Anterior-posterior Motion Research Articles

Comparison of Spinal Cord Motion Versus Vertebral Body Motion During Magnetic Resonance Imaging–Guided Radiation Therapy (MR-IGRT)

An a priori assumption of all currently available IGRT methods is that vertebral (VB) body position is an accurate surrogate for spinal cord (SC) position, since the spinal cord is not well visualized by x-ray based imaging (kV:kV, CBCT). A new MR-IGRT system has been developed which consists of a split 0.35T MR scanner straddled by three 60Co heads mounted on a ring gantry which share a common isocenter. Given the superior ability for MR to visualize the SC, we sought to use MR-IGRT to compare the relative motion of the SC versus the VB. Three healthy volunteers were immobilized in vacuum immobilization bags and underwent volumetric MR at baseline (t0) and again in 5 minute intervals during the course of a mock treatment on a MR-IGRT system. The mock treatment was repeated for 2 additional fractions by removing the patient from the immobilization and then restarting the process completely. The MR protocol was a true fast imaging with steady state precession T2*/T1-weighted volumetric scan with a 1.5 x 1.5 mm resolution and field of view selected based on patient size. Images were imported into a third party treatment planning system, and registrations were performed at the T5 VB level for each patient and each fraction with t0 as reference using either (1) the VB or (2) the SC. Registrations were performed via automated registration with a narrow field of view followed by manual adjustment by the clinician. Differences in motion in the lateral and anterior-posterior (AP) directions and 2D in-plane shifts between SV and VB were calculated. All 3 volunteers were able to complete the course of mock treatment. The SC was well visualized with a high level of contrast between SC and surrounding CSF. Average difference in lateral motion of SC relative to VB across all 3 fractions for patients 1, 2, and 3 was -0.7 +/- 0.4 mm, -0.8 +/- 0.5 mm, and -0.4 +/- 0.3 mm. Average difference in AP motion was -0.1 +/- 0.6 mm, -0.1 +/- 0.5 mm, and 0.2 +/- 0.3 mm. Average difference in 2D motion was 0.9 +/- 0.4 mm, 0.9 +/- 0.5 mm, 0.6 +/- 0.3 mm. No time trends were noted across the 30 minute treatment. Maximum lateral, AP, and VS between SC and VB across all patients and all fractions was -1.4 mm, -1.2 mm, and 1.8 mm, respectively. The SC is well visualized with MR-IGRT and for the first time patient specific shifts can be made directly based on SC position rather than VB as a surrogate. A small but consistent difference in calculated shifts was observed when shifting based on SC versus VB, largely in the lateral direction. Average differences in a clinically relevant 2D shift were generally < 1 mm, but were up to 1.8 mm at certain time points. Confirmed in a larger cohort, such data may also be informative for generation of SC planning risk volume margins at a population level.

Clinical use of electronic portal imaging to analyse tumor motion variation during a 3D-conformal prostate cancer radiotherapy using online target verification and implanted markers

Purpose: To evaluate the daily treatment setup variation and the interfraction and intrafraction prostate motion with portal imaging and implanted fiducial markers during irradiation with a 3D conformal radiotherapy for localized prostate cancer patients. Methods : By remote verification, shifts from isocenteric positioning and inter/intra-fraction prostate motion were investigated for 34 patients treated supine with escalated dose conformal radiotherapy. To limit the effect of inter-fraction prostate motion, patients were planned and treated with an empty rectum and a comfortably full bladder. Daily pre-therapy and treatment electronic portal images were obtained for anterior and lateral treatment fields according to an on-line target localization protocol using three gold markers. From these images, random and systematic set-up errors were measured by matching corresponding patients’ gold markers on reference digitally reconstructed radiographs (DRR). Superior-inferior, anterior-posterior and lateral motions were measured from the displacement of the gold markers implanted into the prostate before planning. A planning target volume (PTV) was derived to account for the measured prostate motion and field placement deviations. Results: Analysis of 1,278 portal images to determine changes in the radiation field during the course of treatment. From the data, random isocenter positioning deviations were 2.66 mm, 2.78 mm and 2.59 mm for vertical, lateral and longitudinal movements respectively. The systematic deviations were 3.15 mm, 3.09 mm and 2.52 mm for vertical, lateral and longitudinal movements respectively. From the verification process, it was realized that 44.7%, 42.8% and 31.4% of the vertical, lateral and longitudinal prostate migrations respectively needed correction/shift. Conclusion : Random set-up errors were small using real-time isocenter placement corrections. Inter-fraction prostate motion remained the largest source of treatment error, and observed motion was greatest at the laterals. In the absence of real-time pre-treatment imaging of the prostate position, using sequential portal films of implanted gold markers, portions of the PTV is missed and surrounding tissues not spared. This research improves quality assurance by confirming the prostate position within the treatment field over the course of therapy. ----------------------------- Cite this article as : Acquah GF, Gustavsson M, Doudoo CO, Agbeve RK, Schiestl B. Clinical use of electronic portal imaging to analyze tumor motion variation during a 3D-conformal prostate cancer radiotherapy using online target verification and implanted markers. Int J Cancer Ther Oncol 2014; 2 (4):02044. DOI : 10.14319/ijcto.0204.4

