Biomechanical Function of Anterior Cruciate Ligament Remnants: Quantitative Measurement With a 3-Dimensional Electromagnetic Measurement System

A study regarding the anterior cruciate ligament remnant: Differences in balance and postural control between remnant-preserving and remnant-non-preserving patients

INTRODUCTION

The anterior cruciate ligament (ACL) is the most frequently injured ligament of the knee. However, quantitative studies on evaluate the postural control influence resulted from the ACL remnant preservation or not are scarce. The aim of this study is to evaluate the postural control of patients submitted to ACL reconstruction with and without preservation of the injured remnant in pre and postoperative periods.

METHODS

Eighteen patients underwent ACL reconstruction and separated into 2 groups according to the preservation or not of the remnant: (I) submitted to ACL reconstruction with preservation of the remnant (10 patients); (II) submitted to ACL reconstruction without preservation of the remnant (8 patients). They were assessed using the Lysholm score and force plate, which evaluated the patient's postural stability for remnant and non-remnant preservation in ACL reconstruction surgery.

RESULTS

Group I showed statistically significant subjective and objective improvements, both at 3 and 6 months. Additionally, improvement of the Lysholm test at 6 months in Group II was also statistically significant. Furthermore, the results of the Friedman test for the VCOP and VY variables of Group I, with support of the injured side in the force plate, showed a statistically significant difference both for pre and postoperative period at 3 months, compared to the 6-month postoperative period. The variables EAC and VX were statistically different for Group II, considering the preoperative period, 3 and 6 months postoperatively.

CONCLUSION

Preserving the ACL remnant in patients with ACL injuries has a positive impact on postural stability during recovery.

The influence of ruptured scar pattern of human anterior cruciate ligament remnant tissue on tendon-bone healing in vivo

The purpose of this study was to determine whether the transplantation of human cells from a non-reattached injured anterior cruciate ligament (ACL) remnant could enhance tendon-bone healing. Human ACL remnant tissue was classified into two groups based on the morphologic pattern as per Crain's classification: (1) non-reattachment group (Crain Ⅳ) and (2) reattachment group (Crain Ⅰ-Ⅲ). Seventy-five 10-week-old immunodeficient rats underwent ACL reconstruction followed by intracapsular administration of one of the following: (1) ACL-derived cells from the non-reattached remnant (non-reattachment group) (n = 5), (2) ACL-derived cells from the reattached tissue (reattachment group) (n = 5), or (3) phosphate-buffered saline (PBS) only (PBS group) (n = 5). Histological (Weeks 2, 4, and 8), immunohistochemical (Week 2), radiographic (Weeks 0, 2, 4, and 8), and biomechanical (Week 8) assessments were performed. Histological evaluation showed high and early healing, induction of endochondral ossification-like integration, and mature bone ingrowth at Week 4 in the non-reattachment group. Microcomputed tomography at Week 4 showed that the tibial bone tunnels in the non-reattachment group were significantly reduced compared to those in the reattachment and PBS groups. Moreover, biomechanical testing showed that ultimate load-to-failure in the non-reattachment group tended to be larger than that in the reattachment group, though not statistically significant. The enhanced healing potential in the non-reattachment group was explained by the increase in intrinsic angiogenesis/osteogenesis. In the subacute phase, the ACL-derived cells with the non-reattached morphologic pattern showed greater and earlier tendon bone healing compared with the cells obtained from the reattached morphologic pattern.

Effect of Remnant Tissues on Outcomes of Anterior Cruciate Ligament Reconstruction at Follow-up Arthroscopy

BACKGROUND

Remnant-preserving anterior cruciate ligament reconstruction (ACLR) is sought to enhance vascularization and maturation of a graft and to produce positive clinical outcomes after reconstruction.

OBJECTIVE

The purpose of this study was to investigate an effect of remnant anterior cruciate ligament (ACL) tissues on outcomes of ACLR 1 year after reconstruction in younger populations.

DESIGN

Retrospective chart review.

SETTING

Inpatient orthopedic surgical and rehabilitation clinic.

SUBJECTS

The subjects were 644 patients who underwent primary ACLR.

INDEPENDENT VARIABLES

The independent variables were age, height, and body weight of the subjects, and the presence of remnant tissue.

