Induction of chondrocyte apoptosis following impact load

A New Method for Creating Impact-Induced Intra-Articular Fractures in a Rabbit Model Induces Severe Post-Traumatic Osteoarthritis

OBJECTIVES

The objective of this work was to develop a model of intra-articular fracture (IAF) in a rabbit and document the speed and severity of degenerative joint changes after fracture fixation.

METHODS

With Institutional Animal Care & Use Committee approval, impact-induced IAFs were created in the distal tibia of 16 New Zealand White rabbits. Fractures were fixed with a plate and screws. Pain and function were monitored at regular postoperative intervals with limb loading analysis. Twelve or 26 weeks after fracture, animals were euthanized for histological assessment of cartilage degeneration and micro-computed tomography analysis of bone histomorphometry.

RESULTS

Eleven animals successfully completed the study. Maximum foot force in the fractured limb was 41% ± 21% lower than preoperative values ( P = 0.006) 12 weeks after fracture and remained 25% ± 13% lower ( P = 0.081) after 26 weeks. Cortical bone mineral density in micro-computed tomography images was 34% ± 13% lower 12 weeks after fracture ( P < 0.001) and remained (42% ± 8%) lower 26 weeks after fracture ( P < 0.001). Twelve weeks after fracture, Mankin scores of cartilage degeneration were significantly higher in the medial talus ( P = 0.007), lateral talus ( P < 0.001), medial tibia ( P = 0.017), and lateral tibia ( P = 0.002) of the fractured limb compared with the uninjured contralateral limb. Average Mankin scores in the talus increased from 12 to 26 weeks (5.9 ± 0.9 to 9.4 ± 0.4; P < 0.001 lateral; 5.4 ± 1.8 to 7.8 ± 2.0; P = 0.043 medial), indicating substantial and progressive joint degeneration.

CONCLUSIONS

The ankle joint of the New Zealand White rabbit provides the smallest available model of impact-induced IAF that can be treated with clinically relevant techniques and replicates key features of healing and degeneration found in human patients.

A2M inhibits inflammatory mediators of chondrocytes by blocking IL-1β/NF-κB pathway

A hallmark of osteoarthritis (OA) is cartilage degeneration, which has been previously correlated with dramatic increases in inflammatory enzymes. Specifically, interleukin-1β (IL-1β) and subsequent upregulation of nuclear factor kappa B (NF-κB) is implicated as an important player in the development of posttraumatic osteoarthritis (PTOA). Alpha 2-macroglobulin (A2M) can inhibit this inflammatory pathway, making it a promising therapy for PTOA. Herein, we demonstrate that A2M binds and neutralizes IL-1β, blocking downstream NF-κB-induced catabolism seen in in vitro. Human chondrocytes (cell line C28) were incubated with A2M protein and then treated with IL-1β. A2M was labeled with VivoTag™ 680 to localize the protein postincubation. The degree of binding between A2M and IL-1β was evaluated through immunoprecipitation (IP). Catabolic proteins, including IL-1β and NF-kB, were detected by Western blot. Pro-inflammatory and chondrocyte-related gene expression was examined by qRT-PCR. VivoTag™ 680-labeled A2M was observed in the cytoplasm of C28 human chondrocytes by fluorescence microscopy. IP experiments demonstrated that A2M could bind IL-1β. Additionally, western blot analysis revealed that A2M neutralized IL-1β and NF-κB in a dose-dependent manner. Moreover, A2M decreased levels of MMPs and TNF-α and increased the expression of cartilage protective genes Col2, Type2, Smad4, and aggrecan. Mostly importantly, A2M was shown to directly neutralize IL-1β to downregulate the pro-inflammatory responses mediated by the NF-kB pathway. These results demonstrate a mechanism by which A2M reduces inflammatory catabolic activity and protects cartilage after joint injury. Further in vivo studies are needed to fully understand the potential of A2M as a novel PTOA therapy.

Experimental animal models of post-traumatic osteoarthritis of the knee

Due to the complex and dynamic nature of osteoarthritis (OA) and post-traumatic osteoarthritis (PTOA), animal models have been used to investigate the progression and pathogenesis of the disease. Researchers have used different experimental models to study OA and PTOA. With an emphasis on the knee joint, this review will compare and contrast the existing body of knowledge from anterior cruciate ligament transection models, meniscectomy models, combination models, as well as impact models in large animals to see how tissues respond to these different approaches to induce experimental OA and PTOA. The tissues discussed will include articular cartilage and the meniscus, with a focus on morphological, mechanical and histological assessments. The goal of this review is to demonstrate the progressive nature of OA by indicating the strong correlation between progressive tissue degeneration, change of mechanical properties, and loss of biochemical integrity and to highlight key differences between the most commonly used experimental animal models.

Articular reductions - how close is close enough? A narrative review

Intra-articular fractures are a unique subset of fractures as they involve a varying extent of damage to cartilage. The impact of this articular fracture causes significant microscopic and macroscopic changes, as well as biomechanical irregularities, which can lead to further cartilage damage, and ultimately cascade down the dreaded path to arthritis. It is generally believed that an anatomic reduction of an articular fracture is the necessary goal of treatment for these injuries, however it yet to be delineated how perfect this reduction has to be. A comprehensive literature review was carried out to create a best available evidence guide to the acceptability of upper extremity and lower extremity articular fracture reductions. Ultimately, a perfect anatomic reduction is the best strategy to minimize abnormal loading and wear patterns, however this should be balanced with the realistic factors of each individual case, such as the level of difficulty, joint involved, surgical timing, and patient activity levels.

Posttraumatic Arthritis After Intra-Articular Distal Femur and Proximal Tibia Fractures

Posttraumatic arthritis (PTA) is a form of joint degeneration that occurs after physical trauma to a synovial joint. Development of PTA is multifactorial and results from mechanical damage at the time of trauma, a cell-mediated inflammatory response, and abnormal articulation due to persistent malalignment or joint instability. Although some risk factors may be unavoidable, preventing the development of PTA of the knee after intra-articular fracture (IAF) requires restoring anatomic articulation and alignment. Reconstruction with total knee arthroplasty is the treatment of choice for PTA and may be a useful primary treatment for IAF in some.

Menisci protect chondrocytes from load-induced injury

Menisci in the knee joint are thought to provide stability, increased contact area, decreased contact pressures, and offer protection to the underlying articular cartilage and bone during joint loading. Meniscal loss or injury is typically accompanied by degenerative changes in the knee, leading to an increased risk for osteoarthritis in animals including humans. However, the detailed mechanisms underlying joint degeneration and the development of osteoarthritis remain largely unknown, and the acute effects of meniscal loss have not been studied systematically. We developed a microscopy-based system to study microscale joint mechanics in living mice loaded by controlled muscular contractions. Here, we show how meniscal loss is associated with rapid chondrocyte death (necrosis) in articular cartilage within hours of injury, and how intact menisci protect chondrocytes in vivo in the presence of intense muscle-based joint loading and/or injury to the articular cartilage. Our findings suggest that loading the knee after meniscal loss is associated with extensive cell death in intact and injured knees, and that early treatment interventions should be aimed at preventing chondrocyte death.

Osteochondral Graft Size Is Significantly Associated With Increased Force and Decreased Chondrocyte Viability

BACKGROUND

Insertion force has been shown to significantly reduce chondrocyte viability during osteochondral allograft transplantation. How graft size influences the required insertion force and chondrocyte viability has yet to be determined. Hypothesis/Purpose: The purpose was to characterize how graft size influences insertion force requirements and chondrocyte viability during osteochondral transplantation. The hypothesis was that larger grafts would require greater force and reduce chondrocyte viability.

STUDY DESIGN

Controlled laboratory study.

METHODS

Four graft sizes-15 × 5 mm, 15 × 10 mm, 25 × 5 mm, and 25 × 10 mm (diameter × depth)-were harvested from 13 thawed fresh-frozen human cadaveric distal femurs. Average, maximum, and cumulative force and number of impacts were recorded for 44 grafts by a surgical mallet embedded with a calibrated force sensor. In a separate experiment, fresh osteochondral tissues were subjected to mechanical loading. To capture a range of clinically important forces, categories were selected to correspond to impaction force data. Chondrocyte viability was assessed with confocal laser microscopy and live/dead staining.

RESULTS

Total force for all grafts averaged 4576 N. Median number of impacts for all grafts was 20 (range, 7-116). The mean number of impacts for 5-mm-deep grafts was 14.2 (95% CI, 10.8-18.6), as compared with 26.3 (95% CI, 19.9-34.4) for 10-mm-deep grafts ( P < .001). The mean cumulative force for 5-mm-deep grafts was 2128 N (95% CI, 1467-3087), as opposed to 4689 N (95% CI, 3232-6803) for 10-mm-deep grafts ( P = .001). For every 1 mm in graft depth, an average of 13.1% (95% CI, 6.2%-20.3%) more impacts are required when controlling for diameter and density ( P < .001). For every 1 mm in graft depth, the force required increases on average by 17.1% (95% CI, 7.7%-27.4%) when controlling for diameter and density ( P = .001). There was a significant reduction in chondrocyte viability for the forces required for graft thickness values >10 mm. Only forces associated with graft thickness <10 mm had chondrocyte viabilities consistently >70%.

