The purpose of this study is to prove whether Japanese patients undergoing primary total hip arthroplasty (THA) for the hip dysplasia were able to return to sport after surgery.

A questionnaire survey was completed by 77 patients in 9 males and 68 females between 1 and 3 years after surgery. Mean age at surgery was 66.1 (range, 49 to 87).

In the 3 years before surgery 40 (51.9%) patients were participating in sport. By 1 to 3 years after surgery 43 (55.8%) patients were participating in sport. A total of 33 (82.5%) had returned to their sporting activities by 1 to 3 years after surgery in groups who played sports before surgery and 7 (17.5%) were unable to do with the most common reason being “cannot move as much as I wanted”. On the other hand, a total of 10 (27%) had started playing sports after surgery. The sports activities after surgery were the most common being walking, radio calisthenics, and swimming as low-impact sports. A total of 27 (73%) did not play sports before or after surgery with the most common reason being “fear of damage to the hip joint”.

In conclusion, when Japanese patients who have undergone THA for hip dysplasia choose to participate in sports, orthopedic surgeons should provide information with which to evaluate the risk of sports activity and recommend appropriate sports activity.

The objective of this study is to determine the in-vivo knee joint kinematics of patients having specially designed knee prosthesis (Bi-surface) at sitting sedentary (seiza) state.

An increase in the demand for TKA has required improvement in the durability and flexibility of knee prostheses. One of the representative cases which have improved knee flexion is Bi-surface knee. Bi-surface knee has two joint surfaces; one for weight bearing and the other for flexion motion which has a unique ball-and-socket joint. This knee prosthesis, having been applied for two decades, has not yet been precisely analyzed how the femoral and tibial components are articulating at deep knee flexion.

Since there is no practical method to measure directly prosthetic kinematics in-vivo; we applied indirect techniques, pattern matching method to the Bi-surface patients. The method has been originated by Banks and Hodge (1964), and we have improved it in order to obtain higher and more reliable accuracies.

The number of subjects examined by X-ray apparatus was 18 knees of 14 patients (3 male and 11 female) who could attain the seiza. Patients were asked to sit at seiza state and their Bi-surface knees were X-ray photographed from lateral side. We focused if the internal rotation was shown at maximum flexion as commonly shown for a normal knee. We also represented the CAD models with the same position/orientation as the data from the pattern matching, thereby investigating the contact states between the ball and socket by viewing them from the desired direction.

The following results were introduced. The mean maximum flexion angle was 144.1° (SD=5.3°), and the mean internal rotation angle at maximum flexion was 15.2° (SD=6.6). The maximum flexion angle among all subjects was 153.3° and internal rotation was 19.5° at that flexion angle. The number of subjects which had (a) contact point(s) on the tibio-femoral and/or ball-socket surface(s) was 5 knees (2 knees had contact point on both the ball-and-socket and the tibio-femoral lateral surfaces, 3 knees had only on either surface) and the other 13 knees had a slight gap between two components.

Correlation was found between the value of the maximum flexion angle and the value of internal rotation angle at that flexion; the subjects of larger maximum flexion angle also demonstrated larger internal rotation angle. This suggests that at deep knee flexion, the tibial internal rotation may play an important role after TKA as a normal knee does. By checking the CAD representations, we found that the tibio-femoral and ball-socket surfaces were separate for most subjects at seiza state. Although serious impingements were not found, it was suggested the risk of subluxation when a patient rises up.

The limitation of our study is that we used simple still X-ray pictures. In order to assess kinematics for ascending from seiza state, kinematic analyses from fluoroscopic images are needed.