Intact Posterior Cruciate Ligament Research Articles

MRI analysis of tibial PCL attachment in a large population of adult patients: reference data for anatomic PCL reconstruction.

BackgroundConsistent reference data used for anatomic posterior cruciate ligament (PCL) reconstruction is not well defined. Quantitative guidelines defining the location of PCL attachment would aid in performing anatomic PCL reconstruction. The purpose was to characterize anatomic parameters of the PCL tibial attachment based on magnetic resonance imaging (MRI) in a large population of adult knees.MethodsThe PCL tibial attachment site was examined in 736 adult knees with an intact PCL using 3.0-T proton density–weighted sagittal MRI. The outcomes measured were the anterior-posterior diameter (APD) of the tibial plateau; angle between the tibial plateau and the posterior tibial ‘shelf’ (the slope where the PCL tibial attachment site was) (PTS); length of the PTS; proximal, central, and distal PCL attachment positions as well as the width of the PCL attachment site; and vertical dimension of the PCL attachment site inferior from the tibial plateau.ResultsThe average APD of the tibia plateau was 33.6 ± 3.5 mm, yielding significant differences between males (35.5 ± 3.0 mm) and females (31.6 ± 2.7 mm), P <.05, and there was a significantly decreasing trend with increasing age in males (P <.05). Mean angle between the tibial plateau and the PTS was 122.4° ± 8.1°, and subgroup analysis showed that the young group had a differently smaller angle (120.9° ± 7.5°) than the middle-aged (123.7° ± 8.2°) and the old (123.4° ± 7.7°) in males population, while there were no significant differences between sexes (P >.05). The proximal, central positions and width of the PCL attachment site were 13.4 ± 3.0 mm, 17.8 ± 3.0 mm and 9.6 ± 2.4 mm along the PTS, with significant differences between males and females (P <.05), and accounted for 60.0 % ± 9.1 %, 80.0 % ± 4.6 % and 43.3 % ± 9.7 % of the PTS respectively, with no significant differences between sexes and among age groups (all P >.05).ConclusionsThis study provides reference data of the tibial PCL attachment based on MRI in the sagittal orientation. In analysis of retrospective data from a large population of adult patients, the quantitative values can be used as references to define the inserted angle and depth of the drill guide, and the exact position and size of the tibial PCL tunnel for performing arthroscopic anatomic PCL reconstruction.

Biomechanical Evaluation of Posterior Cruciate Ligament Reconstruction With Quadriceps Versus Achilles Tendon Bone Block Allograft.

Background:Long-term studies of posterior cruciate ligament (PCL) reconstruction suggest that normal stability is not restored in the majority of patients. The Achilles tendon allograft is frequently utilized, although recently, the quadriceps tendon has been introduced as an alternative option due to its size and high patellar bone density.Purpose/Hypothesis:The purpose of this study was to compare the biomechanical strength of PCL reconstructions using a quadriceps versus an Achilles allograft. The hypothesis was that quadriceps bone block allograft has comparable mechanical properties to those of Achilles bone block allograft.Study Design:Controlled laboratory study.Methods:Twenty-nine fresh-frozen cadaveric knees were assigned to 1 of 3 groups: (1) intact PCL, (2) PCL reconstruction with Achilles tendon allograft, or (3) PCL reconstruction with quadriceps tendon allograft. After reconstruction, all supporting capsular and ligamentous tissues were removed. Posterior tibial translation was measured at neutral and 20° external rotation. Each specimen underwent a preload, 2 cyclic loading protocols of 500 cycles, then load to failure.Results:Construct creep deformation was significantly lower in the intact group compared with both Achilles and quadriceps allograft (P = .008). The intact specimens reached the greatest ultimate load compared with both reconstructions (1974 ± 752 N, P = .0001). The difference in ultimate load for quadriceps versus Achilles allograft was significant (P = .048), with the quadriceps group having greater maximum force during failure testing. No significant differences were noted between quadriceps versus Achilles allograft for differences in crosshead excursion during cyclic testing (peak-valley [P-V] extension stretch), creep deformation, or stiffness. Construct stiffness measured during the failure test was greatest in the intact group (117 ± 9 N/mm, P = .0001) compared with the Achilles (43 ± 11 N/mm) and quadriceps (43 ± 7 N/mm) groups.Conclusion:While the quadriceps trended to be a stronger construct with a greater maximum load and stiffness required during load to failure, only maximum force in comparison with the Achilles reached statistical significance. Quadriceps and Achilles tendon allografts had similar other biomechanical characteristics when used for a PCL reconstruction, but both were inferior to the native PCL.Clinical Relevance:The quadriceps tendon is a viable graft option in PCL reconstruction as it exhibits a greater maximum force and is otherwise comparable to the Achilles allograft. These findings expand allograft availability in PCL reconstruction.

