Chapter 55 Decision Making and Surgical Treatment of Posterior Cruciate Ligament Ruptures

The proper management of injuries to the posterior cruciate ligament (PCL) and other ligaments of the knee involves a series of decisions based on knowledge of diagnosis, reconstruction options and techniques, and rehabilitation concepts.^70,⁷⁶ The clinician must be able to diagnose and treat a spectrum of knee injuries, from an isolated PCL rupture to a combined injury involving other knee ligaments (Box 55-1). This chapter will review the current knowledge of the function of the PCL—both alone and in concert with other ligament systems—that form the basis for the diagnosis of abnormal translations and rotations that result in different types of knee subluxations requiring surgical restoration (Box 55-2). Legitimate controversy exists about the treatment of complete PCL ruptures because of the absence of a true natural history study, short-term clinical results of PCL reconstructions, and lack of randomized controlled trials of sufficient numbers of patients to form conclusions.

Box 55-1 Spectrum of Posterior Cruciate Ligament Injuries

Posterior Cruciate Ligament Rupture, Isolated

A Partial

B Complete

1 Bone avulsion

2 Ligament insertion peel-off

3 Ligament substance

Posterior Cruciate Ligament Rupture Combined With Other System Abnormality

Lower limb malalignment

Neuromuscular system

Peripheral vascular system

Cutaneous, skin

^* Classified according to the system described in Noyes FR, Stabler CL: A system for grading articular cartilage lesions at arthroscopy. Am J Sports Med 17:505–513, 1989.

Box 55-2

From Noyes FR, Barber-Westin SD: Posterior cruciate ligament: diagnosis, operative techniques, and clinical outcomes. In Noyes FR (ed): Noyes’ knee disorders: surgery, rehabilitation, clinical outcomes, Philadelphia, 2009, Saunders, pp 503–576.

Clinical Effects of Posterior Tibial Subluxation of the Posterior Cruciate Ligament–Deficient Knee

• PCL forces up to 50% body weight occur during level walking

• Higher PCL forces occur during stair climbing, ascending and descending stairs

• Posterior tibial subluxation occurs in PCL-deficient knees during activities of daily living in high knee flexion positions, but not at low flexion positions, when medial-lateral ligaments are intact and smaller posterior shear forces are present

• Patients with chronic PCL deficiency frequently note an anterior shifting of the tibia as the tibial moves forward from its subluxated position when they attempt to stand from a seated position.

• Significantly increased contact pressures in medial tibiofemoral and patellofemoral compartments in PCL-deficient knees

• Loss of medial meniscus function because of posterior tibial subluxation

The steps to diagnose and treat associated problems in knees with PCL ruptures must be systematically accomplished; they are reviewed in this chapter. These include varus malalignment, deficiency of the posterolateral structure (PLS) abnormal gait mechanics including knee hyperextension, and severe muscle atrophy. The detection and treatment of these problems are critical, because failure to correct associated conditions properly may result in an undesirable outcome. Many of these problems are found in patients with chronic knee instabilities who may also have lost one or both menisci and demonstrate advanced articular cartilage damage. In these knees, the goal is to restore knee function for daily activities. Surgical advances in treating acute PCL ruptures hopefully will prevent the chronically unstable knee and resultant arthritis that often occur in younger athletes.

This chapter will also review advances from our center in PCL graft selection and surgical techniques designed to reduce the morbidity of the procedure. There are different surgical approaches available for acute knee injuries, dislocated knees with multiple ligament ruptures, chronic knees, and revision knees. Important decisions must be made regarding the placement of single- and two-strand graft constructs. In addition, differences exist in the postoperative rehabilitation program, depending on the surgical procedure(s) performed.⁸² A detailed analysis and surgical treatment of other knee disorders that accompany PCL ruptures has been previously published; this chapter represents a synopsis of this work.⁷⁶

Posterior Cruciate Ligament Anatomy

The PCL arises from a depression posterior to the intra-articular upper surface of the tibia and courses anteromedially behind the ACL to the lateral surface of the medial femoral condyle (Fig. 55-1).¹²² The PCL has an average length of 38 mm and width of 13 mm.^36,¹³¹ The cross-sectional area of the PCL varies and increases from tibial to femoral insertions.⁴² The PCL is approximately 50% larger than the ACL at its femoral origin and 20% larger at its tibial insertion. The anterior meniscofemoral ligament (ligament of Humphry) courses anterior to the PCL, and the posterior meniscofemoral ligament (ligament of Wrisberg) runs obliquely behind the PCL. At least one meniscofemoral ligament is present in 91% of knees, and both ligaments may be found in 50% of knees in young individuals (Box 55-3).^41,^42,⁶⁵

Figure 55-1 The PCL femoral and tibial attachments. Note the prominent posterior meniscofemoral ligament and broad posterior tibial attachment.

(From Noyes FR, Barber-Westin SD: Posterior cruciate ligament: diagnosis, operative techniques, and clinical outcomes. In Noyes FR [ed]: Noyes’ knee disorders: surgery, rehabilitation, clinical outcomes, Philadelphia, 2009, Saunders, pp 503–576.)

Box 55-3

From Noyes FR, Barber-Westin SD: Posterior cruciate ligament: diagnosis, operative techniques, and clinical outcomes. In Noyes FR (ed): Noyes’ knee disorders: Surgery, rehabilitation, clinical outcomes, Philadelphia, 2009, Saunders, pp 503–576.

Meniscofemoral Ligaments

• Most knees have at least one meniscofemoral ligament (MFL).

• One third of knees have both meniscofemoral ligaments.

• There are insufficient data to support a functional role of these structures.

• Identify anterior MFL and posterior MFL (when present) to determine true PCL anatomic footprint for graft placement.

• In some knees with isolated PCL ruptures, secondary ligament restraints, including the MFL structures, resist posterior tibial subluxation, particularly at low knee flexion angles.

• The best position to test for maximum posterior translation is 90 degrees of knee flexion, neutral tibial rotation.

• The amount of posterior translation after PCL rupture is determined by secondary restraints and will vary depending on physiologic laxity.

Free nerve endings and mechanoreceptors that are believed to have a proprioceptive function in the knee ⁴⁹ have been identified in the femoral and tibial attachment sites and on the surface of the PCL.^47,¹⁰⁶

The traditional division of the PCL into separate anterolateral and posteromedial bundles oversimplifies PCL fiber function. The PCL is a complex anatomic structure comprised of a continuum of fibers of different lengths and attachment characteristics. The length-tension behaviors of the fibers that resist posterior tibial translation (with knee flexion) are controlled primarily by femoral attachment regions.* The distal fibers lengthen with increasing knee flexion and the proximal fibers shorten with knee flexion.^65,¹⁰⁵

Variation exists among knees in the shape of the PCL femoral attachment, from the common elliptical shape to a more rounded and thicker shape (Fig. 55-2).⁶⁵ The most accurate measurement system that describes the femoral attachment site uses a clock reference position, with one set of measurement lines perpendicular to the articular cartilage edge and the other set parallel to the femoral shaft.

