The Journal of Bone & Joint Surgery

The Journal of Bone & Joint Surgery, Volume 92, Issue 1

Scientific Articles | January 01, 2010

Cognition Following Computer-Assisted Total Knee Arthroplasty: A Prospective Cohort Study

Craig T. Haytmanek, MD¹; Aidin Eslam Pour, MD¹; Camilo Restrepo, MD¹; Jain Nikhil, BS¹; Javad Parvizi, MD, FRCS¹; William J. Hozack, MD¹

¹ Rothman Institute of Orthopedics, 925 Chestnut Street, Philadelphia, PA 19107. E-mail address for W.J. Hozack: research@rothmaninstitute.com

View Disclosures and Other Information

Disclosure: In support of their research for or preparation of this work, one or more of the authors received, in any one year, outside funding or grants in excess of $10,000 from Stryker Orthopaedics. Neither they nor a member of their immediate families received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. A commercial entity (Stryker Orthopaedics) paid or directed in any one year, or agreed to pay or direct, benefits in excess of $10,000 to a research fund, foundation, division, center, clinical practice, or other charitable or nonprofit organization with which one or more of the authors, or a member of his or her immediate family, is affiliated or associated.

A commentary by Bassam A. Masri, MD, FRCSC, is available at www.jbjs.org/commentary and as supplemental material to the online version of this article.

Investigation performed at the Rothman Institute of Orthopedics, Philadelphia, Pennsylvania

J Bone Joint Surg Am, 2010 Jan 01;92(1):92-97. doi: 10.2106/JBJS.H.00497

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Abstract

Background:

A substantial number of patients experience postoperative cognitive changes following total joint arthroplasty. The change in mental status may be the result of fat and bone-marrow-debris embolization. We hypothesized that the use of computer-assisted total knee arthroplasty, which does not involve the use of intramedullary alignment rods, would produce less fat and bone-marrow-debris embolization and, hence, fewer changes in mental status.

Methods:

Forty-seven patients who underwent total knee arthroplasty with use of a computer-assisted navigation system and forty-eight patients who underwent conventional total knee arthroplasty without the assistance of computer navigation were followed prospectively. The validated Folstein Mini-Mental State Examination (MMSE) was used to assess the mental status of the patients. The test was administered preoperatively, serially postoperatively while the patient was in the hospital, and at six months. Medication and oxygen requirements were recorded.

Results:

On the basis of the numbers studied, no significant differences in postoperative pain-medication or oxygen requirements were found between the group treated with computer-assisted navigation (the navigation group) and the group treated with conventional total knee arthroplasty (the control group). The mean postoperative MMSE score was 88.9 points in the navigation group and 89.3 points in the control group (p = 0.844). Twenty-five patients in the navigation group and thirty-six patients in the control group completed the test at six months. The mean score at that time was 95.3 points in the navigation group and 96.3 points in the control group (p = 0.514).

Conclusions:

Further research is needed to determine if fat and bone-marrow-debris embolization is truly decreased by the use of computer-assisted total knee arthroplasty and if such a reduction has any clinical relevance.

Level of Evidence:

Therapeutic Level II. See Instructions to Authors for a complete description of levels of evidence.

Figures in this Article

Introduction

Introduction | Materials and Methods | Results | Discussion | References

A substantial number of patients, possibly up to 50% according to some reports, experience changes in mental status following total knee arthroplasty¹. Among other causes, passage of fat or bone-marrow-debris emboli into the brain may be the reason for the change in mental status. In one series of forty-one patients undergoing total hip or knee arthroplasty, over half had detectable intraoperative cerebral emboli². The likely cause of embolization in patients undergoing total knee arthroplasty is increased intramedullary pressure secondary to the use of intramedullary alignment rods³.

Kalairajah et al.⁴ found a significant difference between computer-assisted total knee arthroplasty and conventional total knee arthroplasty done with intramedullary alignment rods in terms of the number of emboli in intracranial vessels detected by transcranial Doppler ultrasonography. However, they did not find a difference between the procedures with regard to the patients' mental test scores on either the first or the third postoperative day, and they suggested that a larger study was needed. It should be noted that they did not disclose which mental status test was used to evaluate the patients.

