Mean Contact Area Research Articles

Partial weight-bearing and range of motion limitation significantly reduce the loads at medial meniscus posterior root repair sutures in a cadaveric biomechanical model.

The aim of this study was to investigate the influence of medial meniscus posterior root avulsion (MMPRA) before and after surgical treatment on the biomechanics of the knee joint, including suture repair forces during daily and crutch-assisted gait movements. MMPRA were investigated in eight human cadaver knee joint specimens by a dynamic knee joint simulator with daily (normal gait, gait with additional rotational movement, standing up, sitting down) and rehabilitation-associated movements (crutch-assisted gait with limited flexion range of motion [30°] and 30% [toe-touch weight-bearing, TTWB] and 50% of body weight [partial weight-bearing, PWB]) with simulated physiologic muscle forces. Each specimen was tested in intact, torn and repaired (transtibial suture) state. The biomechanical parameters were: medial mean contact pressure and area, knee joint kinematics, medial displacement of the posterior meniscus horn and loading on the anchoring suture. Significant reduction of the contact area due to the avulsion was observed in all movements except for PWB and sitting down. MMPRA repair significantly increased the contact areas during all movements, bringing them to levels statistically indistinguishable from the initial state. MMPRA resulted in a medial displacement up to 12.8 mm (sitting down) and could be reattached with a residual displacement ranging from 0.7 mm (PWB) to 5.7 mm (standing up), all significantly (p < 0.001) reduced compared to the torn state. The mean peak anchoring suture load increased from TTWB (77 N), PWB (91 N) to normal gait (194 N), gait rotation (207 N), sitting (201 N; p < 0.01) and to standing up (232 N; p = 0.03). Surgical treatment of MMPRA allows restoration of physiological knee joint biomechanics. Crutch-assisted movements reduce the loading of the repair suture, thus likewise the risk for failure. From a biomechanical point of view, crutch-assisted movements are recommended for the early rehabilitation phase after MMPRA repair. Level V.

Load Distribution After Serial Resection of the Posterior Horn of the Lateral Meniscus and Subsequent Meniscal Allograft Transplant: A Biomechanical Study

Background: Data are lacking as to when a meniscal allograft transplant (MAT) may be biomechanically superior to a partially resected lateral meniscus. Hypothesis: Lateral MAT using a bone bridge technique would restore load distribution and contact pressures in the tibiofemoral joint to levels superior to those of a partial lateral meniscectomy. Study Design: Controlled laboratory study. Methods: Eleven fresh-frozen human cadaveric knees were evaluated in 5 lateral meniscal testing conditions (native, one-third posterior horn meniscectomy, two-thirds posterior horn meniscectomy, total meniscectomy, MAT) at 3 flexion angles (0°, 30°, and 60°) under a 1600-N axial load. Pressure sensors were used to acquire contact pressure, contact area, and peak contact pressure within the tibiofemoral joint. Results: Limited (one-third and two-thirds) partial lateral posterior horn meniscectomy showed no significant increase in mean and peak contact pressures as well as no significant decrease in contact area compared with the intact state. Total meniscectomy significantly increased mean contact pressure at 0° and 30° (P = .008 and P < .001, respectively), increased peak contact pressure at 30° (P = .04), and decreased mean contact area in all flexion angles compared with the native condition (P < .01). Lateral MAT significantly improved mean contact pressure compared with total meniscectomy at 0° and 30° (P = .002 and P = .003, respectively) and increased contact area at 30° and 60° (P = .003 and P = .009, respectively), although contact area was still significantly smaller (24.1%) after MAT relative to the native meniscus (P = 0.015). However, allograft transplant did not result in better tibiofemoral contact biomechanics compared with limited partial meniscectomy (P > .05). Conclusion: The peripheral portion of the lateral meniscus provided the most important contribution to the distribution of contact pressure across the tibiofemoral joint in the cadaveric model. Total meniscectomy significantly increased mean and peak contact pressure in the cadaveric model and decreased contact area. Lateral MAT restored contact biomechanics close to normal but was not superior to the partially meniscectomized status. Clinical Relevance: Surgeons should attempt to preserve a peripheral rim of the posterior lateral meniscus. Meniscal allograft transplant appears to improve but not normalize mean contact pressure and contact area relative to total lateral meniscectomy.

Does plantar pressure in short-term standing differ between modular insoles selected based upon preference or matched to self-reported foot shape?