Figure 55-2 Composite of the shapes of different PCL insertion sites as seen on lateral views. Variability is noted between specimens from an oval to an elliptical PCL footprint configuration. Note the differences in the anterior to posterior and proximal to distal dimensions in the PCL footprint. The most common shape of the PCL footprint is elliptical. A, Fibers insert proximally to the intercondylar roof. The PCL footprint is smaller in its anteroposterior dimension. B, Prominent posterior meniscofemoral ligaments. C, More oval PCL attachment, with greater proximal to distal width.

(From Mejia EA, Noyes FR, Grood ES: Posterior cruciate ligament femoral insertion site characteristics. Importance for reconstructive procedures. Am J Sports Med 30: 643–651, 2002.)

In general, the PCL attachment extends from high in the notch (11:30 to 5 o’clock on a right knee) along the medial femoral condyle. The anterior portion of the PCL attachment follows the articular cartilage within 2 to 3 mm of its edge and gradually recedes deeper with the notch until, at the 5 o’clock position, the posterior third is 5 mm from the articular margin. Therefore, the distal boundary of the PCL femoral attachment is furthest away from the cartilage margin posteriorly.

The distance of the distal edge of the attachment to the articular cartilage margin is 3.2 ± 0.8 mm at the roof, 5.8 ± 2.2 mm at its midportion, and 7.9 ± 2.2 mm at its “lowest” extent.¹⁰⁵ The proximal edge of the PCL is usually straight or partially oval, with the attachment tapered in width along its posterior portion.

A clear understanding of the anatomy of the native PCL is critical in determining what portion of the ligament will be reconstructed. The terms high, low, shallow, and deep are only general descriptors. Because there may be confusion regarding femoral graft tunnel placement during PCL reconstruction, the PCL femoral attachment is described using the rule of thirds (Fig. 55-3A, B) to define the proximal-middle-distal thirds (deep to shallow in the femoral notch), and anterior-middle-posterior thirds (high to low), with a small posterior oblique portion in the sagittal plane.^65,⁶⁷ This provides a grid for the identification of the tunnel locations for the graft strands and is preferred over the historical division of an anterolateral or posteromedial bundle (see Fig. 55-3C).

Figure 55-3 A, Rule of thirds. The PCL footprint is divided into anterior, middle, and posterior thirds. The anterior third extends past the midline (12:30 o’clock, left knee) and the posterior region extends to 5 o’clock. The smaller posterior oblique portion of the PCL footprint is also represented. The PCL footprint is elliptical in most knees, but variations exist. B, Rule of thirds. The PCL footprint is further divided into distal, middle, and proximal thirds. This allows for more exact referencing of graft strand placement during PCL reconstruction. The PCL fibers in the distal two thirds lengthen with knee flexion whereas the proximal fibers shorten. The reverse occurs with knee extension. C, Typical division of anterolateral and posteromedial bundles provides an incorrect description of PCL fiber length change, because it describes anterior PCL fibers that lengthen (AL) and posterior fibers (PL) that shorten with knee flexion.

Vascular Anatomy and Variations

The PCL is covered with a well-vascularized synovial sleeve that contributes to its blood supply. The distal portion also receives some vascular supply from capsular vessels originating from the inferior and middle genicular arteries and the popliteal artery.

Detailed knowledge of posteromedial knee anatomy, especially the vascular structures, is required to avoid complications when using a posteromedial approach for a tibial inlay PCL reconstruction. The popliteal artery originates at the adductor hiatus and passes through the popliteal fossa. Before passing deep to the fibrous arch over the soleus muscle, it divides into the anterior and posterior tibial arteries at the distal aspect of the popliteus muscle.

At the level of the knee joint, four major arteries are distributed—the medial and lateral sural arteries, a cutaneous branch that travels with the small saphenous vein to supply superficial tissues, and the middle genicular artery. The medial and lateral inferior genicular arteries are given off just distal to the knee joint.

Two branches deserve particular attention. The medial inferior genicular artery arises from the medial aspect of the distal portion of the popliteal artery and runs medially, deep to the medial head of the gastrocnemius, and approximately 2 to 3 mm from the superior surface of the popliteus muscle. It continues around the medial aspect of the proximal tibia, deep to the superficial MCL (SMCL). The middle genicular artery arises at the level of the femoral condyles proximal to the joint line and passes anteriorly to pierce the oblique popliteal ligament and posterior joint capsule and supply the cruciate ligaments.

This normal vascular pattern has been reported to occur in approximately 88% of knees.^20,⁶³ In approximately 5% to 7%, the popliteal artery will divide at least 1 inch or more proximal to the distal border of the popliteus muscle.¹⁴ In slightly less than half of these knees, with a high division of the popliteal artery, the anterior tibial artery passes anteriorly, not posteriorly, to the popliteus muscle belly.¹²⁹ A number of variations of the anterior tibial artery were described by Mauro and colleagues.⁶³ Therefore, with a tibial inlay approach, the dissection is always performed proximal to the popliteus muscle using a meticulous technique, because the anterior tibial artery is at risk for transection in approximately 3% to 4% of knees.

An unusual variation in the vascular pattern involves the popliteal artery passing medially and then beneath the medial head of the gastrocnemius. Various subtypes of this abnormal pattern have been described. An abnormal vascular pattern may manifest clinically as the popliteal artery entrapment syndrome, which is characterized by vascular claudication symptoms.^52,^102,¹¹⁸ Arterial insufficiency occurs most commonly with entrapment of the artery deep to the medial gastrocnemius muscle, but may also occur when the artery is entrapped deep to the popliteus muscle (persistence of ventral component of artery), or entrapped deep to an abnormal accessory head of the gastrocnemius. A history of pain in the lower extremity with activity but none at rest, particularly in a young patient, should alert the surgeon to the possibility that an abnormal vascular pattern may exist. Further evaluation with magnetic resonance imaging (MRI) or angiography may be warranted.^30,⁵⁵

Posterior Cruciate Ligament Fiber Function

The femoral attachment location of a PCL graft strongly influences graft tension and the ability of the reconstruction to restore posterior stability.* Investigations by Grood and associates³⁸ and Sidles and coworkers¹¹⁵ have demonstrated that the femoral attachment location, and not the tibial attachment location, determines the graft tibiofemoral separation distance with knee flexion-extension.

