3D Knee Model Research Articles

Anatomic double-bundle transtibial anterior cruciate ligament reconstruction restores graft length changes but leads to larger graft bending angles.

The purpose of this study was to evaluate the femoral tunnel position using a modified anatomic transtibial (TT) double-bundle anterior cruciate ligament reconstruction (DBACLR) and to investigate the knee kinematics, graft length and graft bending angle following DBACLR. Ten patients who underwent DBACLR using the modified TT technique were included in the study. All patients performed a single-legged lunge under a dual fluoroscopic imaging system to assess the 6 degrees of freedom tibiofemoral kinematics. Femoral tunnel position was evaluated via postoperative three-dimensional (3D) computed tomography. The area centroids of anteromedial (AM) and posterolateral (PL) bundles were determined on 3D knee models. The lengths of AM and PL bundles, as well as graft bending angle at the femoral tunnel aperture, were measured by created virtual fibres. The reconstructed knee rotated more externally compared with the contralateral knee between 0° and 60° (p ≤ 0.049). There is no significant difference in the length change of AM bundle (n.s.) and PL bundle (n.s.) between the two sides from 0° to 120° during the lunge motion. The maximum graft bending angle at the femoral tunnel aperture occurred at 0° of knee flexion, with the AM graft bending angle was 72.6° ± 9.0° and the PL graft bending angle was 90.3° ± 9.7°. The modified TT technique used in this study could achieve anatomical ACL reconstruction, restoring graft length change patterns compared to contralateral knees. However, residual rotational instability of the reconstructed knee was observed after DBACLR, despite achieving anatomic tunnel placement. Therefore, double-bundle reconstruction may not sufficiently address the persistent rotational instability of the knee. Additionally, larger graft bending angles at the femoral tunnel aperture were found with the modified TT technique. Therefore, further improvement to the TT technique should focus on reducing the graft's curvature while maintaining the anatomical properties of the knee joint. The findings of this study highlight the need for improved surgical techniques to address residual rotational instability and optimise graft curvature. These improvements are crucial for enhancing patient outcomes and long-term joint function following ACL reconstruction. Level II.

An in-vitro three-dimensional surgical simulation technique to predict tibial tunnel length in transtibial posterior cruciate ligament reconstruction

BackgroundDuring the transtibial posterior cruciate ligament (PCL) reconstruction, drilling depth excessively longer than the tibial tunnel length (TTL) is an important reason to cause popliteal neurovascular bundle injury when preparing the tibial tunnel. This study aims to develop an in-vitro three-dimensional surgical simulation technique to determine the TTL in anteromedial (AM) and anterolateral (AL) approaches.MethodsA total of 63 knees’ 3-dimensional (3D) computed tomography models were included in this study. The SuperImage system was used to reconstruct the 3D knee model and locate the tibial PCL site. The established 3D knee model and the coordinates of the tibial PCL site were imported into Rhinoceros 3D modeling software to simulate AM and AL tibial tunnel approaches with different tibial tunnel angles (TTA). The TTL and the tibial tunnel height (TTH) were measured in this study.ResultsIn AM and AL tibial tunnel approaches, the TTL showed a strong correlation with the TTA (for AM: r = 0.758, p < 0.001; for AL: r = 0.727, p < 0.001). The best fit equation to calculate the TTL based on the TTA was Y = 1.04X + 14.96 for males in AM approach, Y = 0.93X + 17.76 for males in AL approach, Y = 0.92X + 14.4 for females in AM approach, and Y = 0.94X + 10.5 for females in AL approach.ConclusionMarking the TTL on the guide pin or reamer could help to avoid the drill bit over-penetrated into the popliteal space to damage the neurovascular structure.

Optimising total knee replacement imaging: a novel 3D printed PET/CT anthropomorphic phantom for metal artefact simulation

