Introduction

In total knee arthroplasty, patients sometimes have pain in the posterolateral part of the knee. One possible cause is the impingement of the popliteus tendon against femoral components. In the literature, the incidence has been reported to be 1–4%. The purpose of this study is to quantify the amount of posterolateral overhang of the femoral component using 3-D templating software.

Restoration of joint line in total knee arthroplasty (TKA) is important for kinematics of knee and ligamentous balance. Especially in revision TKA, it may be difficult to identify the joint line. The aim of this study is to define the relationship between epicondyles and articular surface using CT based three-dimensional digital templating sofware $“Athena” (Soft Cube, Osaka, Japan).

137 knees with osteoarthritis, all caces were grade 2 or lower in Kellgren-Lawrence index, were investigated. Perpendicular lines were dropped from the prominences of the medial and lateral femoral epicondyles to the most distal points of articular surfaces and distances of the lines were measured on the axial and coronal planes. The femoral width was measured as the distance between medial and lateral epicondyles. Each of the distance described above was converted to a ratio by dividing by the femoral width.

On the axial plane, the average distance from epicondyles to the posterior articular surfaces were 29.4±2.2mm on the medial side and 21.2±2.3mm on the lateral side. The average of the femoral width was 75.2±4.1mm. On coronal plane, the average distance from epicondyles to the distal articular surfaces were 25.2±2.8mm on the medial side and 21.4±2.5mm on the lateral side.

The ratio for the distance from epicondyles to the distal and posterior joint line compared to femoral width was 0.39±0.02, 0.28±0.03, 0.33±0.03 and 0.28±0.03. The distance from epicondyles to the distal and posterior joint line correlates with the femoral width of the distal femur. This information can be useful in determining appropriate joint line.

Several anatomical landmarks are preferable in order to achieve the precise decision of femoral component rotation in order to achieve a satisfying result in total knee arthroplasty (TKA). The posterior condylar axis (PCA) is apparent and allows minimization of interobserver error compared with the transepicondylar axis or anterior-posterior axis. The rotation angle based on PCA observed during surgery differs from the angle measured on pre-and postoperative epicondylar view, because X-rays do not reflect the posterior condylar cartilage. We investigated the influence of the posterior condylar cartilage on setting the rotation angle of the femoral component in 184 knees in 112 patients with varus osteoarthritis undergoing TKA.

Medial and lateral thickness of the resected posterior femoral condyle was measured before and after removing the cartilage to determine its thickness. The amount of rotation angle influenced by the cartilage is expressed as an inverse trigonometric function (arctangent) of the distance between the posterior condylar surfaces and the difference in thickness between the medial and lateral cartilage.

Average thickness of the lateral and medial cartilage turned out to be 2.1±0.7mm and 0.7±0.7mm, respectively. The average rotation angle influenced by this difference was calculated to be 1.7±1.3°. These findings suggest that using PCA as a guide to determine the rotation angle of the femoral component results in approximately 1.5–2.0° of excess external rotation in varus osteoarthritis. Because of significant individual variability in condylar twist angle, formed by the intersection of the clinical epicondylar axis with the PCA, preoperative CT or epicondylar view is recommended in order to calculate this angle in each subject. Thickness of the posterior condylar cartilage should be taken into consideration when finalizing the rotation angle of the femoral component by PCA in addition to transepicondylar and anterior-posterior axis.

Introduction: Appropriate femoral component alignment is important for long-term survival of total knee arthroplasty (TKA). Valgus angle of femoral component is recommended as the angle between mechanical axis and anatomical axis of the femur. Intramedullary guide system is widely used for determining the valgus positioning of femoral component. Entry point of intramedullary guide is one of the key factors for determining valgus angle of femoral component. Some investigators have shown appropriate entry points of intramedullary guide, however, it is still unclear. In this study, appropriate entry point of intramedullary guide system was calculated using three-dimensional digital templating software “Athena” (Soft Cube, Osaka, Japan).

Method: Forty-one knees in 34 osteoarthritis patients except valgus deformity (30 females and 4 males, mean age 75.1 years) received TKA and were simulated using “Athena” from January 2009 to March 2009. All cases were grade III or IV in Kellgren-Lawrence index. Radiograph and CT scan image were used for determination of appropriate entry point of femur using “Athena”. The anatomical axis of femur was defined as a line connecting the midpoints of femoral AP and lateral diameter, at 60 mm and 110 mm proximal to the center of intercondylar notch. Two coordinate systems were configured as representation of entry points. One was at the center of intercondylar notch defined as the point of origin in axial view of CT image and the line parallel to the clinical epicondylar axis (cTEA) defined as X-axis. Another coordinate system was the same point of origin but parallel to the line between trochlear groove and the center of intercondylar notch (AP line) defined as Y-axis.