MAIN OUTCOME MEASURES

The outcome measure was the number of subjects with secondary infra-articular injuries at a follow-up arthroscopy after ACLR. The odds ratio was calculated and compared between the remnant-preserving ACLR (ACLR-P) and remnant-resecting (ACLR-R) groups to investigate the effect of remnant tissues on postoperative outcomes.

RESULTS

A total of 416 cases met our inclusion criteria and were included in this study. There were 136 cases (49 males and 87 females) in the ACLR-P group with the mean age (±SD) of 17.86 ± 2.85 years. There were 280 cases (106 males and 174 females) in the ACLR-R group, and the mean age (±SD) was 18.13 ± 2.73 years. Of 136 cases in the ALCR-P group, 54 (39.7%) had abnormal arthroscopic findings that lead to a surgical intervention. Of 280 patients in the ACLR-R group, 128 (45.7%) had abnormal findings. Odds ratio was 0.78 [95% confidence interval (CI), 0.51-1.18; P = 0.24]. Four cases in the ACLR-P group and 8 in the ACLR-R group were diagnosed with ACL retear during follow-up arthroscopy. Odds ratio was 1.03 (95% CI, 0.30-3.48; P = 0.96).

CONCLUSIONS

The presence of ACL remnant tissues did not have a significant effect on outcomes 1 year after reconstruction. However, there was a trend that lower percentage of patients with remnant-preserving ALCR had abnormal arthroscopic findings that lead to a surgical treatment at follow-up arthroscopy 1 year after initial reconstruction. The presence of remnant tissues did not have a significant effect on retear rate.

The Reliability of Classifying the Morphology of Anterior Cruciate Ligament Remnants during Surgery

Arthroscopic classification of the torn anterior cruciate ligament (ACL) morphology is fundamental for clinical studies on emerging techniques such as repair and preservation. At present, the most acknowledged classification is Crain description of four morphological patterns. The purpose of the study was to analyze the intra- and interobserver reliability of Crain classification in patients undergoing ACL reconstruction surgeries. The study included 101 patients who had ACL reconstruction surgery between the years 2014 and 2017. The morphological pattern of ACL remnant scar formation during surgery was observed and classified according to Crain by three orthopaedic surgeons. Inter- and intraobserver reliabilities were measured using kappa statistics. Intraobserver reliability for the Crain classification ranged from 0.63 to 0.83 (substantial to almost perfect agreement). Interobserver reliability was 0.51 (moderate agreement). In almost a third of the cases, observers reported on additional morphological pattern of scar formation that was not well defined by Crain. A modified classification of four patterns was suggested: (A) without scar tissue, (B) with adhesion to the femoral notch (wall or roof), (C) with adhesion to the notch and posterior cruciate ligament (PCL), and (D) with adhesion to the PCL. Reanalysis of these four morphological configurations resulted in interobserver reliability of 0.82 (almost perfect agreement). In conclusion, the Crain classification of torn ACL remnant morphology has moderate interobserver reliability; however, a suggested classification with modified and additional configurations has almost perfect reliability and may be useful for studies on ACL repair and preservation.

Anterior cruciate ligament remnant-preserving and re-tensioning reconstruction: a biomechanical comparison study of three different re-tensioning methods in a porcine model

BACKGROUND

With the developments in the arthroscopic technique, anterior cruciate ligament (ACL) remnant-preserving reconstruction is gradually gaining attention with respect to improving proprioception and enhancing early revascularization of the graft. To evaluate the mechanical pull-out strength of three different methods for remnant-preserving and re-tensioning reconstruction during ACL reconstruction.

METHODS

Twenty-seven fresh knees from mature pigs were used in this study. Each knee was dissected to isolate the femoral attachment of ACL and cut the attachment. An MTS tensile testing machine with dual-screw fixation clamp with 30° flexion angle was used. The 27 specimens were tested after applying re-tensioning sutures with No. 0 polydioxanone (PDS), using the single stitch (n = 9), loop stitch (n = 9), and triple stitch (n = 9) methods. We measured the mode of failure, defined as (1) ligament failure (longitudinal splitting of the remnant ACL) or (2) suture failure (tearing of the PDS stitch); load-to-failure strength; and stiffness for the three methods. Kruskal-Wallis test and Mann-Whitney U-test were used to compare the variance of load-to-failure strength and stiffness among the three groups.

