Determination of the in situ loads on the human anterior cruciate ligament

Physiologic Preoperative Knee Hyperextension Is Not Associated With Postoperative Laxity, Subjective Knee Function, or Revision Surgery After ACL Reconstruction With Hamstring Tendon Autografts

BACKGROUND

There is concern that physiologic knee hyperextension may be associated with inferior outcomes after anterior cruciate ligament reconstruction (ACLR) using hamstring tendon (HT) autografts.

PURPOSE

To assess whether there is an association between contralateral passive preoperative knee hyperextension (≤-5°) and postoperative anterior knee laxity, subjective knee function, or revision surgery after ACLR using HT autografts.

STUDY DESIGN

Cohort study; Level of evidence, 3.

METHODS

Patients without concomitant ligament injuries who underwent primary ACLR using an HT autograft at Capio Artro Clinic, Stockholm, Sweden, between January 1, 2005, and December 31, 2018, were identified. The cohort was dichotomized into the hyperextension group (≤-5°) and the no hyperextension group (>-5°) depending on preoperative contralateral passive knee extension degree. Anterior knee laxity (KT-1000 arthrometer; 134 N) was assessed preoperatively and at 6 months postoperatively. The Knee injury and Osteoarthritis Outcome Score (KOOS) was collected preoperatively and at 1, 2, and 5 years postoperatively. Patients who underwent revision ACLR at any institution in Sweden within 5 years of the primary surgery were identified in the Swedish National Knee Ligament Registry.

RESULTS

A total of 6104 patients (53.5% male) for whom knee range of motion measurements were available were identified (hyperextension group [≤-5°]: 2350 [38.5%]; mean extension, -6.1°± 2.3° [range, -20° to -5°]; no hyperextension group [>-5°]: 3754 [61.5%]; mean extension, 0°± 1.4° [range, -4° to 15°]). There were no intergroup differences in anterior knee laxity preoperatively (hyperextension group, 3.6 ± 2.8 mm; no hyperextension group, 3.7 ± 2.7 mm; P = .24) or postoperatively (hyperextension group, 1.8 ± 2.3 mm; no hyperextension group, 1.8 ± 2.2 mm; P = .41). The only significant but nonclinically relevant intergroup differences were seen in the KOOS Symptoms subscale at the 1-year follow-up (hyperextension group, 81.4 ± 16.0; no hyperextension group, 80.3 ± 16.5; P = .03) and in the Sport and Recreation subscale at the 5-year follow-up (hyperextension group, 73.0 ± 25.6; no hyperextension group, 75.7 ± 24.3; P = .02). No other significant intergroup differences were noted preoperatively or at 1, 2, or 5 years postoperatively in any of the KOOS subscales. The overall revision ACLR rate at ≤5 years after the primary surgery was 4.9% (302 of 6104 patients). The hazard for revision ACLR in the no hyperextension group (4.5%; 170 of 3754 patients) was not significantly different from that in the hyperextension group (5.6%; 132 of 2350 patients) (hazard ratio, 0.89; 95% CI, 0.71 to -1.12; P = .34). A subsequent subanalysis showed that the hazard of revision ACLR in patients with no hyperextension was not significantly different from that of patients with ≤-10° of extension (5.8%; 27 of 467 patients) (hazard ratio, 0.91; 95% CI, 0.61 to 1.36; P = .65).

CONCLUSION

Preoperative passive contralateral knee hyperextension (≤-5°) was not associated with postoperative anterior knee laxity, subjective knee function, or revision surgery ≤5 years after ACLR using HT autografts. Therefore, the presence of knee hyperextension alone should not be considered a contraindication per se for the use of HT autografts in ACLR.

Magnetic Resonance Imaging of Anterior Cruciate Ligament Injury

The Anterior Cruciate Ligament (ACL) is considered the most commonly injured ligament of the knee. Magnetic Resonance Imaging (MRI) has become an indispensable imaging tool and modality of choice for assessing and managing knee conditions. This article outlines an effective MRI imaging technique that improves the diagnostic accuracy of ACL injuries of the knee, covering the appropriate pulse sequences and optimal imaging planes. Furthermore, the article provides a comprehensive review of the appearance of complete and partial ACL tears on MRI in the acute and chronic phases. In addition, it identifies and illustrates the primary MRI signs (signs related to the absence or abnormal visualization of the ACL fibers) and secondary MRI signs (signs related to the mechanism of injury or associated knee injuries) of ACL injury.

Loading mechanisms of the anterior cruciate ligament

This review identifies the three-dimensional knee loads that have the highest risk of injuring the anterior cruciate ligament (ACL) in the athlete. It is the combination of the muscular resistance to a large knee flexion moment, an external reaction force generating knee compression, an internal tibial torque, and a knee abduction moment during a single-leg athletic manoeuvre such as landing from a jump, abruptly changing direction, or rapidly decelerating that results in the greatest ACL loads. While there is consensus that an anterior tibial shear force is the primary ACL loading mechanism, controversy exists regarding the secondary order of importance of transverse-plane and frontal-plane loading in ACL injury scenarios. Large knee compression forces combined with a posteriorly and inferiorly sloped tibial plateau, especially the lateral plateau-an important ACL injury risk factor-causes anterior tibial translation and internal tibial rotation, which increases ACL loading. Furthermore, while the ACL can fail under a single supramaximal loading cycle, recent evidence shows that it can also fail following repeated submaximal loading cycles due to microdamage accumulating in the ligament with each cycle. This challenges the existing dogma that non-contact ACL injuries are predominantly due to a single manoeuvre that catastrophically overloads the ACL.

Clinical Outcomes and Postoperative Complications After All-Epiphyseal Double-Bundle ACL Reconstruction for Skeletally Immature Patients

Background

The treatment strategy for pediatric anterior cruciate ligament (ACL) tears, especially in patients with open physes, remains controversial.

Purpose

To assess clinical outcomes and postoperative complications after all-epiphyseal double-bundle ACL (DB-ACL) reconstruction for patients with open physes.

Study Design

Cohort study; Level of evidence, 3.

Methods

Included were 102 patients aged ≤15 years who underwent ACL reconstruction at a single institution and had a minimum of 2 years of follow-up. Of these patients, 18 had undergone all-epiphyseal DB-ACL reconstruction (mean age, 12.4 ± 1.2 year) and 84 had undergone conventional DB-ACL reconstruction (mean age, 14.1 ± 0.9 year). The outcomes of the all-epiphyseal group were compared with those of the conventional group. Objective clinical outcomes included KT-1000 arthrometer measurements of side-to-side difference in anterior tibial translation, Lachman test grade, and pivot-shift test grade. Radiographic angular deformity (defined as >3° of the side-to-side difference in femorotibial angle) and incidence of second ACL injury were also compared.

Results

The postoperative side-to-side difference in laxity significantly improved from 6.1 ± 2.4 to 0.6 ± 0.9 mm in the all-epiphyseal group (P = .001), and postoperative laxity was similar to that of the conventional group (0.4 ± 0.8 mm; P = .518). A Lachman grade 1 positive result was observed in 20% of the all-epiphyseal group and 3% of the conventional group (P = .042), and a pivot-shift grade 1 positive result was observed in 22% of the all-epiphyseal group and 4% of the conventional group (P = .074). A total of 4 patients (26.7%) in the all-epiphyseal group and 4 (6.1%) in the conventional group demonstrated angular deformity (P = .035). The incidence of postoperative ipsilateral ACL tear was 16.7% in the all-epiphyseal group and 23.8% in the conventional group (P = .757). The incidence of contralateral ACL tear was 11.1% in the all-epiphyseal group and 14.3% in the conventional group (P ≥ .999).

