Anatomic Relation Between the Posterior Cruciate Ligament and the Joint Capsule Leonardo Addêo Ramos, Rogério Teixeira de Carvalho, Moisés Cohen, Ph.D., and Rene Jorge Abdalla, Ph.D.
Purpose: The aim of this anatomic study on cadavers was to determine the anatomic relation between the posterior cruciate ligament (PCL) and the posterior joint capsule attachment. Methods: Thirty knees were dissected by means of a posterior approach to the knee. The presence of the posterior popliteal ligament and Wrisberg meniscofemoral ligament was observed and a U-shaped capsulotomy was performed while preserving the distal insertion of the ligament. After detaching the PCL and determining its area on the tibia, we determined its geometric center and posterior margin and measured the distances between the tibial insertion of the capsule and these points. Results: The distance between the center of the PCL and the posterior capsule was 10.3 mm, and the distance between the posterior margin of the PCL and the capsule was 1.7 mm. The posterior popliteal ligament was easy to see in all the specimens, measuring around 42 mm in length. The Wrisberg meniscofemoral ligament was seen in 12 specimens. Conclusions: We can conclude that the distances from the center of the tibial insertion and the margin of the PCL to the joint capsule were 10.3 mm and 1.7 mm, respectively, thus enabling greater knowledge of the anatomy of the posterior compartment of the knee. Clinical Relevance: Our findings provide anatomic data that increase the safety and knowledge regarding the surgical procedures related to the PCL, because we have supplied information that can contribute to obtaining the best arthroscopic view of this area, thus decreasing the risk of vascular and nerve damage. Key Words: Knee—Posterior cruciate ligament—Anatomy—Capsule.
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any posterior cruciate ligament (PCL) reconstruction techniques have been described, but unfortunately, none of them is free from complications.1-5 Among the complications are avascular necrosis of the femur, fracture of the tibial plateau, diminished mobility, deep vein thrombosis, and nerve lesions.
From the Sports Traumatology Sector, Department of Orthopedics and Traumatology, Federal University of São Paulo, São Paulo Medical School, São Paulo, Brazil. The authors report no conflict of interest. Received January 23, 2008; accepted July 20, 2008. Address correspondence and reprint requests to Rene Jorge Abdalla, Ph.D., Sports Traumatology Sector, Department of Orthopedics and Traumatology, Federal University of São Paulo, São Paulo Medical School, Av Abílio Soares, 227 CJ 31 Paraíso, São Paulo, Brazil. E-mail:
[email protected] © 2008 by the Arthroscopy Association of North America 0749-8063/08/2412-0839$34.00/0 doi:10.1016/j.arthro.2008.07.011
The most worrisome complication is neurovascular lesions of the popliteal region.1-5 This complication may occur while the guides and drill bits for constructing the tibial tunnel are being put in place, given that only the posterior capsule separates the PCL from the popliteal artery.4,5 In-depth anatomic knowledge and knowledge of reconstruction techniques are fundamental for preventing this type of complication. These are determining factors for the success of the procedure. The greatest challenges in performing a surgical procedure on the PCL are familiarity with the anatomy (vessels and nerves of the posterior knee) and surgical technique. To our knowledge, this is the first study showing the relation between the tibial insertion of the PCL and tibial posterior capsule insertion, increasing the safety of procedures involving these structures. The aim of this study was to perform an anatomic analysis of the posterior region of the knee to observe the relation between the posterior capsule and the
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tibial insertion of the PCL. Our hypothesis is that a space exists between the tibial insertion of the PCL and the posterior capsule that can provide an area that makes possible a better view of the intra-articular space. METHODS This study used 30 knees from fresh cadavers. There were 16 right knees and 14 left knees. The mean age of the donors was 58 years (range, 30 to 73 years); they were all male donors, and their mean height was 167 cm (SD, 8 cm). The knees were dissected by use of a posterior access route. Specimens that presented signs of ligament injury or fracture of the tibial plateau were excluded from the study. An S-shaped posterior incision of approximately 30 cm in length was made, starting laterally on the thigh and curving medially after reaching the medial head of the gastrocnemius and then heading inferiorly to the tibia. An opening was made in the subcutaneous tissue, and the short saphenous vein and medial sural cutaneous nerve were identified, which would serve as a guide for the popliteal fossa (Fig 1). The neurovascular structures were identified, and the branches were dissected and then retracted laterally. The middle genicular artery was resected, and all the neurovascular structures were moved away to the medial face of the popliteal fossa for better viewing.
