Tibial spine volume is smaller in ACL-injured athletes compared to healthy athletes.

PURPOSE: The aim of this study was to investigate whether the whole tibial spine volume and femoral intercondylar notch volume are risk factors for anterior cruciate ligament (ACL) injury. The hypothesis was that the whole tibial spine volume and femoral notch volume would be smaller in athletes who sustained ACL injury than in athletes with no history of ACL injury. METHODS: Computed tomography scans of both knees were acquired and three-dimensional bone models were created using Mimics to measure whole tibial spine volume and femoral notch volume. Tibial spine volume, femoral notch volume and each of these volumes normalised by tibial plateau area were compared between the ACL-injured and the ACL-intact group. RESULTS: Fifty-one athletes undergoing unilateral anatomical ACL reconstruction (17 female, 34 male: average age 22.0 ± 7.5) and 19 healthy collegiate athletes with no previous knee injury (eight female, 11 male: average age 20.1 ± 1.3) were included in this study. The whole tibial spine volume in the ACL-injured group (2.1 ± 0.5 cm3) was 20.7% smaller than in the ACL-intact group (2.7 ± 0.7 cm3) (p = 0.005). No differences were observed between the femoral notch volume in the ACL-injured group (9.5 ± 2.1 cm3) and the ACL-intact group (8.7 ± 2.7 cm3) (n.s.). CONCLUSIONS: The main finding of this study was that the whole tibial spine volume of the ACL-injured group was smaller than the ACL-intact group. A small tibial spine volume can be added to the list of anatomical risk factors that may predispose athletes to ACL injury. LEVEL OF EVIDENCE: Level Ⅲ.

Symmetry in knee arthrokinematics in healthy collegiate athletes during fast running and drop jump revealed through dynamic biplane radiography.

OBJECTIVE: Changes in cartilage contact area and/or contact location after knee injury can initiate and exacerbate cartilage degeneration. Typically, the contralateral knee is used as a surrogate for native cartilage contact patterns on the injured knee. However, symmetry in cartilage contact patterns between healthy knees during high-impact activities is unknown. METHOD: Tibiofemoral kinematics were measured on 19 collegiate athletes during fast running and drop jump using dynamic biplane radiography and a validated registration process that matched computed tomography (CT)-based bone models to the biplane radiographs. Cartilage contact area and location were measured with participant-specific magnetic resonance imaging (MRI)-based cartilage models superimposed on the CT-based bone models. Symmetry in cartilage contact area and location was assessed by the absolute side-to-side differences (SSD) within participants. RESULTS: The SSD in contact area during running (7.7 ± 6.1% and 8.0 ± 4.6% in the medial and lateral compartments, respectively) was greater than during drop jump (4.2 ± 3.7% and 5.7 ± 2.6%, respectively) (95% CI of the difference: medial [2.4%, 6.6%], lateral [1.5%, 4.9%]). The average SSD in contact location was 3.5 mm or less in the anterior-posterior (AP) direction and 2.1 mm or less in the medial-lateral (ML) direction on the femur and tibia for both activities. The SSD in AP contact location on the femur was greater during running than during drop jump (95% CI of the difference: medial [1.6 mm, 3.6 mm], lateral [0.6 mm, 1.9 mm]). CONCLUSION: This study provides context for interpreting results from previous studies on tibiofemoral arthrokinematics. Previously reported differences between ligament-repaired and contralateral knee arthrokinematics fall within the range of typical SSDs observed in healthy athletes. Previously reported arthrokinematics differences that exceed SSDs found in these healthy athletes occur only in the presence of anterior cruciate ligament (ACL) deficiency or meniscectomy.

Toward the Identification of Distinct Phenotypes: Research Protocol for the Low Back Pain Biological, Biomechanical, and Behavioral (LB3P) Cohort Study and the BACPAC Mechanistic Research Center at the University of Pittsburgh.

As a member of the Back Pain Consortium (BACPAC), the University of Pittsburgh Mechanistic Research Center's research goal is to phenotype chronic low back pain using biological, biomechanical, and behavioral domains using a prospective, observational cohort study. Data will be collected from 1,000 participants with chronic low back pain according to BACPAC-wide harmonized and study-specific protocols. Participation lasts 12 months with one required in person baseline visit, an optional second in person visit for advanced biomechanical assessment, and electronic follow ups at months 1, 2, 3, 4, 5, 6, 9, and 12 to assess low back pain status and response to prescribed treatments. Behavioral data analysis includes a battery of patient-reported outcomes, social determinants of health, quantitative sensory testing, and physical activity. Biological data analysis includes omics generated from blood, saliva, and spine tissue. Biomechanical data analysis includes a physical examination, lumbopelvic kinematics, and intervertebral kinematics. The statistical analysis includes traditional unsupervised machine learning approaches to categorize participants into groups and determine the variables that differentiate patients. Additional analysis includes the creation of a series of decision rules based on baseline measures and treatment pathways as inputs to predict clinical outcomes. The characteristics identified will contribute to future studies to assist clinicians in designing a personalized, optimal treatment approach for each patient.

