Introduction

The objective of this study was to investigate the incidence of steroid-induced osteonecrosis (ON) among male and female rabbits.

Transposition osteotomy of the acetabulum (TOA) was the first periacetabular osteotomy for the osteoarthritis hips due to acetabular dysplasia, in which the acetabulum was transposed with articular cartilage. TOA improves coverage of the femoral head to restore congruity and stability, and also prevent further osteoarthritis deterioration and induce regeneration of the joint. Many good clinical outcomes have been reported for such periacetabular osteotomies for osteoarthritis of the hips at an early stage. In contrast, the clinical outcome is controversial for those hips at an advanced stage, in which the joint space has partly disappeared. The purpose of this study was to investigate whether TOA is an appropriate option for treatment of osteoarthritis of the hips at the advanced stage by comparing with matched control hips at the early stage.

Between 1998 and 2001, TOA was performed in 104 hips of 98 patients.

Sixteen of 17 hips (94%) with osteoarthritis at the advanced stage were examined and compared with 37 matched control hips at the early stage. The mean age at the operation was 48(38–56) and the mean follow-up period was 88 (65–107) months. TOA corrected the acetabular dysplasia and significantly improved containment of the femoral head.

No hips had secondary operations including THA. Clinical scores were also significantly improved in both of the groups. In the advanced osteoarthritis cases, there was a tendency for abduction congruity before transposition osteotomy of the acetabulum to reflect the clinical outcome.

TOA is a promising treatment option for the advanced osteoarthritis of the hips as well as for those patients at the early stage when preoperative radiographs show good congruity or containment of the joint.

An artificial articular cartilage is being investigated for use in joint replacement. The low elastic modulus lining on the bearing surface is used to promote a continuous lubricant film between the articulating surfaces and hence reduce both friction and wear.

Polyvinyl formal (PVF) as an artificial articular cartilage was proposed to prolong the service life of joint replacement. The major raw material of the PVF was a polyvinyl alcohol (PVA) hydrogel, which was one of the few polymers with hydrophilic properties. It is anticipated to realize a wide range of clinical applications due to its high water-holding capacity and high biocompatibility. However, a major problem with PVA hydrogel is its low wear resistance. The PVF was made by performing a chemical cross-linking reaction in PVA, and its pore diameter, porosity, and beam density could be controlled by varying the concentrations of cross-linking agent (formaldehyde) and catalyst (sulfuric acid).

The knee joint simulator was used for investigating the wear performance of the PVF. The load and motion cycles were taken from ISO 14243-3. The peak load was 2.6 kN, and the walking cycle was 1.0 seconds. The lower PVF specimen represented the flat tibial component of the joint, and the femoral component was artificial knee joint which made from Co-Cr-Mo alloy. The lubricant was a waterbased liquid containing the principal constituents of synovial fluid.

The PVF survived for more than 1.0 million cycles. Enlargement of the PVF creep deformation by prolongation of simulating time was not obvious. Although the tribological property in fatigue wear produced by ploughing friction was inadequate, it was obvious that the PVF was a potential material for developing a load bearing system with hydration lubrication.

Total knee arthroplasty (TKA) has become one of the most successful procedures in orthopedics, and its survival rates are reportedly greater than 90% after 15 years.

Malpositioning of the component, however, can lead to various failures, such as aseptic loosening, instability, polyethylene wear, and patellar dislocation. Navigation systems for TKA have been developed to improve postoperative alignment. Many clinical and experimental studies of these navigation systems have shown that the accuracy of implanted components has improved.

We have compared the alignment of 150 total knee replacements implanted using a computed tomography-based navigation system and using the conventional alignment guide system when performed by a single surgeon. The knees were evaluated using full-length weight-bearing anteroposterior radiographs and computed tomography scans. For the navigated group, the average hip-knee-ankle angle, the femoral component angle to the femoral mechanical axis, and the tibial component angle to the mechanical tibial axis were 179.5, 89.4 and 89.7 degrees. The rotational femoral and tibial component angles to the planning axis were 0.6 and 0.3 degrees. The ideal angles of all alignments in the navigated group were obtained at significantly higher rates than in the conventional group. Our results demonstrated significant improvements in component positioning with CT-based navigation system, especially with respect to rotational alignment.

