The posterolateral corner of the knee. Anatomy, biomechanics and management of injuries

Optimal Implant Positioning Following Total Knee Arthroplasty Using Predictive Dynamic Simulation

In this paper, a novel method is proposed for the determination of the optimal subject-specific placement of knee implants based on predictive dynamic simulations of human movement following total knee arthroplasty (TKA). Two knee implant models are introduced. The first model is a comprehensive 12-degree-of-freedom (DoF) representation that incorporates volumetric contact between femoral and tibial implants, as well as patellofemoral contact. The second model employs a single-degree-of-freedom equivalent kinematic (SEK) approach for the knee joint. A cosimulation framework is proposed to leverage both knee models in our simulations. The knee model is calibrated and validated using patient-specific data, including knee kinematics and ground reaction forces. Additionally, quantitative indices are introduced to evaluate the optimality of implant positioning based on three criteria: balancing medial and lateral load distributions, ligament balancing, and varus/valgus alignment. The knee implant placement is optimized by minimizing the deviation of the indices from their user-defined desired values during predicted sit-to-stand motion. The method presented in this paper has the potential to enhance the results of knee arthroplasty and serve as a valuable instrument for surgeons when planning and performing this procedure.

CT of Periarticular Adult Knee Fractures: Classification and Management Implications

Periarticular knee fractures, which include fractures of the distal femur, tibial plateau, and patella, account for 5%-10% of musculoskeletal injuries encountered in trauma centers and emergency rooms. These injuries are frequently complex, with articular surface involvement. Surgical principles center on reconstruction of the articular surface as well as restoration of limb length, alignment, and rotation to reestablish functional knee biomechanics. Fixation principles are guided by fracture morphology, and thus, CT with multiplanar reformats and volume rendering is routinely used to help plan surgical intervention. Fractures involving the distal femur, tibial plateau, and patella have distinct management considerations. This comprehensive CT primer of periarticular knee fractures promotes succinct and clinically relevant reporting as well as optimized communication with orthopedic trauma surgeon colleagues by tying fracture type and key CT findings with surgical decision making. Fracture patterns are presented within commonly employed fracture classification systems, rooted in specific biomechanical principles. Fracture typing of distal femur fractures and patellar fractures is performed using Arbeitsgemeinschaft für Osteosynthesefragen/Orthopedic Trauma Association (AO/OTA) classification schemes. Tibial plateau fractures are graded using the Schatzker system, informed by a newer explicitly CT-based three-column concept. For each anatomic region, the fracture pattern helps determine the surgical access required, whether bone grafting is warranted, and the choice of hardware that achieves suitable functional outcomes while minimizing the risk of articular collapse and accelerated osteoarthritis. Emphasis is also placed on recognizing bony avulsive patterns that suggest ligament injury to help guide stress testing in the early acute period. ©RSNA, 2024 Supplemental material is available for this article.

Towards a validated musculoskeletal knee model to estimate tibiofemoral kinematics and ligament strains: comparison of different anterolateral augmentation procedures combined with isolated ACL reconstructions

BACKGROUND

Isolated ACL reconstructions (ACLR) demonstrate limitations in restoring native knee kinematics. This study investigates the knee mechanics of ACLR plus various anterolateral augmentations using a patient-specific musculoskeletal knee model.

MATERIALS AND METHODS

A patient-specific knee model was developed in OpenSim using contact surfaces and ligament details derived from MRI and CT data. The contact geometry and ligament parameters were varied until the predicted knee angles for intact and ACL-sectioned models were validated against cadaveric test data for that same specimen. Musculoskeletal models of the ACLR combined with various anterolateral augmentations were then simulated. Knee angles were compared between these reconstruction models to determine which technique best matched the intact kinematics. Also, ligament strains calculated by the validated knee model were compared to those of the OpenSim model driven by experimental data. The accuracy of the results was assessed by calculating the normalised RMS error (NRMSE); an NRMSE < 30% was considered acceptable.

RESULTS

All rotations and translations predicted by the knee model were acceptable when compared to the cadaveric data (NRMSE < 30%), except for the anterior/posterior translation (NRMSE > 60%). Similar errors were observed between ACL strain results (NRMSE > 60%). Other ligament comparisons were acceptable. All ACLR plus anterolateral augmentation models restored kinematics toward the intact state, with ACLR plus anterolateral ligament reconstruction (ACLR + ALLR) achieving the best match and the greatest strain reduction in ACL, PCL, MCL, and DMCL.

CONCLUSION

The intact and ACL-sectioned models were validated against cadaveric experimental results for all rotations. It is acknowledged that the validation criteria are very lenient; further refinement is required for improved validation. The results indicate that anterolateral augmentation moves the kinematics closer to the intact knee state; combined ACLR and ALLR provide the best outcome for this specimen.

Computer-based analysis of different component positions and insert thicknesses on tibio-femoral and patello-femoral joint dynamics after cruciate-retaining total knee replacement

BACKGROUND

Positioning of the implant components and tibial insert thickness constitute critical aspects of total knee replacement (TKR) that influence the postoperative knee joint dynamics. This study aimed to investigate the impact of implant component positioning (anterior-posterior and medio-lateral shift) and varying tibial insert thickness on the tibio-femoral (TF) and patello-femoral (PF) joint kinematics and contact forces after cruciate-retaining (CR)-TKR.

METHOD

A validated musculoskeletal multibody simulation (MMBS) model with a fixed-bearing CR-TKR during a squat motion up to 90° knee flexion was deployed to calculate PF and TF joint dynamics for varied implant component positions and tibial insert thicknesses. Evaluation was performed consecutively by comparing the respective knee joint parameters (e.g. contact force, quadriceps muscle force, joint kinematics) to a reference implant position.

RESULTS

The PF contact forces were mostly affected by the anterior-posterior as well as medio-lateral positioning of the femoral component (by 3 mm anterior up to 31 % and by 6 mm lateral up to 14 %). TF contact forces were considerably altered by tibial insert thickness (24 % in case of + 4 mm increase) and by the anterior-posterior position of the femoral component (by 3 mm posterior up to 16 %). Concerning PF kinematics, a medialised femoral component by 6 mm increased the lateral patellar tilt by more than 5°.

CONCLUSIONS

Our results indicate that regarding PF kinematics and contact forces the positioning of the femoral component was more critical than the tibial component. The positioning of the femoral component in anterior-posterior direction on and PF contact force was evident. Orthopaedic surgeons should strictly monitor the anterior-posterior as well as the medio-lateral position of the femoral component and the insert thickness.

