JBJS | Radiographic Analysis of Low Contact Stress Meniscal Bearing Total Knee Replacements

The Journal of Bone & Joint Surgery, Volume 83, Issue 2

Articles | February 01, 2001

Radiographic Analysis of Low Contact Stress Meniscal Bearing Total Knee Replacements

James M. Hartford, MD; Daxes Banit, MD; Keith Hall, MD; Herbert Kaufer, MD

Investigation performed at the Division of Orthopaedic Surgery, University of Kentucky, Chandler Medical Center, Lexington, Kentucky
James M. Hartford, MD Daxes Banit, MD Keith Hall, MD Herbert Kaufer, MD Division of Orthopaedic Surgery, University of Kentucky, Chandler Medical Center, K414 Kentucky Clinic, 740 South Limestone, Lexington, KY 40536
No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. No funds were received in support of this study.

The Journal of Bone & Joint Surgery. 2001; 83:229-229

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Abstract

Background: Meniscal bearing total knee replacements were developed to decrease the contact stresses on polyethylene and to reduce polyethylene wear. The kinematics of meniscal bearing knee replacements is poorly understood. The present study was designed to evaluate, with radiographic analyses, the motion of the meniscal bearings and the femoral rollback of the Low Contact Stress meniscal bearing knee replacement during knee flexion.

Methods: Eighty-one Low Contact Stress meniscal bearing total knee replacements in seventy-six male patients were assessed on fluoroscopically centered lateral radiographs made with the knee in full extension and in full flexion at an average of six years (range, twenty-four to 147 months) after the operation. The distance and direction of motion of the meniscal bearings and the center contact position of the femoral condyles were measured. Knee evaluations were performed with use of the Knee Society rating system.

Results: The average range of motion of the knees, measured on lateral radiographs, was 90° (range, 45° to 136°). As they moved from terminal extension to terminal flexion, thirty-nine knees (48%) exhibited anterior motion of both bearings and sixteen (20%) demonstrated posterior motion of both bearings. Ten knees (12%) had reciprocal motion of the two bearings (one bearing moving anteriorly and one bearing moving posteriorly) with flexion, nine knees (11%) had motion of only one bearing, and seven knees (9%) had no motion of either bearing. When moving from full extension to full flexion, eighteen knees (22%) demonstrated femoral rollback, six knees (7%) showed no change in the position of femoral contact, and fifty-seven knees (70%) exhibited anterior sliding of the femoral condyles. Flexion of the knees demonstrating femoral rollback averaged 104° (range, 76° to 128°), and flexion of the knees demonstrating anterior sliding averaged 94° (range, 45° to 125°). The difference was significant (p = 0.03). According to the Knee Society rating system, the average clinical score for the entire group was 76 points (range, 27 to 100 points) and the average functional score for the entire group was 72 points (range, 30 to 100 points). The average clinical score was 79 points (range, 27 to 98 points) for the knees that exhibited anterior sliding of the femoral condyles and 87 points (range, 52 to 100 points) for those exhibiting femoral rollback (p = 0.09). The average functional scores were 64 points (range, 30 to 100 points) and 72 points (range, 45 to 100 points), respectively (p = 0.15).

Conclusions: Radiographic analysis of meniscal bearing total knee replacements demonstrated an average anterior motion of both the medial and the lateral meniscal bearing of 4.7 mm (range, 1 to 14 mm) in thirty-nine knees (48%) as they moved from terminal extension to terminal flexion. Sixty-three knees (78%) demonstrated no femoral rollback as they were flexed. Knees with anterior sliding of the condyles had a significantly smaller average range of flexion (p = 0.03) and a lower average Knee Society score than did knees demonstrating femoral rollback. We believe that lack of rollback indicates a functional insufficiency of the posterior cruciate ligament.

Figures in this Article

Introduction

Introduction | Materials and Methods | Results | Discussion | References

Goodfellow and O'Connor^1,2 introduced the meniscal bearing knee replacement (the Oxford knee) in 1976. This prosthesis provided a mobile congruent articulating surface that offered greater contact surface area and reduced contact stresses on the polyethylene³. The reason for the development of the meniscal bearing knee was to reduce polyethylene stresses and wear and thus to increase the longevity of the prosthesis.

