The phenomenon of "ligamentization": anterior cruciate ligament reconstruction with autogenous patellar tendon

Reconstruction of the anterior cruciate ligament (ACL) with patellar tendon (PT) is a common procedure for the symptomatic ACL-deficient knee. Questions regarding graft incorporation, viability, and nutrition of the transplanted tissue are of concern. This relates to the graft's response to its new intrasynovial milieu and new physical forces. These factors were studied in a rabbit model of ACL reconstruction using PT and were evaluated with histological and biochemical parameters with respect to time. A histological and biochemical metamorphosis of the grafted PT occurred in this study. Autografts demonstrated a gradual assumption of the microscopic properties of normal ACL; by 30 weeks postoperatively, cell morphology was ligamentous in appearance. Normally, type III collagen is not observed in PT, however, a gradual increase in its concentration was seen in the grafts; by 30 weeks its concentration (10%) was the same as in normal ACL. Similarly, glycosaminoglycans content increased from its normally low level in PT to that found in native ACL. Collagen-reducible crosslink analysis demonstrated that grafted tissue changed from the normal PT pattern of low dihydroxylysinonorleucine (DHLNL) and high histidinohydroxymerodesmosine (HHMD) to the pattern seen in normal ACL (high DHLNL and low HHMD) by 30 weeks. These data suggest that when PT is placed in the anatomic and environmental milieu of the ACL, a "ligamentization" of the grafted tissue results; also the autograft initially depends on synovial fluid nutrition, as revascularization occurs after 6 weeks.     

Origin of replacement cells for the anterior cruciate ligament autograft

A rabbit model for anterior cruciate ligament (ACL) reconstruction using autogenous avascular patellar tendon (PT) was utilized to study the early events of graft incorporation. Histological observations demonstrated that autografts were centrally acellular with a peripheral rim of cells at 2 weeks, a central focal proliferation of cells at 3 weeks, and a cellular homogeneous distribution by 4-weeks postoperation. Graft necrosis followed by cellular proliferation suggested that a different population of cells other than the native PT fibroblasts may be inhabiting the graft. The extrinsic contribution of cells was studied by selective destruction of native PT cells with liquid nitrogen immersion prior to reconstruction of the ACL. The intrinsic contribution of cells was evaluated by sequestration of the PT graft in a semipermeable membrane before it was used to reconstruct the ACL. Histological analysis of tissue that was liquid N2 treated, used as an autograft, and then harvested 3-weeks postoperation revealed fibroblastic incorporation of the graft. In contrast, no cells were observed in semipermeable membrane sequestered autografts. These data suggest that autogenous ACL autografts of PT origin are repopulated by cells of external origin. In vitro control studies that were carried out in parallel demonstrated that PT fibroblasts could survive in tissue culture, but not in the synovial environment of the ACL. This suggests that fibroblasts from different sources have different, tissue-specific nutritional requirements.     

Substitution of the anterior cruciate ligament: a long-term histologic and biomechanical study with autogenous pedicled grafts of the iliotibial band in dogs

This paper reports the experience with anterior cruciate ligament (ACL) substitution by standardized pedicled strips of the iliotibial band, fixed to the tibia and femur with a bone-peg fixation technique. Thirty-two young adult (+/- one year old) Labrador dogs were used for the experiments (58 transplant knees and six controls). The posttransplantation period ranged from day zero to three years postoperatively. Of the transplants, there were five failures. Forty-seven knees served for gross, photographic, and histologic examination. In 17 knees, the transplants were submitted to tensile testing in an Instron testing machine. The behavior of the ACL transplants was as follows: the transplants became necrotic in a short period of time, but after day four, a process of creeping substitution took place. At 12-16 weeks, a newly formed ligament was seen with a striking macroscopic resemblance to the normal ACL. However, its collagen fibers were coarser and more undulant, and they were fixed to the bony interfaces with Sharpey-like fibers. When these rather good-looking ACLs were subjected to mechanical testing and compared with normal ACLs, the results were less satisfactory. Mechanically, the substituted ACLs were 45% less stiff than normal ligaments, the yield point was at one-third, and the ultimate load was 40% of that of a normal ACL (deformation rate, 5 mm/min). Normal ACLs rupture at their tibial insertion. The transplants ruptured intraligamentarily. A striking finding was that the substituted ligament did not derotate when all the other ligamentous and capsular structures were cut. There was no torsional arrangement of their component bundles. Although the substituted ACL has an excellent histological and macroscopic appearance, its mechanical properties are inferior.     