Recently, we established a new method for 3D reconstruction from postoperative CT images in order to accurately measure the alignment of the component relative to any designed plane. The results showed that the discrepancy between the two-dimensional and three-dimensional evaluations was 0.3 ± 1.8 (−2.7–3.4) degrees.

The coronal femoral angle for 36 knees (97.3%) and the coronal tibial angle for all the 37 knees (100%) were obtained within 3 degrees from the optimal angle. It is possible to measure the postoperative alignment for TKA more accurately on the basis of the defining plane. Three-dimensional analysis is necessary to evaluate the accuracy of the navigation system.

We conclude that navigation system is a very useful tool for achieving proper postoperative alignment. Controversy still exists regarding accuracy in rotational alignment with image-free navigation, but our results showed that CT-based system significantly improved accuracy of rotational alignment. We should keep using and improving the systems to establish more simplified and accurate systems.

Combined anteversion (CA) is defined as the sum of the anteversions of acetabular and femoral components. In this study, we determined the appropriate CA in a variety of femoral versions using a total hip arthroplasty model. In addition, we also examined the usefulness of a changeable neck to improve range of hip motion in these cases.

Using a THA model, the range of motion (ROM) was tested in various CA values obtained by changing the anteversion of a cup in six increments after setting the femoral anteversion to 20° or 60° anteversion and 20° retroversion. The angle of the changeable neck was changed in 11 increments of 5°. To evaluate stability, the range of internal rotation at 90° flexion, the external rotation at 0° extension, and the range flexion was measured when any impingement occurred prior to dislocation. We defined the required ROM that met 40° internal rotation, 30° external rotation, and 110° flexion.

In normal 20° anteversion group, the required ROM was achieved with CA between 30° and 50° without using any changeable necks. In excessive anteversion 60° group, the range of external rotation was less than 10° even when the acetabular component was set 10° retroverted, because of the bone impingement between the greater trochanter and the posterior acetabulum. When 25° retroverted changeable neck was used, ROM improved to 30° external rotation and satisfied the required ROM. In 20° retroversion group, the internal rotation angle was 31° even when the acetabular component was opened 35° anteverted, because of anterior neck-liner impingement. When 25° anteverted changeable neck was used, ROM improved to 39° internal rotation and 130° flexion.

In cases with normal anteversions, the required ROM can be achived by adjusting CA. In cases with excessive anteversion or retroversion, there was a limitation of the CA adjustment. The use of changeable necks allows for further improvement of ROM by compensating femoral anteversions.

Treating Crowe type 3 or 4 of hips tends to be technically difficult when performing total hip arthroplasty (THA) due to the severely dysplastic acetabulum and proximal femur in addition to a high dislocation of the hip. Since the socket is limited to being placed at the original hip center, a femoral shortening osteotomy is often required in order to prevent neurovascular problems. This osteotomy will need the stability of the femoral stem with both the proximal and the distal femoral bones. We used the modular S-ROM stem, which has a valuable proximal structure and a distal flute structure to stabilize the stem with the proximal and distal femoral fragments. The purpose of this study was to report the clinical and radiographic results of the primary THA with a shortening osteotomy while also using the S-ROM prosthesis.

Between 1994 and 2004, primary THA using the S-ROM prosthesis was performed on 7 hips in 6 cases (1 male, 5 females). Crowe type 3 or 4 was observed in one and 6 hips, respectively. The mean age at operation was 56 years old (range 51~60). The mean follow-up period was 41 months (range 24~56 months). Four hips had previously undergone a subtrochanteric valgus osteotomy. All hips underwent a step-cut femoral osteotomy at the proximal metaphysis for the shortening and/or correction of angulations with on-lay chip bone grafts. All of the used stems were straight type. The clinical outcome was evaluated using the clinical scoring system of hip joints established by the Japanese Orthopaedic Association (JOA). According to a 100 point scale, pain was determined to be 40, ROM was 20, gait was 20 and ADL was 20.

