Viscoelastic and failure properties of two configurations of triple-folded hamstring tendons used for anterior cruciate ligament (ACL) reconstruction.

BACKGROUND: Hamstring autografts are commonly used for anterior cruciate ligament (ACL) reconstruction. Different folding techniques exist in tripling the semitendinosus. Few anatomical studies exist in evaluating their viscoelastic properties. The purpose of this study was to characterize and compare the viscoelastic and failure properties of two hamstring graft configurations, the "Z" construct and "2" construct. METHODS: Ten matched pairs of fresh-frozen cadaveric semitendinosus hamstring grafts were used to create the "2" configuration or "Z" configuration. The biomechanical testing consisted of four phases: preconditioning, where graft dimensions (mm) were measured; stress relaxation, where load, displacement and time data were collected and equilibrium relaxation (%) was calculated; dynamic creep, where the total construct elongation was calculated; and ramp-to-failure, where maximum failure load was recorded. RESULTS: The "2" configuration demonstrated recorded forces (N) significantly greater at each time point when compared to the "Z" configuration during stress relaxation (p = 0.003). The "2" configuration exhibited significantly less construct elongation (mm) during dynamic creep at 10 cycles (p = 0.008) and 2000 cycles (p = 0.0001). The maximum measured load at failure was significantly greater in the "2" configuration constructs than "Z" configuration (p = 0.013). Moreover, the axial loads at 2, 3 and 4 mm of displacement were, on average, greater in the "2" configuration than "Z" configuration (p = 0.152; p = 0.080; p = 0.012), respectively. CONCLUSION: The results of this study provide support for folding techniques for tripled grafts to provide higher viscoelastic and failure properties for techniques with less suture interfaces. Future studies can potentially evaluate the clinical significance of these findings.

Histomorphological Alterations of Human Anterior Cruciate Ligament Grafts During Mid-Term and Long-Term Remodeling.

OBJECTIVE: The aim of the present paper is to analyze mid-term and long-term alterations of human anterior cruciate ligament (ACL) grafts during the remodeling process with special regards to cellularity, α-smooth muscle protein (αSMP) expression, and crimp length in comparison to the native ACL. METHODS: A total of 34 patients were included (23 male and 11 female). Biopsies of 13 semitendinosus tendon and 14 patellar tendon autografts were obtained during surgical revision secondary to an ACL reconstruction. According to the interval between the index procedure and sample collection, the patients were divided into four groups: 4-12 months, 13-60 months, 61-108 months, and >108 months. Seven samples of native ruptured ACL tissue obtained during surgical intervention served as control. All biopsies were taken from the intraligamentous part of the ACL or the graft. Histomorphological and immunohistochemical analyses were conducted after samples were stained using hematoxylin-eosin, Giemsa, and αSMP enzyme-labeled antibodies. The total cell density, the numbers of fibroblasts and fibrocytes, the fibroblast/fibrocyte ratio, the number of αSMP+ cell nuclei, and the percentage of αSMP+ cells per fibroblast as well as the crimp lengths were determined using light microscopy. RESULTS: In the early phase of remodeling, the grafts featured extensively high total cell counts (1021.2 ± 327.8, P = 0.001), with high numbers of fibroblasts (841.4 ± 245.2, P = 0.002), fibrocytes (174.5 ± 113.0, P = 0.04), and αSMP+ cells (78.3 ± 95.0, P = 0.02) compared to controls (390.1 ± 141.7, 304.5 ± 160.8, 65.6 ± 31.4 and 2.3 ± 2.6, respectively). Thereafter, the numbers of all cell entities decreased. After more than 108 months, the percentage of αSMP+ cells per fibroblast reached physiological values (ratio 1.3 ± 1.0, P = 0.41; control 0.8 ± 0.8), while the total cell count (834.3 ± 183.7, P = 0.001) as well as the numbers of fibroblasts (663.5 ± 192.6, P = 0.006) and fibrocytes (134.1 ± 73.0, P = 0.049) remained significantly high. The fibroblast/fibrocyte ratio showed no significant alterations over the course of time compared to the controls. The collagen crimp lengths were elongated by tendency in the early phase (28.8 ± 12.9 mm, P = 0.15; control 20.7 ± 2.2 mm) and significantly shortened over time, with the lowest values in the long term (14.8 ± 2.0 mm, P = 0.001). The comparison of biopsies from semitendinosus tendon and patellar tendon autografts revealed no significant differences for any of the histomorphological parameters investigated. CONCLUSION: This study reveals distinctive mid-term and long-term immunomorphological alterations during human ACL graft remodeling. These data clearly indicate that the remodeling is a process that continues for 9 years or more. Furthermore, it seems to be a process of adaptation rather than full restoration. Even in the long run, several biological properties of the native ACL are not completely reestablished.