兔异体冻干跟腱移植重建前交叉韧带后胶原表型的变化

目的 观察兔异体冻干跟腱重建前交叉韧带(ACL)后移植物Ⅰ型及Ⅲ型胶原的表达.方法 应用兔异体冻干跟腱重建ACL,手术后3、12、26、52周取移植物,行组织学观察,并应用免疫荧光共聚焦技术(CLSM)检测移植物Ⅰ型及Ⅲ型胶原表达的平均荧光值.结果 术后52周,异体移植物组织形态与正常ACL基本一致;正常ACL细胞周围主要表达I型胶原(57.10±5.04),几乎不表达Ⅲ型胶原(6.09±1.34);术后3周,移植物Ⅲ型胶原阳性表达开始增加,12～26周达到高峰,移植后52周仍有Ⅲ型胶原阳性表达(13.17±2.26),与ACL比较差异有统计学意义(P＜0.05);术后3周,移植物Ⅰ型阳性表达开始减少,12周后逐渐增加,52周Ⅰ型胶原阳性表达(52.69±2.76)仍与正常ACL比较差异有统计学意义(P＜0.01).结论 异体跟腱重建ACL后,重建后移植物组织形态与正常ACL基本一致,但移植物胶原基质组成与正常ACL存在明显差异.     

The adverse effects of sectioning the posterior cruciate ligament in rabbits

This study examined the changes in the structural properties of the femur-anterior cruciate ligament —tibia complex (FATC) and the histologic changes of the anterior cruciate ligament (ACL) following sectioning of the posterior cruciate ligament (PCL) of 20 rabbits. The PCL in the right knee was sectioned through an arthrotomy. The left knee underwent arthrotomy only and was used as a control. The animals were killed 3 and 6 months postoperatively. The tensile properties of the FATCs were tested, and the ACLs were histologically examined using polarized light microscopy and transmission electron microscopy. There were significant decreases in the ultimate load following sectioning of the PCL, although there were no significant changes in the stiffness. There were no significant differences in either the crimp period or the crimp amplitude of the ACL following sectioning of the PCL. There were significant increases in the number of collagen fibrils per square micrometer, and significant decreases in the collagen fibril diameter and proportion of total collagen fibril area per square micrometer following sectioning of the PCL. These findings suggest that isolated PCL injury may cause pathological changes in the ACL and its insertion sites.     

保留残余束支及残端纤维重建前交叉韧带

[目的]探讨保留残余的束支以及断端纤维进行前交叉韧带重建的方法及意义。[方法]关节镜下证实前交叉韧带损伤47例,其中部分束支断裂15例,完全断裂26例,韧带松弛6例。对前交叉韧带部分损伤的束支或韧带松弛者予以保留,对完全断裂的残端不做清理,采用自体四股腘绳肌腱单束重建前交叉韧带,股骨端采用Rigid-Fix固定,胫骨端采用IntraFix固定。[结果]术后均得到随访,时间12~24个月,平均19个月,术后膝关节稳定性增强,Lysholm膝关节功能评分,术前平均68.6分,术后平均94.9分,较术前提高26.3分。Lachman试验阴性43例,弱阳性3例,阳性1例。按Insall膝关节疗效评定标准,优38例,良9例。[结论]保留残余韧带重建ACL,有助于移植肌腱再血管化和本体感觉的建立,有利于维持膝关节的稳定性。     

