Total knee arthroplasty (TKA) is a successful procedure for end stage arthritis of the knee that is being performed on an exponential basis year after year. Most surgeons agree that soft tissue balancing of the TKA is a paramount to provide a successful TKA. We utilized a set of retrieved lower extremities with an existing TKA to measure the laxity of the knee in all three planes to see if wear scores of the implants correlated to the laxity measured. This data has never been reported in the literature. IRB approval was obtained for the local retrieval program. Each specimen was retrieved after removing the skin, subcutaneous tissue and muscle from mid thigh to mid tibia. The femur, tibia and fibula were then transversely cut to remove the specimen for testing. Each specimen was then imaged using a flouroscopic imaging unit (OEC, Inc) in the AP, Lateral and sunrise views. These images were used to analyze whether there were any signs of osteolysis. Each specimen was mounted into a custom knee testing machine (Little Rock AR). Each specimen then was tested at full extension, 30, 60, and 90 degrees of flexion. At each flexion angle the specimen was subjected to a 10Nm varus and valgus torque, a 1.5Nm internal and external rotational torque and a 35N anterior and posterior directed force. Each specimen's implants were removed to record manufacturer and lot numbers. Polyethylene damage scores (Hood et al. JBMR 1983) were then calculated in the medial, lateral and backside of the polyethylene insert as well as on the medial and lateral femoral condyle. (Figure 1) Correlation coefficients were then calculated to show any relationship with soft tissue balancing in all three planes and wear scores.Introduction
Methods
When performing total knee arthroplasty (TKA), surgeons often utilize a posterior-stabilized (PS) design which compensates for the loss of the posterior cruciate ligament (PCL). These designs attempt to replicate normal knee kinematics and loading using a cam and post to provide posterior restraint of the tibia during flexion. However, these designs may not be able to compensate for the increase in flexion space or the inherent loss of coronal stability after PCL release compared to a cruciate retaining (CR) design. This study aimed to compare stability of PS and CR TKA designs by assessing laxity in three planes. The specimens utilized in this study were lower extremities from fresh cadavers of donors who had previously undergone a total knee replacement (Medical Education and Research Institute (Memphis, TN) and Restore Life USA (Johnson City, TN)). IRB approval was obtained prior to performing the study. Twenty-three knee specimens (8 left, 15 right) were retrieved and all skin, subcutaneous tissue and muscle was removed. The femur and tibia were cut transversely 180 mm superior and inferior to the knee joint line, respectively, and specimens were mounted in a custom knee testing machine. Specimens were tested with the knee joint at full extension and at 30, 60, and 90 degrees of flexion. Laxity was assessed at 1.5 Nm of internal and external torque and 10 Nm varus and valgus torque, as well as a 35 N anterior and posterior force. Laxity was expressed as degrees of tibial displacement in the coronal plane under a varus/valgus torque and degrees of displacement in the transverse plane under an internal/external torque, as well as mm of anterior or posterior displacement. TKA components were retrieved to determine PS or CR design and grouped accordingly.Introduction
Methods
Repair of the arthrotomy is a performed at the end of every total knee arthroplasty (TKA). After the arthrotomy is performed, most surgeons attempt to close the arthrotomy with the medial and lateral edges anatomically approximated. If no landmarks are made prior to performing the arthrotomy however, there is a risk that anatomic approximation may not be obtained. This study looked into the biomechanical changes in stiffness of the knee before and after a medial parapatellar approach repaired with an anatomic, and shifted capsular repair with the medial side of the arthrotomy shifted up or down when repaired to determine if capsular closure may have an effect on the stiffness of the joint. Fourteen cadaveric TKA specimens were retrieved through the Medical Education and Research Institute (Memphis TN). For each specimen tested, the skin and muscle tissue was removed, and the femur and tibia were cut transversely 180 mm from the joint center. Specimens were fixed in extension in a custom knee testing platform (Little Rock AR) and subjected to a 10 Nm varus and valgus torque and a 1.5 Nm internal and external rotational torque. The angle at which these moments occurred was recorded, and each test was repeated for 0, 30, 60, and 90 degrees of flexion. After tests were performed on retrieved TKA specimens, a fellowship trained orthopedic surgeon vented the knee capsule by making an incision with a number 10 scalpel blade in a horizontal nature to provide a landmark for anatomic reapproximation. Tests were repeated as before, after which the surgeon performed a standard arthrotomy and repaired it using #0 suture and a neutral alignment. Sutures were cut and the repair was repeated using upward 5 mm shift and downward 5 mm shift of the medial side of the arthrotomy during the repair. All tests were repeated after each repair technique. Any increase or decrease in laxity after capsule repair was referenced to the TKA laxity tested prior to an arthrotomy being performed.Introduction:
Methods:
Soft tissue balancing is a part of every total knee arthroplasty (TKA) surgery. Traditionally, balancing the varus knee has been approached by releasing portions of the medial soft tissue sleeve in a sub-periosteal nature off of the proximal tibia, but this may lead to undue laxity or residual pain about the area the release was performed. More recently, “pie crusting” of the medial soft tissue sleeve has been used to balance the varus knee without compromising the structural integrity of the ligament. This technique may provide advantages over a sub-periosteal release by targeting only medial tight bands that can be palpated with the capsule distracted in 90 degrees of flexion and full extension. This study aims to biomechanically validate the pie crusting technique of the medial soft tissue sleeve and compare the results to those of standard medial releases that have been previously reported. Six cadaveric TKA specimens were retrieved through the Medical Education and Research Institute (Memphis TN). For each specimen tested, the skin and muscle tissue was removed, and the femur and tibia were cut transversely 180 mm from the joint center. Specimens were fixed in extension in a custom knee testing platform (Little Rock AR) and subjected to a 10 Nm varus and valgus torque. The angle at which these moments occurred was recorded, and each test was repeated for 0, 30, 60, and 90 degrees of flexion. After tests were performed on TKA specimens, a fellowship trained orthopedic surgeon performed “pie crusting,” making alternating stab patterns with a number 11 scalpel blade along the anterior half of the superficial medial collateral ligament (SMCL) or posterior half of the SMCL including the posterior oblique ligament (POL). Three specimens had the anterior capsule pie crusted first and three had the posterior pie crusting performed first, followed by complete pie crusting. After two stages of pie crusting, the medial soft tissue sleeve was released off of the proximal tibia in a sub-periosteal fashion for comparison. Laxity was defined as the angles at which valgus torque equaled 10 Nm. Any increase or decrease in laxity was referenced to the normal TKA laxity.Introduction:
Methods
Soft tissue balancing during Total Knee Arthroplasty (TKA) is a step every surgeon takes during surgery. Coronal and transverse plane mechanical alignment is another parameter that surgeons address during surgery in an attempt to decrease wear and increase longevity. To date, a correlation between laxity, component wear patterns, and alignment of the tibial and femoral implant components has not been established. Theoretically, suboptimal alignment and poor soft tissue balancing should increase polyethylene wear and decrease implant survivorship, contributing to implant loosening and costly revision surgeries. This study utilizes a retrieval program of functioning TKAs obtained at the time of necropsy. By utilizing CT scans, mechanical laxity testing, and polyethylene damage scores, we aimed to determine if any correlation between proper alignment and ligament balancing to polyethylene damage scores exists. Computed Tomography (CT) scans were performed on 17 cadaveric knees containing TKAs obtained from the Medical Education and Research Institute (Memphis TN) using a GE Brightspeed scanning system with a 1.25 mm slice thickness. Transverse slices from these scans were used to calculate the femoral and tibial component rotation for each specimen. Component rotation was determined by utilizing previously published methods (Berger et al), and component mismatch was defined as the difference in rotation angles of the femoral and tibial components. After removal of skin, subcutaneous and muscle tissue, the tibia and femur of each leg was cut transversely, and the specimens were mounted in a custom knee testing machine (Little Rock, AR). Specimens were subjected to a 10 Nm varus and valgus torque and a 1.5 Nm internal and external rotation torque. Data was continuously recorded, and the angle or displacement at each torque or force was noted. Each test was performed at full extension and 30, 60, and 90 degrees of flexion. TKA components were then removed from the cadaveric knees, cleaned of PMMA, and visually inspected for wear using a grading system with 10 wear areas on the articulating surface of the polyethylene tibial insert (Hood et al). Scores were assigned based on severity of 7 different degradation characteristics, and were separated based on medial or lateral compartment. The maximum possible total score was 210 for each knee. The average length of TKA implantation was 10 years. The coronal angle at +10 Nm (varus) moment ranged from 5 to 12 degrees, while the angle under a −10 Nm (valgus) moment ranged from 7 to 11 degrees across 10 specimens. The average component rotational mismatch was 20.5 degrees. The average overall medial wear score was 8.8, while the lateral average was 9.6. Wear scores showed a higher correlation to laxity in the medial compartment than the lateral side (Figures 1 and 2).Methods:
Results:
