Single-Strand "Short Isometric Construct" Medial Collateral Ligament Reconstruction Restores Valgus and Rotational Stability While Isolated Deep MCL and Superficial MCL Reconstruction Do Not.

BACKGROUND: Historical MCL (medial collateral ligament) reconstruction (MCLR) techniques have focused on the superficial MCL (sMCL) to restore valgus stability while frequently ignoring the importance of the deep MCL (dMCL) in controlling tibial external rotation. The recent recognition of the medial ligament complex importance has multiple studies revisiting medial anatomy and questioning contemporary MCLR techniques. PURPOSE: To assess whether (1) an isolated sMCL reconstruction (sMCLR), (2) an isolated dMCL reconstruction (dMCLR), or (3) a novel single-strand short isometric construct (SIC) would restore translational and rotational stability to a knee with a dMCL and sMCL injury. STUDY DESIGN: Controlled laboratory study. METHODS: Biomechanical testing was performed on 14 fresh-frozen cadaveric knee specimens using a custom multiaxial knee activity simulator. The specimens were divided into 2 groups. The first group was tested in 4 states: intact, after sectioning the sMCL and dMCL, isolated sMCLR, and isolated dMCLR. The second group was tested in 3 states: intact, after sectioning the sMCL and dMCL, and after single-strand SIC reconstruction (SICR). In each state, 4 loading conditions were applied at 0°, 20°, 40°, 60°, and 90° of knee flexion: 8-N·m valgus torque, 5-N·m external rotation torque, 90-N anterior drawer, and combined 90-N anterior drawer plus 5-N·m tibial external rotation torque. Anterior translation, valgus rotation, and external rotation of the knee were measured for each state and loading condition using an optical motion capture system. RESULTS: sMCL and dMCL transection resulted in increased laxity for all loading conditions at all flexion angles. Isolated dMCLR restored external rotation stability to intact levels throughout all degrees of flexion, yet valgus stability was restored only at 0° of flexion. Isolated sMCLR restored valgus and external rotation stability at 0°, 20°, and 40° of flexion but not at 60° or 90° of flexion. Single-strand SICR restored valgus and external rotation stability at all flexion angles. In the combined anterior drawer plus external rotation test, isolated dMCL and single-strand SICR restored stability to the intact level at all flexion angles, while the isolated sMCL restored stability at 20° and 40° of flexion but not at 60° or 90° of flexion. CONCLUSION: In the cadaveric model, single-strand SICR restored valgus and rotational stability throughout the range of motion. dMCLR restored rotational stability to the knee throughout the range of motion but did not restore valgus stability. Isolated sMCLR restored external rotation and valgus stability in early flexion. CLINICAL RELEVANCE: In patients with anteromedial rotatory instability in the knee, neither an sMCLR nor a dMCLR is sufficient to restore stability.

Pelvic tilt affects superolateral coverage, but not superomedial coverage of the femoral head following periacetabular osteotomy.

BACKGROUND: Pelvic tilt is an important sagittal parameter that varies greatly among individuals. The objective of this study was to quantify the effect of pelvic tilt on femoral head coverage and range of motion in a dysplastic population following periacetabular osteotomy. METHODS: Twenty-three dysplastic hips from 19 patients (17 female, 2 male) were included in this study. Three-dimensional models were reconstructed using pre-operative CT images, and patient-specific neutral pelvic tilt was obtained on an anteroposterior X-ray. Following a simulated periacetabular osteotomy, the pelvic tilt was changed from -15° to +15°, and the effects on femoral head coverage and hip range of motion was quantified using a customized MATLAB program. FINDINGS: Pelvic tilt did not significantly affect total femoral head coverage (P > 0.2). However, a 15° anterior tilt from neutral resulted in a 17.72 ± 9.45% increase in anterolateral coverage and a 23.96 ± 7.48% decrease in posterolateral coverage (P < 0.0001), as well as an 18.2 ± 8.4° loss of internal rotation at 90° of hip flexion. Contrarily, posterior pelvic tilt led to a 26.79 ± 9.04% reduction in anterolateral coverage (P < 0.0001) and an 18.02 ± 9.57% increase in posterolateral coverage (P < 0.0001), and the maximum internal rotation increased 11.8 ± 3.7°. INTERPRETATION: While pelvic tilt did not affect total femoral head coverage, it had a significant impact on the distribution of coverage within the superolateral region of the femoral head. Anterior pelvic tilt led to increased anterolateral coverage, but also had a negative impact on hip range of motion. An optimal surgical plan should achieve adequate coverage while not significantly limiting the patient's mobility.

