Movement of the posterior cruciate ligament during knee flexion--MRI analysis

Technique and Outcomes of Posterior Cruciate Ligament Repair With Augmentation

Background

Posterior cruciate ligament (PCL) injuries to the knee are uncommon, and ideal surgical management of these injuries is unclear. Current surgical techniques include PCL reconstruction with remnant debridement, remnant-preserving techniques, and primary PCL repair. Augmentation of PCL repairs and reconstructions has been proposed to protect repairs or grafts in the postoperative period.

Purpose

To describe PCL repair with the hamstring autograft augmentation technique and examine our preliminary midterm outcomes from a sequential cohort of patients.

Study Design

Case series; Level of evidence, 4.

Methods

The authors identified patients at their institution who underwent remnant-preserving primary PCL repair with hamstring autograft augmentation for both isolated tears and tears associated with multiligament knee injury (MLKI). Patient-reported outcomes were evaluated at a minimum 2-year follow-up using the International Knee Documentation Committee (IKDC) subjective knee form, the 12-item Short Form Survey, and a custom return-to-play questionnaire. Patient-reported outcomes data were summarized, and the predictors of outcomes from the descriptive data and clinical measures were further examined.

Results

A total of 23 patients with a mean follow-up of 5.3 years met the inclusion criteria. Of these patients, 87% were associated with MLKI. The mean IKDC score was 87.7. Approximately 83% of patients were able to successfully return to their sport or occupation. Among 19 athletes, only 2 reported being unable to return to their preinjury level of sport because of limitations from their PCL surgery. Patient-reported outcome scores and return to sport or occupation did not have a statistically significant association with age, sex, body mass index, time from injury to surgery, or follow-up time.

Conclusion

Outcomes of our cohort with remnant-preserving primary PCL repairs with hamstring autograft augmentation demonstrated comparable clinical outcomes to previously published PCL data. The advantages of remnant preservation, primary repair, and augmentation with an independent hamstring autograft reconstruction are combined within this technique.

Preoperative Factors Predicting the Preservation of the Posterior Cruciate Ligament in Total Knee Arthroplasty

Objective

Predicting the successful preservation of posterior cruciate ligament (PCL) in total knee arthroplasty (TKA) is an important step for preoperative planning to secure the satisfactory outcomes. We aimed to examine the preoperative factors predicting the successful preservation of the PCL in cruciate‐retaining TKA and the outcome of sacrificing the PCL.

Methods

In this retrospective study, we analyzed TKAs consecutively performed by a single surgeon between January 2019 and August 2021 who had been preoperatively planned to undergo implantation of cruciate‐retaining (CR) prostheses. The outcome of the current study was whether the PCL was retained or sacrificed. Anterior‐stabilized (AS) tibial bearings when the PCL was sacrificed as needed were used intraoperatively. Age, sex, body mass index (BMI), and preoperative diagnosis from the patients' medical records were obtained. The medial‐lateral width of epicondyle (MLW), the medial posterior condyle height (MPCH), the lateral posterior condyle height (LPCH), the ratio of MLW and MPCH, the ratio of MLW and LPCH, the Insall–Salvati index, and the severity of the varus or valgus deformity were measured using preoperative radiographs. Univariate and multivariate regression were fitted to assess the association of these factors with the successful retention of PCL. To examine the influence of sacrifice of the PCL on the surgical procedure, the size of the tibial and femoral components, the thickness of the polyethylene insert, and the rate of patella replacement between the CR group and AS group were also compared using t tests or chi‐square tests.

Results

Among 307 TKAs included, PCL was sacrificed with concurrent use of AS prostheses in 89 (29.0%) procedures. Knees with rheumatoid arthritis (P < 0.01), lower Insall–Salvati index (P < 0.01), and more severe varus deformity (P = 0.011) were at a higher risk of sacrificing the PCL intraoperatively. There was no significant difference in age, sex, BMI, MLW, MPCH, LPCH, ratio of MLW and MPCH, ratio of MLW and LPCH, size of the tibial and femoral components, or replacement of the patella between the CR and AS groups. Converting from CR to AS was associated with a higher risk of using a thicker polyethylene insert (P < 0.01).

