David C. Ackland

Moment arms of the muscles crossing the anatomical shoulder

The objective of the present study was to determine the instantaneous moment arms of 18 major muscle sub‐regions crossing the glenohumeral joint during coronal‐plane abduction and sagittal‐plane flexion. Muscle moment‐arm data for sub‐regions of the shoulder musculature during humeral elevation are currently not available. The tendon‐excursion method was used to measure instantaneous muscle moment arms in eight entire upper‐extremity cadaver specimens. Significant differences in moment arms were reported across sub‐regions of the deltoid, pectoralis major, latissimus dorsi, subscapularis, infraspinatus and supraspinatus (P < 0.01). The most effective abductors were the middle and anterior deltoid, whereas the most effective adductors were the teres major, middle and inferior latissimus dorsi (lumbar vertebrae and iliac crest fibers, respectively), and middle and inferior pectoralis major (sternal and lower‐costal fibers, respectively). In flexion, the superior pectoralis major (clavicular fibers), anterior and posterior supraspinatus, and anterior deltoid were the most effective flexors, whereas the teres major and posterior deltoid had the largest extensor moment arms. Division of multi‐pennate shoulder muscles of broad origins into sub‐regions highlighted distinct functional differences across those sub‐regions. Most significantly, we found that the superior sub‐region of the pectoralis major had the capacity to exert substantial torque in flexion, whereas the middle and inferior sub‐regions tended to behave as a stabilizer and extensor, respectively. Knowledge of moment arm differences between muscle sub‐regions may assist in identifying the functional effects of muscle sub‐region tears, assist surgeons in planning tendon reconstructive surgery, and aid in the development and validation of biomechanical computer models used in implant design.

Sensitivity of model predictions of muscle function to changes in moment arms and muscle-tendon properties: A Monte-Carlo analysis

Hill-type muscle models are commonly used in musculoskeletal models to estimate muscle forces during human movement. However, the sensitivity of model predictions of muscle function to changes in muscle moment arms and muscle-tendon properties is not well understood. In the present study, a three-dimensional muscle-actuated model of the body was used to evaluate the sensitivity of the function of the major lower limb muscles in accelerating the whole-body center of mass during gait. Monte-Carlo analyses were used to quantify the effects of entire distributions of perturbations in the moment arms and architectural properties of muscles. In most cases, varying the moment arm and architectural properties of a muscle affected the torque generated by that muscle about the joint(s) it spanned as well as the torques generated by adjacent muscles. Muscle function was most sensitive to changes in tendon slack length and least sensitive to changes in muscle moment arm. However, the sensitivity of muscle function to changes in moment arms and architectural properties was highly muscle-specific; muscle function was most sensitive in the cases of gastrocnemius and rectus femoris and insensitive in the cases of hamstrings and the medial sub-region of gluteus maximus. The sensitivity of a muscles function was influenced by the magnitude of the muscles force as well as the operating region of the muscle on its force-length curve. These findings have implications for the development of subject-specific models of the human musculoskeletal system.

Moment arms of the shoulder musculature after reverse total shoulder arthroplasty.

BACKGROUND Reverse total shoulder arthroplasty is known to increase the moment arm of the middle subregion of the deltoid during shoulder abduction; however, at present, comprehensive data regarding the shoulder muscle moment arm through the full range of abduction and flexion are not available. The purpose of this study was twofold: (1) to measure the instantaneous moment arms of thirteen subregions of major muscles spanning the glenohumeral joint during abduction and flexion of the shoulder after reverse total shoulder arthroplasty and (2) to compare these data with the muscle moment arms previously measured preoperatively in the anatomical shoulders. METHODS Reverse total shoulder arthroplasty was performed on eight entire cadaveric upper extremities. The specimens were mounted onto a dynamic testing apparatus, and the instantaneous abductor/adductor and flexor/extensor moment arms of subregions of the deltoid, latissimus dorsi, pectoralis major, teres major, and subscapularis muscles (a total of thirteen subregions) were measured with use of the tendon excursion method. These muscle moment arms were compared with those measured preoperatively in the anatomical shoulders. RESULTS Reverse total shoulder arthroplasty resulted in significant increases in the abductor moment arms of the anterior subregion of the deltoid (mean increase = 10.4 mm; 95% confidence interval = 7.5 to 13.3 mm) and the middle subregion of the deltoid (mean increase = 15.5 mm; 95% confidence interval = 10.8 to 20.3 mm) as well as recruitment of the posterior subregion of the deltoid as an abductor. The superior subregion of the pectoralis major (the clavicular fibers) and anterior subregion of the deltoid were the most effective flexors and had a substantial potential to initiate flexion. The adductor and extensor moment arms of the teres major, latissimus dorsi subregions, and inferior and middle subregions of the pectoralis major increased substantially after the arthroplasty. The subscapularis subregions behaved as extensors, abductors, and adductors after the arthroplasty; this was in contrast to their roles in the anatomical shoulder, in which they were mainly flexors and adductors. CONCLUSIONS Reverse total shoulder arthroplasty increases the moment arms of the major abductors, flexors, adductors, and extensors of the glenohumeral joint, thereby reducing muscle effort during common tasks such as lifting and pushing.

