Simple geometry tribological study of osteochondral graft implantation in the knee

A Finite Element Model to Investigate the Stability of Osteochondral Grafts Within a Human Tibiofemoral Joint

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. However, factors that cause graft subsidence are not well understood. The aim of this study was to develop finite element (FE) models of osteochondral grafts within a tibiofemoral joint, suitable for an investigation of parameters affecting graft stability. Cadaveric femurs were used to experimentally calibrate the bone properties and graft-bone frictional forces for use in corresponding image-based FE models, generated from µCT scan data. Effects of cartilage defects and osteochondral graft repair were measured by examining contact pressure changes using further in vitro tests. Here, six defects were created in the femoral condyles, which were subsequently treated with osteochondral autografts or metal pins. Matching image-based FE models were created, and the contact patches were compared. 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 that were accurately described in the resultant pressure maps and were well represented in the FE models. Cartilage defects and repair quality were experimentally measurable with good agreement in the FE model pressure maps. Model confidence was built through extensive validation and sensitivity testing. It was found that specimen-specific properties were required to accurately represent graft behaviour. The final models produced are suitable for a range of parametric testing to investigate immediate graft stability.

Challenges in osteoarthritis treatment

Osteoarthritis (OA) is the most common form of arthritis and a degenerative joint cartilage disease that is the most common cause of disability in the world among the elderly. It leads to social, psychological, and economic costs with financial consequences. The principles of OA treatment are to reduce pain and stiffness as well as maintain function. In recent years, due to a better understanding of the underlying pathophysiology of OA, a number of potential therapeutic advances have been made, which include tissue engineering, immune system manipulation, surgical technique, pharmacological, and non-pharmacological treatments. Despite this, there is still no certain cure for OA, and different OA treatments are usually considered in relation to the stage of the disease. The purpose of the present review is to summarize and discuss the latest results of new treatments for OA and potential targets for future research.

Comparative efficacy of osteochondral autologous transplantation and microfracture in the knee: an updated meta-analysis of randomized controlled trials

INTRODUCTION

More than 19% of patients undergoing knee arthroscopies suffers from articular cartilage defects. The chondral or osteochondral lesion has negative impacts on the knee joints function and the life quality of patients. However, the treatment remains challenging as hyaline cartilage is not renewable. The purpose of this study was to systematically analyze the data of randomized controlled trials for comparing the postoperative outcomes between osteochondral autologous transplantation (OAT) and microfracture (MF) procedure. We hypothesized that the outcomes were better in OAT than MF procedure.

MATERIALS AND METHODS

A systematic literature search of the EMBASE, Pubmed, and Cochrane Library databases was conducted based on PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. The outcome measures include: the rate of excellent or good results, the rate of return to sports, the failure rate, osteoarthritis rate, International Cartilage Repair Society (ICRS) score, Lysholm Knee Score, and Tegner scale. The statistical analysis was completed using Review Manager (RevMan, version 5.3) software.

RESULTS

The systematic search identified 7 studies with a total of 346 patients. The pooled result showed significant differences between the two groups in the rate of return to sports and failure. The following outcome scores showed significant improvement (pre- vs postoperatively): Lysholm score (p = 0.02), Tegner scale (p < 0.00001), and ICRS score (p < 0.00001). The differences were not significant in the excellent or good results and the rate of osteoarthritis.

CONCLUSION

The patients in OAT group may return to play quicker, even return to pre-injury level of activity compared to the MF group. OAT is better than MF procedure in accordance with Lysholm score, Tegner score, ICRS score, and the rate of failure. However, few studies have reported long-term outcomes and there has no uniform criteria for safe return to sports. Further research is needed.

LEVEL OF EVIDENCE

Level II, meta-analysis of randomized controlled trials.

In vitro method to quantify and visualize mechanical wear in human meniscus subjected to joint loading

The mechanical wear and tear of soft connective tissue from repetitive joint loading is a primary factor in degenerative joint disease, and therefore methods are needed to accurately characterize wear in joint structures. Here, we evaluate the accuracy of using a structured light 3D optical scanning system and modeling software to quantify and visualize volume loss in whole human meniscus subjected to in vitro joint loading. Using 3D printed meniscus replicas with known wear volumes, we determined that this novel imaging method has a mean accuracy of approximately 13 mm3, corresponding to a mean error of less than 7% when measuring meniscal volumetric changes of 0.2 cm3 (size of a pea). The imaging method was then applied to measure the in vitro wear of whole human menisci at four time points when a single cadaveric knee was subjected to one million cycles of controlled joint loading. The medial and lateral menisci reached steady state volumetric reductions of 0.72 cm3 and 0.34 cm3 per million cycles, respectively. Colorimetric maps of linear wear depth revealed high wear and deformation in the posterior regions of both the medial and lateral menisci. For the first time, this study has developed a method to accurately characterize volume loss in whole meniscus subjected to in vitro joint loading. This 3D scanning method offers researchers a new investigative tool to study mechanical wear and joint degeneration in meniscus, and other soft connective tissues.

