The purpose of this article is to present the challenges of dealing with the morbidly obese patient suffering from degenerative knee arthrosis. Surgery should only be undertaken when conservative management has failed and comorbidities optimized. Owing to risks related to comorbidities, diligence is necessary before proceeding with surgery to lessen the chance of complications—especially infection. Evaluation, conservative treatments, preoperative optimization, and surgical options are discussed.
Obesity is directly linked to the development of osteoarthritis of the knee. Many of these patients will present themselves to the treating orthopedic surgeon with severe pain and disability. The morbidly obese patient may be more severely affected by their arthrosis due to its effect on their mobility and quality of life. The goal of the treating orthopedic surgeon should be to maintain a patient’s mobility, improve or maintain quality of life, and provide pain relief while minimizing risk and complications of treatment.
The purpose of this article is to present the challenges that one faces when dealing with the morbidly obese patient population suffering from degenerative knee arthrosis and provide guidance for treatment options.
The number of patients requiring total knee arthroplasty (TKA) over the next 10 to 20 years is expected to exponentially increase. Many of these patients with degenerative arthritis of the knee suffer from obesity. Bourne and colleagues have shown that patients with morbid obesity (body mass index [BMI] >40) have a 32 times greater likelihood than those who are normal weight (BMI <25) of requiring a total knee replacement. A linear relationship has been established with decreasing levels of glycosaminoglycans (and presumably poorer health of articular cartilage) with increasing BMI. Additionally patients who are morbidly obese present sooner for intervention, often presenting on the order of a decade younger than patients of normal weight. The treating orthopedic surgeon therefore will continue to deal with this complex patient subgroup and their unique challenges. Several studies have investigated the effect of obesity on the results of total knee arthroplasty. Depending on the parameters of the study and the level of obesity variable results have been reported. Whereas many patients will be obese (BMI >30) and fare well with surgical intervention, the patient subset that truly challenges the surgeon is the morbidly obese (BMI >40). Many surgeons will choose not to offer patients of this size treatment owing to a perceived increased risk of complications as well as difficulty in performing surgery.
The evaluation of a patient who is morbidly obese with knee arthrosis begins with a thorough history and physical examination. Important comorbidities to define include coronary artery disease, diabetes mellitus, and obstructive sleep apnea syndrome (OSAS). A history of venous thromboembolism (VTE), whether deep vein thrombosis or pulmonary embolus, should be noted. It is not uncommon for this patient population to suffer from chronic venous stasis (sometimes with ulcers) or lymphedema. On physical examination it is important to note the overall size and shape of the extremity. Patients may have a relatively normal-appearing leg and display truncal obesity, while others will have a significant amount of adiposity throughout their extremity. The patient with a normal-appearing leg does not provide as much of a surgical challenge. Range of motion should be measured paying careful attention to possible flexion contractures as well as limitations of knee flexion. Patients with a large amount of thigh and calf adiposity will have soft tissue constraints to their knee flexion. This constraint or thigh-calf impingement is important to note, as this will limit their flexion. Also if one cannot flex the knee to at least 60 degrees in the office setting (limitation due to soft tissue impingement), one will have great difficulty placing the tibial component at the time of surgery.
As in all patients with degenerative joint disease conservative treatment should be optimized before considering surgical options. The patient’s obesity should be frankly discussed outlining its effect on their arthrosis and mobility and the challenges they face if and when surgical intervention is entertained. A program of weight loss should be recommended and a referral to a dietician or nutrition consultant should be offered. Often the morbidly obese patient has difficulty with a weight loss program because of knee arthrosis and its limitations on their mobility. Some of these patients may be candidates for an evaluation by a surgeon specializing in gastric surgery (gastric bypass, gastric sleeve). A study at the Mayo Clinic specifically looked into the effect of bariatric surgery before undergoing total joint arthroplasty. Although the sample size was small, 20 patients underwent bariatric surgery and went on to have a successful joint replacement. The patients’ BMI reduced from an average of 49 to 29 and there was an average wait of 23 months from time of bariatric surgery to joint replacement. This wait time is necessary for weight loss and to return to a noncatabolic state so they can heal their wound. If patients are taken for surgery before this time they are at risk for wound breakdown and infection from a relatively malnourished state. For a patient with end-stage arthrosis with issues with mobility and pain, this a very long time to wait for surgery.
For patients with extremely large limbs in which the soft tissue impingement will not allow access to the joint or there is such a large abdominal panniculus that the knee cannot be accessed, surgery should not be entertained. These patients must lose weight and often will require bariatric intervention. Unfortunately, bariatric surgery is not without its own risks and not all patients will be a candidate or have a successful result of this intervention. In addition, the surgery is often considered elective by insurance plans and patients will have difficulty getting coverage. The orthopedic surgeon must be the patient’s advocate when this occurs and be willing to support the patient with documentation supporting the impact of their obesity on their disease as well as the benefits of bariatric surgery before joint arthroplasty.