FIGURE 1. View of posterior region of knee, with access to popliteal fossa, showing medial sural cutaneous nerve (arrow) between lateral head of gastrocnemius (GLH) and medial head of gastrocnemius (GMH).
FIGURE 2.
View of neurovascular bundle in popliteal fossa.
The lateral and medial heads of the gastrocnemius muscle were identified and detached from their origin next to the femoral condyles, thus finally exposing the posterior capsule of the knee (Fig 2). After identification of its structures and limits, a U-shaped capsulotomy was performed based on its tibial insertion (Fig 3). After identifying the PCL, as well as the Wrisberg meniscofemoral ligament when present, we detached the tibial insertion of the PCL. The tibial insertion area is easily identified because of its coloring, which is different from that of the adjacent subchondral bone. As described by Sheps et al.6 and Edwards et al.,7 we marked a square area formed superiorly by a depression immediately posterior to the posterior insertions of the posterior horns of the menisci and inferiorly by the tibial margin and the medial and lateral margins of the plateaus next to the menisci. We determined the geometric center of this square and its posterior margin, corresponding to the mean point of the distances in millimeters between the sides superior, inferior, lateral, and medial to the quadrilateral, by identifying the reflection point of the posterior capsule on the tibia. This point is rigorously identified with the region proximal to the capsule to articulate posteriorly in the exact point of convergence of fibers’ attachment to the tibia. We marked its insertion to avoid its detachment from the tibia; this procedure was always carried out by the same researcher with the severity maximum technique (Fig 4). With the aid of a precision pachymeter (Mitutoyo, São Paulo, Brazil), we made measurements from the center of the square and the posterior margin to the
RELATION BETWEEN PCL AND JOINT CAPSULE
FIGURE 3.
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(A) U-shaped capsulotomy with tibial base. (B) Posterior capsulotomy showing posterior septum of knee (arrow) and PCL.
posterior capsule (distances C and P, respectively). This pachymeter has a precision of 0.05 mm, which is acceptable according to internationally recognized norms and recommendations (callipers in accordance to DIN 862, JIS B 7507). RESULTS Measurements of the distances between the geometric center of the tibial insertion of the PCL and the insertion of the posterior capsule were made. The mean distance found was 10.3 mm (SD, 0.75 mm) for distance C and 1.7 mm (SD, 0.4 mm) for distance P. The insertion of the PCL in the tibia could be viewed well and palpated, and it was clearly determined in all the knees studied. The presence of the Wrisberg meniscofemoral ligament was identified in only 12 knees (40%); the Humphrey anterior meniscofemoral ligament was not observed because of the dissection technique used. The anterolateral and posteromedial bands could be identified only after dissection associated with observation of their tension during flexion-extension movements of the knee.
The femoral origin of the joint capsule was above the femoral condyles and extended as far as the posterior margin of the tibial plateau. The middle genicular artery was always found above the fabella ligament. The mean length of the oblique popliteal ligament was 42 mm (SD, 3.9 mm). On the anterior face of the posterior joint capsule, there was a septum characterized by a triangular thickening that was formed by fatty tissue wrapped in a thin synovial membrane in the medial region, thereby dividing the posterior region of the knee. In its upper third, it presented the entry point for the bundle of the middle genicular artery (Fig 3). DISCUSSION The principal findings of this study were the distances from the center of the tibial insertion and the margin of the PCL to the joint capsule: 10.3 mm and 1.7 mm, respectively. In our review of the literature regarding the anatomy of the PCL and its topographic relations, we did not find any articles mentioning the distance between the posterior capsule and the tibial insertion.
