Introduction. Hoffa fractures are rare, intra-articular fractures of the femoral condyle in the coronal plane and involving the weight-bearing surface of the distal femur. Surgical fixation is warranted to achieve stability, early mobilisation and satisfactory knee function. We describe a unique type of Hoffa fracture in the coronal plane with sagittal split and intra-articular comminution. There is scant evidence in current literature with regards to surgical approaches, techniques and implants. We report of our case with a review of the literature. Case report. A 40 year old male motorcyclist was involved in a high speed road traffic collision. X-rays confirmed displaced unicondylar fracture of the lateral femoral condyle. CT showed sagittal split of the Hoffa fragment and intra-articular comminution. MRI showed partial rupture of the anterior cruciate ligament. The patient underwent definitive surgical treatment via a midline skin incision and lateral parapatellar approach using cannulated screws, headless compression screws and anti-glide plate. Weightbearing was commenced at 8 weeks. Arthroscopy and adhesiolysis was performed at 12 weeks to improve range of motion. The patient was discharged at one year with a pain-free, functional knee. Discussion. Hoffa fractures are high-energy fractures, often seen in young male motorcyclists with flexed and slightly abducted knee. Most papers recommend surgical fixation, however there is no widely accepted surgical method or rehabilitation regime. Varying surgical approaches, screw direction, choice of implants, and post-operative care have been described. Surgical approach depends on the configuration of the fracture. The medial/lateral parapatellar approach is commonly used as it does not compromise future arthroplasty, but it does not allow access to fix posterior comminution. Arthroscopic-assistance may be used with good outcomes and less tissue dissection. AP screws are widely reported in the literature, most likely due to easier access to the fracture site. PA screws may provide better stability, but access is more difficult. Fixation often involves passing screws through the articular surface, therefore the area damaged should be kept to a minimum by using the smallest possible screw; headless compression screws leave a smaller footprint in the articular cartilage. Locking plate augmentation generally gives good outcomes. Conclusion. Hoffa fractures are rare and difficult to treat. Surgical treatment is the best choice for optimum post-operative knee function. There is no consensus on choice of surgical approaches, techniques and implants, as these are dependent on fracture configuration. In this particular case we emphasise the importance of using an anti-glide plate to address the sagittal component. Despite the need for a secondary procedure, the treatment has had positive outcomes and may be used as a guide for treatment of future Hoffa fractures of a similar sub-type

Soft tissue balancing is critical to successful knee arthroplasty. Pre-operative planning ensures that the surgeon is prepared for any eventuality. We report a large femoral exostosis resulting in gross instability, requiring revision to a constrained implant. An 81 year old female presented with osteoarthritis of the left knee. Xray showed a medial bony mass. CT noted a large bony exostosis arising from the posteromedial femoral condyle. Review showed the exostosis was not related to the medial collateral ligament (MCL). At surgery, the exostosis was noted to be tenting the MCL – excision resulted in complete flaccidity. A trial of the Biomet AGC prosthesis revealed gross medial instability. The decision was taken to convert to a DePuy Sigma TC3 system. Whilst removing TC3 trial components, a lateral condyle fracture occurred. This was fixed with a 1/3 tubular plate and interfragmentary screw. The TC3 system and an AGC patellar button were found to be congruent. A small lateral release was performed, the deep MCL was replaced with tagging sutures through the MCL and the pes anserinus. At 9 weeks post operatively, the patient was pain free and mobilising independently. The knee was stable, with range of movement from 0 to 110 degrees. To our knowledge, this is the first report of such a complication in the literature. It highlights that despite optimal preoperative planning, the surgeon must be prepared to adapt to the situation at hand. It also highlights the importance of having ‘bail out’ options available on shelf when performing routine surgery

Despite the growing success of OCA transplantation in treating large articular cartilage lesions in multiple joints, revisions and failures still occur. While preimplantation subchondral drilling is intended to directly decrease allograft bioburden and has been associated with significant improvements in outcomes after OCA transplantation, the effects of size, number, and spacing of subchondral bone drill sites have not been fully evaluated. This study aimed to investigate the effects of drill size with or without pulse-lavage of OCA subchondral bone by quantifying remnant marrow elements using histomorphometry. With IRB and ACUC approvals, human and canine OCAs were acquired for research purposes. Portions of human tibial plateau OCAs acquired from AATB-certified tissue banks that would otherwise be discarded were recovered and sectioned into lateral and medial hemiplateaus (n=2 each) with a thickness of 7 mm. Canine femoral condyles and tibial plateaus were split into lateral and medial components with a thickness of 7 mm (n=8). Using our clinical preimplantation preparation protocol, holes were drilled into the subchondral bone of each condyle and hemiplateau OCA using either 1.6 mm OD or 3.2 mm OD drill bits from the cut surface to the cortical subchondral bone plate. One femoral condyle and one hemiplateau per drill bit size were pulse-lavaged while the corresponding OCAs were not. The mean total %-fill remaining marrow elements for each treatment group was calculated. Little to no quantifiable bone marrow element retention was noted to remain within the subchondral bone of human or canine OCA specimens after subchondral drilling of allograft bone with either drill bit size evaluated and with or without pulse-lavage. The %-fill was consistent across zones, ranging from 1-5%. This project was designed to provide a preliminary histologic evaluation of the effects of drill size on OCA preimplantation preparation efficacy based on amount of remaining bone marrow elements in human and canine femoral condyle and tibial plateau specimens. Based on these initial findings, choice of drill bit size for OCA subchondral drilling may need to be based on the associated biomechanical effects rather than effects on donor bone marrow element removal