Result: In the coordinate system that defined the cTEA as the X-axis, the average of entry point was 0.3± 0.30 mm medial (range, −4.8~ 4.7mm) and 11.6 ± 0.52mm anterior (range, 3.1~ 16.5mm) to the center of intecondylar notch. In the other coordinate system that defined AP line as the Y-axis, the average of entry point was 2.6± 0.29 mm medial (range, −1.5~ 6.3mm) and 11.2±0.52 mm anterior (range, 2.8~ 16.0mm) to the center of intercondylar notch.

Discussion: In this study, the appropriate entry point of intramdullary guide was slightly medial and about 11mm anterior to the center of intercondylar notch on average. However, individual entry point varied considerably in distance. These data indicates that it is important to simulate the appropriate entry point of intramedullary guide in preoperative planning.

Achieving deep flexion of knee after total knee arthroplasty (TKA) is particularly desirable in some Asian and Middle Eastern who have daily or religious customs typically use full knee flexion. After TKA, some patients complained about anterior knee pain during deep knee flexion. We evaluated the efficacy of arthroscopic fat pad resection in a series of patients suffering from anterior knee pain associated with high flexion achievement after TKA.

The efficacy of fat pad resection via arthroscopy for treating anterior knee pain associated with high flexion angle (average = 133.1°) was evaluated in eight knees of eight patients among 207 knees performed between 1996 and 1999. The mean age of patients was 71.1 years when the primary TKA was performed. All implatants were posterior stabilized type (IB-II, Nexgen PS and LPS). The symptom of anterior knee pain during deep knee flexion developed within one year after TKA in all cases. In addition to pain in eight knees, two patients have crepitation as the knee was flexed and extended and three patients had hydrarthrosis. Impingement and fibrosis of fat pad were confirmed, and fibrous structures were removed by arthroscopy.

Before arthroscopy, the symptom obviously subsided after injection of local anesthesia into infrapatellar fat pad. Patellar clunk syndrome is also soft tissue impingement and suprapatellar fibrous nodule becomes entrapped intercondylar notch on the femoral component during knee flexion. On this point, these cases does not cause by patellar clunk syndrome. After fat pad resection, the symptom disappeared, and keeps symptom-free after a mean follow-up of six years five months in all cases. Any complications following fat pad resection, such as patella baja and necrosis, were not experienced.

Those cases achieving higher flexion angle tended to experience severe pain and shorter time interval between TKA and arthroscopic surgery, suggesting impingement of the infrapatellar fat pad is closely related to deep flexion after TKA. These results demonstrate that the anterior knee pain due to repetitive infrapatellar fat pad impingement is one of the complications during deep knee flexion after TKA, and the arthroscopic fat pad resection is useful to relief the anterior knee pain. Because of our experience with patients encountering anterior knee pain, we have begun to remove 70 to 80% of the fat pad during the primary TKA procedure since 1999, and until today, none developed anterior knee pain thought to be associated with fat pad impingement, patellar baja nor patellar necrosis. We suggest that fat pad resection is necessary to prevent the anterior knee pain due to fat pad impingement during deep flexion in TKA.

To make rectangular flexion and extension gap is an important goal in total knee arthroplasty (TKA). The purpose of this study was to determine the AP and rotational position of the femora component to obtain rectangular flexion with reference to the anatomical landmarks.

One hundred and twenty seven varus osteoarthritic knees (87 patients) undergoing TKA from June 2004 to March 2006 were included (72 women and 15 men, mean age 74.4 years). All operations were performed with Vanguard PS, Biomet (Warsaw, IN U.S.A.). The position of femoral component was determined using a modified Ranawat block (Equiflex^™) to obtain the rectangular flexion gap equal to extension gap. This instrument uses the balanced soft tissue sleeve in extension as a guide to create a balanced flexion gap. The flexion gap asymmetry after TKA was evaluated as the angle between the posterior condylar axis (PCA) and the tibial cutting line (TCL) by axial radiography of the distal femur. (Tokuhara et. al., JBJS (88-B), 2006). Briefly, axial radiography of the distal femur of flexed knee was obtained with a 1.5kg distraction force in ankle joint. This technique led to clear visualization of the asymmetry of the flexion gap. Femoral component rotation was evaluated using pre- and post-operative axial radiography of the distal femur (Kanekasu et. al., CORR (434), 2005). Condylar twist angle (CTA) is the angle between the CEA and the PCA. The rotational position femoral component relative to the PCA was calculated by subtracting post-operative CTA from pre-operative CTA. In addition, the thicknesses of resected bone from the lateral and medial posterior femoral condyles were measured.

The asymmetry of the flexion gap was 1.6±2.4° with slight laxity in the lateral side. The average amount of external rotation of the femoral component relative PCA was on 6.2 ±2.5°. The thickness of resected bone from the posterior lateral and medial condyles were 4.7 ± 2.1 mm and 8.6 ±2.1 mm respectively.

The results of this study have shown that, for a well-balanced flexion gap, femoral component should be excessively rotated by 3 degrees compared to current recommendation (Parallel to SEA) As for the AP position, the average amount of medial bone resection is equal to the implant thickness (9 mm). This information is useful for the modification of measured resection technique to obtain rectangular flexion gap.