On the femur, the proximal-distal location of a graft has a greater effect on the attachment separation distance than the anterior-posterior location (Figs. 55-4 and 55-5), which forms the basis for the rule of thirds. A graft placed in the distal and middle thirds lengthens with knee flexion, whereas a graft placed in the proximal third lengthens with knee extension.

Figure 55-4 Contour map for a typical knee. The number on each contour line indicates the magnitude of the maximum length change. Line A-A represents the most isometric line and runs almost in the AP direction. Point CR indicates the intersection of the best-fit flexion axis with the lateral surface of the medial femoral condyle. Note that line A-A passes near point CR. The curves at the right show the changes in the tibiofemoral separation distances that occurred for selected femoral attachments. Attachments proximal to the isometric line were shorter at 90 degrees than at full extension. Attachments distal to the line were longer at 90 degrees. Attachments along line A-A had a length at 90 degrees that was almost identical to its length at 0 degrees.

(From Grood ES, Hefzy MS, Lindenfeld TN: Factors affecting the region of most isometric femoral attachments. Part I: The posterior cruciate ligament. Am J Sports Med 17:197–207, 1989.)

Figure 55-5 Left, The curves show the average tibiofemoral separation distance versus knee flexion for three femoral attachment sites located along the most isometric line. Right, The bar chart shows the average and standard deviation of the difference between the maximum and minimum tibiofemoral separation distance for each of the three femoral attachment sites.

(From Grood ES, Hefzy MS, Lindenfeld TN: Factors affecting the region of most isometric femoral attachments. Part I: The posterior cruciate ligament. Am J Sports Med 17:197–207, 1989.)

In an investigation at our laboratory,¹⁰⁵ the changes in tibiofemoral length for seven peripheral attachment sites at the proximal and distal origins located around the circumference of the PCL femoral attachment were studied. The data confirm that proximal PCL fibers lengthen with knee extension and distal fibers lengthen with knee flexion (Fig. 55-6). In Figure 55-7, the flexion angles in which the fiber length elongations were the least (within 5% of the maximum length and, therefore, the functional zone) are graphed for each attachment point. The data as a whole show a progressive loading of fibers from distal to proximal within the PCL attachment with increasing knee flexion. There is a smaller effect proceeding from anterior to posterior. These data contradict the description of PCL fiber function that divides the PCL into an anterolateral bundle (which lengthen with knee flexion) and posteromedial bundle (which shorten with knee flexion).

Figure 55-6 Changes in attachment separation distance (in mm) are measured with progressive knee flexion under a 100-N posterior load. Distal fibers lengthen with knee flexion; proximal fibers shorten with knee flexion.

(From Saddler SC, Noyes FR, Grood ES, et al: Posterior cruciate ligament anatomy and length-tension behavior of PCL surface fibers. Am J Knee Surg 9:194–199, 1996.)

Figure 55-7 The change in attachment separation distance curves have been shifted to begin at the measured absolute length of each fiber. The darker area for each curve represents the 5% strain for each fiber. This in theory represents the functional range of knee flexion for each fiber. Note that this model predicts that the proximal-anterior fiber will function over the longest functional range.

(From Saddler SC, Noyes FR, Grood ES, et al: Posterior cruciate ligament anatomy and length-tension behavior of PCL surface fibers. Am J Knee Surg 9:194–199, 1996.)

The surgeon has the option of placing a PCL graft strand into different regions of the PCL femoral attachment site that determine the functional range of the graft with knee flexion and the knee flexion position to tension the graft. In a study from our laboratory,⁵⁷ one- and two-stand PCL reconstructions were attached in three different locations within the PCL femoral footprint. A 50-N posterior force was applied to the tibia for the single-stand construct and a 100-N force was applied to the two-strand PCL reconstruction. The tension in the graft stands was adjusted to restore posterior translation to within ±1 mm of the intact knee. The complex behavior of a two-strand PCL reconstruction is shown in Figure 55-8, in which the two strands were placed into the more distal locations and tensioned at 90 degrees. Both strands shared the applied load as shown. In contrast, a two-strand construct, in which one strand was placed anterior and the second strand was placed more proximally, resulted in a reciprocal loading relationship between strands (Fig. 55-9). In both situations, posterior translation limits were restored to normal.

Figure 55-8 The graph shows the strand tension (A) and change in posterior translation from intact (B) for the one shallow and two shallow two-strand reconstruction with a 100-N posterior force. The T indicates the flexion angle at which the strands were tensioned. The shaded area for posterior translation represents the translation for the intact knee ±1 mm. The photographs show the (A) one shallow and (B) three shallow femoral tunnel placements.

(From Mannor DA, Shearn JT, Grood ES, et al: Two-bundle posterior cruciate ligament reconstruction. An in vitro analysis of graft placement and tension. Am J Sports Med 28: 833–845, 2000.)

Figure 55-9 The graph shows the strand tension (A) and change in posterior translation from intact (B) for the one shallow and two-deep two-strand reconstruction with a 100-N posterior force. The T indicates the flexion angle where the strands were tensioned. The shaded area for posterior translation represents the translation for the intact knee ±1 mm. C, Photograph shows the two-deep femoral tunnel placement.

(From Mannor DA, Shearn JT, Grood ES, et al: Two-bundle posterior cruciate ligament reconstruction. An in vitro analysis of graft placement and tension. Am J Sports Med 28: 833–845, 2000.)

Another investigation at our laboratory ¹¹⁰ confirmed that a proximal to distal change in the femoral position of the second bundle of a two-bundle construct markedly affects bundle tension and function. A middle placement of the second bundle produced load sharing, which is more ideal in terms of graft function in the long term for preventing posterior tibial subluxation with increasing knee flexion. These concepts are used to select PCL graft attachment locations and tensioning, described in the operative techniques section (see later). The surgeon should select graft attachment locations that have the least amount of change in tibiofemoral length, and tension the graft at the knee flexion position at which the graft length is the longest (and therefore functional). If a graft is tensioned at a knee flexion angle at which the tibiofemoral fiber length is at its shortest, the graft will initially constrain knee flexion or extension and fail as the graft (tibiofemoral distance) lengthens with further knee flexion or extension.

Diagnosis of Posterior Cruciate Ligament Function and Knee Joint Subluxations

Posterior Translation

The normal anterior and posterior translation knee limits are shown in Figure 55-10A.⁴⁰ The increase in these limits when the PCL is cut is shown in Figure 55-10B and the further increase in these limits when the PLS is also sectioned is shown in Figure 55-10C.

