In vivo elongation of the anterior cruciate ligament and posterior cruciate ligament during knee flexion

BACKGROUND: Most knowledge regarding cruciate ligament function is based on in vitro experiments. PURPOSE: To investigate the in vivo elongation of the functional bundles of the anterior cruciate ligament and posterior cruciate ligament during weightbearing flexion. HYPOTHESIS: The biomechanical role of functional bundles of the anterior cruciate ligament and posterior cruciate ligament under in vivo loading is different from that measured in cadavers. STUDY DESIGN: In vivo biomechanical study. METHODS: Elongation of the anterior cruciate ligament and posterior cruciate ligament was measured during a quasi-static lunge using imaging and 3-dimensional computer-modeling techniques. RESULTS: The anterior-medial bundle of the anterior cruciate ligament had a relatively constant length from full extension to 90 degrees of flexion. The posterior-lateral bundle of the anterior cruciate ligament decreased in length with flexion. Both bundles of the posterior cruciate ligament had increased lengths with flexion. CONCLUSION: The data did not demonstrate the reciprocal function of the 2 bundles of the anterior cruciate ligament or the posterior cruciate ligament with flexion observed in previous studies. Instead, the data suggest that there is a reciprocal function between the anterior cruciate ligament and posterior cruciate ligament with flexion. The anterior cruciate ligament plays a more important role in low-flexion angles, whereas the posterior cruciate ligament plays a more important role in high flexion. CLINICAL RELEVANCE: Understanding the biomechanical role of the knee ligaments in vivo is essential to reproduce the structural behavior of the ligament after injury (especially for 2-bundle reconstructions) and thus improve surgical outcomes.     

Isolated posterior cruciate ligament injuries of the knee

Isolated injuries of the posterior cruciate ligament (PCL) are rare in comparison to other ligamentous knee injuries, resulting in a lack of evidence-based literature regarding their treatment. Although consensus exists regarding the nonoperative management of asymptomatic grade I injuries, the treatment of high-grade symptomatic PCL insufficiency remains a matter of debate. A variety of reconstructive procedures have been advocated on the basis of biomechanical data, however, the clinical benefit of these anatomic reconstructive techniques have yet to be conclusively proven in randomized trials. This article attempts to provide the treating physician with a concise overview of the etiology and diagnosis of isolated PCL injuries as well as an objective review of contemporary surgical treatment options and outcomes as reported in the current literature.     

Proprioception in the posterior cruciate ligament deficient knee

This study was undertaken to evaluate knee proprioception in patients with isolated unilateral posterior cruciate ligament (PCL) injuries. Eighteen subjects with isolated PCL tears were studied 1–234 months after injury. The threshold to detect passive motion (TTDPM) was used to evaluate kinesthesia and the ability to passively reproduce passive positioning (RPP) to test joint position sense. Two starting positions were tested in all knees: 45 ° (middle range) and 110 ° (end range) to evaluate knee proprioception when the PCL is under different amounts of tension. TTDPM and RPP were tested as the knee moved into flexion and extension from both starting positions. A statistically significant reduction in TTDPM was identified in PCL-injured knees tested from the 45 ° starting position, moving into flexion and extension. RPP was statistically better in the PCL-deficient knee as tested from 110 ° moving into flexion and extension. No difference was identified in the TTDPM starting at 110 ° or in RPP with the presented angle at 45 ° moving into flexion or extension. These subtle but statistically significant findings suggest that proprioceptive mechanoreceptors may play a clinical role in PCL-intact and PCL-deficient patients. Further, it appears that kinesthesia and joint position sense may function through different mechanisms. Received: 5 September 1998 Accepted: 25 May 1999     

