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Figure 1:

Figure 1

1A represents the OCA plug recipient's site, an osteochondral surface with a centralized lesion, with a 2 mm: 8mm cartilage/bone ratio. 1B represents OCA plug constructs. Light brown color represents the bone portion, and orange brown represent the cartilage region. The bone/cartilage ratio of plug A matches that of the recipient site (for control purposes).

Figure 2

Figure 2

Simulation of an osteochondral allograft within its recipient site. The blue region represents the area through which an even load of 5000 newtons (N) was applied.

Figure 3:

Figure 3

3A illustrates an intact state without a cartilage lesion, and 3B illustrates a centralized osteochondral lesion 8 millimeters in diameter, both with 5000N of downward force in the vertical axis. The continuous color column indicates the total von Mises stress in the model.

Figure 4:

Figure 4

Illustration of each plug (A-E) within the standardized recipient bone block, each with 5000N of downward force in the vertical axis. The continuous color column indicates the total von Mises stress in the model.

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ABSTRACT

OBECTIVE

The purpose of this study is to evaluate the impact that osteochondral allograft cartilage thickness has on contact pressures, and to simulate whether a mismatch of the subchondral bony interface relative to the host-recipient site results in altered biomechanics.

METHODS

Properties of articular cartilage and bone were incorporated into a finite element model to create a simulated osteochondral lesion (diameter: 10mm, height: 10mm, cartilage thickness: 2mm, subchondral bone thickness: 8mm). Five osteochondral plugs were constructed to fill the defect, with cartilage-to-bone ratios between 1:9 and 1:1. The plugs were inserted and given a static downward force of 5000N. Resultant stresses and displacements were measured.

RESULTS

The 2:8 cartilage-to-bone ratio plug, matched with the recipient site, was deemed optimal based on its resultant stress and displacement. The 1:9 plug displaced less than the 2:8 match and endured greater stress per unit of cartilage volume, whereas the 3:7 plug also displayed similar displacement to the 1:9 plug but had greater cartilage volume and was able to distribute less stress per unit of cartilage volume. The 4:6 plug displaced to a similar extent as the 3:7 plug but displayed a unique pattern of strain. The 5:5 plug was considered non-functional, as the majority of displacement was seen in the cartilage of the recipient site rather than in the plug itself.

CONCLUSION

The relationship between the cartilage-to-bone ratio in osteochondral allografts and that of their surroundings significantly impacts the distribution of stresses and predilection for micro-motion at the repair site.

INTRODUCTION

Osteochondral allografts (OCA) are often indicated in patients with large chondral or osteochondral defects, who fail non-operative management, do not have diffuse joint disease and are not candidates for total knee arthroplasty.3x3Cavendish, PA, Everhart, JS, Peters, NJ, Sommerfeldt, MF, and Flanigan, DC. Osteochondral Allograft Transplantation for Knee Cartilage and Osteochondral Defects: A Review of Indications, Technique, Rehabilitation, and Outcomes. JBJS Rev. 2019; 7: e7

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OCA has been shown to result in good long-term outcomes, and in a recent systematic review, Chahal et al. reported a survivorship of 82% at a mean 5-year of follow-up.4x4Chahal, J, Gross, AE, Gross, C, Mall, N, Dwyer, T, Chahal, A, Whelan, DB, and Cole, BJ. Outcomes of osteochondral allograft transplantation in the knee. Arthroscopy. 2013; 29: 575–588

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Thus, while overall a successful operation, there is still a considerable failure rate present with room for improvement. The risk factors for failure of an osteochondral allograft implantation are an important area to study with several patient characteristics such as age, body mass index (BMI), defect size, and alignment having been identified as significant variables.11x11Krych, AJ, Robertson, CM, and Williams, RJ 3rd. Cartilage Study G. Return to athletic activity after osteochondral allograft transplantation in the knee. Am J Sports Med. 2012; 40: 1053–1059

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, 13x13Merkely, G, Ackermann, J, and Gomoll, AH. The Role of Hypertension in Cartilage Restoration: Increased Failure Rate After Autologous Chondrocyte Implantation but Not After Osteochondral Allograft Transplantation. Cartilage. 2020; : 1947603519900792

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, 16x16Thomas, D, Shaw, KA, and Waterman, BR. Outcomes After Fresh Osteochondral Allograft Transplantation for Medium to Large Chondral Defects of the Knee. Orthop J Sports Med. 2019; 7: 2325967119832299

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However, less is known about the characteristics of the OCA graft itself.