Effects of flexibility and strength training on peak hamstring musculotendinous strains during sprinting.

BACKGROUND: Hamstring injury is one of the most common injuries in sports involving sprinting. Hamstring flexibility and strength are often considered to be modifiable risk factors in hamstring injury. Understanding the effects of hamstring flexibility or strength training on the biomechanics of the hamstring muscles during sprinting could assist in improving prevention strategies and rehabilitation related to these injuries. The purpose of this study was to determine the effects of altering hamstring flexibility or strength on peak hamstring musculotendinous strain during sprinting. METHODS: A total of 20 male college students (aged 18-24 years) participated and were randomly assigned to either a flexibility intervention group or a strength intervention group. Each participant executed exercise training 3 times a week for 8 weeks. Flexibility, sprinting, and isokinetic strength testing were performed before and after the 2 interventions. Paired t tests were performed to determine hamstring flexibility or strength intervention effects on optimal hamstring musculotendinous lengths and peak hamstring musculotendinous strains during sprinting. RESULTS: Participants in the flexibility intervention group significantly increased the optimal musculotendinous lengths of the semimembranosus and biceps long head (p ≤ 0.026) and decreased peak musculotendinous strains in all 3 bi-articulate hamstring muscles (p ≤ 0.004). Participants in the strength-intervention group significantly increased the optimal musculotendinous lengths of all 3 hamstring muscles (p ≤ 0.041) and significantly decreased their peak musculotendinous strain during sprinting (p ≤ 0.017). CONCLUSION: Increasing hamstring flexibility or strength through exercise training may assist in reducing the risk of hamstring injury during sprinting for recreational male athletes.

Evaluation of patellar tendon with shear wave elastography after anterior cruciate ligament reconstruction using hamstring tendons.

OBJECTIVES: This study aims to evaluate the characteristics of patellar tendons (PTs) of patients who underwent anterior cruciate ligament reconstruction (ACLR) with hamstring tendon autograft using shear wave elastography (SWE). PATIENTS AND METHODS: This prospective study was conducted between August 2017 and February 2018. We performed brightness mode (B-mode) ultrasound and SWE on 21 patients (20 males, 1 female; mean age 32 years; range, 19 to 42 years) who underwent ACLR with a single-bundle transtibial technique using quadruple hamstring autografts and 14 healthy controls (13 males, 1 female; mean age 35 years; range, 25 to 47 years). Length and thickness of the PT were evaluated with B-mode ultrasound, while elasticity values were evaluated with SWE in the patient and control groups. RESULTS: The mean SWE value of the patient group on the operated side was 25.30 (min-max=16.60-46.20) and on the non-operated side 23.20 (min-max=12.40-44). There were no statistically significant differences regarding PT elasticity, thickness, or length between the groups (p>0.05). CONCLUSION: There were no differences regarding elasticity, length, or thickness between the operated and healthy knees detected with SWE. Upcoming research should focus on tendon biopsy and biochemical analyses for the identification of possible intrastructural changes of the tendon due to collagen synthesis after ACLR with hamstring autograft.

Effects of flexibility and strength interventions on optimal lengths of hamstring muscle-tendon units.