Rupture of the Posterior Cruciate Ligament: Preoperative and Postoperative Assessment.

Posterior cruciate ligament (PCL) ruptures are not common, but reconstruction is increasing because PCL-deficient knees are prone to develop osteoarthritis. Preoperative MRI may confirm a total or partial disruption of PCL fibers. An overstretched PCL is often mistaken for an intact PCL while the knee is functionally PCL deficient, resulting in false-negative MRI reports. Posterior translation of the medial condyle is a useful indirect sign on imaging. Preoperative stress radiographs are used to quantify the degree of PCL deficiency, and posterior translation determines whether to treat conservatively or with surgery. Early postoperative imaging is performed to evaluate tunnel placement and fixation devices. Late postoperative imaging is performed to assess graft rupture, arthrofibrosis, or tunnel widening. Pre- and postoperative imaging plays an important part in planning and treating functionally PCL-deficient knees and PCL ruptures.

Biomechanical evaluation of a novel dynamic posterior cruciate ligament brace

BackgroundUse of a rigid brace or cast immobilization is recommended in conservative treatment or postoperative rehabilitation after a posterior cruciate ligament injury. To prevent the loss of knee joint function and muscle activity often associated with this, a flexible knee brace has been developed that allows an adjustable anteriorly directed force to be applied to the calf in order to prevent posterior tibial translation. The purpose of this biomechanical study was to evaluate the impact of this novel dynamic brace on posterior tibial translation after posterior cruciate ligament injury and reconstruction. MethodsA Telos stress device was used to provoke posterior tibial translation in seven human lower limb specimens, and stress radiographs were taken at 90° of knee flexion. Posterior tibial translation was measured in the native knees with an intact posterior cruciate ligament; after arthroscopic posterior cruciate ligament dissection with and without a brace; and after posterior cruciate ligament reconstruction with and without a brace. The force applied with the brace was measured using a pressure sensor. FindingsPosterior tibial translation was significantly reduced (P=0.032) after application of the brace with an anteriorly directed force of 50N to the knees with the dissected posterior cruciate ligament. The brace also significantly reduced posterior tibial translation after posterior cruciate ligament reconstruction in comparison with reconstructed knees without a brace (P=0.005). InterpretationPosterior tibial translation was reduced to physiological values using this dynamic brace system that allows an anteriorly directed force to be applied to the calf.

The effect of graft strength on knee laxity and graft in-situ forces after posterior cruciate ligament reconstruction.

Surgical reconstruction is generally recommended for posterior cruciate ligament (PCL) injuries; however, the use of grafts is still a controversial problem. In this study, a three-dimensional finite element model of the human tibiofemoral joint with articular cartilage layers, menisci, and four main ligaments was constructed to investigate the effects of graft strengths on knee kinematics and in-situ forces of PCL grafts. Nine different graft strengths with stiffness ranging from 0% (PCL rupture) to 200%, in increments of 25%, of an intact PCL’s strength were used to simulate the PCL reconstruction. A 100 N posterior tibial drawer load was applied to the knee joint at full extension. Results revealed that the maximum posterior translation of the PCL rupture model (0% stiffness) was 6.77 mm in the medial compartment, which resulted in tibial internal rotation of about 3.01°. After PCL reconstruction with any graft strength, the laxity of the medial tibial compartment was noticeably improved. Tibial translation and rotation were similar to the intact knee after PCL reconstruction with graft strengths ranging from 75% to 125% of an intact PCL. When the graft’s strength surpassed 150%, the medial tibia moved forward and external tibial rotation greatly increased. The in-situ forces generated in the PCL grafts ranged from 13.15 N to 75.82 N, depending on the stiffness. In conclusion, the strength of PCL grafts have has a noticeable effect on anterior-posterior translation of the medial tibial compartment and its in-situ force. Similar kinematic response may happen in the models when the PCL graft’s strength lies between 75% and 125% of an intact PCL.

Biomechanical analysis of posterior cruciate ligament reconstruction with aperture femoral fixation.

The goal of this study was to determine whether single-tunnel-double-bundle-equivalent posterior cruciate ligament (PCL) reconstruction using an aperture femoral fixation device better replicated normal knee kinematics than single-bundle reconstruction. Eight fresh-frozen human cadaver knees underwent arthroscopically assisted PCL reconstruction and were examined with a robotic testing system to assess knee joint kinematics under combinations of applied internal, neutral, and external rotational tibial torque and anteroposterior translational forces at 0°, 30°, 60°, 90°, and 120° flexion. Three conditions were tested: (1) intact PCL; (2) single-tunnel PCL reconstruction with anterolateral and posteromedial bundle fixation at 90°/90° (single bundle); and (3) 90°/0° (double-bundle equivalent), respectively. Posterior tibial translation was the primary outcome measure. Compared with the intact knee, double-bundle-equivalent reconstruction under external tibial torque allowed greater posterior translation across the flexion arc as a whole (P=.025) and at 30° flexion (P=.027) when results were stratified by flexion angle. No other kinematic differences were found with single-bundle or double-bundle-equivalent fixation, including mediolateral translation and both coupled and isolated tibial rotation (P>.05). Single-bundle PCL reconstruction closely approximated native knee rotational and translational kinematics, whereas double-bundle-equivalent reconstruction permitted increased posterior translation with applied external tibial torque, particularly at lower flexion angles. Single-bundle PCL reconstruction provides knee stability similar to the intact condition, making it a practical alternative to conventional double-bundle PCL reconstruction. The authors found that double-bundle-equivalent reconstruction provided no advantage to justify its clinical use.

The usefulness of the oblique coronal plane in knee MRI on the evaluation of the posterior cruciate ligament

Imaging findings of posterior cruciate ligament (PCL) injury may be equivocal, particularly when the patient has suffered a partial ligament tear. Some PCLs are positioned more horizontally, making it difficult to diagnose injury based on routine imaging planes alone due to partial volume artifact. To evaluate the diagnostic accuracy of combining oblique coronal imaging (PCL view) with traditional orthogonal views for PCL evaluation. This retrospective study included 20 patients with PCL injury and 43 patients with intact PCL who underwent PCL view imaging. Anatomic identification of PCL pathology on the orthogonal magnetic resonance imaging (MRI) sequences and PCL views was evaluated. Subjective scoring of the PCL was performed by two radiologists who assessed the possibility of a PCL tear based on an entire length view, an entire width view, and margin sharpness according to a 4-point scale. Diagnostic accuracy using these two views was evaluated by calculating the sensitivity, specificity, and accuracy. Arthroscopic and clinical findings were used as the reference standard. Total scores for the PCL view were higher than those of orthogonal views (P < 0.001). Both readers found that anatomic identification using the full width view and sharp margin to be superior using the PCL view compared with the orthogonal views (P < 0.001). The specificities and accuracies were higher in cases where an additional PCL view was provided, but did not show statistical significance. PCL view provides better anatomic evaluation of the PCL and mild improvement in the specificity and accuracy.

Improving the clinical efficiency of T2⁎ mapping of ligament integrity

Current MR methods use T2⁎ relaxation time as a surrogate measure of ligament strength. Currently, a multi-echo voxel-wise least squares fit is the gold standard to create T2⁎ maps; however, the post-processing is time-intensive and serves as a stopgap for clinical use. The study objective was to determine if an alternative method could improve post-processing time without sacrificing fidelity of T2⁎ values for eventual translational use in the clinic. Using a 6 echo FLASH sequence, three different methods were used to determine intact posterior cruciate ligament (PCL) median T2⁎ Two of these methods utilized a voxel-wise method to establish T2⁎ maps: (1) a current “gold standard” method using a voxel-wise 6 echo least-squares fit (6LS) and (2) a voxel-wise 2 echo point T2⁎ determination (2MM). The third method used median ligament signal intensity and a single nonlinear least-squares fit (6LSROI) instead of a voxel-wise basis. The resulting median T2⁎ values of the PCL and computational time were compared. The median T2⁎ values were 42% higher using the 2MM compared to the 6LS method (p<0.0001). However, a strong correlation was found for the median T2⁎ values between the 2MM and 6LS methods (R2=0.80). The median T2⁎ values were not significantly different between the 6LS and 6LSROI methods (p=0.519). Using the 2MM (which provides a regional map) and the 6LSROI (which efficiently provides the median T2⁎ value) methods in tandem would take only minutes of post-processing computational time compared to the 6LS method (~540min), and hence would facilitate clinical application of T2⁎ maps to predict ligament structural properties as a patient outcome measure.

Reverse Segond Fracture Variant Without Posterior Cruciate Ligament Injury

Objectives:Reverse Segond fracture, which was described as the association of an avulsion of deep capsular portion of medial collateral ligament and tears of both posterior cruciate ligament (PCL) and medial meniscus, is an extremely rare injury, unlike Segond fracture. The aim is to report successful surgical treatment of a case with “Reverse Segond Fracture” with intact PCL.Methods:The patient was a 16 years old male, who admitted to emergency department of our Level I trauma center after a pedestrian traffic accident. The main complaint was pain on left knee and shoulder. Physical examination revealed mainly limitation in range of motion (ROM) of relevant joints. Radiology revealed Reverse Segond fracture in the left knee and associated left clavicula mid-shaft fracture. Imaging with MRI and CT revealed neither PCL injury or additional ligamentous pathologies of knee. MRI only revealed medial meniscus tear.Results:In surgery, avulsed bony portion of Reverse Segond fracture was fixed to tibia with a suture anchor and a cannulated screw securely under medial meniscus. Peripheral longitudinal medial meniscus tear was fixed with a 2-0 absorbable suture. Clavicle was internally fixed meanwhile. Knee range of motion (ROM) was started early on postoperative first day, then augmented progressively. The patient was mobilized partially-weight bearing after 1.5 months and returned to his active daily life after 2.5 months. He was without any residual complaints after a final follow-up period of 26 months.Conclusion:This case report would be evaluated as a Reverse Segond Fracture variant, as no injury to PCL was noted, in contrast to its original definition in the relevant literature, which is also scarse. To the best of knowledge, this is the first report of successful surgical treatment of a case with Reverse Segond Fracture variant without PCL tear in the relevant literature.

Kinematic Analysis of the Posterior Cruciate Ligament, Part 2

Background: A more thorough understanding of the posterior cruciate ligament (PCL) has led to an increase in awareness and treatment of complex PCL injuries. Controversy exists about whether PCL reconstruction (PCLR) using an anatomic single-bundle (aSB) or anatomic double-bundle (aDB) technique is the most effective. Hypothesis: An aDB PCLR provides significantly better anterior-posterior and rotatory knee stability compared with an aSB PCLR and more closely recreates normal knee kinematics. Study Design: Controlled laboratory study. Methods: A total of 18 match-paired, cadaveric knees (mean age, 54.8 years; range, 51-59 years; 5 male and 4 female pairs) were used to evaluate the kinematics of an intact PCL, an aSB and aDB PCLR, and a complete sectioned PCL. A 6 degrees of freedom robotic system was used to assess knee stability with a 134-N applied posterior tibial load, 5-N·m external and internal rotation torques, 10-N·m valgus and varus rotation torques, and a coupled 100-N posterior tibial load and 5-N·m external rotation torque at 0°, 15°, 30°, 45°, 60°, 75°, 90°, 105°, and 120°. Results: The aDB PCLR had significantly less posterior translation than the aSB PCLR at all flexion angles of 15° and greater. The largest difference in posterior translation was seen at 105° of flexion, where the aSB PCLR had 5.3 mm (P = .017) more posterior translation than the aDB PCLR. The aDB PCLR also had significantly less internal rotation than the aSB PCLR at all tested angles of 90° and greater. Neither reconstruction was able to fully restore native knee kinematics. Conclusion: An aDB PCLR more closely approximated native knee kinematics when compared with an aSB PCLR. Specifically, the aDB PCLR demonstrated significantly more restraint to posterior translation at flexion angles between 15° and 120° and less internal rotational laxity at high flexion angles 90° to 120°. Clinical Relevance: Comparison of the 2 reconstruction techniques illustrates the time-zero kinematic advantage imparted by the addition of the posteromedial bundle reconstruction. The benefit is most pertinent for resistance to posterior translation across a full range of flexion and rotational stability beyond 90° of knee flexion.

