自体半腱肌腱股薄肌腱重建前交叉韧带术后肌腱再生的临床研究

目的 :应用超声仪观察切取半腱肌腱股薄肌腱重建前交叉韧带后肌腱的再生情况。方法 :39例用自体半腱肌腱股薄肌腱重建前交叉韧带患者 ,术后平均 13个月行双侧半腱肌腱股薄肌腱超声检查 ,了解肌腱再生情况并对比其长度和截面积的变化。结果 :超声检查显示 39例患者中有肌腱再生 2 6例 ,再生率为 72 %。再生肌腱长度和截面积与对侧肌腱相比无明显差异。 2 6例患者半腱肌腱股薄肌肌腹有萎缩。结论 :切取半腱肌腱股薄肌腱重建前交叉韧带后肌腱能够再生。     

Magnetic resonance imagination of the peroneus longus tendon after anterior cruciate ligament reconstruction

Several studies report that tendons can regenerate after harvesting. These studies have been performed especially in patellar and hamstring tendons. At our institution, 10 cm length of full thickness peroneus longus tendon has been harvested to reconstruct torn anterior cruciate ligament since 1997 as a different graft source. The aim of this study was to investigate whether the peroneus longus tendon used the anterior cruciate ligament reconstruction has a regeneration potential or not. Twelve patients, who had originally undergone harvesting of the peroneus longus tendon for the primary surgery of the anterior cruciate ligament reconstruction, underwent magnetic resonance imaging (MRI). Images of both legs were acquired simultaneously with the use of the scanner’s extremity coil, as we aimed to compare harvested peroneus longus tendon with the other leg’s peroneus longus tendon (healthy side) for evaluation of the regeneration potential. The average age of the patients was 31 years. There were eight right and four left legs. The average time interval was 52 months between ligament surgery and MRI. In all patients, a varying amount of the regeneration of the peroneus longus tendon was seen on the MRI images. Although the extent of PLT regeneration in proximal sections seemed better than in mid- and distal sections, there was no statistical difference between sections (P = 0.130). These data show that the peroneus longus tendon has a regeneration potential after harvesting for anterior cruciate ligament reconstruction.     

Regeneration of the hamstring tendons after harvesting for arthroscopic anterior cruciate ligament reconstruction: a histological study in 11 patients

The purpose of our study is to evaluate whether the hamstring tendons can regrow after harvesting for anterior cruciate ligament (ACL) reconstruction and whether the regenerate tissue can be histologically characterized as tendinous. Eleven of the patients (eight female and three male; mean age, 23 years; range 17–37 years) consented to participate in this study. One year after the ACL reconstruction, surgical biopsy was done. Regeneration of the tendon was detected macroscopically in 9 of the 11 patients. Histologically and immunohistochemically, the regenerated tendons closely resembled normal ones. The results of this study show the hamstring tendons can regenerate after harvesting for the ACL reconstruction.     

The "ligamentization" process in human anterior cruciate ligament reconstruction with autogenous patellar and hamstring tendons: a biochemical study

BACKGROUND: There is little information documenting whether the phenomenon of "ligamentization," as proposed by Amiel, occurs in the human anterior cruciate ligament after clinically effective reconstruction. To clarify this point, we analyzed biochemical differences between the native anterior cruciate ligament; the patellar, semitendinosus, and gracilis tendons; and anterior cruciate ligaments reconstructed with autografts. STUDY DESIGN: Cohort study; Level of evidence, 2. METHODS: Fifty patients who underwent arthroscopically assisted anterior cruciate ligament reconstruction using either semitendinosus and gracilis tendon or bone-patellar tendon-bone autografts were selected for the study. Samples of grafted tissue were collected during arthroscopy and quantitatively analyzed for collagen content and the amount of reducible and nonreducible crosslinks at 4 to 6 postoperative months in patients with semitendinosus and gracilis tendon grafts and at 11 to 13 months in all patients with semitendinosus and gracilis tendon or bone-patellar tendon-bone grafts. RESULTS: The total collagen content and nonreducible/reducible crosslink ratios increased significantly during the postoperative period (P < .05). The dihydroxylysinonorleucine/hydroxylysinonorleucine ratio was 3.11 +/- 0.56 in the native anterior cruciate ligament, 1.21 +/- 0.47 in the patellar tendon, and 3.59 +/- 1.58 in the anterior cruciate ligaments reconstructed with bone-patellar tendon-bone autografts 1 year after surgery. The dihydroxylysinonorleucine/hydroxylysinonorleucine ratio in both semitendinosus and gracilis tendons was less than 1.0. However, in anterior cruciate ligaments reconstructed with semitendinosus and gracilis tendon autografts, it was 2.34 +/- 0.98 at 4 to 6 months and 3.43 +/- 1.61 at 11 to 13 months after the operation. CONCLUSIONS: After anterior cruciate ligament reconstruction with autografts, biochemical characteristics of the graft resembled those of the native anterior cruciate ligament. These findings suggest that, regarding the amount of collagen crosslinks and their architecture, the phenomenon of ligamentization occurs in the successfully reconstructed human anterior cruciate ligament within 1 year after operation.     

