Sedentary Work Exerting up to 10 pounds (4.5 kg) of force occasionally and/or a negligible amount of force frequently or constantly to lift, carry, push, pull, or otherwise move objects, including the human body. Sedentary work involves sitting most of the time, but may involve walking or standing for brief periods of time. Jobs are sedentary if walking and standing are required only occasionally and other sedentary criteria are met.

Light Work Exerting up to 20 pounds (9.1 kg) of force occasionally and/or up to 10 pounds (4.5 kg) of force frequently, and/or negligible amount of force constantly to move objects. Physical demand requirements are in excess of those for Sedentary Work. Light Work usually requires walking or standing to a significant degree. However, if the use of the arm and/or leg controls requires exertion of forces greater than that for Sedentary Work and the worker sits most the time, the job is rated Light Work.

Medium Work Exerting up to 50 (22.7 kg) pounds of force occasionally, and/or up to 25 pounds (11.3 kg) of force frequently, and/or up to 10 pounds (4.5 kg) of forces constantly to move objects.

Heavy Work Exerting up to 100 pounds (45.4 kg) of force occasionally, and/or up to 50 pounds (22.7 kg) of force frequently, and/or in excess of 20 pounds (9.1 kg) of force constantly to move objects.

Very Heavy Work Exerting in excess of 100 pounds (45.4 kg) of force occasionally, and/or in excess of 50 pounds (22.7 kg) of force frequently, and/or in excess of 20 pounds (9.1 kg) of force constantly to move objects.

Job Classification

In most duration tables, five job classifications are displayed. These job classifications are based on the amount of physical effort required to perform the work. The classifications correspond to the Strength Factor classifications described in the United States Department of Labor's Dictionary of Occupational Titles. The following definitions are quoted directly from that publication.

Sedentary Work Exerting up to 10 pounds (4.5 kg) of force occasionally and/or a negligible amount of force frequently or constantly to lift, carry, push, pull, or otherwise move objects, including the human body. Sedentary work involves sitting most of the time, but may involve walking or standing for brief periods of time. Jobs are sedentary if walking and standing are required only occasionally and other sedentary criteria are met.

Light Work Exerting up to 20 pounds (9.1 kg) of force occasionally and/or up to 10 pounds (4.5 kg) of force frequently, and/or negligible amount of force constantly to move objects. Physical demand requirements are in excess of those for Sedentary Work. Light Work usually requires walking or standing to a significant degree. However, if the use of the arm and/or leg controls requires exertion of forces greater than that for Sedentary Work and the worker sits most the time, the job is rated Light Work.

Medium Work Exerting up to 50 (22.7 kg) pounds of force occasionally, and/or up to 25 pounds (11.3 kg) of force frequently, and/or up to 10 pounds (4.5 kg) of forces constantly to move objects.

Heavy Work Exerting up to 100 pounds (45.4 kg) of force occasionally, and/or up to 50 pounds (22.7 kg) of force frequently, and/or in excess of 20 pounds (9.1 kg) of force constantly to move objects.

Very Heavy Work Exerting in excess of 100 pounds (45.4 kg) of force occasionally, and/or in excess of 50 pounds (22.7 kg) of force frequently, and/or in excess of 20 pounds (9.1 kg) of force constantly to move objects.

Knee Replacement, Total


Related Terms

  • Knee Arthroplasty
  • Knee Joint Replacement
  • TKR

Specialists

  • Occupational Therapist
  • Orthopedic (Orthopaedic) Surgeon
  • Physiatrist (Physical Medicine and Rehabilitation Specialist)
  • Physical Therapist

Comorbid Conditions

Factors Influencing Duration

The individual’s motivation, ability to participate in rehabilitation, underlying medical conditions, type of implants, and work requirements will influence disability periods. Results are better for individuals with osteoarthritis than for individuals with rheumatoid arthritis, as rheumatoid patients usually have disease in multiple other joints. Procedure complications may increase length of disability periods. The underlying disease process may also determine the duration of disability.

The largest published study of return to work after knee replacement (Styron) found that 94% returned to work and that the mean time to return to work was 8.9 weeks. Factors predicting faster return to work were a sense of personal urgency to return to work, female sex, self-employment, higher mental health scores, higher physical function scores, and having a handicapped accessible workplace. Factors associated with a slower return to work were having less pre-operative pain, having a more physically demanding job, and receiving workers’ compensation.