Conclusion

Rheumatoid arthritis, lower Insall–Salvati index, and more severe varus deformity were associated with an increased risk of sacrificing the PCL in TKAs planned to undergo implantation CR prostheses. Converting to AS tibial bearing may result in a thicker polyethylene insert. These factors should be carefully considered for the appropriate selection of prosthesis type preoperatively.

Two positioned MRI can visualize and detect the location of peripheral rim instability with snapping knee in the no-shift-type of complete discoid lateral meniscus

INTRODUCTION

We evaluated the efficacy of two positioned magnetic resonance imaging (MRI) for visualizing the snapping phenomenon and detecting peripheral rim instability (PRI) in no-shift-type complete discoid lateral meniscus (CDLM).

MATERIALS AND METHODS

The records of 39 patients diagnosed with no-shift-type CDLM under routine MRI who underwent arthroscopic surgery were reviewed. The snapping phenomenon and meniscal shift on two positioned MRI in full extension and deep flexion were evaluated and calculated the agreement between these findings. The positive predictive value (PPV), sensitivity, and specificity of meniscal shift on two positioned MRI for predicting PRI were calculated; PRI was further investigated according to anterior and posterior location. The hypotheses of this study were asfollows: (1) Two positioned MRI can visualize the snapping phenomenon and (2) Meniscal shift on two positioned MRI is an important predictive sign of detecting the instability site in no-shift-type CDLM.

RESULTS

The κ values between the snapping phenomenon and meniscal shift on two positioned MRI were 0.84. The snapping and two positioned MRI findings had high PPV (1.0, 0.96), sensitivity (0.82, 0.85), and specificity (1.0, 0.91) for predicting overall PRI. For anterior PRI, the snapping and posterior shift on two positioned MRI had moderate and high PPV (0.78, 0.9), high sensitivity (0.9, 0.9), and specificity (0.8, 0.89). The anterior shift on two positioned MRI findings predicted posterior PRI with high PPV (1.0) and specificity (1.0).

CONCLUSIONS

Two positioned MRI visualized the snapping phenomenon. Meniscal shift on two positioned MRI was an important predictive sign of overall PRI, anterior PRI, and posterior PRI in no-shift-type CDLM.

In Vivo Knee Kinematics: How Important Are the Roles of Femoral Geometry and the Cruciate Ligaments?

BACKGROUND

While posterior cruciate-retaining (PCR) implants are a more common total knee arthroplasty (TKA) design, newer bicruciate-retaining (BCR) TKAs are now being considered as an option for many patients, especially those that are younger. While PCR TKAs remove the ACL, the BCR TKA designs keep both cruciate ligaments intact, as it is believed that the resection of the ACL greatly affects the overall kinematic patterns of TKA designs. The objectives of this study are to assess the in vivo kinematics for subjects implanted with either a PCR or BCR TKA and to compare the in vivo kinematic patterns to the normal knee during flexion. These objectives were achieved with an emphasis on understanding the roles of the cruciate ligaments, as well as the role of changes in femoral geometry of nonimplanted anatomical femurs vs implanted subjects having a metal femoral component.

METHODS

Tibiofemoral kinematics of 50 subjects having a PCR (40 subjects) or BCR (10 subjects) TKA were analyzed using fluoroscopy while performing a deep knee bend activity. The kinematics were compared to previously published normal knee data (10 subjects). Kinematics were determined during specific intervals of flexion where the ACL or PCL was most dominant.

RESULTS

In early flexion, subjects having a BCR TKA experienced more normal-like kinematic patterns, possibly attributed to the ACL. In mid-flexion, both TKA groups exhibited variable kinematic patterns, which could be due to the transitional cruciate ligament function period. In deeper flexion, both TKA functioned more similar to the normal knee, leading to the assumption that the PCL was properly balanced and functioning in the TKA groups. Interestingly, during late flexion (after 90°), the kinematic patterns for all three groups appeared to be statistically similar.

