In medical terms, TAR most commonly refers to thrombocytopenia-absent radius syndrome, a rare genetic condition present at birth. But the acronym appears in several different medical contexts, including orthopedic surgery and hernia repair, and the word “tar” itself has a separate meaning in dermatology. Here’s what each one involves and why it matters.
TAR Syndrome: A Rare Genetic Condition
Thrombocytopenia-absent radius syndrome is a congenital disorder defined by two features: a shortage of platelets (the blood cells responsible for clotting) and the absence of the radius bone in both forearms. The radius is the bone on the thumb side of your forearm. What makes TAR syndrome unusual compared to similar skeletal conditions is that affected individuals still have their thumbs, while people with other absent-radius conditions typically do not.
TAR syndrome is rare, occurring in roughly 0.42 cases per 100,000 live births, with an overall prevalence estimated between 1 in 100,000 and 1 in 200,000. The low platelet count tends to be most severe during infancy and often improves with age. In some cases, platelet levels eventually reach normal ranges.
Beyond the forearms, TAR syndrome can involve other skeletal differences. The ulna (the other forearm bone) is sometimes underdeveloped or absent. Some people have webbed or fused fingers, curved pinky fingers, or abnormalities in the upper arms, legs, or hip sockets. Facial features like a small lower jaw, prominent forehead, or low-set ears can also occur.
What Causes TAR Syndrome
TAR syndrome results from mutations in a gene called RBM8A, which provides instructions for making a protein involved in cell function. Most people with the condition have a mutation in one copy of this gene and a deletion of genetic material from chromosome 1 that eliminates the other copy. A smaller number have mutations in both copies without the chromosome deletion. Either way, the result is a reduced amount of the protein the gene produces, which disrupts normal development of blood cells and bone.
Total Ankle Replacement
TAR also stands for total ankle replacement (sometimes called total ankle arthroplasty), a surgical procedure for people with end-stage ankle arthritis. The operation removes damaged bone and cartilage from the ankle joint and replaces them with artificial components, similar in concept to a hip or knee replacement.
The ideal candidate is someone with significant ankle arthritis who is reasonably mobile, has a healthy body weight, stable alignment in the foot and ankle, and retains at least some range of motion. The surgery is performed under general anesthesia, typically with a nerve block for pain control. Surgeons access the joint through an incision on the front of the ankle, carefully preserving surrounding tendons, blood vessels, and nerves before removing damaged bone and fitting the prosthetic components.
Modern ankle implants have strong survival rates. One study following patients for an average of eight years found that 97.4% of prostheses were still intact at both five and ten years. When accounting for all revision surgeries, including minor ones, the revision-free rate was 81.5% at five years and 74.7% at ten years.
Transversus Abdominis Release
In abdominal surgery, TAR refers to transversus abdominis release, a technique used to repair large or complex hernias in the abdominal wall. These are typically ventral or incisional hernias where the gap in the abdominal wall muscle is wider than 10 centimeters or involves more than a quarter of the abdominal wall surface.
The technique works by releasing one of the deep abdominal muscle layers, which allows the surgeon to bring the separated edges of the abdominal wall back together at the midline. A large piece of surgical mesh is then placed in a deep plane behind the muscle to reinforce the repair. This approach avoids extensive cutting through the skin and fat layers, which reduces wound complications compared to older hernia repair methods.
Recovery from this surgery requires a hospital stay of several days. Patients typically experience mild to moderate pain for a few weeks and are advised to avoid heavy lifting, strenuous activity, and exercise for at least six weeks. An abdominal binder is often recommended during recovery. While there’s usually an immediate improvement in the hernia, final results take three to six months to fully appear.
Coal Tar in Dermatology
Outside of acronyms, the word “tar” in medicine usually refers to coal tar, a topical treatment for skin conditions like psoriasis. Coal tar has been used for this purpose for hundreds of years and remains available in shampoos, ointments, creams, and foams, both over the counter and by prescription.
Coal tar appears to work by slowing down the rapid skin cell growth that drives psoriasis plaques. It may also reduce inflammation, relieve itching, and have mild antimicrobial effects, though its exact mechanism is still not fully understood. Concentrations range from 2% in foam formulations (useful for hard-to-treat areas like the scalp, skin folds, and palms) up to 6% crude coal tar ointment applied under bandages for thicker plaques on the hands and feet.
Coal tar does come with practical downsides. It can stain skin and clothing, though skin staining fades after you stop using it. More importantly, it makes your skin significantly more sensitive to sunlight. After applying coal tar, you should avoid direct sun exposure and tanning beds for at least 72 hours, and make sure all residue is removed from your skin before going outdoors.