Should cemented or cementless knee implants be used in patients who are obese?
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Click here to read the Cover Story, "Surgeons advise healthy skepticism for cementless TKA."
Good long-term fixation can be achieved
The controversy over fixation in the obese patient population undergoing TKA remains unsolved.
Historically, many studies have shown obese patients, particularly morbidly obese patients (BMI of greater than 40 kg/m2) are at higher risk for aseptic loosening due to higher stress on the implant-cement-bone interface. This has led many surgeons to augment cemented fixation by using stems to off-load the stress on those interfaces. Long-term, however, there are concerns that this mechanical fixation when subject to repeated stress may break down over time and lead to an increased incidence of aseptic loosening.
There is emerging evidence that biological fixation with cementless implants may provide more durable long-term fixation. Recent studies published in the last 5 years demonstrate excellent results of cementless TKA in the obese patient population. Graham S. Goh, MD, and colleagues evaluated a consecutive series of 406 primary cementless TKA and matched these 1:1 with cemented TKA in patients with a BMI of greater than 35 kg/m2. Both groups demonstrated 7-year survivorship of 99%, indicating cementless fixation is durable in this patient population. Brent J. Sincrope, MD, and colleagues performed a retrospective study comparing clinical results of cemented vs. cementless primary TKA with a posterior stabilized TKA design in morbidly obese (BMI of 40 kg/m2 or greater) patients with minimal 5-year follow-up. There were five failures requiring revision in the cementless group, including one for aseptic tibial loosening (0.9%). In the cemented group, there were 22 failures requiring revision, including 16 implants for aseptic loosening (18.8%). Survivorship with aseptic loosening as the endpoint was 99.1% in the cementless cohort vs. 88.2% in the cemented cohort at 8 years.
However, it is important to keep in mind that obesity is not the only factor at play and issues other than just the patient’s weight must be taken into consideration. Many obese patients have other risk factors that may lead to poor bone quality, such as poor nutrition and a more sedentary lifestyle. The patient must have acceptable bone quality that allows for initial fixation. Several TKA studies demonstrate that cementless implants have some micromotion early but are durable once ingrown, whereas cemented implants may be stable early but move over time.
Emerging data would suggest that good long-term fixation with cementless knees in obese patients can be achieved. However, we must look at all factors other than just obesity in isolation. More data are needed to fully understand the ramification of fixation in the obese population, but results to date are encouraging.
- References:
- Goh GS, et al. J Arthroplasty. 2022;doi:10.1016/j.arth.2021.12.038.
- King BA, et al. J Knee Surg. 2022;doi:10.1055/s-0042-1748900.
- Silverstein RS, et al. Current Orthopaedic Practice. 2021;doi:10.1097/BCO.0000000000001029.
- Sinicrope BJ, et al. J Arthroplasty. 2019;doi:10.1016/j.arth.2018.10.016.
Bryan D. Springer, MD, is the fellowship director at OrthoCarolina Hip and Knee Center and professor of orthopedic surgery at Atrium Musculoskeletal Institute in Charlotte, North Carolina.
Antibiotic-impregnated cement preferred
As porous ingrowth technologies evolve, it is important to know their most efficacious applications and limitations. There are many variables in cemented and cementless prostheses, and other factors that influence clinical performance. This is a timely debate as the prevalence of obesity in the United States is about 42% and increasing. The risk of knee osteoarthritis in the obese is seven to eight times that of the nonobese.
It has long been recognized that obesity and misalignment are risk factors for total knee failure. The tibial component is most at risk for loosening. With cement, this can be mitigated by techniques that improve the initial cement bond strength and/or adding a short tibial stem. A 3D porous ingrowth surface can have higher resistance to tension failure compared to cement and be less likely to loosen in alignment outliers and/or the obese. Digital planning, navigation, robotic assist and intraoperative digital imaging can reduce alignment outliers.
The risk of periprosthetic joint infection is roughly doubled with obesity. Obesity may be associated with diabetes, which is also a risk factor for PJI. An advantage of fixation with cement is the option to add antibiotics. Antibiotic-impregnated bone cement decreases the occurrence of PJI in TKA. While the benefits and risks of antibiotic-impregnated bone cement for all patients are debated, most agree that there is a net benefit in patients at increased risk for PJI. A related consideration is the community standard of care. If an obese patient develops a PJI following a cementless TKA, the implanting surgeon may be accused of negligence for not using a knee with antibiotic-impregnated cement. An antimicrobial coating on a total knee prosthesis is an attractive concept that remains to be delivered. So for now, I prefer antibiotic-impregnated cement in obese patients.
- References:
- Billi F, et al. Bone Joint J. 2019;doi:10.1302/0301-620X.101B1.BJJ-2018-0500.R1.
- Garceau SP, et al. J Arthroplasty. 2020;doi:10.1016/j.arth.2020.01.084.
- Kwong LM, et al. Bone Joint J. 2014;doi:10.1302/0301-620X.96B11.34327.
- Ritter MA, et al. J Bone Joint Surg Am. 2011;doi:10.2106/JBJS.J.00772.
- Xu T, et al. Chin J Traumatol. 2022;doi:10.1016/j.cjtee.2022.06.001.
Thomas P. Schmalzried, MD, is a physician specialist at Harbor-UCLA Medical Center in Torrance, California.
Bone quality crucial for cementless TKA
Irrespective of BMI, the choice of whether to utilize cemented or cementless fixation in TKA depends entirely on the quality and viability of the host bone. Rigid mechanical fixation of a porous material against viable host bone is essential for successful ingrowth and osseointegration. Bone quality has been demonstrated to correlate with mechanical stability, with suboptimal fixation observed in osteoporotic bone models. Wolf’s Law states that bone density is enhanced under greater compressive stress, and one could postulate this to be advantageous in the obese patient which would enhance bone density and subsequent mechanical fixation of cementless TKA. Due to high loosening rates of cemented TKA in obese patients, some recent publications have reported excellent survivorship with cementless fixation of contemporary TKA in obese patients.
We recently reported our experience with cementless TKA patients, where excellent fixation and survivorship was observed with 99% survivorship out to 11 years relative to aseptic loosening in a patient cohort with a mean BMI of 35 kg/m2 (range of 21 kg/m2 to 57 kg/m2). However, in our clinical practice, patients with clinical osteoporosis or poor bone quality observed intraoperatively were precluded from receiving cementless TKA implants, representing a confound in investigating obesity as an isolated variable. Therefore, our results are biased in only utilizing cementless TKA in obese patients with good bone quality. In addition, emerging evidence demonstrates that many obese patients are nutritionally malnourished and, if sedentary and inactive, will exhibit varying degrees of osteoporosis and poor bone quality. Therefore, patient activity, overall nutritional status and subsequent bone quality are critical in determining whether an obese patient is appropriate for cementless fixation in TKA.
In summary, cementless fixation in the active and nutritionally optimized obese patient with adequate bone quality has shown excellent clinical results and should be considered the ideal fixation in this specific group of patients.
- References:
- Bagsby DT, et al. J Arthroplasty. 2016;doi:10.1016/j.arth.2016.01.025.
- Helvie PF, et al. J Arthroplasty. 2023;doi:10.1016/j.arth.2023.02.009.
- Meneghini RM, et al. J Knee Surg. 2011;doi:10.1055/s-0031-1280879.
R. Michael Meneghini, MD, is the CEO of the Indiana Joint Replacement Institute and professor of clinical orthopedic surgery at Indiana University School of Medicine in Indianapolis.
Editor’s note: This article was updated on June 22, 2023, to correct wording that misidentified the type of procedure performed. The editors regret this error.
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