A descriptive analysis of the upper limb patterns during gait in individuals with cerebral palsy.

Patients with cerebral palsy (CP) are characterized by a large diversity of gait deviations; thus, lower limb movements during gait have been well-analyzed in the literature. However, the question of upper limb movements and, more particularly, arm movements during gait has received less attention for CP patients as a function of the disease type (Hemiplegic, HE or Diplegic, DI). Thus, the aim of this study was to investigate upper limb movements for a large group of CP patients; we used a retrospective search, including upper limb kinematic parameters and 92 CP patients (42 females and 50 males, mean±standard deviation (SD); age: 15.2±6.7 years). The diagnoses consisted of 48 HE and 44 DI. A control group of 15 subjects (7 females and 8 males, age: 18.4±8.4 years) was included in the study to provide normal gait data. For the DI patients and CG, 88 arms and 30 arms were analyzed, respectively. For the HE patients, 48 affected arms and 48 non-affected arms were analyzed. The kinematic parameters selected and analyzed were shoulder elevation angles; elbow flexion angles; thorax tilt and obliquity angles; hand vertical and anterior-posterior movements; and arm angles. Several gait parameters were also analyzed, such as the gait profile score (GPS) and normalized speed. Statistical analyses were performed to compare CG with the affected and non-affected upper limbs of HE patients and with the two upper limbs of DI patients. The results show that HE and DI patients adopt abnormal upper limb movements. However, DI patients have greater shoulder, elbow, thorax and arm angle movements compared with HE patients. However, HE patients adopt different movements between their affected and non-affected arms. Thus, the patients used their upper limbs to optimize their gait more where gait deviations were more important. These observations confirm that the upper limbs must be integrated into rehabilitation programs to improve inter-limb coordination.

In-vivo evaluation of the kinematic behavior of an artificial medial meniscus implant: A pilot study using open-MRI

BackgroundIn this pilot study we wanted to evaluate the kinematics of a knee implanted with an artificial polycarbonate-urethane meniscus device, designed for medial meniscus replacement. The static kinematic behavior of the implant was compared to the natural medial meniscus of the non-operated knee. A second goal was to evaluate the motion pattern, the radial displacement and the deformation of the meniscal implant. MethodsThree patients with a polycarbonate-urethane implant were included in this prospective study. An open-MRI was used to track the location of the implant during static weight-bearing conditions, within a range of motion of 0° to 120° knee flexion. Knee kinematics were evaluated by measuring the tibiofemoral contact points and femoral roll-back. Meniscus measurements (both natural and artificial) included anterior–posterior meniscal movement, radial displacement, and meniscal height. FindingsNo difference (P>0.05) was demonstrated in femoral roll-back and tibiofemoral contact points during knee flexion between the implanted and the non-operated knees. Meniscal measurements showed no significant difference in radial displacement and meniscal height (P>0.05) at all flexion angles, in both the implanted and non-operated knees. A significant difference (P≤0.05) in anterior–posterior movement during flexion was observed between the two groups. InterpretationIn this pilot study, the artificial polycarbonate-urethane implant, indicated for medial meniscus replacement, had no influence on femoral roll-back and tibiofemoral contact points, thus suggesting that the joint maintains its static kinematic properties after implantation. Radial displacement and meniscal height were not different, but anterior–posterior movement was slightly different between the implant and the normal meniscus.

Deficits in Hip-Ankle Coordination in Female Athletes who Suffer a Second Anterior Cruciate Ligament (ACL) Injury after ACL Reconstruction and Return to Sport

Objectives:Athletes who return to sport after ACL reconstruction (ACLR) are at increased risk of future ACL injury. Proprioceptive deficits at the knee, known to be present at thetime of ACL injury, may persist for up to 2 years after ACLR. Coordinated movements of the hip and ankle are critical in the absence of normal knee proprioception during dynamic athletic movements. Failure to optimally position the knee may make the passive structures susceptible to pathologic stresses that increase the risk of subsequent ligament or graft failure. The purpose of this work was to prospectively determine if altered lower extremity coordination patterns exist in female athletes, who go on to suffer a second ACL injury to either limb, after ACLR and return to sport (RTS). The study tested the hypothesis that female athletes who sustained a second ACL injury would demonstrate altered lower extremity coordination patterns indicative of persistent neuromuscular deficits at the time of return to sport compared to female athletes who would not subsequently sustain a second ACL injury.Methods:Sixty-one female athletes, who sustained an ACL injury, underwent ACLR, completed rehabilitation and were medically cleared for RTS were enrolled in this study. Hip-ankle coordination was assessed on all athletes prior to RTS as they performed a dynamic postural coordination task. The task required participants to stand on a single leg and track the anterior-posterior (AP) movement of an oscillating 3-D square target displayed on a computer monitor. Participants tracked the target with the head so as to maintain a constant perceived distance between their head and the target by matching the amplitude and frequency of the target oscillations. Fourteen patients sustained a second ACL injury within 12 months of RTS (ACLR2). Fourteen matched subjects after ACLR, who did not suffer a second ACL injury (ACLR1), were selected for comparative analysis. Cross-recurrence quantification analysis (Figure 1) was used to characterize hip-ankle coordination patterns through the variable cross-maxline (CML). A group (ACLR1 vs. ACLR2) X target speed (slow vs. fast) X leg (affected vs. unaffected) mixed-model analysis of variance was used to identify coordination differences.Results:A significant main effect of group was observed (p = 0.02), and indicated that the ACLR1 group exhibited more stable hip-ankle coordination overall (M = 166.2 ± 18.9) compared to the ACLR2 group (M = 108.4 ± 10.1), irrespective of target speed or tested leg. A leg x group interaction was also observed (p = .04). A Mann-Whitney test was employed due to unequal variances between groups, and indicated that the affected leg of the ACLR1 group exhibited more stable coordination (M = 187.1 ± 23.3)compared to the affected leg of the ACLR2 group (M = 110.13 ± 9.8), p = 0.03.Conclusion:Hip-ankle coordination was altered in female athletes who subsequently sustain a second ACL injury after initial ACLR and RTS. Failure to appropriately coordinate lower extremity movement between the adjoining proximal and distal hip and ankle in the absence of normal knee proprioception, may place the knee in a high-risk position and increase the likelihood of a second ACL injury in this population.

Trunk kinematics during walking in persons with multiple sclerosis: the influence of body weight support.

Although body weight supported (BWS) treadmill training (TT) leads to some improvements in walking ability, it has not been proven that it is more effective than other walking therapies in persons with multiple sclerosis (PwMS). One possible explanation could be that BWSTT focuses on the cyclic movement of the lower extremities while the trunk is passively suspended in the harness. This study aimed to assess the 3 dimensional trunk and pelvis movements during BWS treadmill walking. 14 PwMS and 14 healthy persons (8 male/20 female; age 23 to 59 years) walked with 0%, 10%, 20%, 30%, 50% and 70% BWS. After a familiarization period, kinematic electromagnetic tracking (Polhemus Liberty™ 240/16) of the trunk and pelvis movements was applied. Statistical analysis consisted of a repeated measures ANOVA with simple contrasts (SPSS 20). This study shows that BWS walking leads in general to smaller maximum trunk and pelvis movement amplitudes compared with walking without BWS, this with exception of the pelvis anterior-posterior movement in healthy subjects. These data help to identify and isolate the effect of different BWS levels in PwMS and in healthy persons and suggest to use BWS lower than 30% for treadmill training.