Stress-shielding resistant design of custom pelvic prostheses using lattice-based topology optimization.

Endoprosthetic reconstruction of the pelvic bone using 3D-printed, custom-made implants has delivered early load-bearing ability and good functional outcomes in the short term to individuals with pelvic sarcoma. However, excessive stress-shielding and subsequent resorption of peri­prosthetic bone can imperil the long-term stability of such implants. To evaluate the stress-shielding performance of pelvic prostheses, we developed a sequential modeling scheme using subject-specific finite element models of the pelvic bone-implant complex and personalized neuromusculoskeletal models for pre- and post-surgery walking. A new topology optimization approach is introduced for the stress-shielding resistant (SSR) design of custom pelvic prostheses, which uses 3D-printable porous lattice structures. The SSR optimization was applied to a typical pelvic prosthesis to reconstruct a type II+III bone resection. The stress-shielding performance of the optimized implant based on the SSR approach was compared against the conventional optimization. The volume of the peri­prosthetic bone predicted to undergo resorption post-surgery decreased from 44 to 18%. This improvement in stress-shielding resistance was achieved without compromising the structural integrity of the prosthesis. The SSR design approach has the potential to improve the long-term stability of custom-made pelvic prostheses.

Changes in psoas muscle size and ambulatory function after internal hemipelvectomy without reconstruction.

Internal hemipelvectomy without reconstruction of the pelvis is a viable treatment for pelvic sarcoma; however, the time it takes to return to excellent function is quite variable. Some patients require greater time and rehabilitation than others. To determine if psoas muscle recovery is associated with changes in ambulatory function, we retrospectively evaluated psoas muscle size and limb-length discrepancy (LLD) before and after treatment and their correlation with objective functional outcomes. T1-weighted MR images were evaluated at three intervals for 12 pelvic sarcoma patients following interval hemipelvectomy without reconstruction. Correlations between the measured changes and improvements in Timed Up and Go test (TUG) and gait speed outcomes were assessed both independently and using a stepwise multivariate regression model. Increased ipsilesional psoas muscle size from three months postoperatively to latest follow-up was positively correlated with gait speed improvement (r = 0.66). LLD at three months postoperatively was negatively correlated with both TUG (r = -0.71) and gait speed (r = -0.61). This study suggests that psoas muscle strengthening and minimizing initial LLD will achieve the greatest improvements in ambulatory function. LLD and change in hip musculature remain substantial prognostic factors for achieving the best clinical outcomes after internal hemipelvectomy. Changes in psoas size were correlated with the amount of functional improvement. Several patients in this study did not return to their preoperative ipsilateral psoas size, indicating that monitoring changes in psoas size could be a beneficial rehabilitation strategy.

Finite element analysis of screw fixation durability under multiple boundary and loading conditions for a custom pelvic implant.

Despite showing promising functional outcomes for pelvic reconstruction after sarcoma resection, custom-made pelvic implants continue to exhibit high complication rates due to fixation failures. Patient-specific finite element models have been utilized by researchers to evaluate implant durability. However, the effect of assumed boundary and loading conditions on failure analysis results of fixation screws remains unknown. In this study, the postoperative stress distributions in the fixation screws of a state-of-the-art custom-made pelvic implant were simulated, and the risk of failure was estimated under various combinations of two bone-implant interaction models (tied vs. frictional contact) and four load cases from level-ground walking and stair activities. The study found that the average weighted peak von Mises stress could increase by 22-fold when the bone-implant interactions were modeled with a frictional contact model instead of a tied model, and the likelihood of fatigue and pullout failure for each screw could change dramatically when different combinations of boundary and loading conditions were used. The inclusion of additional boundary and loading conditions led to a more reliable analysis of fixation durability. These findings demonstrated the importance of simulating multiple boundary conditions and load cases for comprehensive implant design evaluation using finite element analysis.