Measurement of Distance Between Femoral Insertion of Fibular Collateral Ligament and Popliteus: A Cadaveric Study in Indian Population

Background

Injuries to posterolateral corner (PLC) of knee are often neglected. The three key components of PLC are lateral collateral ligament (LCL), popliteofibular ligament (PFL) and popliteus tendon (PT). For adequate reconstruction, anatomic location of these ligaments should be well understood.

Material and methods

Twenty formalin fixed cadaveric knees were dissected. PT and LCL identified. Circumference of the two structures marked with pen just after cutting them close to bone surface. Distance between the centre of LCL and PT was measured along with the measurement of distal femoral medio-lateral dimension (MLD) and Anteroposterior dimension (ALD) of lateral condyle.

Result

The mean distance between PT and LCL measured in 20 specimens was 8.3 ± 0.84 mm, with a range of 7 mm to 10 mm. MLD was 81.0 ± 3.6 mm and APD was 62.7 ± 3.2 mm.

Conclusion

The distance in Indian population is significantly smaller compared to the western. This has clinical implication in drilling the tunnels for PLC reconstruction.

MRI evaluation of the peripheral attachments of the lateral meniscal body: the menisco-tibio-popliteus-fibular complex

PURPOSE

To determine, identify and measure the structures of the menisco-tibio-popliteus-fibular complex (MTPFC) with magnetic resonance imaging (MRI) in knees without structural abnormalities or a history of knee surgery.

METHODS

One-hundred-and-five knees without prior injury or antecedent surgery were analyzed by means of MRI. The average age was 50.1 years ± 14.8. All the measurements were performed by three observers. The peripherical structures of the lateral meniscus body were identified to determine the location, size, and thickness of the entire MTPFC. The distance to other "key areas" in the lateral compartment was also studied and compared by gender and age.

RESULTS

The lateral meniscotibial ligament (LMTL) was found in 97.1% of the MRIs, the popliteofibular ligament (PFL) in 93.3%, the popliteomeniscal ligaments (PML) in 90.4% and the meniscofibular ligament (MFL) in 39%. The anteroposterior distance of the LMTL in an axial view was 20.7 mm ± 3.9, the anterior thickness of the LMTL was 1.1 mm ± 0.3, and the posterior thickness of the LMTL 1.2 mm ± 0.1 and the height in a coronal view was 10.8 mm ± 1.9. The length of the PFL in a coronal view was 8.7 mm ± 2.5, the thickness was 1.4 mm ± 0.4 and the width in an axial view was 7.8 mm ± 2.2.

CONCLUSIONS

The MTPFC has a constant morphological and anatomical pattern for three of its main ligaments and can be easily identified and measured in an MRI; the MFL has a lower prevalence, considering a structure difficult to identify by 1.5 T MRI.

Magnetic resonance imaging evaluation of common peroneal nerve injury in acute and subacute posterolateral corner lesion: a retrospective study

Objective

To evaluate qualitative and quantitative magnetic resonance imaging (MRI) criteria for injury of the common peroneal nerve (CPN) in patients with acute or subacute injuries in the posterolateral corner (PLC) of the knee, as well as to evaluate the reproducibility of MRI evaluation of CPN alterations.

Materials and Methods

This was a retrospective study of 38 consecutive patients submitted to MRI and diagnosed with acute or subacute injury to the PLC of the knee (patient group) and 38 patients with normal MRI results (control group). Two musculoskeletal radiologists (designated radiologist A and radiologist B, respectively) evaluated the images. Nerve injury was classified as neurapraxia, axonotmesis, or neurotmesis. Signal strength was measured at the CPN, the tibial nerve (TN), and a superficial vein (SV). The CPN/TN and CPN/SV signal ratios were calculated. The status of each PLC structure, including the popliteal tendon, arcuate ligament, lateral collateral ligament, and biceps tendon, was classified as normal, partially torn, or completely torn, as was that of the cruciate ligaments. For the semiquantitative analysis of interobserver agreement, the kappa statistic was calculated, whereas a receiver operating characteristic (ROC) curve was used for the quantitative analysis.

Results

In the patient group, radiologist A found CPN abnormalities in 15 cases (39.4%)-neurapraxia in eight and axonotmesis in seven-whereas radiologist B found CPN abnormalities in 14 (36.8%)-neurapraxia in nine and axonotmesis in five. The kappa statistic showed excellent interobserver agreement. In the control group, the CPN/TN signal ratio ranged from 0.63 to 1.1 and the CPN/SV signal ratio ranged from 0.16 to 0.41, compared with 1.30-4.02 and 0.27-1.08, respectively, in the patient group. The ROC curve analysis demonstrated that the CPN/TN signal ratio at a cutoff value of 1.39 had high (93.3%) specificity for the identification of nerve damage, compared with 81.3% for the CPN/SV signal ratio at a cutoff value of 0.41.

Conclusion

CPN alterations are common in patients with PLC injury detected on MRI, and the level of interobserver agreement for such alterations was excellent. Calculating the CPN/TN and CPN/SV signal ratios may increase diagnostic confidence. We recommend systematic analysis of the CPN in cases of PLC injury.

The Menisco-Tibio-Popliteus-Fibular Complex: Anatomic Description of the Structures That Could Avoid Lateral Meniscal Extrusion

PURPOSE

To analyze, quantify, and redefine the anatomy of the peripheral attachments of the lateral meniscal body to further understand how the structures might play a part in preventing meniscal extrusion and how it might be applied to surgical techniques.

METHODS

Ten nonpaired fresh-frozen cadaveric knees without prior injury, a surgical history, or gross anatomic abnormality were included. There were 5 right and 5 left knees, and 50% were from male donors and 50% were from female donors. All the dissections were performed by a group of 3 experts in knee surgery (2 knee surgeons and 1 anatomy professor who oversaw the design of the dissection protocol and guided this protocol). The main peripheral structures associated with the lateral meniscus body were dissected to determine the insertion, size, thickness, and location of the lateral meniscotibial ligament (LMTL), popliteofibular ligament (PFL), and popliteomeniscal ligament (PML). The distance to various landmarks in the lateral compartment was also determined using an electronic caliper. Moreover, a histopathologic study was carried out.