Kinematic Analysis of the Posterior Cruciate Ligament, Part 1

Background: The posterior cruciate ligament (PCL) is composed of 2 functional bundles and has an essential role in knee function and stability. There is, however, a limited understanding of the role of each individual bundle through the full range of knee flexion. Hypothesis: Both bundles provide restraint to posterior tibial translation across a full range of knee flexion. At higher angles of knee flexion (>90°), the intact PCL also imparts significant rotational stability. Study Design: Controlled laboratory study. Methods: Twenty matched-paired, human cadaveric knees (mean age, 55.2 years; range, 51-59 years; 6 male and 4 female pairs) were used to evaluate the kinematics of an intact, anterolateral bundle (ALB) sectioned, posteromedial bundle (PMB) sectioned, and complete PCL sectioned knee. A 6 degree of freedom robotic system was used to assess knee stability with an applied 134-N posterior tibial load, 5-N·m external and internal rotation torques, 10-N·m valgus and varus torques, and a coupled 100-N posterior tibial load and 5-N external rotation torque at 0°, 15°, 30°, 45°, 60°, 75°, 90°, 105°, and 120°. Results: All sectioned states had significant increases compared with intact in posterior translation, internal rotation, and external rotation at all tested flexion angles, with the exception of the ALB sectioned state at 75° of flexion for external rotation. The significant increases (mean ± standard deviation) in posterior translation during a 134-N posterior tibial load at 90° of flexion were 0.9 ± 0.6 mm, 2.6 ± 1.8 mm, and 11.7 ± 4.0 mm for the PMB, ALB, and complete PCL sectioned states, respectively, compared with the intact state. The largest significant increases in internal rotation were in the PMB and complete PCL sectioned states at 105° of flexion, 1.3° ± 1.0° and 2.8° ± 2.1°, respectively. Conclusion: Both the ALB and the PMB assume a significant role in resisting posterior tibial translation, at all flexion angles, suggesting a codominant relationship. The PCL provided a significant constraint to internal rotation beyond 90° of flexion. Clinical Relevance: This information broadens the understanding of native knee kinematics and provides a template for the evaluation of single- and double-bundle PCL reconstructions.

Histopathological changes in the human posterior cruciate ligament during aging and osteoarthritis: correlations with anterior cruciate ligament and cartilage changes

ObjectivesTo determine the histological patterns of posterior cruciate ligament (PCL) degeneration during aging and in relation to changes in articular cartilage and anterior cruciate ligament (ACL) across the entire adult...