Prolonged workplace standing is commonplace and associated with a range of lower limb issues. Evaluating footwear interventions aiming to modify plantar pressure during standing is essential as the body is static, creating a different requirement for footwear. Previous research associates medial midfoot pressure with greater perceived comfort and identifies arch height as the most variable element of foot shape. Targeting footwear mass customization within this area may better address differences within the target wearers. This study aims to evaluate a modular insole system for its ability to modify plantar pressure during standing. Twenty-five participants completed a static and dynamic standing protocol for 60 seconds whilst measuring in-shoe peak and mean plantar pressure (KPa) and contact area (%). Individuals wore three insole options targeted towards different medial arch shapes (A– low arch, B– medium arch, C– high arch) and rated them for comfort. Participants received guidance to self-identify foot shape (low, medium, or high arch). Comparisons were drawn across the three insole profiles and between the insole rated as most comfortable (preferred), and the insole that matched the self-identified foot shape (matched). As insole arch height increased, medial midfoot pressure and contact area significantly increased, alongside significant reductions in first metatarsal pressure and contact. Preference was spread across insoles A, B, and C (56%, 32%, 12% of participants, respectively). Sixteen participants had different matched and preferred insoles, with significantly greater medial midfoot pressure and contact in the matched insole. The modular insole enabled different wear experiences, however, results suggest that individuals selected insoles lower than their foot shape. Providing adequate medial arch support enables redistribution of pressure which may enable greater comfort during the workday.

Higher contact pressure of the lateral tibiofemoral joint in lateral extra-articular tenodesis with tensioned graft in external rotation than in neutral rotation: A biomechanical study

ObjectiveTo determine the mean contact pressure, peak contact pressure, and mean contact area of the lateral tibiofemoral joint in lateral extra-articular tenodesis (LET) with tension on the graft in tibial neutral and external rotation. MethodsA total of eight Thiel-embalmed cadaveric knees were prepared and divided into two groups (4 knees in each group): the LET-NR group (lateral extra-articular tenodesis tension in neutral rotation) and (2) the LET-ER group (lateral extra-articular tenodesis tension in external rotation). Each knee was prepared according to the corresponding technique. A hydraulic testing system (E10000, Instron) simulates an axial load of 735 ​N for 10 ​s in each group. ResultsThe LET-ER group exhibited a statistically significant higher peak contact pressure compared to the LET-NR group. The peak contact pressure values in the LET-NR and LET-ER groups were 702.3 ​± ​233.9 ​kPa and 1235.5 ​± ​171.4 ​kPa, respectively (p ​= ​0.010, 95% CI, −888.0 to −178.5). The mean contact pressure values in the LET-NR and LET-ER groups were 344.9 ​± ​69.0 ​kPa and 355.3 ​± ​34.9 ​kPa, respectively (p ​= ​0.796, 95% CI, −105.1–84.2). The mean contact area values in the LET-NR and LET-ER groups were 36.8 ​± ​3.1 mm2 and 33.3 ​± ​6.4 mm2, respectively (p ​= ​0.360, 95% CI, −5.2–12.2). ConclusionsThe peak contact pressure of the lateral tibiofemoral joint is greater in LET when the graft is tensioned in external rotation than in neutral rotation. However, no statistically significant difference in the mean contact pressure or the mean contact area was observed between the two groups. Level of evidenceIII.

Incorporating patient-specific hip orientation from weightbearing computed tomography affects discrete element analysis-computed regional joint contact mechanics in individuals treated with periacetabular osteotomy for hip dysplasia.

Computational models of the hip often omit patient-specific functional orientation when placing imaging-derived bony geometry into anatomic landmark-based coordinate systems for application of joint loading schemes. The purpose of this study was to determine if this omission meaningfully alters computed contact mechanics. Discrete element analysis models were created from non-weightbearing (NWB) clinical CT scans of 10 hip dysplasia patients (11 hips) and oriented in the International Society of Biomechanics (ISB) coordinate system (NWB-ISB). Three additional models were generated for each hip by adding patient-specific stance information obtained via weightbearing CT (WBCT) to each ISB-oriented model: (1) patient-specific sagittal tilt added (WBCT-sagittal), (2) coronal and axial rotation from optical motion capture added to (1; WBCT-combo), and (3) WBCT-derived axial, sagittal, and coronal rotation added to (1; WBCT-original). Identical gait cycle loading was applied to all models for a given hip, and computed contact stress and contact area were compared between model initialization techniques. Addition of sagittal tilt did not significantly change whole-joint peak (p = 0.922) or mean (p = 0.871) contact stress or contact area (p = 0.638). Inclusion of motion-captured coronal and axial rotation (WBCT-combo) decreased peak contact stress (p = 0.014) and slightly increased average contact area (p = 0.071) from WBCT-sagittal models. Including all WBCT-derived rotations (WBCT-original) further reduced computed peak contact stress (p = 0.001) and significantly increased contact area (p = 0.001). Variably significant differences (p = 0.001-1.0) in patient-specific acetabular subregion mechanics indicate the importance of functional orientation incorporation for modeling applications in which local contact mechanics are of interest.

