Thomas R. Hunt III, MD
Division of Orthopaedic Surgery, The University of Alabama, Birmingham School of Medicine, 930 Faculty Office Tower, 510 20th Street South, Birmingham, AL 35294-3409, USA
CMC joint fractures and fracture/dislocations involving the fingers are relatively common injuries that infrequently result in chronic disability. Persistent pain and dysfunction, usually manifesting as diminished grip strength, typically result from late instability and secondary joint degeneration from missed or maltreated fourth and fifth CMC joint injuries, or from multiple CMC joint fracture/dislocations caused by high energy trauma. As is the case with Bennett's fractures, symptomatic post-traumatic arthritis involving the small finger CMC joint is less frequent than might otherwise be expected, perhaps because of the relatively unconstrained nature of both joints . The laxity may confer a certain degree of protection in the post-traumatic state. Similarly, degenerative joint changes manifesting as meta-carpal bosses are infrequently symptomatic, and when present, rarely necessitate surgical treatment. This article reviews the relevant anatomy and epidemiology, and details treatment algorithms for symptomatic patients who have degenerative and post-traumatic problems affecting the finger CMC joints.
Anatomy, pathomechanics, and epidemiology
The finger carpometacarpal joints define the fixed unit of the hand, serving as the base for digital mobility. Stability is conferred primarily thorough the extensive ligamentous labyrinth .
The author is a consultant to the Arthrotek/Biomet Corporation and an education consultant for Stryker Corporation.
E-mail address: [email protected]
The second and third CMC joints are highly constrained by the ligamentous anatomy as well as by the joint contours. In addition to other articulations, the second metacarpal base keys into the trapezium as an inverted "V," and the third meta-carpal base keys into the capitate, often with a dor-soradial proximal projection providing a degree of added stability. Allowed motion in these joints is less than 5° . Progressively more mobility is noted ulnarly. Most authors estimate a 15° flexion/extension arc for the fourth CMC joint and a 30° arc for the fifth CMC joint. The articular anatomy of the fifth CMC joint is variable, but generally resembles that seen in the trapeziometa-carpal joint of the thumb with a concave (volar/ dorsal) hamate facet and a correspondingly convex metacarpal base. This shallow, concavocon-vex "saddle joint'' allows for flexion/extension, rotation, and translation , facilitating cupping and flattening of the palm as well as opposition of the fifth ray.
The most frequent injuries, fractures of the fourth and fifth metacarpal bases with or without dorsal dislocation, result from striking a solid object with a clenched fist in the majority of cases, and a direct blow to the area in a minority of cases . Yoshida and colleagues  duplicated the pathomechanics of a closed fist blow using a cadaver model, and found that specific patterns of injury were dependent on direction and degree of applied force, position of the joint, and liga-mentous constraints. Plain radiographs significantly underestimated the extent and complexity of the injury produced. Kjaer-Petersen and coworkers  reported on their treatment of 64 in-tra-articular fifth metacarpal base fractures using both closed and open techniques. The majority of the fractures included the commonly observed volar radial fragment held reduced to the fourth metacarpal base via strong intermetacarpal ligaments. They improved the intra-articular reduction in fewer than 55% of patients despite ''relatively easy'' elimination of subluxation. Not only is it difficult to appreciate the full spectrum of injury radiographically, but reduction and stabilization of the fragments may be problematic.
Despite relative consensus regarding the path-omechanics, resulting pathoanatomy, and the requirement for correction of joint subluxation, authors disagree on the need for anatomic joint restoration and the long-term impact of articular incongruity on patient outcome and even on radiographic endpoints. Lundeen and Shin  retrospectively reviewed 22 patients who had isolated intra-articular fractures of the base of the fifth metacarpal at an average of 43 months following injury. All fractures were treated by closed reduction and cast immobilization. Twenty patients reported good or excellent results despite radiographic evidence of mild arthrosis in 9. Outcome was independent of specific fracture pattern, degree of subluxation, or intra-articular incongruity and arthrosis, as judged using plain radiographs. Kjaer-Petersen and colleagues  also found that quality of the reduction did not seem to directly influence outcome, and the result was not impacted by the presence of arthrosis at median follow-up time of 4.3 years; however, 39% of their patients sampled by questionnaire complained of intermittent pain with gripping, and 49% of their patients examined demonstrated decreased grip strength. Bora and Didizian  tied outcome to fracture displacement. One of 7 patients who had displaced fractures in their series required arthrodesis. Decreased grip strength was the most common disabling symptom.
Despite some studies indicating a high frequency of symptoms following these common injuries, most surgeons rarely see patients who have significant chronic complaints after adequate initial treatment of CMC fracture/dislocations. The need for surgical treatment in this population of patients is even less common. Pellegrini  hypothesized that in the case of Bennett's fractures, normal joint surface incongruity and infrequent contact of the metacarpal's displaced articular surface with the remainder of the joint may exert a protective effect over late post-traumatic sequelae of residual articular fracture deformity. This same concept may be applicable to fifth CMC joint injuries, so called ''reverse Bennett's fractures.''
Degenerative arthritis involving the finger CMC joints usually presents as a dorsal carpo-metacarpal boss projecting from the radial third metacarpal base or the ulnar second metacarpal base, often involving the capitate, and accompanied by a ganglion cyst in 30% of cases . The hypertrophic bony spurs are thought to result from repetitive forces acting on these two rigid joints that serve as the stable pillars of the hand. Fusi and colleagues  obtained a history of direct trauma to the region in 24% of their operated patients. Carpometacarpal bosses are equally common in men and women. These patients typically present for treatment in their 20s and 30s , though significant symptoms related to these hypertrophic changes are uncommon.
Was this article helpful?
Did You Know That Herbs and Spices Have Been Used to Treat Rheumatoid Arthritis Successfully for Thousands of Years Do you suffer with rheumatoid arthritis Would you like to know which herbs and spices naturally reduce inflammation and pain 'Treating Rheumatoid Arthritis with Herbs, Spices and Roots' is a short report which shows you where to start.