Collagen fibril populations in human anterior cruciate ligament allografts. Electron microscopic analysis

Machine learning to mechanically assess 2D and 3D biomimetic electrospun scaffolds for tissue engineering applications: Between the predictability and the interpretability

Currently, the use of autografts is the gold standard for the replacement of many damaged biological tissues. However, this practice presents disadvantages that can be mitigated through tissue-engineered implants. The aim of this study is to explore how machine learning can mechanically evaluate 2D and 3D polyvinyl alcohol (PVA) electrospun scaffolds (one twisted filament, 3 twisted filament and 3 twisted/braided filament scaffolds) for their use in different tissue engineering applications. Crosslinked and non-crosslinked scaffolds were fabricated and mechanically characterised, in dry/wet conditions and under longitudinal/transverse loading, using tensile testing. 28 machine learning models (ML) were used to predict the mechanical properties of the scaffolds. 4 exogenous variables (structure, environmental condition, crosslinking and direction of the load) were used to predict 2 endogenous variables (Young's modulus and ultimate tensile strength). ML models were able to identify 6 structures and testing conditions with comparable Young's modulus and ultimate tensile strength to ligamentous tissue, skin tissue, oral and nasal tissue, and renal tissue. This novel study proved that Classification and Regression Trees (CART) models were an innovative and easy to interpret tool to identify biomimetic electrospun structures; however, Cubist and Support Vector Machine (SVM) models were the most accurate, with R2 of 0.93 and 0.8, to predict the ultimate tensile strength and Young's modulus, respectively. This approach can be implemented to optimise the manufacturing process in different applications.

Time-series biological responses toward decellularized bovine tendon graft and autograft for 52 consecutive weeks after rat anterior cruciate ligament reconstruction

There is an essential demand for developing biocompatible grafts for knee anterior cruciate ligament reconstruction (ACLR). This study investigated cell infiltration into decellularized bovine tendon xenografts using a rat knee ACLR model. Twelve-week-old Sprague–Dawley rats were used. At weeks 1, 2, 4, 8, 16, 26, and 52 (each period, n = 6) after ACLR, rats receiving decellularized bovine tendon (group D, n = 42) or autologous tendon (group A, n = 42) as grafts underwent peritibial bone tunnel bone mineral density (BMD), histological, and immunohistological assessments. BMD increased over time in both the groups until week 16 and then remained unchanged without exhibiting significant differences between the groups. Initially, cellularity in group D was lower than that in group A; however, by weeks 4–8, both the groups were comparable to the native anterior cruciate ligament group and cellularity remained unchanged until week 52. Initially, group A had more M1 macrophages, indicating inflammation, whereas group D had more M2 macrophages, indicating tissue regeneration. Nonetheless, the M1 and M2 macrophage counts of both the groups were comparable at most times. This study revealed the excellent recellularization and tendon–bone integration abilities of decellularized tendons using a cross-species model.

Graft healing after anterior cruciate ligament reconstruction (ACLR)

Anterior cruciate ligament reconstruction (ACLR) is a commonly performed procedure in Orthopaedic sports medicine. With advances in surgical techniques providing better positioning and fixation of the graft, subsequent graft failure to certain extent should be accounted by poor graft healing. Although different biological modulations for enhancement of graft healing have been tried in different clinical and animal studies, complete graft incorporation into bone tunnels and the “ligamentization” of the intra-articular part have not been fully achieved yet. Based on the understanding of graft healing process and its failure mechanism, the purpose of this review is to combine both the known basic science & clinical evidence, to provide a much clearer picture of the obstacle encountered in graft healing, so as to facilitate researchers on subsequent work on the enhancement of ACL graft healing.

[A correlation study between the Mohawk expression level and the collagen fiber diameter of hamstring tendon graft after anterior cruciate ligament reconstruction]

OBJECTIVE

To evaluate the correlation between the Mohawk (MKX) expression level and the collagen fiber diameter of autologous hamstring tendon graft during the stable graft remodeling phase after anterior cruciate ligament (ACL) reconstruction.

METHODS

Between January 2018 and August 2018, patients who underwent arth-roscopic single-bundle anatomical ACL reconstruction with autologous hamstring tendons for at least 48 months and also underwent second-look arthroscopy were enrolled in study. During the second-look arthroscopic procedures, ACL graft biopsies were performed from the surface of central part of the ligament. MKX expressions of ACL grafts were analysed by real-time fluorescent quantitative PCR (qRT-PCR). The ultrastructure of collagen fibers of grafts were evaluated by transmission electron microscopy, which included average diameter of collagen fibers (D c), average diameter of large-diameter collagen fibers (D L), average diameter of small-diameter collagen fibers (D S), and large-small collagen fibers ratio (R L/S). The correlation between MKX expression level and graft collagen fiber diameter was calculated.

RESULTS

Twenty-six patients met the selection criteria and their ACL graft specimens were enrolled in the study. The interval between ACL reconstruction and second-look arthroscopy was 52-128 months, with an average of 78.6 months. Arthroscopic graft remodeling score was 3-6 (mean, 4.8). There were 17 cases of excellent remodeling and 9 cases of fair remodeling. All ACL grafts showed typical bimodal distributions of both large-diameter collagen fibers and small-diameter collagen fibers, but the ultrastructural characteristics of the graft collagen fibers were different according to different remodeling status under arthroscopy. The D C, D L, D S, and R L/S of the graft specimens were (65.2±9.3) nm, (91.6±10.5) nm, (45.7±8.6) nm, and 0.73±0.12, respectively. The relative expression level of MKX was 1.42±0.11, which was positively linearly correlated with D C, D L, and R L/S, and the correlation coefficient was statistically significant ( r=0.809, P=0.000; r=0.861, P=0.000; r=0.942, P=0.000), while there was no significant correlation between D S and relative expression level of MKX ( r=0.147, P=0.238). Regression analysis showed that the relative expression level of MKX could predict the D C, D L, and R L/S results of the ACL graft specimens ( P<0.05).

CONCLUSION

After autologous hamstring tendon grafts stepped into stabilized remodeling phase, MKX expression level could predict the diameter measurement results of collagen fibers and be used as an important evaluation basis for graft collagen anabolic metabolism.

Quadriceps Tendon Autograft in Anterior Cruciate Ligament Reconstruction: A Systematic Review

PURPOSE

To systematically review the current evidence to ascertain whether quadriceps tendon autograft (QT) is a viable option in anterior cruciate ligament reconstruction.

METHODS

A literature review was conducted in accordance with Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines. Cohort studies comparing QT with bone-patellar tendon-bone autograft (BPTB) or hamstring tendon autograft (HT) were included. Clinical outcomes were compared, with all statistical analyses performed using IBM SPSS Statistics for Windows, version 22.0, with P < .05 being considered statistically significant.