RESULTS

Ligament failure occurred in all cases in the single stitch group and in all but one case in the triple stitch group. Suture failure occurred in all cases in the loop stitch group and in one case in the triple stitch group. The load-to-failure strength was significantly higher with loop stich (91.52 ± 8.19 N) and triple stitch (111.1 ± 18.15 N) than with single stitch (43.79 ± 11.54 N) (p = 0.002). With respect to stiffness, triple stitch (2.50 ± 0.37 N/mm) yielded significantly higher stiffness than the other methods (p = 0.001).

CONCLUSIONS

The results suggested that loop stitch or triple stitch would be a better option for increasing the mechanical strength when applying remnant-preserving and re-tensioning reconstruction during ACL reconstruction.

Objectifying the Pivot Shift Test

The pivot shift test is utilized for assessment of rotatory instability in the anterior cruciate ligament (ACL) deficient knee. There are multiple reports of the pivot shift maneuver, and there is a lack of consensus among clinicians as to a standardized maneuver. Measurement devices are a feasible option to evaluate rotatory knee instability, objectively or quantitatively. Traditionally, measurement systems have been invasive systems. More recently, electromagnetic system, inertial sensor, or imaging analysis systems, specifically with the utilization of a tablet computer, have emerged as noninvasive, and more importantly, validated options. It is important to recognize that anatomic structures other than the ACL contribute to rotatory knee stability. Addressing the tibial slope, anterolateral structures of the knee, specifically the iliotibial band, and menisci during ACL surgery may decrease residual pivot shift in an attempt to improve clinical outcomes and prevent reinjury. This review article describes the pivot shift maneuver, objective measurement tools, and clinical applications of the pivot shift test.

Quantitative assessment of neural elements in a rat model using nerve growth factor after remnant-preserving anterior cruciate ligament reconstruction: a histological and immunofluorescence pilot study

Background

Immunofluorescence analyses of anterior cruciate ligament (ACL) allografts following remnant-preserving ACL reconstruction using Achilles tendon allografts have provided evidence for the presence of neural elements. In this study, we aimed to examine the expression of neural elements and quantify the presence of neural cells in ACL remnants and Achilles allografts using nerve growth factor (NGF) therapy after remnant-preserving ACL reconstruction.

Methods

Experiments were conducted on 5 pairs of rats (approximately 8 weeks old and weighing 320 g at the time of surgery). Longitudinally, split Achilles tendons from the paired rats were freshly frozen and later defrosted with warm saline and allografted onto the right ACL of the other rat that was partially detached at the femoral attachment site. A sham operation was conducted on the left knee to be used as a control. NGF was injected into both knee joints every week for 6 weeks after surgery. The presence of neural cells in the ACL of the sham-operated knee, allografted Achilles tendon, and ACL remnant was examined 6 weeks post-surgery using H and E and immunofluorescent staining.

Results

H and E staining did not reveal neural cells in any of the three groups. However, immunofluorescence analysis showed the presence of nestin-positive neural elements in the normal ACL tissues as well as ACL remnants. Additionally, neural elements were examined in 7 of the 8 (87.5%) allograft tissues. Quantitative analysis showed no difference in the number or area of nuclei among the three groups. However, the number and area of neural cells in the Achilles allografts were significantly lower than those in the other two groups (p = 0.000 and p = 0.001, respectively).

Conclusion

Our observations indicate that ACL remnants promote the new ingrowth and persistence of neural cells. We suggest that the ingrowth of neural elements can support the persistence and new ingrowth of mechanoreceptors, thereby enhancing the functional stability of knee joints. Moreover, the expression of neural cells in the Achilles allografts was lower than that in normal ACL tissues and ACL remnants in the quantitative evaluation, thereby confirming the essential role of ACL remnants in knee joint functionalization.

The Anterolateral Structure of the Knee Does Not Affect Anterior and Dynamic Rotatory Stability in Anterior Cruciate Ligament Injury: Quantitative Evaluation With the Electromagnetic Measurement System

BACKGROUND

The biomechanical function of the anterolateral structure (ALS), which includes the anterolateral joint capsule and anterolateral ligament (ALL), remains a topic of debate.

