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Orthopaedic Proceedings
Vol. 104-B, Issue SUPP_13 | Pages 65 - 65
1 Dec 2022
Rosario R Coleman R Arruda E Grant J
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The goal of this study was to identify the effect of mismatches in the subchondral bone surface at the native:graft interface on cartilage tissue deformation in human patellar osteochondral allografts (OCA). Hypothesis: large mismatches in the subchondral bone surface will result in higher stresses in the overlying and surrounding cartilage, potentially increasing the risk of graft failure. Nano-CT scans of ten 16mm diameter cadaveric patellar OCA transplants were used to develop simplified and 3D finite element (FE) models to quantify the effect of mismatches in the subchondral bone surface. The simplified model consisted of a cylindrical plug with a 16 mm diameter (graft) and a washer with a 16 mm inner diameter and 36 mm outer diameter (surrounding native cartilage). The thickness of the graft cartilage was varied from 0.33x the thickness of native cartilage (proud graft subchondral bone) to 3x the thickness of native cartilage (sunken graft subchondral bone; Fig. 1). The thickness of the native cartilage was set to 2 mm. The surface of the cartilage in the graft was matched to the surrounding native cartilage. A 1 MPa pressure was applied to the fixed patellar cartilage surface. Scans were segmented using Dragonfly and meshed using HyperMesh. FE simulations were conducted in Abaqus 2019. The simplified model demonstrated that a high stress region occurred in the cartilage at the sharp bony edge between the graft and native subchondral bone, localized to the region with thinner cartilage. A 20% increase in applied pressure occurs up to 50μm away from the graft edge (primarily in the graft cartilage) for grafts with proud subchondral bone but varies little based on the graft cartilage thickness. For grafts with sunken subchondral bone, the size of the high stress region decreases as the difference between graft cartilage and native cartilage thickness decreases (Fig. 2-4), with a 200 μm high stress region occurring when graft cartilage was 3x thicker than native cartilage (i.e., greater graft cartilage thickness produces larger areas of stress in the surrounding native cartilage). The 3D models reproduced the key features demonstrated in the simplified model. Larger differences between native and graft cartilage thickness cause larger high stress regions. Differences between the 3D and simplified models are caused by heterogeneous cartilage surface curvature and thickness. Simplified and 3D FE analysis confirmed our hypothesis that greater cartilage thickness mismatches resulted in higher cartilage stresses for sunken subchondral bone. Unexpectedly, cartilage stresses were independent of the cartilage thickness mismatch for proud subchondral bone. These FE findings did not account for tissue remodeling, patient variability in tissue mechanical properties, or complex tissue loading. In vivo experiments with full-thickness strain measurements should be conducted to confirm these findings. Mismatches in the subchondral bone can therefore produce stress increases large enough to cause local chondrocyte death near the subchondral surface. These stress increases can be reduced by (a) reducing the difference in thickness between graft and native cartilage or (b) using a graft with cartilage that is thinner than the native cartilage. For any figures or tables, please contact the authors directly


Orthopaedic Proceedings
Vol. 104-B, Issue SUPP_12 | Pages 74 - 74
1 Dec 2022
Changoor A Suderman R Wood B Grynpas M Hurtig M Kuzyk P
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Large cartilage lesions in younger patients can be treated by fresh osteochondral allograft transplantation, a surgical technique that relies on stable initial fixation and a minimum chondrocyte viability of 70% in the donor tissue to be successful. The Missouri Osteochondral Allograft Preservation System (MOPS) may extend the time when stored osteochondral tissues remain viable. This study aimed to provide an independent evaluation of MOPS storage by evaluating chondrocyte viability, chondrocyte metabolism, and the cartilage extracellular matrix using an ovine model. Femoral condyles from twelve female Arcott sheep (6 years, 70 ± 15 kg) were assigned to storage times of 0 (control), 14, 28, or 56 days. Sheep were assigned to standard of care [SOC, Lactated Ringer's solution, cefazolin (1 g/L), bacitracin (50,000 U/L), 4°C storage] or MOPS [proprietary media, 22-25°C storage]. Samples underwent