Joint degeneration may make a total knee arthroplasty (TKA) a requirement for pain relief and function. However, the presence of ipsilateral limb osteomyelitis (OM) makes surgical management extremely challenging. We report the experience of a high volume revision knee surgeon managing ipsilateral limb multi resistant OM and the outcome of subsequent TKA. Four consecutive patients were identified who had either ipsilateral femoral or tibial chronic osteomyelitis treated prior to undergoing TKA. Surgery to eradicate the osteomyelitis involved a Lautenbach compartmental debridement, and where necessary, healing by secondary intention. The decision to proceed to a TKA was based on history, clinical examination and radiological findings of advanced osteoarthritic change. The patients had a mean age of 50 years. They had a background of multi-organism OM and underwent single-stage TKAs at an average of 63 months following eradication of the underlying OM. Three patients did well but had complications associated with poor skin and soft tissues, and abnormal bone anatomy. One patient developed an infection and following a re-revision had an arthrodesis. The results for the four cases are summarised in Table 1. We have highlighted that patients with ipsilateral limb multi resistant OM are a difficult cohort to manage

Purpose. The purpose of this study is to analyse regional differences in the microstructural and mechanical properties of the distal femur depending on osteoarthritic changes using micro-images based on finite element analysis. Materials and Methods. Distal femur specimens were obtained from ten donors composed of 10 women with OA (mean age of 65 years, ranging from 53 to 79). As controls, the normal distal femur was sampled from age and gender matched donors consisting of 10 women(mean age of 67 years, ranging from 58 to 81). The areas of interest were six regions of the condyles of the femur(Lateral-Anterior, Middle, Posterior; Medial=Anterior, Middle, Posterior). A total of 20 specimens were scanned using the micro-CT system. Micro-CT images were converted to micro-finite element model using the mesh technique, and micro-finite element analysis was then performed for assessment of the mechanical properties. Results. Trabecular bones from the distal femur in control and OA groups exhibited different microstructural and mechanical properties in the same region. BV/TV, Tb.N, Tb.S and Yield strength were different between LA and MMsignificantly (p=0.005). In control group, the lateral anterior region of the distal femur reflected subchondral trabecular remodeling, while in advanced OA group, the medial middle region showed prominent changes in the microstructural and mechanical properties. Conclusion. The authors concluded that with aging and the progress of primary OA, changes of patello-femoral reaction force induced subchondral trabecular changes of the anterolateral region initially, and then progressed to the medial middle and posterior region in advanced OA

Purpose. The purpose of this study is to investigate the relationship between the angles made by the reference axes on the computerized tomography (CT) images and comparison of the knee alignment between healthy young adults and patients who is scheduled to have total knee arthroplasty. Materials and Methods. This study was conducted in 102 patients with osteoarthritis of knee joint who underwent preoperative computerized tomography (CT). The control group included 50 patients having no arthritis who underwent CT of knee. Axial CT image of the distal femur were used to measure the angles among the the anteroposterior (AP) axis, the posterior condylar axis (PCA), clinical transepicondylar axis (cTEA) and the surgical transepicondylar axis (sTEA). Then, the differences in amounts of rotation between normal and osteoarthritic knee was evaluated. Results. The mean angle between cTEA and PCA in the osteoarthritis group was 5.0°±2.2, whereas that in the control group was 5.5°±2.0. The mean angle between cTEA and sTEA in the osteoarthritis group was 3.7°±0.8, whereas that in the control group was 4.3°±0.6. The mean angle between AP axis and PCA in the osteoarthritic group was 93.25°±2.0, whereas in the control group was 96.3°±1.9. There was significant differences in angles between AP axis and PCA. But, no significant difference was seen in angles between cTEA and PCA, cTEA and sTEA in two groups. Conclusion. In result of this study, the angle between cTEA and PCA showed an average external rotation of 5.0° in osteoarthritic group. More external rotation was needed for the femoral component alignment than 3° recommended in usual total knee arthroplasty. The angle between AP axis and PCA is decreased in osteoarthritic knee compared with normal knee. But, osteoarthritic change of knee joint had no significant effect on the relationships of other axes

