface and surface of the implant, thus generating a compressive force at the bone-to-prothesis interface. The anchoring mechanism has been successfully been integrated into the tibial tray component of a partial knee replacement; an implant component that has a clinical history of revision due to loosening. A detailed investigation into the pulloff strength, wear debris generation, compressive-force properties, and susceptibility to tibial bone fracture was carried out on the anchor technology when integrated in a standard tibial tray of a partial knee replacement. When tested in rigid polyurethane bone foam (Sawbones, Grade 15) the pulloff strength of the construct increased by 360% when utilizing the anchor. The tibial tray and anchor construct were cycled under compressive loading and demonstrated no evidence of interface corrosion or wear debris generation after 1 million cycles. In addition, the anchor mechanism was shown to generate 340N of compressive force at the tibial tray-to-bone interface when evaluated with pressure sensitive film (Fuji Prescale, Medium Grade). Finally, the ultimate compressive load to induce tibial fracture was shown to increase by 17% for the anchored tray as compared to a traditional keeled tray when tested in an anatomic tibial sawbones model; and by 19% when evaluated in human cadaveric tibias. For any figures or tables, please contact authors directly

Purpose. The Birmingham Mid-Head Resection (BMHR) is a bone-conserving, short-stem alternative to hip resurfacing for patients with compromised femoral head anatomy. It is unclear, however, if an uncemented, metaphyseal fixed stem confers a mechanical advantage to that of a traditional hip resurfacing in which the femoral prosthesis is cemented to the prepared femoral head. Thus, we aimed to determine if a metaphyseal fixed, bone preserving femoral component provided superior mechanical strength in resisting neck fracture compared to a conventional hip resurfacing arthroplasty. Method. Sixteen matched pairs of human cadaveric femurs were divided evenly between specimens receiving a traditional epiphyseal fixed hip resurfacing arthroplasty (BHR) and those receiving a metaphyseal fixed BMHR. Pre-preparation scaled digital radiographs were taken of all specimens to determine anatomical parameters as well as planned stem-shaft angles and implant sizes. A minimum of 10 degrees of relative valgus alignment was planned for all implants and the planned stem-shaft angles and implant sizes were equal between femur pairs. Prior to preparation, bone mineral density scans of the femurs were obtained. Prepared specimens were potted, positioned in single-leg stance and tested to failure using a mechanical testing machine. Load-displacement curves were used to calculate construct stiffness, failure energy and ultimate failure load. Results. Human cadaveric femur pairs were well matched for anatomic parameters and BMD with no statistically significant differences in neck-shaft angle (p=0.110), neck width (p=0.173), femoral offset (p=0.224) or neck BMD (p=0.525). There was a statistically significant difference between failure loads for femurs prepared with a BHR and those prepared with a BMHR (p<0.001). Femurs prepared with a BHR (7012 N, SD 2619) failed at an average of 1578 N (SD 865) greater than paired femora prepared with a BMHR (5434 N, SD 2297), representing a 24% increase in failure load. Both construct stiffness and failure energy were not statistically different between groups (p>0.065). Transcervical vertical shear fractures accounted for 19 of 32 failures, the remaining 11 were subcapital fractures. There were no fractures observed at the base of the femoral neck for either implant. Conclusion. A metaphyseal fixed, bone conserving femoral implant does not provide superior mechanical strength nor increased resistance to femoral neck fracture compared to a conventional hip resurfacing arthroplasty

Computer navigation in total knee arthroplasty (TKA) has proven to significantly reduce the number of outliers in prosthesis positioning and to improve mechanical leg alignment. Despite these advantages the acceptance of navigation technologies is still low among orthopaedic surgeons. The time required for navigation might be a reason for the low acceptance. The aim of the study was to test whether software and instrument improvements made in an established navigation system could lead to a significant navigation acquisition time reduction. An improved and the current version of the TKA navigation software were used to perform surgery trials on a human cadaveric specimen by two experienced orthopaedic surgeons. A significant effect of the “procedure” (navigation software version) on the navigation time (p< 0.001) was found, whereas the difference between surgeons was not significant (p= 0.2). There was no significant interaction between surgeon and navigation software version (p= 0.5). The improved version led to a significant navigation acquisition time reduction of 28%. Software and instrument improvements led to a statistically significant navigation acquisition time reduction. The achieved navigation acquisition time decrease was independent from surgeon. Specific instrument and software improvements in established navigation systems may significantly decrease the surgery time segments where navigation takes place. However, the total navigation acquisition time is low in comparison to the total surgery time