Conclusion

All-epiphyseal DB-ACL reconstruction for skeletally immature patients achieved satisfactory clinical outcomes compared with conventional DB-ACL reconstruction. The incidence of ipsilateral graft rupture was relatively high in both groups. The all-epiphyseal group had a significantly higher incidence of angular deformity.

[Research progress of lateral femoral notch sign in diagnosis of anterior cruciate ligament rupture]

Objective

To summarize the relationship between lateral femoral notch sign (LFNS) and anterior cruciate ligament (ACL) rupture.

Methods

The relevant literature of LFNS at home and abroad in recent years was retrospectively reviewed, and its mechanism, diagnostic criteria and influencing factors in diagnosis of ACL rupture were summarized and analyzed.

Results

The LFNS is associated with rotational stability of the knee. As an indirect sign of ACL rupture, the LFNS has high clinical diagnostic value, especially the diagnosis of ACL rupture with lateral meniscus injury.

Conclusion

The diagnostic criteria and influencing factors of LFNS in diagnosis of ACL rupture are still unclear and controversial, which needs further study.

Suture tape augmentation improves laxity of MCL repair in the ACL reconstructed knee

PURPOSE

Medial collateral ligament (MCL) injury is very common and surgical repair is sometimes necessary. Especially in the setting of simultaneous anterior cruciate ligament reconstruction (ACLR) as the ACL is the secondary restraint against valgus stress. The goal of this study was to evaluate knee biomechanics after suture repair of the MCL augmented with suture tape, as compared to MCL repair alone, in the setting of concomitant ACL reconstruction (ACLR).

METHODS

Fifteen fresh-frozen human cadaveric knees were tested using a six-degrees-of-freedom robotic system under four loadings: (a) an 89.0 N anterior tibial load, (b) a 5.0 Nm internal and external rotation torque, (c) a 10.0 Nm valgus load, (d) a 7.0 Nm valgus load combined with 5.0 Nm internal rotation torque as a static simulated pivot-shift. The tested conditions were ACLR with the following states: (1) MCL intact, (2) MCL deficient, (3) MCL Repair, and (4) MCL repair augmented with suture tape (MCL Repair + ST). Under the different knee loadings, the tibial displacement, and the force in either the intact MCL, suture repaired MCL or repaired MCL-suture tape complex was measured.

RESULTS

While neither the MCL Repair nor the MCL Repair + ST restored valgus rotation to the MCL intact state, displacement was significantly smaller after MCL Repair + ST (p < 0.05). The knee rotation under external rotation torque in MCL Repair + ST did not differ MCL intact (n.s.), while with MCL Repair the rotation was significantly greater (p < 0.05). MCL Repair + ST did not cause an over-constraint of the knee in any of the tested loading conditions.

CONCLUSION

In a combined ACL-reconstruction-MCL-repair model, MCL Repair augmented with suture tape improved valgus and external rotation laxity when compared to MCL suture repair alone. Suture tape augmentation may provide this additional means of stabilization and can be added at the time of surgical repair of the MCL. Clinically this may result in lower failure rates and less residual laxity after MCL repair, as well as shorter immobilization times and faster return to play.

Single-Bundle Versus Double-Bundle Arthroscopic Anterior Cruciate Ligament Reconstruction: Comparison of Long-Term Functional Outcomes

Objective

To compare long-term functional results of ACL reconstruction with a single bundle (SB) and double bundle (DB).

Methods

Sixty patients who underwent ACL reconstructions from January 2007 to December 2008 were retrospectively evaluated (30 SB and 30 DB ACL reconstructions). Clinical and functional outcomes were measured pre- and postoperatively in terms of anterior drawer test, Lachman’s test, pivot shift test, KT1000 side-to-side difference, range of motion, International Knee Documentation Committee Scoring, Lysholm knee scoring scale (LKS), and Tegner activity level scale. The period of follow-up was 10 years.

Results

Clinical outcome measured showed that anterior drawer test result were equally normal for both groups (93.3%; p > 0.995); however, the Lachman test was 76.7% in the DB group and 56.7% in the SB group (p > 0.100), the pivot shift was 83% in the DB group and 50% in the SB group (p < 0.001), and KT1000 was 76.7% in the DB group and 56.7% in the SB group (p > 0.100). Regarding the functional outcome, it favored the DB group of patients, with the LKS being statistically significant (p < 0.007) and the Tegner activity level scale p-value being <0.001

Conclusions

DB ACL reconstruction produces better rotational stability and gives superior functional outcome in terms of return to pre-injury activity level in comparison to SB reconstruction. DB ACL reconstruction using hamstring tendon autograft produces better functional results at 10 years follow-up.

Computational frame of ligament in situ strain in a full knee model

The biomechanical function of connective tissues in a knee joint is to stabilize the kinematics-kinetics of the joint by augmenting its stiffness and limiting excessive coupled motion. The connective tissues are characterized by an in vivo reference configuration (in situ strain) that would significantly contribute to the mechanical response of the knee joint. In this work, a novel iterative method for computing the in situ strain at reference configuration was presented. The framework used an in situ strain gradient approach (deformed reference configuration) and a detailed finite element (FE) model of the knee joint. The effect of the predicted initial configuration on the mechanical response of the joint was then investigated under joint axial compression, passive flexion, and coupled rotations (adduction and internal), and during the stance phase of gait. The inclusion of the reference configuration has a minimal effect on the knee joint mechanics under axial compression, passive flexion, and at two instances (0% and 50%) of the stance phase of gait. However, the presence of the ligaments in situ strains significantly increased the joint stiffness under passive adduction and internal rotations, as well as during the other simulated instances (25%, 75% and 100%) of the stance phase of gait. Also, these parameters substantially altered the local loading state of the ligaments and resulted in better agreement with the literature during joint flexion. Therefore, the proposed computational framework of ligament in situ strain will help to overcome the challenges in considering this crucial biological aspect during knee joint modeling. Besides, the current construct is advantageous for a better understanding of the mechanical behavior of knee ligaments under physiological and pathological states and provide relevant information in the design of reconstructive treatments and artificial grafts.

Size and Shape of the Human Anterior Cruciate Ligament and the Impact of Sex and Skeletal Growth: A Systematic Review

BACKGROUND

High rates of anterior cruciate ligament (ACL) injury and surgical reconstruction in both skeletally immature and mature populations have led to many studies investigating the size and shape of the healthy ligament. The purposes of the present study were to compile existing quantitative measurements of the geometry of the ACL, its bundles, and its insertion sites and to describe effects of common covariates such as sex and age.

METHODS

A search of the Web of Science was conducted for studies published from January 1, 1900, to April 11, 2018, describing length, cross-sectional area, volume, orientation, and insertion sites of the ACL. Two reviewers independently screened and reviewed the articles to collect quantitative data for each parameter.

RESULTS

Quantitative data were collected from 92 articles in this systematic review. In studies of adults, reports of average ACL length, cross-sectional area, and volume ranged from 26 to 38 mm, 30 to 53 mm, and 854 to 1,858 mm, respectively. Reported values were commonly found to vary according to sex and skeletal maturity as well as measurement technique.

CONCLUSIONS

Although the geometry of the ACL has been described widely in the literature, quantitative measurements can depend on sex, age, and measurement modality, contributing to variability between studies. As such, care must be taken to account for these factors. The present study condenses measurements describing the geometry of the ACL, its individual bundles, and its insertion sites, accounting for common covariates when possible, to provide a resource to the clinical and scientific communities.

CLINICAL RELEVANCE

Quantitative measures of ACL geometry are informative for developing clinical treatments such as ACL reconstruction. Age and sex can impact these parameters.