Injuries to the posterior cruciate ligament of the knee

The posterior cruciate ligament (PCL) is the strongest ligament about the knee and is approximately twice as strong as the anterior cruciate ligament. Its main function is to prevent the posterior dislocation of the tibia in relation to the femur, providing 95% of the strength to resist the tibial posterior displacement. Along with the anterior cruciate ligament (ACL) the PCL controls the passive 'screw home' mechanism of the knee in terminal knee extension. It also provides mechanical support for the collateral ligaments during valgus or varus stress of the knee. PCL ruptures are uncommon apparently due to its strong fibre structure. The most frequent injury mechanism in isolated PCL tears is a direct blow on the anterior tibia with the knee flexed thus driving the tibia posteriorly. Automobile accidents (in which the knee hits the dashboard) and soccer injuries (in which an athlete receives a blow to the anterior surface of the tibia during knee flexion) characteristically produce this type of injury. In other PCL injury mechanisms (hyperextension, hyperflexion or rotational injuries with associated valgum/varum stress), other knee structures are also often damaged. The most characteristic diagnostic finding in a knee with a PCL rupture is the 'posterior sag sign' meaning the apparent disappearance of the tibial tubercle in lateral inspection when the knee is flexed 90 degrees. This is due to gravity-assisted posterior displacement of the tibia in relation to the femur. A positive posterior drawer test performed at 90 degrees of flexion and a knee hyperextension sign are sensitive but nonspecific tests. False negative findings are frequent, especially in acute cases. If necessary, the clinical diagnosis of the PCL tear can be verified by magnetic resonance imaging, examination under anaesthesia, arthroscopy, or a combination of these modalities. If a PCL avulsion fragment has been dislocated, surgical treatment is recommended. In isolated, complete midsubstance tears of the PCL the majority of the recent studies recommend conservative treatment, since abnormal residual posterior laxity1 in most of these knees is consistent with functional stability and minimal symptoms. This has been the case even in athletes. In isolated PCL tears, the outcome seems to depend more on the muscular (quadriceps) status of the knee than on the amount of residual posterior laxity. Therefore, the conservative treatment protocol emphasises intensive quadriceps exercises, and only a short (under 2 weeks) immobilisation period followed by early controlled activities and early weightbearing.(ABSTRACT TRUNCATED AT 400 WORDS)     

Dysfunction of the posterior cruciate ligament in total knee arthroplasty

Purpose  

Total knee arthroplasty (TKA) is typically carried out either with retention (CR) of the posterior cruciate ligament (PCL) or with sacrifice of this ligament and implantation of a posterior stabilised (PS) prosthesis. This paper investigates a comparison of PCL function in knees treated for osteoarthritis with TKA where the PCL is preserved to those knees treated with TKA and posterior stabilisation.     

The effect of posterior knee capsulotomy on posterior tibial translation during posterior cruciate ligament tibial inlay reconstruction

PURPOSE: To measure the biomechanical effect of the surgical capsulotomy made during a posterior cruciate ligament reconstruction using the tibial inlay technique. HYPOTHESIS: The posterior capsule contributes to posterior tibial stability. STUDY DESIGN: Controlled laboratory experiment. METHODS: Six knee specimens were tested on a robotic testing system from 0 degrees to 120 degrees of flexion with the posterior cruciate ligament intact and resected and with a posterior capsulotomy identical to that performed during tibial inlay reconstruction (sham surgery). A longitudinal incision with medial and lateral soft tissue stripping sufficient to mount an inlay bone block and pass an Achilles tendon graft into the knee was made in the oblique popliteal ligament, muscle belly of the popliteus, and posterior capsule. The posterior tibial translation was measured under a posterior tibial load of 130 N at multiple flexion angles. RESULTS: Capsulotomy increased the posterior laxity compared with the posterior cruciate ligament-resected knee at every flexion angle. An additional 0.97 +/- 0.48 mm, 0.65 +/- 0.47 mm, 0.56 +/- 0.33 mm, 0.48 +/- 0.38 mm, and 0.94 +/- 0.60 mm of posterior laxity was recorded at 0 degrees, 30 degrees, 60 degrees, 90 degrees, and 120 degrees of flexion, respectively. These values were all statistically significant (P < .001). CONCLUSIONS: A posterior capsulotomy alone, without associated posteromedial or posterolateral disruption, produces additional posterior tibial translation in vitro compared with posterior cruciate ligament-deficient knee with intact capsule. CLINICAL RELEVANCE: Damage to the posterior capsule may contribute to the residual posterior laxity noted clinically after posterior cruciate ligament reconstruction.     