CONCLUSION

Subjects having a PCR TKA experienced greater weight-bearing flexion than the BCR TKA group. Subjects having a BCR TKA exhibited a more normal-like kinematic pattern in early and late flexion. The normal knee subjects achieved greater lateral condyle rollback and axial rotation compared to the TKA groups.

In vivo static and dynamic lengthening measurements of the posterior cruciate ligament at high knee flexion angles

PURPOSE

Rehabilitation is an important aspect of both non-operative and operative treatments of knee ligament tear. Posterior cruciate ligament (PCL) non-operative treatment consists of a step-by-step rehabilitation protocol and is well described. It goes from rest (phase I) to strengthening exercises (phase IV). More specific and high-intensity exercises such as cutting, sidestepping or jumps are, however, not described in detail, as no in vivo data exist to tell how these exercises constrain the ligaments and whether they have the same effect on all of them, in particular regarding lengthening. The goal of this study was to measure the ligament lengthening in static knee flexion based on 3D reconstructions from magnetic resonance imaging (MRI) and from motion capture and ligament simulation during dynamic exercises.

METHODS

The knee of nine volunteers was first imaged in a closed-bore MRI scanner at various static knee flexion angles (up to 110°), and the corresponding lengthening of the PCL and the other major knee ligaments was measured. Then, the volunteers underwent motion capture of the knee where dynamic exercises (sitting, jumping, sidestepping, etc.) were recorded. For each exercise, knee ligament elongation was simulated and evaluated.

RESULTS

According to the MRI scans, maximal lengthening occurred at 110° of flexion in the anterior cruciate ligament and 90° of flexion in the PCL. Daily living movements such as sitting were predicted to elongate the cruciate ligaments, whereas they shortened the collateral ligaments. More active movements such as jumping put the most constrain to cruciate ligaments.

CONCLUSION

This study provides interesting insights into a tailored postoperative regimen. In particular, knowing the knee ligament lengthening during dynamic exercises can help better define the last stages of the rehabilitation protocol, and hence provide a safe return to play.

Effects of Suture and Tourniquet on Intraoperative Kinematics in Navigated Total Knee Arthroplasty

BACKGROUND

To investigate the effects of suture (soft tissue closure) and air tourniquet use on intraoperative kinematics in navigated total knee arthroplasty.

METHODS

The study included 20 patients with varus-type knee osteoarthritis who underwent primary posterior-stabilized total knee arthroplasty using computed tomography (CT)-based navigation. Intraoperative tibiofemoral kinematics from maximum extension to maximum flexion were measured using the computed tomography-based navigation. The measurements were performed 3 times as follows: measurement 1: before suture (tourniquet on), measurement 2: after suture (tourniquet on), and measurement 3: after tourniquet removal. Details of kinematics including knee joint gap, tibiofemoral rotational angles, and anteroposterior (AP) distance between the femur and tibia were compared among the 3 measurements and statistically evaluated.

RESULTS

On the medial side, there was no significant difference among the 3 measurements in the extension gap, but measurement 1 showed a significantly larger flexion gap compared with the other 2 measurements. On the lateral side, there was no significant difference between the extension and flexion gaps in all measurements. The anteroposterior distance in measurement 1 showed that the femur was positioned significantly more anterior to the tibia at 10° and 20° of flexion compared with the other 2 measurements after suture. There was no significant difference among the 3 measurements in the tibiofemoral rotation angles.

CONCLUSION

These results found that the effect of suture and tourniquet was minimal, and that intraoperative kinematics can effectively evaluate postoperative passive kinematic conditions.

On the role of the patella, ACL and joint contact forces in the extension of the knee

Traditional descriptions of the knee suggest that the function of the patella is to facilitate knee extension by increasing the moment arm of the quadriceps muscles. Through modelling and evidence from the literature it is shown in this paper that the presence of the patella makes the ability of the quadriceps to rotate the thigh greater than their ability to rotate the tibia. Furthermore, this difference increases as the knee is flexed, thus demonstrating a pattern that is consistent with many human movements. This paper also shows that the anterior cruciate ligament plays a previously unheralded role in extending the shank and that translation at the tibiofemoral and patellofemoral joints is important in improving the capacity for thigh rotation when the knee is flexed. This study provides new insights as to how the structure of the knee is adapted to its purpose and illustrates how the functional anatomy of the knee contributes to its extension function.