Hamstring腱在体内重塑与转归的组织学研究

目的探讨游离Hamstring腱作为替代腱重建前十字韧带（anterior cruciate ligament，ACL）后在体内的重塑与转归过程，初步确定其术后在体内成熟的时间。方法33例关节镜下自体同侧游离4-5股Hamstring腱重建ACL的患者在行关节镜下再视手术时，于移植腱体中下段取活检组织进行组织学观察。重建术至再视手术的平均时间为11．9个月。替代腱依据重建术至再视手术的时段分为1月～、4月～、7月～、10月～、13月～、18月～和25月～组。将替代腱与正常ACL和半腱肌腱组织进行对比。结果重建ACL的Hamstring腱随植入时间延长，组织结构呈现其胶原纤维由不规则排列逐步向同向排列，排列不规则的菱形成纤维细胞逐步向较规则排列的椭圆形类纤维细胞转变，且细胞数目逐渐减少，血管腔数目也不断减少。上述的重塑变化主要发现在7月～组以前，其后各组重塑变化过程缓慢。结论自体游离Hamstring腱重建ACL术后具有良好的早期存活、加快再血管化和重塑过程的组织特性。其术后的重塑与成熟过程与自体髌腱相似，自体Hamstring腱在体成熟的时间为7-9个月。     

Anterior cruciate ligament reconstruction: Allograft versus autograft

Purpose: This study was performed to compare the minimal 2-year outcome of anterior cruciate ligament (ACL) reconstruction using bone–patellar tendon–bone (BPTB) allografts versus autografts, both augmented with an iliotibial band tenodesis. Type of Study: Retrospective review. Methods: Forty-six of 52 BPTB ACL reconstructions using allografts and 33 of 37 BPTB ACL reconstructions using autografts were followed up at a mean of 2.75 and 3.36 years, respectively. All patients had an iliotibial band tenodesis. Evaluations included the Lysholm II scale, a questionnaire, physical examination findings, and KT-1000 arthrometry. Results: No statistically significant differences were seen between groups in Lysholm II scores or in any subjective category. Most patients (91% allograft; 97% autograft) had good to excellent Lysholm II scores. Sixty-five percent of allograft patients and 73% of autograft patients returned to their preinjury activity level. More allograft patients complained of retropatellar pain (16% v 9% for autograft patients). Fifty-three percent of allograft patients versus 23% of autograft patients had a flexion deficit of 5° or more when compared with the normal contralateral side. When comparing KT-1000 side-to-side differences, we found no significant differences between groups. Ninety-one percent of both groups had maximum side-to-side differences less than 5 mm. Three allograft patients (6.5%) had traumatic ruptures at 12, 19, and 43 months postoperatively versus none in the autograft group. All three allograft patients who sustained postoperative traumatic ruptures had received fresh frozen, nonirradiated allografts. Conclusions: Results of ACL reconstruction using allografts or autografts augmented with an iliotibial band tenodesis were comparable. The BPTB autograft should remain the gold standard, although the BPTB allograft in ACL reconstruction is a reasonable alternative.Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 19, No 5 (May-June), 2003: pp 453–462     

Small Size Autograft versus Large Size Allograft in Anterior Cruciate Ligament Reconstruction

BackgroundA small autograft diameter negatively affects functional outcomes, knee stability, and the risk of rerupture after anterior cruciate ligament (ACL) reconstruction, whereas the strength of allograft decreases over time. Therefore, it is not clear whether the use of smaller autografts or the use of larger allografts in ACL yields better results. The aim of this study was to compare the outcome of smaller autografts and larger allografts for ACL reconstruction.MethodsFifty-one patients who underwent ACL reconstruction with hamstring tendon autografts (size ≤ 8 mm) and 21 patients who underwent ACL reconstruction with allografts (size ≥ 10 mm) were included in our study. All patients underwent the same aggressive early postoperative rehabilitation program. There were no significant differences between the autograft and allograft groups regarding the preoperative patient age, sex, time from injury to surgery, and average follow-up time.ResultsThe mean diameter of the 4-stranded hamstring tendon grafts used as autografts was 7.48 ± 0.33 mm and the mean diameter of the allografts was 10.76 ± 0.67 mm. According to specific tests for the ACL (anterior drawer, Lachman, and pivot shift) and clinical evaluation tests (Lysholm knee scoring scale and International Knee Documentation Committee questionnaire), the final follow-up results were significantly better than the preoperative status in both autograft and allograft ACL reconstruction groups. Therefore, there were no significant differences between the autograft and allograft groups preoperatively and at the final follow-up.ConclusionsThe large size of the graft in ACL reconstruction has been reported to affect results positively. However, in our study, we could not find any significant differences between the smaller size autografts and larger size allografts in terms of inadequacy, rerupture, and final follow-up functional results. Although allografts were significantly larger than autografts, we did not have the positive effect of larger size grafts. Smaller size autografts were as effective as the larger size allografts.     

