Impact loading of articular cartilage during transplantation of osteochondral autograft

Effect of Press-Fit Size on Insertion Mechanics and Cartilage Viability in Human and Ovine Osteochondral Grafts

OBJECTIVE

The osteochondral allograft procedure uses grafts constructed larger than the recipient site to stabilize the graft, in what is known as the press-fit technique. This research aims to characterize the relationships between press-fit size, insertion forces, and cell viability in ovine and human osteochondral tissue.

DESIGN

Human (4 donors) and ovine (5 animals) articular joints were used to harvest osteochondral grafts (4.55 mm diameter, N = 33 Human, N = 35 Ovine) and create recipient sites with grafts constructed to achieve varying degrees of press fit (0.025-0.240 mm). Donor grafts were inserted into recipient sites while insertion forces were measured followed by quantification of chondrocyte viability and histological staining to evaluate the extracellular matrix.

RESULTS

Both human and ovine tissues exhibited similar mechanical and cellular responses to changes in press-fit. Insertion forces (Human: 3-169 MPa, Ovine: 36-314 MPa) and cell viability (Human: 16%-89% live, Ovine: 2%-76% live) were correlated to press-fit size for both human (force: r = 0.539, viability: r = -0.729) and ovine (force: r = 0.655, viability: r = -0.714) tissues. In both species, a press-fit above 0.14 mm resulted in reduced cell viability below a level acceptable for transplantation, increased insertion forces, and reduced linear correlation to press-fit size compared to samples with a press-fit below 0.14 mm.

CONCLUSIONS

Increasing press-fit size required increased insertion forces and resulted in reduced cell viability. Ovine and human osteochondral tissues responded similarly to impact insertion and varying press-fit size, providing evidence for the use of the ovine model in allograft-related research.

Compressibility of Osteochondral Autograft Transfer Donor Grafts: A Comparison of Different Donor Regions and How Much Shortening Occurs of Plugs After Impaction

Background

Osteochondral autograft transfer (OAT) is a useful technique for full-thickness cartilage lesions of the distal femur. Various techniques recommend harvesting a plug 2 mm longer than the recipient hole to allow for graft impaction. Grafts with limited compressibility may not sit flush when impacted.

Purpose

To compare the compressibility/shortening of OAT donor plug regions from the distal femur of human cadaveric knees after impaction.

Study Design

Controlled laboratory study.

Methods

A total of 20 cadaveric knees (mean age, 70.3 ± 8.4 years) were divided into 4 donor regions: medial intercondylar (IC) notch, lateral IC notch, medial trochlea, and lateral trochlea. Each region was subdivided into 4 zones: far superior (FSZ), middle superior (MSZ), middle inferior (MIZ), and far inferior (FIZ). A total of 320 grafts (6-mm diameter, 15-mm depth) were extracted, and a custom-built machine was used to strike the graft 5 times using a predetermined energy of 0.11 J. The graft length was measured initially and after each impact. Statistical analysis of the compressibility for each of the 4 regions and all 16 zones was performed utilizing analysis of variance, with post hoc testing using the Fisher's least significant difference.

Results

Compression in the lateral IC notch, medial IC notch, medial trochlea, and lateral trochlea was 2.4 ± 1.5, 2.1 ± 0.7, 3.1 ± 2.2, and 2.1 ± 0.6 mm, respectively, with significant differences between the 4 regions (P < .01) and the most compression in the medial trochlea (P < .01). Subgroup analysis showed that the lateral trochlea had higher compressibility for FIZ versus MIZ (P = .02) and the lateral IC notch had higher compressibility for FSZ versus FIZ and MIZ (P < .05 for both).

Conclusion

Compressibility varied between OAT donor sites in the distal femur. OAT donor grafts showed the highest compressibility in the medial trochlea (3.1 mm) and lateral IC notch FSZ (3.0 mm).

Clinical Relevance

The lateral trochlea, medial IC notch, and the lower zones of the lateral IC notch grafts should not be oversized more than 2 mm in length, as these grafts may not compress adequately.

Comparison of Initial Stability of Oblong, Large Circular, and Multiple-Plug "Snowman" Osteochondral Autografts for Elongated Focal Cartilage Lesions: A Biomechanical Study in a Porcine Model

Background:

Distal femoral osteochondral allograft transplantation (OAT) is an effective treatment of osteochondral lesions in the knee measuring >2 cm² in select patients. Prior studies have demonstrated that the morphology of the plug can affect graft-host interference fit. To our knowledge, there are no data comparing the initial biomechanical stability of standard cylindrical plugs with multiple-plug and oblong-plug morphologies.

Hypothesis:

Large cylindrical single-plug (LCSP) and oblong single-plug (OSP) grafts will have greater pull-out strength, and therefore greater initial stability, than multiple-plug (MP) grafts in a cadaveric porcine femur model.

Study Design:

Controlled laboratory study.

Methods:

A total of 55 porcine distal femurs were divided into 3 groups—LCSP (n = 18), OSP (n = 19), and MP (n = 18)—according to the plug morphology used. The method of graft harvesting and implantation was based on technique guides for the respective implant systems. The sizes (length × width × depth) of the osteochondral defects created in each of the groups were approximately 20.2 × 20.2 × 9.4–mm for the LCSP group, 14.4 × 30.5 × 7.9–mm for the OSP group, and 14.8 × 14.8 × 9.9–mm for the MP group. Tensile testing was performed on each graft to determine pull-out strength.

Results:

The pull-out strength was significantly lower in the OSP group (65.7 N) versus the LCSP (133 N; P = .0005) and the MP (117.6 N; P = .001) groups. There was no statistically significant difference in pull-out strength between the LCSP and MP groups (P = .42). There were no statistically significant differences in displacement at maximum load among any 2 of the 3 groups.

Conclusion:

These findings suggest that while initial stability may play a role in the clinical outcomes of osteochondral allograft (OCA) implantation, the biological milieu in vivo for each graft setting perhaps has a greater impact on the success of an OAT procedure. Further study is needed on the relationship between OCA biomechanics and clinical outcomes of OAT.

The Effect of Fatigue on Leg Muscle Activation and Tibial Acceleration During a Jumping Task

CONTEXT

Lower-extremity stress fractures (SFx) are a common occurrence during load-bearing activities of jumping and landing. To detect biomechanical changes during jumping postinjury, a fatigue model could be used.

OBJECTIVE

To evaluate muscle activation in the lower leg and tibial accelerations (TAs) prefatigue to postfatigue following a jumping task in those with and without a history of SFx.