RESULTS

The average thickness of the LMTL was 0.62 ± 0.18 mm (95% confidence interval [CI], 0.49-0.75 mm); that of the PFL-PML area was 1.05 ± 0.27 mm (95% CI, 0.85-1.24 mm). The anteroposterior distance measured 15.80 ± 4.80 mm (95% CI, 12.40-19.30 mm) for the LMTL and 10.40 ± 1.70 mm (95% CI, 9.21-11.63 mm) for the PFL-PML area. The anteroposterior distance of the whole menisco-tibio-popliteus-fibular complex (MTPFC) was 28.20 ± 4.95 mm (95% CI, 24.70-31.70 mm). The average distance from the MTPFC to the posterior horn of the lateral meniscal root was 29.30 ± 2.29 mm (95% CI, 27.60-30.90 mm), whereas that to the anterior horn was 32.00 ± 4.80 mm (95% CI, 28.60-35.50 mm). The average distance from the tibial insertion of the LMTL to the articular surface was 5.59 ± 1.22 mm (95% CI, 4.72-6.46 mm). In all the anatomic components of the knee, a consistent morphologic and histologic pattern was observed between the fibers of the LMTL, PFL, and PML and those of the lateral meniscal body, making up the proposed MTPFC.

CONCLUSIONS

A consistent anatomic pattern has been identified between the lateral meniscal body and the LMTL, PFL, and PML, forming an interconnected complex that would seem appropriate to denominate the MTPFC. A precise study of this region and appropriate nomenclature for it could contribute to a better understanding of the mechanism of lateral meniscal injuries at this level, as well as the development of surgical techniques to treat these lesions and prevent extrusion.

CLINICAL RELEVANCE

This study contributes to the understanding of the lateral meniscal body attachments and the functions they serve. This will lead to improvements in the treatment of lesions in this region, including the development of surgical techniques.

Recent Issues in Musculoskeletal Anatomy Research and Correlation with MRI

MRI 영상은 관절 내 질환의 평가에 중요한 검사기법이며, 관절 MRI 영상의 해석을 위해선 견고한 해부학적 지식이 바탕이 되어야 한다. 관절의 해부학 분야에서는, 새로운 구조물이 발견되기도 하며, 과거에 보고되었으나 기능을 알지 못하던 구조물이 새롭게 주목을 받기도 한다. 본 종설에서는 최근 십여 년간 활발하게 연구되어온 견관절 회전근개 케이블(rotator cable) 및 상관절막(superior capsule), 슬관절의 후외측(posterolateral corner) 및 전외측 인대 복합(anterolateral ligament complex), 발목관절의 원위부 경비골 인대결합(distal tibiofibular syndesmosis) 등의 최근 연구 결과를 소개하고, 이를 MRI 영상을 통해 확인해 보았다.

A Biomechanical Comparison of the Arciero and LaPrade Reconstruction for Posterolateral Corner Knee Injuries

Background:

Injury to the posterolateral corner (PLC) of the knee requires reconstruction to restore coronal and rotary stability. Two commonly used procedures are the Arciero reconstruction technique (ART) and the LaPrade reconstruction technique (LRT). To the authors’ knowledge, these techniques have not been biomechanically compared against one another.

Purpose:

To identify if one of these reconstruction techniques better restores stability to a PLC-deficient knee and if concomitant injury to the proximal tibiofibular joint or anterior cruciate ligament affects these results.

Study Design:

Controlled laboratory study.

Methods:

Eight matched-paired cadaveric specimens from the midfemur to toes were used. Each specimen was tested in 4 phases: intact PLC (phase 1), PLC sectioned (phase 2), PLC reconstructed (ART or LRT) (phase 3), and tibiofibular (phase 4A) or anterior cruciate ligament (phase 4B) sectioning with PLC reconstructed. Varus angulation and external rotation at 0º, 20º, 30º, 60º, and 90º of knee flexion were quantified at each phase.

Results:

In phase 3, both reconstructions were effective at restoring laxity back to the intact state. However, in phase 4A, both reconstructions were ineffective at stabilizing the joint owing to tibiofibular instability. In phase 4B, both reconstructions had the potential to restrict varus angulation motion. There were no statistically significant differences found between reconstruction techniques for varus angulation or external rotation at any degree of flexion in phase 3 or 4.

Conclusion:

The LRT and ART are equally effective at restoring stability to knees with PLC injuries. Neither reconstruction technique fully restores stability to knees with combined PLC and proximal tibiofibular joint injuries.

Clinical Relevance:

Given these findings, surgeons may select their reconstruction technique based on their experience and training and the specific needs of their patients.

Rater agreement reliability of the dial test in the ACL-deficient knee

Background

Posterolateral rotatory instability (PLRI) of the knee can easily be missed, because attention is paid to injury of the cruciate ligaments. If left untreated this clinical instability may persist after reconstruction of the cruciate ligaments and may put the graft at risk of failure. Even though the dial test is widely used to diagnose PLRI, no validity and reliability studies of the manual dial test are yet performed in patients. This study focuses on the reliability of the manual dial test by determining the rater agreement.

Methods

Two independent examiners performed the dial test in knees of 52 patients after knee distorsion with a suspicion on ACL rupture. The dial test was performed in prone position in 30°, 60° and 90° of flexion of the knees. ≥10° side-to-side difference was considered a positive dial test. For quantification of the amount of rotation in degrees, a measuring device was used with a standardized 6 Nm force, using a digital torque adapter on a booth. The intra-rater, inter-rater and rater-device agreement were determined by calculating kappa (κ) for the dial test.

Results

A positive dial test was found in 21.2% and 18.0% of the patients as assessed by a blinded examiner and orthopaedic surgeon respectively. Fair inter-rater agreement was found in 30° of flexion, κ_F = 0.29 (95% CI: 0.01 to 0.56), p = 0.044 and 90° of flexion, κ_F = 0.38 (95% CI: 0.10 to 0.66), p = 0.007. Almost perfect rater-device agreement was found in 30° of flexion, κ_C = 0.84 (95% CI: 0.52 to 1.15), p < 0.001. Moderate rater-device agreement was found in 30° and 90° combined, κ_C = 0.50 (95% CI: 0.13 to 0.86), p = 0.008. No significant intra-rater agreement was found.

Conclusions

Rater agreement reliability of the manual dial test is questionable. It has a fair inter-rater agreement in 30° and 90° of flexion.

Submeniscal Portal for Horizontal Cleavage Tear with Parameniscal Cyst of the Lateral Meniscus

Horizontal cleavage tears of the medial and lateral meniscus can be difficult to treat using the standard anteromedial or anterolateral arthroscopy portals. In this Technical Note, we present a new surgical technique to better manage the inferior leaflet of horizontal cleavage tears of the medial and lateral meniscus and their associated parameniscal cysts.

