Systematic review of cadaveric studies on anatomic posterior cruciate ligament reconstruction: the landmarks in anatomic posterior cruciate ligament reconstruction.

Recently, several new techniques for anatomic posterior cruciate ligament reconstruction (PCLR) have emerged and are believed to restore the normal anatomy of the posterior cruciate ligament more accurately. Despite the latest trend, the optimal methods for anatomic PCLR remain controversial. The purpose of this research is to review surgical techniques for PCLR in cadaver studies and suggest consistent and reproducible technical criteria. For the review of the literature, MEDLINE and EMBASE were screened for articles on anatomic PCLR. Only basic science studies on PCLR performed on human cadavers and written in English were included. Seventeen studies were included in this systematic review. Only the tunnel positions, graft types, and surgical techniques were reported in the majority of the studies. There were many variations of the reported tunnel positions, graft types, and surgical techniques among the studies. In most studies, surgical techniques for consistent and reproducible anatomic PCLR were not explained clearly. Therefore, high level medical research should be encouraged in order to establish standard surgical techniques for anatomic PCLR.

Introduction

In recent years, more and more attention has been directed towards biomechanics of the anatomic posterior cruciate ligament reconstruction (PCLR). Past studies showed that PCLR would neither prevent the knee from developing osteoarthritis nor fully restore the normal knee kinematics1). However, during the past decade, there has been rapid development in surgical techniques for PCLR, such as the double-bundle technique2,3,4,5,6,7). Consistent and reproducible surgical techniques increase the possibility to replicate the native anatomy of the knee and facilitate anatomic PCLR. Basic science studies, for instance cadaver studies, have demonstrated benefits of anatomic PCLR, and thus have been used as a template when evaluating new surgical techniques. There is an expectation that more anatomic PCLR techniques will enable more accurate restoration of the intact knee kinematics and reduce the incidence of osteoarthritis after PCLR2,8). However, utilization of the term 'anatomic' with regard to PCLR can be misleading because some PCLR surgical techniques designed to better replicate the native anatomy can still be performed nonanatomically. A more specific definition of the anatomic PCLR has recently been proposed: the functional restoration of the knee laxity, graft force, and knee kinematics2,9). Such definition provides a means to evaluate currently published clinical trials and basic science studies on PCLR from the perspective of anatomic accuracy. Overall, there is a scant amount of data on anatomic PCLR, but research has been actively carried out on the confirmation of ligament insertion sites, tunnel positioning techniques, graft types, and graft fixation methods. On the other hand, researches using anatomic landmarks, such as the medial intercondylar ridge, medial bifurcate ridge, and posterior edge of shelf, or regarding preoperative planning or imaging techniques for postoperative evaluation are rare. The purpose of this research was to review surgical techniques for anatomic PCLR in cadaver studies and to suggest consistent and reproducible technical criteria. Therefore, a descriptive analysis was performed on surgical data reports. We hypothesized that the description of surgical techniques in those reports would be insufficient and thus it would not be feasible to set up clinical settings for anatomic PCLR.

Methods

A systematic and descriptive review on surgical techniques for PCLR was undertaken. Clinical trials were excluded from this systematic review; cadaver studies on anatomic PCLR were included in this study. Only studies providing a description of surgical techniques and involving human cadavers were eligible for inclusion.

A systematic electronic search was performed using the MEDLINE via PubMed and EMBASE databases. Studies that were published between 1999 and 2013 were included. The search was carried out by 2 observers in 2013. The following key search terms were used in all fields: 'posterior cruciate ligament' OR 'PCL' AND 'anatomic' OR 'anatomical' AND 'reconstruction' OR 'surgery' AND '1999:2013'. The search was restricted to English. Review articles, studies that were covered by 2 databases, clinical studies, and animal studies were excluded. Selection of studies was done by reading the abstracts, and if necessary, the full texts. For inclusion into the review, two authors independently analyzed the full texts using the aforementioned criteria. Any disagreements between the 2 observers were discussed to reach an agreement. Finally, the reference lists of the selected studies were investigated to identify additional studies that had not been found through our electronic search.

There are no established criteria yet to determine whether a PCLR is performed anatomically or not. So we initially decided to include all papers in which the authors stated that the reconstructive surgical procedure was 'anatomic'. However, considering the recent emphasis on the concept of 'anatomic' PCLR, we deemed it would be unfair to include all PCLR papers. Therefore, we analyzed the anatomic degree of reconstruction in those studies based on the assessment of the insertion site of the footprint of posterior cruciate ligament, tunnel position, and anatomical landmarks (medial intercondylar ridge, medial bifurcate ridge, and posterior edge of shelf), since most authors did not state their technique was 'anatomic'. The anatomical landmarks are displayed in Table 1.