Medical Codes

ICD-9-CM:
00.80 - Revision of Knee Replacement, Total (All Components); Replacement of Femoral, Tibial, and Patellar Components (All Components)
81.5 - Joint Replacement of Lower Extremity
81.54 - Total Knee Replacement; Bicompartmental; Tricompartmental; Unicompartmental (Hemijoint); Partial Knee Replacement
81.55 - Revision of Knee Replacement, Not Otherwise Specified

Overview

© Reed Group
Total knee replacement, or knee arthroplasty, is a surgical procedure in which the worn, damaged surfaces of the knee joint are replaced with metal and high-density plastic. Total knee replacement may result in general pain relief, deformity correction, and resumption of most normal activity.

The knee joint is the largest in the body. It contains three different bones that join together to form the knee: thigh bone (femur), shin bone (tibia), and kneecap (patella). The bones are lined with a tough, elastic tissue (articular cartilage) that cushions the bones and keeps them from rubbing together. Tough bands of tissue (ligaments) attached to the femur and tibia provide stability. Long thigh muscles provide knee strength. The capsule-like tissue lining (synovial membrane) creates a lubricant (synovial fluid) that nourishes the cartilage, which lacks blood supply. The kneecap protects the joint and anchors the tendons, while stabilizing the joint with additional support from the muscles.

Over time, cartilage lining the ends of the bones wears away due to aging, disease, or trauma. When the bones rub together, deformities and significant pain occur. As the joint wears, pieces of the cartilage and bone (debris) are shed. The debris then irritates the lining of the knee. For a time, this irritation can be treated conservatively through medication, physical therapy, crutches, canes, walkers, or minor surgical procedures. When these treatments lose their effectiveness and the deformities or pain become severe, reconstructive surgery is the recommended treatment.

The most common reason for knee replacement surgery is gradual degeneration of bone and joints (osteoarthritis). Rheumatoid arthritis (inflammation of the tissue around the joints) is a second cause of knee deterioration. A third cause for knee replacement is post-traumatic arthritis, a form of arthritis caused by knee injury. The pain from post-traumatic arthritis sometimes manifests many years after the injury.

Source: Medical Disability Advisor



Reason for Procedure

Pain relief from osteoarthritis, or rheumatoid arthritis, or injury to the knee, and restoration of knee function are the primary indications for total knee replacement. The decision to perform the procedure is not based on x-ray findings alone, which may, in fact, show extensive changes in the joint in individuals with minor symptoms and no functional problem. The two main determining criteria for surgery are pain and loss of function.

Until recently, knee replacement implants (prostheses) were affixed to the individual's bones with bone cement and were expected to function for 10 to 15 years. Because of this time constraint, knee arthroplasty was often delayed until the individual was older. Technology has recently advanced to allow biological fixation of implants to the bone (bony ingrowth). The latest addition to this fixation process is the use of hydroxyapatite (a substance normally found in bone that promotes bone growth) in the prosthesis. Studies of cementless designs at 10 to 12 years show a 95% rate of prosthesis survival (Palmer).

The currently accepted standard for total knee replacement in the US is a cemented femur and cemented tibial component (Palmer). A cemented patella button is also placed.

Today, individuals are enjoying prostheses that may now be in place for more than 20 years without revision.

Source: Medical Disability Advisor



How Procedure is Performed

A total knee replacement is usually performed with the individual under general anesthesia, but the procedure can be performed under regional anesthesia. The choice of which to use is a complicated issue and can be affected by the individual's comorbid medical conditions, if any. The choice of anesthesia is ultimately left up to the anesthesiologist with input from the surgeon. Postoperative care, especially pain control and prophylactic measures against blood clots (thrombosis), may differ following regional anesthesia (Crockarell).

The damaged joint surfaces are removed and replaced with a metal and polyethylene implant.

Source: Medical Disability Advisor



Prognosis

The short-term outlook for total knee replacement is excellent. Most individuals can stand the morning after surgery and begin to exercise that day. With the support of walkers or crutches, individuals can walk with confidence, climb stairs, and ride in a car by the time they leave the hospital. Physical therapists can instruct the individual in motion exercises that are the key to a good result; these activities should continue for several months. Some swelling, aching, and numbing are normal during this time. Many individuals are able to return to their normal activities within 6 weeks after surgery.

Cemented knee replacement components are immediately stable, and can withstand full weight bearing as soon as the patient tolerates it. Uncemented implants that depend on bony ingrowth to achieve stability require a period of partial weight bearing to allow for that ingrowth before the implant is stable, and before full weight bearing can safely occur.

