Bone microstructure as an indicator of digging ability in moles (Talpidae, Eulipotyphla).

Talpid moles (Talpidae, Eulipotyphla) are mammals highly specialised in burrowing using their forelimbs. Fossoriality has allowed moles to expand their ecological niche by enabling access to subterranean resources and spaces. This specialisation in burrowing has led to adaptations in the forelimb bones of moles for humeral rotation digging, a distinctive strategy unparalleled among other diggers. While bone robustness has been examined in moles through external morphology, the adaptation of bone microstructure to digging strategy remains unclear. Based on two assumptions, (1) the humerus of moles is subjected to a torsional load due to humeral rotation digging, and (2) the magnitude of torsional load correlates with the compactness of the substrate in which the individuals can dig, we hypothesised that humeral rotation digging influences bone microstructure. Comparative analyses of transverse sections from the humeri and femora of three mole species (Mogera imaizumii, Mogera wogura and Urotrichus talpoides; Talpidae) and an outgroup eulipotyphlan (Suncus murinus; Soricidae) revealed that (1) vascular canals distributed in the humeri of moles align more predominantly circumferential along the bone walls, indicating an adaptation to the torsion generated by humeral rotation digging, and (2) the laminarity of vascular canals, particularly in Mogera species compared with Urotrichus, potentially reflects differences in the magnitude of load due to substrate compactness during digging. The aligned vascular canals are distinctive traits not observed in mammals employing other digging strategies. This suggests that vascular canal laminarity can be an indicator of not only humeral rotation digging in fossorial animals, but also the variation of eco-spaces in talpid species.

A Soft-Tissue Landmark to Assess Humeral Component Rotation in Total Elbow Arthroplasty.

HYPOTHESIS: Assessing the rotational alignment of the humeral component during total elbow arthroplasty is dependent upon bony landmarks that can be absent or altered in cases of distal humerus fractures, revision arthroplasty, severe bone loss, or deformity. We hypothesize that the intermuscular septum can be used as a reliable soft-tissue landmark to set the rotation of the humeral component intra-operatively when previously described bony landmarks are not reliable or present. MATERIALS AND METHODS: Forty-eight unpaired cadaveric human subjects (mean age and standard deviation 63 ± 12 years; 24 males, 24 females) underwent computed tomography (CT) scans. The geometric centers of the trochlea and capitellum were assessed, and the line through these two points was set as the flexion-extension axis (FEA) of the elbow. The intermuscular septum axis (IMSA) was drawn proximal to the olecranon fossa and at least 4 cm proximal to the most distal point of the articular surface, where the posterior humeral cortex was flat. The angles between the FEA and IMSA were calculated and compared using a two-tailed t-test. Regression analysis was used to assess the inter- and intra-observer reliability of the IMSA. RESULTS: The IMSA was externally rotated 10.3° ± 2.8 compared to the FEA (p < 0.001 and confidence interval (CI) of 2.8 with α set to 0.01). The inter- and intra-observer reliability of the IMSA was high, with an R-value of 0.91 and 0.97, respectively. CONCLUSIONS: The intermuscular septum can be used as a soft-tissue landmark to set humeral component rotation and is 10.3° externally rotated with respect to the FEA of the ulnohumeral joint.

Fossorial mammals emphasise the forelimb muscle moment arms used for digging: New indices for reconstruction of the digging ability and behaviours in extinct taxa.

Among fossorial mammals, forelimbs are major digging apparatuses for dwelling, sheltering and foraging underground. Forelimb-diggers have independently evolved in many lineages of mammals; thus, the method of digging with forelimbs varies by taxon. Therefore, the reconstruction of digging behaviours in extinct animals leads us to understand the evolutionary process of fossorial adaptation in each lineage. However, no morphological index was found to reconstruct if, or how, extinct taxa dug with forelimbs. In this study, we used the shoulder and elbow muscle moment arms in relation to the out-force lever on the manus as indices of the efficiency of motions. The mechanical advantage of two shoulder motions (medial rotation and retraction) and three elbow motions (extension, flexion and adduction) was measured in 381 extant mammal specimens representing 332 species, 279 genera, 103 families and 24 orders. Assuming that both forelimb-digging and -paddling in water require relatively high-output moment arm efficiency, the studied taxa were categorised into four groups based on the presence or absence of forelimb-digging and -paddling abilities. We found that the efficiencies of all five muscle moment arms in the forelimb-diggers and -paddlers were higher than those of the non-diggers and non-paddlers. Furthermore, among the forelimb-diggers, the taxa that dig compact substrates or frequently burrow tend to emphasise the muscle moment arms compared to the taxa that dig loose substrates or dig less frequently. The comparison among the 53 extant forelimb-diggers revealed that the efficiency marked among the five muscle moment arms reflects the difference in digging strategy: humeral rotation diggers emphasise the shoulder medial rotator and elbow adductor, hook-and-pull diggers emphasise the shoulder retractor and elbow flexor and scratch diggers emphasise the shoulder retractor and elbow extensor. We propose that these indices will be powerful tools for reconstructing the fossorial behaviours of extinct mammals. Applying these indices to extinct taxa, Ceratogaulus, Ernanodon, Metacheiromys and Prozaedyus are capable of more efficient forelimb-digging, and each may have adopted different digging strategies.

