Introduction

Range of motion (ROM) simulation of the hip is useful to understand the maximum impingement free ROM in total hip arthroplasty (THA). In spite of a complex multi-directional movement of the hip in daily life, most of the previous reports have evaluated the ROM only in specific directions such as flexion-extension, abduction-adduction, and internal - external rotation at 0° or 90° of hip flexion. Therefore, we developed ROM simulation software (THA analyzer) to measure impingement free ROM in any positions of the hip. Recent designs of the hip implants give a wider ROM by increasing the head diameter and then, bone to bone impingement can be a ROM limit factor particularly in a combination of deep flexion, adduction and internal rotation of the hip. Therefore, the purpose of this study were to observe an individual variation in the pattern of the bone impingement ROM in normal hip bone models using this software, to classify the bone impingement ROM mapping types and to clarify the factors affecting the bone impingement type.

In total hip arthroplasty (THA), acetabular cup orientation is critical for avoiding edge-loading and implant-implant impingement, which may lead to serious complications such as dislocation, mechanical loosening, accelerated wear, or implant breakage. Many studies recommended to place the acetabular cup radiographically at an inclination of <50° to avoid edge-loading. Simultaneously, larger prosthetic ROMs than the patients’ ROM during daily activities are needed to minimize impingement related complications. Several three-dimensional computer simulation studies have been done for optimal cup orientation to avoid prosthetic impingement within possible hip ROMs in the late 1990s. However, the reference angles in the directions of flexion, extension, external rotation and internal rotation at 90 ° flexion as possible hip ROMs have not been consistent in previous simulation studies. Thus, different reference angles of hip ROMs resulted in different optimal cup orientation. Therefore, to give accurate information about the reference hip ROM, we measured passive hip ROMs intraoperatively using a navigation system in 91 patients.

Pelvic and femoral coordinate systems referred a functional pelvic plane in the supine position and a retrocondylar plane, respectively. The neutral position of the hip ROM was defined as the position in which corresponding axes of the pelvic and femoral coordinate systems were parallel. Maximum flexion, extension, external rotation and abduction were 120°, 36 °, 43 ° and 55 °, respectively. Moreover, we investigated the hip ROM during five traditional Japanese hip positions which required large hip flexion and internal rotation angles in five healthy female volunteers by a 3D image matching technique using an open-configuration MRI. Maximum flexion was 122 ° and maximum internal rotation was 40 ° at more than 90 ° of flexion position. Therefore, we recommended using 120 ° for flexion, 40 ° for extension, 40 ° for external rotation and 40 ° for internal rotation at 90 ° flexion as the reference ROM when calculating an optimum cup orientation.

We calculated radiographic cup anteversion, when radiographic cup inclination was 40 °, without prosthesis impingement in the reference hip ROMs using computer aided design models of prosthesis, which included a cementless CentPillar stem with a head 32mm in diameter and cementless Trident cup with a flat liner. The results showed the optimal cup target zone existed when the stem anteversion was between 20 ° and 45 °. The size of the target zone was widest when the stem anteversion was 30 °, and then it was plus or minus 5 ° of inclination and anteversion from the center of the zone. To eliminate outliers of cup orientation form the target zone, a computer assisted system such as navigation is recommended.