The objectives of the study were to investigate demographic, injury and surgery/treatment-associated factors that could influence clinical outcome, following Autologous Chondrocyte Implantation (ACI) in a large, “real-world”, 20 year longitudinally collected clinical data set. Multilevel modelling was conducted using R and 363 ACI procedures were suitable for model inclusion. All longitudinal post-operative Lysholm scores collected after ACI treatment and before a second procedure (such as knee arthroplasty but excluding minor procedures such as arthroscopy) were included. Any patients requiring a bone graft at the time of ACI were excluded. Potential predictors of ACI outcome explored were age at the time of ACI, gender, smoker status, pre-operative Lysholm score, time from surgery, defect location, number of defects, patch type, previous operations, undergoing parallel procedure(s) at the time of ACI, cell count prior to implantation and cell passage number. The best fit model demonstrated that for every yearly increase in age at the time of surgery, Lysholm scores decreased by 0.2 at 1-year post-surgery. Additionally, for every point increase in pre-operative Lysholm score, post-operative Lysholm score at 1 year increased by 0.5. The number of cells implanted also impacted on Lysholm score at 1-year post-op with every point increase in log cell number resulting in a 5.3 lower score. In addition, those patients with a defect on the lateral femoral condyle (LFC), had on average Lysholm scores that were 6.3 points higher one year after surgery compared to medial femoral condyle (MFC) defects. Defect grade and location was shown to affect long term Lysholm scores, those with grade 3 and patella defects having on average higher scores compared to patients with grade 4 or trochlea defects. Some of the predictors identified agree with previous reports, particularly that increased age, poorer pre-operative function and worse defect grades predicted poorer outcomes. Other findings were more novel, such as that a lower cell number implanted and that LFC defects were predicted to have higher Lysholm scores at 1 year and that patella lesions are associated with improved long-term outcomes cf. trochlea lesions

The clinical success of osteochondral autografts is heavily reliant on their mechanical stability, as grafts which protrude above or subside below the native cartilage can have a negative effect on the tribological properties of the joint [1]. Furthermore, high insertion forces have previously been shown to reduce chondrocyte viability [2]. Commercial grafting kits may include a dilation tool to increase the diameter of the recipient site prior to insertion. The aim of this study was to evaluate the influence of dilation on the primary stability of autografts. Six human cadaveric femurs were studied. For each femur, four 8.5 × 8mm autografts were harvested from the trochlear groove and implanted into the femoral condyles using a Smith & Nephew Osteochondral grafting kit. Two grafts were implanted into dilated recipient sites (n=12) and two were implanted with no dilation (n=12). Insertion force was measured by partially inserting the graft and applying a load at a rate of 1 mm/min, until the graft was flush with the surrounding cartilage. Push-in force was measured by applying the same load, until the graft had subsided 4mm below congruency. Significance was taken as (p<0.05). Average maximum insertion force of dilated grafts was significantly lower (p<0.001) than their non-dilated equivalent [28.2N & 176.7N respectively]. There was no significant difference between average maximum push-in force between the dilated and non-dilated groups [1062.8N & 1204.2N respectively]. This study demonstrated that significantly less force is required to insert dilated autografts, potentially minimising loss of chondrocyte viability. However, once inserted, the force required to displace the grafts below congruency remained similar, indicating a similar degree of graft stability between both groups

Introduction. Degenerative meniscal tears are the most common meniscal lesions, representing huge clinical and socio-economic burdens. Their role in knee osteoarthritis (OA) onset and progression is well established and demonstrated by several retrospective studies. Effective preventive measures and non-surgical treatments for degenerative meniscal lesions are still lacking, also because of the lack of specific and accurate animal models in which test them. Thus, we aim to develop and validate an accurate animal model of meniscus degeneration. Method. Three different surgical techniques to induce medial meniscus degenerative changes in ovine model were performed and compared. A total of 32 sheep (stifle joints) were subjected to either one of the following surgical procedures: a) direct arthroscopic mechanical meniscal injury; b) peripheral devascularization and denervation of medial meniscus; c) full thickness medial femoral condyle cartilage lesion. In all the 3 groups, the contralateral joint served as a control. Result. From a visual examination of the knee joint emerged a clear difference between control and operated groups, in the menisci but also in the cartilage, indicating the onset of OA-related cartilage degeneration. The meniscal and cartilaginous lesions were characterized by different severity and location in the different groups. For instance, a direct meniscal injury caused cartilaginous lesions especially in the medial part of the condyles, and the other approaches presented specific signature. Evaluation of scoring scales (e.g. ICRS score) allowed the quantification of the damage and the identification of differences among the four groups. Conclusion. We were effectively able to develop and validate a sheep model of meniscal degeneration which led to the onset of OA. This innovative model will allow to test in a pre-clinical relevant setting innovative approaches to prevent meniscal-related OA. Funding. Project PNRR-MAD-2022-12375978 funded by Italian Ministry of Health