Another recent study compared the histologic evidence of fat and bone-marrow-debris emboli between conventional and computer-navigated total knee arthroplasty⁵. The investigators obtained arterial blood samples before insertion of a femoral alignment rod or cutting of the distal part of the femur and then at various times over the next forty-eight hours. They found no significant difference in the prevalence of fat or bone-marrow-debris embolization between the two groups.

The authors of another study compared the mental status of patients who had undergone unilateral total knee arthroplasty with that of patients who had undergone simultaneous bilateral total knee arthroplasty, anticipating that there would be more severe compromise of the mental status after the bilateral procedures¹. All of the patients underwent conventional total knee arthroplasty and were tested preoperatively, on the third postoperative day, and six weeks after the surgery with use of the Folstein Mini-Mental State Examination. The authors found no significant difference in mental status between the two groups.

With these somewhat conflicting studies as a background, we initiated a direct comparison of the mental status of patients treated with conventional total knee arthroplasty with that of patients treated with computer-navigated total knee arthroplasty. We hypothesized that patients undergoing computer-assisted total knee arthroplasty, a procedure that does not involve use of an intramedullary guide, would have a lower rate of embolism and hence a reduced prevalence of changes in mental status as compared with those undergoing conventional total knee arthroplasty. Our intention was to study fifty consecutive patients who had undergone conventional total knee arthroplasty and fifty who had undergone computer-navigated total knee arthroplasty and compare their Folstein Mini-Mental State Examination scores daily during their hospital stay and at six months postoperatively.

Materials and Methods

Introduction | Materials and Methods | Results | Discussion | References

One hundred consecutive patients were prospectively enrolled into two groups from July 2005 to March 2006. Our institutional review board approved this prospective study. The investigation was registered in a public registry (ID number: NCT00830986). All patients provided informed consent to participate.

Fifty patients underwent total knee arthroplasty with the Stryker computer-assisted navigation system (Stryker-Leibinger, Freiburg, Germany) (the navigation group) and fifty patients underwent conventional total knee arthroplasty without the assistance of computer navigation (the control group). The operation that the patient received depended on the surgeon performing the surgery, as one surgeon utilized the navigation system and three performed conventional total knee arthroplasty. The demographic data on all patients are presented in Table I.

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TABLE I Demographic Data

Parameters	Navigation Group	Control Group	Total
No. of patients	47	48	95
Male/female	19/28	13/35	32/63
No. of bilateral cases	6	10	16
Age*(yr)	66.1 (40-87)	66.1 (41-82)
Height*(cm)	169.4 (152-185)	166.1 (150-188)
Body mass index*(kg/m2)	31.7 (21.6-44)	30.3 (22.3-45.5)
Mean operative time*(min)
Unilateral	64.6 (43-95)	71.1 (31-125)
Bilateral	128 (112-144)	135.3 (94-172)
Mean ASA (American Society of Anesthesiologists) category*	2.7 (2-4)	2.7 (2-3)

*The values are given as the mean with the range in parentheses.

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TABLE I Demographic Data

Parameters	Navigation Group	Control Group	Total
No. of patients	47	48	95
Male/female	19/28	13/35	32/63
No. of bilateral cases	6	10	16
Age*(yr)	66.1 (40-87)	66.1 (41-82)
Height*(cm)	169.4 (152-185)	166.1 (150-188)
Body mass index*(kg/m2)	31.7 (21.6-44)	30.3 (22.3-45.5)
Mean operative time*(min)
Unilateral	64.6 (43-95)	71.1 (31-125)
Bilateral	128 (112-144)	135.3 (94-172)
Mean ASA (American Society of Anesthesiologists) category*	2.7 (2-4)	2.7 (2-3)

*The values are given as the mean with the range in parentheses.