No difference in anterior tibial translation with and without posterior cruciate ligament in less invasive total knee replacement

PurposeThe relative advantages of cruciate retaining or cruciate resecting total knee replacement are still controversial. If the posterior cruciate ligament (PCL) is preserved, it should be properly balanced. In a previous study, it was demonstrated that increasing the flexion gap leads to an anterior translation of the tibia relative to the femur. Based on these results, we hypothesized that cutting the PCL increases the flexion gap and lessens anterior tibial translation.MethodsThe amount of anterior tibial translation versus distraction force in the flexion gap was measured in 88 total knee replacements with a less invasive midvastus approach using a custom-made tensioner. Measurements were performed with intact and resected PCL.ResultsThe difference in tibial translation with and without PCL is not significant. A 1-mm increase in the flexion gap led to an average anterior translation of 0.6 mm with intact PCL and 0.4 mm with cut PCL, which is less than that reported in a previous study.ConclusionsThe results have not confirmed our initial hypothesis. The reasons for this may be other soft tissue structures that prevent anterior tibial translation, such as the collateral ligaments, and/or the extensor apparatus. Moreover, the knee flexion angle for the used specific implant may play a role.Level of evidenceProspective comparative study, Level II.

Retrospective Analysis of Total Knee Arthroplasty Cases for Visual, Histological, and Clinical Eligibility of Unicompartmental Knee Arthroplasties

We retrospectively analyzed 97 total knee arthroplasty cases with medial osteoarthritis from seven participating surgeons in our teaching hospital to determine the percentage of patients who met the following eligibility criteria for unicompartmental knee arthroplasty (UKA): healthy cartilage in the lateral compartment based on (1) visual analysis, (2) histological analysis and (3) absence of UKA contraindications based on clinical analysis. The cases with healthy lateral cartilage, intact anterior cruciate ligament and posterior cruciate ligament, lack of patello-femoral arthritis, preoperative range of motion (ROM) greater than 90, and genu varum less than 10° represented 21% of the 97 cases studied. This percentage would likely have been higher had the cases been assessed earlier in the disease process. It was concluded that there is the potential to utilize UKA more frequently in the future.

The Triple PCL Sign: Bucket Handle Tears of Both Medial and Lateral Menisci in a Chronically ACL-Deficient Knee

Bucket handle tears of both menisci in the setting of acute or chronic anterior cruciate ligament (ACL) tears of the same knee have rarely been reported in the literature. This article presents a case of a bucket handle tear affecting both the medial and lateral menisci in a patient with chronic ACL rupture. Both bucket handle tears were displaced and locked in the intercondylar notch. A new magnetic resonance image (MRI) sign suggested on sagittal view is called the triple PCL sign, comprising the intact posterior cruciate ligament (PCL) and the 2 displaced fragments in the intercondylar notch from the two bucket handle tears. The precise diagnosis of this condition is of obvious importance for optimal operative planning. While finding the displaced fragment from the medial meniscus is expected to cause the double PCL sign, the torn ACL may have made it easier to visualize the bucket handle tear of the lateral meniscus in the same sagittal plane as the PCL. Only 5 other reports mention bimeniscal bucket handle tears of both the medial and lateral menisci in association with an ACL tear. None have shown the suggested triple PCL sign because of lack of overlap between the 2 bucket handle tears in the coronal plane while lying in the intercondylar notch causing them not to fall in the same sagittal plane. Our patient showed some overlap between the 2 meniscal fragments while lying in the notch to create the triple PCL sign on sagittal MRI.

Early Results of Total Knee Arthroplasty with a Low Contact Stress Anteroposterior Glide

To present early results of 400 consecutive low contact stress (LCS) anteroposterior (AP) glide total knee arthroplasties (TKAs) performed by a single surgeon. 304 consecutive patients aged 30 to 96 (mean, 66) years underwent 400 TKAs using LCS AP glides performed by a single surgeon. Only patients with an intact posterior cruciate ligament, a fixed flexion deformity of <15 degrees, and a valgus deformity of <15 degrees were included. Patients were assessed pre- and post-operatively using the American Knee Society (AKS) and Hospital for Special Surgery (HSS) scores. Range of motion was measured using a goniometer. AP and lateral radiographs were assessed for radiolucencies and osteolysis. The mean follow-up period was 4.2 (range, 1-8) years. The mean fixed flexion improved to 1 from 11 degrees and the mean active flexion improved to 120 from 111 degrees. Both AKS and HSS scores improved significantly. There were 28 anterior soft tissue impingements; 9 of them were in the first year of the study. Thereafter, the anterior lip of the bearing was modified and any offending osteophytes, soft tissue, or fat pads were excised. Of 39 (10%) knees that underwent re-operation (16 were due to anterior soft tissue impingement), 20 (5%) did not require change of the AP glide bearing and the remaining 19 were converted to a rotating platform bearing. No patellar baja was noted after fat pad excision. No patient had catastrophic wear or failure of the polyethylene bearing. The survival rate of the AP glide bearing was 95%. The early-to-mid-term outcomes of the LCS AP glide TKA are promising.

