12 The Knee

12

The Knee

Brian G. Evans

This chapter discusses the anatomy, biomechanics, and pathology of the knee. The function of the knee is provided primarily by the soft tissue.

Therefore, injury to these soft tissue structures has significant impact upon the stability of the knee.

Anatomy

The osseous anatomy of the knee consists of the proximal tibia, distal femur, and the patella (Fig. 12-1). The distal femur consists of the medial and lateral condyles, the medial and lateral epicondyles, the femoral troch- lear groove, and the intercondylar notch. The medial condyle is larger and extends slightly distal compared to the lateral condyle. Both condyles are covered with articular cartilage. The trochlear groove lies on the anterior aspect of the distal femur between the medial and lateral femoral condyles.

This surface is also covered by articular cartilage and serves as the site of articulation of the patella. The lateral rim of the trochlear groove is fre- quently more prominent than the medial side to allow for proper patellar tracking along the femur.

The epicondyles serve as the site of insertion of several important struc- tures. The deep and superficial medial collateral ligaments (MCL) attach to the medial epicondyle. The proximal margin of the medial epicondyle is enlarged and serves as the site of insertion of the adductor magnus (the adductor tubercle). The lateral or fi bular collateral ligament (LCL) attaches to the lateral epicondyle. Inferior to the attachment of the LCL is the inser- tion of the popliteal muscle at the junction of the lateral condyle and epi- condyle. The medial and lateral heads of the gastrocnemius muscle originate from the medial and lateral posterior femoral condyles. The intercondylar notch is the site of the femoral attachment of the cruciate ligaments. The anterior cruciate ligament (ACL) attaches in the posterolateral aspect of the notch, and the posterior cruciate ligament (PCL) attaches in the antero- medial aspect of the notch.

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The proximal tibial surface is composed of the medial and lateral pla- teaus and the intercondylar eminence. The medial plateau is larger and extends further posterior compared to the lateral plateau. The surface of the medial plateau is relatively flat. The lateral tibial plateau is, in fact, slightly convex. Both the tibial plateaus are covered with articular carti- lage. The intercondylar eminence is the site of attachment menisci and the cruciate ligaments.

The patella is a sesamoid bone within the tendon of the quadriceps mechanism. There are two major facets on the patella, the medial and lateral facets. There is significant variability in the size and orientation of these facets. However, normally the lateral facet is broader and the medial facet is more acutely oriented to the femoral trochlea.

The osseous anatomy of the knee provides little to the stability of the knee. Stability and function are therefore provided by the complex soft tissue envelope around and in the knee (Figs. 12-2, 12-3). The soft tissue components of the knee can be divided into several components: static restraints (ligaments), dynamic restraints (muscles and tendons), and the menisci. The static restraints are represented by the medial collateral liga- ment (MCL), lateral collateral ligament (LCL), anterior cruciate ligament (ACL), and posterior cruciate ligament (PCL). These structures resist valgus and varus stress as well and anterior and posterior translation of the Figure 12-1. Bony anatomy and major ligamentous structures of the flexed knee joint (anterior view).

Posterior cruciate ligament Deep medial collateral ligament Anterior cruciate ligament Medial meniscus Coronary ligament

Patellar tendon Lateral

collateral ligament Lateral meniscus Femoral (trochlear)

groove Lateral condyle Medial condyle

Grant’s notch Intercondylar notch Tibial spines Tibial plateaus

Ligament of Humphry Lateral collateral

ligament

Popliteal tendon Popliteal hiatus (recess) Coronary ligament (meniscotibial)

Lateral meniscus

Transverse ligament

Anterior cruciate ligament

Capsule Deep medial collateral ligament Superficial medial collateral ligament Medial meniscus

Figure 12-2. Cross section of the knee demonstrating the menisci and associated ligaments.

