Unhappy triad
Musculoskeletal system
Congenital disorders
Degenerative and metabolic disorders
Degenerative disc disease
Legg-Calve-Perthes disease
Osgood-Schlatter disease (traction apophysitis)
Osteomalacia and rickets
Osteopetrosis
Osteoporosis
Osteosclerosis
Paget disease of bone
Spinal disc herniation
Spinal stenosis
Spondylolisthesis
Spondylolysis
Spondylosis
Calcium pyrophosphate deposition disease (pseudogout)
Gout
Osteoarthritis
Compartment syndrome
Rhabdomyolysis
Infectious, immunologic, and inflammatory disorders
Ankylosing spondylitis
Antiphospholipid syndrome
Dermatomyositis
Juvenile idiopathic arthritis
Limited systemic sclerosis (CREST syndrome)
Mixed connective tissue disease
Polymyositis
Psoriatic arthritis
Raynaud phenomenon
Reactive arthritis
Rheumatoid arthritis
Scleroderma
Sjogren syndrome
Systemic lupus erythematosus
Osteomyelitis
Septic arthritis
Spondylitis
Baker cyst
Bursitis
Iliotibial band syndrome
Inclusion body myopathy
Patellofemoral pain syndrome
Polymyalgia rheumatica
Temporomandibular joint dysfunction
Transient synovitis
Traumatic and mechanical disorders
Lordosis, kyphosis, and scoliosis
Sciatica
Achilles tendon rupture
Anterior cruciate ligament injury
Meniscus tear
Patellar tendon rupture
Slipped capital femoral epiphysis
Sprained ankle
Unhappy triad
Carpal tunnel syndrome
Erb-Duchenne palsy
Klumpke paralysis
Sciatica
Thoracic outlet syndrome
Ulnar claw
Winged scapula
Dislocated shoulder
Radial head subluxation (Nursemaid elbow)
Rotator cuff tear
Other disorders
Musculoskeletal system pathology review
Bone disorders: Pathology review
Gout and pseudogout: Pathology review
Muscular dystrophies and mitochondrial myopathies: Pathology review
Pediatric musculoskeletal disorders: Pathology review
Myalgias and myositis: Pathology review
Rheumatoid arthritis and osteoarthritis: Pathology review
Scleroderma: Pathology review
Seronegative and septic arthritis: Pathology review
Sjogren syndrome: Pathology review
Systemic lupus erythematosus (SLE): Pathology review
Bone tumors: Pathology review
Back pain: Pathology review
Summary
An unhappy triad, also known as O'Donoghue's triad, is a common injury that occurs in the knee joint. It involves damage to the anterior cruciate ligament (ACL), medial collateral ligament (MCL), and medial meniscus. The injury usually occurs as a result of a sudden forceful twist or impact on the knee joint, such as during a sports activity. The lateral meniscus may also be involved in some cases. This injury is typically treated with surgery and physical therapy.