Flexion is an important outcome variable after total knee arthroplasty. Traditionally, matched implant-bone resections of the distal and posterior aspects of the femur are used to prevent loss of knee flexion or extension. However, given limited implant sizes, resection of these portions of the femur may affect the shape of the knee. Variations in the anterior aspects of the femur along with implant size constraints may increase trochlear groove height in the anterior compartment, increase the arc that the extensor mechanism must travel, and thereby decrease passive flexion. We determined the trochlear groove height change in 55 patients after primary total knee arthroplasties. The thickness of the replaced lateral and medial anterior flanges increased by 1.1 +/- 2.6 mm and 0.5 +/- 2.2 mm, respectively, whereas the change in trochlear groove thickness was 0 +/- 1.1 mm. We examined varying amounts of patellofemoral buildup in a cadaver model to observe the effect on passive range of motion of the knee. A 2-mm and 4-mm buildup of the anterior cortex resulted in flexion loss of 1.8 degrees and 4.4 degrees, respectively. The change in the shape of the anterior aspect of the femur may have small effects on flexion but they may not be clinically important.

Stiffness of the medial (MCL) and lateral (LCL) collateral ligaments was compared between a group of 10 patients undergoing total knee arthroplasty for varus degenerative osteoarthritis (OAP), a group of 10 osteoarthritic cadaveric knees (OAC), and a group of 10 non-osteoarthritic cadaveric knees (NOA). A load4ongation curve was obtained for the medial and lateral compartments of each knee using an instrumented Moreland spreader. A strain gage (SG) was attached to the spreader handle and strain was calibrated to load applied against the spread distance. In extension, medial compartment stiffness of the OAP, OAC, and NOA groups

The following finite element study was conducted to determine whether increased body weight, femoral retroversion, and varus hip loading could sufficiently raise physeal shear strains and stresses above the yield point and predispose an adolescent hip to a slip. A computer tomography scan of a 13-year-old child with slipped capital femoral epiphysis was used to generate a solid model of the proximal femur and physis. The model was parameterized using 3-dimensional software to generate three difference angles of femoral neck version-neutral, 15 degrees retroversion, and 15 degrees anteversion. Loads of 2.7 times body weight in a 46- and 86-kg child were applied to the proximal femur to model stance on one leg. In addition, the loading vector was reoriented at various degrees of varus to study the effect of varus loading on physis shear. The results demonstrated that physis stress, strain, and displacement increased with greater body weight, retroversion, and varus displacement of the loading vector. Physis shear strain in hips with a combination of varus loading and femoral neck retroversion exceeded the reported ultimate strain values for cartilaginous soft tissues. The finite element models suggest that in an overweight child, the combination of retroversion and varus hip load may be sufficient to increase physeal strains above the yield point and result in a slip.

No abstract