DESIGN

Repeated-measures.

SETTING

Athletic Training Research Lab.

PARTICIPANTS

A total of 30 active college-aged students with and without a history of lower-extremity (leg or foot) SFx (15 males and 15 females; 21.5 [5.04] y, height = 173.5 [12.7] cm, weight = 72.65 [16.4] kg).

INTERVENTION

A maximal vertical jump on one leg 3 times with arms folded across the chest prefatigue to postfatigue was performed. Fatigue protocol was standing heel raises on a custom-built platform at a pace controlled by a metronome until task failure was reached. Legs were tested using a randomized testing order. Electromyographic (EMG) surface electrodes were placed on the medial gastrocnemius, soleus, and tibialis anterior following a standardized placement protocol. A triaxial accelerometer was attached to the proximal anteromedial surface of the tibia.

MAIN OUTCOME MEASURES

Linear envelopes of the medial gastrocnemius, soleus, and tibialis anterior and peak accelerations (resultant acceleration takeoff and landing).

RESULTS

Significant interaction for leg × test for tibialis anterior with a posttest difference between SFx and control (P = .05). There were decreases in EMG linear envelope following fatigue for medial gastrocnemius (P < .01) and tibialis anterior (P = .12) pretest to posttest. At takeoff, TA was greater in the SFx contralateral leg in comparison with the control leg (P = .04). At landing, TA was greater in posttest (P < .01) and in the SFx leg compared with SFx contralateral (P = .14).

CONCLUSION

A decrease in muscle activity and an increase in TA following fatigue were noted for all subjects but especially for those with a history of SFx.

Endogenous cell recruitment strategy for articular cartilage regeneration

In the absence of timely and proper treatments, injuries to articular cartilage (AC) can lead to cartilage degeneration and ultimately result in osteoarthritis. Regenerative medicine and tissue engineering techniques are emerging as promising approaches for AC regeneration and repair. Although the use of cell-seeded scaffolds prior to implantation can regenerate and repair cartilage lesions to some extent, these approaches are still restricted by limited cell sources, excessive costs, risks of disease transmission and complex manufacturing practices. Recently developed acellular scaffold approaches that rely on the recruitment of endogenous cells to the injured sites avoid these drawbacks and offer great promise for in situ AC regeneration. Multiple endogenous stem/progenitor cells (ESPCs) are found in joint-resident niches and have the capability to migrate to sites of injury to participate in AC regeneration. However, the natural recruitment of ESPCs is insufficient, and the local microenvironment is hostile after injury. Hence, an endogenous cell recruitment strategy based on the combination of chemoattractants and acellular scaffolds to effectively and specifically recruit ESPCs and improve local microenvironment may provide new insights into in situ AC regeneration. This review provides a brief overview of: (1) the status of endogenous cell recruitment strategy; (2) the subpopulations, potential migration routes (PMRs) of joint-resident ESPCs and their immunomodulatory and reparative effects; (3) chemoattractants and their potential adverse effects; (4) scaffold-based drug delivery systems (SDDSs) that are utilized for in situ AC regeneration; and (5) the challenges and future perspectives of endogenous cell recruitment strategy for AC regeneration. STATEMENT OF SIGNIFICANCE: Although the endogenous cell recruitment strategy for articular cartilage (AC) regeneration has been investigated for several decades, much work remains to be performed in this field. Future studies should have the following aims: (1) reporting the up-to-date progress in the endogenous cell recruitment strategies; (2) determining the subpopulations of ESPCs, the cellular and molecular mechanisms underlying the migration of these cells and their anti-inflammatory, immunomodulatory and reparative effects; (3) elucidating the chemoattractants that enhance ESPC recruitment and their potential adverse effects; and (4) developing advanced SDDSs for chemoattractant dispatch. Herein, we present a systematic overview of the aforementioned issues to provide a better understanding of endogenous cell recruitment strategies for AC regeneration and repair.

Macroscopically healthy articular cartilage with fibrillar-scale early tissue degeneration subject to impact loading results in greater extent of cell-death

From previous investigations it has been shown that there exists healthy-appearing articular cartilage that contains collagen fibril network destructuring. It is hypothesised that such sub-micron scale destructuring not only presents an increased vulnerability to tissue scale damage following impact loading, but an increase in cell death as well. Cartilage-on-bone blocks from 12 patellae, six healthy (G0) and the other six with sub-micron fibrillar destructuring (G1), were obtained and subject to 2.3 J impact loading. Two sets of sub-samples were obtained for each block tested. One set was used to examine for the live/dead cell response using calcein-AM and propidium iodide staining, imaged with confocal microscopy. The tissue microstructural matrix was imaged from the other matched set, unstained and in its fully hydrated state, using differential interference contrast optical light microscopy. High speed imaging of the impact was used to calculate the velocity changes or coefficient of restitution (COR) and used as a proxy of energy that the tissue absorbed. A previously defined tissue matrix damage score was used to quantify the extent of fracturing and cracking in the matrix. The cell death (PCD) was counted and presented as a percentage against all cells live plus dead. The energy absorbed was 36.5% higher in G1 than in G0 (p = 0.034). However, the damage score and PCD of samples in the G1 group was much larger than the G0 group, ~300% and 161% respectively. Microscopy showed that cell death is associated to both matrix compaction and further fibrillar destructuring from the ECM to the territorial matrix regions of the chondron. Following impact loading, cartilage tissue that appears normal but contains sub-micron fibrillar matrix destructuring responds with significantly increased cell death.

An Expert Consensus Statement on the Management of Large Chondral and Osteochondral Defects in the Patellofemoral Joint

Background

Cartilage lesions of the patellofemoral joint constitute a frequent abnormality. Patellofemoral conditions are challenging to treat because of complex biomechanics and morphology.

Purpose

To develop a consensus statement on the functional anatomy, indications, donor graft considerations, surgical treatment, and rehabilitation for the management of large chondral and osteochondral defects in the patellofemoral joint using a modified Delphi technique.

Study Design

Consensus statement.

Methods

A working group of 4 persons generated a list of statements related to the functional anatomy, indications, donor graft considerations, surgical treatment, and rehabilitation for the management of large chondral and osteochondral defects in the patellofemoral joint to form the basis of an initial survey for rating by a group of experts. The Metrics of Osteochondral Allografts (MOCA) expert group (composed of 28 high-volume cartilage experts) was surveyed on 3 occasions to establish a consensus on the statements. In addition to assessing agreement for each included statement, experts were invited to propose additional statements for inclusion or to suggest modifications of existing statements with each round. Predefined criteria were used to refine statement lists after each survey round. Statements reaching a consensus in round 3 were included within the final consensus document.