While some degree of anatomic variation exists, the native knee articular cartilage is usually between 2-4 millimeters thick. In theory, different levels of cartilage thickness may absorb different levels of load, thus altering joint contact pressures.12x12Malekipour, F, Whitton, C, Oetomo, D, and Lee, PV. Shock absorbing ability of articular cartilage and subchondral bone under impact compression. J Mech Behav Biomed Mater. 2013; 26: 127–135

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, 15x15Schmitz, RJ, Wang, HM, Polprasert, DR, Kraft, RA, and Pietrosimone, BG. Evaluation of knee cartilage thickness: A comparison between ultrasound and magnetic resonance imaging methods. Knee. 2017; 24: 217–223

Abstract | Full Text | Full Text PDF | PubMed | Scopus (41)
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Altered joint contact pressures can increase load and early articular cartilage wear, impacting the implanted osteochondral graft and potentially leading to degenerative changes in the joint.8x8Dabiri, Y and Li, LP. Altered knee joint mechanics in simple compression associated with early cartilage degeneration. Comput Math Methods Med. 2013; 2013: 862903

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While it is known that an OCA graft being left proud or recessed just 1mm can alter joint contact pressures, it remains unclear of whether the subchondral bony interface needs to be level compared to the corresponding native subchondral bone plate, and if any changes in this relationship result in altered joint mechanics.

The purpose of the current study is to evaluate, using a finite element model, the impact that osteochondral allograft cartilage thickness has on contact pressures, and to simulate whether a mismatch of the subchondral bony interface relative to the host-recipient site results in altered contact pressures or biomechanics. Finite element analysis is a tool used to analyze stress-strain relationships within a model, or scaffold, by dividing it into multiple smaller blocks or elements and assessing each individually. It allows for a cost-effective and efficient way to preliminarily assess complex anatomic structures before delving into cadaver or clinical-based studies. Our hypothesis is that alterations in the location of the subchondral plate/tidemark between an OCA graft and the recipient site will alter contact pressures.

METHODS

Model Design

Using 123Design software (v. 14.2.2, Autodesk 2015) an osteochondral surface with a centralized lesion model was created. This was simulated as a cylinder 20 millimeters in height and 25 millimeters in diameter, with a 2-millimeter cartilage/8-millimeter bone proportion, matching Plug A cartilage/bone ratio (Figure 1A). Subsequently, five configurations of osteochondral plugs were designed using the same software. These osteochondral plugs were designed with a height of 10 millimeters, a diameter of 10 millimeters, and cartilage-to-bone ratios ranging from 1:9, to 1:1. The rendered simulations of these plugs can be seen in Figure 1B. The simulated plugs were reviewed and processed in order to remove imperfections, using the software MeshLab (v. 2016.12, Pablo Cignoni, Visual Computing Lab) and optimized (correction of errors, closure of design flaws, and removal of self-intersecting or incomplete geometries in the design) on Meshmixer (v. 3.4.35, Autodesk).

Figure 1: Opens large image

Figure 1

1A represents the OCA plug recipient's site, an osteochondral surface with a centralized lesion, with a 2 mm: 8mm cartilage/bone ratio. 1B represents OCA plug constructs. Light brown color represents the bone portion, and orange brown represent the cartilage region. The bone/cartilage ratio of plug A matches that of the recipient site (for control purposes).

Finite Element Analysis

Once these elements were complete, a finite element simulation was created with the following parameters: length units in centimeters, angular units in degrees, and default relative tolerance set to 1 × 10−6. This simulation was performed using COMSOL, a computer-based software utilized in modeling and implementation of finite element designs. The simulation elements were configured as an assembly of components, with the same relative tolerance. These settings allowed for the highest fidelity possible with the original images. The properties of cortical bone and cartilage for the current simulation were assigned according to the built-in software materials library. The specific material properties are listed in Table 1.