The meniscus is at the cornerstone of knee joint function, imparting stability and ensuring shock absorption, load transmission, and stress distribution within the knee joint. However, it is very vulnerable to injury and age-related degeneration. Meniscal tears are reported as the most common pathology of the knee with a mean annual incidence of 66 per 100,000. Knee osteoarthritis progresses more rapidly in the absence of a functional meniscus. Historically, tears extending to the avascular inner portion of the meniscus (white-white zone, “WW”), such as radial tears were considered as untreatable and were often resected, due to the lack of vascularity in the WW zone. Perfusion-based anatomical studies performed on cadaveric menisci in the 1980s shaped the current dogma that human meniscus has poor regenerative capacity, partly due to limited blood supply that only reaches 10 to 25% of the meniscus, commonly referred to as red-red zone (“RR”). Previous studies, including those utilizing animal models have shown mobilization of Mesenchymal Stem Cells (MSCs) upon injury into the WW zone, and successful MSC recruitment when administered externally to the injury site. We and others have recently reported positive outcomes of repaired tears in the inner zone of patients. We hypothesized that the “avascular” white-white zone of the meniscus possesses regenerative capacity due to a resident stem/progenitor cell population. Further, we sought to redefine the presence of microvessels in all meniscal zones using advanced stereology and imaging modalities. Fifteen menisci from fresh human cadaveric knees (mean age: 21.53±6.53 years) without evidence of previous injury were obtained from two tissue banks (JRF, Centennial, CO) and Biosource Medical (Lakeland, FL) and utilized for this study. The use of cadaveric specimens for research purposes was approved by the institutional review board. Tibial plateaus were dissected to harvest medial and lateral menisci along their entire length. The RR, red-white (RW) and WW zones were dissected and separated into three thirds from the inner aspect to the marginal border of the meniscus and their wet weights recorded (Fig.1A). Meniscus tissue cellular content in each zone was obtained from dissociation of meniscus tissue using 0.02% w/v pronase (Millipore) for 1h at 37oC, followed by 18h 0.02% w/v collagenase II (Worthington) at 37oC with shaking. Isolated cells were characterized immediately after harvest using flow cytometry with antibodies against MSCs surface markers (CD105, CD90, CD44 and CD29) as well as respective isotype controls. Further, meniscal cells were cultured and split twice when confluence was reached, characterized at P2 and compared to bone marrow-derived MSCs (BM-MSCs) using the same markers. Self-renewal of cells was assessed using colony forming unit (CFU) assay. Differentiation assays were performed to assess whether colony-forming cells retained multilineage potential. For morphological examination of bigger vessels, samples were fixed in 10% formalin for 1 week, paraffin embedded, sectioned (4 μm thick) and stained with H&E and Masson's trichrome. Presence of microvessels was assessed by CD31 immunofluorescence staining. Further, menisci were cleared using the uDisco protocol labeled with the TO-PRO®-3 stain, a fluorescent dye that stains cell nuclei and imaged using light-sheet microscopy. All continuous data are presented as mean ±standard deviation. Non-repeated measures analysis of variance (ANOVA) and Tukey-Kramer HSD post hoc analysis were performed on sample means for continuous variables. Statistical significance was set at p < 0 .05. Menisci were successfully cleared using a modified uDISCO procedure, imaged and analyzed for total cell density. As expected, bigger vessels were observed in RR but not in WW. However, immunofluorescent staining for CD31 showed a subset of CD31+endothelial cells present in the WW zone, indicating the presence of small vessels, most likely capillaries. In order to assess whether enzymatic digestion had a differential result depending on meniscus zone due to cellular content, we analyzed yields per meniscus per zone. The wet weight of different zones (WW:RW:RR) was at a ratio of ∼1:3:5 respectively, however, the ratio of cells isolated from each zone was at ∼1:4:20, indicating that RR has a denser population of mononuclear cells. However, the difference between all zones in cell yields was not significant. The clonogenic potential of isolated cells was shown to be non-significantly different between the three zones. Differentiation of isolated cells to osteogenic lineage using osteogenic media in vitroshowed no difference between the three zones. Flow cytometry analysis of cells from the three meniscal zones displayed presence of two distinct subpopulations of cells immediately after isolation. One subpopulation was positive to MSC surface markers and the other negative. Additionally, flow cytometry of cultured meniscal cells at P2 displayed that the entire cell population was CD44+CD105+CD29+CD90+, suggesting that culturing meniscal cells results in selection of stem/progenitor cells (plastic adherence). Surface marker expression analysis showed differential expression patterns between markers depending on zone. Similar fraction of cells was detected to express both MSC markers CD90 and CD105 (7–10%) and similar fraction of cells expressed both MSC markers CD29 and CD44 (1–2%) in all three zones, indicating similar density of resident stem/progenitor cells in each zone. Importantly, WW showed significantly higher expression for all four MSC markers compared to the RR zone, indicating higher relative density of stem/progenitor resident cells in the WW zone. Our results determine that CD31-expressing microvessels were present in all zones, including the WW zone, which was previously considered completely avascular. Additionally, stem/progenitor cells were shown to be present in all three zones of the menisci, including the WW zone, showcasing its regenerative potential. For any figures or tables, please contact the authors directly

