Biomechanical outcomes after bioenhanced anterior cruciate ligament repair and anterior cruciate ligament reconstruction are equal in a porcine model

Multiple injections of leukoreduced platelet rich plasma reduce pain and functional impairment in a canine model of ACL and meniscal deficiency

Platelet rich plasma (PRP) is used to treat many musculoskeletal disorders. We used a canine model to determine the effects of multiple intra-articular injections of leukoreduced PRP (ACP) on anterior cruciate ligament healing, meniscal healing, and progression of osteoarthritis (OA). With Animal Care and Use Committee (ACUC) approval, 12 dogs underwent partial ACL transection and meniscal release in one knee. At weeks 1, 2, 3, 6, and 8 after insult, dogs were treated with intra-articular injections (2 ml) of either ACP (n = 6) or saline (n = 6). Dogs were assessed over 6 months to determine comfortable range of motion (CROM), lameness, pain, effusion, kinetics, and radiographic and arthroscopic assessments. At 6-month endpoint, dogs were assessed for ACL material properties and histopathology. Saline-treated dogs had significantly (p < 0.04) more CROM loss, significantly (p < 0.01) more pain, significantly (p < 0.05) more severe lameness, significantly (p < 0.05) lower function, and significantly (p < 0.05) lower %Total Pressure Index in affected hindlimbs compared to ACP-treated dogs. Radiographic OA increased significantly (p < 0.01) over time within each group. Arthroscopically, saline-treated knees showed moderate to severe synovitis, further ACL disruption, and medial compartment cartilage loss, and ACP-treated knees showed evidence of ACL repair and less severe synovitis. ACL material properties in ACP-treated knees were closer to normal than in saline-treated knees, however, the differences were not statistically significant. ACL histopathology was significantly (p< 0.05) less severe in ACP-treated knees compared to saline-treated knees. Five intra-articular injections of leukoreduced PRP had beneficial effects for ACL healing, improved range of motion, decreased pain, and improved limb function for up to 6 months in this model.

Platelets and plasma stimulate sheep rotator cuff tendon tenocytes when cultured in an extracellular matrix scaffold

The addition of platelet-rich plasma (PRP) to rotator cuff repair has not translated into improved outcomes after surgery. However, recent work stimulating ligament healing has demonstrated improved outcomes when PRP or whole blood is combined with an extracellular matrix carrier. The objective of this study was to evaluate the effect of three components of blood (plasma, platelets, and macrophages) on the in vitro activity of ovine rotator cuff cells cultured in an extracellular matrix environment. Tenocytes were obtained from six ovine infraspinatus tendons and cultured over 14 days in an extracellular matrix scaffold with the following additives: (1) plasma (PPP), (2) plasma and platelets (PAP), (3) plasma and macrophages (PPPM), (4) plasma, platelets and macrophages (PAPM), (5) phosphate buffered saline (PBS), and (6) PBS with macrophages (PBSM). Assays measuring cellular metabolism (AlamarBlue), proliferation (Quantitative DNA assay), synthesis of collagen and cytokines (SIRCOL, TNF-α and IL-10 ELISA, and MMP assay), and collagen gene expression (qPCR) were performed over the duration of the experiment, as well as histology at the conclusion. Plasma was found to stimulate cell attachment and spreading on the scaffold, as well as cellular proliferation. Platelets also stimulated cell proliferation, cellular metabolism, transition of cells to a myofibroblast phenotype, and contraction of the scaffolds. The addition of macrophages did not have any significant effect on the sheep rotator cuff cells in vitro. In vivo studies are needed to determine whether these changes in cellular function will translate into improved tendon healing.

Stem cell therapy: a promising biological strategy for tendon-bone healing after anterior cruciate ligament reconstruction

Tendon-bone healing after anterior cruciate ligament (ACL) reconstruction is a complex process, impacting significantly on patients' prognosis. Natural tendon-bone healing usually results in fibrous scar tissue, which is of inferior quality compared to native attachment. In addition, the early formed fibrous attachment after surgery is often not reliable to support functional rehabilitation, which may lead to graft failure or unsatisfied function of the knee joint. Thus, strategies to promote tendon-bone healing are crucial for prompt and satisfactory functional recovery. Recently, a variety of biological approaches, including active substances, gene transfer, tissue engineering and stem cells, have been proposed and applied to enhance tendon-bone healing. Among these, stem cell therapy has been shown to have promising prospects and draws increasing attention. From commonly investigated bone marrow-derived mesenchymal stem cells (bMSCs) to emerging ACL-derived CD34+ stem cells, multiple stem cell types have been proven to be effective in accelerating tendon-bone healing. This review describes the current understanding of tendon-bone healing and summarizes the current status of related stem cell therapy. Future limitations and perspectives are also discussed.

Anterior Cruciate Ligament Preservation: Early Results of a Novel Arthroscopic Technique for Suture Anchor Primary Anterior Cruciate Ligament Repair

PURPOSE

To propose a technique of arthroscopic suture anchor primary anterior cruciate ligament (ACL) preservation for patients with proximal avulsion ACL tears that maintain excellent tissue quality.

METHODS

We performed a retrospective review and early follow-up of 11 consecutive cases of ACL preservation. Patients were included if they had a proximal avulsion tear and excellent tissue quality confirmed to be adequate for repair during arthroscopy. Patients were excluded if these criteria were not met or if patients had multiligamentous injury patterns or significant arthrosis. The ACL was reinforced with a No. 2 FiberWire (Arthrex, Naples, FL) and a No. 2 TigerWire (Arthrex) and was anchored to the femoral footprint by two 4.75-mm BioComposite SwiveLock suture anchors (Arthrex). The surgical procedures were performed at 3 different hospitals by a single surgeon. Anterior stability was determined with a KT-1000 arthrometer (MEDmetric, San Diego, CA). Clinical outcomes were measured using the Lysholm score, modified Cincinnati score, Tegner activity score, Single Assessment Numeric Evaluation, and subjective and objective International Knee Documentation Committee (IKDC) scores.