Concomitant latissimus dorsi tendon transfer during reverse total shoulder arthroplasty does not improve active external rotation or clinical outcomes in patients with external rotation deficit.

BACKGROUND: To assess the role of latissimus dorsi tendon transfer (LDT) concomitant with reverse total shoulder arthroplasty in patients with external rotation (ER) deficit secondary to severe rotator cuff deficiency with and without glenohumeral arthritis. METHODS: Patients with a positive external lag sign and <10° of active external rotation (aER) treated with reverse shoulder arthroplasty at a single institution with a minimum 12-month follow-up were retrospectively identified from a prospective database. Basic demographic information along with preoperative and postoperative range of motion (ROM) measures, American Shoulder and Elbow Surgeons score (ASES), Visual Analog Scale (VAS) pain, and Subjective Shoulder Value scores were obtained. Statistical analysis was performed to compare ROM and functional outcomes between patients who underwent concomitant LDT and those with no transfer (NT). RESULTS: The LDT (n = 31) and NT (n = 33) groups had similar age, sex distributions, and follow-up length average (24 vs. 30 months). No differences were found between groups at baseline, final follow-up, or magnitude of change for ASES, VAS pain, and Subjective Shoulder Value scores. Baseline ROM measures were similar, except for the LDT group having slightly less aER (-8° vs. 0°; P = .004). In addition, all postoperative ROM measures including aER were similar, except for a slight improvement in active internal rotation in the NT group. The majority of patients were satisfied with their outcome (LDT 84% (n = 26); NT 87% (n = 27); P = .72). CONCLUSION: Patients with ER deficit secondary to severe rotator cuff deficiency with and without glenohumeral arthritis undergoing reverse total shoulder arthroplasty do not have significantly improved ER or patient-reported outcome measures with LDT.

The effect of neck muscle fatigue on shoulder humeral rotation joint position sense.

INTRODUCTION: Cervical extensor muscle (CEM) fatigue causes decrements in upper limb proprioceptive accuracy during constrained single-joint tasks. This study used a novel humeral rotation joint position sense (JPS) measurement device to compare JPS accuracy in participants who received acute CEM fatigue vs. non-fatigued controls. METHODS: Participants had vision occluded and were passively guided into postures of internal humeral rotation from a baseline posture before and after a CEM fatigue or control protocol. Mixed model repeated measures ANOVAs were used to verify fatigue and compared absolute, constant, and variable JPS error between groups. RESULTS: CEM fatigue was verified via pre-post reduction in CEM strength, and myoelectric indicators of fatigue. However, between-group comparisons of absolute, constant, and variable JPS error were not statistically significant, despite having large effect sizes. DISCUSSION: Contrary to prevailing literature, unconstrained humeral rotation JPS did not appear to be affected by CEM fatigue in this study. However, between-group differences in JPS error were dwarfed by inter-trial variability, which likely arose due to the unconstrained nature of this task, conflating chances for a Type II error. Future research should perform a kinematic analysis of task constraints to highlight potential compensatory mechanisms obscuring significant findings in this otherwise robust effect.

Effects of gleno-humeral joint centre mislocation on gleno-humeral kinematics and kinetics.

The gleno-humeral (GH) rotation centre is typically estimated using predictive or functional methods, however these methods may lead to location errors. This study aimed at determining a location error threshold above which statistically significant changes in the values of kinematic and kinetic GH parameters occur. The secondary aims were to quantify the effects of the direction of mislocation (X, Y or Z axis) of the GH rotation centre on GH kinematic and kinetic parameters. Shoulder flexion and abduction movements of 11 healthy volunteers were recorded using a standard motion capture system (Vicon, Oxford Metrics Ltd, Oxford, UK), then GH kinematic and kinetic parameters were computed. The true position of the GH rotation centre was determined using a low dose x-ray scanner (EOS™ imaging, France) and this position was transferred to the motion data. GH angles and moments were re-computed for each position of the GH rotation centre after errors of up to ± 20 mm were added in increments of ± 5 mm to each axis. The three-dimensional error range was 5 mm to 34.65 mm. GH joint angle and moment values were significantly altered from 10 mm of three-dimensional error, and from 5 mm of error on individual axes. However, errors on the longitudinal and antero-posterior axes only caused very small alterations of GH joint angle and moment values respectively. Future research should develop methods of GH rotation centre estimation that produce three-dimensional location errors of less than 10 mm to reduce error propagation on GH kinematics and kinetics.