Sonography of injury of the posterior cruciate ligament of the knee

OBJECTIVE: To describe the sonographic appearance of injury of the posterior cruciate ligament (PCL) of the knee. DESIGN AND PATIENTS: Eleven patients (6 men, 5 women) with an average age of 36 years (range 17-70 years), referred for magnetic resonance (MR) imaging evaluation of knee pain, had PCL injury according to standard MR imaging criteria. Sonography was performed after the MR examination by the author, who was aware of the MR findings. Both the affected and contralateral asymptomatic PCL were scanned sonographically in the longitudinal plane with a curvilinear transducer, and their diameters were measured on the scanner using electronic calipers. Bilateral PCL sonography and measurement were also performed on 12 patients with other acute knee injuries but normal PCLs according to MR imaging ("non-PCL-injured knee cohort"), and on 10 normal volunteers. RESULTS: All PCLs were hypoechoic, regardless of injury. The injured PCLs had an average diameter of 0.88 cm (range 0.54-1.21 cm), while the contralateral PCLs had an average diameter of 0.51 cm (range 0.30-0.84 cm) (signed rank test, P<0.001). One patient also had focal discontinuity of the PCL. There was no statistical difference between the diameters of the right and left PCLs of the non-PCL-injured knee cohort (signed rank test, P=0.1) nor between those of the volunteers (signed rank test, P=0.6). The average difference in diameter between the injured and contralateral PCLs was statistically significant versus the difference between the non-PCL-injured knee cohort's PCLs (Mann-Whitney test, P=0.0001) and versus the difference between the volunteers' PCLs (Mann-Whitney test, P=0.0001). CONCLUSION: PCL injury is manifested sonographically either as enlargement of the entire ligament, appreciated by comparison with the contralateral normal PCL, or by focal disruption of the ligament.     

An isolated rupture of the posterior cruciate ligament results in reduced preoperative knee function in comparison with an anterior cruciate ligament injury

Purpose

To investigate differences in preoperative knee function (Knee Injury and Osteoarthritis Outcome Score, KOOS), the time period from injury to surgery, and associated injuries when comparing primary isolated posterior cruciate ligament (PCL) and primary anterior cruciate ligament (ACL) reconstructions.

Methods

Isolated primary ACL and PCL reconstructions registered in the Norwegian National Knee Ligament Registry from 2004 through 2010 were included (n = 71 primary PCLs and 9,649 primary ACLs). Linear regression analysis was used to evaluate the preoperative KOOS subscale values.

Results

The preoperative KOOS in the PCL group (n = 71) and ACL group (n = 9,649) was significantly different for the subscales symptoms (mean difference, ?8.4; 95 % CI: ?12.8 to ?4.0), pain (mean difference, ?15.9; 95 % CI: ?20.3 to ?11.4), activities of daily living (mean difference, ?12.9; 95 % CI: ?17.4 to ?8.4), sport and recreation (mean difference, ?15.9; 95 % CI: ?22.6 to ?9.3), and quality of life (mean difference, ?7.9; 95 % CI: ?12.4 to ?3.5). The primary isolated PCL-reconstructed knees had a median time from injury to surgery of 21 months in comparison with 8 months for ACL injuries. The ACL-injured knees had more associated injuries (meniscus and full-thickness cartilage lesions) than the PCL-injured knees.