Table 1Material Properties of Cortical Bone and Cartilage
PropertyCortical BoneCartilageUnit
Density1,9081.1 × 107kg/cm3
Young's (Elastic) modulus1,500,000,0001,100Pa
Poisson's ratio0.560.13-
View Table in HTML

Using the COMSOL library, a Solid Mechanics study in stationary conditions was chosen. The loads in the simulation were applied onto the articular surface of the model, as shown in figure 2. The load applied 5,000 newtons, as a total force in perpendicular direction to the surface of the model. This force was adapted based on a study by Bergmann et al., who found that peak forces within the knee can reach beyond 5,000 newtons with low-level activities such as jogging.1x1Bergmann, G, Bender, A, Graichen, F, Dymke, J, Rohlmann, A, Trepczynski, A, Heller, MO, and Kutzner, I. Standardized loads acting in knee implants. PLoS One. 2014; 9: e86035

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Once these parameters were set, the software displayed a finite mesh across the model, with a triangular configuration. Forces generated in the model were calculated individually on each triangle of this mesh, and then, all individual solutions extrapolated to a final solution representative of the entire system. The simulations produced are most in line, clinically, with the point in time immediately after insertion of the osteochondral plug, as it does not take into account the ensuing healing that will occur between the osseous portion of the plug and its surroundings. Healing between the bony interface of the plug and surroundings may either allow for greater distributions of forces in the subchondral region or reduce the degree of axial compression in the plug.

Figure 2 Opens large image

Figure 2

Simulation of an osteochondral allograft within its recipient site. The blue region represents the area through which an even load of 5000 newtons (N) was applied.

RESULTS

The calculations generated a non-convergent solution for the model. The intact cartilage state demonstrates uniform distribution of stresses and uniform cartilage deformation with the application of force, while the lesion state demonstrates an uneven distribution of deformation across the cartilage, with significant stress concentrated at the edges of the lesion (figure 3).

Figure 3: Opens large image

Figure 3

3A illustrates an intact state without a cartilage lesion, and 3B illustrates a centralized osteochondral lesion 8 millimeters in diameter, both with 5000N of downward force in the vertical axis. The continuous color column indicates the total von Mises stress in the model.

Among the simulations with inserted osteochondral plugs, the majority of cases (A, B, C, D) primarily demonstrated displacement (i.e. compression) within the cartilage of the plug, with only a modest level of displacement seen in the surrounding recipient site, when the compressive force was applied (figure 4). These findings occur given that 1. There is discontinuity between the cartilage of the plug and that of the recipient site, thus creating two separate systems through which stresses can be distributed; and 2. The cartilage volume of the plug is a fraction of that of the recipient site, thus causing the former to compress to a greater extent than the latter when equal forces are applied to both.

Figure 4: Opens large image

Figure 4

Illustration of each plug (A-E) within the standardized recipient bone block, each with 5000N of downward force in the vertical axis. The continuous color column indicates the total von Mises stress in the model.

Plug A was considered to be optimal given its matched cartilage-to-bone ratio (CBR) with the recipient site. Its resultant stresses are within physiological range and displacements are predicted towards the subjacent bone (figure 4A). Plug B, with a lower CBR than the recipient site and thus lower cartilage volume, displaced to a lesser extent than plug A and consequently endured greater stress per unit of cartilage volume (figure 4B). Additionally, the predicted resultant force of plug B is outwards of the lesion, indicating that this may lead to some degree of micromotion of the plug within the site following OCA transplantation. While plug C was displaced to an extent similar to that of plug B, plug C had greater cartilage volume and was therefore able to distribute less stress per unit of cartilage volume than plug B, allowing plug C to act more similarly to the optimal model, plug A (figure 4C). Plug D displaces to a similar extent as plug C despite having a greater cartilage volume but displays a unique pattern of strain – the cartilage of the plug deforms in two zones (figure 4D). However, similar to plug B, plugs C and D have increased outward resultant forces, which may translate clinically to micromotion within the recipient site following transplantation. In plug E, although the measured level of stress is similar to the previous plugs, the majority of displacement was seen in the cartilage of the surrounding recipient site as opposed to in the plug itself (figure 4E). Of note, the displacement and distribution of stresses in the simulation of plug E are remarkably similar to that of lesion model seen in figure 3B.

A summary of each simulation's cartilage properties, total stress, and direction of resultant force in the cartilage of the plug following application of force can be found in Table 2. Given that the simulation with plug A was considered optimal, Table 2 also compares the non-matched plugs to plug A and provides an efficacy rating of the plugs. The efficacy rating is a theoretical prediction of the plugs’ abilities to distribute stress while lowering the risk of micromotion within the recipient site, relative to one another. Although plug E appeared to have a better stress-per-volume value than plug D, relative to plug A, it was considered the most inferior given that the stress was largely assumed by the cartilage of the recipient site rather than the plug itself.