weekly media changes. Chondrocyte viability was assessed using Calcein AM/Ethidium Homodimer and reported as percent live cells and viable cell density (VCD). Metabolism was evaluated with the Alamar blue assay and reported as Relative Fluorescent Units (RFU)/mg. Electromechanical properties were measured with the Arthro-BST, a device used to non-destructively compress cartilage and calculate a quantitative parameter (QP) that is inversely proportional to stiffness. Proteoglycan content was quantified using the dimethylmethylene blue assay of digested cartilage and distribution visualized by Safranin-O/Fast Green staining of histological sections. A two-way ANOVA and Tukey's post hoc were performed. Compared to controls, MOPS samples had fewer live cells (p=0.0002) and lower VCD (p=0.0004) after 56 days of storage, while SOC samples had fewer live cells (p=0.0004, 28 days; p=0.0002, 56 days) and lower VCD (p=0.0002, 28 days; p=0.0001, 56 days) after both 28 and 56 days (Table 1). At 14 days, the percentage of viable cells in SOC samples were statistically the same as controls but VCD was lower (p=0.0197). Cell metabolism in MOPS samples remained the same over the study duration but SOC had lower RFU/mg after 28 (p=0.0005) and 56 (p=0.0001) days in storage compared to controls. These data show that MOPS maintained viability up to 28 days yet metabolism was sustained for 56 days, suggesting that the conditions provided by MOPS storage allowed fewer cells to achieve the same metabolic levels as fresh cartilage. Electromechanical QP measurements revealed no differences between storage methods at any individual time point. QP data could not be used to interpret changes over time because a mix of medial and lateral condyles were used and they have intrinsically different properties. Proteoglycan content in MOPS samples remained the same over time but SOC was significantly lower after 56 days (p=0.0086) compared to controls. Safranin-O/Fast Green showed proteoglycan diminished gradually beginning at the articular surface and progressing towards bone in SOC samples, while MOPS maintained proteoglycan over the study duration (Figure 1). MOPS exhibited superior viability, metabolic activity and proteoglycan retention compared to SOC, but did not maintain viability for 56 days. Elucidating the effects of prolonged MOPS storage on cartilage properties supports efforts to increase the supply of fresh osteochondral allografts for clinical use. For any figures or tables, please contact the authors directly


Orthopaedic Proceedings
Vol. 95-B, Issue SUPP_22 | Pages 76 - 76
1 May 2013
Minas T
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Although cartilage repair has been around since the time of open Pridie drilling, clinical outcomes for newer techniques such as arthroscopic debridement, microfracture (MFX), osteochondral autograft transfers (OATS), osteochondral allograft transplantation and Autologous Chondrocyte Implantation (ACI) are still finding their place in treating injured knees. Early mechanical symptoms are best managed by a gentle arthroscopic debridement of loose articular flaps. This allows the surgeon to assess the defect size, location in the tibio-femoral or patellofemoral joint, status of the cartilage overall and patients response to the intervention. If the symptom improvement is not satisfactory to the patient, after assessing background factors that will influence the results of a cartilage repair procedure, (alignment of the patellofemoral joint or axial alignment, ligament stability and status of the meniscus), the surgeon can choose the best procedure for that individual based on the expected outcomes of the various cartilage repair techniques while addressing the background factors. As all the techniques have failures and informed discussion with the patient prior to performing the procedure is critical in avoiding disappointment for the patient and the surgeon. The repair technique used should incorporate considerations of the defect size, location, and the patient age, activity level, expectations and ability to comply with the longer rehabilitation needed for biological procedures as compared to prosthetic implants


Orthopaedic Proceedings
Vol. 97-B, Issue SUPP_1 | Pages 73 - 73
1 Feb 2015
Minas T