Although there are several reports of excellent long-term survival after cemented total hip arthroplasty (THA), cemented acetabular components are prone to become loose when compared with femoral components. On the other hand, the survival of cementless acetabular components has been reported to be equal or better than cemented ones and the use of cementless acetabular components is increasing. However, most of the reports on survival after THA are for patients with primary hip osteoarthritis (OA) and there is no report of 20-year survival of cementless THA for patients with hip dysplasia. It is supposed to be more difficult to fix cementless acetabular components for OA secondary to hip dysplasia than primary OA. The purposes of this study were to review retrospectively the 20-year survival of cemented and cementless THA for hip dysplasia and to compare the effect of fixation methods on the long-term survival for patients with hip dysplasia. We retrospectively reviewed all patients with OA secondary to hip dysplasia treated with a cemented Bioceram hip system between 1981 and 1987, and a cementless cancellous metal Lübeck hip system between 1987 and 1991. We excluded patients aged more than 60 years, males, and Crowe 4 hips. The studied subjects were 70 hips of cemented THA (Group-C) and 57 hips of cementless THA (Group-UC). Both hip implants had a 28-mm alumina head on polyethylene articulation. The mean age at operation was 50.5 years (range, 36–60 years) in Group-C and 50.0 years (range, 29–60 years) in Group-UC. The mean BMI was 23.2 kg/m² in Group-C (range, 17.3–29.3 kg/m²) and 22.9 kg/m² in Group-UC (range, 18.8–28.0 kg/m²). There were no significant differences in age and BMI between the two groups. The average follow-up period was 18.0 years in Group-C and 18.4 years in Group-UC. In Group-C, revision was performed in 33 hips due to aseptic cup loosening (30 hips), stem loosening (one hip), and loosening of both components (two hips). In Group-UC, revision was performed in 10 hips due to stem fracture secondary to distal fixation (4 hips), cup loosening (three hips), polyethylene breakage (two hips), and extensive osteolysis around the stem (one hip). The survival at 20 years regarding any revision as the endpoint was 51% in Group-C and 84% in Group-UC. This difference was significant using Log-rank test (P=0.006). The cup survival at 20 years was 54% in Group-C and 92% in Group-UC. This difference was also significant (P = 0.0003). The stem survival at 20 years was 95% in Group-C and 92% in Group-UC. This difference was not significant (P = 0.4826). Cementless THA showed a higher survival rate at 20 years for hip dysplasia than cemented THA because of the excellent survival of the acetabular component without cement. We conclude that cementless THA with the cancellous metal Lübeck hip system led to better longevity at 20 years than cemented THA with the Bioceram for patients with OA secondary to hip dysplasia.

Using a larger diameter femoral head in total hip arthroplasty (THA) has advantages in terms of the increased joint stability and range of motion. And the wear resistance of highly cross-linked polyethylene (HXLPE) even combined with a larger head has already been demonstrated by in vitro studies. The purpose of this study was to compare the in vivo wear of Longevity HXLPE sockets against 32 mm and 26 mm heads at a 5-year follow-up.

From November 2000 to November 2001, 51 primary cementless THAs were performed with a 26 mm cobalt-chromium head and a Longevity HXLPE socket (Zimmer). A cohort of 32 mm cobalt-chromium heads was comprised of 51 THAs with the same prosthesis performed from December 2001 to December 2003. No significant differences between the groups were observed in gender, age, and BMI, however, polyethylene liners with 32 mm heads were significantly thinner than those with 26 mm heads. Two-dimensional linear wear was measured using PolyWare software on annual x-rays, and total head penetration rates at postoperative 5-year and steady state wear rates were calculated. In addition, periprosthetic osteolysis was evaluated.

At the 5-year follow-up, the total head penetration rates were 0.047±0.022 mm/year with 26 mm heads and 0.048±0.026 mm/year with 32 mm heads. The steady state wear rates were −0.008 mm/year with 26 mm heads and 0.001 mm/year with 32 mm heads. No significant differences were seen between the two groups (p=0.82 and p=0.24). Osteolysis was not observed around pros-theses in any hips.

At the 5-year follow-up, the wear rate of Longevity HXLPE was very low. A Longevity HXLPE socket will undergo the same level of wear whether with a 32 mm head or a 26 mm head.

Ceramic heads and highly cross-linked polyethylene (HXLPE) as bearing surface materials have been introduced to reduce the production of polyethylene wear particles. The present study hypothesized that the wear rate of HXLPE could be further reduced when combined with a ceramic head. The purpose of this study was to compare the in vivo wear of Longevity HXLPE against cobalt-chromium and zirconia heads after a minimum 5-year follow-up.

