FRACTURE DISLOCATIONS OF THE PROXIMAL INTERPHALANGEAL JOINT BY RICHARD KANG, MD, AND PETER J. STERN, MD Fracture dislocations of the proximal interphalangeal joint may occur by several different mechanisms of injury and are of 3 basic fracture patterns: palmar lip fractures, dorsal lip fractures, and pilon fractures. Proper treatment of these injuries is predicated on maintenance of concentric reduction of the joint, restoration of joint stability, and institution of early motion. Anatomic reconstitution of the articular surface, though ideal, is less important. Many methods are available to treat these injuries. Understanding the fracture within the context of a stability-based classifi- cation system helps to guide in the selection of the most appropriate treatment. Copyright © 2002 by the American Society for Surgery of the Hand racture dislocations of the proximal interphalan- lanx: (1) palmar lip fractures, (2) dorsal lip fractures, geal joint are common injuries that, when inad- and (3) pilon fractures (Fig 1). These fracture patterns Fequately understood, can be confusing for the are the result of characteristic mechanisms of injury. physician to treat. Worse, inappropriate treatment can Pure hyperextension may cause an avulsion fracture lead to a dysfunctional joint secondary to persistent pain, from the base of the middle phalanx. More commonly, stiffness, and posttraumatic degenerative arthrosis. A however, PIPJ fracture dislocations occur as a result of thorough understanding of the biomechanics of the in- an axial load, the specific fracture pattern depending jured proximal interphalangeal joint, the principles of its on the amount of flexion of the PIPJ at the time of treatment, and the available treatment options is essen- axial loading. tial to the proper management of these injuries. Palmar lip fractures at the articular base of the middle phalanx are the most frequently encountered FRACTURE TYPES AND MECHANISMS OF INJURY PIPJ fracture dislocation type (Fig 1A). With hyper- roximal interphalangeal joint (PIPJ) fracture dis- extension only, the palmar plate may rupture at its Plocations can be classified into 3 types based on distal insertion on the middle phalanx, which can the fracture geometry of the base of the middle pha- result in pure dorsal dislocation of the middle phalanx on the proximal phalangeal head. Alternatively, the palmar plate may avulse a fragment of bone from the From the Department of Orthopaedic Surgery, University of Cincin- palmar lip of the middle phalanx; these fracture frag- nati, Cincinnati, OH. Address reprint requests to Peter J. Stern, MD, 2800 Winslow Ave, ments vary in size and displacement, but are generally Suite 401, Cincinnati, OH 45206. E-mail: [email protected] not comminuted. Fracture dislocation of the PIPJ owing to axial loading of the joint in some degree of Copyright © 2002 by the American Society for Surgery of the Hand 1531-0914/02/0202-0004$35.00/0 flexion results in a fracture of the category coined doi:10.1053/jssh.2002.33317 impaction shear fractures.1 In this category, an axial JOURNAL OF THE AMERICAN SOCIETY FOR SURGERY OF THE HAND ⅐ VOL. 2, NO. 2, MAY 2002 47 48 FRACTURE DISLOCATIONS OF THE PIP JOINT ⅐ KANG & STERN surface of the base of the middle phalanx are spared. There may also be injury to the hyaline cartilage of the head of the proximal phalanx. Dorsal lip fractures of the middle phalanx occur in an analogous fashion as palmar lip fractures (Fig 1B) though they are less common. Hyperflexion of the PIPJ may result in rupture of the central tendon through its substance or its insertion; the central tendon may also avulse a fragment of dorsal bone from the base of the middle phalanx. Axial load with the PIPJ in extension leads to a dorsal lip fracture of the base of middle phalanx from an impaction shear mechanism similar to that described for palmar lip fractures.2 Pilon fractures of the PIPJ have been defined by Stern et al3 as those in which both the palmar and dorsal cortical margins of the base of the middle phalanx are disrupted and the central articular surface is extensively comminuted and impacted into the underlying metaphyseal bone (Fig 1C).3 They result from a high-energy axial load applied to the PIPJ in full extension. JOINT STABILITY FIGURE 1. Proximal interphalangeal fracture dislocation ractures of the base of the middle phalanx may types. (A) Palmar lip fracture with dorsal subluxation. A V- lead to instability of the proximal interphalangeal shaped gap can be appreciated between the head of the F proximal phalanx and the intact dorsal base of the middle joint. Several anatomic and biomechanical factors phalanx because of lack of articular congruency. (B) Dorsal must be considered in understanding the tendency lip fracture with palmar