RESULTS

Ten of eleven patients had good subjective and clinical outcomes after ACL preservation surgery at a minimum of 2 years' and mean of 3.5 years' follow-up. The mean Lysholm score was 93.2; the mean modified Cincinnati score was 91.5; the preoperative Tegner activity score was maintained postoperatively in 8 of 10 patients; the mean Single Assessment Numeric Evaluation score was 91.5; the mean subjective IKDC score was 86.4; and the objective IKDC score was A in 9 of 11 patients, B in 1 patient, and C in 1 patient. KT-1000 measurements were available in 8 of 11 patients, with 7 of 8 showing a side-to-side difference of less than 3 mm on maximum manual testing and 1 showing a 6-mm difference.

CONCLUSIONS

Preservation of the native ACL using the described arthroscopic primary repair technique can achieve short-term clinical success in a carefully selected subset of patients with proximal avulsion-type tears and excellent tissue quality.

LEVEL OF EVIDENCE

Level IV, therapeutic case series.

Primary Repair of the Anterior Cruciate Ligament: A Systematic Review

PURPOSE

To describe the clinical and preclinical research conducted on primary repair of the anterior cruciate ligament (ACL) during the past 10 years.

METHODS

A systematic search of PubMed, the Cochrane Central Register of Controlled Trials, and Embase was performed for all English-language studies published between 2003 and April 2014 on primary repair of the ACL.

RESULTS

Twenty-six studies met the inclusion and exclusion criteria. In the clinical research group, 8 studies (166 patients; age range, 10 to 71 years) met the inclusion and exclusion criteria and were largely long-term clinical outcome studies, based on the original cohorts from the 1970s and 1980s, and suggested high failure rates, additional surgery, and revision for instability. A subset of patients, however, achieved good to excellent subjective and objective long-term outcomes. In the preclinical research group, 18 studies met the inclusion and exclusion criteria and were based on an ACL transection model; they suggested that (1) stabilization of the knee with an internal suture strut improved the healing and biomechanical properties of the repaired ACL, (2) "enhancing" the repair with biological collagen-platelet composite augmentation improved healing and mechanical strength, (3) younger age and skeletal immaturity seem to correlate with improved histologic healing and biomechanical properties, (4) enhanced primary repair of the ACL may reduce post-traumatic osteoarthritis, and (5) the native ACL biomechanically outperformed the repaired ACL.

CONCLUSIONS

Although long-term human studies suggest collectively unacceptable outcomes for open primary repair of the ACL, a subset of patients achieved acceptable long-term results. ACL transection model animal studies showed improved healing and biomechanics with primary suture repair stabilization, early intervention, biological augmentation techniques, and younger age. Primary repair of the ACL may be an effective treatment modality for an appropriately selected subset of patients.

LEVEL OF EVIDENCE

Level IV, systematic review of preclinical and clinical Level IV studies.

Biomechanical Outcomes of Bridge-enhanced Anterior Cruciate Ligament Repair Are Influenced by Sex in a Preclinical Model

BACKGROUND

Despite the well-established role of sex on the anterior cruciate ligament (ACL) injury risk, its effects on ACL surgical outcomes remain controversial. This is particularly critical when developing novel surgical techniques to treat the injury because there are limited data existing on how these procedures will respond in each sex. One such approach is bridge-enhanced ACL repair, in which primary suture repair of the ACL is augmented with a bioactive scaffold saturated with autologous blood. It has shown comparable biomechanical outcomes to ACL reconstruction in preclinical models.

QUESTIONS/PURPOSES

We asked (1) whether sex affects the biomechanical outcomes of bridge-enhanced ACL repair; and (2) if suture type (absorbable or nonabsorbable), used to repair the torn ACL, can minimize the potential sex discrepancies in outcomes after 15 weeks of healing in a large animal preclinical model.

METHODS

Seventeen (eight males, nine females) Yorkshire pigs (Parson's Farms, Hadley, MA, USA) underwent bilateral ACL transection and received bridge-enhanced ACL repair with an absorbable suture (n=17) on one side and with a nonabsorbable suture (n=17) on the other side. The leg receiving the absorbable suture was randomized within each animal. ACL structural properties and AP knee laxity for each knee were measured after 15 weeks of healing. Mixed linear models were used to compare the biomechanical outcomes between sexes and suture groups.

RESULTS

When treated with absorbable suture, females had a lower ACL linear stiffness (females, 11 N/mm [range, 8-42]; males, 31 N/mm [range, 12-56]; difference, 20 N/mm [95% confidence interval {CI}, 4-36]; p=0.032), ACL yield (females, 121 N [range, 56-316]; males, 224 N [range, 55-538]; difference, 103 N [95% CI, 6-200]; p=0.078), and maximum load (females, 128 N [range, 63-332]; males, 241 N [range, 82-538]; difference, 114 N [95% CI, 15-212]; p=0.052) than males after 15 weeks of healing. Female knees treated with absorbable suture had a lower linear stiffness (absorbable, 11 N/mm [range, 8-42]; nonabsorbable, 25 N/mm [range, 8-64]; difference, 14 [95% CI, 2-26] N; p=0.054), ACL yield (absorbable, 121 N [range, 56-316]; nonabsorbable, 230 N [range, 149-573]; difference, 109 N [95% CI, 56-162]; p=0.002), and maximum load (absorbable, 128 N [range, 63-332]; nonabsorbable, 235 N [range, 151-593]; difference, 107 N [95% CI, 51-163]; p=0.002) along with greater AP knee laxity at 30° (absorbable, 9 mm [range, 5-12]; nonabsorbable, 7 mm [range, 2-13]; difference, 2 mm [95% CI, 1-4]; p=0.034) than females treated with nonabsorbable suture. When repaired using nonabsorbable suture, the biomechanical outcomes were similar between female and male knees (p>0.10).