A prospective cohort study was performed in 102 cementless total hip arthroplasties (THAs) with the Longevity HXLPE socket (Zimmer) between June 2000 and October 2001. Same prostheses were used in all cases both acetabular cups (Trilogy; Zimmer) and femoral stems (Versys Fiber Metal Taper; Zimmer). 26-mm zirconia heads (NGK) or 26-mm cobalt-chromium heads (Zimmer) were randomly used in 51 hips each. A minimum 5-year follow-up was completed for 47 hips with zirconia heads and 46 hips with cobalt-chromium heads. Two-dimensional linear wear of Longevity HXLPE was measured using computer-assisted methods (PolyWare) on annual x-rays, and total head penetration rates and steady state wear rates were calculated. In addition, periprosthetic osteolysis was evaluated.

At a mean 6-year follow-up, the total head penetration rates were 0.034±0.016 mm/year (zirconia) and 0.031±0.015 mm/year (cobalt-chromium). The steady state wear rates were −0.01 mm/year (zirconia) and −0.01 mm/year (cobalt-chromium). No significant difference was seen between the two groups (p=0.4 and p=0.91). Osteolysis was not observed around prostheses in any hips.

In conclusion, no advantage was seen for the zirconia head compared with the cobalt-chromium head in this time period.

To analyze the long term results of a third generation ceramic on ceramic bearing in cementless total hip arthroplasty (THA), we reviewed the clinical and radiological results of 100 consecutive THAs performed in 86 patients (68 females, 80 hips; 18 males, 20 hips) between 1996 and 1998. The average age at operation was 55 years with a range of 26 to 73 years. The diagnoses were osteoarthritis in 83 hips, osteonecrosis in 10 hips and rheumatoid arthritis in 7 hips. The articulation was composed of a hemispherical titanium porous bead-coated cup (AnCA), a Biolox Forte alumina ceramic cup liner and a ball with a diameter of 28-mm. The modular ceramic liner was fixed directly to the metal cup without polyethylene sandwich or metal rim. A press-fit technique of 1 mm under-reaming without screws was used for cup fixation. The ceramic head was fixed to a 12/14 taper cone of a modular neck which allowed changes in neck-shaft angle, anteversion, and offset. All operations were performed via a posterolateral approach under general anesthesia. To measure the cup orientation, an ellipse was fitted to the acetabular component rim on the early postoperative AP radiographs using computer software. The average cup inclination and anteversion in the radiographic definition were 41 (range 28 to 63) and 17 (range 3 to 34) degrees, respectively. 22 cups were outside the Lewinnek safe zone. All patients were radiographically evaluated in term of implant stability at two years using Engh’s criteria. All of the acetabular components radiologically were judged to be bone-ingrown stable at two years except one cup. 98 stems were judged to be bone-ingrown stable and the remaining two stems were judged to be fibrous stable at two years. After two years, all patients except for two were followed up clinically and radiologically for at least 10 years or until revision or death. One unstable cup was revised at 2.5 years. This case had a previous Chiari’s pelvic osteotomy and insufficient press-fit of the cup was assumed to have led to loosening. One of the two fibrous stable stems was revised at six years due to aseptic loosening. One rheumatoid arthritis hip with stable bone ingrown fixation developed late infection at six years and was revised. One stable cup showed chipping of the acetabular liner at 8 years and required revision. The orientation of this cup was 55 degrees of inclination and 17 degrees of anteversion and the high inclination was thought to be related to the ceramic liner chipping. The remaining hips showed no osteolysis or loosening at the final follow-up. There were no squeaking hips. The 10-year survivorships with the endpoint of mechanical loosening or revision were 96.7% and 95.6%, respectively. We conclude that the third generation ceramic on ceramic hip bearing without polyethylene sandwich provided long term stability and eliminated periprosthetic osteolysis.

The anterior pelvic plane (APP) through the bilateral anterior superior iliac spines (ASIS) and pubic tuberosities is often used as a pelvic reference in measuring orientation of the acetabular cup in total hip arthroplasty. Apophyses such as ASIS are, however, anatomically variable among patients and APP does not always represent the functional pelvic tilt in the sagittal plane in each patient. Therefore, malposition of the cup and recurrent dislocation may occur even though the cup is placed in a safe zone when measured against APP. We analyzed dynamic pelvic tilt angle in the sagittal plane using a motion analysis system after THA and we found a case of recurrent dislocation due to an unusual APP tilt.