Chewing efficiency and contact area discrepancies in Angle's class I and II malocclusion: A comparative study

ObjectiveThe study aimed to assess and compare both the chewing efficiency and the contact area between class I and class II of Angle’s malocclusions. Material and methodsA total of 120 individuals aged between 19 and 30 years were examined and were divided into two groups according to Angle’s class (Class I and class II). The chewing efficiency was quantified using the ViewGum software and two-colored chewing gum. The contact area was quantified using modeling wax and MATLAB software. All data were collected, then, analyzed using SPSS software 21. Data normality was checked through kurtosis test. Descriptive results were calculated. Matched sample t-tests were used to compare chewing efficiency measurements between right and left sides. Independent t-tests were used to compare chewing efficiency and the contact area between class I and class II of Angle’s malocclusions. Linear regression and Pearson correlation were used to assess the correlation between chewing efficiency and the contact area. The significance level was fixed at p = 0.05. ResultsFor group 1, the mean hue value on both sides was 0.086 ± 0.058. For group 2, it was 0.095 ± 0.055. The difference between both groups was statistically significant (p = 0.03). For group 1, the mean contact area was 49.91 ± 21.47 mm2. For group 2, it was 51.42 ± 19.76 mm2. The difference was statistically not significant (p = 0.4). The correlation between the contact area and the chewing efficiency in both groups was statistically significant and it was negative (in class I p = 0 and R = -0.616; in class II p = 0.01 and R = −0.408). ConclusionThe Chewing is better for patients with Angle’s Class I malocclusion. The contact area is higher. Larger occlusal contact area leads to higher masticatory efficiency. Further studies should be conducted.

Radial and longitudinal meniscus tears show different gapping patterns under stance phase conditions.

Meniscal tearing can increase the contact pressure between the tibia and femur by causing gapping of torn meniscus tissue. The aim of this study was to quantify gapping behavior of radial and longitudinal tears and their impact on peak contact pressure and mean contact area. Twelve porcine knee joints underwent unicondylar, convertible osteotomy for exact tear application and consecutive suturing. Six tantalum marker beads were positioned along meniscus tears. The joints were preloaded with sinusoidal loading cycles ranging between 0 N and 350 N. Peak load was held constant and two synchronized Roentgen stereophotogrammetric analysis x-ray images were obtained to evaluate gapping, peak contact pressure and mean contact area in the native, torn and repaired states. There was no change in gapping or peak contact pressure in longitudinal tear. By contrast, the radial tear led to a significant gapping when compared to the native state, while the inside-out suture was able to restore gapping in parts of the meniscus. An increase in contact pressure after radial tear was detected, which was again normalized after suturing. The most important finding of the study is that longitudinal tears did not gap under pure axial loading, whereas radial tears tended to separate the tear interfaces.

The Effects of Structural Characteristics of the Rollator on the Elderly’s Gait Strategies in Various Walking Environments

A rollator, one of the most widely used among walking assistance devices, can assist the elderly with stable walking in their daily lives. In this study, we investigated how the structural characteristics of two types of rollators affect the upper and lower extremity muscle activity and plantar pressure of the elderly in various walking environments. We quantified muscle activity (upper and lower limbs) and plantar pressure (mean force, peak pressure, and contact area) of 11 older adults walking in various environments (flat, obstacle, uneven, and sloped terrain) using two types of rollators. Upper extremity muscle activity was highest in the obstacle terrain and the uneven terrain, and a significant difference was found due to the structural differences of the rollator. Additionally, it was observed that lower extremity muscle activity and plantar pressure patterns appeared in accordance with the gait strategy to maintain stability in an unstable or inclined walking environment. In other words, it was confirmed that the weight of the rollator, the size of the wheel, grip type, and the auxiliary tools had a great effect on the upper and lower extremity muscle activity and plantar pressure of the elderly during walking. From the results of this study, it can be suggested that it is absolutely necessary to consider the biomechanical characteristics of the elderly and the structure of the rollator, which appear differently depending on the walking environment, in the development of walking aids. In the future, more clinical data will be collected, and based on this a rollator that can safely assist the elderly in various walking environments will be developed.

Comparison of interfragmentary compression across simulated condylar fractures repaired using four techniques.