There are few published reports on the in vivo kinematics of meniscal bearing total knee replacements. Bradley et al.⁴ performed an early radiographic analysis of the Oxford unicompartmental knee replacement and found posterior motion of the meniscal bearings on the tibia as the knee moved from extension to flexion. The purposes of our study were to examine the direction and degree of motion of the meniscal bearings and the femoral center contact point of the Low Contact Stress meniscal bearing total knee replacement (DePuy, Warsaw, Indiana) and to identify any association between the knee kinematics and the clinical outcome.

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Fig. 1-A:: Fluoroscopically centered lateral radiographs of a meniscal bearing knee replacement in full extension (Fig. 1-A) and full flexion (Fig. 1-B).

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Fig. 1-B:: Fluoroscopically centered lateral radiographs of a meniscal bearing knee replacement in full extension (Fig. 1-A) and full flexion (Fig. 1-B).

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Fig. 2-A:: Lateral radiographs showing anterior sliding of the femoral condyles. The black arrows represent the center contact point, and the open arrows identify the positions of the radiopaque markers embedded in the polyethylene meniscal bearing.

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Fig. 2-B:: Lateral radiographs showing anterior sliding of the femoral condyles. The black arrows represent the center contact point, and the open arrows identify the positions of the radiopaque markers embedded in the polyethylene meniscal bearing.

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Fig. 3-A:: Lateral radiographs showing femoral rollback. The black arrows represent the center contact point, and the open arrows identify the positions of the radiopaque markers embedded in the polyethylene meniscal bearing.

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Fig. 3-B:: Lateral radiographs showing femoral rollback. The black arrows represent the center contact point, and the open arrows identify the positions of the radiopaque markers embedded in the polyethylene meniscal bearing.

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TABLE I: Position of the Femoral Condyles and Range of Motion

Position of Femoral Condyles	Range of Motion* (deg)
Extension			Flexion			Arc of Motion
Rollback (n = 18)	3 (-7-12)	}	p = 0.03	104 (76-128)	}	p = 0.03	101 (69-136)	}	p = 0.009
Anterior sliding (n = 57)	7 (-3-29)	94 (45-125)	87 (45-120)
Neutral (n = 6)	7 (0-20)		87 (70-100)		80 (60-100)

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

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TABLE I: Position of the Femoral Condyles and Range of Motion

Position of Femoral Condyles	Range of Motion* (deg)
Extension			Flexion			Arc of Motion
Rollback (n = 18)	3 (-7-12)	}	p = 0.03	104 (76-128)	}	p = 0.03	101 (69-136)	}	p = 0.009
Anterior sliding (n = 57)	7 (-3-29)	94 (45-125)	87 (45-120)
Neutral (n = 6)	7 (0-20)		87 (70-100)		80 (60-100)

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

Materials and Methods

Introduction | Materials and Methods | Results | Discussion | References

Eighty-one Low Contact Stress meniscal bearing total knee replacements in seventy-six men were prospectively evaluated at our institution. The patients were evaluated during routine yearly follow-up in the Veterans' Administration orthopaedic clinic. The routine yearly follow-up includes determination of Knee Society clinical and functional scores as well as fluoroscopically centered flexion and extension lateral radiographs. The University of Kentucky and the Lexington Veterans' Administration Institutional Review Board had approved the use of the clinical data for research. Informed consent was obtained from each subject who participated in this study. The average age at the time of the operation was sixty-six years (range, forty-five to eighty-two years). The average time from the operation to fluoroscopic evaluation was six years (range, twenty-four to 147 months). The diagnosis at the time of the operation was osteoarthritis in seventy-eight knees and rheumatoid arthritis in three knees. All of the operations were performed at one institution by two surgeons who routinely use the Low Contact Stress posterior cruciate ligament-retaining meniscal bearing knee prosthesis for total knee arthroplasties. To ensure objectivity, the operating surgeons did not participate in this study. The knees were independently evaluated by one of us (J.M.H.). All of the total knee replacements were primary procedures. No revision knee replacements or conversions from high tibial osteotomy were included in the study.

The Knee Society clinical and functional rating scores were determined for each knee⁵. The Knee Society clinical score was based on an evaluation of pain, range of motion, joint stability in the anteroposterior and mediolateral planes, and alignment of the knee. The functional score was based on an evaluation of the distance that the patient was able to walk, his or her ability to ascend and descend stairs, and the need for assistive devices (cane, crutch, or walker) while walking.

