Proximal symphalangism is a rare genetic condition in which some middle finger or toe joints do not form normally and stay stiff or fused. It is usually present from birth, and many living with Proximal symphalangism are noticed in infancy or childhood when fingers do not bend as expected. In plain terms, it means the affected digits may have limited movement, and some people also have mild differences in hearing. Proximal symphalangism is not usually life-shortening, but the features can last lifelong and vary from one person to another. Treatment focuses on support, such as hand therapy, hearing care when needed, and sometimes surgery for selected cases, especially if early signs of Proximal symphalangism are affecting daily activities.
How many people live with Proximal symphalangism?
There is no single reliable recent count of how many people live with proximal symphalangism worldwide or in the United States. Major rare-disease references describe it as very rare, but they do not give a clear global or U.S. number.
Overview
Proximal symphalangismSymptoms
Proximal symphalangism mainly affects the fingers and sometimes toes, causing joints to be stiff or fused. Common signs of proximal symphalangism include fingers that do not bend normally, limited hand movement, and differences in finger shape.
Outlook and prognosis
For most people with proximal symphalangism, life expectancy is normal, and symptoms are usually stable rather than worsening over time. Many adapt well, though finger stiffness, toe changes, and sometimes hearing loss can affect daily activities and need ongoing support.
Causes and risk factors
Proximal symphalangism usually results from a change in NOG or GDF5. It often runs in families in a dominant pattern, meaning one changed copy from either parent can cause it. No lifestyle or environmental risks are known.
Genetic influences
Genetics are central to proximal symphalangism. It is usually caused by inherited gene changes, most often in NOG or GDF5, and different variants can affect how severe proximal symphalangism is within the same family.
Diagnosis
Proximal symphalangism is usually diagnosed by its clinical features, especially fingers or toes that do not bend normally. X-rays can show fused joints, and genetic tests may confirm the diagnosis of proximal symphalangism.
Treatment and drugs
Treatment for proximal symphalangism focuses on keeping the hands and feet as comfortable and useful as possible. Many living with proximal symphalangism benefit from hand therapy, stretching, pain relief when needed, and sometimes surgery if fused joints greatly limit movement or function.
Symptoms
Some fingers may stay unusually straight and not bend well, which can make small hand movements awkward. In medical terms, this is proximal symphalangism; in everyday life, it shows up as finger or toe joints that are partly or fully joined from birth. The early features of proximal symphalangism are often subtle in babies and become clearer as hand use increases. Features can range from mild stiffness in a few digits to toe involvement or, less often, other joint or hearing changes.
The middle joint of one or more fingers may bend very little or not at all because the joint is joined more than usual. This is often easiest to notice when trying to make a fist or curl the fingers around an object.
Affected fingers may look unusually straight and hold the same position while the rest of the hand bends. The change is often painless, but the hand can look and move differently from other people's hands.
The usual skin fold over the stiff joint may be faint or missing because that joint does not move much. In children, this can be one of the early features of proximal symphalangism that families notice.
Buttons, pens, tools, sports grips, or musical instruments can take more effort when fingers cannot flex normally. Daily impact depends on how many digits are involved and whether one or both hands are affected.
How people usually first notice Proximal symphalangism?
The first signs of Proximal symphalangism are usually noticed in infancy or early childhood, when parents or doctors see that one or more fingers or toes do not bend normally at the middle joint and can look unusually straight or stiff. Some children are first picked up because their hands seem less flexible during play, dressing, or grasping small objects, while others are noticed after a routine exam or an X-ray shows that nearby bones have formed more like a single rigid segment than a moving joint. In some families, how Proximal symphalangism is first noticed is even earlier, because a relative has the same finger or toe shape and prompts a closer look.
Types of Proximal symphalangism
Proximal symphalangism is a genetic joint condition, and the main variants of proximal symphalangism are usually defined by the gene involved. In day-to-day life, many living with proximal symphalangism notice fingers that do not bend normally, making tasks like gripping a pen, buttoning clothes, or playing certain sports harder. The different variants can look similar, but they may differ in which joints are affected and whether features such as hearing loss are also present. Not everyone will experience every type.
Type 1
This form is most often linked to changes in the NOG gene. People with type 1 often have stiff or fused middle finger joints, especially in the ring or little fingers, and some also have affected toe joints. Conductive hearing loss can occur in some families, so this type may involve more than the hands and feet.