Results

A total of 28 experts (100% response rate) completed 3 rounds of surveys. After 3 rounds, 36 statements achieved a consensus, with over 75% agreement and less than 20% disagreement. A consensus was reached in 100.00% of the statements relating to functional anatomy of the patellofemoral joint, 88.24% relating to surgical indications, 100.00% relating to surgical technical aspects, and 100.00% relating to rehabilitation, with an overall consensus of 95.5%.

Conclusion

This study established a strong expert consensus document relating to the functional anatomy, surgical indications, donor graft considerations for osteochondral allografts, surgical technical aspects, and rehabilitation concepts for the management of large chondral and osteochondral defects in the patellofemoral joint. Further research is required to clinically validate the established consensus statements and better understand the precise indications for surgery as well as which techniques and graft processing/preparation methods should be used based on patient- and lesion-specific factors.

Evidence that reduction in volume protects in situ articular chondrocytes from mechanical impact

Chondrocytes, the resident cells in articular cartilage, carry the burden of producing and maintaining the extracellular matrix (ECM). However, as these cells have a low proliferative capacity and are not readily replaced, chondrocyte death due to extreme forces may contribute to the pathogenesis of osteoarthritis (OA) after injury or may inhibit healing after osteochondral transplantation, a restorative procedure for damaged cartilage that requires a series of mechanical impacts to insert the graft. Consequently, there is a need to understand what factors influence the vulnerability of in situ chondrocytes to mechanical trauma. To this end, the objective of this study was to investigate how altering cell volume by different means (hydrostatic pressure, uniaxial load, and osmotic challenge with and without inhibition of regulatory volume decrease) affects the vulnerability of in situ chondrocytes to extreme mechanical forces. Using a custom experimental platform enabling testing of viable and intact murine cartilage-on-bone explants, we established a strong correlation between chondrocyte volume and vulnerability to impact injury wherein reduced volume was protective. Moreover, we found that the volume-perturbing interventions did not affect cartilage ECM mechanical properties, suggesting that their effects on chondrocyte vulnerability occurred at the cellular level. The findings of this study offer new avenues for novel strategies aimed at preventing chondrocyte loss during osteochondral grafting or to halting the progression of cell death after a joint destabilizing injury.

Effects of Proud Large Osteochondral Plugs on Contact Forces and Knee Kinematics: A Robotic Study

BACKGROUND

Osteochondral allograft (OCA) transplantation is used to treat large focal femoral condylar articular cartilage defects. A proud plug could affect graft survival by altering contact forces (CFs) and knee kinematics.

HYPOTHESIS

A proud OCA plug will significantly increase CF and significantly alter knee kinematics throughout controlled knee flexion.

STUDY DESIGN

Controlled laboratory study.

METHODS

Human cadaver knees had miniature load cells, each with a 20-mm-diameter cylinder of native bone/cartilage attached at its exact anatomic position, installed in both femoral condyles at standardized locations representative of clinical defects. Spacers were inserted to create proud plug conditions of +0.5, +1.0, and +1.5 mm. CFs and knee kinematics were recorded as a robot flexed the knee continuously from 0° to 50° under 1000 N of tibiofemoral compression.

RESULTS

CFs were increased significantly (vs flush) for all proudness conditions between 0° and 45° of flexion (medial) and 0° to 50° of flexion (lateral). At 20°, the average increases in medial CF for +0.5-mm, +1-mm, and +1.5-mm proudness were +80 N (+36%), +155 N (+70%), and +193 N (+87%), respectively. Corresponding increases with proud lateral plugs were +44 N (+14%), +90 N (+29%), and +118 N (+38%). CF increases for medial plugs at 20° of flexion were significantly greater than those for lateral plugs at all proudness conditions. At 50°, a 1-mm proud lateral plug significantly decreased internal tibial rotation by 15.4° and decreased valgus rotation by 2.5°.

CONCLUSION

A proud medial or lateral plug significantly increased CF between 0° and 45° of flexion. Our results suggest that a medial plug at 20° may be more sensitive to graft incongruity than a lateral plug. The changes in rotational kinematics with proud lateral plugs were attributed to earlier contact between the proud plug's surface and the lateral meniscus, leading to rim impingement with decreased tibial rotation.

CLINICAL RELEVANCE

Increased CF and altered knee kinematics from a proud femoral plug could affect graft viability. Plug proudness of only 0.5 mm produced significant changes in CF and knee kinematics, and the clinically accepted 1-mm tolerance may need to be reexamined in view of our findings.

Biomechanics of osteochondral impact with cushioning and graft Insertion: Cartilage damage is correlated with delivered energy

Articular cartilage is susceptible to impact injury. Impact may occur during events ranging from trauma to surgical insertion of an OsteoChondral Graft (OCG) into an OsteoChondral Recipient site (OCR). To evaluate energy density as a mediator of cartilage damage, a specialized drop tower apparatus was used to impact adult bovine samples while measuring contact force, cartilage surface displacement, and OCG advancement. When a single impact was applied to an isolated (non-inserted) OCG, force and surface displacement each rose monotonically and then declined. In each of five sequential impacts of increasing magnitude, applied to insert an OCG into an OCR, force rose rapidly to an initial peak, with minimal OCG advancement, and then to a second prolonged peak, with distinctive oscillations. Energy delivered to cartilage was confirmed to be higher with larger drop height and mass, and found to be lower with an interposed cushion or OCG insertion into an OCR. For both single and multiple impacts, the total energy density delivered to the articular cartilage correlated to damage, quantified as total crack length. The corresponding fracture toughness of the articular cartilage was 12.0 mJ/mm². Thus, the biomechanics of OCG insertion exhibits distinctive features compared to OCG impact without insertion, with energy delivery to the articular cartilage being a factor highly correlated with damage.

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.

