Chapter 139 Thromboembolic Disease and Unicompartmental Knee Arthroplasty

Keith R. Berend, Adolph V. Lombardi, Jr., Michael J. Morris

While debate continues over the indications and contraindications for unicondylar arthroplasty (UKA), the procedure is no doubt a minimally invasive, conservative treatment for unicompartmental arthritis of the knee.^8,^15,^17,^21,²³ UKA is by definition minimally invasive and lends itself to rapid recovery techniques and protocols.^2,¹⁸ There is a certain risk of developing thromboembolic disease (VTD)—namely, deep venous thrombosis (DVT) and pulmonary embolism (PE)—with any lower extremity arthroplasty. However, UKA may be more like an arthroscopy in terms of VTD risk and less aggressive methods of prophylaxis may be applicable in these cases.

Initially, Warwick and Whitehouse ²⁴ and Warwick and colleagues²⁵ reported a 0.1% incidence of fatal PE if no prophylaxis was used following primary TKA. In the eyes of the surgeon and patient, prevention of PE and possible subsequent sudden death is the most critical aspect of prophylactic therapy.^6,¹¹ We have previously described a multimodal prophylaxis program using aspirin and mechanical devices as the baseline option for patients following total knee and total hip arthroplasty.³ Subsequently, we specifically investigated the incidence of symptomatic VTD and the prevention of VTD in UKA patients.¹⁰ In that report of 423 patients, no symptomatic VTD events were seen.

We have again reviewed our experience using the multimodal approach for VTD prevention in a consecutive series of 1000 medial, mobile-bearing UKAs. This chapter outlines the findings of that study and presents a protocol that appears to be safe and effective for preventing VTD and for reducing anticoagulation associated risks following UKA.

Increased risk of surgery site complications has been reported using the American College of Chest Physicians guidelines.^5,⁷ A risk stratification protocol for choosing which patients in the postarthroplasty period should be given type 1A recommended prophylaxis and those for whom this aggressive treatment may be unnecessary may balance the increased risk of surgical site complications with the risk of VTD.

Study Designs

In an identical fashion to our previous reports, a retrospective review of clinical records from our electronic database was performed to identify all patients between July 2004 and July 2008 who underwent minimally invasive, mobile-bearing, medial UKA performed by the senior authors (AVL, KRB). Clinic and hospital records were reviewed to document the VTD prophylaxis measures used, any inpatient variances involving VTD, and any VTD within the first 90 days of surgery. Any perioperative death was attributed to VTD and included in the review. The mortality status was known for all patients.

We previously published our protocol for stratifying the risk of VTD and our protocol for establishing appropriate prophylaxis based on patient-specific risk factors.^3,¹⁰ This multimodal protocol included a preoperative evaluation by a single, specialized, general medical consulting group who make initial recommendations for prophylaxis. All UKA patients received intermittent pneumatic compression devices, either foot pumps or calf compression devices. These devices were initiated intraoperatively on the nonoperative limb and continued bilaterally when the patient arrived in the recovery room and throughout the hospital stay. Hypotensive regional anesthetic was used with an intrathecal narcotic and local anesthetic spinal injection. Antithrombotic stockings were placed on both legs following surgery. In patients who were not identified as having any significant additional risk factors for VTD, oral aspirin was given for 6 weeks postoperatively. In patients with additional risk factors, subcutaneous low-molecular-weight heparin 9 LMWH was used for 2 weeks, with transition to aspirin for an additional 4 weeks. Patients who are at extreme risk, such as those with a previous history of VTD, or those patients on chronic coumadin preoperatively, were transitioned to coumadin with LMWH. In those cases, coumadin was used for 6 weeks or chronically if required by the patient for other medical indications.

As a review, the multimodal prophylactic protocol with aspirin was used in our previous study in 82% of cases. Coumadin alone was used in 1.6%, low-molecular-weight heparin for 2 weeks followed by aspirin in 8.1%, and clopidogrel (Plavix) was used in aspirin-allergic patients in 0.7%. In 6.4% of cases, the patient was considered at significantly increased risk with multiple additional risk factors or had been on coumadin preoperatively and was transitioned using LMWH to coumadin. We consider this to be an accurate representation of our clinical pathways for UKA patients and these data will not be reexamined in this chapter.

Ambulation with full weight bearing and range of motion exercises were initiated on the operative day. Rapid discharge from the hospital and utilization of outpatient physical therapy were encouraged.

The rate of wound-related complications, infections, and transfusions is also reported, because these may be attributable to VTD prophylaxis.

Study Results

There was one symptomatic DVT identified during the follow-up period (0.1%) and no symptomatic PE was identified. No patient underwent a positive radiologic workup for DVT or PE.

There were four wound related complications, including hematoma, that required return to the operating room during the study period (0.4%). One case of deep infection occurred (0.1%). In five patients, a transfusion was required for low hemoglobin and failure to progress with physical therapy because of lethargy (0.5%). Thus, the overall bleeding and wound complication risk is 1% in UKA using the risk stratification and multimodal prophylaxis protocols.

