Radiographic study on the tibial insertion of the posterior cruciate ligament

a Departamento de Ortopedia, Santa Casa de São Paulo, São Paulo, SP, Brasil
b Serviço de Ortopedia e Traumatologia, Hospital Israelita Albert Einstein, Universidade Federal de São Paulo (Unifesp), São Paulo, SP,Brasil
c Instituto de Ortopedia, Hospital das Clínicas, Faculdade de Medicina, Universidade de São Paulo (USP), São Paulo, SP, Brasil
d Escola Paulista de Medicina, Universidade Federal de São Paulo (Unifesp), São Paulo, SP, Brasil

Introduction

Anatomical positioning of the graft is a requisite for achiev-ing a good result from posterior cruciate ligament (PCL)reconstructions.1-3Success in surgical treatments for PCLinjuries is related to precise restoration of PCL anatomy.4In a recent published paper, the anatomical location andmeasurements of the tibial insertions of the PCL weredescribed.

Improper positioning of the tunnels in PCL reconstructionmay cause shortening or lengthening of the graft during kneeflexion and, ultimately, failure.

For the function of the reconstructed ligament to be nor-mal, anatomical reconstruction of its anterolateral (AL) andposteromedial (PM) bands should be envisaged, given thatbiomechanical studies have shown that PCL reconstructionwith a double band is superior to reconstruction with a singleband.

Correct demarcation of the insertion sites of the AL andPM bands of the PCL and the correlated radiographic imagesmight assist in providing greater precision for surgical recon-struction of this ligament.

Computed tomography is a potentially useful tool for eval-uating the locations of bone tunnels, which even has thepossibility of generating three-dimensional reconstructions,13although their use in the operating theater is not possible.

Magnetic resonance is less effective for evaluating the posi-tioning of the tunnels in cruciate ligament reconstructions,because interference screws or other metal artifacts used ingraft fixation may interfere with image quality

The aim of our study was to define the radiographic dis-tances from the centers of the tibial insertions of the bandsof the posterior cruciate ligament to the medial and lateralcortical bone of the tibia, on radiographs in anteroposteriorview, and from these centers to the most proximal point of thefacet of the PCL, on radiographs in lateral view, so that thesemight guide the creation of anatomical tunnels during opera-tions and so that these might serve as analytical parametersfor positioning bone tunnels after these operations.

Methods

The insertions of the AL and PM bands of the PCL were eval-uated in 20 anatomical specimens from the knees of adultcadavers (11 right and 9 left knees). The specimens were notpaired and their sex and age data were unknown. All the kneespresented intact anterior and posterior cruciate ligaments andnone of them showed any macroscopic signs of arthrosis.

Before the dissection, the specimens were fixed in 10% for-mol and were conserved in a mixture of 2.5% phenol, 2.5%formol and 1% sodium chloride. Following this, they were keptin liquid glycerin for 60 days.

We identified and isolated the tibial insertions of the AL andPM bands of the PCL and then resected them. The centers ofthe bands were determined from the intersection of the diam-eters of the height and width and were indicated by means ofmetal markers that were glued directly onto the bone, usingspecial glue. Markers of different format were used for eachband (Fig. 1).

Digital radiographs were produced in anteroposterior (AP)view, with the knee extended, and in absolute lateral view,with the knee flexed at 30?. The radiographs were producedusing the following technical standardization: distance fromthe tube to the specimens of 120 cm; voltage of 48 kV anddosage of 5 mAs.

On the AP radiographs, the locations of the insertion sitesof the AL and PM bands were established, in percentages, fromthe ratio of the distance from the insertion point of each bandto the medial border of the tibia, divided by the largest medio-lateral measurement of the superior tibial joint face (Fig. 2).

On the lateral radiographic images, we traced a line abovethe inclined region of the most proximal portion of the tibia,i.e. the insertion site of the PCL, defined by Moorman et al.as the "facet of the PCL".14We measured the size of the facetof the PCL and the distances from the most proximal pointof this line to the insertions of the AL and PM bands (Fig. 3).The ImageJ software was used to measure all of the distancesdescribed above.

Results

On all the radiographic images analyzed, the center of theinsertion of the PM band was distal and medial to the centerof the insertion of the AL band.

The mean distance from the center of the insertion of theAL band to the medial border of the tibia was 40.68 ± 4.10 mm,which corresponded to 52.32 ± 4.55% of the mediolateral mea-surement of the superior tibial joint face.