Magnetic Resonance Imaging of the Lumbar Spine: Recommendations for Acquisition and Image Evaluation from the BACPAC Spine Imaging Working Group.

Management of patients suffering from low back pain (LBP) is challenging and requires development of diagnostic techniques to identify specific patient subgroups and phenotypes in order to customize treatment and predict clinical outcome. The Back Pain Consortium (BACPAC) Research Program Spine Imaging Working Group has developed standard operating procedures (SOPs) for spinal imaging protocols to be used in all BACPAC studies. These SOPs include procedures to conduct spinal imaging assessments with guidelines for standardizing the collection, reading/grading (using structured reporting with semi-quantitative evaluation using ordinal rating scales), and storage of images. This article presents the approach to image acquisition and evaluation recommended by the BACPAC Spine Imaging Working Group. While the approach is specific to BACPAC studies, it is general enough to be applied at other centers performing magnetic resonance imaging (MRI) acquisitions in patients with LBP. The herein presented SOPs are meant to improve understanding of pain mechanisms and facilitate patient phenotyping by codifying MRI-based methods that provide standardized, non-invasive assessments of spinal pathologies. Finally, these recommended procedures may facilitate the integration of better harmonized MRI data of the lumbar spine across studies and sites within and outside of BACPAC studies.

How Many Trials Are Needed to Estimate Typical Lumbar Movement Patterns During Dynamic X-Ray Imaging?

Dynamic biplane radiographic (DBR) imaging measures continuous vertebral motion during in vivo, functional tasks with submillimeter accuracy, offering the potential to develop novel biomechanical markers for lower back disorders based on true dynamic motion rather than metrics based on static end-range of motion. Nevertheless, the reliability of DBR metrics is unclear due to the inherent variability in movement over multiple repetitions and a need to minimize radiation exposure associated with each movement repetition. The objectives of this study were to determine the margin of uncertainty (MOU) in estimating the typical intervertebral kinematics waveforms based upon only a small number of movement repetitions, and to determine the day-to-day repeatability of intervertebral kinematics waveforms measured using DBR. Lumbar spine kinematics data were collected from two participant groups who performed multiple trials of flexion-extension or lateral bending to assess the uncertainty in the mean estimated waveform. The first group performed ten repetitions on the same day. Data from that group were used to estimate MOU as a function of the number of repetitions. The second group performed five repetitions on each of two separate days. MOU was not only movement-specific, but also motion segment-specific. Using just one or two trials yielded a relatively high MOU (e.g., >4 deg or 4 mm), however, collecting at least three repetitions reduced the MOU by 40% or more. Results demonstrate the reproducibility of DBR-derived measurements is greatly improved by collecting at least three repetitions, while simultaneously minimizing the amount of radiation exposure to participants.

Posterior tibial slope and meniscal slope correlate with in vivo tibial internal rotation during running and drop jump.

PURPOSE: The relationship between tibial bony and meniscus anatomy and knee kinematics during in vivo, high-impact activities remains unclear. This study aimed to determine if the posterior tibial slope (PTS) and meniscal slope (MS) are associated with in vivo anterior-posterior translation and internal tibia rotation during running and double-leg drop jumps in healthy knees. METHODS: Nineteen collegiate athletes performed fast running at 5.0 m/s on an instrumented treadmill and double-leg drop jump from a 60 cm platform while biplane radiographs of the knee were acquired at 150 Hz. Tibiofemoral kinematics were determined using a validated model-based tracking process. Medial and lateral PTS and MS were measured using magnetic resonance imaging (MRI). RESULTS: In fast running, more internal tibia rotation was associated with greater PTS (ρ = 0.336, P = 0.039) and MS (ρ = 0.405, P = 0.012) in the medial knee compartment. In the double-leg drop jump, more internal tibia rotation was associated with greater PTS (ρ = 0.431, P = 0.007) and MS (ρ = 0.323, P = 0.005) in the medial knee compartment, as well as a greater PTS in the lateral knee compartment (ρ = 0.445, P = 0.005). CONCLUSION: These findings suggest that the medial and lateral PTS and medial MS are associated with the amount of knee rotation during high-impact activities. These in vivo findings improve our understanding of ACL injury risk by linking bone and meniscus morphology to dynamic kinematics.

