Physiological sagittal plane patellar kinematics during dynamic deep knee flexion.

PURPOSE: Lateral radiographic views can be easily taken and have reveal considerable information about the patella. The purpose of this study was to obtain sagittal plane patellar kinematics data through the entire range of knee flexion under weight-bearing conditions. METHODS: Patellar flexion angles relative to the femur and tibia and anterior-posterior and proximal-distal translations of the patella relative to the femur and tibia were measured from 0 to 165° knee flexion in nine healthy knees using dynamic radiographic images. RESULTS: The patella flexed relative to the femur and tibia by two thirds times and one third times the knee flexion angle, respectively. The patella translated in an arc relative to the femur and tibia as the knee flexed. In early flexion, the superior and centroid points translated anteriorly and then the patella translated posteriorly relative to the femur. All three points of the patella translated posteriorly relative to the tibia during a full range of flexion. An average of four and three millimetres proximal patellar translation relative to the tibia was demonstrated from 0 to 20° and 140 to 160° knee flexion, respectively. CONCLUSIONS: Physiological sagittal plane patellar kinematics, including patellar flexion angles and translations relative to the femur and tibia, showed generally similar patterns for each subject. Measurements of dynamic radiographic images under weight-bearing activities may enhance the opportunity to identify patellar pathological conditions.

In vivo healthy knee kinematics during dynamic full flexion.

Healthy knee kinematics during dynamic full flexion were evaluated using 3D-to-2D model registration techniques. Continuous knee motions were recorded during full flexion in a lunge from 85° to 150°. Medial and lateral tibiofemoral contacts and femoral internal-external and varus-valgus rotations were analyzed as a function of knee flexion angle. The medial tibiofemoral contact translated anteroposteriorly, but remained on the center of the medial compartment. On the other hand, the lateral tibiofemoral contact translated posteriorly to the edge of the tibial surface at 150° flexion. The femur exhibited external and valgus rotation relative to the tibia over the entire activity and reached 30° external and 5° valgus rotations at 150° flexion. Kinematics' data during dynamic full flexion may provide important insight as to the designing of high-flexion total knee prostheses.

Cutting error of the distal femur in total knee arthroplasty by use of a navigation system.

The aim of this study was to evaluate the alignment of the distal femoral cutting surface using a navigation system to determine the accuracy of bone cutting. We evaluated 20 knees in 20 patients. After cutting the distal femur, the cutting surface was validated using the navigated cutting block adapter, and the angular difference between the cutting surface and that preoperatively planned in the sagittal and coronal planes was recorded. The average error of all knees was 1.6° ± 2.2° in extension, and 14 (70%) of 20 knees were cut in an extended position. Our tendency is to cut the distal femur in an extended position with the first femoral cut in the sagittal plane.

Modified gap-balancing technique in total knee arthroplasty: evaluation of the post-operative coronal laxity.

It is unknown how intra-operative soft-tissue balance affects post-operative knee kinematics during different functional tasks. In order to clarify this relationship, the intra-operative varus-valgus balance and post-operative knee kinematics were compared for 17 patients who underwent total knee arthroplasty using a modified gap technique. The intra-operative balance was recorded with a tensor device, and in vivo knee kinematics of lunging, kneeling and non-weight-bearing knee extension were analyzed with 3D-to-2D model registration techniques. Femoral condylar separation from the tibial articular surface also was investigated. The post-operative varus-valgus angle in 90 degrees kneeling had a strong relationship with the intra-operative varus-valgus angle, while there was a weak relationship for the non-weight-bearing motion at 0 degrees and 90 degrees flexion. Articular surface separation was an uncommon observation, seen in 2.2% of images during non-weight-bearing motion and in none of the lunging or kneeling images. The modified gap technique appears effective providing stable knee arthroplasty kinematics during in vivo activities with minimal articular separation in non-weight-bearing motion.

Knee kinematics in medial osteoarthritis during in vivo weight-bearing activities.

Dynamic knee kinematics were analyzed for medial osteoarthritic (OA) knees in three activities, including two types of maximum knee flexion. Continuous x-ray images of kneeling, squatting, and stair climbing motions were taken using a large flat panel detector. CT-derived bone models were used for the model registration-based 3D kinematic measurements. Three-dimensional joint kinematics and contact locations were determined using two methods: bone-fixed coordinate systems and by interrogation of CT-based bone model surfaces. The femur exhibited gradual external rotation with knee flexion for kneeling and squatting activities, and gradual internal rotation with knee extension for stair climbing. From 100 degrees to 120 degrees flexion, contact locations showed a medial pivot pattern similar to normal knees. However, knees with medial OA displayed a femoral internal rotation bias and less posterior translation when compared with normal knees. A classic screw-home movement was not observed in OA knees near extension. Decreased variability with both activities and methods of calculation were demonstrated for all three activities. In conclusion, the weight-bearing kinematics of patients with medial OA differs from normal knees. Pathological changes of the articulating surfaces and the ligaments correspond to observed abnormalities in knee kinematics.

Total knee arthroplasty following failed high tibial osteotomy: mid-term comparison of posterior cruciate-retaining versus posterior stabilized prosthesis.

