The influence of full-thickness supraspinatus tears on abduction moments: the importance of the central tendon

BACKGROUND

Detachment of the central tendon of the supraspinatus from its insertion is considered to be crucial to functional deficit. The aim of the present study was to assess the function of the supraspinatus in terms of abduction moments by introducing different tear configurations to assess the functional effect of the central tendon insertion.

METHODS

Ten fresh frozen shoulders from five cadavers were prepared for testing. A testing protocol was established to measure the abduction moment of the supraspinatus under physiological loading tailored to the anthropometrics of each specimen. Four conditions were tested: intact supraspinatus; complete detachment of portion of the supraspinatus tendon anterior to the main central tendon; detachment of the main central tendon; and detachment of the region of the supraspinatus posterior to the main central tendon.

RESULTS

There was a significant and large reduction in abduction moment when the central tendon was sectioned (p < 0.05). A smaller reduction in abduction moment was found when the regions anterior and posterior to the main central tendon were sectioned (p < 0.05).

CONCLUSIONS

The central tendon is vital in the role of functional arm abduction through force transmission through the intact rotator cuff. Reinsertion of the central tendon in the correct anatomical location is desirable to optimize functional outcome of surgery.

A Patient-Specific Foot Model for the Estimate of Ankle Joint Forces in Patients with Juvenile Idiopathic Arthritis

Juvenile idiopathic arthritis (JIA) is the leading cause of childhood disability from a musculoskeletal disorder. It generally affects large joints such as the knee and the ankle, often causing structural damage. Different factors contribute to the damage onset, including altered joint loading and other mechanical factors, associated with pain and inflammation. The prediction of patients’ joint loading can hence be a valuable tool in understanding the disease mechanisms involved in structural damage progression. A number of lower-limb musculoskeletal models have been proposed to analyse the hip and knee joints, but juvenile models of the foot are still lacking. This paper presents a modelling pipeline that allows the creation of juvenile patient-specific models starting from lower limb kinematics and foot and ankle MRI data. This pipeline has been applied to data from three children with JIA and the importance of patient-specific parameters and modelling assumptions has been tested in a sensitivity analysis focused on the variation of the joint reaction forces. This analysis highlighted the criticality of patient-specific definition of the ankle joint axes and location of the Achilles tendon insertions. Patient-specific detection of the Tibialis Anterior, Tibialis Posterior, and Peroneus Longus origins and insertions were also shown to be important.

Scaling and kinematics optimisation of the scapula and thorax in upper limb musculoskeletal models

Accurate representation of individual scapula kinematics and subject geometries is vital in musculoskeletal models applied to upper limb pathology and performance. In applying individual kinematics to a model׳s cadaveric geometry, model constraints are commonly prescriptive. These rely on thorax scaling to effectively define the scapula׳s path but do not consider the area underneath the scapula in scaling, and assume a fixed conoid ligament length. These constraints may not allow continuous solutions or close agreement with directly measured kinematics.

A novel method is presented to scale the thorax based on palpated scapula landmarks. The scapula and clavicle kinematics are optimised with the constraint that the scapula medial border does not penetrate the thorax. Conoid ligament length is not used as a constraint. This method is simulated in the UK National Shoulder Model and compared to four other methods, including the standard technique, during three pull-up techniques (n=11). These are high-performance activities covering a large range of motion.

Model solutions without substantial jumps in the joint kinematics data were improved from 23% of trials with the standard method, to 100% of trials with the new method. Agreement with measured kinematics was significantly improved (more than 10° closer at p<0.001) when compared to standard methods. The removal of the conoid ligament constraint and the novel thorax scaling correction factor were shown to be key. Separation of the medial border of the scapula from the thorax was large, although this may be physiologically correct due to the high loads and high arm elevation angles.

The influence of extreme speeds on scapula kinematics and the importance of controlling the plane of elevation

BACKGROUND

The effect of high-speed movement on scapula kinematics is not clear from the literature. Understanding these effects is important for clinicians examining, managing and understanding scapula kinematic pathologies: impingement, glenohumeral instability, muscle patterning instability and athletic injuries. The scapula tracking methodology and the lack of quantified control of the movement's plane of elevation limits previous studies. The aim of the present study is to use improved dynamic scapula kinematic measurement to assess differences during planar movements across different speeds. Athletic and maximal speeds, neglected in previous studies, are the focus.

METHODS

Thirteen subjects performed slow, fast and maximal scapula plane abduction and forward flexion. A previously validated skin-fixed scapula tracker was used and optimally calibrated. A stiff board controlled the plane of elevation. Scapula kinematics were consistent with the literature.

FINDINGS

Large and statistically significant differences were found to exist between scapula kinematics at slow speeds compared to fast and maximal speeds in lateral rotation and protraction. Although some differences were observed in the plane of elevation between speeds, these were not considered to effect the conclusions.

INTERPRETATION

The speed of movement should be considered an important factor affecting scapula kinematics. Clinical studies analysing muscle recruitment strategies and causes of injury in athletic tasks must account for changing kinematics rather than extrapolating slow or static measures and effective clinical examination and management of pathology must take these kinematic changes into account. Control of the plane of movement is challenging and its effectiveness must be quantified in future kinematic studies.