Bone morphology features associated with knee kinematics may not be predictive of ACL elongation during high-demand activities.

PURPOSE: Bony morphology has been proposed as a potential risk factor for anterior cruciate ligament (ACL) injury. The relationship between bony morphology, knee kinematics, and ACL elongation during high-demand activities remains unclear. The purpose of this study was to determine if bone morphology features that have been associated with ACL injury risk and knee kinematics are also predictive of ACL elongation during fast running and double-legged drop jump. METHODS: Nineteen healthy athletes performed fast running and double-legged drop jump within a biplane radiography imaging system. Knee kinematics and ACL elongation were measured bilaterally after using a validated registration process to track bone motion in the radiographs and after identifying ACL attachment sites on magnetic resonance imaging (MRI). Bony morphological features of lateral posterior tibial slope (LPTS), medial tibial plateau (MTP) depth, and lateral femoral condyle anteroposterior width (LCAP)/lateral tibial plateau anteroposterior width (TPAP) were measured on MRI. Relationships between bony morphology and knee kinematics or ACL elongation were identified using multiple linear regression analysis. RESULTS: No associations between bony morphology and knee kinematics or ACL elongation were observed during fast running. During double-legged drop jump, a greater range of tibiofemoral rotation was associated with a steeper LPTS (ß = 0.382, p = 0.012) and a deeper MTP depth (ß = 0.331, p = 0.028), and a greater range of anterior tibial translation was associated with a shallower MTP depth (ß = - 0.352, p = 0.018) and a larger LCAP/ TPAP (ß = 0.441, p = 0.005); however, greater ACL elongation was only associated with a deeper MTP depth (ß = 0.456, p = 0.006) at toe-off. CONCLUSION: These findings indicate that observed relationships between bony morphology and kinematics should not be extrapolated to imply a relationship also exists between those bone morphology features and ACL elongation during high-demand activities. These new findings deepen our understanding of the relationship between bony morphology and ACL elongation during high-demand activities. This knowledge can help identify high-risk patients for whom additional procedures during ACL reconstruction are most appropriate.

Preoperative quantitative pivot shift does not correlate with in vivo kinematics following ACL reconstruction with or without lateral extraarticular tenodesis.

PURPOSE: Quantitative pivot shift (QPS) testing using PIVOT technology can detect high- and low-grade rotatory knee instability following anterior cruciate ligament injury or reconstruction (ACLR). The aim of this project was to determine if preoperative QPS correlates with postoperative knee kinematics in the operative and contralateral, healthy extremity following ACLR with or without lateral extraarticular tenodesis (LET) using a highly precise in vivo analysis system. A positive correlation between preoperative QPS and postoperative tibial translation and rotation following ACLR with or without LET in the operative and healthy, contralateral extremity was hypothesized. METHODS: Twenty patients with ACL injury and high-grade rotatory knee instability were randomized to undergo anatomic ACLR with or without LET as part of a prospective randomized trial. At 6 and 12 months postoperatively, in vivo kinematic data were collected using dynamic biplanar radiography superimposed with high-resolution computed tomography scans of patients' knees during downhill running. Total anterior-posterior (AP) tibial translation and internal-external tibial rotation were measured during the gait cycle. Spearman's rho was calculated for preoperative QPS and postoperative kinematics. RESULTS: In the contralateral, healthy extremity, a significant positive correlation was seen between preoperative QPS and total AP tibial translation at 12 months postoperatively (rs = 0.6, p < 0.05). There were no additional significant correlations observed between preoperative QPS and postoperative knee kinematics at 6 and 12 months postoperatively in the operative and contralateral, healthy extremity for combined isolated ACLR and ACLR with LET patients as well as isolated ACLR patients or ACLR with LET patients analyzed separately. DISCUSSION: The main finding of this study was that there was a significant positive correlation between preoperative QPS and total AP tibial translation at 12 months postoperatively in the contralateral, healthy extremity. There were no significant correlations between preoperative QPS and postoperative in vivo kinematics at 6 and 12 months following ACLR with or without LET. This suggests that QPS as measured with PIVOT technology does correlate with healthy in vivo knee kinematics, but QPS does not correlate with in vivo kinematics following ACLR with or without LET.

Does Femoral Head Translation Vary by Sex and Side in Asymptomatic Hips During a Weightbearing Apprehension Test?