OBJECTIVES: The aim of the present study was to determine the effects of altering both hamstring flexibility and strength on hamstring optimal lengths. DESIGN: Controlled laboratory study. METHODS: A total of 20 male and 20 female college students (aged 18-24 years) participated in this study and were randomly assigned to either a flexibility intervention group or a strength intervention group. Passive straight leg raise and isokinetic strength test were performed before and after interventions. Paired T-tests were performed to determine hamstring flexibility or strength intervention effects on hamstring optimal lengths. RESULTS: Male participants in the flexibility intervention group significantly increased range of hip joint flexion (P=0.001) and optimal lengths of semimembranosus and biceps long head (P≤0.026). Male participants in the strength intervention group significantly increased hamstring strength (P=0.001), the range of hip joint flexion (P=0.037), and optimal lengths of all three bi-articulated hamstring muscles (P≤0.041). However, female participants did not significantly increase their hamstring optimal lengths in either intervention groups (P≥0.097) although both groups significantly increased the range of hip joint flexion and strength (P≤0.009). CONCLUSION: Hamstring optimal lengths can be modified through flexibility intervention as well as strength intervention for male participants, but not for female participants in this study. Hamstring optimal lengths should be considered as hamstring flexibility measures in future prospective studies to identify potentially modifiable risk factors for hamstring injury.

Hamstring muscle-tendon unit lengthening and activation in instep and cut-off kicking.

Hamstring muscle strain injury is one of the most common injuries in sports involving sprinting and kicking. Studies examining hamstring kinematics and activations are rich for sprinting but lacking for kicking. The purpose of this study was to examine kinematics and activations of hamstring muscles in instep and cut-off kicking tasks frequently performed in soccer. Videographic and electromyographic (EMG) data were collected for 11 male soccer-majored college students performing the two kicking tasks. Peak hamstring muscle-tendon unit lengths, elongation velocities, and maximum linear envelop EMG data were identified and compared among hamstring muscles and between kicking tasks. Hamstring muscles exhibited activated elongations before and after the contact of the kicking foot with the ball. The muscle-tendon unit lengths peaked in the follow-through phase. The peak elongation velocity of the semimembranosus was significantly greater than that of the semitendinosus and biceps femoris (p = 0.001). The maximum linear envelop EMG of the biceps femoris was significantly greater than that of the semimembranosus (p = 0.026). The potential for hamstring injury exists in the follow-through phase of each kicking task. The increased hamstring muscle-tendon unit elongation velocities in kicking tasks may explain the more severe hamstring injuries in kicking compared to sprinting.

The effect of cyclic knee motion on the elongation of four-strand hamstring autograft in anterior cruciate ligament reconstruction: an in-situ pilot study.

BACKGROUND: Pretension of the viscoelastic graft by cyclic knee motion has been confirmed to decrease the graft creep and improve the outcome of anterior cruciate ligament (ACL) reconstruction. The purpose of the present study was to investigate the effect of cyclic knee motion on the elongation of the four-strand hamstring tendon autograft in situ and to explore the stable level cycle, in which the tendon length achieved a stable level. METHODS: The study was performed with 53 consecutive patients undergoing transtibial ACL reconstruction with four strand hamstring tendon from Aug 2013 to Apr 2015. 43 males and 10 females were included with mean age of 29 ± 10 years. The pretension of the tendons was operated by cyclical knee motion ranging from 0 to 110°after the femoral fixation with Endo-button. The tendon length after 10, 20, 30 and 40 cycles was measured respectively and compared by repeated measure ANOVA. Then multivariate logistic regression was used to investigate the effect of the patients' parameters (age, gender, height, body weight, tendon length, etc.) on the elongation of the graft and the stable level cycle. RESULTS: The mean lengthening of the graft at 10, 20, 30 and 40 times was 3.0 ± 1.4 mm, 4.3 ± 1.5 mm, 4.8 ± 1.7 mm and 4.8 ± 1.8 mm respectively. No significant correlation was found between the elongation and the patients' parameters. There was significant difference of the tendon length from 0 to 30 cycles (F = 264.8, df = 1.95, p<0.001). However, the tendon length achieved a stable level after 30 cycles and the median elongation from 30 cycles to 40 cycles was 0 (0-1) mm with no significant difference (F = 2.039, p = 0.159). The male and female tendon length achieved to a stable level at 20 cycles and 30 cycles respectively but with no significant difference (p = 0.074). CONCLUSIONS: The four-strand hamstring tendon was elongated after cyclic knee motion and the elongation achieved a stable level after 30 cycles for the transtibial technique. Both of the tendon elongation and the stable level cycle were not correlated with patients' gender, age, preoperative duration, graft diameter and length.

Comparison of interobserver agreement between the evaluation of bicipital and the patellar tendon reflex in healthy dogs.

