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Posterior Cruciate Ligament Injuries
The treatment of posterior cruciate ligament (PCL) injuries is a controversial topic in orthopaedic surgery. In contrast to anterior cruciate ligament (ACL) injuries, for which an abundance of basic science and clinical data is available, the PCL has only recently become a topic of intense investigation. PCL injuries are less common compared with ACL injuries, and thus studies on outcomes are underpowered, making it difficult to draw definitive conclusions regarding management. However, recent biomechanical and clinical data have highlighted the importance of the PCL in knee stability and function. Injury to the PCL, which acts as the primary restraint to posterior tibial translation, may lead to instability, pain, diminished function, and eventually arthrosis.
The purpose of this chapter is to discuss the evaluation, diagnosis, and management of PCL injuries and to present the relevant historic and recent literature on these topics. After a brief review of the pertinent components of the history, physical examination, and imaging modalities, we discuss important considerations in decision-making and treatment options in patients with PCL injuries, as well as our preferred surgical technique and outcomes of surgical management of PCL injuries. Decision-making in this patient population is largely dependent on the grade of PCL injury and the presence or absence of concomitant ligamentous injuries in the knee. We also focus on the latest evidence regarding transtibial versus the tibial inlay technique, single- versus double-bundle methods of reconstruction, and the outcomes of these various surgical treatment options.
History
The true incidence and prevalence of PCL injuries are unknown and difficult to estimate because many of these injuries, particularly prior to the introduction of magnetic resonance imaging (MRI), were not diagnosed. The reported incidence of PCL injuries has differed depending on the population studied. The incidence is as low as 3% in the outpatient setting and as high as 37% in the traumatic setting. Traumatic injuries and sports-related injuries account for the majority of PCL injuries. A prospective analysis of patients presenting with acute hemarthrosis of the knee and diagnosed with a PCL injury demonstrated that 56.5% of patients were trauma victims, whereas 32.9% had a sports-related injury. Yet isolated PCL injuries were infrequent in this cohort, with 96.5% being part of a multiligamentous injury. Similarly, in a retrospective cohort of 494 patients with PCL insufficiency, Schulz et al. found traffic accidents (45%) and athletic injuries (40%) to be the most common causes of injury. Among specific sports, the incidence of PCL injury tends to be greater in those involving contact, such as football, soccer, and rugby. In the cohort reviewed by Schulz and colleagues, skiing and soccer were the sports with the highest incidence of PCL injuries. Overall, the incidence of PCL injury has been estimated to be relatively low in athletes across a variety of sports.
Important information can be obtained from the history of the patient presenting with acute knee pain or trauma. Any patient with knee pain and swelling with a high-energy mechanism of injury should be suspected of having a PCL injury, another capsuloligamentous injury, or both. Patients commonly report the inability to bear weight, instability, and decreased knee range of motion (ROM). In contrast to ACL injuries, which often result from a noncontact event, PCL injuries are typically due to external trauma. The classic “dashboard injury” pattern results from a posteriorly directed force on the anterior aspect of the proximal tibia with the knee in a flexed position. In patients with a higher energy mechanism of injury, it is possible that a knee dislocation occurred at the time of the injury even if the knee is reduced at the time of the evaluation.
In athletics, the typical mechanism of isolated PCL injury is a direct blow to the anterior tibia ( Fig. 100.1A ) or a fall onto the knee with the foot plantar flexed. When the foot is in a position of dorsiflexion, the force is transmitted to the patella and distal femur, decreasing the risk of injury to the PCL ( Fig. 100.2 ). Noncontact mechanisms of injury, although less common, have also been reported. Most commonly, this mechanism of injury occurs via forced hyperflexion of the knee (see Fig. 100.1B ). In a small cohort reported by Fowler and Messieh, these injuries would often lead to incomplete tearing of the PCL with the posteromedial (PM) fibers intact. Knee hyperextension has also been described as a mechanism of injury, which is usually combined with a varus or valgus force that results in multiple ligament injury (see Fig. 100.1C ). Isolated injuries may have more subtle presentations, with patients reporting stiffness, swelling, and pain located in the back of the knee or pain with deep knee flexion (squatting and kneeling). In contrast to acute ACL tears, a “pop” is not usually reported with acute isolated PCL injuries and athletes are often able to continue to play. Reports of anterior knee pain, difficulty ascending stairs, and instability are common when patients present in the chronic phase of an isolated PCL injury.
