The Numbers Speak for Themselves

Osteoarthritis is the leading cause of disability in the general population of the United States.^1,2 The Centers for Disease Control confirms that approximately 1 in 3 adults with arthritis reported limitation in their usual activities. Arthritis of the knee alone afflicts more than 4 million people, and research shows 14 percent of individuals interviewed within the age group of 40 to 79 described knee pain with disability on most days of the previous month.³ Because of the increase in life expectancy within most societies of the western world, the high prevalence of OA is expected to increase further in upcoming years. For example, the number of first-time total knee replacements (TKR) is expected to skyrocket 673 percent to 3.48 billion by 2030.⁵

Osteoarthritis is also associated with extensive direct and indirect costs and represents a considerable burden for the healthcare system and society as a whole. In the United States, the cost of medical care and lost productivity is estimated at $86.2 billion. In the year 2000, hospital costs in the United States for TKR surgery topped $11 billion.^5,6 Beyond this condition’s economic burden, arthritis affects the quality of life for those afflicted and is associated with disabling one’s activities of daily living. Physical therapy is among the treatment options for people who suffer from osteoarthritis and intends to prevent physical impairment and restore functional ability through the use of exercise, physical modalities, and patient education. Current evidence supports the effectiveness and safety of moderate- to high-intensity aerobic and strengthening exercises for osteoarthritis. It is important to note that participation in recreational activities does not replace the need for therapeutic exercises.

It’s in the Joints

OA is a degenerative condition that affects subchondral bone, joint synovium, tendons, ligaments, muscles, and particularly large weight-bearing joints. The affected cartilage initially develops small tears at the articular surface, which eventually results in larger tears. The cartilage eventually fragments off into joints with cartilage-forming cells called chondrocytes replicating in an attempt to keep up with the cartilage loss. Over time, these cells eventually are unable to produce at the rate of degeneration and the underlying bone becomes exposed.

Risk factors associated with knee OA are genetic predisposition, obesity (i.e., body mass index > 30 kg/m2), advancing age, and physically demanding occupations.³ OA is particularly common in older patients, but can occur in the younger population either through genetics or, more commonly, because of previous joint trauma. Symptoms of OA include pain during and/or after use, joint stiffness, swelling, crepitus, and loss of motion.

Several methods exist that can help diagnose knee and other forms of OA. The Kellgren and Lawrence System is the most universally accepted method for classifying degrees of OA and is based on radiographic findings.⁷ The Kellgren and Lawrence System uses four radiographic features: joint space narrowing, osteophytes, subchondral sclerosis, and subchondral cysts. Another method of staging called the Outerbridge method classifies articular cartilage damage based on the arthroscopic findings in patients affected with OA. The four grades are:

• Grade I — Softening and swelling
• Grade II — Fragmentation and fissuring < 0.5 inches
• Grade III — Fragmentation and fissuring > 0.5 inches
• Grade IV — Erosion down to the subchondral bone

The American College of Rheumatology recommends a combination of history, physical examination, and laboratory tests as the three methods to help diagnose OA of the knee.⁸ However, simple clinical criteria diagnose OA of the knee with a sensitivity of 89 percent and a specificity of 88 percent.^8,9 (See sidebar.)

Criteria to Diagnose Knee Osteoarthritis^8,9

1. Knee pain, < 38 years, bony enlargement
2. Knee pain, > 39 years, bony enlargement, morning stiffness > 30 minutes
3. Knee pain, bony enlargement, morning stiffness > 30 minutes, crepitus with active motion
4. Knee pain, >38 years, bony enlargement, morning stiffness > 30 minutes, crepitus with active motion

Medical Management

Physicians may use acetaminophen (Tylenol) as a first-line therapy for patients with mild OA symptoms who do not have contraindications to this medication.¹⁰ However, for people with moderate to severe OA, or for those with mild OA symptoms who do not respond to acetaminophen, nonsteroidal anti-inflammatory medications are commonly prescribed.¹⁰

NSAIDs, while useful in the management of OA, are not without potentially dangerous adverse effects. NSAIDs can cause kidney toxicity by causing reduced blood flow and sodium retention. This can result in renal failure in addition to hypertension, edema, and congestive heart failure.¹⁰ NSAIDs can also affect the stomach, resulting in gastritis and gastric ulcers in patients seen by physical therapists. Additionally, it is not uncommon for people, including outpatient physical therapy patients, to mix over-the-counter NSAIDs with prescription medication, compounding the risk for GI complications.^11,12 Finally, NSAIDs can block the antithrombotic effect of aspirin, interfering with the therapeutic effects of aspirin therapy taken by patients for the management of cardiovascular disease.