Ground reaction force and center of mass velocity during turning

Examining whole-body center of mass (COM) motion is one of method being used to quantify dynamic balance and energy during gait. One common method for estimating the COM position is to apply an anthropometric model to a marker set and calculate the weighted sum from known segmental COM positions. Several anthropometric models are available to perform such a calculation. However, to date there has been no study of how the anthropometric model affects whole-body COM calculations during gait. This information is pertinent to researchers because the choice of anthropometric model may influence gait research findings and currently the trend is to consistently use a single model. In this study we analyzed a single stride of gait data from 103 young adult participants. We compared the whole-body COM motion calculated from 4 different anthropometric models (Plagenhoef et al., 1983; Winter, 1990; de Leva, 1996; Pavol et al., 2002). We found that anterior-posterior motion calculations are relatively unaffected by the anthropometric model. However, medial-lateral and vertical motions are significantly affected by the use of different anthropometric models. Our findings suggest that the researcher carefully choose an anthropometric model to fit their study populations when interested in medial-lateral or vertical motions of the COM. Our data can provide researchers a priori information on the model determination depending on the particular variable and how conservative they may want to be with COM comparisons between groups.

The Effects of Balance Exercise on an Unstable Platform and a Stable Platform on Static Balance

The purpose of this study is to observe how balance exercise on an unstable platform and on a stable platform affects balance ability. The subjects were 35 adults in their 20s and were randomly assigned to a stable platform group and an unstable platform group. They performed balance exercise three times per week for six weeks. Balance exercise introduced by previous research was modified and complemented for use in this study. Balance ability of the subjects was measured through center of pressure(COP) area, medial-lateral displacement, and anterior-posterior displacement using a portable balance platform BT4. There was significant difference in the COP area between the unstable platform exercise group and the stable platform exercise group. In comparison in differences between the unstable platform exercise group and the stable platform exercise group after the exercise, there was significant difference in anterior-posterior movement. Therefore, exercise on an unstable platform is more effective than exercise on a stable platform in strengthening balance ability.

SU‐E‐J‐45: Design and Study of An In‐House Respiratory Gating Phantom Platform for Gated Radiotherapy

Purpose:The main purpose of this work was to develop an in‐house low cost respiratory motion phantom platform for testing the accuracy of the gated radiotherapy system and analyze the dosimetric difference during gated radiotherapy.Methods:An in‐house respiratory motion platform(RMP) was designed and constructed for testing the targeting accuracy of respiratory tracking system. The RMP consist of acrylic Chest Wall Platform, 2 DC motors, 4 IR sensors, speed controller circuit, 2 LED and 2 moving rods inside the RMP. The velocity of the movement can be varied from 0 to 30 cycles per minute. The platform mounted to a base using precision linear bearings. The base and platform are made of clear, 15mm thick polycarbonate plastic and the linear ball bearings are oriented to restrict the platform to a movement of approximately 50mm up and down with very little friction.Results:The targeting accuracy of the respiratory tracking system was evaluated using phantom with and without respiratory movement with varied amplitude. We have found the 5% dose difference to the PTV during the movement in comparison with stable PTV. The RMP can perform sinusoidal motion in 1D with fixed peak to peak motion of 5 to 50mm and cycle interval from 2 to 6 seconds. The RMP was designed to be able to simulate the gross anatomical anterior posterior motion attributable to respiration‐induced motion of the thoracic region.Conclusion:The unique RMP simulates breathing providing the means to create a comprehensive program for commissioning, training, quality assurance and dose verification of gated radiotherapy treatments. Create the anterior/posterior movement of a target over a 5 to 50 mm distance to replicate tumor movement. The targeting error of the respiratory tracking system is less than 1.0 mm which shows suitable for clinical treatment with highly performance.