Effects of knee flexion angle and loading conditions on the end-to-end distance of the posterior cruciate ligament: a comparison of the roles of the anterolateral and posteromedial bundles

BACKGROUND

It is commonly accepted that the anterolateral (AL) bundle of the posterior cruciate ligament (PCL) is tight in flexion and that the posteromedial (PM) bundle is tight in extension. However, a recent in vivo study showed that both bundles were tight in extension.

PURPOSE

To investigate the effects of knee flexion angle, rotational torque, and anterior/posterior translational force on the end-to-end distance between the femoral and tibial insertion sites of each bundle of the PCL.

STUDY DESIGN

Descriptive laboratory study.

METHODS

Cadaveric knees (10 specimens) were mounted on a robotic system, and the relative positional data between the femur and tibia were acquired during passive flexion/extension, with an applied 5-N·m rotational torque and an applied 89-N translational force. The bony surface and PCL insertion data were acquired with a 3-dimensional scanner after gross dissection and were superimposed onto the positional data. The end-to-end distance between the 2 PCL insertion sites of the femur and tibia was measured.

RESULTS

The end-to-end distance increased from full extension to 90° for both the AL (9.2 ± 1.8 mm; from 30.0 to 39.2 mm) and PM bundles (5.8 ± 2.2 mm; from 32.0 to 37.7 mm). With an internal rotational torque, the end-to-end distance of the PM bundle increased significantly (P < .05) at 0°, 30°, and 60° of knee flexion. Under a posterior translational force at 90° of knee flexion, the length of both bundles increased to their longest measurements (AM bundle: 40.6 ± 4.2 mm; PM bundle: 38.4 ± 3.8 mm).

CONCLUSION

The end-to-end distance of the AL and PM bundles of the PCL increased in flexion, and this pattern was maintained during tests with posterior translational force. The PM bundle was more affected by the rotational torque than was the AL bundle.

CLINICAL RELEVANCE

Both bundles of the PCL may serve a greater functional role in flexion than in extension. The PM bundle might be more important for the control of rotation than the AL bundle. Posterior translation at 90° of knee flexion could be the most stressful condition for both bundles of the PCL, which may have implications for an injury mechanism.

The isometry of two different paths for remnant-preserving posterior cruciate ligament reconstruction

PURPOSE

It is reported that the length of the posterior cruciate ligament (PCL) fibres increases as the knee flexes, and the magnitude of the length change reaches up to 9.8 mm throughout the range of motion, which exceeds the range of failure strain. Therefore, we postulated that a compensatory mechanism must be recruited to overcome this large strain in order to maintain physiologic function as a key component of joint kinematics. Our main objective was to compare the length change pattern for the linear distance between the femoral and tibial tunnels with the length change patterns derived from a real isometer test of different curvatures.

METHODS

We utilized ten intact cadaveric knees and created a vertical femoral tunnel (5 mm medial to the roof of the intercondylar notch and 5 mm proximal from the articular margin) and lateral tibial tunnels (5 mm proximal to the posterior bony ridge on the lateral side of the PCL fibre) and performed a 3D-CT scan at 0º, 30º, 60º, 90º, and 120º. The distances between the femoral and tibial tunnels were calculated from the 3D coordinates. Real isometry was checked both (1) over the PCL and (2) under the PCL using an isometer with an accuracy of 0.1 mm.

RESULTS

The path over the PCL had the longest intra-articular length, followed by the path under the PCL, and the lengths measured by CT, respectively. The path over the PCL had a more curved path compared with the path under the PCL and the lengths measured by CT. The lengths measured by CT showed significantly larger excursion than the real isometer test. The path over the PCL showed the least excursion through the range of motion, followed by the path under the PCL, and the lengths measured by CT, respectively.