A computational method for estimating trunk muscle activations during gait using lower extremity muscle synergies.

One of the surgical treatments for pelvic sarcoma is the restoration of hip function with a custom pelvic prosthesis after cancerous tumor removal. The orthopedic oncologist and orthopedic implant company must make numerous often subjective decisions regarding the design of the pelvic surgery and custom pelvic prosthesis. Using personalized musculoskeletal computer models to predict post-surgery walking function and custom pelvic prosthesis loading is an emerging method for making surgical and custom prosthesis design decisions in a more objective manner. Such predictions would necessitate the estimation of forces generated by muscles spanning the lower trunk and all joints of the lower extremities. However, estimating trunk and leg muscle forces simultaneously during walking based on electromyography (EMG) data remains challenging due to the limited number of EMG channels typically used for measurement of leg muscle activity. This study developed a computational method for estimating unmeasured trunk muscle activations during walking using lower extremity muscle synergies. To facilitate the calibration of an EMG-driven model and the estimation of leg muscle activations, EMG data were collected from each leg. Using non-negative matrix factorization, muscle synergies were extracted from activations of leg muscles. On the basis of previous studies, it was hypothesized that the time-varying synergy activations were shared between the trunk and leg muscles. The synergy weights required to reconstruct the trunk muscle activations were determined through optimization. The accuracy of the synergy-based method was dependent on the number of synergies and optimization formulation. With seven synergies and an increased level of activation minimization, the estimated activations of the erector spinae were strongly correlated with their measured activity. This study created a custom full-body model by combining two existing musculoskeletal models. The model was further modified and heavily personalized to represent various aspects of the pelvic sarcoma patient, all of which contributed to the estimation of trunk muscle activations. This proposed method can facilitate the prediction of post-surgery walking function and pelvic prosthesis loading, as well as provide objective evaluations for surgical and prosthesis design decisions.

Bilateral asymmetry of bone density adjacent to pelvic sarcomas: A retrospective study using computed tomography.

Limb-salvaging hemipelvectomy surgeries involving allograft or custom prosthesis reconstruction require high quality remaining pelvic bone for adequate device fixation. Modeling studies of custom pelvis prosthesis designs typically mirror contralateral pelvic bone material properties to the ipsilateral pelvis. However, the extent of bone material property and geometric symmetry, and thus the appropriateness of mirroring, remains unknown and should be considered when designing or analyzing the performance of pelvic prostheses. This study investigates preoperative differences between ipsilateral and contralateral pelvic bone for patients with a pelvic sarcoma. Computed tomography (CT) data were obtained retrospectively from eight patients with a pelvic sarcoma. Subject-specific computational models of the pelvic bones were constructed from the CT data. Bilateral asymmetry of bone material properties and cross-sectional areas between the ipsilateral and contralateral hemipelvis were quantified at points adjacent to the pelvic sarcoma. Large bilateral asymmetry (>20%) in trabecular but not cortical bone density was observed within 20 mm of the tumor location. Differences in trabecular bone density typically declined with increased distance from the tumor. The greatest bilateral difference in cross-sectional area occurred within 10 mm of the tumor boundary for three patients and within 40 mm from the tumor site for four patients. Our results suggest that pelvic sarcomas can cause significant bilateral asymmetries in trabecular bone density for patients with a pelvic sarcoma. These differences should be taken into account when designing custom implants for this patient population.

Heterogeneous material mapping methods for patient-specific finite element models of pelvic trabecular bone: A convergence study.