CONCLUSION

Insertion force increases significantly with increasing graft depth. Controlling for diameter and bone density, a 1-mm increase in graft depth is associated with 13.1% more impacts and 17.1% more force. Chondrocyte viability was significantly reduced to <70% at average forces associated with grafts thicker than 10 mm.

CLINICAL RELEVANCE

Based on the current data, graft depth is an important consideration for surgeons when sizing osteochondral allograft transplant for chondral lesions of the knee.

Multiscale Strain as a Predictor of Impact-Induced Fissuring in Articular Cartilage

Mechanical damage is central to both initiation and progression of osteoarthritis (OA). However, specific causal links between mechanics and cartilage damage are incompletely understood, which results in an inability to predict failure. The lack of understanding is primarily due to the difficulty in simultaneously resolving the high rates and small length scales relevant to the problem and in correlating such measurements to the resulting fissures. This study leveraged microscopy and high-speed imaging to resolve mechanics on the previously unexamined time and length scales of interest in cartilage damage, and used those mechanics to develop predictive models. The specific objectives of this study were to: first, quantify bulk and local mechanics during impact-induced fissuring; second, develop predictive models of fissuring based on bulk mechanics and local strain; and third, evaluate the accuracy of these models in predicting fissures. To achieve these three objectives, bovine tibial cartilage was impacted using a custom spring-loaded device mounted on an inverted microscope. The occurrence of fissures was modulated by varying impact energy. For the first objective, during impact, deformation was captured at 10,000 frames per second and bulk and local mechanics were analyzed. For the second objective, data from samples impacted with a 1.2 mm diameter rod were fit to logistic regression functions, creating models of fissure probability based on bulk and local mechanics. Finally, for the third objective, data from samples impacted with a 0.8 mm diameter rod were used to test the accuracy of model predictions. This study provides a direct comparison between bulk and local mechanical thresholds for the prediction of fissures in cartilage samples, and demonstrates that local mechanics provide more accurate predictions of local failure than bulk mechanics provide. Bulk mechanics were accurate predictors of fissure for the entire sample cohort, but poor predictors of fissure for individual samples. Local strain fields were highly heterogeneous and significant differences were determined between fissured and intact samples, indicating the presence of damage thresholds. In particular, first principal strain rate and maximum shear strain were the best predictors of local failure, as determined by concordance statistics. These data provide an important step in establishing causal links between local mechanics and cartilage damage; ultimately, data such as these can be used to link macro- and micro-scale mechanics and thereby predict mechanically mediated disease on a subject-specific basis.

Increased cytokine levels and histological changes in cartilage, synovial cells and synovial fluid after malleolar fractures

BACKGROUND

Malleolar fractures are among the most common fractures in the human skeleton with a high risk of later development of post-traumatic osteoarthritis (OA). The acute ankle injury initiates a sequence of events potentially leading to progressive articular surface damage resulting from inflammatory changes in cartilage, synovial tissue and synovial fluid. We hypothesised that in the acute phase of ankle fracture, these changes occur at the same time in the different tissues.

METHODS

Specimens of chondral tissue, synovial tissue and synovial fluid were collected from 16 patients with acute articular ankle fracture (study group). Additional samples were obtained from five male fresh cadavers within 12 hours of death (control group). Chondral tissue was assessed for cellularity, irregularities and chondrocyte disarray. Synovial tissue was assessed for synovitis, proteoglycans and collagen deposition. Synovial fluid was assessed for cytokines IL-2, IL-6, IL-10, IL-17, IFN-γ and TGF-β1.

RESULTS

Chondral tissue showed discontinuity in the tidemark between cartilage and subchondral bone, chondrocyte disarray, increased cellularity (both at the cartilage surface and subchondral bone), articular surface irregularities and increased deposition of proteoglycans and collagen fibres. Synovial tissue showed a statistically significant difference between the study and control groups in the concentration per tissue area of both thin collagen fibres (p=0.0274) and thick collagen fibres (p<0.0001). Cytokine concentrations in synovial fluid samples were significantly higher in ankle fracture tissue compared with controls for IL-2 (p=0.0002), IL-6 (p<0.0001), IL-10 (p=0.002) and IL-17 (p<0.0001). No statistically significant differences were observed for IFN-γ (p=0.06303) and TGF-β1 (p=0.8832).

CONCLUSION

We observed a pattern of simultaneous and interrelated pathological changes in cartilage, subchondral bone, synovial tissue and synovial fluid after acute malleolar fracture. As the observed inflammatory changes could lead to the development of OA, a more thorough knowledge of these early processes could be helpful to find strategies for prevention or delay of this common complication.

Targeted designed variants of alpha-2-macroglobulin (A2M) attenuate cartilage degeneration in a rat model of osteoarthritis induced by anterior cruciate ligament transection

Background

The study was performed to evaluate whether targeted alpha-2-macroglobulin (A2M) variants have a similar or enhanced function at wild-type (wt)-A2M to attenuate cartilage degeneration in vivo.

Methods

In and ex-vivo experiment, bovine cartilage explants (BCE) were incubated with TNF-α and IL-1β with or without wt-A2M or A2M variants. Cartilage catabolism was measured in culture supernatant by sulfated glycosaminoglycan (sGAG). In an in-vivo experiment, 2-month-old male Wistar rats (n = 77) were randomly divided into seven groups and treated with different doses of A2M or its variants by intra-articular injection at 24 hours and day 14 after anterior cruciate ligament transection (ACLT), receiving (1) ACLT/PBS; (2) ACLT/wt-A2M (0.153 mg); (3) ACLT/CYT-108 A2M (0.153 mg); (4) ACLT/CYT-108 A2M (0.077 mg); (5) ACLT/CYT-98 A2M (0.153 mg); (6) ACLT/CYT-98 A2M (0.077 mg); or (7) sham/PBS. The joints and synovial lavage were collected 8 weeks after surgery. Fluorescence molecular tomography was used to monitor inflammation in vivo using probes ProSense and MMPSense at 24 hours, and weeks 2, 4, and 6 after surgery. The cartilage damage was quantified using Osteoarthritis Research Society International score and matrix metalloproteinase (MMP)-3, -13, collagen (Col) X, Col 2, Runx2, and aggrecan (Acan) were detected by immunohistochemical analysis (IHC), ELISA, and RT-PCR.

Results

A2M variants inhibited catabolism in the BCE model by up to 200% compared with wt-A2M. ProSense and MMPSense were dramatically increased in all groups after surgery. Supplemental A2M or its variants reduced ProSense and MMPSense compared with the PBS treatment. Less cartilage damage, lower MMP-13 and Col 2 degraded product, and stronger Col 2 synthesis were detected in animals treated with A2M or its variants compared with PBS-treated animals. A2M and its variants enhanced Col 2 and Acan synthesis, and suppressed MMP-3, MMP-13, Runx2, and Col X production. A2M-108 variant demonstrated less cartilage damage compared with wt-A2M and A2M-98 variant.

Conclusion

The targeted variants of A2M have a chondroprotective effect similar to wt-A2M. However, A2M-108 variant has enhanced function to attenuate cartilage degeneration compared with wt-A2M.

Using diet-induced obesity to understand a metabolic subtype of osteoarthritis in rats

Osteoarthritis (OA) in obese individuals is often attributed to joint loading. However, a subtype of OA, Metabolic OA, may be due to obesity-related intrinsic factors but remains to be evaluated experimentally against a known OA progression model.

OBJECTIVE

To evaluate if obesity contributes to OA onset using a high fat/high sucrose diet-induced obesity (DIO) model with anterior cruciate ligament-transected rats (ACL-X).

METHODS

Sprague Dawley rats (n = 33) consumed high fat/high sucrose or chow diets for 12 weeks, were randomized to one of three groups: a unilateral ACL-X group, sham surgery group, or naïve non-surgical group. These animals were followed for an additional 16 weeks. At sacrifice, body composition, knee joint Modified Mankin scores, and 27 serum and synovial fluid cytokines and adipokines were measured.

RESULTS

Experimental limbs of obese ACL-X, obese Sham, and lean ACL-X animals had similar Modified Mankin scores that were greater than those obtained from lean Sham and naïve animals. Obese contralateral limbs had similar OA damage as ACL-X and Sham limbs of obese and ACL-X limbs of lean animals. Obese contralateral limb Modified Mankin scores had a strong correlation (r = 0.75, P < 0.001) with body fat percentage. Serum leptin and synovial fluid IP10/CXCL10 best described Modified Mankin scores in contralateral limbs of obese animals.

CONCLUSIONS

Mechanical factors produced OA damage in experimental limbs, as expected. Interestingly, OA damage in obese contralateral limbs was similar to mechanically perturbed limbs, suggesting that obesity may induce OA in a non-mechanical manner.

Nitric oxide-associated chondrocyte apoptosis in trauma patients after high-energy lower extremity intra-articular fractures

BACKGROUND

The primary goal of this study was to identify nitric oxide (NO)-induced apoptosis in traumatized chondrocytes in intra-articular lower extremity fractures and the secondary goal was to identify the timeline of NO-induced apoptosis after injury.