RESULTS

We identified 15 clinical trials with 1,910 patients. In all included studies, QT resulted in lower rates of anterior knee pain than BPTB. There was no difference in the rate of graft rupture between QT and BPTB or HT in any of the studies reporting this. One study found that QT resulted in greater knee stability than BPTB, and another study found increased stability compared with HT. One study found that QT resulted in improved functional outcomes compared with BPTB, and another found improved outcomes compared with HT, but one study found worse outcomes compared with BPTB.

CONCLUSIONS

Current literature suggests QT is a viable option in anterior cruciate ligament reconstruction, with published literature showing comparable knee stability, functional outcomes, donor-site morbidity, and rerupture rates compared with BPTB and HT.

LEVEL OF EVIDENCE

Level III, systematic review of Level I, II, and III studies.

Ligamentization of Autogenous Hamstring Grafts After Anterior Cruciate Ligament Reconstruction: Midterm Versus Long-term Results

BACKGROUND

In previous studies, unimodal, small-diameter collagen fibrils have been commonly observed as the final collagen ultrastructure of the implanted grafts used in anterior cruciate ligament (ACL) reconstruction. However, the native ACL and hamstring tendon show bimodal collagen fibril distribution, consisting of both large- and small-diameter collagen fibrils.

HYPOTHESIS

Bimodal collagen fibril distribution of the graft is a common phenomenon after ACL reconstruction with hamstring tendon grafts and is time dependent.

STUDY DESIGN

Controlled laboratory study.

METHODS

A total of 52 patients who underwent double-bundle ACL reconstruction using autogenous hamstring tendons and who also underwent second-look arthroscopic surgery were enrolled. The patients were divided into 2 groups according to the time interval between the 2 operations: the midterm group (27 patients), with a 13- to 30-month time interval between operations, and the long-term group (25 patients) with a 31- to 62-month interval. During the second-look arthroscopic procedures, ACL graft biopsies were performed. Normal ACL tissues were harvested from 9 patients who underwent total knee replacement, and biopsy specimens of the to-be-grafted semitendinosus tendon tissues were also harvested from another 9 patients who underwent ACL reconstruction with hamstring tendons, which were designated as normal controls. Graft vascularity, cellularity, metaplasia, cellular metabolism, and collagen fibril distribution were analyzed.

RESULTS

Large-diameter (>100 nm) collagen fibrils were detected in 81.5% of the specimens in the midterm group and in 68.0% of the specimens in the long-term group. A typical bimodal distribution mode was observed in 62.6% of the specimens in the midterm group and in 52.0% of the specimens in the long-term group. There was no significant difference between groups with respect to the presence of large-diameter collagen fibrils, bimodal distribution, graft vascularity, cellularity, metaplasia, or cellular metabolic status.

CONCLUSION

Graft ultrastructural maturation, characterized by large-diameter collagen fibrils and a bimodal collagen fibril distribution, is a common phenomenon and is not time dependent in the midterm to long term.

CLINICAL RELEVANCE

After hamstring tendon ACL reconstruction, the implanted grafts can transform into ACL-like tissue with a similar ultrastructure and metabolism, implying their usefulness as grafts.

The Use of a Green Fluorescent Protein Porcine Model to Evaluate Host Tissue Integration into Extracellular Matrix Derived Bionanocomposite Scaffolds

When using heterogeneous extracellular matrix (ECM) derived scaffolds for soft tissue repair, current methods of in vivo evaluation can fail to provide a clear distinction between host collagen and implanted scaffolds making it difficult to assess host tissue integration and remodeling. The purpose of this study is both to evaluate novel scaffolds conjugated with nanoparticles for host tissue integration and biocompatibility and to assess green fluorescent protein (GFP) expressing swine as a new animal model to evaluate soft tissue repair materials. Human-derived graft materials conjugated with nanoparticles were subcutaneously implanted into GFP expressing swine to be evaluated for biocompatibility and tissue integration through histological scoring and confocal imaging. Histological scoring indicates biocompatibility and remodeling of the scaffolds with and without nanoparticles at 1, 3, and 6 months. Confocal microscope images display host tissue integration into scaffolds although nonspecificity of GFP does not allow for quantification of integration. However, the confocal images do allow for spatial observation of host tissue migration into the scaffolds at different depths of penetration. The study concludes that the nanoparticle scaffolds are biocompatible and promote integration and that the use of GFP expressing swine can aid in visualizing the scaffold/host interface and host cell/tissue migration.

Factors affecting return to play after anterior cruciate ligament reconstruction: a review of the current literature

Anterior cruciate ligament reconstruction has been reported to produce normal or near-normal knee results in > 90% of patients. A recent meta-analysis suggested that, despite normal or near-normal knees, many athletes do not return to sports. Rates and timing of return to competitive athletics are quite variable depending on the graft type, the age of the patient, the sport, and the level of play. Even when athletes do return to play, often they do not return to their previous level. Graft failure, subjective physical factors, and psychological factors, including fear of reinjury and lack of motivation, appear to play a large role in patients' ability to return to sporting activities.

Experimental remodellation of extracorporeal irradiated autogenous and allogenic patellar grafts

BACKGROUND

Irradiated autografts have been used to aid the recovery of bone defects, and the results are well documented. Recently, bone allografts with tendinous attachments have been used to restore the function of joints. Similar reconstructions can be performed with irradiated autografts. However, little information is available on the biology of extracorporeal irradiated tendon autografts.

QUESTIONS/PURPOSES

An experimental rabbit model was used to investigate the quality of healing and remodeling of the irradiated autogenous patellar tendon graft after 3 and 12 weeks using immunohistochemical and morphometric analyses.

METHODS

New Zealand rabbits (n = 40) were randomly divided into autograft and allograft groups. The right knees of all animals served as the control (sham). The patellar tendon graft of the control right knee was reimplanted into its original location without any processing, while the patellar tendon of the left knee in the autograft group was reimplanted into the original location after 50 Gy irradiation. In the allograft group, the patellar tendon was sutured to the knee of another rabbit following 50 Gy irradiation. Five rabbits from each group were sacrificed and examined histologically.

RESULTS

There were significant differences in the number of fibroblasts after 12 weeks between allograft and sham groups (P = 0.002). On the other hand, there were no differences between the allograft and autograft groups at the 12th week (P = 0.139). The difference in fibroblast numbers between autograft and allograft groups was statistically significant after the 3rd week (P < 0.05). Collagen fibril thickness was different between both the allograft and sham groups (P = 0.002) and the allograft and autograft groups at the 12th week (P = 0.000). Collagen fibrils were thicker in the sham and autograft groups compared with the allograft group at the 3rd week of evaluation (P < 0.05). The Ki67 index was significantly different between the allograft and sham groups at the 12th week (P < 0.032), while there was no difference between the allograft and autograft groups (P > 0.05). At the 3rd week, Ki67 reactivity was higher in the allograft group compared with the other two groups (P < 0.05).