BACKGROUND: Hip microinstability is an increasingly recognized source of pain and dysfunction but has no agreed upon diagnostic criteria and the pathophysiology remains unclear. It has been suggested that pain associated with microinstability is caused by excess translation of the femoral head. Recent research indicates that single-plane femoral head translation can be reliably measured using dynamic ultrasonography during a supine clinical examination; however, the overall accuracy of that technique has not been established, and the range of femoral head translation values that are found in individuals with no history of surgery or symptomatic pathology is unknown. QUESTIONS/PURPOSES: (1) How much femoral head translation is present in native, uninjured hips during a weightbearing apprehension position for females and males? (2) How large is the side-to-side difference in hip translation and rotation within the same individual in females and males with no history of surgery or pain during the weightbearing apprehension position? (3) What differences exist in femoral head translation and rotation when comparing females to males? METHODS: Twenty-two young adults (11 males, 11 females; mean age 22 ± 2 years; BMI 22 ± 5 kg/m2) with no history of hip pain, no known hip injury, and who never had hip surgery participated in this study. High-resolution CT images of the femur and pelvis were acquired for each participant, and the bone tissue was segmented from the CT volume. Synchronized biplane radiographs were collected during a neutral standing trial and during a static weightbearing apprehension position in which the participant extended, externally rotated, and abducted at their back hip while standing with their feet split in the AP direction. A validated volumetric model-based tracking technique was used to match the patient-specific bone models to the biplane radiographs with an accuracy of 0.3 mm for translation and 0.8° for rotation. Translation of the center of the femoral head relative to the center of the acetabulum and rotation of the femur relative to the pelvis from neutral to the weightbearing apprehension position were calculated. Sex-based differences in hip kinematics were assessed by bivariate linear regression. RESULTS: The median (range) translation during the weightbearing apprehension position in females was 0.9 mm (0.2 to 2.7 mm), which was less than in the 1.3 mm (0.2 to 2.6 mm) translation found in males (median difference of 0.5 mm; p = 0.04). The median absolute side-to-side difference in translation during the pivot was 1.4 mm (0.1 to 3.8 mm) in females and 1.3 mm (0.1 to 4.4 mm) in males. CONCLUSION: These findings demonstrate that the femoral head translates the same under bodyweight loading as previously observed during supine exam, showing the inherent stability of the hip with no history of surgery or symptomatic pathology. This study also provides normal values for comparison with individuals who have suspected microinstability. Future directions for research include directly comparing biplane radiography to alternative imaging techniques, such as dynamic ultrasound, for identifying hip microinstability and identifying threshold values for symptomatic hip microinstability. LEVEL OF EVIDENCE: Level III, prognostic study.

Improved Outcomes Following Arthroscopic Superior Capsular Reconstruction May Not Be Associated With Changes in Shoulder Kinematics: An In Vivo Study.

PURPOSE: To determine the in vivo effects of superior capsule reconstruction (SCR) on glenohumeral kinematics during abduction and to compare those kinematics results with patient-reported outcomes, range of motion, and strength. METHODS: Dynamic biplane radiography was used to image 10 patients with irreparable rotator cuff tears while performing scapular plane abduction pre- and 1-year post-surgery. Shoulder kinematics were determined by matching subject-specific computed tomography-based bone models to the radiographs using a validated tracking technique. RESULTS: No change was detected in static acromiohumeral distance (-0.7 ± 2.1 mm; P = .35); however, average dynamic acromiohumeral distance decreased (2.7 ± 1.2 mm to 2.3 ± 1.0 mm; P = .035) from pre- to 1-year post-surgery, respectively. The humeral head position was 0.5 ± 0.5 mm more superior 1-year post-surgery compared with pre-surgery (P = .01). Glenohumeral abduction increased from pre-surgery (150 ± 20°) to 1-year post-surgery (165 ± 10°) (P = .04) and all patient-reported outcomes improved from pre-surgery to 1-year post-surgery (all P < .002). A more posterior shift in humeral head position was associated with improved American Shoulder and Elbow Surgeons Shoulder Score from pre-surgery to 1-year post-surgery (r = 0.71, P = .02). CONCLUSIONS: These data suggest that SCR may not depress the humeral head during functional abduction, as previously postulated, and postoperative improvements in subjective and clinical outcomes may be affected by mechanisms other than changes in shoulder kinematics. CLINICAL RELEVANCE: In vivo kinematics changes after SCR are small and do not correspond to previously postulated changes.

The effect of lateral extra-articular tenodesis on in vivo cartilage contact in combined anterior cruciate ligament reconstruction.