CONCLUSIONS

Females had significantly worse biomechanical outcomes than males when the repairs were performed using absorbable sutures. However, the use of nonabsorbable sutures ameliorated these differences between males and females.

CLINICAL RELEVANCE

The current findings highlight the critical role of sex on the biomechanical outcomes of bridge-enhanced ACL repair in a relevant large animal model. Better understanding of the mechanisms responsible for these observations using preclinical models and concomitant clinical studies in human patients may allow for additional development of sex-specific surgical and rehabilitative strategies with potentially improved outcomes in women.

Electron beam sterilization does not have a detrimental effect on the ability of extracellular matrix scaffolds to support in vivo ligament healing

Extracellular matrix (ECM) scaffolds have been used to enhance anterior cruciate ligament (ACL) repair in large animal models. To translate this technology to clinical care, identifying a method which effectively sterilizes the material without significantly impairing in vivo function is desirable. Sixteen Yorkshire pigs underwent ACL transection and were randomly assigned to bridge-enhanced ACL repair-primary suture repair of the ACL with addition of autologous blood soaked ECM scaffold--with either (i) an aseptically processed ECM scaffold, or (ii) an electron beam irradiated ECM scaffold. Primary outcome measures included sterility of the scaffold and biomechanical properties of the scaffold itself and the repaired ligament at 8 weeks after surgery. Scaffolds treated with 15 kGy electron beam irradiation had no bacterial or fungal growth noted, while aseptically processed scaffolds had bacterial growth in all tested samples. The mean biomechanical properties of the scaffold and healing ligament were lower in the electron beam group; however, differences were not statistically significant. Electron beam irradiation was able to effectively sterilize the scaffolds. In addition, this technique had only a minimal impact on the in vivo function of the scaffolds when used for ligament healing in the porcine model.

Effect of low-temperature ethylene oxide and electron beam sterilization on the in vitro and in vivo function of reconstituted extracellular matrix-derived scaffolds

Reconstituted extracellular matrix (ECM)-derived scaffolds are commonly utilized in preclinical tissue engineering studies as delivery vehicles for cells and growth factors. Translation into clinical use requires identifying a sterilization method that effectively removes bacteria but does not harm scaffold function. To determine effectiveness of sterilization and impact on ECM scaffold integrity and function, low-temperature ethylene oxide and 15 kGy electron beam irradiation techniques were evaluated. Scaffold sterility was assessed in accordance to United States Pharmacopeia Chapter 71. Scaffold matrix degradation was determined in vitro using enzymatic resistance tests and gel electrophoresis. Scaffold mechanics including elastic modulus, yield stress and collapse modulus were tested. Lastly, 14 Yorkshire pigs underwent ACL transection and bio-enhanced ACL repair using sterilized scaffolds. Histologic response of ligament, synovium, and lymph nodes was compared at 4, 6, and 8 weeks. Ethylene oxide as well as electron beam irradiation yielded sterile scaffolds. Scaffold resistance to enzymatic digestion and protein integrity slightly decreased after electron beam irradiation while ethylene oxide altered scaffold matrix. Scaffold elastic modulus and yield stress were increased after electron beam treatment, while collapse modulus was increased after ethylene oxide treatment. No significant changes in ACL dimensions, in vivo scaffold resorption rate, or histologic response of synovium, ligament, and lymph nodes with either terminal sterilization technique were detectable. In conclusion, this study identifies two methods to terminally sterilize an ECM scaffold. In vitro scaffold properties were slightly changed without significantly influencing the biologic responses of the surrounding tissues in vivo. This is a critical step toward translating new tissue engineering strategies to clinical trials.

Bio-enhanced repair of the anterior cruciate ligament

Suture repair of the anterior cruciate ligament (ACL) has been widely abandoned in favor of ACL reconstruction, largely because of the high rates of failure and unreliability of the outcomes after suture repair. However, there have been recent basic science studies that suggest that combining a suture repair with a biological adjunct may improve the results of suture repair of the ACL, with several studies in large animal models showing equivalent strength of an ACL treated with bio-enhanced repaired to that of an ACL graft at 3, 6, and 12 months after surgery. In addition, the groups treated with bio-enhanced repair had significantly less osteoarthritis when compared with the animals undergoing ACL reconstruction. These findings have led to a renewed interest in bio-enhanced primary repair as a way to make repair of the ACL a viable option for a select group of patients in the future.

Increased platelet concentration does not improve functional graft healing in bio-enhanced ACL reconstruction

PURPOSE

The use of an extracellular matrix scaffold (ECM) combined with platelets to enhance healing of an anterior cruciate ligament (ACL) graft ("bio-enhanced ACL reconstruction") has shown promise in animal models. However, the effects of platelet concentration on graft healing remain unknown. The objectives of this study were to determine whether increasing the platelet concentration in the ECM scaffold would (1) improve the graft biomechanical properties and (2) decrease cartilage damage after surgery.

METHODS

Fifty-five adolescent minipigs were randomized to five treatment groups: untreated ACL transection (n = 10), conventional ACL reconstruction (n = 15) and bio-enhanced ACL reconstruction using 1× (n = 10), 3× (n = 10) or 5× (n = 10) platelet-rich plasma. The graft biomechanical properties, anteroposterior (AP) knee laxity, graft histology and macroscopic cartilage integrity were measured at 15 weeks.

RESULTS

The mean linear stiffness of the bio-enhanced ACL reconstruction procedure using the 1× preparation was significantly greater than traditional reconstruction, while the 3× and 5× preparations were not. The failure loads of all the ACL-reconstructed groups were equivalent but significantly greater than untreated ACL transection. There were no significant differences in the Ligament Maturity Index or AP laxity between reconstructed knees. Macroscopic cartilage damage was relatively minor, though significantly less when the ECM-platelet composite was used.

CONCLUSIONS

Only the 1× platelet concentration improved healing over traditional ACL reconstruction. Increasing the platelet concentration from 1× to 5× in the ECM scaffold did not further improve the graft mechanical properties. The use of an ECM-platelet composite decreased the amount of cartilage damage seen after ACL surgery.

Addition of autologous mesenchymal stem cells to whole blood for bioenhanced ACL repair has no benefit in the porcine model

BACKGROUND

Coculture of mesenchymal stem cells (MSCs) from the retropatellar fat pad and peripheral blood has been shown to stimulate anterior cruciate ligament (ACL) fibroblast proliferation and collagen production in vitro. Current techniques of bioenhanced ACL repair in animal studies involve adding a biologic scaffold, in this case an extracellular matrix-based scaffold saturated with autologous whole blood, to a simple suture repair of the ligament. Whether the enrichment of whole blood with MSCs would further improve the in vivo results of bioenhanced ACL repair was investigated.

HYPOTHESIS

The addition of MSCs derived from adipose tissue or peripheral blood to the blood-extracellular matrix composite, which is used in bioenhanced ACL repair to stimulate healing, would improve the biomechanical properties of a bioenhanced ACL repair after 15 weeks of healing.

STUDY DESIGN

Controlled laboratory study.

METHODS

Twenty-four adolescent Yucatan mini-pigs underwent ACL transection followed by (1) bioenhanced ACL repair, (2) bioenhanced ACL repair with the addition of autologous adipose-derived MSCs, and (3) bioenhanced ACL repair with the addition of autologous peripheral blood derived MSCs. After 15 weeks of healing, the structural properties of the ACL (yield load, failure load, and linear stiffness) were measured. Cell and vascular density were measured in the repaired ACL via histology, and its tissue structure was qualitatively evaluated using the advanced Ligament Maturity Index.

RESULTS

After 15 weeks of healing, there were no significant improvements in the biomechanical or histological properties with the addition of adipose-derived MSCs. The only significant change with the addition of peripheral blood MSCs was an increase in knee anteroposterior laxity when measured at 30° of flexion.

CONCLUSION

These findings suggest that the addition of adipose or peripheral blood MSCs to whole blood before saturation of an extracellular matrix carrier with the blood did not improve the functional results of bioenhanced ACL repair after 15 weeks of healing in the pig model.

CLINICAL RELEVANCE

Whole blood represents a practical biologic additive to ligament repair, and any other additive (including stem cells) should be demonstrated to be superior to this baseline before clinical use is considered.

Bridge-enhanced ACL repair: A review of the science and the pathway through FDA investigational device approval

Injuries to the anterior cruciate ligament (ACL) are currently treated with replacement of the torn ligament with a graft of tendon harvested from elsewhere in the knee. This procedure, called "ACL reconstruction," is excellent for restoring gross stability to the knee; however, there are relatively high graft failure rates in adolescent patients (Barber et al. in Arthroscopy 30(4):483-491, (2014); Engelman et al. in Am J Sports Med, (2014); Webster et al. in Am J Sports Med 42(3):641-647, (2014)), and the ACL reconstruction procedure does not prevent the premature osteoarthritis seen in patients after an ACL injury (Ajuied et al. in Am J Sports Med, (2013); Song et al. in J Sports Med 41(10):2340-2346, (2013); Tourville et al. Am J Sports Med 41(4):769-778, (2013)) .Thus, new solutions are needed for ACL injuries. Researchers have been investigating the use of scaffolds, growth factors and cells to supplement a suture repair of the ACL (bridge-enhanced repair; also called bio-enhanced repair in prior publications). In this paper, we will review the varied approaches which have been investigated for stimulating ACL healing and repair in preclinical models and how one of these technologies was able to move from promising preclinical results to FDA acceptance of an investigational device exemption application for a first-in-human study.

Regeneration of the anterior cruciate ligament: Current strategies in tissue engineering

Recent advancements in the field of musculoskeletal tissue engineering have raised an increasing interest in the regeneration of the anterior cruciate ligament (ACL). It is the aim of this article to review the current research efforts and highlight promising tissue engineering strategies. The four main components of tissue engineering also apply in several ACL regeneration research efforts. Scaffolds from biological materials, biodegradable polymers and composite materials are used. The main cell sources are mesenchymal stem cells and ACL fibroblasts. In addition, growth factors and mechanical stimuli are applied. So far, the regenerated ACL constructs have been tested in a few animal studies and the results are encouraging. The different strategies, from in vitro ACL regeneration in bioreactor systems to bio-enhanced repair and regeneration, are under constant development. We expect considerable progress in the near future that will result in a realistic option for ACL surgery soon.

Transcription factor Mohawk controls tenogenic differentiation of bone marrow mesenchymal stem cells in vitro and in vivo

Mohawk homeobox (MKX) has been demonstrated as a tendon/ligament specific transcription factor. The aim of this study was to investigate the role of MKX in ligament/tenogenic differentiation of bone marrow derived mesenchymal stem cells (BMMSCs). Human BMMSCs were treated with 50 ng/ml BMP-12 or transduced with MKX or scleraxis (SCX) adenoviral vector. Gene expression analysis was performed by quantitative reverse transcribed polymerase chain reaction (qRT-PCR). Rat BMMSCs were seeded in a collagen scaffold and transplanted into a rat Achilles tendon defect model. Tenogenesis related gene expressions and histological features were analyzed. BMP-12 induced tenogenesis in BMMSCs as indicated by increased COL1a1, TNXB, DCN and SCX mRNA, and MKX expression increased simultaneously. Rat BMMSCs enhanced defect repair and were still detectable 3 weeks after transplantation. Increased expressions of COL1a1, TNC and TNMD in vivo were also correlated with upregulated MKX. Adenoviral MKX promoted expression of COL1a1, TNXB, and TNMD in BMMSCs. This study demonstrated that MKX gene expression is enhanced during the tenogenic differentiation of BMMSCs in vitro and in vivo, and the adenoviral overexpression of MKX increases tendon extracellular matrix gene expression and protein production. Thus, MKX is a key factor for tenogenic differentiation of MSCs.

A normative study of the synovial fluid proteome from healthy porcine knee joints

Synovial fluid in an articulating joint contains proteins derived from the blood plasma and proteins that are produced by cells within the joint tissues, such as synovium, cartilage, ligament, and meniscus. The proteome composition of healthy synovial fluid and the cellular origins of many synovial fluid components are not fully understood. Here, we present a normative proteomics study using porcine synovial fluid. Using our optimized method, we identified 267 proteins with high confidence in healthy synovial fluid. We also evaluated mRNA expression data from tissues that can contribute to the synovial fluid proteome, including synovium, cartilage, blood, and liver, to better estimate the relative contributions from these sources to specific synovial fluid components. We identified 113 proteins in healthy synovial fluid that appear to be primarily derived from plasma transudates, 37 proteins primarily derived from synovium, and 11 proteins primarily derived from cartilage. Finally, we compared the identified synovial fluid proteome to the proteome of human plasma, and we found that the two body fluids share many similarities, underlining the detected plasma derived nature of many synovial fluid components. Knowing the synovial fluid proteome of a healthy joint will help to identify mechanisms that cause joint disease and pathways involved in disease progression.

Updates in biological therapies for knee injuries: anterior cruciate ligament

There have been many advances in anterior cruciate ligament reconstruction (ACLR) techniques incorporating biological treatment. The aim of this review is to discuss the recent contributions that may enlighten our understanding of biological therapies for anterior cruciate ligament (ACL) injuries and improve management decisions involving these enhancement options. Three main biological procedures will be analyzed: bio-enhanced ACL repair, bio-enhanced ACLR scrutinized under the four basic principles of tissue engineering (scaffolds, cell sources, growth factors/cytokines including platelet-rich plasma, and mechanical stimuli), and remnant-preserving ACLR. There is controversial information regarding remnant-preserving ACLR, since different procedures are grouped under the same designation. A new definition for remnant-preserving ACLR surgery is proposed, dividing it into its three major procedures (selective bundle augmentation, augmentation, and nonfunctional remnant preservation); also, an ACL lesion pattern classification and a treatment algorithm, which will hopefully standardize these terms and procedures for future studies, are presented.

A novel silk-based artificial ligament and tricalcium phosphate/polyether ether ketone anchor for anterior cruciate ligament reconstruction - safety and efficacy in a porcine model

Loss of ligament graft tension in early postoperative stages following anterior cruciate ligament (ACL) reconstruction can come from a variety of factors, with slow graft integration to bone being widely viewed as a chief culprit. Toward an off-the-shelf ACL graft that can rapidly integrate to host tissue, we have developed a silk-based ACL graft combined with a tricalcium phosphate (TCP)/polyether ether ketone anchor. In the present study we tested the safety and efficacy of this concept in a porcine model, with postoperative assessments at 3months (n=10) and 6months (n=4). Biomechanical tests were performed after euthanization, with ultimate tensile strengths at 3months of ∼370N and at 6months of ∼566N - comparable to autograft and allograft performance in this animal model. Comprehensive histological observations revealed that TCP substantially enhanced silk graft to bone attachment. Interdigitation of soft and hard tissues was observed, with regenerated fibrocartilage characterizing a transitional zone from silk graft to bone that was similar to native ligament bone attachments. We conclude that both initial stability and robust long-term biological attachment were consistently achieved using the tested construct, supporting a large potential for silk-TCP combinations in the repair of the torn ACL.

Anterior cruciate ligament regeneration using mesenchymal stem cells and collagen type I scaffold in a rabbit model

PURPOSE

The objective of this study was to determine whether using mesenchymal stem cells (MSC) seeded in a collagen type I scaffold would be sufficient to regenerate the torn anterior cruciate ligament (ACL).

METHODS

Anterior cruciate ligament transection was performed on both knees in 10 New Zealand rabbits and then repaired with as follows: suture alone (suture-treated group, n = 6), suture associated with collagen type I scaffold (collagen type I scaffold-treated group, n = 8) or suture associated with autologous MSC seeded on collagen type I scaffold (MSC/collagen type I scaffold-treated group, n = 6). At 12-week post-intervention, the animals were killed and the ACLs were characterised macroscopically and histologically. Data of the 3 groups were against normal ACL (normal group, n = 10).

RESULTS

Macroscopic observation found that in MSC/collagen type I scaffold group, 33% of specimens showed a complete ACL regeneration, with a tissue similar to the normal ACL. Regeneration was not observed in the group treated with suture alone or associated with collagen type I scaffold without cells. In the latter, only a reparative attempt at the ends was observed. Histological analysis of the regenerated ACL showed a tissue with organised collagen and peripheric vessels.

CONCLUSIONS

These results provide evidence that the use of MSC seeded in a collagen type I scaffold in the treatment of ACL injuries is associated with an enhancement of ligament regeneration. This MSC-based technique is a potentially attractive tool for improving the treatment of ACL ruptures.

T2 * MR relaxometry and ligament volume are associated with the structural properties of the healing ACL

Our objective was to develop a non-invasive magnetic resonance (MR) method to predict the structural properties of a healing anterior cruciate ligament (ACL) using volume and T2 * relaxation time. We also compared our T2 *-based structural property prediction model to a previous model utilizing signal intensity, an acquisition-dependent variable. Surgical ACL transection followed by no treatment (i.e., natural healing) or bio-enhanced ACL repair was performed in a porcine model. After 52 weeks of healing, high-resolution MR images of the ACL tissue were collected. From these images, ligament volumes and T2 * maps were established. The structural properties of the ligaments were determined via tensile testing. Using the T2 * histogram profile, each ligament voxel was binned based on its T2 * value into four discrete tissue sub-volumes defined by specific T2 * intervals. The linear combination of the ligament sub-volumes binned by T2 * value significantly predicted maximum load, yield load, and linear stiffness (R(2)  = 0.92, 0.82, 0.88; p < 0.001) and were similar to the previous signal intensity based method. In conclusion, the T2 * technique offers a highly predictive methodology that is a first step towards the development of a method that can be used to assess ligament healing across scanners, studies, and institutions.

