Other precursors include the presence of bone marrow lesions that can form as sequelae to knee OA. These lesions are associated with thinner tibial cartilage and greater overall cartilage loss within the knee joint, and the more severe the lesions are as seen on magnetic resonance imaging (MRI) tests, the more likely the OA will progress and a joint replacement will be needed in as little as 4 years (Tanamas et al., 2010). The risk factor for developing bone marrow lesions in knees with OA is strongly linked to mechanical knee alignment issues and meniscal pathology, with insufficient evidence of an association between physical activity and bone marrow lesions (Lim et al., 2013). The incidence of total joint replacements for patients with RA, an autoimmune disease that causes inflammation, pain, and structural changes within the joints, has declined after peaking in the 1990s, indicating other interventions for this disease are increasingly more successful (Louie & Ward, 2010). Indeed, the improvement of disease-modifying antirheumatic agents appears to be slowing the progression of the joint destruction caused by the disease (Kahlenberg & Fox, 2011). This may be in patients’ best interest as TKA in the presence of RA increases the risk for prosthetic joint infections (Ravi et al., 2012). In addition, patients with RA have a higher revision rate within 5 years of TKA (Ravi et al., 2012). Arthroplasty designs Advancement in the design and componentry of knee arthroplasty devices continues in an effort to prolong the longevity of the implant and reduce the rate of revisions. TKA devices can be described in two basic categories; fixed bearing and mobile bearing devices. Earlier device designs were fixed bearing devices that remain reliable, with 90% still functioning well at 10 years (Bo et al., 2014). Rotating hinge designs (Figure 3) are a more constrained device and are used primarily for unstable knee joints due to ligament insufficiency and for revision procedures. Cruciate retaining devices maintain the integrity of the PCL to facilitate the gliding mechanics associated with normal knee kinetics; however, these devices require careful tensioning of the PCL. An alternate to PCL-sparing devices are posterior stabilized devices, which contain a post to prevent posterior subluxation in place of the function of the PCL (Verra et al., 2013). Figure 3: Rotating Hinge Arthroplasty Design
Contraindications that may preclude TKA surgery can include any factor that may affect a successful outcome or put the patient at risk for serious complications or death, such as active infection, severe muscular weakness, unstable cardiovascular disease or venous stasis of the operative leg, recurrent urinary tract or kidney infections, multiple comorbidities, or dementia (Crockarell & Guyton, 2013). Morbid obesity does not necessarily preclude TKA, but it presents a potential caution for TKA, as the risk of complications, including infection, and decreased function postoperatively are increased in the patient with a BMI > 30 kg/m 2 (Crowe et al., 2015; D’Apuzzo, Novicoff, & Browne, 2015; Santaguina et al., 2008; Si et al., 2015). Conversely, obesity is a predisposing factor that may hasten the need for a patient to undergo TKA. In one study, patients with a BMI of 35 kg/m 2 or greater were on average nearly 8 years younger than their slimmer counterparts at the time of surgery (Gandhi, Wasserstein, Razak, Davey, & Mahomed, 2010). Other conditions that can complicate TKA surgery include the presence of osteoporosis or any other medical condition that could compromise the structural integrity of the underlying bony surfaces that may collapse or fracture during the operative procedure (Alden, Duncan, Trousdale, Pagnano, & Haidukewych, 2010). osteolysis (localized inflammation resulting in bone resorption) along the bone-implant interface resulting in loosening of the component. Mobile bearing devices were designed to reduce abnormal loading at the bone-cement-device interface; however, numerous studies and recent systematic reviews consistently show no advantage of one type of device design over another with respect to patient outcomes (Bo et al., 2014; Hofstede et al., 2015; Kim et al., 2012; Kim, Park, & Kim, 2016; Moskal & Capps, 2014; Smith, Jan, Mahomed, Davey, & Gandhi, 2011; Verra et al., 2013). Figure 4: Mobile Bearing Arthroplasty Design
Note. ©Adobe Stock | NICOLAS LARENTO.
Recently there has been a growing interest in gender-specific devices to address anatomical differences between men and women. The goal of these devices is to improve congruency in the knee components in women. In a recent meta-analysis of 253 studies examining outcomes based on gender-specific implants for knees and hips, no differences were found in functional mobility or patient satisfaction when comparing gender-specific implants and unisex ones (Johnson, Costa, & Mont, 2011). Other newer developments have included high-flexion implants that are meant to provide patients with greater than 120º of knee flexion, enabling squatting activities. High-flexion implants are associated with an increased risk of femoral component loosening, secondary to the increased forces on the implant-cement interface during full squatting movements, particularly between 120º to 145º of flexion (Zelle, Janssen, Van Eijden, De Waal Malefit, & Verdonschot, 2011).
Note. ©Adobe Stock | JASON WINTER
Mobile bearing devices (Figure 4) were developed to provide dual-surface articulation at both the upper and lower surfaces of the polyethylene insert to reduce polyethylene wear and to allow more natural knee kinematics (Huang, Liau, & Cheng, 2007). Aseptic loosening is one of the key reasons for revision surgery and it is believed that abnormal loading may contribute to aseptic loosening. Aseptic loosening occurs from polyethylene component wear from friction in the implant joint surfaces. This results in particulate debris, which can lead to
Book Code: PTNY3622B
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