Posterior cruciate ligament

Medial meniscus Coronary ligament (meniscotibial ligament)

Superficial medial collateral ligament

Popliteus muscle

Soleal line

Anterior cruciate ligament Anterior

meniscofemoral ligament (ligament of Humphry)

Posterior

meniscofemoral ligament (ligament of Wrisberg)

Lateral meniscus Popliteus tendon (under arcuate ligament)

Arcuate ligament

Lateral collateral ligament

Figure 12-3. Posterior aspect of the knee joint.

tibial relative to the femur. The MCL consists of two layers. The deep MCL spans from the medial epicondyle of the femur to the proximal tibial border just below the medial tibial plateau. The superficial MCL has the same femoral origin; however, the ligament has a broad tibial insertion extending 6 to 10 cm below the tibial plateau along the posteromedial border of the tibia. The LCL is a more-discrete band along the lateral aspect of the knee.

It spans from the lateral epicondyle to the fibular head.

The anterior cruciate ligament resists the anterior translation of the tibia relative to the femur. The ligament runs from the anterior aspect of the tibial eminence to the posterolateral aspect of the femoral notch. The posterior cruciate ligament resists posterior translation of the tibia relative to the femur and resists hyperextension of the knee. The ligament extends from the posterior aspect of the intercondylar eminence and proximal tibia in the midline to the anteromedial aspect of the femoral intercondylar notch.

The dynamic restraints in the knee are the muscles and tendons that cross the knee joint. These muscles are broadly divided into those that act to extend the knee and those which act to flex the knee. The extensor muscles are the quadriceps femoris and the tensor fascia lata. The quadri- ceps is a group of four muscles, all inserting onto the patella and patellar tendon, which in turn inserts on the anterior tibial tubercle. The muscles that make up the quadriceps are the rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius; these are all supplied by the femoral nerve. The tensor fascia lata originates on the pelvic brim and inserts at Gerdy’s tubercle on the proximal anterior lateral tibia. The tensor fascia lata is innervated by the superior gluteal nerve.

The primary flexors of the knee are the hamstring muscles—the semi- membranosus, semitendinosus, and the biceps femoris—and the sartorius and gracilis. The hamstring muscles originate on the ischium and insert on the posteromedial and posterolateral proximal tibia. They receive their innervation from the sciatic nerve; all are innervated by the tibial division of the sciatic nerve, except the short head of the biceps, which is innervated by the peroneal division of the sciatic nerve. The sartorius originates from the anterosuperior iliac spine and the gracilis originates from the pubis.

Both these muscles with the semitendinosus insert into the proximal medial tibia in the pes anserine (goose’s foot, relating to the appearance of the three tendons inserting together). The sartorius is innervated by the femoral nerve and the gracilis by the obturator nerve.

The other muscles that serve to flex the knee are the gastrocnemius and popliteus, which extend from the posterior aspect of the femoral condyles to the calcaneus and proximal tibia, respectively.

The menisci are two crescent-shaped cartilaginous structures attached

to the proximal tibial surface. These structures serve two purposes in the

knee. They increase the surface area for weight-bearing, therefore reducing

the peak stress in the articular cartilage, and they also provide a small

degree of stability to the knee by changing the flat tibial articular surface to a cupped surface. The menisci are composed of dense organized carti- lage tissue.

Biomechanics of the Knee

The mechanical axis of the lower extremity extends from the center of rotation of the hip to the center of the ankle joint. This axis normally crosses the knee joint in the lateral third of the medial tibial plateau. The normal anatomic alignment of the knee is in 7 degrees of valgus. When the knee is loaded, the medial compartment experiences 60% and the lateral compartment 40% of the weight-bearing stress. This difference in the applied load in the normal knee is the reason the medial tibial plateau and medial femoral condyle are larger than the lateral side. Patients with significant angular deformity in the knee have altered weight-bearing, which results in increased stress in the medial (with varus or bowlegged deformity) or lateral (with valgus or knock-knee deformity) compartment.

The increased stress frequently results in early arthritis in the overused compartment of the knee.

The highest joint forces, however, are found in the patellofemoral articu- lation. Forces as high as five- to eightfold body weight can be noted for activities such as stair climbing and jumping. The function of the patella has been controversial; however, most now recognize the role of the patella in providing a mechanical advantage to the quadriceps tendon. The patella moves the line of pull of the quadriceps further away from the center of rotation, therefore acting as a lever and reducing the force required to extend the knee. Patients who have had the patella removed because of arthritis or trauma are noted to have approximately 30% reduction in the force in the quadriceps compared to patients with a patella.