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Cartilage is known to have limited intrinsic repair capabilities and cartilage defects can progress to osteoarthritis (OA). OA is a major economic burden of the 21st century, being among the leading causes of disability. The risk of disability from knee OA is as great as that derived from cardiovascular disease; a fact that becomes even more concerning when considering that even isolated cartilage defects can cause pain and disability comparable to that of severe OA. Several cartilage repair procedures are in current clinical application, including microfracture, osteochondral autograft transfer, osteochondral allograft transplantation, and autologous chondrocyte implantation (ACI). Given the economic challenges facing our health care system, it appears prudent to choose procedures that provide the most durable long-term outcome. Comparatively few studies have examined long-term outcomes, an important factor when considering the substantial differences in cost and morbidity among the various treatment options. This study reviews the clinical outcomes of autologous chondrocyte implantation at a minimum of 10 years after treatment of chondral defects of the knee. Mean age at surgery was 36 ± 9 years; mean defect size measured 8.4 ± 5.5cm2. Outcome scores were prospectively collected pre- and postoperatively at the last follow up. We further analyzed potential factors contributing to failure in hopes of refining the indications for this procedure. Conclusions: ACI provided durable outcomes with a survivorship of 71% at 10 years and improved function in 75% of patients with symptomatic cartilage defects of the knee at a minimum of 10 years after surgery. A history of prior marrow stimulation as well as the treatment of very large defects was associated with an increased risk of failure


Orthopaedic Proceedings
Vol. 98-B, Issue SUPP_21 | Pages 72 - 72
1 Dec 2016
Heard S Miller S Schachar R Kerslake S
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Chondral defects on the patella are a difficult problem in the young active patient and there is no consensus on how to treat these injuries. Fresh osteochondral allografts are a valid option for the treatment of full-thickness osteochondral defects and can be used to restore joint function and reduce pain. The primary purpose of this study was to investigate the clinical and subjective outcomes of a series of patients following fresh osteochondral allograft transplantation for isolated chondral defects of the patella. A series of 5 patients underwent surgery using an open approach for graft transplantation. A strict protocol for the allograft tissue was followed. Transplant recipients must be aged <60, have a full-thickness, isolated chondral lesion and have failed previous traditional treatments. The fresh allografts are hypothermically stored at 4°C in X-VIVO10 media for up to 30 days to maintain cartilage viability. Pre- and post-operative clinical measures including knee stability, range of motion, and quadriceps girth were completed. Post-operative plain radiographs were completed including weight-bearing AP, lateral and skyline views. Patient-centred outcome measures including the Knee Osteoarthritis Outcome Score (KOOS) and the Knee Society Score (KSS) were gathered a minimum of 1-year post-operative. Descriptive and demographic data were collected for all patients. A paired t-test was employed to determine the difference between the pre-operative and post-operative outcomes. All patients were female, with a mean age of 27.4 (SD 3.65). Knee ligament stability was similar pre- and post-operatively. Knee ROM assessment of flexion and extension demonstrated a less than 10° increase from pre to post-operative. Quadriceps girth measurements demonstrated a mean change of 0.5 cm from pre- to post-operative for the surgical limb. Post-operative radiographs demonstrated incorporation of the graft in 4/5 cases within 6-months of surgery. One patient developed fragmentation of the graft after 18-months, and one patient had a subsequent trochleoplasty for persistent pain. The mean KOOS domain scores demonstrated significant improvement (p<0.05) as follows: Symptoms pre-op = 28.57, post-op = 55; Pain pre-op 28.89, post-op = 57.22; ADLs pre-op = 48.92, post-op = 66.18; Sports/Recreation pre-op = 6, post-op = 32; and QoL pre-op = 12.5, post-op = 42.5. Mean pre-op surgical versus non-surgical limb KSS scores were 107.4 and 179 respectively. The mean post-op surgical versus non-surgical limb KSS scores were 166 and 200. Isolated chondral defects of the patella can cause substantial pain, reduced function, and can be challenging to address surgically. This series of 5 cases demonstrated improved function, KOOS and KSS for 4/5 patients. To our knowledge this is a novel biological procedural technique for this problem, which has shown promising results making it a viable treatment option for young active patients with osteochondral defects of the patella