CONCLUSION

Our findings suggested that a more curved PCL path has better isometry because the curvature of the PCL compensates for the length change between 0º and 60º flexion. In remnant preservation PCL reconstruction, the passage of graft over the PCL would have increased intra-articular length and better isometry compared with straight under the PCL path.

LEVEL OF EVIDENCE

Basic science study.

The intact posterior cruciate ligament not only controls posterior displacement but also maintains the flexion gap

BACKGROUND

The PCL is a strong stabilizer of the knee and provides posterior stability to the tibia. However, sagittal alignment of the PCL with the knee at 90° flexion suggests the PCL might play a role not only in posterior stabilization but also in maintaining the flexion gap.

QUESTIONS/PURPOSES

We determined whether the intact PCL helps maintain the flexion gap.

METHODS

We examined axial radiographs and gravity sag views of 17 patients with chronic isolated unilateral PCL injury. The flexion gap was defined as the mean value of the medial and lateral distances between the femoral and tibial bones on the axial radiograph. Increase in the flexion gap and posterior laxity were determined by comparing the patients' injured and contralateral uninjured knees.

RESULTS

The flexion gap of PCL injured knees (median, 7.5 mm; range, 5.3-11.5 mm; medial median, 6.2 mm; medial range, 3.7-8.3 mm; lateral median, 7.9 mm; lateral range, 5.3-11.5 mm) was larger than that seen in uninjured knees (median, 5.0 mm; range, 4.0-7.6 mm; medial median, 4.6 mm; medial range 3.4-7.1 mm; lateral median, 5.6; lateral range, 4.5-11.2 mm). The increment in the medial distance was similar to that in the lateral distance. Posterior laxity of injured knees was 9.1 (median); 5.4 to 15.2 (range) mm greater than that of uninjured knees. We found no correlation between posterior laxity and the flexion gap increment.

CONCLUSIONS

Our data suggest the intact PCL controls posterior displacement and maintains the flexion gap.

The influence of patella height on soft tissue balance in cruciate-retaining and posterior-stabilised total knee arthroplasty

PURPOSE

Although the patella reduced or everted position has recently been recognised as an important factor influencing soft tissue balance during assessment in total knee arthroplasty (TKA), the influence of patella height on soft tissue balance has not been well addressed. Therefore, the relationship between soft tissue balance and patella height was investigated and differences between cruciate-retaining (CR) and posterior-stabilised (PS) TKA were compared.

METHODS

Forty consecutive patients blinded to the type of implant received, were randomised prospectively. Using lateral radiographs, pre-operative patella height was measured. Using an offset-type tensor designed to measure the soft tissue balance with a reduced patellofemoral (PF) joint and femoral component in place, soft tissue balance was intra-operatively assessed in CR TKA (n = 20) and PS TKA (n = 20) in osteoarthritic patients. The joint component gap and varus ligament balance at zero, ten, 45, 90 and 135° of knee flexion with the patella reduced were measured.

RESULTS

In PS TKA, the joint component gap positively correlated with patella height at 90 and 135° of knee flexion. However, there was no correlation between joint component gap and patella height at other flexion angles in PS TKA and any flexion angle in CR TKA. Varus ligament balance showed no significant correlation with patella height in either CR or PS TKA.

CONCLUSION

Analysis of soft tissue balance and patella height only showed a positive correlation in joint component gap at a high flexion angle (90 and 135°) in PS TKA but not in other parameters examined. Pre-operative measurement of patella height may be an important factor for predicting an intra-operative flexion gap in PS TKA.