No hips had undergone any revision surgery as of the most recent follow-up. Union was achieved at the osteotomy site in all hips. Neither osteolysis nor a loosening of the implant was radiographically observed. The mean JOA score before THA and at the last follow-up was 41 (31–48) and 81 (62–91) points, respectively. The mean postoperative days to start full weight bearing was 53 days (range 49~70). In two cases (28%), a procedure using circular wiring was performed to treat a crack in the proximal femur.

The S-ROM prosthesis was thus found to be useful for primary THA with a shortening metaphyseal femoral osteotomy for hips in patients with Crowe type 3 or 4 developmental dysplasia.

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.

Minimally invasive surgery (MIS) for unicompartmental knee arthroplasty (UKA) has become increasingly popular. However, wound problems may be encountered with longitudinal skin incisions. This probably occurs because the skin is under excessively high tension during MIS. We have been using transverse incisions for MIS-UKA. We describe the surgical technique and an experimental study for assessing blood flow in the skin around the knee.

A 5–7 cm transverse skin incision was made from the medial edge of the patella at the level of 1–2 cm proximal to the joint line. The capsule was incised along the medial parapatellar up to the proximal two-thirds of the patella, and a few cm were also cut along the distal end of the vastus medialis. Because skin on the anterior aspect of the knee is more flexible in the longitudinal direction, exposure is easy even with a small incision.

Experimental study: We measured the direction of blood flow on the anterior aspect of the knee using laser flowmetry. Nine normal subjects were examined. A probe was attached to the skin on the medial parapatellar region, and two 7 cm long parallel depressors were applied bilaterally on the sides of the probe. The depressors were placed longitudinally or transversely under 30N of compression force, and then blood flow was recorded.

Blood flow was markedly increased due to congestion when the depressor was placed longitudinally. On the contrary, changes in blood flow were significantly lower when the depressor was placed transversely.

Transverse incision can lead to better exposure and permit an smaller incision. Moreover, transverse incisions are less invasive to the skin’s circulation and leave less distinctive scars than longitudinal incisions.

Kinematics of mobile bearing TKA has been evaluated by fluoroscopic studies. However, these studies focused on the relative motion between the femoral component and the tibial tray. The purpose of this study was to investigate the kinematics of the polyethylene insert in mobile bearing TKA under dynamic conditions using a custom-made 6-DOF kneesimulator.

The mobile bearing TKA used in this study had a ågstopåh on the tibial tray, allowing rotation and translation. The implants were mounted on the knee simulator. Vertical load and 5-DOF motions were regulated according to the kinematic data from the literature. The knee simulating test was conducted under three different conditions including a static condition and dynamic conditions of 0.5 Hz and 1.0 Hz. Four metal balls mounted on the insert were observed with two cameras, and position of the insert was calculated. Contact pressure on the insert was also measured using a tactile sensor.

Under the static condition, the femoral component kept almostfull contact with the insert. However, the insert shifted posteriorly with impingement to the stop under the 0.5 Hz condition. Under the 1.0 Hzcondition, antero-posterior translation of the insert was larger with impingement to the stop in both directions and contact pressure was greater.

To our knowledge, no study on the motion of the insert of the mobile bearing TKA has been reported. In the present study, the insert showed different motion and contact stress according to the given condition, in spite of the same relative motion between the femoral component and the tibial tray.

Polyethylene wear in total knee arthroplasty (TKA) is a complex and mutifactorial process. It is generally recognized that wear is directly related to a material wear factor, contact stress, and sliding distance. Conventional methods of predicting polyethylene wear in TKA mainly focus on peak contact stress or subsurface shear stress using finite element method analysis. By incorporating kinematics and contact stress, a new predictor for polyethylene wear in TKA (“Wear Index”) has been developed. The Wear Index was defined by multiplying deformation by femoro-tibial sliding velocity. The purpose of this study was to determine the predictive value of the Wear Index for polyethylene wear in TKA using both a numeric and an in vitro model.