ACL/MCL transection affects knee ligament insertion distance of healing and intact ligaments during gait in the Ovine model

The objective of this study was to assess the impact of combined transection of the anterior cruciate and medial collateral ligaments on the intact and healing ligaments in the ovine stifle joint. In vivo 3D stifle joint kinematics were measured in eight sheep during treadmill walking (accuracy: 0.4±0.4 mm, 0.4±0.4°). Kinematics were measured with the joint intact and at 2, 4, 8, 12, 16 and 20 weeks after either surgical ligament transection ( n=5) or sham surgery without transection ( n=3). After sacrifice at 20 weeks, the 3D subject-specific bone and ligament geometry were digitized, and the 3D distances between insertions (DBI) of ligaments during the dynamic in vivo motion were calculated. Anterior cruciate ligament/medial collateral ligament (ACL/MCL) transection resulted in changes in the DBI of not only the transected ACL, but also the intact lateral collateral ligament (LCL) and posterior cruciate ligament (PCL), while the DBI of the transected MCL was not significantly changed. Increases in the maximal ACL DBI (2 week: +4.2 mm, 20 week: +5.7 mm) caused increases in the range of ACL DBI (2 week: 3.6 mm, 20 week: +3.8 mm) and the ACL apparent strain (2 week: +18.9%, 20 week: +24.0%). Decreases in the minimal PCL DBI (2 week: −3.2 mm, 20 week: −4.3 mm) resulted in increases in the range of PCL DBI (2 week: +2.7 mm, 20 week: +3.2 mm). Decreases in the maximal LCL DBI (2 week: −1.0 mm, 20 week: −2.0 mm) caused decreased LCL apparent strain (2 week: −3.4%, 20 week: −6.9%). Changes in the mechanical environment of these ligaments may play a significant role in the biological changes observed in these ligaments.

Quadriceps force in relation of intrinsic anteroposterior stability of TKA design

Decreased quadriceps strength and fatigue is suspected to be one of the contributing factors for anterior knee pain and malfunction after total knee arthroplasty (TKA). The purpose of this in vitro study was to investigate the amount of quadriceps force required to extend the knee isokinetically after TKA in dependence of different prosthesis designs and the state of the posterior cruciate ligament (PCL). Eight fresh frozen human knee specimens underwent testing in a kinematic device simulating an isokinetic knee extension cycle from 120° of flexion to full extension. The quadriceps force was measured after implantation of a cruciate retaining (CR) TKA (Genesis II, Smith&Nephew, Memphis, TN, USA) applying a conventional CR (11 mm) and a highly conforming (deep dished, DD) polyethylene (PE) inlay consecutively before and after resection of the PCL. Finally, tests were repeated with a posterior-stabilized (PS) design. Simulating a physiological knee extension, no significant differences in the average quadriceps force were detected between the cruciate preserving inlays (CR 1,146.57 ± 88.04 N, DD 1,150.19 ± 97.54 N, P = 0.86) as long as the PCL was intact. After resection of the PCL, the required quadriceps force increased significantly for both designs (CR 1,203.17 ± 91.51 N, P < 0.01 and DD 1,191.88 ± 80.07 N, P < 0.03). After implantation of the posterior stabilized femoral component quad force decreased to its initial levels with forces significantly lower compared to the PCL deficient knees provided with a CR or DD (PS 1,130.91 ± 107.88 N, P < 0.01) inlay. With a deficient PCL there were no statistical differences for the DD design in comparison with CR in mean quad forces (CR 1,203.17 ± 91.51 N vs. DD 1,191.88 ± 80.07 N, P = 0.50) nor in peak forces (CR 1,729.44 ± 161.86 N, DD 1,688.66 ± 123.18 N, P = 0.17). At intact PCL peak quad forces and mean forces beyond 70° of flexion could be shown to be significantly lower with a PS TKA design in comparison with cruciate preserving designs such as CR and DD. In the PCL deficient knee quad forces with a highly conforming implant (DD) and CR were significantly higher than with a PS TKA. The use of PS implants in all PCL deficient knees seems to be advisable

