Anatomy and Biomechanics of the Posterior Cruciate Ligament and Their Surgical Implications

Activity-Dependent Compensation at the Hip and Ankle at 8 Years After the Reconstruction of Isolated and Combined Posterior Cruciate Ligament Injuries

BACKGROUND

After posterior cruciate ligament reconstruction (PCLR), functional deficits at the knee can persist. It remains unclear if neighboring joints compensate for the knee during demanding activities of daily living.

PURPOSE

To assess long-term alterations in lower limb mechanics in patients after PCLR.

STUDY DESIGN

Descriptive laboratory study.

METHODS

A total of 28 patients who had undergone single-bundle unilateral isolated or combined PCLR performed stair navigation, squat, sit-to-stand, and stand-to-sit tasks at 8.2 ± 2.2 years after surgery. Motion capture and force plates were used to collect kinematic and kinetic data. Then, 3-dimensional hip, knee, and ankle kinematic data of the reconstructed limb were compared with those of the contralateral limb using statistical parametric mapping.

RESULTS

Side-to-side differences at the knee were primarily found during upward-driven movements at 8 years after surgery. The reconstructed knee exhibited lower internal rotation during the initial loading phase of stair ascent versus the contralateral knee (P = .005). During the sit-to-stand task, higher flexion angles during the midcycle (P = .017) and lower external rotation angles (P = .049) were found in the reconstructed knee; sagittal knee (P = .001) and hip (P = .016) moments were lower in the reconstructed limb than the contralateral limb. In downward-driven movements, side-to-side differences were minimal at the knee but prominent at the ankle and hip: during stair descent, the reconstructed ankle exhibited lower dorsiflexion and lower external rotation during the midcycle versus the contralateral ankle (P = .006 and P = .040, respectively). Frontal hip moments in the reconstructed limb were higher than those in the contralateral limb during the stand-to-sit task (P = .010); during squats, sagittal hip angles in the reconstructed limb were higher than those in the contralateral limb (P < .001).

CONCLUSION

Patients after PCLR exhibited compensations at the hip and ankle during downward-driven movements, such as stair descent, squats, and stand-to-sit. Conversely, residual long-term side-to-side differences at the knee were detected during upward-driven movements such as stair ascent and sit-to-stand.

CLINICAL RELEVANCE

After PCLR, side-to-side differences in biomechanical function were activity-dependent and occurred either at the knee or neighboring joints. When referring to the contralateral limb to assess knee function in the reconstructed limb, concentric, upward-driven movements should be prioritized. Compensations at the hip and ankle during downward-driven movements lead to biases in long-term functional assessments.

Sonographic Characterization of the Pericruciate Fat Pad with the Use of Compression Elastography-A Cross-Sectional Study among Healthy and Post-Injured Patients

Background: The pericruciate fat pad (PCFP) in the knee joint is still insufficiently studied despite its potential role in knee pathologies. This is the first reported study which aimed to clarify the characteristics of the PCFP in healthy individuals and contrast them with cases of post-traumatic injuries. Methods: Conducted as a retrospective cross-sectional study (n = 110 knees each) following STROBE guidelines, it employed grayscale ultrasound with echogenicity measurement, compression elastography with elasticity measurement, and Color Doppler for blood flow assessment. Results: PCFP showed a homogenic and hyperechoic echostructure. The echogenicity of the PCFP was higher than that of the posterior cruciate ligament (PCL) (p < 0.001, z-score = 8.97) and of the medial head of gastrocnemius (MHG) (p = 0.007, z-score = 2.72) in healthy knees, but lower than subcutaneous fat (SCF) (p < 0.001, z-score = -6.52). Post-injury/surgery, PCFP echogenicity surpassed other structures (p < 0.001; z-score for PCL 12.2; for MHG 11.65 and for SCF 12.36) and notably exceeded the control group (p < 0.001, z-score = 8.78). PCFP elasticity was lower than MHG and SCF in both groups, with significantly reduced elasticity in post-traumatic knees (ratio SCF/PCFP 15.52 ± 17.87 in case group vs. 2.26 ± 2.4 in control group; p < 0.001; z-score = 9.65). Blood flow was detected in 71% of healthy PCFPs with three main patterns. Conclusions: The main findings, indicating increased echogenicity and reduced elasticity of PCFP post-trauma, potentially related to fat pad fibrosis, suggest potential applications of echogenicity and elasticity measurements in detecting and monitoring diverse knee pathologies. The description of vascularity variations supplying the PCFP adds additional value to the study by emphasizing the clinically important role of PCFP as a bridge for the middle genicular artery on its way to the inside of the knee joint.

