Results of Cemented vs Cementless Primary Total Knee Arthroplasty Using the Same Implant Design

Background

Although cemented total knee arthroplasty (TKA) continues to be the gold standard, there are patient populations with higher failure rates with cemented TKAs such as the obese, morbidly obese, and younger active males. Cementless TKA usage continues to increase because of the potential benefits of long-term biologic fixation similar to the rise in cementless total hip arthroplasty. The purpose of this study was to evaluate the clinical and radiographic results of cementless TKA using a novel highly porous cementless tibial baseplate.

Micromotion Analysis of Various Tibial Constructs in Moderate Tibial Defects in Revision Total Knee Arthroplasty

BackgroundThe purpose of this study is to compare the micromotion of various tibial reconstruction strategies including short cemented and long cementless stems with or without metaphyseal augmentation.MethodsA moderate tibial bone defect was milled into dual density polyurethane test blocks. Mechanical testing was performed on 4 test constructs: (1) short cemented stem (75-mm total length) alone; (2) short cemented stem with a symmetric metaphyseal cone; (3) a press-fit (175-mm total length) diaphyseal engaging tibial construct without a cone, and (4) the same press-fit tibial construct with a metaphyseal cone augment. Micromotion of the baseplate/cone construct with respect to the tibia block was measured during a stair descent loading profile for 10,000 cycles. The peak-to-peak micromotion of these various tibial constructs was compared. Unpaired t-tests were used to evaluate differences in peak-to-peak micromotion among the various tibial constructs tested. An analysis of variance was performed for final validation.ResultsThe cemented short stem demonstrated similar varus/valgus displacement, internal/external rotation, compression, and lift-off micromotion values under loading compared to a cementless long stem. A tibial cone improved compression and lift-off micromotion for both cemented and cementless constructs. A short 50-mm cemented stem with a cone demonstrated a lower micromotion at the anterior SI location compared to a press-fit 150-mm cementless stem without a tibial cone.ConclusionsA short cemented tibial component with a cone achieved similar micromotion during simulated stair descent compared to a cementless diaphyseal press-fit implant in cases of moderate tibial defects     

Initial Stability of Cemented vs Cementless Tibial Components Under Cyclic Load

Background

Cement fixation of total knee components remains the gold standard despite resurgence in cementless fixation with the goal of long-term durable fixation. Initial stability is paramount to achieve bony ingrowth of cementless components.

A Biomechanical Comparison of the Effect of Baseplate Design and Bone Marrow Fat Infiltration on Tibial Baseplate Pullout Strength

BackgroundEarly clinical results of a new total knee arthroplasty (TKA) implant design show promise for improved outcomes and patellofemoral function scores. However, reports of early tibial component-cement interface debonding requiring revision have been published. This study investigated the biomechanical properties of three different tibial baseplates to understand potential causes of failure.MethodsPFC Sigma (control), Attune (1st generation) and Attune S+ (2nd generation) tibial baseplates were implanted into 4th generation sawbone tibia models using a standardized technique. Three of each baseplate were cemented with and without additional bovine bone marrow fat. All models were tested to failure with measured axial distraction force. Implant type, presence or absence of bovine marrow and load to failure were all recorded and compared. Two-way ANOVA followed by post-hoc pairwise comparisons were used to determine statistical significance, which was set to P < .05.ResultsThe 2nd generation tibial baseplates required significantly more force to failure. The presence of bovine marrow significantly reduced the pullout force of the implant designs overall. No significant difference was detected between the 1st generation and control baseplates. Failure mode for each model was also noted to be different irrespective of the presence or absence of bone marrow fat.ConclusionThe 2nd generation baseplates required significantly more force to failure compared with older designs. The presence of bone marrow during cementation of a tibial base plate significantly decreased axial pullout strength of a tibial baseplate in this laboratory model. All 1st generation baseplates exhibited debonding at the cement-implant interface.     

