Medial Shift Research Articles

Effect of radial meniscal tear on in situ forces of meniscus and tibiofemoral relationship.

To clarify the effect of the radial tear of the lateral meniscus on the in situ meniscus force and the tibiofemoral relationship under axial loads and valgus torques. Ten intact porcine knees were settled to a 6-degree of freedom robotic system, while the force and 3-dimensional path of the knees were recorded via Universal Force Sensor (UFS) during 3 cycles of 250-N axial load and 5-Nm valgus torque at 15°, 30°, 45°, and 60° of knee flexion. The same examination was performed on the following 3 meniscal states sequentially; 33, 66, and 100% width of radial tears at the middle segment of the lateral meniscus, while recording the force and path of the knees via UFS. Finally, all paths were reproduced after total lateral meniscectomy and the in situ force of the lateral meniscus were calculated with the principle of superposition. The radial tear of 100% width significantly decreased the in situ force of the lateral meniscus and caused tibial medial shift and valgus rotation at 30°-60° of knee flexion in both testing protocols. Under a 250-N axial load at 60° of knee flexion, the in situ force decreased to 36±29N with 100% width of radial tear, which was 122±38N in the intact state. Additionally, the tibia shifted medially by 2.1±0.9mm and valgusrotated by 2.5±1.9° with the complete radial tear. However, the radial tear of 33 or 66% width had little effect on either the in situ force or the tibial position. A radial tear of 100% width involving the rim significantly decreased the in situ force of the lateral meniscus and caused medial shift and valgus rotation of the tibia, whereas a radial tear of up to 66% width produced only little change. The clinical relevance is that loss of meniscal functions due to complete radial tear can lead to abnormal stress concentration in a focal area of cartilage and can increase the risk of osteoarthritis in the future.

The Influence of Articular Cartilage Thickness Reduction on Meniscus Biomechanics.

ObjectiveEvaluation of the biomechanical interaction between meniscus and cartilage in medial compartment knee osteoarthritis.MethodsThe finite element method was used to simulate knee joint contact mechanics. Three knee models were created on the basis of knee geometry from the Open Knee project. We reduced the thickness of medial cartilages in the intact knee model by approximately 50% to obtain a medial knee osteoarthritis (OA) model. Two variants of medial knee OA model with congruent and incongruent contact surfaces were analysed to investigate the influence of congruency. A nonlinear static analysis for one compressive load case was performed. The focus of the study was the influence of cartilage degeneration on meniscal extrusion and the values of the contact forces and contact areas.ResultsIn the model with incongruent contact surfaces, we observed maximal compressive stress on the tibial plateau. In this model, the value of medial meniscus external shift was 95.3% greater, while the contact area between the tibial cartilage and medial meniscus was 50% lower than in the congruent contact surfaces model. After the non-uniform reduction of cartilage thickness, the medial meniscus carried only 48.4% of load in the medial compartment in comparison to 71.2% in the healthy knee model.ConclusionsWe have shown that the change in articular cartilage geometry may significantly reduce the role of meniscus in load transmission and the contact area between the meniscus and cartilage. Additionally, medial knee OA may increase the risk of meniscal extrusion in the medial compartment of the knee joint.

In Vivo Kinematics of Healthy and Osteoarthritic Knees During Stepping Using Density-Based Image-Matching Techniques.

The purpose of this study was to investigate in vivo kinematics in healthy and osteoarthritic (OA) knees during stepping using image-matching techniques. Six healthy volunteers and 14 patients with a medial OA knee before undergoing total knee arthroplasty performed stepping under periodic anteroposterior radiograph images. We analyzed the three-dimensional kinematic parameters of knee joints using radiograph images and CT-derived digitally reconstructed radiographs. The average extension/flexion angle ranged 6°/53° and 16°/44° in healthy and OA knees, with significant difference in extension (P = .02). The average varus angle was -2° and 6° in healthy and OA knees, with a significant difference (P = .03). OA knees showed 1.7° of significantly larger varus thrust (P = .04) and 4.2 mm of significantly smaller posterior femoral rollback (P = .04) compared with healthy knees. Coronal limb alignment in OA knees significantly correlated with varus thrust (R2 = .36, P = .02) and medial shift of the femur (R2 = .34, P = .03). Both normal and OA knees showed no transverse plane instability, including anteroposterior, mediolateral directions, or axial rotation. In conclusion, OA knees demonstrated different kinematics during stepping from normal knees: less knee extension, larger varus thrust, less posterior translation, and larger medial shift.

