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In vivo anteroposterior femorotibial translation: A multicenter analysis
Abstracts from the AAHKS Seventh Annual Meeting Methods: 100 consecutive cases were prospectively studied. The radiologist reading, clinical management and outcome of each case was carefully reviewed. The amount of dollars billed for the radiologist interpretation was noted for each exam. Results: A total of 398 studies in 100 patients were done. Ninety-six preoperative, 71 intra-operative and 192 postoperative roentgenographic studies were reviewed. These reports took an average time of 1.71 days to get to the chart (SD + / - 2.45). The total radiological professional fees billed to Medicare in these cases was $11,054. The radiologist's Interpreta~on was not useful in the clinical management or affected the outcome in any case. Discussion and Conclusions: Assuming that each surgeon takes one xray on every arthroplasty case, the total actual savings to Medicare of not having a radiologist reading these studies could reach $1.9 million per year. If two intrahospital x-ray studies are performed per procedure (pre, intra or post op), the savings are $3.81 million per year. These cost reductions are achieved at no sacrifice to quality of care or outcome. Numerous areas of excessive spending with no improvement in outcome exist in the treatment of Medicare patients. These areas should be identified and eliminated before surgical fees are lowered even further.
P A P E R # 28 IS THE ROUTINE EXAMINATION OF SURGICAL SPECIMENS WORTHWHILE IN PRIMARY TOTAL KNEE ARTHROPLASTY? Jose H e m a n Forero, MD, Mark W. Pagnano, MD, Jacksonville, FL, Giles R. Scuderi, MD, Steven E Harwin, MD Introduction: Given the present health-care climate in which emphasis has been placed on both cost-containment and outcomes, we were interested in determining the utility of routine pathological examination of surgical specimens obtained during primary total knee arthroptasty (TKA). In particular, we sought to determine if and when the pathologic diagnosis differs from the clinical diagnosis, does such a difference alter clinical management of the patient, and what are the costs associated with the collection of routine surgical specimens during primary TKA. Methods: Between 1993 and 1996, 2,035 primary TKAs were performed for a variety of diagnoses at a sIngle institution. In each case, both bone and tissue specimens were sent for routine pathological review. The medical record for every patient was reviewed to determine the preoperative clinical diagnosis, the intraoperative findIngs and the results of the pathological examination. When a discrepancy was noted between the clinical diagnosis and pathological diagnosis, the medical record was further scrutinized to determine if subsequent treatment was altered. Results: Six hundred ninety-two of the TKAs were in male patients and 1,343 in females. The mean age of the patients was 67 years (range 21 to 93 years). The TKA was performed on 973 right knees and 1,062 left. In 8 cases there was a discrepancy between the clinical and pathological diagnosis. In none of those cases was the subsequent treatment of the patient altered as a result of the pathological findings. Conclusions: This study suggests that the routine pathological review of surgical specimens from primary TKAs is of little clinical value. In no case was the subsequent management of a patient altered because of the pathological diagnosis. Costs for the routine pathological examination of a TKA surgical specimen ranged from $195 to $300 at our institution. In those selected cases where the clinical circumstances or surgical findings are aberrant, it remains prudent for the surgeon to submit surgical specimens for pathological review. This study, however, suggests a re-examination of hospital bylaws, as well as local and state regulations that mandate the routine pathological examination of surgical specimens from primary TKAs.
