Flexion contracture (Fig. 21.1)

This may result from tightness in one or more of the structures on the palmar aspect of the joint^1,2:

Fig. 21.1 Flexion contracture may result from tightness of structures volar to the joint, including skin, flexor tendon sheath, tendons, volar palmar plate, and accessory collateral ligaments. In addition, a bone block may impede joint motion, whereas dorsal tendon adhesions may limit the ability to extend the joint.

Extension contracture

Limitation of flexion (extension contracture) (Fig. 21.2) can be caused by one or more structures on the dorsal aspect of the joint.^1,2 However, they too can result from a “jamming” effect of volar structures that block flexion, such as a bone block or palmar plate adhesions.

Fig. 21.2 (A) Extension contracture may result from tightness of dorsal structures, including skin, extensor tendons, collateral ligaments and joint capsule, and well as from a bone block. Volar structures may also impede the ability to flex the joint. (B) In addition, adhesions in the lumbrical canal and of the transverse retinacular ligament fibers may impede both flexion and joint extension.

Bone

This may be a true block or result from intraarticular incongruity. Chondral fractures may not be radiographically apparent and so may present a diagnostic problem (Fig. 21.3). Persistent waxing and waning joint swelling with limited flexion may result from a chondral fracture, which is more likely at the MP joint. Questioning of the patient may lead to recollection of an injury that could have caused the proximal phalangeal base to impinge on the metacarpal head. Surgical exploration may reveal the chondral fracture and consequently loose body in the joint. Computed tomography scanning may help in arriving at the correct diagnosis.

Fig. 21.3 (A) This patient had an osteochondral fracture involving the metacarpal head after a finger “jam” and presented with inability to flex at the MP joint and joint swelling. The fracture involved about one-third of the articular surface but was still attached by a single collateral ligament. (B) Bone fixation restored perfect joint function.

Seesaw effect

This results when a contractural element spans two joints. Presence of this sign helps in the diagnosis of structures that potentially contribute to a stiff joint.⁷ If one joint in a contracted system is flexed, the other joint can then be extended, and vice versa. This is seen, for example, when a longitudinal volar skin scar crosses both proximal and distal interphalangeal joints. The DIP joint can be extended only if the PIP joint is flexed. A similar effect is seen with adherent extrinsic flexor or extensor tendons (Fig. 21.4). For example, flexion of MP joints in the presence of a flexor tendon adhesion over the proximal phalanx has no effect on the flexion contracture of the PIP joint. If the adhesion lies proximal to the MP joint, flexion of that joint results in correction of the contracture apparently present in the PIP joint. Furthermore, with flexor tendon adhesions, passive flexion of the affected joint exceeds active flexion, provided the extensor tendon is healthy. Similarly, in the presence of a Volkmann contracture of the flexors in the forearm, passive extension of the finger joints is reduced with the wrist extended and not if the wrist is flexed.

Fig. 21.4 By adjusting the joints proximal to the joint that appears to be the cause of the contracture, the primary problem may be revealed. (A) If a patient had a PIP flexion contracture, flexion of the MP joint in the presence of flexor tendon adhesion at the proximal phalanx has no effect on the PIP flexion contracture. (B) If the flexor tendon adhesion is proximal to the MP joint, flexion of that joint will result in correction of the PIP joint contracture.

If the extrinsic extensor tendon is adherent to the metacarpal, the limitation of extensor tendon excursion distal to that joint prevents simultaneous flexion of MP and PIP joints. This is the test for extrinsic tightness (Fig. 21.5A).^8,9 The test of Bunnell for intrinsic tightness results from the seesaw phenomenon in which the band acts across two joints but is an extensor of one joint and a flexor of the adjacent joint.¹⁰ If the intrinsic musculotendinous system is foreshortened, extension of the MP joint either actively or passively increases the tone in the system and restrains flexion of the PIP joint. This is tested by passively extending the MP joint and passively flexing the PIP joint (Fig. 21.5B). If flexion of the PIP joint is greater when the MP joint is flexed than when it is extended, intrinsic tightness is present. In the swan-neck deformity, not only is there an extension contracture of the PIP joint, but that joint hyperextends because of volar plate laxity. There is dorsal displacement of the lateral bands at the PIP joint. This slackens the distal tension on the extensor mechanism because of the fixed attachment of the central tendon at the PIP joint. Thus there is unopposed force of the flexor digitorum profundus at the distal joint, which then drops into flexion (Fig. 21.6A).⁹

Fig. 21.5 (A) Test for extrinsic tightness. When the MP joint is flexed (arrow), passive PIP joint flexion is increasingly difficult. (B) Test for intrinsic tightness. When the MP joint is extended (arrow), passive PIP joint flexion is more difficult. (C) Boutonniere test. The oblique retinacular ligament is foreshortened so that when the PIP joint is extended (arrow), passive DIP joint flexion is difficult. (D) Central slip tendon excision is performed for extrinsic extensor tightness and wing tendon excision (oblique fibers and lateral bands) for intrinsic tightness – either of which might cause PIP hyperextension.