There are no efficient treatment options for osteoarthritis (OA) that delay further progression. Besides osteoinduction, there is growing evidence of also anti-inflammatory, angiogenetic and neuroprotective effects of biodegradable magnesium-based biomaterials. Their use for the treatment of cartilage lesions in contrast is not well-evaluated yet. Mg-cylinders were analysed in an in vitro and in vivo OA model. In vitro, SCP-1 stem cell line was analysed under inflammatory conditions and Mg-impact. In vivo, small Mg- and WE43 alloy-cylinders (1mm × 0,5mm) were implanted into the subchondral bone of the knee joint of 24 NZW rabbits after establishment of OA. As control, another 12 rabbits received only drill-holes. µCT-scan were performed and assessed for changes in bone volume and density. After euthanasia, cartilage was evaluated macroscopically and histologically after Safranin-O-staining. Furthermore, staining with CD271 directed antibody was performed to assess neuro-reactivity. In vitro, an increased gene expression of extracellular matrix proteins as collagen II or aggrecan even under inflammatory conditions was observed under Mg-impact. In vivo, µCT evaluation revealed twice-elevated values for bone volume in femoral condyles with Mg-cylinders compared to controls while density remained unchanged. Cartilage showed no significant differences between the groups. Mg- and WE-samples showed significantly lower levels of CD271+ cells in the cartilage and bone of the operated joints than in non-operated joints, which was not the case in the Drilling-group. Furthermore, bone in operated knees of Drilling-group showed a strong trend to an increase in CD271+ cells compared to both Cylinder-groups. Counting of CD271+ vessels revealed that this difference was attributable to a higher amount of these vessels. The in vitro results indicate a potential cartilage regenerative activity of the degradable Mg-based material. While so far there was no positive effect on the cartilage itself in vivo, implantation of Mg-cylinders seemed to reduce pain-mediating vessels. Acknowledgements: This work is funded by the German Research Foundation (DFG, project number 404534760). We thank Björn Wiese for production of the cylinders

Autologous osteochondral grafting has demonstrated positive outcomes for treating articular cartilage defects by replacing the damaged region with a cylindrical graft consisting of bone with a layer of cartilage, taken from a non-loadbearing region of the knee. Despite positive clinical use, factors that cause graft subsidence or poor integration are relatively unknown. The aim of this study was to develop finite element (FE) models of osteochondral grafts within a tibiofemoral joint and to investigate parameters affecting osteochondral graft stability. Initial experimental tests on cadaveric femurs were performed to calibrate the bone properties and graft-bone frictional forces for use in corresponding FE models, generated from µCT scan data. The effects of cartilage defects and osteochondral graft repair were measured by examining contact pressure changes using in vitro tests on a single cadaveric human tibiofemoral joint. Six defects were created in the femoral condyles which were subsequently treated with osteochondral autografts or metal pins. Matching µCT scan-based FE models were created, and the contact patches were compared. Sensitivity to graft bone properties was investigated. The bone material properties and graft-bone frictional forces were successfully calibrated from the initial tests with good resulting levels of agreement (CCC=0.87). The tibiofemoral joint experiment provided a range of cases to model. These cases were well captured experimentally and represented accurately in the FE models. Graft properties relative to host bone had large effects on immediate graft stability despite limited changes to resultant cartilage contact pressure. Model confidence was built through extensive validation and sensitivity testing, and demonstrated that specimen-specific properties were required to accurately represent graft behaviour. The results indicate that graft bone properties affect the immediate stability, which is important for the selection of allografts and design of future synthetic grafts. Acknowledgements. Supported by the EPSRC-EP/P001076