The reliability of reflex-assessment is currently debatable, with current literature regarding the patellar tendon reflex (PTR) as highly reliable, while the biceps tendon reflex (BTR) is regarded to be of low reliability in the dog. Such statements are, however, based on subjective observations rather than on an empirical study. The goals of this study were three-fold: (1) the quantification of the interobserver agreement (IA) on the evaluation of the canine bicipital (BTR) and patellar tendon (PTR) reflex in healthy dogs, (2) to compare the IA of the BTR and PTR evaluation and (3) the identification of intrinsic (sex, age, fur length, weight) and extrinsic (observer´s expertise, body side) risk factors on the IA of both reflexes. The observers were subdivided into three groups based on their expected level of expertise (neurologists = highest -, practitioners = middle-and veterinary students = lowest level of expertise). For the BTR, 54 thoracic limbs were analyzed and compared to the evaluation of the PTR on 64 pelvic limbs. Each observer had to evaluate the reflex presence (RP) (present or absent) and the reflex activity (RA) using a 5-point ordinal scale. Multiple reliability coefficients were calculated. The influence of the risk factors has been calculated using a mixed regression-model. The Odds Ratio for each factor was presented. The higher the level of expertise the higher was the IA of the BTR. For RP(BTR), IA was highest for neurologists and for RA(BTR) the IA was lowest for students. The level of expertise had a significant impact on the degree of the IA in the evaluation of the bicipital tendon reflex: for the RA(BTR), practitioners had a 3.4-times (p = 0.003) and students a 7.0-times (p < 0.001) higher chance of discordance. In longhaired dogs the chance of disagreement was 2.6-times higher compared to shorthaired dogs in the evaluation of RA(BTR) (p = 0.003). Likewise, the IA of the RP(PTR) was the higher the higher the observers´ expertise was with neurologists having significantly highest values (p < 0.001). The RA(PTR) has been evaluated more consistent by practitioners and students than the RA(BTR). For practitioners this difference was significant (< 0.01). Our data suggests that neurologists assess the bicipital and patellar tendon reflex in dogs most reliably. None of the examined risk factors had a significant impact on the degree of IA in the evaluation of RP(PTR), while students had a 4.4-times higher chance of discordance when evaluating the RA(PTR) compared to the other groups. This effect was significant (p < 0.001). Neurologists can reliably assess the bicipital and patellar tendon reflex in healthy dogs. Observer´s level of expertise and the fur length of the dog affect the degree of IA of RA(BTR). The influence of the observer´s expertise is higher on the evaluation of the BTR than on the PTR.

The mechanical properties of fresh versus fresh/frozen and preserved (Thiel and Formalin) long head of biceps tendons: A cadaveric investigation.

Human cadaveric specimens commonly serve as mechanical models and as biological tissue donors in basic biomechanical research. Although these models are used to explain both in vitro and in vivo behavior, the question still remains whether the specimens employed reflect the normal in vivo situation. The mechanical properties of fresh-frozen or preserved cadavers may differ, and whether they can be used to reliably investigate pathology could be debated. The purpose of this study was to therefore examine the mechanical properties of cadaveric long biceps tendons, comparing fresh (n=7) with fresh-frozen (n=8), formalin embalmed (n=15), and Thiel-preserved (n=6) specimens using a Universal Testing Machine. The modulus of elasticity and the ultimate tensile strength to failure was recorded. Tensile failure occurred at an average of 12N/mm2 in the fresh group, increasing to 40.1N/mm2 in the fresh-frozen group, 50.3N/mm2 in the formalin group, and 52N/mm2 in the Thiel group. The modulus of elasticity/stiffness of the tendon increased from fresh (25.6MPa), to fresh-frozen (55.3MPa), to Thiel (82.5MPa), with the stiffest being formalin (510.6MPa). Thiel-preserved and formalin-embalmed long head of biceps tendons and fresh-frozen tendons have a similar load to failure. Either the Thiel or formalin preserved tendon could therefore be considered as alternatives for load to failure studies. However, the Young's modulus of embalmed tendons were significantly stiffer than fresh or fresh frozen specimens, and these methods might be less suitable alternatives when viscoelastic properties are being investigated.

The significant effect of the medial hamstrings on dynamic knee stability.

