[Show abstract][Hide abstract] ABSTRACT: The present study demonstrates that femoral head separation from the acetabular component can occur under weight-bearing conditions
during gait and an abduction-adduction activity in subjects implanted with various designs of THA. The incidence and magnitude
is greatest in those with MOP THA and least in subjects implanted with an AOA THA. Potential detrimental effects resulting
from hip joint separation include premature polyethylene wear, component loosening secondary to impulse loading conditions
and late hip instability. The reduced hip separation observed in AOA THA subjects is likely related to the increased wetability
of this material as well as reduced diametral clearance typically seen in hard-on hard bearings which results in a cohesive
fluid film lubrication regime.
[Show abstract][Hide abstract] ABSTRACT: Frontal plane kinematics including condylar lift-off and medial to lateral translation were investigated in 10 patients who had total knee arthroplasty with a mobile-bearing rotating platform or a similar implant that had been modified with a posterior stabilizer. The rotating platform had condylar lift-off (average, 2 mm) and medial tibial translation (average, 4.3 mm) in all implants tested. The posterior-stabilized prosthesis had significantly less condylar lift-off (average, 1.2 mm) and medial translation (average, 1.7 mm). The difference is attributed to constraint of the posterior stabilizer mechanism in the frontal plane. The important kinematic functions of frontal plane condylar lift-off and medial to lateral translation must be accounted for by contemporary total knee prosthetic designs because abnormalities may lead to abnormal wear and loss of prosthetic fixation.
Clinical Orthopaedics and Related Research 12/2001; · 2.79 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Sagittal plane patellofemoral kinematics was determined for 81 subjects while performing a weight-bearing deep knee bend under fluoroscopic surveillance. Fourteen normal knees, 12 anterior cruciate ligament (ACL)-deficient knees, and 55 total knee arthroplasties (TKAs) were assessed. Of TKAs, 39 had resurfacing with a dome-shaped patella, 8 had resurfacing with an anatomic mobile-bearing patella, and 8 were unresurfaced. TKA patellae experienced more superior patellofemoral contact and higher patellar tilt angles compared with the normal knees and ACL-deficient knees (P <.05). Patellofemoral separation at 5 degrees (+/-3 degrees ) extension was seen in 86% cruciate-retaining and 44% cruciate-stabilized TKAs and 8% ACL-deficient knees but not in the normal knees or mobile-bearing TKAs (P <.05). The patellar kinematic patterns for subjects having a TKA were more variable than subjects having either a normal knee or an ACL-deficient knee. Kinematic abnormalities of the prosthetic patellofemoral joint may reduce the effective extensor moment after TKA.
The Journal of Arthroplasty 09/2001; 16(6):706-14. · 2.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Numerous supporting structures assist in the retention of the femoral head within the acetabulum of the normal hip joint including the capsule, labrum, and ligament of the femoral head (LHF). During total hip arthroplasty (THA), the LHF is often disrupted or degenerative and is surgically removed. In addition, a portion of the remaining supporting structures is transected or resected to facilitate surgical exposure. The present study analyzes the effects of LHF absence and surgical dissection in THA patients. Twenty subjects (5 normal hip joints, 10 nonconstrained THA, and 5 constrained THA) were evaluated using fluoroscopy while performing active hip abduction. All THA subjects were considered clinically successful. Fluoroscopic videos of the normal hips were analyzed using digitization, while those with THA were assessed using a computerized interactive model-fitting technique. The distance between the femoral head and acetabulum was measured to determine if femoral head separation occurred. Error analysis revealed measurements to be accurate within 0.75mm. No separation was observed in normal hips or those subjects implanted with constrained THA, while all 10 (100%) with unconstrained THA demonstrated femoral head separation, averaging 3.3mm (range 1.9-5.2mm). This study has shown that separation of the prosthetic femoral head from the acetabular component can occur. The normal hip joint has surrounding capsuloligamentous structures and a ligament attaching the femoral head to the acetabulum. We hypothesize that these soft tissue supports create a passive, resistant force at the hip, preventing femoral head separation. The absence of these supporting structures after THA may allow increased hip joint forces, which may play a role in premature polyethylene wear or prosthetic loosening.