The human myotendinous junction: An ultrastructural and 3D analysis study

The myotendinous junction (MTJ) is a specialized structure in the musculotendinous system, where force is transmitted from muscle to tendon. Animal models have shown that the MTJ takes form of tendon finger‐like processes merging with muscle tissue. The human MTJ is largely unknown and has never been described in three dimensions (3D). The aim of this study was to describe the ultrastructure of the human MTJ and render 3D reconstructions. Fourteen subjects (age 25 ± 3 years) with isolated injury of the anterior cruciate ligament (ACL), scheduled for reconstruction with a semitendinosus/gracilis graft were included. Semitendinosus and gracilis tendons were stripped as grafts for the ACL reconstruction. The MTJ was isolated from the grafts and prepared for transmission electron microscopy (TEM) and focused ion beam/scanning electron microscopy. It was possible to isolate recognizable MTJ tissue from all 14 patients. TEM images displayed similarities to observations in animals: Sarcolemmal evaginations observed as finger‐like processes from the tendon and endomysium surrounding the muscle fibers, with myofilaments extending from the final Z‐line of the muscle fiber merging with the tendon tissue. The 3D reconstruction revealed that tendon made ridge‐like protrusions, which interdigitiated with groove‐like indentations in the muscle cell.     

Biochemical properties of collagen from ligaments and periarticular tendons of the human knee

The biochemical properties of collagens from the periarticular connective tissues of the human knee (ligaments, semitendinosus and gracilis tendons, and the iliotibial band) were investigated in subjects ranging from 20 to 70 years of age. Although the total collagen content of most tissues was more than 90% of the dry weight, the anterior cruciate ligament and the iliotibial band had relatively low collagen contents. There were no significant changes in the tissue collagen content with aging. However, the anterior cruciate ligament and the patellar tendon of the 20-year-old subject had a higher content of soluble collagen than the other ligaments and tendons. The iliotibial band of the 20-year-old subject contained more collagen that was soluble by a combination of salt, sodium citrate extractions and pepsin digestion. Dihydroxylysinonorleucine was the major reducible cross-link of collagen from all the ligaments. The amount of dihydroxylysinonorleucine in the anterior cruciate ligament of the 20-year-old subject was much higher than that in the other ligaments. In contrast, the tendons and the iliotibial band contained a large amount of histidino-hydroxymerodesmosine and hydroxylysinonorleucine, while the patellar tendon was the only tendon with a significant content of dihydroxylysinonorleucine. Hydroxypyridinium non-reducible cross-links were more abundant in collagens from ligaments than in collagens from the other tissues. The cross-link study and the analysis of collagen solubility showed that patellar tendon collagen more closely resembled the collagen from the anterior cruciate ligament than that from periarticular tendons. It was also shown that the anterior cruciate ligament contains relatively immature collagen compared with the other ligaments. Our findings may contribute to an improved understanding of the functions of the ligaments and tendons around the knee joint. In addition, the data may provide some useful pointers that will help in selection of periarticular tissues as appropriate substitutes for ligament replacement.     

Evaluation of hamstring strength and tendon regrowth after harvesting for anterior cruciate ligament reconstruction

BACKGROUND: It is generally thought that tissue regeneration and good functional recovery can be expected after anterior cruciate ligament reconstruction using the hamstring tendons. However, persistent strength deficit in deep knee flexion has also been reported. HYPOTHESIS: Morphologic regeneration of the harvested hamstring tendon is not necessarily associated with its functional recovery. STUDY DESIGN: Retrospective follow-up study. METHOD: Twenty-eight patients who underwent anterior cruciate ligament reconstruction with hamstring graft were evaluated after a minimum period of 2 years. Status of tendon regrowth was assessed by magnetic resonance imaging. To specifically analyze the functional deficit after graft harvest, the isometric hamstring strength was examined in a sitting position at 90 degrees of flexion and a prone position at 90 degrees and 110 degrees of flexion. Then, the strength data were correlated with the extent of tendon regeneration. RESULTS: In 22 of the 28 patients, a regrowth of the semitendinosus tendon was found, whereas regeneration of the gracilis tendon was observed in 13 patients. In the evaluation of hamstring strength, the isometric peak torque was reduced to 86.2%, 54.6%, and 49.1%, respectively, in the aforementioned 3 postures as compared with the contralateral side. CONCLUSIONS: Significant functional deficit of hamstring strength remains regardless of morphologic regeneration.     