Impact insertion of osteochondral grafts: Interference fit and central graft reduction affect biomechanics and cartilage damage

An osteochondral graft (OCG) is an effective treatment for articular cartilage and osteochondral defects. Impact of an OCG during insertion into the osteochondral recipient site (OCR) can cause chondrocyte death and matrix damage. The aim of the present study was to analyze the effects of graft-host interference fit and a modified OCG geometry on OCG insertion biomechanics and cartilage damage. The effects of interference fit (radius of OCG - radius of OCR), loose (0.00 mm), moderate (0.05 mm), tight (0.10 mm), and of a tight fit with OCG geometry modification (central region of decreased radius), were analyzed for OCG cylinders and OCR blocks from adult bovine knee joints with an instrumented drop tower apparatus. An increasingly tight (OCG - OCR) interference fit led to increased taps for insertion, peak axial force, graft cartilage axial compression, cumulative and total energy delivery to cartilage, lower time of peak axial force, lesser graft advancement during each tap, higher total crack length in the cartilage surface, and lower chondrocyte viability. The modified OCG, with reduction of diameter in the central area, altered the biomechanical insertion variables and biological consequences to be similar to those of the moderate interference fit scenario. Micro-computed tomography confirmed structural interference between the OCR bone and both the proximal and distal bone segments of the OCGs, with the central regions being slightly separated for the modified OCGs. These results clarify OCG insertion biomechanics and mechanobiology, and introduce a simple modification of OCGs that facilitates insertion with reduced energy while maintaining a structural interference fit. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:377-386, 2018.

Review of the biomechanics and biotribology of osteochondral grafts used for surgical interventions in the knee

A review of research undertaken to evaluate the biomechanical stability and biotribological behaviour of osteochondral grafts in the knee joint and a brief discussion of areas requiring further improvement in future studies are presented. The review takes into consideration osteochondral autografts, allografts, tissue engineered constructs and synthetic and biological scaffolds.

UPDATING ON DIAGNOSIS AND TREATMENT OF CHONDRAL LESION OF THE KNEE

The treatment of chondral knee injuries remains a challenge for the orthopedic surgeon, mainly owing to the characteristics of the cartilage tissue, which promote low potential for regeneration. Chondral lesions can be caused by metabolic stimulation, or by genetic, vascular and traumatic events, and are classified according to the size and thickness of the affected cartilage. Clinical diagnosis can be difficult, especially due to insidious symptoms. Additional tests, as Magnetic Resonance Imaging (MRI), may be needed. The treatment of these lesions usually starts with non-operative management. Surgery should be reserved for patients with detached chondral fragments, blocked range of motion, or the failure of non-operative treatment. The surgical techniques used for the treatment of partial thickness defects are Debridement and Ablation. These techniques aim to improve symptoms, since they do not restore normal structure and function of the cartilage. For full-thickness defects (osteochondral lesion), available treatments are Abrasion, Drilling, Microfracture, Osteochondral Autologous and Allogeneic Transplantation, and biological techniques such as the use of Autologous Chondrocyte Transplantation, Minced Cartilage and stem cells.

Influence of basal support and early loading on bone cartilage healing in press-fitted osteochondral autografts

PURPOSE

The influence of basal graft support combined to early loading following an osteochondral autograft procedure is unclear. It was hypothesized that bottomed grafts may allow for early mobilization by preventing graft subsidence and leading to better healing.

METHODS

Osteochondral autografts were press fitted in the femoral condyles of 24 sheep (one graft per animal). In the unbottomed group (n = 12), a gap of 2 mm was created between graft and recipient bone base. In the bottomed group (n = 12), the graft firmly rested on recipient bone. Animals were allowed immediate postoperative weightbearing. Healing times were 3 and 6 months per group (n = 6 per subgroup). After killing, histological and histomorphometric analyses were performed.

RESULTS

Unbottomed grafts at 3 months showed significantly more graft subsidence (P = 0.024), significantly less mineralized bone (P = 0.028) and significantly worse cartilage and subchondral bone plate healing (P = 0.034) when compared to bottomed grafts. At 6 months, no differences were seen. Compared to the native situation, unbottomed grafts showed significantly more graft subsidence (P = 0.024), whereas bottomed grafts did not. Cystic lesions were seen in both groups. Osteoclasts were closely related to the degree of bone remodelling.

CONCLUSION

In the animal model, in the case of early loading, bottomed osteochondral autografts have less chance of graft subsidence. Evident subsidence negatively influences the histological healing process. In the osteochondral autograft procedure, full graft support should be aimed for. This may allow for early mobilization, diminish graft subsidence and improve long-term integration.

The effect of platelet-rich plasma on osteochondral defects treated with mosaicplasty

PURPOSE

This study investigated the efficacy of platelet-rich plasma (PRP) on articular surfaces on which the mosaicplasty technique was performed. Our hypothesis was that PRP can accelerate the osseointegration process and enhance the quality of articular integrity after the mosaicplasty procedure.

METHODS

Standard defects were created in the femoral groove of both patellofemoral joints of 12 New Zealand rabbits. PRP solution was placed inside the defect before fixation of the osteochondral autografts and injected inside the involved joint after capsular closure of the tested knees. The contralateral knees served as the control sides. The animals were euthanized three or six weeks after mosaicplasty, and both limbs were assessed according to Pineda's histological grading scale. Significance level was set at p ≤ 0.05 a priori, and the Mann-Whitney U test was used for statistical analysis.

RESULTS

Histologic findings at the interface between the transferred autograft and the original cartilage revealed better integration of the adjacent surfaces in the mosaicplasty with PRP group three weeks after the procedure; the difference was significant (p < 0.05). However, no significant difference in the transition zone was observed between the groups six weeks after the experiment (p = 0.59).

CONCLUSIONS

Our animal model showed that adjunctive use of PRP produced a better healing response and resulted in superior histological scores after three weeks compared with the mosaicplasty-only procedure. Interpretation of our results is important in terms of rapid return to previous activity levels. Thus, application of PRP can represent a valid therapeutic option for improving the efficacy of mosaicplasty by stimulating the local healing response.

Articular cartilage repair: procedures versus products

This review discusses the current perspectives and practices regarding the treatment of articular cartilage injury. Specifically, the authors have delineated and examined articular cartilage repair techniques as either surgical procedures or manufactured products. Although both methodologies are used to treat articular cartilage injury, there are obvious advantages and disadvantages to the application of both, with the literature providing few recommendations on the most suitable regimen for the patient and surgeon. In recent times, cell-based tissue engineering products, predominantly autologous chondrocyte implantation, have been the subject of much research and have become clinically popular. Herein, we review the most used procedures and products in cartilage repair, compare and contrast their outcomes, and evaluate the issues that must be overcome in order to improve patient efficacy in the future.