A case report of anterior cruciate ligament and posterolateral corner reconstruction using tendon graft preserved in situ

INTRODUCTION

Combined anterior cruciate ligament (ACL) and posterolateral corner (PLC) reconstruction are a rare clinical entity in orthopedic literature, whose management requires different types of tendon grafts. Missed PLC injury leads to the failure of ACL repair due to the joint instability.

PRESENTATION OF CASE

We are presenting a case of posttraumatic right ACL, PLC and lateral meniscus injury. The patient was taken to theatre for arthroscopic meniscectomy, ACL and PLC reconstruction. We had to harvest bilateral Gracilis and semitendinosus tendon grafts. Intraoperatively, we used a pump and after meniscectomy and ACL reconstruction the knee was quite swollen; we opted to offer a two-staged procedure for PLC reconstruction. Hence we had to preserve the graft in situ for the next procedure. Posterolateral corner reconstruction was done in a week's time and preserved ligament was found to be intact.

DISCUSSION

The fact that we did not have a tissue bank or facilities for cryopreservation of the harvested tendons at -80 °C or with liquid nitrogen at -179 °C yet we had to keep the harvested tendons safe.

CONCLUSION

In case of absence of graft and bone bank, tendon graft was in situ and found intact and ready to be used after seven days.

Normal Magnetic Resonance Imaging Anatomy of the Capsular Ligamentous Supporting Structures of the Knee

Recognition of the normal magnetic resonance (MR) imaging appearances of the capsular ligaments of the knee is of great importance. These ligaments contribute to stability of the knee joint and are frequently injured. In this article, we describe the normal MR imaging anatomy of the capsular ligaments of the knee including the lateral and medial collateral ligamentous complexes, the extensor mechanism, and the supporting ligamentous structures of the proximal tibiofibular joint. Normal MR imaging findings and important anatomic variants of the neurovascular structures of the knee are also described.

Using three-dimensional isotropic SPACE MRI to detect posterolateral corner injury of the knee

BACKGROUND

Reliable magnetic resonance imaging (MRI) diagnosis is important in cases of posterolateral corner (PLC) injury due to the limitations of physical examination in patients with multi-ligament injury.

PURPOSE

To document the appearance of PLC of the knee on three-dimensional (3D) isotropic MR images, and to determine the significance of MRI findings in patients with confirmed posterolateral rotatory instability.

MATERIAL AND METHODS

Twenty-five patients that underwent surgery for posterolateral instability, and 25 individuals with normal MRI constituted the study cohort. The PLC appearances (popliteofibular, fabellofibular, arcuate ligaments, popliteomeniscal fascicle) were analyzed using 3D isotropic proton density sequence and routine two-dimensional (2D) MRI. In addition, the "fibular cap" sign was evaluated. Statistical analysis was performed using the Chi-square and McNemar's tests.

RESULTS

Thickening of popliteofibular, fabellofibular, arcuate ligaments, and popliteomeniscal fascicle was significantly more frequent in the PLC injury group than in the control group (P < 0.05). The sensitivity and specificity of 3D MRI for popliteofibular, fabellofibular, arcuate ligaments, and popliteomeniscal fascicle injury were 63/92%, 54/100%, 46/100%, and 58/92%, respectively. On comparing 3D and 2D images with respect to injury detectability (grade 3 or 4), both modalities visualized injuries, but 3D detected grade 3 or grade 1 rather than grade 4 or 0, respectively. The fibular cap sign was observed significantly more frequently in PLC group, with 58% sensitivity and 100% specificity, and was better observed by 3D than 2D (P < 0.05).

CONCLUSION

3D MRI is a valid modality for detecting PLC abnormalities as it visualizes pathologies in each component and exhibits the positive fibular cap sign.

MRI injury patterns in surgically confirmed and reconstructed posterolateral corner knee injuries

PURPOSE

The posterolateral corner (PLC) of the knee is anatomically complex with similarly complex MR imaging findings in acutely injured knees. The purpose of this study was to define the MRI pattern of injury in cases of PLC disruption requiring surgery because of clinical instability.

METHODS

The knee MRIs of 22 patients who underwent surgical repair and/or reconstruction of PLC injury were retrospectively reviewed. The fibular collateral ligament (FCL), popliteus tendon (PT), biceps femoris (BF), popliteofibular ligament (PFL), arcuate ligament (AL), and fabellofibular ligament (FFL) were evaluated and graded as follows: complete tear, high-grade partial tear, low-grade partial tear, and normal.

RESULTS

In the 22 cases of PLC injury that necessitated surgery, a constellation of findings involving the larger structures of the PLC was identified. Of the FCL, PT, and BF (considered larger structures), at least two were abnormal in all 22 injury cases. Of the PFL, AL, and FFL (considered smaller structures), the PFL appeared abnormal in 19 cases, yet neither the AL nor FFL were confidently characterized in the injury group.

CONCLUSION

The larger structures of the PLC are easily evaluated using standard MRI techniques. This study identified a predictable pattern of imaging findings involving these more easily assessed structures in those patients who were felt to be clinically unstable and underwent surgical reconstruction, as at least two were abnormal in all 22 cases. The smaller structures of the PLC are difficult to assess with MRI; however, direct visualization of their involvement on MRI is not necessary to report a clinically unstable PLC injury. Emphasis of this simplified but critical analysis of the FCL, BF and PT on MRI scans reviewed by radiologists and orthopaedic surgeons may help to prevent delayed diagnosis of unstable PLC injuries.

LEVEL OF EVIDENCE

III.

The popliteal fibular ligament in acute knee trauma: patterns of injury on MR imaging

OBJECTIVE

To describe the patterns of injury associated with injury to the popliteofibular ligament injury.

MATERIALS AND METHODS

A retrospective review was performed of 180 MRI scans undertaken for acute knee trauma. Scans were excluded if the time of injury was over 4 weeks from the time of the scan, or if there was a history of septic arthritis, inflammatory arthropathy, previous knee surgery, or significant artefact. An agreed criterion for assessing the structures of the posterolateral ligamentous complex was defined and in each scan, the popliteofibular ligament (PFL) was scored as normal or injured. The menisci, ligaments, and tendons of each knee were also assessed.

RESULTS

The mean age was 25.7 years (range, 9-65 years) and 72.2% (n = 130) patients were male. The PFL was injured in 36 cases (20%). There is a significant association between PFL injury and ACL rupture (p = 0.0001), ITB injury (p = 0.0001), PCL injury (p = 0.0373), in addition to associations with injury to other posterolateral corner structures including the lateral collateral ligament (p = 0.0001), biceps femoris tendon (p = 0.0014), and popliteus tendon (p = 0.0014). Of our series of PFL injuries, nine cases (25%) were associated with further injuries of posterolateral corner structures and in 27 cases (75%) the PFL was the only posterolateral corner structure torn.