Introduction. The ACTIVE(Advanced Cartilage Treatment with Injectable-hydrogel Validation of the Effect) study investigates safety and performance of a novel dextran-tyramine hydrogel implant for treatment of small cartilage defects in the knee (0.5-2.0cm2). The hydrogel is composed of a mixture of natural polymer conjugates that are mixed intra-operatively and which cross-link in situ through a mild enzymatic reaction, providing a cell-free scaffold for cartilage repair. Method. The ACTIVE study is split into a safety (n=10) and a performance cohort (n=36). The Knee Injury and Osteoarthritis Outcome Score (KOOS), pain (numeric rating scale, NRS), Short-Form Health Survey (SF-36) were compared at baseline and 3, 6, and 12 months after surgery. The primary performance hypothesis is an average change in the KOOS from baseline to 12 months (ΔKOOS) greater than a minimal clinically important change (MIC) of 10. No statistical tests were performed as these are preliminary data on a smaller portion of the total study. Result. All patients of the safety cohort (n=10, mean age±SD, 30±9 years) were treated with the hydrogel for a symptomatic (NRS≥4) cartilage defect on the femoral condyle or trochlear groove (mean size±SD, 1.2±0.4cm2). No signs of an adverse foreign tissue reaction or serious adverse events were recorded within the safety cohort. At final follow-up mean KOOS±SD was 66.9±23.5, mean NRS resting±SD was 1.3±1.9, NRS activity±SD was 3.8±2.9 and mean SF-36±SD was 72.0±10.9. ΔKOOS was 21. One patient sustained new knee trauma prior to final follow-up, affecting final scores considerably. When excluded, ΔKOOS was 24(n=9). Conclusion. These promising initial findings provide a solid basis for continuation and expansion of this unique cartilage treatment. The MIC of 10 was surpassed. Though, results should be interpreted cautiously as they are based solely on preliminary data of the first 10 patients. Acknowledgements. Study is sponsored by Hy2Care, producer of the CartRevive®(dextran-tyramine) Hydrogel implant

Rotator cuff tears are common, with failure rates of up to 94% for large and massive tears. 1. For such tears, reattachment of the musculotendinous unit back to bone is problematic, and any possible tendon-bone repair heals through scar tissue rather than the specially adapted native enthesis. We aim to develop and characterise a novel soft-hard tissue connector device, specific to repairing/bridging the tendon-bone injury in significant rotator cuff tears, employing decellularised animal bone partially demineralised at one end for soft tissue continuation. Optimisation samples of 15×10×5mm. 3. , trialled as separate cancellous and cortical bone samples, were cut from porcine femoral condyles and shafts, respectively. Samples underwent 1-week progressive stepwise decellularisation and a partial demineralisation process of half wax embedding and acid bathing. Characterisations were performed histologically for the presence/absence of cellular staining in both peripheral and central tissue areas (n=3 for each cortical/cancellous, test/PBS control and peripheral/central group), and with BioDent reference point indentation (RPI) for pre- and post-processing mechanical properties. Histology revealed absent cellular staining in peripheral and central cancellous samples, whilst reduced in cortical samples compared to controls. Cancellous samples decreased in wet mass after decellularisation by 45.3% (p<0.001). RPI measurements associated with toughness (total indentation depth, indentation depth increase) and elasticity (1st cycle unloading slope) showed no consistent changes after decellularisation. X-rays confirmed half wax embedding provided predictable control of the mineralised-demineralised interface position. Initial optimisation trials show proof-of-concept of a soft-hard hybrid scaffold as an immune compatible xenograft for irreparable rotator cuff tears. Decellularisation did not appreciably affect mechanical properties, and further biological, structural and chemical characterisations are underway to assess validity before in vivo animal trials and potential clinical translation

In this study, we aimed to investigate tibiofemoral and allograft loading parameters after OCA transplantation using tibial plateau shell grafts to characterize the clinically relevant biomechanics that may influence joint kinematics and OCA osseointegration after transplantation. The study was designed to test the hypothesis that there are significant changes in joint loading after tibial plateau OCA transplantation that may require unique post-operative rehabilitation regimens in patients to restore balance in the knee joint. Fresh-frozen cadaveric knees (n=6) were thawed and mounted onto a 6 DOF KUKA robot. Specimens were size matched to +2 mm for the medial-to-lateral width of the medial tibial hemiplateaus. Three specimens served as allograft recipient knees and three served as donor knees. Recipient knees were first tested in their native state and then tested with size-matched medial tibial hemiplateau shell grafts (n=3) prepared from the donor knees using custom-cut tab-in-slot and subchondral drilling techniques. Tekscan sensors were placed in the joint spaces to evaluate the loading conditions under 90N biaxial loading at full extension of the knee before and after graft placement. The I-Scan system used in conjunction analyzed the total force, pressure distribution, peak pressure, and center of force within the joint space. Data demonstrated significant difference (p<0.05) in joint space loading after graft implantation compared to controls in both lateral and medial tibial plateaus. The I-Scan pressure mapping system displayed changes in femoral condylar contact points as well. The results demonstrated that joint space loading was significantly different (p<0.05) between all preoperative and postoperative cadaveric specimens. Despite the best efforts to size match grafts, slight differences in the host's joint geometry resulted in shifts of contact areas between the tibial plateau and femoral condyle therefore causing either an increase or decrease in pressure measured by the sensor. This concludes that accuracy in graft size matching is extremely important to restoring close to normal loading across the joint and this can be further ensured through postoperative care customized to the patient after OCA surgery