PurposeArthroplasty phantoms, including total knee replacement (TKR) phantoms, have been frequently used to test metal artefact reduction methods applied to positron emission tomography/computed tomography (PET/CT) images. These phantoms generally simulate either simple anatomical features or simple activity distribution around the metal inserts in the PET/CT scans. 3D printing has been used recently to fabricate fillable anthropomorphic phantoms that accurately simulate volume and geometry. This study aims to describe the process of image segmentation, phantom modelling, 3D printing and validation of a population-based fillable TKR phantom that simulates human TKR PET/CT metal artefacts.Methods10 participants (5 male and 5 female) were scanned using 3T MRI and the images were segmented to create average male and average female 3D knee models, inversely with void cortical and porous trabecular compartments for 3D printing and contrast media. Virtual total knee replacement (TKR) surgery was implemented on these models to prepare the insertion locations for knee prosthetic implants. Subsequently, TKR models were printed using a 3D photopolymer resin printer and then injected with normal saline to test the phantoms for any leaks. Subsequently, diluted iodinated contrast media was injected into the cortical compartment and saline with 18F-FDG was injected into the trabecular compartment and the phantom was scanned with PET/CT. The images were then evaluated and compared to the human knee radiographic features reported in the literature.ResultsPhantoms were shown to be fluid-tight with distinct compartments. They showed comparable volume and geometry to the segmented human MRI knees. The phantoms demonstrated similar values for x-ray attenuation and Hounsfield units (HU) to the literature for both cortical and trabecular compartments. The phantoms displayed a uniform distribution for the radioactive tracer, resembling that seen in human trabecular bone PET. TKR phantom PET/CT images with metal inserts replicated the clinical metal artefacts seen clinically in the periprosthetic area.ConclusionThis novel, 3D-printed, and customisable phantom effectively mimics the geometric, radiographic and radiotracer distribution features of real TKRs. Importantly, it simulates TKR image metal artefacts, making it suitable for repeatable and comprehensive evaluation of various metal artefact reduction methods in future research.

The optimal tibial tunnel placement to maximize the graft bending angle in the transtibial posterior cruciate ligament reconstruction: a quantitative assessment in three-dimensional computed tomography model.

The graft bending angle created by the graft and the tibial tunnel has inevitably occurred during the transtibial posterior cruciate ligament (PCL) reconstruction. However, few studies quantitively analyzed this angle. This study aimed to (I) explore the optimal tibial tunnel placement to maximize the graft bending angle in the PCL reconstruction; (II) reveal the effect of the tibial tunnel placement on the graft bending angle. This was an in-vitro surgical simulation study based on the three-dimensional (3D) computed tomography (CT). A total of 55 patients who took CT scanning for knee injuries were selected (April 2020 to January 2022) from the local hospital database for review. The 3D knee models were established on the Mimics software based on the knees' CT data. Using the Rhinoceros software to simulate the transtibial PCL reconstruction on the 3D CT knee model. The anteromedial and anterolateral tibial tunnel approaches were simulated with different tibial tunnel angle. The graft bending angle and tibial tunnel length (TTL) with different tibial tunnel angles were quantitively analyzed. The graft bending angle in anterolateral approach with a 50° tibial tunnel angle was significantly greater than it in anteromedial approach with a 60° tibial tunnel angle (P<0.001). There was no difference of the graft bending angle between the anterolateral approach with a 40° tibial tunnel angle and the anteromedial approach with a 60° tibial tunnel angle (P>0.05). The graft bending angle showed a strong correlation with the tibial tunnel angle (for anteromedial approach: r=0.759, P<0.001; for anterolateral approach: r=0.702, P<0.001). The best-fit equation to calculate the graft bending angle based on the tibial tunnel angle was Y = 0.89*X + 59.05 in anteromedial tibial tunnel approach (r2=0.576), and was Y = 0.78*X + 80.21 anterolateral tibial tunnel approach (r2=0.493). The graft bending angle and TTL will significantly increase as the tibial tunnel angle becomes greater. Maximizing the tibial tunnel angle (50° tibial tunnel angle) in the anterolateral approach could provide the greatest graft bending angle in the PCL reconstruction. No matter how the tibial tunnel angle is changed in the anteromedial approach, using anterolateral approach might reduce the killer turn effect more effectively than using anteromedial approach.

3D Printed Models of Trochlear Dysplasia and Trochleoplasty Simulation for Trainee Education

Trochlear dysplasia is a major contributor to patellofemoral instability and subsequent failure of isolated soft tissue reconstruction procedures in the treatment of recurrent patellar dislocation and/or subluxation. Trochleoplasty procedures aim to address abnormal osseous trochlear morphologic factors that contribute to patellar maltracking. However, teaching these techniques is limited by the lack of reliable training models for trochlear dysplasia and trochleoplasty simulation. Although a cadaveric knee model of trochlear dysplasia for trochleoplasty simulation has been recently described, cadaveric knees are less amenable for use in trochleoplasty planning and surgeon training because of the absence of reliable, natural dysplastic anatomic relationships, such as suprapatellar spurs due to the rarity of dysplastic cadavers and the high cost of cadaveric specimens. Furthermore, readily available sawbone models represent “normal” osseous trochlear morphology and are difficult to modify and bend due to their material composition. Given this, we have developed a cost-effective, reliable, and anatomically accurate three-dimensional (3D) knee model of trochlear dysplasia for trochleoplasty simulation and trainee education.