PURPOSE: While hamstring autograft is a popular option for the general population, BTB autograft is still significantly more popular among professional athletes due to concerns of altering knee kinematics with hamstring harvest. This study seeks to quantify the contribution of the medial hamstrings to knee stability. METHODS: Valgus knee laxity, anterior tibial translation, and rotational motion were measured in eight fresh-frozen cadaveric knees after forces were applied on the tibia in each plane (coronal, sagittal, and axial). Four muscle loading conditions were tested: (1) physiologic fully loaded pes anserinus, (2) semitendinosus only loaded, (3) gracilis only loaded, and (4) unloaded pes anserinus. The protocol was then repeated with the ACL transected. RESULTS: In the ACL intact knee, the neutral position of the tibia with an unloaded pes anserinus was significantly more externally rotated (p < 0.01) and anteriorly translated (p < 0.05) at all knee flexion angles than a tibia with a physiologic loaded pes anserinus. Applying an external rotation torque significantly increased external rotation for the fully unloaded (p < 0.001), gracilis only loaded (p < 0.001), and semitendinosus only loaded (p < 0.01) conditions at all flexion angles. Applying a valgus torque resulted in a significant increase in laxity for the fully unloaded condition only at 30° of flexion (p < 0.05). Applying an anterior tibial force resulted in significant increase in anterior translation for the fully unloaded condition at all flexion angles (p < 0.01), and for the gracilis only loaded condition in 30° and 60° of flexion (p < 0.05). Similar results were seen in the ACL deficient model. CONCLUSION: The medial hamstrings are involved in rotational, translational, and varus/valgus control of the knee. Applying anterior, external rotation, and valgus forces on the hamstring deficient knee significantly increases motion in those planes. Harvesting the gracilis and semitendinosus tendons alters native knee kinematics and stability. This is clinically relevant and should be a consideration when choosing graft source for ACL reconstruction, especially in the elite athlete population.

Anatomy of proximal attachment, course, and innervation of hamstring muscles: a pictorial essay.

Hamstring injuries are very common in sports medicine. Knowing their anatomy, morphology, innervation, and function is important to provide a proper diagnosis, treatment as well as appropriate prevention strategies. In this pictorial essay, based on anatomical dissection, the detailed anatomy of muscle-tendon complex is reviewed, including their proximal attachment, muscle course, and innervation. To illustrate hamstrings' role in the rotational control of the tibia, the essay also includes the analysis of their biomechanical function.Level of evidence V (expert opinion based on laboratory study).

Activation of biceps femoris long head reduces tibiofemoral anterior shear force and tibial internal rotation torque in healthy subjects.

The anterior cruciate ligament (ACL) provides resistance to tibial internal rotation torque and anterior shear at the knee. ACL deficiency results in knee instability. Optimisation of muscle contraction through functional electrical stimulation (FES) offers the prospect of mitigating the destabilising effects of ACL deficiency. The hypothesis of this study is that activation of the biceps femoris long head (BFLH) reduces the tibial internal rotation torque and the anterior shear force at the knee. Gait data of twelve healthy subjects were measured with and without the application of FES and taken as inputs to a computational musculoskeletal model. The model was used to investigate the optimum levels of BFLH activation during FES gait in reducing the anterior shear force to zero. This study found that FES significantly reduced the tibial internal rotation torque at the knee during the stance phase of gait (p = 0.0322) and the computational musculoskeletal modelling revealed that a mean BFLH activation of 20.8% (±8.4%) could reduce the anterior shear force to zero. At the time frame when the anterior shear force was zero, the internal rotation torque was reduced by 0.023 ± 0.0167 Nm/BW, with a mean 188% reduction across subjects (p = 0.0002). In conclusion, activation of the BFLH is able to reduce the tibial internal rotation torque and the anterior shear force at the knee in healthy control subjects. This should be tested on ACL deficient subject to consider its effect in mitigating instability due to ligament deficiency. In future clinical practice, activating the BFLH may be used to protect ACL reconstructions during post-operative rehabilitation, assist with residual instabilities post reconstruction, and reduce the need for ACL reconstruction surgery in some cases.

Biceps femoris fascicle length during passive stretching.