The morphological effects of synthetic augmentation in posterior cruciate ligament reconstruction

The treatment of posterior cruciate ligament (PCL) injuries remains controversial. Due to various problems, PCL reconstruction has not consistently produced the knee stability desired. Biological graft tissue undergoes a remarkable healing process comprising different phases. The strength of autogenous graft material decreases soon after operation. During this early healing phase synthetic augmentation could protect the graft tissue from overloading or overstretching, supporting the tissue revitalization and remodeling process. In order to evaluate the morphological effects of the ligament augmentation device (LAD) on a free patellar tendon autograft in PCL reconstruction, a comparative study in sheep was conducted. In 24 mature sheep, the PCL was replaced with either a patellar tendon autograft alone or a patellar tendon autograft augmented by the LAD. The LAD was fixed at both ends. After the operation the animals were not immobilized. Tibial fixation was released 8 weeks postoperation. The autografts of both groups were histologically evaluated after 2, 6, 16, 26, 52, and 104 weeks. In addition to necrotic and degenerative alterations, a remarkable inflammatory reaction could be seen in the LAD-augmented autografts early postoperation. Compared with the nonaugmented autografts, tissue formation and remodeling were delayed in the augmented group. After 1 and 2 years, the morphology of the autograft tissue was similar in both the augmented and nonaugmented group and differed from that of a normal PCL. The LAD was surrounded by a chronic inflammatory reaction, and collagen fiber ingrowth into the LAD was not observed. Using transmission electron microscopy, small diameter collagen fibrils were predominant in the graft tissue of both groups. Thus, a better remodeling of the autograft tissue in the presence of the LAD could not be demonstrated in this particular study. The value of synthetic augmentation of biological grafts in PCL reconstruction seems to be questionable at present.Supported by the Deutsche Forschungsgemeinschaft     

Evaluation of bone incorporation of patellar tendon autografts and allografts for ACL reconstruction using CT

Anterior cruciate ligament (ACL) reconstruction is a relatively common orthopedic procedure, with patellar tendon frequently a graft source. However, controversy exists regarding the decision to use autograft or allograft patellar tendon tissue. This experimental study used computed tomography (CT) to compare the percentage of bone graft incorporation following ACL reconstruction using autografts and allografts. Fifty consecutive patients undergoing ACL reconstruction were included in the study. The tibial bone plug was imaged with CT 1 week, 2 months, and 5 months postoperatively. Four images from each completed scan were analyzed for percentage of incorporation of the bone graft. The results of autograft and allograft incorporation for each of the time intervals were compared. No statistically significant difference was found in the amount of bone incorporation at the tibial bone plug 1 week, 2 months, and 5 months. Clinical concerns regarding slower or less complete healing of allograft bone tissue compared to autograft are not supported with regard to the grafts studied.     

Healing phases in autogenous posterior cruciate ligament replacement. A decision aid for after-care. A biomechanical and histologic study

In a sheep model for reconstruction of the posterior cruciate ligament using the central one-third of the autogenous patellar tendon and immediate mobilization, the incorporation course was studied biomechanically, histomorphometrically and radiographically at eight different points in time up to 1 year after surgery. Four different phases of autograft healing were demonstrated on the basis of the histological events. The biomechanical data were correlated with the morphological findings. Phase 1--necrosis--was characterized by a maximum of necrotic autograft tissue 2 weeks postoperatively. Initially, graft strength was determined by the surgical fixation strength. During phase 2--revitalization--the autograft showed cellular proliferation and revascularization, starting from the periphery. The autograft was determined to be weakest during this phase. Phase 3--collagen formation--revealed a marked increase in newly formed collagen tissue between weeks 12 and 16. A significant increase in maximum load and stress was measured. In phase 4--remodeling--the longest phase, the collagen tissue appeared more compact and less cellular. The fiber bundles were arranged more longitudinally. However, the biomechanical properties remained clearly below that of a normal posterior cruciate ligament.     

