The effect of gamma irradiation on anterior cruciate ligament allograft biomechanical and biochemical properties in the caprine model at time zero and at 6 months after surgery

Evaluation criteria for musculoskeletal and craniofacial tissue engineering constructs: a conference report

Over the past 20 years, tissue engineering (TE) has evolved into a thriving research and commercial development field. However, applying TE strategies to musculoskeletal (MSK) and craniofacial tissues has been particularly challenging since these tissues must also transmit loads during activities of daily living. To address this need, organizers invited a small group of bioengineers, surgeons, biologists, and material scientists from academia, industry, and government to participate in a two and half-day conference to develop general and tissue-specific criteria for evaluating new concepts and tissue-engineered constructs, including threshold values of success. Participants were assigned to four breakout groups representing commonly injured tissues, including tendon and ligament, articular cartilage, meniscus and temporomandibular joint, and bone and intervertebral disc. Working in multidisciplinary teams, participants first carefully defined one or two important unmet clinical needs for each tissue type, including current standards of care and the potential impact of TE solutions. The groups then sought to identify important parameters for evaluating repair outcomes in preclinical studies and to specify minimally acceptable values for these parameters. The importance of in vitro TE studies was then discussed in the context of these preclinical studies. Where data were not currently available from clinical, preclinical, or culture studies, the groups sought to identify important areas of preclinical research needed to speed the development process. This report summarizes the findings of the conference.

Effect of cryoprotectant incubation time on handling properties of allogeneic tendons prepared for knee ligament reconstruction

Soft tissue tendon allografts prepared for anterior cruciate ligament reconstruction are becoming increasingly popular; although concerns exist regarding increased long-term laxity and traumatic rupture rates. This qualitative study evaluated the tissue handling properties of human tibialis posterior tendons prepared using a patented process to improve allograft remodeling and ligamentization under differing cryoprotectant incubation times over 60-min rehydration. Tendons that had been incubated for 8 h had smaller diameters than those that were incubated for 2 h (8.5 +/- 1.5 mm vs. 9.1 +/- 1.3 mm, p = 0.02). Qualitative tissue handling property results indicated that the 8-h incubation had a negative affect on tissue color. Both incubation time and rehydration time influenced tensile stiffness, compressive resilience, and ease of tissue handling for allograft preparation with the 8-h group displaying poorer results. This study concludes that an 8-h cryoprotectant incubation time is detrimental to qualitative allogeniec tibialis posterior tendon properties. Both groups tended to improve with longer rehydration times, however the 8-h incubation group remained actively dehydrated as evidenced by its smaller diameter and poorer tissue handling properties. Suboptimally rehydrated tendons would be more likely to accrue damage during allograft preparation or during implantation.

Graft healing in anterior cruciate ligament reconstruction

Graft healing within the bone tunnel after anterior cruciate ligament (ACL) reconstruction is still a complex, poorly understood biological process that is influenced by multiple surgical and postoperative variables. However, remarkable advances in knowledge of this process have been made based primarly on animal models. According to the findings of this review, some surgical and postoperative variables are known to directly affect time-course and quality of graft-tunnel healing. The type of graft, graft motion, and fixation methods have shown to directly affect time-course and quality of graft-tunnel healing. Therefore, the application of early and aggressive rehabilitation protocols should be cautious when using soft-tissue graft, allografts, and direct or aperture type of fixation for ACL reconstruction. With regard to graft placement, several cadaveric models showed biomechanical advantages of a more anatomical graft location; however, there are no studies that explore the relationship between graft placement and healing process. The precise effect of graft tensioning, graft/tunnel diameter disparity, and graft length within the bone tunnel in the graft healing process remains unclear and requires more research. To enhance graft-tunnel healing, tissue-engineering approaches, including the use of growth factors, mesenchymal stem cells, and periosteum graft augmentation, have been tested on animal models. These have shown promising results in terms of enhancement of bone-graft healing rate.

Remodeling of ACL allografts is inhibited by peracetic acid sterilization

Sterilization of allografts for anterior cruciate ligament (ACL) reconstruction has become an important prerequisite to prevent disease transmission. However, current sterilization techniques impair the biological or mechanical properties of such treated grafts. Peracetic acid (PAA) has been successfully used to sterilize bone allografts without these disadvantages and does not impair the mechanical properties of soft tissue grafts in vitro. We asked whether PAA sterilization would influence recellularization, restoration of crimp length and pattern, and revascularization of ACL grafts during early healing. We used an in vivo sheep model for open ACL reconstruction. We also correlated the histologic findings with the restoration of anteroposterior stability and structural properties during load-to-failure testing. PAA slowed remodeling activity at 6 and 12 weeks compared to nonsterilized allografts and autografts. The mechanical properties of PAA grafts were also reduced compared to these control groups at both time points. We conclude PAA sterilization currently should not be used to sterilize soft tissue grafts typically used in ACL reconstruction.

The effect of donor age and low-dose gamma irradiation on the initial biomechanical properties of human tibialis tendon allografts

BACKGROUND

Most tissue banks recover and irradiate tibialis tendon allografts from donors aged up to 65 years. It is unknown whether donor age and low-dose gamma irradiation affect the initial biomechanical properties of tibialis allografts.

HYPOTHESIS

Donor age up to 65 years and low-dose gamma irradiation do not significantly affect the initial biomechanical properties of tibialis allografts.

STUDY DESIGN

Controlled laboratory study.