Double-bundle anterior cruciate ligament reconstruction using bone-patellar tendon-bone allograft: technique and 2- to 5-year follow-up

BACKGROUND

Nonanatomic transtibial single-bundle anterior cruciate ligament reconstruction (SB-ACLR) with a bone-patellar tendon-bone (BPTB) allograft has been used for a long time and has shown the same satisfactory clinical results as an autograft; however, it has not been reported if a double-bundle ACLR (DB-ACLR) could be performed with a BPTB allograft and achieve even better results.

HYPOTHESIS

The DB-ACLR with a BPTB allograft is technically feasible and will be superior to the SB technique in restoring better anterior and rotating stability.

STUDY DESIGN

Cohort study; Level of evidence, 2.

METHODS

The study was performed with 56 patients, and 52 (25 in the DB group and 27 in the SB group) of them were followed up at 2 to 5 years. With an irradiated deep-frozen BPTB allograft, a standard single-incision arthroscopic technique was used, and the graft was fixed with bioabsorbable interference screws on both the femoral and tibial sides. Outcome assessment at final follow-up included International Knee Documentation Committee (IKDC), Tegner, and Lysholm scores; side-to-side difference by conventional KT-2000 arthrometer; total anteroposterior (AP) laxity by the back-pushing KT-2000 arthrometer; pivot shift (0, +, ++); range of motion (ROM); and isokinetic muscle strength evaluation.

RESULTS

Mean follow-up was 47.3 ± 11.5 and 58.2 ± 6.6 months for the DB group and SB group, respectively. A statistically significant difference in favor of the DB group was found with the total AP laxity at 30° (P < .05). The overall incidence of pivot shift in the DB group (4% ++) was significantly lower than that in the SB group (26%: 19% + and 7% ++; P = .029). No significant differences were found between the 2 groups in terms of IKDC score, Lysholm score, Tegner score, conventional KT-2000 arthrometer anterior laxity, ROM, and muscle strength.

CONCLUSION

A DB-ACLR with a BPTB allograft is feasible and achieved more satisfactory results than the transtibial SB technique in terms of total AP stability and rotational stability in spite of no significant differences among other clinical parameters.

The "ligamentization" process in anterior cruciate ligament reconstruction: what happens to the human graft? A systematic review of the literature

BACKGROUND

Surgical anterior cruciate ligament reconstruction using tendon grafts has become the standard to treat the functionally unstable anterior cruciate ligament-deficient knee. Although tendons clearly differ biologically from ligaments, multiple animal studies have shown that the implanted tendons indeed seem to remodel into a ligamentous "anterior cruciate ligament-like" structure.

PURPOSE

The goal of this study was to systematically review the current literature on the "ligamentization" process in human anterior cruciate ligament reconstruction.

STUDY DESIGN

Systematic review.

METHODS

A computerized search using relevant search terms was performed in the PubMed, MEDLINE, EMBASE, and Cochrane Library databases, as well as a manual search of reference lists. Searches were limited to studies examining the healing of the intra-articular portion of the tendon graft based on biopsies of this graft obtained from a living human.

RESULTS

Four studies were determined to be appropriate for systematic review, none of them reaching a level of evidence higher than 3. All reports considered autografts. Biopsy specimens were evaluated by light or electron microscopy and analyzed for vascularization, cellular aspects, and appearance of extracellular matrix. All authors universally agreed that the tendon grafts survive in the intra-articular environment. Based on changes observed in the healing grafts with regard to vascularization, cellular aspects, and properties of the extracellular matrix, different chronologic stages in the ligamentization process were discerned.

CONCLUSION

The key finding of this systematic review is that a free tendon graft replacing a ruptured human anterior cruciate ligament undergoes a series of biologic processes termed "ligamentization." The graft seems to remain viable at any time during this course. Histologically, the mature grafts may resemble the normal human anterior cruciate ligament, but ultrastructural differences regarding collagen fibril distribution do persist. Different stages of the ligamentization process are described, but no agreement exists on their time frame. Problematic direct transmission of animal data to the human situation, the limited number of reports considering the ligamentization process in humans, and the potential biopsy sampling error attributable to superficial graft biopsies necessitate further human studies on anterior cruciate ligament graft ligamentization.

Regeneration and repair of tendon and ligament tissue using collagen fibre biomaterials

Collagen fibres are ubiquitous macromolecular assemblies in nature, providing the structures that support tensile mechanical loads within the human body. Aligned type I collagen fibres are the primary structural motif for tendon and ligament, and therefore biomaterials based on these structures are considered promising candidates for mediating regeneration of these tissues. However, despite considerable investigation, there remains no collagen-fibre-based biomaterial that has undergone clinical evaluation for this application. Recent research in this area has significantly enhanced our understanding of these complex and challenging biomaterials, and is reinvigorating interest in the development of such structures to recapitulate mechanical function. In this review we describe the progress to date towards a ligament or tendon regeneration template based on collagen fibre scaffolds. We highlight reports of particular relevance to the development of the underlying biomaterials science in this area. In addition, the potential for tailoring and manipulating the interactions between collagen fibres and biological systems, as hybrid biomaterial-biological ensembles, is discussed in the context of developing novel tissue engineering strategies for tendon and ligament.

Electron microscopy of the remodelling process in hamstring tendon used as ACL graft

The purpose of the present study was to make a histological analysis of the remodelling process of hamstring tendon graft used as Anterior Cruciate Ligament (ACL). The hamstring graft of eight patients was biopsied at different follow-up times from 1 to 10 years. The specimens were analysed with transmission electron microscopy (TEM) at ultrastructural level comparing them with a native ACL and a native hamstring graft. The hamstring graft was found to undergo ultrastructural changes in terms of number and diameter of fibrils with the major changes occurring in the first 2 years. At longer times after surgery (48 and 120 months) no important further changes were evident and the ultrastructure did not vary substantially from 2 to 10 years. In conclusion, the hamstring tendon used as ACL graft undergoes a transformation process but does not match the ultrastructure pattern of a normal ACL up to 10 years.