A numerical model for fibril remodeling in articular cartilage

BackgroundCollagen fibrils of articular cartilage have a distinct organization in mature human knee joints. It seems that a mechanobiological process drives the remodeling of newborn collagen fibrils with maturation. Therefore, the goal of the present study was to develop a collagen fibril remodeling algorithm that describes the unique collagen fibril organization in a 3D knee model. MethodA fibril-reinforced, biphasic cartilage model was used with a cuboid and a 3D human knee joint geometries. An isotropic collagen fibril distribution was assigned to the cartilage at the start of the analysis. Each fibril was rotated towards the direction that resulted in a maximum stretch at each time increment of the loading cycle. ResultsThe resulting pattern for the collagen fibrils was compared with split line patterns of porcine knee joint cartilage and also data published in the literature. Fibrils on the articular surface had a radial pattern towards the geometrical centroid of the tibial and femoral cartilage. In the tibiofemoral contact regions of superficial zone, fibrils were oriented circumferentially and randomly. In the porcine samples, the split-line patterns were similar to those obtained theoretically. Depth-wise organization of fibril network was characterized by fibrils perpendicular to the subchondral bone in the deeper layers, and fibrils parallel to the surface of cartilage in the superficial zone. ConclusionsThe maximum stretch criterion, coupled with a biphasic constitutive model, successfully predicted the collagen fibril organization observed in the articular cartilage throughout the depth and on the articular surface.

MATHEMATICAL MODEL AND FEA ANALYSIS OF PROSTHETIC KNEE JOINT

One of the challenges in creating a 3D human knee joint model is accurately defining the area of interest. Prior studies employed simplified bone models, which could potentially compromise the precision of the analysis, posing a contemporary issue. To address this, a multi-step technique was adopted to mitigate the problem and enhance the accuracy of the human knee joint model using analytical and simulation methods. In this endeavour, healthy male knee scanning data were used to reconstruct 3D knee models. Various types of units were employed to segment different parts of the bones. The knee model comprised distinct bone components, and cartilages were created by removing and distinguishing bone layers. For representation, the knee models of a person in both a standing position and while ascending stairs were represented by linear spring elements. Extensive analysis calculations were conducted to validate these models.

3D Killer Turn Angle in Transtibial Posterior Cruciate Ligament Reconstruction Is Determined by the Graft Turning Angle both in the Sagittal and Coronal Planes.

ObjectiveDuring the transtibial posterior cruciate ligament (PCL) reconstruction, surgeons commonly pay more attention to the graft turning angle in the sagittal plane (GASP), but the graft turning angle in the coronal plane (GACP) is always neglected. This study hypothesized that the three‐dimensional (3D) killer turn angle was determined by both the GASP and GACP, and aimed to quantitively analyze the effects of the GASP and GACP on the 3D killer turn angle.MethodsThis was an in‐vitro computer simulation study of transtibial PCL reconstruction using 3D knee models. Patients with knee injuries who were CT scanned were selected from the CT database (April 2019 to January 2021) at a local hospital for reviewing. A total of 60 3D knees were simulated based on the knees' CT data. The femoral and tibial PCL attachment were located on the 3D knee model using the Rhinoceros software. The tibial tunnels were simulated based on different GASP and GACP. The effects of the GASP and GACP on the 3D killer turn angle were quantitatively analyzed. One‐way analysis of variance was used to compare the outcomes in different groups. The regression analysis was performed to identify variables of the GASP and GACP which significantly affected 3D killer turn angle.ResultsThe 3D killer turn angle showed a significant proportional relationship not only with the GASP (r 2 > 0.868, P < 0.001), but also with the GACP (r 2 > 0.467, P < 0.001). Every 10° change of the GACP caused 2.8° to 4.4° change of the 3D killer turn angle, whereas every 10° change of the GASP caused 6.4° to 9.2° change of the 3D killer turn angle.ConclusionsThe 3D killer turn angle was significantly affected by both the GASP and GACP. During the transtibial PCL reconstruction, the proximal anterolateral tibial tunnel approach could increase the 3D killer turn angle more obviously compared with the most distal anteromedial tibial tunnel approach. To minimize the killer turn effect, both the GASP and GACP were required to be considered to increase.

