Anatomy and Function of the Menisci

The knee (tibiofemoral) joint is the largest and one of the most complex joints in the body as it allows you to flex and extend your knee as well as rotate it horizontally. The knee provides both strength and flexibility while being loose enough to allow the freedom for quick movements and changes in directions. It is not the bones inside the knee that provides stability, instead it is the soft tissue (tendons, ligaments, muscles, menisci) that hold the femur (thigh bone), the tibia (shinbone), the fibula (the slender bone in the lower leg) and the patella (kneecap) together at the joint.

The knee cap (patella) is a bone embedded within a tendon that rests over a groove at the bottom of the rounded femur and the top of the flat tibia. It protects the bones and soft tissue in your knee joint and slides when your knee moves, giving leverage to your leg muscles. The tendons in the knee are tough cords of tissue that connect muscle to bone and help control movement of your joint. The upper leg muscles provide your knees with mobility (extension, flexion and rotation) and strength. The quadriceps muscles (located on the front of your thigh rectus femoris, vastus lateralis, vastus medialis, vastus intermedius) straighten your legs, and the hamstring muscles (located on the back of your thigh semitendinosus, semimembranosus, biceps femoris) bend your knees.

As well as providing stability, the tendons, ligaments, articular cartilage, meniscus and other soft tissue in the joint provide cushioning and protect the bones. A type of slick, hard but flexible tissue known as articular cartilage (also called hyaline cartilage) covers the surface ends of the tibia and femur at your knee joint, allowing them to move easily against one another. It is generally 1/8 to 1/4 inch thick. A thick, stringy, egg-like fluid (synovial fluid) found inside the knee capsule, lubricates your knee joint and, along with the meniscus and articular cartilage reduces friction.

The soft tissue structure in the knee includes 2 menisci, the medial meniscus (located on the inside of the knee) and lateral meniscus (located on the outside of the knee). These crescent-shaped pads of fibrocartilage rest on the tibial condyles (rounded ends of the tibia bone) and form a concave surface for the femoral condyles (rounded ends of the femur bone) to rest on. These cover approximately 2/3 of the tibia surface and are thicker on the outside and thinner on the inside appearing triangular in cross section. They fill the space between the leg bones and cushion the femur so it doesn't slide off or rub against the tibia.

The two menisci are joined together within the knee joint by the transverse ligament. The menisci also attach to leg muscles which help the menisci maintain their position during movement. The semimembranosus and quadriceps attach to both menisci. The lateral meniscus attaches to the popliteus below the knee and the femur via the posterior cruciate ligament (PCL). On the inner part of the knee, the ends of the menisci (known as the anterior and posterior horns) are attached to the tibia and joint capsule and along the exterior edge of the meniscus by the coronary ligaments. These ligaments are loose which allows the meniscus to pivot freely. However, the medial meniscus does not move as freely in the joint as the lateral meniscus and as a result is torn more frequently.

The blood flow to the menisci comes from the inferior genicular artery. This artery supplies blood to the perimeniscal plexus which provides oxygen and nutrients to the synovial and capsular tissues around the menisci and within the knee joint. The coronary ligaments attached to the meniscus, transport the blood from the perimeniscal plexus (network of blood vessels) into the peripheral of the menisci. The anterior and posterior horns of the menisci also receive a good amount of blood as they are covered by a vascular synovium. The interior part of the meniscus is avascular, having no direct blood supply.

The Function of the Meniscus

The menisci play a very important role in the proper working of the knee. Essentially, they serve as cushions to decrease the stress caused by weight bearing and forces on the knees. They work like shock absorbers, supporting the load by compressing and spreading the weight evenly within the knee. Even while walking, the pressure put on the knee joints can be 2 - 4 times your own body weight; when you run these forces increase up to 6 - 8 times your body weight and are even higher when landing from a jump. By increasing the area of contact inside the joint by nearly 3 times, the menisci reduce the load significantly (dispersing between 30 and 55% of the load).

As weight is applied to the meniscus they are compressed and are forced to extend out from between the femur and tibia. However, the circular design of the menisci provides circumference tension (referred to as 'Hoop Stress') to resist this extension and provide stability as the load compresses. If the meniscus is torn at the peripheral rim, circumference tension is compromised and the meniscus loses its ability to transfer the load and the joint begins to suffer. In fact, if part of the peripheral is removed or the tear extends to the periphery, the load on the knee joint may increase by up to 350% causing stress and pain. However, if the tear remains on the interior without disrupting the periphery of the meniscus, the meniscus is still able to disperse the load without stress and pain.

