Extramedullary Guides Research Articles

The Deep-MCL Line: A Reliable Anatomical Landmark to Optimize the Tibial Cut in UKA.

The extramedullary guides for the tibial resection during medial unicompartmental knee arthroplasty (UKA) are inaccurate, with an error risk in coronal and sagittal planes and cut thickness. It was our hypothesis that the use of anatomical landmarks for the tibial cut can help the surgeon to improve accuracy. The technique described in this paper is based on the use of a simple and reproducible anatomical landmark. This landmark is the line of insertion of the fibers of the deep medial collateral ligament (MCL) around the anterior half of the medial tibial plateau called the "Deep MCL insertion line". The used anatomical landmark determines the orientation (in the coronal and sagittal planes) and the thickness of the tibial cut. This landmark corresponds to the line of insertion of the fibers of the deep MCL around the anterior half of the medial tibial plateau. A consecutive series of patients who underwent primary medial UKA between 2019 and 2021 were retrospectively reviewed. A total of 50 UKA were included. The mean age at the time of surgery was 54.5 ± 6.6 years (44-79). The radiographic measurements showed very good to excellent intra-observer and inter-observer agreements. The limb and implant alignments and the tibial positioning were satisfying, with a low rate of outliers and good restoration of the native anatomy. The landmark of the insertion of deep MCL constitutes a reliable and reproducible reference for the tibial cut axis and thickness during medial UKA, independent of the wear severity.

Extramedullary Tibial Guide Alignment Is Not Affected by Excess Lower Limb Fat Distribution in Total Knee Arthroplasty.

BackgroundThe goal of this study is to investigate whether excess lower limb fat distribution affects tibial guide alignment in conventional total knee arthroplasty (TKA) with extramedullary guides. A thicker soft tissue envelope may affect the accuracy of extramedullary cutting guide placement and subsequent instrumentation. Previous studies have used body mass index (BMI) to stratify patients, a poor proxy of lower limb fat distribution, which may explain conflicting results reported on this topic to date. This study overcomes this issue by using a novel, radiographic anthropometric index to assess lower limb fat distribution.MethodologyThis is a single-surgeon, single-implant, single-centre retrospective series of 102 consecutive primary TKAs. The suprapatellar fat index (SPFI) and BMI were recorded for all patients, and postoperative tibial component alignment measurements were calculated. Secondary outcome measures included femoral component alignment, femorotibial alignment, length of hospital stay, tourniquet time, blood loss, and complications/reoperations.ResultsIn this study, 102 patients (average age of 69) had an average BMI of 30.8 kg/m2 (19.2-45.5 kg/m2) and an average SPFI of 0.26 (0.09-0.57). Multiple regression analysis demonstrated that increasing leg fat distribution did not affect tibial component alignment in the coronal or sagittal plane.ConclusionsExcess lower limb fat distribution, simply measured using the SPFI, does nothave a significant effect on tibial component positioning when extramedullary guides are used in conventional TKA.

The impact of custom cutting guides on patient satisfaction and residual symptoms following total knee arthroplasty

BackgroundCustom cutting guides (CCGs) in total knee arthroplasty (TKA) use preoperative three-dimensional (3-D) imaging to manufacture cutting blocks specific to a patient's anatomy. The purpose of this study was to evaluate the impact of CCGs versus standard intramedullary and extramedullary guides on patient-reported satisfaction and residual symptoms following TKA. MethodsA retrospective, multicenter study was performed to compare a magnetic resonance imaging-based CCG system versus standard instrumentation. All patients received the same, cemented, fixed-bearing, cruciate-retaining component, and had a primary diagnosis of osteoarthritis. Data was collected by an independent, third party survey center blinded to surgical technique that administered telephone questionnaires assessing patient satisfaction and symptoms. Patient age, gender, minority status, education level, income, length of follow-up, and pre-arthritic UCLA scores were considered potential confounders and accounted for using multivariate logistic regression analyses. Results448 patients (107 CCGs, 341 standard) were successfully interviewed. At a mean follow-up of threeyears, there was no difference in percentage of patients reporting their knee to feel “normal” (74% CCG versus 78% standard, p=0.37). Residual symptoms including knee stiffness (37% CCG versus 28% standard, p=0.08) and difficulty getting in and out of car (34% CCG versus 30% standard, p=0.40) remained high. Multivariate regression analyses demonstrated no differences between the two cohorts for both patient-reported satisfaction and residual symptoms (odds ratios 0.72 to 1.48; p=0.10 to 0.81). ConclusionWhen interviewed by an independent, blinded third party, the use of CCGs in TKA did not improve patient-reported satisfaction or residual symptoms versus the use of standard alignment guides.