Lines of action and stabilizing potential of the shoulder musculature.

The objective of the present study was to measure the lines of action of 18 major muscles and muscle sub‐regions crossing the glenohumeral joint of the human shoulder, and to compute the potential contribution of these muscles to joint shear and compression during scapular‐plane abduction and sagittal‐plane flexion. The stabilizing potential of a muscle was found by assessing its contribution to superior/inferior and anterior/posterior joint shear in the scapular and transverse planes, respectively. A muscle with stabilizing potential was oriented to apply more compression than shear at the glenohumeral joint, whereas a muscle with destabilizing potential was oriented to apply more shear. Significant differences in lines of action and stabilizing capacities were measured across sub‐regions of the deltoid and rotator cuff in both planes of elevation (P < 0.05), and substantial differences were observed in the pectoralis major and latissimus dorsi. The results showed that, during abduction and flexion, the rotator cuff muscle sub‐regions were more favourably aligned to stabilize the glenohumeral joint in the transverse plane than in the scapular plane and that, overall, the anterior supraspinatus was most favourably oriented to apply glenohumeral joint compression. The superior pectoralis major and inferior latissimus dorsi were the chief potential scapular‐plane destabilizers, demonstrating the most significant capacity to impart superior and inferior shear to the glenohumeral joint, respectively. The middle and anterior deltoid were also significant potential contributors to superior shear, opposing the combined destabilizing inferior shear potential of the latissimus dorsi and inferior subscapularis. As potential stabilizers, the posterior deltoid and subscapularis had posteriorly‐directed muscle lines of action, whereas the teres minor and infraspinatus had anteriorly‐directed lines of action. Knowledge of the lines of action and stabilizing potential of individual sub‐regions of the shoulder musculature may assist clinicians in identifying muscle‐related joint instabilities, assist surgeons in planning tendon reconstructive surgery, aid in the development of rehabilitation procedures designed to improve joint stability, and facilitate development and validation of biomechanical computer models of the shoulder complex.

Knee kinematics and joint moments during gait following anterior cruciate ligament reconstruction: a systematic review and meta-analysis

Background Abnormal gait after anterior cruciate ligament reconstruction (ACLR) may contribute to development and/or progression of knee osteoarthritis. Objective To conduct a systematic review and meta-analysis of knee kinematics and joint moments during walking after ACLR. Methods We searched seven electronic databases and reference lists of relevant papers, for cross-sectional, human-based observational studies comparing knee joint kinematics and moments during level walking in individuals with ACLR, with the uninjured contralateral knee or healthy individuals as a control. Two independent reviewers appraised methodological quality (modified Downs and Black scale). Where possible, data were pooled by time post-ACLR (RevMan), otherwise narrative synthesis was undertaken. Results Thirty-four studies were included. Meta-analysis revealed significant sagittal plane deficits in ACLR knees. We found greater knee flexion angles (standardised mean difference: 1.06; 95% CI 0.39 to 1.74) and joint moments (1.61; 0.87 to 2.35) <6 months post-ACLR, compared to healthy controls. However, lower peak knee flexion angles were identified 1–3 years (−2.21; −3.16 to −1.26) and ≥3 years post-ACLR (−1.38, −2.14 to −0.62), and lower knee flexion moment 6–12 months post-ACLR (−0.76; −1.40 to −0.12). Pooled data provided strong evidence of no difference in peak knee adduction moment >3 years after ACLR (vs healthy controls) (0.09; −0.63 to 0.81). No transverse plane conclusions could be drawn. Conclusions Sagittal plane biomechanics, rather than the knee adduction moment, appear to be more relevant post-ACLR. Better understanding of sagittal plane biomechanics is necessary for optimal post-operative recovery, and to potentially prevent early onset and progression of knee OA after ACLR. Trial registration number PROSPERO systematic review protocol registration number CRD4201400882 2.