INTRODUCTION:. Management of developmental dysplasia of hip in adult is challenging and needs more to be understood in terms of ideal implant, position of acetabulum and operative technique. Patient may present very late, usually when osteoarthritic changes develop followed by pain. Operative management is difficult because of hypoplastic femoral medullary canal and shallow acetabulum filled with soft tissues. Altered anatomy of neurovascular structures also pose a risk of being injured during surgery. AIMS:. The goal of this study was to evaluate late results of total hip arthroplasty in adults after a minimum of 5 years follow-up. MATERIAL:. 45 Total hip arthroplasties in 40 patients were performed for painful hip dysplasia between 2003 and 2012. These 45 procedures were performed in 40 patients mean aged 32 +/− 14 years [17–56]. 29 patients (32 hips) were males and 11 patients (13 hips) were females. Non cemented total hip arthroplasty was done in all cases with mean follow up of 6 years. Of the 45 hips, 6 were neglected, dislocated hips with proximal migration of femoral head. In such patients sub-trochanteric osteotomy was done to bring the femoral head up to the level of Acetabulum. 5 patients (5 hips) were lost to follow up; consequently, the functional results were evaluated for 40 hips (35 patients). Harris hip score was used to evaluate the functional and clinical results. RESULTS and CONCLUSION:. Harris hip score improved in all patients. We concluded from this series that total hip replacement should be considered in all patients with painful dysplastic hip. Key words: Developmental Dyplasia Hip, Total Hip Arthroplasty

Introduction:. Unicompartmental knee arthroplasty has been shown to have lower morbidity, quicker rehabilitation and more normal kinematics compared to conventional TKA, but subchondral defects, or severe osteoarthritic changes, of the medial compartment may complicate component positioning. Successful UKA in these patients requires proper planning and exact placement of the components to ensure adequate and stable fixation and proper postoperative kinematics. This study presents a series of three patients with spontaneous osteonecrosis of the knee receiving a UKA with CT-based haptic robotic guidance. Methods:. This series includes two females and one male with spontaneous osteonecrosis of the medial femoral condyle who underwent outpatient mini-incision medial UKA using the MAKO Surgical Rio Robotic Arm System. Pre-operatively all patients were found to have pain with weight bearing that would not improve despite non-arthroplasty treatment. Results:. The first patient was a 69 year old female (BMI of 22.85) with a left medial femur size 3, tibia size 4, bearing size 4×8 mm. The patient improved her ROM from 3–112° pre-operatively to 0–130° at 18 months post-operatively. The second patient was a 69 year old female (BMI of 25.68) with a right medial size 2 femur and 3 tibia and a 3×9 mm bearing. ROM increased from 0–120° pre-operatively to 0–145° at 2 year follow-up. The third patient was a 74 year old male (BMI of 26.5) who underwent previous knee arthroscopy with subsequent SPONK. Conclusion:. The difficulty in treatment of SPONK with UKA solutions includes planning for the full coverage of the ON lesions while also addressing alignment, tracking and balancing needs simultaneously. Using the advanced planning tools of the MAKO Rio software, full coverage of ON lesions can be safely planned and verified preoperatively. The intraoperative flexibility of the system allows surgeon to map out the lesions intraoperatively, where visible, and aid in the proper implant positioning and size adjustment as necessary

Purpose. The purpose of this study is to analysis and compare the micro-structural and mechanical properties of subchondral trabecular bone of non-osteoarthritic and osteoarthritic distal femur using a micro-images based on finite element analysis. Materials and Methods. Fifteen distal femur were harvested from the eight cadevers(5 males, 3 females; non-OA, 10, OA, 5). The subchondral trabeculae were obtained from the middle of artticular surface of distal femurs(Fig. 1). Cylinderical saw with 10 mm diameter was used to acquire trabecular bone core. Total 15 specimens were scanned using micro-CT (SkyScan-1172, SKYSCAN, Belgium) at 24.9ãŽ> of spatial resolution under 70ãŽ,'s voltage and current of 141ãŽ,. 