* Denotes that somethingof value was received Presenters are boldface
231
PAPER # 29 *THE CRUCIATE LIGAMENTS IN TOTAL KNEE ARTHROPLASTY: A KINEMATIC ANALYSIS James B. Stiehl, MD, Milwaukee, WI, Douglas A. Dennis, MD, Richard D. Komistek, PhD, Jean M. Cloutier, MD Introduction: Prostheses for total knee arthroplasty (TKA) are available in a wide variety of designs with techniques that spare both cruciate ligaments, the posterior cruciate ligament, or sacrifice both ligaments. Recent studies have used video fluoroscopy to accurately define knee kinematics invivo. This study compares the performance of TKA with various treatments of the posterior cruciate ligament. Method: Twelve patients with an anterior/posterior cruciate (ACL/PCL) sparing TKA, 8 patients with a posterior eruciate (PCL) sparing TKA, and 20 patients with a posterior cruciate ligament sacrificing (PS) mobile bearing TKA were studied while performing a deep knee bend under invivo weight-bearing conditions using video fluoroscopy. The videos were analyzed using an iterative model fitting technique that fits 3D CAD solid models of the femur and then the tibia onto 2D fluoroscopic silhouette images. Total knee patients selected had an excellent clinical result (>90/ 90 KSS) and had a minimum of 12 months follow-up. At 0 °, 30 °, 60° and 90° degrees of flexion, fluoroscopic images were matched with the best 3D CAD image found in the femoral and tibial component silhouette libraries. Digitization was then utilized to determine the position of femorotibial contact at various increments of flexion. By definition, positive was noted to be anterior to the mid-tibia plane and negative was posterior. The relative error of 0.75 m m was determined using a six degree of freedom apparatus that allowed for the femoral and tibial component to be oriented to known positions. Results: The femorotibial contact position of all three groups started posterior to the mid-line in extension. All 12 patients with the ACL/PCL sparing TKA lacked full extension and were measured in 15° of flexion. At extension, the initial AP position was ACL/PCL, -7.05 ram. (-0.5 to -13.0); PCL, 12.12 ram(-10.3 to -13.29); PS, -1.5 (3.6 to -6.3). At 30 ° and 60 ° flexion, the ACL/PCL and PS TKAs showed slight rollback while the PCL TKAs demonstrated anterior translation (ACL/PCL, -8. I ram; PS, 2.8 ram; PCL, -10.41 ram). At full flexion, the ACL/PCL, PCL, and PS TICAs all showed anterior translation (ACL/PCL, -7.9mm; PS, 0.9ram; PCL, -9.5mm). Discussion: Similar to our prior experience, the PCL TKA in this study started posterior in extension and demonstrated progressive anterior translation with flexion. In contrast, the ACL/PCL and PS TKAs demonstrated a slight degree of rollback from 0 ° to 60 ° of flexion. The ACL/PCL TKAs remained posterior to the mid-line in most positions. This finding coupled with the lack of full extension would suggest a subtle technical imbalance in attempth-tg to create the "four bar linkage" found in the normal knee. The PS TKAs demonstrated the most favorable kinematics, remaining nearly mid-line throughout motion and showing little tendency for anterior translation in deep flexion.
PAPER # 30 *IN VIVO ANTEROPOSTERIOR FEMOROTIBIAL TRANSLATION: A MULTICENTER ANALYSIS Douglas A. Dennis, MD, Denver, CO, Richard D. Komistek, PhD, Clifford W. Colwell, Jr., MD, Richard D. Scott, MD, Thomas S. Thornhill, MD, Chitranjan S. Ranawat, MD Introduction: The objective of this study is to determine in vivo femorotibial contact patterns for subjects having a posterior cruciate retaining (PCR) or posterior cmciate substituting (P$) implanted knee. Methods: Femorotibial contact of 72 subjects implanted with total knee arthroplasty (TKA), performed by five surgeons, was analyzed using video fluoroscopy. Thirty-one subjects were implanted with a posterior cruciate retaining TKA with a fiat polyethylene insert (PCR-F), 12 with a PCR-TKA with a curved insert (PCR-C), and 29 with a posterior cruciate substituting (PS) TKA. Each subject performed successive deep knee bends to maxim u m flexion. Video images at 0, 30, 60 and 90 degrees of flexion were downloaded onto a workstation computer. Femorotibial contact paths were
