RISK FACTORS: BODY MASS INDEX (BMI)

Several high-quality studies were reviewed which investigated the relationship between BMI and patient outcomes after surgical management of knee osteoarthritis. The average pre-operative objective knee society score was 55.88 (range-34 to 74) which improved to 71.84 (range-51 to 89) at six weeks and to 92.79 (range-71 to 100) at six months. Following this improvement, the scores remained steady at the last follow up with mean score being 93.01 (range-72 to 100) (Agarwala 2020, Benjamin 2001).

The functional knee scores before surgery averaged 52.91(range-30 to 75). The score at six weeks were 62.33 (range-35 to 85) which improved significantly at six months to 80.63 (range- 45 to 100). The scores at the last follow up remained the same as the 12 months follow up (Agarwala 2020). During follow-up, 2.1% of patients had SSI (Ahmed 2016). No significant difference between the obese and non-obese groups (Amin 2006).

Regarding the Oxford Knee Score, wound complications were significantly higher (p < 0.001) at a rate of 17% in patients with a BMI of 40 and greater compared with 9% in patients with a BMI of less than 40. (Baker 2012). As BMI increased, knee flexion degree, KOOS and Lysholm scores also decreased significantly (Basdelioglu 2020). At baseline, gait velocity and knee ROM were significantly lower in obese patients compared with those in the nonobese group, and obese patients were more symptomatic than nonobese patients, and their improvement was significantly higher (WOMAC scores) (Bonneyfoy 2017).

While readmission rates were higher in obese patients (Sloan 2020, Basdelioglu 2020), there was no difference in outcomes in obese patients undergoing bilateral total knee arthroplasty (Ogur 2020).

There was also an increase in complications such as infections and bleeding (Shih 2004).

Benefits/ Harms of Implementation

While there is a significant benefit of pain improvement and function in obese patients who undergo TKA, there is increased risk of SSIs. Regarding implant-specific considerations, the practitioner should consult implant manufacturers’ guidelines before surgery, as they may caution against the use of particular implants in patients with high BMI.

Outcome Importance

The outcome of TKA in non-morbidly obese patients is comparable to non-obese patients with excellent post-operative objective and functional scores. However, the risk of SSIs may increase in obese patients after TKA.

Cost Effectiveness / Resource Utilization

Several high-quality studies show that there is an increased risk of SSIs in obese patients after TKA. Several studies also highlighted increased length of stay and use of resources such as antibiotics and the need for consulting services which may increase the cost.

Acceptability

The recommendation comes with varying acceptability. Some surgeons may feel some loss of autonomy with clinical decision making when deciding who is indicated for surgery.

Feasibility

There have been a number of high-quality studies showing comparable postoperative functional outcomes between non-obese and obese patients. As such, it may be more feasible for surgeons to consider the overall health of the patient. If the patient has several risk factors that may contribute to a poor outcome, then it may be more reasonable to better optimize this patient before surgery. If the patient has only one risk factor such as obesity, delaying surgery may cause further functional issues and poor quality of life.

Future Research

Future research should include more studies on functional outcomes in obese patients.