2-D images with were established by an imaging software (TomoNT, SKYSCAN, Belgium) as shown in Fig. 2. Histomorphologic index, trabeculae thickness (Tb.Th), trabecular separation (Tb.Sp), bone volume (BV), bone volume fraction (BV/TV), structure model index(SMI) were determined by the ANT software (Table 1). Based on 2-D images, a finite element model was reconstructed (Fig. 3). Finite element analysis was done using BIONIX (CANTIBIO, Suwon, Korea). Yield stress (MPa), Stiffness was calculated with ANSYS 10.0(ANSYS, Inc) (Fig. 4). Results. The descriptive statistics of the microstructural and mechanical parameters are presented in Fig. 4. The results showed that trabecular bone of osteoarthritic distal femur had a decrease in Tb.Th, BV/TV and had an increase in Tb.Sp and SMI than non-osteoarthritic group. There was a decrease in the yield stress. Conclusion. The results of bone morphometry index and strength showed that subchondral trabeculae of osteoarthritic group was more degenerative structure and decreased strength. And, this results are contribution to understand the osteoarthritic change in bone remodeling aspect

Introduction. There is a controversy with regard to the treatment of osteoarthritis (OA) of the knee in patients with considerable deformities of the femoral or tibial shafts. Some surgeons prefer to correct the deformity while performing TKA at the level of the knee joint. However, this technique requires accurate planning and execution of the planned cuts. In addition, the use of intramedullary guides in such cases may not be possible or desirable and may lead to complications. There is a strong indication for using navigation in such cases. Methods. The navigation technique was used in both laboratory and clinical setting, First, we compared between navigational and conventional techniques in performing TKA in 24 plastic knee specimens (Sawbones, Sweden) that have osteoarthritic changes and complex tibial or femoral deformities. A demo kit for conventional instrumentation of posterior stabilised TKA (Scorpio, Stryker) was used for 12 cases and an image-free navigation system (Stryker) was used for a corresponding 12 cases. There were 4 different deformities; severe mid-shaft tibial varus, severe distal third femoral valgus, complex deformity distal femur and deformity following a revision TKA. The surgical procedures were performed by 3 arthroplasty surgeons, each surgeon operated on 8 knee specimens (4 knees in each arm of the study with 4 different deformities). Deformities were corrected at the level of the knee joint during TKA without prior osteotomies. For conventional techniques, surgeons used a combination of both intramedullary and extramedullary guides. Postoperative long leg radiographs were used to assess coronal alignment. Second, we used the same navigational technique clinically to perform TKA in patients with extra-articular deformities. Results. Using both navigational and conventional techniques, it was possible to indirectly correct shaft deformities by adjusting the inclination of bone cuts at the level of the knee joint. The amount of bone cutting at distal femur and proximal tibia were variable depending on the location and direction of the deformity. There was no compromise of collateral ligaments or patellar tendons in both techniques. However, the accuracy of restoring normal alignment was better in navigational techniques. The results of the clinical cases are still in progress waiting analysis of a longer term follow up. Discussion. Navigational techniques eliminated the use of both intramedullary and extramedullary guides. The improved accuracy with navigational techniques led to better alignment that can improve functional and survival outcome of similar cases of TKA in real patients

[Introduction]. It is said that the mechanical stress is a main factor to advance degenerative osteoarthritis. Therefore, to keep the joint stability is very important to minimize mechanical stress. Methods to evaluate bone-related factor are almost established, especially in hip dysplasia. On the other hand, it is unclear how much each soft tissue contribute to the joint stability. In this study we evaluated the soft tissue contribution for hip joint stability by distraction testing using MTS machine. [Materials & Methods]. We used seven fresh frozen hips from four donors, whose race was all western and reason of death was not related to hip disease in all cases. Average age of them at death was 83 years old. Mean average weight and height were each 52 kg and 162 cm. We retrieved hemi pelvis and proximal femur which kept hip joint intact. We removed all other soft tissue except iliofemoral ligament, pubofemoral ligament, ischiofemoral ligament and capsule. The hemi-pelvis mounted on angular-changeable fixator and the femur fixed to MTS machine (Figure 1). XY sliding table was used to minimize the horizontal direction stress during distraction. MTS machine was set to pull the femur parallel to its shaft by 0.4 mm/sec velocity against pelvis after 10N compression and to keep 5 mm