Physical Examination
Posterior Drawer Test
The posterior drawer test was described initially by Hughston et al. in 1976 and later by Clancy et al. in 1983 and is considered the most accurate clinical test to assess the integrity of the PCL, with a sensitivity of 90% and 99% specificity. The results of this examination also guide treatment recommendations. A posteriorly directed force is placed on the proximal tibia with the patient lying supine and the knee flexed to 90 degrees. This test can be performed with the tibia in neutral, external, and internal rotation. It is important to remember that with a PCL injury, the tibia subluxes posteriorly. Thus it is important to first apply an anteriorly directed force to reduce the posterior subluxation before applying the posteriorly directed force ( Fig. 100.3 ). In cases of isolated PCL tears, a decrease occurs in posterior tibial translation with internal tibial rotation. The superficial medial collateral ligament (MCL) and posterior oblique ligament act as a secondary restraint with the tibia in internal rotation. Translation is measured as the change in distance of step-off between the medial tibial plateau relative to the medial femoral condyle. It is critical to examine the contralateral knee, because the normal relationship between the medial tibial plateau and medial femoral condyle is variable, with the plateau normally resting on average 1 cm anterior to the condyle. Understanding this relationship is also critical in avoiding a false-positive anterior drawer test. The presence or lack of a firm end point should also be noted.
The amount of posterior translation observed during the posterior drawer test is used to grade the PCL injury. In grade I injuries, 0 to 5 mm of increased posterior translation is observed compared with the contralateral knee, but the anterior step-off of the plateau relative to the condyle is maintained. Grade II injuries are defined as those with 6 to 10 mm of posterior translation, which results in the plateau being flush with, but not posterior to, the medial femoral condyle. In both grade I and II injuries, the PCL is usually partially torn. With grade III injuries, posterior translation exceeds 10 mm and the medial tibial plateau displaces posterior to the medial femoral condyle during the posterior drawer test. This finding usually represents a complete tear of the PCL and could also represent a combined PCL and posterolateral corner (PLC) injury.
Posterior Sag Test (Godfrey Test) and Quadriceps Active Test
The posterior sag test may be positive in patients with complete PCL tears or partial tears. The patient lies supine with the hip and knee flexed to 90 degrees and the limb supported at the foot by the examiner. The anterior aspect of the proximal tibia is viewed from the side and compared with the uninjured, contralateral knee. Gravity displaces the tibia posterior to the femur in the case of a complete tear ( Fig. 100.4 ). The quadriceps active test can aid in the diagnosis of complete tears. With this test, the patient lies supine and the knee is placed at 90 degrees of flexion. While the examiner stabilizes the foot, the patient is asked to contract the quadriceps isometrically. In the presence of a complete tear of the PCL (grade III), the patient will achieve dynamic reduction of the posteriorly displaced tibia.
External Rotation of the Tibia (Dial Test)
The dial test is performed to evaluate for concomitant injuries to the PLC, which will affect decision-making and treatment options because these patients are more likely to require surgery. The dial test is performed with the patient positioned prone or supine, while an external rotation force is applied to both feet with the knee positioned at 30 degrees and then 90 degrees of flexion. The degree of external tibial rotation is measured by comparing the medial border of the foot with the axis of the femur. It is essential to compare the results with the contralateral side because wide variability of external rotation is possible at these positions. More than a 10-degree side-to-side difference is considered abnormal. At all degrees of knee flexion, the popliteus complex portion of the PLC is the primary restraint to external rotation, but its effect is maximal at 30 degrees. An increase of 10 degrees or more of external rotation at 30 degrees of knee flexion, but not at 90 degrees, is considered diagnostic of an isolated PLC injury. Increased external rotation at both 30 and 90 degrees of knee flexion suggests a combined PCL and PLC injury.
Reverse Pivot-Shift Test
The reverse pivot-shift test is also used to assess combined injuries and is performed with the patient supine. The knee is passively extended from 90 degrees of flexion with the foot externally rotated and a valgus force applied to the tibia. A positive result is observed when the posteriorly subluxed lateral tibial plateau is abruptly reduced by the iliotibial band at 20 to 30 degrees of flexion. A positive test typically indicates injury to the PCL and another capsuloligamentous structure, usually the PLC.