The menisci also assist with the proper movement (arthrokinematic) of the femur and tibia during flexion and extension. Flexion and extension images here They help stabilize the knees when in motion, reduce friction within the joint, and lubricate and protect the articular cartilage surrounding the tips of the bones from damage due to wear and tear.

What is Fibrocartilage?

The menisci are composed of tissue called fibrocartilage which is tougher and contains more fiber than other types of cartilage in the body. The collagen fibers are woven into dense tissue that is resistant to stretching and extending in various directions. This makes fibrocartilage excellent for cushioning the knee joint that is required to move multidirectionally.

The amount of blood vessels in the fibrocartilage throughout the meniscus varies. The outer one-third of the meniscus is vascular, which means there is an abundance of blood vessels to allow blood to the area. The central part of each meniscus has fewer blood vessels and the inner third does not contain any. As a result, a tear on the outer peripheral of the meniscus can heal faster than one on the inner portion. Tears in the innermost part of the meniscus may not heal completely due to the lack of blood supply. Without proper nutrition (blood supply) the menisci may partially disintegrate resulting in less cushioning and protection within the joint. Proper blood flow ensures nutrients and oxygen reach the area and metabolic waste is removed from the fibrocartilage. When functioning properly, the knee joint naturally receives blood flow through movement and the pumping action of body weight shifting from knee to knee. However, other therapies such as Ultrasound and Blood Flow Stimulation Therapy will promote more blood flow, even when the knee is at rest. Greater blood flow results in faster and more complete healing when meniscus or ligament damage occurs.

Knee Ligaments

Ligaments are strong, elastic-like tissues that connect bone to bone and provide stability and protection to your knee joint by limiting the forward and backward movement of the shin bone. The knee has 2 collateral (parallel) ligaments and 2 cruciate (crossing) ligaments. The medial collateral ligament (MCL) and the lateral collateral ligament (LCL) provide support to the knee by limiting the sideways motion of the joint and resisting extreme rotation in a partially flexed position. The anterior cruciate ligament (ACL) and the posterior cruciate ligament (PCL) stabilize the knee by limiting the rotation and the forward and backward movement of the joint.

The MCL is the most commonly injured of the collateral ligaments. Injury is often a result of a blow to the outer side of the knee during sports. Since the MCL is attached to the medial meniscus, damage to the medial meniscus often occurs when the MCL is injured during a hard hit to the knee. The cruciate ligaments (ACL and PCL) are strong and thick providing stability to the joint. Together they work to prevent extreme knee motions of any kind. As a result, any damage to a cruciate ligament can cause noticeable instability in the knee. An ACL injury, the most common cruciate ligament injury, occurs when the knee is locked with the foot planted and the knee is twisted quickly. Athletes required to make sudden directional changes or to slow down quickly as well as those in contact sports are at high risk for ACL tears. Minor tears may go unnoticed immediately and will appear a few hours later with pain and swelling. More serious ACL tears are accompanied by severe pain and often a popping sound. The knee may feel as though something has snapped and walking or bending the knee is usually impossible.

The medial collateral ligament (MCL) and anterior cruciate ligament (ACL) are ligaments of interest to meniscus tear sufferers because meniscus tears that occur due to force trauma are sometimes accompanied by tears to the MCL and/or ACL. When the meniscus, MCL and ACL are injured in combination it is referred to as the "unhappy triad".

What Happens When the Meniscus is Injured?

A meniscus injury is one of the most common knee injuries. Menisci tend to get injured during movements that forcefully twist your knee while bearing weight (this is very prevalent in younger populations) or they tend to grow weaker with age, and tear as a result of minor injuries or movements. When your meniscus is damaged and/or torn, it starts to move abnormally inside the joint, which can cause it to become caught between the bones of the joint (femur and tibia). Your knee then becomes swollen, painful and difficult to move. These injuries can be difficult to heal because blood supply (which helps your body heal itself) is often limited to the outside edge of the menisci.