Figure 55-10 The curves show the limits of anterior and posterior translation (vertical axis) when a 100-N AP force was applied. A, Intact knees. The curves show the average limits of motion and the standard deviation for nine knees. The range of total AP translation of the intact knee is shown shaded green in A-C. B, Posterior cruciate ligament (PCL) cut first. The increase in posterior translation after cutting the PCL is shown in the blue shaded area (PCL deficit). The limit of posterior translation, and therefore the amount of increase, is controlled by the remaining intact structures. The unshaded portion (+ PLS deficit) shows the added increase when the posterolateral structures (FCL, capsule, PMTL) were cut after the PCL had first been removed. A concurrent external rotation took place with this cut. C, Posterolateral structures cut first. There was only a small increase (PLS deficit) in the posterior limit near full extension when the posterolateral structural elements were cut first. A concurrent external rotation was also present.

(Adapted from Noyes FR, Barber-Westin SD: Function of the posterior cruciate ligament and posterolateral ligament structures. In Noyes FR [ed]: Noyes’ knee disorders: surgery, rehabilitation, clinical outcomes, Philadelphia, 2009, Saunders, pp 467–502.)

The PCL is a primary restraint to posterior tibial translation throughout knee flexion, with the exception of a small increase in posterior translation at full extension when the PLS is cut. A knee that demonstrates increased posterior translation at 30 to 45 degrees of knee flexion, similar to the posterior translation limit at 90 degrees, indicates associated injury to the PLS and the medial structures. In a knee with a combined deficiency of the PCL and PLS, the abnormal posterior tibial translation is at least four to five times the normal limit throughout knee flexion.

The PLS represents one of the most important secondary restraints and has a major effect on lateral tibiofemoral compartment translation. There are marked differences in the amount of posterior tibial translation between isolated and combined PCL injuries. Although the amount of posterior translation may vary among knees,⁴⁰ it is generally appreciated clinically that a 10-mm or greater abnormal displacement at 90 degrees flexion indicates some deficiency of the secondary restraints in addition to the PCL. Furthermore, the posterior tibial displacement progressively increases at low flexion angles with injury or stretching of the secondary ligament restraints. The abnormal forces placed on the patellofemoral and tibiofemoral compartments are expected to increase as greater posterior tibial displacements occur.¹¹⁶ Clinically, it is advantageous to reconstruct the PCL before the loss of these secondary restraints. Otherwise, the PCL graft is placed under greater forces because the secondary restraints are not able to share a portion of the load in resisting posterior tibial subluxation. In chronic cases, in which the secondary restraints are deficient, we recommend surgical reconstruction of these structures during the PCL reconstruction to allow load sharing and protection of the PCL graft during the healing process. The individual function of each of the posterolateral structures has been previously published.⁷¹

Varus and Valgus Rotations

Injury to the fibular collateral ligament (FCL) and posterolateral structures (popliteus muscle–tendon–ligament unit [PMTL], popliteofibular ligament [PFL], and posterolateral capsule) results in increases in lateral joint opening under varus loads and increases in posterior subluxation of the lateral tibial plateau with external tibial rotation. With these ligament injuries, the PCL is placed under higher than normal loading conditions. Figures 55-11 and 55-12 show the relationship of the primary ligamentous restraints to medial and lateral joint opening and the PCL.³⁹ Normally, a small force is present in the PCL to both varus and valgus loads.⁶¹ With injury to medial or lateral structures, the PCL and anterior cruciate ligament (ACL) may be placed in the role of a primary restraint that is not ideal, because their mechanical advantage in the center of the knee joint is not suited to resist medial and lateral joint openings. These biomechanical findings indicate the importance of determining an abnormal medial or lateral joint opening (subluxation) that requires surgical reconstruction. The failure to correct such associated subluxations places the PCL graft reconstruction under high in vivo forces postoperatively and risks graft failure.

Figure 55-11 The percentage contributions to the medial restraints by the ligaments and capsule at 5 mm of medial joint opening and 25 degrees of flexion. The error bars represent ± one standard error of the mean.

(Adapted from Noyes FR, Grood ES: The scientific basis for examination and classification of knee ligament injuries. In Noyes FR [ed]: Noyes’ knee disorders: surgery, rehabilitation, clinical outcomes, Philadelphia, 2009, Saunders, pp 47–88.)

Figure 55-12 The percentage contributions to the lateral restraints by the ligaments and capsule at 5 mm of lateral joint opening and 25 degrees of flexion. The error bars represent ± one standard error of the mean.

Careful examination of the knee preoperatively and under anesthesia is required to determine whether abnormal motions and other ligament injuries are present that require reconstruction at the same time as the PCL. During the arthroscopic examination, the gap test confirms that excessive medial or lateral joint opening is not present, which would place abnormal loads on a PCL graft (Fig. 55-13). The goal is to restore function of any insufficient ligamentous structure in one surgical setting. Both the ACL and PCL function in combination with the medial and lateral ligamentous structures in a complex system of primary and secondary restraints that establish the limits to rotations and translations that normally occur in the knee joint. Any insufficiency of two ligamentous structures results in a combination of subluxations involving the medial and lateral tibiofemoral compartments (see later).

Figure 55-13 A, Arthroscopic demonstration of the lateral joint opening—gap test. The amount of lateral joint opening is measured with the knee at 25 degrees flexion. B, Knees with insufficiency of the posterolateral structures will demonstrate 12 mm of joint opening at the periphery of the lateral tibiofemoral compartment, 10 mm of opening at the midportion of the compartment, and 8 mm at the inner most medial edge.

(From Noyes FR, Barber-Westin SD: Primary, double, and triple varus knee syndromes: diagnosis, osteotomy techniques, and clinical outcomes. In Noyes FR [ed]: Noyes’ knee disorders: surgery, rehabilitation, clinical outcomes, Philadelphia, 2009, Saunders, pp 821–895.)