Type 2
This form is most often linked to changes in the GDF5 gene. Many with type 2 have a similar pattern of finger joint stiffness or fusion, but hearing problems are usually less prominent than in type 1. The number of joints involved and how much movement is limited can still vary from one person to another.
Can I slow down the onset of symptoms?
No, there is no good evidence that lifestyle changes or medical treatment can meaningfully delay the start of symptoms in proximal symphalangism, because it is usually an inherited condition that affects how some finger joints develop before birth. Things like exercise, diet, sleep, or supplements have not been shown to prevent it or push symptoms back, although early care with a hand specialist or hand therapist may help some people protect comfort and make daily tasks easier once stiffness is noticed. There are no well-established preventive medicines for delaying onset, but early support can still help many living with this condition use their hands as well as possible.
What genetics can tell you about symptoms
Yes. In proximal symphalangism, the exact genetic change can help predict which joints are affected, how stiff the fingers or toes may be, and whether other features, especially hearing loss, are more likely to be part of the picture. Genetics can also give clues about severity and whether signs are obvious at birth or noticed later in childhood, although symptoms can still vary even among relatives with the same variant.
Causes and risk factors
The genetic causes of proximal symphalangism usually involve a change in how finger or toe joints separate before birth. Doctors most often find changes in genes called NOG or GDF5, and these changes may be inherited from a parent or happen for the first time in a child. Some risks are written in our DNA, passed down through families. Family history is the main risk factor for proximal symphalangism. Sex, diet, and everyday exposures are not known to cause it, and growth, repetitive hand use, or past injuries may only make stiffness or limited motion easier to notice.
What are the most common causes or risk factors?
Proximal symphalangism is most often caused by an inherited change in a gene that helps the small joints in the fingers or toes form before birth, so the main risk factor is having a parent or other close family member with the condition. In some people, the gene change happens for the first time in the child, even when there is no family history. There are no well-established lifestyle, diet, or environmental risk factors.
Environmental and biological risk factors
For proximal symphalangism, experts have not identified clear environmental exposures or non-genetic body factors that reliably increase the chance of it occurring. Researchers are still exploring how outside influences interact with our inner biology. In practice, the known non-genetic risk factors for proximal symphalangism are very limited, and no specific medicine, infection, pollution exposure, or pregnancy-related factor has been firmly linked to it in a consistent way.
Genetic risk factors
When finger joints are stiff from birth or early childhood, the reason is often genetic. If you are looking into the genetic causes of proximal symphalangism, the main known causes are changes in genes that help joints separate normally before birth. Some risk factors are inherited through our genes. A close family history is often the biggest clue, although features can vary even within the same family.
NOG gene: The most common known cause of proximal symphalangism is a change in the NOG gene. This gene helps control how developing bones and joints separate before birth, so a change can leave a finger joint partly or fully fused. In some families, NOG changes are also linked with hearing loss or extra areas of bone fusion.
GDF5 gene: Changes in GDF5 can also cause proximal symphalangism, though they are less common than NOG-related cases. This gene helps shape the growth of bones and joints in the hands and feet during early development. The exact features can differ from one family to another.
Dominant inheritance: Proximal symphalangism is often passed down in an autosomal dominant pattern, meaning one altered copy of the gene can be enough to cause it. If one parent has the condition-causing change, each child has a 1 in 2, or 50%, chance of inheriting it. Risk is not destiny—it varies widely between individuals.
New variant: Sometimes proximal symphalangism happens because of a new genetic change in the child, even when neither parent is affected. This is called a de novo change, and it means the condition can appear for the first time in a family. Genetic testing can help confirm whether this is the cause.
Lifestyle risk factors
For people living with proximal symphalangism, daily habits do not cause the condition, but they can influence stiffness, pain, hand function, and the strain placed on nearby joints. When people ask how lifestyle affects proximal symphalangism, the main issues are joint protection, activity choices, repetitive hand use, and injury prevention. Supportive routines may help preserve comfort and function, while unhelpful habits can worsen symptoms or secondary problems.
Frequent gripping, pinching, typing, tool use, or gaming can overload already stiff finger joints. This may increase pain, fatigue, and irritation in nearby joints that are trying to compensate for limited motion.