subluxation. (C) Pilon fracture. Both toward subluxation or dislocation of the middle pha- palmar and dorsal cortical margins are fractured and the central articular fracture fragments are impacted and commi- lanx on the head of the proximal phalanx. An under- nuted. (Adapted and reprinted with permission.1) standing of PIPJ stability is central to a functionally useful classification that is helpful in guiding appro- priate treatment of PIPJ fracture dislocations. load across the PIPJ drives the middle phalangeal base In palmar lip fractures, the normally cup-shaped onto the proximal phalangeal head. Because of the base of the middle phalanx is converted into one with flexed position of the PIPJ, the axial load creates a a dorsal proximal to palmar distal orientation (Fig 2). palmar to dorsal force gradient across the articular Combining this anatomic alteration with the loss of surface of the base of the middle phalanx with greater the restraint of the palmar plate at the palmar base of force concentrated at its palmar aspect. The palmar the middle phalanx allows the central slip of the base of the middle phalanx is thus sheared off and, extensor tendon to subluxate or dislocate the base of with continued displacement of the proximal phalan- the middle phalanx dorsally onto the head of the geal head, the palmar fracture fragment is then im- proximal phalanx. This tendency is facilitated by the pacted into the underlying metaphyseal bone, nearly pull of the flexor digitorum superficialis, which tilts always causing fracture comminution.2 This fracture the base of the middle phalanx dorsally about the pattern may involve up to 80% of the palmar aspect of articular margin of the fracture.4 Restoration of sta- the middle phalanx base; by definition, however, the bility is predicated on reestablishing the palmar but- dorsal cortex and some portion of the dorsal articular tress by restoring the articular geometry of the palmar FRACTURE DISLOCATIONS OF THE PIP JOINT ⅐ KANG & STERN 49 extension is then obtained to confirm stability of the reduction. If the joint subluxates or dislocates, it is necessary to identify the degree of flexion at which this occurs; use of fluoroscopy is especially helpful in this determination. In an analogous way, dorsal lip fractures may result in subluxation or dislocation in a palmar direction. The pull of the flexor digitorum superficialis, no longer opposed by the central slip of the extensor tendon, acts to subluxate or dislocate the base of the middle phalanx palmarward. CLASSIFICATION FIGURE 2. Mechanisms of instability in palmar lip fractures. The pull of the intact central slip of the extensor mechanism ased on fracture pattern and joint stability, a is able to subluxate or dislocate the base of the middle classification system for fracture dislocations of phalanx over the head of the proximal phalanx because of (1) B the slope of the fractured base of the middle phalanx, (2) the the proximal interphalangeal joint has been estab- loss of the palmar plate restraint, and (3) the tilting moment lished that is useful with respect to selection of the about the fracture margin caused by the pull of the flexor best option for treatment of these injuries (Table 1).1 digitorum superficialis. P1, proximal phalanx; P2, middle pha- lanx; EXT, central tendon; VP, palmar plate; FDS, flexor digitorum superficialis. (Adapted and reprinted with permis- Palmar Lip-Fracture Classification sion.1) This classification builds on previous ones that have stratified PIPJ fracture dislocations according to the base of the middle phalanx with respect to joint percentage of fractured palmar articular surface at the congruency and concentricity. base of the middle phalanx.4,5 Fractures that involve Given that the primary variable in the earlier- less than 30% are usually, but not always, stable; 30% mentioned scenario is the fracture itself, it stands to to 50% are of tenuous stability; and greater than 50% reason, then, that the size of the fracture fragment(s) is are unstable (Fig 3). By adding the assessment of the major determinant of stability of the injured clinical stability to those based purely on anatomic PIPJ. Though in large part true, equally important is criteria, this classification divides palmar lip fractures the determination of the clinical stability of the re- into 3 functional groups: stable, tenuous, and un- duced PIPJ fracture dislocation by physical examina- stable.1 tion. After digital block anesthesia, the surgeon re- Stable fracture dislocations involve less than 30% of duces the PIPJ and watches for subluxation or the palmar articular base of the middle phalanx, and, dislocation while the patient actively extends the after reduction, the joint remains stable with the PIPJ joint. A true lateral