Basic science of anterior cruciate ligament injury and repair

Injury to the anterior cruciate ligament (ACL) is one of the most devastating and frequent injuries of the knee. Surgical reconstruction is the current standard of care for treatment of ACL injuries in active patients. The widespread adoption of ACL reconstruction over primary repair was based on early perception of the limited healing capacity of the ACL. Although the majority of ACL reconstruction surgeries successfully restore gross joint stability, post-traumatic osteoarthritis is commonplace following these injuries, even with ACL reconstruction. The development of new techniques to limit the long-term clinical sequelae associated with ACL reconstruction has been the main focus of research over the past decades. The improved knowledge of healing, along with recent advances in tissue engineering and regenerative medicine, has resulted in the discovery of novel biologically augmented ACL-repair techniques that have satisfactory outcomes in preclinical studies. This instructional review provides a summary of the latest advances made in ACL repair. Cite this article: Bone Joint Res 2014;3:20-31.

Histologic Predictors of Maximum Failure Loads Differ between the Healing ACL and ACL Grafts after 6 and 12 Months In Vivo

Background:

Bioenhanced anterior cruciate ligament (ACL) repair, where the suture repair is supplemented with a biological scaffold, is a promising novel technique to stimulate healing after ACL rupture. However, the histological properties of a successfully healing ACL and how they relate to the mechanical properties have not been fully described.

Purpose:

To determine which histological features best correlate with the mechanical properties of the healing ACL repairs and ACL grafts in a porcine model at 6 and 12 months after injury.

Study Design:

Controlled laboratory study.

Methods:

A total of 48 Yucatan mini-pigs underwent ACL transection followed by: (1) conventional ACL reconstruction with bone–patellar tendon–bone (BPTB) allograft, (2) bioenhanced ACL reconstruction with BPTB allograft using a bioactive scaffold, or (3) bioenhanced ACL repair using the same bioactive scaffold. After 6 and 12 months of healing, structural properties of the ACL or graft (yield and failure load, linear stiffness) were measured. Following mechanical testing, ACL specimens were histologically analyzed for cell and vascular density and qualitatively assessed using the advanced Ligament Maturity Index.

Results:

After 6 months of healing, the cellular organization subscore was most predictive of yield load (r² = 0.98), maximum load (r² = 0.89), and linear stiffness (r² = 0.95) of the healing ACL, while at 12 months, the collagen subscore (r² = 0.68) became the best predictor of maximum load. For ACL grafts, the reverse was true, with the collagen subscore predictive of yield and maximum loads at 6 months (r² = 0.55) and graft cellularity predictive of maximum load of the graft at 12 months (r² = 0.50).

Conclusion:

These findings suggest there may be key biological differences in development and maintenance of ACL tissue after repair or reconstruction, with early ligament function dependent on cellular population of the repair but early graft function dependent on the maintenance of organized collagen.

Clinical Relevance:

Bioenhanced ACL repair shows promising potential as an alternative clinical treatment for ACL injury. This study contributes to the understanding of the cellular contribution to mechanical characteristics of the healing ACL in both repaired and reconstructed ACLs.

Application of Platelet-Rich Plasma to Disorders of the Knee Joint

IMPORTANCE

The promising therapeutic potential and regenerative properties of platelet-rich plasma (PRP) have rapidly led to its widespread clinical use in musculoskeletal injury and disease. Although the basic scientific rationale surrounding PRP products is compelling, the clinical application has outpaced the research.

OBJECTIVE

The purpose of this article is to examine the current concepts around the basic science of PRP application, different preparation systems, and clinical application of PRP in disorders in the knee.

EVIDENCE ACQUISITION

A systematic search of PubMed for studies that evaluated the basic science, preparation and clinical application of platelet concentrates was performed. The search used terms, including platelet-rich plasma or PRP preparation, activation, use in the knee, cartilage, ligament, and meniscus. Studies found in the initial search and related studies were reviewed.

RESULTS

A comprehensive review of the literature supports the potential use of PRP both nonoperatively and intraoperatively, but highlights the absence of large clinical studies and the lack of standardization between method, product, and clinical efficacy. Conclusions and Relevance. In addition to the call for more randomized, controlled clinical studies to assess the clinical effect of PRP, at this point, it is necessary to investigate PRP product composition and eventually have the ability to tailor the therapeutic product for specific indications.

Biology of anterior cruciate ligament injury and repair: Kappa delta ann doner vaughn award paper 2013

Anterior cruciate ligament (ACL) injuries are currently treated by removing the injured ligament and replacing it with a tendon graft. Recent studies have examined alternative treatment methods, including repair and regeneration of the injured ligament. In order to make such an approach feasible, a basic understanding of ACL biology and its response to injury is needed. Identification of obstacles to native ACL healing can then be identified and potentially resolved using tissue engineering strategies-first, with in vitro screening assays, and then with in vivo models of efficacy and safety. This Perspectives paper outlines this path of discovery for optimizing ACL healing using a bio-enhanced repair technique. This journey required constructing indices of the functional tissue response, pioneering physiologically based methods of biomechanical testing, developing, and validating clinically relevant animal models, and creating and optimizing translationally feasible scaffolds, surgical techniques, and biologic additives. Using this systematic translational approach, "bio-enhanced" ACL repair has been advanced to the point where it may become an option for future treatment of acute ACL injuries and the prevention of subsequent post-traumatic osteoarthritis associated with this injury.

Biomechanical evaluation of augmented and nonaugmented primary repair of the anterior cruciate ligament: an in vivo animal study

PURPOSE

The purpose of this study was to evaluate in a sheep model the biomechanical performance of augmented and nonaugmented primary repair of the anterior cruciate ligament (ACL) following transection at the femoral end during a 12-month postoperative observation.