Chondral defects in the knee have cartilage biomechanical differences due to defect size and orientation. This study examines how the tibiofemoral contact pressure is affected by increasing full-thickness chondral defect size on the medial and lateral condyle at full extension. Isolated full-thickness, square chondral defects increasing from 0.09cm. 2. to 1.0cm. 2. were created sequentially on the medial and lateral femoral condyles of six human cadaveric knees with intact ligaments and menisci. Chondral defects were created 1.0cm from the femoral notch posteriorly. The knees were fixed to a uniaxial load frame and loaded from 0N to 600N at full extension. Contact pressures between the femoral and tibial condyles were measured using pressure mapping sensors. The peak contact pressure was defined as the highest value in the 2.54mm. 2. area around the defect. The location of the peak contact pressure was determined relative to the centre of the defect. Peak contact pressure was significantly different between (4.30MPa) 0.09cm. 2. and (6.91MPa) 1.0cm. 2. defects (p=0.04) on the medial condyle. On the lateral condyle, post-hoc analysis showed differences in contact pressures between (3.63MPa) 0.09cm. 2. and (5.81MPa) 1.0cm. 2. defect sizes (p=0.02). The location of the stress point shifted from being posteromedial (67% of knees) to anterolateral (83%) after reaching a 0.49cm. 2. defect size (p < 0.01) in the medial condyle. Conversely, the location of the peak contact pressure point moved from being anterolateral (50%) to a posterolateral (67%) location in defect sizes greater than 0.49cm. 2. (p < 0.01). Changes in contact area redistribution and cartilage stress from 0.49cm. 2. to 1.0cm. 2. impact adjacent cartilage integrity. The location of the maximum stress point also varied with larger defects. This study suggests that size cutoffs exist earlier in the natural history of chondral defects, as small as 0.49cm. 2. , than previously studied, suggesting a lower threshold for intervention

Introduction and Objective. Distal femoral fractures are commonly treated with a straight plate fixed to the lateral aspects of both proximal and distal fragments. However, the lateral approach may not always be desirable due to persisting soft-tissue or additional vascular injury necessitating a medial approach. These problems may be overcome by pre-contouring the plate in helically shaped fashion, allowing its distal part to be fixed to the medial aspect of the femoral condyle. The objective of this study was to investigate the biomechanical competence of medial femoral helical plating versus conventional straight lateral plating in an artificial distal femoral fracture model. Materials and Methods. Twelve left artificial femora were instrumented with a 15-hole Locking Compression Plate – Distal Femur (LCP-DF) plate, using either conventional lateral plating technique with the plate left non-contoured, or the medial helical plating technique by pre-contouring the plate to a 180° helical shape and fixing its distal end to the medial femoral condyle (n=6). An unstable extraarticular distal femoral fracture was subsequently simulated by means of an osteotomy gap. All specimens were tested under quasi-static and progressively increasing cyclic axial und torsional loading until failure. Interfragmentary movements were monitored by means of optical motion tracking. Results. Initial axial stiffness was significantly higher for helical (185.6±50.1 N/mm) versus straight (56.0±14.4) plating, p<0.01. However, initial torsional stiffness in internal and external rotation remained not significantly different between the two fixation techniques (helical plating:1.59±0.17 Nm/° and 1.52±0.13 Nm/°; straight plating: 1.50±0.12 Nm/° and 1.43±0.13Nm/°), p≥0.21. Helical plating was associated with significantly higher initial interfragmentary movements under 500 N static compression compared to straight plating in terms of flexion (2.76±1.02° versus 0.87±0.77°) and shear displacement under 6 Nm static rotation in internal (1.23±0.28° versus 0.40±0.42°) and external (1.21±0.40° versus 0.57±0.33°) rotation, p≤0.01. In addition, helical plating demonstrated significantly lower initial varus/valgus deformation than straight plating (4.08±1.49° versus 6.60±0.47°), p<0.01. Within the first 10000 cycles of dynamic loading, helical plating revealed significantly bigger flexural movements and significantly lower varus/valgus deformation versus straight plating, p=0.02. No significant differences were observed between the two fixation techniques in terms of axial and shear displacement, p≥0.76. Cycles to failure was significantly higher for helical plating (13752±1518) compared to straight plating (9727±836), p<0.01. Conclusions. Although helical plating using a pre-contoured LCP-DF was associated with higher shear and flexion movements, it demonstrated improved initial axial stability and resistance against varus/valgus deformation compared to straight lateral plating. Moreover, helical plate constructs demonstrated significantly improved endurance to failure, which may be attributed to the less progressively increasing lever bending moment arm inherent to this novel fixation technique. From a biomechanical perspective, helical plating may be considered as a valid alternative fixation technique to standard straight lateral plating of unstable distal femoral fractures