Equine condylar fractures are commonly repaired using cortex screws applied in lag fashion. Inadequate interfragmentary compression can lead to post-operative complications. Lateral condylar fractures were simulated in 21 cadaver limbs (8 third metatarsals, 13 third metacarpals). In each limb, pressure-sensitive film (Prescale®, Fuji Photo Film Co.) was placed in each osteotomy prior to repair with 4.5 mm diameter cortex screws placed in lag fashion. Screws were placed in linear (L), triangular (T), linear plus a washer (LW) and sequentially tightened triangular configurations (TD1). All screws were tightened to a torque of 4 Nm. Pressure prints obtained were scanned using dedicated software (Fuji FPD-8010E, Fuji Photo Film Co.). A Bayesian Network (BN) model was developed to investigate the impact and interrelationship of each factor on interfragmentary compression. Sixty-three repairs (20*L, 24* T, 11*TD1, and 8*LW) performed on 21 limbs were included in the analysis. The BN predicted mean contact area (±s.d.) for pressures within the operating range of the prescale film [≥2.5 Megapascals (MPa) ≤ 10 MPa] by L, T, TD1 and LW repairs were 403mm2 ± (140), 411 mm2 ± (120), 403 mm2 ± (120), and 366mm2 ± (70). The mean contact area (± s.d.) created by L, T, TD1 and LW repairs at pressures >10 MPa were 112 mm2 ± (48), 167 mm2 ± (67), 142 mm2 ± (50), and 100mm2 ± (27). When pressures ≥2.5 MPA to ≤10 MPa were considered, the construct (T or L), washer and screw tightening sequence variables had a very low effect on interfragmentary contact area. At pressures >10 MPa BN sensitivity findings were 16.3, 5.03, and 0.133% for construct, washer and screw tightening sequence. The BN model indicated that triangular repair configuration had a weak influence in the ≥2.5 MPa ≤ 10 MPa range and a moderate influence in the <10 MPa range, on interfragmentary compression. The addition of a washer and the screw tightening sequence had a weak influence on interfragmentary compression at all pressure ranges. The results show that triangular repairs create larger interfragmentary contact areas at greater interfragmentary pressure in simulated condylar fractures, however it is unknown if this results in improved repair stability in the clinical scenario.

Biomechanical Analysis Evaluating Meniscal Extrusion After Knotless Suture Anchor Fixation for Segmental Medial Meniscal Allograft Transplantation.

Segmental medial meniscal allograft transplantation (MAT) has been shown to restore knee biomechanics; however, stable fixation of the transplantation is critical to avoid extrusion and maximize healing. To evaluate the degree of meniscal extrusion and biomechanical function of segmental medial MAT performed with meniscocapsular sutures versus repair augmentation with knotless suture anchors. Controlled laboratory study. Segmental midbody medial meniscectomy and subsequent segmental medial MAT were performed on 10 fresh-frozen cadaveric knees. The knees were then loaded in a dynamic tensile testing machine to 1000 N for 60 seconds at 0°, 30°, 60°, and 90° of flexion, and 4 conditions were tested: (1) intact, (2) segmental defect, (3) inside-out segmental repair, and (4) anchor plus inside-out segmental repair of the medial MAT. Meniscal extrusion was measured using high-fidelity ultrasound imaging. The mean contact area and the mean and peak contact pressures were assessed with submeniscal pressure-mapping sensors. Data from testing conditions were compared with 2-way repeated-measures analysis of variance, with pairwise comparison using the Bonferroni method. At 90° of flexion, the segmental defect state showed a higher degree of meniscal extrusion compared with all other states (P ≤ .012). There was no difference in the degree of meniscal extrusion between the intact state and the inside-out repair or anchor plus inside-out segmental repair states at all knee flexion angles (P > .05). There was no significant difference in the mean and peak contact pressures among the 4 states at all flexion angles except that at 0° of knee flexion there was significantly lower peak contact pressure at the medial compartment after anchor plus inside-out segmental repair compared with the segmental defect state (P = .048). Meniscal extrusion was not significantly increased at any flexion angle after segmental resection. The addition of knotless anchors did not improve meniscal extrusion or contact pressures/area compared with capsular repair alone. The addition of knotless anchors did improve contact mechanics from the segmental defect state, but only at 0° of flexion. The addition of knotless suture anchors to segmental meniscal transplantation increased stabilization of the meniscus at full extension compared with repair with sutures alone. This increased stabilization may lead to better long-term outcomes.

Poster 286: Biomechanical Analysis Evaluating Meniscal Extrusion Following Knotless Suture Anchor Fixation for Segmental Medial Meniscus Allograft Transplantation