Histologic analysis of the tibial bone tunnel after anterior cruciate ligament reconstruction using solvent-dried and gamma-irradiated fascia lata allograft

Anterior cruciate ligament (ACL) reconstruction using free tendon graft requires biologic fixation in the bone tunnel. This report describes the intratunnel histology retrieved from a 47-year-old woman who underwent high tibial osteotomy 17 months after ACL reconstruction using a hybrid graft (a solvent-dried and gamma-irradiated fascia lata allograft as a core wrapped with iliotibial autograft). The patient underwent revision because of pain resulting from osteoarthrotic change, and the graft appeared to be taut and healthy on second-look arthroscopy. The sample was taken from the site of the metaphyseal osteotomy site. Histologic examination of the samples was performed with a light microscope (H&E and Masson trichrome stain). Biologic fixation of the graft to the bone was evident from observation of collagen fiber continuities, resembling Sharpey fibers. Integration of the autograft and allograft seemed to have occurred; the junction between the allograft and the autograft could not be determined. However, there was a difference in ligamentization depending on location. In the peripheral region of the graft (the autograft region), the collagen fibers showed a distinct crimped pattern; the fibroblasts were arranged regularly along the major axis of the collagen fiber bundle. In the central part of the graft (the allograft region), remodeling seemed to be delayed. There were acellular, bubbly or myxoid degeneration areas in which the fiber bundles were less oriented and there was increased vascularity.Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 17, No 8 (October), 2001: E32     

Donor-site morbidity and anterior knee problems after anterior cruciate ligament reconstruction using autografts

The authors review the current knowledge on donor site–related problems after using different types of autografts for anterior cruciate ligament (ACL) reconstruction and make recommendations on minimizing late donor-site problems. Postoperative donor-site morbidity and anterior knee pain following ACL surgery may result in substantial impairment for patients. The selection of graft, surgical technique, and rehabilitation program can affect the severity of pain that patients experience. The loss or disturbance of anterior sensitivity caused by intraoperative injury to the infrapatellar nerve(s) in conjunction with patellar tendon harvest is correlated with donor-site discomfort and an inability to kneel and knee-walk. The patellar tendon at the donor site has significant clinical, radiographic, and histologic abnormalities 2 years after harvest of its central third. Donor-site discomfort correlates poorly with radiographic and histologic findings after the use of patellar tendon autografts. The use of hamstring tendon autografts appears to cause less postoperative donor-site morbidity and anterior knee problems than the use of patellar tendon autografts. There also appears to be a regrowth of the hamstring tendons within 2 years of the harvesting procedure. There is little known about the effect on the donor site of harvesting fascia lata and quadriceps tendon autografts. Efforts should be made to spare the infrapatellar nerve(s) during ACL reconstruction using patellar tendon autografts. Reharvesting the patellar tendon cannot be recommended due to significant clinical, radiographic, and histologic abnormalities 2 years after harvesting its central third. It is important to regain full range of motion and strength after the use of any type of autograft to avoid future anterior knee problems. If randomized controlled trials show that the long-term laxity measurements following ACL reconstruction using hamstring tendon autografts are equal to those of patellar tendon autografts, we recommend the use of hamstring tendon autografts because there are fewer donor-site problems.Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 17, No 9 (November-December), 2001: pp 971–980     

Effectiveness of lateral slide exercise in an anterior cruciate ligament reconstruction rehabilitation home exercise program