Coronal subluxation of the proximal tibia relative to the distal femur after opening wedge high tibial osteotomy

BackgroundThe coronal subluxation of the proximal tibia relative to the distal femur is a common radiological finding in patients with knee osteoarthritis. The purpose was to evaluate whether the coronal subluxation was corrected after opening wedge high tibial osteotomy (OWHTO), and whether this subluxation was one cause of inconsistency between the actual and predicted alignments (correction loss). MethodsFifty-one patients (55 knees) were treated with OWHTO. The change of location between the intersection points of the femoral and tibial axes on the tibial plateau (subluxation-C), the change of location between the lines through the most lateral points of the lateral femoral and tibial condyles (subluxation-L), and joint space angle (JSA) were compared in standing knee radiographs before and one year after OWHTO. The subluxation-C and subluxation-L were converted to a percentage of the tibial plateau width. ResultsThe mean subluxation-C of 6.5% before OWHTO significantly increased to a mean subluxation-C of 7.3% one year after OWHTO. The mean subluxation-L of 6.3% and JSA of 4.5° before OWHTO significantly decreased to a subluxation-L of 1.8% and JSA of 3.3° one year after OWHTO. The change in subluxation-L correlated with the change in femorotibial angle and correction loss (r=0.634, P<0.001 and r=0.463, P<0.001, respectively). ConclusionThe proximal tibia shifted medially relative to the distal femur after OWHTO. This medial shift correlated with the correction loss. The coronal subluxation might be one cause of correction loss.

Anatomic and dosimetric changes in patients with head and neck cancer treated with an integrated MRI-tri-60Co teletherapy device.

Prior studies have relied on CT to assess alterations in anatomy among patients undergoing radiation for head and neck cancer. We sought to determine the feasibility of using MRI-based image-guided radiotherapy to quantify these changes and to ascertain their potential dosimetric implications. 6 patients with head and neck cancer were treated with intensity-modulated radiotherapy (IMRT) on a novel tri-60Co teletherapy system equipped with a 0.35-T MRI (VR, ViewRay Incorporated, Oakwood Village, OH) to 66-70 Gy in 33 fractions (fx). Pre-treatment MRIs on Fx 1, 5, 10, 15, 20, 25, 30 and 33 were imported into a contouring interface, where the primary gross tumour volume (GTV) and parotid glands were delineated. The centre of mass (COM) shifts for these structures were assessed relative to Day 1. Dosimetric data were co-registered with the MRIs, and doses to the GTV and parotid glands were assessed. Primary GTVs decreased significantly over the course of IMRT (median % volume loss, 38.7%; range, 29.5-72.0%; p < 0.05) at a median rate of 1.2%/fx (range, 0.92-2.2%/fx). Both the ipsilateral and contralateral parotid glands experienced significant volume loss (p < 0.05, for all) and shifted medially during IMRT. Weight loss correlated significantly with parotid gland volume loss and medial COM shift (p < 0.05). Integrated on-board MRI can be used to accurately contour and analyze primary GTVs and parotid glands over the course of IMRT. COM shifts and significant volume reductions were observed, confirming the results of prior CT-based exercises. Advances in knowledge: The superior resolution of on-board MRI may facilitate online adaptive replanning in the future.

Anterior Cruciate Ligament Injuries Alter the Kinematics of Knees With or Without Meniscal Deficiency