The treatment of joint-fractures is a common task in orthopaedic surgery causing considerable health costs and patient disabilities. Percutaneous techniques have been developed to mitigate the problems related to open surgery (e.g. soft tissue damage), although their application to joint-fractures is limited by the sub-optimal intra-operative imaging (2D- fluoroscopy) and by the high forces involved. Our earlier research toward improving percutaneous reduction of intra-articular fractures has resulted in the creation of a robotic system prototype, i.e. RAFS (Robot-Assisted Fracture Surgery) system. We propose a robot-bone attachment device for percutaneous bone manipulation, which can be anchored to the bone fragment through one small incision, ensuring the required stability and reducing the “biological cost” of the procedure. It consists of a custom-designed orthopaedic pin, an anchoring system (AS secures the pin to the bone), and a gripping system (GS connects the pin and the robot). This configuration ensures that the force/torque applied by the robot is fully transferred to the bone fragment to achieve the desired anatomical reduction. The device has been evaluated through the reduction of 9 distal femur fractures on human cadavers using the RAFS system. The devices allowed the reduction of 7 fractures with clinical acceptable accuracy. 2 fractures were not reduced: in one case the GS failed and was not able to keep the pin stationary inside the robot (pin rotates inside the GS). The other fracture was too dislocated (beyond the operational workspace capability of the robot). A more stable GS will be designed to avoid displacements between the pin and the robot

