What is Bone?

 

What is Bone?

Bones in our body are living tissue. They are made of cells, vitamins, minerals, and proteins.  Bones have a blood supply, and will bleed if broken.  We are born with over 250 soft bones. When we are born, the skeleton is made predominately of cartilage.  As we mature, the cartilage grows and is eventually replaced by hard mature bone. Some of these cartilage bones later fuse together during maturity.  When the skeleton matures, the total becomes 206 bones.

The major functions of bones are to:

·        Provide structural support for the body and a lever system for movement

·        Provide protection of vital organs

·        Provide an environment for marrow for blood production

·        Act as an active storage area for minerals (such as calcium and phosphorous)

 

 

What is bone made of?

1.   Bone matrix

The majority of bone is made of the bone matrix, or osteoid.  Calcified bone contains about 25% organic matrix (of which 2-5% of which are cells, the rest is collagen and proteins), 5% water and 70% inorganic mineral (hydroxyapatite).  Bone is formed by the hardening of this matrix.

2.   Bone cells

Cells in our bones are responsible for bone production, maintenance and modeling.  There are three types of bone cells: osteoblasts, osteocytes, and osteoclasts.

·        Osteoblasts: bone cells which are responsible for creating bone matrix.  Minerals are then deposited into the matrix, making the bone become hardened and strong.  

·        Osteocytes: as osteoblasts create bone matrix, the matrix becomes mineralized, calcified and turns hard.  As a result, these osteoblasts become “trapped” within the matrix.  At this time the osteoblasts mature and turn into osteocytes.  Osteocytes are still connected to another and to osteoblasts via small canals within bone and are able to communicate with each other via hormones. 

·        Osteoclasts: bone cells which dismantle or resorb bone matrix.  These cells use bone-resorbing enzymes to digest and degrade bone.  This releases minerals from the bone matrix back into the blood. 

 

Modified from http://www.ucl.ac.uk/cdb/research/arnett/boneturnovercopy.jpg

 

 

What kinds of bone exist?

Bone is composed of two types of tissue: Cortical bone and Cancellous bone

1. Cortical/Compact/Dense bone:  hard outer layer, which is strong, dense and tough.  It has minimal gaps and spaces. This compact tissue gives bones their smooth, white, and solid appearance.  Eighty percent of the total bone mass of an adult skeleton is made of compact bone.

2. Cancellous/Trabecular bone:  spongy inner layer. Trabecular bone is light and significantly less dense than compact bone.  Trabecular bone has a sponge like appearance.  Within the spaces of this bone are blood vessels which provide nutrients to bone and bone marrow.   Twenty percent of the adult skeleton is made of trabecular bone.  However, as the trabecular bone is very porous, it has nearly ten times the surface area of compact bone. 

Within the two types of bone tissue (cortical and cancellous), two types of bone can be identified on a microscopic level: woven bone and lamellar bone.  These types are distinguished according to the pattern of collagen forming the osteoid:



Matos  et al. Journal of Orthopaedic Surgery and Research 2008 34

·        Woven bone is characterized by a haphazard organization of collagen fibers and is mechanically weak.

·        Lamellar bone is characterized by a regular parallel alignment of collagen into parallel sheets known as lamellae.   Lamellar bone is mechanically strong.

Woven bone is produced when osteoblasts produce osteoid or bone substance rapidly. Woven bone is found in fetal bones.  Later, the woven bone is replaced by remodeling and the replacement with the stronger lamellar bone. In adults, woven bone is formed in fracture repair.  Following a fracture, woven bone is removed and lamellar bone is deposited in its place.  This process is called “bony substitution”.

Does bone change?

Bone has the ability to alter its form over time.  It can increase in size over time (bone growth or bone modelling).  It may also alter its shape after a fracture (bone remodeling).

Bone modeling

Modeling is when bone resorption and bone formation occur on separate surfaces of the bone.   An example of this process is during long bone increases in length and diameter, where activity occurs on two surfaces of the bone. Bone modeling occurs during birth to adulthood and is responsible for gain in skeletal mass to adult form over time.