Journal of Biomechanics 06/2001; 34(5):623-9. · 2.72 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We describe our experience with in vivo dynamic fluoroscopy that uses simple 2-plane video fluoroscopy of subjects performing maneuvers such as deep knee-bends, gait, and stair climbing after total knee arthroplasty (TKA). Kinematic analysis has evolved from 2-dimensional vector calculations to automated 3-dimensional computer-assisted design matching techniques that are accurate to 0.75-mm translation and 0.75 degrees rotation and that allow simultaneous determination of medial and lateral condyle contact positions. TKAs that retain the posterior cruciate ligament (PCL) have consistently shown posterior contact in extension and anterior translation with flexion with a large variability among subjects. PCL-stabilized implants and mobile bearings with high conformity have posterior femoral rollback more consistent with normal knees--which is a function of prosthetic geometry. Condylar liftoff and screw-home rotation are typical kinematic features of all TKAs.
American journal of orthopedics (Belle Mead, N.J.) 05/2001; 30(4):287-93.
[Show abstract][Hide abstract] ABSTRACT: In summary, if TKRs are to be performed in patients who are younger and more active than those who had the initial procedures in the 1970s and 1980s, better wear performance is imperative for long-term durability, especially if surgeons continue to consider the versatility associated with modular knee-replacement systems to be a necessity. At least with some designs, including the Oxford knee and the LCS knee, the results after a minimum follow-up of 10 years are comparable with the best results after arthroplasty with fixed-bearing designs in terms of wear, loosening, and osteolysis (Table 7). As with fixed-bearing designs, there are additional challenges in terms of optimizing bearing-surface conformity and improving kinematics. Improvements in future designs of mobile-bearing total knee replacements should include better control of bearing mobility patterns to reduce the prevalence of the abnormal kinematic motions that have been observed in fluoroscopic evaluations.
[Show abstract][Hide abstract] ABSTRACT: We carried out weight-bearing video radiological studies on 40 patients with a total knee arthroplasty (TKA), to determine the presence and magnitude of femoral condylar lift-off. Half (20) had posterior-cruciate-retaining (PCR) and half (20) posterior-cruciate-substituting (PS) prostheses. The selected patients had successful arthroplasties with no pain or instability. Each carried out successive weight-bearing knee bends to maximum flexion, and the radiological video tapes were analysed using an interactive model-fitting technique. Femoral lift-off was seen at some increment of knee flexion in 75% of patients (PCR TKA 70%; PS TKA 80%). The mean values for lift-off were 1.2 mm with a PCR TKA and 1.4 mm with a PS TKA. Lift-off occurred mostly laterally with the PCR TKA, and both medially and laterally with the PS TKA. Separation between the femoral condyles and the articular surface of the tibia was recorded at 0 degrees, 30 degrees, 60 degrees and 90 degrees of flexion. Femoral condylar lift-off may contribute to eccentric polyethylene wear, particularly in designs of TKA which have flatter condyles. Coronal conformity is an important consideration in the design of a TKA.
Journal of Bone and Joint Surgery - British Volume 02/2001; 83(1):33-9. · 2.69 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The purpose of this study was to determine to what extent hip joint separation occurs during normal gait on a treadmill and an abduction/adduction leg-lift maneuver in patients who have undergone total hip arthroplasty (THA). Eight patients who had a total of 10 successful unconstrained THAs (Harris Hip Scores >90) performed successive gait motions on an electronically powered treadmill and an abduction/adduction leg lift while under fluoroscopy. The fluoroscopic video images were analyzed using a 3-dimensional model-fitting technique that converts 2-dimensional fluoroscopic images into 3-dimensional real-time images. Hip joint separation was determined to be present if the amount of separation was >0.75 mm, the calculated linear error. During both activities, all 10 THAs experienced femoral head/acetabular component separation. For gait, the maximum amount of separation was 2.8 mm, while the minimum amount was 0.8 mm (average, 1.2 mm). For abduction/adduction leg lift, the maximum amount of separation was 3.0 mm, while the minimal amount was 1.7 mm (average, 2.4 mm). It appears that the femoral head separates from the acetabular component but remains in contact with the superior-most tip of the component. Potential detrimental effects resulting from hip joint separation include premature polyethylene wear and component loosening. Wear may be enhanced because of the creation of multidirectional wear vectors or excessive loads resulting from eccentric femoral head pivoting. These data may be valuable in hip simulation studies to better duplicate wear patterns observed in retrieval analysis.
The Journal of Arthroplasty 09/2000; 15(6):702-9. · 2.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In vivo weight-bearing fluoroscopic kinematic analysis using an interactive model fitting technique with 3-dimensional computer-aided design solid models was done using 16 anterior and posterior (bicruciate)-sparing and 6 posterior cruciate-sparing total knee arthroplasties (TKAs). All patients had a satisfactory clinical result with a minimum of 12 months' follow-up. The femorotibial contact position of TKAs started posterior to the midline in extension. Bicruciate TKAs revealed gradual posterior femoral rollback and limited anterior-posterior translation but remained posterior to the sagittal plane midline in all positions. Posterior cruciate-sparing TKAs began significantly posterior in extension, demonstrated progressive anterior translation with flexion, and had exaggerated medial condyle translation on deep knee bend. The posterior cruciate-retaining TKAs of this study had the most abnormal kinematic performance.
The Journal of Arthroplasty 09/2000; 15(5):545-50. · 2.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: To determine patellofemoral contact patterns in two-dimensions for normal and implanted patients.
An in vivo, weightbearing fluoroscopy analysis of 14 subjects with normal knees, 12 with anterior cruciate ligament deficient knees, 14 with a posterior cruciate retaining implant, and 25 with a posterior cruciate substituting implant.
Most previous experimental studies involving the knee joint have been either in vitro or under nonweightbearing conditions.
Subjects were studied under fluoroscopic surveillance performing deep knee bends to maximum flexion. Video images were analyzed on a computer with a two-dimensional technique of digitizing discrete points on the patella, femur, and tibia.
The contact position, measured from the patella mass center, was inferior on the patella at extension and moved superior during flexion. Average contact positions of the implanted knee groups were more superior than the normal knee group throughout the flexion cycle. Analysis of patellar tilt angle demonstrated a flexed posture of the patella relative to the tibia. Increase in patellar tilt angle with increasing femorotibial flexion was substantially greater in implanted knees versus normal knees. Separation of the patella from the femur in full extension was absent in normal knees, but present in 86% and 44% of posterior cruciate retaining and posterior cruciate substituting total knee arthroplasties, respectively.
The patellofemoral kinematics of the total knee arthroplasties analyzed in the study was statistically different than the normal and anterior cruciate ligament-deficient knees. The kinematic variations observed between normal and implanted knees may be related to disturbed femorotibial kinematics previously observed to occur following total knee arthroplasty.
Patellofemoral complications, including polyethylene wear, are a major concern in total knee arthroplasty. Since the causes of polyethylene wear are multi-factorial, abnormal patellofemoral kinematics may play a role in patellar failure.
[Show abstract][Hide abstract] ABSTRACT: Video fluoroscopy and computer photogrammetry was used to evaluate 20 knees with posterior cruciate ligament (PCL) retaining and 19 knees with PCL sacrificing total knee arthroplasties (TKAs) with a mobile bearing total condylar prosthesis compared with 10 normal patients. In extension, femorotibial contact was posterior for TKA patients (P<.05) and demonstrated anterior translation from 60 degrees-90 degrees flexion. However, posterior rollback with limited translation was seen from 0 degrees-40 degrees, which may reflect the high congruity of this prosthesis. Fifty percent of meniscal bearing implants demonstrated bearing translation. Kinematics and weight-bearing range of motion were similar with PCL retention or sacrifice.
The American journal of knee surgery 01/2000; 13(1):13-8.
[Show abstract][Hide abstract] ABSTRACT: The objective of this study was to analyze the effects of off-loading knee braces in patients diagnosed with symptomatic unicompartmental osteoarthritis. Under fluoroscopic surveillance, 15 patients were asked to perform normal gait on a treadmill. Each patient was asked initially to walk without using a knee brace and then to walk while wearing a brace. The fluoroscopic images of the patients at heel-strike were downloaded to a workstation computer. Condylar separation angle of the knee joint and the distances from the medial and lateral femoral condyles to the tibial plateau (condylar separation) were measured. Twelve of 15 patients (80%) reported relief of pain and demonstrated condylar separation of the degenerative compartment with the use of the off-loading brace. The 3 patients who did not demonstrate condylar separation were obese, making accurate brace fitting difficult. The average change in condylar separation and condylar separation angle was 1.2 mm (range, 0.0-4.5 mm) and 2.2 degrees (range, 0.0 degrees-7.8 degrees). This study demonstrated that condylar separation of a degenerative knee compartment can be achieved with off-loading braces with subsequent subjective relief of knee pain.
