Camptodactyly affects less than 1 % of the population and is usually asymptomatic [2, 3]. The anomaly generally occurs sporadically; however, it can be inherited in an autosomal dominant pattern with variable expressivity and incomplete penetrance. Bilateral deformities occur in approximately two-thirds of cases and the little finger is almost always involved. Multiple digits can be affected, with less frequent involvement of the radial digits. The thumb is not involved. Metacarpophalangeal (MCP) joint hyperextension can accompany PIP flexion contractures.

When the initial presentation is during infancy, males and females are equally affected. Females are more commonly affected when the initial presentation is during adolescence.

Benson classified patients into three types. Type I is an isolated anomaly of the little finger PIP joint that presents in infancy and can involve up to two fingers. Type II has the same clinical features but presents in adolescence. Type III is characterized by severe contractures, bilateral involvement, multiple digits, and other associated congenital anomalies. Type III camptodactyly presents at birth and is seen as a manifestation of a more generalized condition (Table 16.1).

The initial presentation of Type I and Type II camptodactyly at infancy and adolescence, respectively, may be related to growth spurts during which flexor–extensor imbalances manifest.

The PIP flexion deformity may be fixed or passively correctible, which has important treatment implications. Foucher proposed subclassifying Type I and II camptodactyly into “stiff” or “correctable” categories to guide his treatment approach [4].

Abnormalities of almost every structure around the PIP joint have been described. Some believe all of these structures are involved but to varying degrees [4, 5]. Others believe that specific abnormalities of the flexor digitorum superficialis (FDS) or the intrinsic musculature [6–8] result in secondary changes with time and growth.

Early descriptions of camptodactyly have noted a tight, contracted, or underdeveloped FDS tendon [1, 9] and suggest that the deformity is the result of an imbalance of flexor and extensor forces. Aberrant FDS tendon origins in the absence of a normal muscle belly have been described and include the A2 pulley, palmar aponeurosis, flexor tendon sheath, and transverse carpal ligament [10].

Surgical explorations by Courtemanche and McFarlane have identified consistent abnormalities of lumbrical muscles, suggesting that these may be the primary etiology of camptodactyly [6–8]. An aberrant lumbrical origin from the flexor retinaculum [11] has also been described. More commonly, aberrant lumbrical insertions have been described and include the FDS tendon [6–8, 12, 13] and MCP joint capsule [6–8]. Inadequate lumbrical muscle function leads to an intrinsic-minus posture, which may lead to the deformity seen with camptodactyly.

Other soft tissue abnormalities include extensor incompetence, collateral ligament contracture, volar plate contracture, and volar skin deficiency [1, 4, 5]. Bony changes can be seen with long-standing deformities [1, 7] and are consistent with growth in the setting of a chronically flexed joint. The head of the proximal phalanx is narrowed in the dorsovolar plane with loss of the normal volar convexity. The articular surface of the middle phalanx base can have a shallow dorsal groove. Radiographic changes were seen in approximately 15 % of patients in McFarlane and Smith’s series [1, 7]. Smith argues that all of these abnormalities are common to all cases of camptodactyly, but to varying degrees. McFarlane argues that aberrations of lumbrical muscle insertion are the unifying cause and all other changes occur secondary to chronic motor imbalance. He points out how previous anatomic studies have demonstrated that normal anatomic variations of the intrinsic muscles occur more frequently in the ulnar digits and that these are the same digits that are involved with camptodactyly.

Differentiation of camptodactyly from other conditions is accomplished through careful history and physical examination. Camptodactyly is seen in the absence of trauma, inflammation, and palpable lesions. The deformity is slowly progressive and generally occurs in isolation. A trigger finger may be associated with a palpable click on extension. Juvenile palmar fibromatosis or Dupuytren’s disease is associated with palpable subcutaneous nodules. A boutonniere deformity should be associated with antecedent trauma and swelling. Inflammatory arthridities manifest with inflammation and more generalized involvement. Symphalangism is characterized by no active or passive joint motion and an absence of skin creases. Arthrogryposis involves generalized muscular and skeletal deficiencies. Pterygium syndrome is usually associated with involvement of multiple joints.

Following a thorough examination of the upper extremity, active and passive range of motion of the PIP joint should be evaluated and the influence of adjacent joint positions should be noted. FDS tightness can be determined by tenodesis effect in which wrist and MCP extension places the FDS on stretch and results in further loss of passive PIP extension. Intrinsic motor deficiency can be assessed using the Bouvier maneuver, in which active PIP extension is tested with the MCP joint stabilized in flexion. Restoration of full PIP extension suggests that inadequate MCP flexion, via the intrinsic muscles, contributes to the deformity. Extensor competence can be tested using an extensor tenodesis test in which full flexion of the wrist and MCP places the extensor system on stretch. This should result in full PIP extension. Long-standing flexion deformities can result in attenuation of the central slip, in which case PIP extension would not occur with this test. Volar skin deficiency can be determined by testing passive PIP extension with the MCP in flexion and in extension. Blanching and loss of passive PIP extension when the MCP is extended suggests volar soft tissue deficiency.

Flexor digitorum profundus (FDP) and FDS function of each finger should be evaluated. Given that the FDP to each finger acts through a common muscle belly, in order to test isolated FDS function to an individual finger, all other digits must be held in extension while finger flexion of the digit of interest is evaluated. The ring and little finger FDS are conjoined in 30 % of people. If PIP flexion is not possible for the little finger, release of the ring finger should result in PIP flexion of both digits if their FDS is conjoined.

Conservative management should be the first line of treatment. PIP contractures of less than 30° rarely have any functional impact, and greater contractures are often well tolerated.