Tibiofemoral Rotational Subluxations

Injury to the FCL and PLS produces an increase in external tibial rotation and a posterior subluxation of the lateral tibial plateau. There are two primary restraints to external tibial rotation, the PLS at low flexion angles and both the PLS and PCL at high flexion angles (Fig. 55-14). Careful examination of knees with suspected injury to these structures may show a marked increase in external tibial rotation and posterior translation of the lateral tibial plateau or only a slight increase in these abnormal knee motions.⁹¹ The clinician’s first goal is to diagnose all the possible knee subluxations and define the extent of injury to the PLS. In 1989, we first reported on a modification of existing rotation tests to diagnose tibial rotatory subluxations of the medial and lateral tibiofemoral compartments more accurately (dial or spin rotation test).⁸⁸ We then studied the amount of increased posterior subluxation of the medial and lateral tibial plateaus that result from injury to the PCL and PLS.⁹¹ We found that sectioning of the PLS results in a significant mean increase in posterior translation of the lateral tibial plateau of 8.0 mm at 30 degrees of flexion over the intact state (P < .01). No significant increase of the lateral tibial plateau occurred at 90 degrees of flexion. There was no significant increase in posterior translation of the medial tibial plateau at either flexion angle. After sectioning both the PCL and PLS, significant increases in posterior translation of the medial and lateral tibial plateaus occurred at 30 and 90 degrees of flexion (P < .01). The increase in posterior translation of the lateral tibial plateau averaged 17.8 and 23.5 mm at 30 and 90 degrees of flexion, respectively, and the increase in posterior translation of the medial tibial plateau averaged 7.6 and 12.3 mm at 30 and 90 degrees, respectively.

Figure 55-14 The limits of internal and external rotation of the tibia when a 5-N torque was applied. The fully extended position, measured in the intact knee, was used as the zero rotation reference. A, Intact knees. The upper curve shows the limit of external rotation. The dashed line shows the average position of the knee during passive flexion with the tibia hanging freely. The range of tibial rotation in the intact knee is shaded in A-C. B, Posterior cruciate ligament cut first. No change was found in external tibial rotation. C, Posterolateral structures (FCL, capsule, PMTL) cut first. Increases in external tibial rotation occurred at low flexion angles. With added PCL sectioning, the increase in external tibial rotation occurred at high flexion angles.

From the results of this study, we concluded that the diagnosis of injury to the PLS should be made based on the final position of the lateral tibial plateau and not on the amount of increased external tibial rotation alone. An increase in external tibial rotation can occur with anterior subluxation of the medial tibial plateau, posterior subluxation of the lateral tibial plateau, or a combination of both subluxations. In a prior investigation,⁸⁶ we found that clinicians often misdiagnose injuries to the PLS because of misinterpretation of the increase in external tibial rotation as a posterior subluxation of the lateral tibial plateau, when in fact there was a subluxation of the medial tibial plateau caused by injury to the medial collateral ligament (MCL) alone or in combination with the ACL.

We have recommended that during the rotation tests to determine rotatory subluxations of the tibial plateaus, the examiner carefully palpate the position of each tibial plateau to determine qualitatively whether an anterior or posterior subluxation is present. We and others ^15,¹⁶ have reported that it is not possible to determine the actual millimeters of translation of the medial and lateral tibial plateaus in reference to the femoral condyle. Thus, a qualitative determination of whether the reference tibial plateau is anteriorly or posteriorly subluxated is recommended. The inability to measure tibiofemoral compartment translations precisely, and to quantify the amount of posterolateral subluxation, creates problems in deciding whether surgical correction is warranted.

A classification system of rotatory subluxations was previously described based on two concepts—determining the final position of the medial and lateral tibial plateaus under defined loading conditions (e.g., with either internal or external tibial rotation at a defined knee flexion angle) and classifying the position of each plateau.⁹¹ There are three possible positions for each plateau: anterior subluxation, normal position, or posterior subluxation. For each of these positions of the lateral tibial plateau, there are three corresponding positions for the medial tibial plateau (Fig. 55-15).

Figure 55-15 Three types of tibiofemoral situations observed with increased external tibial rotation. A, Abnormal posterior translation of the lateral tibial plateau (at 30 degrees of knee flexion under the loading conditions described in the study). B, Abnormal anterior translation of the medial tibial plateau under loading conditions of 5 Nm at 30 degrees of knee flexion. C, Abnormal posterior translation of the lateral tibial plateau plus abnormal anterior translation of the medial tibial plateau after sectioning both the medial and lateral ligament structures. AS, Anterior subluxation; FCL, lateral collateral ligament; LTP, lateral tibial plateau; MCL, medial collateral ligament; MTP, medial tibial plateau; N, normal position; PLS, posterolateral structures (FCL, PMTL); PMC, posterior medial capsule; PS, posterior subluxation.

(From Noyes FR, Stowers SF, Grood ES, et al: Posterior subluxations of the medial and lateral tibiofemoral compartments. An in vitro ligament sectioning study in cadaveric knees. Am J Sports Med 21:407–414, 1993.)

When a posterior subluxation of the lateral tibial plateau is positively identified by the described tibiofemoral rotation test, the examiner performs additional tests to determine whether ruptures exist to other ligamentous structures. The amount of lateral joint opening at 0 and 20 degrees of knee flexion should be determined (and quantified by stress radiography when possible) to determine the integrity of the FCL and PLS.⁴⁰ The presence of a varus recurvatum in both the supine and standing positions must be carefully assessed. The difference in results of these tests between the injured and contralateral normal knee is compared because of inherent physiologic looseness that is present in some individuals. The different type of subluxations after posterolateral injuries depends on whether there is a concomitant rupture to the ACL or PCL.

Clinical Evaluation

Physical Examination

A comprehensive examination of the knee joint is required to detect all abnormalities (Fig. 55-16). This includes assessment of the following: (1) patellofemoral joint and extensor mechanism malalignment; (2) patellofemoral and tibiofemoral crepitus, indicative of articular cartilage damage; (3) gait abnormalities (excessive hyperextension or varus thrust) during walking and jogging⁸⁷; and (4) abnormal knee motion limits and subluxations compared with the contralateral knee.⁸⁸

Figure 55-16 Manual knee tests. A and B, Posterior drawer test at 90 degrees knee flexion. C, Lachman test. D, Valgus manual test for medial joint opening. E, Valrus manual test for lateral joint opening. F, Dial test at 90 degrees of knee flexion in neutral tibial rotation and maximum external tibial rotation (G). Varus recurvatum in the supine (H) and standing (I) positions.

Experienced clinicians are aware that patients with chronic deficiency of the PCL and PLS may develop an abnormal gait pattern, which is characterized by excessive knee hyperextension during the stance phase.⁸⁷ Subjective complaints of knee instability and giving way during routine daily activities, along with severe quadriceps atrophy, often accompany this gait abnormality. Gait analysis and retraining are required in patients who demonstrate abnormal knee hyperextension patterns before proceeding with any ligament reconstruction. The failure to do so may lead to failure of reconstructed ligaments if the abnormal gait pattern is resumed postoperatively.