Development of robust finite element models to investigate the stability of osteochondral grafts within porcine femoral condyles

Osteoarthritis (OA) is the most prevalent chronic rheumatic disease worldwide with knee OA having an estimated lifetime risk of approximately 14%. Autologous osteochondral grafting has demonstrated positive outcomes in some patients, however, understanding of the biomechanical function and how treatments can be optimised remains limited. Increased short-term stability of the grafts allows cartilage surfaces to remain congruent prior to graft integration. In this study methods for generating specimen specific finite element (FE) models of osteochondral grafts were developed, using parallel experimental data for calibration and validation. Experimental testing of the force required to displace osteochondral grafts by 2 mm was conducted on three porcine knees, each with four grafts. Specimen specific FE models of the hosts and grafts were created from registered μCT scans captured from each knee (pre- and post-test). Material properties were based on the μCT background with a conversion between μCT voxel brightness and Young's modulus. This conversion was based on the results of the separate testing of eight porcine condyles and optimization of specimen specific FE models. The comparison between the experimental and computational push-in forces gave a strong agreement with a concordance correlation coefficient (CCC) = 0.75, validating the modelling approach. The modelling process showed that homogenous material properties based on whole bone BV/TV calculations are insufficient for accurate modelling and that an intricate description of the density distribution is required. The robust methodology can provide a method of testing different treatment options and can be used to investigate graft stability in full tibiofemoral joints.

An experimental simulation model to assess wear of the porcine patellofemoral joint

A range of surgical techniques and osteochondral interventions have been developed for early stage chondral/osteochondral repair interventions in the knee however, methods for functional, pre-clinical assessment of these therapies are limited. In this study, a method for simulating physiological loading and motion in the porcine patellofemoral joint was developed using a 6-axis simulator. As an example of how the method can be used, the influence of surgical positioning of osteochondral allografts in the patella on cartilage wear, deformation and damage and graft stability was investigated in this porcine patellofemoral joint model. The functional performance of allografts implanted either optimally (flush with the cartilage surface) or 1 mm proud of the cartilage surface was compared to a positive control (stainless steel pin implanted 1 mm proud of the cartilage surface), a negative control (no intervention) and a defect model. Allografts implanted flush with the surrounding cartilage could restore the articulating surface of the patella resulting in low wear, damage and deformation of the opposing cartilage surface, similar to that of the negative control group. Implanting the graft proud of the patella surface resulted in cartilage lesions on the femoral trochlea (ICRS grade 2) and a cartilage volume difference of 2.0 ± 3.9 mm3; the positive controls resulted in more severe lesions, a higher volume difference (14.2 ± 7.4 mm3) which in some cases exposed subchondral bone (ICRS grade 4). Defects in the patella caused deformation of the opposing cartilage surface. All grafts implanted in the patella subsided over the duration of the study. This study demonstrated a method that can be used to evaluate osteochondral repair strategies in the patellofemoral joint applying physiological loading and motions.

Influence of the Mechanical Environment on the Regeneration of Osteochondral Defects

Articular cartilage is a highly specialised connective tissue of diarthrodial joints which provides a smooth, lubricated surface for joint articulation and plays a crucial role in the transmission of loads. In vivo cartilage is subjected to mechanical stimuli that are essential for cartilage development and the maintenance of a chondrocytic phenotype. Cartilage damage caused by traumatic injuries, ageing, or degradative diseases leads to impaired loading resistance and progressive degeneration of both the articular cartilage and the underlying subchondral bone. Since the tissue has limited self-repairing capacity due its avascular nature, restoration of its mechanical properties is still a major challenge. Tissue engineering techniques have the potential to heal osteochondral defects using a combination of stem cells, growth factors, and biomaterials that could produce a biomechanically functional tissue, representative of native hyaline cartilage. However, current clinical approaches fail to repair full-thickness defects that include the underlying subchondral bone. Moreover, when tested in vivo, current tissue-engineered grafts show limited capacity to regenerate the damaged tissue due to poor integration with host cartilage and the failure to retain structural integrity after insertion, resulting in reduced mechanical function. The aim of this review is to examine the optimal characteristics of osteochondral scaffolds. Additionally, an overview on the latest biomaterials potentially able to replicate the natural mechanical environment of articular cartilage and their role in maintaining mechanical cues to drive chondrogenesis will be detailed, as well as the overall mechanical performance of grafts engineered using different technologies.