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FIGURE 4. (A) View of posterior compartment of knee. The reflected posterior capsule (CAP), medial meniscus (MM), lateral meniscus (LM), PCL, medial femoral condyle (MC), and lateral femoral condyle (LC) should be noted. (B) View after resection of PCL, showing square area between medial and lateral menisci and showing distances C and P.
Arthroscopy of the posterior region of the knee continues to be an uncommon procedure. Warnings regarding the risk of injury to the neurovascular popliteal structure have been widely described in the literature; however, damage to the popliteal artery was first described in a case report by Makino et al.8 in 2005, and it was later described as a rare complication in the literature.2,4,5,9-15 Most orthopaedists consider PCL reconstruction to be risky, but during some procedures, it becomes necessary. In reconstructing the PCL, anatomic knowledge and skill in performing arthroscopy in this region of the knee are important. Among the procedures described for dealing with this region are synovectomy, meniscal lesion removal from loose bodies, and PCL reconstruction.9,16 There is no consensus in the literature regarding the best way to reconstruct the PCL. PCL reconstruction can be performed by means of a double- or singletunnel technique or by an inlay technique; instruments can be inserted through the anteromedial or posteromedial portal.13 However, all of these approaches re-
quire surgeons to have knowledge of the posterior region of the knee.1,3-5,12,17-19 The tibial insertion region of the PCL consists of an area located 1.5 cm from the joint surface, with a square-shaped area of 153 ⫾ 37 mm2 delimited by the posterior margin of the tibia and the posterior insertions of the medial and lateral menisci. This area encompasses a depression between the posterior margins of the medial and lateral menisci and corresponds to the center of tibial plateaus in the coronal plan.6,7,20 Previously, this limit was determined by a depression posterior to the tibial spines and the insertion of the anterior cruciate ligament. The posterior limit is easily determined from the posterior border of the tibia. The whole insertion region of the PCL was visible because of the change in color seen on the subchondral bone when the PCL was totally removed from this location (Fig 2). The distance from this ligament to the popliteal artery is between 1.1 and 10.3 mm, depending on the degree of knee flexion.4,18 Some authors have recorded the distance from the popliteal artery to the
RELATION BETWEEN PCL AND JOINT CAPSULE PCL and correlated this with the degree of knee flexion.2,4,5,9-12 Matava et al.4 described the distance between the PCL and the popliteal artery and correlated this with the degree of knee flexion. They found that this distance was maximal at 100° of knee flexion, with measurements of 9.9 mm in the axial plane and 9.3 mm in the sagittal plane, using magnetic resonance imaging for these measurements. However, there are other factors that could influence the distance between these structures, such as the pressure during arthroscopy and the debridement of the posterior capsule.4,9 The difficult access and proximity to neurovascular structures make PCL reconstruction a difficult procedure. Veltri et al.2 determined that the critical moment in PCL reconstruction, in relation to the risk of neurovascular lesion, was the moment when the guidewire and drill bit were introduced to construct the tibial tunnel. Many surgeons use the visualization for control of the progression of the guidewires and drill; however, this technique can allow errors of interpretation depending on the rotation of the knee and can cause image intensification and overlapping of images. Other techniques have also been described to avoid this dramatic complication, such as marking of the drill bit with adhesive tape to determine the length of the tunnel, use of devices to limit the progression of the drill bit and guidewires, use of fluoroscopy, use of direct palpation with a finger through the posteromedial portal, use of conical drill bits, use of better positioning of the knee in flexion to increase the distance to the popliteal artery, and use of posteromedial portals or inlay techniques.2,4,5,9-12 We believe, however, that the direct visualization and identification of the posterior compartment in association with these other techniques can provide a safe method of approaching this region. The only structure that separates the neurovascular bundle and the tibial insertion of the PCL is the joint capsule. Thus full viewing of the tibial point of entry is important while creating the tibial tunnels to avoid neurovascular lesions. Attempting to elevate this region is recommended.4,9 Ahn et al.9 recently showed that release of the posterior capsule increases the distance between the tibial insertion of the PCL and the popliteal artery. Posterior capsulotomy, as described by these authors, along with dissection of the posterior insertion of the capsule, provides an increase in the volume of the posterior compartment that enables better viewing of the insertion of the PCL, thereby diminishing the risk of neurovascular lesions.