Diagnostic Clinical Tests

The medial posterior tibiofemoral step-off on the posterior drawer test is performed at 90 degrees of flexion. The amount of posterior tibial translation will vary among knees with isolated PCL ruptures because of physiologic laxity or injury to the secondary posterolateral or medial soft tissue restraints. Posterior tibial translation progressively increases with injury to the secondary restraints.

The exact determination of the extent of a PCL tear (partial versus complete) can be difficult, but is essential from a therapeutic standpoint. The clinical posterior drawer test can be highly subjective, with the forces applied too variable to allow accurate determination of the status of the PCL. MRI is not always accurate for diagnosing partial PCL tears. Frequently, this test may indicate that the ligament is completely ruptured; however, ligament continuity may still exist, with some portions functioning to limit posterior tibial subluxation to only a few millimeters.⁹⁶

The quantitative measurement of posterior tibial subluxation in knees with PCL ruptures or reconstruction is therefore important.⁴³ The knee arthrometer is the most frequently used device to measure posterior tibial translation following PCL injury and reconstruction. However, this device underestimates the true amount of posterior translation in PCL-deficient and reconstructed knees, often by several millimeters.^58,¹²¹ Stress radiography is the most accurate and reproducible technique currently available.^25,^28,^98,¹⁰⁷ We recommend that PCL clinical investigations incorporate stress radiography to provide a more valid measure of posterior tibial translation (Figs. 55-17 and 55-18).

Figure 55-17 Lateral stress radiograph of a PCL-deficient knee demonstrating a 19-mm posterior drop-back (involved-noninvolved knee, 70 degrees knee flexion, 89 N).

(From Noyes FR, Barber-Westin SD: Treatment of complex injuries involving the posterior cruciate and posterolateral ligaments of the knee. Am J Knee Surg 9: 200–214, 1996.)

Figure 55-18 Results of lateral stress radiography on 20 patients with PCL deficiency (9 complete ruptures and 11 partial ruptures). The differences in the measurements between complete and partial PCL ruptures for the medial tibial plateau, lateral tibial plateau, and average of both plateaus were statistically significant (P < .01). Differences in the KT-1000 and posterior drawer measurements between complete and partial PCL ruptures were not significant. The KT measurements at 70 degrees flexion underestimated the magnitude of posterior tibial subluxation for complete PCL ruptures.

(From Hewett TE, Noyes FR, Lee MD: Diagnosis of complete and partial posterior cruciate ligament ruptures. Stress radiography compared with KT-1000 arthrometer and posterior drawer testing. Am J Sports Med 25: 648–655, 1997.)

The integrity of the ACL is determined by Lachman and pivot shift tests. The result of the pivot shift test is recorded on a scale of 0 to 3, with a grade of 0 indicating no pivot shift; grade 1, a slip or glide; grade 2, a jerk with gross subluxation or clunk; and grade 3, gross subluxation, with impingement of the posterior aspect of the lateral side of the tibial plateau against the femoral condyle. Knee arthrometer testing may be done at 20 degrees of flexion (134-N force) to quantify total anteroposterior (AP) displacement.

Medial and lateral ligament insufficiency are determined by varus and valgus stress testing at 0 and 30 degrees of knee flexion. The surgeon estimates the amount of joint opening (in millimeters) between the initial closed contact position of each tibiofemoral compartment, performed in a constrained manner to avoid internal or external tibial rotation, to the maximal opened position. The result is recorded according to the increase in the tibiofemoral compartment of the affected knee compared with that of the opposite normal knee.

The tibiofemoral rotation dial test at 30 and 90 degrees is done to determine whether increases in external tibial rotation exist with posterior subluxation of the lateral tibial plateau (see earlier).⁸⁸

The presence of a varus recurvatum in both the supine and standing positions is carefully assessed.

Imaging Studies

Radiographs taken during the initial examination include AP, lateral at 30 degrees of knee flexion, weight-bearing posteroanterior (PA) at 45 degrees of knee flexion, and patellofemoral axial views.

Posterior stress radiographs are done with an 89-N force applied to the proximal tibia (see Figs. 55-17 and 55-18).⁴³ A lateral radiograph is taken of each knee at 90 degrees of flexion. The limb is placed in neutral rotation with the tibia unconstrained and the quadriceps relaxed. The difference in posterior tibial displacement between the injured knee and contralateral knee is recorded. More than 8 mm of increase in posterior tibial translation on stress testing indicates a complete PCL rupture.¹⁰⁷

Medial or lateral stress radiographs may be required of both knees. The patient is seated (0 degree of knee extension) in neutral tibial rotation with the tibia unconstrained. Approximately 89 N of varus or valgus force is applied and comparison made of the medial or lateral tibiofemoral compartment opening between knees (in millimeters).

Full standing radiographs of both lower extremities, from the femoral heads to the ankle joints, are done in knees in which varus lower extremity alignment is detected on clinical examination. The mechanical axis and weight-bearing line are measured to determine whether a high tibial osteotomy (HTO) is indicated before PCL reconstruction.^24,⁸⁵ If the varus malalignment is not corrected, there is a risk that a PCL or ACL graft may fail because of the varus thrusting forces and concurrent increased lateral joint opening, producing high graft tension loads.⁷⁴

Management Considerations

Posterior Cruciate Ligament Natural History

The treatment of complete isolated PCL ruptures remains controversial because of the unknown natural history of this injury in regard to long-term symptoms, functional limitations, and risk of joint arthritis. Although some studies that included patients with partial PCL deficiency have reported that patients do well when treated conservatively,* others^6,^19,^23,⁴⁸ have described noteworthy symptoms and functional limitations years after the injury, which can be disabling. A high percentage of knees with complete PCL ruptures develop articular cartilage deterioration over time; this usually occurs on the medial femoral condyle and patellofemoral surfaces because of increased joint pressures.^6,^34,^35,¹²³ Posterior tibial subluxation after PCL rupture has a deleterious effect to the knee, similar to that of a medial meniscectomy, because there is loss of medial meniscus function and increased joint contact stress. Posterior tibial subluxation results in a loss of normal joint kinematics (see Box 55-2) and in coupled external tibial rotation with joint loading. Accordingly, a PCL rupture has a more deleterious effect in a varus-angulated knee with associated loss of the medial meniscus and, in particular, larger athletes desiring a return to strenuous athletics. All these factors result in substantial medial tibiofemoral loads and risk of joint deterioration.