Impact of Use of Intramedullary and Extramedullary Guides on Tibial Component Geometry in Total Knee Replacements: A Systematic Review and Meta-Analysis.

Mechanical guides in total knee arthroplasty are divided into intramedullary and extramedullary systems, designed to give accurate reference, to enable the surgeon to perform a tibial cut which is perpendicular to the mechanical axis. We conducted a systematic review and meta-analysis of levels 1 and 2 published data which directly compares the two methods of alignment, with outcomes of interest being the mean tibial component angle to the mechanical axis and the number of outliers from the optimal range. The PRISMA (preferred reporting items for systematic reviews and meta-analysis) guidance was followed. A search was conducted of online databases Medline PubMed; EMBASE; ISI Web of Science, and the Cochrane library, using the Boolean search string ([intramedullary OR extramedullary] AND knee AND [arthroplasty OR replacement]). Numerical data pertaining to tibial component alignment (TCA), the mechanical tibiofemoral angle, the tibial slope, and the number of outliers from optimal TCA were collated, and used to establish pooled results. No constraints on the search in terms of year of publication or language were instituted. Intrastudy bias was assessed using the Jadad score for randomized controlled trials and the Newcastle Ottawa score for prospective cohort studies. A total of 1,896 titles were reviewed. Following abstract review and full review of relevant articles, 10 publications were included for analysis, of which 8 were suitable to include for meta-analysis. No trials showed a significant difference in the mean TCA. Two trials showed an increased number of outliers in the extramedullary group and two studies showed an increased number of outliers in the intramedullary group. Pooled data from studies which included these outcomes showed no advantage for either system in limiting the number of outliers from the optimal TCA (relative risk, 0.99; 95% confidence interval [CI], 0.87-1.14; p = 0.004), and no significant difference in mean TCA (standardized mean difference, -0.07; 95% CI, -0.22 to 0.08; p = 0.000). Based on our results, no advantage can be attributed to the type of mechanical guide used in obtaining an adequate tibial cut.

Extramedullary guides versus PSI versus portable navigation for tibial alignment in total knee arthroplasty

Extramedullary guides versus PSI versus portable navigation for tibial alignment in total knee arthroplasty

Extramedullary Guides Versus Portable, Accelerometer-Based Navigation for Tibial Alignment in Total Knee Arthroplasty: A Randomized, Controlled Trial: Winner of the 2013 HAP PAUL Award

Extramedullary (EM) tibial alignment guides have demonstrated a limited degree of accuracy in total knee arthroplasty (TKA). The purpose of this study was to compare the tibial component alignment obtained using a portable, accelerometer-based navigation device versus EM alignment guides. One hundred patients were enrolled in this prospective, randomized controlled study to receive a TKA using either the navigation device, or an EM guide. Standing AP hip-to-ankle and lateral knee-to-ankle radiographs were obtained at the first, postoperative visit. 95.7% of tibial components in the navigation cohort were within 2° of perpendicular to the tibial mechanical axis, versus 68.1% in the EM cohort (P<0.001). 95.0% of tibial components in the navigation cohort were within 2° of a 3° posterior slope, versus 72.1% in the EM cohort (P=0.007). A portable, accelerometer-based navigation device decreases outliers in tibial component alignment compared to conventional, EM alignment guides in TKA.

Safe and Accurate Utilization of Patient-specific Guides in Total Knee Arthroplasty

Patient-specific guides (PSG) are an emerging technology in total knee arthroplasty (TKA). This technology utilizes advanced imaging modalities to create 3-dimensional models of a patient’s unique anatomy. This model is then utilized in conjunction with computer software to preoperatively determine bony resection, implant sizing, and implant placement. The PSG are then utilized intraoperatively to efficiently and accurately reproduce the preoperative plan. We believe proper use of the PSG relies on proper exposure, confirming proper guide placement, and checking for accurate bony resection. All 2 of these objectives can be achieved by honoring traditional methods and utilizing traditional tools such as extramedullary guides, calipers, and styluses. In this article, we describe our preferred technique for safely and accurately performing a total knee arthroplasty using PSG.