Unlike hip replacements, dislocation of knee replacements is very rare, but ligamentous instability may be present after surgery if contracted ligaments required release, or if less than optimally sized or positioned components are present. Thus the surgeon will dictate the time at which partial weight bearing and the time at which full weight bearing may occur.

The long-term outlook after total knee replacement is also very good. One group of findings suggests that individuals with well-performed knee replacements can expect a 91% to 96% chance that their knee replacement will be in place and functioning at 14 to 15 years (Palmer). Individuals can influence these odds by maintaining an ideal weight, exercising, protecting against infection, and avoiding impact sports.

Source: Medical Disability Advisor



Rehabilitation

Ideally, rehabilitation begins before total knee replacement surgery by assessing the individual's medical and social condition to determine what might be required postoperatively for a successful outcome. The main goal of rehabilitation is to restore function by controlling pain, improving range of motion, and strengthening the knee (Ranawat). Pre-operative exercises to increase lower extremity muscle strength may be beneficial as surgical outcomes are better for those with stronger quadriceps (Kaplan). Also, pre-operative gait instruction may facilitate early postoperative ambulation. Anti-thrombolytics will be used during surgery and postoperatively throughout rehabilitation until mobility is restored (Kaplan).

Therapy will be directed by the surgeon, who knows what implant, what implant fixation (cemented or non-cemented), and what ligamentous stability is present.

Individuals who undergo total knee replacement may receive both physical and occupational therapy. Occupational therapy is helpful after surgery for instruction in self-care, equipment needs, and activities of daily living modifications. The occupational therapist should assess and train individuals in use of adaptive equipment such as an elevated commode, tub seat, reacher, long-handled shoe horn, and long-handled sponges, because these facilitate independence in activities of daily living in the postoperative period.

Physical therapy begins in the hospital and continues on an outpatient basis. The first goal of physical therapy is to control pain, initiate safe transfers and ambulation, and begin range of motion of the operative knee. Weight bearing status is determined by the physician's protocol, and individuals may use assistive devices as needed for independent ambulation on level and uneven surfaces. Cold packs may be used to decrease pain and swelling, with care used to protect the surgical wound.

The second goal of physical therapy emphasizes functional to full knee range of motion. Range of motion restrictions are determined by the surgical approach and type of prosthesis used. Common clinical practice includes use of continuous passive motion machines combined with physical therapy to facilitate recovery and knee motion. Continuous passive motion may decrease the length of hospital stay (Milne; Kaplan). Occasionally, manipulation under anesthesia to break internal scar tissue (adhesions) is performed if there is insufficient range of motion for functional mobility (Kaplan). Aquatic therapy may be useful for some individuals, especially if land exercises are not tolerated (Bartels).

Physical therapy's final goal is to increase knee and hip strength, normalize gait, and increase functional abilities. Because many individuals experience an abnormal (antalgic) gait or limb weakness preoperatively, continued gait training and strengthening exercises may take longer than anticipated. All weight-bearing and strengthening exercises should be continued under the direct guidance of the surgeon to protect the integrity of the knee prosthesis. Therapy may need to focus on specific muscle groups depending on the postoperative issues, which can include joint contracture, quadriceps or gastrocnemius weakness, and foot malalignment. Therapies may include braces, shoe lifts, and foot orthoses (Ulrich).

Besides undergoing supervised rehabilitation, the individual should be instructed in a home exercise program to be practiced daily, and continued independently under physician supervision after the completion of rehabilitation (Fitzgerald; Roos). Most patients can return to medium work categories; however, high-impact sports are usually advised against (Kaplan).

FREQUENCY OF REHABILITATION VISITS
Surgical
SpecialistKnee Replacement, Total
Physical or Occupational TherapistUp to 24 visits within 12 weeks
The table above represents a range of the usual acceptable number of visits for uncomplicated cases. It provides a framework based on the duration of tissue healing time and standard clinical practice.

Source: Medical Disability Advisor



Complications

Although blood clots of the leg veins (thrombophlebitis) are not rare, death from this malady has been almost totally eliminated with use of support stockings, knee motion machines, and blood thinning medications (such as low-dose warfarin, low molecular weight heparin, and aspirin). Risk factors for developing thrombophlebitis include a previous history of thromboembolism, heart attack (myocardial infarction), prolonged immobility, and estrogen use. Individuals without a previous history of thromboembolism may receive drugs to guard against blood clots (chemical prophylaxis) for up to 2 weeks after surgery. Individuals with a history of thromboembolism may receive chemical prophylaxis for up to 6 weeks after surgery (Crockarell).