MATERIALS AND METHODS

This is a prospective collection of samples of human cartilage harvested at the time of surgery to measure apoptotic cell death and the presence of NO by immunohistochemistry. Three patients met the criteria for control subjects and eight patients sustained high-energy intra-articular fractures and were included in the study. Subjects who sustained intra-articular acetabular, tibial, calcaneal and talus fracture had articular cartilage harvested at the time of surgical intervention. All 8 patients underwent open reduction and internal fixation of the displaced intra-articular fractures. The main outcome measures were rate of apoptosis, degree of NO-induced apoptosis in chondrocytes, and the timeline of NO-induced apoptosis after high-energy trauma.

RESULTS

The percentage of apoptotic chondrocytes was higher in impacted samples than in normal cartilage (56 vs 4 %), confirming the presence of apoptosis after intra-articular fracture. The percentage of cells with NO was greater in apoptotic cells than in normal cells (59 vs 20 %), implicating NO-induction of apoptosis. The correlation between chondrocyte apoptosis and increasing time from injury was found to be -0.615, indicating a decreasing rate of apoptosis post injury.

CONCLUSIONS

The data showed the involvement of NO-induced apoptosis of chondrocytes after high-energy trauma, which decreased with time from injury.

[Suprapatellar approach to tibial medullary nailing with electromagnetic field-guided distal locking]

Closed tibial shaft fractures are the domain of intramedullary nailing. With the introduction of new nail designs and technologies, even small, dislocated distal fragments can be anatomically aligned and safely fixed. Unsolved or to a lesser degree controlled are the problems of distal locking in the freehand technique, which can still be difficult and can lead to a significant radiation exposure, and how to control very short proximal tibial fragments in metaphyseal tibial fractures or tibial segmental fractures, where the proximal fracture line also runs through the metaphysis.By using a suprapatellar approach, i.e. a skin incision proximal to the patella with an entry point into the tibial bone from within the knee at the same site as for a standard infrapatellar approach, and then nailing the tibia in a semi-extended position, i.e. the knee is only flexed 10-20°, the intraoperative dislocation of a short proximal fragment can be avoided. The main indications for semi-extended tibial nailing are a short diaphyseal fragment in an isolated tibial shaft fracture, a segmental fracture where the proximal fracture line is metaphyseal and in patients where infrapatellar soft tissues are compromised.The use of the electromagnetic guidance system SureShot® generates reliable and reproducible results, reduces the operating time and is independent from radiation for distal locking.

Effect of hyaluronic acid on chondrocyte apoptosis

OBJECTIVE:

To determine the percentage of apoptotic cells in a contusion model of osteoarthritis (OA) and to assess whether intra-articular injection of high doses of hyaluronic acid (HA) immediately after trauma reduces chondrocyte apoptosis.

METHODS:

Forty knees from adult rabbits were impacted thrice with a 1 kg block released through a 1 meter tall cylinder (29.4 Joules). Subsequently, 2 mL of HA was injected in one knee and 2 mL saline in the contra-lateral knee. Medication were administered twice a week for 30 days, when animals were sacrificed. Specimens were prepared for optical microscopy exam and terminal deoxynucleotidyl transferase end labeling assay (TUNEL).

RESULTS:

The apoptosis rate in the contusion model was 68.01% (± 19.73%), a higher rate than previously described. HA significantly reduced the rate of apoptosis to 53.52% (± 18.09) (p <0.001).

CONCLUSION:

Intra-articular HA administration started immediately after trauma reduces impact-induced chondrocyte apoptosis rates in rabbits.

Level of Evidence I, Experimental Study.

Identification of α2-macroglobulin as a master inhibitor of cartilage-degrading factors that attenuates the progression of posttraumatic osteoarthritis

OBJECTIVE

To determine if supplemental intraarticular α2-macroglobulin (α2 M) has a chondroprotective effect in a rat model of osteoarthritis (OA).

METHODS

Using Western blotting, mass spectrometry, enzyme-linked immunosorbent assay (ELISA), and immunohistochemistry, α2 M was identified as a potential therapeutic agent through a comparison of α2 M concentrations in serum, synovial fluid (SF), and cartilage from normal subjects and patients with OA. In cultured chondrocytes, the effects of α2 M on interleukin-1 (IL-1)-induced cartilage catabolic enzymes were evaluated by Luminex assay and ELISA. In vivo effects on cartilage degeneration and matrix metalloproteinase 13 (MMP-13) concentration were evaluated in male rats (n = 120) randomized to 1 of 4 treatments: 1) anterior cruciate ligament transection (ACLT) and saline injections, 2) ACLT and 1 IU/kg injections of α2 M, 3) ACLT and 2 IU/kg injections of α2 M, or 4) sham operation and saline injections. Rats were administered intraarticular injections for 6 weeks. The concentration of MMP-13 in SF lavage fluid was measured using ELISA. OA-related gene expression was quantified by real-time quantitative polymerase chain reaction. The extent of OA progression was graded by histologic examination.

RESULTS

In both normal subjects and OA patients, α2 M levels were lower in SF as compared to serum, and in OA patients, MMP-13 levels were higher in SF than in serum. In vitro, α2 M inhibited the induction of MMP-13 by IL-1 in a dose-dependent manner in human chondrocytes. In the rat model of ACLT OA, supplemental intraarticular injection of α2 M reduced the concentration of MMP-13 in SF, had a favorable effect on OA-related gene expression, and attenuated OA progression.

CONCLUSION

The plasma protease inhibitor α2 M is not present in sufficient concentrations to inactivate the high concentrations of catabolic factors found in OA SF. Our findings suggest that supplemental intraarticular α2 M provides chondral protection in posttraumatic OA.

Radiologic outcome and patient-reported function after intramedullary nailing: a comparison of the retropatellar and infrapatellar approach

OBJECTIVES

The purpose of this study was to compare the patient-reported functional outcomes after intramedullary nailing of the tibia through a retropatellar or infrapatellar approach. Radiographic assessment of nail entry point and accuracy of fracture reduction were included to aid in the identification of variables that may explain any difference in patient-reported outcomes.

DESIGN

A retrospective radiographic and questionnaire-based assessment of patient-reported outcomes and complications after tibial nailing for trauma or limb reconstruction through a retropatellar or infrapatellar approach.

SETTING

Regional limb reconstruction unit within a university teaching hospital.

PATIENTS/PARTICIPANTS

Two consecutive series of 38 patients with intramedullary tibial nails inserted through a retropatellar approach, and 36 patients with a tibial nail inserted through an infrapatellar approach.

INTERVENTION

Tibial nail insertion through either a retropatellar or infrapatellar approach.

MAIN OUTCOME MEASURES

Patient-reported outcomes and complication rates and radiographic assessment of fracture reduction and nail insertion entry point.

RESULTS

No significant difference was seen in Kujala score as a measure of anterior knee pain (P = 0.217), either in the physical (P = 0.372) or mental (0.504) components of the SF-12 between the groups, although there was a trend toward symptomatic intrusive knee pain in the infrapatellar group. A more accurate fracture reduction, both in terms of angulation (P = 0.003) and translation (P = 0.010) in the coronal plane, was seen in the retropatellar group. The entry point for nail insertion was more accurate in both the sagittal (P = 0.011) and coronal (P = 0.014) planes.

CONCLUSIONS

Retropatellar tibial nail insertion is not associated with more anterior knee pain when compared with infrapatellar nail insertion but is associated with more accurate nail insertion and fracture reduction.

LEVEL OF EVIDENCE

Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.

Automated generation of tissue-specific three-dimensional finite element meshes containing ellipsoidal cellular inclusions

Finite element analysis provides a means of describing cellular mechanics in tissue, which can be useful in understanding and predicting physiological and pathological changes. Many prior studies have been limited to simulations of models containing single cells, which may not accurately describe the influence of mechanical interactions between cells. It is desirable to generate models that more accurately reflect the cellular organisation in tissue in order to evaluate the mechanical function of cells. However, as the model geometry becomes more complicated, manual model generation can become laborious. This can be prohibitive if a large number of distinct cell-scale models are required, for example, in multiscale modelling or probabilistic analysis. Therefore, a method was developed to automatically generate tissue-specific cellular models of arbitrary complexity, with minimal user intervention. This was achieved through a set of scripts, which are capable of generating both sample-specific models, with explicitly defined geometry, and tissue-specific models, with geometry derived implicitly from normal statistical distributions. Models are meshed with tetrahedral (TET) elements of variable size to sufficiently discretise model geometries at different spatial scales while reducing model complexity. The ability of TET meshes to appropriately simulate the biphasic mechanical response of a single-cell model is established against that of a corresponding hexahedral mesh for an illustrative use case. To further demonstrate the flexibility of this tool, an explicit model was developed from three-dimensional confocal laser scanning image data, and a set of models were generated from a statistical cellular distribution of the articular femoral cartilage. The tools presented herein are free and openly accessible to the community at large.