A modified anatomical posterior cruciate ligament reconstruction technique using the posterior septum and posterior capsule as landmarks to position the low tibial tunnel

BACKGROUND

Lowering the exit position of the tibial tunnel can improve the clinical efficacy of posterior cruciate ligament (PCL) reconstruction, however, there is no unified positioning standard. This study aimed to use novel soft tissue landmarks to create a low tunnel.

METHODS

A total of 14 human cadaveric knees and 12 patients with PCL injury were included in this study. Firstly, we observed the anatomical position between the PCL, posterior septum, and other tissue, and evaluated the relationship between the center of the low tibial tunnel (SP tunnel) and posterior septum and distal reflection of posterior capsule, and using computed tomography (CT) to evaluate distance between the center of the SP tunnel with bony landmarks. Then, evaluated the blood vessels content in the posterior septum with HE staining. Finally, observed the posterior septum and distal reflection of the posterior capsule under arthroscopy to explore the clinical feasibility of creating a low tibial tunnel, and assessed the risk of surgery by using ultrasound to detect the distance between the popliteal artery and the posterior edge of tibial plateau bone cortex.

RESULTS

In all 14 cadaveric specimens, the PCL tibial insertions were located completely within the posterior medial compartment of the knee. The distance between the center of the SP tunnel and the the articular surface of tibial plateau was 9.4 ± 0.4 mm. All SP tunnels retained an intact posterior wall, which was 1.6 ± 0.3 mm from the distal reflection of the posterior capsule. The distances between the center of the SP tunnel and the the articular surface of tibial plateau, the champagne glass drop-off were 9.2 ± 0.4 mm (ICC: 0.932, 95%CI 0.806-0.978) and 1.5 ± 0.2 mm (ICC:0.925, 95%CI 0.788-0.975) in CT image. Compared with the posterior capsule, the posterior septum contained more vascular structures. Last, all 12 patients successfully established low tibial tunnels under arthroscopy, and the distance between the posterior edge of tibial plateau bone cortex and the popliteal artery was 7.8 ± 0.3, 9.4 ± 0.4 and 7.4 ± 0.3 mm at 30°, 60° and 90° flexion angels after filling with water and supporting with shaver in posterior-medial compartment of knee joint.

CONCLUSIONS

A modified low tibial tunnel could be established in the PCL anatomical footprint by using the posterior septum and posterior capsule as landmarks.

Cruciate and Collateral Ligaments: 2-Dimensional and 3-Dimensional MR Imaging-Aid to Knee Preservation Surgery

Being a major load-bearing and dynamic functional joint of the body, the knee joint is prone to injuries to the menisci and ligaments. Injury to one or more of these structures leads to accelerated or premature osteoarthritis and chronic debilitation. The estimated cost of these injuries in terms of diagnosis, treatment, rehabilitation, and person-hours lost amounts to over a billion dollars annually. Understanding the relevant anatomy of knee cruciate and collateral ligaments, their biomechanical functional role, and imaging considerations are essential to assist multi-disciplinary communications and timely patient treatments for improved management. MRI is considered the gold standard over other imaging modalities like X-ray, ultrasound (US), and Computed Tomography (CT) for diagnosing and assessing such injuries. High-resolution 2D and 3D MRI are considerably helpful in planning for knee preservation surgery, and this article reviews the role of such imaging as a valuable aid to knee preservation surgery in pre-and post-operative states. Relevant arthroscopy correlations have been illustrated.

Morphological Risk Factors for Posterior Cruciate Ligament Tear and Tibial Avulsion Injuries of the Tibial Plateau and Femoral Condyle

BACKGROUND

Identification of morphological risk factors associated with the knee that threaten ligaments is important for understanding injury mechanisms and prevention. However, the morphological risk factors for posterior cruciate ligament (PCL) lesions are not clearly understood.

PURPOSE

To investigate whether the medial tibial depth (MTD), medial and lateral posterior tibial slope, asymmetry of the medial and lateral slopes, radius of the sagittal plane medial femoral condyle, coronal tibial slope, and notch width index (NWI) were risk factors for PCL intrasubstance tearing (PCLIT) and tibial avulsion fractures (PCLAF).