Contact sports or activities with falls, jamming, or direct blows to the fingers can aggravate symptoms and cause additional hand injuries. Protecting the hands during sport may lower the risk of fractures, sprains, or worsening functional limitations.
Avoiding hand and upper-limb movement completely can reduce strength and dexterity over time. Gentle, regular movement and therapist-guided exercises may help maintain function and reduce stiffness around affected joints.
Using awkward grips or forcing fingers through movements they cannot perform can strain tendons and neighboring joints. Adaptive tools, larger handles, and ergonomic techniques may make daily tasks less painful and more efficient.
Risk prevention
Proximal symphalangism is usually present from birth, so there is no known way to prevent the condition itself if someone has the gene change that causes it. For many living with proximal symphalangism, prevention is really about protecting hand and foot function, limiting pain or strain, and catching related joint or hearing issues early. Some prevention is universal, others are tailored to people with specific risks.
If proximal symphalangism runs in your family, genetic counseling can help you understand the chance of passing it on and what testing options may be available. This can be useful when planning a pregnancy or making sense of a child’s diagnosis.
Gentle use of the hands and avoiding repeated heavy gripping or forceful twisting may help reduce strain on stiff joints affected by proximal symphalangism. In daily life, this can mean choosing tools with thicker handles or taking breaks during tasks like typing, crafting, or using hand tools.
Early review by a hand specialist or therapist may help maintain function and teach safer movement patterns. While fused joints cannot be unfused with exercise, therapy can support nearby joints and help with everyday tasks such as buttoning clothes or opening jars.
Stiff fingers or toes may change how force travels through the hand or foot, so protecting against falls, sports injuries, and crush injuries matters. Well-fitting shoes, protective gear for activities, and sensible pacing can help lower the chance of added joint problems.
Can you prevent Proximal symphalangism?
Usually, no. Proximal symphalangism is a rare inherited condition where some finger or toe joints do not form in the usual way and can be stiff or joined together, so there is no proven way to prevent it. If it runs in your family, talking with a genetics specialist before pregnancy may help you understand the chances of passing it on, but it cannot guarantee prevention.
Transmission
Proximal symphalangism is not infectious, so it cannot be passed from one person to another through touch, kissing, sex, sharing food, or being near someone who has it. Instead, the genetic transmission of Proximal symphalangism usually happens from parent to child.
Many living with Proximal symphalangism have a parent with the condition, and each child of an affected parent often has a 1 in 2, or 50%, chance of inheriting it. In some families, it starts for the first time because of a new gene change, so a child can have Proximal symphalangism even when neither parent is affected.
When to test your genes
Genetic testing is most useful if you were born with stiff, straight finger joints, have relatives with similar hand or foot findings, or doctors suspect a related bone condition. A confirmed result can clarify the diagnosis, guide orthopedic and hearing evaluations when relevant, and inform family planning.
Diagnosis
Many living with Proximal symphalangism first seek answers when stiff fingers or toes make small daily tasks harder, such as gripping a pen or bending the toes inside shoes. Diagnosis is often based on the typical pattern seen on exam and then confirmed with imaging or genetic tests. Getting a diagnosis is often a turning point toward answers and support.
Doctors look for fingers or toes that do not bend normally at the middle joint, especially the index, middle, ring, and little fingers. They also check how much movement is present and whether the pattern fits Proximal symphalangism rather than a past injury or arthritis.
Some conditions have a genetic link, meaning they can run in families. A detailed family and health history can help show whether close relatives have had similar stiff digits, toe changes, or hearing problems.
X-rays can show whether the middle joints are partly formed, narrowed, or fused, which is a key clue in the diagnosis of Proximal symphalangism. Imaging findings also help rule out other bone and joint conditions present from birth.
Genetic tests may be offered to look for a change in a gene known to affect joint development. The genetic diagnosis of Proximal symphalangism can confirm the cause, help with family counseling, and sometimes clarify the chance of the condition appearing in relatives.
How is Proximal symphalangism diagnosed?
Doctors usually diagnose proximal symphalangism by checking how the fingers or toes move, asking whether the stiffness has been there since birth or runs in the family, and taking X-rays. The X-rays can show that one or more of the middle joints are partly or fully joined together, which explains why those fingers or toes do not bend normally. A genetic test may be used to confirm the diagnosis or help guide family planning, but it is usually used along with the exam and X-rays, not instead of them.
