Total knee arthroplasty (TKA) for obese patient entails more preoperative comorbidities and complications, and shorter longevity. This article is a retrospective review comparing longevity of the constrained implant with a standard prosthesis. Patient-specific data, Knee Society Scores, complications, and revisions were recorded and compared. No statistical differences were found. The constrained condylar knee for obese patients improves the intramedullary alignment of the prosthesis and supports the surrounding soft tissues. The clinical results are similar to a standard implant in the nonobese with similar longevity at midterm follow-up.
Key points
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Total knee arthroplasty for the obese patient is associated with a greater number of preoperative comorbidities, more perioperative complications, and a shorter longevity than the patient with a normal body mass index.
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The purpose of this retrospective study is to determine if the clinical result and longevity of the constrained implant in the obese patient is the same as that of the normal weight patient with a standard prosthesis.
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The constrained condylar knee for obese patients facilitates the operative procedure by improving the intramedullary alignment of the prosthesis and supporting the surrounding soft tissues. The clinical results are similar to standard implants in the nonobese with similar longevity at midterm follow-up.
Introduction
According to the World Health Organization (WHO), obesity is a global epidemic and incidence is expected to surpass undernutrition. In the United States, 1 in 3 adults are obese. Furthermore, obesity is an independently recognized modifiable risk factor for the development and progression of osteoarthritis (OA). Compared with normal weight patients, obese patients have a 3-fold to 5-fold increased risk of developing knee OA. It is thought that increased body mass results in increased forces across a joint, thus progressing OA. Other studies demonstrate that arthritis has earlier onset in the obese than that shown by radiographic progression.
Total knee arthroplasty (TKA) in the obese patient presents a challenge for both the patient and the surgeon. Obesity is associated with several systemic medical comorbidities, including type II diabetes, obstructive sleep apnea, cardiovascular disease, cancer, and other musculoskeletal pathologic conditions. Compared with nonobese patients, obese patients have longer operative times, longer hospital stays, and higher morbidity and mortality.
The surgery, itself, can be fraught with difficulty. Intraoperatively, the increased adiposity makes dissection and retraction of soft tissues more difficult and obscures bony landmarks typically needed for extramedullary alignment techniques. Together, these factors can contribute to component malalignment and may portend a worse outcome. Additionally, postoperative periprosthetic joint infection (PJI) is of great concern to both the patient and surgeon. Obese patients have 3.3 to 9.0 times higher prevalence of PJI than the normal weight patient.
Component alignment is critical to a successful TKA. A study by Werner and colleagues suggests that as little as 3° of malalignment of the mechanical axis can result in altered load distribution between the medial and lateral compartments of the implant. In obese patients, increased forces borne by the implant coupled with improper component alignment may ultimately predispose a prosthetic joint to premature failure. Given the difficulty with extramedullary alignment techniques in the obese, a combination of intramedullary cutting guides as well as intramedullary prosthetic stems for both the tibial and femoral components can support correct alignment in the coronal plane ( Fig. 1 ).
Furthermore, the obese knee can have a decreased arc of motion compared with a nonobese knee secondary to the excess adipose tissue on the posterior aspect of the lower extremity. This excess adipose may cause the thigh to contact the calf at 100° (or less) of flexion ( Fig. 2 ). This decrease in the thigh-to-calf angle leads to abnormal forward pressure on the posterior tibia as the knee flexes ( Fig. 3 ). When a posterior stabilized knee design is used, the tibia will shift forward with forced flexion and the polyethylene post can dislocate beneath the femoral cam. The posterior stabilized constrained condylar knee (CCK) designs include increased constraint in the coronal plane as well as a higher post with increased jump distance for dislocation. Given the increase in thigh girth, this additional constraint may prevent dislocation.
In the present study, a CCK implant was used in all of the obese patients (body mass index [BMI]>30), both for the added stability in the sagittal plane and for coronal alignment in the operating room. The intramedullary stems also decrease the total surgical time by facilitating the positioning of the components with respect to the intramedullary canals.
The authors sought to answer 2 questions with our study: Would the obese patients have similar clinical results (as defined by the Knee Society Scores and designated complications) and would the CCK allow similar longevity compared with a matched group of normal weight patients with a standard primary posterior stabilized knee implant?
Introduction
According to the World Health Organization (WHO), obesity is a global epidemic and incidence is expected to surpass undernutrition. In the United States, 1 in 3 adults are obese. Furthermore, obesity is an independently recognized modifiable risk factor for the development and progression of osteoarthritis (OA). Compared with normal weight patients, obese patients have a 3-fold to 5-fold increased risk of developing knee OA. It is thought that increased body mass results in increased forces across a joint, thus progressing OA. Other studies demonstrate that arthritis has earlier onset in the obese than that shown by radiographic progression.
Total knee arthroplasty (TKA) in the obese patient presents a challenge for both the patient and the surgeon. Obesity is associated with several systemic medical comorbidities, including type II diabetes, obstructive sleep apnea, cardiovascular disease, cancer, and other musculoskeletal pathologic conditions. Compared with nonobese patients, obese patients have longer operative times, longer hospital stays, and higher morbidity and mortality.
The surgery, itself, can be fraught with difficulty. Intraoperatively, the increased adiposity makes dissection and retraction of soft tissues more difficult and obscures bony landmarks typically needed for extramedullary alignment techniques. Together, these factors can contribute to component malalignment and may portend a worse outcome. Additionally, postoperative periprosthetic joint infection (PJI) is of great concern to both the patient and surgeon. Obese patients have 3.3 to 9.0 times higher prevalence of PJI than the normal weight patient.
Component alignment is critical to a successful TKA. A study by Werner and colleagues suggests that as little as 3° of malalignment of the mechanical axis can result in altered load distribution between the medial and lateral compartments of the implant. In obese patients, increased forces borne by the implant coupled with improper component alignment may ultimately predispose a prosthetic joint to premature failure. Given the difficulty with extramedullary alignment techniques in the obese, a combination of intramedullary cutting guides as well as intramedullary prosthetic stems for both the tibial and femoral components can support correct alignment in the coronal plane ( Fig. 1 ).
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