Reverse shoulder glenoid baseplate fixation: a comparison of flat-back versus curved-back designs and oval versus circular designs with 2 different offset glenospheres

In this glenoid loosening study, we compared the fixation strength of multiple generic reverse shoulder glenoid baseplates that differed only in backside geometry and shape and size to optimize design from a fixation perspective. The fixation strength of 4 generic baseplates was quantified in a low-density polyurethane substrate to isolate the contribution of baseplate profile and size (25 mm circular vs 25 × 34 mm oval) and backside geometry (flat back vs curved back) on fixation using 2 center-of-rotation glenospheres (0mm and 10mm lateral). The cyclic test simulated 55° of abduction as a 750 N load was continuously applied to induce a variable shear and compressive load. Before and after cyclic loading, baseplate displacement was measured in the directions of the applied static shear and compressive loads. Each generic baseplate was cyclically tested 7 times with each offset glenosphere for a total of 56 samples. Circular baseplates were associated with significantly more shear displacement in both the superior-inferior (SI) and anterior-posterior (AP) directions after cyclic loading than oval baseplates. No such significant differences in fixation were observed between flat-back and curved-back baseplates. Circular baseplates were also associated with significantly more SI and AP shear displacement with 10 mm glenospheres than with 0 mm glenospheres. No significant difference in SI or AP motion was observed with oval baseplates between 0 mm and 10 mm glenospheres. Our results suggest that baseplate shape and size affects fixation strength more than backside geometry. The 25 × 34 mm oval baseplates showed better fixation characteristics than their 25 mm circular counterparts; no discernible difference in fixation was observed between flat-back and curved-back baseplates.

Anti-phase action between the angular accelerations of trunk and leg is reduced in the elderly

Quiet standing posture in humans has often been modeled as a single inverted pendulum pivoting around the ankle joint. However, recent studies have suggested that anti-phase action between leg and trunk segments plays a significant role in stabilizing posture by reducing the acceleration of the center of mass (COM) of the body. The aim of this study is to test the hypothesis that anti-phase action is attenuated in the elderly compared to the young. The anterior–posterior movements of leg and trunk segments were measured using 4 laser displacement sensors from 22 healthy young subjects (age range, 20–35 years) and 38 healthy elderly subjects (age range, 57–80 years) standing quietly for 30s twice. To focus on the segmental action between trunk and legs, we applied constraints (i.e., wooden splints) on each segment. We found that the velocity and acceleration of the COM (standard deviation of the time series was evaluated) were significantly higher for the elderly subjects than for young subjects. The increase in the acceleration of the COM resulted not only from an increase in the angular acceleration of the segments but also from the reduction of their anti-phase relationship, as demonstrated by an index that quantifies the degree of cancelation between both segments. We conclude that the degree of anti-phase action between trunk and leg segments during quiet standing is smaller for elderly subjects than for young subjects, and that this change of the anti-phase action due to aging resulted in increased COM acceleration in the elderly subjects.

In vivo kinematics of medial unicompartmental osteoarthritic knees during activities of daily living

Few studies exist describing unicompartmental osteoarthritic knee kinematics. Moreover, the role of the anterior cruciate ligament (ACL) in the determination of knee kinematics has not been fully described. The objective of the current study was to analyze the in vivo kinematics of knees with medial osteoarthritis (OA) and intact ACL during closed and open chained motion. Eight patients scheduled for UKA diagnosed with primary medial OA underwent knee CT-scans and video-fluoroscopy. Fluoroscopic analysis included stair climbing, chair rising and leg extension. Three-dimensional bone positions were obtained from each image by iterative procedures using a CAD-model-based shape-matching technique. Patterns of axial rotation and anterior-posterior (AP) motion of the medial and lateral femoral condyle were obtained with specific software. The femur reported an overall external rotation relative to the tibia from extension to flexion in all tasks. Average AP translation of the medial femoral condyle were smaller in open-chained tasks than in weight-bearing conditions. Average AP motion of the lateral femoral condyle reported an overall posterior translation with knee flexion. The absent natural "screw-home" mechanism and the lack of medial condyle posterior translation was explained by bone-cartilage defects and meniscal degeneration. Relevant findings were the kinematic pattern differences between weight-bearing and open chained activities, suggesting that in biphasic muscle contraction and unloaded conditions, the function of the cruciate ligaments was not physiological. The kinematics of knees with medial OA and intact ACL differed from healthy knees.