Inhibition of cell-matrix adhesions prevents cartilage chondrocyte death following impact injury

Focal adhesions are transmembrane protein complexes that attach chondrocytes to the pericellular cartilage matrix and in turn, are linked to intracellular organelles via cytoskeleton. We previously found that excessive compression of articular cartilage leads to cytoskeleton-dependent chondrocyte death. Here we tested the hypothesis that this process also requires integrin activation and signaling via focal adhesion kinase (FAK) and Src family kinase (SFK). Osteochondral explants were treated with FAK and SFK inhibitors (FAKi, SFKi, respectively) for 2 h and then subjected to a death-inducing impact load. Chondrocyte viability was assessed by confocal microscopy immediately and at 24 h post-impact. With no treatment immediate post-impact viability was 59%. Treatment with 10 µM SFKi, 10 μM, or 100 µM FAKi improved viability to 80%, 77%, and 82%, respectively (p < 0.05). After 24 h viability declined to 34% in controls, 48% with 10 µM SFKi, 45% with 10 µM FAKi, and 56% with 100 µM FAKi (p < 0.01) treatment. These results confirmed that most of the acute chondrocyte mortality was FAK- and SFK-dependent, which implicates integrin-cytoskeleton interactions in the death signaling pathway. Together with previous findings, these data support the hypothesis that the excessive tissue strains accompanying impact loading induce death via a pathway initiated by strain on cell adhesion receptors.

Posttraumatic Chondrocyte Apoptosis in the Murine Xiphoid

OBJECTIVE

To demonstrate posttraumatic chondrocyte apoptosis in the murine xiphoid after a crush-type injury and to ultimately determine the pathway (i.e., intrinsic or extrinsic) by which chondrocytes undergo apoptosis in response to mechanical injury.

DESIGN

The xiphoids of adult female wild-type mice were injured with the use of a modified Kelly clamp. Postinjury xiphoid cartilage was analyzed via 3 well-described independent means of assessing apoptosis in chondrocytes: hematoxylin and eosin staining, terminal deoxynucleotidyl transferase dUTP nick end labeling assay, and activated caspase-3 staining.

RESULTS

Injured specimens contained many chondrocytes with evidence of apoptosis, which is characterized by cell shrinkage, chromatin condensation, nuclear fragmentation, and the liberation of apoptotic bodies. There was a statistically significant increase in the number of chondrocytes undergoing apoptosis in the injured specimens as compared with the uninjured specimens.

CONCLUSIONS

Chondrocytes can be stimulated to undergo apoptosis as a result of mechanical injury. These experiments involving predominantly cartilaginous murine xiphoid in vivo establish a baseline for future investigations that employ the genetic and therapeutic modulation of chondrocyte apoptosis in response to mechanical injury.

Effects of cartilage impact with and without fracture on chondrocyte viability and the release of inflammatory markers

Post-traumatic arthritis (PTA) frequently develops after intra-articular fracture of weight bearing joints. Loss of cartilage viability and post-injury inflammation have both been implicated as possible contributing factors to PTA progression. To further investigate chondrocyte response to impact and fracture, we developed a blunt impact model applying 70%, 80%, or 90% surface-to-surface compressive strain with or without induction of an articular fracture in a cartilage explant model. Following mechanical loading, chondrocyte viability, and apoptosis were assessed. Culture media were evaluated for the release of double-stranded DNA (dsDNA) and immunostimulatory activity via nuclear factor kappa B (NF-κB) activity in Toll-like receptor (TLR) -expressing Ramos-Blue reporter cells. High compressive strains, with or without articular fracture, resulted in significantly reduced chondrocyte viability. Blunt impact at 70% strain induced a loss in viability over time through a combination of apoptosis and necrosis, whereas blunt impact above 80% strain caused predominantly necrosis. In the fracture model, a high level of primarily necrotic chondrocyte death occurred along the fracture edges. At sites away from the fracture, viability was not significantly different than controls. Interestingly, both dsDNA release and NF-κB activity in Ramos-Blue cells increased with blunt impact, but was only significantly increased in the media from fractured cores. This study indicates that the mechanism of trauma determines the type of chondrocyte death and the potential for post-injury inflammation.

Development of an in vitro model of injury-induced osteoarthritis in cartilage explants from adult horses through application of single-impact compressive overload

OBJECTIVE

To develop an in vitro model of cartilage injury in full-thickness equine cartilage specimens that can be used to simulate in vivo disease and evaluate treatment efficacy.

SAMPLE

15 full-thickness cartilage explants from the trochlear ridges of the distal aspect of the femur from each of 6 adult horses that had died from reasons unrelated to the musculoskeletal system.

PROCEDURES

To simulate injury, cartilage explants were subjected to single-impact uniaxial compression to 50%, 60%, 70%, or 80% strain at a rate of 100% strain/s. Other explants were left uninjured (control specimens). All specimens underwent a culture process for 28 days and were subsequently evaluated histologically for characteristics of injury and early stages of osteoarthritis, including articular surface damage, chondrocyte cell death, focal cell loss, chondrocyte cluster formation, and loss of the extracellular matrix molecules aggrecan and types I and II collagen.

RESULTS

Compression to all degrees of strain induced some amount of pathological change typical of clinical osteoarthritis in horses; however, only compression to 60% strain induced significant changes morphologically and biochemically in the extracellular matrix.

CONCLUSIONS AND CLINICAL RELEVANCE

The threshold strain necessary to model injury in full-thickness cartilage specimens from the trochlear ridges of the distal femur of adult horses was 60% strain at a rate of 100% strain/s. This in vitro model should facilitate study of pathophysiologic changes and therapeutic interventions for osteoarthritis.

Computational investigation of in situ chondrocyte deformation and actin cytoskeleton remodelling under physiological loading

Previous experimental studies have determined local strain fields for both healthy and degenerate cartilage tissue during mechanical loading. However, the biomechanical response of chondrocytes in situ, in particular the response of the actin cytoskeleton to physiological loading conditions, is poorly understood. In the current study a three-dimensional (3-D) representative volume element (RVE) for cartilage tissue is created, comprising a chondrocyte surrounded by a pericellular matrix and embedded in an extracellular matrix. A 3-D active modelling framework incorporating actin cytoskeleton remodelling and contractility is implemented to predict the biomechanical behaviour of chondrocytes. Physiological and abnormal strain fields, based on the experimental study of Wong and Sah (J. Orthop. Res. 2010; 28: 1554-1561), are applied to the RVE. Simulations demonstrate that the presence of a focal defect significantly affects cellular deformation, increases the stress experienced by the nucleus, and alters the distribution of the actin cytoskeleton. It is demonstrated that during dynamic loading cyclic tension reduction in the cytoplasm causes continuous dissociation of the actin cytoskeleton. In contrast, during static loading significant changes in cytoplasm tension are not predicted and hence the rate of dissociation of the actin cytoskeleton is reduced. It is demonstrated that chondrocyte behaviour is affected by the stiffness of the pericellular matrix, and also by the anisotropy of the extracellular matrix. The findings of the current study are of particular importance in understanding the biomechanics underlying experimental observations such as actin cytoskeleton dissociation during the dynamic loading of chondrocytes.

Subject-specific analysis of joint contact mechanics: application to the study of osteoarthritis and surgical planning

Advances in computational mechanics, constitutive modeling, and techniques for subject-specific modeling have opened the door to patient-specific simulation of the relationships between joint mechanics and osteoarthritis (OA), as well as patient-specific preoperative planning. This article reviews the application of computational biomechanics to the simulation of joint contact mechanics as relevant to the study of OA. This review begins with background regarding OA and the mechanical causes of OA in the context of simulations of joint mechanics. The broad range of technical considerations in creating validated subject-specific whole joint models is discussed. The types of computational models available for the study of joint mechanics are reviewed. The types of constitutive models that are available for articular cartilage are reviewed, with special attention to choosing an appropriate constitutive model for the application at hand. Issues related to model generation are discussed, including acquisition of model geometry from volumetric image data and specific considerations for acquisition of computed tomography and magnetic resonance imaging data. Approaches to model validation are reviewed. The areas of parametric analysis, factorial design, and probabilistic analysis are reviewed in the context of simulations of joint contact mechanics. Following the review of technical considerations, the article details insights that have been obtained from computational models of joint mechanics for normal joints; patient populations; the study of specific aspects of joint mechanics relevant to OA, such as congruency and instability; and preoperative planning. Finally, future directions for research and application are summarized.

Effect of combined traumatic impact and radial transection of medial meniscus on knee articular cartilage in a rabbit in vivo model

PURPOSE

The purpose of this study was to test the hypothesis that combined meniscectomy and traumatic impact accelerate early degeneration of articular cartilage in the knee versus meniscectomy alone.

METHODS

A previously published in vivo rabbit cartilage impact model was used combined with radial transection of the medial meniscus posterior horn versus meniscal transection alone. Rabbits were killed 3 months after surgery. Quantitative histologic analysis of the articular cartilage proteoglycan depth and glycosaminoglycan (GAG) fraction was performed at the site of impact on the posterior femoral condyle (PFC) and at the distal femoral condyle (DFC) overlying the meniscectomy in the surgical knee and the contralateral control knee.