Physiologic Preoperative Knee Hyperextension Is a Predictor of Failure in an Anterior Cruciate Ligament Revision Cohort: A Report From the MARS Group

BACKGROUND

The occurrence of physiologic knee hyperextension (HE) in the revision anterior cruciate ligament reconstruction (ACLR) population and its effect on outcomes have yet to be reported. Hypothesis/Purpose: The prevalence of knee HE in revision ACLR and its effect on 2-year outcome were studied with the hypothesis that preoperative physiologic knee HE ≥5° is a risk factor for anterior cruciate ligament (ACL) graft rupture.

STUDY DESIGN

Cohort study; Level of evidence, 2.

METHODS

Patients undergoing revision ACLR were identified and prospectively enrolled between 2006 and 2011. Study inclusion criteria were patients undergoing single-bundle graft reconstructions. Patients were followed up at 2 years and asked to complete an identical set of outcome instruments (International Knee Documentation Committee, Knee injury and Osteoarthritis Outcome Score, WOMAC, and Marx Activity Rating Scale) as well as provide information regarding revision ACL graft failure. A regression model with graft failure as the dependent variable included age, sex, graft type at the time of the revision ACL surgery, and physiologic preoperative passive HE ≥5° (yes/no) to assess these as potential risk factors for clinical outcomes 2 years after revision ACLR.

RESULTS

Analyses included 1145 patients, for whom 2-year follow-up was attained for 91%. The median age was 26 years, with age being a continuous variable. Those below the median were grouped as "younger" and those above as "older" (age: interquartile range = 20, 35 years), and 42% of patients were female. There were 50% autografts, 48% allografts, and 2% that had a combination of autograft plus allograft. Passive knee HE ≥5° was present in 374 (33%) patients in the revision cohort, with 52% being female. Graft rupture at 2-year follow-up occurred in 34 cases in the entire cohort, of which 12 were in the HE ≥5° group (3.2% failure rate) and 22 in the non-HE group (2.9% failure rate). The median age of patients who failed was 19 years, as opposed to 26 years for those with intact grafts. Three variables in the regression model were significant predictors of graft failure: younger age (odds ratio [OR] = 3.6; 95% CI, 1.6-7.9; P = .002), use of allograft (OR = 3.3; 95% CI, 1.5-7.4; P = .003), and HE ≥5° (OR = 2.12; 95% CI, 1.1-4.7; P = .03).

CONCLUSION

This study revealed that preoperative physiologic passive knee HE ≥5° is present in one-third of patients who undergo revision ACLR. HE ≥5° was an independent significant predictor of graft failure after revision ACLR with a >2-fold OR of subsequent graft rupture in revision ACL surgery. Registration: NCT00625885 ( ClinicalTrials.gov identifier).

Knee kinematics in anatomic anterior cruciate ligament reconstruction with four- and five-strand hamstring tendon autografts

An alternative to the gold standard fourstrand hamstring tendon autograft for anterior cruciate ligament (ACL) reconstruction is the five-strand graft. The rationale for its use is to increase graft width to better restore the anatomical footprint and biomechanical properties of the native ACL when unable to create a four-strand graft of 8 mm in diameter. To date, there are no trials assessing the use of this wider graft and its effect on the kinematics of the knee. The aim of this study was to determine whether the use of a wider five-strand hamstring tendon autograft in ACL reconstructive surgery better replicated the kinematics of a normal non-injured knee than the gold standard four-strand graft. Forty-four patients (27 operative and 17 normal control) were recruited for this study over a 12-month period. Twenty patients underwent anterior cruciate ligament reconstruction with the four-strand hamstring tendon autograft construct and seven with the five-strand construct. All patients underwent kinematic testing using the KneeKG System (EMOVI, CA) according to a strict testing protocol. The operative group underwent testing at six (T1) and twelve (T2) weeks postoperatively. Analysis of variance was used to compare six degrees of freedom kinematic data across groups and correlations were made between kinematic data and intraoperatively measured graft width. Postoperative kinematic data revealed no statistically significant differences between graft types. At 12 weeks significant differences were seen between the four-strand and control group in the flexion/extension cycle in the preloading phase and at terminal stance. Significant correlations were seen between graft width and rotational stability at Preloading (Pearson’s r=0.415) and Maximum Internal Rotation (Femoral Width Pearson’s r=0.456 and Tibial Width Pearson’s r=0.476) at 12 weeks regardless of graft type.

This study demonstrated that to achieve anatomic knee kinematics in primary ACL reconstruction in the first 12 weeks postoperatively, a technique to optimise autograft width using a five-strand hamstring tendon autograft is useful. A relationship was found between graft width and more stable rotational kinematics of the knee during walking, regardless of graft type.

Digital image correlation-aided mechanical characterization of the anteromedial and posterolateral bundles of the anterior cruciate ligament

The anterior cruciate ligament (ACL) is one of the most commonly injured soft tissue structures in the articular knee joint, often requiring invasive surgery for patients to restore pre-injury knee kinematics. There is a pressing need to understand the role of the ACL in knee function, in order to select proper replacements. Digital image correlation (DIC), a non-contact full field displacement measurement technique, is an established tool for evaluating non-biological materials. The application of DIC to soft tissues has been in the nascent stages, largely due to patterning challenges of such materials. The ACL is notoriously difficult to mechanically characterize, due to the complex geometry of its two bundles and their insertions. This paper examines the use of DIC to determine the tensile mechanical properties of the AM and PL bundles of ovine ACLs in a well-known loading state. Homogenous loading in the mid-substance of the bundles provides for accurate development of stress/strain curves using DIC. Animal to animal variability is reduced, and the bundles are stiffer than previously thought when tissue-level strains are accurately measured.

STATEMENT OF SIGNIFICANCE

The anterior cruciate ligament (ACL), a major stabilizing ligament of the articular knee joint, is one of the most commonly injured soft tissue structures in the knee. Often, invasive surgery is required to restore pre-injury knee kinematics, and there are several long-term consequences of ACL reconstructions, including early-onset osteoarthritis. The role of the ACL in knee stability and motion has received much attention in the biomechanics community. This paper examines the use of a non-contact full-field displacement measurement technique, digital image correlation, to determine the tensile mechanical properties of the ACL. The focus of this work is to investigate the intrinsic mechanical properties of the ACL, as new knowledge in these areas will aid clinicians in selecting ACL replacements.

Determination of the in situ mechanical behavior of ankle ligaments

The mechanical behavior of ankle ligaments at the structural level can be characterized by force-displacement curves in the physiologic phase up to the initiation of failure. However, these properties are difficult to characterize in vitro due to the experimental difficulties in replicating the complex geometry and non-uniformity of the loading state in situ. This study used a finite element parametric modeling approach to determine the in situ mechanical behavior of ankle ligaments at neutral foot position for a mid-sized adult foot from experimental derived bony kinematics. Nine major ankle ligaments were represented as a group of fibers, with the force-elongation behavior of each fiber element characterized by a zero-force region and a region of constant stiffness. The zero-force region, representing the initial tension or slackness of the whole ligament and the progressive fiber uncrimping, was identified against a series of quasi-static experiments of single foot motion using simultaneous optimization. A range of 0.33-3.84mm of the zero-force region was obtained, accounting for a relative length of 6.7±3.9%. The posterior ligaments generally exhibit high-stiffness in the loading region. Following this, the ankle model implemented with in situ ligament behavior was evaluated in response to multiple loading conditions and proved capable of predicting the bony kinematics accurately in comparison to the cadaveric response. Overall, the parametric ligament modeling demonstrated the feasibility of linking the gross structural behavior and the underlying bone and ligament mechanics that generate them. Determination of the in situ mechanical properties of ankle ligaments provides a better understanding of the nonlinear nature of the ankle joint. Applications of this knowledge include functional ankle joint mechanics and injury biomechanics.