Comparison of humeral rotation co-activation of breast cancer population and healthy shoulders.

Upper limb morbidities are common amongst the breast cancer population (BCP) and have a direct impact on independence. Comparing muscle co-activation strategies between BCP and healthy populations may assist in identifying muscle dysfunction and promote clinical interpretation of dysfunction, which could direct preventative and therapeutic interventions. The purposes of this study were to define humeral rotation muscle co-activation of a BCP and to compare it with a previously defined co-activation relationship of a healthy population. Fifty BCP survivors performed 18 isometric internal and external rotation exertions at various postures and intensities. Surface and intramuscular electrodes recorded shoulder muscle activity. BCP co-activation was predicted at r(2)=0.77 during both exertion types. Humeral abduction angle and task intensity were important factors in the prediction of co-activation in both populations. Comparisons made between populations identified differing muscle strategies used by BCP to maintain postural control. Compared to healthy co-activation, the BCP demonstrated greater activation of internal (IR) and external rotator (ER) type muscles during their respective rotation type. The BCP demonstrated increased (⩾8.7%) activation of pectoralis major. This study has provided insight into how BCP muscles compensate during dysfunction. Continued advancement of this knowledge can provide more understanding of dysfunction, promote generation of evidence-based therapies, and can be useful in biomechanical modeling.

Comparative analysis of acromiohumeral distances according to the locations of the arms and humeral rotation.

[Purpose] The purpose of this study was to compare the potential effects of resistance exercise according to the positions of the arms and the rotation of the humerus on the subhumeral acromial space. [Subjects] The study subjects were 34 subjects without shoulder pain. [Methods] Ultrasonographic measurements of the acromiohumeral distance of the subjects were made at three shoulder positions: 90° flexion, scaption at 90° abduction, and 90° abduction in an upright sitting position. The subjects were instructed to vertically push against a table to the maximum level with the humerus in internal, neutral, and external rotation. The measurements were made three times in each position. [Results] There was a significant difference in acromiohuneral distance between neutral and internal rotation of the humerus, and between external rotation and internal rotation of the humerus. In the scaption position, there was a significant difference between neutral and internal rotation of the humerus, and between external rotation and internal rotation of the humerus. In the 90° flexion position, there was a significant difference between neutral and internal rotation, and between neutral and external rotation. There was a significant difference between the flexion position and the abduction position, and between the flexion position and the scaption position. In terms of the internal rotation of the humerus, there was a significant difference between 90° flexion and 90° abduction. [Conclusion] These findings can be applied in exercises prescribed to increase the acromiohumeral distance and to aid the treatment and evaluation of shoulder dysfunctions.

Early outcomes of staged bilateral reverse total shoulder arthroplasty: a case-control study.

Some surgeons are reluctant to perform a reverse total shoulder arthroplasty (RTSA) on both shoulders because of concerns regarding difficulty with activities of daily living post-operatively as a result of limited rotation of the shoulders. Nevertheless, we hypothesised that outcomes and patient satisfaction following bilateral RTSA would be comparable to those following unilateral RTSA. A single-surgeon RTSA registry was reviewed for patients who underwent bilateral staged RTSA with a minimum follow-up of two years. A unilateral RTSA matched control was selected for each shoulder in those patients undergoing bilateral procedures. The Constant-Murley score (CMS), American Shoulder and Elbow Surgeons (ASES) score, Subjective Shoulder Values (SSV), visual analogue scale (VAS) for pain, range of movement and strength were measured pre- and post-operatively. The mean CMS, ASES, SSV, VAS scores, strength and active forward elevation were significantly improved (all p < 0.01) following each operation in those undergoing bilateral procedures. The mean active external rotation (p = 0.63 and p = 0.19) and internal rotation (p = 0.77 and p = 0.24) were not significantly improved. The improvement in the mean ASES score after the first RTSA was greater than the improvement in its control group (p = 0.0039). The improvement in the mean CMS, ASES scores and active forward elevation was significantly less after the second RTSA than in its control group (p = 0.0244, p = 0.0183, and p = 0.0280, respectively). Pain relief and function significantly improved after each RTSA in those undergoing a bilateral procedure. Bilateral RTSA is thus a reasonable form of treatment for patients with severe bilateral rotator cuff deficiency, although inferior results may be seen after the second procedure compared with the first.