Discussion
TKA is a safe and effective procedure used to treat osteoarthritis of the knee and improve patients’ quality of life.15 About 700,000 TKAs are performed annually in the United States.16 Because of improvements in preventive medicine and medical technology, life expectancy is increasing, and TKAs are now being performed in higher numbers and in an older patient population. Over the next few decades, these developments will lead to more postoperative complications. It is projected that, by 2030, the need for TKAs in the United States will increase by 673% to 3.48 million.17 Postoperative complications are rare but unfortunately often lead to poor outcomes or even mortality.18 To help minimize the number of postoperative complications, we must understand the safety of tourniquet use in TKA. Other investigators have concluded that tourniquet use is unsafe in patients with preoperative vascular calcifications on plain radiographs.7,8,11 The present study, designed to elucidate whether preoperative evidence of knee arterial calcification may predispose TKA patients to postoperative wound complication or VTE, had some important findings.
In our study, wound complication and VTE occurred in a considerable number of patients after TKA. Despite exceeding the number of patients calculated by the power analysis, our population may have been inadequate to fully detect statistical significance. Thus, our conclusion of failing to reject the null hypothesis may have been because of sample size, a type II error. We found that, after primary TKA, 3.04% of patients developed wound complications and 4.77% VTE. According to the literature, the incidence of infection after primary TKA is between 0.5% and 12%, and that of VTE reported within 3 months after TKA is 1.3% to 10%.13,14 Although we had 100% VTE prophylaxis, meeting the standard of care, VTE after TKA remains a postoperative complication.19 This study also found that a considerable percentage of primary TKA patients (23.59%) had preoperative calcification of the knee arteries. To our knowledge, this study was the first to quantify the incidence of knee arterial calcification in patients who underwent TKA.
Preoperative calcification of the knee arteries in patients who underwent TKA did not increase the risk for wound complication, VTE, or arterial damage. These calcifications, however, do pose an increased systemic vascular risk.20 Calcification of the vascular wall predicts increased cardiovascular risk, independent of classical cardiovascular risk factors.3,18,21-24 Clinically, patients who have both diabetes and calcifications are at significant excess risk for total mortality, stroke mortality, and cardiovascular mortality, compared with patients with diabetes but without such calcifications. They also had a significantly higher incidence of coronary heart disease events, stroke events, and lower extremity amputations.25,26
All our patients underwent tourniquet-assisted TKA. Although previous studies have indicated that tourniquet use may increase arterial complications and wound complications or even limb loss in patients with calcified arteries, we did not find this link.7,27 Our population had no reported arterial complications related to tourniquet use. Other, smaller studies have had similar findings. Vandenbussche and colleagues28 prospectively studied 80 TKA cases randomized to tourniquet use or no tourniquet use and found no postoperative nerve palsies, wound infections, wound healing problems, or hematomas. Our study is also in accord with studies that have reported tourniquet use did not increase risk for DVT.29 Therefore, unlike earlier data, our data demonstrated that tourniquet use in patients with knee arterial calcification was safe.7,27,30,31
Patients with calcification were more likely to have the medical comorbidities of hypertension, diabetes, hyperlipidemia, and CAD. All these comorbidities are linked to the development of arterial calcification, or atherosclerotic occlusive disease.32,33 As life expectancy and the need for TKA increase, it is likely that a larger percentage of TKA patients will have preoperative radiographic evidence of knee arterial calcification. Although current dogma is that tourniquet-assisted TKA is contraindicated for patients with preoperative radiographic evidence of femoral-popliteal calcification, our study results showed that this calcification should not affect preoperative TKA planning for these patients.
We divided our patients into 3 categories: those with proximal calcification (above the joint line), those with distal calcification (below the joint line), and those with both proximal and distal calcification. Location of arterial calcification did not have an effect on their rates of postoperative wound complication or VTE. We hypothesized that patients with proximal calcification would be at increased risk for direct arterial injury and subsequent wound complication because the tourniquet is placed proximally. Previous research has indicated that arterial occlusion and subsequent wound complication can occur because of low blood flow stemming from tourniquet use.7 Further, intraoperative manipulation (flexing) of a knee with calcified vessels causes arterial complications after TKA because these vessels are less elastic than nonatheromatous vessels.31 However, we found no such effect. At the same time, having arterial calcification might also be an indication of venous disease in this location,12 which may be especially important for proximal calcifications. Proximal DVT more likely is a precursor to pulmonary embolic events than distal DVT is.31,34 However, we found no difference in VTE rates among the 3 arterial location groups, which is supported by studies that have found that tourniquet use does not increase DVT incidence.29,35-40