Ultrastructural collagen fibril alterations in the patellar tendon 6 years after harvesting its central third

BACKGROUND: Clinically, donor site problems are common, even in the long term after anterior cruciate ligament reconstruction using patellar tendon autograft. However, there is a lack of knowledge in terms of the mid- and long-term ultrastructural appearance of the previously harvested tendon in humans. HYPOTHESIS: The patellar tendon does not regain normal ultrastructure 6 years after harvesting its central third and leaving the defect open. STUDY DESIGN: Case-control study; Level of evidence, 3. METHODS: Thirteen patients were included in the study. Biopsy specimens were obtained from the central and lateral thirds of the patellar tendon under ultrasound guidance 71 months (range, 68-73 months) after the reconstruction. Ten biopsy specimens from other subjects with asymptomatic patellar tendons served as controls. The sections were evaluated using transmission electron microscopy. Longitudinal sections were used for morphological evaluation, and the fibril diameter was measured on the transverse sections and grouped into 5 diameter classes. RESULTS: All control specimens were found to have a compact extracellular matrix with regularly oriented collagen fibrils. Specimens from the lateral part of the harvested tendons displayed a more heterogeneous extracellular matrix. In 3 specimens, the extracellular matrix was different from that of the control specimens. Specimens from the central part of the harvested tendons displayed an even more heterogeneous extracellular matrix, with 8 specimens judged as heterogeneous. The fibril diameter in control specimens displayed the most heterogeneous pattern, and all 5 fibril classes were present. All fibril classes were found in the lateral biopsy specimens from the previously harvested tendons, but the 2 smallest fibril classes (0-30 and 31-60 nm) were significantly more dominant compared with control specimens (P < .0001). In the central specimens from the previously harvested tendons, only the 3 smallest size classes were found (P < .0001 vs controls). CONCLUSION: Six years after harvesting its central third and leaving the defect open, the patellar tendon revealed a "more heterogeneous matrix" with changes in ultrastructural morphology and relative fibril diameter distribution compared with normal control tendon.     

Ultrasonographic and power Doppler evaluation of the patellar tendon ten years after harvesting its central third for reconstruction of the anterior cruciate ligament: comparison of patients without or with anterior knee pain

BACKGROUND: The long-term morphologic changes in the patellar tendon after harvesting its central third for the reconstruction of the anterior cruciate ligament have not been reported. HYPOTHESIS: Sonographic morphologic changes in the harvested patellar tendon are common 10 years after the harvesting procedure. STUDY DESIGN: Retrospective cohort study. METHODS: Thirty-one patients who had undergone an anterior cruciate ligament reconstruction using central-third bone-patellar tendon-bone autograft with a closure of the patellar tendon defect were included in this study. An ultrasonographic and Power Doppler examination was performed at a mean follow-up of 10 years. RESULTS: Ultrasonography of the harvested patellar tendon showed intratendinous calcification in 9 patients, hypoechoic lesion in 20 patients, hyperechoic lesion in 1 patient, and peritendinous changes in 1 patient. Only 3 (9.7%) of the 31 patients had no changes in the harvested patellar tendon. No abnormality was visible in the contralateral (normal) patellar tendons of the 31 patients. The harvested patellar tendon was significantly thicker than the contralateral patellar tendon (P < 0.05). CONCLUSIONS: Sonographic morphologic changes of the patellar tendon were common 10 years after the harvesting procedure, although no evidence of inflammatory process, as could be seen in Power Doppler flow, was found inside of any patellar tendon.     

Magnetic resonance imaging evaluation of the patellar tendon after use of its central one-third for anterior cruciate ligament reconstruction.