The tibial crest as a practical useful landmark in total knee arthroplasty

BackgroundThe middle one-third of the tibial crest in the coronal plane and the fibula in the sagittal plane are known as landmarks for extramedullary guides in total knee arthroplasty (TKA). However, there are few foundational anatomic studies about them. We conducted this study to confirm whether these landmarks are reliable. MethodsWe evaluated 100 Japanese knees using 3D imaging software. We examined our data for correlations between the angle of deviation from the mechanical axis and patient-specific factors (i.e. hip-knee-ankle angle, tibial length, tibial bowing, and tibial torsion) to determine whether there are any individual factors affecting their reliability. ResultsThe mean angles between each of the axes defined by the fibula and the tibial crest with the mechanical axis were 2.9°±0.6° of valgus and 0.7°±0.9° of varus in the coronal plane and 2.2°±0.8° of posterior and 3.6°±1.0° of anterior inclination in the sagittal plane. The middle one-third of the tibial crest (TCL) was revealed as a useful landmark, especially in female patients, who possess TCLs that were within 3° of the tibial mechanical axis in the coronal plane. There were no patient-specific factors strongly affecting reliability of these landmarks. ConclusionsWe can use these landmarks even if the patient has tibial bowing or severe varus deformity. Although not considering soft tissue thickness, our study demonstrated that the tibial crest in the coronal and sagittal planes could be useful guidelines in performing TKAs. Level of evidenceII

Are MRI-based, patient matched cutting jigs as accurate as the tibial guides?

The aim of this study is to evaluate the accuracy of VISIONAIRE (Smith & Nephew Inc., Memphis, TN, USA) Patient Matched cutting tibial jigs in comparison with extramedullary (EM) tibial instrumentation by analysing data as detected by intra-operative use of VectorVision knee navigation software from BrainLAB (Redwood City, CA, USA). Twelve patients were selected for unilateral total knee replacement (TKR). They underwent a full-length weight-bearing anteroposterior (AP) radiograph and magnetic resonance imaging (MRI). During surgery, once the EM guides were placed and fixed on the tibia, the orientation in the coronal and sagittal planes was checked by the navigator and then compared with the data obtained by measuring the orientation of VISIONAIRE Patient Matched cutting tibial jigs. An unsatisfactory result was considered an error ≥2° in both coronal and sagittal planes for the tibial component as a possible error of 4° could result. In the coronal plane the mean deviation of the EM tibial guides from the ideal alignment (0°) was 0.7 ± 0.39° and of the VISIONAIRE was 129 ± 1.55° (P = 0.22). In the sagittal plane the mean deviation of the EM tibial guides from 3° of posterior slope was -1.62 ± 1.78° and of the VISIONAIRE was +1.16 ± 4.29° (P < 0.05). Negative values indicate a more posterior slope from the ideal and positive values an anterior slope. This preliminary study documented only a fair accuracy of the method with a consistent risk of error of more of 3° especially in the sagittal plane. We could speculate that the problem in the sagittal plane was due to the fact that the pre-operative protocol does not include a lateral X-ray projection of the knee and only includes an AP standing X-ray of the straight leg and MRI.

Extramedullary versus intramedullary tibial cutting guides in megaprosthetic total knee replacement

BackgroundIn a standard total knee replacement, tibial component alignment is a key factor for the long term success of the surgery. The purpose of this study is to compare the accuracy of extramedullary and intramedullary tibial cutting guides used in indigenous and imported implants respectively, in positioning of the tibial components in megaprosthetic knee replacements.MethodsA comparative study of the accuracy of extramedullary and intramedullary tibial cutting guides was carried out in 92 megaprosthetic knee replacements for distal femoral tumors. For the proximal tibia cut for tibial component placement, an extramedullary guide was used in 65 patients and an intramedullary guide was used in 27 patients. Tibial component alignment angles were measured in postoperative X-rays with the help of CAD software.ResultsThere was more varus placement in coronal plane with extramedullary cutting guide (−1.18 +/− 2.4 degrees) than the intramedullary guide (−0.34 +/− 2.31 degrees) but this did not reach statistical significance. The goal of 90 +/− 2 degrees alignment of tibial component was achieved in 54% of patients in the extramedullary group versus 67% in the intramedullary group. In terms of sagittal plane alignment, extramedullary guide showed less accurate results (2.09 +/− 2.4 degrees) than intramedullary guide (0.50 +/− 3.80 degrees) for tibial component alignment, though 78% of patients were aligned within the goal of 0–5 degrees of tibial slope angle in extramedullary group versus 63% in intramedullary group. The mean error in the measurements due to rotation of the knee during taking the X-rays was less than 0.1 degrees and distribution of the X-rays with the rotation of knee was similar in both the groups.ConclusionsOverall, in megaprosthetic knee replacement intramedullary guides gave more accurate results in sagittal plane and exhibited similar variability as of extramedullary guides in coronal plane.

