Many recent knee prostheses are designed aiming to the physiological knee kinematics on tibiofemoral joint, which means the femoral rollback and medial pivot motion. However, there have been few studies how to design a patellar component. Since patella and tibia are connected by a patellar tendon, tibiofemoral and patellofemoral motion or contact forces might affect each other. In this study, we aimed to discuss the optimal design of patellar component and simulated the knee flexion using four types of patellar shape during deep knee flexion.

Our simulation model calculates the position/orientation, contact points and contact forces by inputting knee flexion angle, muscle forces and external forces. It can be separated into patellofemoral and tibiofemoral joints. On each joint, calculations are performed using the condition of point contact and force/moment equilibrium. First, patellofemoral was calculated and output patellar tendon force, and tibiofemoral was calculated with patellar tendon force as external force. Then patellofemoral was calculated again, and the calculation was repeated until the position/orientation of tibia converged.

We tried four types of patellar shape, circular dome, cylinder, plate and anatomical. Femoral and tibial surfaces are created from Scorpio NRG PS (Stryker Co.). Condition of knee flexion was passive, with constant muscle forces and varying external force acting on tibia. Knee flexion angle was from 80 to 150 degrees.

As a result, the internal rotation of tibia varied much by using anatomical or plate patella than dome or cylinder shape. Although patellar contact force did not change much, tibial contact balances were better on dome and cylinder patella and the medial contact forces were larger than lateral on anatomical and plate patella. Thus, the results could be divided into two types, dome/cylinder and plate/anatomical. It might be caused by the variations of patellar rotation angle were large on anatomical and plate patella, though patellar tilt angles were similar in all the cases. We have already reported that the anatomical shape of patella would contact in good medial-lateral balance when tibia moved physiologically, therefore we have predicted the anatomical patella might facilitate the physiological tibiofemoral motion. However, the results were not as we predicted. Actually our previous and this study are not in the same condition; we used a posterior-stabilized type of prosthesis, and the post and cam mechanism could not make the femur roll back during deep knee flexion.

It might be better to choose dome or cylinder patella to obtain the stability of tibiofemoral joint, and to choose anatomical or plate to the mobility.

Treatment of the femoral head necrosis with severe extensive collapse in young adults and adolescents are still challenging. We thought preserve the joint and bone stock were important factor for the treatment of femoral head necrosis in young patients. We reviewed the posterior rotational osteotomy for younger patients with severe osteonecrosis. The advantages of posterior rotational osteotomy are; the necrotic area is moved to non-weight bearing portion. The posterior column artery is shifted medially without vascular damage by rotation. Postoperative uncollapsed anterior viable areas are moved to the loaded portion below the acetabular roof in flexed positions. Eighty five hips of 66 young adults (less than 50 years old, mean age; 31 years) with extensive necrosis treated by posterior rotational osteotomy were reviewed with more than 5 year follow up with a mean of 9 years. Results of 13 hips of 12 adolescents (mean age; 14 years) with extensive collapsed necrosis treated by this procedure were also studied with a mean of 6.5 years. A mean degree of posterior rotation was 121. Recollapse was prevented in 77 hips (91%) of adults, and all 13 hips of adolescents on final AP radiographs. Collapsed lesion was remodeled well and resphericity of the postoperative transferred medial collapsed femoral head on final AP radiographs was observed. However, some of the cases were out of indication of the joint preserving procedure showing extensive lesion. In these cases, we performed the MAYO conservative stem for preserving bone stock. Radiological results of 26 hips with osteonecrosis treated by MAYO stem (mean age 42 years, minimum 5 year follow-up. mean; 6.7 years) showed that 2 mm subsidence in one, osteointegration of zone 2, 6 in 93%, no entire lucent line. No hips were revised for late loosening associated with osteolysis. CT imaging indicated that spot welds of zone 2, 6 were found in 100ï¼ï¿½, stress shielding of zone 1, 5 (23.5ï¼ï¿½). These operations were useful particularly for younger patients.

Introduction: Since 2004, in addition to the original curved varus osteotomy for osteonecrosis of the femoral head, we have intentionally performed anterior or posterior rotation without incising the articular capsule to obtain a more extensive viable area in the loaded portion. We investigated the extent of viable area on the loaded portion after this modified operation.