Background: Numerous studies have investigated kinematic alterations in patients with an isolated anterior cruciate ligament (ACL) injury. However, a substantial proportion of patients with injured ACLs also have concomitant meniscal tears. Purpose: To evaluate the in vivo alteration of knee kinematics after an ACL tear, with or without a combined medial or lateral meniscal tear, during level walking activity. Study Design: Controlled laboratory study. Methods: Fifty-six patients with unilateral ACL-deficient (ACLD) knees were studied. Among these patients, 15 had isolated ACL injuries (group 1), 15 had combined ACL and medial meniscal injuries (group 2), 15 had combined ACL and lateral meniscal injuries (group 3), and 11 had combined ACL and medial/lateral meniscal injuries (group 4). The kinematics of each knee was determined using an optical tracking system during treadmill gait. Range of motion (ROM) and kinematic alterations were compared between the contralateral ACL-intact (ACLI) and ACLD knees. Results: All ACLD knees, with or without meniscal deficiency, had significantly less flexion than the ACLI knees (~3°-8°; P < .05). In groups 1, 3, and 4, the injured knees exhibited more femoral external rotation by approximately 1° to 2° (P < .05). Group 4 showed posterior femoral translation (anterior tibial translation) in the swing phase (~13 mm), while groups 2 and 3 showed increased anterior femoral translation (~2-3 mm). During medial-lateral translation, patients in group 2 had a more medial femoral shift (~4 mm) relative to the tibia initially, while those in group 4 exhibited a lateral femoral shift. Conclusion: The results indicate that meniscal injuries alter the kinematics of the ACLD knee when compared with knees with an isolated ACL injury. The location of the meniscal tear also affects knee kinematics. Clinical Relevance: Considering the varying effects of meniscal injuries on knee joint kinematics, these data provide insight into the pathological function of the ACL-injured knee joint during walking.

A reduction in the knee adduction moment with medial thrust gait is associated with a medial shift in center of plantar pressure

The knee adduction moment (KAM) is an established marker of compartmental load distribution across the tibiofemoral joint. Research suggests a link between the magnitude of the KAM and center of plantar pressure (COP) thus alterations in the two may be related. The objective of this study was to investigate whether the COP predictably shifts when the KAM is reduced through a gait adaptation. Twenty healthy adults underwent gait analysis walking with their normal gait pattern and with medial thrust gait, a gait adaptation known to significantly reduce the KAM. Simultaneous COP and 3-D kinetics were acquired to allow for a comparison of the change in COP to the change in the KAM. The COP was quantified by determining a customized medial-lateral pressure index (MLPI) which compares the COP tracing line during the first and second halves of stance to the longitudinal axis of the foot. Linear regressions assessing the association between the changes in KAM and MLPI indicated that 48.3% (p=0.001) of the variation in MLPI during the first half of stance can be explained by the KAM during the same period. A trend was observed between the association between the KAM and MLPI during the second half of stance (R2=0.16, p=0.080). Backwards elimination regression analysis was used to explore whether simultaneous consideration of the KAM and other potential confounding factors such as sagittal plane knee moments and speed explained variance in the MLPI during the first half of stance. Only the KAM exhibited explanatory power (β=0.695, p=0.001). During medial thrust gait, a reduction in the KAM was associated with a medial shift in the MLPI, and an increase in the KAM was associated with a lateral shift in the MLPI, especially in the first half of the stance phase. Together, these results demonstrate an inherent link between foot pressure and the KAM during medial thrust gait, and suggest that manipulating foot pressure may be a biomechanical mechanism for an intervention designed to improve loading conditions at the knee.

73. Neurophysiological features of motor cortex excitability and plasticity in Subcortical Ischemic Vascular Dementia: A TMS mapping study

The aim of this study was to evaluate neurophysiological features of M1 excitability and plasticity in Subcortical Ischemic Vascular Dementia (SIVD), by means of TMS mapping technique. Seven SIVD and nine AD patients, along with nine control subjects were tested. The M1 excitability was studied by resting thresholds, area and volume of active cortical sites for forearm and hand’s examined muscles. For M1 plasticity, coordinates of the hot-spot and the center of gravity (CoG) were evaluated. The correlation between the degree of hyperexcitability and the amount of M1 plastic rearrangement was also calculated. Multivariate analysis of excitability measures demonstrated similarly enhanced cortical excitability in AD and SIVD patients with respect to controls. SIVD patients showed a medial and frontal shift of CoG from the hot-spot, not statistically different from that observed in AD. A significant direct correlation was seen between parameters related to cortical excitability and those related to cortical plasticity. The results suggest the existence of common compensatory mechanisms in different kind of dementing diseases supporting the idea that cortical hyperexcitability can promote cortical plasticity. This study characterizes neurophysiological features of motor cortex excitability and plasticity in SIVD, providing new insights on the correlation between cortical excitability and plasticity.