METHODS

Forty sheep were randomly assigned to nonaugmented or augmented primary ACL repair using a polyethylene terephthalate (PET) band. At two, six, 16, 26 and 52 weeks postoperatively four sheep in each group were sacrificed and biomechanical testing performed.

RESULTS

Compared with nonaugmented primary ACL repair, the PET-augmented repair demonstrated superior biomechanical results from 16 weeks postoperatively onwards in terms of anterioposterior (AP) laxity, tensile strength and ligament stiffness. The augmentation device works as a stress shield during the ligament healing process. The nonaugmented ACL repair also resulted in ligament healing, but the biomechanical properties were at a significantly lower level.

CONCLUSION

These results support the previously reported histological findings following augmented primary ACL repair. This animal study on the healing capacity of the ACL may provide some important contributions to how primary healing in certain types of ruptures can be achieved.

CLINICAL RELEVANCE

I.

Effect of platelet-rich plasma on the biologic activity of the human rotator-cuff fibroblasts: A controlled in vitro study

To assess the in vitro effect of platelet-rich plasma (PRP) on biological activity of the human rotator cuff fibroblasts and to describe the optimal dose-response to maximize cellular stimulation while reducing potential risk. Rotator cuff (RC) fibroblasts of n = 6 patients (mean age of 65.2 years) undergoing arthroscopic cuff tear reconstruction were cultured in vitro for 21 days and stimulated with PRP in three different concentrations (1-, 5-, and 10-fold). Samples were obtained for DNA and GAG measurement at 1, 7, 14, and 21 days. The biological outcomes were regressed on the PRP concentration. The application of PRP significantly influenced the fibroblast proliferation and activity of the human rotator cuff with elevated glycosaminoglycan (GAG) and DNA levels. The dosage of PRP had the significantly highest impact on this proliferation using a onefold or fivefold application. PRP has a significant effect on fibroblast proliferation of the human rotator cuff in vitro with an optimal benefit using a onefold or fivefold PRP concentration. This study justifies further in vivo investigations using PRP at the human rotator cuff.

The effect of notchplasty in anterior cruciate ligament reconstruction: a biomechanical study in the porcine knee

INTRODUCTION

Notchplasty is frequently performed by many orthopaedic surgeons during anterior cruciate ligament (ACL) reconstruction. The effect of notchplasty on tunnel placement and knee biomechanics with ACL reconstruction is not known.

METHODS

Twelve (n = 12) porcine knees were tested using a robotic testing system. Four knee states were compared: (1) intact ACL, (2) ACL-deficient, (3) anatomic single bundle (SB) ACL reconstruction and (4) anatomic SB ACL reconstruction with a 5-mm notchplasty. The graft was fixed at 60° of flexion (full extension of porcine knee is 30°) with an 80-N tension. The knees were subjected to two loading conditions: an 89-N anterior tibial load (ATT) and 4 Nm internal (IR) and external tibial (ER) rotational torques. The kinematics and in situ force obtained from the different knee conditions were compared.

RESULTS

There were no significant differences between pre- and post-notchplasty in the ER at 30° and 60° of knee flexion (n.s.). However, a significant difference was found between pre- and post-notchplasty in ATT at 30° and 60° of flexion (p < 0.05). The in situ force in the anatomic SB reconstruction with notchplasty was significant lower than the intact and anatomic reconstructed ACL pre-notchplasty at 30°, 60° and 90° of knee flexion (p < 0.05). In response to the IR tibial torque, there were significant differences between pre- and post-notchplasty in IR at 60° (p < 0.05) of knee flexion.

CONCLUSION

Notchplasty had greater effect on anterior stability than rotational stability. This change in knee kinematics could be detrimental to a healing bone graft, ligamentization and could lead to failure of the reconstruction in early post-operative period.

Use of a bioactive scaffold to stimulate anterior cruciate ligament healing also minimizes posttraumatic osteoarthritis after surgery

BACKGROUND

Although anterior cruciate ligament (ACL) reconstruction is the treatment gold standard for ACL injury, it does not reduce the risk of posttraumatic osteoarthritis. Therefore, new treatments that minimize this postoperative complication are of interest. Bioenhanced ACL repair, in which a bioactive scaffold is used to stimulate healing of an ACL transection, has shown considerable promise in short-term studies. The long-term results of this technique and the effects of the bioenhancement on the articular cartilage have not been previously evaluated in a large animal model.

HYPOTHESES

(1) The structural (tensile) properties of the porcine ACL at 6 and 12 months after injury are similar when treated with bioenhanced ACL repair, bioenhanced ACL reconstruction, or conventional ACL reconstruction, and all treatments yield results superior to untreated ACL transection. (2) After 1 year, macroscopic cartilage damage following bioenhanced ACL repair is similar to that in bioenhanced ACL reconstruction and less than in conventional ACL reconstruction and untreated ACL transection.

STUDY DESIGN

Controlled laboratory study.

METHODS

A total of 64 Yucatan mini-pigs underwent ACL transection and randomization to 4 experimental groups: no treatment, conventional ACL reconstruction, bioenhanced ACL reconstruction using a bioactive scaffold, and bioenhanced ACL repair using a bioactive scaffold. The biomechanical properties of the ligament or graft were examined and macroscopic assessments of the cartilage surfaces were performed after 6 and 12 months of healing.

RESULTS

The structural properties (ie, linear stiffness, yield, and maximum loads) of the ligament after bioenhanced ACL repair were not significantly different from those in bioenhanced ACL reconstruction or conventional ACL reconstruction but were significantly greater than those in untreated ACL transection after 12 months of healing. Macroscopic cartilage damage after bioenhanced ACL repair was significantly less than that in untreated ACL transection and bioenhanced ACL reconstruction, and there was a strong trend (P = .068) for less macroscopic cartilage damage than in conventional ACL reconstruction in the porcine model at 12 months.