RESULTS

The articular cartilage in the knees that underwent isolated meniscectomy did not differ significantly from the contralateral control knees for any measured value. The knees with a combined insult had a lower GAG fraction (P = .03) at the PFC and a greater depth of proteoglycan loss at both the PFC (P = .02) and the DFC (P = .04) versus contralateral controls. Compared with meniscectomy alone, the combined-insult knees had a greater depth of proteoglycan loss at the DFC (P = .005).

CONCLUSIONS

On the basis of early results using GAG fraction and proteoglycan depth, combined traumatic impact and meniscectomy are more damaging to articular cartilage than meniscectomy alone.

CLINICAL RELEVANCE

A knee with a combination of meniscal injury and articular cartilage impact may be at particularly high risk for early joint degeneration.

An In Vivo Lapine Model for Impact-Induced Injury and Osteoarthritic Degeneration of Articular Cartilage

OBJECTIVE

In this study, we applied a spring-loaded impactor to deliver traumatic forces to articular cartilage in vivo. Based on our recent finding that a 0.28-J impact induces maximal catabolic response in adult bovine articular cartilage in vitro using this device, we hypothesize that this impact will induce the formation of a focal osteoarthritic defect in vivo.

DESIGN

The femoral condyle of New Zealand White rabbits was exposed and one of the following procedures performed: 0.28 J impact, anterior cruciate ligament transection, articular surface grooving, or no joint or cartilage destruction (control). After 24 hours, 4 weeks, or 12 weeks (n = 3 for each time point), wounds were localized with India ink, and tissue samples were collected and characterized histomorphometrically with Safranin O/Fast green staining and Hoechst 33342 nuclear staining for cell vitality.

RESULTS

The spring-loaded device delivered reproducible impacts with the following characteristics: impact area of 1.39 ± 0.11 mm(2), calculated load of 326 ± 47.3 MPa, time-to-peak of 0.32 ± 0.03 ms, and an estimated maximal displacement of 25.1% ± 4.5% at the tip apex. The impact resulted in immediate cartilage fissuring and cell loss in the surface and intermediate zones, and it induced the formation of a focal lesion at 12 weeks. The degeneration was defined and appeared more slowly than after anterior cruciate ligament transection, and more pronounced and characteristic than after grooving.

CONCLUSION

A single traumatic 0.28 J impact delivered with this spring-loaded impactor induces focal cartilage degeneration characteristic of osteoarthritis.

Mandibular lateral shift induces the increased expression of TGF-β, VEGF, and Col-II in the condyle of rat temporomandibular joints

OBJECTIVE

The present study evaluates histologic changes to and expression of angiogenic factors in rats with mandibular functional shift (MFS).

STUDY DESIGN

After 1, 2, and 4 weeks of MFS, rats in the experimental and control groups were killed. Histologic micrographs of the ipsilateral condyle cartilage were obtained. The localization and expression of vascular endothelial growth factor (VEGF), transforming growth factor beta (TGF-β), and type-II collagen (Col-II) in temporomandibular joints (TMJs) were evaluated through immunohistochemical staining.

RESULTS

The results showed that structural changes in the condyle cartilage could be observed 2 weeks after MFS. TGF-β expression reached its peak 2 weeks post-MFS, whereas VEGF and Col-II reached their peaks 4 weeks posttreatment.

CONCLUSIONS

Compressive forces applied to the TMJ could enhance the expressions of VEGF, TGF-β, and Col-II, and activate angiogenesis. The proteins appear to play important roles in the remodeling of the TMJ.

Cell volume regulation in chondrocytes

Chondrocytes are the cells within cartilage which produce and maintain the extracellular matrix. Volume regulation in these cells is vital to their function and occurs in several different physiological and pathological contexts. Firstly, chondrocytes exist within an environment of changing osmolarity and compressive loads. Secondly, in osteoarthritic joint failure, cartilage water content changes and there is a notable increase in chondrocyte apoptosis. Thirdly, endochondral ossification requires chondrocyte swelling in association with hypertrophy. Regulatory volume decrease (RVD) and regulatory volume increase (RVI) have both been observed in articular chondrocytes and this review focuses on the mechanisms identified to account for these. There has been evidence so far to suggest TRPV4 is central to RVD; however other elements of the pathway have not yet been identified. Unlike RVD, RVI appears less robust in articular chondrocytes and there have been fewer mechanistic studies; the primary focus being on the Na(+)-K(+)-2Cl(-) co-transporter. The clinical significance of chondrocyte volume regulation remains unproven. Importantly however, transcript abundances of several ion channels implicated in volume control are changed in chondrocytes from osteoarthritic cartilage. A critical question is whether disturbances of volume regulation mechanisms lead to, result from or are simply coincidental to cartilage damage.

Biomechanical influence of cartilage homeostasis in health and disease

There is an urgent demand for long term solutions to improve osteoarthritis treatments in the ageing population. There are drugs that control the pain but none that stop the progression of the disease in a safe and efficient way. Increased intervention efforts, augmented by early diagnosis and integrated biophysical therapies are therefore needed. Unfortunately, progress has been hampered due to the wide variety of experimental models which examine the effect of mechanical stimuli and inflammatory mediators on signal transduction pathways. Our understanding of the early mechanopathophysiology is poor, particularly the way in which mechanical stimuli influences cell function and regulates matrix synthesis. This makes it difficult to identify reliable targets and design new therapies. In addition, the effect of mechanical loading on matrix turnover is dependent on the nature of the mechanical stimulus. Accumulating evidence suggests that moderate mechanical loading helps to maintain cartilage integrity with a low turnover of matrix constituents. In contrast, nonphysiological mechanical signals are associated with increased cartilage damage and degenerative changes. This review will discuss the pathways regulated by compressive loading regimes and inflammatory signals in animal and in vitro 3D models. Identification of the chondroprotective pathways will reveal novel targets for osteoarthritis treatments.

Post-traumatic osteoarthritis: improved understanding and opportunities for early intervention

Even with current treatments of acute joint injuries, more than 40% of people who suffer significant ligament or meniscus tears, or articular surface injuries, will develop osteoarthritis (OA). Correspondingly, 12% or more of all patients with lower extremity OA have a history of joint injury. Recent research suggests that acute joint damage that occurs at the time of an injury initiates a sequence of events that can lead to progressive articular surface damage. New molecular interventions, combined with evolving surgical methods, aim to minimize or prevent progressive tissue damage triggered by joint injury. Seizing the potential for progress in the treatment of joint injuries to forestall OA will depend on advances in (1) quantitative methods of assessing the injury severity, including both structural damage and biologic responses, (2) understanding of the pathogenesis of post-traumatic OA, taking into account potential interactions among the different tissues and the role of post-traumatic incongruity and instability, and (3) application of engineering and molecular research to develop new methods of treating injured joints. This paper highlights recent advances in understanding of the structural damage and the acute biological response following joint injury, and it identifies important directions for future research.

Cartilage viability and catabolism in the intact porcine knee following transarticular impact loading with and without articular fracture

Posttraumatic arthritis commonly develops following articular fracture. The objective of this study was to develop a closed joint model of transarticular impact with and without creation of an articular fracture that maintains the physiologic environment during loading. Fresh intact porcine knees were preloaded and impacted at 294 J via a drop track. Osteochondral cores were obtained from the medial and lateral aspects of the femoral condyles and tibial plateau. Chondrocyte viability was assessed at days 0, 3, and 5 postimpact in sham, impacted nonfractured, and impacted fractured joints. Total matrix metalloproteinase (MMP) activity, aggrecanase (ADAMTS-4) activity, and sulfated glycosaminoglycan (S-GAG) release were measured in culture media from days 3 and 5 posttrauma. No differences were observed in chondrocyte viability of impacted nonfractured joints (95.9 ± 6.9%) when compared to sham joints (93.8 ± 7.7%). In impacted fractured joints, viability of the fractured edge was 40.5 ± 27.6% and significantly lower than all other sites, including cartilage adjacent to the fractured edge (p < 0.001). MMP and aggrecanase activity and S-GAG release were significantly increased in specimens from the fractured edge. This study showed that joint impact resulting in articular fracture significantly decreased chondrocyte viability, increased production of MMPs and aggrecanases, and enhanced S-GAG release, whereas the same level of impact without fracture did not cause such changes.

The effect of storage medium tonicity on osteochondral autograft plug diameter

PURPOSE

The purpose of this study was to investigate the effect of differing storage medium on osteochondral plug diameter.

METHODS

Four storage conditions were evaluated: air, hypotonic solution (sterile water), isotonic saline solution (0.9% sodium chloride), and hypertonic saline solution (3.0% sodium chloride). Four osteochondral plugs were acquired (4.5-mm harvesting system) from each of 10 fresh calf femurs and randomized to 1 of 4 storage media (N = 40). Micro-computed tomography was used to evaluate the precise diameter of each plug. After a time 0 scan, each plug was placed in a designated storage medium and rescanned at 3 time points over approximately 1 hour. A region of interest was identified from approximately 1 to 6 mm proximal to the tidemark. Custom software automatically calculated the diameter of each plug.