Blood clots of the leg arteries (arterial thrombosis) occur in only 0.03% to 0.17% of cases but are devastating and can lead to amputation. They are more likely to occur in individuals with significant vascular disease; those individuals should seek a vascular surgery consultation prior to knee replacement (Palmer). Methods of detecting postoperative blood clots include x-ray (venography) with contrast media, and duplex ultrasound.

Infection in a total knee replacement is relatively rare but can be disastrous. Its incidence ranges from 2.6% to 1.6% of cases, depending on the study consulted (Crockarell). Some infections cause symptoms and problems early after surgery, while other infections develop and present even years later, perhaps due to bacteria in the blood stream lodging about the "foreign body" or joint implant. Symptoms of infection include swelling (edema), redness (erythema), tenderness, and painful range of motion. Sudden (acute) onset of pain in a previously pain-free and well-functioning knee replacement may also accompany the onset of infection (Crockarell).

Like other complications, an infection is better avoided than treated. In increasing numbers of hospitals, all joint replacement surgery is performed in special laminar flow operating rooms designed to keep out dust, germs, and unclean air. The surgeons also wear full-body "space suits." These full-body suits, worn over normal scrubs, allow the surgeons to move and breathe without spreading germs, because an exhaust tube carries contaminated, dirty air out of the room. An infection rate of less than 0.5% in joint replacement surgeries is achievable in some hospitals. With proactive use of deterrents, such as preventive (prophylactic) antibiotics, ultraviolet light, and meticulous and expeditious surgery, the overall occurrence of postoperative infections is 1% (Palmer). To prevent the late infections, patients who have had a knee replacement are advised to see a physician and, usually, to be treated early on with antibiotics for significant infections (e.g. urinary tract infection). Similarly they are advised to take prophylactic antibiotics before medical procedures known to cause transient bacteria in the bloodstream (bacteremia), procedures including cleaning the teeth by a dental hygienist and colonoscopy.

Formation of obstructive scar tissue (arthrofibrosis) follows surgery in approximately 1% of cases (Palmer). Initially treated with conservative measures, such as anti-inflammatory medication and physical therapy, it can also be treated more aggressively with continuous passive motion (CPM), and follow-up (revision) surgery.

Instability of the replaced knee is a cause of 10% to 22% of the revision surgery (2nd knee replacement of the same knee). This instability is usually due to mechanical factors not fully addressed at the time of the initial surgery. Individuals with unstable knees after knee replacement require either revision surgery, or safeguards such as limited ambulation, bracing, and crutches (Parratte).

Other long-term complications, such as wear, stiffness, or loosening of prosthetic parts, relate as much to the individual's behavior as to surgical success. However, knees with prosthetic-part problems can usually be improved through revision surgery.

Source: Medical Disability Advisor



Ability to Work (Return to Work Considerations)

Sedentary work and light work can be performed sooner if done sitting. Work restrictions early after surgery, before full recovery, typically include limited use of the knee, including avoidance of kneeling, squatting, twisting, jumping, climbing, prolonged standing, and walking. Prolonged sitting is also to be avoided because of potential for increased swelling of the lower extremity. Restrictions may become permanent.

Use of prescribed medications will require review of drug policies. Work release time for rehabilitation will be required.

Risk: The long term problems are component wear (wearing out the metal and plastic parts) and loosening. There is no consensus statement on what work activities should be, or should not be, recommended after knee replacement surgery. The best published analogy is the data on consensus among surgeons on recommendations for sports participation.

A published study shows that when surveyed, joint replacement surgeons are over time relaxing their recommended sports restrictions, as sports related stresses have been less of factor in late loosening or wear than anticipated (Healy).

According to the study, the 2005 survey of Knee Society surgeons found there was consensus that bowling, bicycling, dancing, golf, swimming, canoeing, and walking/hiking were safe. The surgeons would “allow with prior experience” rowing, cross-country skiing, downhill skiing, doubles tennis, and horseback riding.

The surgeons could not reach consensus on fencing, roller skating, weight lifting, baseball, gymnastics, handball, hockey, rock climbing, squash/racquetball, singles tennis, and weight machines.

The surgeons consensus was clearly to not recommend basketball, football, jogging, soccer, and volleyball.