Patient-specific finite element (FE) models of bone require the assignment of heterogeneous material properties extracted from the subject's computed tomography (CT) images. Though node-based (NB) and element-based (EB) material mapping methods (MMMs) have been proposed, the sensitivity and convergence of FE models to MMM for varying mesh sizes are not well understood. In this work, CT-derived and synthetic bone material data were used to evaluate the effect of MMM on results from FE analyses. Pelvic trabecular bone data was extracted from CT images of six subjects, while synthetic data were created to resemble trabecular bone properties. The numerical convergence of FE bone models using different MMMs were evaluated for strain energy, von-Mises stress, and strain. NB and EB MMMs both demonstrated good convergence regarding total strain energy, with the EB method having a slight edge over the NB. However, at the local level (e.g., maximum stress and strain), FE results were sensitive to the field type, MMM, and the FE mesh size. The EB method exhibited superior performance in finer meshes relative to the voxel size. The NB method converged better than did the EB method for coarser meshes. These findings may lead to higher-fidelity patient-specific FE bone models.

Kinematics of monoblock bicompartmental knee arthroplasty during weight-bearing activities.

PURPOSE: There is an increased interest in treating arthritis of the medial and patellofemoral compartments without using a total knee arthroplasty. The purpose of this study was to measure kinematics in knees with a monoblock bicompartmental arthroplasty to see whether maintaining the cruciate ligaments and lateral compartment resulted in consistent kinematics more similar to healthy knees than those observed in replaced knees. METHODS: The kinematics of ten knees with monoblock bicompartmental arthroplasty were observed using fluoroscopy during three weight-bearing activities. Model-image registration techniques were used to quantify the three-dimensional motions of the knee joints. RESULTS: During kneeling, lunging, and stair-step activities, the medial condyle remained relatively close to the centre of the tibial plateau, while the lateral condyle typically moved posteriorly with flexion. Knees generally exhibited motion patterns consistent with retained cruciate ligament function, but individual patterns varied significantly. CONCLUSIONS: Bicompartmental knee arthroplasty has the potential to retain more natural knee function. Improved tools for aligning the implants and increased implant sizing options may be required to achieve highly consistent results and realize the clinical benefit of a knee arthroplasty with intact cruciate ligaments. LEVEL OF EVIDENCE: III.

Effect of tibial plateau leveling osteotomy on patellofemoral alignment: a study using canine cadavers.

Tibial plateau leveling osteotomy (TPLO) has been shown to alter the biomechanics of the femorotibial joint; however, the effect of TPLO on patellofemoral (PF) joint alignment remains unknown. The purpose of this study was to evaluate PF joint kinematics before and after cranial cruciate ligament (CrCL) transection and following TPLO in a cadaveric stifle model with set patellar tendon load, tested in passive range of motion at 90°, 105°, 120°, 135° and 150° of flexion. The PF joint poses were measured on mediolateral projection radiographs using a two-dimensional computer digitization technique. In the subluxated CrCL-deficient stifle, the PF joint had an increase in patellar tilt angle. In the reduced CrCL-deficient stifle treated by TPLO, there was distal and caudal displacement of the patella relative to the femur and a decreased patellar tilt angle. The estimated patellar moment arm following TPLO was not different from the control stifle. On the basis of these results, TPLO alters PF joint kinematics. The changes in PF joint alignment induced by TPLO may be a biomechanical factor predisposing to patellar tendonitis following TPLO.

Physiological sagittal plane patellar kinematics during dynamic deep knee flexion.

PURPOSE: Lateral radiographic views can be easily taken and have reveal considerable information about the patella. The purpose of this study was to obtain sagittal plane patellar kinematics data through the entire range of knee flexion under weight-bearing conditions. METHODS: Patellar flexion angles relative to the femur and tibia and anterior-posterior and proximal-distal translations of the patella relative to the femur and tibia were measured from 0 to 165° knee flexion in nine healthy knees using dynamic radiographic images. RESULTS: The patella flexed relative to the femur and tibia by two thirds times and one third times the knee flexion angle, respectively. The patella translated in an arc relative to the femur and tibia as the knee flexed. In early flexion, the superior and centroid points translated anteriorly and then the patella translated posteriorly relative to the femur. All three points of the patella translated posteriorly relative to the tibia during a full range of flexion. An average of four and three millimetres proximal patellar translation relative to the tibia was demonstrated from 0 to 20° and 140 to 160° knee flexion, respectively. CONCLUSIONS: Physiological sagittal plane patellar kinematics, including patellar flexion angles and translations relative to the femur and tibia, showed generally similar patterns for each subject. Measurements of dynamic radiographic images under weight-bearing activities may enhance the opportunity to identify patellar pathological conditions.