A dynamic study of the anterior cruciate ligament of the knee using an open MRI

Recent anatomical and radiological studies of the anterior cruciate ligament (ACL) suggest the ACL length and orientation change during knee flexion, and an open MRI sequencing during knee flexion enables a dynamic ACL analysis. This study's goal is to describe a normal ACL using a 1T open MRI and, in particular, variations in length and insertion angles at different degrees of flexion. Twenty-one volunteers with clinically healthy knees received a dynamic MRI with their knees in hyperextension, neutral position, and flexed at 45° and 90° angles. For each position, two radiologists measured the ACL lengths and angles of the proximal insertion between the ACL's anterior edge and the roof of the inter-condylar notch. Additionally, we measured the ACL's and the tibial plateau's distal angle insertion between their anterior edges and then compared these with the nonparametric Wilcoxon test. The ACL had a significant extension between the 90° flexion and all other positions (hyperextension: 31.75 ± 2.5 mm, neutral position: 32.5 ± 2.6 mm, 45°: 35.6 ± 1.6 mm, 90°: 35.6 ± 1.6 mm). There was also a significant increase of the angle insertion between the proximal 90° flexion and all other positions, as well as between hyperextension and bending to 45° (hyperextension: 2.45° ± 3.7°, neutral: 13.4° ± 9.7°, 45°: 33 25 ± 9.3, 90: 51.85° ± 9.3°). Additionally, there is a significant increase in the distal angle insertion for all positions (hyperextension: 133.2° ± 5.4°, neutral position: 134.95° ± 4.4°, 45°: 138.35° ± 5.9°, 90°: 149.15° ± 8.6°). Our study is the first to exhibit that a dynamic MRI has a significant ACL extension in vivo during bending. This concept opens the way for further studies to improve the diagnosis of traumatic ACL injuries using a dynamic MRI.

Anatomic anterior cruciate ligament reconstruction: a changing paradigm

Injury to the anterior cruciate ligament (ACL) of the knee is potentially devastating for the patient and can result in both acute and long-term clinical problems. Consequently, the ACL has always been and continues to be of great interest to orthopaedic scientists and clinicians worldwide. Major advancements in ACL surgery have been made in the past few years. ACL reconstruction has shifted from an open to arthroscopic procedure, in which a two- and later one-incision technique was applied. Studies have found that traditional, transtibial arthroscopic single-bundle reconstruction does not fully restore rotational stability of the knee joint, and as such, a more anatomic approach to ACL reconstruction has emerged. The goal of anatomic ACL reconstruction is to replicate the knee's normal anatomy and restore its normal kinematics, all while protecting long-term knee health. This manuscript describes the research that has changed the paradigm of ACL reconstruction from traditional techniques to present day anatomic and individualized concepts.

Deconstructing the Anterior Cruciate Ligament: What We Know and Do Not Know About Function, Material Properties, and Injury Mechanics

Anterior cruciate ligament (ACL) injury is a common and potentially catastrophic knee joint injury, afflicting a large number of males and particularly females annually. Apart from the obvious acute injury events, it also presents with significant long-term morbidities, in which osteoarthritis (OA) is a frequent and debilitative outcome. With these facts in mind, a vast amount of research has been undertaken over the past five decades geared toward characterizing the structural and mechanical behaviors of the native ACL tissue under various external load applications. While these efforts have afforded important insights, both in terms of understanding treating and rehabilitating ACL injuries; injury rates, their well-established sex-based disparity, and long-term sequelae have endured. In reviewing the expanse of literature conducted to date in this area, this paper identifies important knowledge gaps that contribute directly to this long-standing clinical dilemma. In particular, the following limitations remain. First, minimal data exist that accurately describe native ACL mechanics under the extreme loading rates synonymous with actual injury. Second, current ACL mechanical data are typically derived from isolated and oversimplified strain estimates that fail to adequately capture the true 3D mechanical response of this anatomically complex structure. Third, graft tissues commonly chosen to reconstruct the ruptured ACL are mechanically suboptimal, being overdesigned for stiffness compared to the native tissue. The net result is an increased risk of rerupture and a modified and potentially hazardous habitual joint contact profile. These major limitations appear to warrant explicit research attention moving forward in order to successfully maintain/restore optimal knee joint function and long-term life quality in a large number of otherwise healthy individuals.

The femoral insertion of the anterior cruciate ligament: discrepancy between macroscopic and histological observations

PURPOSE

To observe the femoral anterior cruciate ligament (ACL) insertion macroscopically, histologically, and immunohistologically.

METHODS

We used 20 embalmed cadaveric knees (mean age, 69.8 ± 5.3 years) for this study. The femoral ACL insertion was observed macroscopically, and areas were measured with digital calipers. The morphology of the ACL insertion was subsequently observed, and the areas were measured histologically and immunohistologically (stained for types I and III collagen). Finally, the macroscopic and microscopic measurements were compared.

RESULTS

Macroscopically, in 16 knees, the proximal ACL fibers spread in a fanlike manner on the medial aspect of the lateral femoral condyle and the femoral insertion was oval. The lengths of the long and short axes of the insertion were 17.7 ± 2.7 mm and 4.6 ± 0.7 mm, respectively. Microscopically, the insertion was located just behind the lateral intercondylar ridge (resident's ridge) and could be divided into the direct and indirect insertions. The direct insertion was 5.3 ± 1.1 mm wide and did not continue to the posterior cartilage. The indirect insertion was located behind the direct insertion, and the posterior ACL fiber stained for type I collagen blended into the posterior cartilage on immunohistologic observations. Another bony ridge was found at the posterior margin of the direct insertion. The widths of the direct insertion were similar between microscopic and macroscopic measurements.

CONCLUSIONS

The femoral ACL insertion observed macroscopically corresponded to the direct insertion observed microscopically. The posterior portion behind the lateral intercondylar posterior ridge was the indirect insertion microscopically and appeared membrane-like macroscopically.

CLINICAL RELEVANCE

Findings from observation of the lateral intercondylar posterior ridge during arthroscopy and consideration of the distance from the posterior cartilage border may contribute to surgeons' decisions about femoral tunnel placement during anatomic ACL reconstruction.

Variations in cell morphology in the canine cruciate ligament complex

Cell morphology may reflect the mechanical environment of tissues and influence tissue physiology and response to injury. Normal cruciate ligaments (CLs) from disease-free stifle joints were harvested from dog breeds with a high (Labrador retriever) and low (Greyhound) risk of cranial cruciate ligament (CCL) rupture. Antibodies against the cytoskeletal components vimentin and alpha tubulin were used to analyse cell morphology; nuclei were stained with 4',6-diamidino-2-phenylindole, and images were collected using conventional and confocal microscopy. Both cranial and caudal CLs contained cells of heterogenous morphologies. Cells were arranged between collagen bundles and frequently had cytoplasmic processes. Some of these processes were long (type A cells), others were shorter, thicker and more branched (type B cells), and some had no processes (type C cells). Processes were frequently shown to contact other cells, extending longitudinally and transversely through the CLs. Cells with longer processes had fusiform nuclei, and those with no processes had rounded nuclei and were more frequent in the mid-substance of both CLs. Cells with long processes were more commonly noted in the CLs of the Greyhound. As contact between cells may facilitate direct communication, variances in cell morphology between breeds at a differing risk of CCL rupture may reflect differences in CL physiology.

Mechanical functions of the three bundles consisting of the human anterior cruciate ligament

PURPOSE

The reconstruction technique to individually reconstruct multi-bundles of the anterior cruciate ligament (ACL) has been improved in the last decade. For further improvement of the technique, the present study was conducted to determine the force sharing among the three bundles (the medial and lateral bundles (AMM and AML) of the anteromedial (AM) bundle and the posterlateral (PL) bundle) of the human ACL in response to hyperextension, passive flexion-extension and anterior force to the knee.