STUDY DESIGN

Cross-sectional study; Level of evidence, 3.

METHODS

Between January 2015 and March 2022, 82 patients with isolated PCLIT, 68 patients with isolated PCLAF, and 82 controls without any ligamentous or meniscal pathologic findings as determined via physical examination and magnetic resonance imaging were included. Values were compared among the 3 groups. Logistic regression analysis was performed to confirm the risk factors. Receiver operating characteristic curves were defined for the morphological indicators and combination of risk factors.

RESULTS

Logistic regression analysis revealed (1) MTD, lateral minus medial posterior tibial slope, radius of the posterior circle of the medial femoral condyle, and NWI as significant independent predictors for PCLIT and (2) MTD and NWI for PCLAF. The areas under the curve combining the 4 indicators for PCLIT and noncontact PCLIT were 0.79 (95% CI, 0.72-0.86) and 0.90 (95% CI, 0.85-0.96), respectively. The area under the curve for the combination of MTD and NWI for PCLAF was 0.78 (95% CI, 0.70-0.86).

CONCLUSION

Decreased MTD and NWI were associated with an increased incidence of PCLIT and PCLAF. Increased asymmetry of the medial and lateral slopes and the radius of the posterior circle of the medial femoral condyle were associated with the presence of PCLIT. In addition, the model of a combination of risk factors showed good predictive ability for noncontact PCLIT. These findings may aid clinicians in identifying patients at risk for PCL lesions. Further studies are warranted for identifying the effect of these factors on biomechanical mechanisms.

A novel meniscofemoral ligament variant intra-substance to the PCL

While much detail is known about each anatomic structure of the knee and its contributory effect on biomechanics, our understanding is still evolving. In particular, the function of the meniscofemoral ligaments and their anatomical variants have yet to be fully described. In this report, a never-before-described anatomical meniscofemoral ligament variant intra-substance to the PCL is presented. Arthroscopists should be aware of the novel variant as a growing number of studies have demonstrated the biomechanical importance of the meniscofemoral ligaments in protecting the lateral meniscus and supporting the function of the PCL.Level of Evidence: IV.

Operative management of isolated posterior cruciate ligament injuries improves stability and reduces the incidence of secondary osteoarthritis: a systematic review

PURPOSE

To evaluate the evidence for operative and non-operative management of isolated posterior cruciate ligament (PCL) injuries.

METHODS

Using Pubmed, EMBASE and Cochrane databases, a systematic review was conducted of studies investigating the treatment of isolated PCL injuries published until July 2020. Quality assessment was performed with the Cochrane risk of bias tool (level I), the Newcastle-Ottowa Scale (level II-III) and the National Institute of Health quality assessment tool (level IV). Clinical outcome measures included residual laxity, return to sports, patient-reported outcome measures, subsequent articular degeneration and complications.

RESULTS

Twenty-seven studies [23 case series, 2 case-control, 1 cohort study and 1 randomized controlled trial (RCT)] including 5197 patients (5199 knees) with a mean age of 29.5 ± 3.6 years (range 15-68) fulfilled the study requirements. Significantly less residual laxity was found after posterior cruciate ligament reconstruction (PCLR) compared to non-operative management (3.43 vs. 5.47 mm, CI: 1.84-2.23, p < 0.001). Both treatment modalities yielded satisfying functional outcomes and a high return to sports (64-77%, mean: 70.3, CI: 67.8-72.2). Osteoarthritis (OA) occurred less frequently following PCLR (21.5 vs. 44.1%, p < 0.001).

CONCLUSION

In the absence of level I RCTs, this systematic review suggests that surgical management for selected isolated PCL injuries is a reasonable option to consider, especially when the surgeon aims at minimizing residual laxity and presumably secondary osteoarthritis.

LEVEL OF EVIDENCE

IV.