Four commercially available total knee prostheses were modeled for this study. Deformation and sliding velocity were calculated based on the three-dimensional geometry of the components and the gait kinematic inputs using Hertz’s formula. One specimen of each of the four types of total knee prostheses was mounted on a custom-designed knee simulator. Vertical loads and flexion-extension uni-axial motion were simulated using computer controlled servohydraulic actuators. The same gait kinematic inputs used in the theoretical study were used in the simulation test. After the simulations, the surface of the tibial insert was examined microscopically and macroscopically and compared with the theoretically generated Wear Index.

This study showed a high correlation between the numeric model and the simulation. The depth of wear on the tibial insert correlated significantly with the Wear Index. Microscopic findings also demonstrated a good correlation between the Wear Index and observed wear patterns. Sliding velocity is an important factor for understanding wear in TKA. In conclusion, this study suggests that the Wear Index is a reliable predictor of polyethylene wear in TKA, as it incorporates both contact stress and kinematics in its calculation.

We evaluated the geometry of the resected femoral surface according to the theory for total knee arthroplasty (TKA) using three-dimensional computed tomography (3D CT).

The 3D CT scans were performed in 44 knees indicated as requiring total knee arthroplasty. The 3D images of the femurs were clipped according to the following procedures. The distal femur was cut perpendicular to the mechanical axis at 10 mm proximal from the medial condyle. Rotational alignment was fixed at 3 degrees external rotation from the posterior condylar line. The anterior condyle was resected using the anterior cortex as the reference point. The posterior condyle was cut at 10 mm anterior from the medial posterior condyle.

The medial-lateral (ML) width/anterior-posterior (AP) length was 1.58 ± 0.14 (mean ± SD). AP length of the 3D images tended to be longer than the box length of the three kinds of components provided when the ML width of the images was approximately equal to that of each component. The widths of medial and lateral posterior condyles of the images were 30.1 ± 3.8 mm and 24.8 ± 3.0 mm, respectively. In all except one case, the widths of the resected medial posterior condyles were greater than those of the medial condyles of all components when those of resected lateral posterior condyles were equal to those of the lateral condyles of the components.

The shapes of the resected femoral surface did not always match those of the components. The configuration of Japanese knee joints is different from that of American knee joints. Components with appropriate geometry should be designed for Japanese patients.

Purpose: Osseointegration is crucial for favorable outcomes after total hip arthroplasty (THA) using cement-less femoral components. Osseointegration is recognized on radiographs as the endosteal spot weld, which is the bony bridge between the implant and surrounding bone (Engh et al, CORR, 1989). The purpose of this study is to evaluate the clinical and radiographic results for patients who had hydroxyapatite (HA)-coated rough surfaced implants compared with those who had identical implants without HA-coating at three-year minimum follow-up.

Methods: Ninety-one patients, one hundred and two hips who had primary THA with titanium arc sprayed rough surfaced femoral implants were retrospectively studied. Sixty-four hips had received HA-coated implants (HA) and 38 hips had an identical component but without HA (Non-HA). Radiographical parameters analyzed included 1) endosteal spot welds, 2) radiolucent lines, 3) calcar responses, 4) pedestal formation, 5) implant loosening, 6) endosteal osteolysis.

Results: At a minimum follow up of 3 years after operation (mean, 5.5 years), the mean Harris hip score was 89.4 points in the HA group and 89.0 points in the Non-HA group. The radiographic analysis did show the significantly earlier appearance of the endosteal spot welds in HA group. The spot welds at 1 and 2 year after operation were present in 48% and 70% of HA group, while 13% and 42% of Non-HA group. There was no significance at 3 years (71% vs 66%). More than 80% of the spot welds were seen at Gruen zone 6 in the both groups. No differences were noted regarding the radiolucent lines, calcar response, pedestal formation between the groups. There were no implant loosening and osteolysis in both groups.