METHODS

Using a 6-DOF robotic system, the human cadaveric knee specimens were subjected to hyperextension, passive flexion-extension and anterior-posterior tests, while recording the 6-DOF motion and force/moment of the knees. The intact knee motions recorded during the tests were reproduced after sequential bundle transection to determine the bundle forces.

RESULTS

The bundle forces were around 10 N at 5 N-m of hyperextension and remained less than 5 N during passive flexion-extension. In response to 100 N of anterior force, the AMM and PL bundle forces were slightly higher than the AML bundle force at full extension. The AMM bundle force remained at a high level up to 90° of flexion, with significant differences versus the AML bundle force at 15°, 30° and 60° of flexion and the PL bundle force at 90° of flexion.

CONCLUSION

The AMM bundle is the primary stabilizer to tibial anterior drawer through wide range of motion, while the AML bundle is the secondary stabilizer in deep flexion angles. The PL bundle is the crucial stabilizer to hyperextension as well as tibial anterior drawer at full extension.

Imaging of the anterior cruciate ligament

The anterior cruciate ligament (ACL) is an important structure in maintaining the normal biomechanics of the knee and is the most commonly injured knee ligament. However, the oblique course of the ACL within the intercondylar fossa limits the visualization and assessment of the pathology of the ligament. This pictorial essay provides a comprehensive and illustrative review of the anatomy and biomechanics as well as updated information on different modalities of radiological investigation of ACL, particularly magnetic resonance imaging.

Current knowledge in the anatomy of the human anterior cruciate ligament

The anterior cruciate ligament (ACL) is one of the most frequently studied structures of the musculoskeletal system and continues to stimulate debate and challenges among researchers and surgeons. The ultimate goal of anatomic reconstruction surgery is to restore the native anatomy as much as possible. However, this requires thorough knowledge of its anatomy. The aim of this article is to review the current knowledge of the anatomy of ACL along with its macrostructural and ultrastructural properties.

Analysis of partial meniscectomy and ACL reconstruction in knee joint biomechanics under a combined loading

BACKGROUND

Despite partial meniscectomies and ligament reconstructions as treatments of choice for meniscal and ligament injuries, respectively, the knee joint osteoarthritis persists.

METHODS

A detailed nonlinear finite element model of the knee joint was developed to evaluate biomechanics of the tibiofemoral joint under 200 N drawer load with and without 1500 N compression preload. The model incorporated composite structure of cartilage and meniscus. The effects on joint response and articular contact pressure of unilateral partial meniscectomy, of changes in prestrain or material properties of the anterior cruciate ligament and of their combination were investigated.

FINDINGS

Compressive preload further increases anterior cruciate ligament strains/forces in drawer loading. Partial meniscectomy and perturbations in anterior cruciate ligament prestrain/material properties, alone or combined, substantially alter the load transfer via covered and uncovered areas of cartilage as well as contact pressure distribution on cartilage. Partial meniscectomy especially when combined with a slacker anterior cruciate ligament diminish the load via affected meniscus generating unloaded regions on the cartilage.

INTERPRETATION

Partial meniscectomy concurrent with a slack anterior cruciate ligament substantially alter cartilage contact pressures. These alterations further intensify in the event of greater external forces, larger meniscal resections and total anterior cruciate ligament rupture, thus suggesting a higher risk of joint degeneration.

Anatomic double-bundle versus single-bundle ACL reconstruction: a comparative biomechanical study in rabbits

Thirty New Zealand white rabbits underwent anterior cruciate ligament (ACL) reconstruction in their right knees; 15 animals underwent a double-bundle anatomic ACL reconstruction using the medial third of the patellar tendon and the semitendinosus tendon. Additionally, 15 animals underwent ACL reconstruction, using a single-bundle semitendinosus tendon autograft. The knees of both groups were evaluated with a device similar to the KT1000 arthrometer onto which a dial indicator was attached (Mitutoyo dial indicator 2050) in 30 degrees and 90 degrees of flexion, preoperatively, after ACL resection and 3 months postoperatively. Statistical analysis of the results revealed that for 90 degrees of knee flexion, the mean estimated anterior shift for the double-bundle technique was 1.92 mm lesser than that of the single-bundle technique (P = 0.006). For 30 degrees of knee flexion, the mean anterior shift was again lesser than that of the single-bundle technique by 0.66 mm, but this difference was not statistically significant. The described double-bundle ACL reconstruction technique resulted in a more stable knee as far as the anterior tibial shift was concerned as compared to a single-bundle ACL reconstruction. This animal model may be potentially useful in the future for the study of other parameters influencing the outcome of the double-bundle ACL reconstruction.

Biomechanics of the goat three bundle anterior cruciate ligament

The goat is a widely used animal model for basic research on the anterior cruciate ligament (ACL), but the biomechanical role of the different bundles [intermediate (IM), anteromedial (AM), posterolateral (PL)] of the ACL is unclear. Therefore, the aim of this study is to describe the biomechanical function of the different bundles and evaluate its use for a double bundle ACL reconstruction model. A CASPAR Stäubli RX90 robot with a six degree-of-freedom load cell was used for measurement of anterior tibial translation (ATT) (mm) and in situ forces (N) at 30 degrees (full extension), 60 degrees , 90 degrees as well as rotational testing at 30 degrees in 14 paired goat knees before and after each bundle was cut. When the AM-bundle was cut, the ATT increased significantly at 60 degrees and 90 degrees of flexion (p < 0.05). When the PL-bundle was cut, the ATT increased only at 30 degrees. However, most load was transferred through the big AM-bundle while the PL-bundle shared significant load only at 30 degrees, with only minimal contribution from the IM-bundle at all flexion degrees. The observed biomechanical results in this study are similar to the human ACL observed previously in the literature. Though anatomically discernible, the IM-bundle plays only an inferior role in ATT and might be neglected as a separate bundle during reconstruction. The goat ACL shows some differences to the human ACL, whereas the main functions of the ACL bundles are similar.

ST/G ACL reconstruction: double strand plus extra-articular sling vs double bundle, randomized study at 3-year follow-up

Several investigators have reported the presence of biomechanical, kinematic, anatomic, fiber orientation patterns and biological differences between the anteromedial bundle and the posterolateral bundle of ACL. The purpose of this prospective randomized study was to compare the clinical, instrumental and X-ray outcome of two ACL reconstruction techniques with hamstring tendons: one with a single intra-articular bundle associated to an extra-articular sling, the second with a more anatomic double-bundle technique that reproduces better the native ACL function. From an initial group of 100 patients who underwent ACL reconstruction, 72 patients (35 single bundle plus lateral plasty and 37 double bundle) were evaluated with IKDC, Tegner score, KT2000 arthrometer, Activity Rating Scale, Psychovitality Questionnaire and Ahlback radiographic score at a mean 3 years follow-up. Double-bundle group showed significantly better results regarding IKDC, ROM, Activity Rating Scale and time to return to sport. Also KT 2000 showed significant differences in objective stability. The double-bundle technique for ACL reconstruction described in this paper has demonstrated significantly better subjective, objective and functional results compared with a double-stranded hamstrings plus extra-articular sling at a minimum 3-year follow-up.

Strain pattern comparison of double- and single-bundle anterior cruciate ligament reconstruction techniques with the native anterior cruciate ligament

PURPOSE

The purpose of this study was to dynamically assess the native strain patterns of the anteromedial bundle (AMB) and posterolateral bundle (PLB) of the anterior cruciate ligament (ACL) and compare these findings with graft bundle strain patterns after double-bundle (DB) ACL reconstruction with tibial fixation under 40 N of tension at 75 degrees knee flexion (AMB) and under 20 N of tension at 20 degrees knee flexion (PLB) and after single-bundle (SB) reconstruction with tibial fixation under 40 N of tension at 20 degrees knee flexion.