RESULTS

The time 0 plug diameter (mean ± 95% confidence interval) for all specimens was 4.66 ± 0.01 mm. There were no significant differences between any of the groups at the baseline scan. There were also no significant differences between the time 0 and subsequent scans of the unsubmerged specimens. However, all of the liquid solutions (hypertonic, isotonic, and hypotonic) resulted in a significant increase in diameter from their baseline scans (P < .05), indicating that a cause may be increased extracellular matrix fluid pressure.

CONCLUSIONS

Placing an osteochondral plug in a liquid solution increased the diameter of the subchondral bone. Size increase from the storage medium appeared to level off within 14 minutes after placement in solution.

CLINICAL RELEVANCE

Increases in diameter of the plug may alter the ease of insertion of the graft, possibly increasing contact pressure on cartilage during plug implantation.

Transplante autólogo de condrócitos

Esta revisão da literatura descreve o processo do transplante autólogo de condrócitos em todas as suas etapas, indicações clínicas, técnica operatória, técnica laboratorial, reabilitação e resultados clínicos. Desde 1994, quando a técnica de ACI foi descrita pela primeira vez, este procedimento foi aprimorado e tornou-se uma das mais importantes alternativas cirúrgicas para o tratamento das lesões condrais do joelho. Nivel de Evidência II, Prospectivo Comparativo.

Mechanical impact induces cartilage degradation via mitogen activated protein kinases

OBJECTIVE

To determine the activation of Mitogen activated protein (MAP) kinases in and around cartilage subjected to mechanical damage and to determine the effects of their inhibitors on impaction-induced chondrocyte death and cartilage degeneration.

DESIGN

The phosphorylation of MAP kinases was examined with confocal microscopy and immunoblotting. The effects of MAP kinase inhibitors on impaction-induced chondrocyte death and proteoglycan (PG) loss were determined with fluorescent microscopy and 1, 9-Dimethyl-Methylene Blue (DMMB) assay. The expression of catabolic genes at mRNA levels was examined with quantitative real-time PCR.

RESULTS

Early p38 activation was detected at 20 min and 1h post-impaction. At 24h, enhanced phosphorylation of p38 and extracellular signal-regulated protein kinase (ERK)1/2 was visualized in chondrocytes from in and around impact sites. The phosphorylation of p38 was increased by 3.0-fold in impact sites and 3.3-fold in adjacent cartilage. The phosphorylation of ERK-1 was increased by 5.8-fold in impact zone and 5.4-fold in adjacent cartilage; the phosphorylation of ERK-2 increased by 4.0-fold in impacted zone and 3.6-fold in adjacent cartilage. Furthermore, the blocking of p38 pathway did not inhibit impaction-induced ERK activation. The inhibition of p38 or ERK pathway significantly reduced injury-related chondrocyte death and PG losses. Quantitative Real-time PCR analysis revealed that blunt impaction significantly up-regulated matrix metalloproteinase (MMP)-13, Tumor necrosis factor (TNF)-α, and ADAMTS-5 expression.

CONCLUSION

These findings implicate p38 and ERK mitogen activated protein kinases (MAPKs) in the post-injury spread of cartilage degeneration and suggest that the risk of post-traumatic osteoarthritis (PTOA) following joint trauma could be decreased by blocking their activities, which might be involved in up-regulating expressions of MMP-13, ADAMTS-5, and TNF-α.

Suprapatellar versus infra-patellar intramedullary nail insertion of the tibia: a cadaveric model for comparison of patellofemoral contact pressures and forces

PURPOSE

To quantify patellofemoral contact pressures and forces during infrapatellar (IP) and suprapatellar (SP) intramedullary tibial nail insertion.

METHODS

Fresh-frozen hemicadavers with intact lower extremities and pelves were used for this study. A standard IP entry portal was used on nine tibiae, whereas an SP entry portal was used in eight tibiae. A digital electronic pressure sensor system was used to dynamically measure peak pressures within the patellofemoral joint during each procedure. Data were continuously recorded from the start to completion of each procedure. Mean pressure and force as well as peak contact pressures recorded were then compared between the two techniques.

RESULTS

Mean patellofemoral pressures and forces as well as peak contact pressures were higher in the SP group than the IP group. The mean peak contact pressure was 0.90 MPa (range, 0.48-1.26 MPa) during IP nailing. The mean peak contact pressure on the patella and femoral condyles was 1.84 MPa (range, 1.09-2.95 MPa) and 2.13 MPa (range, 1.10-2.86 MPa), respectively, during SP nailing.

CONCLUSIONS

It is known that structural integrity of articular cartilage is compromised at impact loads exceeding 25 MPa, and chondrocyte apoptosis can occur at sustained loads of as little as 4.5 MPa in immature bovine cartilage. The results of this study indicate that although the patellofemoral contact pressures are higher with SP nail insertion, they remain below the values reported to be detrimental to articular cartilage. Based on these data, we do not believe that the SP entry portal poses a significant risk to the viability or structural integrity of the articular cartilage of the patellofemoral joint. Clinical correlation is needed.

Optical coherence tomography detection of subclinical traumatic cartilage injury

OBJECTIVES

Posttraumatic arthritis is a major cause of disability. Current clinical imaging modalities are unable to reliably evaluate articular cartilage damage before surface breakdown, when potentially reversible changes are occurring. Optical coherence tomography (OCT) is a nondestructive imaging technology that can detect degenerative changes in articular cartilage with an intact surface. This study tests the hypothesis that OCT detects acute articular cartilage injury after impact at energy levels resulting in chondrocyte death and microstructural changes, but insufficient to produce macroscopic surface damage.

METHODS

Bovine osteochondral cores underwent OCT imaging and were divided into a control with no impact or were subjected to low (0.175 J) or moderate (0.35 J) energy impact. Cores were reimaged with OCT after impact and the OCT signal intensity quantified. A ratio of the superficial to deep layer intensities was calculated and compared before and after impact. Chondrocyte viability was determined 1 day after impact followed by histology and polarized microscopy.

RESULTS

Macroscopic changes to the articular surface were not observed after low and moderate impact. The OCT signal intensity ratio demonstrated a 27% increase (P = 0.006) after low impact and a 38% increase (P = 0.001) after moderate impact. Cell death increased by 150% (P < 0.001) and 200% (P < 0.001) after low and moderate energy impacts, respectively. When compared with unimpacted controls, both Mankin histology and David-Vaudey polarized microscopy scores increased (P = 0.036 and P = 0.002, respectively) after moderate energy impact.

CONCLUSIONS

This study shows that OCT detects acute cartilage changes after impact injury at levels insufficient to cause visible damage to the articular surface but sufficient to cause chondrocyte death and microscopic matrix damage. This finding supports the use of OCT to detect microstructural subsurface cartilage damage that is poorly visualized with conventional imaging.

Oxidant conditioning protects cartilage from mechanically induced damage

Articular cartilage degeneration in osteoarthritis has been linked to abnormal mechanical stresses that are known to cause chondrocyte apoptosis and metabolic derangement in in vitro models. Evidence implicating oxidative damage as the immediate cause of these harmful effects suggests that the antioxidant defenses of chondrocytes might influence their tolerance for mechanical injury. Based on evidence that antioxidant defenses in many cell types are stimulated by moderate oxidant exposure, we hypothesized that oxidant preconditioning would reduce acute chondrocyte death and proteoglycan depletion in cartilage explants after exposure to abnormal mechanical stresses. Porcine cartilage explants were treated every 48 h with tert-butyl hydrogen peroxide (tBHP) at nonlethal concentrations (25, 100, 250, and 500 microM) for a varying number of times (one, two, or four) prior to a bout of unconfined axial compression (5 MPa, 1 Hz, 1800 cycles). When compared with untreated controls, tBHP had significant positive effects on post-compression viability, lactate production, and proteoglycan losses. Overall, the most effective regime was 100 microM tBHP applied four times. RNA analysis revealed significant effects of 100 microM tBHP on gene expression. Catalase, hypoxia-inducible factor-1alpha (HIF-1alpha), and glyceraldehyde 6-phosphate dehydrogenase (GAPDH) were significantly increased relative to untreated controls in explants treated four times with 100 microM tBHP, a regime that also resulted in a significant decrease in matrix metalloproteinase-3 (MMP-3) expression. These findings demonstrate that repeated exposure of cartilage to sublethal concentrations of peroxide can moderate the acute effects of mechanical stress, a conclusion supported by evidence of peroxide-induced changes in gene expression that could render chondrocytes more resistant to oxidative damage.

AUTOLOGOUS CHONDROCYTE TRANSPLANTATION-SERIES OF 3 CASES

Hyaline cartilage covers joint surfaces and plays an important role in reducing friction and mechanical loading on synovial joints such as the knee. This tissue is not supplied with blood vessels, nerves or lymphatic circulation, which may be one of the reasons why joint cartilage has such poor capacity for healing. Chondral lesions that reach the subchondral bone (osteochondral lesions) do not heal and may progress to arthrosis with the passage of time. In young patients, treatment of chondral defects of the knee is still a challenge, especially in lesions larger than 4 cm. One option for treating these patients is autologous chondrocyte transplantation/implantation. Because this treatment does not violate the subchondral bone and repairs the defect with tissue similar to hyaline cartilage, it has the theoretical advantage of being more biological, and mechanically superior, compared with other techniques. In this paper, we describe our experience with autologous chondrocyte transplantation/implantation at the Institute of Orthopedics and Traumatology, Hospital das Clínicas, University of Sâo Paulo, through a report on three cases.