In vivo open-bore MRI reveals region- and sub-arc-specific lengthening of the unloaded human posterior cruciate ligament

Open-bore MRI scanners allow joint soft tissue to be imaged over a large, uninterrupted range of flexion. Using an open-bore scanner, 3D para-sagittal images of the posterior cruciate ligament (PCL) were collected from seven healthy subjects in unloaded, recumbent knee extension and flexion. PCL length was measured from one 2D MRI slice partition per flexion angle, per subject. The anterior surface of the PCL lengthened significantly between extension and flexion (p<0.001). Conversely, the posterior surface did not. Changes were not due to the PCL moving relative to the 2D slice partition; measurements made from 3D reconstructions, which compensated for PCL movement, did not differ significantly from measurements made from 2D slice partitions. In a second experiment, videos of knee flexion were made by imaging two subjects at several flexion angles. Videos allowed soft tissue tracking; examples are included. In a third experiment, unloaded knees of seven healthy, recumbent subjects were imaged at extension and at 40°, 70°, 90°, 100°, 110° and 120° flexion. The distance between PCL attachments increased between extension and 100°, and then decreased (p<0.001). The anterior surface of the PCL lengthened over the flexion angles measured (p<0.01). The posterior surface of the PCL lengthened between extension and 40° and then shortened (p<0.001). Both attachment separation and anterior surface length increased dramatically between extension and 40°, but varied less afterwards. Results indicate that PCL dynamics differ between terminal extension and active function sub-arcs. Also, attachment separation cannot predict the lengthening of all parts of the PCL, nor can lengthening of one part of the PCL predict the lengthening of another part. A potential connection between lengthening and loading is discussed. We conclude that low-field MRI can assess ligament lengthening during flexion, and that the dynamics of the PCL for any given region and sub-arc should be measured directly.

The influence of patella height on intra-operative soft tissue balance in posterior-stabilized total knee arthroplasty

PURPOSE

Although the patella reduced or everted position has recently been recognized as an important factor in influencing soft tissue balance during the assessment in total knee arthroplasty (TKA), the influence of patella height on soft tissue balance has not been well addressed. We therefore investigated the effect of patella height by comparing soft tissue balance between high [Insall-Salvati index (ISI) > 1] and low patella patients (ISI ≦ 1).

METHODS

Using a tensor designed to facilitate soft tissue balance measurements with a reduced patellofemoral joint and femoral component in place, we intra-operatively assessed the joint component gap and ligament balance of posterior-stabilized (PS) TKAs in 30 osteoarthritic patients performed at 0, 10, 45, 90, and 135° of flexion, with the patella reduced.

RESULTS

When comparing the two groups, the component gaps of the higher patella group showed a larger trend than those of the lower patella group, with significant differences at 90 and 135° of knee flexion. Moreover, the joint component gap positively correlated with ISI at 90 and 135° of knee flexion.

CONCLUSION

Patella higher group showed significant larger component gaps than patella lower group in high flexion angles (90 and 135°). Pre-operative measurement of patellar height can help predict intra-operative soft tissue balance in PS TKA.

LEVEL OF EVIDENCE

III.

REHABILITATION PROTOCOL AFTER ISOLATED POSTERIOR CRUCIATE LIGAMENT RECONSTRUCTION

To create a rehabilitation protocol following reconstruction of the posterior cruciate ligament (PCL), through a literature review. The literature review was conducted in the Medline and Embase databases, to search for data on biomechanical concepts and analyses relating to the posterior cruciate ligament of the knee. The search strategy was set up using the following rules: problem or injury in association with anatomical location terms; or surgical intervention procedure in association with rehabilitation terms. We began the process in this manner and subsequently introduced restrictions on certain terms to improve the search specificity. To design the protocol, a table was created for better data assessment, based on the time that elapsed between surgery and the start of physiotherapy. A rehabilitation protocol was created to improve weight-bearing control in the initial weeks after surgery, with the aid of a knee brace. Our aim was to achieve gains in total range of motion of the knee, which should be attained by the third month, thereby avoiding contractures resulting from the tissue healing process. Strengthening exercises and sensory-motor training were guided accordingly, thus avoiding overload on the graft and respecting the healing phases. The protocol proposed through this review was based on the current evidence relating to this subject.

Joint mechanics measurement using magnetic resonance imaging

Magnetic resonance imaging-based methods for measuring the mechanics of human joints have been successfully applied to quantitatively evaluate biomechanics in a wide variety of joints, pathologies, and interventions. The objective of this review was to provide a detailed overview of methods in the literature for measuring joint kinematics, meniscal and ligament movement, and cartilage strain using MRI.