The exclusion criteria were less than twelve years of education, an inability to read and write in English, a history of mental illness, Parkinson disease, depression, dementia, and current use of an antidepressant and/or antipsychotic medication. On the basis of these criteria, three patients in the navigation group and two patients in the control group were excluded from the study.

The American Society of Anesthesiologists (ASA) values for the navigation group and the control group were compared^6-8. This system, which is used to classify the physical status of patients preoperatively, has six categories. Category 1 includes normal healthy patients; Category 2, patients with mild systemic disease; Category 3, those with severe systemic disease; Category 4, those with severe systemic disease that is a constant threat to life; Category 5, those who are not expected to survive without surgery; and Category 6, brain-dead patients who are considered for organ removal for donor purposes. No significant difference in the ASA category was found between the navigation and control groups in the present study (p = 0.844).

All patients underwent a primary total knee arthroplasty with the use of cemented Stryker Scorpio components (Stryker Orthopaedics, Mahwah, New Jersey) with a cemented patellar button. A vertical midline incision was used in all knees, and the bone cuts were made in the same sequence in all cases. Minimally invasive surgery was not attempted in any case. The variable distinguishing the two groups was the use of femoral intramedullary alignment jigs in the conventional total knee arthroplasty group and the use of single bicortical tracking pins in the tibia and femur in the computer-navigation group. No drains were used. The mean operative time was 64.6 minutes (range, forty-three to ninety-five minutes) for the unilateral computer-navigated procedures and 71.1 minutes (range, thirty-one to 125 minutes) for the unilateral conventional procedures (p = 0.189). The mean operative time was 128 minutes (range, 112 to 144 minutes) for the bilateral navigation procedures and 135.3 minutes (range, ninety-four to 172 minutes) for the bilateral conventional procedures (p = 0.77). The same postoperative protocol, including the use of continuous passive motion and physical therapy, was followed for each patient.

During the patients' hospital stay, blood oxygen saturation levels and the need for oxygen administration, vital signs, hemoglobin levels, the need for blood transfusion, and all medications administered were recorded (Table II). The pain medication needs were compared between the groups after conversion of the dosage of the administered pain medication to an equivalent amount of morphine with use of the equianalgesic conversion formula^9,10.

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TABLE II Comparison of Oxygen Saturation, Hemoglobin Levels, Blood Transfusion Requirements, and Narcotic Use Between Navigation and Control Groups

Variable	Navigation Group*	Control Group*	P Value
Oxygen saturation (%)	96.8 (96-100)	96.3 (94-100)	0.932
Hemoglobin level (g/L)	108 (84-124)	102 (84-118)	0.0856
Blood transfusion (units)	1.6 (1-3)	1.3 (1-4)	0.0784
Narcotic use (units†)	36.9 (15.3-60.5)	41.6 (17.3-62.8)	0.562

*The values are given as the mean with the range in parentheses.
†The dosage of the administered pain medication was converted to an equivalent amount of morphine with use of the equianalgesic conversion formula^9,10.

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TABLE II Comparison of Oxygen Saturation, Hemoglobin Levels, Blood Transfusion Requirements, and Narcotic Use Between Navigation and Control Groups

Variable	Navigation Group*	Control Group*	P Value
Oxygen saturation (%)	96.8 (96-100)	96.3 (94-100)	0.932
Hemoglobin level (g/L)	108 (84-124)	102 (84-118)	0.0856
Blood transfusion (units)	1.6 (1-3)	1.3 (1-4)	0.0784
Narcotic use (units†)	36.9 (15.3-60.5)	41.6 (17.3-62.8)	0.562

The 30-point Folstein Mini-Mental State Examination (MMSE)¹¹ was administered to all patients in the preoperative holding area, before administration of any medication, to obtain a baseline measurement, and it was also administered a few hours postoperatively. The examination was then performed on each postoperative day in the hospital and at six months postoperatively. The scores obtained on the postoperative days in the hospital were averaged to determine a single postoperative score. We utilized the MMSE because it is easily administered at the bedside, is fairly brief, and has been validated¹¹ for assessment of the component of interest in this study. When comparing the two groups, we normalized the 30-point scale of the MMSE to a scale of 100 points.