distance for 5 seconds. We measured the force at 1 mm, 3 mm, 5 mm distraction. In case the joint was dislocated, the maximum force just before dislocation was recorded. The specimen was changed its posture as neutral (flexion0° abduction0° external rotation0°), flexion (flexion60° abduction0° external rotation0°), abduction (flexion0° abduction30° external rotation0°) and extension (extension20° abduction0° external rotation0°). Each position was measured in six sequential conditions, which are normal, Incised iliofemoral ligament, Circumferentially incised capsule, resected capsule, labral radial tear and resected labrum. After measurement joint surface was observed to evaluate the joint condition. [Results]. We excluded the one specimen two hips by osteoarthritic change of joint surface. The average force needed for 5 mm distraction in normal condition at neutral, flexion, extension and abduction posture was each 95.8N, 52.7N, 162.8N and 94.2N. The force was biggest in extension posture and smallest in flexion posture. The force was statistically reduced from 95.8N to 31.5N after iliofemoral ligament incision in neutral position. The force was also statistically reduced from 145.6N to 31.9N after Circumferential capsule incision in extension posture (Figure 2). In all posture, traction force was reduced after capslotomy and all hip dislocated in all cases. [Discussion]. We could conclude that iliofemoral ligament works much in neutral and extension posture, and capsule helps its work in extension more than in neutral posture. We have reported the zona orbicularis will be important as joint stabilizer before. Capsule including zona orbicularis makes hip joint more stable in any posture because dislocation happened easily after capsule resection in all posture

Introduction. Hip Arthrodesis had been considered as a useful surgical option in young adult patient with high activity demands suffering from osteoarthritis of the hip. Although the procedure surely eliminates pain of the hip joint, it can also cause disorders of the adjacent joints in addition to the complete loss of motion, might consequently deteriorate the activity of daily living. The purpose of this retrospective study was to investigate the efficacy and drawback of hip arthrodesis, focusing on the effect of this procedure on the adjacent joints. Materials and Methods. From 1976 to 1989, 29 hip arthrodesis were performed and 22 hips were followed up (1 died, 6 lost). Disorders led to arthrodesis were septic arthritis (1 hip), post-traumatic (1), osteonecrosis (1), primary osteoarthritis (3), and secondary osteoarthritis due to DDH (16). The average age at surgery was 38 years (range, 19–53 years, 6 men and 16 women). Hip arthrodesis was indicated for young active adults with end stage osteoarthritis, who had normal or mild osteoarthritis in contralateral hip and needed physical labor. The hip was positioned in 30 degrees of flexion, 0 to 5 degree of external rotation, and 0 to 5 degree of abduction. Clinical and radiographic assessment was done for these patients. The clinical follow-up consisted of questionnaire which assessed ability of typical Japanese daily living movement and patient's satisfaction. The condition of the adjacent joints was evaluated clinically and radiographically. Results. After an average follow-up of 22 years (range15-28), no patients complained of pain in the fused hip joint. On the other hand, pain in the adjacent joints was seen frequently. Seventeen (77%) of 22 patients had low back pain and one of these patients, who had severe low back pain, required conversion of arthrodesis to THA. Ten patients (45%) had contralateral hip pain and 8 (36%) of whom subsequently needed THA. All patients who required THA had early stage osteoarthritis when they underwent arthrodesis. Ten patients (45%) had knee pain (5 in the ipsilateral and 5 in the contralateral knee). Radiographic progression of osteoarthritis in adjacent joints was also seen frequently, namely, 9 in lumbar spine, 11 in contralateral hip, 6 in ipsilateral and 6 in contralateral knee. Although pain in the involved hip disappeared, activity of daily living was severely deteriorated (impossible to clip nail: 88%, ride a bicycle: 94%, use a Japanese toilet: 75%, sit in Japanese style: 50%). As a result, only 4 patients (18%) were satisfied with the hip arthrodesis. Discussion. The satisfaction of hip arthrodesis was unexpectedly poor despite of pain relief of involved hip joint. One of essential reasons was activity of daily living in Japanese style, which requires relatively deep flexion in hip and knee. Compensation of limited movement in hip might cause pain and progression of osteoarthritic change in adjacent joints. Another vital reason was that we indicated this procedure for bilateral DDH case whose contralateral hip had early stage osteoarthritis, ended up with THA in most cases