Haptically guided robotic technology in total hip arthroplasty: a cadaveric investigation.

The longevity of total hip arthroplasty (THA) continues to improve with advancements in design and bearing materials. However, the incidence of dislocation and impingement-related failures continue to rise, with the inability of the surgeon to achieve optimal component orientation cited as a cause. Computer-assistance has been shown to increase the accuracy of component orientation and robotic-assistance has been developed to translate this advantage into precise surgical execution. We sought to validate a haptically-guided robotic arm system in performing THA with the aim of comparing the accuracy of robotic-assisted acetabular cup placement to manual placement. We implanted 12 acetabular components in 6 cadaveric pelvises comparing robotic-assistance on one side with manual implantation on the other. We measured planned and actual center of rotation (COR), cup position, leg-length equalization and offset for each THA using computed tomography and the robotic platform. The root-mean-square (RMS) error for the robotic-assisted system was within 3 degrees for cup placement and within 1 mm for leg-length equalization and offset when compared to computed tomography. The robotic-assisted system was significantly more accurate than manual implantation in reproducing the COR and cup orientation, as determined by a preoperative plan. The RMS error for manual implantation compared to robotic-assistance was 5 times higher for cup inclination and 3.4 times higher for cup anteversion (p < 0.01). Robotic-assistance is more accurate than manual implantation in achieving optimal cup orientation. It has the ability to eliminate human error from THA and should be considered in light of THA failures due to component malposition.

In vivo healthy knee kinematics during dynamic full flexion.

Healthy knee kinematics during dynamic full flexion were evaluated using 3D-to-2D model registration techniques. Continuous knee motions were recorded during full flexion in a lunge from 85° to 150°. Medial and lateral tibiofemoral contacts and femoral internal-external and varus-valgus rotations were analyzed as a function of knee flexion angle. The medial tibiofemoral contact translated anteroposteriorly, but remained on the center of the medial compartment. On the other hand, the lateral tibiofemoral contact translated posteriorly to the edge of the tibial surface at 150° flexion. The femur exhibited external and valgus rotation relative to the tibia over the entire activity and reached 30° external and 5° valgus rotations at 150° flexion. Kinematics' data during dynamic full flexion may provide important insight as to the designing of high-flexion total knee prostheses.

Unicompartmental knee arthroplasty: is robotic technology more accurate than conventional technique?

BACKGROUND: Robotic-assisted unicompartmental knee arthroplasty (UKA) with rigid bone fixation "can significantly improve implant placement and leg alignment. The aim of this cadaveric study was to determine whether the use of robotic systems with dynamic bone tracking would provide more accurate UKA implant positioning compared to the conventional manual technique. METHODS: Three-dimensional CT-based preoperative plans were created to determine the desired position and orientation for the tibial and femoral components. For each pair of cadaver knees, UKA was performed using traditional instrumentation on the left side and using a haptic robotic system on the right side. Postoperative CT scans were obtained and 3D-to-3D iterative closest point registration was performed. Implant position and orientation were compared to the preoperative plan. RESULTS: Surgical RMS errors for femoral component placement were within 1.9 mm and 3.7° in all directions of the planned implant position for the robotic group, while RMS errors for the manual group were within 5.4mm and 10.2°. Average RMS errors for tibial component placement were within 1.4mm and 5.0° in all directions for the robotic group; while, for the manual group, RMS errors were within 5.7 mm and 19.2°. CONCLUSIONS: UKA was more precise using a semiactive robotic system with dynamic bone tracking technology compared to the manual technique.