METHODS

The mean strain pattern of the AMB and PLB of the native ACL of 4 cadaveric knees was measured via differential variable reluctance transducers and 2-dimensional kinematic analysis during passive manual knee flexion-extension under a constant axial compression load. Measurements were repeated after DB and SB ACL reconstruction. Celeration line assessments with a split-middle technique were performed to quantify percent strain/knee flexion-extension angle change at reciprocating bundle function transition points.

RESULTS

The DB ACL reconstruction technique displayed reciprocating AMB and PLB strain patterns that more closely replicated those of the native ACL. The SB ACL reconstruction technique tended to replicate AMB strain patterns, suggesting poor bundle function differentiation.

CONCLUSIONS

The DB ACL reconstruction with differential AMB and PLB tensioning more closely replicated native ACL strain patterns than the SB ACL reconstruction. The SB ACL reconstruction that we used closely simulated native ACL AMB strain patterns; however, PLB function was not restored.

CLINICAL RELEVANCE

The DB ACL reconstruction more closely replicated the AMB and PLB strain patterns of the native ACL.

Anterior cruciate ligament reconstruction with double bundle versus single bundle: experimental study

OBJECTIVE

To test an intra-articular reconstruction of the anterior cruciate ligament of the knee in 10 human cadavers by replacing 2 anterior cruciate ligament bundles, with the purpose of producing a surrogate that would be structurally more similar to the anatomy of the anterior cruciate ligament and would provide the knee with more stability.

METHODS

We reconstructed the anteromedial and posterolateral bundles using a quadriceps muscle tendon graft that included a patellar bone segment. The anteromedial bundle was replaced in 10 knees (5 right and 5 left knees from different cadavers) by a quadriceps-bone tendon graft, and the anteromedial and posterolateral bundles were replaced in the matching pairs of these knees. In the latter, the bone segment was fixed to the tibia, and the tendinous portion of the graft was divided longitudinally creating two 5-mm wide bundles that were inserted individually into the femur through 2 independent bone tunnels. Then, the knees were tested mechanically to evaluate the tibial anterior dislocation in relation to the femur, as well as the rigidity of the graft. The control group was formed by the knees with intact anterior cruciate ligaments, before being resected to be reconstructed.

RESULTS

The results obtained did not show superiority of double-bundle reconstruction over single-bundle reconstruction, and neither technique provided the knee with the same stability and rigidity of the intact anterior cruciate ligament.

CONCLUSION

Our hypothesis, based on the anatomy and biomechanics of the knee, that reconstruction of the anterior cruciate ligament using 2 bundles would result in a more anatomic reconstruction and provide better containment of the anterior tibial translation was not supported by the results of this study.

Comparison of fixation methods of double-bundle double-tibial tunnel ACL reconstruction and double-bundle single-tunnel technique

An experimental study was conducted in order to evaluate biomechanical methods of single-bundle reconstruction in ACL and compare it with a new double-bundle double-tibial tunnel technique. Twenty-four porcine cadaver knees, divided into 4 groups of 6 knees each and 48 proper extensors of the fourth toe tendons, were used for the fixation techniques. In groups A and B, a double-bundle technique with a single femoral and tibial tunnel was used, fixed to a femoral and tibial post with screws and with buttons, respectively. In groups C and D, a double-bundle technique (technique Delta) with two separate tibial tunnels was used, fixed to a femoral and tibial post with screws and with buttons, respectively. A material testing system (Instron) was used for anteriorly translating the tibia until failure. The femoral and tibial post as a fixation method is superior to the conventional buttons technique. The more anatomical double-bundle reconstruction technique provided significantly higher structural properties and smaller loss of fixation compared with the single-bundle reconstruction technique. The comparison of the two techniques gave superior results to the femoral and tibial screws over the buttons. The double-bundle technique attempts to restore the anterior stability of the knee joint.

Biomechanical evaluation of two techniques for double-bundle anterior cruciate ligament reconstruction: one tibial tunnel versus two tibial tunnels

BACKGROUND

This research was undertaken to determine whether there is a need for a second tibial tunnel in anatomic anterior cruciate ligament reconstruction.

HYPOTHESIS

Anatomic two-bundle reconstruction with two tibial tunnels restores knee anterior tibial translation in response to 134 N and to 5-N.m internal tibial torque combined with 10-N.m valgus torque more closely to normal than does double-bundle reconstruction with one tibial tunnel.

STUDY DESIGN

Controlled laboratory study.

METHODS

Ten cadaveric knees were subjected to a 134-N anterior tibial load at 0 degrees, 30 degrees, 60 degrees, and 90 degrees and to 5-N.m internal tibial torque and 10-N.m valgus torque at 15 degrees and 30 degrees. Resulting knee kinematics and in situ force in the anterior cruciate ligament or replacement graft were determined by using a robotic/universal force-moment sensor testing system for (1) intact, (2) anterior cruciate ligament-deficient, (3) double-bundle/one tibial tunnel, and (4) double-bundle/two tibial tunnels.

RESULTS

Anterior tibial translation for the reconstruction with two tibial tunnels was significantly closer to that of the intact knee than was the reconstruction with one tibial tunnel at 0 degrees and 30 degrees of flexion (0 degrees = 3.82 vs 6.0 mm, P < .05; 30 degrees = 7.99 vs 11 mm, P < .05). The in situ force normalized to the intact anterior cruciate ligament for the reconstruction with two tibial tunnels was significantly higher than the in situ force of the reconstruction with one tibial tunnel (30 degrees = 89 vs 82 N, P < .05). With a combined rotatory load, the anterior tibial translation of specimens with a tibial two-tunnel technique was significantly lower than that of specimens with one tunnel (0 degrees = 5.7 vs 8.4 mm, P < .05; 30 degrees = 7.5 vs 9.5 mm, P < .05).

CONCLUSIONS

Anatomic reconstruction with two tibial tunnels may produce a better biomechanical outcome, especially close to extension.

CLINICAL RELEVANCE

At the time of initial fixation, there appears to be a small biomechanical advantage to the second tibial tunnel in the setting of two-bundle anterior cruciate ligament reconstruction.

Anterior cruciate ligament anatomy and function relating to anatomical reconstruction

Recently, the interest in surgical techniques that reconstruct the anteromedial (AM) and the posterolateral (PL) bundles of the anterior cruciate ligament (ACL) has risen. This review focuses on the structural as well as the mechanical properties of the ACL and the anatomical details of the femoral origin, midsubstance, and tibial insertion of AM and PL bundles of the ACL. The terminology of AM and PL bundles is chosen according to the tibial insertion and determined by their functional tensioning pattern throughout knee flexion. Close to extension the AM is moderately loose and the PL is tight. As the knee is flexed, the femoral attachment of the ACL becomes more horizontally oriented, causing the AM bundle to tighten and the PM bundle to loosen up. The ACL has been described to be restraint to anterior tibial displacement and internal tibial rotation. The rotational component might be represented by the PL bundle. The femoral origin has an oval shape with the center of the AM close to over-the-top position and the center of the PL close to the anterior and inferior cartilage margin. Tibial and femoral insertions of the ACL are over 3.5 times larger when compared to the midsubstance and tunnel placement is more challenging because of the limited size of potential grafts selection of tunnel site placement. For reconstruction, both bone-patellar tendon-bone (BPTB) and quadrupled hamstring grafts are used. Structural properties of a 10 mm wide BPTB or quadrupled hamstring graft have been reported to be comparable with those of the native ACL.