CONCLUSIONS

PFL injury is not uncommon in acute knee trauma and is associated with significant internal derangement of the knee, especially anterior cruciate ligament rupture, ITB sprain, and injury to other structures within the posterolateral corner.

Co-simulation of neuromuscular dynamics and knee mechanics during human walking

This study introduces a framework for co-simulating neuromuscular dynamics and knee joint mechanics during gait. A knee model was developed that included 17 ligament bundles and a representation of the distributed contact between a femoral component and tibial insert surface. The knee was incorporated into a forward dynamics musculoskeletal model of the lower extremity. A computed muscle control algorithm was then used to modulate the muscle excitations to drive the model to closely track measured hip, knee, and ankle angle trajectories of a subject walking overground with an instrumented knee replacement. The resulting simulations predicted the muscle forces, ligament forces, secondary knee kinematics, and tibiofemoral contact loads. Model-predicted tibiofemoral contact forces were of comparable magnitudes to experimental measurements, with peak medial (1.95 body weight (BW)) and total (2.76 BW) contact forces within 4-17% of measured values. Average root-mean-square errors over a gait cycle were 0.26, 0.42, and 0.51 BW for the medial, lateral, and total contact forces, respectively. The model was subsequently used to predict variations in joint contact pressure that could arise by altering the frontal plane joint alignment. Small variations (±2 deg) in the alignment of the femoral component and tibial insert did not substantially affect the location of contact pressure, but did alter the medio-lateral distribution of load and internal tibia rotation in swing. Thus, the computational framework can be used to virtually assess the coupled influence of both physiological and design factors on in vivo joint mechanics and performance.

Medium-term (5-year) comparison of the functional outcomes of combined anterior cruciate ligament and posterolateral corner reconstruction compared with isolated anterior cruciate ligament reconstruction

PURPOSE

To present a 5-year comparison of the functional outcomes of combined anterior cruciate ligament (ACL) and posterolateral corner (PLC) reconstruction with those of isolated ACL reconstruction.

METHODS

All patients were reviewed clinically and completed knee function questionnaires prospectively, by use of the International Knee Documentation Committee (IKDC) 2000, Knee Injury and Osteoarthritis Outcome Score (KOOS), and Lysholm scoring systems, preoperatively and at 1, 2, and 5 years postoperatively. Patients who underwent combined ACL-PLC reconstruction were identified and reviewed. These patients had intact lateral collateral ligaments. A comparison group was created from a group of patients who underwent isolated ACL reconstruction. The ACL group was selected to have the same profile with regard to age, sex, and meniscal procedure.

RESULTS

There were 25 patients in the ACL-PLC group and 100 in the ACL group. All patients underwent restoration of their PLC function as shown on dial testing. The preoperative values for all KOOS measures and the Lysholm score were significantly lower in the ACL-PLC group than in the ACL group (P < .001). The IKDC score was not significantly different. All knee scores showed a significant improvement in both groups postoperatively at 1, 2, and 5 years (P < .001). At 5 years, the KOOS symptoms subscore (P < .001), KOOS pain subscore (P < .001), KOOS sports subscore (P < .001), KOOS quality-of-life subscore (P < .05), KOOS activities-of-daily living subscore (P < .001), aggregate score for all KOOS parameters (P < .001), and Lysholm score (P < .001) were significantly lower in the ACL-PLC group than in the ACL group. At 5 years, the IKDC scores were not significantly different. All patients in the ACL-PLC group resumed preinjury employment, and 23 of 25 had resumed sports.

CONCLUSIONS

Combined ACL-PLC injuries have greater morbidity than isolated ACL injuries. However, return to work and sporting activity is possible in most cases after combined ACL-PLC reconstruction. The KOOS for sport outcomes suggests that sports were resumed at lower functional levels.

LEVEL OF EVIDENCE

Level III, case-control study.

Posterolateral and posteromedial corner injuries of the knee

Posterolateral (PLC) and posteromedial (PMC) corners of the knee represent complex anatomic regions because of intricate soft tissue and osseous relationships in small areas. Concise knowledge of these relationships is necessary before approaching their evaluation at imaging. Magnetic resonance imaging offers an accurate imaging diagnostic tool to establish normal anatomy and diagnose and characterize soft tissue and osseous injury. It is important to carefully evaluate the PLC and PMC structures on magnetic resonance imaging before planned surgical intervention to avoid potential complications resulting from occult injury.

Meniscofibular ligament: morphology and functional significance of a relatively unknown anatomical structure

Purpose. A relatively unknown ligamentous structure of the posterolateral corner of the knee joint, the so-called meniscofibular ligament (MFL), was investigated as regards its macroscopic morphology, its histological features, and its reaction to knee movements. Material and Methods. MFL was exposed on 21 fresh-frozen unpaired knee joints. Its microscopic morphology was examined utilizing for comparison the fibular collateral and the popliteofibular ligament. Results. MFL was encountered in 100% of the specimens as a thin striplike fibrous band extending between the lower border of the lateral meniscus and the head of the fibula. MFL was tense during knee extension and external rotation of the tibia, whereas its histological features were similar to those of fibular collateral and popliteofibular ligament. Discussion. Its precise histological nature is studied as well as its tension alterations during knee movements. The potential functional significance of the MFL with respect to its role in avoidance of lateral meniscus and lateral coronary ligament tears is discussed. Conclusions. MFL presumably provides an additional protection to the lateral meniscus during the last stages of knee extension, as well as to the lateral coronary ligament reducing the possibility of a potential rupture.

Biomechanical comparisons between 4-strand and modified Larson 2-strand procedures for reconstruction of the posterolateral corner of the knee

BACKGROUND

The posterolateral corner (PLC) resists tibial varus angulation, external rotation, and, to a lesser extent, posterior translation. It is important that reconstructions of posterolateral knee injuries restore joint laxity and patient function, but residual laxities are often observed.

HYPOTHESIS

The knee laxity after a new 4-strand PLC reconstruction would be closer to normal than after a 2-strand "modified Larson" reconstruction.

STUDY DESIGN

Controlled laboratory study.

METHODS

Fourteen intact cadaveric knees were mounted in a 6 degrees of freedom rig and subjected to the following external loading conditions: a 90-N posterior tibial force, a 5-N·m external rotation torque, and 5-N·m varus moment. Knee kinematics were recorded with an active optical tracking system for the intact, PLC-deficient, modified Larson PLC reconstruction and 4-strand PLC reconstruction.