A biomechanical comparison of three hybrid linear-circular external fixator constructs.

OBJECTIVE: To evaluate the stiffness, displacement, ring deformation and bone model motion of 3 configuations of linear-circular hybrid fixator constructs loaded in axial compression, craniocaudal and mediolateral bending, and torsion. STUDY DESIGN: Biomechanical evaluation. SAMPLE POPULATION: Three hybrid construct configurations with 8 replicates/configuration. METHODS: Construct Ia used a single, 84 mm, incomplete ring and 2 tensioned olive wires to stabilize 1 bone segment and a primary hybrid rod with 3 fixation pins to stabilize the other bone segment. Constructs Ia(d) and Ib were similar to Ia with the addition of a secondary diagonal hybrid rod. Construct Ib had a fixation pin inserted orthogonally from the diagonal rod. Constructs were loaded for 10 cycles in each mode of loading using a materials testing machine. Ring deformation was assessed by obtaining serial ring measurements. Bone model motion at the fracture gap as a result of loading was also calculated. RESULTS: Axial compression: constructs Ia(d) and Ib were significantly stiffer than construct Ia. Craniocaudal bending: Construct Ib was significantly stiffer than construct Ia. Mediolateral bending: there were no significant differences between constructs. Torsion: Construct Ib was significantly stiffer than constructs Ia and Ia(d) . Permanent ring deformation did not occur. Bone model translational motion decreased in constructs Ia(d) and Ib compared to construct Ia. CONCLUSIONS: Addition of a secondary hybrid rod as well as biplanar fixation pin placement improved construct stiffness in several loading modes.

Accuracy of dynamic tactile-guided unicompartmental knee arthroplasty.

Unicompartmental knee arthroplasty (UKA) can achieve excellent clinical and functional results for patients having single-compartment osteoarthritis. However, UKA is considered to be technically challenging to perform, and malalignment of implant components significantly contributes to UKA failures. It has been shown that surgical navigation and tactile robotics could be used to provide very accurate component placement when the bones were rigidly fixed in a stereotactic frame during preparation. The purpose of this investigation was to determine the clinically realized accuracy of UKA component placement using surgical navigation and tactile robotics when the bones are free to move. A group of 20 knees receiving medial UKA with dynamically referenced tactile-robotic assistance was studied. Implant placement errors were comparable with those achieved using tactile robotics with rigid stereotactic fixation.

Effect of tibial tuberosity advancement on the contact mechanics and the alignment of the patellofemoral and femorotibial joints.

OBJECTIVE: To evaluate the effect of tibial tuberosity advancement (TTA) on patellofemoral (PF) contact mechanics, and alignment of the PF and femorotibial (FT) joints in cranial cruciate ligament (CrCL)-deficient stifles of dogs. STUDY DESIGN: Ex vivo biomechanical study. ANIMALS: Unpaired cadaveric hind limbs (n=9). METHODS: Digital pressure sensors placed in the PF joint were used to measure contact force, contact area, peak and mean contact pressure, and peak pressure location with the limb under an axial load of 30% body weight and a stifle angle of 135°. The FT and PF poses were obtained using a 2-dimensional computer digitization technique. Each specimen was tested under normal, CrCL-deficient, and TTA-treated conditions. Data was normalized and analyzed, after testing for normality by Wilk-Shapiro, using 1 sample T-test, paired T-test, and ANOVA; P≤.05 was considered significant. Bonferroni's correction was used when needed. RESULTS: A significant cranioproximal tibial displacement and increase in patellar tilt were found in the CrCL-deficient joints. Both FT and PF alignments were restored after TTA. Contact areas and peak pressure did not vary between conditions. Peak pressure location displaced proximally from intact to CrCL-deficient condition and returned to normal after TTA. Total force measured in the CrCL-deficient stifle and TTA conditions were significantly lower than in the control. CONCLUSION: TTA restored the normal FT and PF alignment, and reduced the retropatellar force by about 20%.