The purpose of this study was to quantify the relative changes in fascicle (FL) and muscle-tendon unit (LMTU) length of the long head of the biceps femoris (BFlh) at different combinations of hip and knee joint positions. Fourteen participants performed passive knee extension trials from 0°, 45° and 90° of hip flexion. FL, LMTU, pennation angle (PA) and effective FL (FL multiplied by the cosine of the PA) of the BFlh were quantified using ultrasonography (US). Three-way analysis of variance designs indicated that at each hip angle, FL and LMTU increased and PA decreased from 90° to 0° of knee flexion. Increasing hip flexion angle from 0° to 90° led to a higher FL and LMTU and a lower PA (p < .05). The average lengthening of the LMTU and effective FL was 28.00 ±â€¯1.82% and 85.88 ±â€¯21.92%, respectively. The average effective FL change accounted for 51.36 ±â€¯7.39% of LMTU change. The relationship between effective FL and LMTU was almost linear with a slope equal to 0.49 ±â€¯0.06 (r2 = 0.52 to 0.97). To achieve greater lengthening of the fascicles of the BFlh, passive stretch with the hip flexed at least 45° and the knee reaching full extension is necessary.

Mechanical Analysis of Extra-Articular Knee Ligaments. Part two: Tendon grafts used for knee ligament reconstruction.

OBJECTIVES: The aim of this study was to provide information about the mechanical properties of grafts used for knee ligament reconstructions and to compare those results with the mechanical properties of native knee ligaments. METHODS: Eleven cadaveric knees were dissected for the semitendinosus, gracilis, iliotibial band (ITB), quadriceps and patellar tendon. Uniaxial testing to failure was performed using a standardized method and mechanical properties (elastic modulus, ultimate stress, ultimate strain, strain energy density) were determined. RESULTS: The elastic modulus of the gracilis tendon (1458±476MPa) (P<0.001) and the semitendinosus tendon (1036±312MPa) (P<0.05) was significantly higher than the ITB (610±171MPa), quadriceps tendon (568±194MPa), and patellar tendon (417±107MPa). In addition, the ultimate stress of the hamstring tendons (gracilis 155.0±30.7MPa and semitendinosus 120.1±30.0MPa) was significantly higher (P<0.001, respectively P<0.05), relative to the ITB (75.0±11.8MPa), quadriceps tendon (81.0±27.6MPa), and patellar tendon (76.2±25.1MPa). A significant difference (P<0.05) could be noticed between the ultimate strain of the patellar tendon (24.6±5.9%) and the hamstrings (gracilis 14.5±3.1% and semitendinosus 17.0±4.0%). No significant difference in strain energy density between the grafts was observed. CONCLUSIONS: Material properties of common grafts used for knee ligament reconstructions often differ significantly from the original knee ligament which the graft is supposed to emulate.

Finite element simulations of different hamstring tendon graft lengths and related fixations in anterior cruciate ligament reconstruction.

As one of the most frequently used grafts in anterior cruciate ligament (ACL) reconstruction, hamstring tendon (HT) grafts are prepared with different lengths and fixed by specific fixations in knee joints. However, there are incomplete studies to investigate both the joint kinematics and graft biomechanics in the ACL reconstructions with different HT graft lengths. In this paper, three different graft lengths (i.e., 30, 50, and 70 mm) were developed in the ACL reconstruction and analyzed using finite element method under two usual clinical test loads (i.e., 134 N anterior tibial drawer and pivot shift test load). The different mechanical properties of the corresponding fixations were also considered for each graft length. It was revealed that the change in HT graft length would cause different strain and stress results in the grafts, but did not greatly influence joint stabilities under the two clinical test loads. The graft reaction force at the femoral fixation was always greatly lower than that at the tibial fixation regardless of load and graft length. The comparison of stress and strain results also indicated that more graft tissues inside the femoral and tibial tunnels could decrease the stress and strain values at the femoral and tibial fixation sites, respectively.

Static tensioning promotes hamstring tendons force relaxation more reliably than cycling tensioning.