Comparison of instantaneous knee kinematics during walking and running

BackgroundAccurate measurements of in-vivo knee joint kinematics are essential to elucidate healthy knee motion and the changes that accompany injury and repair. Although numerous experimental measurements have been reported, the accurate non-invasive analysis of in-vivo knee kinematics remains a challenge in biomechanics. Research questionThe study objective was to investigate in-vivo knee kinematics before, at, and after contact during walking and running using a combined high-speed dual fluoroscopic imaging system (DFIS) and magnetic resonance (MR) imaging technique. MethodsThree-dimensional (3D) knee models of ten participants were created using MR images. Knee kinematics during walking and running were determined using high-speed DFIS. The 3D knee models were then related to fluoroscopic images to obtain in-vivo six-degrees-of-freedom knee kinematics. ResultsBefore contact knee flexion, external femoral rotation, and proximal-distal distance were 11.9°, 3.4°, and 1.0 mm greater during running compared to walking, respectively. Similar differences were observed at initial contact (9.9°, 7.9°, and 0.9 mm, respectively) and after contact (6.4°, 2.2°, and 0.8 mm, respectively). Posterior femoral translation at initial contact was also increased during running compared to walking. SignificanceThis study demonstrated accurate instantaneous in-vivo knee kinematic characteristics that may further the understanding of the intrinsic biomechanics of the knee during gait.

Poster 228: Comparison of Isometric Properties Between the Medial Patellofemoral Complex Fibers

Objectives:The medial patellofemoral complex (MPFC) has a broad attachment on the patella and quadriceps tendon. Recent anatomic studies have demonstrated a corresponding elongated footprint on the medial femur in which the proximal fibers constitute the MQTFL and the distal fibers form the MPFL. Reconstruction of the MPFL and MQTFL have traditionally been described using the midpoint of the femoral footprint (Schottle’s point) while varying the graft’s position on the patella or quadriceps tendon. The purpose of this study was to compare graft isometry of MPFL, MQTFL, and MPFC reconstruction when using a standard femoral tunnel versus the corresponding anatomic femoral tunnel, and to identify the morphologic risk factors that influence each reconstruction technique.Methods:3D digital knee models were created from dynamic CT images of asymptomatic knees of patients with contralateral patellar instability. Knee models were grouped into 10° intervals and graft length, or distance between the defined points on the femur and extensor mechanism were measured in the following conditions: 1) standard MQTFL (sMQTFL), between the midpoint of the femoral footprint and the quadriceps tendon attachment, 2) anatomic MQTFL (aMQTFL), between the proximal femoral footprint and quadriceps tendon attachment, 3) standard MPFL (sMPFL), between the femoral footprint midpoint and the patellar attachment, 4) anatomic MPFL (aMPFL), between the distal femoral footprint and patellar attachment, and 5) MPFC, between the midpoints of the femoral and quadriceps tendon/patellar attachments. Changes in graft length between 0°and 40° flexion were compared for each reconstruction technique and assessed for their relationship to morphologic risk factors using stepwise multiple regression analyses.Results:12 knees were included in this study (3M, 9F; mean age 23.1+/-8.0y). Mean graft length was significantly greater at 0° than 40° in all reconstructive techniques (p<0.001 to p=0.045). Graft length changes showed no significant differences between reconstructive techniques when using corresponding anatomic femoral tunnels (aMQTFL, aMPFL, aMPFC). When compared to aMPFC (8.8mm), graft length changes were greater in sMQTFL (11.3, p=0.005) and smaller in sMPFL (6.9, p=0.037); however 2/12 (16.7%) of the sMPFL had unfavorable length change patterns that were tighter in flexion than extension. Overall, proximal reconstructions (aMQTFL and sMQTFL) were the most sensitive to the presence of morphologic risk factors (R=.933, R2=0.87 and R=0.898,R2=0.81, respectively) with patella alta having the greatest effect. In contrast, the distal reconstructions (aMPFL and sMPFL) did not have a significant relationship with risk factors but trended toward a significant relationship with TTTG distance (p=0.072 and 0.064, respectively).Conclusions:For MQTFL and MPFL reconstructions, using the corresponding anatomic femoral attachment showed more favorable length change patterns over using the currently described standard femoral tunnel. Overall, graft length changes in proximal (quadriceps tendon) reconstructions were more sensitive to the presence of patella alta, while distal (patellar) reconstructions were influenced by TTTG distance. Further studies are needed to identify the optimal reconstructive technique based on each patient-specific morphologic patterns in the treatment of patellar instability.

The Permissive Safe Angle of the Tibial Tunnel in Transtibial Posterior Cruciate Ligament Reconstruction: A Three-Dimensional Simulation Study.