Conclusions: These results suggest that the use of HA-coating does provide improved fixation in the early periods and the possibility of improved durability.

Flexion after total knee arthroplasty (TKA) has recently been improved by changing implant designs, surgical techniques and early postoperative rehabilitation protocols. Especially for Asian people, deep knee flexion is essential because of their life style. Small numbers of patients can achieve full flexion after TKA, however, most current prostheses are not designed to allow deep knee flexion safely. Furthermore, the kinematics involved in knee flexion greater than 90 degrees in cases of TKA is still unknown, even though fluoroscopic studies have shown the paradoxical anterior femoral translation in posterior cruciate retaining (CR) TKA with knee flexion up to 90 degrees. The purpose of this study was to determine the femoro-tibial contact pattern in deep knee flexion.

The knee that had been operated upon was passively flexed from 90 degrees up to the maximum flexion under anesthesia soon after the surgery. Lateral roentgenograms of the knee were taken during flexion, and the three-dimensional kinematics was analyzed using image-matching techniques. Nine patients with CR type were included.

The average maximum flexion angle was 131.8 °. The contact point moved posteriorly with deep knee flexion except for one patient. Five out of nine patients showed external rotation of the femoral condyle. Two patients showed internal rotation, and the other two exhibited no rotational movement. None of the patients showed dislocation or disengagement of the components. At the maximum flexion, the edge of the posterior flange of the femoral component contacted the polyethylene insert.

This study was performed under non-weight-bearing conditions, but deep knee flexion is not usually performed in weight-bearing conditions. Most of the CR type showed posterior roll back during deep knee flexion. The design of the posterior flange of the femoral component should be changed to prevent damage to the polyethylene.

Introduction: Correct rotational alignment of the femoral component is an important factor for successful total knee arthroplasty. This study evaluated relationship between the transepicondylar axis and the posterior condylar axis in normal, varus, and valgus knees.

Methods: Thirty normal knees (mean age: 66.2 years), 30 osteoarthritic knees with varus deformity (67.9 years), and 25 osteoarthritic knees with valgus deformity (70.7 years) were evaluated using magnetic resonance imaging. Femo-rotibial angle on standing anteroposterior radiograph was 185° in the varus knees and 166.1° in the valgus knees. In the transverse view, the angle between the transepicondylar axis and the posterior condylar axis, and the angle between the line perpendicular to the anteroposterior (AP) axis and the posterior condylar axis were measured in each group.

Results: Transepicondylar line showed 6.4° of external rotation in the normal knees and 6.1 of external rotation in the varus knees relative to the posterior condylar axis. However, transepicondylar axis of the valgus knee showed 11.6° of external rotation. This angle was significantly larger than that of normal knee and varus knee (p < 0.05). The line perpendicular to the AP axis was externally rotated from the posterior condylar axis in 6.3° in the normal knees, 6.6° in the varus knees, and 8.8° in the valgus knees. The external rotational angle in the valgus knees was significantly larger than that of the normal and varus knees (p < 0.05).

Discussion and conclusion: These results suggest that there is no hypoplasia of the posterior part of the medial condyle in varus knees, however, posterior part of the lateral condyle in valgus knee is severely distorted. Based on the results of this study, 3 to 5 degrees of external rotation relative to the posterior condyles is not large enough to achieve correct rotational alignment for valgus knees.

Introduction: Analyses of the 3-D kinematics of TKA in vivo using the x-ray image matching techniques have been widely reported. However, the accuracy of those techniques has seemed not to be discussed enough. To demonstrate more accurate technique for those analyses, we developed the new calibration flame to detect the geometry of the x-ray source and more accurate image matching methods.