For the six-month test, the MMSE was changed, with the help of a staff psychiatrist, from 30 to 28 points by eliminating the spatial reasoning portions to facilitate use over the telephone. This modification of the MMSE has not been validated to our knowledge. This score was also converted to a 100-point scale for comparison. All patients were contacted at six months following the total knee arthroplasty. Some patients chose not to answer the questionnaire by telephone. All testing was done by a medical student or a research fellow.

Statistical Analysis

Noncategorical variables (continuous data) were assessed with a t test. A value was considered to be significant when alpha was <0.05 at a 95% confidence level. A multivariate analysis to isolate the influence of the tested factors was also conducted.

Source of Funding

Stryker Orthopaedics provided funding for this study.

Results

Introduction | Materials and Methods | Results | Discussion | References

The preoperative mean MMSE score was 88.9 points (range, 70 to 100 points) in the navigation group and 90.6 points (range, 73.3 to 100 points) in the control group (p = 0.397). Postoperatively, the navigation group had a mean MMSE score of 88.9 points (range, 74.2 to 100 points) and the control group had a mean MMSE score of 89.3 points (range, 67.5 to 99.2 points) (p = 0.844). At six months, twenty-five of the forty-seven patients in the navigation group and thirty-six of the forty-eight patients in the control group were tested with the 28-point modified MMSE. The mean score at six months was 95.3 points (range, 75 to 100 points) in the navigation group and 96.3 points (range, 75 to 100 points) in the control group (p = 0.514).

No substantial difference between the two groups was found with regard to oxygen requirements, hemoglobin levels, the need for blood transfusion, chemistry panels, or narcotic use. Oxygen saturation levels also remained comparable between the two groups throughout the inpatient monitoring period (Table II).

In the control group, the preoperative MMSE score (mean, 90.6 points [range, 73.3 to 100 points]) did not differ significantly from the postoperative score (mean, 89.3 points [range, 67.5 to 99.2 points]) (p = 0.466). However, the six-month MMSE score (mean, 96.3 points [range, 75 to 100 points]) was significantly higher than the preoperative score (p = 0.000) and the postoperative score (p = 0.000).

In the navigation group, the preoperative MMSE score (mean, 88.9 points [range, 70 to 100 points]) did not differ significantly from the postoperative MMSE score (mean, 88.9 points [range, 74.2 to 100 points]) (p = 0.969). However, there was a significant difference between the preoperative score and the six-month score (mean, 95.3 points [range, 75 to 100 points]) (p = 0.003) and between the postoperative score and the six-month score (p = 0.002).

When we compared the unilateral and bilateral cases in the navigation group, we found, with the small numbers studied, no significant difference in the preoperative scores (mean, 88.7 points [range, 76.7 to 100 points] for the unilateral group and mean, 95 points [range, 90 to 100 points] for the bilateral group) (p = 0.241), the postoperative scores (mean, 86.6 points [range, 70 to 100 points] for the unilateral group and mean, 91.6 points [range, 93.3 to 96.6 points] for the bilateral group) (p = 0.983), or the six-month scores (mean, 95 points [range, 75 to 100 points] for the unilateral group and mean, 98.2 points [range, 96.4 to 100 points] for the bilateral group) (p = 0.530) (Table III).

When we compared the unilateral and bilateral cases in the control group, we identified, with the small numbers studied, no significant difference in the preoperative scores (mean, 90.3 points [range, 80 to 100 points] for the unilateral group and mean, 91.3 points [range, 73.3 to 100 points] for the bilateral group) (p = 0.735), the postoperative scores (mean, 87.6 points [range, 56.6 to 100 points] for the unilateral group and mean, 87 points [range, 76.6 to 96.6 points] for the bilateral group) (p = 0.455), or the six-month scores (mean, 95.7 points [range, 75 to 100 points] for the unilateral group and mean, 97 points [range, 94.4 to 100 points] for the bilateral group) (p = 0.464) (Table III).

