Muscle strength measurements of the Hand - Handen Team Zeeland

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Ton A.R. Schreuders, JW Brandsma, HJ Stam the metacarpo-phalangeal (MCP) joint. The first palmar interosseous (1 PI) muscle is more active in tip pinch activities. In Type II, the insertion into the lateral band of the extensor apparatus (d.) is responsible for an important extension force at the proximal interphalangeal (PIP) joints. The first palmar interosseous also produces some supination of the index finger to get good approximation of the pulps. In this respect we might consider the 1 PI as an “opponens indices” muscle in tip pinch activities. Without interossei the finger is unstable and will collapse into the “claw” (i.e. intrinsic minus) position of flexed IP joints and (hyper-) extension of the MCP joint: therefore the interosseous are sometimes referred to as the “anti-claw” muscles. 35 The primary function of the interossei is MCP flexion/stabilisation with extension of the interphalangeal (IP) joints. This is especially evident during pinch in which the collapse of the index PIP joint is apparent in, often > 90°, flexion. This is a sign of interosseous muscle weakness and sometimes referred to as the Mannerfelt sign. 20 (Figure 2). FIGURE 2. Mannerfelt and Froment sign on left hand of patient with ulnar nerve paralysis. Recording the moments of the intrinsic muscles that were generated after electrical stimulation Lauer et al. 43 found that the dorsal interossei muscles were strong abductors of the fingers and generated a significant moment in MCP joint flexion and IP joint extension. Similarly, Ketchum et al. 34 found that the interossei muscles of the index finger contribute 73% to the overall moment for flexion of the MCP joint. 34 Li et al. 44 investigated the role of the intrinsic finger flexor muscles during finger flexion tasks. When an external force is applied proximally to the PIP joint, the extensor mechanism (intrinsic muscle group) is the largest component (70%) on force production of all flexors. Thus the interossei muscles are important flexors of the MCP joint together with the long flexors: flexor digitorum profundus (FDP) and flexor digitorum superficiales (FDS). However, at the PIP joint level the long flexors, primarily the FDS, and the interossei are antagonists. When the PIP joint is flexed, some reduction of the extension moment of the interossei takes place, due to the volar displacement of the lateral bands (of about 4-mm) at the PIP joint level. At full flexion of both the PIP and distal interphalangeal (DIP) joints, the lateral bands approach the flexion-extension axis of the PIP joint, thereby minimising the extensor moment. 2 The action of the interossei muscles can be studied separately from the extensor digitorum communis (EDC) muscles in patients with a radial nerve paralysis. If the patient is asked to extend the fingers, no extension of the MCP will occur, but the finger IP joints will extend because of the ulnar and median nerve innervated interosseous and lumbrical muscles. However, in some patients the fingers, especially the index, can be extended in the MCP joint to some degree, especially with the wrist flexed; this is probably because the angle of attachment of the dorsal interossei muscles is only 0°- 5°. When the tension on the extensor tendon is increased due to the flexed wrist, this angle will go beyond the 0° and thus the interosseous muscle becomes an extensor of the MCP joint. The angle of approach to the extensor mechanism for the palmar interossei muscles is 20°-25° and for the lumbrical muscles 35°. 28 The index finger is deprived of all long flexors and the lumbrical muscles in patients with a high median nerve paralysis. The only active muscles are the long extensors and the two interossei. In 6
Muscle strength measurements of the Hand an attempt to flex the fingers the index finger will remain extended, and is accurately described as the “pointing finger” where the IP joints are fully extended and the MCP joint flexed. In high median nerve paralysis the long finger is also deprived of the long flexor, but will usually flex in grip. This is due to the attachments between the FDP tendons of the long finger and the ring finger and is called the Quadriga phenomena. 45 46 This term suggests a symmetrical organisation of the four tendons; however, the connections between the FDP of the index and middle finger are usually absent, and a strong connection between the flexor pollicis longus (FPL) and the FDP of the index finger can exist. 1.1.2 Pathokinesiology (paralyses, consequences for prehension/ADL, shortening) The deficiency mentioned in textbooks due to loss of interossei is usually that of controlled abduction and adduction of the fingers. The loss of this action is important for those who play musical instruments or operate keyboards, but in most patients this is not recognised as a severe deficit. The loss of the interossei function of MCP flexion and PIP extension is a much more significant loss. In acute paralysis of the interossei muscles it will sometimes only be visible as a mild hyperextension at the MCP joints and slight flexed position of the PIP joints when the patient is asked to extend the fingers. However, this deformity usually progresses depending on the natural joint laxity of the hands, i.e. long, thin and hypermobile fingers will develop a socalled claw hand much quicker than thick, stiff fingers. In the mobile hands the volar ligamentous structures stretch more easily, causing increased hyperextension and subsequently less PIP extension. Extension of the PIP joints is only possible by contraction of the EDC when the MCPs are 'blocked', either actively (internally) through muscle contraction or passively (externally) through the examiners hand or a splint, preventing hyperextension of the MCP joints. In the latter situation this is called assisted extension, which is used as a test to assess the integrity of the extensor apparatus. Other factors that may contribute to the development of a claw hand are: hand dominance, continued use of the hand (or the lack of), compliance of the patient to perform the routine exercises to prevent joint stiffness, and use of (night) splints. Without interosseous the hand can still make a full fist, but the pattern of movement is changed (the MCP flexion takes place later than usual). The contribution of the interossei muscles in grip strength measurements will be discussed later. In patients with a “high” ulnar lesion, the FDP muscles of the 4th and 5th fingers are paralysed and less clawing is often visible because the flexion moment at the PIP joints is decreased compared to a “low” ulnar palsy. We might conclude from this observation that clawing is also the result of visco-elastic tension of FDP. When the ulnar nerve recovers, the 4th and 5th finger will show an increasing clawing. Maintaining the length of the FDPs, i.e. preventing flexor tightness, therefore also helps to prevent clawing. Another sign of interossei muscle weakness was first described by Andre- Thomas in 1917 and is called the Thomas sign. 47 (p. 518) (Figure 3). This is the tendency (compensation) of a patient with weak interossei muscles of the fingers to automatically flex the wrist in an attempt to gain a better opening of the hand, i.e. MCP extension, by means of increasing the pull on the EDC. This in fact increases the hyperextension of the MCP joints and adds to the progress of the development of the claw hand. This “trick” movement is adopted very quickly and even when the interossei have regained their strength, will often take a long time to “un-learn”. In longstanding paralyses of the interossei, e.g. when the ulnar nerve could not be repaired or did not recover, the PIP joints are continuously in a flexed position. This will cause a gradual stretching of the dorsal expansion (sometimes called the tri-angular ligament) over the PIP joint, which secures the lateral bands of the extensor tendon in their dorsal position. In 7
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Muscle strength measurements of the Hand - Handen Team Zeeland

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