Collateral Ligament Assessment
Varus and valgus stress tests are used to assess the lateral collateral ligament (LCL) portion of the PLC. The tests are performed with the knee in full extension and in 30 degrees of flexion. Although an isolated PCL injury does not significantly affect varus or valgus stability, increased varus opening at 30 degrees of knee flexion indicates an injury to the LCL and possibly the popliteus complex. If a significant degree of varus opening is noted at full extension, a combined injury of the PLC, PCL, and/or ACL is likely present.
Gait and Limb Alignment
The evaluation of gait and limb alignment is particularly important for persons with chronic injury of the PCL or the PLC. In these patients, varus alignment, external rotation, and varus thrust may be observed. Compromised function of the stabilizers of the lateral knee can lead to excessive posterolateral rotation and varus opening (or thrust) in the stance phase of gait.
Imaging
Radiography
In the acute setting, plain radiographs of the knee should be performed, including bilateral standing anteroposterior, flexion posteroanterior 45 degrees with weight bearing, and Merchant patellar and lateral radiographs. These views are evaluated for posterior tibial subluxation, avulsion fractures, posterior tibial slope, and tibial plateau fractures. Tibial plateau fractures often indicate a high-energy injury with multiligament involvement. Bony avulsion fractures can be seen at the insertion of the PCL and at the fibular head, medial tibial plateau (medial Segond fracture), or the tibial tubercle. Identification of bony avulsion injuries of the PCL, when recognized acutely, may be repaired primarily with superior results compared with late reconstruction. Identification of tibial tubercle fractures is also critical. The unopposed pull of the hamstrings causes posterior tibial subluxation in this scenario, which can become fixed within a short time, requiring open reduction. Medial Segond fractures represent a medial capsular avulsion in PCL injuries that may be associated with a peripheral medial meniscus tear. Lastly, long leg hip-to-ankle views are critical to evaluate overall lower extremity alignment, particularly varus, in chronic or revision cases.
Stress radiographs are not necessary to diagnose a PCL injury but may be helpful to differentiate between complete and partial PCL tears. However, these radiographs are most commonly used for research purposes. In a retrospective review of 21 patients with partial or complete PCL tears, Hewett and colleagues found that stress radiographs were more accurate than KT-1000 measurements in diagnosing PCL tears. With the knee flexed to 70 degrees and an 89-N weight suspended from the tibia at the level of the tibial tubercle, a lateral radiograph was taken. The mean translation of the medial tibial plateau was 12.2 mm in the presence of a complete tear compared with 5.2 mm seen with a partial tear as confirmed with diagnostic arthroscopy. The magnitude of posterior tibial translation during stress radiography has been correlated with the presence of combined ligament injury. In a cadaveric study by Sekiya et al., the authors demonstrated that greater than 10 mm of posterior tibial translation on stress radiography correlated with the presence of a PLC injury in addition to a complete disruption of the PCL. It should be noted that the accuracy of stress radiography may be decreased by patient guarding and partial reduction of the tibia with quadriceps activation; in addition, this infrequently performed examination is operator dependent. Stress radiographs can also be influenced by tibial rotation, and thus some authors have concluded that physical examination may be equally sensitive to stress radiographs in determining the presence and extent of a PCL tear.
Magnetic Resonance Imaging
MRI has become the imaging modality of choice for confirming the presence of an acute PCL tear and to diagnose associated injuries with a sensitivity of up to 100%. The location and physical characteristics of the tear can also be assessed with MRI and may have implications for prognosis and treatment. MRI may be less sensitive in the diagnoses of chronic tears. The normal PCL appears dark on T1- and T2-weighted sequences and is curvilinear in appearance. In contrast, chronic tears of the PCL can heal and assume the aforementioned curvilinear appearance; thus MRIs are much less sensitive for chronic PCL tears, and the appearance of a normal shape of the ligament should not be used as a criterion for a normal PCL.