RESULTS

With external tibial torque, the rotational laxity in 4-strand reconstruction was significantly less than in the PLC-deficient (P < .0001) and modified Larson reconstruction (P = .0112) and did not differ significantly from intact laxity at any angle of flexion. In response to posterior load, posterior translation did not change in any of the tested conditions, while the coupled external rotation laxity in 4-strand PLC reconstruction was significantly less than in the PLC-deficient (P < .0001) and modified Larson reconstruction (P < .0486) and was not significantly different from the intact movements for both reconstructions. The varus angulation-versus-flexion curves were significantly different between the PLC-deficient and both PLC reconstructions (P < .0001). The varus laxity was not significantly different between the modified Larson reconstruction, the 4-strand reconstruction, and the intact knee.

CONCLUSION

This study showed that the rotational knee laxity in response to both external rotation and posterior translation load were significantly better after the 4-strand PLC reconstruction than after the modified Larson reconstruction, although significant differences were not found between the 2 procedures for varus laxity.

CLINICAL RELEVANCE

The 4-strand PLC reconstruction may produce a better biomechanical outcome, especially during external rotation and posterior translation tibial load. The authors suggest that this relates to load sharing among 4 graft strands crossing the joint.

Posterolateral corner injuries of the knee: a serious injury commonly missed

We retrospectively reviewed the hospital records of 68 patients who had been referred with an injury to the posterolateral corner of the knee to a specialist knee surgeon between 2005 and 2009. These injuries were diagnosed based on a combination of clinical testing and imaging and arthroscopy when available. In all, 51 patients (75%) presented within 24 hours of their injury with a mean presentation at eight days (0 to 20) after the injury. A total of 63 patients (93%) had instability of the knee at presentation. There was a mean delay to the diagnosis of injury to the posterolateral corner of 30 months (0 to 420) from the time of injury. In all, the injuries in 49 patients (72%) were not identified at the time of the initial presentation, with the injury to the posterolateral corner only recognised in those patients who had severe multiple ligamentous injuries. The correct diagnosis, including injury to the posterolateral corner, had only been made in 34 patients (50%) at time of referral to a specialist knee clinic. MRI correctly identified 14 of 15 injuries when performed acutely (within 12 weeks of injury), but this was the case in only four of 15 patients in whom it was performed more than 12 weeks after the injury. Our study highlights a need for greater diligence in the examination and investigation of acute ligamentous injuries at the knee with symptoms of instability, in order to avoid failure to identify the true extent of the injury at the time when anatomical repair is most straightforward.

Posterior knee pain

Posterior knee pain is a common patient complaint. There are broad differential diagnoses of posterior knee pain ranging from common causes such as injury to the musculotendinous structures to less common causes such as osteochondroma. A precise understanding of knee anatomy, the physical examination, and of the differential diagnosis is needed to accurately evaluate and treat posterior knee pain. This article provides a review of the anatomy and important aspects of the history and physical examination when evaluating posterior knee pain. It concludes by discussing the causes and management of posterior knee pain.

Single-bundle versus double-bundle posterior cruciate ligament reconstruction

PURPOSE

The purpose of this report is to present a systematic review of the literature to compare knee kinematics and clinical outcomes after single-bundle versus double-bundle posterior cruciate ligament reconstruction.

METHODS

Systematic review of the literature by PubMed search, reference review, and search of Arthroscopy identified the relevant biomechanical and clinical studies. The studies were critically evaluated to determine potential advantages of single-bundle or double-bundle reconstructions in anteroposterior stability, graft tension, rotational stability, and functional outcome.

RESULTS

Biomechanical comparisons evaluating anteroposterior stability described either no difference or increased stability with double-bundle reconstructions. Comparing these results is complicated by differential graft choices, tensioning techniques, and tunnel anatomy. Biomechanical studies of graft tension describe conflicting results regarding the optimal reconstruction technique. Recent studies of rotational stability suggest no advantage of double-bundle reconstruction in the setting of concomitant posterolateral corner repair but suggest a possible advantage in the setting of subtle posterolateral corner injury. Three retrospective clinical studies of single- and double-bundle reconstructions with methodologic limitations described no difference in clinical outcome.

CONCLUSIONS

The superiority of single-bundle or double-bundle posterior cruciate ligament reconstruction remains uncertain.

A comparison of modified Larson and 'anatomic' posterolateral corner reconstructions in knees with combined PCL and posterolateral corner deficiency

Different methods to reconstruct damaged posterolateral structures are available, but there has been little work studying their relative performance in combined PCL plus posterolateral corner (PLC) deficiency. We hypothesized that an 'anatomic' reconstruction with three graft bundles crossing the joint line would restore knee laxity closer to normal than a modified two-bundle Larson reconstruction. In a controlled laboratory study, the kinematics of cadaveric knees were measured electromagnetically with posterior drawer, external rotation, or varus rotation loads applied, with the knee at sequential stages: intact, PCL-deficient; PCL plus PLC-deficient; modified Larson reconstruction; anatomic PLC reconstruction. The graft bundles were tensioned sequentially to restore specific degrees of freedom to intact values of laxity at specific angles of knee flexion. A significant difference was not found between the two reconstructions. Both reconstructions restored external rotation and varus laxity to normal. Both restored posterior drawer to that caused by isolated PCL deficiency, but did not restore posterior laxity to normal. It was concluded that, with appropriate graft tensioning, both PLC reconstructions could restore both external rotation and varus laxity to normal, but not posterior drawer. The three-stranded anatomical reconstruction did not perform better than the modified two-strand Larson technique. Both of these isolated PLC reconstructions in knees with combined PCL plus PLC deficiency restored the knees to the laxity condition of an isolated PCL-deficiency, they could not reduce posterior drawer to normal.

Control of laxity in knees with combined posterior cruciate ligament and posterolateral corner deficiency: comparison of single-bundle versus double-bundle posterior cruciate ligament reconstruction combined with modified Larson posterolateral corner reconstruction

BACKGROUND

Although many posterior cruciate ligament (PCL) injuries are in combination with posterolateral corner (PLC) injuries, there has been little research on combined injury reconstruction; the literature includes differing recommendations.

HYPOTHESIS

Combined PCL plus PLC reconstruction corrects the abnormal posterior translation, varus, and external rotation laxities caused by combined PCL plus PLC deficiency. Furthermore, double-bundle PCL plus PLC reconstruction restores laxity closer to normal than single-bundle PCL plus PLC reconstruction.

STUDY DESIGN

Controlled laboratory study.