Objectives. We studied subchondral intraosseous pressure (IOP) in an animal model during loading, and with vascular occlusion. We explored bone compartmentalization by saline injection. Materials and Methods. Needles were placed in the femoral condyle and proximal tibia of five anaesthetized rabbits and connected to pressure recorders. The limb was loaded with and without proximal vascular occlusion. An additional subject had simultaneous triple recordings at the femoral head, femoral condyle and proximal tibia. In a further subject, saline injections at three sites were carried out in turn. Results. Loading alone caused a rise in subchondral IOP from 11.7 mmHg (. sd. 7.1) to 17.9 mmHg (. sd. 8.1; p < 0.0002). During arterial occlusion, IOP fell to 5.3 mmHg (. sd. 4.1), then with loading there was a small rise to 7.6 mmHg (. sd. 4.5; p < 0.002). During venous occlusion, IOP rose to 20.2 mmHg (. sd. 5.8), and with loading there was a further rise to 26.3 mmHg (. sd. 6.3; p < 0.003). The effects were present at three different sites along the limb simultaneously. Saline injections showed pressure transmitted throughout the length of the femur but not across the knee joint. Conclusion. This is the first study to report changes in IOP in vivo during loading and with combinations of vascular occlusion and loading. Intraosseous pressure is not a constant. It is reduced during proximal arterial occlusion and increased with proximal venous occlusion. Whatever the perfusion state, in vivo load is transferred partly by hydraulic pressure. We propose that joints act as hydraulic pressure barriers. An understanding of subchondral physiology may be important in understanding osteoarthritis and other bone diseases. Cite this article: M. Beverly, S. Mellon, J. A. Kennedy, D. W. Murray. Intraosseous pressure during loading and with vascular occlusion in an animal model. Bone Joint Res 2018;7:511–516. DOI: 10.1302/2046-3758.78.BJR-2017-0343.R2

Focal knee resurfacing implants (FKRIs) are typically intended to treat focal cartilage defects in middle-aged patients. All currently available FKRIs are (partly) composed of metal, which potentially leads to degeneration of the opposing articulating cartilage and hampers follow-up using magnetic resonance imaging (MRI). The purpose of this study was to investigate the in vivo osseointegration process of a novel non-degradable thermoplastic polycarbonate-urethane (TPU) osteochondral implant. Bi-layered implants measuring 6 mm in diameter, with a double-curvature to match the approximate curvature of the goat medial femoral condyle were fabricated. TPU implants were composed of an articulating Bionate® II 80A top layer, and a Bionate® 75D bottom layer (DSM Biomedical, Geleen, the Netherlands) which is intended to osseointegrate. A biphasic calcium phosphate coating formulation, optimized during a prior in vitro study, was applied to half of the TPU implants, while the other half was left uncoated. Bi-layered metal implants (articulating cobalt-chromium top layer and titanium bottom layer) were used as positive control implants. Eight implants per group were implanted bilaterally in the medial femoral condyle of the stifle joints in 12 Dutch milk goats. 18F-sodium fluoride (18F-NaF) positron emission tomography-computed tomography (PET-CT) scanning was performed at 3 and 12 weeks postoperatively, and the corrected maximum standard uptake values (cSUVmax) was calculated to assess the peri-implant bone metabolism. After sacrifice 12 weeks postoperatively, bone histomorphometric analysis was performed to assess the bone-to-implant contact area (BIC). Student's T-test was used in case of normal distribution and the Mann-Whitney-U-test was used in case of abnormal distribution for comparison of BIC and cSUVmax. The BIC value of 10.27 ± 4.50% (mean ± SD) for the BCP-coated TPU implants was significantly (P=0.03) higher than the 4.50 ± 2.61% for the uncoated TPU implants. The uncoated TPU implants scored significantly (P=0.04) lower than the BIC of 12.81 ± 7.55% for the metal implants, whereas there was no significant difference between BCP-coated TPU implants and the metal implants (P=0.68). There was a strong correlation between the cSUVmax values and the BIC values at 12 weeks (Pearson's R=0.74, P=0.001). The cSUVmax values significantly decreased between 3 and 12 weeks for the metal implants (p=0.04). BCP-coated TPU implants followed a similar trend but did not reach statistical significance (p=0.07). cSUVmax in the uncoated TPU implants did not show a significant difference between the time-points (p=0.31). Osseointegration of BCP-coated TPU implants did not significantly differ from metal implants. 18F-NaF PET-CT is a feasible modality to assess osseointegration patterns and showed a similar trend between the BCP-coated and metal implants. Hence, an implant fully composed of TPU may avoid the typical metal-related drawbacks of currently available FKRIs. Long-term follow-up studies are advocated to address the effects of the implant to the opposing cartilage, and are therefore warranted