Lastly, MRI provides important information on the status of the menisci, articular cartilage, and other ligaments in the knee, because concomitant injuries affect treatment decision-making and prognosis. Bone bruises have been found in 83% of grade II and III PCL injuries on MRI, but in contrast to the bone bruise associated with ACL tears, the location is variable. The utility of MRI for the diagnosis of associated injuries to the PLC has previously been evaluated. With use of thin-slice coronal oblique T1-weighted images through the entire fibular head, LaPrade and colleagues were able to identify injury to the posterolateral structures with an accuracy of 68.8% to 94.4%, depending on the structure. Similarly, Theodorou et al. found that MRI has an accuracy of 79% to 100% for the diagnoses of posterolateral injuries confirmed with arthroscopy.
Bone Scan
Although a bone scan is not frequently used, it can be useful in the evaluation and management of chronic PCL injuries. In particular, patients with these injuries are predisposed to early medial and patellofemoral compartment chondrosis. In the setting of an isolated PCL-deficient knee with medial or patellofemoral compartment pain and normal radiographs, a bone scan to assess these compartments may be indicated. Increased uptake suggests that surgical intervention may be beneficial, although this supposition has not been proven definitively.
Decision-Making
Decision-making in the treatment of PCL injuries is dependent on the natural history of the disease, with most treatment recommendations made on the basis of symptoms, activity level, grade of the injury, and associated injuries. As with any orthopaedic ailment, operative intervention should be chosen only if it results in superior outcomes compared with nonsurgical management. Controversy exists regarding PCL treatment because the extent to which posterior laxity causes symptoms or accelerates the development of degenerative joint disease (DJD) is unclear. However, a computational knee kinematic study by Kang et al. suggests that PCL deficiency leads to significantly increased contact forces on the patellofemoral joint as well as PLC structures during normal gait. Furthermore, it is unknown whether reconstruction sufficiently mitigates laxity to result in clinical improvement and slow the development of DJD. Reducing posterior laxity with reconstruction may improve long-term outcomes in patients with PCL injuries, and yet residual laxity is common even after reconstruction. Some investigators propose that isolated PCL tears follow a benign course in the short term without reconstruction but that diminishing results may be seen at a later point. To date, no study has demonstrated that PCL reconstruction can prevent the development of DJD.
Controversy remains regarding indications for nonoperative versus operative management because few clinical studies have sufficient sample sizes and duration of follow-up to draw definitive conclusions. Additionally, a variety of PCL reconstructions are currently used, and the treatment of isolated PCL injuries is often reported in conjunction with combined injuries, such as PLC injuries, making outcome studies relatively heterogeneous. Currently most studies are retrospective in nature and use various outcome measurements, which make comparisons difficult. Until randomized prospective clinical trials are conducted, this debate will likely continue. The next section reviews the results of nonoperative management of PCL injuries and conclude the section with our decision-making rationale.
Nonoperative Treatment
Many studies have found favorable outcomes when isolated PCL injuries are treated conservatively. Parolie and Bergfeld evaluated patient satisfaction in 25 persons with isolated PCL tears that had resulted from sporting injuries at a minimum of 2 years of follow-up. These investigators found that 68% of patients returned to their previous level of activity and 80% were satisfied with their knee function. They evaluated laxity and found no correlation with DJD. More recently, Shelbourne and Muthukaruppan prospectively evaluated 215 conservatively treated patients with isolated PCL tears. Their study focused on patients with grade II laxity or less. These investigators found that subjective scores did not correlate with the degree of laxity and mean scores did not decrease with time from injury. They were unable to identify any risk factors that would predict which patients would have a decline in knee function over time. Patel et al., in another recent retrospective review of 57 patients with grade A or B PCL tears, a grading system proposed by MacGillivray and colleagues also found that functional scores did not correlate with the degree of PCL laxity. Lysholm knee scores were excellent in 40% and good in 52%. Patel et al. found grade I medial compartment osteoarthritis (OA) in seven knees, grade II in three knees, and mild patellofemoral OA in four knees at an average of 6.8 years of follow-up. They concluded that most patients with acute, isolated PCL tears do well with nonoperative management at intermediate follow-up. Furthermore, a more recent study by Shelbourne and colleagues showed that at an average of 14.3 years follow-up 89% (39/44) of individuals with isolated grade I or II PCL injuries treated nonoperatively showed full ROM, good quadriceps strength, and minimal OA.