Obesity affects collagen fibril diameter and mechanical properties of tendons in Zucker rats

Obesity is currently considered to be a world epidemic and one of the major public health problems in many countries, whose incidence is increasing at alarming rates. Genetically obese Zucker rats are used as a model of obesity and were employed in the present study. Tendons transmit contractile force from muscles to bone, thus permitting articular movement. The objective of our study was to analyze the ultrastructural, biochemical, and biomechanical alterations that occur in the deep digital flexor tendon of obese Zucker rats compared to lean animals. Ultrastructural analysis showed differences in collagen fibril diameter distribution and mass-average diameter between obese and lean animals. Regarding mechanical parameters, there was a significant difference in maximum displacement and strain. Hydroxyproline content was higher in obese animals. In view of the excess weight and peculiar conditions to which the tendon of obese animals is submitted, we concluded that obesity provokes alterations in the composition and organization of tendon extracellular matrix components. These alterations might be related to organizational and structural modifications in the collagen bundles, influencing the mechanical properties of the tendon and the progression to a pathological state.

Comparative and morphological analysis of commonly used autografts for anterior cruciate ligament reconstruction with the native ACL: an electron, microscopic and morphologic study

Ligaments and tendons are similar in composition but differ in proportion and arrangement. Tendons are being used as grafts for the ACL reconstruction. Their microscopic structure has not been sufficiently studied and compared to the native ACL. A null hypothesis was declared stating that the anterior cruciate ligament should be histological, morphologically and functionally different from the tendon grafts used for ACL reconstruction. We investigated similarities and differences of the structure of ACL and tendons used as a graft tissue for ACL reconstruction. In this study, standardized samples of quadriceps, hamstrings (semitendinosus and gracilis) and patellar tendons, and the ACL were harvested from 26 autopsies (average age 36.4) and were investigated using light and electron microscopy, immunohistochemistry and morphometry. The thickness of the collagen fibrils, collagen organization and diameter, the fibril/interstitium ratio, density of fibroblasts and blood vessels, and distribution of the collagen type I, III and V fibrils were analyzed. The semitendinosus showed the highest density of fibroblasts and blood vessels, while the gracilis the highest fibril/interstitium ratio. No differences regarding the thickness of collagen fibrils and distribution of fibrils were found. The ACL had the highest concentration of type III and V collagen fibrils as well as elastic fibers. The histological and ultrastructural appearance of the ACL differs from those of the tendons used as graft, for ACL reconstruction. Its ultrastructure is varied and complex, with its collagen fibers bundles lying in many directions.

Serial evaluation of human anterior cruciate ligament grafts by contrast-enhanced magnetic resonance imaging: comparison of allografts and autografts

PURPOSE

The purpose of this study was to clarify the difference in remodeling between allografts and autografts in anterior cruciate ligament reconstruction.

METHODS

We examined 24 knees with bone-patellar tendon-bone allografts and 20 knees with central-third bone-patellar tendon-bone autografts. Surgical patients from January 1997 to December 2002 were included in the study, and more than 1 year had passed since surgery. The mean postoperative follow-up was 24.0 months in the allograft group and 21.3 months in the autograft group. Patients with a positive Lachman test were excluded. The operative method and postoperative rehabilitation programs were the same. All allografts were provided by Tokai Regional Bone Bank, the only regional bone bank in Japan. Contrast-enhanced magnetic resonance imaging (1.0 T, T1-weighted, sagittal section, infusion of 0.2-mL/kg gadolinium-diethylenetriamine pentaacetic acid [Gd-DTPA]) was performed for all knees at 1, 4, 6, and 12 months after surgery and performed for some knees irregularly thereafter. The signal/noise quotient (SNQ) of grafts was calculated by use of magnetic resonance imaging based on the method of Weiler et al. (2001) as follows: SNQ = (Signal of ACL graft - Signal of quadriceps tendon)/Signal of background.

RESULTS

The SNQ of allografts was significantly lower than for autografts 12 months after surgery. As for the SNQ 1 month after surgery, there was no difference before or after Gd-DTPA infusion in the allografts; however, the SNQ was significantly higher after Gd-DTPA infusion in autografts. The SNQ after Gd-DTPA infusion continued to increase until 12 to 24 months in the allograft group but peaked at 4 or 6 months in the autograft group.

CONCLUSIONS

Compared with autologous tendons, allogeneic tendons have a slower onset and rate of revascularization.

LEVEL OF EVIDENCE

Level III, retrospective comparative study.

"Biological failure" of the anterior cruciate ligament graft

Anterior cruciate ligament (ACL) reconstruction has the best chance for success when the graft undergoes extensive biologic remodeling and incorporation after implantation. There are many factors that can lead to graft failure and possible revision surgery. These include patient selection; surgical technique such as graft placement and tensioning; the use of allograft versus autograft; mechanical factors such as secondary restraint laxity; lack of a correct, carefully controlled post-operative rehabilitation program; and biological factors. When a patient presents with knee instability following ligament reconstruction and there is no history of a new trauma or identifiable technical error, biological failure should be considered. However, the biologic response of the grafted tissue is closely linked to the mechanical and biochemical environment into which the graft is placed. Thus, the "biological failure" of the ACL graft is a complex pathological entity whose cause is not fully understood. Failure may be initiated by early extensive graft necrosis, disturbances in revascularization, problems in cell repopulation and proliferation, and as well difficulties in the ligamentization process. However, further study of the biological characterization of a failed graft placed in a correct mechanical environment is warranted.

Anterior cruciate ligament reconstruction : quadriceps versus patellar autograft

The bone-patellar tendon-bone has been widely used and considered a good graft source. The quadriceps tendon was introduced as a substitute graft source for bone-patellar tendon-bone. We compared the clinical outcomes of anterior cruciate ligament reconstructions using central quadriceps tendon-patellar bone and bone-patellar tendon-bone autografts. We selected 72 patients who underwent unilateral anterior cruciate ligament reconstruction using bone-patellar tendon-bone between 1994 and 2001 and matched for age and gender with 72 patients who underwent anterior cruciate ligament reconstruction using quadriceps tendon-patellar bone. All patients were followed up for more than 2 years. We assessed anterior laxity, knee function using the Lysholm and International Knee Documentation Committee scores, and quadriceps strength, the means of which were similar in the two groups. More patients (28 or 39%) in the bone-patellar tendon-bone group reported anterior knee pain than in the quadriceps tendon-patellar bone group (six patients or 8.3%). Anterior cruciate ligament reconstruction using the central quadriceps tendon-patellar bone graft showed clinical outcomes comparable to those of anterior cruciate ligament reconstruction using the patellar tendon graft, with anterior knee pain being less frequent in the former. Our data suggest the quadriceps tendon can be a good alternative graft choice.

LEVEL OF EVIDENCE

Level III Therapeutic study.