232
The Journal of Arthroplasty Vol. 13 No. 2 February 1998
then determined for the medial (MC) a n d lateral (LC) condyles u s i n g a n iterative model fitting technique. Femorotibial contact anterior to the tibial midline in the sagittal plane w a s denoted as positive a n d contact posterior w a s denoted as negative. Results: The average contact position for the subjects h a v i n g a PCR-implanted knee with a fiat insert was: at full extension LC = -5.1 (-0.5 to -10.2) a n d MC = -2.9 (+4.5 to -9.0) m m ; at 30 ° of knee flexion LC = -7.1 (-0.4 to -10.8) a n d MC = -3.9 (+5.4 to -11.7) m m ; at 60 ° of knee flexion LC = -7.3 (-2 to -14.9) a n d MC = -2.9 (+2.1 to -13.4) ram; at 90 ° of knee flexion LC = -5.6 (0.3 to -12.4) a n d MC =-3.0 (+4.5 to -9.3) m m . The average contact position for the subjects having a PCR-implanted kne~ with a c u r v e d insert was: at full extension LC =-5.9 (-2.7 to -9.1) a n d MC = -4.8 (-0.5 to -11.7) ram; at 30 ° of knee flexion LC = -6.9 (-3.1 to -11.1) a n d MC -- -5.0 (-0.4 to -9.7) nun; at 60 o of knee flexion LC = -5.9 (-3.1 to -7.8) a n d MC = -3.8 (0.0 to -9.7) ram; at 90 ° of knee flexion LC = -5.7 (-3.8 to -9.3) a n d MC = -2.9 (-0.8 to -5.3) m m . The average contact position for subjects h a v i n g a PS TKA was: at full extension LC = -2.0 (1.52 to -6.2) a n d MC = -4.6 (+0.7 to -10.5) ram; at 30 ° of knee flexion LC = -7.4 (-4.5 to -11.2) a n d MC = -6.7 (-2.3 to -10.8) ram; at 60 ° of knee flexion LC = -7.2 (-4.5 to -10.5) a n d MC = -5.1 (+1.0 to -8.8) ram; at 90° of knee flexion LC = -8.5 (-5.2 to -11.0) a n d MC = -5.1 (+0.5 to -10.8) ram.
Discussion and Conclusion: Data from this mutticenter s t u d y is remarkably similar to previous fluoroscopy data from a single surgeon series, demonstrating a lack of c u s t o m a r y posterior femoral rollback (PFR) in both PCR designs, conversely d e m o n s t r a t i n g an average anterior femoral translation with knee flexion. PFR, less t h a n in n o r m a l knees, routinely w a s observed in PS TKA, attributed to e n g a g e m e n t of the cam-post mechanism. The a b n o r m a l anterior femoral translation observed in PCR TKA m a y be a factor in p r e m a t u r e polyethylene w e a r observed in retrieval studies.
P A P E R # 31
*MODULAR TIBIAL INSERT M I C R O M O T I O N : A C O N C E R N W I T H CONTEMPORARY KNEE IMPLANTS Nancy L. Parks, MS, Alexandria, VA, L. D. T. Tun Topoleski, PhD, G e r a r d A. Engh, MD, Joshua Emperado, BS Introduction: osteolysis has become a cause of knee arthroplasty failure since m o d u l a r tibia] c o m p o n e n t s became commonplace. Debris caused b y m i c r o m o t i o n at the insert/baseplate interface has been implicated. 1 This s t u d y measures the m a g n i t u d e of micromotion in m o d u l a r tibial c o m p o nents. Methods: Anteroposterior (AP) a n d medial lateral (ML) motion w a s measured with a n MTS machine. Three n e w tibial implants of each of nine c o n t e m p o r a r y designs were tested. The implants included snap-fit, peripheral capture, dovetail, a n d pin a n d clip locking mechanisms. The insert a n d baseplate were c l a m p e d into 2 independent frames a n d linear displacement u n d e r static loads of 100N, 200N, a n d 400N w a s m e a s u r e d with a n extensometer. Results: All tibial inserts m o v e d at least 100 microns relative to the m e t a l fibial baseplate in either the AP or ML direction (see Table). Dovetail designs m o v e d primarily in the direction parallel to the dovetails, whereas snap-fit designs m o v e d equally in the AP a n d ML directions. Variation in insert micromotion between implants of the same design w a s more t h a n 500 microns in all designs tested.
in all the implants tested. The tolerances of the m o d u l a r insert locking m e c h a n i s m are not tightly controlled b y implant manufacturers. A n ind u s t r y - w i d e lack of quality control yields a pool of implants with w i d e variations in insert motion. This relative motion m a y be a n unappreciated source of w e a r debris in total knees. 1. Wasielewski, Parks, et al. 1997 AAOS Meeting, San Francisco, CA.
P A P E R # 32 T O T A L KNEE ARTHROPLASTIES FOR PATIENTS W I T H EXTENSOR M E C H A N I S M DEFICIENCY
James F. Wenz, MD, Baltimore, MD, Michael A. Mont, MD, James A. Shaw, MD, Ronald Delanois, MD, Dennis Lennox, MD, D a v i d S. H u n g e r f o r d , MD Introduction: A lack of a functional knee extensor mechanism is considered a relative contraindication to performing a total knee arthroplasty. These patients are typically r e c o m m e n d e d as candidates for knee arthrodesis. This s t u d y examined the outcome of patients with total knee arthroplasties w h o h a d absolute or functional deficiencies of their extensor mechanism. Material and Methods: This was a multi-center review of patients with deficiencies of their extensor mechanism. There were two g r o u p s studied; (1) patients w h o preoperatively (pre-TKA) h a d a non-functional extensor m e c h a n i s m a n d (2) patients w h o post operatively (post-TKA) developed a functional extensor deficiency. The extensor m e c h a n i s m deficiency w a s defined as a muscle grade p o w e r of less than 3 or less points. Patients were characterized clinically b y Knee Society scores in addition to radiographic evaluation. Other clinical parameters studied utilized various functional instruments a n d special attention w a s paid to the patient's ability to a m b u l a t e with or without aids such as braces or crutches. Results: Five patients were in G r o u p 1 (pre-op deficiency) with the foll o w i n g diagnoses; poliomyehfis (2 patients), proximal tibial plateau fracture (1 patient), a n d an absent extensor mechanism after successfully treated d e e p infection (2 patients). Six patients were in G r o u p 2 (post-operative deficiency) secondary to femoral nerve palsy (1 patient), patella tendon r u p t u r e s (4 patients), a n d after flap reconstructive closure of an extensive w o u n d (1 patient). There were five m e n a n d six w o m e n w h o h a d a n average age of 67 years (range, 42 to 81) a n d were followed for a m e a n of 4.5 y e a r s (range, 2 - 7). All patients h a d Knee Society scores greater t h a n 75 points a n d were pleased with their outcome. None of the patients w o u l d h a v e considered a knee arthrodesis at a n y time d u r i n g the course of their treatment. Five patients needed extension braces or knee immobilizers for a m b u l a t i o n a n d six patients required only the use of a cane for long walks. N o patient w e n t into functional knee recurvatum. Discussion and Conclusions: The five patients w h o u n d e r w e n t total knee arthroplasty with absent extensor function pre-operatively did well functionally. In addition, 6 other patients w h o post-TKA developed a n extensor dysfunction have maintained satisfactory function. Total knee arthroplasty in patients with deficiencies of extensor m e c h a n i s m should be considered in select patients as an alternative to knee arthrodesis.
P A P E R # 33 M e a n displacement in microns: 100N AP . . . . . ge (range) • 469 (221-1073) ML average (range) ~t 287 (66 - 750)
200N 695 (193-1030) 535 (125 - 1381)
400N 1052 (342-1523)] 985 (312 - 1160)
]
*CEMENTLESS ACETABULAR C O M P O N E N T S IN PRIMARY TOTAL H I P A R T H R O P L A S T Y AT TEN YEARS J o h n Clohisy, MD, Boston, ARIA,William H. Harris, MD
Discussion and Conclusion: Locking mechanisms of contemporary, m o d u lar tibial implants d o not eliminate motion between the insert a n d baseplate. E n o u g h motion to create fretting at the m o d u l a r interface occurred
* Denotes that something of value was received Presenters are boldface
Introduction: The optimal type of acetabular fixation in p r i m a r y total hip arthroplasty remains controversial. We report our results with a porous acetabular c o m p o n e n t at an average 10 years follow-up.
Methods: Two h u n d r e d thirty-seven p r i m a r y total hip replacements in 213 patients were performed between J a n u a r y 1984 a n d December 1987 using a Harris-Galante porous coated acetabular component with screw fixation. O n e h u n d r e d fifteen patients were male a n d 98 female. The m e a n age w a s 63 years (range, 39 - 85). All hips were evaluated clinically a n d radiographically at a n average 122 m o n t h s (range, 84 - 144).
P A P E R # 28 IS THE ROUTINE EXAMINATION OF SURGICAL SPECIMENS WORTHWHILE IN PRIMARY TOTAL KNEE ARTHROPLASTY? Jose H e m a n Forero, MD, Mark W. Pagnano, MD, Jacksonville, FL, Giles R. Scuderi, MD, Steven E Harwin, MD Introduction: Given the present health-care climate in which emphasis has been placed on both cost-containment and outcomes, we were interested in determining the utility of routine pathological examination of surgical specimens obtained during primary total knee arthroptasty (TKA). In particular, we sought to determine if and when the pathologic diagnosis differs from the clinical diagnosis, does such a difference alter clinical management of the patient, and what are the costs associated with the collection of routine surgical specimens during primary TKA. Methods: Between 1993 and 1996, 2,035 primary TKAs were performed for a variety of diagnoses at a sIngle institution. In each case, both bone and tissue specimens were sent for routine pathological review. The medical record for every patient was reviewed to determine the preoperative clinical diagnosis, the intraoperative findIngs and the results of the pathological examination. When a discrepancy was noted between the clinical diagnosis and pathological diagnosis, the medical record was further scrutinized to determine if subsequent treatment was altered. Results: Six hundred ninety-two of the TKAs were in male patients and 1,343 in females. The mean age of the patients was 67 years (range 21 to 93 years). The TKA was performed on 973 right knees and 1,062 left. In 8 cases there was a discrepancy between the clinical and pathological diagnosis. In none of those cases was the subsequent treatment of the patient altered as a result of the pathological findings. Conclusions: This study suggests that the routine pathological review of surgical specimens from primary TKAs is of little clinical value. In no case was the subsequent management of a patient altered because of the pathological diagnosis. Costs for the routine pathological examination of a TKA surgical specimen ranged from $195 to $300 at our institution. In those selected cases where the clinical circumstances or surgical findings are aberrant, it remains prudent for the surgeon to submit surgical specimens for pathological review. This study, however, suggests a re-examination of hospital bylaws, as well as local and state regulations that mandate the routine pathological examination of surgical specimens from primary TKAs.
* Denotes that somethingof value was received Presenters are boldface
231
PAPER # 29 *THE CRUCIATE LIGAMENTS IN TOTAL KNEE ARTHROPLASTY: A KINEMATIC ANALYSIS James B. Stiehl, MD, Milwaukee, WI, Douglas A. Dennis, MD, Richard D. Komistek, PhD, Jean M. Cloutier, MD Introduction: Prostheses for total knee arthroplasty (TKA) are available in a wide variety of designs with techniques that spare both cruciate ligaments, the posterior cruciate ligament, or sacrifice both ligaments. Recent studies have used video fluoroscopy to accurately define knee kinematics invivo. This study compares the performance of TKA with various treatments of the posterior cruciate ligament. Method: Twelve patients with an anterior/posterior cruciate (ACL/PCL) sparing TKA, 8 patients with a posterior eruciate (PCL) sparing TKA, and 20 patients with a posterior cruciate ligament sacrificing (PS) mobile bearing TKA were studied while performing a deep knee bend under invivo weight-bearing conditions using video fluoroscopy. The videos were analyzed using an iterative model fitting technique that fits 3D CAD solid models of the femur and then the tibia onto 2D fluoroscopic silhouette images. Total knee patients selected had an excellent clinical result (>90/ 90 KSS) and had a minimum of 12 months follow-up. At 0 °, 30 °, 60° and 90° degrees of flexion, fluoroscopic images were matched with the best 3D CAD image found in the femoral and tibial component silhouette libraries. Digitization was then utilized to determine the position of femorotibial contact at various increments of flexion. By definition, positive was noted to be anterior to the mid-tibia plane and negative was posterior. The relative error of 0.75 m m was determined using a six degree of freedom apparatus that allowed for the femoral and tibial component to be oriented to known positions. Results: The femorotibial contact position of all three groups started posterior to the mid-line in extension. All 12 patients with the ACL/PCL sparing TKA lacked full extension and were measured in 15° of flexion. At extension, the initial AP position was ACL/PCL, -7.05 ram. (-0.5 to -13.0); PCL, 12.12 ram(-10.3 to -13.29); PS, -1.5 (3.6 to -6.3). At 30 ° and 60 ° flexion, the ACL/PCL and PS TKAs showed slight rollback while the PCL TKAs demonstrated anterior translation (ACL/PCL, -8. I ram; PS, 2.8 ram; PCL, -10.41 ram). At full flexion, the ACL/PCL, PCL, and PS TICAs all showed anterior translation (ACL/PCL, -7.9mm; PS, 0.9ram; PCL, -9.5mm). Discussion: Similar to our prior experience, the PCL TKA in this study started posterior in extension and demonstrated progressive anterior translation with flexion. In contrast, the ACL/PCL and PS TKAs demonstrated a slight degree of rollback from 0 ° to 60 ° of flexion. The ACL/PCL TKAs remained posterior to the mid-line in most positions. This finding coupled with the lack of full extension would suggest a subtle technical imbalance in attempth-tg to create the "four bar linkage" found in the normal knee. The PS TKAs demonstrated the most favorable kinematics, remaining nearly mid-line throughout motion and showing little tendency for anterior translation in deep flexion.
PAPER # 30 *IN VIVO ANTEROPOSTERIOR FEMOROTIBIAL TRANSLATION: A MULTICENTER ANALYSIS Douglas A. Dennis, MD, Denver, CO, Richard D. Komistek, PhD, Clifford W. Colwell, Jr., MD, Richard D. Scott, MD, Thomas S. Thornhill, MD, Chitranjan S. Ranawat, MD Introduction: The objective of this study is to determine in vivo femorotibial contact patterns for subjects having a posterior cruciate retaining (PCR) or posterior cmciate substituting (P$) implanted knee. Methods: Femorotibial contact of 72 subjects implanted with total knee arthroplasty (TKA), performed by five surgeons, was analyzed using video fluoroscopy. Thirty-one subjects were implanted with a posterior cruciate retaining TKA with a fiat polyethylene insert (PCR-F), 12 with a PCR-TKA with a curved insert (PCR-C), and 29 with a posterior cruciate substituting (PS) TKA. Each subject performed successive deep knee bends to maxim u m flexion. Video images at 0, 30, 60 and 90 degrees of flexion were downloaded onto a workstation computer. Femorotibial contact paths were
232
The Journal of Arthroplasty Vol. 13 No. 2 February 1998
then determined for the medial (MC) a n d lateral (LC) condyles u s i n g a n iterative model fitting technique. Femorotibial contact anterior to the tibial midline in the sagittal plane w a s denoted as positive a n d contact posterior w a s denoted as negative. Results: The average contact position for the subjects h a v i n g a PCR-implanted knee with a fiat insert was: at full extension LC = -5.1 (-0.5 to -10.2) a n d MC = -2.9 (+4.5 to -9.0) m m ; at 30 ° of knee flexion LC = -7.1 (-0.4 to -10.8) a n d MC = -3.9 (+5.4 to -11.7) m m ; at 60 ° of knee flexion LC = -7.3 (-2 to -14.9) a n d MC = -2.9 (+2.1 to -13.4) ram; at 90 ° of knee flexion LC = -5.6 (0.3 to -12.4) a n d MC =-3.0 (+4.5 to -9.3) m m . The average contact position for the subjects having a PCR-implanted kne~ with a c u r v e d insert was: at full extension LC =-5.9 (-2.7 to -9.1) a n d MC = -4.8 (-0.5 to -11.7) ram; at 30 ° of knee flexion LC = -6.9 (-3.1 to -11.1) a n d MC -- -5.0 (-0.4 to -9.7) nun; at 60 o of knee flexion LC = -5.9 (-3.1 to -7.8) a n d MC = -3.8 (0.0 to -9.7) ram; at 90 ° of knee flexion LC = -5.7 (-3.8 to -9.3) a n d MC = -2.9 (-0.8 to -5.3) m m . The average contact position for subjects h a v i n g a PS TKA was: at full extension LC = -2.0 (1.52 to -6.2) a n d MC = -4.6 (+0.7 to -10.5) ram; at 30 ° of knee flexion LC = -7.4 (-4.5 to -11.2) a n d MC = -6.7 (-2.3 to -10.8) ram; at 60 ° of knee flexion LC = -7.2 (-4.5 to -10.5) a n d MC = -5.1 (+1.0 to -8.8) ram; at 90° of knee flexion LC = -8.5 (-5.2 to -11.0) a n d MC = -5.1 (+0.5 to -10.8) ram.
Discussion and Conclusion: Data from this mutticenter s t u d y is remarkably similar to previous fluoroscopy data from a single surgeon series, demonstrating a lack of c u s t o m a r y posterior femoral rollback (PFR) in both PCR designs, conversely d e m o n s t r a t i n g an average anterior femoral translation with knee flexion. PFR, less t h a n in n o r m a l knees, routinely w a s observed in PS TKA, attributed to e n g a g e m e n t of the cam-post mechanism. The a b n o r m a l anterior femoral translation observed in PCR TKA m a y be a factor in p r e m a t u r e polyethylene w e a r observed in retrieval studies.
P A P E R # 31
*MODULAR TIBIAL INSERT M I C R O M O T I O N : A C O N C E R N W I T H CONTEMPORARY KNEE IMPLANTS Nancy L. Parks, MS, Alexandria, VA, L. D. T. Tun Topoleski, PhD, G e r a r d A. Engh, MD, Joshua Emperado, BS Introduction: osteolysis has become a cause of knee arthroplasty failure since m o d u l a r tibia] c o m p o n e n t s became commonplace. Debris caused b y m i c r o m o t i o n at the insert/baseplate interface has been implicated. 1 This s t u d y measures the m a g n i t u d e of micromotion in m o d u l a r tibial c o m p o nents. Methods: Anteroposterior (AP) a n d medial lateral (ML) motion w a s measured with a n MTS machine. Three n e w tibial implants of each of nine c o n t e m p o r a r y designs were tested. The implants included snap-fit, peripheral capture, dovetail, a n d pin a n d clip locking mechanisms. The insert a n d baseplate were c l a m p e d into 2 independent frames a n d linear displacement u n d e r static loads of 100N, 200N, a n d 400N w a s m e a s u r e d with a n extensometer. Results: All tibial inserts m o v e d at least 100 microns relative to the m e t a l fibial baseplate in either the AP or ML direction (see Table). Dovetail designs m o v e d primarily in the direction parallel to the dovetails, whereas snap-fit designs m o v e d equally in the AP a n d ML directions. Variation in insert micromotion between implants of the same design w a s more t h a n 500 microns in all designs tested.
in all the implants tested. The tolerances of the m o d u l a r insert locking m e c h a n i s m are not tightly controlled b y implant manufacturers. A n ind u s t r y - w i d e lack of quality control yields a pool of implants with w i d e variations in insert motion. This relative motion m a y be a n unappreciated source of w e a r debris in total knees. 1. Wasielewski, Parks, et al. 1997 AAOS Meeting, San Francisco, CA.