Once you have a meniscus tear, you have an increased risk of developing knee arthritis because these shock absorbers are weakened. They slowly wear away with knee movements and are not able to protect your articular cartilage on the surface of the knee joint as much as before.

While some meniscus tears can be repaired, most cannot be fixed.  The torn piece is removed through the arthroscope in the operating room.  The tear itself and the removal of the loose piece result in increased forces on the surfaces of the joint which then can lead to a progression of arthritis.  In a small number of cases, pain from the arthritis can progress after surgery to remove the torn meniscus.  It is the tear, not the surgery, that leads to the continued pain and progression of arthritis.


Patients must understand that, if they have a torn meniscus in the face of arthritis, their pain may not be completely resolved by an arthroscopic surgery.  In a small number of cases, the pain from the arthritis may even increase.

In the USA, 61 of 100,000 people experience an acute tear of the meniscus at some point in their life (850,000 meniscus surgeries are performed in the USA each year, estimates indicate that at least twice this number of meniscus procedures are performed internationally). Health professionals used to believe the meniscus had no function and removed it if injured, however we now know it plays an integral role in knee joint mechanics and function.

Thanks,

JTM, MD

Interesting Knee Arthroscopy Pictures

Here are some interesting knee scope pictures. 

This is the under surface of the patella or knee cap.  Above the metal instrument, you can see a small bare spot in the joint cartilage.  This is arthritis that occurs over time.  It is a wear and tear process that causes the cartilage to thin out a wear away as we age.  Such is life.

Another view of the arthritis.

This is the medial joint space.  Here you can see the torn meniscus cartilage at the end of the gold color metal probe.  Above the probe and the meniscus is the joint cartilage.  There are 2 type of cartilage in the knee: meniscus cartilage and joint cartilage.  They both have different functions in protecting our knees.  Joint cartilage covers the end of the bone and is the cushion we walk on between the bone surfaces.  The meniscus cartilage functions as a shock absorber and stabilizer of the joint. 

Here you can see both a meniscus tear and arthritis of the joint.  Arthritis is a break down or wearing away of the joint cartilage.

The probe is on the arthritic joint surface.

Arthritis medial femoral condyle.

The torn meniscus has been removed.  The arthritis on the joint surface cannot be cleaned and trimmed further.  This may continue to bother the patient over time.  The pain from the meniscus tear will resolve.  If there is pain from arthritis, there are other options to help this patient.

Meniscus tear removed.  Arthritis remains.  This is the best that can be done arthroscopically for arthritis of the knee.

This is the other side of the joint: lateral.  Notice the degenerative meniscus.  It is shredded at the inner margin.  There is no significant arthritis here on the joint surface.

Lateral joint.  Degenerative meniscus.  No arthritis.

Notice the probe on the shredded meniscus edge.

Shredded meniscus edge.  No arthritis.

In a case like this, the pain from the meniscus tear on the medial side will resolve after surgery since the torn flap has been removed.  The pain from the arthritis may persist.  It can then be treated with other options: anti-inflammatories, therapy, viscosupplementation, other surgery as a last option.

Thanks,

JTM, MD

Antibiotic Prophylaxis for Bacteremia in Patients with Joint Replacements

As an orthopedic surgeon, I have a large number of patients whose shoulders and knees I have replaced.   I also have many more patients who have metal implants related to fracture repair and metal or plastic anchor implantation from rotator cuff surgery.  The question of prophylactic antibiotics always comes up.  Dentists are apparently under the impression that antibiotics may only be needed for the first 2 years after a joint replacement.  This, I assume, was based on a study by dentists not orthopedic surgeons.

If I put a joint replacement in your body, you will always need prophylactic antibiotics for dental work and other procedures as written by the AAOS below.  Always means always and forever, for the rest of your life. 

From the AAOS as of 2009...

This statement represents the AAOS’ current recommendations on this topic. The AAOS regularly reviews and updates all informational statements as new technology, evidence, or policy is developed. It is possible that these current recommendations may change as the result of the ongoing clinical guidelines development process around the topic of antibiotic prophylaxis for total joint patients undergoing dental procedures. As such, clinicians are encouraged to consider the recommendations in the context of their specific clinical situation and consult, where appropriate, other sources of clinical, scientific, or regulatory information prior to making a treatment decision. Clinicians are encouraged to check the AAOS website for the most up-to-date information.