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The findings from this study have shown that the mean distance between the center of the area of tibial insertion of the PCL and the tibial insertion of the joint capsule is 10.3 mm. This may determine how much space within the joint can be obtained, thus allowing arthroscopic viewing of the introduction of the guidewires during the procedure of constructing the tibial tunnel, without progression of the guidewire outside of the joint (where there is no direct viewing). The distance between the posterior margin of the PCL and capsule was only 1.7 mm, but with debridement of this area, we were able to increase this distance and thus enable better viewing of this anatomic region and increased safety in relation to the distance from the popliteal artery.9 The posterior capsule of the knee is a complex structure formed by various expansions of the insertion of the semimembranosus and popliteal muscles. LaPrade et al.21 conducted an anatomic study with the aim of identifying its structures and standardizing the nomenclature for these structures. In agreement with that study, we observed that the oblique popliteal ligament was the largest structure in the posterior capsule and that it was easily identifiable. It originates in the region of the lateral femoral condyle, in an area of thickening of the capsule, and its distal insertion is next to the tendon of the semimembranosus, in the posteromedial region of the knee. It has a mean length of 42 mm, and it was used as an anatomic marker for performing the capsulotomy. In the anatomic study by LaPrade et al., this ligament was also observed to be the largest structure in the posterior capsule, measuring 10.4 mm in width in its most central portion and 48 mm in length. In a study using cadavers, Park et al.22 showed that posterior capsulotomy led to increased posterior translation of the knee. The results from those studies suggest that this ligament may have a biomechanical function in preventing knee hyperextension and external rotation, and they should serve as a basis for future studies. In all the knees we evaluated, the insertion of the middle genicular artery was above this ligament. Thus we consider that this ligament is an important anatomic marker for avoiding injury to this artery, particularly in inlay reconstructions of the PCL. The middle genicular artery penetrates between the condyles in a septum that divides the posterior compartment of the knee into 2. The presence of this septum does not pose a risk for the posterior approach to the knee, and it can be safely resected in its lower third. The middle genicular artery emerges in the upper part of this septum, but there is no need for
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surgical manipulation of this area when dealing with the posterior compartment of the knee.16 During this procedure, we performed blunt dissection of this septum, to expose the posterior compartment. In agreement with Ahn et al.,9,16 we believe that dealing with the posterior septum is important for dissection of the posterior capsule and can be performed safely. We believe that our findings can contribute to the technique of PCL reconstruction by supplying information on the distance between the area of insertion of the PCL and the capsule, allowing local management without the risk of disrupting this capsule, and allowing a direct arthroscopic view, thus enabling the procedure to be safer. The limitations of this study are that we were not able to measure lesser distances than 0.05 mm; therefore, we used an instrument for manual measurements; in addition, the insertion area to the joint capsule was often difficult to determine, especially given the histologic findings in individuals of older ages. Through the natural process of aging, degenerative changes occur and these impede appropriate identification of the anatomic structures. CONCLUSIONS We can conclude that the distances from the center of the tibial insertion and the margin of the PCL to the joint capsule were 10.3 mm and 1.7 mm, respectively, thus enabling greater knowledge of the anatomy of the posterior compartment of the knee.
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