Effect of exogenous IGF-1 on chondrocyte apoptosis in a rabbit intraarticular osteotomy model

Insulin-like growth factor-1 (IGF-1) has been shown to protect chondrocytes from apoptosis in vitro. IGF-1 expression may also assist in maintaining a fully differentiated chondrocyte phenotype. Theoretically, posttraumatic administration of IGF-1 may inhibit chondrocyte apoptosis. This study is to determine if administration of IGF-1 after fracture inhibits apoptosis in vivo. Twenty-four mature female New Zealand white rabbits were randomized to control and IGF-1 groups. All subjects underwent standardized medial femoral condyle fracture and repair. Fibrin clot was administered in all subjects, with 25 mcg/ml IGF-1 in the clot in half the subjects. Half of the animals in each group were sacrificed at 2 weeks and half at 4 weeks, specimens were fixed and underwent TUNEL staining. Two-week controls showed significantly higher rate of apoptosis than 2-week IGF-1 subjects (21 +/- 6 vs. 12 +/- 6, p = 0.04). Likewise, 4-week controls showed significantly higher rate of apoptosis than 2-week IGF-1 subjects (23 +/- 7 vs. 10 +/- 2, p = 0.01). There was no significant administration difference between 2-week control and 4-week control subjects, or between 2-week IGF-1 and 4-week IGF-1 subjects. Intraarticular IGF-1 at the time of fracture repair appears to inhibit chondrocyte apoptosis in vivo, as judged by TUNEL staining, in this animal model. If administration of IGF-1 inhibits human chondrocyte apoptosis in vivo, this may lead to interventions that may reduce posttraumatic arthritis after fracture.

Progressive chondrocyte death after impact injury indicates a need for chondroprotective therapy

BACKGROUND

Impact injury to articular cartilage can lead to posttraumatic osteoarthritis.

HYPOTHESES

This study tests the hypotheses that (1) chondrocyte injury occurs after impact at energies insufficient to fracture the cartilage surface, and that (2) cartilage injury patterns vary with impact energy, time after injury, and cartilage thickness.

STUDY DESIGN

Controlled laboratory study.

METHODS

Fresh bovine osteochondral cores were randomly divided into 5 groups: (1) control, (2) 0.35 J, (3) 0.71 J, (4) 1.07 J, and (5) 1.43 J impact energies. Cores were subjected to computer-controlled impact loading and full-thickness sections were then prepared and incubated in Dulbecco's Modified Eagle's Medium/F12 at 37 degrees C. Adjacent sections were harvested 1 and 4 days after impact for viability staining and fluorescent imaging. The area of dead and living chondrocytes was quantified using custom image analysis software and reported as a percentage of total cartilage area.

RESULTS

The highest impact energy fractured the cartilage in all cores (1.43 J, n = 17). Seventy-three percent and 64% of the osteochondral cores remained intact after lower energy impacts of 0.71 J and 1.07 J, respectively. At lower energy levels, fractured cores were thinner (P <.01) than those remaining intact. In cores remaining intact after impact injury, chondrocyte death increased with increasing impact energy (P <.05) and with greater time after impact (P <.05). A progressive increase in dead cells near the bone/cartilage interface and at the articular surface was observed.

CONCLUSION

These data showing progressive chondrocyte death after impact injury at energies insufficient to fracture the cartilage surface demonstrate a potential need for early chondroprotective therapy.

CLINICAL RELEVANCE

These data show that efforts to reduce chondrocyte morbidity after joint injury may be a useful strategy to delay or prevent the onset of posttraumatic osteoarthritis.

Chondrocyte death and cartilage degradation after autologous osteochondral transplantation surgery in a rabbit model

BACKGROUND

Autologous osteochondral transplantation surgery requires an impact force on the graft that may cause chondrocyte death and matrix degradation. This study attempted to determine the degree to which this occurs in a rabbit model shortly after the procedure.

HYPOTHESIS

Impaction of a press-fit autologous osteochondral graft in vivo results in chondrocyte necrosis, apoptosis, and matrix degradation at early time points.

STUDY DESIGN

Controlled laboratory study.

METHODS

Twenty New Zealand White rabbits underwent unilateral osteochondral transplantation (OT) surgeries, and 10, bilateral sham surgeries. Fifteen animals were sacrificed at time zero (10 sham-0 limbs, 10 OT-0 limbs), and 15, 4 days after surgery (10 sham-4 limbs, 10 OT-4 limbs). Chondrocyte viability/necrosis was determined with cell vital staining. Chondrocyte apoptosis was determined by TUNEL, Bcl-2, and M30 assays. Cartilage matrix degradation was determined by routine light and polarized light microscopy and COL2-3/4C(short) immunohistochemistry. Statistical analysis was performed with a 2-way analysis of variance (P < .05).

RESULTS

There were significantly fewer viable cells in OT-4 than in sham-4. A similar difference in cell viability was found in OT-0 versus sham-0. There were more TUNEL-positive cells in OT-4 as compared with OT-0, sham-0, and sham-4; however, there was little or no staining of Bcl-2 and M30. Mankin scores were higher in both OT groups versus both sham groups at time zero and day 4. The OT-4 group had positive staining for COL2-3/4C(short) that corresponded with a loss of collagen birefringence at the superficial zone.

CONCLUSION

Osteochondral transplantation procedures performed by tamping a press-fit graft induce chondrocyte necrosis and matrix metalloproteinase-mediated cartilage matrix degradation. However, apoptosis was not found to a major contributor to cell death in this model.

CLINICAL RELEVANCE

Results of osteochondral transplantation procedures may be improved by atraumatic insertion and fixation techniques or by pharmacologic agents that can block these degradative processes.

Mechanical compression of articular cartilage induces chondrocyte proliferation and inhibits proteoglycan synthesis by activation of the ERK pathway: implications for tissue engineering and regenerative medicine

Articular cartilage is recalcitrant to endogenous repair and regeneration and is thus a focus of tissue engineering and regenerative medicine strategies. A prerequisite for articular cartilage tissue engineering is an understanding of the signal transduction pathways involved in mechanical compression during trauma or disease. We sought to explore the role of the extracellular signal-regulated kinase 1/2 (ERK 1/2) pathway in chondrocyte proliferation and proteoglycan synthesis following acute mechanical compression. Bovine articular cartilage explants were cultured with and without the ERK 1/2 pathway inhibitor PD98059. Cartilage explants were statically loaded to 40% strain at a strain rate of 1/s for 5 s. Control explants were cultured under similar conditions but were not loaded. There were four experimental groups: (a) no load, without inhibitor; (b) no load, with the inhibitor PD98059; (c) loaded, without the inhibitor; and (d) loaded, with the inhibitor PD98059. The explants were cultured for varying durations from 5 min to 5 days and were then analysed by biochemical and immunohistochemical methods. Mechanical compression induced phosphorylation of ERK 1/2, and this was attenuated with the ERK 1/2 pathway inhibitor PD98059 in a dose-dependent manner. Chondrocyte proliferation was increased by mechanical compression. This effect was blocked by the inhibitor of the ERK 1/2 pathway. Mechanical compression also led to a decrease in proteoglycan synthesis that was reversed with inhibitor PD98059. In conclusion, the ERK 1/2 pathway is involved in the proliferative and biosynthetic response of chondrocytes following acute static mechanical compression.

Intraoperative acoustic evaluation of living human cartilage of the elbow and knee during mosaicplasty for osteochondritis dissecans of the elbow: an in vivo study

BACKGROUND

Autologous osteochondral mosaicplasty for osteochondritis dissecans of the capitellum is being used increasingly in adolescent patients. Little research has been published on the material properties of living human cartilage of the elbow and knee.

HYPOTHESIS

The cartilage of the osteochondritis dissecans lesion is detected as degenerated by ultrasound. The material properties of the cartilage of the intact part of the elbow are not different from those of the intact knee except in thickness.

STUDY DESIGN

Descriptive laboratory study.

METHODS

The authors studied 10 young male athletes with osteochondritis dissecans of the capitellum who underwent mosaicplasty. An acoustic probe was used for measurement, and the wavelet transform method was used. Three parameters were used: signal intensity (index of cartilage stiffness), signal duration (index of roughness), and signal interval (index of thickness).

RESULTS

The cartilage of the osteochondritis dissecans lesion had lower signal intensity than did the intact part of the capitellum. The cartilage of the radial head opposite the capitellum had significantly lower signal intensity and higher signal duration than did other sites. The signal intensity of the radial head was significantly higher in early-stage patients than in late-stage patients, although the macroscopic view was almost all intact. The signal intensity of the plug was decreased significantly after grafting.

CONCLUSION

The osteochondritis dissecans lesion had lower signal intensity than did the intact part of the capitellum. Although the macroscopic view looked intact, the radial head cartilage was degenerated as measured acoustically.