Evaluation of the Painful Knee

History

The history should begin with the chief complaint and how long the patient has noticed the problem. The specific location of pain, any radiation, the nature of the pain (ache, burning, stabbing, etc.), and any exacerbating or ameliorating factors are included. In particular, the relationship of the pain to activity and rest are important to note. Commonly, pain in the musculo- skeletal system is relieved with rest. Severe pain that is present at rest sug- gests a septic process or neoplasm, which may be primary or metastatic.

Knee problems frequently begin with an injury. A detailed history

describing the injury can be very helpful in determining the structures that

are injured. The nature of any external force contacting the knee and the

position of the knee at the time of injury should be elicited. Did an audible or palpable pop occur at the time of the injury? Shifting or abnormal movement of the knee may also have been noted at the time of injury. The degree and nature of any swelling around the knee is important to record.

In addition to a description of the injury, it is helpful to inquire about the patient’s ability to use the knee after the injury: Was the patient able to weight-bear? Was the onset of pain or swelling immediate or delayed?

Could the patient flex or extend the knee after injury? These are important questions to ask the patient after a knee injury.

In addition to pain, patients with knee problems complain of mechanical problems in the knee. Patients may note an inability to fully bend or straighten the knee, which is referred to as locking of the knee. Locking can be a result of a loose body in the knee becoming lodged between the femoral condyle and tibial plateau, similar to a wedge “doorstop.” The patients who note intermittent locking of the knee are usually able to relieve the locked knee by gently moving the knee without weight-bearing.

This maneuver allows the loose fragment to be released from between the femur and tibia, and motion will be restored. However, inability to fully fl ex and extend the knee can also be noted in patients with large effusions and in patients with ligament injuries.

Instability is another frequent complaint of patients with knee injuries.

Patients observe that their knee shifts or buckles with particular activities.

Instability can result from two general etiologies. The first are ligamentous injuries. As noted previously, the stability of the knee is a result of the liga- ments that cross from the tibia to the femur. Disruption of the ligaments will result in alteration of knee function; the knee may shift or sublux with activity. The second common cause of a knee buckling or giving-way are problems in the patellofemoral joint. Instability of the patella in the troch- lear groove will result in a giving-way sensation as the patella subluxes.

Damage to the articular surfaces of the patella or the trochlear groove will result in pain as the patella tracks over the trochlea; this can occasionally lead to a sharp acute pain that leads to the quadriceps releasing its contrac- tion while the patient is weight-bearing on the leg as a result of a primitive reflex arc. The patient notes a giving-way or buckling sensation in the knee, and a few patients may actually fall as a result.

The majority of knee complaints are aggravated by activities. The spe- cific problems the patient has encountered are important to note. Patients commonly have difficulty ascending and descending stairs. Frequently, descending stairs will be the most symptomatic as this places high stress across the patellofemoral joint. Bicycling can also aggravate the patello- femoral joint. Activities that involve quadriceps contraction with the knee in flexion may result in subluxation in patients with patellar instability.

Patients with meniscal tears have difficulty squatting and may notice

snapping or pain when rising from a chair or ascending stairs. Activities

that involve stopping and turning or cutting will result in the knee

shifting or giving-way if there is insufficiency in the collateral or cruciate ligaments.

Physical Examination

Physical examination of the patient with a knee complaint begins with inspection. Observation of the alignment of the lower extremity should demonstrate a normal 7 degree valgus (knock-knee) angle at the knee when a patient is standing. Deformity of the leg in varus or valgus beyond 7 degrees can be associated with either a ligamentous or osseous deficiency.

Any swelling, bruising, or ecchymosis should be recorded.

Next, the evaluation should focus on the patient’s gait. Normal gait involves range of motion from 0 to 65 degrees of flexion. The gait should have a smooth cadence, with the length of each step being equal on the left and right sides. The knee should not demonstrate any sudden shift to either the lateral or medial side. If abnormal lateral motion is noted, this is recorded as a medial or lateral thrust.

The knee should then be examined with the patient sitting with the legs over the edge of the examining table. The position of the patella should be anterior and symmetrical. The patellar tracking can then be followed by asking the patient to flex and extend the knee with the examiner palpating the patella. There should be little lateral movement. Crepitus may also be noted as a grinding sensation between the patella and the femoral trochlear groove.