Stages of Proximal symphalangism
Proximal symphalangism does not have defined progression stages. This is because it is a structural difference present from birth, rather than a condition that typically moves through mild, moderate, and severe phases over time. People with proximal symphalangism usually come to medical attention when stiff fingers or toes make everyday movements harder, and doctors usually start with a conversation about symptoms and family history, followed by an exam of joint movement. To confirm how proximal symphalangism is diagnosed, doctors often use X-rays to show whether the middle joints are partly or fully fused, and follow-up is usually based on hand function, comfort, and any changes in daily activities.
Outlook and prognosis
The outlook for people with proximal symphalangism is generally excellent, because the condition is usually nonprogressive and most affected individuals have a normal life expectancy. The main long-term issues are reduced finger mobility, stiffness, and sometimes functional limitations with fine motor tasks, while hearing loss can occur in some genetic forms and may need monitoring and treatment. Symptoms can vary widely even within the same family, ranging from mild joint fusion with little disability to more noticeable hand impairment. Surgery or hand therapy may improve function in selected cases, but outcomes depend on which joints are fused and how severe the limitation is. Mortality is not thought to be increased in isolated proximal symphalangism, and prognosis is mainly determined by hand function and whether there are associated features such as conductive or mixed hearing loss.
Long-term effects
Many living with Proximal symphalangism have fingers or toes that stay stiff over the long term because some of the small joints do not form or move in the usual way. In day-to-day life, this can mean trouble fully bending certain fingers, making a tight fist, gripping small objects, or fitting into some shoes if the toes are involved. Long-term effects vary widely, and the pattern can be mild in some families and more noticeable in others. Doctors may also watch for related bone or hearing changes, since these can occur in some people with Proximal symphalangism.
The main long-term effect is lifelong stiffness or fusion of the middle joints in the fingers, and sometimes the toes. For many, this limits fine hand movements rather than causing major day-to-day pain.
People with Proximal symphalangism may have lasting trouble with tasks that need finger bending, such as buttoning clothes, opening jars, or gripping a pen for long periods. Early symptoms of Proximal symphalangism are often noticed in childhood, but the hand differences usually remain into adult life.
When the toes are involved, they may be stiff or less flexible than usual over time. This can affect balance slightly, make some footwear less comfortable, or change the way the foot bears pressure.
Some people also have extra or unusually shaped bones in the hands or feet, or changes in nearby joints as they grow. These features are usually stable, but they can add to reduced movement or make the fingers look shorter or broader.
How is it to live with Proximal symphalangism?
Living with proximal symphalangism often means that some finger joints, and sometimes toe joints, do not bend normally because the bones are joined or partly joined. For many people, this causes stiff fingers, a reduced grip for tasks like buttoning clothes, writing, typing, or playing certain sports or instruments, while others have only mild limits and adapt well over time. Family members, teachers, and coworkers may need to understand that hand function can vary from day to day and that some tasks take longer or need simple adjustments, but many people with proximal symphalangism live full, active lives by finding ways to work around the stiffness.
Treatment and drugs
Proximal symphalangism is usually treated by focusing on day-to-day function, since the fused finger or toe joints themselves cannot be separated with medicine. Many people with proximal symphalangism do not need active treatment if hand and foot use is good, but some may benefit from hand therapy, stretching guidance, splints, or shoe changes if stiffness makes writing, gripping, or walking less comfortable. Supportive care can make a real difference in how you feel day to day. Surgery is uncommon, because results can be limited when joints are formed this way from birth, but a specialist may consider it in selected cases if there is significant pain, a major difference in function, or another bone problem that can be corrected.
Can you cure Proximal symphalangism?
No, there is no cure for proximal symphalangism, a genetic condition in which some finger or toe joints are born stiff or joined together. Treatment cannot undo the joint changes, but it may help with comfort and day-to-day function through hand therapy, splints, pain relief if needed, and sometimes surgery in selected cases. Many people living with this condition do best with care that focuses on movement, grip, and making everyday tasks easier.
Non-drug treatment
Living with proximal symphalangism often means fingers or toes feel unusually stiff from an early age, which can make tasks like gripping a button, holding a pencil, or fitting into certain shoes more awkward. There is no therapy that can reverse the joint fusion itself, so treatment focuses on comfort, function, and support for any related problems such as hearing changes. Supportive therapies can improve day-to-day use of the hands and feet, and for many families looking for non-surgical treatment for proximal symphalangism, that is the main goal.