Table 2Summary of Simulation and Efficacies Relative to Plug A.
ModelTotal Cartilage Volume (mm3)Recipient Cartilage Height (mm)Plug Cartilage Height (mm)Sum of Total Stress in Model (MPa)Direction of Plug Cartilage Resultant ForceStress/Cartilage Volume (MPa/mm3)Ratio of Stress/Cartilage Volume to Plug AEfficacy Rating
A981.752.002.00445,000Inward453.271.001
B903.212.001.003,410,000Outward3775.448.334
C1060.292.003.00508,000Outward479.121.062
D1138.832.004.00555,000Outward487.341.083
E1217.372.005.001,280,0001051.452.325
View Table in HTML

DISCUSSION

The most important finding in this study was that the relationship between the cartilage-to-bone ratio (CBR) of an osteochondral allograft and that of its surrounding block impacts the degree and directionality to which stresses are distributed within the joint, as demonstrated by our finite element analysis. An allograft with a CBR different from that of its surrounding block was unable to tolerate the same level of stress as one with a matched CBR. Moreover, the allograft with the largest difference in CBR compared to its surrounding block was unable to tolerate the applied load entirely. Therefore, a higher CBR seems to lead to a situation with very little forces on the plug and more on the surrounding unit.

The finite element analysis method was first introduced into the field of orthopaedics when Brekelmans et al. evaluated a new way to analyze the mechanical behavior of skeletal parts.2x2Brekelmans, WA, Poort, HW, and Slooff, TJ. A new method to analyse the mechanical behaviour of skeletal parts. Acta Orthop Scand. 1972; 43: 301–317

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Since then, this methodology has been used in various applications, such as to assess the viability of a procedure or implant where directly measuring in vivo forces and stresses would otherwise be difficult, if not impossible. For instance, Koh et al. used the finite element method to evaluate the biomechanical effects of meniscal allograft transplantation,10x10Koh, YG, Lee, JA, Kim, YS, and Kang, KT. Biomechanical influence of lateral meniscal allograft transplantation on knee joint mechanics during the gait cycle. J Orthop Surg Res. 2019; 14: 300

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and Sano et al. used it to evaluate factors affecting the stress distribution of the proximal tibia after a uni-compartmental knee arthroplasty.14x14Sano, M, Oshima, Y, Murase, K, Sasatani, K, and Takai, S. Stress Analysis of the Proximal Tibia using Finite Element Method after Unicompartmental Knee Arthroplasty. J Nippon Med Sch. 2020;

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These analyses have subsequently largely corroborated by clinical studies.14x14Sano, M, Oshima, Y, Murase, K, Sasatani, K, and Takai, S. Stress Analysis of the Proximal Tibia using Finite Element Method after Unicompartmental Knee Arthroplasty. J Nippon Med Sch. 2020;

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, 20x20Yoon, JR, Kim, TS, Lee, YM, Jang, HW, Kim, YC, and Yang, JH. Transpatellar approach in lateral meniscal allograft transplantation using the keyhole method: can we prevent graft extrusion?. Knee Surg Sports Traumatol Arthrosc. 2011; 19: 214–217

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Thus, the use of finite element analysis can be considered effective in assessing and predicting biomechanical properties in the setting of an orthopaedics procedure.

Transplantation of osteochondral allografts has generally favorable outcomes – a systematic review by Chahal et al. reported a 82% clinical survivorship and a mean postoperative patient satisfaction rate of 86% at a mean 5-year follow-up,4x4Chahal, J, Gross, AE, Gross, C, Mall, N, Dwyer, T, Chahal, A, Whelan, DB, and Cole, BJ. Outcomes of osteochondral allograft transplantation in the knee. Arthroscopy. 2013; 29: 575–588

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while a separate systematic review by Hurley et al. reported rates of return-to-sport ranging from 77%.6x6Crawford, ZT, Schumaier, AP, Glogovac, G, and Grawe, BM. Return to Sport and Sports-Specific Outcomes After Osteochondral Allograft Transplantation in the Knee: A Systematic Review of Studies With at Least 2 Years' Mean Follow-Up. Arthroscopy. 2019; 35: 1880–1889

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However, rates of failure of the procedure, defined by multiple studies as revision of OCA, conversion to arthroplasty, or gross failure of OCA on second-look arthroscopy, have been reported as between 9.9% to 20%.6x6Crawford, ZT, Schumaier, AP, Glogovac, G, and Grawe, BM. Return to Sport and Sports-Specific Outcomes After Osteochondral Allograft Transplantation in the Knee: A Systematic Review of Studies With at Least 2 Years' Mean Follow-Up. Arthroscopy. 2019; 35: 1880–1889

