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In-vivo kinematic analysis of a total knee prosthesis retaining the anterior and posterior cruciate ligaments
Abstracts from the AAHKS Seventh Annual Meeting Discussion: At 5 to 11 year follow-up, the efficacy of PCL retaining total knee.arthroplasty in patients with rheumatoid arthritis was excellent. The revision rate in the RA group was much lower and there was no aseptic loosening. Furthermore, in contrast to reports of late instability with PCL retaining TKA in patients with rheumatoid arthritis, this study found late instability due to PCL attenuation does not occur more frequently in patients with RA and only accounts for a failure rate of 1% at an average follow-up of 8.8 years.
POSTER #15 THROMBOEMBOLISM AFTER TOTAL KNEE ARTHROPLASTY: THE ROLE OF PNEUMATIC COMPRESSION AND ASPIRIN PROPHYLAXIS Douglas E MacMillan, Jr., MS, Christopher M. Larson, MD, Chapel Hill, NC, Paul E Lachiewicz, MD Introduction: The optimal prophylaxis for thromboembolism (TE) after total knee arthroplasty (TKA) remains controversial. Methods: The study group consisted of 323 TKAs performed by one surgeon. Between 1983 - 1991, aspirin prophylaxis alone (ASA) was used. In 1991, knee-high sequential compression devices were added to the previous prophylaxis (ASA/SCD). All patients were prospectively monitored for TE by experienced vascular technologists using doppler venous examination between 1983 - 1986 and Duplex ulfrasonography between 1986 1996. In the ASA group, there were 131 patients (168 knees); 37 patients had bilateral one-stage TKA and 4 patients (5 knees) had a prior history of TE. In the ASA/SCD group, there were 123 patients (155 knees); 32 patients had bilateral one-stage TKA and 3 patients (3 knees) had a prior history of TE. Results: The overall incidence of TE was 12.8% (30 patients). The incidence of TE in the ASA group was 15.9% (21 patients), with one symptomatic DVT. The location was calf/tibial in 10, popliteal in 6, and femoral in 5. There was one patient with a possible symptomatic nonfatal pulmonary embolism vs. cardiac ischemic event. The incidence of TE in the A S A / SCD group was 7.4% (9 patients), with no symptomatic DVT. The location was caLf/tibial in 6 patients, popllteal in 1, and femoral in 2. There was a significant difference in the incidence of DVT between the two groups (p = 0.035). A history of previous DVT was a significant risk factor for a new DVT (p = 0.0003). The incidence of DVT after bilateral, one-stage TKAs was 23.7% for the ASA and 12.5% for the ASA/SCD group. The incidence of DVT in patients with bilateral, one-stage TKA was 18.6% compared to 9.2% for patients with unilateral TKA (p = 0.03). Discussion: There was a significant reduction in the incidence of DVT after TKA using SCD and aspirin prophylaxis compared to aspirin prophylaxis alone. A prior history of DVT and bilateral, onestage TKA were significant risk factors for DVT. Aspirin and SCDs used together are a safe and effective means of DVT prophylaxis after TKA.
POSTER #16 *IN-VIVO KINEMATIC ANALYSIS OF A TOTAL KNEE PROSTHESIS RETAINING THE ANTERIOR AND POSTERIOR CRUCIATE LIGAMENTS William R. Kennedy, MD, Sarasota, FL, Douglas A. Dennis, MD, Richard D. Komistek, PhD, Scott Walker, David L. Roter, MD The objective of this study was to determine the in-vivo kinematics of knees having an ACL retaining TKA. Ten patients having an AXIOM@ ACL retaining implant underwent fluoroscopic evaluation while performing a deep knee bend to maximum flexion. An image matching process that overlays 3D solid CAD models onto the 2D fluoroscopic silhouette was used. The video analysis was downloaded to a workstation computer to determine the kinematics of this prosthesis in the tibio-femoral articulation.
* Denotes that somethingof value was received Presenters are boldface
241
The lateral condyles for all ten subjects contacted the tibia anterior to the midpoint of the tibia in the sagittal plane at full extension. The average contact position at full extension for the lateral condyle was 4.2mm anterior to the midpoint of the tibia in the sagittal plane. As the knee flexed, each of the knees rolled in the posterior direction on the lateral side, on average, to a position 9.2ram posterior at 90 degrees of flexion. On average, the medial condyle contact point also rolled back in the posterior direction from 4.8ram anterior at full extension to 1.8 man posterior at 90 degrees of flexion. This was 6.6ram of rollback. The lateral condyle of this prosthesis duplicated the femoral tibial rollback of the lateral condyle seen in the normal knee. The medial pivot motion seen in the normal knee was not produced in the TKA patient, but demonstrafed medial condyle rollback instead of the anterior slide seen in previous studies on PCR implanted knees. In full extension, the lateral condyles of the normal knee contacted the tibia 4-10ram anterior to the tibial midline in the sagittal plane. As the normal knee flexes the lateral condyle rolls back to a position of 6 - 12mm posterior. Since all posterior cruciate retaining knees slide anterior during flexion, this study shows that the retained anterior cruciate ligament is extremely important to ensure posterior femoral rollback in total knee surgery.