The patients had a radiographic examination consisting of fluoroscopically centered lateral non-weight-bearing radiographs made with the knee in full extension (Fig. 1-AFig. 1-A) and in full flexion (Fig. 1-BFig. 1-B). A Polydoras 80S fluoroscope (Siemens, New York, N.Y.) was used. The patients were placed in a lateral position, with the lateral aspect of the knee to be examined lying on the fluoroscopic table. The fluoroscopic beam projected from medial to lateral. The patients were first instructed to fully extend the knee so that the terminal extension lateral radiograph could be made. The patients were then instructed to bend the knee as far as they could comfortably do so for the terminal flexion radiograph. The true fluoroscopic center of the knee was identified, and permanent copies were made with the knee in both terminal extension and terminal flexion.

Radiopaque markers embedded in the polyethylene bearing by the manufacturer were used to identify the position of the bearings on the lateral radiographs. The center of the tibial plateau was identified through the center of the tibial keel, and the position of the marker was measured with use of the center point of the tibial plateau as the reference point. Both the distance and the direction of movement of the meniscal bearings were documented. The measurements were made on the permanent copies. Radiographic parallax allowed identification of the medial and lateral bearings, with the medial bearing measuring slightly larger than the lateral bearing on the lateral radiograph. The anteroposterior measurements of six femoral condylar prostheses on lateral radiographs were determined and were compared with the actual anteroposterior measurements of the femoral condylar prostheses. The magnifications were 12%, 15%, and 16% for two prostheses each. The lateral measurements on all of the radiographs were then adjusted to account for a clinically standard 15% radiographic magnification.

The center contact point of the femoral condyles with the meniscal bearings was identified on the lateral radiographs. The direction and distance of motion of the center contact point were also measured from the center of the tibial plateau, which was used as the reference point. The degree of flexion as well as the arc of motion from full extension to full flexion was measured on the two fluoroscopically centered radiographs. The amount of extension was documented in terms of flexion. A negative number denoted hyperextension of the knee. Terminal extension, terminal flexion, and the arc of motion were documented. These three parameters were compared between knees demonstrating femoral rollback and those demonstrating anterior sliding of the femoral condyles with use of a Student t test from the statistical package of Microsoft Excel 98 (Redmond, Washington).

The Knee Society clinical and functional scores were also compared, with use of the Student t test, between the patients exhibiting femoral rollback and those demonstrating anterior sliding of the femoral condyles. Again, the analysis was performed with use of the statistical package of Microsoft Excel 98.

A stratification of the time from the operation to the time of evaluation was performed to assess the changes in meniscal motion. Eighteen knees were evaluated two to four years after the operation; forty-four, four to eight years after the operation; and nineteen, eight to twelve years after the operation. Significance was assessed with analysis of variance (StatView; SAS Institute, Cary, North Carolina).

For all analyses, significance was determined by a p value of less than 0.05.

Results

Introduction | Materials and Methods | Results | Discussion | References

Eighty-one knees were evaluated. The average arc of motion, as determined fluoroscopically, was 90° (range, 45° to 136°). According to the Knee Society system, the average clinical score was 76 points (range, 27 to 100 points) and the average functional score was 72 points (range, 30 to 100 points).

Forty-three (53%) of the eighty-one medial bearings slid anteriorly during flexion, twenty-three (28%) slid posteriorly, and fifteen (19%) had no motion. Fifty-one (63%) of the eighty-one lateral bearings slid anteriorly, twenty-two (27%) moved posteriorly, and eight (10%) did not move. Overall, ninety-four bearings (58%) moved anteriorly, forty-five (28%) moved posteriorly, and twenty-three (14%) had no motion.

On the average, the medial bearings that moved anteriorly translated 4.4 mm (range, 1 to 14 mm), the lateral bearings that moved anteriorly translated 5.0 mm (range, 1 to 12 mm), the medial bearings that moved posteriorly translated 4.7 mm (range, 1 to 13 mm), and the lateral bearings that moved posteriorly translated 4.7 mm (range, 1 to 12 mm).

Reciprocal bearing motion (bearings moving in opposite directions) was identified in ten knees (12%). Motion of only one bearing with no movement of the other bearing was found in nine knees (11%). Synchronous bearing motion (both bearings moving in the same direction) was the most prevalent bearing motion, occurring in fifty-five knees (68%). Of the knees demonstrating synchronous bearing motion, thirty-nine demonstrated anterior motion and sixteen demonstrated posterior motion. Seven knees (9%) demonstrated no motion of either bearing.