HYPOTHESIS

The ALS contributes to knee joint stability during the Lachman test and the pivot-shift test in anterior cruciate ligament (ACL)-deficient knees.

STUDY DESIGN

Controlled laboratory study.

METHODS

Fourteen fresh-frozen hemipelvis lower limbs were used. For 7 specimens, the anterior one-third of the ALS and the residual ALS were cut intra-articularly with a radiofrequency device. Subsequently, the ACL was cut arthroscopically. For the other 7 specimens, the ACL was cut first, followed by the anterior one-third of the ALS and the residual ALS intra-articularly. During the procedures, the iliotibial band (ITB) was kept intact. At each condition, the anterior tibial translation (ATT) during the manual Lachman test and the acceleration of posterior tibial translation (APT) and the posterior tibial translation (PTT) during the manual pivot-shift test were measured quantitatively with an electromagnetic measurement system. The mean values of those parameters were compared among 6 groups (ACL intact, one-third ALS cut, all ALS cut, ACL cut, ACL/one-third ALS cut, and ACL/all ALS cut).

RESULTS

The mean ATTs during the Lachman test and the mean APTs and PTTs in the ACL-cut conditions (ACL cut, ACL/one-third ALS cut, and ACL/all ALS cut) were significantly larger than those under the ACL-intact conditions (ACL intact, one-third ALS cut, all ALS cut) (P < .01). However, no statistically significant differences were observed among the intact, one-third ALS-cut, and all ALS-cut conditions, within the ACL-intact or ACL-cut conditions.

CONCLUSION

Intra-articular dissection of the ALS did not increase the ATT during the Lachman test or the APT and PTT during the pivot-shift test under the intact condition of the ITB, regardless of the integrity of the ACL. When the ITB is intact, the ALS does not have a significant role in either anterior or dynamic rotatory knee stability, while the ACL does.

CLINICAL RELEVANCE

Recent growing interest about ALL reconstruction or ALS augmentation may not have a large role in controlling either anterior or dynamic rotatory knee instability in isolated ACL-deficient knees.

The detached stump of the torn anterior cruciate ligament adheres to the femoral notch wall and then to the posterior cruciate ligament within 6 months from injury

PURPOSE

To evaluate the progressive changes in the morphology of traumatic ruptures of the anterior cruciate ligament (ACL) over time. A secondary objective was evaluating their correlation with meniscal tears or chondral lesions.

METHODS

The study included one hundred and one patients who underwent ACL reconstruction surgery of the knee after a definite date of injury. The torn ACL remnant morphological pattern was assessed and classified during arthroscopy. A correlation analysis was performed between the pathological features of the remnant and the time length from injury. In addition, correlation between ACL remnant subtypes and meniscal tears or chondral lesions was evaluated.

RESULTS

At surgery there were four distinct ACL tear morphological patterns that were correlated to the time span from injury (r = 0.61, p < 0.001) and ended with scarring of the femoral remnant to the posterior cruciate ligament. The early pattern was noticed within median time of 2.6 months from injury and appeared as a separate stump with no scar tissue. The following two patterns appeared within 6 months from injury and were characterized by adhesion of scar tissue to different locations in the femoral notch. The last morphological pattern appeared as adherence of the ACL stump to the posterior cruciate ligament. This pattern was seen in some patients within 6 months from injury but was the dominant pattern later on and was also correlated with meniscal tears.

CONCLUSIONS

During the first 3 months from injury the gross morphological features of the torn ACL remnant showed no scar. This phase was followed by scarring of the femoral remnant at first to the femoral notch, and eventually to the posterior cruciate ligament within 6 months from injury and later on. Therefore, further research on the healing potential of the human ACL stump and its biological environment should be focused on the first 3 months from injury.

STUDY DESIGN

Case series; Level of evidence, 4.

The concomitant lateral meniscus injury increased the pivot shift in the anterior cruciate ligament-injured knee

PURPOSE

Concomitant meniscus injuries in the anterior cruciate ligament (ACL) have been suggested to exacerbate rotational laxity. However, the effect is supposed to be so small, if any, that some quantitative pivot-shift measurement is needed. The purpose of this prospective study was to determine the effect of meniscus tear on rotational laxity in ACL-deficient knees by an quantitative measurement. It was hypothesized that a concomitant meniscus tear, especially a lateral one, would induce greater pivot shift.