Objectives: Segmental medial meniscus allograft transplantation (MAT) has been shown to restore knee biomechanics, however, stable fixation of the transplant is critical to avoid extrusion and maximize healing. The purpose of this study was to evaluate the degree of meniscal extrusion and biomechanical function of segmental MAT performed with meniscocapsular sutures versus repair augmentation with knotless suture anchors. Methods: Ten fresh frozen cadaveric knees underwent central midbody medial meniscectomy (15-mm defect) and subsequently segmental medial MAT. Knees were loaded in a dynamic tensile testing machine to 1000 N for 20 seconds at 0°, 30°, 60°, and 90° of flexion. Four conditions were tested: (1) intact, (2) segmental defect, (3) inside-out segmental repair, and (4) anchors plus inside-out segmental repair of the MAT. Meniscal extrusion was measured for each test state using high-fidelity ultrasound imaging by three independent observers. Submeniscal medial and lateral pressure-mapping sensors assessed the mean contact pressure, peak contact pressure, mean contact area, and pressure mapping. Assessment of inter- and intraobserver reliability of measurements were done using intraclass correlation coefficients. A two-way repeated measures ANOVA was computed in order to evaluate whether there is a significant interaction between meniscal states and knee flexion angles on the outcome variables. If the P value was ≤ 0.05, a pairwise comparison of the means was determined using the Bonferroni method. Results: At 0° of knee flexion, the segmental defect demonstrated the statistically significant higher degree of meniscal extrusion (2.08 mm ± 0.78 mm) compared with intact (1.02 mm ± 0.86 mm, P = 0.039) and anchor plus inside-out segmental repair (1.44 mm ± 0.76 mm, P = 0.044), but not for an inside-out segmental repair (1.55 mm ± 0.49 mm, P = 0.08). The segmental defect state also showed a higher degree of meniscal extrusion compared with all other states at 90° of knee flexion (P &lt; 0.01). There was no difference in the degree of meniscal extrusion between the intact state and the inside-out repair or anchor plus inside-out segmental repair in all knee flexion angles (P &gt; 0.05). Three observers showed good-to-strong intra-rater and moderate-to-strong inter-rater reliabilities for extrusion measurements. There was no significant difference in the mean contact pressure and peak contact pressure among four states in all knee flexion angles for both medial and lateral compartments except for that at 0° of knee flexion, there was a significantly lower peak pressure at the medial compartment after anchor plus inside-out segmental repair compared with the segmental defect state (P = 0.048). The medial contact area of the intact state was significantly higher than the other states at 0° of knee flexion (P &lt; 0.05). However, the lateral contact area after anchor plus inside-out repair showed no significant difference compared with the intact state (P = 0.13). Conclusions: Segmental meniscus transplantation mechanics may be improved at full extension (0° of knee flexion) with the addition of knotless anchors. However, in terms of meniscus extrusion, the knotless anchors provided limited benefit over inside-out repair. Overall, a robust repair is achieved of a segmental meniscus with sutures and knotless anchors. Although, additional work is needed to assess long-term in vivo results.

Paper 23: Taking the Load Off: Effect of Varus Producing Distal Femoral Osteotomy and High Tibial Osteotomy on Compartment Pressures and Contact Area in Varying Stages of Knee Flexion

Objectives: Study Objective: Evaluate mean contact area, mean contact pressure, and peak contact pressure in the medial and lateral compartment of the knee following varus producing high tibial osteotomy and distal femoral osteotomy in varying states of knee flexion (0*, 30*, 60*, 90*). Background: Genu valgum causes mechanical pressure to be transferred to the lateral compartment. In patients with valgus alignment and a diseased lateral compartment, both lateral opening wedge distal femoral osteotomy (DFO) and high tibial closing wedge osteotomy (HTO) can be used to unload a diseased lateral compartment of the knee. To the best of our knowledge, there are no biomechanical studies investigating how a DFO and HTO affect lateral compartment contact pressure and area in varying states of flexion. Prior anatomic studies have shown that, in valgus knees, the tibial wear is posterior. Additional, biomechanical studies have indicated that DFO exerts the greatest effect in full extension but it’s effect is decreased as flexion angle rises. Hypothesis: Medial closing wedge high tibial osteotomy will significantly decrease contact area, mean contact pressure and peak contact pressure in the lateral knee compartment through knee flexion to a greater extent compared to lateral opening wedge distal femoral osteotomy. Methods: Lateral opening wedge DFO and medial closing wedge HTO was performed, correcting a mean of 8°, in 10 cadaveric knees using plate fixation. Tibio- femoral contact pressure of the medial and lateral compartment was measured in 0°, 30°, 60°, and 90° of knee flexion before and after osteotomy using thin electronic sensors (K-scan Model 4000, 1500 psi; Tekscan Inc, South Boston, MA) and load applied through an Instron device (Instron, Norwood, MA). Peak contact pressure (PCP), average contact pressure (ACP), and contact area (CA) were measured for each condition. Mixed-effects regression analyses were used to compare the change in variables before and after osteotomy and between flexion angles. Results: The lateral ACP was significantly decreased in the HTO state when compared to native in 30° (p=0.015), 60° (p=0.0199), and 90° (p&lt;0.0001) of flexion. The lateral ACP was also significantly decreased in the HTO state when compared to the DFO state in 60° (p=0.0093) and 90° of flexion (p&lt;0.0001). Following DFO, the lateral ACP returned to that of the native state in 60° (p=1.000) and 90° (p=1.000) of flexion. The medial ACP was significantly increased when compared to both the native and HTO state in 60° (p&lt;0.001; p=0.015) and 90° (p&lt;0.0001; p=0.0435) of flexion. Conclusions: With varus corrections of &lt;10°, medial closing HTO is more effective at unloading the lateral compartment than lateral opening DFO. This effect is amplified as the knee flexion angle increases.