Introduction and Objective. TKA have shown both excellent long-term survival rate and symptoms and knee function improvement. Despite the good results, the literature reports dissatisfaction rates around 20%. This rate of dissatisfaction could be due to the overstuff that mechanically aligned prostheses could produce during the range of motion. Either size discrepancy between bone resection and prosthetic component and constitutional mechanical tibiofemoral alignment (MTFA) alteration might increase soft tissue tension within the joint, inducing pain and functional limitation. Materials and Methods. Total knee arthroplasties performed between July 2019 and September 2020 were examined and then divided into two groups based on the presence (Group A) or absence (Group B) of patellofemoral overstuff, defined as a thickness difference of more than 2 mm between chosen component and bone resection performed, taking into account at least one of the following: femoral medial and lateral condyle, medial or lateral trochlea and patella. Based on pre and post-operative MTFA measurements, Group A was further divided into two subgroups whether the considered alignment was modified or not. Patients were assessed pre-operatively and at 6 months post-op using the Knee Society Score (KSS), Oxford Knee Score (OKS), Forgotten Joint Score (FJS), Visual Analogue Scale (VAS) and Range of Motion (ROM). Results. One hundred total knee arthroplasties were included in the present study, 69 in Group A and 31 in group B. Mean age and BMI of patients was respectively 71 and 29.2. The greatest percentage of Patellofemoral Overstuff was found at the distal lateral femoral condyle. OKS, KSS functional score, and FJS were statistically significant higher in patients without Patellofemoral Overstuff. Therefore, Group A patients with a non-modified MTFA demonstrated statistically significant better KSS, ROM and FJS. Conclusions. Patellofemoral Overstuff decrease post-operative clinical scores in patients treated with TKA. The conventional mechanically aligned positioning of TKA components might be the primary cause of prosthetic overstuffing leading to worsened clinical results. Level of evidence: III; Prospective Cohort Observational study;

Medial meniscus tear has been proposed as a potential etiology of spontaneous osteonecrosis of the knee (SONK). Disruption of collagen fibers within the meniscus causes meniscal extrusion, which results in alteration in load distribution in the knee. A recent study has demonstrated high incidence of medial meniscus extrusion in the knee with SONK. Our purpose was to determine whether the extent of medial meniscus extrusion correlates with the severity of SONK in the medial femoral condyle. Anteroposterior and lateral knee radiographs were taken with the patients standing. Limb alignment was expressed as the femorotibial angle (FTA) obtained from the anteroposterior radiograph. The stage of progression of SONK was determined according to the radiological classification system described by Koshino. After measurement of anteroposterior, mediolateral, and superoinferior dimensions of the hypointense T1 signal intensity lesion of MRI, its ellipsoid volume was calculated with the three dimensions. Meniscal pathology (degeneration, tear, and extrusion) were also evaluated by MRI. Of the 18 knees with SONK, we found 5 knees at the radiological stage 2 lesions, 9 knees at the stage 3, and 4 knees at the stage 4. Whereas the ellipsoid volume of SONK lesion significantly increased with the stage progression, the volume was significantly greater at stage 4 than stage 2 or 3. All the 18 knees with SONK in the present study showed substantial extrusion (> 3mm) and degeneration of the medial meniscus. While medial meniscal extrusion increased with the stage progression, medial meniscus was significantly extruded at stage 3 or 4 compared with stage 2. A significant increase in FTA was found with the stage progression. FTA was significantly greater at stage 4 than stage 2 or 3. Multiple linear regression analysis revealed that medial meniscus extrusion and FTA were useful predictors of the volume of SONK lesion. This study has clearly shown a significant correlation between the extent of medial meniscus extrusion and the stage and volume of SONK lesion. Degeneration and tears of the medial meniscus in combination with extrusion may result in loss of hoop stress distribution in the medial compartment, which could increase the load in the medial femoral condyle. In addition to meniscal pathology, knee alignment can influence load distribution in the medial compartment biomechanically. Multiple linear regression analysis indicates that an increase in FTA concomitant with a greater extrusion of medial meniscus could result in greater lesion and advanced radiological stage of SONK. Taken together, alteration in compressive force transmission through the medial compartment by meniscus extrusion and varus alignment could develop subchondral insufficiency fractures in the medial femoral condyle, which is considered to be one of the main contributing factors to SONK development. There was high association of medial meniscus extrusion and FTA with the radiological stage and volume of SONK lesion. Increased loading in the medial femoral condyle with greater extrusion of medial meniscus and varus alignment may contribute to expansion and secondary osteoarthritic changes of SONK lesion