Validation Is Crucial in Head and Neck Translational Imaging Research

based on daily contours. Statistical significance was determined by the 2-tailed t test, while correlations were assessed by the Spearman coefficient. Results: Primary GTVs decreased significantly in volume over the course of IMRT (median % volume loss, 38.7%; range, 29.5-72.0%; P<.05) at a median rate of 1.2% per fraction (range, 0.92%-2.2% per fraction). Both ipsilateral and contralateral parotid glands underwent significant volume loss (P<.05). Median percentage of volume loss of ipsilateral parotid glands was 31.1% (2.3%-43.9%), and median rate of volume loss was 0.97% per fraction (0.07%-1.4% per fraction). Contralateral parotids experienced a median percentage of volume loss of 21.8% (4.0%-40.5%) and median shrinkage rate of 0.68% per fraction (0.13%-1.3% per fraction). Both ipsilateral and contralateral parotids shifted medially during IMRT. Weight loss correlated significantly with parotid gland volume loss and medial COM shift (P<.05). Dose received by the primary GTVs and parotids did not significantly change during treatment. Median difference between administered mean dose at fraction 33 and planned dose per fraction was 0.008 Gy (-0.060.18 Gy) for ipsilateral and 0.01 Gy (-0.12-0.27 Gy) for contralateral parotids. Conclusion: Integrated on-board MRIs from a tri-Co teletherapy system can be used to accurately contour and analyze primary GTVs and parotid glands over the course of IMRT. COM shifts and significant volume reductions of the primary tumors and parotids were observed, confirming the results of CT-based studies. The enhanced resolution of the MRIs acquired may facilitate online adaptive replanning in the future. Despite anatomic changes during IMRT, significant dosimetric shifts were not always apparent. Author Disclosure: G. Raghavan: None. A.U. Kishan: None. M. Cao: None. Y. Yang: None. A.M. Chen: None.

Gait analysis before and after corrective osteotomy in patients with knee osteoarthritis and a valgus deformity

PurposeIn this prospective study, the changes in kinetics and kinematics of gait and clinical outcomes after a varus osteotomy (tibial, femoral or double osteotomy) in patients with osteoarthritis (OA) of the knee and a valgus leg alignment were analysed and compared to healthy subjects.MethodsTwelve patients and ten healthy controls were included. Both kinetics and kinematics of gait and clinical and radiographic outcomes were evaluated.ResultsThe knee adduction moment increased significantly postoperatively (p < 0.05) and almost similar to the control group. Patients showed less knee and hip flexion/extension motion and moment during gait pre- and postoperatively compared to the controls. A significant improvement was found in WOMAC [80.8 (SD 16.1), p = 0.000], KOS [74.9 (SD 14.7), p = 0.018], OKS [21.2 (SD 7.5), p = 0.000] and VAS-pain [32.9 (SD 20.9), p = 0.003] in all patients irrespective of the osteotomy technique used. The radiographic measurements showed a mean hip knee ankle (HKA) angle correction of 10.4° (95 % CI 6.4°–14.4°).ConclusionIn patients with knee OA combined with a valgus leg alignment, the varus-producing osteotomy is a successful treatment. Postoperatively, the patients showed kinetics and kinematics of gait similar as that of a healthy control group. A significant increase in the knee adduction moment during stance phase was found, which was related to the degree of correction. The HKA angle towards zero degrees caused a medial shift in the dynamic knee loading. The medial shift will optimally restore cartilage loading forces and knee ligament balance and reduces progression of OA or the risk of OA. A significant improvement in all clinical outcomes was also found.Level of evidenceIII.

Prediction of elbow joint contact mechanics in the multibody framework

Computational multibody musculoskeletal models of the elbow joint that are capable of simultaneous and accurate predictions of muscle and ligament forces, along with cartilage contact mechanics can be immensely useful in clinical practice. As a step towards producing a musculoskeletal model that includes the interaction between cartilage and muscle loading, the goal of this study was to develop subject-specific multibody models of the elbow joint with discretized humerus cartilage representation interacting with the radius and ulna cartilages through deformable contacts. The contact parameters for the compliant contact law were derived using simplified elastic foundation contact theory. The models were then validated by placing the model in a virtual mechanical tester for flexion-extension motion similar to a cadaver experiment, and the resulting kinematics were compared. Two cadaveric upper limbs were used in this study. The humeral heads were subjected to axial motion in a mechanical tester and the resulting kinematics from three bones were recorded for model validation. The maximum RMS error between the predicted and measured kinematics during the complete testing cycle was 2.7mm medial-lateral translation and 9.7° varus–valgus rotation of radius relative to humerus (for elbow 2). After model validation, a lateral ulnar collateral ligament (LUCL) deficient condition was simulated and, contact pressures and kinematics were compared to the intact elbow model. A noticeable difference in kinematics, contact area, and contact pressure were observed for LUCL deficient condition. LUCL deficiency induced higher internal rotations for both the radius and ulna during flexion and an associated medial shift of the articular contact area.