Effects of Lateral Opening-Wedge Distal Femoral Osteotomy on Meniscal Allograft Transplantation: A Biomechanical Evaluation

Background: Lateral meniscal deficiency with valgus malalignment increases the rate of lateral compartment osteoarthritis. Lateral meniscal allograft transplantation (LMAT) with a concomitant varus-producing opening-wedge distal femoral osteotomy (DFO) is an option yet to be evaluated biomechanically. Purpose/Hypothesis: The purpose of this study was to clarify the biomechanical effects of the realignment procedure in the setting of LMAT. We hypothesized that (1) given the dependence of the lateral compartment on the lateral meniscus, a DFO and increasing degrees of varus would be insufficient to restore lateral compartment pressures to normal from a lateral meniscus-deficient state, and that (2) LMAT would restore lateral compartment pressures to the intact state while DFO would decrease lateral compartment pressures for any given state of the meniscus. Study Design: Controlled laboratory study. Methods: Ten cadaveric knees underwent opening-wedge varus-producing DFO secured by an external fixator. Anatomic alignment was standardized to 6° of mechanical valgus, and each joint was tested in full extension. Submeniscal placement of thin film pressure sensors allowed for the recording of contact pressure, peak contact pressure, and contact area. The specimens were loaded on a biaxial dynamic testing machine with loading angles between 9° valgus and 6° varus of mechanical alignment. Conditions tested included intact meniscus, meniscal deficiency, and meniscal transplantation. Results: Isolated varus-producing DFO to 6° in the meniscus-deficient state failed to restore joint pressures and contact areas to the intact state, with significant changes in mean contact pressure (175%), mean peak contact pressure (135%), and contact area (–41%) (all P &lt; .05 vs intact), while LMAT restored all outcome measures (all P &gt; .05 compared with intact). After LMAT, every additional 1° of DFO correction contributed to a decrease in the mean contact pressure, peak pressure, and contact area of 5.6% (–0.0479 N/mm2), 5.9% (–0.154 N/mm2), and 1.4% (–6.99 mm2) for the lateral compartment and 7.3% (+0.034 N/mm2), 12.6% (+0.160 N/mm2), and 4.3% (+20.53 mm2) for the medial compartment, respectively. Conclusion: Isolated DFO was inadequate to restore load distribution in meniscus-deficient knees, while concomitant LMAT restored near normal forces and improved the lateral compartment biomechanical profile. Clinical Relevance Our findings support the concomitant use of LMAT and varus-producing DFO in the setting of lateral meniscal deficiency with valgus malalignment. This study provides tools for the orthopaedic surgeon to individualize the correction for each patient.

Impact of Radiocapitellar Interposition Arthroplasty on Ulnohumeral Joint Biomechanics.

Radial head excision has been shown to increase contact pressures within the ulnohumeral joint. Radiocapitellar interposition arthroplasty with the use of a soft tissue graft is an alternative for the treatment of isolated radiocapitellar arthritis or with failure of radial head replacement. We investigated contact pressures and contact area within the ulnohumeral joint after radial head excision (RHE) compared to radiocapitellar interposition arthroplasty with dermal autograft (RCIA). Six fresh-frozen cadaver elbows were tested on a custom dynamic elbow frame. A pressure sensor was inserted into the intact elbow joint, and mean contact pressure, peak contact pressure, contact area, and force within the ulnohumeral joint were recorded at 0°, 30°, 60°, 90°, and 120° of flexion as a valgus load was applied to the elbow. The radial head was then excised and specimens were retested. Finally, a dermal graft matched to the size of the resected radial head was inserted in the radiocapitellar space and the specimens were tested a third time. At 90° of flexion, contact pressure within the ulnohumeral joint was significantly lower with RCIA compared with RHE (110.8 kPa vs. 216.8 kPa.; P = 0.013). Mean peak contact pressure was also significantly lower with RCIA compared with RHE at 90° (279.4 vs. 626.7 kPa; P =0.025). No statistically significant differences were seen in mean contact area or force between the three testing conditions at any flexion position. RCIA with a dermal graft reduced contact pressures within the ulnohumeral joint compared to radial head excision at 90° of flexion without a significant change in contact area or contact force.

Validity and reliability of the XSENSOR in-shoe pressure measurement system.