Other investigators have also found good initial clinical outcomes with nonoperative treatment but have found deterioration at extended follow-up. Boynton and Tietjens observed 38 patients with isolated tears for a mean of 13.4 years. Of these patients, eight had subsequent meniscal injuries and surgery. Of the remaining 30 patients with normal menisci, 24 (81%) had occasional pain, 17 (56%) had occasional swelling, and a positive increase in articular cartilage degeneration was seen on radiographs over time. Fowler and Messieh prospectively followed up 13 patients with acute isolated PCL tears that were confirmed by arthroscopy and treated with physiotherapy. All patients had a good subjective functional score according to the Houston criteria, but objective scores were good in only 3 patients and only fair in the other 10 patients.
Although relatively good results have been observed with nonoperative treatment, it should be noted that many of the patients in these series had grade II laxity or less and not all patients achieved a normal outcome, especially patients with grade III injuries. The benign course observed may be due to the integrity of the secondary restraints and various portions of the PCL complex remaining intact in persons with less serious injuries. Tibial slope may also affect the stability of the PCL deficient knee. In a cadaveric study, increasing the posterior tibial slope decreased the static posterior instability of the PCL/PLC-deficient knee, whereas decreasing the tibial slope increased posterior instability and the magnitude of the reverse pivot-shift test.
Despite acceptable clinical results with nonoperative treatment, it is well understood that PCL deficiency alters knee kinematics and the distribution of load during activity. In an uninjured knee, numerous biomechanical studies have shown that the PCL plays a significant role in tibiofemoral joint stability throughout an active and passive ROM especially in the presence of a posteriorly directed tibial force, while it has been shown that the PCL-deficient knee experiences increased contact pressures in the patellofemoral and medial compartments. Logan et al. evaluated the effect of PCL rupture on tibiofemoral motion during squatting with use of MRI. They concluded that PCL deficiency is similar to a medial meniscus resection and results in a “fixed” anterior subluxation of the medial femoral condyle (posterior subluxation of the medial tibial plateau). This subluxation changes the kinematics of the knee and may explain the increase in medial compartment OA seen in PCL-deficient knees. Currently more attention is being placed on additional injuries that are commonly associated with grade III tears that lead to greater instability and more severely altered biomechanics.
Although it is known that the kinematics of the knee are altered in the presence of a PCL injury, specific prognostic factors that predict outcome have proven elusive. In many studies the time from injury and objective instability have not correlated well with final outcome and radiographic changes. Surgical reconstruction is not recommended for isolated grade I injuries. Because many patients with isolated grade II posterior laxity only improve to grade I laxity with reconstruction, we agree with other authors that operative intervention in these patients may not offer improved outcome when compared with nonoperative treatment. The treatment of acute isolated grade III PCL injuries is controversial. In these patients, some surgeons favor a more aggressive approach involving PCL reconstruction, whereas others recommend nonsurgical treatment. In cases with greater than 10 mm of abnormal posterior laxity, the clinician should remember to have a high index of suspicion for a combined ligamentous injury involving the PLC.
Level I evidence does not currently exist to support strong recommendations on the management of PCL injuries. However, based on the previously described data, we recommend nonoperative management for the treatment of acute and chronic isolated grade I and II PCL injuries ( Figs. 100.5 and 100.6 ). Operative management is reserved for chronic isolated grade III PCL injuries with symptoms of pain or instability when an adequate course of conservative treatment has failed. In addition, surgical treatment is usually recommended for acute and chronic combined ligamentous injuries. The treatment of acute grade III PCL tears is controversial, with some surgeons recommending PCL reconstruction and others recommending nonoperative treatment. Lastly, open reduction and internal fixation are recommended for acute avulsion fractures at the PCL tibial attachment site.
Treatment Options
Nonoperative Treatment
As discussed in the previous section, nonoperative treatment is recommended in patients with acute, isolated grade I or II PCL tears. Nonoperative management is aimed at counteracting the forces of gravity and the hamstring muscles, which act to sublux the tibia posteriorly on the femur. Pierce and colleagues have recently reviewed the literature on rehabilitation protocols for nonoperative and operative treatment of PCL injuries. Based on the finding of the reviewed studies, a three-phase rehabilitation protocol was recommended. We follow a similar protocol at our institution.