Allografts in the Treatment of Anterior Cruciate Ligament Injuries

Symptomatic knee instability is a common complaint among athletic individuals after a torn anterior cruciate ligament (ACL) of the knee. Allograft ACL reconstruction has gained popularity for primary and revision reconstructions. This graft choice has become popular with good intermediate term results combined with decreased operative times, hospital costs, and improved immediate postoperative pain and function. Intermediate follow-up has demonstrated similar results with autograft reconstructions, without the addition of donor site morbidity. Multiple allograft options exist for ACL reconstruction. The most commonly selected grafts include patellar tendon, Achilles tendon, and tibialis allografts. The use of a tibialis allograft provides a stout graft for reconstruction, while minimizing bone tunnel size. Bone-patella-bone allografts provide bone to bone fixation options with flexibility in tunnel selection sizing.

Periarticular ligament changes following ACL/MCL transection in an ovine stifle joint model of osteoarthritis

Anterior cruciate ligament (ACL) injuries often lead to significant functional impairment, and are associated with increased risk for induction of degenerative joint disease. However, few studies have described the effect of ligament transection on the remaining intact knee ligaments. This study sought to determine specifically what impact combined ACL/medial collateral ligament (MCL) transection had on the remaining intact knee ligaments, particularly from the histological, biochemical, and molecular perspectives. Twenty weeks post-ACL/MCL transection, the cut ends of sheep MCLs were bridged by scar, while the posterior cruciate ligaments (PCLs) and lateral collateral ligaments (LCLs) seemed gross morphologically normal. Water content and cell density increased significantly in the MCL scars and the intact PCLs but were unchanged in the LCLs. Collagen fibril diameter distribution was significantly altered in both MCL scar tissue and uninjured PCLs from transected joints. MMP-13 mRNA levels in MCL scars and PCLs from ligament transected joints were increased, while TIMP-1 mRNA levels were significantly decreased in the PCLs only. This study has shown that some intact ligaments in injured joints are impacted by the injury. The joint appears to behave like an integrated organ system, with injury to one component affecting the other components as the "organ" attempts to adapt to the loss of integrity.

Neoligamentization process of BTPB used for ACL graft: histological evaluation from 6 months to 10 years

Following anterior cruciate ligament (ACL) reconstruction with the middle third part patellar tendon, the graft undergoes histological rearrangement due to biomechanical action, which transforms it into a structure similar to the normal ACL. The purpose of our study was to make a qualitative and quantitative histological evaluation, by transmission electron microscopy (TEM), of the neoligamentization process of a bone-patellar tendon-bone (BTPB) graft used as pro-ACL at different follow-up times. We analysed the ultrastructure of collagen fibrils by focusing on their size and distribution with respect to a normal patellar tendon and a normal ACL used as controls. Our results showed that up to 24 months follow-up, progressive ultrastructural changes towards the normal ACL were observed. At longer times after surgery (48 and 120 months) no further changes were evident and the ultrastructure showed a marked reduction in large fibrils, which was typical of the control patellar tendon, and a significant increase in small fibrils. The ultrastructure seemed to combine fibrils from two different morphological units. The BPTB graft used as ACL underwent a transformation process for up to two years. After that period the transformation ceased and for ten years failed to reach the ultrastructural aspect of a normal ACL. However, from an architectural point of view the graft was slowly transformed into a structure similar to ACL with respect to the different mechanical stresses the ligament has to sustain.

Is the increase in type III collagen of the patellar tendon graft after ligament reconstruction really caused by "ligamentization" of the graft?

To test the hypothesis that extrinsic cells that infiltrate the devitalized patellar tendon (PT) synthesize type III collagen even in the environmental milieu of the native PT, we conducted the present experimental study using the rat in situ frozen-thawed PTs. Tissue culture showed no cell outgrowth from the tendons immediately after the freeze-thaw treatment. Analysis by RT-PCR showed that the expression level of type III procollagen mRNA in the frozen-thawed tendon was significantly higher than that in the sham-operated tendon at 6 and 12 weeks. Immunohistological findings showed positive type III collagen staining around cells that had infiltrated the necrotized tendon at 3, 6, and 12 weeks. In addition, the elastic modulus of the in situ frozen-thawed tendon at 6 weeks was significantly less than that of the sham-operated tendon. The present study indicates that extrinsic cells that had infiltrated the devitalized PT synthesized type III collagen at least for 12 weeks even in the environmental milieu of the native PT. These findings raised the question whether the increase in type III collagen of the PT graft after ACL reconstruction is really caused by "ligamentization," the adaptation of the PT graft to the ACL environment.

Self-Reported Patient Outcomes after ACL Reconstruction with Allograft Tissue

PURPOSE

Self-reported outcomes after primary ACL reconstruction using allograft tissues were compared at > or = 5 yr (group 1) and at 2-4 yr (group 2) after surgery.

METHODS

The IKDC Subjective Knee Evaluation and Current Health Assessment and the Knee Outcome Survey Activities of Daily Living Scale (KOS-ADLS) and the Sports Activity Scale (KOS-SAS) were mailed to 335 consecutive former patients at > or = 2 yr after surgery.

RESULTS

Surveys were completed and returned by 64.6% of former patients. Time after surgery for group 1 (N = 90) and group 2 (N = 116) was 7.8 +/- 2.7 and 2.8 +/- 0.8 yr, respectively. Groups did not differ for IKDC Subjective Knee Evaluation or KOS-ADLS scores, although group 1 displayed a lower mean KOS-SAS score. Pooled IKDC Subjective Knee Evaluation scores were 42.7% normal (A), 22.8% nearly normal (B), 24.8% abnormal (C), or 9.7% severely abnormal (D). Pooled standardized IKDC Subjective Knee Evaluation z scores were -0.80 +/- 1.4 standard deviations below the reported population mean for unimpaired individuals with 33.5% scoring at or above the normative population mean, 28.2% scoring < 1 standard deviation below the normative population mean, 18.8% scoring between 1 and 2 standard deviations below the normative population mean, and 19% scoring > or = 2 standard deviations below the normative population mean. Pooled KOS-ADLS scores were 62.1% (> or = 90%), 18% (89-80%), 10.2% (79-70%), and 9.7% (< 70%). Pooled KOS-SAS scores were 49.5% (102/206, > or = 90%), 25.7% (53/206, 89-80%), 9.7% (20/206, 79-70%), and 15.1% (31/206, < 70%). Groups displayed comparable knee function before injury and at the time of the survey. Pooled knee-function scores decreased from 9.5 +/- 1.6 before injury to 8 +/- 2.5 current function (84% return). Both groups displayed decreases in current sports activity level from strenuous to moderate and frequency from 4-7 to 1-3 times per week.

CONCLUSIONS

Self-reported outcomes did not differ between groups for the IKDC Subjective Knee Evaluation or for the KOS-ADLS score, although group 1 displayed decreased mean KOS-SAS scores, suggesting decreased perceived sporting activity knee function at > or = 5 yr after surgery. Decreased sports activity level and frequency are comparable with self-reported outcome studies after primary ACL reconstruction using autograft tissues.

