With no flexor tendon attachment, there is little point in keeping the residual middle phalanx. The proximal phalanx must be shortened to at least remove all articular cartilage in order to avoid a pseudobursa, and more commonly to the neck of the proximal phalanx to avoid the stump being too long when the patient makes a fist. During initial amputation, the digital nerves should simply be divided proximal to the skin flaps and allowed to retract back into the soft tissues. If a subsequent neuroma develops, that can be dealt with by a number of techniques. The flexor and extensor tendon ends should be allowed to retract in order to avoid a quadriga effect. In cases where the FDS insertion remains intact, there may be useful PIP joint flexion, in which case it may be worth using a local flap to preserve digital length. FDP retraction may result in paradoxical extension of the injured digit when trying to flex the fingers caused by tension through the lumbrical. This is uncommon and is dealt with on an elective basis with division of the lumbrical. The fish-mouth incision should be designed to provide a longer volar skin flap, as this is sensate and provides better soft-tissue padding for the new fingertip (Fig. 84.1).1–3 Fig. 84.1 A “fish-mouth” incision design creates volar and dorsal skin flaps for amputation stump coverage. The volar skin flap should be designed slightly longer, such that it can be wrapped over the distal stump, to provide more durable and sensate coverage.
Revision ray amputation is usually an elective procedure following initial care of a more distal digital amputation. The main purpose is to close the interdigital gap to stop objects falling through. A secondary potential benefit is an improvement in cosmesis. Power grip, key grip, pronation, and supination power are usually reduced after ray amputation, so must be considered when pursuing a ray amputation for cosmetic reasons.1–3 Ray amputation may also be used primarily in trauma and tumor management, or for removal of a poorly functioning previously reconstructed digit.
3. Kakar S. Digital amputations. In: Wolfe SW, Hotchkiss RN, Pederson WC, Kozin SH, Cohen MS, eds. Green’s Operative Hand Surgery. 7th ed. Philadelphia, PA: Elsevier; 2017: 1708–1752
The border digits can be transposed to close the gap from the third or fourth ray amputations.1 The base of the fifth metacarpal should still be preserved in order to protect the insertions of the ECU and FCU tendons. Likewise, the index metacarpal base should be preserved to protect the ECRL and FCR tendon insertions. The osteotomy is performed at the metaphyseal flare. Ray amputations usually result in 15 to 20% reduction in grip strength and narrowing of the palm.2–4
Transection of the radius and ulna should be at the same level. The distal radioulnar joint should be preserved rather than fused where possible to allow pronation and supination. While the tendons are often divided under traction to allow proximal retraction, this is not appropriate if future hand transplantation is a possibility as length should be preserved in this scenario. The minimum length considered useful for a forearm prosthesis is 8 to 10 cm of residual radius and ulna length.1–3
Allodynia is the perception of a painful sensation following what is normally a non-noxious stimulus, such as a burning sensation in response to a light touch. Mild symptoms can be quite common after digital amputation during the early stages of scar maturation and reinnervation; however, this usually settles with desensitization exercises. If allodynia persists, becomes severe, or is associated with trophic changes to the soft tissues, it may be part of a complex regional pain syndrome. Six weeks is too early for formation of a neuroma, and this would usually present as a pinpoint site of tenderness over the digital nerve stump or external scar, leading to an “electric shock” sensation or “shooting pain.” It is rather late for development of a postoperative infection and if infection was present the digit would usually be painful, swollen, tender, and warm. Cold intolerance is a recognized complication of digital amputation but would not present in this way.1–3
The lumbrical plus deformity may occur following a partial amputation of the finger. The PIP joint extends during attempts to actively flex the joint because the retracted FDP tendon remains attached to the lumbrical muscles in the palm. FDP contraction, therefore, pulls on the lumbrical muscle, causing flexion of the metacarpophalangeal (MCP) joint and extension of the IP joint. The lumbrical plus deformity can be prevented by securing the FDP to the A4 pulley during revision amputation; however, care must be taken when performing such a procedure as there is a risk of causing a quadriga effect instead. For this reason, it is not commonly performed. If the FDP tendon is overly advanced or tensioned in the injured digit, the action of FDP in the remaining digits is compromised. This is because the FDP tendons share a common muscle belly and if one is significantly tighter than the others, normal flexion in the remaining digits is restricted. Intrinsic minus deformity is a condition where the finger MCP joints are hyperextended and the PIP joints are flexed. This is because the normal function of the intrinsics is restricted, causing an imbalance between the strong extrinsics and the deficient intrinsics. It is typically observed in association with an ulnar nerve motor branch injury.1
The quadriga effect is where one of the FDP tendons is functionally shorter than the others. As this muscle group has a mass action, when the tightest FDP fully flexes, the remaining digits cannot fully flex and consequently display an active flexion lag or reduced power in grip. The main causes of this are either an overly tight FDP tendon repair to a single digit or after digital terminalization where the FDP is sutured to the extensor tendon or pulleys during the amputation procedure. Patients tend to complain of weak grip with an inability to actively make a full fist. Therefore, it is important when performing digital terminalization that the FDP is allowed to retract into the palm without distal tethering. One potential issue with doing so, however, is that the FDP may then pull on the lumbricals proximally and cause an lumbrical plus deformity. These risks have to be balanced when performing such surgery; however, lumbrical plus is uncommon and readily dealt with if it arises by release of the lumbrical in the palm; so, this may be preferable to producing a quadriga effect.1–3