BACKGROUND: Graft elongation might be a major reason for increased anterior laxity after anterior cruciate ligament (ACL) reconstruction. This study analyzed the force relaxation values and their stabilization when single strands of the gracilis and semitendinosus tendons underwent cyclic and static tensioning at 2.5% strain level, and compared the efficiency of static and cyclic tensioning in promoting force relaxation. METHODS: Eighteen gracilis tendons and 18 semitendinosus tendons from nine male cadavers (mean age: 22.44years) were subjected to 10 in vitro cyclic loads at 2.5% strain level, or to a static load at 2.5% strain level. RESULTS: During cyclic loading, the reduction in force values tended to stabilize after the sixth cyclic load, while, in the case of static loading, this stabilization occurred by the second minute. Comparing static and cyclic loading, the gracilis tendon had similar mechanical responses in both conditions, while the semitendinosus tendon showed greater force relaxation in static compared with cyclic loading. CONCLUSIONS: Considering that the semitendinosus tendon is the main component of the hamstring graft, its biomechanical response to loading should guide the tensioning protocol. Therefore, static tensioning seems more effective for promoting force relaxation of the semitendinosus tendon than cyclic tensioning. The gracilis tendon showed a similar mechanical response to either tensioning protocols.

A Biomechanical Comparison of Allograft Tendons for Ligament Reconstruction.

BACKGROUND: Allograft tendons are frequently used for ligament reconstruction about the knee, but they entail availability and cost challenges. The identification of other tissues that demonstrate equivalent performance to preferred tendons would improve limitations. Hypothesis/Purpose: We compared the biomechanical properties of 4 soft tissue allograft tendons: tibialis anterior (TA), tibialis posterior (TP), peroneus longus (PL), and semitendinosus (ST). We hypothesized that allograft properties would be similar when standardized by the looped diameter. STUDY DESIGN: Controlled laboratory study. METHODS: This study consisted of 2 arms evaluating large and small looped-diameter grafts: experiment A consisted of TA, TP, and PL tendons (n = 47 each) with larger looped diameters of 9.0 to 9.5 mm, and experiment B consisted of TA, TP, PL, and ST tendons (n = 53 each) with smaller looped diameters of 7.0 to 7.5 mm. Each specimen underwent mechanical testing to measure the modulus of elasticity (E), ultimate tensile force (UTF), maximal elongation at failure, ultimate tensile stress (UTS), and ultimate tensile strain (UTε). RESULTS: Experiment A: No significant differences were noted among tendons for UTF, maximal elongation at failure, and UTϵ. UTS was significantly higher for the PL (54 MPa) compared with the TA (44 MPa) and TP (43 MPa) tendons. E was significantly higher for the PL (501 MPa) compared with the TP (416 MPa) tendons. Equivalence testing showed that the TP and PL tendon properties were equivalent or superior to those of the TA tendons for all outcomes. Experiment B: All groups exhibited a similar E. UTF was again highest in the PL tendons (2294 N) but was significantly different from only the ST tendons (1915 N). UTϵ was significantly higher for the ST (0.22) compared with the TA (0.19) and TP (0.19) tendons. Equivalence testing showed that the TA, TP, and PL tendon properties were equivalent or superior to those of the ST tendons. CONCLUSION: Compared with TA tendons, TP and PL tendons of a given looped diameter exhibited noninferior initial biomechanical strength and stiffness characteristics. ST tendons were mostly similar to TA tendons but exhibited a significantly higher elongation/UTϵ and smaller cross-sectional area. For smaller looped-diameter grafts, all tissues were noninferior to ST tendons. In contrast to previous findings, PL tendons proved to be equally strong. CLINICAL RELEVANCE: The results of this study should encourage surgeons to use these soft tissue allografts interchangeably, which is important as the number of ligament reconstructions performed with allografts continues to rise.

Risk of iatrogenic injury to the infrapatellar branch of the saphenous nerve during hamstring tendon harvesting: A meta-analysis.

INTRODUCTION: Our goal was to conduct a comprehensive analysis of studies reporting data on the rate of injury to the infrapatellar branch of the saphenous nerve following hamstring tendon graft harvesting with respect to the type of incision over the pes anserinus. METHODS: A broad search through all major electronic databases was conducted to identify articles eligible for inclusion. All available data were extracted and pooled into the analysis. RESULTS: Eleven studies (n = 1,050 patients) were included in the meta-analysis. The study revealed that a vertical incision during hamstring tendon harvesting over the pes anserinus was associated with the highest rate of injury with a pooled rate of 51.4% (95% confidence interval [CI], 34.6-67.2%). This was followed by oblique and horizontal incisions with pooled rates of 26.0% (95% CI,1.3-61.3%) and 22.4% (95% CI, 5.4-45.5%), respectively. CONCLUSIONS: We highly recommend the use of the shortest possible oblique incision during hamstring tendon harvesting over the pes anserinus. Muscle Nerve 56: 930-937, 2017.