Self-reported outcomes after anterior cruciate ligament reconstruction: an internal health locus of control score comparison

PURPOSE

The purpose of this study was to evaluate the influence of high or low internal health locus of control (HLOC) scores on knee function and sports activity self-reports.

METHODS

The Multidimensional HLOC Scale, the Knee Outcome Survey (KOS) Activities of Daily Living Scale (ADLS) and Sports Activity Scale (SAS), and the 2000 International Knee Documentation Committee (IKDC) Subjective Knee Evaluation and Current Health Assessment surveys were mailed to 335 subjects at a minimum of 2 years after anterior cruciate ligament reconstruction.

RESULTS

Of the subjects, 198 returned completed surveys at 5.1 +/- 2.9 years after surgery. Compared with the group with low internal HLOC scores, the group with high internal HLOC scores had better KOS-ADLS scores (89.6 +/- 13.7 v 77.4 +/- 23.9, P < .0001), KOS-SAS scores (85.2 +/- 18 v 70 +/- 29, P < .0001), global ADLS ratings (90.7 +/- 12.8 v 77.4 +/- 23.9, P < .0001), global SAS ratings (81.8 +/- 20.6 v 70 +/- 29.4, P < .0001), 2000 IKDC Subjective Knee Evaluation scores (80.9 +/- 17.7 v 68.3 +/- 25.2, P < .0001), and 2000 IKDC Current Health Assessment scores for physical function (90.2 +/- 14 v 80.5 +/- 24.6, P = .001), social function (92.6 +/- 14.8 v 85.8 +/- 21.1, P = .014), bodily pain (80.7 +/- 17.7 v 68.7 +/- 24.6, P < .001), mental health (77.9 +/- 14.2 v 70.6 +/- 19.2, P = .005), and vitality (65.1 +/- 19 v 58.8 +/- 21, P = .04). Current knee function scores (8.7 +/- 1.8 v 7.1 +/- 2.9, P < .0001) and KOS-SAS sports activity level scores (chi(2) = 11.2, P = .01) were also higher in the group with high internal HLOC scores compared with the group with low scores.

CONCLUSIONS

Patients with high internal HLOC scores were more satisfied with knee function.

LEVEL OF EVIDENCE

Level IV, prognostic case series.

Ultrastructural Differences in Cranial Cruciate Ligaments from Dogs of Two Breeds with a Differing Predisposition to Ligament Degeneration and Rupture

Cranial (anterior) cruciate ligament (CCL) samples were obtained from dogs of the Labrador retriever (LR) and greyhound (GH) breeds, of which the former but not the latter is predisposed to CCL rupture. Electron microscopy revealed that the collagen fibril diameters of GHs were larger than those of LRs (P=0.03). Histological examination revealed a "fibrocartilaginous" appearance of CCLs in seven of eight GHs, and, to a lesser extent, in three of eight LRs. The formation of fibrocartilage is clearly not a disadvantage to the healthy racing GH, and cannot be regarded as a pathological degeneration in this breed. It is suggested that fibrocartilage is formed as a beneficial physiological adaptation to the compression of CCLs caused by tensile stress as a result of the tightening of two twisted bands. Fibrocartilage would appear to protect CCLs in the GH, but it may be indicative of a mild degenerative change, which may eventually lead to rupture in the LR.

Treatment of anterior cruciate ligament injuries, part I

Anterior cruciate ligament injuries are common among athletes. Although the true natural history remains unclear, anterior cruciate ligament injuries are functionally disabling; they predispose the knee to subsequent injuries and the early onset of osteoarthritis. This article, the first in a 2-part series, was initiated with the use of the PubMed database and a comprehensive search of articles that appeared between January 1994 to the present, using the keywords anterior cruciate ligament. A total of 3810 citations were identified and reviewed to determine the current state of knowledge about the treatment of these injuries. Articles pertaining to the biomechanical behavior of the anterior cruciate ligament, the prevalence of anterior cruciate ligament injury, the natural history of the anterior cruciate ligament-deficient knee, injuries associated with anterior cruciate ligament disruption, risk factors for anterior cruciate ligament injury, indications for treatment of anterior cruciate ligament injuries, and nonoperative and operative treatments were obtained, reviewed, and served as the basis for part I. Part II, to be presented in another issue of this journal, includes technical aspects of anterior cruciate ligament surgery, bone tunnel widening, graft healing, rehabilitation after reconstruction, and the effect of sex, age, and activity level on the outcome of surgery. Our approach was to build on prior reviews and to provide an overview of the literature for each of the before-mentioned areas of study by summarizing the highest level of scientific evidence available. For the areas that required a descriptive approach to research, we focused on the prospective studies that were available; for the areas that required an experimental approach, we focused on the prospective, randomized controlled trials and, when necessary, the highest level of evidence available. We were surprised to learn that considerable advances have been made during the past decade regarding the treatment of this devastating injury.

The role of macrophages in the tissues regeneration stimulated by the biomaterials

Allogenic grafted tissues are subjected to biodegradation and replaced by the regenerate. To minimize the immune response and improve the rebuilding of tissues there was developed a technology to treat tissues with a cells elimination and dosed out extraction of proteoglycanes (Alloplant. With aim to clarify the role of macrophages in the tissues regeneration resulting implantation the biomaterials 112 rats were injected the allogenic and xenogenic (rabbit's) pulverized biomaterials in the form of suspension. Injections were performed subcutaneously into the animals' back by the base of the tail. The control group (14 rats) were injected a physiologic saline. Animals were killed by ether inhalation on day 2, 4, 7, 14, 30, 90 and 180 and tissue sections were studied by light and electron microscopy. The study showed the key role of the macrophages in resorption of the allogenic biomaterial and formation of the newly-formed tissue. Implantation of the biomaterial induced activity a great number of the mature macrophages, which completely lysed and resorbed the biomaterial particles. Expression TNFalpha was significantly higher whereas expression TGF-beta1 was significantly lower. With xenogenic biomaterial implantation there were less macrophages, their activity was restricted. Macrophages containing large vacuoles with an active endo- and exocytosis were revealed in the allogenic biomaterial implantation and were named 'matrix-forming macrophages'. We may suppose that these macrophages synthesize (or re-synthesize) proteoglycan component of the newly-formed collagen fibers. There was put forward a hypothesis about the two component mechanism of the collagen fibers formation.

Ultrastructural study of the extra-articular Leeds-Keio ligament prosthesis

BACKGROUND

There have been several histological studies of the Leeds-Keio ligament in anterior cruciate ligament reconstruction, but there have been few of the Leeds-Keio ligament in the extra-articular portion.