Treatment of Acute Posterior Cruciate Ligament Ruptures

Controversy exists in regard to the treatment of midsubstance complete PCL ruptures, primarily because of the lack of a scientifically proven operative procedure that can restore posterior stability and PCL function predictably. In comparison, surgical procedures to reattach the native PCL in cases of bony avulsion injuries or peel-off injuries directly at the PCL attachment site have more predictable healing rates.^5,^54,^127,¹²⁸ Even in cases of PCL rupture directly at the attachment site, there is usually sufficient ligament substance for a direct repair.

Augmentation of partial PCL tears is controversial.^2,^46,¹³² Graft reconstruction of the so-called posteromedial portion of the PCL has been described in which the anterolateral bundle is still intact and functional. The senior author (FN) has not performed augmentation procedures to date.

The treatment rationale for patients with acute PCL ruptures is shown in Figure 55-19.⁷⁶ The algorithm is divided into three major sections based on the PCL tear (partial, complete, or combined with other ligament ruptures). The 10-mm division is somewhat arbitrary.

Figure 55-19 Treatment algorithm for acute PCL ruptures.

The rules to treat partial or acute isolated PCL tears are shown in Box 55-4. In our experience, 4 weeks of protection to allow initial healing of a complete PCL rupture will frequently restore partial PCL function, with less than 10-mm residual posterior tibial subluxation. The initial PCL healing process involves low tensile strength and an additional 4 to 6 weeks of protection is recommended, including avoiding athletics, running, walking on downhill grades, walking down stairs, or other high knee flexion activities that load the PCL. Even in knees with a complete PCL tear and more than 10 mm of increased posterior tibial displacement, healing of the disrupted PCL fibers may still occur, although a residual posterior tibial subluxation of a few millimeters (with a hard end point) will remain. Knees in which partial PCL function has been restored should be routinely followed, with repeat stress radiographs obtained at 6 months and over the next few years to determine PCL function. These partial PCL tears seldom require reconstruction. A repeat MRI with fast spin-echo cartilage sequences¹⁰¹ helps determine the integrity of the articular cartilage and provides important information for counseling the patient on athletic activities to decrease the risk of future joint arthritis.

Box 55-4

Rules to Treat Partial or Acute Isolated Posterior Cruciate Ligament Tears

1 Immobilize for 4 weeks in a full knee extension brace or bivalved cylinder cast to maintain tibiofemoral reduction. Use quadriceps isometrics, electrical muscle stimulation, leg raises, and 25% weight bearing.

2 Obtain a lateral radiograph to verify that no posterior tibial subluxation exists, which can occur in up to 50% of knees.

3 At 2 weeks, the therapist initiates 0 to 90 degrees of motion, maintaining an anterior tibial translation load. The patient must sleep in the brace and is not allowed unsupervised knee motion to prevent posterior tibial subluxation,

4 At 4 weeks, the patient is allowed to perform active quadriceps extension out of the brace, 50% weight bearing, and crutch support, maintaining brace protection.

5 At 5 to 6 weeks, the patient is weaned from the brace and crutch support, full knee flexion is allowed, and our rehabilitation protocol is followed to protect the healing PCL fibers.

In cases of complete isolated midsubstance PCL ruptures that have more than 10 mm of increased posterior tibial displacement, and the patient is seen late after the injury and the above program cannot be instituted, one treatment approach in athletes and strenuous occupations is PCL graft reconstruction before the secondary restraints stretch out, with subsequent reinjuries. We believe that in athletic individuals, PCL reconstructive procedures have advanced to the point where more predictable results can be expected to restore sufficient PCL function to prevent gross posterior tibial subluxation. Studies have demonstrated, at least in the short term, that most patients with acute PCL ruptures treated with reconstruction are able to return to various levels of sports activities.⁷³ Additional factors to be weighed in the decision to perform early surgery on an isolated PCL rupture (with >10 mm posterior displacement at 90 degrees flexion) include athletic goals, body weight, medial meniscus or tibiofemoral joint damage, patellofemoral joint damage, and varus malalignment, because these factors add to the effects of the residual posterior subluxation in increasing knee joint loads and subsequent joint deterioration. Sedentary patients with a complete PCL rupture and more than 10 mm of posterior translation (90 degrees flexion) are not considered surgical candidates; however, they are followed as described earlier.

Patients with a PCL disruption and other ligament injuries have an obvious posterior tibial drop back without a firm end point on posterior drawer testing, and 10 mm or more of posterior tibial subluxation. In almost all these knees, some increase in medial or lateral joint opening or external tibial rotation can be detected, although the findings may be subtle. There may be physiologic laxity of other ligament structures without a true injury that allow for the gross posterior tibial subluxation.

In knees that have associated posterolateral ruptures, acute anatomic repair is required within 14 days before scarring occurs and the ability to restore these structures anatomically is lost. A similar situation exists for the medial ligament structures; however, these tissues are easier to reconstruct later if surgery cannot be performed during the ideal time period for anatomic repair. There may exist a displaced meniscus tear requiring early treatment. As a word of caution, a displaced meniscus should be reduced into the tibiofemoral joint by 3 weeks to prevent meniscus shortening and scarring, which compromise a future repair and result in loss of meniscus function. Even in knees that have marked soft tissue swelling and edema, and in which major ligament reconstruction is contraindicated, a meniscus repair procedure using all-inside techniques can be performed to reduce the meniscus to a normal tibiofemoral position. The mistake is to wait until 6 weeks or later, expecting that the meniscus repair can be performed at that time.

Too frequently, major ligament surgery in dislocated knees performed under acute conditions results in joint arthrofibrosis, compromising the result. Patients should be carefully selected for acute multiligament repairs, realizing that there are proven techniques for reconstruction of the ruptured ligaments performed later under more ideal conditions. When surgery is performed on acute combined PCL and posterolateral ruptures, the procedure includes the use of appropriate grafts to restore lateral stability and allow an early protected range of knee motion program.⁷⁷ Most acute knee dislocations should be treated in a staged approach, first by treating the acute injury and then determining whether a ligament reconstruction should be performed within the 10- to 14-day envelope or delayed. When early surgery is not advisable, the knee is protected for the first 4 weeks to prevent posterior tibial subluxation, as described earlier for acute isolated PCL ruptures. A lateral radiograph is obtained with the knee placed in a posterior plaster shell and a soft bolster positioned beneath the calf to prevent posterior tibial subluxation. The capsular tissues heal in 7 to 10 days to provide enough stability to prevent recurrence of dislocation.

There is a select group of morbidly obese patients who sustain serious knee dislocations with minimal trauma. The lack of protective muscle function and extreme body weight place abnormal tensile loads on ligament reconstructions, and a high rate of failure of a PCL reconstruction is expected. The preferred treatment for these patients is short-term plaster immobilization (and occasionally external fixation) to allow healing of soft tissues, followed by rehabilitation to return muscle function and knee motion. Only in exceptional circumstances would operative repair (acute or chronic) be warranted in these patients, although consideration for surgical reconstruction is warranted after appropriate weight reduction.