Magnetic resonance imaging was used to evaluate the remaining patellar tendon after its central one-third had been harvested for anterior cruciate ligament reconstruction. Twenty patients were studied at either 6 weeks, 4, 6, 9, or 18 months postoperatively. The average thickness, width, cross-sectional area, and signal intensity of the operated and contralateral non-operated tendons were calculated and compared for each magnetic resonance imaging scan. A significant increase in the thickness was noted at all periods of followup, but no change in width occurred despite the defect being closed at the time of surgery. High signal intensity was present in the early periods, which signified edema and scar tissue. Signal intensity decreased at subsequent follow-up periods until at 18 months the operated tendon appeared normal. These findings indicate that the patellar tendon has the potential to regenerate and remodel in the postoperative period.     

The influence of locally applied platelet-derived growth factor-BB on free tendon graft remodeling after anterior cruciate ligament reconstruction

BACKGROUND: Ligaments and tendons do not gain mechanical properties of the native tissue after injury or grafting. PURPOSE: To determine the influence of platelet-derived growth factor on tendon graft remodeling. STUDY DESIGN: Laboratory animal study. METHODS: Forty-eight sheep underwent anterior cruciate ligament reconstruction and were sacrificed after 3, 6, 12, and 24 weeks. In 6 animals at each time point, platelet-derived growth factor was locally delivered via coated sutures. After mechanical testing, tissue samples were taken for histologic, immunohistochemical, and electron microscopy evaluations. RESULTS: With platelet-derived growth factor treatment, cross-sectional area was significantly lower at 3 and 12 weeks. Load to failure was significantly higher at 6 weeks. Tensile stress was significantly higher at 3 and 12 weeks. Crimp length was significantly higher at 3 and 6 weeks. Vascular density was significantly higher at 6 weeks. Electron microscopy showed a significantly higher collagen fibril amount at 12 weeks. Differences in these parameters at other time points were not significant. CONCLUSIONS: There were alterations in several but not all time points. The local application of platelet-derived growth factor alters the tissue's mechanical properties during free tendon graft remodeling after anterior cruciate ligament reconstruction. Growth factors present a promising tool toward the complete mechanical restitution of a healing ligament substitute.     

A radiographic and histologic evaluation of the patellar tendon after harvesting its central third

Nineteen consecutive patients undergoing anterior cruciate ligament reconstruction using the central third of the ipsilateral patellar tendon were included in the study. Serial magnetic resonance images revealed that the donor-site gap in the tendon decreased with time (mean follow-up, 26 months). The thickness was significantly increased compared with the intact contralateral patellar tendon, regardless of when the magnetic resonance imaging was performed. Ultrasonography showed the same findings at a mean follow-up of 26 months. Histologic evaluation of the repair tissue in the central part of the tendon, as well as the tissue in the peripheral part of the patellar tendon at the donor site, revealed a significant increase in cellularity and vascularity as compared with normal control tendons. Thus, 2 years after the harvesting procedure, the patellar tendon displayed significant radiographic and histologic abnormalities. On the basis of these findings, reharvest of the patellar tendon, at least up to 2 years after primary harvest, cannot be recommended.     

Revision anterior cruciate ligament reconstruction with hamstring tendon autograft: 5- to 9-year follow-up

BACKGROUND: The results of revision anterior cruciate ligament reconstruction are limited in the current literature, and no studies have previously documented the outcome of revision anterior cruciate ligament reconstruction using solely hamstring tendon grafts. HYPOTHESIS: Revision anterior cruciate ligament reconstruction with 4-strand hamstring tendon graft affords acceptable results and is comparable to reported outcomes with the bone-patellar tendon-bone graft. STUDY DESIGN: Case series; Level of evidence, 4. METHODS: Fifty-seven consecutive revision anterior cruciate ligament reconstructions with the hamstring tendon graft and interference screw fixation were assessed a mean time of 89 months (range, 60-109 months) after surgery. Assessment included the International Knee Documentation Committee knee ligament evaluation, instrumented laxity testing, and radiologic examination. RESULTS: Of the 50 knees reviewed, 5 (10%) had objective failure of the revision anterior cruciate ligament reconstruction. Of the 45 patients with functional grafts, knee function was normal or nearly normal in 33 patients (73%). An overall grade of normal or nearly normal was found in 56% of patients. The mean side-to-side difference on manual maximum testing was 2.5 mm (range, -1 to 4 mm). Degenerative changes on radiographs were identified in 23% of patients at the time of surgery, increasing to 56% of patients at review. The status of the articular cartilage at the time of revision surgery was the most significant contributor to successful outcome. CONCLUSION: Revision anterior cruciate ligament reconstruction with hamstring tendon graft and interference screw fixation affords acceptable results at a minimum of 5 years' follow-up. Good objective results can be obtained, but subjectively, the results appear inferior to those of primary anterior cruciate ligament reconstruction in the literature, which may be related to the high incidence of articular surface damage in this patient population. We recommend that, when available, hamstring tendon autografts should be considered for revision anterior cruciate ligament reconstruction.     