Introduction. Total-knee-arthroplasty (TKA) is used to restore knee function and is a well-established treatment of osteoarthritis. Along with the widely used fixed bearing TKA design, some surgeons opt to use mobile bearing designs. The mobile-bearing TKA is believed to allow for more freedom in placement of the tibial plate, greater range of motion in internal-external (IE) rotation and greater constraint through the articular surface. This current study evaluates 1) the kinematics of a high constraint three condyle mobile bearing TKA, 2) the insert rotation relative to the tibia, and 3) compares them with the intact knee joint kinematics during laxity tests and activities-of-daily-living (lunge, level walking, stairs down). We hypothesize that 1) in contrast to the intact state the anterior-posterior (AP) stability of the implanted joint increases when increasing compression level while 2) maintaining the IE mobility, and that 3) the high constraint does not prevent differential femorotibial rollback during lunge. Methods. Six fresh-frozen human cadaveric knee joints with a mean donor age of 64.5 (±2.4) years and BMI of 23.3 (±7.3) were tested on a robot (KR140, KUKA) in two different states: 1) intact, 2) after implantation of a three condyle mobile bearing TKA. The tibia plateau and the insert of each tested specimen were equipped with a sensor to measure the insert rotation during testing. Laxity tests were done at extension and under flexion (15°, 30°, 45°, 60° 90°, 120°) by applying subsequent forces in AP and medial-lateral (ML) of ±100N and moments in IE and varus-valgus (VV) rotation (6Nm/4Nm, 12 Nm/-). Testing was performed under low (44N) and weight bearing compression (500N). Loading during the lunge, level walking and stairs descent activity was based on in-vivo data. Resulting data was averaged and compared with the kinematics of the intact knee. Results. Increasing the joint compression resulted in a 90% reduced AP laxity (increased stability) for the implanted case while the intact knee laxity stayed similar. In high compression the implanted IE mobility was reduced by 45% for low and mid flexion angles and by 20% for high flexion angles, while the intact knee IE mobility was reduced by 30% at low and mid flexion and 20% at high flexion. The trend of the rollback behaviour was similar for the implanted and intact joints and showed higher lateral than medial rollback (Figure 3 A). The average insert-rotation was highest during level walking (+ 5° to −2.5°) and lowest during lunge (−3.5° to 2.5° over flexion). Conclusion. The established hypotheses were supported by the above listed results. Increasing the joint compression in the mobile bearing design stabilized the knee in the AP direction and maintained the IE mobility similar to the intact knee. This can be directly related to the design of the TKA articular surface, which has a high impact on constraint as soon as the joint is loaded. However, the high constraint of the TKA did not prevent differential rollback

Introduction. Although cementless press-fit femoral total knee arthroplasty (TKA) components are routinely used in clinical practice, the effect of the interference fit on primary stability is still not well understood. Intuitively, one would expect that a thicker coating and a higher surface roughness lead to a superior fixation. However, during implant insertion, a thicker coating can introduce more damage to the underlying bone, which could adversely influence the primary fixation. Therefore, in the current study, the effect of coating thickness and roughness on primary stability was investigated by measuring the micromotions at the bone-implant interface with experimental testing. Methods. A previous experimental set-up was used to test 6 pairs of human cadaveric femurs (47–60 years, 5 females) implanted with two femoral component designs with either the standard e.motion (Total Knee System, B. Braun, Germany) interference fit of 350 µm (right femurs) or a novel, thicker interference fit of 700 µm (left femurs). The specimens were placed in a MTS machine (Figure 1) and subjected to the peak loads of normal gait (1960N) and squat (1935N), based on the Orthoload dataset for Average 75. Varus/valgus moments were incorporated by applying the loads at an offset relative to the center of the implants, leading to a physiological mediolateral load distribution. Under these loads, micromotions at the implant-bone interface were measured using Digital Image Correlation (DIC) at different regions of interest (ROIs – Figure 1). In addition, DIC was used to measure opening and closing of the implant-bone interface in the same ROIs. Results. After comparing the micromotions and opening of the two implant designs, we found no significant differences between the standard and novel coating. Loading was a significant factor for both opening (P<0.0001) and micromotions (P=0.019), where the squat produced higher micromotions than gait. Opening was seen anteriorly (MA, LA), and was higher during squat. Closing was noticed distally (MD, LD), particularly during gait (Figure 2). During gait (Figure 3), the highest micromotions were found in the posterior condyles (CM, MP), followed by the medial anterior region (MA). For squat, the largest micromotions were in the anterior flange (ANT), followed by the distal regions (LD, MD). Discussion. In the current study, the primary stability of the same implant with two different coating thicknesses was evaluated. The results demonstrate that increasing the coating thickness does not automatically influence the primary stability of a femoral TKA component. This is likely due to abrasion and damage of the underlying trabecular during implant insertion, which also was observed in previous experiments. The exact relation between coating thickness or interference fit and primary implant stability still remains subject to debate. Obviously, the primary implant stability is compromised when the interference fit is too low. However, the current results suggest that there is a threshold beyond which further improvement of the fixation is not possible. The exact magnitude of this threshold is unknown, and may depend on coating characteristics and bone quality, and requires further evaluation, possibly utilizing a hybrid approach of experimental and computational techniques

