Extensors tendons of hand Functional anatomy M Al-Maiyah April 2007

Introduction 1 Extensor tendons injuries (ETI) are common due to their relatively exposed and superficial location. Extensor tendons in fingers (in comparison to flexors) are thinner, less substantial and less likely to hold sutures. Majority of ETI are at joint levels, so penetrating wounds prone to enter the underlying joint (MCP, IPJ).

Introduction 2 Lacerating & avulsion ETI usually not associated with tendon ends retraction: Multiple soft tissue attachments and interconnections. Paratenon surrounds the extensor tendons over the dorsum of hands, so those tendons do not separate widely when lacerated. Because of this some injuries (Esp. fingers) could be treated by splinting only. However, they do retract at wrist level

Anatomy 1 Extensor mechanism more complex than flexor mechanism Extensors tendons   ExtrinsicIntrinsic

picture

Anatomy 2 Ex. Tendons enter the hand beneath Extensor Retinaculum. E. R (~ 5 cm). It consists of 2 layers. 6 tunnels; 5 fibro-osseous & one fibrous (the 5 th, contains EDM). At this level, tendons have synovial sheaths. At MP joint level communis tendons are joined by by juncturae tendinum. Centred around ring finger.

Anatomy 3 When evaluating an injured hand, a lacerated tendon my be overlooked if finger extension in partially maintained through juncturae tendinum

Anatomy 4 There are many normal variations. EPL, EPB, EIP & EDM have more independent origin and action. EDC, has limited independent action. Its tendon to the little finger is absent in 50 % of cases. EIP at MP joint is usually ulnar to the EDC tendon to the Index finger. EDM over the metacarpal and wrist level is usually represented by two tendons.

Anatomy 5 At MP joint, Ext. tendon held centralised over the joint by the conjoined tendons of intrinsic muscles and the sagittal band. Any injury to this hood may result in subluxation or dislocation of the Extensor tendon.

Anatomy 6 EIP transfer may associated with extension lag of the Index finger and to avoid this the tendon should be sectioned proximal to the hood.

Anatomy 7 At the finger level; the extensor tendon trifurcate into central slip (attached into the dorsal base of middle phalanx) and two lateral slips which attach to the dorsum of distal phalanx. The lateral bands displace volarly in flexion and dorsally in extension.

Anatomy 8 The intrinsic tendons from lumbricals and interosseous muscles join the extensor mechanism at about proximal phalanx and continue distally to DIP. At MP joint level, The intrinsic tendons are palmer to the joint, so they act as flexors, while at PIP are dorsal to PIP so they act as extensors of PIP & DIP.

Anatomic Variations 1 Extensor carpi radialis Intermedius & Accessory tendons Incidence 12%- 24% Arises between ECRL & ECRB and usually inserted on index or middle finger metacarpal. It might be suitable for tendon transfer.

Anatomic Variations 2 Extensor Medii Proprius: (10 %) A muscle analogous to EIP with same origin but inserts to the extensor aponeurosis of the middle finger. It may be covered by EDC tendon. Its insertion always medial and distal to EDC tendon.

Anatomic Variations 3 Extensor Indicis et Medii Communis: (3.4 %) It is an anomalous EIP that splits and inserts into both the index and middle fingers Extensor Digitorum Brevis Manus:(3%) An abnormal muscle on the dorsum of hand. Usually fusiform, soft mass on the dorsum of the hand, between the index and middle finger metacarpals. It may become painful, then should be differentiated from dorsal wrist ganglion or tumour

Anatomic Variations 4 Other extensor tendons variations and multiplicity Double EIP tendon Single to triple EDC tendon to the ring finger. Absent, Single or double EDC to the little finger A knowledge of these variations is useful in the identification and repair of these structures as well as in utilising them in reconstructive procedures