Manuscript: Irreducible Dorsal Dislocation of the Index MCP Joint with Superimposed Sesamoid Bone
James Thomas, Nader Paksima
Dorsal dislocation of the Metacarpophalangeal (MCP) joint is common. Irreducible dorsal dislocation of the MCP joint however, are rare and require open reduction. Any dislocation that requires operative reduction is by definition, a complex dislocation.
We present a 79-year-old (y.o.) right hand dominant (RHD) male who came in with the chief complaint of an inability to use his left index finger after tripping while walking. Radiographs revealed dorsally dislocated left index MCP with a superimposed sesamoid bone. He was diagnosed with an irreducible left index finger MCP dislocation, after failure of closed reduction in the ED. The patient was operated on, using the dorsal approach to incise the volar plate longitudinally
Presence of a sesamoid bone within the joint space is pathognomonic for an irreducible dorsal MCP dislocation. Irreducible dorsal MCP dislocations are rare and require operative reduction.
Irreducible dorsal MCP dislocations occur due to an axial load that puts a digit into hyperextension, pushing the metacarpal head in a volar direction. In an irreducible dorsal dislocation, the volar plate is torn and imposed in the joint space, preventing reduction. Incorrect reduction techniques, namely straight traction, can transform a simple dislocation into a complex one. Furthermore, fractures may be present in up to 50% of MCP dislocations. There is also a possibility of complications, such as avascular necrosis (AVN) and arthritis. Simple dislocations are defined as those that can be reduced by closed reduction. Complex dislocations require open reduction due to a displaced volar plate. The metacarpal (MC) head can be trapped within numerous palmar structures. Following dislocation, the MC head is deviated to the radial edge of the flexor tendons. This results in a tearing of the fibrocartilaginous volar plate and its displacement over the dorsal surface of the head of the MC. The fibrocartilaginous plate is now wedged between the proximal phalanx and the MC head. The collateral ligaments now hold the phalanx in this new abnormal position. Simultaneously, the pair of transverse fibers of the palmar fascia also maintains this abnormal position: the natatory ligament (distal) applies pressure to the dorsum of the bone, while the superficial transverse ligament (proximal) applies pressure to the volar portion.
The presence of a sesamoid bone within the joint space is pathognomonic for an irreducible dorsal MCP dislocation. Here we present a case of an irreducible index finger dorsal MCP dislocation that resulted in the volar plate being shifted above the MC head with an interposed sesamoid.
A 79 y.o. RHD male presented with a primary complaint of inability to use his left index finger after tripping while walking. Apart from the pain, there was associated swelling and edema. A left upper extremity physical exam revealed the following: intact skin; tender left MCP joint with obvious deformity; inability to flex and extend left index MCP; decreased active and passive ROM of left finger MCP, but full ROM for all MCP, PIP, and DIP joints of all other digits; decreased sensation over the radial side of the index finger; capillary refill in less than two seconds for all fingers. These findings, along with the radiographs, led to a high index of suspicion for a dorsal MCP dislocation.
The case was diagnosed as an irreducible left index finger MCP dorsal dislocation after failure to achieve closed reduction in the ED. Figure 1. and Figure 2. above show AP and oblique radiographs of the dorsal MCP dislocation with a sesamoid bone interposed within the joint space, respectively. The patient was indicated for open reduction via a dorsal incision. Incision of the ulnar sagittal bands was performed to retract the extensor tendons, after which dorsal MCP capsulotomy was completed. The sesamoid bone was interposed in the joint space on the ulnar aspect, while the volar plate was interposed dorsally. After subsequent longitudinal incision of the volar plate, the sesamoid bone was pushed volar, and reduction was successful. Finally, the dorsal osteochondral fragments were excised and a dorsal blocking splint was placed. Figures 3, 4a, 4b, and 4c, show radiographs of pre-reduction, anterior-posterior post-reduction, lateral post-reduction, and oblique post-reduction, respectively.
Following reduction the joint was stable and did not need to be pinned. The sagittal hood fibers were repaired and the skin sutured. The patient was placed on a splint with the MCP in 70 degrees of flexion for one week. Hand therapy was initiated at one week, allowing full active range of motion, while protecting the collateral ligaments and preventing hyperextension of the MCP joint.
Open reduction for irreducible dorsal MCP dislocations can be achieved via two primary incisions: volar or dorsal. The dorsal approach was first described by Farabeuf in 1876, and the volar approach by Kaplan in 1957. Both approaches have advantages and disadvantages. According to Kaplan et al., the volar incision allows the division of all the constricting bands. The fiborcartilagenous plate , the taut natatory ligament and the superficial transverse metacarpal ligament, which allows reduction of the joint .
Durakbasa et al studied seven cases of isolated, closed, complex dorsal MCP dislocation that were treated using the volar surgical approach. The volar plate was found to impede reduction in all the cases. At final follow-up (median 91 months), MCP range of motion (ROM), grip power, stability, and sensation were normal. The primary advantage of the volar approach is the direct visualization of the MC head. Furthermore, the longitudinally split volar plate can be repaired as well.
Becton et al noted significant drawbacks to the volar approach. Using the volar approach increases the chances of lacerating the digital nerves. The volar dislocation of the MC head pushes the digital neurovascular structures even more palmar, thereby significantly increasing the risk should the volar approach be used. Furthermore, there is limited view of the cartilaginous volar plate. Becton et al argues that the dorsal approach through the skin and extensor tendon would give full exposure of the volar plate, as well as pose no risk to laceration of the digital nerves and vessels. Finally, accurate reduction and fixation of the osteochondral fragments is possible with a dorsal approach. We chose to use the dorsal approach because of these concerns.
Patients presenting with an irreducible dorsally dislocated MCP joint need open reduction for treatment. Additionally, the presence of a sesamoid bone within the MCP joint is pathognomonic for an irreducible dorsal MCP dislocation. Finally, when considering what surgical approach to use, bear in mind the advantages and disadvantages of both. The dorsal approach is mostly used, as it poses no risk of lacerating the digital nerves and vessels.
- Becton, J. L., J. D. Christian, Jr., H. N. Goodwin, and J. G. Jackson, 3rd. "A Simplified Technique for Treating the Complex Dislocation of the Index Metacarpophalangeal Joint | The Journal of Bone & Joint Surgery." A Simplified Technique for Treating the Complex Dislocation of the Index Metacarpophalangeal Joint | The Journal of Bone & Joint Surgery. The Journal of Bone and Joint Surgery, July 1975. Web. 24 July 2016.
- DeCoster, Thomas A., Deborah McGrew, and George E. Omer. "Complex Dorsal Dislocation of the Metacarpophalangeal Joint: The Deep Transverse Metacarpal Ligament as a Barrier to Reduction."The Iowa Orthopaedic Journal. U.S. National Library of Medicine, 1988. Web. 25 July 2016.
- Dennison, David G. "Hand – Finger Dislocations and Ligament Injuries." Key Topics in Orthopaedic Trauma Surgery (1999): 80-81. Web.
- Durakbaza, Oguz, and Bulent Guneri. "The Volar Surgical Approach in Complex Dorsal Metacarpophalangeal Dislocations." The Volar Surgical Approach in Complex Dorsal Metacarpophalangeal Dislocations. Elsevier, June 2009. Web. 24 July 2016.
- Kaplan, Emanuel B. "Dorsal Dislocation of the Metacarphophalangeal Joint of the Index Finger." The Journal of Bone and Joint Surgery (1957): 1081-086. 1957. Web. 22 July 2016.