METHODS

Fifty-seven unilateral ACL-injured patients (26 men and 31 women, mean age: 24 ± 10 years) were included. The pivot-shift test was performed prior to ACL reconstruction, while a quantitative evaluation using an electromagnetic system to determine tibial acceleration and a clinical grading according to the IKDC were performed. Meniscus injuries were diagnosed arthroscopically, and concomitant meniscus tear was confirmed in 32 knees.

RESULTS

The clinical grade was not different between the ACL-injured knees of patients with and without meniscus tear (n.s.). Tibial acceleration did not show a statistical significant difference (meniscus-injured knees: 1.6 ± 1.1 m/s² versus meniscus-intact knees: 1.2 ± 0.7 m/s², n.s.). However, the subgroup analysis demonstrated that there was increased tibial acceleration in ACL-deficient knees with lateral meniscus tear (2.1 ± 1.1 m/s², n = 13) compared with meniscus-intact knees (p < 0.05), whereas rotational laxity did not increase in the medial meniscus-injured and bilateral-injured knees (1.2 ± 0.9 m/s², n = 12, n.s. and 1.4 ± 1.1 m/s², n = 7, n.s., respectively).

CONCLUSION

A concomitant meniscus tear, especially a lateral meniscus tear, has a significant impact on rotational laxity in ACL-injured knees. When a large pivot shift is observed in the ACL-injured knee, a concomitant meniscus tear should be suspected and an aggressive treatment would be considered. Meniscus injuries should be inspected carefully when substantial pivot shift is encountered in ACL-injured knees.

LEVEL OF EVIDENCE

Diagnostic study, Level III.

Anatomic Anterior Cruciate Ligament Reconstruction Using Hamstring Tendons Restores Quantitative Pivot Shift

Background:

It is still uncertain how surgical reconstruction of the anterior cruciate ligament (ACL) is able to restore rotatory laxity of the involved joint. The desired amount of restraint applied by the ACL graft, as compared with the healthy knee, has not been fully clarified.

Purpose:

To quantify the ability of single-bundle anatomic ACL reconstruction using hamstring tendons in reducing the pivot-shift phenomenon immediately after surgery under anesthesia.

Study Design:

Case series; Level of evidence, 4.

Methods:

An inertial sensor and image analysis were used at 4 international centers to measure tibial acceleration and lateral compartment translation of the knee, respectively. The standardized pivot-shift test was quantified in terms of the side-to-side difference in laxity both preoperatively and postoperatively with the patient under anesthesia. The reduction in both tibial acceleration and lateral compartment translation after surgery and the side-to-side difference were evaluated using the Wilcoxon signed-rank test. Alpha was set at P < .05.

Results:

A total of 107 patients were recruited for the study, and data were available for 89 patients. There was a statistically significant reduction in quantitative rotatory knee laxity between preoperatively (inertial sensor, 2.55 ± 4.00 m/s²; image analysis, 2.04 ± 2.02 mm) and postoperatively (inertial sensor, –0.54 ± 1.25 m/s²; image analysis, –0.10 ± 1.04 mm) between the involved and healthy joints, as measured by the 2 devices (P < .001 for both). Postoperatively, both devices detected a lower rotatory laxity value in the involved joint compared with the healthy joint (inertial sensor, 2.45 ± 0.89 vs 2.99 ± 1.10 m/s², respectively [P < .001]; image analysis, 0.99 ± 0.83 vs 1.09 ± 0.92 mm, respectively [P = .38]).

Conclusion:

The data from this study indicated a significant reduction in the pivot shift when compared side to side. Both the inertial sensor and image analysis used for the quantitative assessment of the pivot-shift test could successfully detect restoration of the pivot shift after anatomic single-bundle ACL reconstruction. Future research will examine how pivot-shift control is maintained over time and correlation of the pivot shift with return to full activity in patients with an ACL injury.

Preservation of remnant with poor synovial coverage has no beneficial effect over remnant sacrifice in anterior cruciate ligament reconstruction

PURPOSE

The purpose of the study was to evaluate the influence of synovial coverage of the remnant on clinical outcomes and graft healing in anterior cruciate ligament (ACL) reconstruction.