3P2-E03 水中上肢リハビリテーション補助用ロボットの開発 : 前腕回内/外運動リハビリテーション装置の開発(リハビリテーションロボティクス・メカトロニクス)

The aim of this study was to develop the novel underwater robotic device to achieve forearm abduction/adduction rehabilitation with master-slave system. The developed system could execute the 5-degree-of-freedom motion (anterior-posterior and vertical motion, and pitch, yaw, and roll rotation). We evaluated this system and the results showed enough functional capability for underwater upper limb rehabilitation, especially in the abduction/adduction rotation in forearm. Further studies are needed to achieve this system and to evaluate the efficacies regaining the for hemiparetic patients.

Movement constraints on interpersonal coordination and communication.

The present study investigated how constraining movement affects interpersonal coordination and joint cognitive performance. Pairs of participants worked cooperatively to solve picture-puzzle tasks in which they conversed to identify differences between pictures in 3 degree-of-constraint conditions: both participants were free to move their hands (free-free; FF); both participants' hands were restrained (restrained-restrained; RR); and the hands of 1 participant were free while the hands of the other participant were restrained (free-restrained; FR). Eye tracking data were collected, and movement was measured at the waist, hand, and head. Data were analyzed using Cross-Recurrence Quantification Analysis (CRQ). Postural sway coordination, gaze coordination, and task performance were predicted to be highest in FF, followed by RR, and then by FR. Results showed the asymmetric FR condition generally exhibited lesser degrees of coordination than the symmetric Conditions FF and RR, and that the patterning of coordination in the symmetric conditions varied across the measured body segments. These results demonstrate that movement restraints affect not only interpersonal postural coordination, but also joint attention. Additionally, significant positive relationships were found between task performance and total amount of anterior-posterior movement measured at the head, hand and waist; number of utterances; and number of differences pairs found in the puzzles. These findings indicate a relationship between movement and task performance consistent with the hypotheses that both interpersonal coordination and cognitive performance are sensitive to local action constraints.

Patterns of Meniscal Damage Associated with Acute ACL Rupture

Patterns of Meniscal Damage Associated with Acute ACL Rupture

Continuous cervical spine kinematics during in vivo dynamic flexion-extension

Background contextA precise and comprehensive definition of “normal” in vivo cervical kinematics does not exist due to high intersubject variability and the absence of midrange kinematic data. In vitro test protocols and finite element models that are validated using only end range of motion data may not accurately reproduce continuous in vivo motion. PurposeThe primary objective of this study was to precisely quantify cervical spine intervertebral kinematics during continuous, functional flexion-extension in asymptomatic subjects. The advantages of assessing continuous intervertebral kinematics were demonstrated by comparing asymptomatic controls with patients with single-level anterior arthrodesis. Study designCervical spine kinematics were determined during continuous in vivo flexion-extension in a clinically relevant age group of asymptomatic controls and a group of patients with C5–C6 arthrodesis. Patient sampleThe patient sample consisted of 6 patients with single-level (C5–C6) anterior arthrodesis (average age: 48.8±6.9 years; 1 male, 5 female; 7.6±1.2 months postsurgery) and 18 asymptomatic control subjects of similar age (average age: 45.6±5.8 years; 5 male, 13 female). Outcome measuresOutcome measures included the physiologic measure of continuous kinematic motion paths at each cervical motion segment (C2–C7) during flexion-extension. MethodsParticipants performed flexion-extension while biplane radiographs were collected at 30 images per second. A previously validated tracking process determined three-dimensional vertebral positions with submillimeter accuracy. Continuous flexion-extension rotation and anterior-posterior translation motion paths were adjusted for disc height and static orientation of each corresponding motion segment. ResultsIntersubject variability in flexion-extension angle was decreased 15% to 46% and intersubject variability in anterior-posterior translation was reduced 14% to 33% after adjusting for disc height and static orientation angle. Average intersubject variability in continuous motion paths was 1.9° in flexion-extension and 0.6 mm in translation. Third-order polynomial equations were determined to precisely describe the continuous flexion-extension and anterior-posterior translation motion path at each motion segment (all R2>0.99). ConclusionsA significant portion of the intersubject variability in cervical kinematics can be explained by the disc height and the static orientation of each motion segment. Clinically relevant information may be gained by assessing intervertebral kinematics during continuous functional movement rather than at static, end range of motion positions. The fidelity of in vitro cervical spine mechanical testing protocols may be evaluated by comparing in vitro kinematics to the continuous motion paths presented.