Femoroacetabular impingement is a condition in which the femoral head/neck region abnormally contacts the acetabulum, limiting the range of motion of the hip and often associated with pain, damage, and loss of function. The pathophysiology of osteoarthritic changes stemming from impingement syndromes has been linked to the shape of the hip; however, little is known about the influence of the soft tissues to this process. In this pilot study, we used computer-assisted navigation technology to track motion on a cadaver that had mild bilateral cam-impingement lesions, and then performed a virtual simulation to locate sites of impingement. We hypothesised that soft tissues contribute to the degree and location of impingement, so we compared impingements across three different dissection states: (i) all soft tissues intact; (ii) post-capsulectomy; with only the labrum and ligamentum teres remaining; and (iii) disarticulated, with labrum and ligamentum teres removed. With ethical approval, we used one fresh frozen cadaver pelvis that was sectioned above the fifth lumbar vertebra and at the knee. The femurs and pelvis were implanted with fiducial screws as an accurate means for surface-based image registration. With all soft tissues intact, tissues were imaged using computed tomography with a slice thickness of 0.625 mm. The CT scans were imported into Mimics (v13.0, Materialise, Belgium) and carefully segmented, with particular detail to the articular regions and fiducials, to create 3D digital models of the pelvis and femurs. On each side, optical local coordinate reference (LCR) bodies were attached at the proximal femur and iliac crest to permit spatial tracking with an Optotrak Certus camera (Northern Digital Inc., Waterloo, Canada). The 3D digital models were imported into the VSS navigation system (iGO Technologies, Kingston, Canada) and scrupulously registered to the anatomy using the fiducial screws and a calibrated probe. The pose of the femur and pelvis were recorded throughout a series of twelve movements involving various combinations of flexion-extension, abduction-adduction, internal-external rotation and circumduction, as well as functional movements typical of a clinical hip screening. Soft tissues were selectively removed and the movements were repeated post-capsulectomy and completely disarticulated. The recorded pose data were applied to the 3D digital models to perform a computational simulation of the movements during the trials. The pose data were expressed in coordinates of the anterior pelvic plane to compute angles of motion in the principal directions (flexion, abduction, rotation). The motion data were further filtered so that only comparable ranges of motion were present for data analysis. Algorithms were developed to determine bone-on-bone impingement locations by finding contact points between the models. Impingement locations were plotted on the digital models of the femur and pelvis in order to establish zones of impingement. The surface area of each impingement zone was computed by using a Crust-based algorithm that triangulated impingement points encompassing a region, and then summed the surface area of each triangle to estimate the total impingement surface area. Upon visual inspection, it was immediately apparent that impingements tended to occur in well-defined regions. On the femur, these were found along aspects of the head-neck junction, especially on or near osteophytes. On the pelvis, impingement regions were found along the acetabular rim and extending into the lunate region. With soft tissues intact, both femurs and pelvis had prominent anterior and posterior impingement zones. In contrast, post-capsulectomy impingement zones were predominately confined to the anterior region. It should be noted, however, that the total impingement area decreased post-capsulectomy, representing only about 25% of the total area of impingements when all soft tissues were intact. This was also true in the disarticulated state. Both femurs had mild posterior cam lesions, the right worse than the left. Impingements were seen at these sites with soft tissues intact, but diminished almost entirely post-capsulectomy. The anterior lesions were located contra coup to these cam lesions. With soft tissues intact, impingements tended to occur in external rotation and abduction. With soft tissues removed there was a pronounced shift towards impingements occurring in internal rotation. Impingements were also noted in large flexion angles and large abduction-adduction angles in the absence of soft tissues. Although it is widely accepted that the hip is spherical in shape and has ball-and-socket