Tribometer for measuring coefficients of friction of uneven surfaces like articular cartilage

To examine coefficients of friction (COFs) of articular cartilage, it is necessary to use cartilage as a friction partner. Irregularities of surfaces require special tribometers and calculation methods. The aim of this study was to establish a tribometer system for measuring a low COF of cartilage and to develop and validate an algorithm that takes the irregularities into consideration. We used a pin-on-plate tribometer that allows a vertical displacement of the pin to follow the surface of the plate and developed an algorithm that takes these irregularities into account. We were, thus, able to take into consideration a forward and backward movement, an upward and downward movement, and different force ratios. The algorithm was validated using a spherical POM (polyoxymethylene) pin against a stainless steel plate at slope angles up to 24°. First examinations with articular cartilage against articular cartilage samples of a stifle joint of a pig were then performed. The newly developed tribometer worked well when POM against a stainless steel hump was examined. The COF increased for slope angles steeper than ±15°. There was an interaction between the COF and the slope angle, but not for the range within ±15°. Cartilage examinations revealed COFs as published in the literature. The tribometer and the algorithm were suitable for the detection of low COF of irregular surfaces of the plate within a range of ±15°. The COF resulting from the forward and backward movements should be averaged.

Biomechanical assessment of the stability of osteochondral grafts implanted in porcine and bovine femoral condyles

Osteochondral grafts are used clinically to repair cartilage and bone defects and to restore the congruent articulating surfaces of the knee joint following cartilage damage or injury. The clinical success of such osteochondral grafts is heavily reliant on the biomechanical and tribological properties of the surgical repair; however, a limited number of studies have investigated these factors. The aim of this study was to evaluate the influence of graft harvesting and implantation technique as well as bone properties on the primary stability of press-fit implanted osteochondral grafts using a series of uniaxial experimental push-in and push-out tests. Animal (porcine and bovine) knees were used to deliver models of different bone properties (elastic modulus and yield stress). The study showed the graft harvesting method using either a chisel or drill-aided trephine to have no influence on primary graft stability; however, the preparation technique for the graft recipient site was shown to influence the force required to push the graft into the host tissue. For example, when the length of the graft was equal to the recipient site (bottomed), the graft was more stable and dilation of the recipient site was shown to reduce short-term graft stability especially in immature or less dense bone tissue. The push-out tests which compared tissue of different skeletal maturities demonstrated that the maturity of both the graft and host bone tissue to influence the stability of the graft. A higher force was required to push out more skeletally mature grafts from mature bone tissue. The study demonstrates the importance of surgical technique and bone quality/properties on the primary stability and ultimately, the success of osteochondral grafts in the knee.

Simple geometry tribological study of osteochondral graft implantation in the knee

Robust preclinical test methods involving tribological simulations are required to investigate and understand the tribological function of osteochondral repair interventions in natural knee tissues. The aim of this study was to investigate the effects of osteochondral allograft implantation on the local tribology (friction, surface damage, wear and deformation) of the tissues in the natural knee joint using a simple geometry, reciprocating pin-on-plate friction simulator. In addition, the study aimed to assess the ability of osteochondral grafts to restore a low surface damage, deformation and wear articulation when compared to the native state. A method was developed to characterise and quantify surface damage wear and deformation of the opposing cartilage-bone pin surface using a non-contacting optical profiler (Alicona Infinite Focus). Porcine 12 mm diameter cartilage-bone pins were reciprocated against bovine cartilage-bone plates that had 6 mm diameter osteochondral allografts, cartilage defects or stainless steel pins (positive controls) inserted centrally. Increased levels of surface damage with changes in geometry were not associated with significant increases in the coefficient of dynamic friction. Significant damage to the opposing cartilage surface was observed in the positive control groups. Cartilage damage, deformation and wear (as measured by change in geometry) in the xenograft (2.4 mm³) and cartilage defect (0.99 mm³) groups were low and not significantly different (p > 0.05) compared to the negative control in either group. The study demonstrated the potential of osteochondral grafts to restore the congruent articular surface and biphasic tribology of the natural joint. An optical method has been developed to characterise cartilage wear, damage and deformation that can be applied to the tribological assessment of osteochondral grafts in a whole natural knee joint simulation model.