Discussion

We have previously published the concept and results of a risk-based multimodal protocol for the prevention of VTD in our patients.³² Furthermore, we have reported on the use of these protocols in UKA patients.¹⁰ Lower extremity arthroplasty patients are stratified into risk categories by a general medical consulting group. All lower extremity patients receive intermittent pneumatic compression devices, either foot pumps or calf compression devices. Hypotensive regional anesthetic in the form of spinal injection with local anesthetic and long-acting narcotic is used in most patients. In a small proportion, femoral nerve blockade is used if a spinal injection is contraindicated. Oral aspirin is the mainstay of the protocol and is administered 6 weeks postoperatively.* If a patient has an additional risk factor for VTD, such as a previous history, subcutaneous LMWH is used for 2 weeks, followed by aspirin. Alternatively, patients may be transitioned to 6 weeks of coumadin if severely increased risk is identified. Patients who are on chronic coumadin treatment for an unrelated medical condition are transitioned to coumadin using a LMWH bridge.

We had previously reported a rate of symptomatic VTD of 1.8% in our review of over 3300 consecutive lower extremity arthroplasties, with DVT in 1.7%.³ Symptomatic or radiographically diagnosed PE was seen in 0.24% in that series using the multimodal protocol. No cases of fatal PE were identified, but death from VTD attributed to other causes could not be excluded. The initial UKA study demonstrated no symptomatic or radiographically diagnosed VTD (DVT or PE) in the consecutive series of 432 UKAs. Additionally, the mortality status of all patients was known and no deaths occurred in the UKA patients during the perioperative period. Of significant note is the stark difference in VTD between the group of 3300 primary and revision total knee and total hip arthroplasties and the UKA group.

To elucidate this possible difference further, this report included 1000 consecutive medial, mobile-bearing UKAs and demonstrated that the multimodal risk stratification protocol results in no symptomatic PE and a 0.1% rate of symptomatic DVT. Chi-square analysis demonstrated a significant reduction in the relative risk of VTD following UKA when compared with total joint arthroplasty (odds ratio, 18; P < .0001). Given that all patients were treated with identical risk stratification and prophylaxis protocols, and the large number of patients studied, the significant variable is the type of arthroplasty. Clearly, UKA carries a significantly lower risk of VTD than total joint arthroplasty. Therefore, it can be concluded that more aggressive measures, such as those recommended by the American College of Chest Physicians (ACCP) guidelines, are unnecessary in UKA.

When stratifying risk of VTD, it is important to understand those factors that may actually increase the risk in UKA patients. These risks do not appear to be the same as in TKA. Age older than 75 years may be a risk factor for VTD, with a 16% rate of proximal DVT reported following THA.²⁶ In the previous report, 10% of UKAs were performed in patients older than 75 years of age without any identifiable VTD. Furthermore, we did not see an increased use of LMWH or coumadin in the older patients, with 83% of younger patients and 84% of older patients in that series receiving the aspirin-based program. Obesity has also been associated with increased risk following lower extremity arthroplasty.¹⁴ Overall, more than 25% of our patients are obese, with a body mass index (BMI) greater than 35 and, again, no VTD has been seen in that group. We do tend to use more alternative modalities such as LMWH or coumadin in these patients. Despite this, more than 75% of obese patients are managed with the aspirin-based therapy. We would argue that in these patients, multimodal prophylaxis, including aspirin, decreases the risk of VTD, but that not all patients with a BMI over 35 need LMWH or coumadin prophylaxis. Previous VTD is the most significant patient-related risk factor for VTD.⁴ In these patients, we use LMWH for 2 weeks, followed by aspirin for 6 weeks, or transition to coumadin if other risk factors are present. These types of higher risk patients represent a minority of patients undergoing UKA in our practice.

Adherence to set guidelines for all patients, without identifying risk factors, may increase the overall risk of complications following lower extremity arthroplasty. The current report highlights the fact that UKA carries a significantly lower risk of VTD than total joint arthroplasty. Burnett and colleagues ⁵ have reported that adherence to the ACCP 1A guidelines significantly increases the risk of surgery site complications following total hip and knee arthroplasty. This increased risk is likely magnified if generalized guidelines are followed for UKA, for which patients are already at a lessened risk of VTD. Jameson and associates⁷ have demonstrated that when national guidelines are set for the prophylaxis of VTD, there is no significant reduction in the rate of VTD. Moreover, they showed a significantly higher risk of surgical complications. This paradox of increased surgical site complications, without a commensurate reduction in VTD risk, has even more significant implications for UKA, in which the overall risk of symptomatic VTD is lessened.

Lower extremity arthroplasty is an independent risk factor for the development of DVT and PE when compared with the general population.^4,^11,¹⁴ A number of studies have advocated the use of coumadin or LMWH in these patients.^1,^6,^9,^22,²⁷ Unfortunately the use of these anticoagulants is also associated with potential surgical site complications, bleeding, and infection.^5,⁷ Minimally invasive UKA may be an exception to the need for aggressive chemoprophylaxis. Price and coworkers¹⁷ and Beard and colleagues² have reported an accelerated protocol and rapid recovery using the Oxford UKA device implanted using a minimally invasive approach. This rapid recovery associated with UKA may be the key to this difference in VTD risk between TKA and UKA. It would appear that minimally invasive UKA carries a substantially lower risk of VTD than other lower extremity arthroplasty procedures, and that aggressive prophylaxis is not safe or warranted for most UKA patients.