CLINICAL RELEVANCE

Not only the cartilage of the capitellum but the cartilage of the radial head are acoustically degenerated in osteochondritis dissecans patients. Plugs might be damaged in the transplanting procedure, and further follow-up is necessary.

The acutely ACL injured knee assessed by MRI: are large volume traumatic bone marrow lesions a sign of severe compression injury?

OBJECTIVES

To map by magnetic resonance imaging (MRI) and quantitative MRI (qMRI) concomitant fractures and meniscal injuries, and location and volume of traumatic bone marrow lesions (BMLs) in the acutely anterior cruciate ligament (ACL) injured knee. To relate BML location and volume to cortical depression fractures, meniscal injuries and patient characteristics.

METHODS

One hundred and twenty-one subjects (26% women, mean age 26 years) with an ACL rupture to a previously un-injured knee were studied using a 1.5T MR imager within 3 weeks from trauma. Meniscal injuries and fractures were classified by type, size and location. BML location and volume were quantified using a multi-spectral image data set analyzed by computer software, edited by an expert radiologist.

RESULTS

Fractures were found in 73 (60%) knees. In 67 (92%) of these knees at least one cortical depression fracture was found. Uni-compartmental meniscal tears were found in 44 (36%) subjects and bi-compartmental in 24 (20%). One hundred and nineteen (98%) knees had at least one BML, all but four (97%) located in the lateral compartment. Knees with a cortical depression fracture had larger BML volumes (P<0.001) than knees without a cortical depression fracture, but no associations were found between meniscal tears and BML volume or fractures. Older age at injury was associated with smaller BML volumes (P<0.01).

CONCLUSION

A majority of the ACL injured knees had a cortical depression fracture, which was associated with larger BML volumes. This indicates strong compressive forces to the articular surface and cartilage at the time of injury, which may constitute an additional risk factor for later knee osteoarthritis development.

Alterations in the vimentin cytoskeleton in response to single impact load in an in vitro model of cartilage damage in the rat

Background

Animal models have provided much information on molecular and cellular changes in joint disease, particularly OA. However there are limitations to in vivo work and single tissue in vitro studies can provide more specific information on individual events. The rat is a commonly used laboratory species but at the current time only in vivo models of rat OA are available to study. The purpose of this study was to investigate the damage that single impact load (SIL) of 0.16J causes in a rat cartilage in vitro model and assess whether this load alters the arrangement of vimentin.

Methods

Rat cartilage was single impact loaded (200 g from 8 cm) and cultured for up to 48 hours (n = 72 joints). Histological changes were measured using a semi-quantitative modified Mankin score. Immunolocalisation was used to identify changes in vimentin distribution.

Results

SIL caused damage in 32/36 cartilage samples. Damage included surface fibrillation, fissures, fragmentation, changes in cellularity and loss of proteoglycan. SIL caused a statistically significant increase in modified Mankin score and chondrocyte clusters over time. SIL caused vimentin disassembly (as evidenced by collapse of vimentin around the nucleus).

Conclusion

This study describes a model of SIL damage to rat cartilage. SIL causes changes in histological/chemical parameters which have been measured using a semi-quantitative modified Mankin score. Single impact load also causes changes in the pattern of vimentin immunoreactivity, indicating vimentin dissassembley. Using a semi-quantitative scoring system the disassembly was shown to be statistically significant in SIL damaged cartilage.

The changes described in this paper suggest that this novel single tissue rat model of joint damage is a possible candidate model to replace in vivo models.

Time Course of Expression of Bcl-2 and Bax in Rabbit Condylar Chondrocytes Following Forward Mandibular Positioning

Objective: To clarify the expression of Bcl-2 and Bax following forward mandibular positioning (FMP) in the condylar chondrocytes of rabbits.

Materials and Methods: Sixty rabbits at 8 weeks of age were randomly allocated to the experimental group (n = 36) and control group (n = 24). Rabbits in the experimental group were induced to FMP by a functional appliance. Six rabbits from the experimental group and four from the control group were sacrificed after 3 days and 1, 2, 4, 8, and 12 weeks, respectively. All the right temporomandibular joints (TMJs) were collected and the expression of Bcl-2 and Bax was evaluated by immunohistochemical staining.

Results: The results showed the expression pattern of Bcl-2 and Bax during 12 weeks after FMP. The expression of Bcl-2 reached the highest level at 1 week, whereas Bax reached its maximal expression after 4 weeks. Subsequently, the expression of Bcl-2 and Bax gradually decreased. The ratio of Bcl-2/Bax began to decrease 3 days after FMP and continued to decline until 12 weeks.

Conclusions: FMP with functional appliances could change the expression of Bcl-2 and Bax, which is related to apoptosis in condylar chondrocytes.

Instability-associated changes in contact stress and contact stress rates near a step-off incongruity

BACKGROUND

Intra-articular fractures can result in articular surface incongruity and joint instability, both of which can lead to posttraumatic osteoarthritis. The purpose of this study was to quantify changes in contact stresses and contact stress rates in incongruous human cadaveric ankles that were either stable or unstable. It was hypothesized that joint instability, superimposed on articular incongruity, would cause significant increases in contact stresses and contact stress rates.

METHODS

Intact human cadaveric ankles were subjected to quasi-physiologic stance-phase motion and loading, and instantaneous contact stresses were captured at 132 Hz. The anterior one-third of the distal part of the tibia was displaced proximally by 2.0 mm, and testing was repeated. Anterior/posterior forces were modulated during loading to cause incongruous ankles to either remain stable or become unstable during loading. Transient contact stresses and contact stress rates were measured for seven ankles under intact, stable-incongruous, and unstable-incongruous conditions. Peak and 95th percentile values of contact stress and contact stress rates for all three conditions were compared to determine the pathomechanical effects of incongruity and instability.

RESULTS

The addition of instability caused 95th percentile and peak contact stresses to increase approximately between 20% and 25% in the unstable-incongruous specimens compared with the stable-incongruous specimens. In contrast, the addition of instability increased the magnitude of peak positive and peak negative contact stress rates by 115% and 170% in the unstable-incongruous specimens compared with the stable-incongruous specimens. Similarly, the 95th percentile contact stress rates increased 112% in the unstable-incongruous specimens compared with the stable-incongruous specimens.

CONCLUSIONS

In human cadaveric ankles, instability superimposed on an existing articular surface incongruity causes disproportionate increases in contact stress rates compared with the increases in contact stresses.

Decreased metalloproteinase production as a response to mechanical pressure in human cartilage: a mechanism for homeostatic regulation

Articular cartilage is optimised for bearing mechanical loads. Chondrocytes are the only cells present in mature cartilage and are responsible for the synthesis and integrity of the extracellular matrix. Appropriate joint loads stimulate chondrocytes to maintain healthy cartilage with a concrete protein composition according to loading demands. In contrast, inappropriate loads alter the composition of cartilage, leading to osteoarthritis (OA). Matrix metalloproteinases (MMPs) are involved in degradation of cartilage matrix components and have been implicated in OA, but their role in loading response is unclear. With this study, we aimed to elucidate the role of MMP-1 and MMP-3 in cartilage composition in response to mechanical load and to analyse the differences in aggrecan and type II collagen content in articular cartilage from maximum- and minimum-weight-bearing regions of human healthy and OA hips. In parallel, we analyse the apoptosis of chondrocytes in maximal and minimal load areas. Because human femoral heads are subjected to different loads at defined sites, both areas were obtained from the same hip and subsequently evaluated for differences in aggrecan, type II collagen, MMP-1, and MMP-3 content (enzyme-linked immunosorbent assay) and gene expression (real-time polymerase chain reaction) and for chondrocyte apoptosis (flow cytometry, bcl-2 Western blot, and mitochondrial membrane potential analysis). The results showed that the load reduced the MMP-1 and MMP-3 synthesis (p < 0.05) in healthy but not in OA cartilage. No significant differences between pressure areas were found for aggrecan and type II collagen gene expression levels. However, a trend toward significance, in the aggrecan/collagen II ratio, was found for healthy hips (p = 0.057) upon comparison of pressure areas (loaded areas > non-loaded areas). Moreover, compared with normal cartilage, OA cartilage showed a 10- to 20-fold lower ratio of aggrecan to type II collagen, suggesting that the balance between the major structural proteins is crucial to the integrity and function of the tissue. Alternatively, no differences in apoptosis levels between loading areas were found – evidence that mechanical load regulates cartilage matrix composition but does not affect chondrocyte viability. The results suggest that MMPs play a key role in regulating the balance of structural proteins of the articular cartilage matrix according to local mechanical demands.

Chondrocyte apoptosis and posttraumatic arthrosis

Apoptosis, or programmed cell death, plays an important role in many normal and pathologic conditions. This article has been designed to introduce the concept of chondrocyte apoptosis and how it may contribute to posttraumatic arthrosis following articular injury. Available means of assessing chondrocyte apoptosis are presented, in addition to the findings of in vitro and in vivo studies of cartilage injury. Unfortunately, despite active research in this area, the exact contribution chondrocyte apoptosis makes following joint injury to the development of posttraumatic arthrosis is unknown.