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TABLE III Comparison of Preoperative, Postoperative, and Six-Month Follow-up MMSE Scores Between Unilateral and Bilateral Cases in Navigation and Control Groups

	Unilateral*	Bilateral*	P Value
Navigation group
Preop. score	88.7 (76.7-100)	95 (90-100)	0.241
Postop. score	86.6 (70-100)	91.6 (93.3-96.6)	0.983
6-mo score	95 (75-100)	98.2 (96.4-100)	0.530
Control group
Preop. score	90.3 (80-100)	91.3 (73.3-100)	0.735
Postop. score	87.6 (56.6-100)	87 (76.6-96.6)	0.455
6-mo score	95.7 (75-100)	97 (94.4-100)	0.464

*The values are given as the mean number of points with the range in parentheses.

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TABLE III Comparison of Preoperative, Postoperative, and Six-Month Follow-up MMSE Scores Between Unilateral and Bilateral Cases in Navigation and Control Groups

	Unilateral*	Bilateral*	P Value
Navigation group
Preop. score	88.7 (76.7-100)	95 (90-100)	0.241
Postop. score	86.6 (70-100)	91.6 (93.3-96.6)	0.983
6-mo score	95 (75-100)	98.2 (96.4-100)	0.530
Control group
Preop. score	90.3 (80-100)	91.3 (73.3-100)	0.735
Postop. score	87.6 (56.6-100)	87 (76.6-96.6)	0.455
6-mo score	95.7 (75-100)	97 (94.4-100)	0.464

*The values are given as the mean number of points with the range in parentheses.

We then eliminated all of the bilateral cases and compared just the unilateral cases in the navigation group with just the unilateral cases in the control group. We found no significant difference in the preoperative scores (mean, 88.7 points [range, 76.7 to 100 points] for the navigation group and mean, 90.3 points [range, 80 to 100 points] for the control group) (p = 0.333), the postoperative scores (mean, 86.6 points [range, 70 to 100 points] for the navigation group and mean, 87.6 points [range, 56.6 to 100 points] for the control group) (p = 0.680), or the six-month scores (mean, 95 points [range, 75 to 100 points] for the navigation group and mean, 95.7 points [range, 75 to 100 points] for the control group) (p = 0.350) (Table IV).

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TABLE IV Comparison of Preoperative, Postoperative, and Six-Month Follow-up MMSE Scores in Unilateral Cases Only Between Navigation and Control Groups

	Navigation Group*	Control Group*	P Value
Preop. score	88.7 (76.7-100)	90.3 (80-100)	0.333
Postop. score	86.6 (70-100)	87.6 (56.6-100)	0.680
6-mo score	95 (75-100)	95.7 (75-100)	0.350

*The values are given as the mean number of points with the range in parentheses.

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TABLE IV Comparison of Preoperative, Postoperative, and Six-Month Follow-up MMSE Scores in Unilateral Cases Only Between Navigation and Control Groups

	Navigation Group*	Control Group*	P Value
Preop. score	88.7 (76.7-100)	90.3 (80-100)	0.333
Postop. score	86.6 (70-100)	87.6 (56.6-100)	0.680
6-mo score	95 (75-100)	95.7 (75-100)	0.350

*The values are given as the mean number of points with the range in parentheses.

Discussion

Introduction | Materials and Methods | Results | Discussion | References

Mental status commonly changes immediately following total knee arthroplasty¹. Fortunately, no lasting cognitive compromise has been documented, to our knowledge. Many factors such as delirium (which may be drug-induced in some cases), hypoxia, and hypotension may contribute to cognitive changes following surgery¹¹. We investigated whether fat and bone-marrow-debris embolism created by increased intramedullary pressures is also a factor affecting cognition following surgery.