METHODS

Cadaveric knee kinematics were measured electromagnetically in 9 knees with posterior drawer, external rotation, and varus rotation loads applied at sequential stages: intact, PCL-deficient, PCL plus PLC-deficient, double-bundle PCL plus modified Larson PLC reconstruction, and single-bundle PCL plus modified Larson PLC reconstruction. Each graft was tensioned using a laxity-matching protocol.

RESULTS

There was no significant difference between single-bundle and double-bundle PCL reconstruction, in combination with the modified Larson reconstruction, at any angle of flexion. Both combined reconstructions restored posterior drawer, external rotation, and varus laxity so that they did not differ significantly from normal.

CONCLUSION

In combined PCL plus PLC deficiency, combined PCL plus PLC reconstruction restored all major laxity limits to normal across the range of knee flexion examined. Double-bundle PCL reconstruction was not better than single-bundle reconstruction in this context.

CLINICAL RELEVANCE

The added complexity of double-bundle reconstruction does not seem to be justified by these results. In combined PCL plus PLC-deficient knees, combined single-bundle PCL plus modified Larson PLC reconstruction was sufficient to restore posterior drawer, external rotation, and varus laxity to normal.

The posterolateral corner of the knee

OBJECTIVE

The purpose of this article is to review the clinical importance and MRI appearances of injuries to the posterolateral corner of the knee.

CONCLUSION

Injuries to the posterolateral corner structures of the knee can cause significant disability due to instability, cartilage degeneration, and cruciate graft failure. Becoming familiar with the anatomy of this region can improve one's ability to detect subtle abnormalities and can perhaps lead to improvements in diagnosing and understanding injuries to this area.

MRI of the popliteofibular ligament: isotropic 3D WE-DESS versus coronal oblique fat-suppressed T2W MRI

OBJECTIVE

The objective was to compare isotropic 3D water excitation double-echo steady state (WE-DESS) MRI with coronal oblique fat-suppressed T2-weighted (FS T2W) images in the identification of the popliteofibular ligament (PFL).

MATERIALS AND METHODS

A prospective analysis of 122 consecutive knee MRIs was performed in patients referred for knee pain from the orthopaedic clinic. In addition to the standard knee sequences, isotropic WE-DESS volume acquisition through the whole knee and coronal oblique FS T2W fast spin echo sequences through the posterolateral corner were obtained. The presence of the popliteus and biceps femoris tendons, lateral collateral and PFL was documented. Anterior cruciate ligament injury was present in 33 cases and these were excluded from the study because of the risk of associated PFL injury, leaving a total of 89 cases. Of the 42 patients in whom arthroscopic evaluation was subsequently obtained, none were found to have an injury to the PFL.

RESULTS

The lateral collateral ligament, biceps femoris and popliteus tendon were identified in all cases on all sequences. The PFL was seen in 81 (91.0%; 95% CI 85.1-97.0%) patients using the WE-DESS sequence and 63 (70.8%; 95% CI 61.3-80.2%) patients using the coronal oblique FS T2W sequence, a statistically significant difference (p < 0.00005).

CONCLUSION

Isotropic 3D WE-DESS MRI significantly enhances our ability to identify the popliteofibular ligament compared with coronal oblique fat-suppressed T2-weighted images.

MR imaging of the posterolateral corner of the knee

The posterolateral corner (PLC) is a complex functional unit, consisting of several structures, which is responsible for posterolateral stabilization. The PLC is not consistently defined in the literature. However, most descriptions include the popliteal tendon (PT), the lateral collateral ligament (LCL), the popliteofibular ligament (PFL) and the posterolateral capsule, which is reinforced by the arcuate ligament (AL) and the fabellofibular ligament (FFL). Knowledge of PLC anatomy, including its variations, and understanding of the biomechanics is important for correct diagnosis of PLC injuries. An overlooked PLC injury can result in chronic instability, chronic pain, and, eventually, in secondary osteoarthritis. Damage to the PLC also has an adverse effect on the outcome of cruciate ligament repair. Isolated lesions of the PLC are rare. PLC lesions are typically associated with injuries of the cruciate ligaments, the menisci, bone and soft tissue. In the acute phase, clinical findings can be difficult to interpret due to pain and swelling. Magnetic resonance (MR) imaging potentially demonstrates the entire spectrum of PLC injuries and associated lesions of the knee, including those that may be overlooked during clinical examination or arthroscopy.

Knee dislocation with lateral side injury: results of an en masse surgical repair technique of the lateral side

BACKGROUND

Knee dislocations with lateral side injury are rare and disabling if not treated.

HYPOTHESIS

An en masse surgical technique to repair the lateral side will provide good stability, and the posterior cruciate ligament will heal when left in situ.

STUDY DESIGN

Case series; Level of evidence, 4.

METHODS

Twenty-three patients underwent an en masse lateral side repair after knee dislocation injury; all but 1 patient had anterior cruciate ligament reconstruction. Physical examination included the International Knee Documentation Committee score, isokinetic strength testing, KT-2000 arthrometer testing, radiography (including varus stress), and magnetic resonance imaging scan. Patients were evaluated subjectively with several surveys.

RESULTS

Mean objective evaluation occurred for 17 patients at 4.6 years postoperatively, and 21 subjective evaluations occurred for 21 patients at 5.6 years postoperatively. The objective overall grade was normal for 10 patients and nearly normal for 7 patients. Lateral laxity was graded as normal in 15 patients and 1+ in 2 patients. The posterior drawer was normal in all but 3 patients, who had 1+ posterior laxity. The postoperative varus stress radiography demonstrated a mean increase of 1.1 +/- 1.7 mm (range, -1.2-4.7) between knees. Magnetic resonance scans showed that the lateral side was thickened but intact in all patients. The posterior cruciate ligament was viewed as healed or intact in all patients but was sometimes seen as elongated or buckled. The mean subjective total scores were 91.3 points for the IKDC survey, 93.0 for the modified Noyes survey, and 8.0 for an activity score, but scores were higher for patients who underwent surgery within 4 weeks from the injury.

CONCLUSIONS

The en masse surgical technique to repair the lateral side combined with an anterior cruciate ligament reconstruction after knee dislocation provides excellent long-term stability. The repaired lateral side and untreated posterior cruciate ligament heal with continuity. Patients can return to high levels of activity.

The importance of the valgus stress test in the diagnosis of posterolateral instability of the knee

BACKGROUND

The diagnosis of posterolateral instability of the knee is often based on a typical indirect mechanism of injury, a history of "giving way" and a positive dial test. Our search of the English literature revealed no mention of including the valgus stress test in the diagnostic protocol for posterolateral instability.