Quantifying variability of intrafractional target motion in stereotactic body radiotherapy for lung cancers

In lung stereotactic body radiotherapy (SBRT), variability of intrafractional target motion can negate the potential benefits of four‐dimensional (4D) treatment planning that aims to account for the dosimetric impacts of organ motion. This study used tumor motion data obtained from CyberKnife SBRT treatments to quantify the reproducibility of probability motion function (pmf) of 37 lung tumors. The reproducibility of pmf was analyzed with and without subtracting the intrafractional baseline drift from the original motion data. Statistics of intrafractional tumor motion including baseline drift, target motion amplitude and period, were also calculated. The target motion amplitude significantly correlates with variations (1 SD) of motion amplitude and baseline drift. Significant correlation between treatment time and variations (1 SD) of motion amplitude was observed in anterior‐posterior (AP) motion, but not in craniocaudal (CC) and left‐right (LR) motion. The magnitude of AP and LR baseline drifts significantly depend on the treatment time, while the CC baseline drift does not. The reproducibility of pmf as a function of time can be well described by a two‐exponential function with a fast and slow component. The reproducibility of pmf is over 60% for the CC motion and over 50% for the AP and LR motions when baseline variations were subtracted from the original motion data. It decreases to just over 30% for the CC motion and about 20% for the AP and LR motion, otherwise. 4D planning has obvious limitations due to variability of intrafractional target motion. To account for potential risks of overdosing critical organs, it is important to simulate the dosimetric impacts of intra‐ and interfractional baseline drift using population statistics obtained from SBRT treatments.PACS number: 87.55.‐x

Passive Anterior Tibial Subluxation in Anterior Cruciate Ligament–Deficient Knees

Background: Abnormal anterior-posterior and rotational motion secondary to anterior cruciate ligament (ACL) insufficiency is typically described in terms of dynamic laxity. An original description of the abnormal tibiofemoral relationship in the setting of ACL insufficiency has highlighted the presence of a fixed anterior tibial subluxation in this population of failed ACL reconstruction (ACLR); however, no study has quantified the degree of tibial subluxation in both the medial and lateral compartments. Purpose: To measure and compare the amount of anterior tibial subluxation among various states of ACL competency, including (1) intact ACL, (2) acute ACL disruption, and (3) failed ACLR (ie, patients requiring revision ACLR). We hypothesized that anterior tibial displacement would be greater in the lateral compartment and in cases of failed ACLR compared with intact and acute ACL injured states. Study Design: Cross-sectional study; Level of evidence, 3. Methods: Using sagittal magnetic resonance imaging (MRI) and a standardized measurement technique, we determined the amount of anterior tibial subluxation relative to a constant posterior condylar reference point. Measurements were performed in both the medial and the lateral compartments and were compared with 1-way analysis of variance. The presence of meniscal tears along with meniscal volume loss and chondral damage was correlated with the amount of subluxation in each group. Results: Compared with the intact ACL state, the medial tibial plateau was positioned more anteriorly relative to the femur in both acute ACL injured knees (mean 1.0 mm) and those that failed ACLR (mean 1.8 mm) (P = .072). In the lateral compartment, there was 0.8 mm of mean anterior tibial displacement after acute ACL injury and 3.9 mm of mean anterior subluxation in patients who failed ACLR (P < .001). Mean anterior displacement of the lateral plateau in patients who failed ACLR was almost 5 times greater than the amount observed in patients with acute ACL injuries. There was no correlation between meniscal/chondral injury and the amount of subluxation. Conclusion: Patients who require revision ACLR have an abnormal tibiofemoral relationship noted on MRI that is most pronounced in the lateral compartment and should be taken into account during revision surgery. These observations may explain the suboptimal clinical results seen in some patients who undergo revision ACLR.