PURPOSE: Lateral extra-articular tenodesis (LET) may confer improved rotational stability after anterior cruciate ligament reconstruction (ACLR). Little is known about how LET affects in vivo cartilage contact after ACLR. The aim of this study was to investigate the effect of LET in combination with ACLR (ACLR + LET) on in vivo cartilage contact kinematics compared to isolated ACLR (ACLR) during downhill running. It was hypothesised that cartilage contact area in the lateral compartment would be larger in ACLR + LET compared with ACLR, and that the anterior-posterior (A-P) position of the contact center on the lateral tibia would be more anterior after ACLR + LET than after ACLR. METHODS: Twenty patients were randomly assigned into ACLR + LET or ACLR during surgery (ClinicalTrials.gov:NCT02913404). At 6 months and 12 months after surgery, participants were imaged during downhill running using biplane radiography. Tibiofemoral motion was tracked using a validated registration process. Patient-specific cartilage models, obtained from 3 T MRI, were registered to track bone models and used to calculate the dynamic cartilage contact area and center of cartilage contact in both the medial and lateral tibiofemoral compartments, respectively. The side-to-side differences (SSD) were compared between groups using a Mann-Whitney U test. RESULTS: At 6 months after surgery, the SSD in A-P cartilage contact center in ACLR + LET (3.9 ± 2.6 mm, 4.4 ± 3.1 mm) was larger than in ACLR (1.2 ± 1.6 mm, 1.5 ± 2.0 mm) at 10% and 20% of the gait cycle, respectively (p < 0.01, p < 0.05). There was no difference in the SSD in cartilage contact center at 12 months after surgery. There was no difference in SSD of cartilage contact area in the medial and lateral compartments at both 6 and 12 months after surgery. There were no adverse events during the trial. CONCLUSION: LET in combination with ACLR may affect the cartilage contact center during downhill running in the early post-operation phase, but this effect is lost in the longer term. This suggests that healing and neuromuscular adaptation occur over time and may also indicate a dampening of the effect of LET over time. (337 /350 words) LEVEL OF EVIDENCE: Level II.

Anterior cruciate ligament reconstruction with lateral extraarticular tenodesis better restores native knee kinematics in combined ACL and meniscal injury.

PURPOSE: To determine if anterior cruciate ligament (ACL) reconstruction (ACLR) with lateral extraarticular tenodesis (LET) is beneficial for restoring knee kinematics with concomitant meniscal pathology causing rotatory knee instability. METHODS: Twenty patients with an ACL tear were randomized to either isolated ACLR or ACLR with LET. Patients were divided into four groups based on the surgery performed and the presence of meniscal tear (MT): ACLR without MT, ACLR with MT, ACLR with LET without MT, and ACLR with LET with MT. Kinematic data normalized to the contralateral, healthy knee were collected using dynamic biplanar radiography superimposed with high-resolution computed tomography scans of patients' knees during downhill running. Anterior tibial translation (ATT) and tibial rotation (TR) as well as patient-reported outcome measures (PROMs) were analyzed at 6- and 12-months postoperatively. RESULTS: At 6 months, ACLR with LET resulted in significantly decreased ATT at heel strike compared to ACLR (ACLR without MT: 0.3 ± 0.8 mm and ACLR with MT: 1.4 ± 3.1 mm vs. ACLR with LET without MT: - 2.5 ± 3.4 mm and ACLR with LET with MT: - 1.5 ± 1.2 mm ATT, p = 0.02). At 6 months, at toe off ACLR with LET better restored ATT to that of the contralateral, healthy knee in patients with meniscal pathology, while in patients without meniscal pathology, ACLR with LET resulted in significantly decreased ATT (1.0 ± 2.6 mm ATT vs. - 2.6 ± 1.7 mm ATT, p = 0.04). There were no significant differences in kinematics or PROMs between groups at 12 months. CONCLUSION: For combined ACL and meniscus injury, ACLR with LET restores native knee kinematics at toe off but excessively decreases ATT at heel strike in the early post-operative period (6 months) without altering knee kinematics in the long term. Future large-scale clinical studies are needed to better understand the function of LET and ultimately improve patient outcomes. LEVEL OF EVIDENCE: III.

Associations between range of motion, strength, tear size, patient-reported outcomes, and glenohumeral kinematics in individuals with symptomatic isolated supraspinatus tears.

