It is recommended in the TKA operation to balance the tension of soft tissues to make the rectangular gap in both flexion and extension because significant imbalance may result in eccentric stress on the polyethylene insert. However, no intensive research has been done on the medial and lateral laxity of the normal knee

X-ray of 50 normal knees were taken under the varus or valgus stress in both extension and flexion at 80 degrees. The angle of lines on the femoral condyles and tibia plateau was measured. The same methods were also done for the 20 osteoarthritis knees.

In extension of the normal knees, the mean angle was 5.06 degrees in varus stress and was 2.46 degrees in valgus stress. In flexion of the normal knees, the mean angle was 5.04 degrees in varus stress and was 1.82 degrees in valgus stress. Therefore, the lateral laxity was significantly larger than the medial laxity in both extension and flexion (p< 0.0001). The lateral laxity was significantly larger also in osteoarthritis knees (p< 0.0001).

There are some arguments about the priority to make the perfect rectangular gaps. The methods to measure the tension of soft tissues during the operation are not accurate and does not always reflect the post-operative tensions. Furthermore, the tension during the operation may be different from dynamic phase such as walking and standing. The present study showed that the mediolateral laxity was asymmetrical in the normal knees. This imbalance may be necessary for the medial pivot movement of the normal knee. These results suggest that a slight lateral laxity is acceptable during TKA operation and may be beneficial to achieve the normal kinematics especially for the cruciate retaining prosthesis.

Aims: This study reports early outcome data from a contemporary tapered cementless stem. Methods: Fifty patients (55 hips) underwent THA and received cement-less femoral and acetabular components (Encore Medical, Austin, TX). All stems were collarless with a 3-dimensional wedge geometry manufactured from titanium alloy with a proximal full circumferential titanium porous coating. There were 19 females and 31 males with an average age and weight of 63(31–81) years and 86(46–114)kg, respectively. Initial diagnosis was osteoarthritis (76%), osteonecrosis (15%), congenital dysplasia (5%), rheumatoid arthritis (2%) and trauma (2%). Patients were followed prospectively and Harris Hip Scores were recorded. Pre-operative, immediate postoperative, and annual radiographs were evaluated for stem and cup position, component migration, and evidence of radiolucent lines and bony adaptation. Results: The average length of follow-up was 2.0±0.4(1.5–3.1) years. There were no cup or stem revisions at this early follow-up interval. The average Harris Hip Score was 95 points (range, 63 to 100). Average cup inclination was 53¡(38¡–65¡). Radiolucent lines around the acetabular cup were infrequent (7%) and were less than 1 mm in width. Stem subsidence was noted on 10 (18%) stems, consistent with the collarless stem geometry. Some medial calcar atrophy was noted in 78% of the hips. Six (11%) stems had distal radiolucent lines > 2 mm in width. One (2%) stem had pedestal formation at the distal stem. Conclusions: Excellent midterm outcomes have been reported for tapered cementless stems with proximal circumferential porous coating. Radiolucent lines in the distal stem zones and mild medial calcar atrophy have not been associated with inferior outcomes up to 10 years.

Aims: This study describes the varied anatomic geometry of the proximal femur as it relates to cementless femoral stem design. Methods: Femoral head offset, neck-shaft angle, and canal width were measured on frontal plane radiographs of undiseased hips from 47 female and 39 male North American patients. Average age and height was 66(21–89) years and 170(152- 193)cm, respectively. Patients were positioned supine with inward pointed toes to achieve femoral internal rotation during radiography. Measurements were corrected for magniþcation and correlated with demographic data. Results: The average femoral head offset and neck-shaft angle was 37±6(25- 53)mm and 131û±6û(119û-145û), respectively. Distal canal width aver aged 11±2(5–16)mm and the canal ßare index was normal in 77% of the femurs, stovepipe in 8% and ßuted in 15%. Signiþcant correlations were as follows. As patient height increased, femoral head offset and distal canal width also increased (p< 0.05). As patient age increased, distal canal width increased and canal ßare index decreased (p< 0.05), becoming more stovepipe in shape. Femoral head offset decreased with increased neck shaft angle. Conclusions: Comparing these data with published data from Eastern populations is useful for determining appropriate cementless stem sizes applicable to different populations. Variation in femoral head offset supports the use of different neck lengths, neck-shaft angles or medialized necks to provide surgeons with stems suitable for restoring leg length and balancing soft tissues. The width of the distal endosteal canal varied widely, suggesting that some patients may beneþt from a smaller or larger distal stem diameter for a given proximal stem size.

Experimental injuries of cartilage and bone were produced by applying shear force to the articular surfaces of the lateral femoral condyles of six-month-old pigs under various loading conditions. The lesions were divided into two groups, 'open' or 'closed', depending on the presence of a crack on the articular surface. Each was further divided into four types according to the depth of penetrating injury: (1) splitting of uncalcified cartilage; (2) splitting at the subchondral plate; (3) subchondral fracture; and (4) intra-articular fracture. When shear force was applied at high speed but with low energy, the articular cartilage surface was the first to crack. At low speed and low energy, splits occurred in the deeper layers first. As the energy increased, both loading conditions eventually resulted in similar open lesions. Experimentally produced shear injuries are useful models for clinical osteochondral fracture, osteochondritis dissecans, and chondromalacia patellae.