Bone remodeling

Remodeling is the replacement of old bone by new bone tissue. It is known as bone turnover.  This occurs in the adult skeleton to maintain bone mass or during fracture healing. This process involves the coupling of bone resorption and bone replacement through the function of the osteoclasts and osteoblasts respectively.



Bone remodeling cycle.  modified from http://www.ns.umich.edu/Releases/2005/Feb05/img/bone.jpg



 

How does bone form?

Osteogenesis is the process of bone tissue formation.  Osteogenesis occurs by two processes: intramembranous ossification and enchondral ossification.

·        Intramembranous ossification occurs in the flat bones of the body (e.g. skull, clavicle, maxilla and mandible). It involves the replacement of connective tissue membrane sheets, known as mesenchyme, with bone tissue and results in the formation of flat bones.

 

·        Enchondral ossification occurs in the long bones of the body (e.g. femur, humerus, and tibia).  It involves the replacement of a hyaline cartilage model in infancy with bone tissue to form the adult skeleton.  As the infant cartilage skeleton matures, it grows in length and width.  As the bones increase in size, the cartilage is replaced by bone tissue.  The length increases through activity in the growth plates of the bones at the ends of the long bones.   The width increases by bone formation via the exterior lining of the bone called the periosteum.

 

 

References:

http://www.iofbonehealth.org/what-is-osteoporosis
http://orthoinfo.aaos.org/topic.cfm?topic=a00232
http://www.healthline.com/health/osteoporosis
http://nihseniorhealth.gov/osteoporosis/whatisosteoporosis/01.html
http://nof.org/

 

My name is Alexandra Burgar.  I am a board certified orthopedic surgeon with a subspecialty in hand and microvascular surgery.  To clarify:  I treat everything from the elbow to the tips of the fingers.  I grew up on Long Island and slowly migrated my way to the west coast.  My practice is located in the Tri-Valley area of the east bay, San Francisco.  I treat all ages of patients, from infants to seniors.  To be seen as a patient, please view the practice website at trivalleyorthopedics.com or call 866-623-7600.

Medical Disclaimer: this blog is for educational purposes only.  The information is not intended nor suited to be a replacement or substitute for professional medical treatment or for professional medical advice relative to a specific medical question or condition. I urge you to always seek the advice of your physician or medical professional with respect to your medical condition or questions.

 

Carpal Tunnel Syndrome

What is Carpal Tunnel Syndrome?

 

Carpal tunnel syndrome is a condition which is brought on by increased pressure in the wrist causing a nerve to be pinched.  The nerve reacts to this pressure by sending singles of numbness, tingling and pain to the hand and occasionally the forearm.  In most instances, releasing the pressure reduces the amount of pinching upon the nerve and alleviates the symptoms.

 

What is the Carpal Tunnel?

 

The carpal tunnel is a channel structure located in the wrist.  It is made of a semi-circle of bones, connected at the tips by a tight ligament called the Transverse Carpal Ligament.  Within this tunnel travel nine tendons which help control the movement of your fingers and the median nerve.  The tendons are lined with tissue which help them glide called the tenosynovium.  The tendons are sturdy and can withstand a lot of motion and force.  The median nerve develops at the neck from nerves leaving the spinal cord, travels down the arm, through the carpal tunnel and into your hand.  The median nerve provides sensation or feeling to the thumb, index, middle and half of the ring finger.  It also provides muscle strength to a small muscle of the thumb.  Unlike the sturdy tendons, the nerve is delicate and vulnerable to changes in pressure. 

 

 

 

What causes Carpal Tunnel Syndrome?

 

The cause of carpal tunnel syndrome is predominantly due to increased pressure in the wrist, or carpal tunnel, which pinches the median nerve at the wrist.  The increased pressure can be caused by multiple reasons:

 

-        swelling of the tendon lining, or tenosynovitis

-        fractures (breaks in the bone), dislocations or arthritis

-        awkward wrist positions, like keeping the wrist in a bent position for long periods of time

-        gripping for long periods of time (ie, driving) brings small muscles into the carpal tunnel for extended periods of time, pinching the nerve

-        fluid retention (ie, pregnancy, especially in the third trimester)

-        other conditions causing increased swelling or inflammation in the body, like diabetes, rheumatoid arthritis and thyroid conditions

-        vibratory tools (ie jackhammers)

 

 

Unfortunately, in most instances, a cause cannot be identified or is unknown.