kinematics, recent work suggests that the osteoarthritic hip is aspherical and that translational motion is present. On a very limited series, this work is supportive of the latter observation: if hip motion is purely spherical, a decrease in impingements post-capsulectomy is exceedingly hard to describe. However, if soft tissues cause translatory motion, then their absence logically should lead to a change in the impingement pattern (which we found). This preliminary study provides a methodology for studying the effects of soft tissue on impingements. We conclude that soft tissues do indeed play an important role in impingement and may even contribute to the development of impingement lesions. Limitations include a small sample size, so further studies are required prior to conclusively establishing impingement patterns in passive kinematics of cadaver hips

Primary internal fixation of uncomplicated scaphoid fractures is growing in popularity due to its advantages over conventional cast fixation. Performing the procedure percutaneously reduces the risk of infection and soft tissue damage, but can be tricky because of the small size and complex three-dimensional (3D) shape of this bone. Computer-assisted navigation has been an invaluable tool in other pin insertion procedures. This in-vitro study aimed to evaluate two different rendering techniques for our navigation interface: (i) 3D volume rendering of the CBCT image to show digitally-reconstructed radiographs of the anatomy, and (ii) volume-slicing, analogous to CT-images. As the shape of the scaphoid is highly variable, a plastic model of the wrist was constructed in order to provide consistency that would not be possible in a cadaver-based study. The plastic model featured a removable scaphoid such that a new one was replaced between trials. Three surgeons each performed eight trials using each of the two navigated techniques (yielding a total of 48 trials for analysis). Central placement of scaphoid fixation has been linked with mechanical stability and improved clinical outcomes, thus the surgical goal was to place a K-wire to maximise both depth from the surface and length of the drill path. The wire was drilled through the scaphoid, from distal to proximal, allowing for post-trial analysis of the drill path. A ceiling-mounted OptoTrak Certus camera (Northern Digital Inc., Canada) and a floor-mounted isocentric 3D CBCT C-arm (Innova 4100, GE Healthcare, France) permitted a registration transformation between the tracking and imaging systems to be computed preoperatively, before each trial, using a custom calibration device. Optical local coordinate reference bodies were attached to the wrist model and a custom drill guide for tracking with the Certus camera. During each trial, a 3D spin image of the wrist model was acquired, and rendered according to the technique under study. For 3D volume rendering, the spin image was rendered as a digitally-reconstructed radiograph (DRR) that could be rotated in three dimensions. In the planning phase, the surgeon positioned a desired drill path on the images. Anterior-posterior and lateral views of the 3D volume rendering were used for navigation during the drilling phase. The real-time orientation of the drill guide was shown relative to these images and the plan on an overhead. For volume-sliced (VS) navigation, the spin image was volume-rendered and sliced along the principal planes (axial, coronal, sagittal) for planning. A slider interface allowed the surgeon to scroll through the slices in each of the planes, as if they were looking at individual CT slices. Once the desired drill path was positioned, the volume-sliced views were reconfigured to show slices along the oblique planes of the planned path for navigation. Following all trials, model scaphoids with wire intact were imaged using CT with a slice thickness of 0.625 mm. The CT series were segmented and used to construct 3D digital models of the wire and drilled scaphoid. Algorithms were developed to determine the minimum distance from the centerline of the wire and the scaphoid surface, and to compute the length of the drill path. Screw breach should be avoided as it disrupts the articular surface and may lead to a sequela of cartilage deterioration and osteoarthritic changes. The shortest distance measure was extrapolated to assess whether a standard fixation screw (Accutrak Mini, 1.78 mm radius) would have breached the scaphoid surface. There were three screw breaches noted in the 3D DRR trials, while only one occurred using volume-slicing. The minimum distance from the centerline of the wire to the scaphoid surface can also be thought of as a “safe zone” for screw breach. Although no difference in the mean distance (μ) was noted between groups (μ. DRR. = 2.3 