The knee should then be examined with the patient supine. For all aspects of the examination, the contralateral knee can be used as a normal control. Effusion or fl uid within the knee can be assessed by placing both hands on the knee, with one below the patella and one above the patella.

Any fl uid in the knee can then be displaced and palpated proximally and distally. The knee can be palpated to determine the specific site of maximum tenderness. The range of motion of the knee is measured with the knee in straight extension as 0 degrees of flexion; normal full flexion is approxi- mately 135 degrees.

The collateral ligaments are then assessed by stabilizing the thigh with one hand and placing a varus or valgus stress on the knee with the other hand. A normal knee has a small amount of medial and lateral laxity in the collateral ligaments. However, any laxity that is excessive, or causes pain to be elicited, should be noted. The cruciate ligaments can also be assessed. The anterior cruciate ligament is best assessed using the Lachman test. The examiner stands by the patient’s feet and stabilizes the femur with one hand holding the distal medial thigh. The tibia is held with a thumb at the lateral joint line. The examiner then attempts to displace the tibia forward in relation to the femur. Translation less than 5 mm should be noted, and the anterior cruciate ligament should be felt to “snap taut.”

Injury to the posterior cruciate ligament can be demonstrated by noting

the degree of recurvatum (back-knee), which can be obtained passively compared to the contralateral knee. Also, with both knees flexed 60 to 90 degrees and the patient supine, the tibia on the deficient side will be noted to sag posteriorly compared to the uninjured leg when viewed from the side. Comparison to the contralateral knee is very important for examina- tion of the collateral and cruciate ligaments.

The menisci are examined by palpation of their outer margin along the joint line at the proximal tibial articular surface. In addition, meniscal tears can be detected by the McMurray maneuver; this is done by flexing the knee internally and externally rotating the tibia and then extending the knee with a valgus force applied. If a reproducible snap is palpated or pain elicited at the joint line, this is suggestive of a tear. Patients with meniscal tears also report pain when asked to squat down with the knees flexed.

Imaging

All the available imaging techniques have been utilized in the evaluation of patients with knee problems. Plain radiographs are the most commonly obtained studies (Fig. 12-4). Plain radiographs are helpful in the evaluation of fractures and subluxation of the joint; in addition, the condition of the articular surfaces can be investigated. The standard series of routine X-

Figure 12-4. Standing anteroposterior (AP) radiograph of both knees in a 70-

year-old woman with osteoarthritis of both knees with a valgus (knock-knee defor-

mity) of both knees. Note the asymmetrical space between the medial and lateral

femoral condyles and the tibial surface.

rays of the knee should include a standing anteroposterior (AP) radiograph of both knees, a lateral view and a merchant or “sunrise view.” The sunrise view is a view taken with the knee in 45 degrees of flexion with the beam directed inferiorly and parallel to the patellar articular surface. There should be a space of 5 to 10 mm between the end of the femoral condyles and the tibial surface and beneath the patellar surface and the femoral trochlea. This “clear space” is in fact occupied by articular cartilage.

R19

A

B

Figure 12-5. (A) Normal T

-weighted magnetic resonance imaging (MRI) sagittal

image of the medial meniscus. (B) Schematic illustration showing the section cut

of (A).

Routine radiography is an excellent tool for the evaluation of the knee for trauma, arthritis, and alignment. Plain radiographs, however, only dem- onstrate the osseous structures. As mentioned earlier, the soft tissues provide the stability and allow the knee to function. Arthrography has been used in the past to evaluate the knee for meniscal pathology. However, this technique is inaccurate and invasive. The development of arthroscopy is a technique that allows the direct visualization of the structures within the knee with a minor surgical procedure. However, this technique is also invasive, and although arthroscopy is accurate, the procedure is relatively expensive compared to an imaging modality alone. Nuclear medicine studies are of limited use in the knee. These studies are sensitive; however, the specificity of these studies is limited. Magnetic resonance imaging (MRI) has provided a dramatic step forward in our ability to diagnose soft tissue injury to the knee. MRI provides accurate and noninvasive evalua- tion of all the soft tissue structures within the knee (Fig. 12-5). MRI is currently the study of choice for the evaluation of intraarticular pathology within the knee.