A 77-year-old woman underwent primary THA 3 years ago and cup re-implantation was done with the use of a 10-degree elevated liner and the head diameter was increased from 26mm to 28 mm after two anterior dislocations. However, posterior dislocation occurred 11 times after this. A second revision was performed with a 36 mm head and cup anteversion was optimized against APP. Further posterior dislocations occurred twice again. To probe the cause of recurrent dislocation, we performed motion analysis using a 6-camera VICON system and the markers were registered to the bone and implant models based on the postoperative CT images. This system visually represents four-dimensional dynamic motions that include the time sequential transitions of components and their posture. The cup had been placed in 6 degrees of radiographic anteversion against APP, and in −13 degrees of radiographic retroversion in supine (FPP), because the pelvic flexion angle in supine was 17.6 degrees. Furthermore, when standing, the pelvic flexion angle increased 10 degrees.

Malposition of the acetabular cup in THA is the most common cause of dislocation. To avoid errors in cup placement, computer navigation systems have been introduced and most of the navigation systems refer APP to establish cup orientation. There are two drawbacks in using APP as the reference. One is that apophyses such as ASIS develop variably in each patient with a resulting variability in APP tilt in the sagittal plane in supine. The other is significant changes in pelvis tilt during various activities of daily living such as standing, walking, and sitting. Therefore, even if cup orientation is acceptable when referencing APP, it can be mal-oriented in a functional position of the pelvis as in this case, which showed proper anteversion against APP but retroversion in supine, standing and sitting.

In conclusion, we found that there exists a case in which APP is not a suitable pelvic reference in determining orientation of the cup.

While numerous studies have examined dislocation caused by basic everyday movements, no objective studies have investigated body positions to minimize risk of dislocation during intercourse. We therefore used a four-dimensional motion analysis system to assess sexual activities in patients who had undergone total hip arthroplasty (THA), to identify body positions displaying less risk of dislocation.

Five body-surface infrared sensors were placed on five healthy female volunteers, and maximum hip joint angle was measured. Subjects were asked to take the following three body positions: supine (missionary); top (woman on top); and kneeling (doggy-style). Angle data obtained using body surface markers were combined with three-dimensional skeletal models extracted using CT images obtained from the 24 joints of 16 patients who had undergone THA, to ascertain angles at which collision with the artificial joint or skeleton would occur.

Collision angle for: supine position at maximum abduction in flexion was 77±16° in flexion and 82±57° in medial rotation; top position at maximum extension was 36±16° in flexion and 68±53° in medial rotation; top position at maximum flexion was 12±9° in flexion and 14±11° in medial rotation; kneeling position at maximum extension was 115±1° in flexion and 127±44° in medial rotation; and kneeling position at maximum flex-ion was 14±8° in flexion and 17±11° in medial rotation.

The present study only assessed risk for dislocation caused by collision with the artificial joint or skeleton, and did not take into account the effects of soft tissue. However, we were able to quantitatively assess angle of the hip joint for some leg positions involved with various common coital positions. The results showed that the supine position at maximum abduction in flexion is relatively safe, since the range of motion before collision would occur was relatively wide. In addition, top and kneeling positions at maximum extension were relatively safe, but caution must be exercised at maximum flexion, as not much extra angle was available in flexion and medial rotation.

We have developed a novel system of 4-dimensional motion analysis after total hip arthroplasty (THA) that can aid in preventing dislocation by assessing safe range of motion for patients in several daily activities.

This system uses skeletal structure data from CT and motion capture data from an infrared position sensor. A 3-D model reconstructed from CT data is combined with the motion capture data. Using this system, we analyzed hip motion when getting up from and sitting down in a chair or picking up an object while sitting in a chair in 17 patients (26 hips) who underwent THA. To assess the accuracy of this system’s measurements, open MRI was used to evaluate positions of skin markers against bones in 5 healthy volunteers in various postures.

No impingement between bones and/or implants was found in any subjects during any activities. However, mean angle at the point of maximum hip flexion was different for each patient. The open MRI results indicated that average error in hip angle of the present system was within 5 degrees for each static posture.