Computer-Assisted Techniques Versus Conventional Guides for Component Alignment in Total Knee Arthroplasty

Optimal alignment of the prosthesis in total knee arthroplasty results in improved patient outcomes. The goal of this study was to determine the most accurate technique for component alignment in total knee arthroplasty by comparing computer-assisted surgery with two conventional techniques involving use of an intramedullary guide for the femur and either an intramedullary or an extramedullary guide for the tibia. One hundred and seven patients were randomized prior to surgery to one of three arms: computer-assisted surgery for both the femur and the tibia (the computer-assisted surgery group), intramedullary guides for both the femur and the tibia (the intramedullary guide group), and an intramedullary guide for the femur and an extramedullary guide for the tibia (the extramedullary guide group). Measurements of alignment on hip-to-ankle radiographs and computed tomography (CT) scans made three months after surgery were evaluated. The operative times and complications were compared among the three groups. The coronal tibiofemoral angle demonstrated, on average, less malalignment in the computer-assisted surgery group (1.91°) than in the extramedullary (3.22°) and intramedullary (2.59°) groups (p = 0.007). The coronal tibiofemoral angle was >3° of varus or valgus deviation in 19% (seven) of the thirty-six patients treated with computer-assisted surgery compared with 38% (thirteen) of the thirty-four in the extramedullary guide group and 36% (thirteen) of the thirty-six in the intramedullary guide group (p = 0.022). The increase in accuracy with computer-assisted surgery came at a cost of increased operative time. The operative time for the computer-assisted surgery group averaged 107 minutes compared with eighty-three and eighty minutes, respectively, for the surgery with the extramedullary and intramedullary guides (p < 0.0001). There was no significant difference in any of the outcomes between the intramedullary and extramedullary guide groups. This study provides evidence that the implant alignment with computer-assisted total knee arthroplasty, as measured with radiography and computed tomography, is significantly improved compared with that associated with conventional surgery with intramedullary or extramedullary guides. This finding adds to the body of evidence showing an improved radiographic outcome with computer-assisted surgery compared with that following conventional total knee arthroplasty.

Anterior border of the tibia as a landmark for extramedullary alignment guide in total knee arthroplasty for varus knees

A disadvantage to using extramedullary alignment guides of the tibia for total knee arthroplasty (TKA) is difficulty in correctly identifying the ankle center. The anterior border of the tibia is easily palpable, as it is not covered by muscles and its shape is convex anteriorly. We hypothesized that appropriate points exist along the anterior border that can be used as landmarks for extramedullary guides. Prior to TKA, computed tomographic images of the entire tibia were obtained from 101 osteoarthritic knees with varus deformities. The relationship between the lines connecting two points on the anterior border and the mechanical axis was evaluated using 3D imaging software. The mean angles between each of 10 determined axes and the mechanical axis varied from 3.2° varus to 2.1° valgus in the coronal plane. In the sagittal plane, all axes referencing the anterior border of the tibia showed anterior inclination to the mechanical axis. The line connecting the medial one-third of the patellar tendon attachment and the distal one-fourth of the anterior border, however, was highly consistent and parallel to the mechanical axis in the coronal plane. This axis can be effectively used as a landmark for extramedullary guides during TKA.

The accuracy of extramedullary guides for tibial component placement in total knee arthroplasty

Anteroposterior radiographs that included the whole tibia were taken before and after 75 total knee arthroplasties in 48 patients. The same tibial extra-medullary alignment guide system was used in every knee. The average tibial component alignment was 0.4 (SD 2.5, range -4.9 to 6.4) degrees of valgus post-operatively. 59 tibial components (78.7%) had a tibial cut within 3 degrees from being perpendicular to the mechanical axis, ten were too valgus (13.3%) and six were too varus (8%). The chance of the tibial components becoming too varus was higher if there was lateral tibial bowing, compared with no tibial bowing (p=0.048). A smaller lateral width of the leg increased the chance of the tibial components becoming too valgus (p=0.047).

