Understanding the biomechanics of the forearm during the dart thrower's motion

This study investigated the contribution of different forearm muscles, namely the flexor carpi ulnaris, extensor carpi radialis longus and brevis, extensor carpi ulnaris and flexor carpi radialis, during the dart thrower's motion. Thirteen healthy participants were recruited. The forearm muscle activation patterns during the dart thrower's motion were measured using surface electromyography. The average root mean square for the extensor carpi ulnaris was found to be the highest during the dart thrower's motion. Muscle activations during the dart thrower's motion were heterogeneous among the participants. The results suggest the rehabilitation protocol for patients with wrist injuries should be reconsidered.

The right turn around: Penrose tourniquet application in paediatrics

INTRODUCTION

Commercially available tourniquets are ill-suited for paediatric patients with limb circumferences smaller than the required mechanism, forcing surgeons to improvise. This study aimed to quantify pressures exerted by the Penrose tourniquet when applied on a phantom model and evaluate the intra-/inter-rater reproducibility of the technique previously proposed.

METHODS

Eight calibrated pressure sensors were distributed evenly along the inner and outer circumference of a silicon-based model. A 30cm-by-3.2 cm ARGYLE Penrose drain, 4-by-4 gauze, marker and ruler were used. The optimal interval for arterial occlusion was determined to be 70% of limb circumference. The tourniquet was secured using two half-knots formed by gauze.

RESULTS

Two-turns of the tourniquet about the model generated mean pressures (SD) of 209.43 (SD:35.98 mmHg) (95%CI: 195.85-224.00 mmHg) (outer-sensor) and 246.32 (SD:61.92 mmHg) (95%CI: 221.02-273.49 mmHg) (inner-sensor). Three-turns generated mean pressures of 302.07 (SD:23.98 mmHg) (95%CI: 292.29-312.53 mmHg) (outer-sensor) and 314.44 (SD:56.70 mmHg) (95%CI: 291.25-338.25 mmHg) (inner-sensor).

CONCLUSION

The Penrose tourniquet has clinical utility, particularly for patients where commercially available tourniquets are not suitable. Current application techniques generate inconsistent pressures. Using the existing model, further refinement can be done to improve the consistency and safety of the application. We recommend using intervals of slightly more than 70% of limb circumference and only two turns of the Penrose tourniquet during application.

LEVEL OF EVIDENCE

V.

Which is the most ergonomic mop? A comparison of three domestic mopping systems

PURPOSE

To assess musculoskeletal risk factors (repetitions, posture, forces) of the upper limb during domestic floor mopping tasks.

METHODS

Two hundred women were surveyed to determine the most common mopping system, mopping patterns and type of flooring used in their homes. The biomechanical demands of the three most common mopping systems were then evaluated in the laboratory. Participants were also asked to rate their perceived levels of exertion and cleanliness of each mopping system.

RESULTS

The use of wet wipes had the highest repetition count and exertion rates during mopping and scrubbing tasks. Higher peak scrubbing forces were noted for the plunge mop. All participants found the cotton fibre mop to be the cleanest. All 3 mops had medium postural risk.

CONCLUSION

The advantages and disadvantages of each mopping system were outlined and may be used by occupational therapists when providing ergonomic advice to patients with upper limb musculoskeletal conditions.

Investigating the functional grip strength of elderly fallers in Singapore

Background:

Static grip strength has been a reliable method for assessing the functional capacity of the individual and can be a useful marker for identifying elderly people at risk of functional deterioration leading to a fall. However, static grip strength alone may not represent the true maximum strength that an individual could exert in his/her daily life, especially if the task requires simultaneous forces from gripping and a forearm twisting action, which is termed as functional isometric grip strength. Hence, the objectives of this study were to determine the differences in the fallers’ grip strengths at static-neutral grip position and during isometric forearm pronation/supination, as well as the differences between the maximum and sustained isometric grip strengths.

Methods:

Data were analysed from 31 elderly people (11 males and 20 females) aged 70 and over. Using a custom-made hand strength measurement device, three measurements were taken: (1) grip strength in neutral forearm position; (2) grip strength during isometric forearm pronation; and (3) grip strength during isometric forearm supination.

Results:

Elderly fallers could only achieve approximately 60%–80% of the maximum normative strength. Additionally, it was found that their functional isometric grip strengths were generally weaker than their static maximal grip strength, especially during isometric supination as either maximum or sustained isometric supination grip strengths (Dominant hand: 10.6 kg and 8.5 kg, respectively (males); 6.0 kg and 4.4 kg, respectively (females)).