ObjectiveTo determine the permissive safe angle (PSA) of the tibial tunnel in transtibial posterior cruciate ligament (PCL) reconstruction based on a three‐dimensional (3D) simulation study.MethodsThis was a computer simulation study of transtibial PCL reconstruction using 3D knee models. CT images of 90 normal knee joints from 2017 to 2020 were collected in this study, and 3D knee models were established based on CT data. The tunnel approaches were subdivided into the anterior 1/3 of the anteromedial tibia (T1), middle 1/2 of the anteromedial tibia (T2), the tibial crest (T3), anterior 1/3 of the anterolateral tibia (T4), middle 1/2 of the anterolateral tibia (T5). Five tibial tunnels (T1–T5) were simulated on the 3D knee models. The PSAs, in different tibial tunnel approaches were measured, and subgroup analyses of sex, age and height were also carried out.ResultsThe mean PSAs of the tibial tunnels with 5 different approaches (T1–T5) were 58.49° ± 6.82°, 61.14° ± 6.69°, 56.12° ± 7.53°, 52.01° ± 8.89° and 49.90° ± 10.53°, respectively. The differences of the mean PSAs between the anteromedial and anterolateral approaches were significant (P < 0.05). However, there was no significant difference of the mean PSA value between the two anteromedial tibial tunnel approaches (T1–T2) (P > 0.05), as well as between the two anterolateral tibial tunnel approaches (T4–T5). The patient's anthropomorphic characteristics of sex, age, and height were not associated with the PSAs.ConclusionsThe PSA varied with the anteromedial, tibial crest and anterolateral approaches for transtibial PCL reconstruction, and surgeons should limit the PCL drill guide by referring to the specific PSA for different surgical approaches.

CORR Insights®: What Is the Maximum Tibial Tunnel Angle for Transtibial PCL Reconstruction? A Comparison Based on Virtual Radiographs, CT Images, and 3D Knee Models.

1Orthopaedic Surgeon, Mammoth Orthopedic Institute, Mammoth Lakes, CA, USA B. B. Gilmer, Mammoth Orthopedic Institute, 85 Sierra Park Road, Mammoth Lakes, CA 93546, USA, Email: [email protected] This CORR Insights® is a commentary on the article “What Is the Maximum Tibial Tunnel Angle for Transtibial PCL Reconstruction? A Comparison Based on Virtual Radiographs, CT Images, and 3D Knee Models” by Teng and colleagues available at: DOI: 10.1097/CORR.0000000000002111. The author certifies that there are no funding or commercial associations (consultancies, stock ownership, equity interest, patent/licensing arrangements, etc.) that might pose a conflict of interest in connection with the submitted article related to the author or any immediate family members. All ICMJE Conflict of Interest Forms for authors and Clinical Orthopaedics and Related Research® editors and board members are on file with the publication and can be viewed on request. The opinions expressed are those of the writer, and do not reflect the opinion or policy of CORR® or The Association of Bone and Joint Surgeons®.

What Is the Maximum Tibial Tunnel Angle for Transtibial PCL Reconstruction? A Comparison Based on Virtual Radiographs, CT Images, and 3D Knee Models.

To minimize the killer turn caused by the sharp margin of the tibial tunnel exit in transtibial PCL reconstruction, surgeons tend to maximize the angle of the tibial tunnel in relation to the tibial plateau. However, to date, no consensus has been reached regarding the maximum angle for the PCL tibial tunnel. In this study we sought (1) to determine the maximum tibial tunnel angle for the anteromedial and anterolateral approaches in transtibial PCL reconstruction; (2) to compare the differences in the maximum angle based on three measurement methods: virtual radiographs, CT images, and three-dimensional (3D) knee models; and (3) to conduct a correlation analysis to determine whether patient anthropomorphic factors (age, sex, height, and BMI) are associated with the maximum tibial tunnel angle. Between January 2018 and December 2020, 625 patients who underwent CT scanning for knee injuries were retrospectively reviewed in our institution. Inclusion criteria were patients 18 to 60 years of age with a Kellgren-Lawrence grade of knee osteoarthritis less than 1 and CT images that clearly showed the PCL tibial attachment. Exclusion criteria were patients with a history of tibial plateau fracture, PCL injuries, tumor, and deformity around the knee. Finally, 104 patients (43 males and 61 females, median age: 38 [range 24 to 56] years, height: 165 ± 9 cm, median BMI: 23 kg/cm2 [range 17 to 31]) were included for analysis. CT data were used to create virtual 3D knee models, and virtual true lateral knee radiographs were obtained by rotating the 3D knee models. Virtual 3D knee models were used as an in vitro standard method to assess the true maximum tibial tunnel angle of anteromedial and anterolateral approaches in transtibial PCL reconstruction. The tibial tunnel's entry was placed 1.5 cm anteromedial and anterolateral to the tibial tubercle for the two approaches. To obtain the maximum angle, a 10-mm- diameter tibial tunnel was simulated by making the tibial tunnel near the posterior tibial cortex. The maximum tibial tunnel angle, tibial tunnel lengths, and perpendicular distances of the tunnel's entry point to the tibial plateau were measured on virtual radiographs, CT images, and virtual 3D knee models. One-way ANOVA was used to compare the differences in the maximum angle among groups, and correlation analysis was performed to identify the relationship of the maximum angle and anthropomorphic factors (age, sex, height, and BMI). The maximum angle of the PCL tibial tunnel relative to the tibial plateau was greater in the anteromedial group than the anterolateral group (58° ± 8° versus 50° ± 8°, mean difference 8° [95% CI 6° to 10°]; p < 0.001). The maximum angle of the PCL tibial tunnel was greater in the virtual radiograph group than the CT image (68° ± 6° versus 49° ± 5°, mean difference 19° [95% CI 17° to 21°]; p < 0.001), the anteromedial approach (68° ± 6° versus 58° ± 8°, mean difference 10° [95% CI 8° to 12°]; p < 0.001), and the anterolateral approach (68° ± 6° versus 50° ± 8°, mean difference 18° [95% CI 16° to 20°]; p < 0.001), but no difference was found between the CT image and the anterolateral groups (49° ± 5° versus 50° ± 8°, mean difference -1° [95% CI -4° to 1°]; p = 0.79). We found no patient anthropomorphic characteristics (age, sex, height, and BMI) that were associated with the maximum angle. Surgeons should note that the mean maximum angle of the tibial tunnel relative to the tibial plateau was greater in the anteromedial than anterolateral approach in PCL reconstruction, and the maximum angle might be overestimated on virtual radiographs and underestimated on CT images. To perform PCL reconstruction more safely, the findings of this study suggest that the PCL drill system should be set differently for the anteromedial and anterolateral approaches, and the maximum angle measured by intraoperative fluoroscopy should be reduced 10° for the anteromedial approach and 18° for the anterolateral approach. Future clinical or cadaveric studies are needed to validate our findings.