STUDY DESIGN: Two-group repeated measures design using a sample of convenience of subjects with anterior cruciate ligament (ACL) reconstructive surgery. OBJECTIVES: To determine the effect of incorporating one specific weight-bearing exercise (lateral slide exercise using a slide board) into an ACL reconstruction home exercise program. BACKGROUND: Reduced clinic visits have increased the importance of home exercise programs in knee ligament reconstruction rehabilitation. Few studies have been conducted to test the efficacy of specific exercises as part of a home-based treatment program on subjects who have undergone ACL reconstruction. METHODS AND MEASURES: Fourteen subjects who underwent patella tendon autograft reconstruction on one of their ACLs were studied. Testing consisted of the following 4 measurements: peak isometric knee extension torque, peak isometric knee flexion torque, maximum lateral step height, and lateral step-up repetitions to fatigue. Subjects were pretested at 8 weeks after surgery and were randomly placed into either a control or experimental group. The postsurgical rehabilitation was similar for both groups, except the experimental group incorporated lateral slide exercise into their home exercise program. All subjects were re-evaluated 14 weeks after surgery. RESULTS: A 2-way repeated measure ANOVA (group by test session), and posthoc testing revealed significant improvements in the slide group for quadricep strength (101.9 +/- 31.3 N m to 140.5 +/- 31.3 N m of torque), while the control group showed no significant increase (125.1 +/- 61.7 N m to 125.8 +/- 45.1 N m of torque). Lateral step height also improved in the slide group (from 22.9 +/- 5.3 cm to 28.7 +/- 5.6 cm), while the control group showed no increase (20.0 +/- 4.5 cm to 20.7 +/- 3.4 cm). Both groups increased in lateral step-up repetitions to fatigue. CONCLUSION: Including lateral slide exercise in a home exercise program after ACL reconstruction appears to improve knee extension strength.     

Collagen-platelet rich plasma hydrogel enhances primary repair of the porcine anterior cruciate ligament.

The anterior cruciate ligament (ACL) fails to heal after suture repair. One hypothesis for this failure is the premature loss of the fibrin clot, or provisional scaffolding, between the two ligament ends in the joint environment. To test this hypothesis, a substitute provisional scaffold of collagen-platelet rich plasma (PRP) hydrogel was used to fill the ACL wound site at the time of suture repair and the structural properties of the healing ACLs evaluated 4 weeks after surgery. Bilateral ACL transections were performed in five 30-kg Yorkshire pigs and treated with suture repair. In each animal, one of the repairs was augmented with placement of a collagen-PRP hydrogel at the ACL transection site, while the contralateral knee had suture repair alone. In addition, six control knees with intact ACLs from three additional animals were used as a control group. No postoperative immobilization was used. After 4 weeks the animals underwent in vivo magnetic resonance imaging to assess the size of the healing ACL, followed by biomechanical testing to determine tensile properties. The supplementation of suture repair with a collagen-PRP hydrogel resulted in significant improvements in load at yield, maximum load, and linear stiffness at 4 weeks. We conclude that use of a stabilized provisional scaffold, such as a collagen-PRP hydrogel, to supplement primary repair of the ACL can result in improved biomechanical properties at an early time point. Further studies to determine the long-term effect of primary repair enhancement are needed.     

Bone–patellar tendon–bone autograft versus LARS artificial ligament for anterior cruciate ligament reconstruction

The optimized graft for use in anterior cruciate ligament (ACL) reconstruction is still in controversy. The bone–patellar tendon–bone (BPTB) autograft has been accepted as the gold standard for ACL reconstruction. However, donor site morbidities cannot be avoided after this treatment. The artificial ligament of ligament advanced reinforcement system (LARS) has been recommended for ACL reconstruction. The purpose of this study is to compare the midterm outcome of ACL reconstruction using BPTB autografts or LARS ligaments. Between July 2004 and March 2006, the ACL reconstruction using BPTB autografts in 30 patients and LARS ligaments in 32 patients was performed. All patients were followed up for at least 4 years and evaluated using the Lysholm knee score, Tegner score, International Knee Documentation Committee (IKDC) score, and KT-1000 arthrometer test. There were no significant differences between the two groups with respect to the data of Lysholm scores, Tegner scores, IKDC scores, and KT-1000 arthrometer test at the latest follow-up. Our study demonstrates that the similarly good clinical results are obtained after ACL reconstruction using BPTB autografts or LARS ligaments at midterm follow-up. In addition to BPTB autografts, the LARS ligament may be a satisfactory treatment option for ACL rupture.     