In addition to weight loss, physical therapy for strength and flexibility, as well as instruction in a safe cardiovascular-focused exercise program, should be attempted. Aerobic programs that minimize impact loading of the joint should be encouraged. The judicious use of corticosteroid injections or viscosupplementation can help the patient to buy time and possibly work on weight loss and mobility before surgical intervention is considered. Bracing has been shown to be helpful in the treatment of knee arthritis. Often the obese and particularly the morbidly obese patients have a limb that is somewhat cone shaped and therefore ill-suited for brace fitting. A lateral or medial heel wedge can be of use in the varus or valgus knee, respectively.
While managing the patient’s disease process conservatively, comorbidities should be optimized before surgical intervention (regardless of the type of surgery planned). Patients with coronary artery disease will require evaluation and clearance by their primary care physician or cardiologist. New cardiac disease may be discovered requiring intervention with stenting or bypass before an elective knee replacement. All patients should have a hemoglobin A1C performed to ensure their blood sugar is well controlled and to ensure they do not have unrecognized diabetes mellitus. Patients should have a value less than 8 before undergoing surgery. A recent review of a national database has shown that patients with poorly controlled or uncontrolled diabetes have higher risk of stroke, urinary tract infection, ileus, postoperative hemorrhage, transfusion, wound infection, and death. Patients should be evaluated for the presence of OSAS as many undergoing total joint arthroplasty will suffer from undiagnosed OSAS at time of surgery. Finally, the patient’s limb should also be optimized for surgery. Chronic lymphedema should be minimized with appropriate lymphedema care, often with the use of custom compression stockings and a referral to a lymphedema nurse or clinic.
By undertaking this approach preoperatively, the risks of complications are minimized and chance of success are improved. This approach commits the patient to take an active role in the process before a major surgical procedure in which their size and comorbidities significantly effect the outcome. Surgery is not scheduled until these preoperative requirements have been met.
Surgical options for knee arthrosis include arthroscopy, osteotomy, and arthroplasty. Knee arthroscopy with debridement and lavage of the joint is not advocated in this patient population and should be avoided. An upper tibial osteotomy for isolated medial compartment arthrosis has been shown to provide reasonable pain relief and maintenance of function for many patients Unfortunately obesity has been shown to be a major predictor of failure for this intervention. However, a corrective osteotomy may play a role in someone with isolated disease who is young and a laborer. Finally, arthroplasty may be offered for end-stage arthrosis of the knee. Unicompartmental knee arthroplasty (UKA) can be of some benefit in the patient with single-compartment involvement, but most patients will require total knee replacement.
Before proceeding to surgery it is important to have proper surgical equipment and implants available. A leg holder that attaches to the operating table is very helpful ( Fig. 1 ). Owing to the severe deformity of some of these knees, collateral ligament insufficiency is common as well as major bone loss or voids. Semiconstrained implants should be readily available, as well as stems, augments, and wedges. A surgical table that can hold a patient greater than 300 pounds is necessary, as well as a bariatric bed for postoperative care.
Surgical process (total knee arthroplasty)
Two surgical assistants can be helpful for limb positioning and retraction. There is no place for minimally invasive knee surgery in this patient population. An attempt is made to exsanguinate the limb and use a standard tourniquet. If a venous tourniquet results, it is best to proceed without and only use the tourniquet for cementation of implants. Large incisions are necessary for adequate exposure and for placing retractors to protect soft tissues ( Fig. 2 ). Patellar eversion will often not be possible because of the thickness of the soft tissues and, therefore, the patella should be subluxated. The sequence of the bony cuts depends on surgeon preference. There is controversy on whether a patella should be resurfaced in these patients. Obese patients have been noted to have more patellar pain whether the patella has been resurfaced or not. Healy and colleagues found that obese patients were more likely to have loosening of their patellar component. If the decision is made to resurface the patella it may or may not be possible to evert the patella because of the large soft tissue envelope. If the patella cannot be reliably everted (and resurfacing is planned), the femoral and tibial cuts can be made first. The patella cut can then be made with the knee in extension. The tibial cut can be difficult to perform owing to an inability to flex the knee. If one makes the distal femoral cut first, it “opens” up the knee, allowing for an easier exposure for the tibial cut. The accuracy of the tibial cut, likewise, can be compromised from the large soft tissue envelope. A traditional extramedullary alignment guide can be used, but standard bony landmarks may not be easily identified. Consideration for an intramedullary alignment guide or computer-assisted navigation may be helpful and eliminate the chance of a poor tibial cut. Lozano and colleagues investigated the use of an intra- versus extramedullary tibial guide as it relates to accuracy of implant position. They did not note any difference in alignment but did note a shorter operative time when using an intramedullary tibial guide in the morbidly obese patient. They concluded that the intramedullary guide allowed for a decreased operative time because of the relative ease of tibial component positioning.