Total Knee Arthroplasty Case File

Total Knee Arthroplasty Case File

Eugene C. Toy, MD, Andrew J. Rosenbaum, MD, Timothy T. Roberts, MD, Joshua S. Dines, MD

CASE 39

A 73-year-old man is seen in the outpatient clinic with complaints of right knee pain, 6 months in duration. He denies recent trauma and is otherwise without significant medical problems. He states that over the past several years, he has had a progressive “dull ache” in his knee. The near constant pain wakes him at least 3 times per week. Last month, he started using a golf cart instead of walking between holes and now borrows a friend’s cane when walking long distances. He states that his right leg feels “unstable.” He denies fevers, weight loss, and recent illnesses, and he takes only acetaminophen as needed for pain relief. Family history is unremarkable. On physical exam of his right knee, there is no obvious effusion, erythema, or drainage. He has joint line tenderness, most prominent on the lateral aspect of his knee, and he exhibits a slight genu valgum. There is crepitus with range of motion. A 5-degree flexion contracture is noted when he is fully extended, and he can only flex the knee to 100 degrees. He is neurovascularly and ligamentously intact. He has brought an x-ray of his right knee, taken last month at his primary care doctor’s office ( Figure 39–1 ).

► What is the most likely diagnosis?

► What are the next steps in the workup for this condition?

► What are the next steps in the management of this condition?

Figure 39–1. AP radiograph of the right knee.

ANSWER TO CASE 39:

Total Knee Arthroplasty                   

Summary: A relatively healthy 73-year-old man presents with progressive right knee pain. His pain is severe enough that it has caused him to change his daily activities, has caused him to start using a cane, and wakes him at night. Exam reveals crepitus, lateral joint line tenderness, and a limited range of motion. He denies a history of traumatic injury and exhibits neither signs nor symptoms of infection.

• Most likely diagnosis: Osteoarthritis (degenerative joint disease) of the right knee.
• Next diagnostic test: Obtain plain radiographs of bilateral knees, including weightbearing posteroanterior and lateral views in approximately 45 degrees of flexion, a tunnel or notch view, and Merchant (sunrise) views of the patellofemoral joint.
• Next step in therapy: Conservative therapy including nonsteroidal antiinflammatory drugs (NSAIDs; ibuprofen, naproxen, diclofenac, or selective COX-2 inhibitors); physical therapy is sometimes recommended to help strengthen the muscles around the knee, including the hamstrings, gastrocsoleus complex, and quadriceps. Assistive devices such as canes, crutches, and walkers can be used as well to offset some of the joint reactive forces stressing the knee.

ANALYSIS

Objectives

1. Recognize the presentation of DJD of the knee and understand the salient aspects of patient history necessary to guide treatment.
2. Develop a standard treatment algorithm for DJD of the knee.
3. Understand the surgical options available for the treatment of knee arthritis.
4. Understand common potential complications after total knee arthroplasty.

Considerations

There are several differential diagnoses that must be considered in any patient with nonacute traumatic joint pain. Common etiologies include osteoarthritis, also referred to as degenerative joint disease (DJD), inflammatory arthritis, osteonecrosis, and posttraumatic arthritis. Given this patient’s atraumatic history and his lack of fevers, joint erythema, or other systemic inflammatory symptomatology, osteoarthritis is the most likely diagnosis. Specifics for workup of these alternate diagnoses are considered later in this chapter. This 73-year-old male presents with signs, symptoms, and radiographic findings consistent with right knee osteoarthritis, specifically the lateral compartment. In a patient who has had no previous intervention to address his symptoms, the first priority is pain relief. There are many options for pain relief, including acetaminophen, NSAIDs, corticosteroid injections, and narcotics. Ideally, narcotics are reserved for short-term relief in individuals with intractable pain, refractory to all other modalities. Following analgesia recommendations, attempts should be made to address pathologic changes in the mechanics of knee. The available treatment options are bracing, physical therapy, and assistive devices for ambulation. Other conservative modalities include intraarticular viscosupplementation with hyaluronic acid analogues or derivatives (Synvisc ®) and corticosteroid injections.