Editorial Commentary: Reduce the Failure Risk: A Challenge to Reduce the Risk of Using Hybrid Graft in Anterior Cruciate Ligament Reconstruction

Hybrid grafting (augmentation of small hamstring autografts with allograft tissue) is preferred by many surgeons for anterior cruciate ligament (ACL) reconstruction. Although a recent, well-conducted, systematic review reported no significant differences in failure risk between hybrid graft and autograft ACL reconstruction, a trend toward a greater failure risk using the hybrid graft existed in many of the included studies. Three potential causes of hybrid graft ACL reconstruction failure that are absent in autograft ACL reconstruction are different levels of graft revascularization and ligamentization, differences in the tendon-bone healing capacity between the allograft and autograft portions in the bone tunnel, and processing of the graft. Research advances in these areas will further reduce the failure risk of hybrid graft ACL reconstruction.     

In vivo anterior cruciate ligament elongation in response to axial tibial loads

Background  The knowledge of in vivo anterior cruciate ligament (ACL) deformation is fundamental for understanding ACL injury mechanisms and for improving surgical reconstruction of the injured ACL. This study investigated the relative elongation of the ACL when the knee is subject to no load (<10 N) and then to full body weight (axial tibial load) at various flexion angles using a combined dual fluoroscopic and magnetic resonance imaging (MRI) technique. Methods  Nine healthy subjects were scanned with MRI and imaged when one knee was subject to no load and then to full body weight using a dual fluoroscopic system (0°–45° flexion angles). The ACL was analyzed using three models: a single central bundle; an anteromedial and posterolateral (double functional) bundle; and multiple (eight) surface fiber bundles. Results  The anteromedial bundle had a peak relative elongation of 4.4% ± 3.4% at 30° and that of the posterolateral bundle was 5.9% ± 3.4% at 15°. The ACL surface fiber bundles at the posterior portion of the ACL were shorter in length than those at the anterior portion. However, the peak relative elongation of one posterolateral fiber bundle reached more than 13% whereas one anteromedial fiber bundle reached a peak relative elongation of only about 3% at 30° of flexion by increasing the axial tibial load from no load to full body weight. Conclusions  The data quantitatively demonstrated that under external loading the ACL experiences nonhomogeneous elongation, with the posterior fiber bundles stretching more than the anterior fiber bundles.     

Cell survival following bone-anterior cruciate ligament-bone allograft transplantation: DNA fingerprints, segregation, and collagen morphological analysis of multiple markers in the canine model

Bone-anterior cruciate ligament-bone allograft transplantation has become recognized as a potential solution to reconstruction of the anterior cruciate ligament (ACL). The purpose of this study was to determine the time-dependent fibrocyte donor cell survival rate after cryopreserved bone-ACL-bone allograft transplantation. Additionally, bony incorporation of the pediculated bone plugs was examined. The ability to successfully transplant allogenous ACL fibrocytes and have them survive has not previously been documented. In this study, DNA fingerprints identified and documented the survival rate of the cellular DNA in transplanted ACL allografts for ACL reconstruction in the knee joints of 10 skeletally mature dogs. At 4, 8, 26 and 52 weeks after ACL allograft transplantation, DNA probes, H & E, Giemsa, Goldner, PAS and polarized light staining was done to demonstrate the time-dependent changes in the allografts after transplantation. At 4 weeks host fibrocytes began to grow into the graft; however, histologically the cells could not be distinguished as to host or donor origin. After 4 weeks the DNA pattern reflected only the band pattern of the host. This reveals the early cellular infiltration activity of the host into the ACL allograft, also demonstrated in the light microscopy stainings. The survival rate of transplanted allogenous ACL fibrocytes had not been documented before this study. There is no evidence that ACL allograft cells survive in the intra-articular environment of the host’s knee. Within 4 weeks ACL allografts became completely repopulated with host cells. The cells that migrate early into the ACL allografts are probably of synovial origin because they are present before revascularization and collagen reorganization occur. We conclude from this study that viable cells in transplanted ACL allografts did not survive longer than 4 weeks after intra-articular transplantation. Advances in molecular biology may offer new approaches to alter or stimulate fibrocyte population and function in the transplanted ACL allograft used for ACL reconstruction. New methods to maintain the viability of donor cells may be necessary to improve the biomechanical and histological properties of autografts or allografts for ACL reconstruction. Received: 21 April 1997