BACKGROUND: Clinical failure associated with nonoperative treatment of rotator cuff tears may be due to inadequate characterization of the individual's functional impairments. Clinically, restricted passive range of motion (ROM) (restrictions imply capsular tightness), limitations in muscle strength, and larger rotator cuff tears are hypothesized to be related to altered glenohumeral kinematics. Understanding these relationships, as well as the relationship between glenohumeral kinematics and patient-reported outcomes (PROs) prior to exercise therapy, may help characterize functional impairments in individuals with rotator cuff tears. The objectives of the study were to describe the baseline presentation of individuals with an isolated supraspinatus tear, including passive ROM, rotator cuff muscle strength, tear size, PROs, and glenohumeral kinematics, and to determine associations among these variables. METHODS: One hundred one individuals with symptomatic isolated supraspinatus tears were recruited for the study and underwent assessments of passive glenohumeral ROM, isometric muscle strength, and ultrasonography to assess anterior-posterior tear size. Glenohumeral kinematics during scapular-plane abduction were measured using biplane radiography. Furthermore, PROs including the American Shoulder and Elbow Surgeons (ASES) score and the Western Ontario Rotator Cuff Index (WORC) score were collected. RESULTS: Individuals presented with decreased ROM, external rotation weakness compared with the uninvolved side, and pain and disability as measured by the ASES and WORC scores. These findings were not associated with glenohumeral kinematics, with the exception of a weak positive association between glenohumeral contact path lengths and WORC scores (ρ = 0.25, P = .03). Tear size was 11.7 ± 5.7 mm, and maximum anterior translation, superior translation, and contact path length were 3.0% ± 3.8% of glenoid width, 3.5% ± 3.8% of glenoid height, and 38.2% ± 20.7% of glenoid size, respectively. CONCLUSION: Individuals with a symptomatic isolated supraspinatus tear presented with decreased ROM, external rotation weakness, and pain and disability as measured by the ASES and WORC scores. However, no abnormal kinematics associated with these limitations were observed. Thus, given that the tear is isolated to the supraspinatus tendon and no capsular restrictions are present, normal function of the glenohumeral joint may be possible during scapular-plane abduction.

Using Simultaneous Confidence Bands to Calculate the Margin of Error in Estimating Typical Biomechanical Waveforms.

Studies of human movement usually collect data from multiple repetitions of a task and use the average of all movement trials to approximate the typical kinematics or kinetics pattern for each individual. Few studies report the expected accuracy of these estimated mean kinematics or kinetics waveforms for each individual. The purpose of this study is to demonstrate how simultaneous confidence bands, which is an approach to quantify uncertainty across an entire waveform based on limited data, can be used to calculate margin of error (MOE) for waveforms. Bilateral plantar pressure data were collected from 70 participants as they walked over 4 surfaces for an average of at least 300 steps per surface. The relationship between MOE and the number of steps included in the analysis was calculated using simultaneous confidence bands, and 3 methods commonly used for pointwise estimates: intraclass correlation, sequential averaging, and T-based MOE. The conventional pointwise approaches underestimated the number of trials required to estimate biomechanical waveforms within a desired MOE. Simultaneous confidence bands are an objective approach to more accurately estimate the relationship between the number of trials collected and the MOE in estimating typical biomechanical waveforms.

Predictions of Anterior Cruciate Ligament Dynamics From Subject-Specific Musculoskeletal Models and Dynamic Biplane Radiography.

In vivo knee ligament forces are important to consider for informing rehabilitation or clinical interventions. However, they are difficult to directly measure during functional activities. Musculoskeletal models and simulations have become the primary methods by which to estimate in vivo ligament loading. Previous estimates of anterior cruciate ligament (ACL) forces range widely, suggesting that individualized anatomy may have an impact on these predictions. Using ten subject-specific (SS) lower limb musculoskeletal models, which include individualized musculoskeletal geometry, muscle architecture, and six degree-of-freedom knee joint kinematics from dynamic biplane radiography (DBR), this study provides SS estimates of ACL force (anteromedial-aACL; and posterolateral-pACL bundles) during the full gait cycle of treadmill walking. These forces are compared to estimates from scaled-generic (SG) musculoskeletal models to assess the effect of musculoskeletal knee joint anatomy on predicted forces and the benefit of SS modeling in this context. On average, the SS models demonstrated a double force peak during stance (0.39-0.43 xBW per bundle), while only a single force peak during stance was observed in the SG aACL. No significant differences were observed between continuous SG and SS ACL forces; however, root mean-squared differences between SS and SG predictions ranged from 0.08 xBW to 0.27 xBW, suggesting SG models do not reliably reflect forces predicted by SS models. Force predictions were also found to be highly sensitive to ligament resting length, with ±10% variations resulting in force differences of up to 84%. Overall, this study demonstrates the sensitivity of ACL force predictions to SS anatomy, specifically musculoskeletal joint geometry and ligament resting lengths, as well as the feasibility for generating SS musculoskeletal models for a group of subjects to predict in vivo tissue loading during functional activities.