Physical therapists can screen for potential medication mishaps and related patient concerns, which should be relayed to the patient’s physician. Pharmacologic management of OA, while an important component in the overall management of OA, is a complex issue and requires diligent medical monitoring to ensure patient safety and effective outcomes.

Intra-articular steroid injections may provide pain relief and have an anti-inflammatory effect on the affected joint. Options for joint injections generally consist of glucocorticoids (i.e., steroids) or hyaluronic acid (HA) products. Steroid injections, such as triamcinalone hexacetonide (Aristospan), represent a short-term option for patients with OA of the knee and result in reduction of pain as soon as one week after injection with benefits lasting potentially for up to a month.¹³ However, such injections carry the potential for complications that range from mild synovitis to infection, tendon weakening or rupture, and nerve damage.¹⁴ As a result, controversial evidence exists regarding frequent administration and usually no more than three injections are recommended per year in any one osteoarthritic joint.

HA is a vital component of both articular cartilage and synovial fluid. Healthy articular cartilage has a balance of extracellular matrix turnover — matrix that is broken down by the body and replaced by new matrix. When an imbalance occurs so that the matrix degradation is greater than matrix production, OA begins its destructive process. The intra-articular injection of HA products — viscosupplementation — is meant to improve the health of affected joints by enhancing the viscoelastic nature (shock absorption and lubrication) of synovial fluid and, in the long term, affect the return of metabolic homeostasis of the joint.¹⁵

Two types of HA products are available in the United States — a low-molecular weight substance that is naturally occurring and a high-molecular weight substance that is derived from rooster combs or bacterial cultures.^16,17 High-molecular weight HA products have been shown to be more effective than low-molecular ones.¹⁸ While viscosupplementation tends to have a later onset of action than steroids, that is, five to 13 weeks versus one week, respectively, it can provide longer-lasting relief, especially since the benefits of steroid injections can wear off after a month.^15,19 Before a decision to give the recommended three- to five-injection course of HA, patients are advised to try conservative therapy for at least three months.

Healthcare providers should be mindful of the role of HA products in the management of knee OA, even though it has been shown to have a modest effect on pain, function, and patient global assessment consisting of outcome tools such as the Health Assessment Questionnaire (HAQ) and Study Short-Form-36 (SF-36).^15,20

As with any joint injection, viscosupplementation is not without adverse effects, such as injection site pain and inflammation and more severe, yet rare, occurrences of severe swelling, vasculitis, hypersensitivity reaction and painful, acute local reaction.²¹

Manual Therapy and Exercise

According to 2004 statistics from the Centers for Medicare and Medicaid Services, therapeutic exercise and manual therapy are two of the most common outpatient therapy claims submitted by physical therapists.²² This information stems from a randomized controlled study, where patients with osteoarthritis of the knee were treated with manual physical therapy and exercise. Clinicians in this study performed joint mobilizations with various grades, locations, and directions of mobilizations. In addition to receiving joint mobilizations, subjects in the treatment group also performed a standardized exercise program that was progressed for each individual patient to provide a training effect to the muscles and range of motion stress to restricted joint tissues. Compared to a no-treatment group, these patients experienced significant improvements in self-perceptions of pain, stiffness, and functional ability and the distance walked in six minutes. The beneficial effects of treatment persisted at four weeks and one year after the conclusion of clinical treatment. The observed improvements were attributed to the physical therapy intervention. What’s more, the study showed that a regimen of manual therapy and exercise could delay or prevent the need for a TKR one year after treatment. Twenty percent of those in the control group had a TKR at the one-year follow-up period, while only 5 percent of those in the treatment group required a TKR.