A pilot trial on kinematic magnetic resonance imaging using a superconducting, horizontally opened, 1.2 T magnetic resonance system

Purpose

This study was performed to introduce and evaluate the potential of kinematic magnetic resonance imaging (KMRI) using a high-field open-magnet magnetic resonance (MR) system.

Methods

We attempted to perform KMRI of healthy volunteers’ lumbar spine and knee in the lateral position and ankle in the supine position utilizing the superconducting, horizontally opened, 1.2 T MR system (OASIS, HITACHI, Tokyo, Japan). For the KMRI of the lumbar spine, the volunteer had to lie on one side while maintaining maximally anteflexed, neutral, and maximally retroflexed positions and remain still for the duration of the acquisition time for each posture. In the same way, KMRI of the knee was performed with the volunteer's knee flexed at 0°, 30°, 60°, 90°, and 120° in the lateral position, and KMRI of the ankle was performed with the volunteer's ankle in maximally dorsiflexed, neutral, and maximally plantarflexed positions while lying in the supine position.

Results

We could acquire higher quality kinematic MR images than those acquired using low-field MR systems. The spinal canal, intervertebral discs and foramina, and facet joints in lumbar spine KMRI; the ligaments, menisci and patellofemoral joint in knee KMRI; and the tibiotalar articulation and peroneal tendon in ankle KMRI were clearly depicted.

Conclusion

The results of our pilot trial indicated that a superconducting horizontally opened, 1.2 T MR system offers high-quality KMRI images and can be utilized for the kinematic diagnosis and evaluation of sports injuries.

A multiple-bundle model to characterize the mechanical behavior of the cruciate ligaments

Measurements of elongations of the cruciate ligaments have been used to study the behaviors of these ligaments in-vitro and in-vivo, mostly based on simplified two-bundle models of the cruciates. The complex fiber anatomy of the cruciates may suggest a complex deformation behavior across the continuum of their substance that cannot be captured by only two measurement points. In this study, a new methodology was introduced to include more detailed fiber anatomy and to take into consideration the wrapping of the PCL around the intercondylar notch of the femur in deep flexion. The method was used in comparison to the conventional two-bundle models on three sample cadaver knees that underwent a passive flexion up to 150°. The elongation ratios of the bundles were measured as the ratio of change in the length of the bundles over their lengths at 0° flexion. The multiple-bundle models showed ranges of variations across the attachment sites of the cruciates which at all flexion angles were significantly larger than those observed from the conventional two-bundle models. When expressed in percentages, at 150° flexion the ranges of variations in the elongation ratio of the bundles were 32.7%±31.9% and 34%±8.6% for the ACL and PCL, respectively. Results of this study showed that important variations of elongation across the body of the cruciates can be obscured to the conventional two-bundle model of the cruciates, and therefore a more detailed bundle configuration is suggested for the purpose of studying elongation behaviors of these ligaments.

Posterior cruciate ligament recruitment affects antero-posterior translation during flexion gap distraction in total knee replacement. An intraoperative study involving 50 patients

BACKGROUND AND PURPOSE

Because of the oblique orientation of the posterior cruciate ligament (PCL), flexion gap distraction could lead to anterior movement of the tibia, which would influence the tibiofemoral contact point. This would affect the kinematics of the TKR. We assessed the flexion gap parameters when the knee is distracted during implantation of a PCL-retaining TKR. Furthermore, the effects of PCL elevation (steep or flat) and collateral ligament releases on the flexion gap parameters were determined.

METHODS

During a ligament-guided TKR procedure in 50 knees, the flexion gap was distracted with a double-spring tensor with 200N after the tibia had been cut. The flexion gap height, anterior tibial translation, and femoral rotation were measured intraoperatively using a CT-free navigation system.

RESULTS

During flexion gap distraction, the greatest displacement was seen in anterior-posterior direction. Mean ratio between increase in gap height and tibial translation was 1 to 1.9, and was highest for knees with a steep PCL (1 to 2.3). Knees with a flat PCL and knees with a ligament release had a larger increase in PCL elevation when the gap was distracted.