APPROACH TO:

Osteoarthritis of the Knee                              

DEFINITIONS

ARTHROPLASTY: The surgical replacement and reconstruction of a functional joint.

OSTEONECROSIS: The death of bone tissue secondary to impaired or disrupted blood supply, often as the result of trauma or disease. Osteonecrosis is marked by severe, localized pain and by structurally weakened bone that may flatten and collapse. This process is also known as aseptic or avascular necrosis (AVN).

POLYMETHYLMETHACRYLATE (PMMA): A synthetic polymer used commonly as cement for the implantation of knee and hip prostheses

CLINICAL APPROACH

Differential Diagnosis

As discussed, there are several causes of knee pain that must be considered before the diagnosis of osteoarthritis is made. Like DJD, inflammatory arthropathies such as gout, chronic septic arthritis, and rheumatologic processes may present with insidious, atraumatic knee pain. Several conditions in this wide spectrum of inflammatory diseases are discussed in greater depth elsewhere in this text. As a general rule, however, if there is suspicion for underlying infectious, rheumatologic, or crystalline process, further workup should be performed and includes obtaining blood and synovial fluid samples. Although the specific laboratory tests to be ordered are chosen on a case-by-case basis, general studies typically always obtained include a complete blood count (CBC), erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), and synovial fluid gram stain, crystal analysis, cell count and aerobic and anaerobic cultures.

    Avascular necrosis of the knee can also be a cause of this gentleman’s pain. There are several etiologies of this condition. First, spontaneous osteonecrosis of the knee, an idiopathic condition that commonly affects women older than 55 years, is typically unilateral and affects only 1 condyle. The other causes include excessive alcohol use, sickle cell anemia, trauma, or corticosteroid use and usually affect patients younger than 45 years. Both conditions may present with slow-onset knee pain, sometimes worst at night, and typically affect the medial compartment. As with DJD, these conditions may respond to arthroplasty when conservative treatments fail.

    Finally, posttraumatic arthritis is an accelerated degenerative process of the knee that results from previous damage to the knee’s articular surfaces. It is managed in much the same way as DJD, with conservative measures first and arthroplasty for end-stage disease.

TREATMENT OF OSTEOARTHRITIS

Nonoperative (Conservative) Treatment

Despite the surgical focus of this text, it must be stressed that the initial management of DJD is almost always nonoperative. The conservative interventions described previously are usually successful in attenuating patients’ DJD symptoms, at least in the short term. How long, exactly, DJD can be managed nonoperatively varies greatly between individuals. Several studies show significant short-term pain relief and functional improvement using corticosteroid injections and viscosupplementation, but results, again, are unpredictable.

    It is important to recognize that none of these aforementioned treatments are a cure for DJD. Therefore, when discussing the natural history of osteoarthritis with patients, it is important to explain that it will progress as long as they partake in weightbearing activities. Because the lifespan of a prosthetic joint is finite —and most prone to wear in younger, active individuals—arthroplasty interventions are generally delayed until the patient can no longer tolerate conservative measures.

Operative Treatment

Once a patient has failed all conservative therapy, surgery may be indicated. There are several surgical options available and include total knee arthroplasty, osteotomies, arthroscopic interventions, and unicompartmental arthroplasty.

Arthroscopy and Osteotomies

Arthroscopic interventions are reserved for young patients with mild, localized disease in the setting of mechanical symptoms (ie, joint clicking, locking, or instability). Arthroscopic treatments are guided at debridement, chondroplasty, and removal of chondral loose bodies commonly found in osteoarthritic disease. Arthroscopy also plays a diagnostic role in determining the severity of arthritic disease, as some patients with advanced, debilitating arthritis may have deceptively benignappearing x-rays.

    Another surgical option that does not involve prostheses are osteotomies, or wedge-shaped bone cuts, that alter the alignment of the knee joint. When patients present with disproportionately worn compartments, the alignment of the knee can be altered to divert weightbearing pressures from the affected side. Ideal patients for this procedure are younger than 50 years, with isolated unicompartmental disease and a normal range of motion. They should also have competent ligaments, active flexion beyond 90 degrees, and minimal evidence of a flexion contracture. A varus or valgus osteotomy can be used to offload the lateral or medial compartments, respectively. In general, varus-producing osteotomies are performed on the femur, and valgus-producing osteotomies are performed on the tibia.