mm, μ. VS. = 2.2 mm), the standard deviation (σ) was significantly higher for the DRR trials (σ. DRR. = 0.50 mm, σ. VS. = 0.37 mm, p < 0.1), suggesting a higher reliability of central placement using VS for navigation. In contrast, the length of the drill paths were significantly longer for the DRR trials (μ = 28.7 mm, σ = 0.66 mm) than for VS-navigation (μ = 28.3 mm, σ = 0.62 mm) at p < 0.1. The surgical goal was to pick a path that maximised both the length of the path, as well as the minimum distance from the scaphoid surface. Algorithms were developed to find the paths that would maximise: (i) the length and (ii) the distance from the surface of the model scaphoid used in this study. The maximum possible length was 29.8mm (with a minimum distance of 2.2mm from the scaphoid surface), and the maximum distance was 3.3mm (with a length of 27.5mm). Therefore, the set of optimal drill paths had length > 27.5 mm, and distance > 2.8 mm. Of the DRR-navigated trials, 11 were below the minimum optimal depth, and only one trial was below the optimal length; 13 of the 24 trials (54%) were of both optimal length and depth. Of the VS-navigated trials, nine were below the minimal optimal distance, and four were below the minimum optimal length; 11 out of 24 trials (46%) were within both the optimal length and depth. From this comparative study, we conclude that VS-navigation was superior in locating a central location for the fixation wire, while DRRs were superior in maximising the depth of the drill path. Thus, we propose a hybrid interface, incorporating both volume-slicing and DRRs, in order to maximise the effectiveness of navigation for percutaneous scaphoid pinning

Osteoarthritic (OA) changes to the bone morphology of the proximal tibia may exhibit load transfer patterns during total knee arthroplasty not predicted in models based on normal tibias. Prior work highlighted increased bone density in transverse sections of OA knees in the proximal-most 10mm tibial cancellous bone. Little is known about coronal plane differences, which could help inform load transfer from the tibial plateau to the tibial metaphysis. Therefore, we compared the cancellous bone density in OA and cadaveric (non-OA) subjects along a common coronal plane. This study included nine OA patients (five women, average age 59.1 ± 9.4 years) and 18 cadaver subjects (four women, average age 39.5 ± 14.4 years). Patients (eight with medial OA and one with lateral OA) received pre-operative CT scans as standard-of-care for a unicompartmental knee replacement. Cadavers were scanned at our institution and had no history of OA which was confirmed by gross inspection during dissection. 3D reconstructions of each proximal tibia were made and an ellipse was drawn on the medial and lateral plateau using a previously published method. A coronal section (Figure 1) to standardize the cohort was created using the medial ellipse center, lateral ellipse center, and the tibial shaft center 71.5mm from the tibial spine. On this section, profile lines were drawn from the medial and lateral ellipse centers, with data collected from the first subchondral bone pixel to a length of 20mm. The Hounsfield Units (HU) along each profile line was recorded for each tibia; a representative graphical distribution is shown in Figure 2. The Area Under the Curve (AUC) was calculated for the medial and lateral sides, which loosely described the stiffness profile through the region of interest. To determine differences between the medial and lateral subchondral bone density, the ratio AUC[medial] / AUC[lateral] was compared between the OA and cadaver cohorts using a two-sample t-test. Data from the sole lateral OA patient was mirror-imaged to be included in the OA cohort. The majority of the OA patients appeared to have higher subchondral bone density on the affected side. Figure 3 compares the medial and laterals sides of each group using the AUC ratio method described above. For the cadaver group the AUC was 1.2 +/− 0.22, with a median of 1.1 [0.9 1.6], smaller than the mean AUC for the OA group, which was 1.4 +/− 0.39, with a median of 1.6 [0.93 2.1]. The p-value was 0.06. The increased density observed in OA patients is consistent with asymmetric loading towards the affected plateau, resulting in localized remodeling of cancellous bone from the epiphysis to metaphysis. From the coronal plane, bone was often observed in OA patients bridging the medial plateau to the metaphyseal cortex. Although the cadaver subjects were normal from history and gross inspection, some subjects exhibited early bone density changes consistent with OA. Future work looks to review more OA scans, extend the work to the distal femur, and convert the HU values to bone elastic moduli for use in finite element modelling