Graft healing does not influence subjective outcomes and shoulder kinematics after superior capsule reconstruction: a prospective in vivo kinematic study.

BACKGROUND: A viable treatment option for young patients with massive, irreparable rotator cuff tears is arthroscopic superior capsule reconstruction (SCR). SCR theoretically improves shoulder stability and function and decreases pain. However, no prospective studies to date have correlated magnetic resonance imaging (MRI) healing with in vivo kinematic data. The purpose of this study was to evaluate the association between graft healing and in vivo kinematics, range of motion (ROM), strength, and patient-reported outcomes (PROs). METHODS: Ten patients (8 men and 2 women; mean age, 63 ± 7 years) with irreparable rotator cuff tears underwent arthroscopic SCR with dermal allograft. Strength was measured with isometric internal rotation and external rotation (ER) at 0° of abduction, ER at 90° of abduction, and scapular-plane abduction, whereas ROM was measured during shoulder flexion, abduction, and ER and internal rotation at 90° of abduction both before and 1 year after SCR. PROs included American Shoulder and Elbow Surgeons, Western Ontario Rotator Cuff Index, and Disabilities of the Arm, Shoulder and Hand surveys that were collected before and 1 year after SCR. Synchronized biplane radiographs were collected at 50 images/s before and 1 year after SCR while patients performed 3 trials of scapular-plane abduction. A validated volumetric tracking technique with submillimeter accuracy determined 6-df glenohumeral and scapular kinematics. The acromiohumeral distance (AHD), humeral head translation, and scapulohumeral rhythm (SHR) were calculated from the in vivo kinematics. Healing at 5 locations was evaluated on 1-year postoperative MRI scans: anterior and posterior glenoid, anterior and posterior humerus, and posteriorly along the infraspinatus. Each subject was given a score from 0 to 5 based on number of sites healed. RESULTS: Of the 10 patients, 9 (90%) had complete (n = 4) or partial (n = 5) healing of the graft whereas 1 (10%) had complete failure at the glenoid. No correlation existed between MRI healing and the AHD, SHR, strength, ROM, or PROs. American Shoulder and Elbow Surgeons, Western Ontario Rotator Cuff Index, and Disabilities of the Arm, Shoulder and Hand scores all significantly improved from before to 1 year after SCR regardless of graft healing. CONCLUSIONS: The rate of complete or partial graft healing on MRI mimics findings of prior reports in the literature. MRI healing was correlated with humeral head anterior-posterior translation but not with the static and dynamic AHDs, SHR, humeral head superior-inferior translation, ROM, strength, or PROs 1 year after SCR. All PROs improved significantly from before to 1 year after SCR regardless of graft status on MRI. In vivo kinematic changes were small after SCR and not clinically significant, and the data suggest that improvements in clinical and functional outcomes may occur in the absence of full graft healing.

Increases in Load Carriage Magnitude and Forced Marching Change Lower-Extremity Coordination in Physically Active, Recruit-Aged Women.

The objective was to examine the interactive effects of load magnitude and locomotion pattern on lower-extremity joint angles and intralimb coordination in recruit-aged women. Twelve women walked, ran, and forced marched at body weight and with loads of +25%, and +45% of body weight on an instrumented treadmill with infrared cameras. Joint angles were assessed in the sagittal plane. Intralimb coordination of the thigh-shank and shank-foot couple was assessed with continuous relative phase. Mean absolute relative phase (entire stride) and deviation phase (stance phase) were calculated from continuous relative phase. At heel strike, forced marching exhibited greater (P < .001) hip flexion, knee extension, and ankle plantar flexion compared with running. At mid-stance, knee flexion (P = .007) and ankle dorsiflexion (P = .04) increased with increased load magnitude for all locomotion patterns. Forced marching (P = .009) demonstrated a "stiff-legged" locomotion pattern compared with running, evidenced by the more in-phase mean absolute relative phase values. Running (P = .03) and walking (P = .003) had greater deviation phase than forced marching. Deviation phase increased for running (P = .03) and walking (P < .001) with increased load magnitude but not for forced marching. With loads of >25% of body weight, forced marching may increase risk of injury due to inhibited energy attenuation up the kinetic chain and lack of variability to disperse force across different supportive structures.

Knee Kinematics of Healthy Adults Measured Using Biplane Radiography.