Reconstruction of anterior cruciate ligament using the doubled tendon graft technique: an experimental study in rabbits

In an attempt to assess reconstruction of the anterior cruciate ligament (ACL) by a new method, 18 New Zealand white rabbits underwent ACL replacement using the medial one-third of the patellar tendon and the semitendinosus tendon, thus partly reproducing the anatomical configuration of the ACL, with the semitendinosus tendon replacing the posterolateral bundle of the ACL and the patellar tendon replacing the anteromedial bundle. The Noulis-Trillat-Lachman test was performed before and after transection of the ACL, after reconstruction and before sacrifice. The animals were divided into four groups and were killed at 3, 6, 12 and 22 weeks after surgery. Femur-ligament-tibia complexes were evaluated postoperatively for gross morphology and histological appearance. The tendons of the first group showed compact parallel fibres with no definitive separation of their bundles and areas of disorganized collagen matrix. Tendons were surrounded by trabecular lamellar bone haphazardly arranged. The tendons of the second, third and fourth groups looked more like normal tendon. The trabecular bone surrounding the tendons formed a tunnel. The Noulis-Trillat-Lachman test result was negative before the procedure, 6.5±0.5 mm on average after transection of the ACL, 1.5±0.6 mm after the procedure, and negative again before sacrifice. The joints of the animals killed at 12 and 22 weeks showed signs of osteoarthritic lesions. Received: 29 May 1997 Accepted: 1 March 1998     

Effect of repeated freezing–thawing on the Achilles tendon of rabbits

The increased use of allograft tissue in the reconstruction of anterior cruciate ligament has brought more focus to the effect of storage and treatment on allograft. The purpose of this study was to observe the effect of histology and biomechanics on Achilles tendon in rabbits through repeated freezing–thawing before allograft tendon transplantation. Rabbit Achilles tendons were harvested and processed according to the manufacture’s protocol of tissue bank, and freezing–thawing was repeated three times (group 1) and ten times (group 2). Those received only one cycle were used as controls. Then, tendons in each group were selected randomly to make for histological observations and biomechanics test. Histological observation showed that the following changes happened as the number of freezing–thawing increased: the arrangement of tendon bundles and collagen fibrils became disordered until ruptured, cells disrupted and apparent gaps appeared between tendon bundle because the formation of ice crystals. There were significant differences between the experimental and control groups in the values of maximum load, energy of maximum load and maximum stress, whereas no significant differences existed in other values such as stiffness, maximum strain, elastic modulus, and energy density. Therefore, repeated freezing–thawing had histological and biomechanical effect on Achilles tendon in rabbits before allograft tendon transplantation. This indicates that cautions should be taken in the repeated freezing–thawing preparation of allograft tendons in clinical application.     

Regeneration of the semitendinosus tendon after its use in anterior cruciate ligament reconstruction: a histologic study of three cases

We describe the histologic course of regenerated tissue simulating the semitendinosus tendon in three patients after anterior cruciate ligament reconstruction with doubled semitendinosus and gracilis tendons. Specimens were retrieved during revision surgery for removal of tibial hardware at 6, 24, and 27 months, respectively. Resisted flexion during physical examination in all patients revealed a "string" on the posteromedial aspect of the knee that was quite evident, suggesting the presence of a regenerated semitendinosus tendon. At surgery, a well-defined fibrous band was identified about 3 cm proximal and medial to the pes anserinus, reproducing the pathway of the native semitendinosus tendon. In the specimen retrieved 6 months postoperatively, a prominent fibroblastic proliferation was observed together with a few vessels surrounded by fibrous tissue; only a few bundles of well-oriented collagen fibers were present, together with scattered rows of spindle-shaped cells. In both of the specimens retrieved 2 years postoperatively, all of the central, thicker portion of each specimen was occupied by well-oriented tendon-like fibers together with uniformly distributed spindle-shaped cells that had the appearance of mature tenocytes arranged in orderly rows. These findings help us to understand the progression of the healing process at the harvest site and the nature of the regenerated semitendinosus tendon, which has previously been investigated only by studies of clinical and functional outcomes and by imaging studies.     