Biomechanics and anterior cruciate ligament reconstruction

For years, bioengineers and orthopaedic surgeons have applied the principles of mechanics to gain valuable information about the complex function of the anterior cruciate ligament (ACL). The results of these investigations have provided scientific data for surgeons to improve methods of ACL reconstruction and postoperative rehabilitation. This review paper will present specific examples of how the field of biomechanics has impacted the evolution of ACL research. The anatomy and biomechanics of the ACL as well as the discovery of new tools in ACL-related biomechanical study are first introduced. Some important factors affecting the surgical outcome of ACL reconstruction, including graft selection, tunnel placement, initial graft tension, graft fixation, graft tunnel motion and healing, are then discussed. The scientific basis for the new surgical procedure, i.e., anatomic double bundle ACL reconstruction, designed to regain rotatory stability of the knee, is presented. To conclude, the future role of biomechanics in gaining valuable in-vivo data that can further advance the understanding of the ACL and ACL graft function in order to improve the patient outcome following ACL reconstruction is suggested.

Anatomic double-bundle anterior cruciate ligament reconstruction

Anterior cruciate ligament (ACL) reconstruction is one of the most common procedures performed by orthopaedic surgeons. The procedure has improved significantly since its inception in 1900 and continues to be intensively studied with outcomes receiving considerable attention. Traditional ACL reconstruction techniques have focused on one portion of the ACL--the anteromedial bundle. Single-bundle ACL reconstruction is the criterion standard and has provided good to excellent results, with many athletes being able to return to sports; however, recently, some authors have noted persistent instability with functional testing and degenerative radiographic changes after single-bundle ACL reconstruction. As a result, several centers have attempted to improve upon the single-bundle technique by reconstructing both the anteromedial and posterolateral bundles of the ACL. This article will present the embryologic, anatomic, and biomechanical rationale for double-bundle ACL reconstruction. In addition, the latest outcomes of double-bundle ACL reconstruction will be presented.

Anatomy of the anterior cruciate ligament double bundle structure: a macroscopic evaluation

INTRODUCTION

Traditional anterior cruciate ligament (ACL) surgery has demonstrated good results, but there is still a subset of unsatisfactory outcomes. Trends in reconstruction technique have changed from bone-patella-tendon-bone to hamstring refixation, and the next step appears to be the double bundle concept.

METHODS

We examined six fresh-frozen cadaver knees to evaluate the double bundle structure, dynamic motion characteristics and the relationship of knee flexion and relative position of the femoral insertion sites of the ACL.

RESULTS

In all knees, we identified an anteromedial (AM) and posterolateral (PL) bundle. The motion pattern demonstrated that the AM and PL bundles are oriented near parallel with the knee extended, and twist around each other as the knee is flexed. The visualization of the femoral footprint anatomy differs with knee flexion.

DISCUSSION

The double bundle model facilitates restoration of the original footprint anatomy and biomechanics more easily than the concept of the ACL as a one-bundle structure and the use of the o'clock position. It is essential to be aware of the degree of knee flexion when drilling the femoral tunnels.

PERSPECTIVE

Anatomic ACL reconstruction is a concept, not a technique, and allows a more refined surgical approach to ACL reconstruction including revision cases and partial ACL tears.

Cadaveric knee observation study for describing anatomic femoral tunnel placement for two-bundle anterior cruciate ligament reconstruction

PURPOSE

The recently developed 2-bundle anterior cruciate ligament (ACL) reconstruction lacks sufficient anatomic background. The purpose of this anatomic study was to describe functional anteromedial (AM) and posterolateral (PL) portions of the natural ACL and to provide a reproducible description of the graft placement. Our hypothesis was that the core functional area of the femoral ACL attachment will be revealed by removing the surface fibrous membranous tissue of the ACL midsubstance and the attachment area.

METHODS

The natural ACL was divided into 2 portions of AM and PL bundles in a flexion position; those bundles were most clearly defined when the knee was in flexion. The surface membrane of the ACL was removed and the margin was marked. The attachment site was removed after documenting its measurements. The knee position was corrected by digital photographs with the femoral bone in the correct lateral position.

RESULTS

The length of the major axis of the AM and PL bundles averaged 9.2 +/- 0.7 mm and 6.0 +/-0.8 mm, respectively. Both lengths of the minor axis of AM and PL bundles averaged 4.7 +/-0.6 mm. The distance from the attachment center of each AM and PL bundle to the posterior bone and articular surface border averaged 6.3 +/- 0.6 mm and 8.6 +/- 0.6 mm, respectively. The center of the AM and PL bundles was described as 1:40 and 3:10 clock positions, respectively, as left knee when the point was defined on the "lateral wall clock" of the intercondylar notch.

CONCLUSIONS

The study described the position and area of each 2-bundle of AM and PL portions of the natural ACL by describing its central structure with the surface membrane removed.

CLINICAL RELEVANCE

The detailed anatomic description of the natural ACL femoral attachment might suggest to surgeons where to make femoral tunnels during 2-bundle reconstruction.

A retrospective study of the midterm outcome of two-bundle anterior cruciate ligament reconstruction using quadrupled semitendinosus tendon in comparison with one-bundle reconstruction

PURPOSE

The objective of the study was to retrospectively compare the outcome of the first series of a 2-bundle anterior cruciate ligament reconstruction technique using quadrupled semitendinosus tendon with that of a 1-bundle reconstruction technique from 1992 through 1996.

TYPE OF STUDY

Case-control study.

METHODS

The 1-bundle group consisted of 56 patients with a follow-up period of 24 months or more (average, 46.5 months). The 2-bundle group consisted of 79 patients with a follow-up period of 24 months or more (average, 40.8 months). Manual knee laxity tests, anterior stability with KT-1000 (manual maximum), and knee extension and flexion strength by Cybex were evaluated using an average and standard deviation, and data were categorized according to the International Knee Documentation Committee (IKDC) classification. The Lysholm scale and the subjective recovery scale were also evaluated.

RESULTS

A statistically greater number of patients in the 1-bundle group were positive (+ or ++) based on the Lachman test (34% in the 1-bundle group and 13% in the 2-bundle group). The average KT-1000 anterior laxity of 2.7 +/- 2.3 mm in the 1-bundle group was statistically greater than the 1.9 +/- 1.9 mm in the 2-bundle group, with a statistical power between 70% and 80%. The total Lysholm knee scale score was 93 points in both groups, and the subjective recovery score was equivalent, 82% in the 1-bundle group and 86% in the 2-bundle group, respectively.

CONCLUSIONS

There was no statistical difference based on the IKDC, Lysholm, and subjective analysis. However, there was a statistical difference in the Lachman test, anterior drawer test, and KT-1000 measurements.

LEVEL OF EVIDENCE

Level III.

A new double-bundle anterior cruciate ligament reconstruction using the posteromedial portal technique with hamstrings

We describe a new double-bundle reconstruction method for ruptured anterior cruciate ligament using a posteromedial portal technique. Reconstruction materials are semitendinosus tendon (STT) and gracilis tendon (GT). STT is used as the substitute for the anteromedial bundle (AMB) and fixed to the tunnels produced on the tibia and the femur. GT is used as the substitute for the posterolateral bundle (PLB) and fixed to the tunnels on the tibia and the femur. This femoral tunnel for the PLB is created through a posteromedial portal. These procedures are performed using the inside-out technique. The posteromedial portal provides an accurate access to the femoral attachment of the PLB. This surgical technique can avoid overlapping of the 2 femoral tunnels and destruction of the posterior cortex of the lateral condyle on the femur during the preparation of the PLB. Our technique does not need another tibial tunnel for the PLB; the 1 tibial tunnel enables double-bundle reconstruction and prevents tibial tunnel expansion.

The effectiveness of reconstruction of the anterior cruciate ligament using the novel knot/press-fit technique: a cadaveric study

BACKGROUND

A variety of fixation devices are used for anterior cruciate ligament reconstruction with hamstring tendon grafts. These devices increase costs and can present artifacts in magnetic resonance imaging as well as complications in revision surgery. Therefore, a novel knot/press-fit technique that requires no implantable devices has been introduced.