Conclusion:

Elderly fallers are weaker when their grip is subjected to additional torque, endurance or both. Hence, these findings have potential implications for designing better screening tools for the geriatric population.

Computational Simulation of Synovial Fluid Kinematics of the Scapholunate Joint

Background: The interaction between wrist kinematics and synovial fluid pressure has yet to be studied. To our knowledge, this is the first study to determine the effect of scapholunate joint kinematics on synovial fluid pressure change using finite volume method. Methods: The carpal bones of a cadaveric hand were obtained from Computed Tomography (CT) scans. CT images of the carpal bones were segmented and reconstructed into 3D model. The 3D synovial fluid model between the scaphoid and lunate was constructed and then used for computational simulations. The kinematics data of scapholunate joint obtained from radioulnar deviation of the wrist was investigated. Results: It was found that the pressure in synovial fluid varied from -1.68 to 2.64 Pa with maximum pressure located at the scaphoid-fluid interface during the radial deviation. For ulnar deviation, the pressure increased gradually from the scaphoid-fluid interface towards the lunate-fluid interface (-1.37 to 0.37 Pa). Conclusions: This new computational model provides a basis for the study of pathomechanics of ligament injury with the inclusion of synovial fluid.

An Exploratory Study Using Semi-Tabular Plate in Zone II Flexor Tendon Repair

Background: This study evaluated the feasibility of using a low-profile titanium (Ti) plate implant, also known as the Ti-button, for Zone II flexor tendon repair. We hypothesize that the use of the Ti-button can distribute the tensile force on the digital flexor tendons to achieve better biomechanical performance.

Methods: Twenty lacerated porcine flexor tendons were randomly divided into two groups and repaired using Ti-button or 6-strand modified Lim-Tsai technique. Ultimate tensile strength, load to 2 mm gap force, and mode of failure were recorded during a single cycle loading test. We also harvested twelve fingers with lacerated flexor digitorum profundus tendons from six fresh-frozen cadaver hands and repaired the tendons using either Ti-button method or modified Lim-Tsai technique. A custom-made bio-friction measurement jig was used to measure the gliding resistance and coefficient of friction of the tendon sheath interface at the A2 pulley.

Results: The ultimate tensile strength, load to 2 mm gap force, stiffness, and gliding resistance of the Ti-button repairs were 101.5 N, 25.7 N, 7.8 N/mm, and 2.2 N respectively. Ti-button repairs had significantly higher ultimate tensile strength and stiffness than the modified Lim-Tsai repair. However, Ti-button also increased the gliding resistance and coefficient of friction but there was no significant difference between the two repair techniques.

Conclusions: Ti-button repair displayed comparable mechanical properties to the traditional repair in terms of 2-mm gap formation and gliding resistance, but with a stronger repair construct. Thus, this deepened our interest to further investigate the potential of using Ti-button implant in Zone II flexor tendon repair by studying both the mechanical and biochemical (tendon healing) properties in more in-depth.

A Biomechanical Comparison of Different Knots Tied on Fibrewire Suture

BACKGROUND

Synthetic sutures such as Fiberwire used in flexor tendon repairs have high tensile strength. Proper application allows early mobilisation, decreasing morbidity from repair rupture and adhesions while preserving range of motion. Suture stiffness can cause poorer knot holding, contributing to gapping, peritendinous adhesions or rupture. Previous studies recommended more throws in knots tied on Fiberwire to prevent knot slippage. These larger knots are voluminous and prominent. In tendon repairs they can cause "catching", increase friction and work of flexion. Other studies advocated certain complicated knots as being more secure. We evaluated several knots and their biomechanical properties with the aim of finding a compact knot with less potential for slippage to maximise strength potential of flexor tendon repairs using Fiberwire.

METHODS

A series of different knots tied on Fiberwire 4-0 sutures were pulled to failure on a mechanical tester. Mean tensile strengths, knot volumes and tensile strength to knot volume ratios were compared.

RESULTS

Tensile strengths and knot volume increased with more throws and loops. Four variations of the square knot (the 4=4=1, 2=2=2=2, 1=1=1=1=1, 2=1=1=1=1 knots) had tensile strengths greater than 35N. The specialised anti-slip knot had highest tensile strength and suture volume but lower strength-to-volume ratio.

CONCLUSIONS

The anti-slip knot had highest tensile strength but it also had the highest volume. The greater strength of repair may not translate into improved clinical outcome. The 1=1=1=1=1 knot has superior knot strength-to-volume ratio with good knot strength adequate for early active mobilisation in flexor tendon repairs.