Table 1

Demographic and Surgical Data from Included Studies

PCL: posterior cruciate ligament, AL: anterolateral, PM: posteromedial, MRI: magnetic resonance imaging, CT: computed tomography, 3D: three-dimensional.

A descriptive review of the reports providing a variety of surgical data was performed with the utilization of a predefined standardized data sheet. The authors filled in a template regarding suggestions for anatomic PCLR, which was used for analysis of the studies (Table 1). The data sheet included a column for all data as well as an additional column for pooling more specific data. The analysis was not performed in a blinded fashion. The data were recorded as either 'reported' or 'not reported'. Also, the ratios of studies presenting certain data to the total included studies were calculated as percentages. Assessments on detailed procedures or methods were not performed. In addition, if an item was recorded as 'reported', more specific data were collected when possible for the purpose of pooling. Consensus was reached through discussion for any disagreements.

Results

There were 185 search results on MEDLINE via PubMed and 123 on EMBASE according to the aforementioned search criteria (Fig. 1). Of these 308 studies, 246 were excluded because the abstracts showed they did not meet the inclusion criteria. Most of the excluded studies were either clinical trials or not written in English. Of the remaining 62 papers, 17 papers were selected by both observers and the rest were excluded after discussion due to disagreement. Therefore, 17 papers were selected for final inclusion of the systematic review2,7,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23). The results of 17 included studies are summarized in Table 2. The 45 studies were excluded mostly because the authors did not claim that their reconstructive technique was anatomic.

Fig. 1

Flow diagram for systematic review of the literature.

Table 2

Summary of the Included Studies

ALB: anterolateral bundle, PMB: posteromedial bundle, PCL: posterior cruciate ligament, AP: anteroposterior, AL: anterolateral, PM: posteromedial, CT: computed tomography, 3D: three-dimensional.

Whether certain surgical data were reported or not reported in the included papers is displayed in Table 3. Visualization indicates presenting diagrams or pictures showing how the femoral or tibial bone is attached in the study. The femoral and tibial insertion sites were visualized in approximately two-thirds of the included studies, whereas only 12% of anatomic studies investigated the actual insertion sites of the PCL. Regarding the use of the medial intercondylar ridge and the medial bifurcate ridge for femoral tunnel positioning, the posterior edge of shelf was rarely used for tibial tunnel positioning (Figs. 2 and 3). The anatomic positions of tunnels or footprints proposed in the studies are described in Table 2.

Table 3

Reporting of Surgical Data in Included Studies

PCL: posterior cruciate ligament, AL: anterolateral, PM: posteromedial, MRI: magnetic resonance imaging, CT: computed tomography, 3D: threedimensional.

Fig. 2

Femoral footprint of the posterior cruciate ligament (imaging was reconstructed using Geomagic Software). (A) a: AL bundle, b: PM bundle, c: medial bifurcate ridge, d: medial intercondylar notch. (B) Femoral footprint at three-dimensional reconstructed imaging. AL: anterolateral, PM: posteromedial.

Fig. 3

Tibial footprint of posterior cruciate ligament (imaging was reconstructed using Geomagic Software). (A) a: AL bundle, b: PM bundle, c: posterior edge of shelf. (B) Tibial footprint at three-dimensional reconstructed imaging. AL: anterolateral, PM: posteromedial.

Seventy-eight percent and 61.7% of the studies included data on the tunnel placement in the femoral and tibial insertion sites, respectively. Seventy-eight percent of them also provided visual proof in their papers (Table 4). Imaging techniques were poorly used in these cadaveric trials: standard radiographs, computed tomography (CT), and three-dimensional CT were used in only 9.1% each. Magnetic resonance imaging was used in 18.2% and the use of other methods such as fluoroscopic images, computer graphics, or gross cadaveric dissection photographs were reported in 27.3%.

Table 4

Proof of Tunnel Placement in the Native Posterior Cruciate Ligament Footprint

The positions of femoral and tibial tunnels were reported to be at a fixed distance from another anatomic structure in 66.5% and 55.9%, respectively. On the femoral side, the authors used the intercondylar roof, PCL insertion site, and the edge of the articular cartilage for guidance of femoral tunnel placement. On the tibial side, authors used the anterior margin of the tibia, the medial border of the tibial plateau, and the vertical distance from the tibial plane as reference points. No superior graft has been identified and graft fixation method was reported in approximately half of the included studies (Table 5).