More than 1,000,000 total joint arthroplasties are performed annually in the United States, of which approximately 7 percent are revision procedures.¹ Deep infections of total joint replacements usually result in failure of the initial operation and the need for extensive revision, treatment and cost. Due to the use of perioperative antibiotic prophylaxis and other technical advances, deep infection occurring in the immediate postoperative period resulting from intraoperative contamination has been markedly reduced in the past 20 years.

Bacteremia from a variety of sources can cause hematogenous seeding of bacteria onto joint implants, both in the early postoperative period and for many years following implantation.² In addition, bacteremia may occur in the course of normal daily life^3-5 and concurrently with dental, urologic and other surgical and medical procedures.⁵ The analogy of late prosthetic joint infections with infective endocarditis is invalid as the anatomy, blood supply, microorganisms and mechanisms of infection are all different.⁶

 

It is likely that bacteremia associated with acute infection in the oral cavity,^7,8 skin, respiratory, gastrointestinal and urogenital systems and/or other sites can and do cause late implant infection.⁸ Practitioners should maintain a high index of suspicion for any change or unusual signs and symptoms (e.g. pain, swelling, fever, joint warm to touch) in patients with total joint prostheses. Any patient with an acute prosthetic joint infection should be vigorously treated with elimination of the source of the infection and appropriate therapeutic antibiotics.^8,9

Patients with joint replacements who are having invasive procedures or who have other infections are at increased risk of hematogenous seeding of their prosthesis. Antibiotic prophylaxis may be considered, for those patients who have had previous prosthetic joint infections, and for those with other conditions that may predispose the patient to infection (Table 1). ^8,10-16 There is evidence that some immunocompromised patients with total joint replacements may be at higher risk for hematogenous infections.^10-18 

However, patients with pins, plates and screws, or other orthopaedic hardware that is not within a synovial joint are not at increased risk for hematogenous seeding by microorganisms.

Given the potential adverse outcomes and cost of treating an infected joint replacement, the AAOS recommends that clinicians consider antibiotic prophylaxis for joint replacement patients with one or more of the following risk factors prior to any invasive procedure that may cause bacteremia. 

Table 1. Patients at Potential Increased Risk of Hematogenous Total Joint Infection^8,10-16,18

• All patients with prosthetic joint replacement
• Immunocompromised/immunosuppressed patients
• Inflammatory arthropathies (e.g.: rheumatoid arthritis, systemic lupus erythematosus)
• Drug-induced immunosuppression
• Radiation-induced immunosuppression
• Patients with co-morbidities (e.g.: diabetes, obesity, HIV, smoking)
• Previous prosthetic joint infections
• Malnourishment
• Hemophilia
• HIV infection
• Insulin-dependent (Type 1) diabetes
• Malignancy
• Megaprostheses

Prophylactic antibiotics prior to any procedure that may cause bacteremia are chosen on the basis of its activity against endogenous flora that would likely to be encountered from any secondary other source of bacteremia, its toxicity, and its cost. In order to prevent bacteremia, an appropriate dose of a prophylactic antibiotic should be given prior to the procedure so that an effective tissue concentration is present at the time of instrumentation or incision in order to protect the patient’s prosthetic joint from a bacteremia induced periprosthetic sepsis. Current prophylactic antibiotic recommendations for these different procedures are listed in Table 2. ¹⁹

Occasionally, a patient with a joint prosthesis may present to a given clinician with a recommendation from his/her orthopaedic surgeon that is not consistent with these recommendations. This could be due to lack of familiarity with the recommendations or to special considerations about the patient's medical condition which are not known to either the clinician or orthopaedic surgeon. In this situation, the clinician is encouraged to consult with the orthopaedic surgeon to determine if there are any special considerations that might affect the clinician’s decision on whether or not to pre-medicate, and may wish to share a copy of these recommendations with the physician, if appropriate. After this consultation, the clinician may decide to follow the orthopaedic surgeon’s recommendation, or, if in the clinician’s professional judgment, antibiotic prophylaxis is not indicated, may decide to proceed without antibiotic prophylaxis.

Table 2.

