Last updated:
10/20/2023
Years published: 2023
NORD gratefully acknowledges Kevin McMahon and Gregory Cichon, MD Candidates, Creighton University School of Medicine, and Ashwin Dalal, MD, Adjunct Visiting Professor, Department of Medical Genetics, Kasturba Medical College, Manipal, Karnataka, India, for the preparation of this report.
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Summary
Tarsal carpal coalition syndrome (TCC) is a rare genetic condition that is primarily characterized by fusion of the bones of the hands, wrists, feet and ankles, but may involve other areas such as the elbow. The most common symptoms are worsening stiffness, pain, immobility and deformity of the affected joints. TCC is caused by changes (pathogenic variants or mutations) in the NOG gene leading to overgrowth of bone or other tissues in the affected joints. Treatment options include physical therapy, occupational therapy and surgery aimed at reducing pain, improving joint mobility, correcting joint deformity and maintaining patient independence. Early diagnosis can lead to improved patient outcomes and better quality of life.
Introduction
TCC was first described in 1985 in a family with multiple affected members. In 2001, multiple genetic pathogenic variants of the NOG gene were reported to be associated with this disorder. Since then, additional pathogenic variants have been identified in this gene and have been associated with a range of similar conditions. Some scientists suggest classifying these conditions as NOG gene-related symphalangism spectrum disorders, where symphalangism refers to the fusion of finger or toe joints. Tarsal carpal coalition syndrome can be differentiated from other NOG gene-related symphalangism spectrum disorders by the absence of conductive hearing loss, abnormal facial features, or asymmetry of spinal curvature and the chest.
The most common initial signs and symptoms of tarsal carpal coalition syndrome are worsening joint stiffness, joint pain and joint deformity. Common complaints include pain with walking and abnormal walking pattern (gait).
Tarsal-carpal coalition syndrome is a progressive disease that is characterized by abnormal development that leads to the fusion of bones in the distal joints. The wrists/hands (carpals, phalanges/fingers) and ankles/feet (tarsals, phalanges/toes) are most affected. Involvement of the hand often is most noticeable in the pinky finger and spreads towards the thumb, but the thumb is often spared. Progressive fusion of the bones in these regions that may cause deformities such as inward or outward twisting of the feet, flat feet, shortening of the fingers or toes (brachydactyly), abnormal curvature of the fingers (clinodactyly) or partial to near complete fusion of the fingers or toes (syndactyly).
These deformities may be detected while a patient is still in the womb, and symptoms such as reduced range of motion in the fingers/toes, elbows and ankles may be seen at birth. There is often a family history of the condition and older family members may have similar but more advanced symptoms such as fixed flexion of joints, fusion of fingers and fusion of many small bones in the hands and/or feet.
If diagnosed at birth, babies with TCC may show stiffness or decreased/absent movement of finger joints, wrists, and elbows, shortening of fingers/toes, and fixed joint deformities such as clubfoot (inward deviation of the foot). In adults, symptoms are often more severe (since symptoms have had a longer time to progress) and may include fixed flexion deformities of the elbows, fusion of the fingers/toes, shortening of the fingers/toes, extensive fusion of the small bones of the hands and feet (carpal & tarsal bones) and limited range of motion in joints such as the fingers/toes, wrist, ankles and elbows. If not initially detected, adults with tarsal carpal coalition syndrome may have a history of delayed fine and gross motor development such as inability to bring things to their mouth, impaired ability to form a fist, difficulty raising their arms above their shoulders or fully straightening or supinating the forearms, trouble placing their thighs on floor when seated with folded legs and a history of abnormal walking gait. This is due to overgrowth of tissues in the affected joints leading to stiffness.
Patients with TCC may have low-to-normal height and weight, but normal intelligence and lifespan.
Tarsal carpal coalition syndrome is caused by changes (pathogenic variants) in the NOG gene. These variants result in a loss of the noggin protein which normally forms a receptor that decreases the concentration of proteins associated with bone and cartilage growth. This excess of bone-forming and cartilage-forming proteins or cells (osteoblasts) leads to oversized growth plates and excess cartilage and bone formation. This causes failure of joint formation and fusion of adjacent bones. Multiple pathogenic variants have been identified that lead to various presentations of TCC with overlapping symptoms. These variants cause abnormal cartilage formation but do not affect the overall shape or length of limbs. Most cases run in families, but some have been isolated (sporadic, non-familial). Different families with similar/identical pathogenic variants may have different symptoms, different severity, or even different NOG gene-related disorders due to differences in gene expression. Though there is variation in presentation, it appears that everyone with a pathogenic variant in the NOG gene has some form of disease with similar findings in males and females.
Tarsal carpal coalition syndrome is an autosomal dominant genetic condition. Dominant genetic disorders occur when only a single copy of a mutated gene is necessary to cause the disease. The mutated gene can be inherited from either parent or can be the result of a changed gene in the affected individual. The risk of passing the mutated gene from an affected parent to a child is 50% for each pregnancy. The risk is the same for males and females.
Tarsal carpal coalition syndrome is a rare condition with a prevalence of 1/1,000,000 in the general population.
Diagnosis of tarsal carpal coalition syndrome begins with recognizing the symptoms of joint stiffness, pain and deformity which are highly suspicious for this condition. Often these suspicions are confirmed by imaging such as CT or MRI which show the characteristic joint fusion, shortening of fingers/toes, deformity of bones and joint deformity. It should be noted that on plain imaging such as x-rays, children under 8 years old may not have enough bone formation to show bone fusion, and instead the cartilage fusion is still causing them to have symptoms. A definitive diagnosis can be made through genetic testing showing characteristic pathogenic variants in the NOG gene.
Treatment
Treatment is mostly aimed at controlling pain and preserving function with physical therapy followed by regular surgeries that involve cutting and reshaping bones to improve alignment or function.
Patients diagnosed as infants may need physical therapy once or twice a month to support range of motion and development of gross motor patterns. They may need casts to stabilize the joints as they grow followed by fitted orthotics for significant joint deformities such as clubfoot. Occupational therapy may be used to help with daily activities and creation of custom assistance devices to help perform daily activities. In all patients, long-term follow-up is recommended due to the progressive nature of this condition and tendency for symptoms to worsen or recur.
Microfractures and progressive ossification (formation or conversion of tissues to bone) lead to pain and can restrict mobility. Physical and occupational therapy can help maintain range of motion, reduce pain and preserve independence and function. When conservative treatments no longer work, surgery is the next option. Surgery involves removal of excess bone and soft-tissue or arthrodesis (surgical immobilization via fusion of adjacent joints). The size of the coalitions (fusion) is the main factor in predicting patient outcomes.
Surgical options are divided into a few main categories: excision (cutting out), arthrodesis (surgical immobilization of a joint by fusion) and osteotomy (cutting and reshaping of bones). All of these options focus on reducing symptoms, correcting deformities and/or improving functionality and appearance. After surgery, the joint is often placed in a plaster cast to allow healing of the bones for approximately 6 weeks. If multiple surgeries are required, there may be a period of up to 8 weeks between surgeries to allow for the initial joint to heal and regain function prior to a second surgery on the contralateral joint, such as the left knee being operated on 8 weeks after surgery on the right knee. Physical therapy may use electrical stimulation to retain strength in the muscles of the affected limb and may conduct training for proper joint utilization if the patient has been affected since infancy (i.e., they never had a normal walking gait due to stiffness of joints in the foot or legs). Patients may need to have frequent or repeated surgeries due to the progressive nature of this condition.
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