Table 5

Fixation Methods Used for Anatomic Posterior Cruciate Ligament Reconstruction

In these studies, either single-bundle PCLR or double-bundle PCLR was used as a tunnel reconstruction method, and superiority between the two methods could not be determined.

Discussion

The growing attention to anatomic PCLR has led to a recent increase in the number of basic science studies evaluating potential benefits and limitations of this technique. However, despite the outcomes of many studies, the true definition of anatomic PCLR has not yet reached a consensus. In this review, it was hypothesized that the description of surgical techniques would be insufficient to set up clinical settings for anatomic PCLR.

This review revealed that data for anatomic PCLR, such as the insertion site and tunnel position, are not sufficient despite the current increase in the number of PCL research. In many studies, femoral tunnel positions were not determined by referring to anatomic sites and the o'clock reference was used instead. However, the size and shape of the PCL insertion site, tibial plateau, and femoral intercondylar notch anatomy are different from patient to patient21,22,24). Therefore, the o'clock reference would not be beneficial for anatomic reconstruction because it provides a non-reproducible generic two-dimensional formula for tunnel placement. The o'clock reference was originally developed to be used with radiographs taken with the knee in extension, which can be quite reliable under this circumstance25). Later, it was also utilized for arthroscopic measurements without taking into consideration that the knee is flexed in this situation. Differences in the knee flexion angle and viewing portal have caused much confusion when using the o'clock description26). The mean tibial tunnel position in the studies we selected for review was 10-15 mm below the articular joint. In cadaveric studies and clinical trials, authors utilize various anatomical landmarks to describe the tibial insertion site23,27,28,29). However, these studies mostly used only one reference value, although at least two coordinates are necessary to define a geographical point, and more are needed for an accurate 3D mapping. Radiological studies also attempted to identify landmarks for definition of the PCL tibial insertion site10,11). However, they did not rely on identical reference points and did not distinguish between the anterolateral and posteromedial bundles28). As evidenced in this review, the accurate methods for tibial tunnel positioning have been rarely reported in many studies, demonstrating the need for a detailed description of the PCL fovea to establish consistent, reproducible anatomical landmarks for surgery.

The increased interest in anatomic PCLR has led to a great number of basic science studies evaluating potential benefits and limitations of this technique2,7,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23). However, the true definition of anatomic PCLR has not reached a consensus, and therefore, the interpretation of 'anatomic' varies from study to study. The aim of many cadaver studies on PCLR is to study the effects of differences in reconstruction techniques and tunnel positions on the knee biomechanics15,16,19,20). Recent research furthermore puts its emphasis on comparisons of surgical methods and approaches for 'anatomic' PCLR6,7,14,15,30). As aforementioned in the present study, superiority between the single-bundle PCLR and doublebundle PCLR with regard to tunnel reconstruction could not be determined. So we believe this should be elucidated in further research. Basic science is the milestone for clinical research and ultimately treatment strategies. Providing detailed description of a surgical method helps readers make an appropriate interpretation of the study results and be assured that the reconstruction was indeed performed in an anatomic fashion. The ideal way to implement this would be to establish standards for describing anatomic techniques, encompassing all essential aspects needed to define anatomic PCLR. Authors, for their part, should strive to provide clear description of their methods using figures, pictures, and diagrams.

Overall, we found that a variety of surgical data were not presented in current cadaver studies on anatomic PCLR. The absence of certain data on surgical techniques does not necessarily imply certain procedures were not performed. However, the recent high standard of medical research requires accuracy when reporting methods and findings. Description of surgical techniques in clinical studies may be considered unimportant; however, it should be addressed in detail in cadaver studies considering that they are used as a template for clinical trials. Anatomic PCLR can be performed in many different ways, and such diversity of methods affects the study outcomes. As a result, in the absence of sufficient description of techniques, it should be difficult to interpret the outcomes and make comparisons with other studies.

There were several limitations of this systematic review. First, it was specifically focused on studies that report on anatomic PCLR techniques in cadaver models. Second, the search was limited to English papers available on MEDLINE via PubMed or EMBASE. Third, the data extraction was not performed in a blinded fashion. However, despite these limitations, we believe this systematic review provides a rare insight into the overall factors of anatomic PCLR and the current status of studies on the technique.

Most basic science studies regarding anatomic PCLR in cadavers do not provide detailed description of surgical techniques for consistent and reproducible anatomic PCLR. Therefore, we believe high level medical research should be encouraged in order to establish standard surgical techniques and delineate the definition of anatomic PCLR.