In-shoe pressure measurement systems are used in research and clinical practice to quantify areas and levels of pressure underfoot whilst shod. Their validity and reliability across different pressures, durations of load and contact areas determine their appropriateness to address different research questions or clinical assessments. XSENSOR is a relatively new pressure measurement device and warrants assessment. Does the XSENSOR in-shoe pressure measurement device have sufficient validity and reliability for clinical assessments in diabetes? Two XSENSOR insoles were examined across two days with two lab-based protocols to assess regional and whole insole loading. The whole insole protocol applied 50-600 kPa of pressure across the insole surface for 30 seconds and measured at 0, 2, 10 and 30 seconds. The regional protocol used two (3.14 and 15.9 cm2 surface area) cylinders to apply pressures of 50, 110 and 200 kPa to each insole. Three trials of all conditions were averaged. The validity (% difference and Root Mean Square Error: RMSE) and repeatability (Bland Altman, Intra-Class Correlation Coefficient: ICC) of the target pressures (whole insole) and contact area (regional) were outcome variables. Regional results demonstrated mean contact area errors of less than 1 cm2 for both insoles and high repeatability (≥0.939). Whole insole measurement error was higher at higher pressures but resulted in average peak and mean pressures error < 10%. Reliability error was 3-10% for peak pressure, within the 15% defined as an analytical goal. Errors associated with the quantification of pressure are low enough that they are unlikely to influence the assessments of interventions or screening of the at-risk-foot considering clinically relevant thresholds. Contact area is accurate due to a high spatial resolution and the repeatability of the XSENSOR system likely makes it appropriate for clinical applications that require multiple assessments.

Biomechanical Analysis of Posterior Open-Wedge Osteotomy and Glenoid Concavity Reconstruction Using an Implant-Free, J-Shaped Iliac Crest Bone Graft

Background: Posterior open-wedge osteotomy and glenoid reconstruction using a J-shaped iliac crest bone graft showed promising clinical results for the treatment of posterior instability with excessive glenoid retroversion and posteroinferior glenoid deficiency. Purpose: To evaluate the biomechanical performance of the posterior J-shaped graft to restore glenoid retroversion and posteroinferior deficiency in a cadaveric shoulder instability model. Study Design: Controlled laboratory study. Methods: A posterior glenoid open-wedge osteotomy was performed in 6 fresh-frozen shoulders, allowing the glenoid retroversion to be set at 0°, 10°, and 20°. At each of these 3 preset angles of glenoid retroversion, the following conditions were simulated: (1) intact joint, (2) posterior Bankart lesion, (3) 20% posteroinferior glenoid deficiency, and (4) posterior J-shaped graft (at 0° of retroversion). With the humerus in the Jerk position (60° of glenohumeral anteflexion, 60° of internal rotation), stability was evaluated by measuring posterior humeral head (HH) translation (in mm) and peak translational force (in N) to translate the HH over 25% of the glenoid width. Glenohumeral contact patterns were measured using pressure-sensitive sensors. Fixation of the posterior J-graft was analyzed by recording graft micromovements during 3000 cycles of 5-mm anteroposterior HH translations. Results: Reconstructing the glenoid with a posterior J-graft to 0° of retroversion significantly increased stability compared with a posterior Bankart lesion and posteroinferior glenoid deficiency in all 3 preset degrees of retroversion (P < .05). There was no significant difference in joint stability comparing the posterior J-graft with an intact joint at 0° of retroversion. The posterior J-graft restored mean contact area and contact pressure comparable with that of the intact condition with 0° of retroversion (222 vs 223 mm2, P = .980; and 0.450 vs 0.550 MPa, P = .203). The mean total graft displacement after 3000 cycles of loading was 43 ± 84 µm, and the mean maximal mediolateral graft bending was 508 ± 488 µm. Conclusion: Biomechanical analysis of the posterior J-graft demonstrated reliable restoration of initial glenohumeral joint stability, normalization of contact patterns comparable with that of an intact shoulder joint with neutral retroversion, and secure initial graft fixation in the cadaveric model. Clinical Relevance: This study confirms that the posterior J-graft can restore stability and glenohumeral loading conditions comparable with those of an intact shoulder.

Transtibial Repair of Lateral Meniscus Posterior Root Tears Improves Contact Biomechanics in Pediatric Cadavers