NULL HYPOTHESIS

The knot/press-fit technique restores knee kinematics as well as the more commonly used EndoButton CL fixation and has similar biomechanical properties as other devices published in the literature.

STUDY DESIGN

Controlled laboratory study.

METHODS

Eight fresh-frozen cadaveric knees (52 +/- 7 years) were tested using a robotic/universal force-moment sensor testing system. The knee kinematics of the intact, anterior cruciate ligament-deficient, EndoButton-reconstructed, and knot/press-fit-reconstructed knee in response to both a 134-N anterior tibial load and a combined rotatory load at multiple knee flexion angles was determined. Differences between the 4 knee states were evaluated with a 2-factor repeated-measures analysis of variance (P < .05). To determine the stiffness and strength of the knot/press-fit fixation, the femur-graft-tibia complex was tested in uniaxial tension.

RESULTS

In response to an anterior tibial load, the anterior tibial translation for the knot/press-fit reconstruction was found to be not significantly different from that of the intact anterior cruciate ligament as well as that of the EndoButton reconstruction (P > .05). In response to a combined rotatory load, neither reconstruction procedure could effectively reduce the coupled anterior tibial translation to that of the intact knee, and no significant difference between the 2 reconstructions could be detected (P > .05). The stiffness of the knot/press-fit complex was found to be 37.8 +/- 9.6 N/mm, and the load at failure was 540 +/- 97.7 N, which is equal to other devices published in the literature.

CLINICAL RELEVANCE

The experiment suggests that the knot/press-fit technique may be a reliable alternative for the femoral fixation of hamstring tendon grafts.

Cruciate coupling and screw-home mechanism in passive knee joint during extension–flexion

The screw-home mechanism and coupling between forces in cruciate ligaments during passive knee joint flexion were investigated for various boundary conditions, flexion axis alignments and posterior cruciate ligaments (PCL)/anterior cruciate ligament (ACL) conditions. A developed non-linear 3D finite element model was used to perform detailed elasto-static response analyses of the human tibiofemoral joint as a function of flexion angle varying from 10 degrees hyper-extension to 90 degrees flexion. The tibia rotated internally as the femur flexed and externally as the femur extended. The re-alignment of the flexion axis by +/-5 degrees rotation about the axial (distal-proximal) axis, transection of the ACL and changes in cruciate ligament initial strains substantially influenced the 'screw-home' motion. On the other hand, restraint on this coupled rotation diminished ACL forces in flexion. A remarkable coupling was predicted between ACL and PCL forces in flexion; forces in both cruciate ligaments increased as the initial strain or pretension in one of them increased whereas they both diminished as one of them was cut or became slack. This has important consequences in joint functional biomechanics following a ligament injury or replacement surgery and, hence, in the proper management of joint disorders.

Effect of changes in cruciate ligaments pretensions on knee joint laxity and ligament forces

The knee joint cruciate ligaments are reconstructed with the rationale to avoid joint instability, recurrent injury, damage to soft tissues and osteoarthritis. Wide range of procedures with different stiffness, pretension, orientation and insertion locations have been proposed with the primary goal to restore the joint laxity. Apart from the general lack of success in preservation of force in the reconstructed ligament itself, the concern, not yet addressed, arises as to the effect of such perturbation on the other intact cruciate ligament. The interaction between cruciate ligament forces is hypothesized in this work. Using a 3-D nonlinear finite element model of the tibiofemoral joint, we examined this hypothesis by quantifying the extent of coupling between cruciate ligaments while varying the prestrain in each ligament under flexion with and without anterior-posterior (A-P) loads. A remarkable coupling was predicted between cruciate ligament forces in flexion thus confirming the hypothesis; forces in both cruciate ligaments increased as initial strain or pretension in one of them increased whereas they both diminished as one of them became slack. Moreover, changes in laxity and in ligament forces as a cruciate ligament prestrained or pretensioned varied with flexion angle and external loads. These findings have important consequences in joint functional biomechanics following a ligament injury or replacement surgery and in selection of laxity matched or ligament force matched pretensioning protocols.

Contribution of biomechanics, orthopaedics and rehabilitation: the past present and future

Biomechanics is a field that has a very long history. From its beginnings in ancient Chinese and Greek literature, the field of orthopaedic biomechanics has grown in the areas of biomechanics of bone, articular cartilage, soft tissues, upper extremities, spine and so on. Bioengineers in collaboration with orthopaedic surgeons have applied biomechanical principles to study clinically relevant problems, improving patient treatment and outcome. In the past 30 years, my colleagues and I have focused our research on the biomechanics of musculoskeletal soft tissues, ligaments and tendons in particular. Therefore, in this review article, the function of the knee ligaments and the associated homeostatic responses secondary to immobilisation and exercise will be described. Research on healing of the medial collateral ligament (MCL) of the knee and possible future approaches in improving the healing of the knee ligaments will be presented. Finally, improvement of the understanding of ligament reconstruction, specifically of the anterior cruciate ligament (ACL), through the use of robotics technology will be included. Throughout the manuscript, specific scientific findings that have guided or changed the clinical management of injury to these soft tissues will be emphasised.

Anatomic reconstruction of the anteromedial and posterolateral bundles of the anterior cruciate ligament using hamstring tendon grafts

PURPOSE

To develop and evaluate an anatomic reconstruction procedure of the posterolateral and anteromedial bundles of the anterior cruciate ligament (ACL).

TYPE OF STUDY

Anatomic study and case series.

METHODS

The femoral attachment of the anteromedial and posterolateral bundles of the ACL was anatomically analyzed with 5 cadaveric knees. Using another 3 cadaveric knees, anatomic reconstruction of the posterolateral and anteromedial bundles was performed with the transtibial technique, and tunnel positioning and graft function in a range of knee motion was observed. Based on this anatomic study, an anatomic reconstruction procedure of the anteromedial and posterolateral bundles was developed using hamstring tendon autografts. This procedure was carried out in 57 consecutive patients with an ACL-deficient knee. The patients were followed-up for a minimum of 24 months.

RESULTS

We developed the arthroscopically assisted anatomic reconstruction procedure of the posterolateral and anteromedial bundles, involving a new method of creating the tibial and femoral tunnels for the posterolateral bundle. To visualize the femoral attachment of the posterolateral bundle, the medial infrapatellar portal was more useful than the lateral portal. In clinical results, the side-to-side difference of anterior laxity averaged 1.0 mm with a standard deviation of 0.9.

CONCLUSIONS

The anatomic reconstruction of the anteromedial and posterolateral bundles using hamstring tendon autografts is clinically practical in the treatment for the ACL-deficient knee.

LEVEL OF EVIDENCE

Level IV.

Experimental and Computational Modeling of Joint and Ligament Mechanics

Quantitative data on the mechanics of diarthrodial joints and the function of ligaments are needed to better understand injury mechanisms, improve surgical procedures, and develop improved rehabilitation protocols. Therefore, experimental and computational approaches have been developed to determine joint kinematics and the in-situ forces in ligaments and their replacement grafts using human cadaveric knee and shoulder joints. A robotic/universal force-moment sensor testing system is used in our research center for the evaluation of a wide variety of external loading conditions to study the function of ligaments and their replacements; it has the potential to reproduce in-vivo joint motions in a cadaver knee. Two types of computational models have also been developed: a rigid body spring model and a displacement controlled spring model. These computational models are designed to complement and enhance experimental studies so that more complex loading conditions can be examined and the stresses and strains in the soft tissues can be calculated. In the future, this combined approach will improve our understanding of these joints and soft tissues during in-vivo activities and serve as a tool to aid surgical planning and development of rehabilitation protocols.

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

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