Quadriceps volumes are reduced in people with patellofemoral joint osteoarthritis

OBJECTIVES This study aimed to (1) compare the volumes of vastus medialis (VM), vastus lateralis (VL), vastus intermedius and rectus femoris and the ratio of VM/VL volumes between asymptomatic controls and patellofemoral joint osteoarthritis (PFJ OA) participants; and (2) assess the relationships between cross-sectional area (CSA) and volumes of the VM and VL in individuals with and without PFJ OA. METHODS Twenty-two participants with PFJ OA and 11 controls aged ≥ 40 years were recruited from the community and practitioner referrals. Muscle volumes of individual quadriceps components were measured from thigh magnetic resonance (MR) images. The CSA of the VM and lateralis were measured at 10 equally distributed levels (femoral condyles to lesser femoral trochanter). RESULTS PFJ OA individuals had smaller normalized VM (mean difference 0.90 cm(3) · kg(-1), α = 0.011), VL (1.50 cm(3) · kg(-1), α = 0.012) and rectus femoris (0.71 cm(3) · kg(-1), α = 0.009) volumes than controls. No differences in the VM/VL ratio were observed. The CSA at the third level (controls) and fourth level (PFJ OA) above the femoral condyles best predicted VM volume, whereas the VL volume was best predicted by the CSA at the seventh level (controls) and sixth level (PFJ OA) above the femoral condyles. CONCLUSION Reduced quadriceps muscle volume was a feature of PFJ OA. Muscle volume could be predicted from CSA measurements at specific levels in PFJ OA patients and controls.

Moment arms of the shoulder muscles during axial rotation

The objective of the present study was to determine the instantaneous moment arms of 18 major muscle sub‐regions crossing the glenohumeral joint in axial rotation of the humerus during coronal‐plane abduction and sagittal‐plane flexion. The tendon‐excursion method was used to measure instantaneous muscle moment arms in eight entire upper‐extremity cadaver specimens. The results showed that the inferior subscapularis was the largest internal rotator; its rotation moment arm peaks were 24.4 and 27.0 mm during abduction and flexion, respectively. The inferior infraspinatus and teres minor were the greatest external rotators; their respective rotation moment arms peaked at 28.3 and 26.5 mm during abduction, and 23.3 and 22.1 mm during flexion. The two supraspinatus sub‐regions were external rotators during abduction and internal rotators during flexion. The latissimus dorsi and pectoralis major behaved as internal rotators throughout both abduction and flexion, with the three pectoralis major sub‐regions and middle and inferior latissimus dorsi displaying significantly larger internal rotation moment arms with the humerus adducted or flexed than when abducted or extended (p < 0.001). The deltoid behaved either as an internal rotator or an external rotator, depending on the degree of humeral abduction and axial rotation. Knowledge of moment arm differences between muscle sub‐regions may assist in identifying the functional effects of muscle sub‐region tears, assist surgeons in planning tendon transfer surgery, and aid in the development and validation of biomechanical computer models.