Dating back to 1873, when Von Bergmann's description appeared¹², fat embolism syndrome has been widely reported in the orthopaedic literature. The route of the emboli must also be considered when changes in mental status are being investigated. The lungs are usually the primary recipients of venous emboli, and it is thought that these emboli can affect blood oxygenation levels. As Kalairajah et al.⁴ and Riding et al.² demonstrated, however, there is clear evidence of emboli bypassing the lungs and entering the systemic circulation, including the cerebral vessels. It is thought that, in order to bypass the lungs and create systemic emboli, the particles must pass through pulmonary precapillary shunts, through recruitable pulmonary vessels, or through the pulmonary capillary bed directly. Also, a patent foramen ovale, which has been documented in 20% to 34% of the population¹³, may allow paradoxical embolism of fat and bone marrow debris.

Gurd's criteria are used to aid in the diagnosis of fat embolism syndrome¹⁴. The major criteria are axillary or subconjunctival petechia, hypoxemia, depression of the central nervous system disproportionate to what would be expected with hypoxemia, and pulmonary edema. The minor criteria include tachycardia, pyrexia, emboli on funduscopic examination, fat in the urine, a sudden unexplainable drop in platelet or hematocrit values, an increasing erythrocyte sedimentation rate, and fat in the sputum. At least one of these major signs and at least four of the minor signs must be present for fat embolism syndrome to be diagnosed^14,15. While fulminant fat embolism syndrome is rare in the setting of total knee arthroplasty, major complications linked to fat embolism have been reported¹⁶.

Bone cement implantation syndrome is another clinical entity described in the literature. The syndrome is characterized by cardiopulmonary disturbances, and Ereth et al.³ showed that patients who underwent total hip arthroplasty with cement had a greater prevalence of decreased cardiac output, increased pulmonary artery pressure, and increased pulmonary vascular resistance than did patients who underwent total hip arthroplasty without cement. Rates of embolization, as monitored with transesophageal echocardiography, were significantly greater during insertion of the prosthesis in total hip arthroplasties performed with cement than they were during insertion in cementless arthroplasties. The authors attributed the higher rates of embolization in the cement group to higher intramedullary pressures created with use of a cemented prosthesis³. While, in the present study, we investigated total knee arthroplasty, we believe that the increased intramedullary pressures created during conventional total knee arthroplasty may have similar, but smaller, embolism-producing effects.

In this study, the six-month follow-up MMSE scores of both groups were significantly higher than the postoperative scores. This finding was anticipated because mental status is commonly compromised in the postoperative period after total knee arthroplasty¹. The six-month follow-up scores for both groups were also significantly higher than the preoperative scores. We postulate that fasting, the stress of being in the preoperative holding area, and the inevitable lack of sleep caused the patients to have a preoperative score that was lower than their true baseline.

It has been suggested that the longer operative times needed for computer-navigated total knee arthroplasty negate any beneficial effect that might be achieved by avoiding the insertion of intramedullary rods⁴. However, the operative times did not differ significantly between the study groups in this study. We believe that the similar operative times were due to the fact that, in our high-volume practice, the navigated procedure was done by a highly trained and experienced surgeon who had performed more than 2500 computer-navigated total knee arthroplasties.

A possible weakness of our study is that the MMSE is not sensitive enough to determine subtle differences in mental status between the two groups. It is also possible that the MMSE is not an appropriate indicator of the effects of fat and bone-marrow-debris emboli. Like us, Kalairajah et al.⁴ found no difference between computer-assisted-arthroplasty and control groups in terms of mental status test scores on the first or third postoperative day; however, they did not describe the method that they used to test mental status. They proposed that a sample size of sixty patients per group tested on the first postoperative day would be needed to show a significant difference. Our study of nearly fifty patients per group falls short of that calculated number, but our follow-up went beyond one postoperative day. Another limitation of our study is the fact that the six-month follow-up could not be completed for every patient. One other weakness relates to intentional exclusion of the "vulnerable" patients with mental health issues and diseases that may have predisposed them to cognition changes. Hence, it is possible that the true incidence of alterations in cognition following total knee arthroplasty is higher than what we reported, as the patients most at risk for an alteration in mental status were excluded.