Materials and Methods: Subjects included 11 patients (13 joints: anterior, 12 joints; posterior, 1 joint) who underwent a modified curved varus osteotomy and anterior or posterior rotation. We investigated the percent of viable area in the preoperative vs. the postoperative weighted portion. In addition, we measured the extent of viable area in the loaded portion when the extent of curved varus osteotomy without rotation was performed based on a schematic drawing.

Results: In this study, the combination of transtrochanteric curved varus osteotomy and anterior or posterior rotation significantly increased the percent viable area from 66% to 85%.

Discussion: The extent of postoperative viable area on the loaded portion might have been increased more than in the original procedure.

Introduction: We studied resphericity of the collapsed femoral head moved medially after posterior rotational osteotomy for osteonecrosis at a mean of 8.5 years follow-up.

Materials and Methods: Twenty-eight hips in 24 patients with osteonecrosis with apparent collapse treated by this operation were studied. All hips had no recollapse at final follow-up. The mean age of patients was 26 years. Twenty-two hips were non-traumatic, 6 were traumatic. The resphericity was studied by ratio (%, medial area of collapse/hip center to superior viable joint surface) at less than 6 months, 3years, and at final follow-up on postoperative antero-posterior radiographs. Disappearance of the subchondral fracture was also observed.

Results and Discussion: The mean ratio of the medial collapse area was 18.4% at less than 6 months, 8.3% at 3years, and 3.4% at final follow-up. Subchondral fracture was seen in 25 of 28 hips at less than 6 months, subchondral fractures disappeared in 17 hips at 3 years, and in 23 hips at final follow-up. We thought that remodeling of the postoperative medial collapsed lesion occurred after this operation.

Purpose of the study: The purpose of this prospective study was to compare insert wear radiographically at minimum three years comparing crosslinked (Duration, Howmedia) versus regular (Stratec Medical) polyethylene.

Material and methods: We used two types of UHMWPE for a series of 140 total hip arthroplasties (THA) (February 1999 – August 2000). Duration polyethylene (Howmedica) was used for 63 implants. This UHMWPE undergoes gamma ray treatment under nitrogen which leads to a stabilization phase under temperature and time conditions enabling preferential formation of cross links between the molecular chains. Vecteur Orthopedic polyethylene implants exposed to gamma radiation under air were used for 62 implants. Eighty-seven patients were reviewed at minimum three years radiological follow-up. This series included 60 women and 27 men, mean age 64 years (range 32–93 years). The trans-trochanteric approach was used in all cases for insertion of a Charnley-Kerboull cemented femoral stem. All cups were cemented (abnormal implant position was an exclusion criterion). Cups were assigned randomly with a permutation table. Wear measurements were made by graphic construction comparing the immediate postoperative and last follow-up anteroposterior pelvis x-rays.

Results: Follow-up was at least 36 months for 87 patients. Mean follow-up for these 87 patients was 49.9 months. Mean wear was 0.32 mm for crosslinked poly-ethylene and 0.35 mm for regular polyethylene. Five patients presented wear ≥ 1 cm for crosslinked poly-ethylene and there were nine patients with ≥ 1 cm for regular polyethylene.

Discussion: In vitro, crosslinked polyethylene exhibits significantly improved mechanical qualities for wear resistance. Several factors can account for differences in polyethylene wear: the size and composition of the prosthetic head, and patient gender, age, activity level and BMI. These factors were comparable in our two groups. It does however appear that even with crosslinked poly-ethylene, after four years implantation, wear is limited, close to the detection level of the measurement method.

Conclusion: The measurement method used in this prospective randomized study of polyethylene wear comparing crosslinked versus regular polyethylene showed no difference between the two groups at four years follow-up.

Introduction: In cases of small and middle size osteonecrosis on conventional antero-posterior (AP) radiographs, we studied the extent of the lesion on AP radiographs at the 45 degrees flexion position for lesions of the anterior area of the femoral head.

Materials and Methods: Classification of Japanese organizing committee was applied for the extent of the lesion on joint surface. Type A lesions occupy the medial one-third or less; Type B, the medial two-thirds or less; Type C-1 occupies more than the medial two-thirds; and Type C-2 extends laterally to the acetabular edge at the neutral position on conventional AP radiographs. Thirty-three hips (25 patients) with small or middle size lesions (Type A;11, Type B;22) were studied. On AP radiographs taken at the 45 degrees flexion position, the extent of the lesion was studied in 33 hips.