Biomechanical Analysis of Distal Clavicle Excision With Acromioclavicular Joint Reconstruction

Background: Acromioclavicular (AC) joint separation is a common injury, usually affecting young adults. Controversy exists regarding whether to excise the distal clavicle when surgical intervention is required. Purpose: To evaluate the biomechanical strength of AC and coracoclavicular (CC) ligament reconstruction with and without concurrent distal clavicle excision. Study Design: Controlled laboratory study. Methods: Nine matched pairs of cadaver shoulders were used. All shoulders were tested with intact CC and AC ligaments, and the ligaments were sectioned. For 1 shoulder in each pair, a 7-mm distal clavicle excision was performed. The contralateral distal clavicle was left intact. Single-tunnel CC ligament reconstruction was performed, and excess graft length was extended and secured across the AC joint to reconstruct the superior AC joint ligaments in all specimens. Specimens were then potted and cyclically loaded for 500 cycles in the anterior-posterior and superior-inferior planes using an MTS Minibionix load frame to evaluate displacement across the AC joint. Results: Regarding the clavicle–intact reconstructed versus the intact state, there was significantly greater AC joint translation in the reconstructed state in the anterior-posterior (20.2 ± 7.0 mm vs 6.0 ± 1.5 mm; P < .001) and superior-inferior directions (12.3 ± 3.3 mm vs 4.2 ± 1.2 mm; P < .001). In the clavicle–excised reconstructed versus the intact state, there was also significantly greater translation in the reconstructed state in the anterior-posterior (21.7 ± 5.1 mm vs 8.9 ± 4.3 mm; P < .001) and superior-inferior directions (12.3 ± 6.1 mm vs 5.8 ± 3.1 mm; P < .001). When the difference in translation between the reconstructed and intact groups in the clavicle-intact versus the clavicle-excised group was compared, no statistically significant difference was noted in anterior-posterior (14.2 ± 7.8 mm vs 12.8 ± 5.0 mm; P = .67) or superior-inferior translation (8.1 ± 2.9 mm vs 6.6 ± 3.9 mm; P = .39). Conclusion: Excision of the distal clavicle did not have a significant effect on anterior-posterior or superior-inferior motion at the AC joint following single-tunnel CC and AC ligament reconstruction. Clinical Relevance: The study suggests that excision of the distal clavicle in this procedure is not associated with increased anterior-posterior or superior-inferior instability in this model.

The influence of total knee arthroplasty geometry on mid-flexion stability: An experimental and finite element study

Fluoroscopic evaluation of total knee arthroplasty (TKA) has reported sudden anterior translation of the femur relative to the tibia (paradoxical anterior motion) for some cruciate-retaining designs. This motion may be tied to abrupt changes in the femoral sagittal radius of curvature characteristic of traditional TKA designs, as the geometry transitions from a large load-bearing distal radius to a smaller posterior radius which can accommodate femoral rollback. It was hypothesized that a gradually reducing radius may attenuate sudden changes in anterior–posterior motion that occur in mid-flexion with traditional discrete-radius designs. A combined experimental and computational approach was employed to test this hypothesis. A previously developed finite element (FE) model of the Kansas knee simulator (KKS), virtually implanted with multiple implant designs, was used to predict the amount of paradoxical anterior femoral slide during a simulated deep knee bend. The model predicted kinematics demonstrated that incorporating a gradually reducing radius in mid-flexion reduced the magnitude of paradoxical anterior translation between 21% and 68%, depending on the conformity of the tibial insert. Subsequently, both a dual-radius design and a modified design incorporating gradually reducing radii were tested in vitro in the KKS for verification. The model-predicted and experimentally observed kinematics exhibited good agreement, while the average experimental kinematics demonstrated an 81% reduction in anterior translation with the modified design. The FE model demonstrated sufficient sensitivity to appropriately differentiate kinematic changes due to subtle changes in implant design, and served as a useful pre-clinical design-phase tool to improve implant kinematics.