Materials and methods: A calibration flame was composed of four ball bearing markers. First, the optimal distributions of those ball markers were determined by computer simulations, and then, using the high-resolutional computed radiography (CR) of a metallic ball taken with the obtained optimal calibration flame, the resolving power of three degrees of freedom (DOF) translations were calculated. Next, the computer-synthesized projected images of the femoral component of TKA were calculated using the estimated x-ray source geometry and experimentally measured geometric data of the prosthesis when the full six DOF poses of the prosthesis were calculated. Matching the computer-synthesized images with the extracted and binalized 2-D CR images of the prosthesis was done automatically using computer in order to minimize the exclusive OR (XOR).

Results: The geometry of the x-ray source was estimated with accuracy of below 0.5 mm in computer simulations. The CR images of the prosthesis were matched with the computer-synthesized images until the XOR reached under one pixel and then, the accuracy of below 1.0 mm translations and 1.0 degrees rotation were recognized for the resolving power of six DOF poses of the prosthesis.

Discussion: The more accurate measurement of full six DOF poses is indispensable to estimate not only the 3-D kinematics but also the contact stresses or predicted polyethylene wear on TKA in vivo. The new calibration flame and the image matching technique we developed appear to be effective for analyses of TKA in vivo.

Introduction: The purpose of this study was to investigate the effects of combination treatments with anticoagulant (warfarin) and a lipid-lowering agent (probucol) on the prevention of steroid-associated osteonecrosis (ON) in rabbits.

Materials and Methods: Male adult Japanese white rabbits were intramuscularly injected once with 20mg/kg body weight of methylprednisolone acetate into the right gluteus medius muscle. These rabbits were divided into three groups: a warfarin plus probucol treatment group (WP Group, n=25), a probucol treatment group (PR Group, n=30), and a non-prophylactic treatment group (NP Group, n=20). Two weeks after the cortico-steroid injection, both femora and humeri were histopathologically examined for the presence of ON, and the sizes of bone marrow fat cells were morphologically examined.

Results: The incidence of ON in the WP Group (5%) was significantly lower than that in the NP Group (70%) (p < 0.0001). The incidence of ON in the PR Group (37%) was significantly lower than that in the NP Group (p < 0.05), but it was significantly higher than that in the WP Group (p < 0.01). The mean size of the bone marrow fat cells was significantly smaller in the WP Group (53.5 ± 4.1μm) than that in the NP Group (60.0 ± 4.0μm) (p < 0.0001). There were no significant differences in the size of bone marrow fat cells between the WP and the PR Groups (52.0 ± 5.0μm).

Discussion: This study experimentally confirmed that anticoagulant plus lipid-lowering agent treatment has a preventative effect on steroid-associated ON in rabbits.

Introduction: When osteonecrosis is located in the medial portion of the femoral head, transtrochanteric curved varus osteotomy (varus), in which the lateral intact area is transposed to the weight-bearing portion, is indicated. The purpose of this study was to evaluate the clinical outcomes of this procedure.

Materials and Methods: Cases consisted of 60 hips in 52 patients with osteonecrosis of the femoral head who had a varus osteotomy from 1981 to 1998. Fifty-five hips out of 60 were followed (follow-up rate: 92%; 5 hips dropped out). The underlying associated factors were alcohol (5), trauma (2), and corticosteroids (40); 8 hips were from patients without a known factor (idiopathic). Nineteen were male and 36 were female. The average age was 34 years at the time of surgery. Forty-three hips were classified as ARCO Stage III-A, 11 in Stage III-B, and 1 in Stage IV.

Results: The average follow-up was 8.1 years (range, 0.8 to 20 years). The average preoperative Harris Hip Score of 51 points improved to an average of 81 at the latest follow-up. Radiographically, osteonecrosis in 46 hips (84%) healed or had no progression of collapse. Nine hips (16%) showed osteoarthritic changes, including progression of collapse, in which 4 cases had undergone conversion to THA. The post-operative intact area ratio in these 4 cases was 16%, while that in the other 51 cases was 70% (p< 0.005).

Discussion: When the intact area remains at the lateral portion of the femoral head, varus osteotomy is useful not only for healing of the necrotic lesion but also for the prevention of osteoarthritis. If the intact area ratio is over 34 % with hip abduction, varus osteotomy is indicated.