The center contact point of the femoral condyles moved anteriorly (anterior sliding) from extension to flexion in fifty-seven knees (70%) (Figs. 2-AFigs. 2-A and 2-B2-B). Eighteen knees (22%) demonstrated posterior movement of the center contact point (rollback) (Figs. 3-AFigs. 3-A and 3-B3-B). Six knees (7%) demonstrated no change in the position of the center contact point of the femoral condyles.

The average flexion of the knees demonstrating femoral rollback was 104° (range, 76° to 128°) (Table ITable I). The average flexion of the knees demonstrating anterior sliding of the condyles was 94° (range, 45° to 125°). The difference was significant (p = 0.03). The average arc of motion of the knees demonstrating rollback was 101° (range, 69° to 136°), whereas the average arc of motion of the knees demonstrating anterior sliding was 87° (range, 45° to 120°). The difference was significant (p = 0.009).

The clinical scores for the knees demonstrating anterior sliding averaged 79 points (range, 27 to 98 points), and those for the knees demonstrating rollback averaged 87 points (range, 52 to 100 points) (p = 0.09). The functional scores for the knees with anterior sliding averaged 64 points (range, 30 to 100 points), and those for the knees with rollback averaged 72 points (range, 45 to 100 points) (p = 0.15). With the numbers available, the differences in the clinical and functional scores between the knees that demonstrated anterior sliding and those that demonstrated femoral rollback were not significant. The clinical and functional scores for the knees that demonstrated no change in the position of the center contact point were 80 points (range, 65 to 90 points) and 55 points (range, 30 to 70 points), respectively.

Motion of the meniscal bearings was examined (with use of absolute values) in relation to the duration of follow-up from the time of the operation. Two to four years after the operation, the average motion was 3.7 mm for the medial bearings and 3.8 mm for the lateral bearings. Four to eight years postoperatively, the average motion was 3.3 and 4.3 mm for the medial and lateral bearings, respectively, and eight to twelve years after the operation, the average motion was 4.6 and 5.1 mm, respectively. The average motion increased from the two to four-year follow-up period to the eight to twelve-year follow-up period. However, analysis of variance showed no significant association (p = 0.9 for the medial bearings and p = 0.6 for the lateral bearings) between the duration of follow-up and the distance of motion of the bearings.

Discussion

Introduction | Materials and Methods | Results | Discussion | References

Meniscal bearing total knee replacements have demonstrated good survival at ten years. Using revision as the end point, Goodfellow and O'Connor¹ reported a success rate of 88% six years after implantation of the Oxford knee in a series of 125 knees. Jordan et al.³, again using revision as the end point, reported a survival rate of 94.6% (95% confidence interval, 92.0% to 97.2%) at eight years in a series of 473 cementless Low Contact Stress meniscal bearing total knee replacements. In a study of 211 knees, Buechel and Pappas⁶ reported that, with revision as the end point, the survival rate of the Low Contact Stress knee replacement was 97% at six years and 90.9% at twelve years, for both the cementless and the cemented cruciate-retaining designs.

Bradley et al.⁴ evaluated the bearing motion of the Oxford knee on flexion and extension radiographs. They identified an average bearing movement of 4.4 mm in the medial compartment and 6.0 mm in the lateral compartment between full extension and 90° of flexion. Using fluoroscopy, Stiehl et al.⁷ performed a limited in vivo analysis of ten patients with a Low Contact Stress posterior cruciate ligament-retaining meniscal bearing total knee replacement while the patients performed deep knee bends. In five of the ten knees, the bearings demonstrated no movement. From 0° to 60° of flexion the knees demonstrated varying patterns of femoral rollback, and from 60° to 90° the knees uniformly demonstrated anterior sliding of the femoral condyles. This anterior sliding of the femoral condyles is consistent with the findings with other posterior cruciate ligament-retaining designs with fixed bearings⁸. In our radiographic analyses of meniscal bearing total knee replacements, 139 bearings (86%) continued to demonstrate motion at an average of five years and ten months after the operation. We were unable to perform a continuous analysis of the bearing movement through the full arc of motion, but between the extremes of motion ninety-four bearings (58%) glided anteriorly and forty-five bearings (28%) demonstrated posterior movement.

Because of the limitations of our fluoroscopic equipment, we could only analyze the motion of the meniscal bearings and the change in the center contact point on non-weight-bearing extension and flexion radiographs of the knee. Although this does not simulate the normal forces produced during walking, our results do demonstrate abnormal kinematics that was similar to that identified by Stiehl et al.⁷. In their examination of meniscal bearing knee replacements with fluoroscopy, Stiehl et al. had the subjects perform deep knee bends. Neither that method nor our method reproduces true kinematic motion of the knee during walking. The deep knee bends used by Stiehl et al. represented a closed-chain model, whereas the active extension and flexion used in our study is an open-chain model.