Fig. 21.6 (A) Swan neck deformity with hyperextension at the PIP joint. Dorsal displacement of the lateral bands slackens distal extensor tension, and so the unopposed flexor digitorum profundus draws the DIP joint into flexion. (B) Boutonniere deformity. The PIP joint drops into flexion because of central slip attenuation, and the lateral bands move volar. Excess extensor pull bypasses the PIP joint and hyperextends the DIP joint. The oblique retinacular ligament foreshortens.

A similar volar to dorsal seesaw effect occurs at the DIP joint secondary to action of the oblique retinacular ligament and lateral bands, resulting in extension contracture at that joint. This occurs with the boutonniere deformity. When the central tendon insertion into the dorsal base of the middle phalanx ruptures or attenuates, the PIP joint drops into flexion and the lateral bands move volar to the axis of motion of that joint.¹¹ They will foreshorten and adhere in that position. Excess extensor pull that secondarily bypasses the PIP joint is imposed dorsally at the DIP joint with consequent recurvature at that joint (Fig. 21.6B). The oblique retinacular ligament is an extensor of the DIP joint and a flexor of the PIP joint.¹¹ It also foreshortens and this permits the DIP joint to be flexed as long as the PIP joint is maintained in flexion. Passively extending the PIP joint brings the DIP joint into extension, making passive flexion increasingly more difficult. This maneuver is the Boutonniere test (Fig. 21.5C).

Volar plate and collateral ligament changes

Changes in the volar plate and collateral ligaments occur with flexion contractures. Flexion and extension contractures can occur at the PIP joint. In contrast, at the MP joints, extension contractures occur, but flexion contracture is rare due to volar plate and collateral ligament anatomy. The volar plate at MP joints is different anatomically from that of interphalangeal joints.

The protected position of MP joints is in flexion. The cam and volar flare shape of the metacarpal head places collateral ligaments in greatest tension during flexion (Fig. 21.7). The MP joint volar plate has criss-crossing bands of fibers that expand with joint extension and are collapsible with flexion.⁶ Thus, the volar plate at the MP joint is considerably longer in extension than in flexion (Fig. 21.8A).

Fig. 21.7 Cam-like action of the collateral ligaments at the MP joint. Collateral ligaments are in greatest tension during flexion because of the cam and volar flare shape of the metacarpal head.

Fig. 21.8 (A) Criss-crossing bands of fibers make up the MP joint volar plate, and these allow expansion with joint extension. (B) The volar plate at the PIP joint is relatively uncollapsible. In contrast to the MP joint, the PIP volar plate slides proximally and distally with joint flexion and extension.

In contrast, the interphalangeal joint collateral ligaments do not change in tightness with joint flexion and extension. The volar plate is relatively uncollapsible. Rather, the volar plate slides proximally and distally with flexion and extension of the joint (Fig. 21.8B). The volar plate is not attached to the proximal phalanx as this would prevent full extension. The assembly lines are the two ridges on the volar lateral surfaces of the phalanx to which are attached the flexor sheath, Cleland ligaments, Grayson ligaments, oblique retinacular ligaments, and transverse retinacular ligaments, and the transverse metacarpal ligament and MP joint volar plate more proximally. Normally, there is no ligament structure between the volar plate of the PIP joint and the assembly line or extension of that joint would not be possible. Two bands (checkreins)^6,12,13 form between the lateral proximal volar plate and the assembly lines after injury. These are pathologic structures (Fig. 21.9). They are thicker at the base attached to the volar plate and have a thinner longer proximal apex attached to the assembly line. The communicating artery of the vincula system passes deep to the checkreins. With interphalangeal joint contracture it is the checkreins that mainly prevent extension. Division of these checkreins and accessory collateral ligaments enables extension at the interphalangeal joint to be achieved when surgery is required. It is virtually never necessary to divide collateral ligaments.

Fig. 21.9 (A) Checkreins are attached by a broad base to the volar plate, and a tapering apex is attached to the assembly line. (B) Release of the PIP flexion contracture requires excision of the checkreins, with care taken not to injure the transverse communicating vessel between the two digital arteries.