In another randomized trial studying manual therapy and exercise for the treatment of knee OA, patients frequently reported 20 to 40 percent relief of symptoms after only two to three clinical treatments of manual therapy and exercise.²³

At present, there are no other recent studies comparing other forms of physical therapy to surgical intervention to treat knee osteoarthritis.

Arthroscopic Surgery for Knee OA

Physical therapists who work in an outpatient setting frequently treat patients following arthroscopic surgery for knee OA. Surprisingly, much disagreement is apparent in the literature about the efficacy of this treatment option, even though it is commonly performed.²⁴ Arthroscopic surgical options for knee OA include debridement of meniscal tears or cartilage lesions and joint lavage. One study that compared joint debridement, lavage, and placebo arthroscopic surgery discovered that the surgical outcomes were no better than those found in the placebo group. However, in the case of meniscal tears, debridement did at least improve patients’ symptoms.²⁵ However, another investigation found that debridement of meniscal tears did not guarantee a successful outcome in patients with knee OA.²⁶ This is possibly due to the amount of exposed bone that may be present after the meniscal debridement.

Excess Weight and Knee OA

Much media attention has been directed to the rising incidence of obesity in the United States. Excess weight has been shown to be a risk factor in osteoarthritis of the knee.^31,32 Physical therapists can serve as educators and referral sources for overweight patients with knee OA. They can suggest their patients consult with a nutritionist, a physician, or both. Physical therapists can also propose one of the many programs available to assist with weight loss, such as Weight Watchers, that patients may engage in under the approval of their physicians.

Physical therapists can also actively assist patients to lose weight through an individualized program for diet and exercise. Because exercise plays a pivotal role in weight loss, this is an area through which physical therapists can directly affect in a patient’s therapy program. A walking program is an important component of a comprehensive treatment plan for knee OA.²³ However, because many patients with knee OA are unable to walk extended distances, exercises that are less weight-bearing, such as aquatic exercises, can be incorporated. Several studies suggest that lower intensity aerobic exercise can selectively burn fat over carbohydrates.^27-32 Exercise intensity is measured by several variables to include max VO2. This is described as the point at which the oxygen consumption of an individual plateaus with no further increase of oxygen despite an additional exercise workload. Exercise intensities that maximize the metabolism of fat are somewhere in the range of 40 percent maximum oxygen uptake to 64 percent VO2 max.³³

Researchers found 64 percent VO2 max to be the ideal exercise intensity for fat metabolism.²⁸ That translates into about 74 percent of maximum heart rate. They further discovered that fat burning was negligible at heart rates of 92 percent max or greater. Therapists should consider these variables when designing exercise programs for patients with knee OA in whom weight loss is desirable. Of further clinical importance, the physical therapist can educate the patient that high intensity aerobic workouts are not necessary for weight loss and benefits can be achieved with moderate aerobic exercise performed on a consistent basis.

Genetics can play a structural role in knee osteoarthritis. Structural deviations that can cause an increase in cartilage degeneration is the amount of genu varus or genu valgus seen at the knee joint. Excessive genu varus gives the patient a bow-legged appearance and can place excess stress on the medial compartment of the knee. Genu valgus will give the appearance of knock knees and cause additional stress and possibly accelerate the degeneration to the cartilage of the lateral compartment of the knee.³⁴

Physical Therapy and Post-TKR

TKR, also referred to as total knee arthroplasty (TKA), is a surgical procedure where worn, diseased, or damaged surfaces of a knee joint are removed and replaced with artificial surfaces. Materials used for resurfacing of the joint are not only strong and durable, but also optimal for joint function as they produce as little friction as possible. The “artificial joint,” or prosthesis, generally has two components, one made of metal, which is usually cobalt-chrome or titanium, or a plastic material, polyethylene.

Classifications of total knee prosthesis: There are four basic categories of knee replacements, with the use of each depending on the degree of mechanical stability provided by the design of the artificial knee. These categories are nonconstrained, semiconstrained, constrained or hinged, and unicondylar. The highly successful nonconstrained implant is the most common type of artificial knee. It is termed nonconstrained because the artificial components inserted into the knee are not linked to each other. In this type, the damaged bone surfaces are replaced, but the person’s own ligaments and muscles are left in their anatomical positions and maintain the mobility of the knee. This is a key feature of this group of artificial implants, helping to maintain the stability of the knee.