The functional position of the pelvis during daily activities must be taken into account when assessing the real risk of dislocation. The present system enables dynamic analysis involving not only alignment of components and bones of each patient, but also individual differences in characteristics of daily motions. Further investigation using this system can help determine safe ranges of motion for preventing hip dislocation, improving the accuracy of individualized guidance for patients regarding postoperative activities.

Alendronate is a potent inhibitor of bone resorptive activity, and has been shown to prevent and restore periprosthetic osteolysis in experimental models. A preliminary study was conducted to examine clinical usefulness of a lendronate treatment.

Twenty-five patients (27 hips) with radiological evidence of osteolysis after cemented total hip arthroplasty were included. Of these, 14 patients (15 hips) were administered 5 mg of alendronate daily (alendronate group), and 11 patients (12 hips) did not receive alendronate treatment (control group). The subjects were followed up for 12 months, using radiological examinations and biochemical markers. The radiological analysis was evaluated blindly by 2 joint arthroplasty experts, each with more than 10 years of experience, without knowledge of alendronate administration.

In the alendronate group, average serum bone alkaline phosphatase and urinary excretion of the N-telopep-tide of type I collagen values decreased from the baseline values after administration of alendronate, to 71% and 76% of baseline at the 3-month examination, and 57% and 62% at the 1-year examination, respectively. In the control group, expansion of osteolysis was found in 5 hips (42%) and no hip showed restoration of osteolysis. In the alendronate group, expansion of osteolysiswas found in 2 hips (13%), and restoration of osteolysis was found in 5 hips (33%). There was a statistically significant difference in ratio of hips with osteolysis restoration between the 2 groups (p< 0.05). In the alendronate group, there was no significant difference in age, average linear wear rate of polyethylene, and the biochemical markers, between the hips with and without diminishment of osteolysis.

Conclusions: The present results indicate that clinicala-lendronate treatment can prevent and restore periprosthetic osteolysis, which is generally thought to require surgical intervention. These findings warrant further study of the effects of duration and dose of alendronate treatment, component materials, and component fixation methods.

Introduction: The purpose of this study is to evaluate the clinical and radiogra phic outcome of patients with secondary osteoarthritis of the hip, who underwent custom-made cementless THA.

Methods: Between January 1994 and June 1997, 98 prim ary cementless custom-made THA’s were performed in 76 patients with secondary osteoarthritis and reviewed at mean 6 years follow-up (range: 4 – 7.5 years). Nine patients had a previous femoral osteotomy. There were 69 females and seven males. The mean age at operation was 54 years (40 – 73 years). Custom-made, 125 mm-long, titanium femoral components with blasted surface were fabricated based on the computerized tomography.

Results: The mean Harris Hip Score improved from 43 to 95 points. 97 patients (99%) had more than 80 points for total score, and 2 patients (2%) had thigh pain at the latest follow-up. Radiographically, 86 hips (87%) showed obviously extensive bone ongrowth onto the middle part of the stem while 8 hips (9%) showed stable fibrous fixation. Four hips (4%) were unstable: more than 2 mm subsidence in 2 hips and more than 2 degrees varus migration in 2 hips. Of these 4 hips, 2 had intraoperative cracks of the poximal femur and 2 had varus positioning of the stem.

Discussion and conclusion: Cementless THA has been advocated to enhance fit and fill of variable hip geometry. However, some clinical studies failed to show that custom implants significantly improve clinical success or implant longevity because their surface finish was not optimal. Custom-made titanium femoral components with blasted surface showed good clinical results. The reasons for radiolographical failures were because of intraoperative technical errors and these might be derived from 125 mm-long stem with maximum canal fill. A shorter stem may be an option because it may improve the feasibility of stem insertion and the distal fill.

Introduction: Progression of collapse in osteonecrosis of the femoral head (ONFH) is greatly influenced by repair reactions, especially bone resorptive activity. This study was performed to test if systemic alendronate treatment, a potent inhibitor of osteoclast activity, can prevent the development of collapse in ONFH.

Materials and Methods: Daily administration of oral alendronate (5mg/day) was started in 14 hips in 11 patients with ONFH (Alendronate group). At the beginning of the study (3, 6, 12 months), plain radiographs, T1-weighted MR imaging, and biochemical makers of osteoclast activity (N-telopeptide of type-I collagen) and osteoblast activity (Bone-specific alkaline phosphatase), were examined. At 12 months, MR imaging was repeated. Eleven hips in 6 patients with ONFH who did not receive alendronate administration were considered as the control group.

Results: There was no significant difference with respect to gender distribution, etiology factors, initial ARCO stages, and extent of necrosis in the two groups. In the alendronate group, there was an early decrease of osteoclast activity at 3 months, with a decrease to 62% at 12 months, while the decrease of osteoblast activity was smaller with 80% at 12 months. Development of collapse was observed in 4 of the 11 hips (36%) in the control group, and in none of the 14 hips in the alendronate group. There was a significant difference of collapse development between the two groups (p=0.026, Mann-Whitney U-test). Signal change on serial MR images was observed in 5 of 9 hips (56%) in the control group, with only one of 9 hips (11%) in the alendronate group.

Discussion: The low incidence of signal change on serial MR images may reflect the decrease of repair activity in the alendronate group. The present study was the first clinical trial to show that alendronate has a significant preventive effect of collapse development in patients with osteonecrosis of the femoral head.

Introduction: In order to investigate the relationship between the degeneration of the acetabular cartilage and the radiological staging of osteonecrosis of the femoral head, the following study was performed.

Materials and Methods: Acetabular cartilage with sub-chondral bone was taken from the superior dome from 34 hips from 30 patients undergoing total hip arthroplasty due to osteonecrosis of the femoral head. The specimens were stained with hematoxylineosin and safranin-O, and were evaluated as to the thinning of cartilage, fibrillation, clefts, and proliferation of chondrocytes. There were 18 females and 12 males with an average age of 49 years. We used the radiological staging system proposed by the working group of the Specific Disease Investigation Committee under the auspices of the Japanese Ministry of Health, Labor and Welfare. There were eight hips in stage IIIA disease (collapse of the femoral head less than 3 mm), 19 hips in stage IIIB disease (collapse 3 mm or greater), and seven stage IV disease hips.

Results: All 34 specimens showed histological abnormalities. In eight stage IIIA hips, six hips were mild and two were moderate histological degeneration. In 19 stage IIIB hips, five hips were mild, six were moderate, and eight had severe arthrosis. Seven stage IV hips had severe arthrosis.

Discussion: Although the radiographs cannot demonstrate early degeneration of cartilage, degenerative changes were present in all stage III hips. Histological degenerative changes in stage IIIB hips were more severe than those in stage IIIA hips. These findings should be kept in mind in treating patients with osteonecrosis of the femoral head.

Introduction: There is controversy over whether the lesions of osteonecrosis of the femoral head (ONFH) will spontaneously decrease. This study reports a longitudinal study of lesion volume using high-resolution serial MRI and recently developed techniques for image registration to realign serial images.

Materials and Methods: Baseline and follow-up (minimum one year later) MRI scans were carried out on 15 patients (18 hips). Accurate subvoxel registration was performed and subtraction images were produced to reveal areas of regional necrotic lesion change. Volume-to-femoral head ratio (VFR) was calculated to normalize the measured volume to the total femoral head volume.

Results: Three of 18 hips showed spontaneous reductions in the size of the lesions. They were all related to steroid use and were within one year after initial steroid treatment The mean volume decrease of these 3 hips was 3.4 ± 2.0 cm³ (SD) and its VFR was 6.8 ± 3.1 % (SD). Mean necrotic lesion volumes at baseline of decreasing lesions and unchanged lesions were 4.6 ± 2.5 cm³ (VFR, 9.1 ± 3.9 %) and 7.5 ± 5.5 cm³ (VFR, 16.7 ± 12.4 %), respectively.

There was no statistically significant difference in baseline lesion volume between decreasing lesions and unchanged lesions.

Discussion: In conclusion, some early lesions within one year after onset can decrease in size on MRI, regardless their size at baseline.