The measurement of joint mechanics and their role in osteoarthritis genesis and progression

Mechanics play a role in the initiation and progression of osteoarthritis. However, our understanding of which mechanical parameters are most important, and what their impact is on the disease, is limited by the challenge of measuring the most important mechanical quantities in living subjects. Consequently, comprehensive statements cannot be made about how mechanics should be modified to prevent, slow or arrest osteoarthritis. Our current understanding is based largely on studies of deviations from normal mechanics caused by malalignment, injury, and deformity. Some treatments for osteoarthritis focus on correcting mechanics, but there appears to be scope for more mechanically based interventions.

A method of isolating viable chondrocytes with proliferative capacity from cryopreserved human articular cartilage

This study aimed to optimise methods of cryopreserving human articular cartilage (AC) tissue for the isolation of late chondrocytes. Human AC specimens from osteoarthritis patients who had undergone total knee replacement were used to optimise the chondrocyte isolation process and the choice of cryoprotective agent (CPA). For AC tissue cryopreservation, intact cored cartilage discs (5 mm diameter) and diced cartilage (0.2-1 mm cubes) from the same sized discs were step cooled and stored in liquid nitrogen for up to 48 h before chondrocyte isolation and in vitro assay of cell viability and proliferative potential. The results showed that 10 % dimethyl sulphoxide in 90 % foetal bovine serum was a successful CPA for chondrocyte cryopreservation. Compared with intact cored discs, dicing of AC tissue into 0.2-1 mm cubes significantly increased the viability and proliferative capacity of surviving chondrocytes after cryopreservation. In situ cross-section imaging using focused ion beam microscopy revealed that dicing of cored AC discs into small cubes reduced the cryo-damage to cartilage tissue matrix. In conclusion, modification of appropriate factors, such as the size of the tissue, cryoprotective agent, and isolation protocol, can allow successful isolation of viable chondrocytes with high proliferative capacity from cryopreserved human articular cartilage tissue. Further studies are required to determine whether these cells may retain cartilage differentiation capacity and provide sufficient chondrocytes for use as implants in clinical applications.

Knee chondral injuries: clinical treatment strategies and experimental models

Articular cartilage has a very limited capacity to repair and as such premature joint degeneration is often the end point of articular injuries. Patients with chondral injury have asymptomatic periods followed by others in which discomfort or pain is bearable. The repair of focal cartilage injuries requires a precise diagnosis, a completed knee evaluation to give the correct indication for surgery proportional to the damage and adapted to each patient. Many of the surgical techniques currently performed involve biotechnology. The future of cartilage repair should be based on an accurate diagnosis using new MRI techniques. Clinical studies would allow us to establish the correct indications and surgical techniques implanting biocompatible and biodegradable matrices with or without stem cells and growth factors. Arthroscopic techniques with the design of new instruments can facilitate repair of patella and tibial plateau lesions.

Axial load-bearing capacity of an osteochondral autograft stabilized with a resorbable osteoconductive bone cement compared with a press-fit graft in a bovine model

BACKGROUND

Osteochondral autografts in mosaicplasty are inserted in a press-fit fashion, and hence, patients are kept nonweightbearing for up to 2 months after surgery to allow bone healing and prevent complications. Very little has been published regarding alternative fixation techniques of those grafts.

HYPOTHESIS

Osteochondral autografts stabilized with a resorbable osteoconductive bone cement would have a greater load-bearing capacity than standard press-fit grafts.

STUDY DESIGN

Controlled laboratory study.

METHODS

Biomechanical testing was conducted on 8 pairs of cadaveric bovine distal femurs. For the first 4 pairs, 6 single osteochondral autografts were inserted in a press-fit fashion on one femur. On the contralateral femur, 6 grafts were stabilized with a calcium triglyceride osteoconductive bone cement. For the 4 remaining pairs of femurs, 4 groups of 3 adjacent press-fit grafts were inserted on one femur, whereas on the contralateral femur, grafts were cemented. After a maturation period of 48 hours, axial loading was applied on all single grafts and on the middle graft of each 3-in-a-row series.

RESULTS

For the single-graft configuration, median loads required to sink the press-fit and cemented grafts by 2 and 3 mm were 281.87 N versus 345.56 N (P = .015) and 336.29 N versus 454.08 N (P = .018), respectively. For the 3-in-a-row configuration, median loads required to sink the press-fit and cemented grafts by 2 and 3 mm were 260.31 N versus 353.47 N (P = .035) and 384.83 N versus 455.68 N (P = .029), respectively.

CONCLUSION

Fixation of osteochondral grafts using bone cement appears to improve immediate stability over the original mosaicplasty technique for both single- and multiple-graft configurations.

CLINICAL RELEVANCE

Achieving greater primary stability of osteochondral grafts could potentially accelerate postoperative recovery, allowing early weightbearing and physical therapy.

Management of articular cartilage defects of the knee

Articular cartilage injuries of the knee present a difficult clinical dilemma and their treatment is controversial. Hyaline articular cartilage is an avascular, low-friction, and wear-resistant weightbearing surface that has limited capacity for self-repair. The optimal treatment for cartilage lesions has yet to be established. Various treatment methods are employed to reestablish a stable cartilage surface, including microfracture, autologous and allograft osteochondral transplantation, autologous chondrocyte implantation, matrix-associated chondrocyte implantation, and scaffold-assisted methods. Treatment algorithms help to guide physicians' decision making in the care of these injuries. In this article, results from outcomes studies as well as prospective randomized clinical trials comparing treatment methods are reviewed, and current practice guidelines are summarized.

Spinal facet joint biomechanics and mechanotransduction in normal, injury and degenerative conditions

The facet joint is a crucial anatomic region of the spine owing to its biomechanical role in facilitating articulation of the vertebrae of the spinal column. It is a diarthrodial joint with opposing articular cartilage surfaces that provide a low friction environment and a ligamentous capsule that encloses the joint space. Together with the disc, the bilateral facet joints transfer loads and guide and constrain motions in the spine due to their geometry and mechanical function. Although a great deal of research has focused on defining the biomechanics of the spine and the form and function of the disc, the facet joint has only recently become the focus of experimental, computational and clinical studies. This mechanical behavior ensures the normal health and function of the spine during physiologic loading but can also lead to its dysfunction when the tissues of the facet joint are altered either by injury, degeneration or as a result of surgical modification of the spine. The anatomical, biomechanical and physiological characteristics of the facet joints in the cervical and lumbar spines have become the focus of increased attention recently with the advent of surgical procedures of the spine, such as disc repair and replacement, which may impact facet responses. Accordingly, this review summarizes the relevant anatomy and biomechanics of the facet joint and the individual tissues that comprise it. In order to better understand the physiological implications of tissue loading in all conditions, a review of mechanotransduction pathways in the cartilage, ligament and bone is also presented ranging from the tissue-level scale to cellular modifications. With this context, experimental studies are summarized as they relate to the most common modifications that alter the biomechanics and health of the spine-injury and degeneration. In addition, many computational and finite element models have been developed that enable more-detailed and specific investigations of the facet joint and its tissues than are provided by experimental approaches and also that expand their utility for the field of biomechanics. These are also reviewed to provide a more complete summary of the current knowledge of facet joint mechanics. Overall, the goal of this review is to present a comprehensive review of the breadth and depth of knowledge regarding the mechanical and adaptive responses of the facet joint and its tissues across a variety of relevant size scales.