Knee Pathology

Soft tissue injury is common in the knee. A knee with a bloody effusion after an injury has an incidence as high as 80% of significant soft tissue injury. The differential diagnosis of a posttraumatic bloody effusion in the absence of an intraarticular fracture are meniscal tear, ACL tear, or a patellar dislocation.

Meniscal Tears

Tears of the meniscus can occur in two settings. One is as the result of a specific injury, which usually involves a twisting injury with the knee in some flexion. Swelling and pain are noted immediately after the injury.

There is increased pain with attempts at movement, and there is a limita- tion in the range of motion. Pain with squatting down or arising from a chair is commonly reported. The torn meniscus can block motion. Occa- sionally the knee can be gently manipulated to reduce the torn meniscal fragment, and motion will be restored. However, the fragment will fre- quently redisplace, and intermittent locking may occur. This form of a tear is usually in younger patients with stout meniscal tissue.

In older individuals, the meniscal tissues soften and the edge becomes

frayed. As this occurs, the frayed edges can become entrapped between

the edges of the bone, initiating a tear that can extend into the meniscal

substance. This tear can occur with little or no trauma with minimal swell-

ing and pain initially. The diagnosis is made by joint line pain, effusion,

and rarely locking. Patients with locking frequently require arthroscopic

surgery to debride the torn portion of the meniscus. In older patients, if the meniscal tear does not cause locking, frequently these can be treated with nonsteroidal antiinflammatory (NSAI) medications and an intraar- ticular corticosteroid injection. These treatments will reduce the effusion and pain. With continued activity, the soft meniscal tissue can be worn down and a stable edge reestablished.

Ligament Injuries

Injury to the ligamentous structures are manifest by instability in the knee.

In addition to pain and swelling, patients report a sense of the knee shifting or giving way, which may occur only with specific activities such as descend- ing stairs or when turning on the loaded extremity. The initial management of these injuries is rest, ice, and elevation. A splint or knee immobilizer can also be helpful to protect the knee. As the initial pain subsides, it is important to begin to work on restoring range of motion, using a brace to protect the injured ligament. As the pain further decreases, strengthening is begun. If after the strengthening program is completed the knee remains unstable, the patient may be a candidate for surgical reconstruction.

Patellofemoral Pathology

The patellofemoral joint is one of the most common areas of pain in the knee. Common complaints are anterior knee pain, which is aggravated by activities involving high loads on a flexed knee such as stair climbing or bicycling. This pain can be the result of degenerative changes in the patel- lofemoral articulation or a result of maltracking of the patella within the trochlear groove. A grinding or snapping sensation may also be noted. Pain is usually relieved by rest; however, if the patient is sitting for a prolonged period of time with the knee flexed, such as in a theater, on a plane, or during a long car ride, anterior knee pain will result. Frequently patients try to change the position of the knee to relieve their discomfort. This symptom is referred to as movie sign and is indicative of degenerative changes in the patellofemoral joint. Softening of the articular surface is referred to as chondromalacia patella; this can be a primary problem or it may be secondary to excessive trauma to the joint caused by maltracking of the patella within the trochlear groove.

The treatment of these conditions is primarily nonoperative. Improving

the patellar tracking can be done through a series of exercises to retrain

the quadriceps and through patellar mobilization exercises. The exercise

program need to be maintained for a minimum of 6 to 8 weeks to demon-

strate benefit. The symptoms frequently recur. If the symptoms are recur-

rent and do not respond to the nonoperative regimen, and patellar

maltracking is evident, operative intervention may be indicated. Operative

intervention is directed at correcting the patellar tracking and maximizing the quadriceps function with postoperative physical therapy.

Arthritis

The management of arthritic symptoms within the knee is similar to man- agement elsewhere in the body. The nonoperative management of arthritis within the knee consists of a five-modality approach. The first line of therapy is the use of NSAI agents, which will reduce the pain and swelling associated with the knee. Although all the NSAI drugs (NSAIDs) function in a similar fashion, there is wide variation in individual patient response.

Therefore, minimally two or three different NSAIDs should be tried. The most common side effect of this course of treatment is dyspepsia.