The semiconstrained implant is a device increasing the stability of the knee. This type of knee replacement has a specific degree of stability engineered into the prosthesis. It is an option in the surgical situation where removal of the medial collateral ligaments or other major ligaments is required. It may also be an option if the surgeon feels the new knee replacement will be generally more stable and functionally successful.

Constraint or hinged variety implants are rarely used as a first choice of surgical options. In this case, the two components of the knee joint are linked together with a hinged mechanism. This type of knee replacement is used when the knee is highly unstable and will not be able to support the other type of knee replacements. It is useful in the treatment of severely damaged knees particularly in very elderly people undergoing a revision replacement procedure. The disadvantage of this type of knee joint is that it is more likely to loosen and fail.

A surgeon can also replace only that area of the knee joint that is severely damaged. In the right circumstance, some surgeons believe it more appropriate to perform a unicondylar knee replacement, also referred to as hemiarthroplasty. This procedure replaces only half of the knee joint—the medial or lateral compartment. It is performed if the damage is limited to one side of the joint only, with the remaining part of the knee joint being relatively spared. Implant fixation — cemented and uncemented prosthesis: A cemented prosthesis is held in place by a type of epoxy cement that attaches the metal to the bone. Although not a standard rule, some orthopedists recommend the cemented joints for people over 65, believing that bones become thinner in the older population and for these people a cemented joint may have better success.

An uncemented prosthesis has a fine mesh of holes on the surface that allows bone to grow into the mesh and attach the prosthesis to the bone. Uncemented prosthesis can produce a tighter bond, yet because it is not initially fastened as tightly as cemented joints, it takes a longer period to heal. This is of clinical importance to the rehabilitation professional because the patient is required to spend more recovery time non-weight-bearing. In some cases a combination of the two types are used. The choice to use a cemented or uncemented artificial knee is usually made by the surgeon based on the patient’s age and lifestyle, and the surgeon’s preference and experiencee.³⁵

A recent development in design — the rotating platform knee implant: Advances in biotechnology are revolutionizing knee replacements on a continuous basis. For instance, a more recent advance is the rotating platform knee, also known as a mobile-bearing knee. To date, the rotating platform knee is the only implant in the United States designed to bend and rotate, helping to accommodate more normal kinematics of the knee joint.

According to the American Academy of Orthopaedic Surgeons, a rotating platform knee may be more appropriate for the younger, more active patient. In a traditional implant, the tibia is topped with a flat metal piece that securely holds the plastic spacer. In the case of the rotating platform knee implant, the plastic spacer can rotate. Because of this feature, the contact between the tibia and femur can be more evenly distributed, resulting in reduced stress and wear on the implant. One disadvantage of this implant compared with traditional designs is that it is less sensitive of imbalance in soft tissues, potentially increasing the chance of dislocation. The cost may also be higher than traditional designs.

General Goals of TKR

TKR is designed to provide painless and unlimited standing, sitting, walking, and other normal activities of daily living. Goals of range of motion may differ among patients and their condition/age; however, generally speaking 110 degrees of flexion and 0 degrees of extension are ideal and sought after by both surgeon and physical therapist. Functionally it requires the knee to have at least 110 degrees of flexion to safely and functionally ascend and descend stairs. It is not uncommon for patients to achieve 120 degrees of flexion, which will only be beneficial for them throughout activities of daily living. However, immediately following the surgery, patients can expect significant declines in knee range of motion, limb strength (in particular the quadriceps muscle), and functional performance, such as transfers, gait, stair climbing, and self-care. All of these variables are addressed in a comprehensive postoperative rehabilitation program.

Pain and swelling: Knee pain and swelling can impede a person’s willingness to move as well as limit the range of motion of the knee and the ability of the quadriceps muscle to contract. Deficits in quadriceps strength are very important as they are highly correlated with a patient’s functional performance.³⁶ Pain can be managed pharmacologically, and it is imperative to encourage patients to follow their physicians’ directions regarding their pain medications. This can allow the patient to tolerate more rehabilitation as well as permit the patient to be more comfortable and provide restful sleep, which can also affect the rehabilitation program.