Results: Seven of 11 hips of Type A on neutral position showed Type A lesions. For the remaining 4 hips, 2 were Type B, 2 were on Type C-1 at 45 degrees flexion position. For 22 hips with Type B on neutral position, 6 were Type B, 12 were Type C-1, 4 were Type C-2 found at the 45 degrees flexion position.

Discussion: AP radiographs at the 45 degrees flexion position revealed more extensive necrotic area in cases of small and middle size lesions comparing with the neutral position. This finding may be related to progression of the disease.

Introduction: We performed rotational open wedge osteotomy ( ROWO ) for Perthes’ disease with an extensive lesion. With this technique, the femoral head was rotated anteriorly, the postero-lateral viable segment was moved below the lateral acetabular roof consequently with the intertrochanteric osteotomy. We reviewed the results of this procedure radiographically.

Materials and Methods: Twenty two cases over 2 years follow up were investigated. Nineteen hips (19 patients) were boys and 3 hips (3 patients) were girls. The patients’ mean age at the time of the operation was 7 years and 9 months and the mean follow-up was 6.5 years. There were 15 hips in fragmentation stage and 7 hips in healing stage. In Catterall Grouping, 19 hips were in Group III and 3 hips were in Group IV. The mean rotation angle was 36 degrees, and the mean varus angle was 21 degrees. We analyzed Stulberg classification and Mose’ rating at the final X-ray.

Results By the Stulberg classification on final X-ray, 3 hips were in class I, 17 hips were in class II, 2 hips were in class III, and class IV and V were not seen. In Mose’ rating, all cases had good or fair results.

Discussion: We conclude that rotational open wedge osteotomy is a beneficial procedure for Perthes’ disease with extensive lesions.

Introduction: We investigated the necrotic area and its shrinkage on stage 1 femoral head necrosis with band pattern low intensity on MRI.

Materials and Methods: Eleven femoral heads (6 patients) with a history of steroid treatment were studied. In heads, band pattern was detected by MRI. The mean age was 40 years.

The location of the lesion shown by the band pattern low intensity was determined by Japanese investigation committee as follows. Type A lesion occupies the medial one-third or less; Type B occupies the medial two-thirds or less; Type C-1 occupies more than the medial two-thirds; and Type C-2 extends laterally to the acetabular edge at the neutral position. Types were observed on initial and final MRIs. The mean follow up was 4 years and 3 months. For the repair patterns, the direction was observed in the anterior and posterior slices of MRIs.

Results: Initial MRIs showed types were Types A, B, C-1, and C-2 in 3, 3, 3, and 2 femoral heads, respectively. At the final observation, no band pattern was noted on the weight-bearing surface in 3 Type-A femoral heads. The femoral head surface was repaired, and the lesion was present only in the non-weight-bearing region. In all of the 3 Type-B femoral heads and 5 Type-C1 and -C-2 femoral heads, the lesion shrank to Type A. The articular surface was covered with normal intensity area from the posterior direction in all femoral heads

Discussion: We believe that the repair occurred during the disease process in stage 1 necrosis.

Introduction: Posterior rotational osteotomy has been used in young patients to treat apparent collapse and extensive osteonecrosis of the femoral head. We have reviewed a series of our patients with greater than 3 year follow-up.

Materials and Methods: Forty-three hips in 32 young patients with non-traumatic femoral head osteonecrosis were treated by posterior rotational osteotomy. All heads were apparently collapsed (Greater than 3mm), and 12 hips showed joint narrowing. Extensive lesions were noted on measurements of the area below the acetabular roof on preoperative AP radiographs. The age of the patients at the time of surgery ranged from 15 to 48 years with a mean of 34 years. There were 13 women and 19 men. Nineteen patients received steroid administration, 9 had alcoholic abuse, 6 had no apparent risk factor. Posterior rotational angle was 60–150 degrees with a mean of 124 degrees. We reviewed radiographically at 3 to 17 years follow-up (mean; 7.6 years).

Results: Re-collapse were prevented in 39 hips (91%) on final follow-up AP radiographs. Progressive joint narrowing was found in 6 hips (14%). Of the remodeling, we observed a collapsed area on the medial portion of 19 hips after posterior rotation. Re-spherical contour was noted on 18 hips. In 12 hips with joint narrowing preoperatively, atrophy of acetabular subchondral bone was seen on 12 hips 6 months postoperatively. A newly formed acetabular bony roof was noted in 11 hips at 2 years postoperatively.