† If a tourniquet is used the entire dose of antibiotic must be infused prior to its inflation

This statement provides recommendations to supplement practitioners in their clinical judgment regarding antibiotic prophylaxis for patients with a joint prosthesis. It is not intended as the standard of care nor as a substitute for clinical judgment as it is impossible to make recommendations for all conceivable clinical situations in which bacteremias may occur. The treating clinician is ultimately responsible for making treatment recommendations for his/her patients based on the clinician’s professional judgment.

Any perceived potential benefit of antibiotic prophylaxis must be weighed against the known risks of antibiotic toxicity, allergy, and development, selection and transmission of microbial resistance. Practitioners must exercise their own clinical judgment in determining whether or not antibiotic prophylaxis is appropriate.

References:

1. Number of Patients, Number of Procedures, Average Patient Age, Average Length of Stay - National Hospital Discharge Survey 1998-2005. Data obtained from: U.S. Department of Health and Human Services; Centers for Disease Control and Prevention; National Center for Health Statistics.
2. Rubin R, Salvati EA, Lewis R: Infected total hip replacement after dental procedures. Oral Surg. 1976;41:13-23.
3. Bender IB, Naidorf IJ, Garvey GJ: Bacterial endocarditis: A consideration for physicians and dentists. J Amer Dent Assoc 1984;109:415-420.
4. Everett ED, Hirschmann JV: Transient bacteremia and endocarditis prophylaxis: A review. Medicine 1977; 56:61-77.
5. Guntheroth WG: How important are dental procedures as a cause of infective endocarditis? Amer J Cardiol 1984;54:797-801.
6. McGowan DA: Dentistry and endocarditis. Br Dent J 1990;169:69.
7. Bartzokas CA, Johnson R, Jane M, Martin MV, Pearce PK, Saw Y: Relation between mouth and haematogenous infections in total joint replacement. BMJ 1994;309:506-508.
8. Ching DW, Gould IM, Rennie JA, Gibson PH: Prevention of late haematogenous infection in major prosthetic joints. J Antimicrob Chemother 1989;23:676-680.
9. Pallasch TJ, Slots J: Antibiotic prophylaxis and the medically compromised patient. Periodontology 2000 1996;10:107-138
10. Rubin R, Salvati EA, Lewis R: Infected total hip replacement after dental procedures. Oral Surg. 1976;41:13-23.
11. Brause BD: Infections associated with prosthetic joints. Clin Rheum Dis 1986;12:523-536.
12. Jacobson JJ, Millard HD, Plezia R, Blankenship JR: Dental treatment and late prosthetic joint infections. Oral Surg Oral Med Oral Pathol 1986; 61:413-417.
13. Johnson DP, Bannister GG: The outcome of infected arthroplasty of the knee. J Bone Joint Surg; 688:289-291.
14. Jacobson JJ, Patel B, Asher G, Wooliscroft JO, Schaberg D: Oral Staphyloccus in elderly subjects with rheumatiod arthritis. J Amer Geriatr Soc 1997;45:1-5.
15. Murray RP, Bourne WH, Fitzgerald RH: Metachronus infection in patients who have had more than one total joint arthroplasty. J Bone Joint Surg 1991;73-A:1469-1474.
16. Poss R, Thornhill TS, Ewald FC, Thomas WH, Batte NJ, Sledge CB: Factors influencing the incidence and outcome of infection following total joint arthroplasty. Clin Orthop 1984;182:117-126.
17. Council on Dental Therapeutics. Management of dental patients with prosthetic joints. J Amer Dent Assoc 1990;121:537-538.
18. Berbari EF, Hanssen AD, Duffy MC, Ilstrup DM, Harmsen WS, Osmon DR: Risk factors for prosthetic joint infection: case-control study. Clin Infectious Dis 1998; 27:1247-1254.
19. Antibiotic Prophylaxis for Surgery. The Medical Letter 2006; 4 (52): 83-88.

© February 2009. Revised June 2010 American Academy of Orthopaedic Surgeons

Thanks,  

JTM, MD

DVT: Deep venous Thrombosis

Bloods clots or DVT can occur after any kind of leg trauma or surgery.  I cannot do a better job than the AAOS has done on their educational web site here.  

Every patient having any kind of lower extremity surgery should review this site.