A paucity of data exists on the treatment of pediatric lateral meniscus root tears (LMPRTs). This study aims to characterize the biomechanics of the lateral knee joint in pediatric cadavers following LMPRT and root repair. Our hypotheses were: (1) compared with the intact state, LMPRT would be associated with decreased contact area; (2) compared with the intact state, LMPRT would be associated with increased contact pressures; and (3) compared with LMPRT, root repair would restore contact area and pressures toward intact meniscus values. Eight cadaver knees (ages 8-12 years) underwent contact area and pressure testing of the lateral compartment. Tekscan pressure mapping sensors covering the tibial plateau were inserted underneath the lateral meniscus. Appropriate pressure load equivalents were applied by a robot at degrees of flexion: 0, 30, 60. Three meniscus conditions were tested: (1) intact, (2) complete root tear, and (3) repaired root tear. Root repairs were performed with transtibial pullout sutures. Statistical analysis was performed. Root tear significantly decreased mean contact area at 30° (P= .0279) and 60° (P= .0397). Root repair increased mean contact area and did not significantly differ from intact states. Differences in contact pressures between meniscus states were not statistically significant. Relative to the intact state. the greatest increase in contact pressures occurred between 0° and 30°. Root repair decreased mean contact pressures at 0° and 30°. At 60°, mean contact pressures of the repair state were closer in magnitude to the tear state than the intact state. Conclusions: LMPRT decreases contact area and increases contact pressures in the lateral knee compartment. Repair of LMPRT improves tibiofemoral contact area at high (>30°) degrees of flexion and contact pressures at low (<30°) degrees of flexion. Transosseous pullout repair is a clinically validated treatment for LMPRT. This study provides baseline biomechanics data of transtibial pullout repair of pediatric LMPRTs.

Evaluation of the contact surface between vertebral endplate and 3D printed patient-specific cage vs commercial cage

Biomechanical study. To evaluate the performance of the contact surface for 3D printed patient-specific cages using CT-scan 3D endplate reconstructions in comparison to the contact surface of commercial cages. Previous strategies to improve the surface of contact between the device and the endplate have been employed to attenuate the risk of cage subsidence. Patient-specific cages have been used to help, but only finite-element studies have evaluated the effectiveness of this approach. There is a possible mismatch between the CT-scan endplate image used to generate the cage and the real bony endplate anatomy that could limit the performance of the cages. A cadaveric model is used to investigate the possible mismatch between 3D printed patient-specific cages and the endplate and compare them to commercially available cages (Medtronic Fuse and Capstone). Contact area and contact stress were used as outcomes. When PS cage was compared to the Capstone cage, the mean contact area obtained was 100 ± 23.6 mm2 and 57.5 ± 13.7 mm2, respectively (p < 0.001). When compared to the Fuse cage, the mean contact area was 104.8 ± 39.6 mm2 and 55.2 ± 35.1 mm2, respectively(p < 0.001). Patient-specific cages improve the contact area between the implant and the endplate surface, reducing the contact stress and the risk of implant subsidence during LIF surgeries.

Effect of modeling femoral version and head-neck offset correction on computed contact mechanics in dysplastic hips treated with periacetabular osteotomy

While correction of dysplastic acetabular deformity has been a focus of both clinical treatment and research, concurrent femoral deformities have only more recently received serious attention. The purpose of this study was to determine how including abnormalities in femoral head-neck offset and femoral version alter computationally derived contact stresses in patients with combined dysplasia and femoroacetabular impingement (FAI). Hip models with patient-specific bony anatomy were created from preoperative and postoperative CT scans of 20 hips treated with periacetabular osteotomy and femoral osteochondroplasty. To simulate performing only a PAO, a third model was created combining each patient’s postoperative pelvis and preoperative femur geometry. These three models were initialized with the femur in two starting orientations: (1) standardized template orientation, and (2) using patient-specific anatomic landmarks. Hip contact stresses were computed in all 6 model sets during an average dysplastic gait cycle, an average FAI gait cycle, and an average stand-to-sit activity using discrete element analysis. No significant differences in peak contact stress (p = 0.190 to 1), mean contact stress (p = 0.273 to 1), or mean contact area (p = 0.050 to 1) were identified during any loading activity based on femoral alignment technique or inclusion of femoral osteochondroplasty. These findings suggest that presence of abnormal femoral version and/or head-neck offset deformities are not themselves predominant factors in intra-articular contact mechanics during gait and stand-to-sit activities. Inclusion of modified movement patterns caused by these femoral deformities may be necessary for models to adequately capture the mechanical effects of these clinically recognized risk factors for negative outcomes.

Morphological Dynamics of Leukemia Cells on TiO2 Nanoparticle Coatings Studied by AFM

Coatings of modified TiO2 nanoparticles (TiO2-m) have been shown to effectively and selectively trap non-adherent cancer cells, with an enormous potential for applications in photodynamic therapy (PDT). Leukemia cells have a remarkable affinity for TiO2-m coatings, adhering to the surface by membrane structures and exhibiting morphologic characteristics of amoeboid locomotion. However, the details of the cell–substrate interaction induced by the TiO2-m coating remain elusive. With the aim to obtain a better understanding of this phenomenon, leukemia cell adhesion to such coatings was characterized by atomic force microscopy (AFM) for short contact times up to 60 min. The cell and membrane morphological parameters mean cell height, contact area, cell volume, and membrane roughness were determined at different contact times. These results reveal cell expansion and contraction phases occurring during the initial stage of adhesion. Subsequently, the leukemic cells reach what appears to be a new resting state, characterized by pinning of the cell membrane by TiO2-m nanoparticle aggregates protruding from the coating surface.