The Journal of Arthroplasty 10/1999; 14(6):738-42. · 2.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Fourteen subjects having a flat on flat condylar posterior cruciate retaining total knee arthroplasty were evaluated under different in vivo weightbearing conditions, with six performing a deep knee bend and eight walking at normal gait. An interactive model fitting algorithm was used to convert two-dimensional fluoroscopic images into three-dimensional computer aided design solid model images. The femorotibial contact positions for the medial and lateral condyle started posterior at full extension. With a deep knee bend the lateral condyle acted as a pivot, and the medial condyle slid in the anterior direction. Five of six had lateral condyle liftoff (maximum 1.6 mm) and abnormal positive screw home motion was seen from 0 degree to 90 degrees flexion. During gait, all femorotibial contact positions were posterior in extension and throughout the cycle. Six of eight patients experienced lateral condyle liftoff (maximum 3.5 mm), but minimal screw home motion was seen. Abnormal medial condyle posteroanterior sliding, lateral condyle liftoff, and erratic screw home motion may be related to abnormal wear characteristics of this flat on flat condylar design.
Clinical Orthopaedics and Related Research 09/1999; · 2.79 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Twenty subjects implanted with the low-contact stress (LCS) cruciate-sacrificing, mobile-bearing total knee arthroplasty underwent dynamic videofluoroscopy during in vivo weight-bearing conditions using a 3-dimensional computer-aided design (CAD) interactive modeling method. Ninety percent of the subjects demonstrated significant lift-off during stance phase of gait. Condylar lift-off was present at both the medial and the lateral condyles. The maximal medial lift-off was 2.12 mm, whereas the greatest lateral lift-off was 3.53 mm. The maximal positive screw-home was 9.6 degrees, whereas the maximal negative or reverse screw-home was 6.2 degrees. The average screw-home rotation was positive 0.5 degrees. In 50% of patients, medial condylar translation was unexpectedly greater than lateral condylar motion. Condylar lift-off and screw-home motion are significant kinematic functions in this rotationally unconstrained total condylar knee arthroplasty.
The Journal of Arthroplasty 05/1999; 14(3):293-9. · 2.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A study was conducted to determine in vivo femorotibial contact patterns for subjects having a posterior cruciate retaining or posterior cruciate substituting total knee arthroplasty. Femorotibial contact of 72 subjects implanted with a total knee replacement, performed by five surgeons, was analyzed using video fluoroscopy. Thirty-one subjects were implanted with a posterior cruciate retaining total knee replacement with a flat polyethylene posterior lipped insert, 12 with a posterior cruciate retaining total knee replacement with a curved insert, and 29 with a posterior cruciate substituting total knee replacement. Each subject performed successive deep knee bends to maximum flexion. Video images at 0 degree, 30 degrees, 60 degrees, and 90 degrees flexion were downloaded onto a workstation computer. Femorotibial contact paths were determined for the medial and lateral condyles using an interactive model fitting technique. Femorotibial contact anterior to the tibial midline in the sagittal plane was denoted as positive and contact posterior was denoted as negative. Analysis of average femorotibial contact pathways of both posterior cruciate retaining designs revealed posterior femorotibial contact in full extension with anterior translation of femorotibial contact commonly observed in midflexion and terminal flexion. In posterior cruciate substituting designs, anterior femoral translation was seen medially at 30 degrees to 60 degrees flexion but rarely was observed laterally. Posterior femoral rollback laterally from full extension to 90 degrees flexion was seen in 100% of subjects implanted with a posterior cruciate substituting total knee replacement, versus 51.6% (posterior lipped polyethylene insert) and 58.3% (curved insert) of those with a posterior cruciate retaining total knee replacement. Data from this multicenter study are remarkably similar to previous fluoroscopy data from a single surgeon series, showing a lack of customary posterior femoral rollback in both posterior cruciate retaining designs, and conversely showing an average anterior femoral translation with knee flexion. Posterior femoral rollback, less than in normal knees, routinely was observed in posterior cruciate substituting total knee arthroplasty, attributed to engagement of the femoral component cam with the tibial post. The abnormal anterior femoral translation observed in posterior cruciate retaining total knee arthroplasty may be a factor in premature polyethylene wear observed in retrieval studies.