Thus sports that involve jumping and landing from a height, or twisting on the limb were felt to be particularly risky for the long term health of the knee replacement.

Capacity: In the published study on return to work by Styron in which 93% of patients returned to their pre-operative job, 27% of knee replacement patients self-rated their jobs as requiring low demand, 46% as moderate, and 27% as high physical demand.

Tolerance: Knee replacement patients in general have somewhat more joint area permanent pain than do hip replacement patients, but as noted most do choose to return to work. For further information on risk, capacity, and tolerance after knee replacement, please refer to "Work Ability and Return to Work," page 245.

Accommodations: Work accommodations include the use of assistive devices for ambulation, frequent rest periods, and avoidance of at-risk activities. Accommodations are conducive to a more rapid return to full-time work. For more information, please refer to "Work Ability and Return to Work," page 232.

Source: Medical Disability Advisor



Maximum Medical Improvement

6 to 12 months after surgery if clinical findings remain stable on 2 consequent visits

Source: Medical Disability Advisor



References

Cited

Bartels, E., et al., eds. "Acquatic Exercise for the Treatment of Knee and Hip Osteoarthritis." Cochrane Database of Systematic Reviews 4 (2007): NA.

Crockarell, John R., and James L. Guyton. "Arthroplasty of the Knee." Campbell's Operative Orthopaedics. Eds. S. Terry Canale and James H. Beaty. 11th ed. Philadelphia: Mosby Elsevier, 2008.

Fitzgerald, J. D., et al. "Patient Quality of Life During the 12 Months Following Joint Replacement." Arthritis and Rheumatism 51 1 (2004): 100-109. National Center for Biotechnology Information. National Library of Medicine. 4 Oct. 2008 <PMID: 14872462>.

Healy, W. L. , et al. "Athletic Activity After Total Joint Arthroplasty." Journal of Bone and Joint Surgery 90 (10) (2008): 2245-2252. National Center for Biotechnology Information. National Library of Medicine. 12 Dec. 2012 <PMID: 18829924>.

Kaplan, Robert J. "Chapter 71 - Total Knee Replacment." Essentials of Physical Medicine and Rehabilitation. Eds. Walter R. Frontera, Julie K. Silver, and Thomas Rizzo. 2nd ed. Philadelphia: Saunders, Elsevier, 2008.

Milne, S., et al. "Continuous Passive Motion Following Total Knee Arthroplasty." Cochrane Database of Systematic Reviews 2 (2003): CD004260. National Center for Biotechnology Information. National Library of Medicine. 4 Oct. 2008 <PMID: 12804511>.

Palmer, Simon H., and Mervyn J. Cross. "Total Knee Arthroplasty." eMedicine. Eds. T. M. DeBerardino, et al. 30 Jan. 2004. Medscape. 18 Feb. 2009 <http://www.emedicine.com/orthoped/topic347.htm>.>.

Parratte, Sebastien, and Mark W. Pagnano. "Instability After Total Knee Arthroplasty." Journal of Bone and Joint Surgery 90 (2008): 184-194. 1 Jan. 2008. 12 Dec. 2012 <http://jbjs.org/article.aspx?articleid=28421>.

Ranawat, C. S., A. S. Ranawat, and A. Mehta. "Total Knee Arthroplasty Rehabilitation Protocol: What Makes the Difference?" Journal of Arthroplasty 18 3 Suppl 1 (2003): 27-30. National Center for Biotechnology Information. National Library of Medicine. 4 Oct. 2008 <PMID: 12730924>.

Roos, E. M. "Effectiveness and Practice Variation of Rehabilitation after Joint Replacement." Current Opinion in Rheumatology 15 2 (2003): 160-162. National Center for Biotechnology Information. National Library of Medicine. 4 Oct. 2008 <PMID: 12598806>.

Styron, J. F. , et al. "Preoperative predictors of returning to work following primary total knee arthroplasty." Journal of Bone and Joint Surgery 93 (1) (2011): 2-10. National Center for Biotechnology Information. National Library of Medicine. 12 Dec. 2012 <PMID: 21209263>.

Talmage, J. B. , J. M. Melhorn, and M. H. Hyman, eds. Work Ability and Return to Work, AMA Guides to the Evaluation of. Second ed. Chicago: AMA Press, 2011.

Ulrich, S. "Focused Rehabilitation Treatment of Poorly Functioning Total Knee Arthoplasties." Clinical Orthopaedics and Related Research 464 (2007): 138-145.

Source: Medical Disability Advisor






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