Occupational or hand therapy can help people with proximal symphalangism make the best use of the movement they do have. Therapy often focuses on grip, fine motor skills, joint protection, and practical ways to manage school, work, or self-care tasks.
Gentle stretching and range-of-motion exercises may help nearby joints stay flexible, even though the fused joint itself will not loosen. A therapist can show safe routines so exercises do not cause strain or frustration.
Some may find that custom splints or soft supports improve positioning or make certain activities easier. These are usually tailored to the person, because not every stiff finger or toe causes the same problems.
Built-up pens, modified utensils, easy-grip handles, and other assistive devices can reduce day-to-day effort. People with proximal symphalangism often benefit most when small changes are matched to the tasks they do most often.
Your genes may have an impact on how drugs work for you
For people with proximal symphalangism, treatment usually focuses on hand and foot function, stretching, and sometimes surgery, not on long-term medicines. At this time, there are no well-established genetic findings that doctors use to choose or adjust common medications specifically for this condition, because the gene changes linked to it mainly affect how joints form rather than how the body handles medicine. If someone living with proximal symphalangism needs pain relief after an injury or surgery, the choice of medicine is usually based on their age, symptoms, and overall health, not on genetic testing for this condition.
Pharmacological treatments
Day-to-day, many people with proximal symphalangism do not need medicine at all, especially if the fused finger or toe joints are not painful. There is no drug that can undo the joint fusion or change the underlying inherited bone development, so medications used for proximal symphalangism are aimed at comfort rather than a cure. Not everyone responds to the same medication in the same way, and treatment is usually based on whether there is pain, swelling, or later wear-and-tear arthritis in nearby joints.
Acetaminophen can help ease mild hand or foot pain linked to proximal symphalangism. It is often a first option when soreness comes and goes after daily use. It does not reduce swelling.
Ibuprofen or naproxen may help if proximal symphalangism causes pain with inflammation, such as after overuse or when nearby joints become irritated. These medicines can reduce both pain and swelling. They are not suitable for everyone, especially people with stomach ulcers, kidney disease, or some heart risks.
Anti-inflammatory gels such as diclofenac can be rubbed onto painful areas when discomfort is limited to one hand or foot region. This may give local relief with less whole-body exposure than tablets. Some people find them useful for mild symptoms or flare-ups.
In some cases, a corticosteroid injection may be used if a nearby joint or tendon becomes inflamed and painful. This is not a routine treatment for the fused joint itself, but it can help selected people with secondary irritation. Relief is usually temporary.
Genetic influences
Many living with proximal symphalangism notice that certain finger or toe joints have been unusually stiff since childhood, and this condition is usually genetic. Proximal symphalangism is most often caused by a change in the NOG gene, and less commonly in GDF5, both of which help joints form and separate normally before birth. It is usually inherited in an autosomal dominant pattern, which means a parent with the condition has a 1 in 2 chance of passing it on to each child. Even with the same gene change, people can have different degrees of joint stiffness, and in some families there can also be hearing changes if tiny bones in the ear are affected. Genetic testing for proximal symphalangism can help confirm the diagnosis and show whether other relatives may also be at risk.
Is Proximal symphalangism genetic?
Genetics are central to proximal symphalangism. It is usually caused by inherited gene changes, most often in NOG or GDF5, and different variants can affect how severe proximal symphalangism is within the same family.
Having a genetic risk is not necessarily a diagnosis
Genetic variants are a normal part of being human and are common across the general population. Most do not directly affect health and simply reflect natural human diversity. For many genes, having a variant associated with a condition suggests a possible link rather than a definite diagnosis, especially when several genes and environmental factors are involved. In some cases, though, a single well-understood variant in a specific gene can be enough to confirm a diagnosis.