This study evaluated the mid-term results of total knee arthroplasty (TKA) following high tibial osteotomy (HTO), comparing posterior cruciate-retaining prostheses to posterior stabilized prostheses. The Knee Society score for the entire group (20 knees) improved significantly from 62 (median) preoperatively to 87 at the latest follow-up. The postoperative Knee Society score of 85 in posterior cruciate-retaining prostheses (8 knees) was significantly inferior to the 94 score in posterior stabilized prostheses (12 knees). Of Knee Society score, Stability and ROM scores (17 and 21, respectively) in posterior cruciate-retaining TKA were inferior to those in posterior stabilized TKA (25 and 24, respectively). Since postoperative knee instability due to posterior cruciate ligament (PCL) insufficiency is thought to contribute to the inferior results of posterior cruciate-retaining prostheses after HTO, PCL-substituting TKA would be suitable for use after HTO.

Co-occurrence of subchondral insufficiency fracture of the femoral head and contralateral femoral neck fracture in a rheumatic patient receiving steroid treatment.

We describe a 79-year-old woman with rheumatoid arthritis who suffered from subchondral insufficiency fracture of the femoral head (SIF) and contralateral femoral neck fracture. Radiographs obtained two months after the onset of thigh pain showed collapse of the right femoral head and contralateral femoral neck fracture. MRI revealed a subchondral serpiginous low-intensity band in the right femoral head on the T2-weighted image. This case report suggests that SIF should be considered in the differential diagnoses of rheumatic patients who suffer from thigh pain without antecedent trauma.

Dynamic activity dependence of in vivo normal knee kinematics.

Dynamic knee kinematics were analyzed for normal knees in three activities, including two different types of maximum knee flexion. Continuous X-ray images of kneel, squat, and stair climb motions were taken using a large flat panel detector. CT-derived bone models were used for model registration-based 3D kinematic measurement. Three-dimensional joint kinematics and contact locations were determined using three methods: bone-fixed coordinate systems, interrogation of CT-based bone model surfaces, and interrogation of MR-based articular cartilage model surfaces. The femur exhibited gradual external rotation throughout the flexion range. Tibiofemoral contact exhibited external rotation, with contact locations translating posterior while maintaining 15 degrees to 20 degrees external rotation from 20 degrees to 80 degrees of flexion. From 80 degrees to maximum flexion, contact locations showed a medial pivot pattern. Kinematics based on bone-fixed coordinate systems differed from kinematics based on interrogation of CT and MR surfaces. Knee kinematics varied significantly by activity, especially in deep flexion. No posterior subluxation occurred for either femoral condyle in maximum knee flexion. Normal knees accommodate a range of motions during various activities while maintaining geometric joint congruency.

Can magnetic resonance imaging-derived bone models be used for accurate motion measurement with single-plane three-dimensional shape registration?

The purpose of this study was to compare three-dimensional (3D) kinematic measurements from single-plane radiographic projections using bone models created from magnetic resonance imaging (MRI) and computed tomography (CT). MRI is attractive because there is no ionizing radiation, but geometric field distortion and poor bone contrast degrade model fidelity compared to CT. We created knee bone models of three healthy volunteers from both MRI and CT and performed three quantitative comparisons. First, differences between MRI- and CT-derived bone model surfaces were measured. Second, shape matching motion measurements were done with bone models for X-ray image sequences of a squat activity. Third, synthetic X-ray images in known poses were created and shape matching was again performed. Differences in kinematic results were quantified in terms of root mean square (RMS) error. Mean differences between CT and MRI model surfaces for the femur and tibia were -0.08 mm and -0.14 mm, respectively. There were significant differences in three of six kinematic parameters comparing matching results from MRI-derived bone models and CT-derived bone models. RMS errors for tibiofemoral poses averaged 0.74 mm for sagittal translations, 2.0 mm for mediolateral translations, and 1.4 degrees for all rotations with MRI models. Average RMS errors were 0.53 mm for sagittal translations, 1.6 mm for mediolateral translations, and 0.54 degrees for all rotations with the CT models. Single-plane X-ray imaging with model-based shape matching provides kinematic measurements with sufficient accuracy to assess knee motions using either MRI- or CT-derived bone models. However, extra care should be taken when using MRI-derived bone models because model inaccuracies will affect the quality of the shape matching results.

Comparing in vivo kinematics of anterior cruciate-retaining and posterior cruciate-retaining total knee arthroplasty.

The purpose of this study was to compare knee kinematics in patients with bi-cruciate preserving total knee arthroplasty and posterior cruciate ligament (PCL) preserving total knee arthroplasty. Five knees received PCL-retaining arthroplasty and nine knees received both cruciate-retaining arthroplasty (ACL/PCL knees). We studied treadmill gait, stair stepping, and maximum flexion activities using lateral fluoroscopy and shape matching. For maximum flexion, the ACL/PCL knees showed 6 mm more posterior translation of the lateral condyle (p < 0.05). For the stair activity, posterior translations of the lateral condyle were significantly greater in the ACL/PCL knees from 30 degrees to 70 degrees flexion (p < 0.05). Both condyles in the ACL/PCL knees showed greater posterior translation in the stance and swing phases of gait than in the PCL knees (p < 0.05). Preserving both cruciate ligaments in total knee arthroplasty appears to maintain some basic features of normal knee kinematics in these activities.