In an analysis of the stabilizing mechanisms of the loaded and unloaded knee joint, Hsieh and Walker⁹ demonstrated that the stability of a loaded knee joint is determined more by the congruity of the condylar surfaces whereas the stability of an unloaded knee joint depends more on the soft tissues. In the model in the study by Stiehl et al.⁷, which utilized a weight-bearing knee, the kinematics of the knee was determined more by condylar congruity, whereas in our study the kinematics was determined more by the soft-tissue constraints of the knee. Because our model removes the quadriceps mechanism as a source of anterior pull on the tibia as seen during walking, our results may understate the extent of anterior sliding of the femoral condyles as compared with that found by Stiehl et al.

Only eighteen knees (22%) in our study demonstrated rollback through the full arc of motion. In fifty-seven knees (70%), the center contact point of the femoral condyles demonstrated anterior motion, suggesting posterior cruciate insufficiency. The knees with rollback had significantly greater flexion (average, 104°) than the knees with anterior sliding (average, 94°) (p = 0.03). The average clinical score of the knees demonstrating rollback was also greater than that of the knees with anterior sliding, although this difference was not significant, with the numbers available (p = 0.09).

The posterior cruciate ligament is thought to help to reproduce normal kinematics and to preserve rollback in cruciate-retaining total knee replacements¹⁰. Goodfellow et al.¹¹ demonstrated that not only the posterior cruciate ligament but also the four-bar linkage of the posterior cruciate ligament and anterior cruciate ligament is necessary to reproduce normal knee kinematics^4,12. Fluoroscopic analysis of posterior cruciate-retaining total knee replacements by Stiehl et al.⁸ verified the inability of the posterior cruciate ligament to reproduce normal knee kinematics and femoral rollback. Our analysis of the Low Contact Stress meniscal bearing total knee replacement confirms this inability of the posterior cruciate ligament to reproduce normal kinematics.

Abnormal kinematics is believed to be detrimental to the longevity of a total knee replacement¹³. Loss of rollback increases the demands on the quadriceps and increases the forces on the patellofemoral articulation^14,15. We identified a decrease in the range of motion and the clinical scores for the majority of meniscal bearing knee replacements that had anterior sliding of the femoral components rather than femoral rollback. The Low Contact Stress meniscal bearing knee was designed to improve congruency of the femorotibial articulating surface. Fifty-five of the eighty-one knees in our series demonstrated motion of the medial and lateral bearings that was either uniformly anterior or uniformly posterior. The design of the curvilinear tracks of the Low Contact Stress total knee replacement requires reciprocal bearing motion to produce congruity in the medial-lateral plane¹⁶. As the bearings move either anteriorly or posteriorly in unison, they must move toward the midline of the knee while the femoral contact points maintain an equal distance between the condyles, creating an incongruity of the femoral condyles on the articular surface of the bearings.

Our radiographic analysis of the Low Contact Stress knee replacement demonstrated continued motion of the meniscal bearings at an average of five years and ten months after the operation. Normal knee kinematics usually was not reproduced, demonstrating insufficiency of the posterior cruciate ligament in the majority of the knees. The knees that did not reproduce normal rollback had, on the average, a decreased range of motion and a decreased clinical score compared with the few knees that had normal kinematic rollback.

Because the bearing tracks are curved, as the knee moves from extension to flexion the medial and lateral bearings are forced either toward the midline or away from the midline. Our study demonstrated that most bearings move together, either posteriorly or anteriorly, as the knee bends. Because the distance between the femoral condyles is fixed, as the bearings move toward or away from each other, condyle-bearing congruity is impaired, leading to edge-loading of the bearings and increased contact stress.