In the first 6 weeks after injury (phase I), rehabilitation is focused on partial weight-bearing, hamstring and gastrocnemius stretching to reduce the posterior pull on the tibia, quadriceps strengthening and prone ROM exercises. In this initial phase, a number of immobilization techniques have been described to decrease stress on the healing ligament. These techniques include bracing the knee locked between 0 and 60 degrees of knee flexion, use of a cylindrical leg cast with a posterior support to prevent posterior displacement of the tibia, and use of a brace with a dynamic anterior drawer to apply an anterior force on the posterior proximal tibia. In phase II, 6 to 12 weeks after injury, the focus is on progressive strengthening, reestablishment of full ROM, and improving proprioception. In phase III, 13 to 18 weeks after the injury occurred, the patient is allowed to begin running and to perform sports-specific exercises, with return to sports allowed 4 to 6 months after the initial injury, assuming quadriceps strength is comparable to that of the contralateral leg. It is important to note that this time frame can be significantly accelerated in the case of elite athletes with potential return to sport as early as 6 to 8 weeks but with the expected risk of increased residual joint laxity.
Operative Treatment
A number of surgical techniques for PCL reconstruction can be considered. Current surgical treatment options include transtibial and tibial inlay reconstruction techniques with single- or double-bundle reconstruction and a variety of fixation methods. Several biomechanical and anatomic studies have been published recently investigating the benefits and pitfalls of these techniques. However, no consensus currently exists on the best method of PCL reconstruction.
Transtibial Tunnel Versus Tibial Inlay Techniques
The transtibial technique is a commonly used method of PCL reconstruction. In this technique, the tibial and femoral tunnels are drilled and the graft must make a sharp turn around the “killer turn” as it surfaces from the tibial tunnel and changes direction before entering the knee joint. This acute turn has been implicated as the cause of graft abrasion with subsequent thinning of the graft and eventual graft rupture or excessive laxity. The residual posterior knee laxity observed clinically after traditional transtibial PCL reconstruction techniques may be related to this acute turn. To address the concern of graft attenuation resulting from this tunnel, the tibial inlay technique was developed and reported by Jakob and Ruegsegger, as well as by Berg. In this technique, direct fixation occurs at the tibial attachment site of the PCL, preventing an acute turn as the graft passes from the tibia to the femoral tunnel.
A number of cadaveric biomechanical studies have compared the transtibial and tibial inlay techniques. Although McAllister et al. found no significant differences in mean knee laxities between the tibial tunnel and tibial inlay techniques at time zero, increased laxity was observed with this technique after cyclic loading. Bergfeld et al. assessed anteroposterior laxity in cadaveric knees undergoing tunnel reconstruction or inlay reconstruction. Minimal differences in anteroposterior laxity were observed in the inlay group when compared with the tunnel group from 30 to 90 degrees of knee flexion and after repetitive loading at 90 degrees of knee flexion. However, evaluation of the grafts after testing demonstrated evidence of graft thinning and attenuation in the tunnel group but not in the inlay group. In a detailed cyclic loading analysis, Markolf and colleagues also evaluated cadaver knees with tibial inlay and transtibial reconstruction. Ten of 31 grafts in the tunnel group failed at the acute angle before 2000 cycles of testing could be completed, whereas all 31 grafts that had been fixed to the tibia with use of the inlay method survived the testing intact. In addition, a significant increase in graft thinning and stretching out was observed in the remaining tunnel grafts that survived testing compared with the inlay grafts.
Thus in vitro analyses comparing the transtibial technique with tibial inlay suggest that although initial knee stability is equivalent, posterior laxity increases with cyclic loading with the transtibial technique when compared with the tibial inlay technique. Attempts have also been made to decrease the effects of the killer turn by reducing the sharp edge at the tibial tunnel exit, but this technique has only been attempted in an animal model. Weimann and colleagues found that rounding the sharp edge of the tibial tunnel decreased graft damage associated with the killer turn in a porcine model of PCL reconstruction. To date, retrospective studies comparing patients undergoing transtibial versus tibial inlay procedures have not shown significant differences in subjective outcome or knee laxity measurements. Thus although the tibial inlay technique may have some biomechanical advantages when tested in a cadaveric model, these advantages have yet to be realized in the clinical setting.