If a nonoperative approach is selected with associated MCL and posteromedial capsular disruptions, the same program is followed, with the lower limb placed in a cylinder cast to allow “stick-down” of the medial soft tissues. Plaster immobilization is required because a soft hinged brace, even if maintained at 0 degree of extension, does not provide sufficient protection to maintain medial joint line closure to allow the disrupted medial tissues to heal. At 7 to 10 days, the cylinder cast is split into an anterior and posterior shell and the therapist assists the patient with range of motion from 0 to 90 degrees in a figure-of-four position, with the hip joint externally rotated to protect the healing medial tissues.

Treatment of Chronic Posterior Cruciate Ligament Ruptures

The algorithm for the treatment of chronic PCL ruptures is shown in Figure 55-20. The symptoms and clinical examination determine the functional limitations, particularly the component of symptoms caused by medial tibiofemoral or patellofemoral arthritis, because these problems are likely to persist after surgical stabilization. Knees with chronic PCL ruptures are arbitrarily divided into three categories—those with varus osseous malalignment (and, rarely, valgus malalignment) in which an osteotomy must be considered, those with an isolated PCL rupture in which reconstruction may or may not be necessary, and those with significant combined ligament injuries that require reconstruction.

Figure 55-20 Treatment algorithm for chronic PCL ruptures.

Patients are entered into a formal rehabilitation program to correct muscular weakness and gait-related problems (hyperextension) when required. The amount of joint arthritis must be determined with accuracy. Radiographs (Merchant view, standing PA at 45 degrees) and MRI articular cartilage fast spin-echo sequences provide valuable information.

In knees with no or only mild articular cartilage damage, an assessment of the patient’s goals and athletic desires may indicate the need to proceed with PCL reconstruction. The indications for surgical reconstruction in these knees are pain and instability with athletics or other activities, swelling, and 10 mm or more of increased posterior tibial translation at 90 degrees flexion.

Patients with chronic PCL deficiency who have severe muscle atrophy, loss of knee motion, or hyperextension gait abnormalities require extensive rehabilitation and gait retraining before reconstruction.⁸⁷

Combined ligament ruptures that produce complex instability patterns require careful clinical assessment to detect all the joint subluxations and ligament deficiencies present. PCL reconstruction is most frequently performed in dislocated knees with gross instability caused by other ligament injuries to the ACL, MCL, or PLS.

The results of PCL reconstruction in knees with chronic ruptures are not as favorable as those that undergo reconstruction for acute injuries. This is because patients present with pain and swelling caused by joint deterioration, which often persists, even though some benefit may be gained from improved knee stability obtained from the operative procedure.⁷³ In these knees, areas of exposed bone are frequently encountered in the medial tibiofemoral compartment, along with diffuse cartilage fragmentation in the patellofemoral joint. In these individuals, even mildly strenuous exercises aggravate the joint arthritis symptoms and cannot be performed. The patient’s initial experience with rehabilitation, and the inability to perform the required rehabilitation exercises, provides important information regarding the amount of joint arthritis that is present and joint symptoms, which are likely permanent.

If a nonoperative approach is elected, the clinician should warn the patient that the return to athletic activities may carry an uncertain prognosis and that although sports may be resumed in the short term, some form of joint arthritis will eventually ensue. It is therefore important to follow the patient at regular intervals. A bone scan may be used to provide some indication of abnormal blood flow dynamics; however, it is our experience that the onset of pain and swelling usually indicates more advanced joint damage and a poor prognosis after PCL reconstruction. An MRI scan with fast spin-echo ¹⁰¹ sequences provides a baseline for repeated studies at 1- to 2-year intervals. The nonoperative treatment protocol of chronic PCL injuries involves educating the patient to avoid activities such as lunges and other high knee flexion activities that increase posterior tibial subluxation.

Operative Techniques: Current Concepts

PCL operative techniques continue to evolve and clinical outcome studies remain limited to allow precise decision making. The senior author’s (FN) recommended surgical approaches and relative advantages and disadvantages of each procedure are shown in Box 55-5.

Box 55-5

Adapted from Noyes FR, Barber-Westin SD: Posterior cruciate ligament: diagnosis, operative techniques, and clinical outcomes. In Noyes FR (ed): Noyes’ knee disorders: surgery, rehabilitation, clinical outcomes, Philadelphia, 2009, Saunders, pp 503–576.

Recommended Surgical Approaches

Tibial Inlay

Reserved for revision knees to bypass misplaced tibial tunnel (staged bone graft may be required)

First, the surgical approach of the all-inside or tibial inlay technique is chosen. The all-inside approach simulates the tibial inlay approach by placing the bone portion of the PCL graft directly at the posterior tibial attachment. In our experience, soft tissue grafts placed through a large tibial tunnel have an increased risk of failure because of delayed graft incorporation. When a soft tissue graft is placed at the tibia, the use of two tibial tunnels is preferred to allow better graft tunnel healing, although sometimes this is not possible in smaller knees. Others have described the historical technique that places the bone plug at the femoral site (inside-out or outside-in tunnel) and the collagenous portion through a single tibial tunnel. The most frequently used graft for this technique is the Achilles tendon-bone (AT-B) allograft. This technique is perhaps the easiest to master and is useful when surgical time is an issue, because it can be more difficult to pass the bone portion of the graft through the tibial tunnel.

Second, a large graft must be used that fills most of the PCL anatomic femoral and tibial footprints. At the femoral attachment, either a two-tunnel or a single rectangular bone plug placement will fulfill this requirement. A single large-diameter femoral tunnel may also be used; however, from a theoretical standpoint, this is considered less ideal, because portions of the graft may be outside the femoral footprint.

Third, the use of a bone-tendon-bone or bone-tendon graft offers the advantage of more secure fixation and superior healing of a bone plug compared with a soft tissue graft without bone plugs. It is important that high-strength graft fixation methods be used to withstand the large forces expected postoperatively.

The fourth principle is to use an autogenous graft in isolated PCL surgical procedures, when possible, because of higher success rates and healing compared with allografts.^72,⁷³ In multiligament knee injuries, allograft tissues are usually required, although an autogenous graft may be harvested from the contralateral side in select knees. In combined ligament reconstructions, a quadriceps tendon–patellar bone (QT-PT) autograft is not removed from the same knee, because this adds to the morbidity of the operative procedure.