POSTER #17 TIBIAL COMPONENT ASYMMETRY IN REVISION TOTAL KNEE ARTHROPLASTY: A CASE FOR TIBIAL COMPONENT OFFSET James P. Jamison, MD, Boston, MA, James V. Bono, ME), Joseph C. McCarthy, MD, Roderick H. Turner, ME) Introduction: Revision total knee arthroplasty presents the surgeon with numerous challenges in the process of restoring a failed prosthesis to one which is functions well and is properly aligned. Loss of tibial bone stock often requires customization with a modular prosthesis in the form of augmentation wedges and blocks, and intramedullary stems. Using tibial intramedullary stems, we have observed that the tibial component does not rest symmetrically upon the underlying tibial plateau. Typically, the tibial component overhangs medially leaving lateral bone uncovered. To avoid medial component overhang, the tibial component has to be downsized, further accentuating the loss of lateral bone coverage and compromising the contact between bone and prosthesis. The purpose of this study is to investigate the asymmetry of tibial component position when an intramedullary stem is used. Methods: Radiographs of 24 patients undergoing revision total knee arthroplasty with a stemmed tibial component from August, 1990, to March, 1997, were reviewed. The same modular revision implant system was used by the senior authors in each case. There were 14 males and 10 females, with an average age of 66.7 years (range: 37-93). Intramedullary tibial stern extensions were used in each case, with an average diameter of 14.9 m m (range: 10 - 20 ram) and an average length of 68.5 m m (range: 30 - 115 man). Augmentation wedges were required in 5 patients, with two I0 degree full medial wedges, one 15 degree full medial wedge, one 15 degree half medial wedge, and one 10 degree half lateral wedge. Measurements of tibial component medial, lateral, anterior, and posterior eccentricity were made and corrected for magnification. Results: The tibial component was noted to be eccentrically positioned on the tibial plateau in 24 of 24 patients, with medial placement noted in 20, lateral in 3, posterior in 17, and anterior in 3. Medial tibial component overhang was encountered in 46% of patients, averaging 2.5 ram (range: 1.7 - 4.3 ram). Of the 11 patients with medial component overhang, the lateral aspect of the tibial plateau was noted to be uncovered by an average of 5.4 ram (range: 1.8 - 9.9 mm) in 8 patients. Discussion & Conclusion: Medial eccentricity of the tibial component was found to be the most common problem (20 of 24) encountered when intramedullary extension stems were used, resulting in medial overhang in 11 of 24 cases despite downsizing of the tibial component. Posterior placement of the tibial component was similarly noted in 17 of 24 cases. This is the result of altered anatomy due to loss of proximal tibial bone stock and the restriction placed on tibial component positioning by the intramedullary stem. These findings suggest that an allowance for lateral and anterior offset be incorporated into tibial component design when used with an intramedullary stem extension.
POSTER #15 THROMBOEMBOLISM AFTER TOTAL KNEE ARTHROPLASTY: THE ROLE OF PNEUMATIC COMPRESSION AND ASPIRIN PROPHYLAXIS Douglas E MacMillan, Jr., MS, Christopher M. Larson, MD, Chapel Hill, NC, Paul E Lachiewicz, MD Introduction: The optimal prophylaxis for thromboembolism (TE) after total knee arthroplasty (TKA) remains controversial. Methods: The study group consisted of 323 TKAs performed by one surgeon. Between 1983 - 1991, aspirin prophylaxis alone (ASA) was used. In 1991, knee-high sequential compression devices were added to the previous prophylaxis (ASA/SCD). All patients were prospectively monitored for TE by experienced vascular technologists using doppler venous examination between 1983 - 1986 and Duplex ulfrasonography between 1986 1996. In the ASA group, there were 131 patients (168 knees); 37 patients had bilateral one-stage TKA and 4 patients (5 knees) had a prior history of TE. In the ASA/SCD group, there were 123 patients (155 knees); 32 patients had bilateral one-stage TKA and 3 patients (3 knees) had a prior history of TE. Results: The overall incidence of TE was 12.8% (30 patients). The incidence of TE in the ASA group was 15.9% (21 patients), with one symptomatic DVT. The location was calf/tibial in 10, popliteal in 6, and femoral in 5. There was one patient with a possible symptomatic nonfatal pulmonary embolism vs. cardiac ischemic event. The incidence of TE in the A S A / SCD group was 7.4% (9 patients), with no symptomatic DVT. The location was caLf/tibial in 6 patients, popllteal in 1, and femoral in 2. There was a significant difference in the incidence of DVT between the two groups (p = 0.035). A history of previous DVT was a significant risk factor for a new DVT (p = 0.0003). The incidence of DVT after bilateral, one-stage TKAs was 23.7% for the ASA and 12.5% for the ASA/SCD group. The incidence of DVT in patients with bilateral, one-stage TKA was 18.6% compared to 9.2% for patients with unilateral TKA (p = 0.03). Discussion: There was a significant reduction in the incidence of DVT after TKA using SCD and aspirin prophylaxis compared to aspirin prophylaxis alone. A prior history of DVT and bilateral, onestage TKA were significant risk factors for DVT. Aspirin and SCDs used together are a safe and effective means of DVT prophylaxis after TKA.