Clinical Orthopaedics and Related Research 12/1998; · 2.79 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: OBJECTIVE: A method has been developed to accurately measure three-dimensional (3-D) femoral-tibial contact positions of artificial knee implants in vivo from X-ray fluoroscopy images using interactive 3-D computer vision algorithms. DESIGN: A computerized graphical (CAD) model of an implant component is displayed as an overlay on the original X-ray image. An image matching algorithm matches the silhouette of the implant component against a library of images, in order to estimate the position and orientation (pose) of the component. The operator further adjusts the pose of the graphical model to improve the accuracy of the match. BACKGROUND: Previous methods for in vivo measurement of joint kinematics make only indirect measurements of joint kinematics, require invasive procedures such as markers or pins, or make simplifying assumptions about imaging geometry which can reduce the accuracy of the resulting measurements. METHODS: Fluoroscopic videos are taken of implanted knees in subjects performing weight-bearing motion. Images from the videos are digitized and stored on a computer workstation. Using computerized model matching, the relative pose of the two knee implant components can be determined in each image. The resulting information can be used to determine where the two components are contacting, the area of the contact region, liftoff angle, and other kinematic data. RESULTS: Accuracy tests done on simulated imagery and in vitro real imagery show that the pose estimation method is accurate to less than 0.5 mm of error (RMS) for translations parallel to the image plane. Orientation error is less than or equal to 0.35 degrees about any axis. Errors are larger for translations perpendicular to the image plane (up to 2.25 mm). In a clinical study, the method was used to measure in vivo contact points, and characterize the kinematic patterns of two different knee implant designs. CONCLUSIONS: The ability to accurately measure knee kinematics in vivo is critical for the understanding of the behavior of knee implant designs and the ultimate development of new, longer lasting implants. RELEVANCE: This work shows that it is possible to accurately measure the three-dimensional position and orientation (pose) of artificial knee implants in vivo from X-ray fluoroscopy images using interactive 3-D computer graphics. The method can be applied to any joint when accurate CAD models are available. The resulting data can be used to characterize the kinematics of current knee implant designs.
[Show abstract][Hide abstract] ABSTRACT: Problems associated with the patellofemoral joint account for nearly half of all total knee arthroplasty (TKA) revisions. Under in vivo conditions, we previously determined that TKA subjects experience patellofemoral separation while performing dynamic, weight-bearing activities. This study investigates the impulse loading conditions that may exist at the time the patella impacts the femur during knee flexion. Fifty-seven subjects (68 knees) performed three successive deep knee bends under fluoroscopic surveillance. Eleven subjects (14 knees) had a posterior cruciate retaining (PCR) TKA, 19 subjects (25 knees) had a posterior cruciate substituting (PS) TKA, 15 subjects (17 knees) had a normal knee, and 12 subjects (12 knees) had an anterior cruciate ligament deficient (ACLD) knee. Velocities of each subjects' patella relative to a fixed point on the tibia were used as input to a mathematical model incorporating the impulse-momentum equation. At full extension, 12 of 14 PCR knees, 11 of 25 PS knees, 1 of 12 ACLD knees, and none of the 17 normal knees exhibited patellofemoral joint separation. The maximum separation, detected in a PCR knee, was 12 mm. The relative force determined upon patellofemoral impact was minimal (1.0 N). Simulated walking conditions for each subject were then entered into the mathematical model at a rate of 100 Hz and the calculated patellofemoral impact forces ranged from 78 N to 213 N. Since impulse loading conditions occur over a very small period of time, it was concluded that capturing fluoroscopy images at a rate of 30 Hz was too slow. Under simulated walking conditions, the impact forces due to impulse loading could contribute to polyethylene failure if these conditions induce fatigue of the polyethylene.
Der Orthopäde 10/1998; 27(9):612-8. · 0.51 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Knee range of motion was determined in 60 patients to assess the effect of weight bearing on maximal knee flexion. Three patient subgroups were investigated: patients with normal knees, patients implanted with posterior cruciate-retaining (PCR) total knee arthroplasty (TKA), and patients implanted with posterior cruciate-substituting (PS) TKA. Maximal knee flexion was determined using videofluoroscopy both in a passive, non-weight-bearing mode and during active weight bearing. Flexion was diminished with weight bearing in all three subgroups (P < .045). Patients with normal knees exhibited significantly greater knee flexion than either TKA subgroup when measured either with or without weight bearing (P < .001). Knee flexion of both TKA subgroups was similar when measured passively without weight bearing. Patients with PS TKA demonstrated greater flexion than patients with PCR TKA when measured in weight bearing (P < .025), despite having less range of motion and lower clinical performance ratings preoperatively. Measurement of knee range of motion in a weight-bearing fashion may be a superior method of assessment of functional capabilities.
The Journal of Arthroplasty 10/1998; 13(7):748-52. · 2.11 Impact Factor