Computed tomography–based three-dimensional modeling of glenoid bone preservation with augmented baseplates

BackgroundReverse total shoulder arthroplasty (rTSA) is a treatment option for a variety of shoulder pathologies, including rotator cuff arthropathy, glenohumeral arthritis, and irreparable rotator cuff tears and fractures. There has been substantial improvement in rTSA implants and surgical techniques, such as augmented baseplates that preserve bone tissue. In this study, we used three-dimensional modeling to determine the extent of bone preservation with augmented baseplates in rTSA.MethodsComputed tomography scans from 50 consecutive patients before they underwent rTSA were used to create three-dimensional models of each glenoid. The virtual positions of reverse shoulder baseplate implants followed strict parameters for adequate fixation as determined through consensus among 4 fellowship-trained shoulder specialists. Parameters for adequate fixations included 100% backside contact, neutral scapular version, and 10° of inferior tilt. The 4 baseplate options trialed on each glenoid were a nonaugmented baseplate, a small 10° half-wedge augment, a medium 20° half-wedge augment, and a large 30° half-wedge augment. The extent of volumetric glenoid bone removal and lateralization of the baseplate was calculated for each scenario.ResultsPreoperative computed tomography imaging showed a mean of 10.7° of retroversion and a reverse shoulder arthroplasty angle of 21.3°. A medium augment (20° half wedge) was determined as optimal in 29 cases, and a large augment (30° half wedge) was considered optimal for the remaining 21 cases. The use of augmented baseplates was calculated to preserve 54% glenoid bone stock (1989 ± 650 mm³ bone removal vs. 4439 ± 1636 mm³ with nonaugmented baseplate; P < .001). The surgeon-selected augmented baseplate was on average 4.1 mm lateral in comparison to the nonaugmented baseplate.ConclusionsThe use of augmented baseplates reduces the volume of bone that needs to be removed in rTSA. Furthermore, augmented baseplates result in relative lateralization of the glenosphere, which has been theorized to improve soft tissue tension and limit impingement and scapular notching. Further exploration of the impact of augmented baseplates on clinical outcomes is needed.     

Undersizing the Tibial Baseplate in Cementless Total Knee Arthroplasty has Only a Small Impact on Bone-Implant Interaction: A Finite Element Biomechanical Study

BackgroundThe tibial component in total knee arthroplasty (TKA) is often chosen to maximize coverage of the tibial cut, which can result in excessive internal rotation of the component. Optimal rotational alignment may require a smaller baseplate with suboptimal coverage that could threaten fixation. We asked: “does undersizing the tibial component of a cementless TKA to gain external rotation increase the risk of bone failure?”MethodsWe developed computational finite element (FE) analysis models from the computed tomography (CT) scans of 12 patients scheduled for primary TKA. The models were implanted with a cementless tibial baseplate that maximized coverage and one or two sizes smaller and externally rotated by 5°. We calculated the risk of bone collapse under loads representative of stair ascent.ResultsUndersizing the implant increased the area at risk of collapse for eight patients. However, the area at risk of collapse for the undersized implant (range, 5.2%-16.4%) was no different (P = .24) to the optimally sized implant (range, 4.5%-17.9%). The bone at risk of collapse was concentrated along the posterior edge of the implant. The area at risk of collapse was not proportional to implant size, and for four subjects undersizing the implant actually decreased the area at risk of collapse.ConclusionWhile implants should maximize coverage of the tibial cut and seek support on dense bone, undersizing the tibial component to gain external rotation had minimal impact on the load transfer to the underlying bone. This FE analysis model of a cementless tibial baseplate may require further validation and additional studies to investigate the long-term biomechanical effects of undersizing the tibial baseplate. In conclusion, while surgeons should strive to use the appropriate tibial baseplate for each patient, our model identified only minor biomechanical consequences of undersizing the implant for the immediate postoperative bone-implant interaction and implant subsidence.     

Metaphyseal Stem Extension Improves Tibial Stability in Cementless Total Knee Arthroplasty

BackgroundThe goal was to determine if the addition of a metaphyseal stem extension limits micromotion of a cementless tibial component during cyclic loading in primary total knee arthroplasty. The hypothesis tested was that the use of a 50-mm stem extension on a cementless tibial component would limit motion compared with an identical cementless component without a stem extension.MethodsThe study used 3 variations of a tibial component from the same total knee arthroplasty system. Group 1 consisted of a cementless tibial component without a stem extension. Group 2 used the same cementless component as group 1, but with the addition of a short 50-mm stem. Group 3 consisted of a cemented tibial component without a stem extension to serve as a “control” (gold standard). The tibial specimens were implanted into a synthetic bone model and tested using a physiological medial-lateral 60/40 load distribution for 5000 cycles.ResultsThe results demonstrated a significant decrease in motion at the anterior region of the cementless stem extension (group 2) components compared with the cementless with no stem extension (group 1). The cementless with stem extension (group 2) demonstrated similar results at all cycles to the cemented (group 3) components at the anterior region.ConclusionThe addition of a short metaphyseal stem (50mm) to a keel plus 4-peg tibial component design provides a significant reduction in micromotion during cyclic loading of a cementless tibial baseplate in a synthetic foam bone model, similar to a cemented implant.     