References

Introduction | Materials and Methods | Results | Discussion | References

GoodfellowJW,O'Connor J. Clinical results of the Oxford knee. Surface arthroplasty of the tibiofemoral joint with a meniscal bearing prosthesis. Clin Orthop,1986;205: 21-42. 20521 1986 [PubMed]

GoodfellowJ,O'Connor J. The mechanics of the knee and prosthesis design. J Bone Joint Surg Br,1978;60: 358-69. 60358 1978 [PubMed]

JordanLR, Olivo JL,Voorhorst PE. Survivorship analysis of cementless meniscal bearing total knee arthroplasty. Clin Orthop,1997;338: 119-23. 338119 1997 [PubMed]

BradleyJ, Goodfellow JW,O'Connor JJ. A radiographic study of bearing movement in unicompartmental Oxford knee replacements. J Bone Joint Surg Br,1987;69: 598-601. 69598 1987 [PubMed]

InsallJN, Dorr LD, Scott RD,Scott WN. Rationale of the Knee Society clinical rating system. Clin Orthop,1989;248: 13-4. 24813 1989 [PubMed]

BuechelFF,Pappas MJ . Long-term survivorship analysis of cruciate-sparing versus cruciate-sacrificing knee prostheses using meniscal bearings. Clin Orthop.,1990;260: 162-9. 260162 1990 [PubMed]

StiehlJB, Dennis DA, Komistek RD,Keblish PA. In vivo kinematic analysis of a mobile bearing total knee prosthesis. Clin Orthop,1997;345: 60-6. 34560 1997 [PubMed]

StiehlJB, Komistek RD, Dennis DA, Paxson RD,Hoff WA. Fluoroscopic analysis of kinematics after posterior-cruciate-retaining knee arthroplasty. J Bone Joint Surg Br,1995;77: 884-9. 77884 1995 [PubMed]

HsiehHH,Walker PS. Stabilizing mechanisms of the loaded and unloaded knee joint. J Bone Joint Surg Am,1976;58: 87-93. 5887 1976 [PubMed]

PagnanoMW, Cushner FD,Scott WN. Role of the posterior cruciate ligament in total knee arthroplasty. J Am Acad Orthop Surg,1998;6: 176-87. 6176 1998 [PubMed]

GoodfellowJW, Kershaw CJ, Benson MK,O'Connor JJ. The Oxford knee for unicompartmental osteoarthritis. The first 103 cases. J Bone Joint Surg Br,1988;70: 692-701. 70692 1988 [PubMed]

MinnsRJ,Campbell J. The mechanical testing of a sliding meniscus knee prosthesis. Clin Orthop,1978;137: 268-75. 137268 1978 [PubMed]

WrightTM,Bartel DL. The problem of surface damage in polyethylene total knee components. Clin Orthop,1986;205: 67-74. 20567 1986 [PubMed]

LewandowskiPJ, Askew MJ, Lin DF, Hurst FW,Melby A. Kinematics of posterior cruciate ligament-retaining and -sacrificing mobile bearing total knee arthroplasties. An in vitro comparison of the New Jersey LCS meniscal bearing and rotating platform prostheses. J Arthroplasty.,1997;12: 777-84. 12777 1997 [PubMed]

MillerRK, Goodfellow JW, Murray DW,O'Connor JJ. In vitro measurement of patellofemoral force after three types of knee replacement. J Bone Joint Surg Br,1998;80: 900-6. 80900 1998 [PubMed]

O'Connor JJ,Goodfellow JW. Theory and practice of meniscal knee replacement: designing against wear. Proc Inst Mech Eng [H],1996;210: 217-22. 210217 1996 [PubMed]

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Fig. 1-A:: Fluoroscopically centered lateral radiographs of a meniscal bearing knee replacement in full extension (Fig. 1-A) and full flexion (Fig. 1-B).

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Fig. 1-B:: Fluoroscopically centered lateral radiographs of a meniscal bearing knee replacement in full extension (Fig. 1-A) and full flexion (Fig. 1-B).

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TABLE I: Position of the Femoral Condyles and Range of Motion

Position of Femoral Condyles	Range of Motion* (deg)
Extension			Flexion			Arc of Motion
Rollback (n = 18)	3 (-7-12)	}	p = 0.03	104 (76-128)	}	p = 0.03	101 (69-136)	}	p = 0.009
Anterior sliding (n = 57)	7 (-3-29)	94 (45-125)	87 (45-120)
Neutral (n = 6)	7 (0-20)		87 (70-100)		80 (60-100)

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

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TABLE I: Position of the Femoral Condyles and Range of Motion

Position of Femoral Condyles	Range of Motion* (deg)
Extension			Flexion			Arc of Motion
Rollback (n = 18)	3 (-7-12)	}	p = 0.03	104 (76-128)	}	p = 0.03	101 (69-136)	}	p = 0.009
Anterior sliding (n = 57)	7 (-3-29)	94 (45-125)	87 (45-120)
Neutral (n = 6)	7 (0-20)		87 (70-100)		80 (60-100)