Pharmacogenetics—how genetics influence drug effects
Stiff finger joints can make everyday tasks like buttoning clothes, gripping a steering wheel, or playing an instrument harder, and in proximal symphalangism that stiffness is present because some joints formed differently before birth. In many families, proximal symphalangism is linked to an inherited change in a gene involved in joint development, which can help confirm the diagnosis and explain why other relatives may have similar hand or foot findings. That genetic result usually does not lead to a special drug treatment, because there is no medicine that can undo a joint that is already fused. Not every difference in response is genetic, but for proximal symphalangism the main role of genetics is to guide the overall treatment plan, including whether hand therapy, supportive care, or sometimes surgery is worth considering. Medicines are usually used only to ease discomfort if it occurs, and there are no well-established gene-based prescribing rules that are specific to this condition. Genetic testing for proximal symphalangism can still be useful, though, because some inherited forms can also affect hearing, so the results may help doctors plan follow-up care and give families a clearer picture of what to expect.
Interactions with other conditions
People living with proximal symphalangism often find that stiffness in the fingers is only part of the picture, because this condition can also occur alongside hearing problems, especially conductive hearing loss caused by changes in the tiny bones of the middle ear. In some families, proximal symphalangism is part of a broader pattern of bone and joint fusion, so the wrists, elbows, ankles, or feet may also be affected, which can make everyday tasks more tiring. Certain diseases may overlap, meaning proximal symphalangism can appear as one feature within a larger inherited skeletal condition rather than as an isolated hand finding. Someone might notice their child has unusually stiff fingers and also needs the TV turned up louder, and that combination can be an important clue for doctors. Because the range and severity vary, people with proximal symphalangism may benefit from care that looks beyond the hands, including hearing checks and an assessment for other joint changes.
How genes can cause diseases
Humans have more than 20,000 genes, each carrying out one or a few specific functions in the body. One gene instructs the body to digest lactose from milk, another tells the body how to build strong bones and another prevents the body's cells from beginning to multiply uncontrollably and developing into cancer. As all of these genes combined are the building instructions for our body, a defect in one of these genes can have severe health consequences.
Through decades of genetic research, we know the genetic code of any healthy/functional human gene. We have also identified that in certain positions on a gene, some individuals may have a different genetic letter from the one you have. We call these hotspots "Genetic Variations" or "Variants" in short. In many cases, studies have been able to show that having the genetic letter "G" in the position makes you healthy, but having the letter "A" in the same position disrupts the gene function and causes a disease. Genopedia allows you to view these variants in genes and summarizes all that we know from scientific research, which genetic letters (Genotype) have good or bad consequences on your health or on your traits.
What other conditions can cause similar symptoms to Proximal symphalangism?
Other conditions that can look similar include multiple synostosis syndrome, an inherited condition where several joints are joined or unusually stiff, and some forms of brachydactyly or camptodactyly, which can cause short, stiff, or bent fingers. In children and adults, joint stiffness from juvenile arthritis or from an old injury to the finger can also be mistaken for proximal symphalangism, especially when the main problem is that the middle finger joints do not bend normally. Doctors usually tell these apart by the pattern of which joints are affected, whether symptoms have been present since birth, and imaging such as X-rays.
History
Long before it had a formal name, families sometimes noticed that certain relatives had fingers or toes that did not bend the way most people’s do. A child might have trouble making a tight fist, playing certain musical instruments, or curling the toes comfortably in some shoes, even though the joints looked otherwise normal. Over time, doctors began to recognize this pattern and describe it in medical writing as proximal symphalangism, a condition in which some of the middle finger or toe joints are stiff because the bones are joined more than usual.
Early descriptions focused on what could be seen on an exam or X-ray, rather than on the underlying cause. In the late 1800s and early 1900s, physicians reported families in which several members shared the same hand and foot pattern, which helped show that this was a distinct condition rather than a simple injury or isolated joint problem. As medical imaging improved, it became easier to see that the affected joints had formed differently during development, and that the stiffness was often present from birth even if it was noticed more clearly later in childhood.
In recent decades, awareness has grown as specialists in hand conditions, orthopedics, and genetics have described a wider range of findings linked with proximal symphalangism. This has helped doctors understand that symptoms can vary from one family to another and even between relatives, with some people having only mild finger stiffness while others have more noticeable limits in movement. Researchers later identified a genetic cause for the condition in many families, which clarified why it tends to run in families, but the clinical picture is still what usually brings people to medical attention.
Today, the history of proximal symphalangism is a good example of how careful observation over many years can improve diagnosis. What was once mainly a curious pattern seen across generations is now better recognized, so people with early symptoms of proximal symphalangism are less likely to be told their joints are simply unusually stiff or that nothing explains the change.