CONCLUSION

Bioenhanced ACL repair produces a ligament that is biomechanically similar to an ACL graft and provides chondroprotection to the joint after ACL surgery.

CLINICAL RELEVANCE

Bioenhanced ACL repair may provide a new, less invasive treatment option that reduces cartilage damage following joint injury.

Scaffolds derived from cancellous bovine bone support mesenchymal stem cells' maintenance and growth

Since bone defects can lead to various disabilities, in recent years, many increasing attempts have been made in bone tissue engineering. In this regard, scaffolds have attracted a lot of attention as three dimensional substrates for cell attachment which improve successful tissue engineering. The aim of the present study was to provide an interconnected porous scaffold to facilitate cell infiltration. To do so, cancellous bone from bovine femur was dissected in fragments and decellularized by physicochemical methods, including snap freeze/thaw, rinsing in hot water and treatment with different solutions of sodium dodecyl sulfate (SDS). Histological analysis and 4',6-diamidino-2-phenylindole staining revealed that the best results were obtained after treatment with 2.5%, 5%, and 8% SDS for 8, 3, or 1 h respectively, which significantly removed bone cells with intact trabeculae geometry. Further characterization of decellularized scaffolds by the compression tests also revealed no significant difference between elastic modulus values of the three different SDS treatments. Moreover, studying the ratio of bone trabeculae to bone surfaces (BT/BS) as assessed by Clemex vision software 3.5 showed that treatment with 2.5% SDS for 8 h resulted in a BT/BS score in the range of native bone and therefore this treatment was used for further experiments. Histological studies and scanning electron microscopy revealed rat mesenchymal stem cells integration, adhesion, and maintenance during the 2 and 7 d of culture in vitro. In conclusion, the present results support the effective role of SDS in cancellous bovine bone decellularization and also propensity of treated samples in providing a suitable three-dimentional environment to support the maintenance and growth of mesenchymal stem cells.

Pediatric ACL injuries: evaluation and management

The anterior cruciate ligament (ACL) is a stabilizing structure to both anterior translation of the tibia with respect to the femur as well as rotation of the knee joint. Children and adolescents are susceptible to these injuries, and there are some who believe the incidence of ACL injuries in this population is increasing due to year round single sport participation. Pediatric ACL injuries are typically seen in several forms: tibial avulsion fractures, partial ACL tears, and full thickness ligament tears. There were and still are some who feel that ACL injuries should be treated non-operatively in the pediatric and adolescent population; however, recent literature refutes this notion. Several factors must be considered during pediatric and adolescent ACL reconstruction, each of which will be examined in this manuscript, including: status of the physis, reconstruction technique, and graft source.

Peripheral blood mononuclear cells enhance the anabolic effects of platelet-rich plasma on anterior cruciate ligament fibroblasts

Use of platelet-rich plasma (PRP) has shown promise in various orthopaedic applications, including treatment of anterior cruciate ligament (ACL) injuries. However, various components of blood, including peripheral blood mononuclear cells (PBMCs), are removed in the process of making PRP. It is yet unknown whether these PBMCs have a positive or negative effect on fibroblast behavior. To begin to define the effect of PBMCs on ACL fibroblasts, ACL fibroblasts were cultured on three-dimensional collagen scaffolds for 14 days with and without PBMCs. ACL fibroblasts exposed to PBMCs showed increased type I and type III procollagen gene expression, collagen protein expression, and cell proliferation when the cells were cultured in the presence of platelets and plasma. However, addition of PBMCs to cells cultured without platelets had no effect. The increase in collagen gene and protein expression was accompanied by an increase in IL-6 expression by the PBMCs with exposure to the platelets. Our results suggest that the interaction between platelets and PBMCs leads to an IL-6 mediated increase in collagen expression by ACL fibroblasts.

Effects of suture choice on biomechanics and physeal status after bioenhanced anterior cruciate ligament repair in skeletally immature patients: a large-animal study

PURPOSE

The objective of this study was to assess the effect of absorbable or nonabsorbable sutures in bioenhanced anterior cruciate ligament (ACL) repair in a skeletally immature pig model on suture tunnel and growth plate healing and biomechanical outcomes.

METHODS

Sixteen female skeletally immature Yorkshire pigs were randomly allocated to receive unilateral, bioenhanced ACL repair with an absorbable (Vicryl) or nonabsorbable (Ethibond) suture augmented by an extracellular matrix-based scaffold (MIACH). After 15 weeks of healing, micro-computed tomography was used to measure residual tunnel diameters and growth plate status, and biomechanical outcomes were assessed.

RESULTS

At 15 weeks postoperatively, there was a significant difference in tunnel diameter with significantly larger diameters in the nonabsorbable suture group (4.4 ± 0.3 mm; mean ± SD) than in the absorbable group (1.8 ± 0.5 mm; P < .001). The growth plate showed a significantly greater affected area in the nonabsorbable group (15.2 ± 3.4 mm(2)) than in the absorbable group (2.7 ± 0.8 mm(2), P < .001). There was no significant difference in the linear stiffness of the repairs (29.0 ± 14.8 N/mm for absorbable v 43.3 ± 28.3 N/mm for nonabsorbable sutures, P = .531), but load to failure was higher in the nonabsorbable suture group (211 ± 121.5 N) than in the absorbable suture group (173 ± 101.4 N, P = .002). There was no difference between the 2 groups in anteroposterior laxity at 30° (P = .5117), 60° (P = .3150), and 90° (P = .4297) of knee flexion.

CONCLUSIONS

The use of absorbable sutures for ACL repair resulted in decreased physeal plate damage after 15 weeks of healing; however, use of nonabsorbable sutures resulted in 20% stronger repairs.

CLINICAL RELEVANCE

Choice of suture type for ACL repair or repair of tibial avulsion fractures may depend on patient skeletal age and size, with absorbable sutures preferred in very young, small patients at higher risk with physeal damage and nonabsorbable sutures preferred in larger, prepubescent patients who may place higher loads on the repair.