In relation to the PM band, the mean distance between thecenter of its insertion and the medial border of the tibia was38.74 ± 4.40 mm, equivalent to 49.85 ± 4.92% of the measure-ment of the distance between the medial and lateral bordersof the superior tibial joint face. The data relating to the tib-ial insertions of the PCL on AP radiographs are presented inTable 1.

In evaluating the lateral-view radiographs, the mean lengthof the facet of the PCL was 15.43 ± 2.47 mm. The mean dis-tances between the most proximal point of the facet of thePCL and the centers of insertion of the AL and PM bands were5.49 ± 1.29 mm and 10.53 ± 2.17 mm, respectively (Table 2).

Discussion

The general orthopedic precept that surgery should repro-duce anatomy suggests that grafts placed far from theirtrue anatomical insertion may present impaired function.14Thus, radiographic guidelines for placing tunnels in surgicaltreatments for PCL injuries are essential for accomplishinganatomical reconstructions.

The radiographic locations of the bands of the PCL are ref-erence points that are independent of the size of the knee.Intraoperative fluoroscopy may therefore be a helpful tool forcorrect placement of the tunnels.

Biomechanical studies have shown that reconstruction ofthe PCL using a double band is superior to reconstruction witha single band.7-9However, the most important factor for goodresults is perfect anatomical placement of the bands.9Somestudies on the PCL have not described the locations of the ALand PM bands separately.

We observed that the center of insertion of the PM band wasalways medial and distal to the center of insertion of the ALband. On AP radiographs, the mean distances from the centersof insertion of the AL and PM bands to the medial border of thetibia were 40.68 ± 4.10 mm and 38.74 ± 4.40 mm, respectively.The center of insertion of the AL band was at a location thatcorresponded to 52.32 ± 4.55% of the mediolateral measure-

ment of the superior tibial joint face. For the center of insertionof the PM band, this location represented 49.85 ± 4.92% of themeasurement of the superior tibial joint face.

Lorenz et al.12studied the insertion of the PCL in 16 kneesfrom cadavers. They found that the common point of the inser-tion of the PCL was located at 49 ± 2% of the mediolateraldiameter of the tibia, in relation to the medial border. In astudy on 10 knees from cadavers using computed tomogra-phy, Greiner et al.13found that the mean distance betweenthe tibial insertion of the PCL and the medial border of the tib-ial plateau was 36.6 mm, equivalent to 49% of the total widthof the tibial plateau.

In a study on 39 knees from cadavers, Edwards et al.17foundthat there was a strong correlation between the positions ofthe centers of the AL and PM bands and the width of the tib-ial plateau, which was 48 ± 4% for the AL band (p < 0.001) and48 ± 5% for the PM band (p < 0.002).

According to Osti et al.,18who evaluated 15 knees fromhuman cadavers, the centers of insertion of the AL and PMbands were found at 47.88% and 50.93% of the total medio-lateral tibial diameter, respectively. Takahashi et al.19studied33 tibias from cadavers and found that the distances from themedial border of the joint cartilage of the tibial plateau to thecenters of the tibial insertions of the AL and PM bands, in rela-tion to the width of the tibial plateau, were 51.0% and 50.0%,respectively.

In our sample, the distance from the most proximal pointof the line traced above the facet of the PCL to the insertionof the AL band was 5.49 ± 1.29 mm and it was 10.53 ± 2.17 mmfor the PM band. According to Osti et al.,18the measurementsfrom the insertions of the AL and PM bands of the PCL to thejoint surface were 5.3 mm and 12.8 mm, respectively. On the

other hand, according to Racanelli and Drez,10in a study on 12knees from human cadavers, the distance from the commoninsertion of the PCL to the tibial joint face was 8 mm.

We fully agree with the statement by Johannsen et al.15thatthe most important findings relate to the lateral radiographicview, which is more frequently used during operations.

The different evaluation measurements that we used herecan be applied to surgical reconstructions of the PCL, both asan aid for creating anatomical tunnels and for postoperativeverification.

Conclusions

Our study established a radiographic model for identifying thesites of the tibial insertions of the bands of the PCL basedon the distances from the centers of their insertions to themedial and lateral cortical bones of the tibia and from thesecenters to the most proximal point of the facet of the PCL. Theresults from our investigation may contribute toward anatom-ical reconstruction of the PCL, since correct positioning ofthe tunnels can be checked using fluoroscopy, before theyare drilled. The data obtained may also aid in analyzing thelocations of the tunnels, after the operation.

Conflicts of interest

The authors declare no conflicts of interest.

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