The second line of treatment of arthritis, the selected use of intraarticu- lar corticosteroid medication, can be effective in patients who have an acute exacerbation of the arthritic pain. The injection can quiet their pain and restore them to a baseline level of discomfort. The injection should not be utilized for the control of baseline pain. If the injection is required at a frequency of greater than one every 6 to 8 weeks, some other course of treatment should be initiated, such as surgery. If the knee is injected more frequently than two to three times per year, the corticosteroid may have a detrimental effect on the articular cartilage.

Physical therapy can be very helpful in the treatment of arthritis of the knee. As the soft tissue sleeve is very important to the function of the knee, by optimizing the function of the soft tissues the symptoms of arthritis can be reduced. Physical therapy should be directed at maintaining the range of motion of the knee and optimizing the strength of the quadriceps and the hamstring muscles. In the late stages of degenerative arthritis, physical therapy may worsen the patient’s symptoms and should be limited to the patient’s tolerance.

Assistive devices such as a cane or crutch may be helpful in the man- agement of arthritis of the knee. These aids can limit the stress across the painful knee and improve the patient’s walking tolerance. The final approach to the management of arthritis of the knee is modification of the patient’s activities, such as sports, the work environment, and possibly arranging special parking for the patient the patient’s car. Frequently, patients with significant knee arthritis are also overweight. Weight loss in these patients can significantly reduce symptoms and the need for other treatment modalities.

Surgical Reconstruction for Arthritis

When all nonoperative measures have failed to relieve the symptoms of

knee arthritis, surgical intervention should be contemplated. The surgical

correction of knee arthritis can be separated into treatments that retain the patient’s articular surfaces and knee replacement. Nonreplacement options include the use of arthroscopy to “clean out” the knee; this proce- dure can remove the small cartilage fragments that accumulate in arthritic joints and debride any loose articular fragments. The pain relief from this procedure, however, is short lived, lasting only 3 to 6 months. Patients should be informed preoperatively that if extensive arthritis is noted during arthroscopy, the pain may be worse after surgery. In that setting, the patient is a candidate for knee replacement.

Patients with osteoarthritis of the knee frequently develop angular deformities. The most common deformity is varus angulation of the knee, which results from erosion of the medial compartment of the knee. As the deformity progresses, a greater portion of the weight-bearing stress is con- centrated in the medial compartment of the knee. Osteotomy is a proce- dure to realign the articulation. The proximal tibia is transected, and a wedge of bone is removed from the lateral aspect. When the two new sur- faces are brought together, the varus deformity is corrected. This proce- dure redistributes some of the weight-bearing stress to the lateral compartment and can result in improved symptoms in the knee. The result is generally successful for 5 to 10 years. Osteotomy is contraindicated in knees that are stiff or unstable. When the symptoms return, knee replace- ment surgery is indicated.

Arthrodesis or fusion of the knee is an option for the management of young active patients, particularly physical laborers. Fusion results in a stiff straight knee that will allow the patient to ambulate and stand for long periods of time without difficulty. However, significant limitations also exist. The gait pattern is significantly abnormal. In addition, patients will have difficulty sitting, particularly in confined spaces such as public trans- portation and theaters. Resection arthroplasty is a procedure in which the articular surfaces are resected and a fibrous pseudoarthrosis forms within the joint space. Pain may be decreased; however, the knee is significantly unstable, requiring a brace for ambulation. Arthrodesis and resection arthroplasty are not commonly performed. Currently, these procedures are reserved for the management of a failed total knee replacement.

Total knee replacement (TKR) is commonly utilized to relieve the symp- toms of knee arthritis and restore function (Fig. 12-6). Approximately 200,000 arthroplasties are performed annually in the United States; the average age of patients receiving a TKR is 70 to 74 years. Successful results can be obtained in more than 95% of patients, with survivorship at 10 to 15 years of 90%. All components are currently fixed with polymethylmeta- crylate (PMMA) bone cement. Noncemented components, those used with porous ingrowth surfaces for bone ingrowth, have been associated with a higher incidence of loosening and pain.

The proximal tibia is cut perpendicular to the long axis of the shaft,

and the femoral articular surface is cut using specific guides to remove the

femoral trochlea and distal and posterior femoral condyles. The ACL is removed; however, the PCL can be resected or retained depending on the design of implant chosen. For proper function of the arthroplasty, the MCL, LCL, and, if retained, PCL must be carefully balanced. The com- ponents are then fixed to the surfaces of the tibia and femur with bone cement. The patella is normally resurfaced as well after resecting the articular surface parallel to the anterior surface.