AIMS/METHODS

To report the histological and ultrastructural findings of two cases of medial patellofemoral ligament reconstruction using the Leeds-Keio ligament, removed 6.1 years and 8.7 years after implantation.

RESULTS

In both cases, the tissue over the Leeds-Keio ligament was a ligament-like tissue. Electron microscopy showed that the diameter of the collagen fibrils in the tissue over the Leeds-Keio ligament was unimodal in the case investigated 6.1 years after implantation but bimodal in the case investigated after 8.7 years.

CONCLUSIONS

The tissue over the Leeds-Keio ligament may continue to grow with prolonged periods of mechanical stress.

Collagen fibril diameter distribution does not reflect changes in the mechanical properties of in vitro stress-deprived tendons

The purpose of this study was to determine if an association exists between the tensile properties and the collagen fibril diameter distribution in in vitro stress-deprived rat tail tendons. Rat tail tendons were paired into two groups of 21 day stress-deprived and 0 time controls and compared using transmission electron microscopy (n = 6) to measure collagen fibril diameter distribution and density, and mechanical testing (n =6) to determine ultimate stress and tensile modulus. There was a statistically significant decrease in both ultimate tensile strength (control: 17.95+/-3.99 MPa, stress-deprived: 6.79+/-3.91 MPa) and tensile modulus (control: 312.8+/-89.5 MPa, stress-deprived: 176.0+/-52.7 MPa) in the in vitro stress-deprived tendons compared to controls. However, there was no significant difference between control and stress-deprived tendons in the number of fibrils per tendon counted, mean fibril diameter, mean fibril density, or fibril size distribution. The results of this study demonstrate that the decrease in mechanical properties observed in in vitro stress-deprived rat tail tendons is not correlated with the collagen fibril diameter distribution and, therefore, the collagen fibril diameter distribution does not, by itself, dictate the decrease in mechanical properties observed in in vitro stress-deprived rat tail tendons.

Electron microscopic evaluation of two-bundle anatomically reconstructed anterior cruciate ligament graft

We investigated the difference in collagen fibrils in the two-bundle anatomically reconstructed anterior cruciate ligament (ACL) and the one-bundle reconstructed ACL. Ten patients with a two-bundle anatomically reconstructed ACL using semitendinosus tendons (Two-ST) were followed for an average of 16 months (7-27 months) and were compared with 15 patients with a one-bundle ACL (One-ST) reconstruction using hamstring tendons followed for an average of 20 months (9-39 months). Biopsy was performed during second-look arthroscopy. The diameter of the collagen fibrils, their density, and the percentage of collagen fibrils were measured using electron micrography. We also investigated biopsy specimens of normal semitendinosus and gracilis tendons from 10 patients. The diameter of the collagen fibrils from hamstring tendons in the Two-ST (45.1 +/- 7.6 nm) was significantly larger than that in the One-ST (40.1 +/- 7.8 nm) ( P < 0.05). The diameter of the collagen fibrils in the normal hamstring tendons was significantly larger than that in the reconstructed ACL with hamstring tendons of the Two-ST and One-ST groups ( P < 0.01). The results of the study revealed that the diameter of collagen fibrils in the Two-ST was significantly greater than that in the One-ST. Hence, the tensile strength of the two-bundle graft may be greater than that of the one-bundle graft.

Anterior cruciate ligament reconstruction using cryopreserved allografts

Primary ACL reconstruction historically has been done using autograft tissues whereas allografts have been limited to revision cases and patients who are older or with lower physical demands because some animal studies suggested a slower biologic incorporation rate. The purpose of the current study was to evaluate the effectiveness of the cryopreserved Achilles tendon allograft in primary ACL reconstruction in a consecutive series of athletes. Fifty consecutive patients with a strenuous or moderate preinjury activity level, as defined by the International Knee Documentation Committee (IKDC), had ACL reconstruction using cryopreserved Achilles tendon allografts secured with bioabsorbable interference screws. Five patients were professional athletes. The average age of the patients was 36 years (range, 17-50 years). A 3- to 5-year followup study was done in all of the patients using the IKDC form. Tunnel widening was measured in the lateral radiographs at the widest level. The overall outcome was normal or nearly normal in 94% of the patients. No failures were reported in this series. Forty-six patients (92%) returned to their same preinjury sport activity level. The average KT-1000 side-to-side difference was 2.3 mm. Average tibial tunnel widening was 2.7 mm (range, 0-6 mm); no significant correlation was observed between increased tunnel size and a fair or poor clinical outcome. This experience shows that favorable results can be obtained with cryopreserved Achilles tendon allografts in athletes in whom avoiding donor site morbidity may be an issue in terms of a prompt return to sport.

Anterior cruciate ligament reconstruction with allograft tendons

Allograft tissue allows reconstruction of the ACL without the donor site morbidity that can be caused by autograft harvesting. Patients who must kneel as a part of their occupation or chosen sport are particularly good candidates for allograft reconstruction. Patients over 45 years of age and those requiring revision ACL surgery can also benefit from the use and availability of allograft tendons. In some cases, patients or surgeons may opt for allograft tendons to maximize the result or morbidity ratio. Despite advances in cadaver screening and graft preparation, there remain risks of disease transmission and joint infection after allograft implantation. Detailed explanation and informed consent is vitally important in cases in which allograft tissue is used.

Future direction of the treatment of ACL ruptures

The future of treatment of the ACL rupture is changing as our understanding of the biology surrounding the ACL continues to increase. It is our expectation that clinically applicable treatments, including the repair of the ACL and the development of a biologically engineered ACL, will occur in the next decade.

Silk matrix for tissue engineered anterior cruciate ligaments

A silk-fiber matrix was studied as a suitable material for tissue engineering anterior cruciate ligaments (ACL). The matrix was successfully designed to match the complex and demanding mechanical requirements of a native human ACL, including adequate fatigue performance. This protein matrix supported the attachment, expansion and differentiation of adult human progenitor bone marrow stromal cells based on scanning electron microscopy, DNA quantitation and the expression of collagen types I and III and tenascin-C markers. The results support the conclusion that properly prepared silkworm fiber matrices, aside from providing unique benefits in terms of mechanical properties as well as biocompatibility and slow degradability, can provide suitable biomaterial matrices for the support of adult stem cell differentiation toward ligament lineages. These results point toward this matrix as a new option for ACL repair to overcome current limitations with synthetic and other degradable materials.

