The correct answer is "compartment syndrome." Compartment syndrome is a surgical emergency in which an injury results in hemorrhage or swelling in an enclosed space that causes dangerously high pressures to build within the enclosed space, resulting in compromised bloodflow to the muscles and nerves within and distal to the space. The symptoms include a cool, pale, pulseless extremity that may also experience paresthesias, and that is visibly swollen and tense. In this case, the patient's right arm exhibits all of these characteristics, and this presentation is highly consistent with compartment syndrome.

The other choices are incorrect. Vasculitis and lupus are both autoimmune conditions that may result in limb swelling, but would be unlikely causes of this patient's presentation, especially in the setting of a recent local trauma to the affected limb. Fat embolism would not account for the patient's constellation of symptoms.There is no evidence of limb necrosis at this stage of the patient's injury. Should the compartment syndrome not be addressed and vascular flow remain compromised by persistently high pressures, then limb ischemia and consequent necrosis could be a downstream effect.

Osgood-Schlatter syndrome of irritation of the patellar ligament at the tibial tuberosity, characterized by painful lumps just below the knee, most often seen in young adolescents. Risk factors may include overzealous exercise but it's ultimately thought to be caused by adolescent bone growth. Osteosarcoma, the most common bone cancer in adolescent populations, can present with pain and a lump or frank swelling. This is caused by actual tumor growth, not by any ligamentous issue. Osteosarcoma does present frequently in the knee, and must be ruled out before a diagnosis of Osgood-Schlatter disease is made. Slipped capital femoral epiphysis causes pain and reduced movement in the hip, rather than the knee. Osteomalacia is a general softening of the bones caused by a deficiency in vitamin D.

Patellofemoral syndrome presents as pain in the front of the knee, sometimes caused by wearing down, roughening, or softening of the cartilage under the kneecap. Osgood-Schlatter disease is a syndrome of irritation of the patellar ligament at the tibial tuberosity, characterized by painful lumps just below the knee, most often seen in young adolescents. Legg-Calvé-Perthes syndrome is due to disruption of blood flow to the femoral head, leading to avascular necrosis. Congenital scoliosis is a spinal deformity characterized by the curving of the spine at an angle greater than 10 degrees on radiography.

Psoriatic arthritis will often show a pencil-in-cup deformity on x-ray. Osteoarthritis will show joint space narrowing, sclerosis, and osteophytes. Rheumatoid arthritis and juvenile rheumatoid arthritis will both show soft tissue swelling, joint space narrowing, and may show marginal erosions.

The correct answer is "ACL, MCL, and Medial meniscus." This is the only answer choice that correctly lists all three components of the "unhappy triad." The unhappy triad is frequently injured in athletes who participate in contact sports, such as football. The injury mechanism often involves a direct, forceful hit to a firmly planted leg. The hit is forceful enough to rupture two ligaments (ACL and MCL), as well as the medial meniscus. The treatment for such an injury involves surgical intervention and a lengthy recovery period, though for patients inclined to partake in the rehabilitation process, they can often return to their desired sports after completion of surgery and rehab.

Swan neck deformity is often seen in patients with rheumatoid arthritis. This is a state in which the distal interphalangeal joint (DIP) becomes hyperflexed (bends toward the palm) while the proximal interphalangeal joint (PIP) is hyperextended (bending away from the palm). Shepherd's crook deformity is seen in Paget's disease of the bone, pencil-in-cup deformity is seen in psoriatic arthritis, and Heberden nodes are frequently seen in the distal phalanges of patients with osteoarthritis.

Duchenne's is the most common and most severe form of muscular dystrophy, accounting for a full 50% of cases of muscular dystrophy in the US. The next most common type is Becker's, followed by myotonic muscular dystrophy and Emery-Dreifuss.

Lambert-Eaton syndrome is a condition of progressive muscle weakness caused by an auto antibodies to presynaptic calcium channels in the neuromuscular junction. This does not allow calcium to enter the presynaptic cell, which is required for neurotransmitter release into the synaptic cleft. Without the release of neurotransmitter, there will be no muscular response. Myasthenia gravis is an autoimmune condition in which antibodies are formed against acetylcholine receptors, and muscular weakness in multiple sclerosis is caused by destruction of myelin in the CNS due to antibodies against oligodendrocytes. Dermatomyositis is an inflammatory connective tissue condition that may be associated with a post-viral autoimmune reaction or triggered by a paraneoplastic syndrome.

Histological findings of dermatomyositis will generally reveal mixed B cell and T cell perivascular inflammatory infiltrate and perifascicular muscle fiber atrophy.

Fibrosed muscle fibers and fatty infiltrates are typical of Duchenne's muscular dystrophy, while granulomas in muscle are rare but may be seen in sarcoidosis and other conditions of granulomatous myositis.

A periorbital heliotrope rash is often seen in dermatomyositis. It is bilateral, symmetric, purpuric, and macular, and erupts over the eyelids and surrounding periorbital area. Malar rash (often called a "butterfly rash") is seen in patients with systemic lupus erythematosus (SLE). Dermatitis herpetiformis is a rash on the elbows and knees generally seen with gluten allergy (celiac disease). Perioral dermatitis is an iatrogenic condition often associated with prolonged use of topical steroid creams.