Background. Based on decellularisation and cleaning processes of trabecular bone and fibrocartilage, an osteochondral allograft has been developed. Material. The chemical process, established thanks to bone and fibrocartilage data, included an efficient viroinactivation step. The raw material was a tibial plateau collected during knee arthroplasty, cut in cylinders strictly selected (>2mm cartilage height and total height between 10 and 16mm). The grafts were freeze-dried and gamma sterilised. Methods. Decellularisation and structure integrity were validated based on histological analysis, before and after treatment. Mesenchymal Stem Cells (MSC) proliferation in contact with the graft was evaluated to validate the biocompatibility. Biomechanics of the cartilage was studied to determine the compressive resistance before and after treatment. Proof of concept has been completed on femoral condyles in a rabbit model: osteochondral allografts of rabbit were prepared from femoral condyles, processed like human allografts and implanted in 6 femoral condyle defects of 4mm diameter and compared to 3 sham-operated sites. Rabbits were sacrificed at 12 weeks. Macroscopic evaluation and histological stainings were carried out to determine bone and cartilage reconstruction. Results. The stainings of processed grafts showed decellularisation, cleaning of bone, porosity of cartilage tissue, decrease in the aggrecan rate and preservation of type II collagen. MSC proliferated inside the trabecular bone and spread at the surface of the cartilage tissue after 3 weeks. Compressive resistance of cartilage before and after processing was similar to literature. Osteochondral rabbit defects were filled with bone and cartilage tissue, with total integration of bone and cartilage repair observed in two ways: cells spreading from lateral cartilage and MSC diffusing from subchondral plate. Conclusions. The decellularised biocompatible osteochondral allograft enhanced cartilage repair in an animal model. Two clinical trials are ongoing in talus and knee osteochondral lesions

Abstract. Objectives. Osteochondral grafting (OCG) is one treatment strategy for osteoarthritis with good clinical results. Decellularised tissues provide a promising alternative to standard autografts or allografts. This study aimed to compare the stability of traditional OCG and decellularised scaffolds upon initial implantation. Methods. Host cubes (N=16) were extracted from porcine femoral condyles around an artificial defect hole. Grafts (N=11) were harvested from the trochlear groove; porcine decellularized osteochondral scaffold (N=5) were prepared. Each host was secured in fixtures and submerged in PBS at 37 ºC. Each graft or scaffold was press fit into one of the hosts, then pushed in for 5 mm, using an indenter (Instron3365) and pushed out in the opposite direction for 10 mm. Parameters analysed were the force required to initiate movement (Dislodging Force) and the maximum force (Max Force). Results. The Dislodging Force of grafts (mean ± std. dev) was 133±15 N for the push in test and 109±11 N for the push out test. This was significantly higher than values for scaffolds: IN 24±1 N and OUT 26±5 N. The Max Force were also larger in the grafts than the scaffolds: IN 152±16 N vs. 41±4 N and OUT 118±14 N vs. 33±3 N. Conclusions. The force required to dislodge a graft or scaffold from a host environment was similar for the push in test and the push out test, suggesting it is a good measure of initial stability. Upon initial implantation, the decellularised scaffolds were easier to dislodge than the OCG. Previously, the decellularisation process was found to soften bone, relative stiffness may thus be an important consideration in graft fixation. A greater press fit may be necessary for decellularised scaffolds in order to achieve the same level of graft stability as natural OCG when used in vivo. Declaration of Interest. (b) declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported:I declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project

Abstract. Objectives. A fibril reinforced multiphasic cartilage model was developed to improve the understanding of the depth-dependent cartilage internal structure and its through thickness biomechanical response. The heterogeneous model of cartilage was validated against full-field strain measurement obtained via Digital Image Correlation (DIC) during free swelling experiments. Methods. Hemi-cylindrical cartilage cores of 5mm diameter were obtained from porcine femoral condyles and humeral heads. The full field behaviour of these samples was monitored using DIC during an osmotic free swelling experiment performed following a standardised protocol [1]. Computational models were created in FEBio (version 2.8, . febio.org. ). The cartilage, submerged in saline solution was represented by a 1×1mm cube [2] with geometry and constrains set up to mimic the experimental conditions. Cartilage was modelled as a multiphasic material represented by one inhomogeneous layer with depth-dependent Young's modulus [3], zonally varied water content and zonally oriented collagen fibrils [4]. Experimental and predicted strain maps were compared to each other both qualitatively and quantitatively. Results. The numerical strain map showed high strain localisation close to the cartilage surface, with strain in this region reaching 40% and 12% for femoral and humeral samples respectively, this finding was confirmed in our experimental results. Strain magnitude gradually decreased with depth, reaching near-zero at around 200μm. This behaviour also matched experimental observations. Conclusions. Both sets of computational strain results exhibited very good agreement with experimental data, both in terms of cartilage through-thickness swelling behaviour and strain magnitude. Our results show the importance of including cartilage structural inhomogeneities and inclusions of collagen fibrils when simulating through-thickness cartilage swelling. These findings highlight the crucial role of collagen fibrils on both tissue solute transport properties as well as the overall biomechanical response of cartilage. Declaration of Interest. (b) declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported:I declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project