Effect of Patellar Resurfacing on Patellofemoral Crepitus in Posterior-Stabilized Total Knee Arthroplasty

BackgroundPatellofemoral crepitus (PC) is a complication of total knee arthroplasty (TKA). Although patellar resurfacing (PR) directly influences the kinematics of the patellofemoral joint, the influence of PR on PC is unclear. The purpose of this study was to investigate the influence of PR on the incidence of PC. MethodsThis study included 84 knees from 69 patients who underwent TKA using the Vanguard Complete Total Knee System, with or without PR (n = 42 each). Clinical evaluation of the incidence of PC; Knee Society Score; and radiographic measurements of patellar tilt, patellar distance, patellar shift, Insall-Salvati ratio, patellar flexion, femorotibial angle; and rotation of the femoral component was performed. Parameters were evaluated preoperatively and at postoperative months 2, 6, 12, and 24. Logistic regression analysis was conducted to investigate the effect of PR on the risk of PC. ResultsThe incidence of PC was significantly higher in the non-PR group than the PR group (33.3% vs 4.8%). The knees of the PR group displayed a significantly increased patellar tilt, medially shifted patella, and decreased patella flexion angle compared with those of the non-PR group. There were no significant differences in the other radiographic parameters or Knee Society Score. The absence of PR was associated with a much higher risk of PC (odds ratio, 10.37; 95% confidence interval, 2.18-10.37). ConclusionPR may decrease the incidence of PC by increasing the patellar tilt and medial shift and positioning the patella more closely parallel to the femur. PR is recommended during TKA with this prosthesis.

Descent of mesonephric duct to the final position of the vas deferens in human embryo and fetus.

Because the ureter arises from the mesonephric or Wolffian duct (WD), the WD opening should migrate inferiorly along the urogenital sinus or future urethra. However, this process of descent has not been evaluated morphometrically in previous studies and we know little about intermediate morphologies for the descent. In the present work, serial sagittal sections of 15 specimens at gestational age 6–12 weeks and serial horizontal sections of 20 specimens at 6–10 weeks were analyzed. Monitoring of horizontal sections showed that, until 9 weeks, a heart-, lozenge- or oval-shape of the initial urogenital sinus remained in the bladder and urethra. Thus, the future bladder and urethra could not be distinguished by the transverse section or plane. The maximum width of the urogenital sinus or bladder at 6–10 weeks was 0.8 mm, although its supero-inferior length reached 5 mm at 10 weeks. During earlier stages, however, the medial shift of the WD was rather evident. Depending on the extent of upward growth of the bladder smooth muscle, the descent of the vas deferens became evident at 10–12 weeks. Development of the urethral rhabdosphincter likely resulted in the differentiation of urogenital sinus into the urethra and bladder before formation of the bladder neck with 3-layered smooth muscles. Development of the prostate followed these morphological changes, later accelerating the further descent of the WD opening. Because of their close topographical relationships, slight anomalies or accidents of the umbilical cord at 10–12 weeks may have a significant effect on normal anatomy.