Conclusion

Surgically treated knees with an isolated rupture of the PCL exhibited worse knee function preoperatively compared with knees with an isolated ACL injury; in addition, the delay to surgery was longer. Meniscal lesions were found more frequently in ACL-injured knees.

Level of evidence

Prospective cohort study, evidence Level I.     

The effect of posterior cruciate ligament deficiency on knee kinematics

BACKGROUND: Alteration of the kinematics of the PCL-deficient knee might be a factor in producing the articular damage. Very little is known about the in vivo weightbearing kinematics of the PCL-deficient knee. HYPOTHESIS: Isolated rupture of the posterior cruciate ligament alters knee kinematics, predisposing the patient to development of early osteoarthritis. STUDY DESIGN: Case series. METHODS: Tibiofemoral motion was assessed using open-access magnetic resonance imaging, weightbearing in a squat, through the arc of flexion from 0 degrees to 90 degrees in 6 patients with isolated rupture of the posterior cruciate ligament in one knee and a normal contralateral knee. Passive sagittal laxity was assessed by performing the posterior and anterior drawer tests while the knees were scanned, again using the same magnetic resonance imaging scanner. The tibiofemoral positions during this stress magnetic resonance imaging examination were measured from midmedial and midlateral sagittal images of the knees. RESULTS: Rupture of the posterior cruciate ligament leads to an increase in passive sagittal laxity in the medial compartment of the knee (P < .006). In the weightbearing scans, posterior cruciate ligament rupture alters the kinematics of the knee with persistent posterior subluxation of the medial tibia so that the femoral condyle rides up the anterior upslope of the medial tibial plateau. This fixed subluxation was observed throughout the extension-flexion arc and was statistically significant at all flexion angles (P < .018 at 0 degrees , P < .013 at 20 degrees , P < .014 at 45 degrees , P < .004 at 90 degrees ). The kinematics of the lateral compartment were not altered by posterior cruciate ligament rupture. The posterior drawer test showed increased laxity in the medial compartment. CONCLUSION: Posterior cruciate ligament rupture alters the kinematics of the medial compartment of the knee, resulting in "fixed" anterior subluxation of the medial femoral condyle (posterior subluxation of the medial tibial plateau). This study helps to explain the observation of increased incidence of osteoarthritis in the medial compartment, and specifically the femoral condyle, in posterior cruciate ligament-deficient knees.     

Injuries to the posterior cruciate ligament and posterolateral structures of the knee

Although the incidence of injuries to the posterior cruciate ligament (PCL) is much lower than with the anterior cruciate, recent evidence suggests that deficiency of the PCL may be a much larger problem than originally thought, in the isolated case or in combination with posterolateral structures. Although advances have been made in understanding PCL injuries, the diagnosis and treatment of PCL insufficiency remain unclear. The natural history of a PCL-deficient knee is just beginning to be understood. Numerous methods have been reported for the surgical repair and reconstruction of the PCL, yielding less than optimal results in many cases. Controversy exists regarding the choice between conservative and surgical treatment in the isolated PCL injury. This article reviews the literature and summarizes the state of the art regarding the PCL and related posterolateral injuries, with an emphasis on anatomy, biomechanics, mechanism of injury, diagnosis and treatment Future directions in PCL research are proposed.     

The influence of functional knee bracing on the anterior cruciate ligament strain biomechanics in weightbearing and nonweightbearing knees