Retrospective Evaluation of the Duracon Periapatite-Coated Tibial Tray : Midterm Results and Factors Affecting Success

This study reports the retrospective radiographic outcome of a series of 63 consecutive total knee arthroplasties using an uncemented hydroxyapatite-coated Duracon cruciate-retaining tibial baseplate (Stryker Howmedica Osteonics Corp, Mahwah, NJ). Sixty-three knees were assessed at a mean follow-up of 65 months. The knees were primarily diagnosed with osteoarthritis with a mean age of 61 years. Radiographic analysis showed 6 knees with tibial baseplate radiolucencies, with all of these resolving or improving over the course of the study. All tibial baseplates were implanted with the concomitant use of autologous bone slurry. There were no reoperations for aseptic loosening, fracture, or patellofemoral problems. This intermediate study demonstrates excellent radiographic outcomes for uncemented hydroxyapatite-coated Duracon cruciate-retaining tibial baseplates and evaluates other factors felt to be important in the success of a cementless implant.     

Micromotion of Cementless Tibial Baseplates: Keels with Adjuvant Pegs Offer More Stability Than Pegs Alone

Initial implant stability is crucial to cementless knee arthroplasty fixation. The objective of this study was to evaluate the stability of two baseplates with different fixation features: a monoblock porous tantalum baseplate featuring two hexagonal pegs alone, and a modular design featuring a keel with four adjuvant cruciform pegs. A physiologically relevant test method previously described was used to evaluate compression and liftoff of the baseplates during stair descent. The porous tantalum baseplate with dual-hex peg fixation experienced greater rocking motions and liftoff compared to the baseplate with a keel and adjuvant pegs. Liftoff and displacement motion is likely deleterious and may inhibit biological fixation due to the physical separation of the baseplate from the bone.     

Correcting retroversion during reverse shoulder arthroplasty for B2 glenoids leads to medialization and worsens impingement on the scapular neck

BackgroundReverse shoulder arthroplasty (RSA) is a viable option for posteriorly-eroded B2 glenoids. But little is known in this setting about the effect of baseplate version on impingement on the scapular neck, which affects the risk of notching, the risk of impingement-related instability, and the passive range of motion (ROM). Correcting retroversion with eccentric reaming leads to medialization to achieve full support of the baseplate, bringing the humerus closer to the scapula and potentially increasing impingement on the scapular neck. We hypothesized that correcting retroversion in B2 glenoids would result in increased medialization and worse impingement on the scapular neck.MethodsTen patients with Walch B2 glenoids underwent a simulated RSA. For each patient, a 25 mm baseplate was digitally implanted along the inferior margin of the glenoid, centered anterior-to-posterior, in 0˚ of inclination, with 100% backside contact, with a 36 mm glenosphere and 145˚ neck-shaft angle. Impingement-free ROM was then simulated with 17 different implant arrangements: baseplate version of P (the pathologic version), −15˚, -10˚, −5˚, 0˚, and baseplate lateralization +0, +3mm, +6mm. Two additional simulations consisted of half-wedge baseplates seated at the best fit (matching the paleoglenoid) and 0˚ version. The primary endpoint was external rotation at the side (ERS), based on in-vivo analyses that reveal this as the primary mode of notching and impingement-related instability. Data was analyzed using paired t-test, analysis of variance (ANOVA), and a multivariable regression analysis.ResultsIn every simulation in every patient, correcting retroversion worsened scapular neck impingement with ERS, the primary mode of notching and impingement-related instability. Overall, implantation in retroversion led to 33% more ERS (P = .02). The magnitude of this effect was much greater with medialized glenoids: 100% more ERS for +0 baseplates and 23% more ERS for +6 (P = .008). Half-wedge baseplates resulted in more ERS than +0 baseplates: 2.3x more at 0˚ version (P = .02). Any correction of version resulted in increased medialization (all P < .01), which led to worse scapular neck impingement. Multiple linear regression analysis showed that baseplate lateralization has the most impact on scapular neck impingement (β = 0.640; P < .001).ConclusionIn B2 glenoids undergoing RSA, correcting the glenoid retroversion with eccentric reaming results in significantly more medialization, worsening scapular neck impingement with ERS. This can increase the risk of notching, may lead to impingement-related instability, and decreases passive ERS.Level of evidenceClinical science study     