AVOIDING POPLITEAL NEURO-VASCULAR INJURY DURING ILIOTIBIAL BAND ACL RECONSTRUCTION

Background:For patients with significant growth remaining, the Iliotibial Band ACL reconstruction technique has proven to be reliable procedure with minimal risk for growth disturbance. Recent dissection studies confirm the neuro-vascular bundle is within 1 cm of the ACL graft over the top position, confirming the importance of careful graft passage technique to avoid neurovascular injury.Purpose:The purpose of this study was to evaluate the over the top graft passage technique using pediatric 3-D knee models. Instrument placement for graft passage was assessed for its proximity to the posterior aspect of the femur, maintaining a safe distance from the neurovascular bundle.Materials and Methods:3D knee models (ages 7, 9, 11 years) were printed from high resolution knee CT scans, including a hinge/pivot mechanism to allow for simulation of knee position during flexion and extension. Various curved tip instruments were used to evaluate the path of the graft passage, with several goals: 1. Allow the instrument to create a graft path through the posterior capsule in the most anatomic femoral position. 2. Keep the tip of the instrument close to posterior and lateral cortex of the femur, to avoid neurovascular injury. The instruments varied in design, arc of curvature, overall length, diameters.Results:Clamp passage was performed using a retrograde approach, i.e. through the notch, passing outside the periosteum of the postero-lateral femur (Figure 1). For some clamps, the arc of the curvature allowed for passage of the instrument with minimal risk of neurovascular injury. For some clamp configurations, the clamps deviated significant from the posterior aspect of the femur during graft passage, which may increase the risk of neurovascular bundle injury. In each case, an instrument was identified that met the criteria for safe passage, but different instruments were required based upon the size of the knee joint.Conclusions:The ITB ACL reconstruction is one of the best options for ACL reconstruction in the skeletally immature. The neurovascular structures are very close to the path for over the top graft placement. Due to the wide range of knee dimensions in this group, different clamp designs may be necessary for optimal over the top graft passage. 3D knee models may guide surgeons for procedure technique and optimal instrument selection for safe graft passage.Figure 1.

High-speed fluoroscopic imaging for investigation of three-dimensional knee kinematics before and after marathon running.

