BMI closely related to the occurrence of osteoarthritis
Up to 2/3 of the elder people at 65 years of age or older suffer from osteoarthritis and lead to disability of disease. With the aging of the population, the incidence of osteoarthritis rises[4]. Jensen et al[5] retrospectively studied 115 osteoarthritis cases underwent TKR, results found that 37% of the patients involve osteoarthritis due to obesity. A lot of evidence demonstrate that the overweight people are prone to knee osteoarthritis, that is the increasing body weight is prior to the occurrence of knee osteoarthritis. Hart et al[6] investigated more than 1 000 women, X-ray shows a relationship between osteoarthritis of the knee and the BMI, higher BMI indicates higher incidence of knee osteoarthritis. From the morphology view, Jan[7] described osteoarthritis patients are taller, heavier, with stronger muscle strength, belonging to another population of obese. This experiment showed patients of normal BMI accounted for only 19.1%, overweight patients 80.9%, of which obese patients 29.1%, indicating that general BMI is closely related with the occurrence of osteoarthritis, therefore, the majority of patients candidate for TKR because of osteoarthritis are obesity.
Follow-up time necessary for knee function and motion range
König et al [8]observed 276 cases of osteoarthritis underwent TKR because of osteoarthritis. Knee score markedly increased and remained stable levels at 2 years postoperation, while function scores reached a peak at 2 years and then decreased. This is mainly due to function scores are influenced greatly by the walking distance, age, BMI, while knee scores were not subjected to the above-mentioned factors. As for the knee joint flexion range after TKR in the functional rehabilitation, would increase over time in short-term, and has no significant change 1 year later.
The clinical follow-up results of Lizaur et al[9] showed significant difference in knee flexion range between postoperation and 3 months, between 3 months and 6 months, between 6 months and 1 year; while no significant difference was observed between 1 year and 2 years, between 2 years and more than 2 years. Malkani et al[10] also found no significant difference between 1 year and 10 years. Therefore the maximum flexion range after TKR requires at least 1 year of follow-up.
In this experiment, the patients were followed up for 12 to 46 months, at an average of 28.3 months, which is convincible for the knee score, function score and range of motion.
Postoperative complications in obese patients following TKR
TKR aims at the elderly, the majority of surgical patients implementing TKR in 1985/1990 in the United States were osteoarthritis patients over the age of 65 years[11]. Osteoarthritis causes pain and loss of function, reduces quality of life. Joint replacement is acceptable for those osteoarthritis patients in who pains cannot be relieved and functional activities can not be improved by drugs, and those can obtain satisfactory clinical efficacy. However, obesity has been considered as constraints of TKR, and may increase the perioperative complications, including infection, extended hospital stay, increased venous thrombosis. Overweight patients are advised to discourage for TKR or informed of unsatisfactory replacement results. It has been reported that obese is associated with postoperative prosthesis loosening of replacement and obese increased the chance of reoperation[12-13]. Some studies have shown that obesity could benefit patients from TKR, even morbidly obese patients[14]. Wound complications do not increase[15-16], and there is no significant difference in the range of motion, knee score, patellofemoral complications between obese and non-obese cases. The confusion and lack of statistical data lead to that many joint surgeons tend to prevent obese patients from TKR[13].
Very different literature reports result from some of the authors may not notice the different activity after TKR. McClung et al [17] have evaluated the relationship between BMI and activity levels after joint replacement, results show that a higher BMI indicates lower activity, they less use their joints, which reduces the anticipated prosthesis wear, that is to say the wear is the result of use, not a matter of time. These articles neglected activity in the evaluation of TKR, the prosthetic wear and the postoperative evaluations after TKR should include the impact of obesity on activity.
This test is an observation and a clear result of the follow-up, the preoperative prediction and assessment of postoperative function have been performed in obese patients, to unify understanding of clinical doctors and patients, and to obtain active patients.
BMI unrelated to TKR
Deshmukh et al[18] pointed out: Obesity has been considered to have a negative impact on TKR patients, overweight patients may be discouraged from TKR surgery, but body mass never be conclusively proved to influence the surgical results. He conducted a follow-up of 1-12 months among 180 osteoarthritis patients underwent TKR surgery operated by the same doctor. Results concluded that BMI is not a negative effect on TKR. Stickles et al[19] studied the relationship between BMI and functional recovery after TKR, after postoperative 1-year follow-up, the linear regression statistical analysis showed that, obese patients similar with other patients, obtained the same functional improvement and satisfaction after TKR, but a larger BMI increased the up-down stairs difficulty at 1 year postoperation.
Hawker et al [13] conducted a follow-up to in 193 cases of 242 311 patients after TKR surgery for 2-7 years in North America between 1985 and 1989. All subjects, regardless of age, BMI and postoperative time, reported no or less pain, 85.2% of patients were satisfactory on postoperative function. At 2-7 years, all patients reported significant and sustained pain relief and functional improvement. The results proved that age and obesity have no negative impact on functional activities after TKR.
Spicer et al[20] divided 285 cases underwent TKR for osteoarthritis into two groups according to BMI = 30. There were no significant differences in KSS score, revision rate, 10-year survival rate and linear imaging lucency line between the two groups, only the incidence of focal osteolysis was 5 times higher than normal group at BMI > 40.
The present experiment results showed: The preoperative functional score in obese group was lower than that in control group, but the knee joint score was fair. In the final follow-up, both the knee score and functional score were significantly increased after TKR in overweight, obese, morbidly obese and control groups. The difference of the level of increase was not statistically significant among groups. Although the maximal range of flexion and extension in obese group was smaller than that in control group, it is still one of the most intuitive indicators in patients, but the range of motion accounts for a small proportion of the scores, therefore less affecting HSS score, and the absolute value is equal, so there was no significant difference.
Characteristics of this study
TKR leads to positive and immediate improvements in the quality of life of patients. No matter age, sex, affected side and BMI, a simple BMI has no impact on the functional recovery after TKR. Obese only increases the difficulty in surgical operation and postoperative care in patients, thus requiring a higher technique for surgeons.
This study is unique in that it controls a number of other confounding factors and determined the influence of BMI on TKR function, while other studies failed to do so. Another feature is the stability of TKR quality (the same group of surgeons, the same prosthesis, and the same disease).