Load Redistribution in Variable Position Wheelchairs in People With Spinal Cord Injury

Abstract

Background/Objective: Tilt and recline variable position seating systems are most commonly used for pressure relief to decrease potential for skin breakdown. This study provides quantitative information on the magnitudes of loading on the seat and back during phases of tilt, recline, and standing. The objective of this study was to show that the amount of force reduction at the seat would differ across these 3 methods within their respective clinical ranges.

Participants: Six able-bodied (AB) subjects (2 men, 4 women) with a median age of 25 years, and 10 subjects (8 men, 2 women) with spinal cord injury (SCI) with a median age of 35.5 years.

Methods: Subjects sat on a power wheelchair with Tekscan pressure mats placed underneath a foam backrest and cushion. Data were collected at 5 positions for each method. Order of position and method tested were randomized. Linear regressions were used to calculate the relationships of normalized seat and backrest forces to seat and backrest angles for each chair configuration.

Results: Normalized seat loads had strong linear relationships with the angles of change in tilt, recline, and standing for both groups. Maximum decreases in seat load occurred at full standing and full recline in the SCI subjects and in full standing in the AB subjects. Loads linearly increased on the back during tilt and recline and linearly decreased during standing for both groups.

Conclusions: Standing and recline offered similar seat load reductions at their respective terminal positions. Standing also reduced loading on the backrest. Recognizing that each method had clinical benefits and drawbacks, the results of this study indicate that tilt, recline, and standing systems should be considered as a means of weight shifting for wheelchair users.     

Accuracy and precision of placement of the glenoid baseplate in reverse total shoulder arthroplasty using a novel computer assisted navigation system combined with preoperative planning: A controlled cadaveric study

HypothesisRTSA glenoid baseplates will be placed more accurately and precisely with the use of preoperative planning and computer navigation compared to the use of preoperative planning and conventional freehand instrumentation alone.Material and methodsFive fellowship trained surgeons preoperatively planned 30 cadaveric scapulae (15 side matched pairs) for an RTSA baseplate using preoperative CT scans and a custom 3D templating software. The specimens were randomized with respect to side and were split into two equal cohorts. One cohort used preoperative planning and conventional freehand instrumentation to implant the baseplate, and the other cohort used preoperative planning and a CT based navigation system to implant the baseplate. Postoperative CT scans were taken, and accuracy and precision for baseplate position and angulation with respect to the preoperative plan was compared for both groups.ResultsGlenoid baseplates placed using the navigation system demonstrated significantly improved accuracy and precision of positioning, based on the preoperative plan, than those placed using conventional freehand instrumentation without navigation for version (1.9 ± 1.9° vs 5.9 ± 3.5°; P = 0.004) and inclination (2.4 ± 2.4° vs 6.3 ± 6.2°; P = 0.026), with a post hoc power > 95% (α = 0.05). No significant difference was noted for anterior/posterior (AP) positioning, superior/inferior (SI) positioning, and reaming depth. A lower standard deviation was observed for AP positioning in the navigated cohort (0.6 mm vs 1.3 mm; P = 0.017).ConclusionPreoperative planning combined with the navigation system used in this side matched pair cadaveric study is more accurate and precise in achieving the desired version and inclination of the glenoid baseplate in RTSA compared to preoperative planning combined with conventional freehand instrumentation alone. The system may offer less benefit improving AP or SI placement as well as reaming depth.     

Dynamic RSA for the evaluation of inducible micromotion of Oxford UKA during step-up and step-down motion

Background and purpose — Implant inducible micromotions have been suggested to reflect the quality of the fixation interface. We investigated the usability of dynamic RSA for evaluation of inducible micromotions of the Oxford Unicompartmental Knee Arthroplasty (UKA) tibial component, and evaluated factors that have been suggested to compromise the fixation, such as fixation method, component alignment, and radiolucent lines (RLLs).

Patients and methods — 15 patients (12 men) with a mean age of 69 (55–86) years, with an Oxford UKA (7 cemented), were studied after a mean time in situ of 4.4 (3.6–5.1) years. 4 had tibial RLLs. Each patient was recorded with dynamic RSA (10 frames/second) during a step-up/step-down motion. Inducible micromotions were calculated for the tibial component with respect to the tibia bone. Postoperative component alignment was measured with model-based RSA and RLLs were measured on screened radiographs.

Results — All tibial components showed inducible micromotions as a function of the step-cycle motion with a mean subsidence of up to ?0.06?mm (95% CI: ?0.10 to ?0.03). Tibial component inducible micromotions were similar for cemented fixation and cementless fixation. Patients with tibial RLLs had 0.5° (95% CI: 0.18–0.81) greater inducible medio-lateral tilt of the tibial component. There was a correlation between postoperative posterior slope of the tibial plateau and inducible anterior-posterior tilt.

Interpretation — All patients had inducible micromotions of the tibial component during step-cycle motion. RLLs and a high posterior slope increased the magnitude of inducible micromotions. This suggests that dynamic RSA is a valuable clinical tool for the evaluation of functional implant fixation.     

Contact Kinematics Correlates to Tibial Component Migration Following Single Radius Posterior Stabilized Knee Replacement

Background

Contact kinematics between total knee arthroplasty components is thought to affect implant migration; however, the interaction between kinematics and tibial component migration has not been thoroughly examined in a modern implant system.

Bone Mineral Density and Cortical-Bone Thickness of the Distal Radius Predict Femoral Stem Subsidence in Postmenopausal Women

BackgroundThe distal radius is an optional site for evaluation of bone quality in postmenopausal women before cementless total hip arthroplasty. We hypothesized that dual-energy X-ray absorptiometry (DXA) and pulse-echo ultrasonometry of the distal radius may help discriminate subjects at high risk of femoral stem subsidence.MethodsA prospective cohort of postmenopausal women with primary hip osteoarthritis underwent total hip arthroplasty with implantation of a parallel-sided femoral stem. Postoperative stem migration was measured using radiostereometric analysis. Preoperatively, subjects had multisite DXA measurement of bone mineral density (BMD) and pulse-echo ultrasonometry of the cortical-bone thickness. The diagnostic abilities of these methods to discriminate <2 mm and ≥2 mm femoral stem subsidence were tested.ResultsThe accuracy of the distal radius BMD and cortical-bone thickness of the distal radius were moderate (area under the curve, 0.737 and 0.726, respectively) in discriminating between <2 mm and ≥2 mm stem subsidence. Women with low cortical-bone thickness of the radius were more likely (odds ratio = 6.7; P = .002) to develop stem subsidence ≥2 mm. These subjects had lower total hip BMD (P = .007) and reduced thickness of the medial cortex of the proximal femur (P = .048) with lower middle (P < .001) and distal (P = .004) stem-to-canal fill ratios.ConclusionFemoral stem stability and resistance to subsidence are sensitive to adequate bone stock and unaltered anatomy. DXA and pulse-echo ultrasonometry of the distal radius may help discriminate postmenopausal women at high risk of stem subsidence.     

Tibial interface wear in retrieved total knee components and correlations with modular insert motion

BACKGROUND: Wear occurring at the interface between the polyethylene insert and metal baseplate of a modular tibial component has become an increasingly common finding at the time of revision total knee arthroplasty. Although this so-called backside wear on retrieved polyethylene inserts has been evaluated in prior studies, wear on retrieved metal baseplates has not been described, to our knowledge. The purposes of the present study were to characterize backside wear on retrieved polyethylene inserts and on the mating surfaces of their corresponding baseplates and to investigate if there is a relationship between backside wear and relative motion of the modular elements. METHODS: Twenty-nine retrieved modular tibial components of twelve fixed-bearing designs were analyzed in vitro with regard to backside wear and relative motion between the polyethylene insert and the metal baseplate. We graded the backside of each polyethylene insert and the mating surface of the metal baseplate for wear with use of a scoring system that consisted of three modes of wear and three levels of severity of wear. Relative motion between the insert and the baseplate was measured in the transverse plane with use of a mechanical testing machine. These measurements were used to compute the insert motion index, which served to quantify unrestricted motion of the insert with respect to the baseplate. RESULTS: The mean insert motion index for the tibial components was 416 micro m (range, 104 micro m to 760 micro m). On a wear-grading scale ranging from 0 to 54 (with 0 indicating no wear), the mean backside wear score was 30 (range, 12 to 48) for the inserts and 28 (range, 7 to 51) for the baseplates. Insert motion was positively correlated with backside polyethylene wear (p = 0.003) and baseplate wear (p < 0.001). Baseplate wear was strongly correlated with backside polyethylene wear (p < 0.001). CONCLUSIONS: Backside wear was correlated with the relative motion between the polyethylene insert and the metal baseplate. New locking mechanism designs directed toward better methods of securing the polyethylene insert to the tibial tray are needed to minimize the generation of particulate wear debris at the modular interface.     

The effect of a tibial baseplate undersurface peripheral lip on cement penetration in total knee arthroplasty

Many total knee arthroplasty (TKA) tibial baseplates have a peripheral lip or cement pocket theoretically to increase cement penetration by decreasing edge escape of the cement squeeze film on baseplate impaction. We reviewed 177 consecutive TKAs (89 nonlipped and 87 lipped baseplates) performed by a single surgeon, using the same third-generation tibial cementation techniques. Cement penetration patterns of the lateral 12 mm of proximal tibia were examined by a semiautomatic computerized digital image analysis technique. Penetration in the lipped baseplate was double that of the nonlipped baseplate at the component's lateral edge (P<.05) and continued to be statistically significantly greater to 4 mm from edge. From 5 to 7 mm, the difference was no longer statistically significant, and from 8 to 12 mm, the penetration was equal.     

How Flat Is the Tibial Osteotomy in Total Knee Arthroplasty?

BackgroundCementless total knee arthroplasty has been developed to decrease the incidence of failure in younger and more active patients. However, failures are still more common in cementless versus cemented components. It is hypothesized that this is triggered by incomplete bone-tray contact. The present study compares the final contact area of a cementless tray as a function of the initial osteotomy flatness.MethodsEight surgeons prepared 14 cadaveric knees for cementless total knee replacement using standard instrumentation. The topography of each osteotomy was captured with a laser scanner; 3-dimensional computer models of the surfaces were generated. After scanning each tibia, the surgeons implanted cementless tibial trays using a manual impactor. Each tibia was then dissected, embedded in mounting resin, and sectioned. The sectioned blocks were observed under stereomicroscopy to identify points of bone-tray contact which were incorporated into the 3-dimensional models. Maps were then generated illustrating depicting contacting and noncontacting areas.ResultsThe mean initial flatness of all specimens was 1.1 ± 0.35 mm. After impaction, 79.4% ± 0.3% of the surface had established bony contact. Of the noncontacting areas, 17.6% were within 0.3 mm of the tray. Only 2.6% of the surface was at distances reported to impede ingrowth. Noncontacting areas were typically located centrally. A trend in decreasing percent contact area with increased flatness tolerance was observed (R² = 0.605).Conclusion(1) There is an inverse correlation between the flatness of the tibial osteotomy and the percentage of the bony surface in contact with underside of the tibial tray. (2) Almost all tray-tibia contact is generated during implantation through flattening of elevated features on the tibial surface. (3) Gaps between the tray and the tibia are consistently located in the central regions of the osteotomy proximal to the medullary canal.     

Change in Acetabular Cup Orientation From Supine to Standing Position and Its Effect on Wear of Highly Crosslinked Polyethylene

Background

The purpose of this study is to measure acetabular cup position and wear of the highly crosslinked polyethylene liner in the supine and standing position for patients at a minimum of 10 years after the operation.

Comparison of each bundle of the spring ligament complex between the standing and supine positions: A multiposture magnetic resonance imaging study

BackgroundThe spring ligament complex (SLC) supports the medial longitudinal arch of the foot, particularly in standing. We evaluated posture-related changes in the thickness and length of the three SLC bundles and their histology.MethodsThe thickness and length of the supramedial calcaneonavicular ligament (smCNL), medioplantar oblique calcaneonavicular ligament (mpoCNL), and inferoplantar calcaneonavicular ligament (iplCNL) were measured in the supine and standing positions, using a multiposture magnetic resonance imaging system, in 72 healthy adult feet. Histological examination was performed for 10 feet from five cadavers.ResultsThe smCNL thickness decreased and its length increased from the supine to the standing position (P < 0.001); no other posture-related effects were noted. Histologically, smCNL fibers overlapped along multiple directions while mpoCNL and iplCNL, fibers were oriented horizontally along the longitudinal axis and vertically along the short axis, respectively.ConclusionThe complex, multidirectional, orientation of the smCNL allows an adaptive response to changes in loading.