Effect of Biceps Reattachment Location on Moment Arm

The ultimate goal of the project is to quantify the effect of biceps tendon attachment location in clinically relevant terms, range of motion and torque generating ability as measured by muscle moment arm. Our hypothesis was that an anatomic repair would recreate native tendon moment arm and forearm rotation, while a non-anatomic insertion would compromise moment arm and forearm rotation. Isometric supination torque and range of motion were measured for the native distal biceps tendon and 4 systematically placed repair points in 6 cadaveric specimens. A computer controlled elbow simulator, which exerts known loads on the forearm applied through the biceps tendon, was adapted to a device capable of measuring isometric forearm torque generated by cadaveric elbows.For torque testing, the biceps tendon was loaded, and the torque generated was measured with the forearm fixed at 60° pronation, neutral, and 60° supination. Range of motion testing was done by incrementally loading the biceps while measuring the supination motion generated using a digital goniometer.Tendon location and forearm position significantly affected the moment arm of the biceps. The native tendon had a mean moment arm of 5.67±2.86 and 10.44±1.45 (mm) in 60° supination and neutral respectively. Anatomic repair in all forearm positions showed no significant difference from the native insertion. However, a centralized anterior repair was significantly lower in supination (0.15 ±3.48) and neutral (7.65 ±1.95) and also produced significantly less supination motion. No difference was observed between all tendon locations in pronation. Clinically, these findings would suggest that patients with a biceps repair might experience the most weakness in a supinated position without experiencing a deficit in the pronated forearm. Surgically, particular attention needs to be paid to the geometry of the tuberosity and location of tendon reattachment as it could play a critical role in maximizing the functional outcomes of patients. The results of this study could help surgeons gain a better understanding of how to optimize their repair and thereby improve the expected outcome of their patients with distal biceps injuries

Challenging the spliceosome machine

BACKGROUND: Using cDNA copies of transcripts and corresponding genomic sequences from the Berkeley Drosophila Genome Project, a set of 24,753 donor and acceptor splice sites were computed with a scanning algorithm that tested for single nucleotide insertion, deletion and substitution polymorphisms. Using this dataset, we developed a progressive partitioning approach to examining the effects of challenging the spliceosome system. RESULTS: Our analysis shows that information content increases near splice sites flanking progressively longer introns and exons, suggesting that longer splice elements require stronger binding of spliceosome components. Information also increases at splice sites near very short introns and exons, suggesting that short splice elements have crowding problems. We observe that the information found at individual splice sites depends upon a balance of splice element lengths in the vicinity, including both flanking and non-adjacent introns and exons. CONCLUSION: These results suggest an interdependence of multiple splicing events along the pre-mRNA, which may have implications for how the macromolecular spliceosome machine processes sets of neighboring splice sites