Introduction. Cementless total knee arthroplasty (TKA) designs are clinically successful and allow for long term biological fixation. Utilizing morselized bone to promote biological fixation is a strategy in cementless implantation. However, it is unknown how bone debris influences the initial placement of the tray. Recent findings show that unseated tibia trays without good contact with the tibial resection experience increased motion. This current study focuses on the effect of technique and instrument design on the initial implantation of a cementless porous tibia. Specifically, can technique or instrument design influence generation of bone debris, and thereby change the forces required to fully seat a cementless tray with pegs?. Methods. This bench top test measured the force-displacement curve during controlled insertion of a modern cementless tibia plate with two fixation pegs. A total of nine pairs of stripped human cadaver tibias were prepared according to the surgical technique. However, the holes for the fixation pegs were drilled intentionally shallow to isolate changes in insertion force due to the hole preparation. A first generation instrument set (Instrument 1.0) and new instrument set design (Instrument 2.0), including a new drill bit designed to remove debris from the peg hole, were used. The tibias prepared with Instrument 1.0 were either cleaned to remove bone debris from the holes or not cleaned. The tibias prepared with the Instrument 2.0 instruments were not cleaned, resulting in three groups: Instrument 1.0 (n=7), Instrument 1.0 Cleaned (n=5), and Instrument 2.0 (n=6). Following tibia resection and preparation of holes for the fixation pegs, the tibias were cut and potted in bone cement ensuring the osteotomy was horizontal. The tibial tray was mounted in a load frame (Enduratec) and the trays were inserted at a constant rate (0.169mm/sec) while recording the force. The test was concluded when the pegs were clearly past the bottom of the intentionally shallow holes. Results. The force-displacement curves from this method were dependent on the instrument used and cleaning of the holes. Instrument 2.0 specimens were inserted about 2 mm past the maximum peg depth before experiencing a significant increased resistance. The Instrument 1.0 Cleaned holes saw an increase in force slightly past the maximum peg depth, while the Instrument 1.0 group saw increase in force around 1 mm before reaching the maximum peg depth. The average insertion force required to reach maximum peg depth was significantly higher (p<0.05) for the Instrument 1.0 group (790.7 N, sd=185.9) than both the Instrument 1.0 Cleaned (429.7 N, sd=116.8) and the Instrument 2.0 group (580.4 N, sd=89.3). The insertion forces at a ‘mid-tunnel’ location, before the increase in resistance, were not affected by drill design as the drill diameters were the same, resulting in the same press fit. Conclusions. Bone debris in fixation feature holes increases the force to fully seat a cementless tibia plate. This suggests there is a cost to leaving morselized bone in place. Removing bone debris through instrument design or surgical technique can ensure that a tibial plate is fully seated at time of implantation, maximizing initial fixation

Aims

Disorders of bone integrity carry a high global disease burden, frequently requiring intervention, but there is a paucity of methods capable of noninvasive real-time assessment. Here we show that miniaturized handheld near-infrared spectroscopy (NIRS) scans, operated via a smartphone, can assess structural human bone properties in under three seconds.