Big Novels/Big Data

Big Novels/Big Data Jessica Pressman (bio) What is the state of the novel in the age of big data? Sometimes, it’s just a question of scale. Novels have much to say about human experience in the midst of a medial shift from the contained codex to the never-ending World Wide Web. Increasingly, it seems, they speak not just in words on the page but through the sheer number of pages they contain. New work by such writers as William T. Vollmann and Karen Tei Yamashita take up lots of space on the shelf, but none quite expresses the commitment to bigness as Mark Z. Danielewski’s ambitious promise to publish an epic twenty-seven volume serial narrative wherein each book is itself a tome. As the earlier reviews indicate, the first and second books in Danielewski’s new Familiar series clock in at over 800 pages—with a third volume of equal immensity due later this year. In short, the trend towards bigness in bookish bulk is about building the novel to scale in an age of big data. But big novels are, of course, nothing new. From the eighteenth and nineteenth-century tome to the heavy hitters of the twentieth-century experimental novel—a lineage including Fielding, Melville, Faulkner, and Stein as much as Joyce, Pynchon, Silko and Wallace—the novel takes up space. Confronted with this older legacy, twenty-first century maximalism must respond to a critical question: is the contemporary trend towards bigness an ironic or expected outcome of the print novel in the moment of the book’s supposed obsolescence due to digital technologies? I would venture to say, yes. The novel has always been a material artifact but this fact is evermore apparent and of increased aesthetic interest in the face of seemingly disembodied digital data. That is, the big book counts its heft as part of its signification, occupying literal space on the bookshelf where its physicality plays an equally vital role in its meaning-making. Literary criticism is also going big. Inspired by computational practices of textual analysis and digital visualization tools, literary critics are exploring “distant reading” (see Franco Moretti) and moving from close reading small objects (a poem, a passage, a theme) to analyzing big data sets of all sorts of literary corpora (the titles of all novels published during a certain time period). It’s an interesting time for literary analysis, when ideas about what counts as reading and how we do it are shifting along with our reading devices and tools. In this moment, the bigness of the print-based and bookbound novel registers particular significance. Both in cahoots with big data and also rebelling against it, the big novel accordingly mimics information overload even as it seems to contain the entire world (and, often, the World Wide Web) within it. Resolute in its bigness, such books proclaim that the novel is here…and it’s not going anywhere. [End Page 14] Jessica Pressman Jessica Pressman is Assistant Professor of English and Comparative Literature at San Diego State University, where she also directs SDSU’s Digital Humanities Initiative (dh.sdsu.edu). She is the author of Digital Modernism: Making It New in New Media (2014), co-author, with Mark C. Marino and Jeremy Douglass, of Reading Project: A Collaborative Analysis of William Poundstone’s Project for Tachistoscope (2015), and co-editor, with N. Katherine Hayles, of Comparative Textual Media: Transforming the Humanities in a Postprint Era (2013). Copyright © 2016 American Book Review

No difference in patellar kinematics between fixed-bearing cruciate-retaining and cruciate-substituting total knee arthroplasty: a cadaveric investigation.

The influence of cruciate-ligament-retaining (CR-TKA) and cruciate-ligament-substituting (CS-TKA) TKA on tibiofemoral kinematics was analysed in many investigations. However, the influence on patellar kinematics is unclear so far. The aim of this study was to compare patellar kinematics of the natural knee with those after CR- and CS-TKA. Patellar kinematics of nine healthy whole-body cadaveric knees before and after CR- and CS-TKA was investigated using a commercial optical computer navigation system. Patellar kinematics of the healthy knee was compared with those after CR- and CS-TKA. No significant difference between the natural knee and the knee after TKA or between both types of TKA for patellar kinematics could be found. Interestingly, both types of TKA resulted in a more medial patellar shift and a contrary patellar tilt and rotation behaviour. CR- and CS-TKA resulted in smaller values for patellar epicondylar distance at all flexion angles. Our study found no influence of prosthesis type on patellar kinematics. Factors like component alignment and prosthesis design seem to be more important in terms of adequate restoration of patellar kinematics in TKA than whether choosing CR- or CS-TKA.

Influence of mediolateral tibial baseplate position in TKA on knee kinematics and retropatellar pressure.

Anterior knee pain is a major reason for unsatisfied patients after total knee arthroplasty (TKA). Since malposition and increased retropatellar peak pressure are supposed to contribute to pain, we conducted this in vitro study to analyse the influence of mediolateral tibial component position on tibiofemoral and patella kinematics as well as retropatellar pressure. Eight fresh frozen cadaver specimens were tested after a fixed-bearing TKA. To evaluate the influence of mediolateral tibial component position, special inlays with 3mm of medialization and lateralization were constructed. For the analysis, a weight-bearing knee rig under a loaded squat from 20° to 120° of flexion was used. Tibiofemoral and patella kinematics were measured with an ultrasonic-based three-dimensional motion analysis system. Additionally, retropatellar pressure distribution was registered with a pressure-sensitive film. Alteration of mediolateral tibial component position by 3mm did not reveal a significant influence on retropatellar peak pressure (7.5±2.5 vs. 7.2±2.6MPa). Regarding tibiofemoral kinematics, 3-mm medialization of the tibial baseplate significantly increased lateral femoral rollback and femorotibial external rotation. Medialization of 3mm also significantly increased the relative medial patella shift and decreased lateral patella tilt. Medialization of the tibial baseplate came along with more lateral rollback and external femorotibial rotation. For the positioning of the tibial baseplate, rotational alignment seems to be more important than mediolateral orientation. Since retropatellar peak pressure remained rather unchanged, the tibial baseplate should be placed by the surgeon looking for a maximal tibial coverage without overhang.