METHODS

One hundred twenty-six tibialis tendon allografts (63 pairs, 37 human donors) were divided into 3 age groups: young (<45 years), middle (46-55 years), and old (56-65 years). Within each age group, half of the paired tendons underwent tensile testing as single-strand grafts and the other half as double-strand grafts. One tendon from each donor pair was randomly assigned to undergo terminal sterilization with an absorbed dose of 1.46 to 1.80 Mrad (14.6-18.0 kGy) gamma irradiation, whereas the other tendon received no irradiation. All tendon grafts were preconditioned with a cyclic load and tested to failure in tension.

RESULTS

Irradiated single-strand tendons in the old age group had a longer displacement at failure compared to the middle but not the young age group. Nonirradiated double-strand tendons in the old age group had a lower failure stress. Single-strand irradiated old tendons had a lower stiffness, and all irradiated young tendons and old double-strand tendons had a higher failure stress compared to nonirradiated tendons.

CONCLUSION

Donor age up to 65 years does not significantly affect the initial failure load, stiffness, or displacement at failure of tibialis allografts. An age-related decrease in failure stress was observed among nonirradiated tendons but not in tendons subjected to irradiation.

CLINICAL RELEVANCE

The results provide biomechanical evidence for use of tibialis allografts from donors up to 65 years of age. Low-dose gamma irradiation does not negatively influence the initial biomechanical properties of tibialis allografts. Further studies examining age and irradiation effects after submaximal cyclic loading conditions are recommended.

Clinical outcomes of allograft versus autograft in anterior cruciate ligament reconstruction

Anterior cruciate ligament (ACL) injuries are the most common complete ligamentous injury to the knee. The optimal graft should be able to reproduce the anatomy and biomechanics of the ACL, be incorporated rapidly with strong initial fixation, and cause low graft-site morbidity. This article reviews the literature comparing the clinical outcomes following allograft and autograft ACL reconstruction and examines current issues regarding graft choice.

Nonirradiated versus irradiated Achilles allograft: in vivo failure comparison

BACKGROUND

Many studies suggest that gamma irradiation decreases allograft strength in a dose-dependent manner. No study has demonstrated that this decrease in strength translates into higher clinical failures.

HYPOTHESIS

Irradiation of allograft tissue will lead to higher early clinical failure in anterior cruciate ligament (ACL) reconstruction.

STUDY DESIGN

Cohort study; Level of evidence, 3.

METHODS

Medical records were reviewed for 90 consecutive patients who had received Achilles allograft reconstruction for unilateral primary ACL injuries at one institution between July 2001 and June 2002. One half of patients received nonirradiated Achilles allograft and the other half received irradiated Achilles allograft at a dose range of 2.0 to 2.5 Mrad. The ACL allograft reconstructions were performed using the same surgical technique. The rehabilitation program was identical for both groups. All clinical failures were recorded.

RESULTS

At least 6 months' follow-up was available on 42 subjects in the nonirradiated group and 33 subjects in the irradiated group. A significant difference was noted in early failure rates between the groups (P <.01). The nonirradiated group had 1 in 42 (2.4%) catastrophic failure. In the irradiated group, 11 of 33 (33%) Achilles tendon grafts failed.

CONCLUSIONS

Less than satisfactory results led the senior authors to discontinue the use of irradiated allografts in ACL surgery. Continued research into alternatives to gamma irradiation is needed.

Lower extremity injuries in the skeletally immature athlete

The heightened intensity of training and competition among young athletes places them at increased risk for both acute and chronic injuries. Prompt recognition and treatment of such injuries are critical to prevent long-term functional disability and deformity. These injuries occur in patterns unique to the skeletally immature athlete, given their developing epiphyses and ossification centers and supporting ligamentous structures. Children and adolescents who participate in recreational and organized sports are particularly susceptible to a broad spectrum of lower extremity injuries involving both the osseous and soft-tissue structures. Fundamental knowledge of the pathophysiology of injury helps the clinician in determining management. Early recognition of acute traumatic injuries, along with preventive regimens and knowledge of both nonsurgical and surgical treatment protocols, has helped to restore and maintain normal lower extremity function in the skeletally immature athlete.

Anterior cruciate ligament reconstruction with a porcine xenograft: a serologic, histologic, and biomechanical study in primates

PURPOSE

This study proposes treatment methods to provide a mechanically competent, immunocompatible, and sterile porcine graft for human knee ligament reconstruction.

METHODS

The anterior cruciate ligament (ACL) was reconstructed by using treated porcine patellar tendon grafts or controls of untreated porcine grafts or allografts in 20 rhesus monkeys. Animals were stratified into 2-, 6-, and 12-month postreconstruction cohorts. Serologic and histologic assessments were performed to evaluate host immunological and cellular response. Healing and functional integrity of the ACL reconstructions were assessed by tensile biomechanical testing.

RESULTS

Untreated porcine grafts were acutely resorbed and rejected, whereas treated porcine grafts and allografts were incorporated by the host as functional grafts. Temporal histologic assessment of treated porcine grafts and rhesus grafts revealed gradual host cellular infiltration and graft collagen remodeling through a similar mechanism of ligamentization. Biomechanical evaluations support graft functional integration with no difference between allograft and treated graft reconstructions.

CONCLUSION

Rhesus allograft and treated porcine grafts presented with similar healing profiles in a long-term evaluation of ACL reconstruction.

CLINICAL RELEVANCE

Immunochemical modification and sterilization of porcine patellar tendon grafts may improve initial biocompatibility and long-term functionality of xenografts in musculoskeletal applications.