Women are affected more often then men, by a ratio of 3:1.  Carpal tunnel syndrome affects people mostly between the ages of 30 to 55.

 

What are the symptoms of Carpal Tunnel Syndrome?

 

The symptoms of carpal tunnel syndrome include numbness, tingling and occasionally pain.  These symptoms occur mostly in the thumb, index, and middle fingers.  These symptoms can worsen at night time due to awkward wrist positions and increased swelling in the hands while sleeping.  The symptoms may even wake people from sleep.  When the symptoms continue for long periods of time, weakness in gripping may occur in the hand.  This is due to the pressure affecting the nerve to the small muscle of the thumb.  As the symptoms progress, people may notice frequently dropping objects, clumsiness and the inability to pick up small objects like a pin.  When the nerve is pinched for a long period of time, permanent damage may occur to where the sensation is lost and the hand remains weak.

 

How do you diagnose Carpal Tunnel Syndrome?

 

Your doctor will take a detailed history of your symptoms, medical history, activities and injuries.  Your doctor will then do a physical examination, checking the neck through the hands to assess the nerve.  They will check for swelling, color changes, strength, motion, coloration and sensation.  They will also perform multiple physical manipulations of your wrist and hand, intentionally increasing the pressure of your carpal tunnel to see if your symptoms are reproducible.  An x-ray may be taken to check for arthritis or other bone conditions in the wrist causing swelling.  Laboratory tests may need to be checked to assess any other medical conditions which can affect the carpal tunnel.  More specific tests may be ordered, such as a Nerve Conduction Test and EMG to assess for the specific condition of the median nerve and rule out pinching of the nerve at another location in the arm or neck. 

 

How do you treat Carpal Tunnel Syndrome?

 

Carpal tunnel syndrome may be treated in a variety of ways. Treatment of carpal tunnel syndrome is dependent on the stage of the disease.  In the early stages of the disease, the symptoms are reversible, and less invasive treatment is recommended.  In later stages of the disease, the nerve may be damaged, and therefore surgery may be recommended to protect it from further injury.  Surgery may also be recommended in those patients whose initial treatment is successful, but the symptoms return.

 

The first mode of treatment is to treat the underlying causes of carpal tunnel syndrome.  If the wrists are kept in awkward positions during the day or night, the doctor may recommend a wrist brace to keep the wrist in a steady, neutral position to keep the pressure off the nerve.  If there is arthritis or swelling, the doctor may recommend therapy and medication such as anti-inflammatories for the hand to reduce the swelling. If the symptoms continue, the doctor may recommend a cortisone injection to the carpal tunnel to alleviate the swelling immediately surrounding the nerve. 

 

When the symptoms of carpal tunnel syndrome continue or are severe, your doctor may recommend surgery.  In surgery, the ligament covering the nerve (the transverse carpal ligament) is cut in half, increasing the space around the nerve and giving it more room to breathe.  By increasing the space surrounding the nerve, the pressure on the nerve is taken away.  If caught early enough, the symptoms of the carpal tunnel syndrome may be completely relieved.  However, if there is any existing damage to the nerve from long term symptoms, these symptoms may not improve.  In these cases, the nerve is protected from any further injury and worsening of the condition. In the majority of cases, the surgery is done as a same day surgery.  The symptoms usually are alleviated within a few days of the surgery, however the symptoms can last up to several months depending on the condition of the nerve.  There are many types of incisions for this surgery, however, the end result is to alleviate the pressure on the nerve.  The incision and surrounding tissue may be sore for weeks or months after the surgery as the tissue recovers.  Ultimately, motion and function return to normal within a couple of months from surgery.  For those patients with severe carpal tunnel syndrome, they can expect a slow continued improvement of their symptoms after surgery for up to one year.