P A P E R # 32 T O T A L KNEE ARTHROPLASTIES FOR PATIENTS W I T H EXTENSOR M E C H A N I S M DEFICIENCY
James F. Wenz, MD, Baltimore, MD, Michael A. Mont, MD, James A. Shaw, MD, Ronald Delanois, MD, Dennis Lennox, MD, D a v i d S. H u n g e r f o r d , MD Introduction: A lack of a functional knee extensor mechanism is considered a relative contraindication to performing a total knee arthroplasty. These patients are typically r e c o m m e n d e d as candidates for knee arthrodesis. This s t u d y examined the outcome of patients with total knee arthroplasties w h o h a d absolute or functional deficiencies of their extensor mechanism. Material and Methods: This was a multi-center review of patients with deficiencies of their extensor mechanism. There were two g r o u p s studied; (1) patients w h o preoperatively (pre-TKA) h a d a non-functional extensor m e c h a n i s m a n d (2) patients w h o post operatively (post-TKA) developed a functional extensor deficiency. The extensor m e c h a n i s m deficiency w a s defined as a muscle grade p o w e r of less than 3 or less points. Patients were characterized clinically b y Knee Society scores in addition to radiographic evaluation. Other clinical parameters studied utilized various functional instruments a n d special attention w a s paid to the patient's ability to a m b u l a t e with or without aids such as braces or crutches. Results: Five patients were in G r o u p 1 (pre-op deficiency) with the foll o w i n g diagnoses; poliomyehfis (2 patients), proximal tibial plateau fracture (1 patient), a n d an absent extensor mechanism after successfully treated d e e p infection (2 patients). Six patients were in G r o u p 2 (post-operative deficiency) secondary to femoral nerve palsy (1 patient), patella tendon r u p t u r e s (4 patients), a n d after flap reconstructive closure of an extensive w o u n d (1 patient). There were five m e n a n d six w o m e n w h o h a d a n average age of 67 years (range, 42 to 81) a n d were followed for a m e a n of 4.5 y e a r s (range, 2 - 7). All patients h a d Knee Society scores greater t h a n 75 points a n d were pleased with their outcome. None of the patients w o u l d h a v e considered a knee arthrodesis at a n y time d u r i n g the course of their treatment. Five patients needed extension braces or knee immobilizers for a m b u l a t i o n a n d six patients required only the use of a cane for long walks. N o patient w e n t into functional knee recurvatum. Discussion and Conclusions: The five patients w h o u n d e r w e n t total knee arthroplasty with absent extensor function pre-operatively did well functionally. In addition, 6 other patients w h o post-TKA developed a n extensor dysfunction have maintained satisfactory function. Total knee arthroplasty in patients with deficiencies of extensor m e c h a n i s m should be considered in select patients as an alternative to knee arthrodesis.
P A P E R # 33 M e a n displacement in microns: 100N AP . . . . . ge (range) • 469 (221-1073) ML average (range) ~t 287 (66 - 750)
200N 695 (193-1030) 535 (125 - 1381)
400N 1052 (342-1523)] 985 (312 - 1160)
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*CEMENTLESS ACETABULAR C O M P O N E N T S IN PRIMARY TOTAL H I P A R T H R O P L A S T Y AT TEN YEARS J o h n Clohisy, MD, Boston, ARIA,William H. Harris, MD
Discussion and Conclusion: Locking mechanisms of contemporary, m o d u lar tibial implants d o not eliminate motion between the insert a n d baseplate. E n o u g h motion to create fretting at the m o d u l a r interface occurred
* Denotes that something of value was received Presenters are boldface
Introduction: The optimal type of acetabular fixation in p r i m a r y total hip arthroplasty remains controversial. We report our results with a porous acetabular c o m p o n e n t at an average 10 years follow-up.
Methods: Two h u n d r e d thirty-seven p r i m a r y total hip replacements in 213 patients were performed between J a n u a r y 1984 a n d December 1987 using a Harris-Galante porous coated acetabular component with screw fixation. O n e h u n d r e d fifteen patients were male a n d 98 female. The m e a n age w a s 63 years (range, 39 - 85). All hips were evaluated clinically a n d radiographically at a n average 122 m o n t h s (range, 84 - 144).