As the use of computer-assisted total knee arthroplasty continues to increase, the advantages and disadvantages need to be considered. The benefit of fewer fat and bone-marrow-debris emboli, as claimed by some, does not seem to have an effect on postoperative mental status as revealed by our comparison of patients treated with conventional and computer-navigated arthroplasty. Further research is needed to elucidate how the emboli form, to determine if their numbers are truly decreased with computer-assisted total knee arthroplasty, and to ascertain if there is any clinical relevance to such a reduction.

References

Introduction | Materials and Methods | Results | Discussion | References

Rex FS; Worland R; Blanco C. Lack of mental-status changes in patients undergoing total knee arthroplasty. J Arthroplasty. 2004;19:635-7.[PubMed][CrossRef]

Riding G; Daly K; Hutchinson S; Rao S; Lovell M; McCollum C. Paradoxical cerebral embolisation. An explanation for fat embolism syndrome. J Bone Joint Surg Br. 2004;86:95-8.[PubMed]

Ereth MH; Weber JG; Abel MD; Lennon RL; Lewallen DG; Ilstrup DM; Rehder K. Cemented versus noncemented total hip arthroplasty-embolism, hemodynamics, and intrapulmonary shunting. Mayo Clin Proc. 1992;67:1066-74.[PubMed]

Kalairajah Y; Cossey AJ; Verrall GM; Ludbrook G; Spriggins AJ. Are systemic emboli reduced in computer-assisted knee surgery?: A prospective, randomised, clinical trial. J Bone Joint Surg Br. 2006;88:198-202.[PubMed]

Kim YH; Kim JS; Hong KS; Kim YJ; Kim JH. Prevalence of fat embolism after total knee arthroplasty performed with or without computer navigation. J Bone Joint Surg Am. 2008;90:123-8.[PubMed][CrossRef]

American Society of Anesthesiologists. New classification of physical status. Anesthesiology. 1963;24:111-4.

Harling DW. Consistency of ASA grading. Anaesthesia. 1995;50:659.[PubMed]

Little JP. Consistency of ASA grading. Anaesthesia. 1995;50:658-9.[PubMed]

Cherny NI. Opioid analgesics: comparative features and prescribing guidelines. Drugs. 1996;51:713-37.[PubMed][CrossRef]

Levy MH. Pharmacologic treatment of cancer pain. N Engl J Med. 1996;335:1124-32.[PubMed] [CrossRef]

Tombaugh TN; McIntyre NJ. The mini-mental state examination: a comprehensive review. J Am Geriatr Soc. 1992;40:922-35.[PubMed]

Von Bergmann E. Ein fall tödlicher Fettembolie. Berl Klin Wochenschr. 1873;10:385-7. German.

Hagen PT; Scholz DG; Edwards WD. Incidence and size of patent foramen ovale during the first 10 decades of life: an autopsy study of 965 normal hearts. Mayo Clin Proc. 1984;59:17-20.[PubMed]

Gurd AR. Fat embolism: an aid to diagnosis. J Bone Joint Surg Br. 1970;52:732-7.[PubMed]

Levy D. The fat embolism syndrome. A review. Clin Orthop Relat Res. 1990;261:281-6.[PubMed]

Orsini EC; Richards RR; Mullen JM. Fatal fat embolism during cemented total knee arthroplasty: a case report. Can J Surg. 1986;29:385-6.[PubMed]

Topics

obesity ; cognition ; computers ; knee replacement arthroplasty ; mini-mental state examination ; embolism ; mental function

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Craig T. Haytmanek, Aidin Eslam Pour, Camilo Restrepo, Jain Nikhil, Javad Parvizi, William J. Hozack; Cognition Following Computer-Assisted Total Knee ArthroplastyA Prospective Cohort Study. The Journal of Bone & Joint Surgery. 2010 Jan;92(1):92-97.

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