knee structure

7/29/2019 Knee Structure

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KNEE STRUCTUREThe knee joint is a junction of three

bones. The femur and the tibia meet toform a hinge joint. In front of them is thepatella (kneecap). The patella sits overthe other bones and slides when the legmovesThe ends of the three bones are coveredwith articular cartilage. This is a toughelastic material that basically cushionsthe joint. Also helping to cushion theknee are two C-shaped pads of cartilage

called menisci. They lie between the tibiaand the femur. There is a lateralmeniscus and a medial meniscus.

Ligaments help to stabilize the knee.These are strong elastic bands oftissue that connect one bone toanother. The four main stabilizingligaments of the knee are the

anterior cruciate ligament (ACL),posterior cruciate ligament (PCL),medial collateral ligament (MCL),and lateral collateral ligament (LCL).

There are two basic groups ofmuscles at the knee. In the front ofthe knee are the quadricepsmuscles that work to straighten theleg out. In the back of the knee arethe hamstring muscles which help to

flex the knee.


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(ACL) INJURIES

ANTERIOR CRUCIATE LIGAMENT

The anterior cruciate ligament (ACL) is important for knee

stabilization. This is located deep inside the knee joint.

The ACL helps control how far the tibia can move in relationship tothe femur.Injuries to the ACL are very common and most of the timeare sports related.

The sports requiring the foot to be planted and the body to changedirections rapidly, such as basketball, are associated with a higherincidence of injury.

Usually injury will occur to the ACL with a sudden hyperextension orrotational force. Depending on the activity or sport the mechanism

may differ somewhat.

Soccer, skiing and football are also three common sports whereACL injuries occur. Often the injured athlete will feel a pop in theknee and have sudden pain.

The athlete may or may not fall to the ground. Skiers will usuallyfall. However, a soccer player or basketball player in mid-stridestopping suddenly and pivoting can suffer an ACL tear and still oftenbe able to ambulate.

Besides the pop, the knee often swells after an ACL injury.It is not uncommon for multiple knee structures to

be hurt in an injury. An ACL, MCL and lateralmeniscal injury is a common triad.

Activities requiring rotational motion about theknee, including twisting, cutting and jumping sports,are not recommended after an ACL tear because ofthe risk of cartilage damage.

The orthopaedic community has realized over thelast several years that long term instability of theknee can lead to early arthritis.

Some activities, however, can be continued with an

ACL lax knee. These are in-line sports such asbicycling, light jogging, roller blading andswimming.

TREATMENT OPTIONSNon-surgical

Conservative care can be used for partial ACL tears when the knee is still stable for a patients activity.


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If one anticipates in-line activities only then a good argument can be made to rehab the knee forstrengthening and range of motion and see how the patient does. Also at times an ACL brace is helpfulin these situations.

Surgical

If one anticipates returning to vigorous sports, such as those mentioned above, or has instability of theknee even with efforts at non-vigorous activities, ACL reconstruction should be strongly considered.

Surgery is done on an outpatient basis using an arthroscope. Weightbearing is usually begunimmediately, as is motion. Physical therapy is also started soon after surgery to aid in function.

SURGICAL TECHNIQUE

There are several surgical techniques for an ACL injury. Most of these are reconstructive techniqueswhere a piece of tendon or ligament is used to replace a torn ACL. Years ago, attempts were made atsuturing the ACL together, but this has been found to typically lead to a very poor result. Betteroutcomes have occurred after a full reconstruction.

There are several choices for graft in an ACL reconstruction. The following are the most common:

Patella Tendon (Autograft)

This involves taking part of the patients patellar tendon adjacent to the patella and a tibial bone block foruse in the reconstruction. This technique has been used for several years and is probably the mostcommon type of reconstruction. This is probably the best choice for most athletes. An incision is made

just below the patella for harvesting this graft. The rest of the work in the knee is done with anarthroscope.

HamstringsHamstrings tendons can also be used for an ACL reconstruction. This may be an option for those whohave had previous patella problems and are not candidates for patellar tendon autograft

Allograft

Allograft tissues are obtained from a cadaver. This is a nice option to have for those undergoing revisionACL surgery whose own patella tendon has already been used. An allograft can also be used in thecase when multiple ligaments are injured. The advantage to this is that there is no need to harvest thepatients own tissue; therefore there may be less discomfort after the surgery. The disadvantage is thatsome reports indicate this type of graft is more likely to stretch and fail than an autograft. Although rare,there is a possibility of disease transmission with donor graft tissue.

NEW TREATMENTS

A new ACL treatment, called ACL shrinkage, is beginning to be performed now. This technique uses aheat shrinkage type technique to tighten up a partially torn ACL. This does not apply to complete ACLtears. Surgery is done arthroscopically. This is a fairly new technique and there are not long termresults out with this yet. One obvious advantage to this, if it should work out, is that with some ACL tearsa reconstruction would not be necessary and hopefully postoperative rehabilitation would be muchquicker.

PROGNOSIS

ACL reconstruction is a common and highly successful procedure and most patients can be expected toreturn to full sports activities with a vigorous rehabilitation program.