HYPOTHESIS

Based on our experience, we hypothesised that a medial collateral ligament (MCL) tear will also produce a positive dial test and that a valgus stress test would provide differential diagnostic information.

METHODS

The MCL's of 14 fresh cadaveric knees (7 cadavers) were cut to simulate a grade 3 tear, taking care not to damage the medial retinaculum or the posteromedial stabilisers of the knee. The amount of tibial external rotation (the dial test) was measured for each knee before and after transection of the MCL.

RESULTS

The results of the dial test after transection of the MCL were similar to those stemming from a solitary injury to the posterolateral corner. There was a significant increase in external rotation of the knee in 30 degrees and 90 degrees of flexion. More over, external rotation in 30 degrees was significantly greater than external rotation in 90 degrees of knee flexion.

CONCLUSIONS

Whenever suspecting a posterolateral complex injury, one has to carefully perform a valgus stress test in 0 degrees and 30 degrees. Although the support of a clinical study is needed in order to make a definite conclusion, the dial test is probably not reliable in the presence of medial instability, and alternative diagnostic measures should be used.

Anterior cruciate ligament tears and associated injuries

Anterior cruciate ligament (ACL) tears are a commonly sustained sports injury, often occurring in association with meniscal tears and trauma to other ligamentous structures around the knee. Diagnosis can often be made clinically, but assessment may be difficult in the acute setting when there is a large joint effusion and severe pain. Plain radiographs may detect the presence of a joint effusion and any associated fractures. However, magnetic resonance imaging is vital for assessing acute knee injuries and plays an important role in deciding treatment options and planning surgical intervention. Some of the associated meniscal and ligamentous injuries can be subtle and may easily be overlooked if these structures are not scrutinized closely. This article will discuss the anatomy of the ACL and the mechanisms and initial clinical assessment of ACL injuries, and review the imaging features of ACL tears and some of the associated injuries, including the posterolateral corner structures. These associated injuries have important implications for determining treatment options and subsequent return to athletic activities.

Combined reconstruction of chronic posterior cruciate ligament and posterolateral corner deficiency

We report a retrospective analysis of the results of combined arthroscopically-assisted posterior cruciate ligament reconstruction and open reconstruction of the posterolateral corner in 19 patients with chronic (three or more months) symptomatic instability and pain in the knee.

All the operations were performed between 1996 and 2003 and all the patients were assessed pre- and post-operatively by physical examination and by applying three different ligament rating scores. All also had weight-bearing radiographs, MR scans and an examination under anaesthesia and arthroscopy pre-operatively. The posterior cruciate ligament reconstruction was performed using an arthroscopically-assisted single anterolateral bundle technique and the posterolateral corner structures were reconstructed using an open Larson type of tenodesis.

The mean follow up was 66.8 months (24 to 110). Pre-operatively, all the patients had a grade III posterior sag according to Clancy and demonstrated more than 20° of external rotation compared with the opposite normal knee on the Dial test. Post-operatively, seven patients (37%) had no residual posterior sag, 11 (58%) had a grade I posterior sag and one (5%) had a grade II posterior sag. In five patients (26%) there was persistent minimal posterolateral laxity. The Lysholm score improved from a mean of 41.2 (28 to 53) to 76.5 (57 to 100) (p = 0.0001) and the Tegner score from a mean of 2.6 (1 to 4) to 6.4 (4 to 9) (p = 0.0001).

We conclude that while a combined reconstruction of chronic posterior cruciate ligament and posterolateral corner instability improves the function of the knee, it does not restore complete stability.

Imaging of the posterolateral corner of the knee

The structures of the posterolateral corner of the knee are increasingly recognized as fulfilling an important role in maintaining knee stability. The posterolateral aspect of the knee is stabilized by a complex anatomy of osseous, myotendinous and ligamentous structures. Unrecognized injuries to this part of the knee are a cause of failure of cruciate ligament reconstruction. This review focuses on the anatomy and common injury patterns involving the posterolateral corner of the knee, with emphasis on magnetic resonance imaging.

The insertion geometry of the posterolateral corner of the knee

We have quantitatively documented the insertion geometry of the main stabilising structures of the posterolateral corner of the knee in 34 human cadavers. The lateral collateral ligament inserted posterior (4.6 mm, sd 2) and proximal (1.3 mm, sd 3.6) to the lateral epicondyle of the femur and posterior (8.1 mm, sd 3.2) to the anterior point of the head of the fibula. On the femur, the popliteus tendon inserted distally (11 mm, sd 0.8) and either anterior or posterior (mean 0.84 mm anterior, sd 4) to the lateral collateral ligament. The popliteofibular ligament inserted distal (1.3 mm, sd 1.2) and anterior (0.5 mm, sd 2.0) to the tip of the styloid process of the fibula. The ligaments had a consistent pattern of insertion and, despite the variation between specimens, the standard deviations were less than the typical size of drill hole used in reconstruction of the posterolateral corner. The data provided in this study can be used in the anatomical repair and reconstruction of this region of the knee.

Topographical histology of the posterolateral corner of the knee, with special reference to laminar configurations around the popliteus tendon: a study of elderly Japanese and late-stage fetuses

We investigated the histology of laminar configurations at the posterolateral corners of 40 knees (18 late-stage fetuses, 22 elderly persons). In the fetuses, the deeply located popliteal fascia and the superficially located inferior geniculate vascular sheath were evident in a space between the popliteus tendon (PT) and the biceps femoris and gastrocnemius. Along, and deep to, the popliteal fascia, the popliteus muscle parenchyma developed into both the PT and another dense connective tissue mass. The PT attached to the fibula (i.e., the fetal popliteofibular ligament) and to the base of the lateral meniscus (i.e., the fetal popliteomeniscal fasciculus). This laminar configuration was essentially maintained in the elderly. The fetal dense connective tissue of the popliteus origin seemed to correspond to the adult arcuate ligament. However, because a connective tissue complex (including the PT and the arcuate and popliteofibular ligaments) was often well developed, the complex involved the inferior geniculate vascular sheath and popliteal fascia. A spectrum of variations was found in how thickly the complex developed. Thus, clear separation of the PT from the surrounding tissues often became difficult. Notably, the connective tissue complex could be peeled in different manners, depending on the site and the individual. Therefore, macroscopic variation in the posterolateral corner, including the apparent absence of some ligaments, seemed to be related to the thickness and number of layers developed by the connective tissue complex, possibly due to an adaptation to the individual's mechanical environment during growth and aging.