Arthroplasty

Before discussing total joint arthroplasty, it is worthy to mention the increasing popularity of unicompartmental knee arthroplasty (UKA). This procedure is restricted to patients with unicompartmental noninflammatory osteoarthritis, deformities of less than 10 degrees (varus or valgus), and an intact anterior cruciate ligament. Medial compartment replacement is by far the most commonly performed UKA, as the prevalence of medial-sided arthritis far exceeds that of isolated lateral disease. In the correct patient population, advantages of UKA over total joint replacement include faster recovery, less rehabilitation, and smaller incisions.

    The most commonly performed procedure for knee arthritis in the United States is total knee arthroplasty (TKA). Typically, patients are older than 50 years, have disease in all 3 compartments, and have experienced changes in their activity levels secondary to pain. TKA involves a resurfacing procedure of the distal femur and proximal tibia and typically the undersurface of the patella. The goals are to reconstruct a stable knee with a functional range of motion, to restore knee alignment and smooth patella tracking, and to relieve pain. There are a great variety of TKA prosthetic designs whose nuances extend beyond the scope of this discussion. Most modern TKA systems, however, share these same goals, and indeed there is no definitive evidence that supports the superiority of one modern TKA system over another.

Complications

The common complications that are associated with TKA include infection, deep vein thrombosis, aseptic loosening, osteolysis, periprosthetic fracture, failure of the extensor mechanism, and postoperative stiffness or arthrofibrosis.

    Infections in an artificial joint, although rare (< 1%), are one of the most devastating complications of TKA. Periprosthetic joint infections (PJIs) can present in a multitude of ways. While some patients present with acute pain, swelling, and redness, others have a more insidious onset of symptoms. In general, any patient with a TKA and new-onset pain should be evaluated for infection, amongst other causes of pain. Diagnosis can be challenging and relies on physical exam findings, laboratory studies (ESR, CRP), and synovial fluid analysis. Although a positive gram stain and/or cultures make the diagnosis easy, many times these tests are negative. When this occurs, many believe that a synovial fluid white blood cell count of greater than 1100 cells/mL and a polymorphonuclear level of greater than 64% is consistent with a PJI, regardless of gram stain and culture findings. The management of PJI is challenging. In general, acute infections (defined as those of less than 3 weeks duration) are treated with a surgical irrigation and debridement and polyethylene exchange. Unfortunately, a PJI of greater than 3 weeks duration requires a complete explantation of the total knee system, placement of an antibiotic-eluting spacer where the total knee was, and 4 to 6 weeks of intravenous antibiotics. After this, a replantation of the total knee may be performed.

    Finally, patients undergoing total joint replacements are notoriously at risk for deep vein thrombosis (DVT). DVTs occur in up to 5% to 15% of patients undergoing arthroplasty and are considered the most common complication of TKA. Most surgeons and hospitals go to considerable lengths to reduce DVT rates, including frequent mobilization postoperatively, placement of sequential compression stockings and compression stockings, and the use of anticoagulation medications such as postoperative heparin, low-molecular-weight heparin, warfarin, aspirin, and several other drugs. Unfortunately, despite significant efforts, the rates of DVT in arthroplasty patients remain relatively high.

COMPREHENSION QUESTIONS

39.1 A 55-year-old construction worker presents to your office with complaints of right knee pain, several years in duration. Examination of the right knee is notable for a slight flexion contraction, painful range of motion (ROM), and palpable crepitus during ROM. The left knee by comparison has a greater, albeit limited ROM that is not painful. Standing radiographs show significant medial and lateral compartmental joint space narrowing with sclerotic and osteophytic changes in bilateral knees. He has not yet been treated for his condition. What is the best next step in the management of this patient?