The patient is mobilized into a chair on the first postoperative day, and full weight-bearing may be allowed immediately. However, a knee immo- bilizer should be utilized to protect the knee from acute flexion while walking, and this is continued until the quadriceps function returns. The critical element of the postoperative therapy is the restoration of motion.

If the motion is not restored within the first 3 to 6 weeks, maturation of the scar tissue will prevent major gains in motion after that point. Many patients can be safely discharged at 3 to 4 days after surgery.

Frequently, however, these patients require home physical therapy to continue to work on range of motion and ambulation in the first few weeks after surgery. The total rehabilitation period after total knee replacement is between 3 and 6 months, although patients are functionally mobile after 2 to 3 weeks. Knee replacement can be performed bilaterally in one stage in medically healthy patients (see Fig. 12-6). The initial increase in debili- tation postoperatively is offset by a reduction in the overall period of rehabilitation after sequential unilateral TKR.

Figure 12-6. Standing AP radiograph of both knees 2 weeks after one-stage

bilateral knee replacements in the 70-year-old female patient whose preoperative

radiograph is shown in Figure 12-4.

Aseptic loosening of the implants after TKR occurs at a low rate. Several studies have documented a 15-year survivorship of greater than 90% and less than 0.5% per year rate of aseptic loosening after cemented TKR. If a TKR is noted to be loose earlier than 5 years postoperatively, it should be evaluated for deep infection. Deep sepsis is associated with early loos- ening after TKR. Young age, marked obesity, and high demand also nega- tively impact upon the long-term survival of the replacement. To date, the best data indicate noncemented TKR are equal to the cemented replace- ment. Several studies suggest poorer results when cement is not used, par- ticularly for fixation of the tibial component. Increased tibial loosening and pain have been noted with these devices. At present. because of the gener- ally increased cost for the noncemented porous-coated implants and poorer clinical results, the use of these devices is difficult to justify.

The majority of the complaints after cemented TKR are from the patel- lofemoral joint, which can be the result of poor soft tissue alignment at the time of arthroplasty and may lead to painful subluxation or dislocation of the patellar component. If inadequate bone is resected from the patella at the time of resurfacing, a marked increase in the patellofemoral stress can be noted, which may become painful. Several authors have advocated not resurfacing the patella. However, several studies now demonstrate a higher rate of patellofemoral complaints after TKR without patellar resurfacing.

If significant patellofemoral arthritis exists at the time of arthroplasty, patients with weight greater than 60 kg and height greater than 160 cm will have more pain postoperatively if the patella is not resurfaced.

The most common complication after TKR is thromboembolic disease (TED). The rate of deep venous thrombosis ranges from 25% to 50% of cases in patients evaluated with venography or duplex Doppler analysis.

Similar to patients receiving total hip replacement (THR), currently it is recommended that all patients receive some form of prophylaxis against TED. Mechanical methods such as the pneumatic compression stockings appear to have a greater benefit after TKR compared to THR. Low-dose Coumadin and aspirin are currently the most commonly utilized medica- tions. The efficacy of low molecular weight heparin is currently under investigation.

Deep infection occurs at a rate of approximately 1% after TKR for osteoarthritis over the life of the implant. The most common organisms are skin flora, primarily Staphylococcus aureus and Staphylococcus epi- dermidis. In particular to knee replacement, the relatively thin soft tissue envelope at the inferior aspect of the skin incision can lead to wound dehiscence and allow entry of the flora into the joint. Any area of skin breakdown after TKR should be treated aggressively to prevent deep infec- tion, particularly in patients with prior incisions and in those with diabetes or significant vascular disease.

If a deep infection is established, the only way to eradicate the infection

is to remove the implants and cement and then thoroughly debride the

joint. A cement spacer is then placed into the joint space, and the patient should receive 6 weeks of intravenous antibiotics. The serum bactericidal titers (SBT) again should exceed 1:8. After 6 weeks, the knee can be reim- planted if adequate soft tissue and bone remains. However, as a result of the inevitable scarring the clinical result is compromised.