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, 9x9Familiari, F, Cinque, ME, Chahla, J, Godin, JA, Olesen, ML, Moatshe, G, and LaPrade, RF. Clinical Outcomes and Failure Rates of Osteochondral Allograft Transplantation in the Knee: A Systematic Review. Am J Sports Med. 2018; 46: 3541–3549

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One way that surgeons try to avoid reoperation and/or graft failure is by matching the topography of the graft to that of its surroundings. While numerous studies have shown that harvesting an allograft from a non-orthotopic area can be done without impacting the topography of the joint or postoperative clinical outcomes,17x17Urita, A, Cvetanovich, GL, Madden, BT, Verma, NN, Inoue, N, Cole, BJ, and Yanke, AB. Topographic Matching of Osteochondral Allograft Transplantation Using Lateral Femoral Condyle for the Treatment of Medial Femoral Condyle Lesions: A Computer-Simulated Model Study. Arthroscopy. 2018; 34: 3033–3042

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, 18x18Wang, D, Jones, KJ, Eliasberg, CD, Pais, MD, Rodeo, SA, and Williams, RJ 3rd. Condyle-Specific Matching Does Not Improve Midterm Clinical Outcomes of Osteochondral Allograft Transplantation in the Knee. J Bone Joint Surg Am. 2017; 99: 1614–1620

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, 19x19Yanke, AB, Urita, A, Shin, JJ, Cvetanovich, GL, Moran, EK, Bach, BR Jr., Cole, BJ, Inoue, N, and Verma, NN. Topographic Analysis of the Distal Femoral Condyle Articular Cartilage Surface: Adequacy of the Graft from Opposite Condyles of the Same or Different Size for the Osteochondral Allograft Transplantation. Cartilage. 2019; 10: 205–213

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the ultimate goal of the procedure remains creating a flush articular surface and avoiding creation of a step-off between the allograft and the edge of the recipient site. D'Lima et al. found on the effects of graft alignment found that leaving the graft proud by as little as 0.25 millimeters can significantly alter the biomechanical loading and distribution of stresses in the knee and jeopardize the graft.7x7DDL, D, CC, P, and W. Colwell, C.J. Osteochondral grafting: effect of graft alignment, material properties, and articular geometry. Open Orthop J. 2009; 3: 61–68

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Similar to how a gross step-off on the articular surface can impact knee biomechanics and graft viability, so can the relationship between the CBR of the allograft and that of the recipient at the site of the lesion, as found in the current study.

Cartilage of the knee serves to reduce friction of articulating bones while also distributing a person's weight-bearing forces to the distal limb. Given that these forces cannot be distributed equally, as local contact pressures within the joint vary based on location and type of activity being performed, articular cartilage thickness throughout the joint has been shown to adapt to chronic loading patterns.5x5Chaudhari, AM, Briant, PL, Bevill, SL, Koo, S, and Andriacchi, TP. Knee kinematics, cartilage morphology, and osteoarthritis after ACL injury. Med Sci Sports Exerc. 2008; 40: 215–222

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A study by Rossom et al. found that areas of the knee joint with higher and more repetitive condylar loading were correlated with thicker cartilage.5x5Chaudhari, AM, Briant, PL, Bevill, SL, Koo, S, and Andriacchi, TP. Knee kinematics, cartilage morphology, and osteoarthritis after ACL injury. Med Sci Sports Exerc. 2008; 40: 215–222

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Thus, when considering transplanting an osteochondral allograft, graft-to-recipient matching should not only include orthotopic and topographical matching, but also CBR matching. Our study has shown that an allograft with a lower CBR than its recipient block is predicted to tolerate less of the applied stress and produce an outward resultant force, when compared to one with a matched CBR. While allografts with a higher CBR than their recipient block were better able to tolerate the applied stress, given the inherently pliant nature of cartilage, a similar outward resultant force was still predicted. A marked difference in CBR between the plug and recipient, as seen with plug E, resulted in a non-functional allograft as the cartilage of the plug was unable to tolerate the applied load; thus, the loading forces were distributed throughout the surrounding recipient site, as if the osteochondral lesion was never filled. As many activities of the knee involve cyclic on-loading and off-loading force, we believe that the predicted outward resultant forces in the non-CBR-matched allografts will lead to micro-motion of the plug within its recipient site potentially leading to improper healing and perhaps even a compromised graft.