Donor cell survival and repopulation after intraarticular transplantation of tendon and ligament allografts

The specific cells within ligaments and tendons are important to maintain the unique structural and material properties of these tissues. The use of tendon and ligament allografts with living cells for ligament reconstruction would be desirable assuming that these cells would survive after transplantation and continue to function. We assessed the fate of donor cells in fresh allografts of the patellar and anterior cruciate ligaments after transplantation. The cells in these allografts used to reconstruct the anterior cruciate ligament did not survive. This was demonstrated using a DNA probe technique that clearly distinguished donor cells from host cells in the Spanish goat model. The donor cells were replaced by host cells in a rapid manner. The host cells that repopulated the allografts assumed the histologic similarity to the fibroblasts they replace. Simultaneous full-thickness skin transplants in the same animals were not rejected during the interval of rapid loss of donor DNA from the allografts. The absence of rejection of the skin grafts at the one-week interval suggests that no pre-existing antibody associated with an immune reaction was responsible for the rapid loss of DNA in the allografts. The clinical basis for utilizing intra-articular allografts with living donor cells needs further justification to account for their increased expense, more complicated surgical logistics, and higher potential risk of disease transmission.

pN collagen type III within tendon grafts used for anterior cruciate ligament reconstruction

This study measured the amount of immature collagen type III present in tendon rafts obtained from anterior cruciate ligament (ACL) reconstructions. These values were compared with those obtained from control grafts typically used for reconstruction--Achilles, patellar, and fascia lata--and also to the normal ACL. Analyses were performed using a commercially available radioimmunoassay (RIA). The RIA made use of a rabbit polyclonal antibody specific to the amino terminus of procollagen type III. The specificity of the Ab was confirmed by a western blot. Fibril diameter of each of the above samples was measured by transmission electron microscopy (TEM). We thus were able to determine if there was a relationship between pN collagen III content and fibril diameter. The mean amount of pN collagen type III in the normal tendon control group was 0.8 +/- 0.3 ng/microg total protein (range 0.0-2.5 ng/microg). There was significantly greater pN collagen III (16 +/- 3.7 ng/microg total protein) in the grafts containing an average fibril diameter <55 nm than in the normal tendons or ACL (P < 0.05). Grafts with an average fibril diameter >55 nm had similar levels of pN collagen III (1.0 +/- 0.79 ng/microg) as the controls. There was also significantly less pN-collagen III within the functional grafts (5.3 +/- 1.9 ng/microg) as compared to failed grafts, (21.6 +/- 5.1 ng/microg, P < 0.05). These results indicate that incomplete processing of procollagen III may be responsible for some of the ultrastructural alterations seen in tendon grafts. Since ultrastructural organization is believed to influence mechanical properties of these tissues. pN collagen III levels may be a possible indicator of ligament or tendon weakness.

Collagenase degradation decreases collagen fibril diameters--an in vitro study of the rabbit medial collateral ligament

Based on the similarity of fibril diameters in healing and grafted ligaments, it has been speculated that all small fibrils represent newly synthesized collagen. Alternatively, small fibrils in grafts could be due to enzymatic degradation of endogenous large fibrils. This study examined the effect of collagenase on collagen fibril diameters in normal NZW rabbit MCLs. Midsubstance MCL slivers were incubated in buffer for 72 or 144 h for comparison with slivers incubated in buffer containing 4 units/ml bacterial collagenase. The samples were examined under TEM for fibril diameter analysis. Mean fibril diameters of 3-day and 6-day collagenase-treated MCLs were significantly reduced, resembling 40-week scar values. These results suggest that collagenase treatment can alter collagen fibril diameter and shape in normal rabbit MCL, thus it is possible that despite their similarity to ligament scars, that at least some small fibrils in ligament grafts may be enzymatically reduced endogenous fibrils.

Current trends in anterior cruciate ligament reconstruction. Part 1: Biology and biomechanics of reconstruction

With today's increasing emphasis on sporting activities, the incidence of anterior cruciate ligament injuries has also increased. Epidemiologic studies estimate that the prevalence of anterior cruciate ligament injuries is about 1 per 3000 Americans. Management of these injuries has evolved from nonoperative treatment to extracapsular augmentation and primary ligament repair to anterior cruciate ligament reconstruction. Treatment of these injuries has significantly improved over the last few decades with the application of knowledge gained from both basic science and clinical research. This article is composed of two parts. The first part reviews the biology and biomechanics of the injured anterior cruciate ligament and the basic science of reconstruction. In the second part, to be published later, current operative concepts of reconstruction, as well as clinical correlations, are reviewed. Summarizing the latest information on basic scientific as well as clinical studies regarding the anterior cruciate ligament, this article intends to demonstrate the correlation between the application of basic science knowledge and improvement of clinical outcomes.

Collagen fibril diameters in the rabbit medial collateral ligament scar: a longer term assessment

Previous transmission electron microscopic investigations of collagen fibril diameters in rabbit medial collateral ligament (MCL) scars have indicated a homogeneous population of small fibrils for the first 40 weeks of healing. In this study, four 8 mm MCL gap scars were studied at 78 weeks of healing and another three at 104 weeks. Results showed increased heterogeneity in the distribution of fibril diameters in all scars, with the appearance of progressively slightly larger fibrils in 78 and 104 week specimens. All longer term scars still contained roughly 90% small fibrils plus some "patches" of larger fibrils, but there was considerable variation between animals in these proportions. No scar contained the fibril populations typical of uninjured adult rabbit MCLs. These results suggest slow but on-going collagen fibril turnover and remodeling in this gap healing rabbit MCL model via currently unidentified mechanisms.

Alterations of glycosaminoglycans during patellar tendon autograft healing after posterior cruciate ligament replacement. A biochemical study in a sheep model

In each of 30 skeletally mature sheep, the posterior cruciate ligament was replaced in one knee by a free patellar tendon autograft using the central third of the ipsilateral patellar tendon. The healing autograft was compared with the contralateral posterior cruciate ligament and the patellar tendons and posterior cruciate ligaments of nonoperated animals. The content of glycosaminoglycans, chondroitin sulfate disaccharides, and dermatan sulfate disaccharides was assessed biochemically at six periods during the 2 years after surgery. The total glycosaminoglycans and chondroitin sulfate disaccharides in the native posterior cruciate ligament was threefold that in the native patellar tendon. In contrast, the amount of dermatan sulfate disaccharides was similar in both the native tendon and native ligament. In the autograft, glycosaminoglycans and chondroitin sulfate disaccharides increased significantly to about 144% and 172%, respectively, of the contralateral posterior cruciate ligament at Week 104. The dermatan sulfate disaccharides in the autograft also showed a significant increase up to Week 26, followed by a remarkable but not significant decrease until the end of the study. In the contralateral posterior cruciate ligament, the dermatan sulfate disaccharides increased significantly between Weeks 52 and 104. Thus, the amount of dermatan sulfate disaccharides was similar in both the autograft and the contralateral posterior cruciate ligament after 2 years. This study suggests that the patellar tendon autograft did not completely assume the biochemical properties of the posterior cruciate ligament.