Patellar tendon length after anterior cruciate ligament reconstruction: a comparative magnetic resonance imaging study between patellar and hamstring tendon autografts

Patellar tendon shortening after anterior cruciate ligament reconstruction may be associated with anterior knee pain or patellofemoral arthritis. The present study was designed to compare postoperative changes in patellar tendon length after anterior cruciate ligament reconstruction between patellar tendon and hamstring tendon autograft. Magnetic resonance images of both knees (operated and healthy) and functional outcome were documented at least 1 year postoperatively in 16 patellar tendon harvested patients and in 32 hamstrings harvested patients. Patellar tendon length, patella length and Insall–Salvati ratio were measured. The operated knee values were compared to the respective values of the non-operated control knees. A significant 4.2 mm or 9.7% patellar tendon shortening in patellar tendon group and a non-significant 1.14 mm or 2.6% shortening in hamstrings group was detected. No significant difference was detected in terms of major shortening—patella baja—(6% for the patellar tendon group vs. 0% for the hamsting group). There was no significant difference in anterior knee problems between the two groups as evidenced by the Shelbourne score (94 for the patellar tendon group vs. 98 for the hamsting group). Harvesting of the patellar tendon for anterior cruciate ligament reconstruction resulted in a significant shortening of the remaining tendon. In contrast harvesting of the hamstring tendons did not affect significantly the patellar tendon length. However, the incidence of patella baja and overall functional outcome was not significantly different between the two groups. Paper presented at the 12th ESSKA 2000 Congress, Innsbruck, Austria, 2006 and also presented at the 5th Biennial ISAKOS Congress, Hollywood, FL, USA, 2005.     

A prospective randomized study of patellar versus hamstring tendon autografts for anterior cruciate ligament reconstruction

BACKGROUND: Bone-patellar tendon-bone graft has been the most commonly used graft material in anterior cruciate reconstructions, but there has been increasing use of hamstring tendon grafts. However, no existing clinical studies show adequate support for the choice of one graft over the other. HYPOTHESIS: Hamstring tendons are equally as good as patellar tendon in anterior cruciate ligament reconstructions. STUDY DESIGN: Prospective randomized clinical trial. METHODS: Ninety-nine patients with laxity caused by a torn anterior cruciate ligament underwent arthroscopically assisted reconstruction with graft randomization according to their birth year. Grafts were either bone-patellar tendon-bone with metal interference screw fixation or double-looped hamstring tendons with metal plate fixation. There were no significant differences between the two groups preoperatively or at operation. Standard rehabilitation included immediate postoperative mobilization without a knee brace, protected weightbearing for 2 weeks, and return to full activity at 6 to 12 months. RESULTS: Forty-three patients in the patellar tendon group and 46 patients in the hamstring tendon group were available for clinical evaluation at a minimum of 21 months after surgery. No statistically significant differences were seen with respect to clinical and instrumented laxity testing, International Knee Documentation Committee Score ratings, isokinetic muscle torque measurements, and Kujala patellofemoral, Lysholm, and Tegner scores. CONCLUSION: Equal results were seen for patellar and hamstring tendon autograft anterior cruciate ligament reconstructions at 2 years after surgery. Both techniques seem to improve patients' performance.     

Influence of medial hamstring tendon harvest on knee flexor strength after anterior cruciate ligament reconstruction. A detailed evaluation with comparison of single- and double-tendon harvest

BACKGROUND: The advantages of hamstring tendon autografts for anterior cruciate ligament reconstruction are well known; however, concerns have arisen regarding the influence of hamstring tendon harvest on postoperative weakness in knee flexion. PURPOSE: To evaluate the influence of hamstring tendon harvest on knee flexion strength in patients undergoing anterior cruciate ligament reconstruction. STUDY DESIGN: Prospective randomized study. METHODS: Ninety patients were randomly assigned at surgery to undergo anterior cruciate ligament reconstruction with either a semitendinosus tendon autograft or a semitendinosus and gracilis tendon autograft. Quadriceps and hamstring muscle strength was tested before surgery and at 6, 12, and 18 months after surgery. RESULTS: There was no significant difference in clinical results between the groups and neither group showed a significant decrease in isokinetic hamstring muscle strength. However, when the subjects' knees were at positions of 70 degrees or more of flexion, both isokinetic and isometric measurements revealed a significant decrease in hamstring muscle strength in both groups. The strength in the group with semitendinosus and gracilis tendons was considerably less than that in the group with semitendinosus tendon alone at 18 months. CONCLUSIONS: Tendon harvest causes significant weakness of hamstring muscle strength at high knee flexion angles, but such weakness can be minimized if the gracilis tendon is preserved.