Management of focal chondral lesion in the knee joint

Articular cartilage does not contain vascular, nervous and lymphatic tissue and chondrocytes hardly participate in the healing or repair process of chondral tissue because of being surrounded by plenty of extracellular matrix. Therefore, the injury to articular cartilage frequently requires an operative treatment. The goal of surgical repair of articular cartilage is to regenerate nearly normal chondral tissue and prevent degenerative arthritis caused by the articular cartilage defect. Microfracture is a kind of cartilage repair procedure that makes a fibrin clot containing mesenchymal stem cells in the chondral lesion. Microfracture is a simple procedure but it has a disadvantage that the repaired tissue is fibrocartilage. Autologous chondrocyte implantation has an advantage that it implants fully differentiated chondrocytes to the lesion, which theoretically produces hyaline cartilage. Its disadvantages are that it is a two stage and a costly procedure. Osteochondral autograft transplantation is a one stage procedure and repairs the lesion with hyaline cartilage. But its limitation is the lack of donor site availability. Surgeons who understand the theoretical background, indications, surgical methods, rehabilitation, complications, and clinical course of cartilage repair procedures can achieve the goal of preventing degenerative arthritis.

Osteochondral autograft transfer for treatment of osteochondritis dissecans of the caudocentral humeral head in dogs

OBJECTIVE

To establish whether osteochondral autograft transfer (OAT) procedures for osteochondritis dissecans (OCD) of the canine caudocentral humeral head would restore articular contour, resurface osteochondral defects, and resolve lameness in dogs with OCD.

STUDY DESIGN

Case series.

ANIMALS

Dogs (n=14) with caudocentral humeral head OCD (16 shoulders).

METHODS

After arthroscopic assessment, the humeral head was exposed by arthrotomy. The OCD lesion was debrided and OATS(™) instrumentation used for resurfacing the defect with osteochondral core grafts collected from the stifle. Recipient sockets were created to maximally resurface articular lesions. Outcomes measures included clinical, radiographic, and arthroscopic examination at 12-18 weeks and clinical examination at 12-46 months (mean, 30.8 months) postoperatively.

RESULTS

Resurfacing of the humeral head was achieved in all dogs. Subjectively, lameness resolved in 9 of 16 limbs by 5-6 weeks postoperatively, and in 13 limbs by 12-18 weeks. Radiographically, all autografts were maintained. On second-look arthroscopy, the grafted section was intact, resilient on probing, satisfactorily conformed to the adjacent articular contour, and grossly appeared consistent with hyaline or fibrocartilage depending on the graft source. Of 12 limbs available for 12-46 months reevaluation, none were considered lame and mild discomfort on shoulder manipulation was recorded for only 1 joint.

CONCLUSIONS

OAT procedures are technically feasible in the caudocentral aspect of the canine humeral head. Articular contour reconstruction, resurfacing of osteochondral defects, and amelioration or resolution of short-term lameness may be achieved.

Chondrocyte function after osteochondral transfer: comparison of concave and plane punches

BACKGROUND

An incongruity between instrument and articular surfaces in osteochondral transfer (OCT) results in unevenly distributed impact forces exerted on the cartilage which may cause a loss of functional chondrocytes. We tested whether a plane instead of a concave design of the punch of an osteotome can reduce these cartilage damages.

METHODS

Osteochondral cylinders were transferred from a donor to a recipient site within porcine humeral heads. Histological sections of the cartilage were assessed for metabolic active chondrocytes by in situ hybridization detecting coll alpha(1)(II) mRNA subsequent to OCT and 24 h thereafter.

RESULTS

The percentage of cartilage harbouring functional chondrocytes in the transferred grafts was 85 +/- 10 and 91 +/- 4% subsequently to OCT using punches with concave or plane surfaces, respectively, and 83 +/- 10% (concave) and 82 +/- 10% (plane) after 24 h. In the superficial layer of the cartilage the percentages were 72 +/- 13% (concave) and 84 +/- 8% (plane) subsequently to OCT, and 68 +/- 15% (concave) and 70 +/- 3% (plane) after 24 h. The analysis did not reveal any statistically significant differences.

CONCLUSIONS

The OCT leads to considerable loss of functional chondrocytes which could not be prevented by the use of a plane instead of a concave punch. Since functional chondrocytes might be of crucial importance for the survival and integration of the graft into the recipient site further work is needed to optimize the OCT procedure.

Current concepts in the diagnosis and treatment of osteochondral lesions of the ankle

Osteochondral lesions of the ankle are a more common source of ankle pain than previously recognized. Although the exact pathophysiology of the condition has not been clearly established, it is likely that a variety of etiological factors play a role, with trauma, typically from ankle sprains, being the most common. Technological advancements in ankle arthroscopy and radiologic imaging, most importantly magnetic resonance imaging, have improved diagnostic capabilities for detecting osteochondral lesions of the ankle. Moreover, these technologies have allowed for the development of more sophisticated classification systems that may, in due course, direct specific future treatment strategies. Nonoperative treatment yields best results when employed in select pediatric and adolescent patients with osteochondritis dissecans. However, operative treatment, which is dependent on the size and site of the lesion, as well as the presence or absence of cartilage damage, is frequently warranted in both children and adults with osteochondral lesions. Arthroscopic microdrilling, micropicking, and open procedures, such as osteochondral autograft transfer system and matrix-induced autologous chondrocyte implantation, are frequently employed. The purpose of this article is to review the history, etiology, and classification systems for osteochondral lesions of the ankle, as well as to describe current approaches to diagnosis and management.

Mechanical effects of surgical procedures on osteochondral grafts elucidated by osmotic loading and real-time ultrasound

Introduction

Osteochondral grafts have become popular for treating small, isolated and full-thickness cartilage lesions. It is recommended that a slightly oversized, rather than an exact-sized, osteochondral plug is transplanted to achieve a tight fit. Consequently, impacting forces are required to insert the osteochondral plug into the recipient site. However, it remains controversial whether these impacting forces affect the biomechanical condition of the grafted articular cartilage. The present study aimed to investigate the mechanical effects of osteochondral plug implantation using osmotic loading and real-time ultrasound.