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MENISCUS

Longitudinal tear Radial tear Bucket handle tear Parrot beak tearThe meniscus is the distal cartilage tissue that is found between the weightbearingbones of the knee joint. It acts as a shock absorber. It is usually very tough andrubbery. It does grow weaker with age and meniscal tears can occur with fairly minorinjuries in older patients. In younger populations a tear is usually the result of a fairlyforceful injury. When the meniscus tears a piece of cartilage can move abnormally inthe joint causing catching, buckling and swelling. Swelling usually occurs initially and

can sometimes continue occurring with a meniscal tear.TREATMENT OPTIONS

If a tear is very small and symptoms resolve quickly and there is just occasionaldiscomfort but no instability, a patient can be treated with an exercise and range ofmotion program. If the symptoms continue then a meniscus can be repaired or partiallyremoved arthroscopically. A large part of a meniscus has no direct blood supply andtherefore spontaneous healing on its own is unusual.To repair a meniscus sutures can be used or new absorbable tact can be used. Using

the newer absorbable tacks all the work can be done without additional incisions in theknee. In cases where a meniscus cannot be repaired just the offending torn tissue isremoved in order to preserve as much cartilage function as possible.

Arthroscopy is done on an outpatient basis. Usually three small incisions in the kneeare used. The patient is begun on immediate weightbearing and to move the knee astolerated.

NEW TECHNIQUES

In certain cases where most of the medial or lateral meniscus has been removed

meniscus transplantation is now being performed. This is where a meniscus istransplanted from a cadaver after being appropriately sized by new measurements andstudies.


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PATELLA

The patella is your kneecap. It is a small bone that sits in front of your knee joint. Itactually is embedded in the quadriceps tendon. It slides in a groove called the trochleaon the femur as the knee moves. The patella has a thick cartilage lining but is also

subject to high stresses.

CHONDROMALACIA PATELLA

This is a Latin term meaning bad cartilage or breakdown or softening of cartilage. It isone of the most common problems of the knee. Running and jumping can aggravatethis condition.

Symptoms include pain in the front of the knee and a crunching or grinding sound withmotion. Swelling can occur at times. Symptoms seem to be worse with climbing up ordown stairs or a hill. Also, getting up from prolonged sitting can cause pain.

The cartilage surface on the underside of the patella becomes soft. Part of the cartilagecan become stringy and flake off at times. Part of the surface may become roughened.The synovium in the knee which is a normal substance that helps lubricate the kneeoint can sometimes be aggravated in this condition and contribute to the grindingfeeling.TreatmentInitial treatment for chondromalacia patella emphasize strengthening activities. Often atherapist is used to teach a patient quadriceps exercises to help the patella become

rebalanced in a sense. Anti-inflammatory medication can be used temporarily as wellas ice. Occasionally, a therapist may teach an athlete taping techniques that arehelpful. In cases not responsive to conservative treatment, arthroscopy may be helpful.

PATELLA MALTRACKING

The normal patella should track in the groove of the femur in a relatively straightmanner. There are varying degrees of malalignment and tracking. In some cases the


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patella may tend to track more to the side of the knee or actually be tilted as it goesback and forth in its groove. On occasion it may actually come partially out of thegroove, which is called subluxation. Some patients have a positive J-sign in which, infull extension, the patella tilts and is pulled strongly to the side of the leg.

The tracking of the patella can be influenced by different things. Most of it is influencedby the anatomical shape of the knee. The following can all contribute to the maltrackingof the patella: shallowness of the femoral groove, the angle of the knees (knock-knees),rotation of the hips, foot positioning on the floor (pronation or flat feet), weakness of thequadriceps, and the shape of the patella.Treatment

Treatment for this emphasizes quadriceps strengthening. The middle muscle of thequadriceps, called the vastus medialis obliquus, or VMO, is the muscle that is focusedon to try to balance the patella in its motion. Occasionally, taping can also help with

this. If conservative measures are not helpful, surgical treatment is reasonable.Rebalancing the kneecap by opening some tissue on the outside of the knee can bedone arthroscopically. Occasionally tightening the medial structures can also help. Inmost patients, this type of surgery would be all that they would need. In some patientswith a significant problem and with patella subluxation or dislocation, a more extensiverealignment procedure is sometimes used.

PATELLA DISLOCATION

When the patella is completely out of its groove it is called dislocated. Features listedabove contributing to maltracking kneecaps can also attribute to a kneecap that is

easier to dislocate. A common scenario is standing full weightbearing on a leg with afoot planted and twisting the opposite way from the leg and feeling a sudden tear or popin the knee with the kneecap dislocating. Sometimes the kneecap will pop back intoplace by itself and sometimes a trip to a medical facility is needed. Once a kneecap hasdislocated, typically the medial structures become loose and it is easier to re-dislocate.The danger of patella dislocation or recurrent dislocation is continued abnormal trackingwith cartilage damage under the kneecap or cartilage being chipped off as the patelladislocates over the edge of the femur.

Treatment

Treatment for this again emphasizes strengthening but surgery is more common for thistype of patella problem. Again, arthroscopic release of the tissues on the outside of theknee will sometimes help prevent further dislocating problems. On occasion, a moreextensive procedure is needed. Either way, strengthening exercises are critical fortreatment.


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VMO RehabilitationWhile monitoring your VMO muscles, making sure you are still getting the contractionsthere; extend the leg by pushing the leg into the towel. Pump the ankle three times, not

letting the tone in that VMO fluctuate. Then slowly and controllably let your leg back

down to the table.Let it relax completely. Tighten it back up. Again pump three times. And again in acontrolled manure lower your leg back down to the table.

1-monitoring your VMO 2-push leg into the towel 3-Lift leg 4-6inches 4-pump ankle 3 times

5-pump ankle 6-pump ankle 7-lower leg 8- relax & repeat

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