[Imaging reasons for periprosthetic femoral fractures during the operation of total hip arthroplasty with anatomic prosthesis].

OBJECTIVE: To explore the imaging reasons for periprosthetic femoral fractures during the operation of total hip arthroplasty with anatomic prosthesis. METHODS: The fracture group consisted of 7 cases with periprosthetic femoral fracture (PPFF) and the non-fracture group 21 cases without PPFF during the operation of total hip arthroplasty (THA) among the 144 cases of primary THA with anatomic prosthesis. The preoperative plain films of hip joint were taken to calibrate the Sharp's angle, centre edge (CE) angle, femoral neck shaft angle, femoral anteversion angle of neck, bowing angle of proximal femoral shaft part, width of narrowest part in proximal femoral shaft. For each case, surgical details, age, height and weight were recorded. The results were analyzed with independent sample t test by software SPSS 17.0. RESULTS: No significant difference existed in general situation, Sharp's angle and CE's angle between two groups. And there were significant differences in femoral neck shaft angle (P = 0.040), femoral anteversion angle of neck (P = 0.026), bowing angle of proximal femoral shaft part (P = 0.024), width of narrowest part in proximal femoral shaft (P = 0.021). CONCLUSION: Dysplasia of proximal femur is a major cause of periprosthetic femoral fracture during the operation of total hip arthroplasty with anatomic prosthesis.

[The etiologies and prevention of patellar instability after un-resurfaced total knee arthroplasty].

OBJECTIVE: To investigate the etiologies and prevention of patellar instability after total knee arthroplasty (TKA). METHODS: From September 1997 to April 2005, 94 patients (105 knees) underwent TKA without patellar resurfacing. All of them were osteoarthritis. Ten patients (14 knees) were performed with Rotation Knee (RK) prostheses. Forty patients were performed with mobile bearing TACK prostheses, and 44 patients with GEMINI prostheses. Subluxation and tilt of patella were evaluated by X-rays before or after operation. RESULTS: The incidence of patellar instability after operation was 28.6% in patients who had genu valgus deformity, and was 29.5% in whom had patellar instability preoperative. The incidence of patellar instability in RK, TACK, and GEMINI group was 28.6%, 20.9%, and 16.7% respectively after operations. Four patients had obvious femoral or tibial components malrotation. CONCLUSIONS: The etiologies of patellofemoral instability include pre-operative conditions, prosthetic design, and improper positioning of the prosthetic component. So the suitable component design and skillful operative technique will help the surgeon to avoid this complication.

[Change in the joint line after total knee arthroplasty].

OBJECTIVE: To investigate the change in joint line after knee arthroplasty. METHODS: A total of 43 patients had 25 primary cruciate-retaining total knee replacements (Link Gemini MKII) and 25 rotational knee replacements (Link Endo-Model Rotational Knee System) sacrificing collateral ligaments and cruciate ligaments. Lateral radiographs were made both preoperatively and postoperatively. The change in the relative position of the joint line preoperatively and postoperatively was defined as the difference between the perpendicular distance from the weight-bearing surface of the tibial plateau to the tibial tubercle of the natural tibia (JL) and perpendicular distance from the weight-bearing surface of the prosthetic tibial component to the tibial tubercle (JL'). This distance was JL'-JL. The statistical differences between 2 groups were analyzed. RESULTS: The distance of JL'-JL was 2.0 mm (-1.3 - 7.2 mm) in 22 patients with Gemini replacement, whereas the distance was 3.1 mm (-1.5 - 12.3 mm) in the other patients with rotational knee system. The difference was significant. CONCLUSIONS: If the collateral ligaments and cruciate ligaments are removed during the knee replacement operations, the prosthetic joint line is likely to be malpositioned proximally. The fibular styloid and medial or lateral epicondylar reference points can be used to determine proper position of the joint line during operation.