Methods

A full-thickness cylindrical osteochondral defect (diameter, 3.5 mm; depth, 5 mm) was created in the lateral lower quarter of the patella. Using graft-harvesting instruments, an osteochondral plug (diameter, 3.5 mm as exact-size or 4.5 mm as oversize; depth, 5 mm) was harvested from the lateral upper quarter of the patella and transplanted into the defect. Intact patella was used as a control. The samples were monitored by real-time ultrasound during sequential changes of the bathing solution from 0.15 M to 2 M saline (shrinkage phase) and back to 0.15 M saline (swelling phase). For cartilage sample assessment, three indices were selected, namely the change in amplitude from the cartilage surface (amplitude recovery rate: ARR) and the maximum echo shifts from the cartilage surface and the cartilage-bone interface.

Results

The ARR is closely related to the cartilage surface integrity, while the echo shifts from the cartilage surface and the cartilage-bone interface are closely related to tissue deformation and NaCl diffusion, respectively. The ARR values of the oversized plugs were significantly lower than those of the control and exact-sized plugs. Regarding the maximum echo shifts from the cartilage surface and the cartilage-bone interface, no significant differences were observed among the three groups.

Conclusions

These findings demonstrated that osmotic loading and real-time ultrasound were able to assess the mechanical condition of cartilage plugs after osteochondral grafting. In particular, the ARR was able to detect damage to the superficial collagen network in a non-destructive manner. Therefore, osmotic loading and real-time ultrasound are promising as minimally invasive methods for evaluating cartilage damage in the superficial zone after trauma or impact loading for osteochondral grafting.

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.

The measurement of joint mechanics and their role in osteoarthritis genesis and progression

Mechanics play a role in the initiation, progression, and successful treatment of osteoarthritis. However, we don't yet know enough about which specific mechanical parameters are most important and what their impact is on the disease process to make comprehensive statements about how mechanics should be modified to prevent, slow, or arrest the disease process. The objectives of this review are (1) to summarize methods for assessing joint mechanics and their relative merits and limitations, (2) to describe current evidence for the role of mechanics in osteoarthritis initiation and progression, and (3) to describe some current treatment approaches that focus on modifying joint mechanics.

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.

Transduction of anti-cell death protein FNK suppresses graft degeneration after autologous cylindrical osteochondral transplantation

This study shows that artificial super antiapoptotic FNK protein fused with a protein transduction domain (PTD-FNK) maintains the quality of osteochondral transplant by preventing chondrocyte death. Cylindrical osteochondral grafts were obtained from enhanced green fluorescent protein (EGFP)-expressing transgenic rats, in which living chondrocytes express green fluorescence, and submerged into medium containing PTD-FNK, followed by transplantation into cartilage defects of wild-type rats by impact insertion simulating autologous transplantation. The tissues were histologically evaluated by hematoxylin-eosin and Safranin-O staining. At 1 week, chondrocyte alignment was normal in the PTD-FNK treatment group, whereas all grafts without PTD-FNK treatment showed mixed cluster cell distribution. At 4 weeks, all grafts with PTD-FNK treatment showed almost normal matrix, whereas two grafts without PTD-FNK treatment showed fibrocartilage. Notably, all grafts with PTD-FNK retained high intensity of Safranin-O staining, but all grafts without PTD-FNK largely lost Safranin-O staining. PTD-FNK significantly suppressed a decrease in the survival rate and the density of EGFP-positive cells at 1 and 2 weeks, and this tendency continued at 4 weeks. The results of terminal deoxynucleotidyl transferase (TdT)-mediated deoxyuridine triphosphate (dUTP)-nick end-labeling staining showed that PTD-FNK inhibited cell death, indicating that PTD-FNK protects chondrocyte death and suppresses graft degeneration.

Apoptosis and gene expression of collagenases but not gelatinases in rabbit disc fragment cultures

OBJECT

The object of this study was to characterize the biological response of isolated intervertebral disc fragments to in vitro culture conditions with respect to cell death and inflammatory and catabolic changes. The acquired data could help to gain a better understanding of the biological reaction of disc tissue when exposed to environmental changes along with altered nutritional and osmotic conditions, as are encountered in different in vitro disc models or disc diseases in vivo.

METHODS

Intervertebral disc anulus fragments were isolated from Burgundy rabbits and cultured in standard media for 3 days. The disc fragments were analyzed for their swelling properties, proteoglycan loss on histological studies, lactate dehydrogenase activity, apoptosis, gene expression of collagenases and gelatinases, and for proinflammatory (MCP-1, IL-8, and IL-6) and apoptosis-associated (TNF-alpha, Fas-L, and caspase 3) genes.

RESULTS

The results demonstrate that disc specimens were swelling, and a loss of proteoglycans with disarrangement of anulus architecture was observed. The disc cells underwent rapid apoptosis with upregulation of various proinflammatory genes. Both collagenases, matrix metalloproteinase (MMP)-1 and MMP-13, were increasingly transcribed, whereas the gelatinases MMP-2 and MMP-9 did not respond or were downregulated.

CONCLUSIONS

Cultured disc fragments swell and undergo necrotic and apoptotic cell death combined with a catabolic gene response and gene expression of proinflammatory and chemoattractant proteins. Some of these findings have been demonstrated before in various spinal disorders. In addition, disc fragments are not suitable for long-term culture if a stable disc metabolism is desired, and the described changes have to be considered when using isolated disc material for in vitro cultures.

Cartilage repair with osteochondral autografts in sheep: effect of biophysical stimulation with pulsed electromagnetic fields

The effect of pulsed electromagnetic fields (PEMFs) on the integration of osteochondral autografts was evaluated in sheep. After osteochondral grafts were performed, the animals were treated with PEMFs for 6 h/day or sham-treated. Six animals were sacrificed at 1 month. Fourteen animals were treated for 2 months and sacrificed at 6 months. At 1 month, the osteogenic activity at the transplant-host subchondral bone interface was increased in PEMF-treated animals compared to controls. Articular cartilage was healthy in controls and stimulated animals. At 6 months, complete resorption was observed in four control grafts only. Cyst-like resorption areas were more frequent within the graft of sham-treated animals versus PEMF-treated. The average volume of the cysts was not significantly different between the two groups; nevertheless, analysis of the variance of the volumes demonstrated a significant difference. The histological score showed no significant differences between controls and stimulated animals, but the percentage of surface covered by fibrous tissue was higher in the control group than in the stimulated one. Interleukin-1 and tumor necrosis factor-alpha concentration in the synovial fluid was significantly lower, and transforming growth factor-beta1 was significantly higher, in PEMF-treated animals compared to controls. One month after osteochondral graft implantation, we observed larger bone formation in PEMF-treated grafts which favors early graft stabilization. In the long term, PEMF exposure limited the bone resorption in subchondral bone; furthermore, the cytokine profile in the synovial fluid was indicative of a more favorable articular environment for the graft.

