Surgical Anatomy. The lower end of the ulna articulates with the superior surface of the triangular fibro-cartilage and the sigmoid cavity of the radius. This joint is maintained by the triangular fibro-cartilage, anterior and posterior radio-ulnar ligaments, and a separate synovial sac. Isolated luxation of this joint is rare but can occur as a complication of Colles' fracture.
Clinically, three types of luxation have been observed: backward, forward, and inward. Backward dislocation occurs behind the postero-internal angle of the radius with intact triangular fibro-cartilage. Forward dislocation displaces the ulna forward and slightly outward, often due to hypersupination. Inward dislocation requires rupture of the interarticular cartilage.
Symptoms include pain, swelling, tenderness, loss of function, deformity, and disturbance in rotary action of the forearm. Chronic luxations may develop gradually as a result of heavy work during bone development stages (Madelung's deformity).
Diagnosis involves palpating the displaced head of the ulna according to displacement direction. Treatment varies by type: backward dislocations require supination; forward dislocations, pronation.
Operative treatment is rarely needed unless as a complication of Colles' fracture or in old cases where bones have grown out of alignment. After-treatment involves immobilization and healing time for ligaments.
Prognosis is excellent if reduction is early but can be poor with unreduced chronic cases, especially affecting rotary action.
Key Takeaways
- Luxations of the lower end of the ulna are rare but can occur as complications of Colles' fracture.
- Three main types of luxation exist: backward, forward, and inward, each with distinct symptoms and diagnostic features.
- Treatment varies based on type and severity; early reduction is crucial for a good prognosis.
Practical Tips
- Palpate the wrist carefully to identify the displaced head of the ulna during diagnosis.
- Use supination or pronation techniques as appropriate for backward or forward luxations, respectively.
- Immobilize the forearm in rotation opposite to that which caused the luxation.
Warnings & Risks
- Failure to diagnose and treat luxations early can lead to chronic issues affecting wrist function.
- Chronic cases may require surgical intervention if non-invasive methods fail.
Modern Application
While modern medical practices have advanced significantly, understanding historical techniques for diagnosing and treating ulnar luxations remains valuable. Early recognition and proper immobilization are still critical today, as they were a century ago.
Frequently Asked Questions
Q: What is the most common type of luxation observed in this chapter?
The backward dislocation is more commonly seen as a complication of 'reversed Colles' fracture' and due to hyperpronation of the wrist.
Q: How can one diagnose an inward luxation of the lower end of the ulna?
Inward luxations are characterized by broadening of the wrist with loss of power in rotary action. They are almost never seen except as a complication of Colles' fracture.
Q: What is Madelung's deformity and how does it relate to chronic backward subluxation?
Madelung's deformity refers to a gradual backward displacement that develops in children due to heavy work during bone development stages, leading to radial deformity and ulnar overgrowth.