Volar plate division necessary for metacarpophalangeal joint dislocation reduction, study finds

SAN FRANCISCO — The volar plate is the primary structure preventing reduction of dislocation in the metacarpophalangeal (MP) joint and must be divided to reduce dislocation, according to a study presented here.

The findings were part of a study by Ahmed M. Afifi, MD, presented at the Combined Annual Meeting of the American Society for Surgery of the Hand and American Society of Hand Therapists, here.

“Most authors believe it is the volar plate that prevents reduction, however there are two other theories that are always mentioned,” Afifi said. “One of them is the transverse of the carpal ligament, forming a continuous dent of the volar plate. The other theory is the noose theory.”

According to Afifi, the results disprove Kaplan’s noose theory — that the flexor tendons, lumbricals, superficial transverse and natatory ligaments cause irreducibility.

An open dissection

Afifi’s team attempted closed reduction on dislocations created in nine cadaveric hands. Irreducible cases were followed up with an open dissection of the joint in the effort to identify the anatomy of the structures surrounding the MP joint as well as the cause of the irreducibility. Six joints were irreducible.

“Our findings show that the flexor tendons were always ulnar to the carpal head, which is in agreement with most of the published literature,“ Afifi said.

In addition, the study noted that the radial digital nerve was superficial (50%) or radial (50%) to the metacarpal head and the lumbrical was usually radial (83%) to the joint. Division of the volar plate was found to be necessary to reduce the dislocation in all cases, whereas division of the deep transverse metacarpal ligament was reported to be less effective.

The study found that the natatory and superficial transverse metacarpal ligaments, flexor tendons and the lumbricals all do not contribute to irreducibility.

“Relief of all the structures forming the noose did not allow induction of dislocation,” Afifi said. “We therefore believe that the noose theory proposed by Kaplan is inaccurate, as based on our cadavers.”

The results, Afifi said, also point toward the volar plate being the primary structure preventing the reduction of MP dislocations.

Furthermore, due to the variability of the structures surrounding the MP joint, Afifi and that careful dissection to prevent iatrogenic injuries is “mandatory.”

Alternative approaches

Moderator Steven Z. Glickel, MD, complimented Afifi on the biomechanical apparatus used in the study to create the dislocations.

“The technique is clever and reproducibly achieved the desired pathology,” Glickel said. “That is the strength of this study.”

Glickel asked Afifi about alternative approaches to treatment, specifically the dorsal approach.

“Proponents of the volar approach say you need to go volarly to release the noose that is wrapped around the carpal head,” Afifi replied. “Based on what we have found, we see that as unnecessary. As you can see, the anatomy is quite variable … it is not always very straightforward. Based on this, I believe the dorsal approach makes more sense.”

Afifi also stated further studies were necessary.

Reference:
Afifi AM, Cheema TA, Medoro A, et al. Anatomy of irreducible metacarpophalangeal joint dislocation in a cadaver model. Paper HS-19. Presented at the Combined Annual Meeting of the American Society for Surgery of the Hand and American Society of Hand Therapists. September 2-5, 2009. San Francisco.