Extramedullary Versus Intramedullary Tibial Alignment Guides for Total Knee Arthroplasty

This retrospective study evaluated whether intramedullary or extramedullary tibial alignment guides are more accurate in assuring correct tibial component positioning in total knee arthroplasties (TKAs). Fifty-five TKAs were performed with the only difference being whether an intramedullary (31) or extramedullary (24) cutting guide was used. Pre- and postoperative tibiofemoral angle, tibial component alignment angle, and femoral component alignment angles were measured and the results were statistically analyzed. We also performed a subgroup analysis on the preoperative varus knees to determine if the presence of a varus deformity would have better results with either the intramedullary or extramedullary cutting guide. The 2-sample t test was used to compare the results of the two groups. The results showed no statistical difference in alignment of the tibial component when using the intramedullary or extramedullary guides.

Identifying the center of the femoral head using ultrasonography to assess the higher accuracy of femoral extramedullary guides in TKA

To identify the center of the femoral head (FHC), which is critical for determining the mechanical axis of the femur in total knee arthroplasty (TKA), we used a high-resolution ultrasound technique in 200 hips in 128 patients with osteoarthritis of the knee. FHC was defined as the intersection of two lines: the maximum diameter of the femoral head between the superior and inferior edges of the head and the maximum diameter of the femoral head between the medial and lateral edges. Ultrasound identified the FHC within 5 mm in 56% of cases and within 10mm in 89.5%. Ultrasound appears to be a highly reliable, noninvasive imaging modality for identifying the FHC preoperatively or even intraoperatively. Therefore, our procedure might ultimately be helpful in establishing the correct alignment of the prosthesis.

Geometric analysis of potential error in using femoral intramedullary guides in total knee arthroplasty

Abstract: Proper component orientation is necessary for the long-term success of a total knee arthroplasty. Femoral component placement has used jigging systems that are based on intramedullary and extramedullary guides. The intramedullary system has been shown to foster more accurate and reproducible placement of the femoral component. This study analyzed and quantified the potential error of the intramedullary guide system. Geometric data of the human femur were obtained from radiographs of 45 cadaver femora in the anteroposterior and lateral views. The correct entry point of the intramedullary rod in the distal femur is the midaxial line of the femoral canal on anteroposterior and lateral radiographs. The position of this point in relation to the mediolateral and anteroposterior dimensions of the distal femur was calculated as a ratio. The average calculated ratios were anteroposterior, 0.53 offset medially; lateral, 0.32 offset anterior. Mathematical models were constructed to quantify the potential varus valgus and flexion extension error of the guide rods. Variables investigated were entry point location, guide rod diameter, guide rod length, and rotation. The surgeon must be cognizant of these potential sources of error to maximize the accuracy of the femoral intramedullary jigging system.

Influence of intramedullary versus extramedullary alignment guides on final total knee arthroplasty component position: A radiographic analysis

A prospective study of 116 consecutive Kinemax cemented posterior cruciate ligament-retaining total knee arthroplasties was carried out. Similar surgical technique was used with a single variable: 61 were implanted using intramedullary guides on the tibia and 55 were implanted using extramedullary guides on the tibia. A radiographic study was performed after at least 1 year of follow-up to evaluate postoperative component position and compare the difference in the accuracy of positioning of the femoral and tibial components. Radiographic analysis showed that satisfactory position was achieved using both types of instrumentation. No statistically significant difference was observed in either the coronal or sagittal plane of the femoral component and the sagittal plane positioning of the tibial component. However, the coronal plane positioning of the tibial component revealed a statistically significant difference ( P <.01), with intramedullary guides being superior to extramedullary guides. Also observed, was that using either technique, patients with less accurate postoperative positioning tended to be obese, with wide intramedullary canals. Patients with significant extraarticular deformities, marked bowing, and those with prior surgery or fractures may not be suitable for intramedullary guides, and they may require the use of extramedullary guides and intraoperative radiographic control. The ideal indication for the use of intramedullary instrumentation is in the patient who is not obese, with no extraarticular deformity, and with a well-defined, but not excessively wide, tibial medullary canal. Since tibial component malalignment in general, and coronal plane malalignment in particular, may adversely affect the long-term survival of total knee arthroplasties, the use of intramedullary alignment instrumentation is recommended when possible.