Axial Rotation Moment Arms of the Shoulder Musculature After Reverse Total Shoulder Arthroplasty

BACKGROUND Reverse total shoulder arthroplasty changes the lines of action of the shoulder muscles, resulting in increases in the moment arms of the major abductors and flexors of the glenohumeral joint; however, at present little is known about the axial rotation capacity of the musculature after this procedure. The purpose of this study was to measure the instantaneous axial rotation moment arms of all of the major muscles spanning the glenohumeral joint during abduction and flexion after reverse total shoulder arthroplasty. METHODS Reverse total shoulder arthroplasty was performed on eight entire cadaveric upper extremities. Specimens were mounted onto a testing apparatus, and the internal/external rotation moment arms of eighteen major muscle subregions involving the subscapularis, supraspinatus, infraspinatus, teres minor, teres major, deltoid, pectoralis major, and latissimus dorsi were measured during abduction and flexion. These muscle moment arms were compared with those measured preoperatively in the anatomical shoulders (i.e., before the arthroplasty). RESULTS Reverse total shoulder arthroplasty resulted in loss of external rotation function in the posterior deltoid subregion. Postoperatively, the inferior subscapularis subregion had the largest internal rotation moment arm overall, whereas the teres minor and the inferior infraspinatus subregion had the greatest external rotation moment arms. The teres minor, infraspinatus, and deltoid subregions were external rotators during abduction, whereas only the teres minor, infraspinatus, and to a small extent the posterior deltoid subregion were external rotators during flexion. CONCLUSIONS Reverse total shoulder arthroplasty results in an overall decrease in the external rotation moment arm of the deltoid and increases in the moment arms of the major internal rotators, including the latissimus dorsi and pectoralis major. Reverse total shoulder arthroplasty may result in complete loss of external rotation function if the teres minor and infraspinatus muscles are damaged.

Shoulder muscle function depends on elbow joint position: An illustration of dynamic coupling in the upper limb

Shoulder muscle function has been documented based on muscle moment arms, lines of action and muscle contributions to contact force at the glenohumeral joint. At present, however, the contributions of individual muscles to shoulder joint motion have not been investigated, and the effects of shoulder and elbow joint position on shoulder muscle function are not well understood. The aims of this study were to compute the contributions of individual muscles to motion of the glenohumeral joint during abduction, and to examine the effect of elbow flexion on shoulder muscle function. A three-dimensional musculoskeletal model of the upper limb was used to determine the contributions of 18 major muscles and muscle sub-regions of the shoulder to glenohumeral joint motion during abduction. Muscle function was found to depend strongly on both shoulder and elbow joint positions. When the elbow was extended, the middle and anterior deltoid and supraspinatus were the greatest contributors to angular acceleration of the shoulder in abduction. In contrast, when the elbow was flexed at 90°, the anterior deltoid and subscapularis were the greatest contributors to joint angular acceleration in abduction. This dependence of shoulder muscle function on elbow joint position is explained by the existence of dynamic coupling in multi-joint musculoskeletal systems. The extent to which dynamic coupling affects shoulder muscle function, and therefore movement control, is determined by the structure of the inverse mass matrix, which depends on the configuration of the joints. The data provided may assist in the diagnosis of abnormal shoulder function, for example, due to muscle paralysis or in the case of full-thickness rotator cuff tears.

Classification of Parkinson's Disease Gait Using Spatial-Temporal Gait Features

Quantitative gait assessment is important in diagnosis and management of Parkinsons disease (PD); however, gait characteristics of a cohort are dispersed by patient physical properties including age, height, body mass, and gender, as well as walking speed, which may limit capacity to discern some pathological features. The aim of this study was twofold. First, to use a multiple regression normalization strategy that accounts for subject age, height, body mass, gender, and self-selected walking speed to identify differences in spatial-temporal gait features between PD patients and controls; and second, to evaluate the effectiveness of machine learning strategies in classifying PD gait after gait normalization. Spatial-temporal gait data during self-selected walking were obtained from 23 PD patients and 26 aged-matched controls. Data were normalized using standard dimensionless equations and multiple regression normalization. Machine learning strategies were then employed to classify PD gait using the raw gait data, data normalized using dimensionless equations, and data normalized using the multiple regression approach. After normalizing data using the dimensionless equations, only stride length, step length, and double support time were significantly different between PD patients and controls (p <; 0.05); however, normalizing data using the multiple regression method revealed significant differences in stride length, cadence, stance time, and double support time. Random Forest resulted in a PD classification accuracy of 92.6% after normalizing gait data using the multiple regression approach, compared to 80.4% (support vector machine) and 86.2% (kernel Fisher discriminant) using raw data and data normalized using dimensionless equations, respectively. Our multiple regression normalization approach will assist in diagnosis and treatment of PD using spatial-temporal gait data.