INTERPRETATION

When the PCL is tensioned, every extra mm that the flexion gap is distracted can be expected to move the tibia anteriorly by at least 1.7 mm (flat PCL), or more if there is a steep PCL. This changes the tibiofemoral contact point, which may have consequences for polyethylene wear.

Twenty-five years of tendon and ligament research

Twenty-five years ago, the Journal of Orthopaedic Research published its first volume, which included five articles covering topics in tendon and ligament research. Since then, the body of tendon and ligament research has continued to increase exponentially. This review summarizes major advancements in tendon and ligament research since the initial publication of this journal. The purpose of this article is not to provide an in-depth review of all of tendon and ligament research, but instead to provide a concise literature review of some of the major and recurring areas of research. The general topics covered over the last 25 years include tissue properties, tendinopathy, healing, and engineered scaffolds.

Joint gap changes with patellar tendon strain and patellar position during TKA

Balancing of the joint gap in extension and flexion is a prerequisite for success of a total knee arthroplasty. The joint gap is influenced by patellar position. We therefore hypothesized the state of the knee extensor mechanism (including the patellar tendon) would influence the joint gap. In 20 knees undergoing posterior-stabilized type total knee arthroplasties, we measured the joint gap and the patellar tendon strain from 0 degrees to 135 degrees flexion with the femoral component in position. When the patella was reduced, the joint gap was decreased at 90 degrees and 135 degrees (by 1.9 mm and 5.5 mm, respectively) compared with the gap with the patella everted. The patellar tendon strain increased with knee flexion. Patellar tendon strain at 90 degrees flexion correlated with the joint gap difference with the patella in everted and reduced positions. This suggests that in addition to the collateral ligaments, the knee extensor mechanism may have an influence on the joint gap. Therefore, accounting for extensor mechanism tightness may be important in achieving the optimal joint gap balance during total knee arthroplasty.

LEVEL OF EVIDENCE

Level IV, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

Function of posterior cruciate ligament bundles during in vivo knee flexion

BACKGROUND

The biomechanical functions of the anterolateral and posteromedial bundles of the posterior cruciate ligament over the range of flexion of the knee joint remain unclear.

HYPOTHESIS

The posterior cruciate ligament bundles have minimal length at low flexion angles and maximal length at high flexion angles.

STUDY DESIGN

Descriptive laboratory study.

METHODS

Seven knees from normal, healthy subjects were scanned with magnetic resonance, and 3-dimensional models of the femur, tibia, and posterior cruciate ligament attachment sites were created. The lines connecting the centroids of the corresponding bundle attachment sites on the femur and tibia represented the anterolateral and posteromedial bundles of the posterior cruciate ligament. Each knee was imaged during weightbearing flexion (from 0 degrees to maximal flexion) using a dual-orthogonal fluoroscopic system. The length, elevation, deviation, and twist of the posterior cruciate ligament bundles were measured as a function of flexion.

RESULTS

The lengths of the anterolateral and posteromedial bundles increased with flexion from 0 degrees to 120 degrees and decreased beyond 120 degrees of flexion. The posteromedial bundle had a lower elevation angle than the anterolateral bundle beyond 60 degrees of flexion. The anterolateral bundle had a larger deviation angle than the posteromedial bundle beyond 75 degrees of flexion. The femoral attachment of the posterior cruciate ligament twisted externally with increasing flexion and reached a maximum of 86.4 degrees +/- 14.7 degrees at 135 degrees of flexion (P < .05).

CONCLUSION

These data suggest that there is no reciprocal function of the bundles with flexion, which is contrary to previous findings. The orientation of the anterolateral and posteromedial bundles suggests that at high flexion, the anterolateral bundle might play an important role in constraining the mediolateral translation, whereas the posteromedial bundle might play an important role in constraining the anteroposterior translation of the tibia.

CLINICAL RELEVANCE

These data provide a better understanding of the biomechanical function of the posterior cruciate ligament bundles and may help to improve the design of the 2-bundle reconstruction techniques of the ruptured posterior cruciate ligament.