What is the distance between the insertion of the distal end of the bicep tendon and the head of the radius?
From {1}:


  Abstract
  PURPOSE:
  There is little information in the literature describing the anatomy of the biceps tendon insertion. The purpose of this study was to map the footprint of the biceps tendon insertion on the bicipital tuberosity and to report on the relevant anatomy to assist surgeons with correct tendon orientation during surgical repair.
  METHODS:
  Fifteen fresh-frozen adult upper extremities were used in this study. The relationships between the long head of the biceps tendon, the short head of the biceps tendon, the muscle bellies, and the distal tendon orientation were examined. The length, width, and area of the biceps tendon insertion were measured.
  RESULTS:
  In all specimens examined, the biceps musculotendinous unit rotated 90 degrees externally from origin to insertion. The long head of the distal tendon was inserted onto the proximal aspect of the bicipital tuberosity, while the short head of the distal tendon was inserted onto the distal aspect of the tuberosity. The lacertus fibrosus, in all specimens, originated from the distal short head of the biceps tendon. On average, the biceps tendon insertion started 23 mm distal to the articular margin of the radial head. The average length of the biceps tendon insertion on the tuberosity was 21 mm, and the average width was 7 mm. The average total area of the biceps tendon insertion (footprint) was 108 mm(2). The average area of the long head of the biceps tendon insertion was 48 mm(2), and the average area of the short head of the biceps tendon insertion was 60 mm(2).
  CONCLUSIONS:
  Landmarks have been identified that will allow anatomic orientation of the distal biceps tendon during operative repair. The distal short head of the biceps tendon has a consistent relationship with the lacertus fibrosus and a distinct insertion on the bicipital tuberosity. The dimensions of the distal biceps tendon footprint have been determined to assist with bone tunnel or suture anchor placement during surgical repair.


(bicipital tuberosity = radial tuberosity)

Some figures from the same study:







FYI:


How correlated are the lengths of tendons in different part of a human body?
How can I measure my tendon length?




References:


{1} Athwal, George S., Scott P. Steinmann, and Damian M. Rispoli. "The distal biceps tendon: footprint and relevant clinical anatomy." The Journal of hand surgery 32, no. 8 (2007): 1225-1229. https://www.ncbi.nlm.nih.gov/pubmed/17923307 ; https://scholar.google.com/scholar?cluster=16116840451671820399&amp;hl=en&amp;as_sdt=0,22 ; http://www.sciencedirect.com/science/article/pii/S0363502307005163 ; http://dx.doi.org/10.1016/j.jhsa.2007.05.027 ; http://sci-hub.cc/10.1016/j.jhsa.2007.05.027