Patients should be supported to comply with wearing compressive stockings as scheduled, if prescribed, not only for deep vein thrombosis protection, but also for edema control. Cold therapy through the use of ice packs or commercially available cooling devices has been shown to decrease pain and swelling.^37,38 Ankle pumping and elevation of patients extremities when they are not on their feet is also a commonly prescribed practice to control edema.

Exercise: Typical exercises after a TKR consist of passive, active assistive, and then active range-of-motion exercises to improve knee joint mobility. Beneficial stretching exercises include the standing calf, supine hamstring, and prone quadriceps stretches. Range of motion (ROM) exercises vary among rehabilitation protocols but have similar goals and techniques. For example, to promote flexion, the patient is instructed to begin in long-sitting or seated position; the knee is brought into end range flexion and held for three seconds, followed by bringing the knee further into flexion as tolerated and held for 30 seconds. To help increase extension the patient is instructed to begin in long sitting position; the knee is then brought into end range extension and comfortably held for three seconds, followed by bringing the knee further into extension and held for 30 seconds. A stationary bicycle also can be helpful to promote knee flexion.

Strengthening exercises begin with static muscle contractions such as quadriceps sets, one set of 10 repetitions with a six-second hold. As the patient progresses in muscle control, closed-chain progression exercises begin as tolerated and can consist of standing terminal knee extensions with one 30-second bout, increasing resistance of extension; seated leg press, one 30-second bout with increased resistance; and step-ups with one 30-second bout increasing step height. Such strengthening exercises help to improve force production around the knee, and gait activities.³⁹

The therapist needs to monitor a patient’s signs, symptoms, and performance levels at each therapy session to ensure constant progress to prevent stagnation or regression. Some discomfort is to be expected in TKR rehabilitation; however, severe pain and swelling for hours after a therapy session is a sign that the program needs to be adjusted. The primary goal of strengthening is to promote independent weight-bearing and safe transfers and ambulation at the level before surgery.

Strengthening of the quadriceps muscle following TKR has been shown to be more highly correlated to functional improvement than other variables, such as ROM or strengthening other muscle groups.^36,40 Quadriceps muscle weakness begins well before TKR surgery in patients with knee OA and is considered to be one of the most important predictors of disability. The quadriceps muscle loses its firing properties and contractile response from pain stimuli, which can actually cause atrophy over a period of time.⁴¹ Therefore, special attention must be paid to ensuring maximal return of force production of this muscle.

Progressive overload of quadriceps through resistance training (without overloading the prosthetic components or joint tissues as evidenced by increasing pain, swelling, and decrease in function) is one method to maximize the strength of this muscle. However, neuromuscular electrical stimulation (NMES) of the quadriceps appears to have a role in the rehabilitation process following TKR surgery. Researchers found that the application of NMES to the quadriceps (10 contractions at a dose greater than 30 percent of voluntary quadriceps strength) along with a volitional quadriceps-strengthening program resulted in better quadriceps muscle activation and performance on the timed-up-and-go test than a volitional exercise program only. ⁴² Other investigators and clinicians have discovered similar results when adding NMES to the rehabilitation program of patients who have undergone TKR surgery.^43,44,45

Because knee OA does not develop overnight, patients can develop muscle imbalances as a result of gait compensations.⁴⁶ Individuals with knee OA have been found to exhibit increased hamstring activation⁴⁷ and more reliance on adductor muscles of the hip⁴⁸ in addition to quadriceps weakness. These imbalances do not disappear simply because a total knee replacement surgery was performed. While TKR addresses the end result of the degenerative process, muscle imbalances that developed before surgery remain afterwards. Such imbalances need to be addressed as part of a patient’s post-TKR rehabilitative process to maximize gait and function.

Third-party payers are keeping a vigilant eye on how their reimbursement dollars are being spent. Those of us in the PT profession need to make sure we are providing the most effective and efficient rehabilitative measures available to our clients, who include insurers as well as those with disabilities and dysfunctions. We can accomplish this objective by using best-practice methods found in evidence-based research and by recording new, efficient, effective interventions in the form of case studies or clinical research. Rehabilitation plays a vital role in the overall management of OA of the knee, and by approaching each patient individually and professionally, we can make clinical decisions that support his or her best interests.