Functional knee braces are commonly prescribed after anterior cruciate ligament injury or reconstruction; however, their ability to protect the ligament, or graft, remains unclear. Our objective was to evaluate the anterior cruciate ligament strain response in braced and unbraced knees during weightbearing and nonweightbearing in combination with three externally applied loads: 1) anterior-posterior shear forces, 2) internal-external torques, and 3) varus-valgus moments. The Legend brace was tested. All external loads were applied to the tibia with the knee flexed to 20 degrees. Reproducible data were obtained from 11 subjects. For anterior shear loads up to 130 N, the brace significantly reduced strain values compared with the unbraced knee during nonweightbearing and weightbearing conditions. For internal torques of the tibia (up to 9 N x m), strain in the braced knee was significantly less than in the unbraced knee when the knee was nonweightbearing only. The brace did not reduce strain values when the knee was subjected to external torques (9 N x m) or varus-valgus moments (10 N x m) in weightbearing and nonweightbearing knees. These data indicate that a functional knee brace can protect the anterior cruciate ligament during anterior-posterior shear loading in the nonweightbearing and weightbearing knee and during internal torques in the nonweightbearing knee.     

The absent posterior drawer test in some acute posterior cruciate ligament tears of the knee

Over a 10 year period, 24 of 54 acute PCL tears in cases of straight medial instability demonstrated an absent or an equivocal posterior drawer test. Most of these (22, 91.6%) were contact injuries, and in the 11 cases where the mechanism of injury was known (45.8%), were incurred by a blow to the outer aspect of the leg while the foot was planted. The ACL was normal in 6 of the 24 knees. The abduction stress test at 0 degree extension was severely positive (2+ or more) in 21 of the 24 knees (87.5%). The phenomenon of an absent or equivocal posterior drawer test in the situation of acute straight medial instability is felt to occur when the mechanism of injury does not stress, strain, or tear the arcuate complex. If the PCL tear is not discovered and repaired, repeated stressful activity stretches the arcuate complex, and the chronically unstable knee subsequently presents with a positive posterior drawer test.     

Positioning of the posterior cruciate ligament

The isometric position in ligament reconstruction is the one in which there is little or no change in the length of the graft with range of motion of the joint. It varies according to the positions of the tunnels that will become the attachment sites of whatever graft is being used. Better understanding of this concept that greatly improved the surgical results of intra-articular reconstructions of the anterior cruciate ligament. Unfortunately, the results of posterior cruciate ligament (PCL) reconstructions have lagged behind. A better understanding of the isometry of the PCL and how it relates to the positioning of a graft at the time of reconstruction should help improve the situation. The current scientific studies on the PCL as they relate to isometry are evaluated and summarised in this paper. The tibial isometric point was universally less sensitive to changes in position than was the femoral isometric point. However, all the points that were evaluated for the tibia fell within the normal insertion area of the PCL. This has important ramifications when extrapolating these laboratory studies to the operating room, where it is imperative to get the tibial tunnel or attachment site distal enough on the tibia so that it will be in the usual anatomic location of the PCL. There is less uniformity when it comes to the femoral isometric point, but once again the isometric point from each of the studies fell within the normal anatomic femoral attachment site. The differences between the selected points may be explained by the different study designs.     

Management of combined anteriorcruciate ligament/posterior cruciate ligament/posterolateral complex injuries of the knee

The multiple ligament injured knee is a complex problem in orthopedic surgery. These injuries may present as acuteknee dislocations, and careful assessment of the extremity vascular status is essential because of the possibility of arterial and/or venous compromise. These complex injuries require a systematic approach to evaluation and treatment. Physical examination and imaging studies enable the surgeon to make a correct diagnosis and formulate a treatment plan. Arthroscopically assisted combined anterior cruciate ligament/ posterior cruciate ligament (ACL/PCL) reconstruction is a reproducible procedure. Knee stability is improved postoperatively when evaluated with knee ligament rating scales, arthrometer testing, and stress radiographic analysis. Posterolateral complex (PLC) injuries combined with ACL/PCL tears are best treated with primary repair as indicated combined with PCL reconstruction using a post of strong autograft (split biceps tendon, biceps tendon, semitendinosus), or allograft (Achilles tendon, bone-patellar tendon-bone) tissue. Surgical timing depends on the injured ligaments, vascular status of the extremity, reduction stability, and overall patient health. The use of allograft tissue is preferred because of the strength of these large grafts and the absence of donor site morbidity.