Knee injuries often occur during or shortly after marathon running, and are linked to altered knee kinematics. The kinematics of healthy knees during pre- and post-marathon running have not been examined with high-speed fluoroscopy. This study aimed to evaluate the effects of marathon running on knee kinematics during walking and running by using a combined high-speed fluoroscopy and MRI technique. Ten healthy runners underwent knee MRI within 24 h before marathon running to construct three-dimensional (3D) knee models. Knee kinematics during treadmill walking and running were evaluated using high-speed fluoroscopy (200hz) within 24 h before and as soon as possible (within 5 h) after marathon running. All pre- and post-marathon measurements were compared. (1) For post-marathon walking, posterior femoral translation increased 1.4 mm at initial contact (p = 0.015); proximal-distal distance of tibia and femur decreased 0.7 mm and 0.8 mm at initial contact and after contact, respectively (p = 0.039, p = 0.046); and valgus femur rotation increased 1.2° after contact (p = 0.027). (2) For post-marathon running, proximal-distal distance decreased 0.7 mm and 1.0 mm at initial contact and after contact (p = 0.011, p = 0.003) respectively; knee flexion decreased 4.3° before contact (p = 0.007); knee flexion increased 1.8° and 2.6° at initial contact and after contact, respectively (p = 0.038, p = 0.011); external femoral rotation increased 1.2° and 1.8° at initial contact and after contact, respectively (p = 0.012, p = 0.037). Valgus femoral rotation after contact increased 2.3° (p = 0.001). Post-marathon changes in valgus and external femoral rotation, knee flexion, posterior femoral translation, and proximal-distal distance may increase the risk of knee injury. This study provides information to better understand the response of the knee to marathon running.

MPFL Length Change Patterns in Asymptomatic Knees of Patients with Contralateral Patellar Instability

Objectives:Recreating the isometry of the medial patellofemoral ligament (MPFL) is critical during patellar stabilization surgery to restore patellar kinematics. The native MPFL is reported to remain constant in length from 0-70°knee flexion in normal knees. However, patients with patellar instability have morphologic abnormalities that may alter the isometric function of the ligament. Length change patterns of the intact MPFL in such patients have not been described.Methods:3D digital knee models were created from dynamic CT images of 10 patients with unilateral patellar instability who were confirmed to have no symptoms on the contralateral knee. At each flexion angle, MPFL length was calculated based on the distance between its known attachment points. Straight line representation of the MPFL was allowed to wrap around the femoral condyle to ensure accurate length measurement. Morphologic characteristics of each knee were recorded, including sulcus angle and lateral trochlear inclination (LTI) as measurements of trochlear dysplasia, trochlear alpha angle to measure trochlear length, tibial tuberosity to trochlear groove (TTTG) distance to measure malalignment, and Caton Deschamps Index (CDI) to measure patellar height. Changes in MPFL length were assessed relative to knee flexion angle in each patient and correlated with morphologic characteristics.Results:10 knees were included in this study, with a mean age of 20.4+/-4.7 yrs. Mean sulcus angle was 153.4+/-8.9°, LTI 14.1+/-4.0°, trochlear alpha angle 66.1+/-5.8°, TTTG distance 18.3+/-3.1mm, CDI 1.1+/-0.1. Mean MPFL length varied from 62.5+/-4.9mm at 50° knee flexion to 74.4+/-3.9mm at 0°, with a 20.1+/-8.8% change in length (p<0.001). No significant length changes were noted between 30° and 50° flexion. Moderate correlation was noted between increasing MPFL length change and measurements of trochlear length (R=-0.55, p=0.017).Conclusions:In the asymptomatic knees of patients with contralateral patellar instability, the calculated MPFL length based on known anatomic attachment points varied by 20.1%, or an average of 12.1mm, between 50° flexion and full extension. This suggests that the isometric function of the intact MPFL in these patients may not reflect previously described findings in anatomically normal patients. Further studies are needed to understand the pathoanatomy related to these changes, as well as the implications for graft placement and assessment of isometry in MPFL reconstruction techniques.

Augmented reality navigation for minimally invasive knee surgery using enhanced arthroscopy

PurposeDuring the minimally invasive knee surgery, surgeons insert surgical instruments and arthroscopy through small incisions, and implement treatment assisted by 2D arthroscopic images. However, this 2D arthroscopic navigation faces several problems. Firstly, the guidance information is displayed on a screen away from the surgical area, which makes hand/eye coordination difficult. Secondly, the small incision limits the surgeons to view the internal knee structures only from an arthroscopic camera. In addition, arthroscopic images commonly appear obscure visions. MethodsTo solve these problems, we proposed a novel in-situ augmented reality navigation system with the enhanced arthroscopic information. Firstly, intraoperative anatomical locations were obtained by using arthroscopic images and arthroscopy calibration. Secondly, tissue properties-based model deformation method was proposed to update the 3D preoperative knee model with anatomical location information. Then, the updated model was further rendered with glasses-free real 3D display for achieving the global in-situ augmented reality view. In addition, virtual arthroscopic images were generated from the updated preoperative model to provide the anatomical information of the operation area. ResultsExperimental results demonstrated that virtual arthroscopic images could reflect the correct structure information with a mean error of 0.32 mm. Compared with 2D arthroscopic navigation, the proposed augmented reality navigation reduced the targeting errors by 2.10 mm and 2.70 mm for the experiments of knee phantom and in-vitro swine knee, respectively. ConclusionOur navigation method is helpful for minimally invasive knee surgery since it can provide the global in-situ information and detail anatomical information.