METHODS

Seventy-five patients who underwent second-look arthroscopy after a single-bundle ACL reconstruction using autologous quadriceps tendon graft were included. The patients were divided into two groups according to whether the remnant was preserved (group P, n = 42) or sacrificed (group S, n = 33). Group P was further classified according to the degree of synovial coverage of the remnant on initial arthroscopic findings: group A (remnant fully covered with synovium, n = 15), group B (synovial coverage >50%, n = 15), and group C (coverage <50%, n = 12). Clinical outcomes including manual laxity tests, KT-2000 side-to-side difference, modified Lysholm score, Tegner activity score, and International Knee Documentation Committee score were evaluated pre-operatively and prior to the second-look arthroscopy. Graft tension, degrees of synovialization, and gross integrity were evaluated on second-look arthroscopic examination.

RESULTS

There were no statistical differences in manual laxity tests, KT-2000 side-to-side difference, and clinical scores between groups P and S. In second-look arthroscopic examination, graft tension showed no difference between the two groups, but gross integrity and synovialization were significantly higher in group P (P = 0.032 and P = 0.008, respectively). In subgroup analysis, only group A showed higher grade regarding gross integrity and synovialization in comparison with group S (P = 0.007 and P < 0.001, respectively).

CONCLUSIONS

Preservation of remnant in ACL reconstruction showed no superiority concerning knee stability and clinical outcomes over remnant sacrificing at post-operative 1-year second-look arthroscopy. Preservation of remnant with good synovial coverage had a positive effect on graft synovialization and maintenance of graft integrity, but this effect was not observed in cases of a remnant with poor synovial coverage. When deciding whether to preserve the remnant or not, the degree of synovial coverage should be considered.

LEVEL OF EVIDENCE

III.

MRI evaluation of the ACL remnant tissue in ACL-deficient knee

PURPOSE

To clarify the relationship between anterior cruciate ligament (ACL) remnant tissue at the time of surgery and preoperative evaluation of ACL-injured knee.

METHODS

A total of 123 patients were enrolled and classified into four groups based on the classification of ACL remnant tissue. To quantify the signal-noise quotient (SNQ), five regions of interest (ROIs), such as tibial, mid, femoral ACL remnant, tendon of quadriceps femoris to normalize the signal intensity of ACL remnant tissue, and background measurements, were measured. Preoperative side-to-side difference (SSD) and SNQ were analyzed.

RESULTS

Significant differences were observed in preoperative SSD of the four groups ( p = 0.021), and a post hoc analysis revealed that SSD in Crain type 2 was significantly smaller than that in Crain type 4 ( p = 0.014). SSD in Crain type 3 was also significantly smaller than that in Crain type 4 ( p = 0.0030). There were significant differences in SNQ at the tibial, mid, and femoral portion in Crain types 2 and 3 ( p < 0.001); SNQ at the tibial portion in Crain type 2 was significantly lower than that at the mid portion ( p = 0.024); and SNQ at the tibial portion in Crain type 3 was significantly lower than that at the mid portion ( p = 0.016). Furthermore, significant differences were observed in SNQ at the tibial portions in the four groups ( p = 0.034), and SNQ at the tibial portions in Crain type 2 was significantly lower than that in Crain type 1 ( p = 0.044). Also, SNQ at the tibial portions in Crain type 3 was significantly lower than that in Crain type 1 ( P = 0.035).

CONCLUSION

The femoral attachment of the ACL remnant tissue may influence the SNQ of the tibial remnant tissue and the stability of the ACL-injured knee.

Anterior cruciate ligament remnant and its values for preservation

Controversy surrounds the remnant-preserving anterior cruciate ligament surgery. Advantages of remnant preservation have been reported in regard to better healing and knee function, although no consensus has been reached. This review article discussed the value and meaning of anterior cruciate ligament remnant preservation in several sections such as effects on healing, remnant classification, biomechanical evaluation, relation to proprioception, animal studies, and clinical studies. We hope that this review will facilitate further discussion and investigation for better treatment of anterior cruciate ligament injuries. So far, the current reviews have not provided sufficient scientific evidence to support the value of preserving the remnant.