While the current study did not include comparative analysis between plugs, it is important to understand which CBR is optimal when a perfect match is unavailable. If choosing between a plug with a slightly lower CBR (e.g. plug B) or its counterpart with a slightly higher CBR (e.g. plug C), it appears that choosing the latter may be superior given its ability to tolerate a higher range of stresses while also exhibiting a lower predicted outward displacement. However, it is best to consider these simulations as a progression rather than as discrete units. As seen with plug D, having a large difference in CBR between the plug and its recipient site can lead to altered patterns of stress distribution. As seen with plug E, a plug with an even higher CBR can render the plug non-functional and thus, inferior to a plug with a slightly lower CBR compared to its surroundings. Additionally, it is also possible that small variations in the mechanical properties of the plug may alter the threshold at which a plug becomes non-functional.

When interpreting the current data, several limitations must be considered. While the current model incorporated the intrinsic properties of articular cartilage and subchondral bone with respect to their density, Young's modulus, and Poisson's ratio, several complexities of the knee joint were not included in the analysis. For instance, the designed geometry omitted articular surface topography, primary and secondary knee stabilizers (e.g. ligaments), the dynamic nature of the joint, and the impact bone healing would have on the analysis. The authors acknowledge the importance of these variables in assessing the joint but believe that the current analysis was sufficient to assess whether the CBR of the allograft with respect to its surrounds plays a role in biomechanical loading. This analysis also assumed a uniform osteochondral lesion size, lesion location, and material properties (e.g. cartilage density) throughout all scenarios. Thus, it would be useful to assess how variance with these measurements can affect our results. Ultimately, the best way to validate the results of this analysis is to simulate similar conditions in a cadaveric study and measure the resulting stresses on the allograft and surrounding recipient joint. An additional consideration that may be addressed in future studies is whether, in the case of a non-matched allograft, the addition of a fixation screw may help reduce graft displacement and/or micromotion. Additionally, the model showed a non-convergent solution. There are several explanations for this, the first being the presence of a non-stationary solution. In other words, the components in the simulation may show movement or displacements. An additional explanation for the non-convergent solution is the presence of multiple similar solutions. Given the circular nature of our simulation, the directions of the forces predicted are equally likely in other directions, generating the non-convergent results.

CONCLUSION

The relationship between the ratio of cartilage-to-bone in an osteochondral allograft and that of its surroundings significantly impacts the distribution of stresses and predilection for micro-motion at the repair site.

Declaration of interests

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Informed Patient Consent

The author(s) should confirm that written informed consent has been obtained from the involved patient(s) or if appropriate from the parent, guardian, power of attorney of the involved patient(s); and, they have given approval for this information to be published in this case report (series).

REFERENCES

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  17. 17Urita, A, Cvetanovich, GL, Madden, BT, Verma, NN, Inoue, N, Cole, BJ, and Yanke, AB. Topographic Matching of Osteochondral Allograft Transplantation Using Lateral Femoral Condyle for the Treatment of Medial Femoral Condyle Lesions: A Computer-Simulated Model Study. Arthroscopy. 2018; 34: 3033–3042
  18. 18Wang, D, Jones, KJ, Eliasberg, CD, Pais, MD, Rodeo, SA, and Williams, RJ 3rd. Condyle-Specific Matching Does Not Improve Midterm Clinical Outcomes of Osteochondral Allograft Transplantation in the Knee. J Bone Joint Surg Am. 2017; 99: 1614–1620
  19. 19Yanke, AB, Urita, A, Shin, JJ, Cvetanovich, GL, Moran, EK, Bach, BR Jr., Cole, BJ, Inoue, N, and Verma, NN. Topographic Analysis of the Distal Femoral Condyle Articular Cartilage Surface: Adequacy of the Graft from Opposite Condyles of the Same or Different Size for the Osteochondral Allograft Transplantation. Cartilage. 2019; 10: 205–213
  20. 20Yoon, JR, Kim, TS, Lee, YM, Jang, HW, Kim, YC, and Yang, JH. Transpatellar approach in lateral meniscal allograft transplantation using the keyhole method: can we prevent graft extrusion?. Knee Surg Sports Traumatol Arthrosc. 2011; 19: 214–217

All authors were fully involved in the study and preparation of the manuscript and each author believes that the manuscript represents honest research. All authors have read and approved the final submitted manuscript.

 

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