Introduction. Various 2D and 3D surfaces are available for cementless fixation of acetabular cups. The goal of these surface modifications is to improve fixation between the metallic cups and surrounding bone. Radiographs have historically been used to evaluate the implant-to-bone fixation around the acetabular cups. In general, a well fixed cup shows no gaps or radiolucency around the cup's outer diameter. In post-operative radiographs, the presence of progressive radiolucent zones of 2mm or more around the implant in the three radiographic zones is indicative of aseptic loosening, as described by DeLee and Charnley [1]. In this cadaveric study, we investigated the X-ray image characteristics of two different types of acetabular shell surfaces (2D and 3D) to evaluate the implant-to-bone interface in the two designs. Methods. Six human cadavers were bilaterally implanted with acetabular cups by an orthopaedic surgeon. 2D surface cups (Trident, Stryker, Mahwah, NJ) and 3D surface cups (Tritanium, Stryker, Mahwah, NJ) were randomized between the left and right acetabula. The surgeon used his regular surgical technique (1 mm under reaming) to implant the acetabular cups. The cadavers were sent for X-ray imaging after the operation, Figure 1A. Following the X-ray imaging, the acetabular cups were carefully resected from the cadavers. Enough bone around the cups was retained for analysis of the implant-to-bone interface by contact X-ray. The acetabular cups with the surrounding bone were fixed in 70% isopropyl alcohol for about a week and subsequently embedded in polymethyl methacrylate. The embedded cups were sectioned at 30° intervals using a diamond saw in the coronal plane, as recommended by Engh et al [2], Figure 1B. The sectioning of the samples produced 6 slices of each cup where the implant-bone interface could easily be visualized for evaluation with contact X-ray. Results. The AP X-rays of the cadavers demonstrated radiolucent lines, as well as gap defects in some cases. The same phenomenon was observed on the contact X-rays of the embedded implant sections as well, where one could easily identify the gap between the metal cup and the surrounding bone. The most striking finding was that, in a few cases, the contact X-rays showed radiolucency around the metal cup whereas the physical section did not seem to have any gaps. This phenomenon is illustrated in Figure 2. Conclusions. The physical gap or radiolucent lines around the acetabular cups have been reported in literature; however, they seem to fill up with time as biological fixation progresses between the surrounding bone and the implant. In our study we found radiolucency that was not associated with the presence of a physical gap. In contrast, we found gaps on physical sections that were not correlated with radiolucencies. This phenomenon may be attributed to the interaction of X-rays with the cup surface modifications. The contact X-ray images demonstrated that radiolucency around cups may not always correlate with physical gaps. Further analysis is required to understand the implications of these findings

Introduction. Accurate placement of total knee arthroplasty (TKA) components is critical for obtaining good long-term clinical outcome. Several contemporary CT- or MRI-based technologies allow surgeons to pre-plan TKA and translate that planning into the operating room. To evaluate TKA component placement, post-operative CT or MRI scans allow comprehensive 3D measurements. However, these are expensive and difficult to obtain in large numbers, and yield an additional radiation dose to the patient (in case of CT). A potential solution to overcome these hurdles exists in using 2D/3D registration techniques. In this technique, a new tool (the X-ray Module, Mimics®, Materialise NV) is used to align one or more post-operative X-rays with the preoperative CT- or MRI-based 3D planning (Figure 1). The aim of this study was to determine the accuracy of this 2D/3D registration technique for determining 3D position of TKA implant components postoperatively. Materials and Methods. A TKA was performed in six human cadaver legs. A CT scan was acquired preoperatively and the bones were segmented using Mimics® to obtain 3D bone models. Post-operatively, a high-resolution CT scan with minimization of metal scatters was acquired and bones and implant components were segmented in Mimics® to obtain the ground truth for their relative position. To apply the novel X-ray based post-op analysis, conventional anteroposterior and lateral radiographs were obtained. The accuracy of the X-ray tool was determined by calculating the angles (varus/valgus, flexion/extension, external/internal rotations) and the distances (anterior/posterior, proximal/distal, medial/lateral) between the centers of gravity of the implants from the X-ray based method and the CT-based ground truth in the anatomical coordinate system of the bone. X-ray based alignment was assessed by an orthopedic surgeon (3 repetitions) and Bland-Altman plots were created to visualize the differences between the ground truth and the X-ray based assessment of the implant position. Results. The differences in rotation between the X-ray and CT analyses are shown in Figure 2 (femur) and Figure 3 (tibia). The average differences between the methods were in the order of 1° or less, except for external/internal rotation, which showed the largest differences (0.23±0.85° for the femur, 0.51±1.91° for the tibia). For the position differences between the X-ray and CT analyses, average differences were smaller than 0.3mm and 0.9mm for the femur and tibia, respectively. Proximal-distal alignment showed larger differences (0.24±0.22 for the femur, −0.87±0.42 mm for the tibia) than the anterior-posterior alignment (−0.07±0.43 for the femur and 0.01±0.21 for the tibia) and the mediolateral alignment (0.17±0.11 for the femur and 0.17±0.15 for the tibia). Discussion. Sub-degree/millimeter accuracy was achieved in all measurements except external/internal rotation. The accuracy of this technology depends on various factors including image quality, geometry of the 3D models and the experience of the observer. Adding additional diagonal radiographs to the X-ray based analysis may help to improve the 2D/3D registration, which may increase the accuracy of the external/internal rotation measurements. This will be subject to further study