Hand tendon injuries are mostly open, with lacerations being the most common, often accompanied by neurovascular injuries or bone and joint injuries, and closed lacerations can also occur. After a tendon rupture, the corresponding joint loses its function. For example, if the flexor digitorum superficialis tendon is ruptured, the proximal interphalangeal joint of the corresponding finger cannot flex; if the flexor digitorum profundus tendon is ruptured, the distal interphalangeal joint cannot flex; if both the superficial and deep flexor tendons are ruptured, neither the proximal nor the distal interphalangeal joints can flex. Since the intrinsic hand muscles remain intact, the flexion of the metacarpophalangeal joint is unaffected. Ruptures of the extensor tendons at different locations result in the inability to extend the corresponding joints and may lead to deformities.

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1. Avulsion of extensor tendon insertion: Mostly caused by poking injuries, sudden flexion of the distal interphalangeal joint leading to the avulsion of the extensor tendon attachment, or local lacerations can also sever it. Manifested as mallet finger deformity, some patients may have associated avulsion fractures.
   1. Open injury: After debridement, the tendon is sutured, and the finger is positioned with the distal interphalangeal joint hyperextended and the proximal interphalangeal joint flexed to relax the extensor tendon. Fixation with gypsum or an aluminum splint for 4–6 weeks.
   2. Closed injury: Fixed in the aforementioned position for 4–6 weeks. If accompanied by a large avulsion fracture, early surgery may be performed using the "pull-out wire technique" to fix the fracture fragment, followed by external fixation with gypsum or an aluminum splint.
   3. Old injury: The proximal tendon retracts, forming scar tissue at the rupture site, causing tendon laxity. If functional impairment is minimal, no treatment is necessary. For significant functional impact, surgical intervention is performed. An S-shaped incision is made on the dorsal side of the distal interphalangeal joint, the skin flap is lifted, and the muscle membrane is overlapped and sutured. Postoperative fixation in the aforementioned position for 4–6 weeks.
2. Central slip rupture of the extensor tendon: During finger flexion, the dorsal prominence of the proximal interphalangeal joint is prone to injury, often accompanied by central slip rupture. Normally, the central slip and lateral bands lie on the dorsal side of the finger's longitudinal axis. After central slip rupture, the lateral bands can still extend the finger. If the central slip is not repaired, with repeated flexion, the lateral bands gradually slide toward the palmar side, losing their extensor function and instead causing flexion of the proximal interphalangeal joint and hyperextension of the distal interphalangeal joint, forming the classic "boutonnière deformity."
3. Injuries to the extensor tendons on the dorsum of the hand, wrist, and forearm: Primary repair of the ruptured extensor tendons should be performed, yielding good results. For ruptures at the dorsum of the wrist, the corresponding portion of the dorsal transverse carpal ligament and synovial sheath should be incised to position the tendon directly under the skin.