Single-Bundle Versus Double-Bundle Reconstruction
Controversy also exists regarding the utility of single- versus double-bundle techniques of PCL reconstruction. The native PCL can be divided into an anterolateral (AL) and a PM bundle ( Fig. 100.7 ). The AL bundle is tight in knee flexion and becomes lax in extension, whereas the PM bundle is tight in knee extension and becomes lax in flexion. The AL bundle is larger in cross-sectional area and thus is most commonly reconstructed in single-bundle procedures ( Fig. 100.8 ). Double-bundle PCL reconstructions were proposed to more closely reproduce the anatomy and biomechanical properties of the intact PCL. Biomechanical studies have indicated that the two bundles demonstrate reciprocal tightening during knee ROM and both are active in reducing posterior tibial translation and external tibial rotation, suggesting that both are required for normal knee kinematics.
Single- versus double-bundle PCL reconstruction have been compared in several biomechanical studies, and some investigators have suggested improved biomechanics with double-bundle reconstruction. Milles et al. compared single-bundle versus double-bundle reconstruction in cadaveric human knees using five different surgical techniques and found increased stiffness and decreased laxity in double-bundle reconstructions at numerous flexion angles. Tsukada et al. compared single AL bundle reconstruction, single PM bundle reconstruction, and double-bundle reconstruction in cadaveric human knees at different angles of knee flexion. The double-bundle reconstruction resisted posterior tibial load better than the AL single bundle at 0 and 30 degrees of knee flexion and better than the PM single bundle at 30, 60, and 90 degrees of knee flexion under the posterior tibial load, leading the authors to conclude that double-bundle reconstruction reduces laxity in extension.
Additional studies have demonstrated potential drawbacks of double-bundle reconstruction, and some studies have been unable to demonstrate a benefit. Whiddon et al. compared single- and double-bundle tibial inlay reconstruction in a cadaver model and found that the double-bundle technique improved rotational stability and posterior translation in knees with a concomitant PLC injury. However, no advantage was seen with a double-bundle reconstruction when compared with a single-bundle reconstruction with regard to posterior translation with the PLC intact. In addition, excessive rotational constraint was observed at 30 degrees. Wiley and colleagues also observed that although posterior laxity was reduced compared with single-bundle reconstruction, overconstraint at 30 degrees of flexion was seen with double-bundle reconstruction. In a comparison of single-bundle AL reconstruction with double-bundle reconstruction in cadaver knees, Markolf and colleagues found that the addition of a PM bundle reduced laxity from 0 to 30 degrees of flexion but at the expense of increased PCL graft forces. Bergfeld et al. compared single- and double-bundle tibial inlay reconstruction in cadaveric knees using Achilles tendon grafts. No differences in translation between the single- and double-bundle reconstruction were observed at any flexion angle.
A number of clinical studies have shown no significant differences in subjective and objective results between single- and double-bundle PCL graft reconstructions. Jain and colleagues performed a retrospective review of 40 patients, 18 of which underwent double-bundle PCL reconstruction and 22 of which underwent single-bundle PCL reconstruction and looked at clinical, functional, and radiologic outcomes at 24 months postoperatively. KT-1000 measurements showed an average side-to-side difference in the double-bundle group of 1.78 mm and 2.4 mm in the single-bundle group ( P < .04). Stress radiographs showed increased posterior tibial translation in the single-bundle group as compared to the double-bundle group. However, both double-bundle and single-bundle groups showed significant functional improvement in Lysholm and IKDC scores with no statistically significant difference between the groups themselves. Furthermore, Hatayama et al., in a retrospective clinical study comparing arthroscopic single-bundle and double-bundle PCL reconstruction showed that at 2-year follow-up of 3/10 patients who underwent double-bundle PCL reconstruction showed rupture of the PM bundle at second-look arthroscopy. Based on the literature to date, we believe evidence is lacking to support the routine use of double-bundle reconstruction. However, this type of reconstruction remains a topic of interest and is undergoing continued investigation in the treatment of PCL injuries.
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