High-load preconditioning of human soft tissue hamstring grafts: An in vitro biomechanical analysis.

PURPOSE: In order to minimize viscoelastic elongation of ACL reconstruction grafts, preconditioning protocols have been employed in clinical practice prior to final graft fixation. The purpose of this study was to evaluate two separate high-load static preconditioning protocols of double-looped semitendinosus-gracilis grafts and compare these results to both a current clinical protocol and a control group with no preconditioning protocol applied. It was hypothesized that a high-load, static preconditioning protocol would minimize graft elongation during a simulated progressive early rehabilitation compared to both the "89 N" clinical protocol and control groups. METHODS: Grafts were randomly allocated into four preconditioning study groups: (1) control (no preconditioning), (2) clinical protocol (89 N for 15 min), (3) high-load, short duration (600 N for 20 s), and (4) high-load, long duration (600 N for 15 min). After preconditioning, grafts were cyclically loaded between 10 and 400 N at 0.5 Hz for 450 cycles to simulate early postoperative rehabilitation. Graft displacement (elongation) was recorded during both preconditioning and cyclic loading. RESULTS: Increased preconditioning load magnitude and duration significantly reduced graft elongation during cyclic loading (p < 0.05) which corresponded to an inverse relationship with increased elongation during preconditioning. The "600 N for 15 min" protocol resulted in significantly less elongation during simulated early rehabilitation than both the control group and the "89 N for 15 min" protocol (p < 0.001, p < 0.05). CONCLUSIONS: Graft elongation during simulated early rehabilitation was significantly reduced by a high-load preconditioning protocol applied for an extended period of time compared to a current common clinical protocol and grafts that were not preconditioned. In addition, the amount of elongation during simulated early rehabilitation was similar between grafts preconditioned using the current clinical practice protocol and the high-load/short-duration protocol, implying that the latter could potentially induce the same viscoelastic changes in soft tissue grafts as the current clinical practice. The "600 N for 20 s" preconditioning protocol may provide similar postoperative results as the clinical protocol, "89 N for 15 min", and also reduce or maintain operative time. A high-load preconditioning protocol that reduces graft elongation may benefit patients undergoing ACL reconstruction, especially for cases of failed primary reconstruction, genu recurvatum, and increased tibial slope, where maintaining graft length is imperative to restore knee stability.

Morphology of the fibular insertion of the posterolateral corner and biceps femoris tendon.

PURPOSE: To clarify the fibular head insertion of the fibular collateral ligament (FCL), popliteofibular ligament (PFL), and biceps femoris tendon and related osseous landmarks on three-dimensional (3-D) images. METHODS: Twenty-one non-paired, formalin-fixed human cadaveric knees were evaluated in this study. The fibular head insertions of the FCL, PFL and biceps femoris tendon were identified and marked. 3-D images were created, and the surface area, location, positional relationships, and morphology of the fibular insertions of the FCL, PFL, and biceps femoris tendon and related osseous structures were analysed. RESULTS: The fibular head had a unique pyramidal shape, and the relationships of the fibular insertion of the FCL, PFL, and biceps femoris tendon were consistent. The fibular head consists of three aspects: lateral aspect, posterior aspect, and proximal tibiofibular facet. The insertions of the FCL, PFL, and biceps femoris tendon were attached to the centre from the distal side of the lateral aspects of the fibular head, posterior aspect of the fibular styloid process, and lateral aspect surrounding the FCL, respectively. The mean surface areas of the FCL and PFL fibular insertions were 100.1 ± 29.5 and 18.5 ± 7.2 mm2, respectively. CONCLUSION: This study showed that the relationships between the characteristic features of the fibular head and insertions of the FCL, PFL, and biceps femoris tendon were consistent. The clinical relevance of this study is that it improves understanding of the anatomy of the insertions of the PLC and biceps femoris tendon.