Thanks,

JTM, MD

Some Arthroscopic Rotator Cuff Repair Pictures

Here are some pictures of a rotator cuff tear, before and after repair.  They are mixed with some diagrams to help you understand the process of rotator cuff repair. 

Normal shoulder viewed from the side.

 

Above is a diagram of a rotator cuff tear similar to the one seen below.

This is a medium sized rotator cuff tear.  The torn tendon (top) has been ripped for the bone (bottom).

An arthroscopic instrument grabs the tendon to check for tendon mobility and excursion.

A plastic anchor is placed in the bone.  This serves as an attachment point for the sutures which will be passed through the torn rotator cuff tendon.

Sutures have bee passed through the tendon on the left and a second anchor will be placed just to the right of the tendon to complete the repair.

Here you can see the repair in progress.  There is a plastic anchor in the bone.  Those purple sutures on the right side are attached to the anchor and have been passed through the tendon.

Second anchor being placed.

 

The repair is completed above.

You can see the repaired tendon.  The gap that could be seen in the first picture is now closed as the sutures pull the tendon to the surface of the bone.  Over 6 weeks this should heal allowing normal shoulder function in most cases.

Another picture of the same repaired tendon.  These sutures are attached to anchors that are buried in the bone.  There is an anchor buried under the tendon on the left of the picture which you cannot see here.  Those sutures are pulled over the edge of the tendon and attached to 2 other anchors completing the repair.

Another view of the repaired tendon.

Below are some pictures from another rotator cuff repair.  

Another tear.  View from inside the joint.  Tear is to the right.  Humeral head on the bottom,  biceps to the left.

Another view of the tear.  Notice the shredded fibers of the tendon.

Here the biceps tendon is inspected.  It appears slightly inflamed but not torn.  An inflamed biceps tendon can cause pain.  The biceps is right behind the metal probe in this picture.

Above a needle is placed through the tear as we are in the process of repair. 

Above we see a metal instrument placed through the tear showing the full extend of the tear as it is lifted away from the bone.  This is a medium sized tear of the supraspinatus tendon.

Another view of the tear as we proceed with repair.  This view is from inside of the joint on the lower surface of the tendon.

Here the camera is looking at the top surface of the tendon.  Notice the fraying of the tendon that results from friction between the tendon itself and the bone spur above.  That metal instrument is touching the bone spur as I am in the process of removing it.

A view of the tear from the top surface of the tendon.  Notice the frayed edges of the tendon.  The tendon has ripped away from the bone seen on the bottom of the photo.

Just another view of the tear.

Repair in progress.  Notice the anchor and sutures on the left.  These are passed through the tendon, tied medially and then attached to a second anchor laterally.  This accomplishes and "double row" or "suture bridge" repair. Two medial anchors and two lateral anchors were used in this repair.

Repair completed. 

Great repair. This repair is water tight as the tendon is compressed to the bone.  The space between the blue sutures is just a few millimeters and will heal well in time.  It takes 6 weeks for the tendon to heal to the bone.  If the patient uses the arm normally before it heals, or if strengthening exercises are started before the tendon is ready, it will pull away from the bone resulting in a failure if the repair.  Listen to your doctor and therapist for guidance regarding your post operative protocol.

I did not draw the above diagrams but I did fix these tendons.  


Thanks,

JTM, MD

Pictures from a Knee Arthroscopy

Here are some intraoperative photos from a recent left knee arthroscopy.  Below is the joint surface of the patella (knee cap).  You can see the fraying of the cartilage which represents early arthritis.  This degree of arthritis may not show up on an x-ray or MRI but, if present, may still cause pain for a patient.

Here is a meniscus tear in the medial meniscus.  You can see that the torn flap of cartilage that is getting pinched between the joint surface.

Another view of the torn meniscus.

Same knee.  Another torn flap of meniscus being trimmed with the metal device seen in the left side of the photo.

This torn flap of meniscus cartilage is getting trapped between the surfaces of the joint.  Just like a stone that got into you shoe, it can cause significant pain when you walk on it.

Here you can see that the torn flap of cartilage has bee trimmed and can no longer cause pain in the knee. 

On the other side of the joint, you can see that the lateral meniscus is normal, with a smooth edge.  No arthritis seen here.

Normal lateral meniscus.

Thanks,

JTM, MD