Medial Subluxation of the Tibia After Anterior Cruciate Ligament Rupture as Revealed by Standing Radiographs and Comparison With a Cadaveric Model

Background: Biomechanical studies indicate that the tibia shifts medially and has a more valgus orientation in the anterior cruciate ligament (ACL)–deficient knee. However, it is not known whether these differences can be detected on standing radiographs. Purpose: To determine whether medial subluxation and more changes in coronal alignment of the tibia are detectable in both weightbearing radiographs and a cadaveric model simulating quiet standing. Study Design: Case series; Level of evidence, 4, and Descriptive laboratory study. Methods: Radiographic data were available for a cross-section of 74 patients with unilateral ACL tears. Tibial subluxation and coronal limb alignment were measured on hip-to-ankle weightbearing radiographs. Eight cadaveric knees were mounted on a 6 degree of freedom robot. Mediolateral position and varus-valgus alignment of the tibia relative to the femur were measured in response to 300-N axial compression simulating quiet standing at 5° and 15° of flexion with the ACL intact and sectioned. Results: Across all 74 patients included in the clinical study, the ACL-injured knee experienced 1.6 ± 2.3 mm (mean ± SD) of medial tibial subluxation compared with the contralateral uninjured knee (P < .001). The 24 patients with isolated ACL rupture exhibited 2.0 ± 1.8 mm of medial subluxation (P < .001). The mean coronal alignment of all 74 patients in the study was 0.7° ± 2.8° varus in the injured limb and 1.3° ± 2.6° varus in the uninjured contralateral limb (P = .0187). In the cadaveric model, the tibia translated 0.4 ± 0.5 mm more medially after sectioning of the ACL at 15° of flexion (P = .0485); however, no changes in coronal alignment were detected. Conclusion: The tibia shifts medially and is less varus in the ACL-deficient knee on standing radiographs. The medial tibial shift is reproduced in an axially loaded cadaveric model. Clinical Relevance: Medial tibiofemoral subluxation seen on frontal plane standing radiograph is an underappreciated sequela of isolated ACL rupture. The ability of ACL reconstruction to restore this aspect of ACL injury is not well understood and should be investigated further. Cadaveric models may be used to directly measure the mechanical effect of subtle changes in mediolateral position on articular contact stress as an indicator of the importance of this finding.

Distinct displacements of the optic radiation based on tumor location revealed using preoperative diffusion tensor imaging.

OBJECT Visual field defects (VFDs) due to optic radiation (OR) injury are a common complication of temporal lobe surgery. The authors analyzed whether preoperative visualization of the optic tract would reduce this complication by influencing the surgeon's decisions about surgical approaches. The authors also determined whether white matter shifts caused by temporal lobe tumors would follow predetermined patterns based on the tumor's topography. METHODS One hundred thirteen patients with intraaxial tumors of the temporal lobe underwent preoperative diffusion tensor imaging (DTI) fiber tracking. In 54 of those patients, both pre- and postoperative VFDs were documented using computerized perimetry. Brainlab's iPlan 2.5 navigation software was used for tumor reconstruction and fiber visualization after the fusion of DTI studies with their respective magnetization-prepared rapid gradient-echo (MP-RAGE) images. The tracking algorithm was as follows: minimum fiber length 100 mm, fractional anisotropy threshold 0.1. The lateral geniculate body and the calcarine cortex were employed as tract seeding points. Shifts of the OR caused by tumor were visualized in comparison with the fiber tracking of the patient's healthy hemisphere. RESULTS Temporal tumors produced a dislocation of the OR but no apparent fiber destruction. The shift of white matter tracts followed fixed patterns dependent on tumor location: Temporolateral tumors resulted in a medial fiber shift, and thus a lateral transcortical approach is recommended. Temporopolar tumors led to a posterior shift, always including Meyer's loop; therefore, a pterional transcortical approach is recommended. Temporomesial tumors produced a lateral and superior shift; thus, a transsylvian-transcisternal approach will result in maximum sparing of the fibers. Temporocentric tumors also induced a lateral fiber shift. For those tumors, a transsylvian-transopercular approach is recommended. Tumors of the fusiform gyrus generated a superior (and lateral) shift; consequently, a subtemporal approach is recommended to avoid white matter injury. In applying the approaches recommended above, new or worsened VFDs occurred in 4% of the patient cohort. Total neurological and surgical morbidity were less than 10%. In 90% of patients, gross-total resection was accomplished. CONCLUSIONS Preoperative visualization of the OR may help in avoiding postoperative VFDs.

