Biomechanics of the distal upper limb

The design and development of a finger joint simulator

Artificial finger joints lack the long-term clinical success seen with hip and knee prostheses. In part, this can be explained by the challenges of rheumatoid arthritis, a progressive disease which attacks surrounding tissues as well as the joint itself. Therefore, the natural finger joints’ biomechanics are adversely affected, and consequently, this imbalance due to subluxing forces further challenges any prosthesis. Many different designs of finger prosthesis have been offered over a period of greater than 50 years. Most of these designs have failed, and it is likely that many of these failures could have been identified had the prostheses been appropriately tested prior to implantation into patients. While finger joint simulators have been designed, arguably only those from a single centre have been able to reproduce clinical-type failures of the finger prostheses tested in them. This article describes the design and development of a finger simulator at Durham University, UK. It explains and justifies the engineering decisions made and thus the evolution of the finger simulator. In vitro results and their linkage to clinical-type failures are outlined to help to show the effectiveness of the simulator. Failures of finger implants in vivo continue to occur, and the need for appropriate in vitro testing of finger prostheses remains strong.

Computerised pinch dynamometry in the assessment of adult hand spasticity

BACKGROUND/AIM

The hand engages with the environment through the grasp, stabilisation, manipulation and release of objects during everyday tasks, activities and routines. Upper motor neuron syndrome following acquired brain injury may negatively impact hand function, reducing strength, range of motion and motor control. It is important for clinicians to reliably measure such impacts, particularly for the impact of intervention and to monitor change in performance over time. Therefore, the aim of this study was to investigate the test-retest reliability and construct validity of Dynamic Computerised pinch Dynamometry for measuring fine hand motor performance following acquired brain injury.

METHODS

The Dynamic Computerised pinch Dynamometry protocol was completed by 36 community dwelling adults and 27 healthy adults using a simulated pinch and release task in lateral and pincer grip positions. Measurements were conducted over two testing occasions approximately five weeks apart. Dynamic Computerised pinch Dynamometry output was evaluated to determine the test-retest reliability and construct validity of the measure.

RESULTS

Test-retest reliability scores using Kendall coefficient of concordance ranged from W = 0.61-0.94. Dynamic Computerised pinch Dynamometry discriminated between participants with and without acquired brain injury (z = 4.97-6.50, P < 0.05) and between the affected and non-affected hand of participants with acquired brain injury (z = 3.37-5.22, P < 0.001).

CONCLUSIONS

Dynamic Computerised pinch Dynamometry in both lateral and pincer positions had fair to excellent test-retest reliability, and had good construct validity for discrimination between participants with and without acquired brain injury as well as between the affected and non-affected hand of participants with acquired brain injury.

BIOMECHANICS OF THE NORMAL AND DISEASED METACARPOPHALANGEAL JOINT: IMPLICATIONS ON THE DESIGN OF JOINT REPLACEMENT IMPLANTS

The metacarpophalangeal (MCP) joint is crucial for hand function, but is frequently affected by arthritis, leading to pain and disability. This paper reviews the biomechanics of the normal and diseased joint in order to help consider the design of improved MCP joint replacement implants. The normal MCP joint enables a large range of motion in flexion/extension and abduction/adduction as well as a few degrees of rotation. A normal joint typically allows 90° flexion, with a grip strength of up to 672 N. The diseased joint has a reduced range of motion (typically 30° flexion) and reduced hand strength compared to the normal joint. Current MCP joint replacement implants generally try to recreate the range of motion of the normal joint; however, many designs are prone to fracture, as they are unable to withstand the conditions of the diseased joint. It may be beneficial for future implant designs to provide just a functional range of motion. Future designs of MCP joint replacement implants need to be more durable and last longer. Careful consideration of the diseased joint, rather than the normal joint, may help to better define the requirements for such implants.

Laparoscopic intracorporal colorectal sutured anastomosis using the Radius Surgical System in a phantom model

BACKGROUND

The Radius Surgical System (RSS) is a manipulator with additional degrees of freedom to enhance the dexterity of laparoscopic suturing. Our aim was to determine the feasibility and potentially added value of laparoscopic intracorporal sutured colorectal anastomosis (RSS) compared with suturing with conventional laparoscopic instruments (CLI).

METHODS

A total of 72 colorectal anastomoses and 30 single sutures using RSS and CLI were performed in the study. The experiment was divided as follows: One surgeon performed 40 colorectal anastomoses using RSS to assess the learning curve and the feasibility of the technique; The same surgeon performed 10 additional colorectal anastomoses with CLI which were then compared to the last 10 cases of the 40 anastomoses with RSS; Fifteen single sutures in the horizontal plane with RSS and 15 with CLI between two segments of colon were performed to compare the traction force to disrupt the suture; Twelve anastomoses were performed by the other three participants to evaluate ergonomy.

RESULTS

Three leakages (7.5%) were found in the 40 anastomoses with RSS but none after the eighth case. There was no stenosis. The mean time for the anastomoses once the learning curve was achieved was 32.7 min. After 21 anastomoses with RSS there was no improvement in the operating time. The quality of the suture was superior with RSS, with a larger anastomosis diameter, higher bursting pressure, and fewer suturing failures being found. The RSS suture withstood a higher traction force. The participants showed more discomfort suturing with CLI.

CONCLUSION

This study demonstrated the feasibility of laparoscopic colorectal anastomosis using RSS. Anastomosis with RSS was shown to be safer. The three participants evaluating ergonomy reflected less discomfort in hand/wrist using RSS. Others ergonomic problems were comparable to CLI.

A test procedure for artificial finger joints

This paper highlights the lack of an agreed testing standard for artificial finger joints. It reviews the anatomy, pathology and biomechanics of finger joints as well as the various designs of finger prostheses and the machines used to test them. While pre-implantation testing should be fundamental, increasing regulation of the biomedical engineering industry will further demand testing of prostheses to pre-agreed standards. Standards relating to the testing of other artificial joints are reviewed before possible parameters for testing finger prostheses are offered.