Population-Based and Personalized Design of Total Knee Replacement Prosthesis for Additive Manufacturing Based on Chinese Anthropometric Data

At present, most total knee replacement (TKR) prostheses on the market are designed according to the sizes of Caucasians. However, extensive studies have indicated that human anatomies differ among different ethnicities. A number of reports have indicated that Chinese TKR patients do not match with available prostheses. In this study, computed tomography (CT) images of 52 knees of Chinese men and women were used for anthropometric measurements. Index and geometric measurements were defined and used for correlation analysis. Key parameters from the measurement results were identified. Detailed geometries of knees were measured as coordinates. A deformable three-dimensional (3D) knee model based on anatomical coordinates correlating with the identified key parameters was generated. A prosthesis was then designed according to the analyzed results. Surface matching analysis, bone resection analysis, and cadaveric trials were conducted and compared with commercial products to validate the proposed design. The femoral component designed by this study resulted in the highest accuracy (root mean square point-to-surface (RMS PS), (1.08 ± 0.20) mm) and lowest amount of resected bone volume (27 412 mm3) in comparison with two commercial knee prostheses. This study suggests a new approach for population-based patient-specific femoral prosthesis design. With a single, easily acquired dimension—namely, epicondyle width (ECW)—as input, a patient-specific femoral prosthesis can be designed according to the analyzed measured data and manufactured by additive manufacturing (AM) methods. Meanwhile, the reconstructed femoral condylar surface was compared with the femoral condylar surface in the original CT scanning data. The average RMS PS distance of the reconstructed femoral condylar surface among all data was (1.10 ± 0.18) mm, which is comparable to other statistical shape modeling methods using multiple radiographs as input data. There is a need to develop an anthropometric-based knee prosthesis for the Chinese population. Based on the anthropometry of the Chinese population, our new design fits Chinese patients better and reserves more bone volume compared with current commercial prostheses, which is an essential step toward AM for personalized knee prostheses.

Graft bending angle of the reconstructed posterior cruciate ligament gradually decreases as knee flexion increases.

The purpose of the study was to determine the change in the graft bending angles at the femoral and tibial tunnel aperture in single-bundle posterior cruciate ligament (PCL) reconstruction. It was hypothesized that different knee flexion and different tunnel directions may affect changes of the femoral and tibial graft bending angle. The right knees of 12 male subjects were scanned with a high-resolution computed tomography scanner at 4 different knee flexion angles (0°, 45°, 90° and 135°). To begin with, the 3D knee models were created and manipulated with the use of several modeling programs. Single-bundle PCL reconstruction was then virtually conducted in a 90° flexion model: The femoral and tibial graft bending angle, according to the various knee flexion angles, was calculated using a special software program. The femoral graft bending angle significantly decreased as the knee flexion increased between 0° and 135° (all p < 0.001). The femoral graft bending angle of the AL graft showed the most obtuse angles among the three types of the graft beyond 45° of knee flexion. For the tibial graft bending angle, the anteromedial tunnel group showed significantly more acute tibial graft bending angle than the anterolateral tunnel group in all three types of the graft at all flexion angles (all p < 0.001). Changes in the femoral graft bending angle were generally affected by different knee flexion angles. The effect of tibial tunnel direction on the tibial graft bending angle was found to be significant. The clinical relevance is that a mostly obtuse femoral graft bending angle was shown by the AL graft among three types of the graft.

Development of patient specific knee joint implant

The main objective of this paper is to generate 3D model of knee from Digital Imaging and Communication in Medical (DICOM) files, which is acquired from CT scan. Now a day so many cases of Total Knee Replacement (TKR) are happens due to various reasons and after TKR, patient satisfies 90% to 95% as reported. In preoperative planning saves the time and boosts the knee replacement surgery and it includes 3D model of knee, which is essential for further prediction of operative decisions. The purpose of this work was to form a procedure for generating 3D solid model of the human knee to be used in an ongoing preoperative planning. 3D Solid models of the distal end of the femur and the tibial plateau were created to approximate the human knee. So, in this work many open source data conversion software’s are used for transformation of DICOM files to Stereo-Lithography (STL) model. Solidworks software gives significant contribution to produce 3D solid models from the scanned data. This 3D model of knee is used for customization of knee implant according to damaged portion of actual knee or required dimensions.