The primary deforming forces in Bennett and Rolando fractures are the Abductor pollicis longus and adductor pollicis.
In a Bennet's or Rolando fracture-dislocation the volar-ulnar fracture fragment is held reduced by the anterior oblique ligament while strong deforming forces pull the remaining metacarpal shaft proximally and dorsally, angulate the shaft ulnarly and supinate the shaft. Most important in these deforming forces are the abductor pollicis longus (APL) inserting on the base of the metacarpal which pulls the metacarpal shaft proximally and dorsally and the adductor pollicis (AP) which inserts on the ulnar base of the proximal phalanx and angulates the metacarpal shaft ulnarly and supinates the shaft. Less important is the extensor pollicis longus (EPL) which inserts on the base of the distal phalanx and also adds to the ulnar angulation of the distal fragment.
Soyer reviews the diagnosis, pathoanatomy, and treatment for fractures at the base of the 1st metacarpal. Understanding the biomechanics, anatomical deforming forces, and the exact fracture pattern aids the treating surgeon in determining the most appropriate method of fixation. The most essential factor for obtaining a good functional result is anatomic restoration of the articular surface.
Elgafy et al. examined the terminal anatomy of the posterior interosseous nerve in their cadaver study - identifing six terminal branches and describing methods to avoid injury. They describe how treating surgeons can maximize function and recovery after base of the 1st metacarpal fractures by understanding these nervous branches and specific fracture pattern treatment to avoid iatrogenic injury to the PIN.
Soyer AD. Fractures of the base of the first metacarpal: current treatment options. J Am Acad Orthop Surg. 1999 Nov-Dec;7(6):403-12. Review.
PMID:11505928 (Link to Abstract)
Elgafy H, Ebraheim NA, Rezcallah AT, Yeasting RA. Posterior interosseous nerve terminal branches. Clin Orthop Relat Res. 2000 Jul;(376):242-51.
PMID:10906882 (Link to Abstract)
Trumble TE (ED). Hand Surgery Update 3: Hand, elbow, and shoulder. American Society for Surgery of the Hand. Rosemont, IL. 2003, PP 47-56