HOJ-2003 v7

Philip E. Blazar, M.D. Assistant Professor in Orthopedic Surgery Harvard Medical School Attending Physician, Department of Orthopaedic Surgery Brigham and Women’s Hospital 75 Francis Street Boston, MA 02115 (617) 732-8550 [email protected] INTRODUCTION Metacarpophalangeal (MP) arthroplasty is the most common and successful joint replacement surgery of the hand. This paper will briefly review the anatomy of the MP joint, and the indications, technique, results and complications of MP arthroplasty. Although MP implants are occasionally performed for post-traumatic or osteoarthritic joints, the literature focuses on patients with rheumatoid or other inflammatory arthritides. These patients can anticipate deformity correction, improved function and highly effective pain relief. The hand is the primary mode of interaction with our environment. Therefore, even minor alterations of hand and wrist function resulting from rheumatoid arthritis (RA) affect the ability to function occupationally, recreationally and in activities of daily life. A multidisciplinary approach involving the rheumatologist, hand surgeon, and hand therapist is advisable in caring for these patients. Because delays in surgical and non-surgical treatment may lead to further disease progression, joint destruction and loss of function, early intervention is imperative. The initial evaluation and subsequent treatment of each patient’s problem are challenging because of the anatomic complexities of the hand and wrist. However, a strong understanding of the relevant anatomy and a systematic approach to patient evaluation allow a logical plan of treatment to be generated. ANATOMY The normal MP joint is a diarthodial, condylar-type joint. The metacarpal head has a greater surface area than the base of the proximal phalanx. The articular surface of the head is convex and has a wider volar surface. The asymmetry of this surface accounts for the tightening of the collateral ligaments when the joint is brought into flexion. This asymmetry also results in a mobile center of rotation to the MP joint, which moves volarly with flexion. The normal synovial membrane of the MP joint is attached around the margins of the articular cartilage with volar and dorsal capsular reflections. The largest synovial fold is found on the dorsal neck of the metacarpal. (10) The arc of motion of the normal MP joint is described as neutral to 90 degrees of flexion, although many individuals will demonstrate variable degrees of hyperextension. Radial and ulnar deviation is maximized in extension and is decreased with flexion and the associated tightening of the collateral ligaments. The MP joint deviates slightly in the ulnar direction with flexion of the digits. The joint is stabilized by ligamentous structures. The collateral ligaments originate on the dorsal aspect of the metacarpal head neck junction and insert on the volar aspect of the proximal phalanx. The collaterals are the primary stabilizers against varus-valgus and dorsal-palmar stresses. The volar plate has a membranous attachment on the neck of the metacarpal and a more fibrous attachment on the base of the proximal phalanx; it acts as the primary stabilizer against hyperextension. The flexor tendon sheath, the intermetacarpal ligaments and the sagittal bands of the extensor hood attach to the volar plate. The accessory collateral ligaments are located volar to the collateral ligaments and insert into the volar plate; they act as stabilizers of the volar plate, as well as secondary stabilizers against varus-valgus stress. The interossei and lumbrical muscles exert a flexion force on the MP joint through their attachments into the extensor hood and proximal phalanx. The sagittal bands aid in extension of the MP joint through their insertion into the volar plate, as well as stabilizing the extensor tendons over the joint itself. The long flexor tendons can exert a flexion moment on the MP joint but their insertions on the distal and middle phalanges require this to occur after interphalangeal joint flexion. PATHOPHYSIOLOGY OF RHEUMATOID MP JOINTS The MP joint is the most common site of involvement in RA. Destruction of the MP joint in RA begins with a proliferative synovitis and progressively leads to a volarly subluxated proximal phalanx with ulnar deviation and destruction of the articular cartilage. MP joint deformities in RA have been extensively described. Characteristic changes occur in the articular surface, soft tissue stabilizing structures and bony supports. (10,16) The primary causative factor producing the MP joint deformities characteristic of RA remains controversial. Zancolli and others have proposed a dynamic deformity, which exists prior to articular destruction. (22) Inflammation of the carpometacarpal joints exaggerates the spread of the metacarpals and