A dataset of knee kinematics in healthy, uninjured adults is needed to serve as a reference for comparison when evaluating the effects of injury, surgery, rehabilitation, and age. Most currently available datasets that characterize healthy knee kinematics were developed using conventional motion analysis, known to suffer from skin motion artifact. More accurate kinematics, obtained from bone pins or biplane radiography, have been reported for datasets ranging in size from 5 to 15 knees. The aim of this study was to characterize tibiofemoral kinematics and its variability in a larger sample of healthy adults. Thirty-nine knees were imaged using biplane radiography at 100 images/s during multiple trials of treadmill walking. Multiple gait trials were captured to measure stance and swing-phase knee kinematics. Six degrees-of-freedom kinematics were determined using a validated volumetric model-based tracking process. A bootstrapping technique was used to define average and 90% prediction bands for the kinematics. The average ROM during gait was 7.0 mm, 3.2 mm, and 2.9 mm in anterior/posterior (AP), medial/lateral (ML), and proximal/distal (PD) directions, and 67.3 deg, 11.5 deg, and 3.7 deg in flexion/extension (FE), internal/external (IE), and abduction/adduction (AbAd). Continuous kinematics demonstrated large interknee variability, with 90% prediction bands spanning approximately ±4 mm, ±10 mm, and ±5 mm for ML, AP, and PD translations and ±15 deg, ±10 deg, and ±6 deg in FE, IE, and AbAd. This dataset suggests substantial variability exists in healthy knee kinematics. This study provides a normative database for evaluating knee kinematics in patients who receive conservative or surgical treatment.

Determining Subject-Specific Lower-Limb Muscle Architecture Data for Musculoskeletal Models Using Diffusion Tensor Imaging.

Accurate individualized muscle architecture data are crucial for generating subject-specific musculoskeletal models to investigate movement and dynamic muscle function. Diffusion tensor imaging (DTI) magnetic resonance (MR) imaging has emerged as a promising method of gathering muscle architecture data in vivo; however, its accuracy in estimating parameters such as muscle fiber lengths for creating subject-specific musculoskeletal models has not been tested. Here, we provide a validation of the method of using anatomical magnetic resonance imaging (MRI) and DTI to gather muscle architecture data in vivo by directly comparing those data obtained from MR scans of three human cadaveric lower limbs to those from dissections. DTI was used to measure fiber lengths and pennation angles, while the anatomical images were used to estimate muscle mass, which were used to calculate physiological cross-sectional area (PCSA). The same data were then obtained through dissections, where it was found that on average muscle masses and fiber lengths matched well between the two methods (4% and 1% differences, respectively), while PCSA values had slightly larger differences (6%). Overall, these results suggest that DTI is a promising technique to gather in vivo muscle architecture data, but further refinement and complementary imaging techniques may be needed to realize these goals.

Unloader knee brace increases medial compartment joint space during gait in knee osteoarthritis patients.

PURPOSE: The purpose of the present study was to investigate the effect of the unloader brace on medial compartment dynamic joint space (DJS) during gait, while simultaneously recording ground reaction force (GRF) in varus knee osteoarthritis (OA) patients using a highly accurate biplane radiography system which allowed continuous measurement of DJS from heel strike through the midstance phase of gait. The hypothesis was that DJS in the medial compartment would be greater with the unloader brace than without the brace during gait. METHODS: After 2 weeks of daily use of the unloader brace, ten varus knee OA patients (age 52 ± 8 years) walked with and without the brace on an instrumented treadmill, while biplane radiographs of the OA knees were acquired at 100 Hz. Medial compartment DJS was determined from heel strike to terminal stance (0-40% of the gait cycle) using a validated volumetric model-based tracking process that matches subject-specific 3D bone models to the biplane radiographs. The GRF during gait was collected at 1000 Hz. Repeated-measures ANOVA was used to explore differences in medial compartment DJS and GRF between the unbraced and braced conditions. A patient-reported subjective questionnaire related to the brace use was collected at the time of the test. RESULTS: Medial compartment DJS was significantly greater with the unloader brace than without the brace during gait (P = 0.005). The average difference was 0.3 mm (95% confidence interval 0.1-0.4 mm). No significant difference was observed in terms of vertical GRF between the two conditions. The questionnaire showed participants felt reduced pain when wearing the brace. CONCLUSION: The unloader brace has the significant effect of increasing medial compartment DJS during gait, which supports the underlying premise that the unloader brace reduces pain by increasing medial joint space during dynamic loading activities. LEVEL OF EVIDENCE: III.