Single versus double bundle in posterior cruciate ligament (PCL) reconstruction: a meta-analysis

Posterior cruciate ligament (PCL) reconstruction can be performed using single bundle (SB) and double bundle (DB) techniques. The present study investigated whether DB PCL reconstruction is superior to SB reconstruction in terms of patient reported outcome measures (PROMs) and joint stability. In December 2021 Embase, Google Scholar, Pubmed, Scopus databases were accessed. All clinical trials comparing SB versus DB reconstruction to address PCL insufficiency in skeletally mature patients were considered. Data from 483 procedures were retrieved. The mean follow-up was 31.0 (28.0 to 107.6) months, and the mean timespan between injury and surgery was 11.3 (6 to 37) months. The mean age of the patients was 29.3 ± 3.8 years. 85 of 483 patients (18%) were women. At a mean of 31.0 months post reconstruction, ROM (P = 0.03) was slightly greater in the SB group, while the Tegner score (P = 0.03) and the Telos stress (P = 0.04) were more favorable in the DB cohort. Similarity was found in instrumental laxity (P = 0.4) and Lysholm score (P = 0.3). The current evidence does not support the use of DB techniques for PCL reconstruction. Both methods could restore knee stability and motion with satisfactory short term patient reported outcome measures. Further high quality clinical trials are required to validate these results on a larger scale.

Prevalence, Biomechanics, and Pathologies of the Meniscofemoral Ligaments: A Systematic Review

Purpose

To systematically review the literature to examine current understanding of the meniscofemoral ligaments (MFLs), their function, their importance in clinical management, and known anatomical variants.

Methods

A systematic review was conducted following Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines using PubMed, EMBASE, and Cochrane databases. Studies were included if they reported on the biomechanical, radiographic, or arthroscopic evaluation of human MFLs, or if they reported on an anatomical variant. These were then categorized as cadaveric, radiographic, or clinical. Biomechanical, radiographic, patient-reported, and functional outcomes data were recorded.

Results

Forty-seven studies were included in the qualitative analysis, and 26 of them were included in the quantitative analysis. Of these, there were 15 cadaveric, 3 arthroscopic, and 9 radiographic studies that reported on the prevalence of MFLs. Overall, when looking at all modalities, the presence of either the anterior or posterior MFL (aMFL, pMFL) has been noted to be 70.8%, with it being the aMFL 17.4% and the pMFL 40.6%. The presence of both ligaments occurs in approximately 17.6% of individuals. Eleven reported on mean MFL length and thickness. When evaluating mean length in both men and women, the aMFL has been reported between 21.6 and 28.3 mm and the pMFL length in this population is between 23.4 and 31.2 mm. Five reported on cross-sectional area. Nine additional papers report anatomical variants.

Conclusions

This review shows that there continues to be a variable incidence of MFLs reported in the literature, but our understanding of their function continues to broaden. A growing number of anatomic and biomechanical studies have demonstrated the importance of the MFLs in supporting knee stability. Specifically, the MFLs serve an important role in protecting the lateral meniscus and augmenting the function of the posterior cruciate ligament.

Clinical Relevance

Our findings will aid the clinician in both identifying and treating pathologies of the meniscofemoral ligaments.

Biomechanical evaluation of a novel transtibial posterior cruciate ligament reconstruction using high-strength sutures in a porcine bone model

Background:

Multiple techniques are commonly used for posterior cruciate ligament (PCL) reconstruction. However, the optimum method regarding the fixation of PCL reconstruction after PCL tears remains debatable. The purpose of this study was to compare the biomechanical properties among three different tibial fixation procedures for transtibial single-bundle PCL reconstruction.

Methods:

Thirty-six porcine tibias and porcine extensor tendons were randomized into three fixation study groups: the interference screw fixation (IS) group, the transtibial tubercle fixation (TTF) group, and TTF + IS group (n = 12 in each group). The structural properties of the three fixation groups were tested under cyclic loading and load-to-failure. The slippage after the cyclic loading test and the stiffness and ultimate failure load after load-to-failure testing were recorded.

Results:

After 1000 cycles of cyclic testing, no significant difference was observed in graft slippage among the three groups. For load-to-failure testing, the TTF + IS group showed a higher ultimate failure load than the TTF group and the IS group (876.34 ± 58.78 N vs. 660.92 ± 77.74 N [P < 0.001] vs. 556.49 ± 65.33 N [P < 0.001]). The stiffness in the TTF group was significantly lower than that in the IS group and the TTF + IS group (92.77 ± 20.16 N/mm in the TTF group vs. 120.27 ± 15.66 N/m in the IS group [P = 0.001] and 131.79 ± 17.95 N/mm in the TTF + IS group [P < 0.001]). No significant difference in the mean stiffness was found between the IS group and the TTF + IS group (P = 0.127).

Conclusions:

In this biomechanical study, supplementary fixation with transtibial tubercle sutures increased the ultimate failure load during load-to-failure testing for PCL reconstruction.