A. Right total knee arthroplasty

B. Right knee medial unicompartmental arthroplasty

C. Right knee lateral unicompartmental arthroplasty

D. NSAIDs and acetaminophen, recommend physical therapy

E. Bilateral knee total arthroplasties

39.2 A 52-year-old woman with a history of rheumatoid arthritis is referred to your clinic with right knee pain. For the past 3 years, her rheumatoid arthritis has been well controlled with a disease-modifying anti-rheumatic drug (DMARD) regimen; however, she continues to have persistent knee pain. On exam you note a comparatively varus right knee with a painful and limited ROM. She is ligamentously intact and is tender to palpation only on the anteromedial aspect of her knee. Radiographs show significant narrowing of the right knee medial compartment, with relative sparing of the patellofemoral and lateral compartments. There are sclerotic and cystic changes on the medial aspect of her knee only. Having failed nonoperative interventions, which of the following is the most appropriate surgical intervention for this patient?

A. Right total knee arthroplasty

B. Right knee lateral unicompartmental arthroplasty

C. Right knee medial unicompartmental arthroplasty

D. Right knee corrective osteotomy

39.3 A 73-year-old woman is on postoperative day 3 for a total knee replacement. The procedure was without complication, but as a result of postoperative pain, she has been slow to mobilize. You are called to evaluate the patient for increasing tachycardia (heart rate 115 beats/minute) and sudden-onset tachypnea (respiratory rate 30 breaths/min). Blood pressure and temperature are within normal limits. She has received a dose of intravenous morphine 30 minutes before your evaluation and currently states her pain is “only a 3/10.” Electrocardiogram, cardiac enzymes, and chest x-ray are obtained and demonstrate no acute changes or abnormalities. She is a smoker and has a history of breast cancer. Which of the following is the most likely diagnosis?

A. Acute myocardial infarction

B. Pneumonia

C. Pulmonary embolism

D. Fat embolism

E. Blood loss anemia with secondary hypovolemia

ANSWERS

39.1 D. Nonoperative measures are almost always trialed before arthroplasty is performed for patients with DJD. Although this patient has radiographic degenerative changes, he is asymptomatic on the left, and thus bilateral TKA would be contraindicated. The presence of bilateral compartment disease is a contraindication to unicompartmental arthroplasty should the patient fail conservative treatment.

39.2 A. Although this patient’s arthritis is confined to the medial space, the presence of rheumatoid arthritis is a contraindication to unicompartmental replacement. Corrective osteotomies may correct the patient’s varus alignment but do nothing to address the underlying joint pathology.

39.3 C. Pulmonary emboli (PE) are an unfortunate and not too uncommon complication of knee or hip arthroplasty. Most occur second to embolized DVTs, which result from immobilizations, surgical trauma, insufficient postoperative thrombus prophylaxis, and underlying risk factors, such as this patient’s history of tobacco use and malignancy. The next step should be a CT angiogram of the chest (the diagnostic gold standard) or a ventilation perfusion scan. Although pneumonia and acute myocardial infarction may account for her symptoms, they are less likely given the normal chest x-ray and cardiac enzymes/electrocardiogram changes, respectively. Blood loss anemia with subsequent hypovolemic shock is also common; however, it is less likely given her normal blood pressure. Fat embolism may occur in the setting of joint replacement procedures, but more often occurs intraoperatively or immediately postoperatively with placement of intramedullary components. Remember that PEs rarely cause electrocardiogram changes and are not typically diagnosable on regular chest x-rays.

    CLINICAL PEARLS    

► Standard radiographic imaging of patient with DJD of the knee includes standing AP radiographs of bilateral knees, extension- and flexion-lateral radiographs of the affected knee, and a Merchant-view radiograph. ► First-line therapies for DJD of the knee are almost always nonoperative in nature. They include interventions such as physical therapy, nonsteroidal anti-inflammatories, and intraarticular corticosteroid injections. ► Total knee arthroplasty is the treatment of choice for end-stage osteoarthritis in patients who have failed conservative measures. ► A synovial fluid white blood cell count of greater than 1100 cells/mL and a polymorphonuclear level of greater than 64% is concerning for a PJI.

REFERENCES

Flynn JM, ed. Knee reconstruction and replacement. In: Orthopaedic Knowledge Update: Ten . Rosemont, IL: American Academy of Orthopaedic Surgeons; 2011:469-478. 

Miller MD, ed. Adult reconstruction. In: Review of Orthopaedics . 5th ed. Philadelphia: Saunders Elsevier; 2008: 306-358.

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