Occasionally, after TKR range of motion of the knee does not progress well. If the patient is less than 2 to 6 weeks past surgery, a gentle manipula- tion of the knee in the operating room under anesthesia may be beneficial.

If the motion cannot be restored, particularly if the patient is beyond 6 weeks after replacement, additional surgery may be necessary to restore functional range of motion.

Summary and Conclusions

The knee is a complex joint with function provided by the combination of osseous and soft tissue structures. The soft tissue envelope plays a signifi - cant role in the pathology of the knee and in the management of these conditions. With careful history, physical examination, and appropriate use of the available diagnostic modalities, knee pathology can be accurately determined and successful treatment instituted. Successful management of knee pathology includes treatment of the specific etiology, but optimal management of the soft tissue envelope with directed physical therapy is essential to an optimal outcome.

Suggested Readings

Heck DA, Murray DG. Biomechanics in the knee. In: Evarts CM (ed) Surgery of the Musculoskeletal System, 2nd ed. New York: Churchill Livingstone, 1990:

3243–3254.

Rand JA, Ilstrup DM. Survivorship analysis of total knee arthroplasty: cumulative rates of survival of 9200 total knee arthroplasties. J Bone Joint Surg 1991;73A:

397–409.

Stern SH, Insall JN. Posterior stabilized prosthesis: results after follow-up of nine to twelve years. J Bone Joint Surg 1992;74A:980–986.

Windsor RE, Bono JV. Infected total knee replacements. J Am Acad Orthop Surg 1994;2:44–53.

Questions

Note: Answers are provided at the end of the book before the index.

12-1. The posterior cruciate ligament limits which motion of the knee?

a. Posterior translation of the tibia relative to the femur

b. Anterior translation of the tibia relative to the femur

c. Valgus opening of the knee

d. Varus opening of the knee e. Hyperflexion of the knee

12-2. Which ligament is removed in all modern knee replacement surgeries?

a. Anterior cruciate ligament b. Posterior cruciate ligament c. Medial collateral ligament d. Lateral collateral ligament e. Patellar ligament

12-3. The most common complication after total knee replacement is:

a. Stiffness b. Infection

c. Instability

d. Deep venous thrombosis e. Neurovascular injury

12-4. A valgus closing wedge osteotomy is indicated for the treatment of:

a. Valgus osteoarthritis with isolated lateral compartment narrowing

b. Varus osteoarthritis with isolated medial compartment narrowing

c. Isolated patellofemoral osteoarthritis d. Rheumatoid arthritis

e. Tricompartmental osteoarthritis

12.5. On postoperative day 3 after a total knee replacement, the patient is noted to have an open area of the wound with a black necrotic edge. The most worrisome complication of this clinical situation is:

a. Deep venous thrombosis b. Infection

c. Poor scar appearance d. Nerve injury

e. Medial collateral ligament rupture

12-6. If a total knee replacement becomes loose before 5 years after implantation, it should be evaluated for what other complication:

a. Osteoporosis b. Stiffness

c. Fracture

d. Neurovascular injury e. Infection

12-7. Resection arthroplasty of the knee is indicated for the treatment of:

a. Osteoarthritis b. Rheumatoid arthritis

c. Chronic knee instability

d. Salvage of the multiply operated failed total knee replacement

e. Ankylosing spondylitis

12-8. When recommending arthroscopy of the knee for a patient with osteoarthritis, the surgeon should inform the patient that:

a. The results are highly successful

b. The long-term success is excellent for pain relief c. The patient may have more pain postoperatively

d. Arthroscopy is necessary before total knee replacement e. Arthroscopy can delay the need for total knee replacement 12-9. Nonoperative management of osteoarthritis of the knee includes:

a. Nonsteroidal antiinflammatory medications

b. Careful use of intraarticular corticosteroid injections c. Physical therapy

d. Use of a cane and weight loss e. All the above

12-10. Patients with chondromalacia of the patella have which of the fol- lowing symptoms?

a. Anterior knee pain with prolonged sitting b. Anterior knee pain when descending stairs

c. Buckling or giving way of the knee with ambulation d. Crepitus in the anterior aspect of the knee

e. All the above