2.1 Metacarpal bones

The five metacarpals form the breadth of the hand, with the index and middle metacarpals acting as a rigid central pillar. The distal transverse arch of the hand is located along the deep metacarpal ligaments, which connect the metacarpal heads. The thumb, ring finger, and little finger metacarpals are the mobile units. A stable base is required for useful finger function, and this is achieved by the width and stability of the four-finger metacarpals, bound tightly together by their basal ligaments and supported by their more mobile distal intermetacarpal ligaments. Unstable fractures of the border metacarpals (index or little) narrow this stable base and result in poorer grip and altered finger function. The metacarpal shaft has dorsal convexity; the concave palmar cortex is denser as this is the compression side with tension on the dorsum.

2.2 Carpometacarpal joints

The capitate articulates with three metacarpals (index, middle, and ring) and the index metacarpal articulates with three carpal bones (trapezium, trapezoid, and capitate). The index and middle carpometacarpal joints are practically immobile. The connection to the ring finger and little finger are mobile, hinge-shaped joints with strong palmar ligaments. The carpometacarpal joint of the thumb is a reciprocally biconcave saddle joint. This allows an extensive range of motion, including some rotation, but provides great stability in compression ( Fig 6.3.4-1 ).

2.3 Metacarpophalangeal joints

When viewed in the sagittal plane, the metacarpal head is cam-shaped and similar to the knee. During flexion, the axis of rotation moves in a palmar direction. The articular surfaces form a condyloid joint: the metacarpal head is narrow dorsally with a widened palmar flare giving progressively more contact with the base of the proximal phalanx with increasing flexion. This anatomical shape, combined with the eccentric origin of the collateral ligament, means that the collateral ligaments are tight in flexion and lax in extension ( Fig 6.3.4-2 ). Hence, the fingers cannot be spread (abducted) unless these joints are extended.

Due to the anatomical arrangement of the collateral ligaments, the metacarpophalangeal joints must always be immobilized at 90° flexion to minimize stiffness.

2.4 Phalanges

The proximal and middle phalanges are divided into the base, shaft, neck, and head (condyles). In contrast to the metacarpals, the phalanges are enveloped by the gliding surfaces of the overlying intrinsic and extrinsic tendons. Fractures or surgical approaches in this area predispose to scar formation and adherence of the overlying extensor tendon. This limits both active and passive movement ( Fig 6.3.4-3 ).

2.5 Interphalangeal joints

These are hinge joints. The heads of the proximal and middle phalanges have two articular condyles that resemble a grooved trochlea ( Fig 6.3.4-4 ) and prevent adduction and abduction. Dynamic stability results from compressive forces, which increase during pinch and grip. Passive stability derives from collateral ligament and palmar aponeurosis tension, which is greatest in full extension.

The proximal and distal interphalangeal joints should be immobilized in extension to minimize joint stiffness ( Fig 6.3.4-5 ).

3.1 Implant selection

Small implants are available in the modular hand system based upon a number of different screw sizes ( Table 6.3.4-1 ). Simple adaption plates have round screw holes while the limited-contact dynamic compression plate (LC-DCP) 2.0 has oval holes to allow eccentric screw insertion and compression with the plate. Angular stable implants are available as small as 1.5 mm. These are useful for the fixation of metaphyseal and articular fractures of the metacarpals and phalanges. Specialized T-, Y-, and H-plates are also available for different fracture patterns, and anatomical plates—designed for specific fracture patterns—provide an accurate solution for certain difficult injuries. The locking compression plate (LCP) 2.0 is usually indicated for metacarpal and proximal phalangeal fractures, whereas the LCP 2.4 is indicated for larger size metacarpals and also for the distal radius. There are a number of special plates that have been designed for the specific anatomy of the distal part of the proximal phalanx ( Fig 6.3.4-7 ); the base of the thumb metacarpal ( Fig 6.4.3-8 ); and the commonly encountered metacarpal neck fracture ( Fig 6.3.4-9 ). The peculiar but consistent anatomical shape of these areas of bone has been difficult to stabilize with conventional implants. Fractures are common in these areas and the introduction of specific anatomical implants has made their stabilization less challenging and more reliable.

3.2 Operating room set-up

After disinfecting the entire hand, wrist, and arm with the appropriate antiseptic right up to the limits of the tourniquet cuff, which allows full exsanguination, the entire upper limb is prepared, which allows repositioning during surgery. If alcohol-based antiseptic is used, care should be taken that it does not run up under the tourniquet since skin damage can occur from prolonged contact with soaked material during surgery. A single-use occlusive hand drape with expandable arm opening is recommended ( Fig 6.3.4-10 ). The image intensifier is also draped.

The surgeon sits beside the patient′s head to gain a good view and access to the dorsum of the hand. The assistant sits opposite the surgeon. The operating room personnel sits at the end of the hand table. Adjustable-height stools and protective lead gowns should be provided for all personnel involved. The image intensifier display screen is placed in full view of the surgical team and the radiographer ( Fig 6.3.4-11 ).