Vertebral endplate trauma induces disc cell apoptosis and promotes organ degeneration in vitro

There is a major controversy whether spinal trauma with vertebral endplate fractures can result in post-traumatic disc degeneration. Intervertebral discs, which are adjacent to burst endplates, are frequently removed and an intercorporal spondylodesis is performed. In any case, the biological effects within the discs following endplate fractures are poorly elucidated to date. The aim of our investigations was therefore to establish a novel disc/endplate trauma culture model to reproducibly induce endplate fractures and investigate concurrent disc changes in vitro. This model is based on a full-organ disc/endplate culture system, which has been validated by the authors before. Intervertebral disc/endplate specimens were isolated from Burgundy rabbits and cultured in standard media (DMEM/F12, 10%FCS). Burst endplate fractures were induced in half of the specimens with a custom-made fracture device and subsequently cultured for 9 days. The biological effects such as necrotic or apoptotic cell death and the expression of pro-apoptotic genes and other genes involved in organ degeneration, e.g. matrix metalloproteinases (MMPs) were analyzed. Cell damage was assessed by quantification of the lactate dehydrogenase (LDH) activity in the supernatant. The expression of genes involved in the cellular apoptotic pathway (caspase 3) and the pro-apoptotic proteins FasL and TNF-alpha were monitored. The results demonstrate that LDH levels increased significantly post trauma compared to the control and remained elevated for 3 days. Furthermore, a constant up-regulation of the caspase 3 gene in both disc compartments was present. The pro-apoptotic proteins FasL and TNF-alpha were up regulated predominantly in the nucleus whereas the MMP-1 and -13 transcripts (collagenases) were increased in both disc structures. From this study we can conclude that endplate burst fractures result in both necrotic and apoptotic cell death in nucleus and annulus tissue. Moreover, FasL and TNF-alpha expression by nucleus cells may lead to continued apoptosis induced by Fas- and TNF-alpha receptor bearing cells. In addition TNF-alpha over-expression has potentially deleterious effects on disc metabolism such as over-expression of matrix proteinases. Taken together, the short term biological response of the disc following endplate fracture exhibits characteristics, which may initiate the degeneration of the organ.

Mechanical behavior of articular cartilage after osteochondral autograft transfer in an ovine model

BACKGROUND

Grafting of autologous hyaline cartilage and bone for articular cartilage repair is a well-accepted technique. Although encouraging midterm clinical results have been reported, no information on the mechanical competence of the transplanted joint surface is available.

HYPOTHESIS

The mechanical competence of osteochondral autografts is maintained after transplantation.

STUDY DESIGN

Controlled laboratory study.

METHODS

Osteochondral defects were filled with autografts (7.45 mm in diameter) in one femoral condyle in 12 mature sheep. The ipsilateral femoral condyle served as the donor site, and the resulting defect (8.3 mm in diameter) was left empty. The repair response was examined after 3 and 6 months with mechanical and histologic assessment and histomorphometric techniques.

RESULTS

Good surface congruity and plug placement was achieved. The Young modulus of the grafted cartilage significantly dropped to 57.5% of healthy tissue after 3 months (P < .05) but then recovered to 82.2% after 6 months. The aggregate and dynamic moduli behaved similarly. The graft edges showed fibrillation and, in some cases (4 of 6), hypercellularity and chondrocyte clustering. Subchondral bone sclerosis was observed in 8 of 12 cases, and the amount of mineralized bone in the graft area increased from 40% to 61%.

CONCLUSIONS

The mechanical quality of transplanted cartilage varies considerably over a short period of time, potentially reflecting both degenerative and regenerative processes, while histologically signs of both cartilage and bone degeneration occur.

CLINICAL RELEVANCE

Both the mechanically degenerative and restorative processes illustrate the complex progression of regeneration after osteochondral transplantation. The histologic evidence raises doubts as to the long-term durability of the osteochondral repair.

Effect of Fatigue on Tibial Impact Accelerations and Knee Kinematics in Drop Jumps

PURPOSE

The principle of specificity suggests that it may be beneficial to undertake plyometric drop-jump training when fatigued. However, this may increase peak-impact accelerations and therefore increase the risk of injury. The aims of the study were to determine if whole-body fatigue (i) increased peak-impact acceleration on the proximal tibia during plyometric drop jumps and (ii) produced associated changes in knee-joint kinematics during landing.

METHODS

Fifteen physically active male subjects performed drop jumps (30 and 50 cm) when nonfatigued and when fatigued. Whole-body fatigue was induced using a treadmill running protocol that incrementally increased effort. Peak-impact acceleration was measured with an accelerometer attached to the proximal tibia. Knee-joint kinematics were assessed during the eccentric phase: angle at initial touch down, maximum angle of flexion, range of motion, and peak angular velocity.

RESULTS

Fatigue caused a significant increase in tibial impact acceleration and peak angular velocity in drop jumps from 30 cm (154.9 +/- 93.8 vs 192.6 +/- 103.9 m x s(-2): 24%; 675.3 +/- 60.7 vs 811.4 +/- 68.9 degrees x s(-1): 20%), but not from 50 cm (222.4 +/- 74.9 vs 234.1 +/- 83.9 m x s(-2): 5%; 962.0 +/- 189.0 vs 984.4 +/- 189.3 degrees x s(-1): 2.6%), with no associated change in the knee-joint angles assessed. It was argued, however, that rather than the neuromuscular system being selectively affected by fatigue at 30 cm and not 50 cm, drop jumps from 50 cm resulted in larger-impact accelerations with the neuromuscular system having only a limited ability to attenuate them per se, whether fatigued or nonfatigued.

CONCLUSION

Care should be taken when performing drop jumps from a height of 30 cm in a fatigued state because of the reduced capacity to attenuate impact accelerations at the tibia, which may be associated with an increased risk of injury.