Letter to the Editor: Early Outcome of TKA with a Medial Pivot Fixed-bearing Prosthesis Is Worse Than With a PFC Mobile-bearing Prosthesis

To the Editor: I read with great interest the article “Early Outcome of TKA with a Medial Pivot Fixed-bearing Prosthesis Is Worse Than With a PFC Mobile-bearing Prosthesis” by Kim et al. [1]. This is an important contribution because comparing two different knee designs in the same patient eliminates many of the patient-dependent variables. In this series, the same surgeon performed the procedures at the same time. I agree with Kim et al. that the unusually high infection rate that led to premature closing of their study reduces the power of some of the conclusions. I would like to comment on the point raised by them regarding the posterior cruciate ligament (PCL). They performed a recession of the PCL in 16% of the Medial Pivot knees. I also selectively recessed the PCL in the first 50 patients I treated with the Medial Pivot prosthesis, but in the last 369 patients I have completely excised the ligament (unpublished data). Range of motion and patient satisfaction are superior in the excised group, including 27 patients with an intact PCL on one side and an excised PCL on the other. Also, they state: “Although we tried to resect an equal amount of bone from the distal and posterior femoral condyles, posterolateral condyles were resected less than posteromedial condyles.” I routinely resect more of the medial femoral condyle for the same reason given by Kim et al. (the medial femoral condyle is larger), but also prepare and place the femoral component in 3° valgus rather than the 5° valgus as they described. These technical points may play an important role in the quality of the results achieved when using the Medial Pivot prosthesis, which is a highly technique-sensitive procedure. Since 1987, I have reviewed patient preferences in knee prostheses when one type of prosthesis is used in one knee and another design in the other. I find patients usually can detect a difference and express a preference [2]. Since that report I evaluated patients with a mobile-bearing prosthesis on one side and a Medial Pivot prosthesis on the other. Among 83 patients, I found 51 (61%) preferred the Medial Pivot side. All the Medial Pivot prostheses were implanted with complete resection of the PCL and using a femoral guide set for 3° valgus. There were no differences in range of motion, infection rate, or other outcomes in these patients. Among patients who preferred the Medial Pivot prosthesis, the reason given was a greater sense of stability, particularly during weightbearing flexion. Patients also stated their Medial Pivot knee felt more natural. I suggest surgeons resect (not recess) the PCL when performing a TKA using the Medial Pivot prosthesis. The results in the patients of Kim et al. may have been quite different if this were part of their technique. Also, there is a small typographical error (the authors stated 98 patients with 198 knees, however, I believe this should be 196 knees) when they state their case numbers.

In Vivo Determination of Total Knee Arthroplasty Kinematics: A Multicenter Analysis of an Asymmetrical Posterior Cruciate Retaining Total Knee Arthroplasty

The objective of this study was to determine if consistent posterior femoral rollback of an asymmetrical posterior cruciate retaining (PCR) total knee arthroplasty was mostly influenced by the implant design, surgical technique, or presence of a well-functioning posterior cruciate ligament (PCL). Three-dimensional femorotibial kinematics was determined for 80 subjects implanted by 3 surgeons, and each subject was evaluated under fluoroscopic surveillance during a deep knee bend. All subjects in this present study having an intact PCL had a well-functioning PCR knee and experienced normal kinematic patterns, although less in magnitude than the normal knee. In addition, a surprising finding was that, on average, subjects without a PCL still achieved posterior femoral rollback from full extension to maximum knee flexion. The findings in this study revealed that implant design did contribute to the normal kinematics demonstrated by subjects having this asymmetrical PCR total knee arthroplasty.