Discussion: These results suggest that this operation is effective for young patients with advanced stage osteonecrosis.

Introduction: The results of noncemented press-fit bipolar hip endoprostheses were reviewed in patients with osteonecrosis of the femoral head.

Materials and Methods: Twenty-nine hips in 24 patients with osteonecrosis of the femoral head were studied. The average follow-up period was 12 years and 5 months (range from 9 years 2 months to 17 years 11 months). All hips were classified as stage 3 or 4 (osteonecrosis) before surgery using the classification method of the Japanese Investigation Committee. Acetabular reaming was performed in 5 hips with stage 4 osteonecrosis.

Results: Four prostheses have been revised to a total hip arthroplasty at the time of follow-up examination. The average clinical hip score of Japanese Orthopaedic Association was 88.9 (98–82) with 23 hips rated excellent and good, and 6 hips rated fair. Radiologically, stem subsidence more than 5 mm occurred in 5 hips and stem loosening occurred in 6 hips (21%). Five hips with stage 4 osteonecrosis (3 hips received acetabular reaming, 2 hips in elderly patients with osteoporosis) developed outer head migration more than 4 mm in both superior and axial direction. Osteolytic lesions, seen on 11 hips in the femur and 3 hips in the acetabulum, appeared at an average of 4.2 years postoperatively.

Conclusion: These results suggest that cementless pressfit bipolar endoprosthesis for osteonecrosis demonstrated a high incidence of acetabular protrusio and osteolysis. Cementless THA with a porous coating stem should be recommended for treatment of osteonecrosis of the femoral head.

Introduction: The progression of the collapse is influenced by the extent and location of the necrotic focus of the necrotic femoral head. The authors studied the extent of the necrotic focus on the joint surface by conventional antero-posterior radiographs in neutral position, and antero-posterior radiographs at the 45 degrees flexion position. The differences of the lesions in these two types of radiographs were analyzed.

Materials and Methods: The conventional antero-posterior radiographs of the neutral position, and the antero-posterior radiographs at the 45 degrees flexion positions in 115 hip joints of 86 patients with non-traumatic osteonecrosis of the femoral head were obtained for this study. These 115 hips showed extensive lesions and could be divided into two groups: Type C-1 or C-2 by classification of the Specific Disease Investigation Committee under the auspices of the Japanese Ministry of Health Labor and Welfare. Type C1 lesions occupy more than the medial 2/3 of the femoral head and C2 lesions extend laterally to the acetabular edge.

Results: At the neutral position, Type C-1 lesions were noted in 42 joints (36%). In these 42 hips, 13 showed Type C-1 (30%) at the 45 degrees flexion position. In contrast, 29 joints (70%) were Type C-2. Type C-2 lesions in 73 joints (64%) were shown in the neutral position. In these 73 hips, Type C-2 lesions were disclosed on 69 joints (95%) in the 45 degrees flexion position and Type C-1 was noted on 4 hips (5%).

Conclusions: Based on these results, the authors propose that location of the lesion on the joint surface varies with different hip positions.

Introduction: Osteonecrosis of the femoral head with joint space narrowing in young patients aged less than fifty years old was treated with posterior rotational osteotomy. Changes of the acetabular roof were observed after operation. Early remodeling of the acetabular roof after operation was studied radiographically.

Materials and Methods: Eighteen hips in 15 patients treated by posterior rotational osteotomy were subjects for this study. The age of the patients ranged from 15 to 50 (mean of 36 years). Eleven patients were women, 4 were men. The etiologic factors were steroid administration in 9 patients, alcoholic abuse in 1 patient, trauma in 7 patients, and no apparent factor in 1 patient. Changes of the acetabular roof on antero-posterior radiographs were observed at 6 months, 1 year, and 2 years postoperatively. Atrophic change and uniform shape of the acetabular roof was studied in each period.

Results: At 6 months after operation, atrophic change was noted on all 18 hips. None of uniform shape was found. Atrophic change of 10 hips (56%) was found 1 year postoperatively. Shape of acetabular roof was improved and uniformed in 8 hips. In all 18 hips 2 years after operation, shape of acetabular roof was remodeled and uniformed.

Discussion: From these results, we thought acetabular roof of femoral head involving necrosis with joint narrowing was remodeled at an early period postoperatively.