Robot-aided in vitro measurement of patellar stability with consideration to the influence of muscle loading.

BackgroundAnterior knee pain is often associated with patellar maltracking and instability. However, objective measurement of patellar stability under clinical and experimental conditions is difficult, and muscular activity influences the results. In the present study, a new experimental setting for in vitro measurement of patellar stability was developed and the mediolateral force–displacement behavior of the native knee analyzed with special emphasis on patellar tilt and muscle loading.MethodsIn the new experimental setup, two established testing methods were combined: an upright knee simulator for positioning and loading of the knee specimens, and an industry robot for mediolateral patellar displacement. A minimally invasive coupling and force control mechanism enabled unconstrained motion of the patella as well as measurement of patellar motion in all six degrees of freedom via an external ultrasonic motion-tracking system. Lateral and medial patellar displacement were measured on seven fresh-frozen human knee specimens in six flexion angles with varying muscle force levels, muscle force distributions, and displacement forces.ResultsSubstantial repeatability was achieved for patellar shift (ICC(3,1) = 0.67) and tilt (ICC(3,1) = 0.75). Patellar lateral and medial shift decreased slightly with increasing flexion angle. Additional measurement of patellar tilt provided interesting insights into the different displacement mechanisms in lateral and medial directions. For lateral displacement, the patella tilted in the same (lateral) direction, and tilted in the opposite direction (again laterally) for medial displacement. With regard to asymmetric muscle loading, a significant influence (p < 0.03, up to 5 mm shift and 8° tilt) was found for lateral displacement and a reasonable relationship between muscle and patellar force, whereas no effect was visible in the medial direction.ConclusionThe developed experimental setup delivered reproducible results and was found to be an excellent testing method for the in vitro analysis of patellar stability and future investigation of surgical techniques for patellar stabilization and total knee arthroplasty. We demonstrated a significant influence of asymmetric quadriceps loading on patellar stability. In particular, increased force application on the vastus lateralis muscle led to a clear increase of lateral patellar displacement.

Nail–medullary canal ratio affects mechanical axis deviation during femoral lengthening with an intramedullary distractor

IntroductionCallus distraction of the femur using an intramedullary distractor has several advantages over the use of external fixators. However, difficulty in controlling the mechanical axis during lengthening may cause deformities and knee osteoarthritis. Purpose of the study is to answer the following questions: (1) is lengthening with an intramedullary device associated with a medial or lateral shift of the mechanical axis? (2) Which factors are associated with varisation/valgisation of the mechanical axis during lengthening? Materials and methodsWe analysed pre-treatment and post-treatment radiographs from 20 patients who underwent unilateral femoral-lengthening procedures using intramedullary distractors. Patients with acute correction of pre-existing deformities or combined ipsilateral femoral and tibial lengthening were excluded. Mechanical axis deviations, osteotomy level, and nail–medullary canal ratio were recorded. ResultsCompared to the preoperative axis, the mechanical axis shifted medially in 7 patients (varisation group) and laterally in 13 patients (valgisation group). The groups did not significantly differ regarding preoperative leg length discrepancy (LLD), mechanical axis alignment, LLD-cause and implants used. The nail–medullary canal ratio significantly differed between groups (p<0.001), being <85% in the varisation group and >85% in the valgisation group. The distance between the lesser trochanter and the osteotomy site was significantly longer in the valgisation group (58.9±16.3mm, middle third of the femur) compared to the varisation group (40.6±11.4mm, proximal third of the femur; p=0.02). ConclusionThe nail–medullary canal ratio should be considered during preoperative planning. To avoid a varisation effect—for example, in cases with pre-existing varus alignment—it would be advisable to perform an osteotomy at the middle third of the femur with implantation of a nail that fully covers the medullary canal at the osteotomy site. Level of evidenceLevel IV, therapeutic study. See Instructions for Authors for a complete description of levels of evidence.