The Incidence of Large Venous Emboli During Total Knee Arthroplasty Without Pneumatic Tourniquet Use

Echogenic venous emboli accompany tourniquet deflation during total knee arthroplasty.Two types of echogenic emboli appear in the central circulation: small venous emboli (miliary emboli) and large venous emboli (masses of echogenic material superimposed on miliary emboli). Presumably, medullary cavity trespass releases small and large echogenic emboli. However, patients undergoing lower extremity procedures with a tourniquet have large echogenic emboli regardless of medullary cavity invasion. Avoiding tourniquet inflation may decrease the release of large venous emboli. Thirteen patients undergoing total knee arthroplasty without pneumatic tourniquet received intramedullary guides and 11 patients received tibial extramedullary guides. Recordings of hemodynamic variables, mixed venous oximetry, end-tidal CO2, and echocardiographic images were made after the induction of anesthesia and for 15 min after femoral prosthesis cementing. Mean arterial pressure did not change during the study, and mean pulmonary arterial pressure increased minimally. Large venous emboli appeared in eight patients, small venous emboli appeared in 12 patients, and no emboli appeared in four patients. Compared with previous investigations of large venous emboli during total knee arthroplasty with a pneumatic tourniquet, multiple logistic regression analysis discloses a 5.33-fold greater risk of large venous embolism accompanied the use of a tourniquet during total knee arthroplasty. Implications: One third of knee replacements performed without a tourniquet demonstrated large emboli. Reducing marrow cavity invasion did not decrease the release of large emboli. Compared with knee replacement without tourniquet, tourniquet use places patients at a 5.33-fold greater risk of having a large emboli. (Anesth Analg 1998;87:439-44)

The incidence of venous emboli during extramedullary guided total knee arthroplasty.

During total knee arthroplasty (TKA), instrumentation of the marrow cavity with an intramedullary guide appears responsible for fatal intraoperative pulmonary embolism. Transesophageal echocardiography demonstrates venous emboli (VE) after tourniquet deflation during intramedullary guided TKA. Extramedullary guides avoid manipulating the marrow cavity. We determined the incidence of VE in 20 patients undergoing extramedullary guided TKA. Recordings of hemodynamic variables, mixed venous oximetry, end-tidal CO2 and N2 tensions, and echocardiograph images occurred after induction of anesthesia, after tourniquet inflation, during cementing, and for 15 min after tourniquet deflation. Large VE appeared in 14 patients and small VE in the other 6 patients. Large VE occurred only after deflation of the tourniquet. Beginning 3 min after tourniquet deflation, mean pulmonary arterial pressures increased from the baseline of 21 +/- 1.0 to 30 +/- 1.3 mm Hg and remained increased for the duration of the procedure. The incidence of large VE with extramedullary guided TKA did not differ compared to the previously reported incidence with intramedullary guided TKA. These data suggest that VE might arise from a thrombogenic effect of the tourniquet rather than from manipulation of the marrow cavity.

The Incidence of Venous Emboli During Extramedullary Guided Total Knee Arthroplasty

During total knee arthroplasty (TKA), instrumentation of the marrow cavity with an intramedullary guide appears responsible for fatal intraoperative pulmonary embolism.Transesophageal echocardiography demonstrates venous emboli (VE) after tourniquet deflation during intramedullary guided TKA. Extramedullary guides avoid manipulating the marrow cavity. We determined the incidence of VE in 20 patients undergoing extramedullary guided TKA. Recordings of hemodynamic variables, mixed venous oximetry, end-tidal CO2 and N2 tensions, and echocardiograph images occurred after induction of anesthesia, after tourniquet inflation, during cementing, and for 15 min after tourniquet deflation. Large VE appeared in 14 patients and small VE in the other 6 patients. Large VE occurred only after deflation of the tourniquet. Beginning 3 min after tourniquet deflation, mean pulmonary arterial pressures increased from the baseline of 21 +/- 1.0 to 30 +/- 1.3 mm Hg and remained increased for the duration of the procedure. The incidence of large VE with extramedullary guided TKA did not differ compared to the previously reported incidence with intramedullary guided TKA. These data suggest that VE might arise from a thrombogenic effect of the tourniquet rather than from manipulation of the marrow cavity. (Anesth Analg 1995;81:757-62)