POSTER #16 *IN-VIVO KINEMATIC ANALYSIS OF A TOTAL KNEE PROSTHESIS RETAINING THE ANTERIOR AND POSTERIOR CRUCIATE LIGAMENTS William R. Kennedy, MD, Sarasota, FL, Douglas A. Dennis, MD, Richard D. Komistek, PhD, Scott Walker, David L. Roter, MD The objective of this study was to determine the in-vivo kinematics of knees having an ACL retaining TKA. Ten patients having an AXIOM@ ACL retaining implant underwent fluoroscopic evaluation while performing a deep knee bend to maximum flexion. An image matching process that overlays 3D solid CAD models onto the 2D fluoroscopic silhouette was used. The video analysis was downloaded to a workstation computer to determine the kinematics of this prosthesis in the tibio-femoral articulation.
* Denotes that somethingof value was received Presenters are boldface
241
The lateral condyles for all ten subjects contacted the tibia anterior to the midpoint of the tibia in the sagittal plane at full extension. The average contact position at full extension for the lateral condyle was 4.2mm anterior to the midpoint of the tibia in the sagittal plane. As the knee flexed, each of the knees rolled in the posterior direction on the lateral side, on average, to a position 9.2ram posterior at 90 degrees of flexion. On average, the medial condyle contact point also rolled back in the posterior direction from 4.8ram anterior at full extension to 1.8 man posterior at 90 degrees of flexion. This was 6.6ram of rollback. The lateral condyle of this prosthesis duplicated the femoral tibial rollback of the lateral condyle seen in the normal knee. The medial pivot motion seen in the normal knee was not produced in the TKA patient, but demonstrafed medial condyle rollback instead of the anterior slide seen in previous studies on PCR implanted knees. In full extension, the lateral condyles of the normal knee contacted the tibia 4-10ram anterior to the tibial midline in the sagittal plane. As the normal knee flexes the lateral condyle rolls back to a position of 6 - 12mm posterior. Since all posterior cruciate retaining knees slide anterior during flexion, this study shows that the retained anterior cruciate ligament is extremely important to ensure posterior femoral rollback in total knee surgery.
POSTER #17 TIBIAL COMPONENT ASYMMETRY IN REVISION TOTAL KNEE ARTHROPLASTY: A CASE FOR TIBIAL COMPONENT OFFSET James P. Jamison, MD, Boston, MA, James V. Bono, ME), Joseph C. McCarthy, MD, Roderick H. Turner, ME) Introduction: Revision total knee arthroplasty presents the surgeon with numerous challenges in the process of restoring a failed prosthesis to one which is functions well and is properly aligned. Loss of tibial bone stock often requires customization with a modular prosthesis in the form of augmentation wedges and blocks, and intramedullary stems. Using tibial intramedullary stems, we have observed that the tibial component does not rest symmetrically upon the underlying tibial plateau. Typically, the tibial component overhangs medially leaving lateral bone uncovered. To avoid medial component overhang, the tibial component has to be downsized, further accentuating the loss of lateral bone coverage and compromising the contact between bone and prosthesis. The purpose of this study is to investigate the asymmetry of tibial component position when an intramedullary stem is used. Methods: Radiographs of 24 patients undergoing revision total knee arthroplasty with a stemmed tibial component from August, 1990, to March, 1997, were reviewed. The same modular revision implant system was used by the senior authors in each case. There were 14 males and 10 females, with an average age of 66.7 years (range: 37-93). Intramedullary tibial stern extensions were used in each case, with an average diameter of 14.9 m m (range: 10 - 20 ram) and an average length of 68.5 m m (range: 30 - 115 man). Augmentation wedges were required in 5 patients, with two I0 degree full medial wedges, one 15 degree full medial wedge, one 15 degree half medial wedge, and one 10 degree half lateral wedge. Measurements of tibial component medial, lateral, anterior, and posterior eccentricity were made and corrected for magnification. Results: The tibial component was noted to be eccentrically positioned on the tibial plateau in 24 of 24 patients, with medial placement noted in 20, lateral in 3, posterior in 17, and anterior in 3. Medial tibial component overhang was encountered in 46% of patients, averaging 2.5 ram (range: 1.7 - 4.3 ram). Of the 11 patients with medial component overhang, the lateral aspect of the tibial plateau was noted to be uncovered by an average of 5.4 ram (range: 1.8 - 9.9 mm) in 8 patients. Discussion & Conclusion: Medial eccentricity of the tibial component was found to be the most common problem (20 of 24) encountered when intramedullary extension stems were used, resulting in medial overhang in 11 of 24 cases despite downsizing of the tibial component. Posterior placement of the tibial component was similarly noted in 17 of 24 cases. This is the result of altered anatomy due to loss of proximal tibial bone stock and the restriction placed on tibial component positioning by the intramedullary stem. These findings suggest that an allowance for lateral and anterior offset be incorporated into tibial component design when used with an intramedullary stem extension.